U.S. patent application number 11/167605 was filed with the patent office on 2005-12-29 for roller for image forming apparatus and method of manufacturing same.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Hong, Seock-deock, Kim, Hyun-Soo, Park, Geun-Yong.
Application Number | 20050286933 11/167605 |
Document ID | / |
Family ID | 35107032 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050286933 |
Kind Code |
A1 |
Kim, Hyun-Soo ; et
al. |
December 29, 2005 |
Roller for image forming apparatus and method of manufacturing
same
Abstract
An image forming apparatus has a plurality of image bearing
bodies in a predetermined sequence, an intermediate transfer medium
for running in contact with each of the plurality of image bearing
bodies, and a plurality of supporting rollers for driving the
intermediate transfer medium. The rollers are manufactured such
that a driven coupler is engaged with the roller body in a
predetermined orientation with a location of a radius deviation
along the circumference of the roller body.
Inventors: |
Kim, Hyun-Soo; (Yongin-si,
KR) ; Park, Geun-Yong; (Suwon-si, KR) ; Hong,
Seock-deock; (Suwon-si, KR) |
Correspondence
Address: |
ROYLANCE, ABRAMS, BERDO & GOODMAN, L.L.P.
1300 19TH STREET, N.W.
SUITE 600
WASHINGTON,
DC
20036
US
|
Assignee: |
Samsung Electronics Co.,
Ltd.
|
Family ID: |
35107032 |
Appl. No.: |
11/167605 |
Filed: |
June 28, 2005 |
Current U.S.
Class: |
399/167 |
Current CPC
Class: |
G03G 15/0194 20130101;
G03G 2215/0119 20130101; G03G 2215/0158 20130101; H04N 1/00
20130101 |
Class at
Publication: |
399/167 |
International
Class: |
G03G 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2004 |
KR |
2004-48837 |
May 24, 2005 |
KR |
2005-43735 |
Claims
What is claimed is:
1. A roller comprising: a roller body having a deviation in its
radius along the direction of circumference; and a driven coupler
engaged with one end of the roller body, for complimentary mating
with a driving coupler and receiving a driving force from the
driving coupler, wherein the roller body has a mark formed on a
predetermined position for indicating a location of the
deviation.
2. The roller of claim 1, wherein the driven coupler comprises a
positioning part for determining a position of engaging with the
driving coupler, and the roller body is engaged with the driven
coupler such that the positioning part maintains a predetermined
set angle with respect to the mark.
3. The roller of claim 1, wherein the mark is provided at a
predetermined angle with respect to a maximum radius deviation
location of the roller body.
4. An image bearing body for use in an image forming apparatus,
comprising: a drum body having a deviation in its radius along the
direction of circumference; and a driven coupler engaged with one
end of the roller body, for complimentary mating with a driving
coupler and receiving a driving force from the driving coupler,
wherein the drum body has a mark formed on a predetermined position
for indicating a location of the deviation.
5. The image bearing body of claim 4, wherein the mark is provided
at a predetermined location with respect to a maximum radius
deviation location.
6. The image bearing body of claim 4, wherein the driven coupler
comprises a positioning part for determining a position of engaging
with the driving coupler, and the driven coupler is engaged with
the drum body such that the positioning part maintains a
predetermined angle with respect to the mark.
7. The image bearing body of claim 6, wherein the driven coupler
comprises a non-circular coupling part formed at one end either in
concave or convex fashion to receive a driving force in an
engagement with the driven coupler, and the positioning part is
extended from the coupling part in a radial direction of the driven
coupler.
8. A method of manufacturing a roller comprising a roller body
having a deviation in its radius along the direction of its
circumference, and a driven coupler engaged with one end of the
roller body, the method comprising the steps of: finding an
interval of the roller body having a radius deviation; and setting
the posture of the driven coupler with respect to the found
interval and engaging the driven coupler with the roller body in
said posture.
9. The method of claim 8, wherein said step of finding an interval
comprises finding a location of maximum radius deviation.
10. The method of claim 9, wherein the step of finding the interval
having a maximum radius deviation comprises the steps of: finding a
point of maximum radius deviation by measuring an end of the roller
body; and forming a mark on the roller body for indicating the
found point of maximum radius deviation.
11. The method of claim 9, wherein the step of engaging the driven
coupler comprises assembling the driven coupler with the roller
body in a manner such that a positioning part of the driven coupler
maintains a predetermined angle with respect to the point of
maximum radius deviation and that the relative positions of
engaging the driven coupler and the driving coupler are
determined.
12. The method of claim 9, wherein the step of engaging the driven
coupler comprises the steps of: supporting the roller body on a
first jig such that the point of maximum radius deviation is
positioned at a predetermined angle with respect to a reference
coordinate axis; supporting the driven coupler on a second jig such
that the driven coupler is positioned at a predetermined angle with
respect to the reference coordinate axis; and moving at least one
of the first and the second jigs to engage the driven coupler with
the roller body.
13. A jig for assembling one or more rollers for use in an image
forming apparatus, the one or more rollers each comprising a roller
body having a radius deviation along a circumference and a driven
coupler adapted to receive a driving force, the jig comprising: a
first receiving portion adapted to receive at least one roller
body; and a second receiving portion adapted to receive at least
one corresponding driven coupler in a predetermined orientation
with respect to the at least one roller body radius deviation.
14. The jig of claim 13, wherein at least one of the first and
second receiving portions are adapted to move with respect to the
other in order to engage the at least one roller body to the at
least one corresponding driven coupler in the predetermined
orientation.
15. The jig of claim 13, wherein the second receiving portion
comprises at least one mating part adapted for complimentary mating
with a non-circular coupling part of the at least one driven
coupler.
16. The jig of claim 15, wherein the mating part has a positioning
part and the coupling part has a complimentary positioning part for
determining the predetermined orientation.
17. The jig of claim 13, wherein one of the mating part and the
coupling part are concave, and the other of the mating part and the
coupling part are convex.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Korean Patent
Application No. 2004-48837 filed Jun. 28, 2004, and Korean Patent
Application No. 2005-43735 filed May 24, 2005, in the Korean
Intellectual Property Office, the disclosures of which are hereby
incorporated by reference. This application is related to U.S.
Patent Applications titled "Image Forming Apparatus Having Reduced
Image Errors From Driving Unit and Method of Manufacturing Same,"
"Image Forming Apparatus Having Reduced Image Errors From Image
Bearing Bodies and Method of Manufacturing Same," and "Image
Forming Apparatus Adapted to Overlap Image Errors From Driving Unit
and Image Bearing Bodies and Method of Manufacturing Same," each
filed on even date herewith.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention:
[0003] The present invention relates to a driving unit for an image
forming apparatus, a color image forming apparatus having the same,
and a method of manufacturing an image forming apparatus having the
driving unit.
[0004] 2. Description of the Related Art:
[0005] Generally, image forming apparatuses are classified into a
monochromatic image forming apparatus and a color image forming
apparatus. The monochromatic image forming apparatus forms an image
in black and white by using only one color developer, while the
color image forming apparatus forms a colorful image by using color
developers such as magenta, cyan, yellow, and black.
[0006] An electrophotographic image forming apparatus forms an
electrostatic latent image by scanning a laser beam onto an organic
photoconductor (OPC), which is electrified by an electrifying unit
to have a predetermined level of electric potential, using a light
exposing unit. The electrostatic latent image is developed using a
developer and then transferred into a visible image on supplied
print paper. In a color image forming apparatus, the electrostatic
latent image is developed by using color developers on the organic
photoconductors and overlapped images are transferred onto an
intermediate transfer medium, such as an Intermediate Transfer Belt
(ITB). The color images overlapped on the intermediate transfer
medium are transferred onto print paper. Subsequently, the print
paper with a color image goes through a series of fixing processes
before it is transferred out of the image forming apparatus.
[0007] FIG. 1 is a structural diagram showing a conventional color
image forming apparatus that performs a two-step transferring
process by using the intermediate transfer medium. Referring to
FIG. 1, the color image forming apparatus comprises a belt 10, a
supporting roller 11, four T1 rollers 12, 13, 14 and 15, four
organic photoconductors 16, 17, 18 and 19, a T2 roller 20, and a
belt driving roller 21.
[0008] Developers each corresponding to K (black), C (cyan), M
(magenta), and Y (yellow) are attached to the electrostatic latent
image area of each of the organic photoconductors 16, 17, 18 and
19. The T1 rollers 12, 13, 14 and 15 are set up to correspond to
the organic photoconductors 16, 17, 18 and 19 with the belt 10
between the organic photoconductors 16, 17, 18 and 19 and the T1
rollers 12, 13, 14 and 15. Accordingly, the developers attached to
the surfaces of the organic photoconductor 16, 17, 18 and 19 are
primarily transferred to the surface of the belt 10 by the
transferring activity of the T1 rollers 12, 13, 14 and 15. Herein,
the respective color images of the organic photoconductors 16, 17,
18 and 19 are transferred onto the belt 10 at predetermined time
intervals so that the color developers transferred to the belt 10
can be overlapped in registration into a complete color image.
Therefore, the color developers are overlapped on the belt 10 to
thereby form a complete color image. Subsequently, the color image
on the belt 10 goes through a secondary transferring process
between the T2 roller 20 and the belt driving roller 21. Also, the
belt driving roller 21 runs the belt 10 at a proper rate.
[0009] The belt 10 and the organic photoconductors 16, 17, 18 and
19 are consumption goods with limited life spans, that must
periodically be replaced.
[0010] A transferring unit including the belt 10 and developing
units including each organic photoconductor 16, 17, 18 or 19 are
typically set up in a detachable manner along with a predetermined
coupling unit and the driving unit for providing power in the image
forming apparatus.
[0011] When the consumption goods, that is, the transferring unit
and the developing units, are replaced, the structure of the
coupling unit for performing relative motion of the driving unit,
the transferring unit, and the developing units is significant.
That is, it is important to connect the transferring unit and the
developing units to have the same rotational axis as the driving
unit. It is also important to realize highly precise color
registration in consideration of the so-called total runout between
the transferring unit and the developing unit. This is particularly
important in view of manufacturing tolerances in the external
circumferential surface of the driving roller of the transferring
unit.
[0012] Herein, the total runout can be understood to include a
phenomenon that the belt 10 rotates at a predetermined rate, but
small changes in the instantaneous rotation rate occur due to the
manufacturing tolerance of the external circumferential surface of
the driving roller. The total runout affects the developing units
in the same period through the belt 10. Therefore, it is important
to equalize the influence of the total runout on the developing
units and improve the quality of a color image.
[0013] Additionally, the organic photoconductors and the driving
roller may have deviations in their radii if the outer
circumferences thereof do not make a perfect circle due to
manufacturing tolerances. Such deviations result in errors of a
composite color image on the belt as the color image partially
stretches or cuts due to the aforementioned deviations in the OPC
rollers and the driving roller.
SUMMARY OF THE INVENTION
[0014] It is, therefore, an object of the present invention to
provide a roller which enables controlling the orientation of a
predetermined radial displacement.
[0015] It is another object of the present invention to provide a
method of manufacturing a roller which enables controlling the
orientation of a predetermined radial displacement.
[0016] It is another object of the present invention to provide an
improved driving unit of an image forming apparatus which enables
minimizing an image error caused due to radial errors in rollers
supporting the belt.
[0017] It is another object of the present invention to provide an
improved image forming apparatus which enables minimizing an image
error caused due to a plurality of image bearing bodies.
[0018] It is another object of the present invention to provide an
improved image forming apparatus which enables minimizing an image
error caused due to a plurality of image bearing bodies and belt
supporting rollers.
[0019] The above aspects and other features of the present
invention can substantially be achieved by providing a roller
including a roller body having a radial displacement along the
direction of its circumference; and a driven coupler engaged with
one end of the roller body, for complimentary mating with a driving
coupler for driving a driving force. The roller body has a mark
formed on a predetermined position for indication of radial
displacement.
[0020] The driven coupler includes a positioning part for
determining a position of engaging with the driving coupler. The
roller body is engaged with the driven coupler such that the
positioning part maintains a predetermined angle with respect to
the mark.
[0021] The mark is preferably provided at a predetermined angle
with respect to a maximum radial displacement location of the
roller body.
[0022] According to one aspect of the present invention, an image
bearing body for use in an image forming apparatus includes a drum
body having a radial displacement along the direction of its
circumference; and a driven coupler engaged with one end of the
roller body, for complimentary mating with a driving coupler for
driving a driving force. The drum body preferably has a mark formed
on a predetermined position for indication of the location of
maximum radial displacement.
[0023] The mark is preferably provided at a predetermined location
with respect to a maximum radial displacement location.
[0024] The driven coupler preferably includes a positioning part
for determining a position of engaging with the driving coupler.
The driven coupler may be engaged with the drum body such that the
positioning part maintains a predetermined angle with respect to
the mark.
[0025] The driven coupler preferably includes a non-circular
coupling part formed at one end either in concave or convex fashion
to receive a driving force in an engagement with the driven
coupler. The positioning part may be extended from the coupling
part in the direction of the radius of the driven coupler.
[0026] According to another aspect of the present invention, a
method of manufacturing a roller including a roller body having a
radial displacement along the direction of its circumference, and a
driven coupler engaged with one end of the roller body, is
provided. The method may include the steps of identifying a
location of radial displacement of the roller body; and setting the
position of the driven coupler with respect to the identified
location and engaging the driven coupler with the roller body in
said position.
[0027] The step of finding the location having a radial
displacement preferably includes the steps of finding a point of
maximum radial displacement by measuring an end of the roller body;
and forming a mark on the roller body for indication of the found
point of maximum radial displacement.
[0028] The step of engaging the driven coupler preferably includes
assembling the driven coupler with the roller body in a manner such
that a positioning part of the driven coupler maintains a
predetermined angle with respect to the point of maximum radial
displacement and that the relative positions of engaging the driven
coupler and the driving coupler are determined.
[0029] The step of engaging the driven coupler preferably includes
the steps of supporting the roller body on a first jig such that
the point of maximum radial displacement is positioned at a
predetermined angle with respect to a reference coordinate axis;
supporting the driven coupler on a second jig such that the driven
coupler is positioned at a predetermined angle with respect to the
reference coordinate axis; and moving the first and the second jigs
relative to each other and thereby engaging the driven coupler with
the roller body.
[0030] According to yet another aspect of the present invention, a
driving unit of an image forming apparatus may include a driving
gear for driving a plurality of image bearing bodies which are
arranged in a predetermined sequence, and a driving gear for
driving a plurality of supporting rollers which support a belt
running on the plurality of image bearing bodies. A distance
between centers of rotation of at least two of the plurality of
driving gears is preferably a positive integral multiple of the
length of circumference of one of the supporting rollers.
[0031] Each of the distances between the centers of rotation of the
plurality of driving gears is preferably a positive integral
multiple of the length of the circumference of at least one of the
supporting rollers.
[0032] One of the supporting rollers may be a driving roller which
receives a driving force in engagement with the driving gear.
[0033] One of the supporting rollers may be a roller having a
radial displacement.
[0034] The driving gear preferably includes first through fourth
driving gears in a predetermined sequence with respect to the
direction of belt running, which satisfy at least one of the
following equations:
[0035] [Equation Set 1]
L1=l.multidot.Sd.multidot.(1.+-.0.05)(l=1, 2, 3, . . . ) (1)
L2=m.multidot.Sd.multidot.(1.+-.0.05)(m=1, 2, 3, . . . ) (2)
L3=n.multidot.Sd.multidot.(1.+-.0.05)(n=1, 2, 3, . . . ) (3)
L4=o.multidot.Sd.multidot.(1.+-.0.05)(o=1, 2, 3, . . . ) (4)
L5=p.multidot.Sd.multidot.(1.+-.0.05)(p=1, 2, 3, . . . ) (5)
L6=q.multidot.Sd.multidot.(1.+-.0.05)(q=1, 2, 3, . . . ) (6)
[0036] where L1 is the distance between the centers of first and
second driving gears,
[0037] L2 is the distance between the centers of second and third
driving gears,
[0038] L3 is the distance between the centers of third and fourth
driving gears,
[0039] L4 is the distance between the centers of first and third
driving gears,
[0040] L5 is the distance between the centers of first and fourth
driving gears,
[0041] L6 is the distance between the centers of second and fourth
driving gears, and
[0042] Sd is the length of the circumference of the one of the
supporting rollers.
[0043] The driving gears are preferably mounted to satisfy all of
the equations in Equation Set 1.
[0044] The driving gears are preferably mounted to satisfy
L1=L2=L3.
[0045] The driving gears are preferably mounted to satisfy
L1=L2=L3, and L1, L2, and L3 are positive integer multiples of
Sd.
[0046] The radius of the supporting rollers is preferably equal to
the radius of the image bearing bodies.
[0047] A plurality of driving couplers are preferably provided to a
center of rotation of each of the plurality of driving gears, to
transmit a driving force in engagement with each of the plurality
of image bearing bodies.
[0048] The driving coupler may include a coupling part configured
to have a non-circular section corresponding to each of the driven
couplers provided to an end of each image bearing body; and a
positioning part provided to a side of the coupling part to
determine a position of engagement such that the driving coupler
engages with the driven coupler at a fixed posture.
[0049] The coupling part may be a coupling recess sunken into an
end of the coupling part in a non-circular shape, and the
positioning part may be a recess sunken into an inner side of the
coupling part to a predetermined depth.
[0050] The driven coupler may include a shaft protruding from an
end toward the center of rotation, and a shaft hole at a bottom of
the coupling recess for engagement with the shaft.
[0051] The coupling part may be a coupling protrusion extending
from an end in a non-circular shape, and the positioning part may
be a protrusion extending from an outer portion of the coupling
protrusion.
[0052] According to yet another aspect of the present invention, an
image forming apparatus preferably includes a plurality of image
bearing bodies arranged in a predetermined sequence; an
intermediate transfer medium running in contact with each of the
plurality of image bearing bodies; and a plurality of supporting
rollers for driving the intermediate transfer medium. A distance
between centers of rotation of at least two image bearing bodies is
a positive integral multiple of the length of the circumference of
at least one of the supporting rollers.
[0053] The image bearing bodies preferably include first to fourth
image bearing bodies which are arranged in a predetermined sequence
with reference to the direction in which the intermediate transfer
medium runs, and the first to fourth image bearing bodies
preferably satisfy at least one of the following equations:
[0054] [Equation Set 1]
L1=l.multidot.Sd.multidot.(1.+-.0.05)(l=1, 2, 3, . . . ) (1)
L2=m.multidot.Sd.multidot.(1.+-.0.05)(m=1, 2, 3, . . . ) (2)
L3=n.multidot.Sd.multidot.(1.+-.0.05)(n=1, 2, 3, . . . ) (3)
L4=o.multidot.Sd.multidot.(1.+-.0.05)(o=1, 2, 3, . . . ) (4)
L5=p.multidot.Sd.multidot.(1.+-.0.05)(p=1, 2, 3, . . . ) (5)
L6=q.multidot.Sd.multidot.(1.+-.0.05)(q=1, 2, 3, . . . ) (6)
[0055] where L1 is the distance between the centers of first and
second driving gears,
[0056] L2 is the distance between the centers of second and third
driving gears,
[0057] L3 is the distance between the centers of third and fourth
driving gears,
[0058] L4 is the distance between the centers of first and third
driving gears,
[0059] L5 is the distance between the centers of first and fourth
driving gears,
[0060] L6 is the distance between the centers of second and fourth
driving gears, and
[0061] Sd is the length of circumference of the one of the
supporting rollers.
[0062] The image bearing bodies are preferably mounted to satisfy
all of the equations in Equation Set 1.
[0063] The image bearing bodies are preferably mounted to satisfy
L1=L2=L3.
[0064] The image bearing bodies are preferably mounted to satisfy
L1=L2=L3, and L1, L2 and L3 are positive integer multiples of
Sd.
[0065] The plurality of supporting rollers preferably include a
driving roller for driving the intermediate transfer medium while
being rotated with a driving force transmitted thereto, and an idle
roller being passive-rotated while supporting the intermediate
transfer medium. Sd defines the length of circumference of a
supporting roller.
[0066] A driving unit is preferably provided for driving the image
bearing bodies and the supporting rollers.
[0067] The driving unit preferably includes a first driving unit
for driving the plurality of image bearing bodies at the same time;
and a second driving unit for driving one of the plurality of
supporting rollers independently.
[0068] The first driving unit preferably includes a plurality of
driving gears provided to correspond to each of the plurality of
image bearing bodies, and rotated in association with each other;
and a first driving motor for providing a driving force to drive
the plurality of driving gears at the same time.
[0069] The second driving unit preferably includes a second driving
motor; and one driving gear engaged with one of the supporting
rollers, and driven by the second driving motor.
[0070] Each of the driving gears and each of the image bearing
bodies preferably include at their corresponding ends, a driving
coupler and a driven coupler for complimentary mating with the
driving coupler.
[0071] The driving and the driven couplers preferably include
coupling parts at their ends provided in a non-circular section and
complimentarily mated with each other; and positioning parts
extended from a side of each of the coupling parts to a
predetermined configuration to determine a posture of engagement of
the driving and driven couplers.
[0072] The image bearing bodies have a radial displacement in which
the radius of the image bearing body varies, and also have
intervals A1, A2, A3 and A4 having a predetermined location of
maximum radial displacement, and the first to fourth image bearing
bodies may be mounted to satisfy one of the following
equations:
[0073] [Equation Set 2]
{2.pi..multidot.l+(.alpha.2-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=L1-
, (l=0, 1, 2, . . . ), (Ro=Ro1=Ro2) {circle around (1)}
{2.pi..multidot.m+(.alpha.3-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=L1-
+L2, (m=0, 1, 2, . . . ), (Ro=Ro1=Ro3) {circle around (2)}
{2.pi..multidot.n+(.alpha.4-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=L1-
+L2+L3, (n=0, 1, 2, . . . ), (Ro=Ro1=Ro4) {circle around (3)}
[0074] where .alpha.1 is the angle, which is measured from the
transfer starting location of the first image bearing body to the
center of the interval Al, in the direction of reverse rotation of
the first image bearing bodies,
[0075] .alpha.2 is the angle, which is measured from the transfer
starting location of the second image bearing body to the center of
the interval A2, in the direction of reverse rotation of the second
image bearing bodies,
[0076] .alpha.3 is the angle, which is measured from the transfer
starting location of the third image bearing body to the center of
the interval A3, in the direction of reverse rotation of the third
image bearing bodies,
[0077] .alpha.4 is the angle, which is measured from the transfer
starting location of the fourth image bearing body to the center of
the interval A4, in the direction of reverse rotation of the fourth
image bearing bodies, and
[0078] Ro1, Ro2, Ro3 and Ro4 are radii of the first through fourth
image bearing bodies.
[0079] The image bearing bodies preferably satisfy L1=L2=L3.
[0080] The image bearing bodies preferably satisfy L1=L2=L3, while
L1, L2 and L3 are positive integer multiples of Sd.
[0081] A driving unit is preferably provided for driving the image
bearing bodies and the supporting rollers, and each of the image
bearing bodies preferably have at one end a driven coupler for
receiving a driving force in engagement with the driving unit.
[0082] The driven couplers preferably each include a positioning
part for determining a position of engagement with respect to the
driving unit. The driven couplers may be engaged such that the
intervals A1, A2, A3 and A4 of the respective image bearing bodies
are formed at a predetermined angle with respect to the positioning
parts.
[0083] The driving unit preferably includes a first driving unit
for driving the first through fourth image bearing bodies at the
same time; and a second driving unit for driving the supporting
rollers independently.
[0084] The first driving unit preferably includes a plurality of
driving gears provided to correspond to the plurality of image
bearing bodies, respectively, rotating altogether in association
with each other, and each having a driven coupler at one end to
engage with the driven coupler; and a first driving motor for
providing a driving force to drive the plurality of driving gears
at the same time.
[0085] The first and second image bearing bodies are preferably
mounted to satisfy the first equation of the equations 2-1, and
satisfy .alpha.1=.alpha.2.
[0086] The first and third image bearing bodies are preferably
mounted to satisfy the third equation of the equations 2-1, and
satisfy .alpha.1=.alpha.3.
[0087] The first and fourth image bearing bodies are preferably
mounted to satisfy the third equation of the equations 2-1, and
satisfy .alpha.1=.alpha.4.
[0088] The first to fourth image bearing bodies are preferably
mounted to satisfy all of the equations 2-1, and satisfy
.alpha.1=.alpha.2=.alpha.3=- .alpha.4.
[0089] The image bearing bodies have a radial displacement in which
the radius of the image bearing body varies, and also have
intervals A1, A2, A3 and A4 having a predetermined locations of
maximum radial displacement, and at least two of the first through
fourth image bearing bodies are mounted to satisfy one of the
following equations:
[0090] [Equation Set 3]
{2.pi..multidot.l+(.alpha.2-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=L1-
, (l=0, 1, 2, . . . ), (Ro=Ro1=Ro2) {circle around (1)}
{2.pi..multidot.m+(.alpha.3-.alpha.2)}.multidot.Ro.multidot.(1.+-.0.05)=L2-
, (m=0, 1, 2, . . . ), (Ro=Ro2=Ro3) {circle around (2)}
{2.pi..multidot.n+(.alpha.4-.alpha.3)}.multidot.Ro.multidot.(1.+-.0.05)=L3-
, (n=0, 1, 2, . . . ), (Ro=Ro3=Ro4) {circle around (3)}
[0091] where .alpha.1 is the angle of center of the interval A1,
measured from the transfer starting location of the first image
bearing body in the direction of reverse rotation of the image
bearing bodies,
[0092] .alpha.2 is the angle of center of the interval A2, measured
from the transfer starting location of the second image bearing
body in the direction of reverse rotation of the image bearing
bodies,
[0093] .alpha.3 is the angle of center of the interval A3, measured
from the transfer starting location of the third image bearing body
in the direction of reverse rotation of the image bearing
bodies,
[0094] .alpha.4 is the angle of center of the interval A4, measured
from the transfer starting location of the fourth image bearing
body in the direction of reverse rotation of the image bearing
bodies, and
[0095] Ro1, Ro2, Ro3 and Ro4 are radii of the first to fourth image
bearing bodies.
[0096] The image bearing bodies preferably satisfy L1=L2=L3.
[0097] The image bearing bodies preferably satisfy L1=L2=L3, while
L1, L2 and L3 may be positive integral multiples of Sd.
[0098] The image bearing bodies are preferably mounted to satisfy
all of the equations 2-2, and satisfy
.alpha.1=.alpha.2=.alpha.3=.alpha.4.
[0099] The image bearing bodies each have a radial displacement in
which the radius of the image bearing body varies, and an interval
A having a maximum radial displacement at a predetermined location,
wherein, when one of the supporting rollers has a radial
displacement in which the radius varies, and an interval B having a
maximum radial displacement, and with reference to a predetermined
(X, Y) coordinate system based on the center of rotation of the
supporting rollers and the image bearing rollers, the image bearing
bodies and the supporting rollers are mounted to satisfy one of the
following equations:
[0100] [Equation Set 4]
Rd.multidot..theta.d=(2.pi..multidot.l+.theta.ox).multidot.Rox.multidot.(1-
.+-.0.05)
(l=1, 2, 3, . . . ), (x=1, 2, 3, . . . ), Rd=z.multidot.Rox,(z=2,
3, 4, 5, . . . ) {circle around (1)}
Rd.multidot..theta.d=Rox.multidot..theta.ox(1.+-.0.05)
Rd=.theta.ox, (x=1, 2, 3, . . . ) {circle around (2)}
(2.pi..multidot.h+.theta.d).multidot.Rd=Rox.multidot..theta.ox(1.+-.0.05)
(h=1,2,3, . . . ), (x=1, 2, 3, . . . ), Rox=k.multidot.Rd, (k=2, 3,
4, 5, . . . ) {circle around (3)}
[0101] where, .theta.d is the angle of the center of the interval B
in the direction of reverse rotation of the supporting rollers
along the axis +X of the (X, Y) coordinate system,
[0102] .theta.ox is the angle measured from the axis +Y of the
(x)th image bearing body in the running direction of the
intermediate transfer medium to the center of the interval A in the
reverse rotational direction of the image bearing body,
[0103] Rox is the radius of the (x)th image bearing body, and
[0104] Rd is the radius of the supporting rollers.
[0105] The axis +X is preferably defined to be parallel with
reference to the running direction of the intermediate transfer
medium, such that when the center of the interval B is positioned
on the axis +X, the speed change of intermediate transfer medium
reaches a maximum.
[0106] When the radius of the supporting rollers is larger than the
radius of the image bearing bodies by interger multiples, the
integer being 2 or more, the image bearing bodies and the
supporting rollers are preferably arranged to satisfy the first
equation of the Equation Set 3.
[0107] When the radius of the image bearing bodies equals the
radius of the supporting rollers, the image bearing bodies and the
supporting rollers are preferably arranged to satisfy the second
equation of Equation Set 3.
[0108] When the radius of the image bearing bodies is larger than
the radius of the supporting rollers by an integer multiple, the
integer being 2 or more, the image bearing bodies and the
supporting rollers are preferably arranged to satisfy the third
equation of Equation Set 3.
[0109] A first driving unit is preferably provided for driving the
image bearing bodies at the same time, and a second driving unit is
preferably provided for driving one of the supporting rollers.
[0110] The image bearing bodies each preferably include a drum
body, a driven coupler engaged with one end of the drum body to
receive a driving force in connection with the first driving
unit.
[0111] The drum body of each of the image bearing bodies preferably
have a mark for indicating the maximum radial displacement interval
A.
[0112] The driven coupler of each of the image bearing bodies
preferably include a positioning part for determining a position of
engagement with the first driving unit, and the image bearing
bodies and the driven couplers are preferably engaged such that the
positioning part is positioned at a predetermined angle with
respect to the mark.
[0113] The supporting rollers each preferably include a roller
body, and a driven coupler engaged with one end of the roller body
to receive a driving force from the second driving unit.
[0114] The driven coupler of each of the supporting rollers
preferably include a positioning part to determine a position of
engagement with respect to the second driving unit, and the roller
body is preferably provided with a mark for indicating the interval
B at a predetermined angle with respect to the positioning
part.
[0115] The image bearing bodies preferably have identical
radii.
[0116] The image bearing bodies are preferably arranged to satisfy
L1=L2=L3.
[0117] The image bearing bodies each have a radial displacement in
which the radius of the image bearing body varies, and an interval
A having a maximum radial displacement at a predetermined location,
wherein when, one of the supporting rollers has a radial
displacement in which the radius varies, and an interval B having a
maximum radial displacement, and with reference to a predetermined
(X, Y) coordinate system based on the center of rotation of the
supporting rollers and the image bearing rollers, the image bearing
bodies and the supporting rollers are mounted to satisfy one of the
following equations:
[0118] [Equation Set 4]
Rd.multidot..theta.d=(2.pi..multidot.l+.theta.ox).multidot.Rox.multidot.(1-
.+-.0.05)
(l=1, 2, 3, . . . ), (x=1, 2, 3, . . . ), Rd=z.multidot.Rox, (z=2,
3, 4, 5, . . . ) {circle around (1)}
Rd.multidot..theta.d=Rox.multidot..theta.ox.multidot.(1.+-.0.05)
Rd=.theta.ox, (x=1, 2, 3, . . . ) {circle around (2)}
(2.pi..multidot.h+.theta.d).multidot.Rd=Rox.multidot..theta.ox.multidot.(1-
.+-.0.05)
(h=1, 2, 3, . . . ), (x=1, 2, 3, . . . ), Rox=k.multidot.Rd, (k=2,
3, 4, 5, . . . ) {circle around (3)}
[0119] where, .theta.d is the angle of center of the interval B in
the direction of reverse rotation of the supporting rollers along
the axis +X of the (X, Y) coordinate system,
[0120] .theta.ox is the angle measured from the axis +Y of the
(x)th image bearing body in the running direction of the
intermediate transfer medium to the center of the interval A in the
reverse rotational direction of the image bearing body,
[0121] Rox is the radius of the (x)th image bearing body, and
[0122] Rd is the radius of the supporting rollers.
[0123] The axis +X is preferably defined to be parallel with
reference to the running direction of the intermediate transfer
medium, such thatwhen the center of the interval B is positioned on
the axis +X, the speed change of intermediate transfer medium
reaches a maximum.
[0124] When the radius of the supporting rollers is larger than the
radius of the image bearing bodies by an integer multiple, the
integer being 2 or more, the image bearing bodies and the
supporting rollers are preferably arranged to satisfy the first
equation of Equation Set 3.
[0125] When the radius of the image bearing bodies equals the
radius of the supporting rollers, the image bearing bodies and the
supporting rollers may be arranged to satisfy the second equation
of Equation Set 3.
[0126] When the radius of the image bearing bodies is larger than
the radius of the supporting rollers by an integer multiple, the
integer being 2 or more, the image bearing bodies and the
supporting rollers are preferably arranged to satisfy the third
equation of the Equation set 3.
[0127] The image bearing bodies are preferably mounted to satisfy
L1=L2=L3.
[0128] The image bearing bodies preferably satisfy L1=L2=L3, while
L1, L2 and L3 are a positive integer multiple of Sd.
[0129] A driving unit is preferably provided for driving the image
bearing bodies and the supporting rollers, and the image bearing
bodies each preferably have a driven coupler at one end to receive
a driving force in connection with the driving unit.
[0130] The driven couplers each preferably have a positioning part
for determining a position of engagement with the driving unit, and
the driven couplers are preferably engaged such that the intervals
A1, A2, A3 and A4 of the respective image bearing bodies are formed
at a predetermined angle with respect to the positioning parts.
[0131] The driving unit preferably includes a first driving unit
for driving the first to fourth image bearing bodies at the same
time; and a second driving unit for driving the supporting rollers
independently.
[0132] The first driving unit preferably includes a plurality of
driving gears provided to correspond to the plurality of image
bearing bodies, respectively, rotating altogether in association
with each other, and each having a driven coupler at one end to
engage with the driven coupler; and a first driving motor for
providing a driving force to drive the plurality of driving gears
at the same time.
[0133] The first and second image bearing bodies are preferably
mounted to satisfy the first equation of equations 2-1, and satisfy
.alpha.1=.alpha.2.
[0134] The first and third image bearing bodies are preferably
mounted to satisfy the third equation of equations 2-1, and satisfy
.alpha.1=.alpha.3.
[0135] The first and fourth image bearing bodies are preferably
mounted to satisfy the third equation of equations 2-1, and satisfy
.alpha.1=.alpha.4.
[0136] The first to fourth image bearing bodies are preferably
mounted to satisfy all of the equations 2-1, and satisfy
.alpha.1=.alpha.2=.alpha.3=- .alpha.4.
[0137] According to yet another aspect of the present invention, an
image forming apparatus preferably includes a plurality of image
bearing bodies arranged in a predetermined sequence, and having a
radial displacement, and also having an interval A having a maximum
radial displacement; an intermediate transfer medium running in
contact with each of the plurality of image bearing bodies; and a
plurality of supporting rollers for guiding the running of the
transfer medium while supporting the transfer medium, and having a
radial displacement in which the radius varies, and also having an
interval B having a maximum radial displacement, wherein, with
reference to a predetermined (X, Y) coordinate system based on the
center of rotation of the supporting rollers and the image bearing
rollers, the image bearing bodies and the supporting rollers are
mounted to satisfy one of the following equations:
[0138] [Equation Set 4]
Rd.multidot..theta.d=(2.pi..multidot.l+.theta.ox).multidot.Rox(1.+-.0.05)
(l=1, 2, 3, . . . ), (x=1, 2, 3, . . . ), Rd=z.multidot.Rox, (z=2,
3, 4, 5, . . . ) {circle around (1)}
Rd.multidot..theta.d=Rox.multidot..theta.ox.multidot.(1.+-.0.05)
Rd=.theta.ox, (x=1, 2, 3, . . . ) {circle around (2)}
(2.pi..multidot.h+.theta.d).multidot.Rd=Rox.multidot..theta.ox.multidot.(1-
.+-.0.05)
(h=1, 2, 3, . . . ), (x=1, 2, 3, . . . ), Rox=k.multidot.Rd, (k=2,
3, 4, 5, . . . ) {circle around (3)}
[0139] where, .theta.d is the angle of center of the interval B in
the direction of reverse rotation of the supporting rollers along
the axis +X of the (X, Y) coordinate system,
[0140] .theta.ox is the angle measured from the axis +Y of the
(x)th image bearing body in the running direction of the
intermediate transfer medium to the center of the interval A in the
reverse rotational direction of the image bearing body,
[0141] Rox is the radius of the (x)th image bearing body, and
[0142] Rd is the radius of the supporting rollers.
[0143] The axis +X is preferably defined to be parallel with
reference to the running direction of the intermediate transfer
medium, such thatwhen the center of the interval B is positioned on
the axis +X, the speed change of intermediate transfer medium
reaches a maximum.
[0144] When the radius of the supporting rollers is larger than the
radius of the image bearing bodies by an integer multiple, the
integer being 2 or more, the image bearing bodies and the
supporting rollers are preferably arranged to satisfy the first
equation of Equation Set 3.
[0145] When the radius of the image bearing bodies equal the radius
of the supporting rollers, the image bearing bodies and the
supporting rollers are preferably arranged to satisfy the second
equation of Equation Set 3.
[0146] When the radius of the image bearing bodies is larger than
the radius of the supporting rollers by an integer multiple, the
integer being 2 or more, the image bearing bodies and the
supporting rollers are preferably arranged to satisfy the third
equation of Equation Set 3.
[0147] A driving unit is preferably provided for driving the image
bearing bodies and the supporting rollers, and the image bearing
bodies each preferably have a driven coupler at one end to receive
a driving force in connection with the driving unit.
[0148] The driven couplers each preferably have a positioning part
for determining a position of engagement with the driving unit, and
the driven couplers are preferably engaged such that the intervals
A1, A2, A3 and A4 of the respective image bearing bodies are formed
at a predetermined angle with respect to the positioning parts.
[0149] The first driving unit preferably includes a plurality of
driving gears provided to correspond to the plurality of image
bearing bodies, respectively, rotating altogether in association
with each other, and each having a driven coupler at one end to
engage with the driven coupler; and a first driving motor for
providing a driving force to drive the plurality of driving gears
at the same time.
[0150] The second driving unit preferably includes a driving gear
provided to correspond to the supporting rollers, and having a
driving coupler at one end for engagement with the driven coupler
which is provided at an end of each of the supporting rollers; and
a second driving motor for driving the driving gear.
BRIEF DESCRIPTION OF THE DRAWINGS
[0151] The above aspects and features of the present invention will
be more apparent by describing certain embodiments of the present
invention with reference to the accompanying drawings, in
which:
[0152] FIG. 1 is a schematic view showing the structure of a
conventional color image forming apparatus;
[0153] FIG. 2 is a schematic view illustrating the structure of an
image forming apparatus according to an embodiment of the present
invention;
[0154] FIG. 3 is a perspective view of a driving unit of FIG.
2;
[0155] FIG. 4A is a perspective view showing an image bearing body
disassembled;
[0156] FIG. 4B is a perspective view showing a driving coupler of
FIG. 3;
[0157] FIG. 4C is a perspective view of a driving roller of FIG.
2;
[0158] FIG. 5 is a perspective view of an image bearing body and a
driving coupler of FIG. 4A according to another embodiment of the
present invention;
[0159] FIG. 6 is a schematic view of a radial displacement caused
due to manufacturing tolerances of the image bearing body and the
driving roller of FIG. 2;
[0160] FIG. 7A is a view of the process of monitoring an end of the
image bearing body of FIG. 4A;
[0161] FIG. 7B is a view of the process of assembling the image
bearing bodies of FIG. 4A;
[0162] FIG. 8A is a schematic structure view of an image forming
apparatus according to a first embodiment of the present
invention;
[0163] FIGS. 8B and 8C are graphs provided to illustrate image
error caused due to manufacturing tolerances in the radius of the
driving roller in the state of FIG. 8A;
[0164] FIG. 9A is a structure view of a conventional image forming
apparatus;
[0165] FIG. 9B is a graph of an image error caused due to
manufacturing tolerances in the radius of the driving roller in the
image forming apparatus shown in FIG. 9A;
[0166] FIG. 10A is a schematic structure view of an image forming
apparatus according to a second embodiment of the present
invention;
[0167] FIG. 10B is a graph of an image error caused due to
manufacturing tolerances in the radius of the driving roller in the
state of FIG. 10A;
[0168] FIG. 11A is a schematic structure view provided for
explanation of another conventional printer;
[0169] FIG. 11B is a graph of an image error caused due to
manufacturing tolerances in the radius of the driving roller in the
state of FIG. 11A
[0170] FIG. 12A is a schematic structure view showing an image
forming apparatus according to a third embodiment of the present
invention;
[0171] FIG. 12B is a graph of an image error caused due to
manufacturing tolerances in the radius of the driving roller in the
state of FIG. 12A;
[0172] FIG. 13 is a structure view of a main part of a conventional
image forming apparatus;
[0173] FIGS. 14A to 14D are schematic views of an image error
caused due to image bearing bodies having radial displacement;
[0174] FIG. 14E is a view of an overlay of image errors which are
caused due to the radial displacement of each image bearing
body;
[0175] FIG. 15A is a schematic structure view of a conventional
image forming apparatus in which an image bearing body having a
radial displacement is employed;
[0176] FIG. 15B is a graph of an image error caused due to the
image bearing bodies of FIG. 15A;
[0177] FIG. 16A through 16D are a schematic structure views of an
image forming apparatus according to a third embodiment of the
present invention;
[0178] FIG. 17A is a schematic perspective view of a jig which is
provided for setting an image bearing body according to an
embodiment of the present invention;
[0179] FIG. 17B is a schematic perspective view of another example
of a jig which is provided for setting an image bearing body
according to an embodiment of the present invention;
[0180] FIG. 18A is a view showing an example in which the driving
roller is larger than the image bearing body;
[0181] FIG. 18B is a graph of an image error caused due to the
driving roller and the image bearing body in the state of FIG.
18A;
[0182] FIG. 18C is a schematic structure view provided for
explanation of an image forming apparatus according to a fourth
embodiment of the present invention;
[0183] FIG. 18D is graph showing an image error caused due to the
driving roller and the image bearing body in the state of FIG.
18C;
[0184] FIG. 19A is a view showing an example where the radii of the
driving roller and the image bearing body are equal;
[0185] FIG. 19B is a graph showing an image error caused due to the
image bearing body and the driving roller in the state of FIG.
19A;
[0186] FIG. 19C is a schematic structure view of an image forming
apparatus according to a fifth embodiment of the present
invention;
[0187] FIG. 19D is a graph provided for explanation of an image
error caused due to the driving roller and the image bearing body
in the state of FIG. 19C;
[0188] FIG. 20A is a schematic structure view showing an example
where the radius of the image bearing body is larger than that of
the driving roller;
[0189] FIG. 20B is a graph provided for explanation of an image
error caused due to the driving roller and the image bearing body
in the state of FIG. 20A;
[0190] FIG. 20C is a schematic structure view provided for
explanation of an image forming apparatus according to an sixth
embodiment of the present invention;
[0191] FIG. 20D is a graph provided for explanation of an image
error caused due to the driving roller and the image bearing body
in the state of FIG. 20C;
[0192] FIG. 21A is a schematic structure view provided for
explanation of an image forming apparatus according to a seventh
embodiment of the present invention;
[0193] FIG. 21B is a schematic view of an image error caused due to
the driving roller in the state of FIG. 21A;
[0194] FIG. 21C is a schematic view of an image error caused due to
the image bearing body in the state of FIG. 21A;
[0195] FIG. 21D is a view provided for explanation of an overlay of
image errors which are caused due to the image bearing body and the
driving roller in the state of FIG. 21A;
[0196] FIG. 22A is a structure view provided for explanation of an
image forming apparatus according to an eighth embodiment of the
present invention;
[0197] FIG. 22B is a schematic view of an image error caused due to
the driving roller in the state of FIG. 22A;
[0198] FIG. 22C is a schematic view of an image error caused due to
the image bearing body in the state of FIG. 22A;
[0199] FIG. 22D is a schematic view of an overlay of image errors
which are caused due to the image bearing body and the driving
roller in the state of FIG. 22A;
[0200] FIG. 23A is a structure view of an image forming apparatus
according to a ninth embodiment of the present invention;
[0201] FIG. 23B is a schematic view of an image error caused due to
the driving roller in the state of FIG. 23A;
[0202] FIG. 23C is a schematic view of an image error caused due to
the image bearing body in the state of FIG. 23A; and
[0203] FIG. 23D is a schematic view of an overlay of image errors
which are caused due to the image bearing body and the driving
roller in the state of FIG. 23A.
[0204] It should be understood that throughout the drawings, like
reference numbers are used to depict like elements features and
structure.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0205] Certain exemplary embodiments of the present invention will
now be described in greater detail with reference to the
accompanying drawings.
[0206] The matters defined in the description such as a detailed
construction and elements are provided to assist in a comprehensive
understanding of the invention. Thus, it should be apparent to
those of ordinary skill in the art that various changes and
modifications can be made to the exemplary embodiments described
herein without departing from the scope and spirit of the
invention. Also, descriptions of well-known functions or
constructions are omitted for clarity and consiceness in describing
exemplary embodiments of the present invention.
[0207] Referring to FIG. 2, an image forming apparatus according to
an embodiment of the present invention includes a plurality of
rotary rollers 30, 40, 50, 60, a belt 70 disposed to run in contact
with the plurality of rotary rollers 30, 40, 50, 60, a plurality of
supporting rollers 80, 91 to support the belt 70, and a driving
unit 100.
[0208] In the embodiment illustrated in FIG. 2, the plurality of
rotary rollers 30, 40, 50, 60 are exemplified as organic
photoconductors (OPCs) which are provided to transfer each of the
color images onto the belt 70 in a certain sequence. More
specifically, in the following description of an exemplary
embodiment, there are four rollers, that is, there are four OPCs
30, 40, 50, 60 disclosed to independently transfer to the belt 70
color images which typically include black (K), cyan (C), magenta
(M) and yellow (Y) color images in an overlaying manner.
[0209] Additionally, in this particular example of an exemplary
embodiment of the present invention, the respective OPCs 30, 40,
50, 60 sequentially transfer the black, cyan, magenta and yellow
color images onto the belt 70 as an overlay of a color image along
the running direction of the belt 70 (The OPCs 30, 40, 50, 60
rotate in a clockwise direction in this example).
[0210] It will be understood that the following described features
of an exemplary embodiment of the present invention are equally
applicable to other situations such as when there are more or fewer
than four OPCs 30, 40, 50, 60 employed. One of ordinary skill in
the art will also understand that the respective OPCs 30, 40, 50,
60 can be arranged along the running direction of the belt 70, in a
different sequence from that which is described herein.
[0211] Developing units 26, 27, 28, 29 for the respective colors
are disposed near, and preferably below the OPCs 30, 40, 50, 60, to
form images in each color on the outer circumference of the OPCs
30, 40, 50, 60. Any suitable generally-known structures can be
applied as the developing units 26, 27, 28, 29, and one will
appreciate that the present invention is not limited to the
structures of the developing units 26, 27, 28, 29 described with
reference to the exemplary embodiment.
[0212] The belt 70 is supported by the driving roller 80, the
supporting roller 91 and a plurality of T1 rollers 93 to run in a
predetermined direction. The belt 70 is run by the rotational force
of the driving roller 80 and receives color images from each of the
OPCs 30, 40, 50, 60 in an overlaying manner. As a result, a full
color image is formed and then transferred onto a printing medium
97 which is passed between the belt 70 and the T2 roller 95. The
driving roller 80 is connected with the driving unit 100 and
receives the driving force from the driving unit 100 to move the
belt 70. The supporting roller 91 may be elastically biased toward
the belt 70 so as to support the belt 70 with a constant
tension.
[0213] Referring to FIGS. 2 and 3, the driving unit 100 includes a
frame 110, a first driving part 101 provided on the frame 110 that
drives the OPCs 30, 40, 50, 60, and a second driving part 103 that
drives the driving roller 80.
[0214] The frame 110 includes a front frame 111 and a rear frame
112 coupled in substantially parallel relation with each other.
[0215] The first driving part 101 includes a first driving motor
121 installed on the frame 110, first main gears, that is, first
through fourth driving gears 123, 124, 125, 126 for each of the
colors corresponding to the OPCs 30, 40, 50, 60, and first driving
couplers 133, 134, 135, 136 provided at the rotational axes of the
first through fourth driving gears 123, 124, 125, 126,
respectively. The first through fourth driving gears 123, 124, 125,
126 are arranged at predetermined intervals, and disposed to rotate
between the frames 111 and 112. Reference numeral 122 of FIG. 2
denotes a shaft gear which is provided to the driving shaft of the
driving motor 121 and drives the respective driving gears 124 and
125. Additionally, reference numeral 127 denotes an idle gear which
moves the driving gears 123, 124, 125, 126 in association with each
other. One driving motor 121 is positioned approximately in the
middle of the four driving gears 123, 124, 125, 126 to rotate the
driving gears 123, 124, 125, 126 in the same direction.
[0216] The first through fourth driving couplers 133, 134, 135, 136
of each color are rotated together with the driving gears 123, 124,
125, 126. The first through fourth driving couplers 133, 134, 135,
136 are constructed such that each is engaged with a driven coupler
at one end of each OPC 30, 40, 50, 60 to transmit driving force.
The driving couplers 133, 134, 135, 136 and driven couplers will be
described in greater detail below.
[0217] The second driving part 103 includes a second driving motor
141 installed on the frame 110, a second main gear, that is, a
fifth driving gear 143 rotatably placed between the frames 111 and
112 and rotated by the second driving motor 141, and a fifth
driving coupler 145 provided at the rotational axis of the fifth
driving gear 143. The fifth driving gear 143 is preferably driven
separately from the first through fourth driving gears 123, 124,
125, 126. The fifth driving coupler 145 is rotated together with
the fifth driving gear 143, and is configured such that it is
complimentarily engaged with the driven coupler at the driving
roller 80 to transmit the driving force. In the exemplary
embodiment, all of the first through fifth driving couplers 133,
134, 135, 136 and 145 are shown to have identical coupling
structures. In addition, other structures of the OPCs 30, 40, 50,
60, and in particular, the structure of the driven couplers can be
understood to be substantially identical in this embodiment.
Accordingly, for the sake of brevity, only the K color OPC 30 and
the first driving coupler 133 will be described as a representative
example of the others. Similarly, description of the first driven
coupler 133 can appropriately replace that of the fifth driving
coupler 145 corresponding to the driving roller 80.
[0218] Meanwhile, being consumables, the OPCs 30, 40, 50, 60 have
limited lifespans that expire when used more than a predetermined
number of times. The OPCs 30, 40, 50, 60 may be separately
installed, or in an alternative example, formed integrally with the
developing units 26, 27, 28, 29 and removably placed in the image
forming apparatus body 25.
[0219] The OPCs 30, 40, 50, 60 are rotated by the driving force
transmitted from the driving unit 100. The OPCs 30, 40, 50, 60 are
each joined with a passive-driven coupling structure for
complimentary mating with the first through fourth driving couplers
133, 134, 135, 136 so that the OPCs 30, 40, 50, 60 receive driving
force from the driving unit 100 when mounted in the image forming
apparatus body 25. Since the respective OPCs 30, 40, 50, 60 can
have essentially the same structure, only the K color OPC 30 for
forming an image in black (K) as shown in FIG. 4A will be
representatively explained below.
[0220] Referring to FIG. 4A, the K color OPC (hereinafter, `OPC`)
30 includes a cylindrical drum body 31, and a driven coupler 33
engaged with one end of the drum body 31. The drum body 31 is
preferably formed of metal material such as stainless steel, and
preferably has the configuration of a cylinder with both ends open.
A photoconductive layer is preferably coated or applied to the
outer circumference of the drum body 31.
[0221] In an exemplary embodiment, one end of the driven coupler 33
is press-fit to an end of the drum body 31. At the other end, the
driven coupler 33 is provided with a coupling part 33a with
non-circular cross section, and a positioning part 33b protruding
from a side of the coupling part 33a with a predetermined shape.
The coupling part 33a is mated with the first driving coupler 133,
shown in FIG. 4B, of the driving unit 100 to transmit driving
force. The positioning part 33b determines the position of the
driven coupler 33, that is, determines a coupling angle of the OPC
30 with respect to the first driving coupler 133. The same
structures as that of the first driven coupler 33 are applied to
the other OPCs 40, 50, 60 and therefore, only the first driven
coupler 33 of the K color OPC 30 will be representatively explained
below.
[0222] The first driven coupler 33 preferably also includes a shaft
33c protruding along the rotational axis of the coupling part 33a.
The shaft 33c is coupled to the shaft hole 133c, shown in FIG. 4B,
of the first driving coupler 133, to guide the first driving
coupler 133 and the first driven coupler 33 to coaxially mated with
each other.
[0223] The first driving coupler 133 preferably also includes a
coupling part 133a sunken from the end in a non-circular
configuration, a positioning part 133b sunken from an inner side of
the coupling part 133a, and a shaft hole 133c. The coupling part
133a is configured in correspondence with the coupling part 33a of
the driven coupler 33, and the positioning part 133b is configured
in correspondence with the positioning part 33b of the driven
coupler 33.
[0224] As shown in FIG. 4C, the driving roller 80 includes a roller
body 81, and a driven coupler 83 coupled with an end of the roller
body 81. The driven coupler 83 may have the same structure as the
driven coupler 33 of the OPC 30 of FIG. 4A. More specifically, the
driven coupler 83 includes a coupling part 83a of a non-circular
cross section, and a positioning part 83b protruding from a side of
the coupling part 83a. The driven coupler 83 of the driving roller
80 is coupled to the fifth driving coupler 145 as shown in FIG. 3.
Because the driven coupler 83 has a substantially identical
configuration as that of the driven coupler 33 of FIG. 4A, the
fifth driving coupler 145 may have essentially the same structure
as that of the first driving coupler 133 which is engaged with the
driven coupler 30. Accordingly, description about the fifth driving
coupler 145 can be replaced with the description about the first
driving coupler 133 described with reference to FIG. 4B.
[0225] The roller body 81 of the driving roller 80 has a
predetermined radius Rd, and a circumference of
Sd=2.pi..multidot.Rd. The circumference `Sd` of the driving roller
80 may be the same or different than the circumference of the OPCs
30, 40, 50, 60, and the detailed operation and effect of each case
will be explained below.
[0226] The first through fourth driving couplers 133, 134, 135, 136
and the driven coupler 33 are preferably configured in an opposing
manner. More specifically, as shown in FIG. 5, the driven coupler
233 is formed on one end of the roller body 231 of the OPC 230, and
the driven coupler 233 preferably has a coupling part 234 sunken in
a non-circular configuration, and a positioning part 235 extending
from the coupling part 234. In this case, the driving coupler 330
corresponding to the driven coupler 233 of the OPC 230 preferably
has, as shown in FIG. 5, a coupling part 331 protruding from an end
in a non-circular configuration, and a positioning part 332
protruding from a side of the coupling part 331. The positioning
part 332 is complimentarily mated with the positioning part 235 of
the driven coupler 233. The driven coupler 233 preferably has a
shaft hole 236, while the driving coupler 330 preferably has a
shaft 233 for complimentary mating with the shaft hole 236.
[0227] In other words, the driven coupler 233 is preferably formed
in a concave manner in the end of the OPC 30, while the end of the
driving coupler 330 corresponding to the driven coupler 233 is
preferably configured in a convex manner. The exemplary embodiment
of FIG. 5 is preferably applied to all of the OPCs 30, 40, 50, 60,
and all of the first through fourth driving couplers 133, 134, 135,
136.
[0228] Although not shown, the structure of the coupler as shown in
FIG. 5 can be applied to the driving roller 80 and the fifth
driving coupler 145 as well. Also, although not described in
detail, a variety of coupler structures can be applied to the
supporting roller 91 as well.
[0229] Meanwhile, the bodies of the rollers such as OPCs 30, 40,
50, 60 or the driving roller 80 are typically mass-produced using a
metal molding process, as is known in the art. An important aspect
in mass-producing roller bodies, that is, in the mass-production of
the drum bodies, is to achieve a perfect circle along the outer
circumference. However, perfect circles have yet to be achieved,
andthere are always tolerances or errors during processing, which
result in the drum body having an imperfect cross section. This
will now be explained in greater detail with reference to the
organic photoconductor 30 as a representative example.
[0230] FIG. 6 illustrates in exaggerated fashion, a `runout`
occurring in the outer circumference of the drum body 31, which is
a radial displacement of the drum body 31 in a predetermined
interval. More specifically, the runout causes a radial
displacement .delta.o, which is a varyation in the radius according
to a rotational cycle of the OPC 30. The radial displacement
.delta.o can be defined by the maximum and minimum values of
variations in the nominal radius appearing as a sinusoidal curve in
one rotational cycle of the drum body 31, that is, in one
rotational cycle of the OPC 30. In this particular embodiment, the
maximum radial displacement of the roller body 31 is +.delta.o, and
the minimum radial displacement is -.delta.o. Additionally, as
shown in FIG. 6, the interval A is defined with reference to the
maximum radial displacement +.delta.o, which contributes to an
image error as will be described below. The range of the interval A
is variable according to the size of the radial displacement
.delta.o.
[0231] As described above, an operator needs to know the interval A
in order to control any influence of the roller body 31 cause by
radial displacement .delta.o. To this end, as shown in FIG. 4A, the
roller body 31 may be indicated with a mark 31a for indication of
the location of interval A. The mark 31a may be formed on the outer
or inner circumference of the roller body 31 to correspond to the
center of the interval A. As can be appreciated, the mark 31a could
also be formed at any predetermined angle away from the center of
the interval A, and still identify the location of interval A.
[0232] As described above, by marking the interval A, the operator
can regulate the relative orientation between the centers of the
positioning part 33b of the driven coupler 33 and the interval A
during assembly of the driven coupler 33 with respect to the drum
body 31. In other words, as shown in FIGS. 4A and 6, marks 31a are
preferably uniformly formed during the manufacturing process at a
position 45 degrees (+45.degree.) away from the center of the
interval A in the rotational direction of the OPC. Then the
positioning part 33b is aligned with the mark 31a, and the drum
body 31 and the driven coupler 33 are engaged with each other. By
assembling all the OPCs in the above-described manner, the
positioning parts 33b of multiple rollers can be positioned in the
same location with respect to the interval A.
[0233] A variety of methods can be employed to align the
positioning part 33b with the mark 31a. For example, as shown in
FIG. 7A, the respective ends of the drum body 31 may be captured
through a camera (not shown), and a captured image may be displayed
through a screen of a predetermined monitor 200. Reference
coordinates (x, y) may be set on the screen 210, together with a
reference complete circle 211. By placing such that the reference
coordinates (x, y) overlap the reference complete circle 211, the
center of the interval A of the captured image, that is, the
maximum radial displacement +.delta.o can be located. Accordingly,
by adjusting such that the maximum radial displacement +.delta.o is
located 315.degree. in the clockwise direction from the +x axis,
the mark 31a is can preferably be indicated on the outer surface,
or on the end of the drum body 31 at a location which corresponds
to the +x axis.
[0234] Next, as shown in FIG. 7B, the drum bodies 31 bearing marks
31a thereon are supported on a first jig 241, with the marks 31a
being located on the +x axis of the reference (x, y) coordinate
system. The driven coupler 33 is supported on a second jig 242, and
in here too, the driven coupler 33 is arranged such that the
positioning part 33b is positioned on the +x' axis of the reference
coordinate system (x', y'). In such a manner, the two jigs 241, 242
are oppositely arranged such that the reference coordinate systems
(x, y) and (x', y') can be aligned with each other. Then by moving
the two jigs 230, 240 towards each other, the driven couplers 33
are respectively joined with the plurality of drum bodies 31 and
therefore, assembled all at the same time with the same relative
orientations. It is possible that the positioning part 33b is
positioned with respect to the center of the interval A of each
drum body 31. Although it has been described above with reference
to one example where the plurality of OPCs are assembled at the
same time, one will understand that this should not be considered
as limiting, because the OPCs can be assembled separately one by
one with the same relative orientations.
[0235] In another example, a structure is separately prepared in
which the drum body 31 is rotatably supported on the first jig 241.
In this case, separate detecting equipment such as a mark sensor or
a monitor detects whether the mark 31a is positioned on the +x axis
while the drum body 31 is rotated. Accordingly, when the mark 31a
is detected to be positioned on the +x axis, the drum body 31 is
stationed, and coupled with the driven coupler 33 such that the
positioning part 33b is oriented with respect to the mark 31a.
[0236] The OPC 30, after being assembled in the manner as described
above, can be positioned in the center of the interval A, which is
-45 degrees from the positioning part 33b. Accordingly, in
consideration of the fact that the interval A is located in
correspondence with the positioning part 33b, it is possible to
minimize the generation of image errors due to deviations in the
radius of the OPC drum at interval A by controlling the positions
of the OPCs during assembling and installing.
[0237] Although it has been described above that the drum body 31
is assembled with the driven coupler 33 with reference to the
interval A having the maximum radial displacement +.delta.o as an
example, it will be appreciated that the initial position of the
positioning part 33b can also be set with reference to other
intervals, such as an interval having -.delta.o, or .delta.o=0.
[0238] In the manner described above, it should also be understood
that the other color OPCs 40, 50, 60 each have an interval A that
can be oriented -45 degrees away from the positioning parts
33b.
[0239] The driving roller 80 also has a runout as a result of
manufacturing processes, and as shown in FIG. 6, has a maximum
radial displacement +.delta.d in the circumferential direction. The
radial displacement +.delta.d due to runout is, as in the case of
the OPC 30, expressed as a sinusoidal curve in a one rotational
cycle of the driving roller, and can be defined by the maximum and
minimum values thereof. In this particular embodiment, the maximum
radial displacement of the driving roller 80 is +.delta.d, and the
minimum radial displacement is -.delta.d. The interval having the
maximum radial displacement +.delta.d is an interval B. The
interval B also influences image errors (described in detail below)
due to the driving roller 80, and can be defined in a variety of
ways. In the same manner as in the assembling of OPC 30, the
driving roller 80 is oriented such that the positioning part 83b
can be positioned at a predetermined rotational angle from the
center of the interval B by controlling the assembly of the roller
body 81 and the driven coupler 83 during the assembling process. In
the following example, the positioning part 83a of the driven
coupler 83 is located 45 degrees (that is, -45.degree.) from the
center of the interval B in an opposite direction with respect to
the rotation of the driving roller 80.
[0240] Meanwhile, the maximum and minimum radial displacements
.+-..delta.d of the driving roller 80 influences the speed of the
belt 70. In other words, the tangential speed maximizes to Vdmax in
the center of the interval B of the driving roller 80. Accordingly,
when the interval B and the belt 70 contact tightly to the driving
roller 80 and therefore, the positions of force application are
aligned with each other, that is, when the direction of the
tangential speed Vdmax runs parallel with the +y axis as shown in
an imaginary line of FIG. 6, the belt 70 runs at maximum speed.
Accordingly, as the running speed of the belt 70 changes, color
images of the OPCs 30, 40, 50, 60 transferred onto the belt 70 may
be distorted so that the images are stretched, blurred or cut.
Because the belt 70 changes speed periodically in a rotational
cycle, the image error periodically occurs on the belt 70 in
correspondence with the rotational cycle of the driving roller
80.
[0241] Methods according to exemplary embodiments of the present
invention to improve image errors caused due to the radial
displacement Ad of the driving roller 80 will be explained below.
In the following explanation, it is assumed that the OPCs 30, 40,
50, 60 and the supporting roller 91 are free from the runout, and
therefore, the radial displacement of the OPCs 30, 40, 50, 60 is
.delta.o=0. Accordingly, it is assumed that the radial displacement
.delta.d of the driving roller 80 is the only influence on the
image being transferred onto the belt 70. As the first step to
minimize image errors, the influence of the driving roller 80 is
minimized and one example of doing so will be described below.
[0242] First, as described above with reference to FIG. 6, it is
assumed that the center of the interval B of the driving roller 80,
which has the maximum radial displacement +.delta.d, is positioned
on the +45.degree. angle when the rotation of the driving roller 80
from the positioning part 83b is expressed by the unit of +angles.
It should be appreciated that the angle of +45.degree. is a random
interval selected for the convenience of explanation. The driving
roller 80 has a predetermined radius Rd and a circumference
Sd=2.pi..multidot.Rd. With the driving roller 80 with the radial
displacement .delta.d being arranged, the OPCs 30, 40, 50, 60 are
arranged to satisfy one of the following six conditions of
equations 1 to reduce image error of the image being overlain on
the belt 70:
[0243] [Equation Set 1]
L1=l.multidot.Sd.multidot.(1.+-.0.05)(l=1, 2, 3, . . . ) (1)
L2=m.multidot.Sd.multidot.(1.+-.0.05)(m=1, 2, 3, . . . ) (2)
L3=n.multidot.Sd.multidot.(1.+-.0.05)(n=1, 2, 3, . . . ) (3)
L4=o.multidot.Sd.multidot.(1.+-.0.05)(o=1, 2, 3, . . . ) (4)
L5=p.multidot.Sd.multidot.(1.+-.0.05)(p=1, 2, 3, . . . ) (5)
L6=q.multidot.Sd.multidot.(1.+-.0.05)(q=1, 2, 3, . . . ) (6)
[0244] Referring to FIG. 2, the distance between the centers C1, C2
of first and second driving gears 123, 124 is L1, the distance
between the centers C2, C3 of second and third driving gears 124,
125 is L2, the distance between the centers C3, C4 of third and
fourth driving gears 125, 126 is L3, the distance between the
centers C1, C3 of first and third driving gears 123, 125 is L4, the
distance between the centers C1, C4 of first and fourth driving
gears 123, 126 is L5, and the distance between the centers C2, C4
of second and fourth driving gears 124, 126 is L6.
[0245] Driving couplers 133, 134, 135, 136 are provided to the
respective driving gears 123, 124, 125, 126, and the OPCs 30, 40,
50, 60 are rotatably engaged with the driving couplers 133, 134,
135, 136. Accordingly, the centers C1, C2, C3, C4 are aligned with
the center of rotation of each of the OPCs 30, 40, 50, 60.
Accordingly, it can be understood that the OPCs 30, 40, 50, 60 are
arranged to satisfy at least one of the equations 1. Of course, L1
refers to the distance between the centers C1, C2 of the K color
OPC 30 and the C color OPC 40, L2 refers to the distance between
the centers C2, C3 of the C color OPC 40 and the M color OPC 50, L3
refers to the distance between the centers C3, C4 of the M color
OPC 50 and the Y color OPC 60, L4 refers to the distance between
the centers C1, C3 of the K color OPC 30 and the M color OPC 50, L5
refers to the distance between the centers C1, C4 of the K color
OPC 30 and the Y color OPC 40, and L6 refers to the distance
between the centers C2, C4 of the C color OPC 40 and the Y color
OPC 60.
[0246] Accordingly, by setting the image forming apparatus system
to satisfy at least one of the equations in Equation Set 1, image
errors due to variations in the radius of the driving roller 80 can
be reduced. FIG. 2 shows a preferred embodiment in which the OPCs
30, 40, 50, 60 are arranged to satisfy all the equations in
Equation Set 1, such that L1=L2=L3=Sd.
[0247] Image errors occur frequently on the image on the belt 70
due to the interval B of the driving roller 80 when the OPCs 30,
40, 50, 60 are arranged to satisfy none of the equations 1, and
this will be described in detail below. In the following three
examples, the radius Rd of the driving roller 80 and the radius Ro
of the OPCs 30, 40, 50, 60 are mainly considered.
[0248] FIG. 8A shows the first example where the driving roller 80
has a bigger radius than the OPC rollers 30, 40, 50, 60 (Rd>Ro).
In the example of FIG. 8A, the OPCs 30, 40, 50, 60 do not satisfy
any of the equations in Equation Set 1. In other words, distances
between any two of the centers C1, C2, C3, C4 of the respective
OPCs 30, 40, 50, 60 are not integer multiples of the circumference
Sd of the driving roller 80.
[0249] With reference to FIG. 8A, it is assumed that the K color
image is initially transferred with the center of the interval B
being positioned at .theta.d (+135.degree.) along the axis +X. As
shown in FIG. 8B, the radial displacement .delta.d repeats in a
sinusoidal manner according to the running distance of the belt 70,
and the interval B appears once in every rotational cycle of the
driving roller 80. With reference to FIG. 8A, it is assumed that
the K image transfer starts from the location F0, and one
rotational cycle of the driving roller 80 starts from when the
location f0 is simultaneously positioned on the axis +x. As shown
in FIG. 8B, the center of the image error Rke of the K image caused
due to the interval B, is centered at the location which is
distanced apart from the location F0 as much as
Rd.multidot..theta.d.
[0250] When the length of the image transferred by each image
bearing body is short enough, that is, when the location F1 where
the K image transfer ends, and the location F2 where the C image
starts transfer, are aligned with each other, the interval of C
image transfer is not influenced by the interval B. Therefore, no
image error due to the interval B does not occur in the C image. In
other words, the K image transfer ends before the belt 70 moves by
the distance of 1 Sd, and the C image transfer starts. Because the
location F3 where the C image transfer ends, is positioned before
the belt 70 moves from the location F0 by the distance of
Sd+Rd.multidot..theta.d, no image error occurs in the C image.
[0251] Next, when it is assumed that the M image transfer location
F4 is the same as the location F3, an image error Rme occurs in the
M image due to the interval B at the location which is a
predetermined distance away from the location F4. Because the
distance L4 is not an integer multiple of Sd, the M image transfer
start location F4 is positioned after one rotational cycle of the
driving roller 80 and the running of the belt 80 as much as t1 from
the location f1 where the second rotational cycle of the driving
roller 80 starts. When the respective color image transfer
intervals are represented in a unit image area P1, the M image
error Rme occurs at different locations from the starting line SL
of the unit image area P1. In other words, two image errors Rke,
Rme appear in the unit image area P1 at a distance apart from one
another by Rd.multidot..theta.d-t1.
[0252] According to the same principle, the location F5 where the M
image transfer ends, and the location F6 where the Y image transfer
starts, are positioned before the belt 70 is run as much as 2Sd,
that is, before the driving roller 80 completes a second rotational
cycle. Accordingly, an image error Rye due to the interval B also
occurs in the Y image. Here, because the Y image transfer start
location F6 is positioned a predetermined distance (t2) from the
location f2 where the second rotational cycle of the driving roller
80 starts, the center of the Y image error Rye occurs away from the
starting line SL by t2+Rd.multidot..theta.d.
[0253] As explained above, when Rd>Ro, there may be a color
image such as a C image, which is not influenced by the interval B
of the driving roller 80 because the OPC rollers complete
revolutions more often than the larger driving roller. Accordingly,
a color OPC 40 which corresponds to the error-free color image,
needs not be considered, but at least two of the
respectively-spaced image errors Rke, Rme, Rye should be aligned
with each other to reduce the frequency of image error occurrence
within the unit image area P1. In the following description, a
method of aligning the K and M image errors Rke, Rme will be
described as one example of the present invention.
[0254] In order to align the two image errors Rke, Rme, the system
is realized to satisfy the fourth equation of the equation set 1.
That is, a distance between the centers C1, C3 of the two OPCs 30,
50 may be set to L4=o.multidot.Sd(o=1, 2, 3, . . . ). To this end,
as indicated by an imaginary line in FIG. 8A, the OPC 50 is
positioned with its center C3 being distanced from the center C1 by
oSd with o=1.
[0255] Accordingly, as the system is set as described above, if the
K image starts to be transferred, the center of the K image error
Rke occurs away from the starting line SL as much as
Rd.multidot..theta.d. The C image is free from an image error as
mentioned above with reference to FIG. 8B.
[0256] Meanwhile, as shown in FIG. 8C, because the center C3 of the
M OPC 50 is positioned at a 1Sd location, that is, at a location f1
where the second rotational cycle of the driving roller 80 starts,
the M image transfer starting location F4 precedes the location F3
where the C image transfer ends. The location F4 is same as the
location f1. Accordingly, the center of the M image error Rme due
to the interval B occurs away from the starting line SL of the unit
image area P1 as much as Rd.multidot..theta.d . As a result, the K
and M image errors Rke, Rme are overlapped at the same relative
location. Because the frequency of image error occurrences can be
reduced in a final form of color image being printed, a higher
quality print is possible. A Y image error Rye has not been
considered in this description. The Y image error Rye may occur at
a different location from the K and M image errors Rke, Rme as
described above with reference to FIG. 8B.
[0257] Of course, the Y image error Rye can also be aligned with
the other image errors, by establishing the system to satisfy the
fourth and third equations of Equation Set 1, or by establishing
the system to satisfy the fourth and fifth equations of Equation
Set 1. The principle according to which K, M, Y image errors Rke,
Rme, Rye are overlapped by satisfying the above conditions, can be
easily understood from the above-mentioned process of aligning the
two image errors. Therefore, a detailed description thereof will be
omitted for the sake of brevity.
[0258] In this particular embodiment, the transfer intervals of
each of the color OPCs 30, 40, 50, 60 are randomly set, and also
the starting and ending points of color images are randomly set for
the convenience of explanation. Accordingly, one will appreciate
that the above particular case should not be construed as limiting.
Various examples are possible under the condition of Rd>Ro, and
the number of image errors of a unit image area can variously
change. It is only clear that, regardless of the number of image
errors, at least two image errors should aligned with each other by
satisfying at least one of the equations in Equation Set 1 to
reduce the total number of occurrences of image errors due to
variations in the radius of the driving roller 80.
[0259] Furthermore, although FIG. 8A depicts that the variable o=1
in the fourth equation of the Equation Set 1, this is just one
example, and it will be appreciated that the same effect is
obtained when the variable o is an integer number which is equal to
or greater than 1.
[0260] A second example of the first step will now be described. As
shown in FIG. 9A, a first example of image errors is described when
none of the equations of Equation Set 1 are met and the driving
roller radius is equal to the OPC roller radius (Rd=Ro), followed
by the description of a method of reducing the image error by
satisfying at least one of the equations in Equation Set 1.
[0261] Referring first to FIG. 9A, it is assumed that the K color
image starts to be transferred when +.delta.d, that is, when the
center of the interval B is at a location .theta.d (135.degree.)
with reference to the axis +X. As shown in FIG. 9B, an image error
Rke due to the interval B occurs away from the K image transfer
starting line SL by a distance of m1=Rd.multidot..theta.d . That
is, the starting line SL of the K image starts from the location
F0, and when the starting line SL reaches the location F1 where the
K image transfer is completed (based on the assumption that one
unit image is completed with one rotational cycle of the driving
roller 80), the center of the interval B of the driving roller 80
is at the initial location (that is, 135.degree. of axis X) as
shown in FIG. 9A. Here, because the distance L1 between the centers
C1, C2 of the two OPCs 30, 40 is longer than the circumference Sd
of the driving roller 80 as much as t3, the belt 70 moves further
from the location F1 by the interval of t3, and the C color image
starts transfer from the location F2. It is assumed for purposes of
illustration that the rotational angle of the driving roller 80
corresponding to the interval t3 is 45.degree.. In this case, the
center of the image error Rce of the C image due to the interval B
occurs away from the location F1 as much as Rd.multidot..theta.d,
but in consideration of the fact that the actual starting line SL
of the C image is F2, the center of the image error Rce occurs away
from the starting line SL of the unit image area P1 as much as
m2=Rd.multidot..theta.d-t3=Rd.multidot.(.theta.d-45.degree.)=Rd.multid-
ot.90.degree.. Accordingly, the distance between the centers of the
two image errors Rke, Rce are away from the unit image area as much
as t3=Rd.multidot.90.degree..
[0262] Additionally, because the distance L2 between the centers
C2, C3 of the C and M OPCs 40, 50 is longer than Sd as much as t3,
the M image starts to be transferred onto the belt 70 when the belt
70 moves from the location F3 where the C image transfer ends, by
t3=Rd.multidot.45.degree.- . The location F4 is at a distance 2t3
from the starting point f2 of the second rotational cycle of the
driving roller 80. Accordingly, when considering the fact that the
center of the M image error Rme due to the interval B occurs at a
distance that the belt 70 is run from the location f2 by
Rd.multidot..theta.d, the actual center of the M image error Rme
occurs away from the starting line SL of the M unit image area P1
by
m3=Rd.multidot..theta.d-2t3=m1-2Rd.multidot.45.degree.=Rd(.theta.d-90.deg-
ree.)=Rd.multidot.45.degree.. As a result, the M image error Rme
occurs at a different location of the unit image area P1 from the K
and C image errors Rke, Rce.
[0263] Referring to FIG. 9A, the distance between the centers C3,
C4 of the M and Y OPCs 50, 60 is exemplified as L3=Sd+2t3. In this
case, the starting point f3 of the third rotational cycle of the
driving roller 80 precedes the location F5 where the M image
transfer ends, by the interval of 2t3. Because the distance of the
two OPCs 50, 60 is further distanced than Sd by the interval of
2t3, the transfer of Y image starts from the location F6 where the
belt 70 is moved further from the location F5 by the interval of
2t3. The location F6 is where the belt 70 is moved from the
location f3 by the interval of 4t3. Accordingly, an image error due
to the interval B does not occur in the third rotational cycle of
the driving roller, and Y image error Rye occurs from a location
which is distanced from the starting location f4 of the fifth
rotational cycle by m1=Rd.multidot..theta.d. The Y image error Rye
occurs because the location f4 is in the Y image transfer interval.
In this situation, the Y image error Rye occurs at a location F6,
which is distanced from the starting line SL of the unit image area
P1 as much as
m4=Sd+m1-4t3=Rd.multidot.2.pi.+Rd.multidot..theta.d-4Rd.multidot.45.degre-
e.=Rd(2.pi.-45.degree.). Because the Y image error Rye occurs in
the unit image area P1 at a different relative location from the
other image errors Rke, Rce, Rme, it affects the image quality. As
described above, when Rd=Ro, at least one image error occurs within
each of the transferred color images. More specifically, although
FIGS. 9A and 9B depict an example where all of the color images are
transferred within one rotational cycle of the OPCs 30, 40, 50, 60,
one color image can be completed by the two rotational cycles of
the OPCs 30, 40, 50, 60. In this case too, one image error occurs
in each of the transferred color images. Accordingly, the image
quality can be greatly improved by aligning at least two image
errors by making at least two of the OPC rollers satisfy at least
one of the equations in Equation Set 1.
[0264] In the following second example of the first step, it will
be exemplified that the system is set to satisfy all of the
equations of Equation Set 1. Referring to FIG. 10A, the system is
set such that distances between the centers C1, C2, C3, C4 of the
OPCs 30, 40, 50, 60 satisfy L1=L2=L3=Sd. In such a situation, when
the center of the interval B of the driving roller is rotated along
the +x axis by .theta.d=135.degree., it is assumed that the K image
is initially transferred onto the belt 70 at a location F0. If it
is assumed that one unit image is formed in one rotational cycle of
the OPCs 30, 40, 50, 60, the distance L1 between the centers C1, C2
of the two OPCs 30, 40 corresponds to an integer multiple of Sd,
that is, L1=1Sd. Accordingly, as shown in FIGS. 10A and 10B, the
distance from the location F0 where the K image transfer starts
until the location F1 where the K image transfer ends, corresponds
to the distance between the location f0 where the first rotational
cycle of the driving roller 80 begins until the location f1 where
the second rotational cycle of the driving roller 80 begins.
Accordingly, a K image error Rke occurs with its center being
located at a distance where the belt 70 is run by
m1=Rd.multidot..theta.d- .
[0265] Next, because the C image transfer start point F2 meets the
location F1, and the location f1 also meets the location F1, the
center of the C image error Rce occurring in the C image due to the
interval B is positioned at the location F1, that is, at a distance
from the starting line SL of the C image by
m1=Rd.multidot..theta.d. As a result, the K and C image errors Rke,
Rce are overlapped at the same location.
[0266] Furthermore, because L1=L2=1Sd, the M image transfer start
point F4 is positioned at the same location as the C image transfer
end location F3, and as the starting point f2 of the third
rotational cycle of the driving roller 80. Because the center of
the M image error Rme due to the interval B is at a
m1=Rd.multidot..theta.d distance from the SL location, which is
identical to the location F3, the K and C image errors Rke, Rce can
be superimposed at the same location.
[0267] Additionally, because L1=L2=L3=Sd, the Y image transfer
start point F6 is at the same location as the M image transfer end
location F5, and as the start point f3 of the fourth rotational
cycle of the driving roller 80. Accordingly, the center of the Y
image error Rye due to the interval B occurs at the location F6,
that is, at a distance from the starting line SL of the unit image
area P1 as much as m1=Rd.multidot..theta.d. Because the Y image
error Rye occurs at the same location as the overlap of the K, C
and M image errors Rke, Rce, Rme, the number of image errors of
unit image area P1 can be greatly reduced, and as a result, the
image quality improves.
[0268] The third example of the first step where Rd<Ro will now
be described.
[0269] FIG. 11A shows the system when Ro=2Rd. In the following
description, it will be assumed that each color image is completed
by one rotation of the OPCs 30, 40, 50, 60. Accordingly, the OPCs
30, 40, 50, 60 rotate once during two rotations of the driving
roller 80 of FIGS. 11A and 11B, and one unit image is formed by one
rotation of the OPCs 30, 40, 50, 60. Referring to FIG. 11A, an
exemplary system is illustrated in which the centers C1, C2, C3, C4
of the respective OPCs 30, 40, 50, 60 do not satisfy any of the
equations of Equation Set 1. In such a situation, the K image is
initially transferred onto the belt 70 when the maximum radial
displacement +.delta.d of the driving roller 80, that is, the
center of the interval B is rotated from the axis +X by .theta.d
(+135.degree.). The location of the interval B, that is, the
location of .theta.d is randomly set for the convenience of
explanation.
[0270] When the K image is transferred onto the belt 70 at the K
image transfer starting point F0, the starting point f0 of the
first rotation of the driving roller 80 meets the location F0.
Accordingly, the center of the first K image error Rke1 due to the
interval B occurs at a distance where the belt 70 is run from the
unit image transfer starting line SL as much as
M1=Rd.multidot..theta.d. Since the K image transfer is completed by
one rotation of the OPC 30, the driving roller 80 rotates twice
during the transfer of the K image. Accordingly, the second K image
error Rke2 occurs at a distance where the belt 70 is run from the
center of the first K image error Rke1 as much as
1Sd=2.pi..multidot.Rd. That is, two K image errors Rke1, Rke2 occur
in one unit image area P1 due to the interval B, and the center of
the second K image error Rke2 occurs away from the SL as much as
Sd+m1.
[0271] Meanwhile, because the distance between the centers C1, C2
of the two OPCs 30, 40 is L1=1Sd+t3, the C image transfer starts at
a location F2 where the belt 70 is run by the interval of t3 from
the starting point f1 of the second rotation of the driving roller
80. Accordingly, the center of the first C image error Rce1, which
is caused due to the interval B in the second rotation of the
driving roller 80, appears at a location where the belt 70 is moved
from the location f1 as much as m1. As a result, the center of the
first C image error Rce1 occurs away from the starting line SL of
the C image transfer by m2=m1-t3. For the convenience of
explanation, the distance corresponding to the interval t3 is
defined to be the length of circumference when the driving roller
80 rotates by 45.degree.. Accordingly,
m2=Rd.multidot..theta.d-Rd.multidot.4-
5.degree.=Rd(.theta.d-45.degree.). As a result, the center of the
first C image error Rce1 is at a different location from the
centers of the two K image errors Rke1, Rke2 in the unit image area
P1.
[0272] The second C image error Rce2 is caused due to the interval
B while the C image is transferred and during the third rotation of
the driving roller 80. The center of the second C image error Rce2
appears at a distance where the belt 80 is moved from the center of
the C image error Rce1 by the interval of Sd. Accordingly, the
center of the second C image error Rce2 is at a distance from the
starting line SL of the C unit image P1 by
m2+Sd=Rd(.theta.d-45.degree.)+2.pi.Rd=Rd.multidot.(2.pi.+90.degree.-
).
[0273] Because the distance between centers C2 and C3 of the C
color OPC 40 and the M color OPC 50 is L2=Sd+t3, the transfer of
the M image starts from the point F4. The transfer staring point F4
of the M color image is away from the point F0 by 2Sd+2t3, that is,
away from the point f2 by 2t3. Accordingly, the center of the first
M color image error Rme1 caused due to the interval B in the unit
image area P1 is positioned away from the point f2 by
m1=Rd.multidot..theta.d. Accordingly, the distance between the
center of the image error Rme1 and the SL of the unit image area P1
during the M image transfer is m3=m1-2t3=Rd.multidot..theta.d-2Rd-
.multidot.45.degree.=Rd.multidot.(.theta.d-90.degree.). The center
of the second M color image error Rme2 caused due to the interval B
occurs away from the center of the image error Rme1 at a position
where the belt 70 is moved by a distance of Sd. Accordingly, the
second M color image error Rme2 occurs away from the SL of the M
color image by
m3+Sd=Rd.multidot.(.theta.d-90.degree.)+2.pi..multidot.Rd=Rd.multidot.(2.-
pi.+45.degree.). Accordingly, the two M color image errors Rme1 and
Rme2 occur at different locations from the K and C color image
errors Rke1, Rke2, Rme 1 and Rme2.
[0274] Referring to FIG. 11A, the distance between the centers C3
and C4 of the M color OPC 50 and the Y color OPC 60 is L3=Sd+2t3.
Accordingly, the transfer starting point F6 of the Y color image is
located at a position where the belt 70 is moved from the point f0
by a distance of 3Sd+4t3. Then, the center of the first Y color
image error Rye1 caused due to the interval B during the fourth
rotation of the driving roller 8 occurs away from the F6 by a
distance of m4. Since the distance between the point F6 and the
point f3 is 4t3, the distance between the point F6 and the point f4
is Sd-4t3. Also, the distance between the point f4 and the first Y
color image error Rye1 is m1. Accordingly,
m4=Sd-4t3+m1=2.pi..multidot.Rd-4Rd.multidot.45.degree.+Rd.multidot..theta-
.d=Rd.multidot.(2.pi.-45.degree.). The second Y color image error
Rye1 occurs at a position where the belt 70 is moved from the
center of the first Y color image Rye1 by a distance of Sd.
Accordingly, the center of the second Y color image error Rye1
occurs away from the SL of the Y color unit image P1 by
m4+Sd=Rd.multidot.(4.pi.-45.degree.). As described above, the Y
color images Rye1 and Rye1 occur at different positions from the K,
C, and M color image errors in the unit image area P1, and as a
result, many image errors occur in the unit image area P1.
[0275] As described above, the number of image errors can be
reduced thief the pair of color image errors occurring in the image
area P1 are aligned with each other. Therefore, the image quality
is improved.
[0276] Hereinafter, a method of aligning the two C and Y color
image errors (Rce1, Rce2)(Rye1, Rye2) with each other will now be
described with reference to FIGS. 12A and 12B. To this end, the
image forming system is arranged to satisfy the sixth equation of
Equation Set 1. That is, the two OPCs 40 and 60 are arranged as
shown in FIG. 12A to satisfy L6=q.multidot.Sd. FIG. 12A shows
L6=3Sd. That is, the distance between the centers C2 and C4 of the
C color and Y color OPCs 40 and 60 is an integer multiple (in this
example, 3) of the outer circumference Sd of the driving roller 80.
The remaining distances L1, L2, L3, L4, AND L5 are not necessarily
integer multiples of the outer circumference Sd. Comparing the
configurations illustrated in FIGS. 11A and 12A, only the Y color
OPC 60 of FIG. 12A varies in location. Therefore, the remaining
OPCs 30, 40, 50 are understood to be arranged at the same position
in FIG. 12A as in FIG. 11A.
[0277] When the K color image is transferred from the point F0 in
the state of FIG. 12A, the K color image transfer is performed
during the two rotational cycles of the driving roller 80.
Accordingly, the first and the second K color image errors
(Rke1)(Rke2) due to the B interval occur at the same location as
shown in FIGS. 11A and 11B. That is, the center of the first K
color image error (Rke1) occurs away from the point f0(F0) at a
distance where the belt 70 is moved by a distance of
m1=Rd.multidot..theta.d, and the center of the second K color image
error (Rke2) occurs away from the point f0 at a distance where the
belt 70 is moved by Sd+m2.
[0278] The first and the second C color image errors (Rce1)(Rce2)
occur at the same location during the transfer of the C color image
as shown in FIG. 11B. That is, as shown in FIG. 12B, the center of
the first C color image error Rce1 occurs away from the point F2
(the transfer starting line SL of the C color unit image) at a
distance where the belt 70 is moved by
m2=m1-t3=Rd.multidot..theta.d-Rd.multidot.45.degree.=Rd(.theta.d-
-45.degree.). The center of the second C color image error Rce2
occurs away from the point f2 at a distance where the belt 70 is
moved past F2 by
m2+Sd=Rd.multidot.(.theta.d-45.degree.)=2.pi..multidot.Rd=Rd.multidot.-
(2.pi.+90.degree.).
[0279] The first M color image error (Rme1) occurs away from the
point F4 at a distance where the belt 70 is moved by a distance of
m3=m1-2t3=Rd.multidot..theta.d-2Rd.multidot.45.degree.=Rd.multidot.(.thet-
a.d-90.degree.). The center of the second M color image error Rme2
occurs away from the point F4 at a distance where the belt 70 is
moved by a distance of
m3+Sd=Rd.multidot.(.theta.d-90.degree.)+2.pi..multidot.Rd=Rd.-
multidot.(2.pi.+45.degree.).
[0280] Since the center C4 of the Y color OPC 60 is distanced away
from the center C2 by a distance of 3Sd, the point F6 from which
the Y color image is transferred is located a distance where the
belt 70 is moved from the point F2 from which the C color mage is
transferred by three times the circumference of Sd (3Sd). Then, the
point F6 is distanced away from the point f4 by t3, and the center
of the first Y color image error Rye1 occurs away from the point f4
by m1 due to the interval B. Accordingly, since the center of the
first Y color image error Rye1 occurs from the point F6, that is,
from the transfer starting line (SL) of the Y color image, at a
distance where the belt 70 is moved by
m4=m1-t3=Rd.multidot..theta.d-Rd.multidot.45.degree.=Rd.multidot.(.theta.-
d--45.degree.)=m2, the two image errors (Rce1, Rye1) are aligned
with each other in the unit image area P1. Also, the center of the
second Y color image error Rye2 occurs away from the point F6 at a
distance where the belt 70 is moved by
m4+Sd=m2+Sd=Rd.multidot.(.theta.d-45.degree.)+2.pi..m-
ultidot.Rd=Rd.multidot.(2.pi.+90.degree.). Accordingly, the second
C image error (Rce2) and the second Y image error (Rye2) of the
unit image area P1 are positioned away from the SL by the same
distance and therefore, are aligned with each other.
[0281] As described above, in the full color image area P1 where
the images are transferred to the belt 70 through all of the four
OPCs 30-60, there are six image errors including the overlay of
image errors (Rke1, Rye1)(Rke2, Rye2), which is 2 errors less than
the 8 image errors occurring in the construction of FIG. 11A.
Accordingly, the image quality can be improved because the number
of image errors decreases and thus, a reliability of a product can
be improved.
[0282] In the above embodiment explained with reference to FIG.
12A, only the distance L6 between the centers of the C and Y color
OPCs 40 and 60 are integer multiples of Sd. However, if at least
one of the remaining distances L1, L2, L3, L4 and L5 satisfies the
same conditions, the number of image errors aligned with each other
can increase. Also, if Ro>Rd and the system is arranged to
satisfy L1=L2=L3=n.multidot.Sd (n=1, 2, 3, . . . ), the 8 image
errors decrease to the four overlaying images, and thus, the image
quality can be improved. Since such an effect can be fully
understood by referring to the previous descriptions with reference
to FIGS. 12A and 12B, a detailed description will be omitted for
the sake of brevity.
[0283] Also, in the description of an exemplary embodiment of the
present invention using the Equation Set 1, the method of
minimizing the occurrence of image errors caused due to the runout
of the driving roller 80 is highlighted. However, this should not
be considered as limiting. If an image error occurs due to a runout
of the supporting roller 91, the occurrence of the image error can
be minimized by using the above method and Equation Set 1 making
any of the lengths L1-L6 equal to an integer multiple of the
circumference of the supporting roller 91.
[0284] That is, the system is arranged to satisfy at least one of
the equations in Equation Set 1 with respect to one of the driving
roller 80 or the supporting roller 91 based on which has a greater
radial displacement and greater effects on the image. On the other
hand, with respect to the other roller, the runout can be minimized
through a post-process such as precision machining, and the
frequency of the image error occurrence caused by the supporting
rollers of the belt 70 can be reduced.
[0285] As described above with reference to FIGS. 4A though 7B,
each OPC 30, 40, 50, 60 has an interval A having the maximum radial
displacement +.delta.o. An image error due to the interval A such
as image blurring, image stretch, and image cut, occurs both in the
color images formed on the respective OPCs 30, 40, 50, 60 and in
the transfer image transferred to the belt 70. These will now be
explained in greater detail with reference to FIG. 13. For example,
in order to form a K color image, the OPC 30 is rotated and a
surface of the OPC 30 rotated in contact with the charging roller
35 is charged with a predetermined electric potential. However,
because the radius Ro of the OPC 30 increases as much as +.delta.0
due to the radial displacement +.delta.o in the interval A, the
interval A has a maximum tangential speed Vmax. Because the
interval A passes more rapidly when being rotated in contact with
the charging roller 35, the interval A receives less electric
charge and thus has a lower electric potential than the other parts
of the OPC 30.
[0286] Also, an electrostatic latent image is formed by scanning
the surface of the OPC 30 with laser beams emitted from a laser
scanning unit 31. During this procedure of forming the latent
image, the interval A has increasing tangential speed Vmax.
Accordingly, the interval A may have a decreasing amount of laser
scan and increasing scan areas. The electrostatic latent image
formed on the OPC 30 passes through the developing roller 33 so
that toner particles are attracted from the developing roller 33 to
the electrostatic latent image. Therefore, a visible image is
obtained. During this procedure, however, the interval A passes in
contact with the developing roller 33 more rapidly, and also, the
amount of laser energy scanned onto the electrostatic latent image
is less. As a result, less developer is attracted to the
electrostatic image, and the developer attracted to the
electrostatic image blurs due to the faster tangential speed. In
summary, the visible image obtained on the surface of the OPC 30
through a series of procedures such as charging, laser scanning,
and developing has an image error such as image blurring, image
stretch, and image cut, in the interval A.
[0287] As described above, the visible image is formed on the
surface of the OPC 30, but has an image error in the interval A
prior to being transferred to the belt 70. The visible image which
is transferred to the belt 70 may have an image error due to the
interval A. As described above, the image error occurs due to the
interval A caused by the runout of the OPC 30, 40, 50, 60,
independently from the runout of the driving roller 80 as described
above. Because one image error occurs in each OPC 30, 40, 50, 60
due to the runout of the OPCs 30, 40, 50, 60, a full color image
may have a great number of image errors. For example, if each OPC
30, 40, 50, 60 is designed to rotate two times to form a unit
image, two image errors may occur in each OPC 30, 40, 50, 60. As a
result, a full color image has total eight image errors due to
variations in radius of the OPCs 30, 40, 50, 60.
[0288] Meanwhile, the center of the interval A, which causes the
image error to occur, can be arranged at a predetermined position
with respect to the positioning part 33b of the driven coupler 33
as explained with reference to FIGS. 4A through 7B. That is, a mark
31a is formed on the drum body 31 at a predetermined angle from the
center of the interval A, and the OPCs 30,40, 50, 60 are assembled
by coinciding the mark 31a with the positioning part 33b. Also, the
OPCs 30, 40, 50, 60 can advantageously be assembled using a jig
without requiring an extra measurement device.
[0289] Hereinafter, an image error occurring when the images are
formed by using the respective OPCs 30, 40, 50, 60, each being
mounted to have the center of the interval A positioned at a
predetermined angle with respect to the positioning part 33b, will
be described. Additionally, a method of reducing the number of
image errors and an effect thereof according to an embodiment of
the present invention will be described.
[0290] The description will mainly focus on the interval A of the
respective OPCs 30, 40, 50, 60 which has radial displacement
+.delta.o. However, the like definition can be applied to an area
having -.delta.o. Because the image error becomes more problematic
in the area having +.delta.o than in the area having -.delta.o, the
description will be made mainly about the area having
+.delta.o.
[0291] For the convenience of the following exemplary explanation,
it is assumed that the driving roller 80 and the supporting roller
91 form complete circles which have no runouts. It is also assumed
that variations in speed of the belt 70 due to a radial
displacement difference of the driving roller 80 and the supporting
roller 91does not occur, and that the belt 70 runs at a constant
speed.
[0292] As shown in FIGS. 14A though 14D, the respective color OPCs
30, 40, 50, 60 are arranged in a manner so that the positioning
parts 33b of the respective driven couplers are positioned at
different angles from one another in a counterclockwise direction
(+angle) from the axis Y. In this state, starting lines SL of unit
images P2 are consecutively transferred to contact position Po1,
Po2, Po3, and Po4 of the belt 70 with respect to the respective
OPCs 30, 40, 50, 60, thereby forming an overlay of color images.
The respective OPCs 30, 40, 50, 60 are arranged to have intervals
A1, A2, A3, and A4, each having a maximum radial displacement
+.delta.o at a predetermined angle from the positioning part 33b.
Also, as shown in FIGS. 14A through 14D, it is assumed that the
respective OPCs have different postures at the beginning of the
transfer. In the following, as case will be described in which the
starting lines SL of the respective unit images P2 are transferred
to the point Po1, Po2, Po3, and Po4 on the +Y axis of the
respective OPCs 30, 40, 50, 60. That is, the postures of the
respective OPCs 30, 40, 50, 60 refers to postures of the respective
OPCs 30, 40, 50, 60 at the beginning of consecutive transfer of the
respective color images K, C, M and Y.
[0293] As shown in FIG. 14A, if a printing starts when the K color
OPC 30 is in contact with the axis +Y, the center of the interval
A1 is positioned with respect to the +Y axis in a counterclockwise
direction by angle .THETA.1. In FIGS. 14A through 14D, the centers
of the intervals A1.about.A4 are distanced from the positioning
part 33b by 45.degree.. Accordingly, the K color image error Oke
occurs at a predetermined position of the unit image area P2 of the
belt 70 due to the interval A1. The image error Oke may include an
image blurring, an image stretch, and an image cut. That is,
because the tangential speed Vmax of the OPC 30 varies more rapidly
in the interval A of the surface of the OPC 30 than the other
intervals, a stretched electrostatic latent image is formed on the
OPC (on the other hand, since the area -.delta.o has a minimum
tangential speed Vmin, a shrunken electrostatic latent image may
occur). If the developing roller 33 performs a developing in
contact with the OPC 30, there occurs an image blurring in the
interval A1 due to difference from a nominal speed of the OPCs.
When the image is transferred to the belt 70 through the above
processes, there occurs a speed difference between the interval A1
and the belt 70 in contact with the interval A1, which results in
the image blurring. The center of the K color image error Oke
occurs away from the starting line SL by
1ok=Rol.multidot..THETA.1.
[0294] As shown in FIG. 14B, the C color OPC 40 has the center of
the interval A2 positioned with respect to the +Y axis such that
.THETA.2=+135.degree.. In this case, the C color image error Oce
occurs in the unit image area P2 due to the interval A2 and at a
different position from that of the K color image error Oke. That
is, the C color image error Oce occurs away from the starting line
at position 1oc=Ro2.multidot..THETA.2.
[0295] Referring to FIG. 14C, the center of the interval A3 of the
M color OPC 50 is positioned with respect to the +Y axis in a
counterclockwise direction such that .THETA.3=+225.degree..
Accordingly, the M color image error Ome occurs in the unit image
area P2 due to the interval A, and occurs at a different position
from the K and C color image errors Oke and Oce. That is, the M
color image error Ome occurs away from the staring line SL at
position 1om=Ro3.multidot..THETA.3.
[0296] Referring to FIG. 14D, the center of the interval A4 of the
Y color OPS 60 is positioned with respect to the +Y axis in a
counterclockwise direction such that .THETA.4=+315.degree..
Accordingly, a Y color image color Oye occurs in the unit image
area P2 due to the interval A4 of the OPC 60, but occurs at
different positions from those of the K, C, M color image errors
(Oke)(Oce)(Ome). That is, the Y color image error occurs away from
the starting line SL at position 1oy=Ro4.multidot..THETA.4.
[0297] Referring to FIGS. 14A and 14D, if Ro1=Ro4=Ro, a distance
between the centers of the image erros Oke and Oce is
1oc-1ok=Ro.multidot.(.THETA- .2-.THETA.1). As a result, since the
color image errors are misaligned in the unit image area P2, the
respective color image errors Oke, Oce, Ome, Oye are located at
different positions on the overlay of color images, which
deteriorates an image quality.
[0298] An example of the above will be described in greater detail
with reference to FIGS. 15A and 15B.
[0299] FIG. 15A shows the OPCs 30, 40, 50, 60 of FIGS. 14A through
14D in a single view. In FIG. 15A, since the respective OPCs 30,
40, 50, 60 are illustrated with reference to staring points Po1,
Po2, Po3, and Po4 for transferring the respective color image, time
is not taken into account in the following description.
[0300] FIG. 15B shows a radial displacement (.delta.ok, .delta.oc,
.delta.om, .delta.oy) per color in the form of sinusoidal curve
according to a rotational cycle of the OPCs 30, 40, 50, 60. In the
drawing, the intervals between centers of each OPC 30, 40, 50, 60
are not considered, and the radial displacement and image error per
color are shown based on transfer points Po1, Po2, Po3, Po4 per
color. The radius of each OPC 30, 40, 50, 60 is uniform, that is,
Ro1=Ro2=Ro3=Ro4=Ro.
[0301] The first graph of FIG. 15B shows a radial displacement
(.delta. ok) according to the rotational cycle of the OPC 30,
assuming that the transfer of the K color OPC 30 starts in a
position shown in FIGS. 14A and 15A. If assuming that an K unit
image is formed when the OPC 30 is once rotated, the transfer of K
color image starts from the point Po1, and therefore, the center of
K image error Oke by the interval A1 occurs in one rotational cycle
(unit image area; P2). That is, a distance traveled by
1ok=Ro.multidot..theta.1=Ro.multidot.45.degree. from the SL point
for the belt 70 to transfer the K color image.
[0302] The second graph of FIG. 15B shows a radial displacement
(.delta. oc) according to rotational cycle of the C color OPC 40
disposed as shown in FIG. 14B. The transfer of C color starts from
the point Po2, and the point Po1, in which the transfer of K color
image starts, aligns with the line SL, in which the transfer of C
color image starts, at the point Po2. Referring to FIG. 15A, the
interval between two points Po1 and Po2 on actual belt 70 is the
distance L1 between the rotation centers C1, C2 of the two OPCs 30,
40. Accordingly, the SL of K color image starting the transfer from
the point Po1 meets the point Po2 after the belt 70 travels L1
distance to start the transfer of C color image. In FIG. 14B, the
interval A2 is located in a phase from the point Po2 to .theta.2
(115.degree.), and therefore, the center of the C color image error
Oce is located in the SL based on one rotational cycle (unit image
area; P2). That is, the distance the belt 70 is traveled is
1oc=Ro.multidot..theta.2- (115.degree.) from the point Po2. If both
of the two image errors Oke, Oce are generated in the unit image
area P2, the graph shows that the interval between the centers of
the two image errors Oke, Oce is
1oc-1ok=Ro.multidot.(.theta.2-.theta.1) as explained in FIG.
14B.
[0303] The third graph of FIG. 15B shows a radial displacement
(.delta. om) according to the rotational cycle of the M color OPC
50 disposed as shown in FIG. 14C. The center of interval A3 is
located on the phase of .THETA.3 (225.degree.) from the point Po3
in which the transfer of M color starts. The M color image error
Ome by the interval A3 is generated in the M color image when the M
OPC 50 is rotated by .theta.3. Accordingly, the center of the M
color image error Oce is generated in the distance where the belt
70 travels from the point Po3 to 1om=Ro.multidot..theta.3. When one
rotational cycle of the OPC 50 is divided into 360.degree., the
distance 1om=Ro.multidot..theta.3 lies at a location which is
rotated by approximately 225.degree. from the point Po3.
Accordingly, the distance between centers of two image errors Oce,
Ome is 1om-1oc=Ro.multidot.(.theta.3-.theta.2). The interval
between points Po2, Po3 represents the distance L2 between the
rotational centers C2, C3 of the two OPCs 40, 50, and the SL of K
color image and C color image aligns at the point Po3 with SL of M
color image superimposed by the OPCs 30, 40.
[0304] The fourth graph of FIG. 15B shows a radial displacement
(.delta. oy) according to rotational cycle of the Y color OPC 60
disposed as shown in FIG. 14D. The center of interval A4 is located
in a phase of.THETA.4 (315.degree.) from the point Po4.
Accordingly, the Y color image error Oye caused by interval A4 is
generated as OPC 60 is rotated by approximately 315.degree. when
one rotational cycle (unit image area;P2) of the OPC 60 is divided
into 360.degree.. The center of the Y color image error Oye is
located in a distance where the belt 70 travels from the point Po4
by 1oy=Ro.multidot..theta.4=Ro.multidot.215.degree.. The interval
between the centers of the two image errors Ome, Oye is
1oy-1om=Ro.multidot.(.theta.4-.theta.3). As each color image is
superimposed, image errors are generated in different positions,
and therefore, the quality of the overlapped color images is
deteriorated.
[0305] As shown in FIG. 15B, the phase of radial displacements
(.delta.ok,.delta.oc,.delta.om,.delta.oy) per each color are
different with respect to one rotational cycle (unit image area;
P2). Accordingly, if assuming that the unit image area P2 is formed
by one rotational cycle of the OPC, the image errors Oke, Oce, Ome,
Oye per each color are generated at different relative positions.
Four image errors are generated at different positions in the unit
image area P2.
[0306] In FIGS. 14A-14D, and 15B, the radius of each OPC 30 to 60
is uniform as Ro, and one unit image is formed by one rotation of
each OPC 30, 40, 50, 60. However, in practice, one unit image may
not correlate with one rotation of an OPC. For example, one unit
image may be formed by one, one and half, or two rotations
according to the size of the radius of OPCs 30, 40, 50, 60.
Accordingly, more than one image error may be introduced for each
OPC per unit image area. Thus, at least four image errors, and
possibly more, are generated in the unit image area of a full color
image, and therefore, image quality is deteriorated.
[0307] In addition, in the foregoing description, it was assumed
that all of the OPC's have the same radius. Of course, as one of
ordinary skill in the art will appreciate, the principles described
above could also be applied if the OPC drums are not all of equal
radius. For example, rather than controlling the distance between
rotation centers of OPCs, the same effect can be obtained by
controlling the distance between contact points of the OPCs. That
is, each OPC has a contact point on the belt 70. By controlling the
length between contact points of OPCs along the belt, image errors
caused by radius deviations in the OPCs can be overlapped, and
thereby reduced. In such a scenario, because the radii are not
equal, the length between centers of rotation may not necessarily
be equal to the length along the belt between contact points.
[0308] If the position of each radial displacement +.delta.of OPCs
30 to 60 is aligned based on the initial transfer point of each OPC
30, 40, 50, 60, that is, if each OPC 30, 40, 50 is adjusted and
arranged to generate each image error Oce, Ome, Oye shifted by a
certain distance, only a single overlapped Ote of four color image
errors is generated. As shown in the fifth graph of FIG. 15B, the
radial displacement .delta.ok,.delta.oc,.delta.om,.delta.oy of each
OPCs 30, 40, 50, 60 appears in a regular pattern in the unit
rotational cycle (unit image area; P2). Because each radial
displacement .delta.ok,.delta.oc,.delta.om- ,.delta.oy in the unit
rotational cycle (unit image area; P2) is aligned, the image errors
Oke, Oce, Ome, Oye per each color are aligned in the same
phase.
[0309] The fifth graph of FIG. 15B shows image errors generated
when each of four OPCs 30, 40, 50, 60 are aligned. However, the
total number of image errors can be greatly reduced even when the
image errors of at least two OPCs are superimposed. Hereinafter, an
exemplary method and operation effect for overlaying image errors
of two or more OPCs will be explained in detail.
[0310] FIGS. 14A-14D, and 15B were previously explained based on a
sequence of transfer points of each OPCs. The following exemplary
description will explain the relationship between OPCs based on the
engagement relationship between each of the OPCs and the driven
couplers corresponding to the OPCs at the time of system
installation.
[0311] Accordingly, description will now be made with reference to
FIGS. 16A to 16D.
[0312] FIG. 16A shows a point when the K color OPC 30 is initially
transferred. The transfer start position with respect to the belt
70 is D1, the position of the K color OPC 30 contacting the belt 70
is E1, and the angle between E1 and the center of the maximum
radial displacement area A1 is .alpha.1 (since the present drawing
differs from FIGS. 14A to 14D which are based on the sequential
transfer points of each OPCs, general angles
.alpha.1.about..alpha.4 are used in FIG. 16A). At this time, the
contacting point between the C color OPC 40 and the belt 70 is D2,
the corresponding position of the C color OPC 40 is E2, and the
angle between the E2 and the center of the maximum radial
displacement area A2 of the C color OPC 40 is .alpha.2. The
position on the belt 70 starting the transfer of the M color OPC 50
is D3, the contacting position of the M color OPC 50 is E3, and the
angle between the E3 and the center of the maximum radial
displacement area A3 is .alpha.3. The contacting point between the
Y color OPC 60 and the belt 70 is D4, the corresponding position of
the Y color OPC 60 is E4, and the angle between the E4 and the
center of the maximum radial displacement area A4 of the Y color
OPC 60 is .alpha.4. The distance between C1 and C2 is L1, the
distance between C2 and C3 is L2, the distance between C3 and C4 is
L3, and the radii of the OPCs 30, 40, 50, 60 are Ro1, Ro2, Ro3,
Ro4. The OPCs may be mounted to meet any one of the following
Equation Set 2.
[0313] [Equation Set 2]
{2.pi..multidot.l+(.alpha.2-.alpha.1)}.multidot.Ro.multidot.(1
.+-.0.05)=L1, (l=0 , 1, 2, . . . ),(Ro=Ro1=Ro2) {circle around
(1)}
{2.pi..multidot.m+(.alpha.3-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=L1-
+L2, (m=0, 1, 2, . . . ), (Ro=Ro1=Ro3) (2)
{2.pi..multidot.n+(.alpha.4-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=L1-
+L2+L3, (n=0, 1, 2, . . . ), (Ro=Ro1=Ro4) {circle around (3)}
[0314] In FIG. 16A, the K color OPC 30 is initially transferred to
the K unit image Pk. The starting line SL of the K unit image Pk
starts from the position D1 on the belt 70 and contacts the point
E1 of the OPC 30. The center of interval A1 is located in the angle
of .alpha.1 along the +Y axis from the point E1. The C color OPC 40
contacts the position D2 on the belt 70, and the center position of
interval A2 is rotated by .alpha.2 from the contacting position E2
on the OPC 40. Likewise, each center of intervals A3 and A4 of the
M color OPC 50 and the Y color OPC 60 is located at the angle
rotated by .alpha.3, .alpha.4 from each E3 and E4.
[0315] The K color image is transferred to the K unit image Pk in
the state of FIG. 16A, and the center of the K image error Oke
caused by the interval A1 appears away from the starting line SL by
b1=Ro.multidot..alpha.1=Ro1.multidot..alpha.1. If the center of the
C color image error Oce generated in the C unit image Pc by the
interval A2 of the C OPC 40 is aligned with the center position of
the image error Oke as the center of the K color image error Oke
reaches the position Po6 contacting the C color OPC 40 and the belt
70 as shown in FIG. 16B, the two image errors Oke, Oce are
superimposed at the same position. Here, the following equation
meets the above conditions.
Ro.multidot..alpha.1+L1=Ro.multidot..alpha.2, (Ro=Ro1=Ro2) (1)
[0316] Because the distance of L1 is within one rotational
circumference length 2.pi..multidot.Ro of the OPC 30, that is,
L1<2.pi..multidot.Ro, the equation (1) may be generalized as
follows:
Ro.multidot..alpha.1+L1=Ro.multidot.(.alpha.2+2.pi..multidot.l),
(l=0, 1, 2, . . . ) (2)
[0317] The above equation (2) can be rewritten as follows:
{2.pi..multidot.l+(.alpha.2-.alpha.1)}.multidot.Ro=L1, (l=0, 1, 2,
. . . ) (3)
[0318] The above equation (3) corresponds to the first equation of
Equation Set 2. If two OPCs 30, 40 are arranged to satisfy equation
(3), the image errors Oke, Oce by the intervals A1, A2 of K color
and C color OPC 30, 40 are superimposed at the same position. More
specifically, when setting each OPCs 30, 40 in the image forming
apparatus, the K color OPC 30 is preferably first set as the S1 and
Ro values are set. Then, if a certain .alpha.1 value of the K color
OPC 30 is substituted using the first equation of the equations 2,
.alpha.2 of the C color OPC 40 can be obtained. Therefore, if the C
color OPC 40 is properly arranged along axes X and Y based on the
obtained .alpha.2, the image errors Oke, Oce can be
superimposed.
[0319] Additionally, as shown in FIG. 16A, the center of K image
error Oke appears away from the starting line SL as much as
b1=Ro.multidot..alpha.1- =Ro1.multidot..alpha.1. If the center of
the M image error Ome generated in the M unit image Pm by the
interval A3 of the M color OPC 50 is aligned with the center of the
K image error Oke as the center of the K image error Oke reaches
the contacting position Po7 with respect to the belt 70 of the M
OPC 50 as shown in FIG. 16C, the two image errors Oke, Ome are
superimposed at the same position. To this end, the two OPCs 30, 50
need to meet the following equation (4).
Ro.multidot..alpha.1+L1+L2=Ro.multidot.(.alpha.3+2.pi..multidot.m),
(m=0, 1, 2, . . . ), (Ro=Ro1=Ro3) (4)
[0320] Rewriting the above equation (4), the second equation of the
Equation Set 2 can be derived as follows:
{2.pi..multidot.m+(.alpha.3-.alpha.1)}.multidot.Ro=L1+L2, (m=0, 1,
2, . . . ), (Ro=Ro1=Ro3) (5)
[0321] In order to align the K color image error Oke with the Y
color image error Oye generated in the unit image Py by the
interval A4 of the Y OPC 60 as shown in FIG. 16D, the center of the
interval A4 needs be located on the point Po8 when the position D1
of the belt 70 is moved from the point Po8 by
b1=Ro.multidot..alpha.1=Ro1.multidot..alpha.1. This condition may
be represented in the following equation (6).
Ro.alpha.1+L1+L2+L3=Ro.multidot.(.alpha.4+2.pi..multidot.n), (n=0,
1, 2, . . . ), (Ro=Ro1=Ro4) (6)
[0322] The above equation (6) can be rewritten as:
{2.pi..multidot.n+(.alpha.4-.alpha.1)}.multidot.Ro=L1+L2+L3, (n=0,
1, 2, . . . ), (Ro=Ro1=Ro4) (7)
[0323] Equation (7) rewritten from the equation (6) corresponds to
the third equation of the Equation Set 2.
[0324] The aforementioned conditions of Equation Set 2 can be used
to control the installation position of OPCs 40, 50, 60 so that
image errors generated by one of the OPCs 40, 50, 60 can be
superimposed on the K color image error Oke generated by the
interval A1 of the K OPC 30.
[0325] Additionally, contrary to the Equation Set 2, in order to
superimpose the image error generated in at least neighboring OPCs
30, 40, 50, 60, the image forming apparatus needs be set to meet at
least one of the following equations.
[0326] [Equation Set 3]
{2.pi..multidot.l+(.alpha.2-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=L1-
, (l=0, 1, 2, . . . ), (Ro=Ro1=Ro2) {circle around (1)}
{2.pi..multidot.m+(.alpha.3-.alpha.2)}.multidot.Ro.multidot.(1.+-.0.05)=L2-
, (m=0, 1, 2, . . . ), (Ro=Ro2=Ro3) {circle around (2)}
{2.pi..multidot.n+(.alpha.4-.alpha.3)}.multidot.Ro.multidot.(1.+-.0.05)=L3-
, (n=0, 1, 2, . . . ), (Ro=Ro3=Ro4) {circle around (3)}
[0327] where, the equation {circle around (1)} of the Equation Set
3 corresponds to the first equation of the Equation Set 2. The
equations represent the conditions to align the image errors Oke,
Oce generated by the two neighboring OPCs 30, 40. Of course the
above equations refer to a distance between centers of rotation of
the OPCs. Alternatively, the distance between points of contact on
the belt 70 of each OPC could be controlled with respect to the
orientation of the OPC rollers.
[0328] The second equation of the Equation Set 3 represents
conditions to align the image errors Oce, Ome generated by the
interval A2, A3 of the C and M color OPCs 30, 40, and the method of
overlapping image errors of the two OPCs 30, 40 can be easily
comprehended through the aforementioned method. In other words, if
.alpha.2 value of the C color OPC 40 is set with set L2 value and
Ro value, .alpha.3 value of the M color OPC 50 can be obtained
through equation {circle around (2)} of the Equation Set 3.
Accordingly, by setting the M color OPC 50 based on .alpha.3 value,
the two image errors Oce, Ome can be superimposed.
[0329] Equation {circle around (3)} of the Equation Set 3
represents conditions to superimpose the image errors Ome, Oye
generated by the intervals A3, A4 of the M and Y color OPCs 50, 60.
At this time, the image errors Ome, Oye of the two OPCs 50, 60 can
be superimposed in the same manner as that explained in FIGS.
16A-16D which is used to superimpose one of the other image errors
Oce, Ome, Oye on the image error Oke by the interval A1 of the K
color OPC 30. In other words, when L3 and Ro are provided as set
values, and the M color OPC 50 is first mounted to a certain
position, .alpha.3 value of the mounted M color OPC 50 can be
obtained. Then .alpha.3 is substituted for equation {circle around
(3)} of Equation Set 3 to obtain .alpha.4 value. Accordingly, when
the Y color OPC 60 is set to correspond to the obtained .alpha.4
value, two image errors Ome, Oye can be superimposed.
[0330] In preferred embodiments of the present invention, the
distances between the centers C1, C2, C3, C4 of each OPC 30, 40,
50, 60 are identically set as L1=L2=L3. Therefore, the Equation Set
2 can be rewritten as follows:
[0331] [Equation Set 4]
{2.pi..multidot.l+(.alpha.2-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=L1-
, (l=0, 1, 2, . . . ), (Ro=Ro1=Ro2) (1)
{2.pi..multidot.m+(.alpha.3-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=2L-
1, (m=0, 1, 2, . . . ), (Ro=Ro1=Ro2=Ro3) (2)
{2.pi..multidot.n+(.alpha.4-.alpha.1)}.multidot.Ro.multidot.(1.+-.0.05)=3L-
1, (n=0, 1, 2, . . . ), (Ro=Ro1=Ro2=Ro3=Ro4) (3)
[0332] In the same manner as described with reference to FIGS. 4A
through 7B, the OPCs 30, 40, 50, 60 are mounted so that the
intervals A1, A2, A3 and A4 of the respective OPCs 30, 40, 50, 60
are disposed at the same phase with respect to the positioning part
33b of the driven coupler 33. Of course the above equations refer
to a distance between centers of rotation of the OPCs.
Alternatively, the distance between points of contact on the belt
70 of each OPC could be controlled with respect to the orientation
of the OPC rollers.
[0333] In this case, L1, Ro and the maximum radial displacement
location on the reference OPC, that is, the location of the
interval A1 (.alpha.1) are obtained. In this embodiment, the K
color OPC 30 is preferably set as the reference OPC. Additionally,
the maximum radial displacement locations (.alpha.2, .alpha.3 and
.alpha.4) of the other OPCS 40, 50, 60 are obtained to satisfy
equations 2 and 3, and the respective OPCs 40, 50, 60 are mounted
accordingly. In order for visual confirmation of the radial
displacement locations, the positioning part 33b of the driven
coupler may be fastened in the factory to have a predetermined
interval (for example, 45.degree.) with respect to the respective
radial displacement locations, as shown in FIG. 4A. Therefore, the
initial position of the OPCs 30, 40, 50, 60 can be determined with
reference to the positioning part 33b.
[0334] After the maximum radial displacement locations (.alpha.2,
.alpha.3 and .alpha.4) of the other OPCS 40, 50, 60 are determined
with respect to the location .alpha.1 of the reference OPC 30, the
OPCs 30, 40, 50, 60 can be mounted in the image forming apparatus
through at least two methods, which will now be described in more
detail.
[0335] As a first method, as described above, the respective OPCs
30, 40, 50, 60 are mounted such that the positioning part 33b of
the driven coupler is positioned at a predetermined angle with
respect to the maximum radial displacement +.delta.o. One of the
OPCs, namely, OPC 30 is connected to the driving coupler 133 as
shown in FIG. 3. In a state that the OPC 30 is mounted, .alpha.1
can be detected using a predetermined detecting device. In this
state, .alpha.2, .alpha.3 and .alpha.4 of the other OPCs 40, 50, 60
are obtained by applying L1, L2, L3, Ro and .alpha.1 to the second
and third equations of Equations Set 2. The maximum radial
displacement +.delta.o of the OPCs 40, 50, 60 are controlled using
the detecting device to meet the obtained .alpha.2, .alpha.3 and
.alpha.4, and the OPCs 40, 50, 60 are engaged with the driving
couplers 134, 135 and 136. According to another example of the
first method, the OPCs 30, 40, 50, 60 may be connected to the
driving couplers 133-136 in a state that the driving coupler 133
connected to the K color OPC 30, which is the reference OPC, is set
to a predetermined position and the other driving couplers 134-136
are positioned corresponding to the obtained .alpha.2, .alpha.3 and
.alpha.4. Of course, the positioning parts of the driving couplers
133-136 can be adjusted by using detecting equipment.
[0336] A second method for setting the OPCs is to use a jig. For
example, as shown in FIG. 17A, a jig device 300 may be used, in
which a plurality of reference drums 330, 340, 350, 360 are
adjustably mounted in a jig frame 310. The reference drums 330,
340, 350, 360 correspond to parts of the color OPCs 30, 40, 50, 60
which are mounted in the image forming apparatus. Intervals between
the reference drums 330, 340, 350, 360 are preferably the same as
those of the driving couplers 133-136 of the driving unit 100 (FIG.
3) where the OPCs are mounted. The reference drums 330, 340, 350,
360 respectively have at the front end thereof driven couplers 333,
343, 353 and 363 corresponding to the driven coupler 33 of the OPCs
30, 40, 50, 60. Accordingly, the driven couplers 333, 343, 353 and
363 are complimentarily mated with the corresponding driving
couplers 133 to 136, respectively. Also, it will be understood that
positioning parts of the driven couplers 333, 343, 353, 363 are
positioned at the same phase as the positioning part 33b of the
driven coupler 33 provided to the substantial OPCs 30, 40, 50, 60,
that is, at a predetermined angle with respect to the maximum
radial displacement +.delta.o of the OPC.
[0337] Meanwhile, the reference drums 330, 340, 350, 360 are
rotatably inserted in adjusting holes 313 formed at predetermined
intervals on the jig frame 310. In addition, the jig frame 310 has
fixing members 320 corresponding to the respective reference drums
330, 340, 350, 360. The plurality of fixing members 320 are
fastened to the jig frame 310 in a threaded manner such that one
end of each is contacted with the reference drums 330, 340, 350,
360 being inserted in the adjusting holes 313. Therefore, as the
fixing member 320 is rotated toward the reference drums 330, 340,
350, 360, the one end is tightly contacted with the reference drums
330, 340, 350, 360, thereby immovably fixing the reference drums
330, 340, 350, 360. On the other hand, as the fixing member 320 is
rotated away from the reference drums 330, 340, 350, 360, the
reference drums 330, 340, 350, 360 and the fixing member 320 are
separated from each other so that the reference drums 330, 340,
350, 360 are rotatable within the adjusting holes 313.
[0338] Using the jig device 300, the positions of the reference
drums 330, 340, 350, 360, instead of the OPCs 30, 40, 50, 60
mounted in the driving unit 100, can be controlled and fixed to
satisfy any of the equations in Equation Set 2 or 3.
[0339] In order to control reference positions of the reference
drums 330, 340, 350, 360, the first method described above can be
used. In other words, .alpha.1 of a predetermined reference drum,
for example, the reference drum 330 is detected and .alpha.2,
.alpha.3 and .alpha.4 of the other reference drums 340, 350, 360
are obtained with respect to .alpha.1. Based on the obtained
.alpha.2, .alpha.3 and .alpha.4, the positions of the respective
reference drums 330, 340, 350, 360 are controlled and fixed in
order using the predetermined detecting device.
[0340] After the reference positions of the reference drums 330,
340, 350, 360 are determined, the jig device 300 and the driving
unit 100 are approached to each other and the driven couplers 333,
343, 353, 363 of the position-controlled reference drums 330, 340,
350, 360 are coupled with the driving couplers 133-136. Since the
driven couplers 333, 343, 353, 363 are fixed, the driving couplers
133-136 appropriately rotate to be connected with the driven
couplers 333, 343, 353, 363. After the driving couplers 133-136 are
position-controlled and coupled with the driven couplers 333, 343,
353, 363, the jig device 300 and the driving unit 10 are moved
relative to the reference drums 330, 340, 350, 360 along an axial
direction of the reference drums 330, 340, 350, 360 so as to
separate the driving couplers 133-136 from the driven couplers 333,
343, 353, 363. Here, the driving unit 100 may be moved by a
dedicated moving jig and connected with the jig device 300 or
alternatively, the jig device 300 may be moved toward the image
forming apparatus, with the driving unit 100 being mounted to the
image forming apparatus, thereby controlling the driving couplers
133-136 of the driving unit 100.
[0341] The driving couplers 133-136, after being connected and
separated with respect to the driven couplers 333, 343, 353, 363,
are then coupled with the driven coupler 33 of the OPCs 30, 40, 50,
60. Since positions of the driving couplers 133-136 are fixed, the
OPCs 30, 40, 50, 60 can be set to satisfy Equations 2 and 3.
[0342] Accordingly, by using the jig device 300, assembling time is
saved in bulk production and radial displacement control of the
OPCs is facilitated.
[0343] FIG. 17B shows a third method of using a jig device 300'.
The jig device 300' as shown in FIG. 17B is similar to that shown
in FIG. 17A, and therefore, the like elements are given the same
reference numerals in the following description. However, in the
jig device 300' of FIG. 17B, the reference drums 330, 340, 350, 360
have driven couplers 333, 343, 353, 363 at one end, respectively,
and also have gears 371, 372, 373, 374 at the other end,
respectively. Idle gears 375 are arranged between the respective
gears 371, 372, 373, 374 such that the respective gears 371, 372,
373, 374 are disposed to rotate in associate with each other. The
reference drums 330, 340, 350, 360 are arranged at predetermined
intervals. Accordingly, by adjusting the position of one reference
drum, the position of the other reference drums can also be
adjusted accordingly. The reference drums are fixed in place when
the positions are adjusted, and the fixing process requires a
fixing member 320. Unlike in FIG. 17A, the respective reference
drums 330, 340, 350, 360 of FIG. 17B are connected so that they can
move in association with each other. Therefore, only a single
fixing member 320 is required to fix one 330 of the reference drums
to fix all of the reference drums 330, 340, 350, 360. For example,
if the first reference drum 330 is fixed by the fixing member 320,
the other reference drums 340, 350, 360 are accordingly fixed due
to the gears 371, 372, 373, 374, 375. By using the jig device 300'
as shown in FIG. 17B to obtain, for example, a value .alpha.1 of
one reference drum 330. Then as the position of the corresponding
reference drum 330 is adjusted based on the obtained value
.alpha.1, values .alpha.2, .alpha.3, .alpha.4 of the other
reference drums 340, 350, 360 are automatically determined, and
accordingly, the position of the reference drums 340, 350, 360 are
also adjusted. As a result, the image bearing bodies can be set
easily and efficiently.
[0344] When the radii Ro of the respective OPCs 30, 40, 50, 60 are
all the same and the distances between centers of the OPCs 30, 40,
50, 60 are all the same (L1=L2=L3=2.pi..multidot.Rox (x=1, 2, 3, .
. . )), .alpha.2, .alpha.3 and .alpha.4 all have the same value.
Therefore, as shown in FIG. 3, the positioning part of the OPCs 30,
40, 50, 60 fastened to the driving couplers 133-136 can be
positioned by uniformly placing the positioning part of the driving
couplers 133-136 which correspond to the OPCs 30, 40, 50, 60 along
the +X axis. As a result, the image errors of each color, generated
by +.delta.o of the OPCs 30, 40, 50, 60, can be controlled to
overlap in the same relative position during the sequential
transfer. As described with reference to FIGS. 4A through 7B, the
+.delta.o of the OPCs 30, 40, 50, 60 can be regulated with respect
to the positioning part 33b of the driven coupler 33, thereby
realizing an embodiment of the present invention.
[0345] To summarize, i) The OPCs 30,40, 50, 60 and the driving
rollers 80 respectively have runouts. In order to advantageously
control the frequency of image errors occurring due to +.delta.o
and +.delta.d by the runout, the OPCs and the driving rollers are
constructed so that the positioning parts 33b and 83b of the driven
couplers 33 and 83 are positioned at certain locations with respect
to +.delta.o and +.delta.d.
[0346] ii) An embodiment and the effect thereof have been
described, with the embodiment satisfying the conditions of the
Equation Set 1 so that at least two of the image errors (Rke, Rce,
Rme, Rye) by the runout of at least one of the driving roller 80
and the supporting roller 91 overlap at the same relative location.
Here, the image errors generated in the image area of the
corresponding OPC can be overlapped according to relative sizes of
the radius Rd of the driving roller 80 and the radius Ro of the OPC
and regardless of the number of image errors generated in a unit
image.
[0347] iii) Hereinbefore, Equation Set 2 and the Equation Set 3
have respectively been described as conditions of superimposition
of at least two of the image errors (Oke, Oce, Ome, Oye) generated
by the runout of the OPCs 30, 40, 50, 60, without regard to the
runout of the driving roller 80 and the supporting roller 91. More
specifically, in order to superimpose any one image error of the
other OPCs 40, 50, 60 with respect to the predetermined OPC 30, the
system is set up to satisfy at least one condition of Equation Set
2 or 3. In order to superimpose the image errors of at least two
neighboring OPCs, the system is set up to satisfy at least one
condition of the Equation Set 3. Equation Sets 2 and 3 can be
generally applied without considering the relative sizes of L1, L2
and L3, which are distances between the centers of the OPCs 30, 40,
50, 60. When L1=L2=L3, the system is set up, generally, on
condition of Equation Set 4. In other words, since the product is
substantially manufactured to satisfy L1=L2=L3, considering
relations in assembly and size with other various parts, frequency
of the image error occurrence can be effectively reduced by
applying any of Equation Sets 2-4.
[0348] As a third step for reducing the frequency of the image
error occurrence, a method for superimposing the image error by the
runout of at least one of the supporting roller 91 and the driving
roller 80 corresponding to the image error by the runout of the
respective OPCs 30, 40, 50, 60 will now be described.
[0349] As described in FIGS. 8A and 8B, for example, the image
error Rke occurs in the image area of the K color OPC 30 caused by
the interval B of the driving roller 80. By the interval B, again,
the image errors Rme and Rye occur as well in the image areas of
other OPCs 50, 60. The image error Oke occurs by the interval A1 of
the K color OPC 30 as described in respect to FIGS. 15A and 15B.
Also, the image errors Oce, Ome and Oye occur by the intervals A1,
A2, A3 and A4 of the other OPCs 40, 50, 60. When at least two of
the image errors respectively generated by the intervals A1-A4 and
B of the OPCs 30, 40, 50, 60 and the driving roller 80 are
superimposed at the same position on the belt 70, influences of the
image errors on the final full color image can be reduced.
[0350] Referring to FIG. 18A, .theta.d refers to an angle formed by
a center of the interval B defining the radial displacement
+.delta.d of the driving roller 80 counterclockwise from the +X
axis, and that .theta.ox refers to an angle formed by the radial
displacement +.delta.o of the OPC disposed at the x-th position in
a running direction of the belt 70 counterclockwise from the +Y
axis. At least one (Rke, for example) of the image errors Rke, Rce,
Rme and Rye, which may be generated by the interval B, can be
superimposed with a corresponding image error (Oke) among the image
errors Rke, Rce, Rme and Rye of the respective OPCs 30, 40, 50, 60,
on the same position on the belt 70, through the following method.
The driving roller 80 and the OPC 30 are positioned so that the
interval A1 of the OPC 30 contacts with the belt 70 at a location
where the maximum tangential speed Vmax of the driving roller 80 by
the interval B has the most influence on the belt 70, that is, when
a direction of the maximum tangential speed Vmax is aligned with
the +Y axis as shown by an imaginary line in FIG. 18A. Thus, in
order to superimpose the image errors by at least one of the
plurality of OPCs 30, 40, 50, 60, for example, the OPC 30, with
respect to the driving roller 80, the system is set up to satisfy
at least one of the following equations in Equation Set 5.
[0351] [Equation Set 5]
Rd.multidot..theta.d=(2.pi..multidot.l+.theta.ox).multidot.Rox.multidot.(1-
.+-.0.05)
(l=1, 2, 3, . . . ), (x=1, 2, 3, . . . ) and
Rd=z.multidot.Rox,(z=2, 3, 4, 5, . . . ) {circle around (1)}
Rd.multidot..theta.d=Rox.multidot..theta.ox (1.+-.0.05)
Rd=.theta.ox, (x=1, 2, 3, . . . ) {circle around (2)}
(2.pi.h+.theta.d)Rd=Rox.multidot..theta.ox(1.+-.0.05)
(h=1, 2, 3, . . . ), (x=1, 2, 3, . . . ) and Rox=k.multidot.Rd,
(k=2, 3, 4, 5, . . . ) {circle around (3)}
[0352] That is, if the system is set up to satisfy at least one of
the equations from Equation Set 5, the image errors occurring due
to the radial displacements of the driving roller 80 and the OPCs
30, 40, 50, 60 are superimposed at the same position on the belt
70, and accordingly, the image error appears only at the
superimposed location of the image.
[0353] First, a case wherein Rox<Rd will be described on the
assumption that .delta.o=.delta.d.
[0354] According to the first equation of Equation Set 5, the image
errors by the driving roller 80 and the objective OPC can be
superimposed when the radius Rd of the driving roller 80 is larger
than the radius Rox of the OPC of interest by integer multiples
equal to or greater than 2.
[0355] This will now be described in greater detail with reference
to FIGS. 18A and 18B. FIG. 18A shows a system which is not set up
to satisfy the first equation of Equation Set 3. Here, the OPC of
interest is the K color OPC 30 being disposed at the first
position, and Rd=2Ro1.
[0356] When Rd=2Ro1, and the driving roller 80 rotates once, the
OPC 30 rotates twice. It is assumed for purposes of this example
that a unit image is formed by two cycles of rotation of the OPC
30. Accordingly, one image error caused by the interval B of the
driving roller 80 and two image errors caused by the interval A1 of
the OPC 30 occur within one unit image area.
[0357] Hereinbelow, a method of aligning the image error caused by
the interval B of the driving roller 80 with one of the two image
errors caused by the interval A1 of the OPC 30 by resetting the
system to satisfy the first equation of Equation Set 5 will be
described with reference to FIG. 18A.
[0358] More specifically, referring to FIG. 18A, a center of the
interval A1 of the OPC 30 is set to .THETA.ox=.THETA.o1=315.degree.
counterclockwise with respect to the +Y axis, and the center of the
interval B is set to .THETA.d=315.degree. clockwise with respect to
the +X axis. When transfer of K image begins in this state, the
center of the image error Rke by the interval B during one
rotational cycle of the belt 70 occurs on a location where the belt
70 is moved from the starting point `Po1` by a distance equal to
Rd.multidot..theta.d. In other words, the center of the image error
Rke, generated in the unit image by the driving roller 80, is
generated at distances of Rd.multidot..theta.d from SL.
[0359] While the driving roller 80 rotates by one cycle, the OPC 30
rotates by two cycles. Therefore, two image errors, that is, first
and second image errors Oke1 and Oke2, casued by the interval A1
are generated within the unit image area.
[0360] A center of the first image error Oke1 occurs at a distance
Rox.multidot..THETA.ox=Ro1.multidot..THETA.o1=Ro1.multidot.315.degree.
away from SL. Since the second image error Oke2 occurs at a
distance 2.pi..multidot.Ro1 away from the first image error Oke1,
the second image error Oke2 is distanced away from SL by
2.pi..multidot.Ro1+Ro1.multidot..-
THETA.o1=(2.pi.+.THETA.o1).multidot.Ro1.
[0361] Therefore, in order to align one of the first and second
image errors Oke1 and Oke2 caused by the interval A1 of the OPC 30
with the image error Rke caused by the interval B of the driving
roller 80 at the same position, the distance Rd.multidot..theta.d
from SL to Rke should be the same as the distance
Rox.multidot..theta.ox=Ro1.multidot..theta.o1 from SL to the first
image error Oke1, or as the distance (2.pi.+.theta.o1).multidot.Ro1
from SL to the second image error Oke2.
[0362] To generalize the above conditions, the first equation of
Equation Set 5 can be obtained as follows.
Rd.multidot..theta.d=(2.pi..multidot.l+.theta.ox).multidot.Rox
(l=1, 2, 3, . . . ), (x=1, 2, 3, . . . ) and Rd=z.multidot.Rox,
(z=2, 3, 4, 5, . . . ) {circle around (1)}
[0363] By applying Rd=2Ro1 to the first equation of the equations
3, the OPC 30 and the driving roller 80 are mounted to satisfy
.THETA.ol=2.multidot..THETA.d.sub.-2.pi.. Because
.THETA.d=315.degree.,
.THETA.ol=630.degree..multidot.2.pi.=270.degree. is satisfied. That
is, when the driving roller 80 is initially positioned at a
position moved by 315.degree. clockwise on the +X axis with respect
to the interval B, according to the first equation of Equation Set
5, the interval A1 of the OPC 30 can be disposed at a position
moved by 270.degree. with respect to the +Y axis as shown in FIG.
18C. Since the interval A1 is pre-positioned, herein, at the phase
45.degree. counterclockwise from the positioning part 33b of the
driven coupler, the interval A1 can be easily adjusted to satisfy
.THETA.o1=270.degree..
[0364] When the OPC 30 and the driving roller 80 are mounted to
satisfy the first equation of the equations 3, the image errors
Oke2 and Rke are superimposed at the same distance, that is, by
Rd.multidot..theta.d=Rd.mu-
ltidot.315.degree.=(2.pi.+.theta.o1).multidot.Ro1=(2.pi.+270.degree.).mult-
idot.Ro1 away from SL. Therefore, only a single overlay Te1 of
superimposed image errors Oke2 and Rke and a non-superimposed image
error Oke1 occur in the K color image.
[0365] As described above, when the first OPC 30 and the driving
roller 80 are arranged so that the image errors thereof are
superimposed, one of the image errors occurring in the interval A2
of the neighboring OPC 40 can be superimposed with the image error
by the driving roller 80. In other words, as shown in FIG. 18C,
since Rd=2Ro2 in the C color OPC 40 as well,
.theta.o2=.theta.o1=270.degree. is satisfied according to the first
equation of Equation Set 3. Therefore, when the interval A2 of the
C color OPC 40 is positioned 270.degree. counterclockwise with
respect to the +Y axis, the center of the second image error Oce2
caused by the interval A2 is distanced away from SL by
Rd.multidot..theta.d, as shown in FIG. 18D. Accordingly, the image
error of the C color OPC 40 can also be superimposed at the same
position as the superimposed image error Te1.
[0366] Since the distance between the neighboring OPCs 30 and 40 is
not considered herein, the image error Rke of the driving roller 80
and the other image errors Oke1 and Oce1 are not necessarily
superimposed. In order to superimpose the image errors Oke1 and
Oke2 caused by the interval A1 with the image errors Oce1 and Oce2
caused by the interval A2, the OPCs 30 and 40 are arranged to
satisfy the first equation of the Equation Set 2. To explain it in
greater detail, the OPCs 30 and 40 have already been positioned to
satisfy the first equation of Equation Set 3. Therefore, as shown
in FIG. 18c, it can be understood that
.theta.o2=.theta.o1=.alpha.2=.alpha.1. By applying .alpha.2
=.alpha.1 to the first equation of the Equation Sets 2 and 3,
L1=2.pi..multidot.l.mult- idot.Ro1 can be satisfied. Because 1 is
an integer, the distance L1 between the centers C1 and C2 is set to
be an integer multiple of a circumference of the OPC 30. When l=1,
the transfer point Po2 of the C image of the OPC 40 is positioned
where the belt 70 is moved from the starting point `Po1` of the K
image by SL. Therefore, the image errors (Oke1, Oke2)(Oce1, Oce2)
caused by the intervals A1 and A2 are superimposed at the same
position. Since the OPCs 30 and 40 are mounted to satisfy the first
equation of Equation Set 5, the superimposed image errors Oke2,
Oce2 are also superimposed with the image error Rke caused by the
interval B of the driving roller 80.
[0367] As can be appreciated from the above description, when the
radius of the driving roller 80 is bigger than the radius of the
objective OPC by an integer multiple equal to or greater than two,
one of the plurality of image errors generated by the OPC of
interest can be superimposed with the image error caused by the
driving roller 80 by setting up the system to satisfy the first
equation of Equation Set 5. In the other plurality of OPCs as well,
one of the image errors caused by the corresponding OPCs can be
superimposed with the image error caused by the driving roller 80
by setting up the system to satisfy the first equation of Equation
Set 5.
[0368] When the system is set up to satisfy the first equation of
Equation Set 2, the image errors generated by the two OPCs 30 and
40 can be overlapped. Thus, the image errors generated by the OPCs
30 and 40 of interest can be reduced.
[0369] It has been illustrated that the image error Rke due to the
driving roller 80 and the image error due to the two OPCs 30 and 40
are overlapped, by way of example of the OPCs 30 and 40. It should
be understood, however, that if at least one of the plurality of
the OPCs 30 through 60 can be selected and set to satisfy the first
equation of Equation Set 5, the same effect can be obtained to
reduce the image error generated due to the selected OPC.
[0370] It has been illustrated that the first equation of Equation
Set 5 and the first equation of Equation Sets 2 and 3 can be
satisfied at the same time by way of example. It should be
understood that the same effect can be obtained from the OPC of
interest when the respective OPCs 30 through 60 satisfy at least
one of the equations from Equations Set 2, while also satisfying
the first equation of Equation Set 5. These scenarios can be
understood from the above description, and will not be described in
detail for the sake of brevity.
[0371] Now a scenario in which the size of the driving roller and
the OPC rollers are equal (Rd=Rox) will be described. It is
assumed, for purposes of this example, that the radius deviations
of the driving roller and the OPC rollers are equal, that is,
.delta.D=.delta.o.
[0372] Referring to FIG. 19A, Rd=Rox=Ro1. Therefore, when the
driving roller 80 rotates one time, the OPC 30 of interest also
rotates one time. Suppose that the OPC 30 rotates two times and
forms a unit image, two image errors Oke1 and Oke2 occur at the K
unit image due to the interval A1 of the OPC 30 as illustrated in
FIG. 19B. Since the interval A1 of the OPC 30 is positioned at the
phase .theta.o1 in the counterclockwise direction with respect to
the +Y axis, the center of the first image error Oke1 occurs away
from the transfer start point Po1 by a distance of
Ro1.multidot..theta.o1. The second image error Oke2 occurs away
from Po1 by a distance of
2.pi..multidot.Ro1+Ro1.multidot..theta.o1. The K unit image has two
image errors Rke1 and Rke2 generated at a certain location caused
by the interval B of the driving roller 80. Still referring to FIG.
19A, the center of the interval B of the driving roller 80 is
located at the phase .theta.d in the clockwise direction with
respect to the +X axis. Accordingly, the first image error Rke1
caused by the interval B appears away from the point Po1 by a
distance of Rd.multidot..theta.d, and the center of the second
image error Rke2 appears away from the point Po1 by a distance of
2.pi..multidot.Rd+Rd.mul- tidot..theta.d as illustrated in FIG.
19B.
[0373] As a result, the distance between the centers of the first
image errors Rke1 and Oke1 is
d1=Ro1.multidot..theta.o1-Rd.multidot..theta.d. Likewise, the
distance between the centers of the second image errors Rke2 and
Oke2 is d1=Ro1.multidot..multidot..theta.o1-Rd.multidot..theta.d-
.
[0374] As Rd=Ro, when the OPC 30 and the driving roller 80 are set
to satisfy the condition d1=0, that is, the condition
Ro1.multidot..theta.o1-Rd.multidot..theta.d, the image errors Oke2
and Oke2 of the OPC 30 can be overlapped with the image errors Rke1
and the Rke2 of the driving roller 80, respectively. As illustrated
in FIG. 19A, .theta.d=225.degree. and .theta.o1=315.degree.. Hence,
when the image errors Oke1 and Oke2 of the OPC 30 overlap the image
errors Rke1 and Rke2 of the driving roller 80, the OPC 30 is set to
.theta.d=.theta.o1=225.deg- ree. as shown in FIG. 19C. Since the
interval A1 of the OPC 30 is predetermined to locate at a specific
phase away from the positioning part of the driven coupler, the
interval A1 of the OPC 30 is set to locate at 225.degree. away from
+Y in the counterclockwise direction as described in the exemplary
embodiments of the present invention. Referring to FIG. 19D, the
radial displacements .delta.o and .delta.d of the OPC 30 and the
driving roller 80 appear on the belt 70 with the same pattern
period and can advantageously be overlapped with each other.
Consequently, only the overlapping images of the image errors Oke1
and Oke2, and Rke1 and Rke2 occur in the unit image, to thus reduce
the total number of the image errors. That is, the unit image area
has only the overlapping error Te3 of Oke1 and Rke1 and the
overlapping error of Te4 of Oke2 and Rke2.
[0375] While the OPC 30 is set for the driving roller 80 to satisfy
the second condition of Equation Set 5, if one of the neighboring
OPCs 40, 50, 60 is set to satisfy one of the conditions of Equation
Set 2 or 3, the image error due to the OPC of interest can be
overlapped with respect to the overlapping error Te3 and Te4. A
detailed description thereof has been provided above in reference
to FIGS. 6A through 16, therefore a detailed description will not
be repeated here for the sake of brevity.
[0376] Now a scenario in which the OPC rollers are larger than the
driving roller (Rd<Rox) will be described. Again, it is assumed
for purposes of this exemplary description that the radius
deviations of the OPCs and the driving roller are equal, that is,
.delta.D=.delta.o. As Rd<Rox, the driving roller 80 has a
shorter rotational cycle than the OPCs 30, 40, 50, 60 in view of
the rotational cycle over a unit of time. As a result, the image
error caused by imperfections in the driving roller 80 occur more
often than caused by the OPC in the unit image area. The number of
image errors can be reduced as a whole by overlapping one of the
plurality of the image errors of the driving roller 80 in the unit
image area, with the image error of the OPC of interest. To this
end, the system is set up to satisfy the third equation of Equation
Set 5. An embodiment of the present invention exemplifies that the
radius Rox of the OPC of interest is two times (c=2) longer than
the radius Rd of the driving roller 80. Suppose that the unit image
of a certain color is formed by four rotations of the driving
roller 80, and correspondingly two rotations of the OPC roller.
Hence, the unit image area has six image errors in total caused by
the driving roller and the particular OPC roller, including four
image errors caused by the driving roller 80 and two image errors
caused by the OPC.
[0377] Referring to FIG. 20A, an example is provided in which the
third equation of Equation Set 3 is not satisfied. The phase of the
center of the interval B of the driving roller 80 is positioned at
.theta.d=225.degree. with respect to the +X axis. If the transfer
of K initiates, the K unit image is transferred onto the belt 70 as
the driving roller 80 rotates four times as illustrated in FIG.
20B. Four image errors Rke1, Rke2, Rke3, and Rke4 caused by the
interval B appear in the unit image area at intervals equal to
2.pi..multidot.Rd. The initial image error Rke1 occurs away from
the transfer start point Po1 by a distance of
Rd.multidot..theta.d=Rd.multidot.225.degree.. The other image
errors Rke2, Rke3, and Rke4 sequentially appear away from the point
Po1 as much as (2.pi..multidot.h+.theta.d).multidot.Rd (h=1, 2,
3).
[0378] The OPC 30 is positioned at .theta.o1=45.degree. away from
the +Y axis in the counterclockwise direction. To transfer the K
unit image area, the OPC 30 rotates two times. Thus, two image
errors Oke1 and Oke2 due to the interval A1 occur with the distance
2.pi..multidot.Ro1 therebetween in the K unit image area as
illustrated in FIG. 20B. The first image error Oke1 occurs at a
position where the belt 70 is moved from the transfer start point
Po1 by a distance of
Ro1.multidot..theta.o1=Ro1.multidot.45.degree.. Therefore, the
distance between the first image errors Oke1 and Rke1 is
d2=Ro1.multidot.(0.5.thet-
a.d-.theta.o1)=Ro1.multidot.(112.5.degree.-45.degree.)=Ro1.multidot.67.5.d-
egree..
[0379] As a result, to overlap the two image errors Oke1 and Rke1,
the distance from Po1 to the image errors Oke1 and Rke1 should be
identical. While the driving roller 80 is set in advance, it is
required to satisfy the condition
Rd.multidot..theta.d=Ro1.multidot.(45.degree.+67.5.degree.)- . The
third equation of Equation Set 5 can be satisfied by setting the
OPC 30 to position at 112.5.degree. from +Y of the interval A1 in
the counterclockwise direction, as illustrated in FIG. 20C. In FIG.
20D, the centers of the two image errors Oke1 and Rke1 are at the
same location, that is, the centers are aligned away from Po1 by a
distance of
Rd.multidot..theta.d=Ro1.multidot..theta.o1=Ro1.multidot.112.5.degree..
The second image error Oke2 of the interval A1 overlaps with the
third image error Rke3 of the interval B. Therefore, the six image
errors in the K unit image area are reduced to four image errors,
to thus reduce the effect of the image errors.
[0380] The image errors caused by other OPCs can be further reduced
by setting the other OPCs to be in phase with the first OPC. That
is, the OPC of interest can be set to satisfy at least one of the
conditions of Equation Sets 2-4 while also satisfying the
conditions of Equation Set 5. In this situation, at least one of
the image errors due to the driving roller 80 can overlap with the
image error of the OPC, and at the same time, the image errors
occurring due to the OPCs can overlap with each other. Therefore,
the number of the image errors can be reduced still more.
[0381] The following is an explanation as to how to overlap the
image error of the driving error 80 with at least one of the image
errors of at least two OPCs at the same location within the unit
image. In this exemplary embodiment of the present invention, it is
exemplified that all the image errors of the plurality of the OPCs
30, 40, 50, 60 are overlapped, and that the overlapping error of
the OPCs 30, 40, 50, 60 is also advantageously overlapped with the
image error of the driving roller 80. Note that the radiuses of the
OPCs 30, 40, 50, 60 in this example are identical.
[0382] Firstly, referring to FIG. 21A, the radius Rd of the driving
roller 80 is greater than the radius Rox of the OPCs 30, 40, 50,
60. The radius of the respective OPCs 30, 40, 50, 60 is identical
Rox=Ro. Distances L1, L2, L3, L4, L5, and L6 defined among the
centers C1-C4 of the OPCS 30, 40, 50, 60 are set to satisfy all of
the conditions of Equation Set 1. That is, the positions of the
OPCs 30,40, 50, 60 are set to satisfy
L1=L2=L3=Sd(2.pi..multidot.Rd). Under these conditions, the image
error due to the interval B of the driving roller 80 appears at the
same location as the overlapping unit image that is transferred
onto the belt 70 by the respective OPCs 30, 40, 50, 60. If the unit
image area is formed during one rotation of the driving roller 80,
the center of color image errors Rke, Rce, Rme, Rye caused by the
interval B is distanced away from the starting line SL by a
distance of Rd.multidot..theta.d(315.- degree.) in the unit image
area, as illustrated in FIG. 21B. Since L1=L2=L3=Sd, the full color
unit image area which passes through the OPCs 30, 40, 50, 60 and is
overlapped on the belt 70, has a single overlapping error Rte from
the image error Rke, Rce, Rme, Rye. Ultimately, by configuring the
system to satisfy all of the conditions of Equation Set 1, the
number of image errors due to the interval B of the driving roller
80 can be reduced to one fourth of the number of errors of Equation
Set 1 is not followed, and the image quality can thereby be
enhanced.
[0383] As discussed previously, the respective OPCs 30, 40, 50, 60
have radial displacement due to runout. Intervals A1, A2, A3, and
A4 of the OPCs 30, 40, 50, 60 cause image errors. To overlap the
image errors due the intervals A1, A2, A3, and A4, as shown in FIG.
21A, is the OPC's are set to satisfy the conditions of Equations
2-1 and 2-2. In short, L1=L2=L3 is satisfied and the radii of the
OPCs 30, 40, 50, 60 are identical. The maximum radial displacement
+.delta.0 of the OPCs 30, 40, 50, 60 is positioned at the same
phase 270.degree. from the +Y axis in the counterclockwise
direction. As constructed above, when the driving roller 80 rotates
one time, the OPCs 30, 40, 50, 60 rotate two times to create the
unit image area.
[0384] Two image errors occur from each of the respective OPCs 30,
40, 50, 60, and the centers of the first image errors Oke1, Oce1,
Ome1, Oye1 caused by the OPCs 30, 40, 50, 60 are positioned away
from the starting line SL by a distance of Ro.multidot.270.degree.,
as illustrated in FIG. 21C. The centers of the second image errors
Oke2, Oce2, Ome2, Oye2 caused by the OPCs 30, 40, 50, 60 are
positioned away from the starting line SL by a distance of
Ro.multidot.(2.pi.+270.degree.). Originally, the full color
overlapping image, which passed through the OPCs 30, 40, 50, 60,
has 8 image errors Oke1, Oce1, Ome1, Oye1 and Oke2, Oce2, Ome2,
Oye2. When the system is set to satisfy the conditions of Equation
Sets 2-4, the overlapping error Ote1 of the first image errors
Oke1, Oce1, Ome1, Oye1 and the overlapping error Ote2 of the second
image errors Oke2, Oce2, Ome2, Oye2 only appear. Thus, the number
of the image errors can be reduced to one fourth of the number of
errors caused when the relative locations of the OPC's are not
controlled according to Equation Set 2.
[0385] The overlapping errors Ote1 and Ote2 caused by the OPCs 30,
40, 50, 60 may appear at different positions from the overlapping
error Rte due to the driving roller 80 as mentioned above. When the
overlapping error Rte is overlapped with one of the overlapping
errors Ote1 and Ote2 by the OPCs 30, 40, 50, 60, the number of the
image errors in the unit image area can be reduced further. To this
end, it is set to satisfy the first equation of Equation Set 5 in
FIG. 21A. That is, Rd=2Rox=2Ro1=2Ro2=2Ro3=2- Ro4. Note that
.theta.ox=.theta.o1=.theta.o2=.theta.o3=.theta.o4=270.degre- e..
Accordingly, the distance Rd.multidot..theta.d between SL and the
center of Rte is the same as the distance
Ro.multidot.(2.pi.+270.degree.) between SL and the center of Ote2.
In other words, as Rd=2Ro and
Rd.multidot..theta.d=2Ro.multidot.315.degree.=Ro.multidot.(2.pi.+270.degr-
ee.), the two overlapping errors Ote2 and Rte are overlapped away
from SL by a distance of Rd.multidot..theta.d.
[0386] As for the scenario when Rd=2Ro, when the system is set to
satisfy the first equation of Equation Set 5 in addition to all of
the conditions of Equation Set 1 and Equation Sets 2-4, the unit
image area has only the first overlapping error Ote1 caused by the
OPCs 30, 40, 50, 60 and only the overlapping error Te5 of the
second overlapping error Ote2 caused by the OPCs 30, 40, 50, 60 and
the overlapping error Rte caused by the driving roller 80, as
illustrated in FIG. 21D. Ultimately, twelve image errors including
four image errors by the driving roller 80 and eight image errors
by the OPCs 30 through 60 can be reduced to two image errors in the
unit image area. Thus. the total number of image errors is reduced
considerably and the image quality is enhanced.
[0387] When Rd=Rox, Equation Set 1, Equation Sets 2-4, and Equation
Set 5 are all satisfied. In this case, the radii of the OPCs 30,
40, 50, 60 are identical Rox=Ro. Referring to FIG. 22A, the
interval B of the driving roller 80 is positioned at the phase
.theta.d away from the +X axis in the clockwise direction. In an
exemplary embodiment of the present invention,
.theta.d=315.degree.. The distance between the centers C1, C2, C3
and C4 of the OPCs 30, 40, 50, 60 is L1=L2=L3=2.pi.Rd=Sd. The
distance between the centers of the OPCs 30, 40, 50, 60 is set to
equal an integer multiple of the circumference of the driving
roller 80. Such a system can satisfy Equation Set 1. To facilitate
the understanding of embodiments of the present invention, suppose
that the unit image area is formed by one rotation of the driving
roller 80, the interval B affects the same phase of the respective
OPCs 30, 40, 50, 60. More specifically, the driving roller 80 of
FIG. 22A needs to rotate four times to transfer the overlapped
color images of the OPCs 30, 40, 50, 60 and form the final full
color image. As illustrated in FIG. 22B, the centers of the image
errors Rke, Rce, Rme, Rye occurring within the color overlapping
image and caused by the interval B are aligned away from the
starting line SL by a distance of
Rd.multidot..theta.d=Rd.multidot.315.degree.. As the OPCs 30, 40,
50, 60 are set to satisfy Equation Set 1, all of the image errors
Rke, Rce, Rme, Rye caused by the interval B appear at the same
location during the image transfer by the OPCs 30, 40, 50, 60,
regardless of the number of the rotations of the driving roller 80.
Consequently, only one overlapping image error Rte occurs.
[0388] The OPCs 30, 40, 50, 60 are installed to satisfy the
condition of Equation Set 2. In more detail, the OPCs 30, 40, 50,
60 are installed such that the intervals A1, A2, A3, and A4 of the
respective OPCs 30, 40, 50, 60 are positioned at the same angle
from the transfer start point Po1, Po2, Po3, and Po4 in the
counterclockwise direction, that is, at the phase
.alpha.1=.alpha.2=.alpha.3=.alpha.4. For further understanding of
an exemplary embodiment of the present invention, .alpha.1-.alpha.4
are set to 315.degree. and it is assumed that one rotation of the
OPCs 30, 40, 50, 60 creates the color unit images. Referring to
FIG. 22C, the centers of the image errors Oke, Oce, Ome, Oye due to
the intervals A1, A2, A3, and A4 of the OPCs 30, 40, 50, 60 appear
away from the starting line SL by a distance of
Ro.multidot..alpha.1=Ro.multidot.315.degree. in the unit image
area. Therefore, the full color unit image area generated by the
OPCs 30, 40, 50, 60 and transferred onto the belt 70 in an
overlapping manner, has only the overlapping image error Ote of the
image errors Oke, Oce, Ome, Oye. The overlapping image Ote is
distanced from the SL by Ro.multidot.315.degree..
[0389] The system of FIG. 22A is set to satisfy the second
condition of Equation Set 3. That is, Rd=Rox, and .theta.o1
(=.alpha.1), .theta.o2 (=.alpha.2), .theta.o3 (=.alpha.3), and
.theta.o4 (=.alpha.4) of the respective OPCs 30, 40, 50, 60 equal
to 315.degree., which is also equal to .theta.d.
[0390] Accordingly, the image errors due to the interval B of the
driving roller 80 overlap with the image errors due to the
intervals A1, A2, A3, and A4 of the respective OPCs 30, 40, 50, 60.
Meanwhile, as shown in FIG. 22B, the image errors Rke, Rce, Rme,
Rye due to the driving roller 80 overlap as the overlapping error
Rte at the same position. The image errors Oke, Oce, Ome, Oye due
to the OPCs 30, 40, 50, 60 also overlap as the overlapping error
Ote at the same position. In this regard, the system is implemented
to further satisfying the second condition of Equation Set 5 so
that the two overlapping errors Rte and Ote can advantageously
overlap at the same position. As a result, as illustrated in FIG.
22D, the unit image area has only the final overlapping error Te6
produced from the two overlapping errors Rte and Ote. The center of
the final overlapping error Te6 is distanced away from SL by
Rd.multidot..theta.d=Ro.multidot..theta.o1=Ro.about..alpha.1. Under
the condition of Rd=Ro, when the second condition of Equation Set
1, Equation Sets 2-4, and Equation Set 5 are satisfied at the same
time, even more image errors in the unit image area can be
overlapped. Hence, the number of the image errors decreases, the
image quality can be enhanced, and the reliability of the product
can be elevated.
[0391] Thirdly, referring to FIG. 23A, a scenario when the OPC
rollers are bigger than the driving roller is described, that is,
when Rox=h.multidot.Rd(h=2, 4, 6 . . . ). To ease the understanding
of embodiments of the present invention, it is exemplified that the
radius Rd of the driving roller 80 is two times longer than the
radius Rox of the OPC. The number of the OPCs of interest is four,
and the radii of the respective OPCs 30, 40, 50, 60 is
Rox=Ro1=Ro2=Ro3=Ro4.
[0392] The distance between the centers C1, C2, C3, and C4 of the
OPCs 30, 40, 50, 60 is L1=L2=L3=2.times.2.pi..multidot.Rd=2Sd.
Accordingly, when the driving roller 80 rotates two times, the
respective OPCs 30, 40, 50, 60 make one rotation. Suppose that two
rotations of the driving roller 80 create the unit image of a
certain color, the interval B of the driving roller 80 produces two
effects on the color unit image areas, as illustrated in FIG. 23B.
Since the distance between the centers of the OPCs 30, 40, 50, 60
is an integer multiple of the circumference of the driving roller
80, the centers of the first image errors Rke1, Rce1, Rme1, Rye1
occurring at each color are aligned away from the starting line SL
by a distance of Rd.multidot..theta.d. The centers of the second
image errors Rke2, Rce2, Rme2, Rye2 are distanced from the starting
line SL by 2.pi..multidot.Rd+Rd.multidot..theta.d. As
.theta.d=180.degree., the first image errors Rke1, Rce1, Rme1, Rye1
appear away from the SL by a distance of Rd.multidot.180.degree.,
as the single overlapping image Rte1. The second image errors Rke2,
Rce2, Rme2, Rye2 appear as the single overlapping image error Rte2
positioned away from SL by a distance of
2.pi..multidot.Rd+Rd.multidot.180.degree.=Rd.multidot.(2.pi.+180.degree.)-
.
[0393] The distances between the centers C1, C2, C3, and C4 of the
OPCs 30, 40, 50, 60, as defined in the first and second equations
of Equation Set 2, are L1=L2=L3=2.pi..multidot.Ro. Since
.alpha.1=.alpha.2=.alpha.3=.- alpha.4=.theta.o1, the centers of the
image errors Oke Oce, Ome, Oye due to the intervals A1, A2, A3, and
A4 of the OPCs 30, 40, 50, 60 are distanced from SL by
Ro.multidot..theta.o1 in the unit image area, as illustrated in
FIG. 23C. Note that in this example .theta.o1=.alpha.1=270.degree..
Accordingly, the image errors Oke, Oce, Ome, Oye due to the OPCs
30, 40, 50, 60 appear as the single overlapping error Ote
positioned away from SL by a distance of
Ro.multidot.270.degree..
[0394] The system of FIG. 23A is set to satisfy the third equation
of Equation Set 5. Since 2Rd=Rox, which is applied to the third
equation of Equation Set 5,
(2.pi..multidot..theta.d).multidot.Rd=Rox.multidot..theta-
.ox=2Rd.multidot..theta.ox. Since .theta.d=180.degree.,
(2.pi.+180.degree.).multidot.Rd=2Rd.multidot..theta.ox. It can be
seen that the above equation can be rearranged to
(2.pi.+180.degree.)=.theta.o- x and .theta.ox=270.degree.. Since
.theta.o1=.theta.o2=.theta.o3=.theta.o4- =270.degree., the
respective OPCs 30, 40, 50, 60, as shown in FIG. 23A, satisfy the
third equation of Equation Set 5. After satisfying the third
equation of Equation Set 5, as aforementioned in reference to FIGS.
23B and 23C, one of the two overlapping errors Rte1 and Rte2 can be
overlapped with the final overlapping error Te7 that overlaps with
the other overlapping error Ote at the same position as illustrated
in FIG. 23D. Because the center of the overlapping image error Ote
due to the OPCs 30, 40, 50, 60 is positioned away from SL by a
distance of Ro.multidot..theta.o1=(2.pi.+.theta.d).multidot.Rd, the
final overlapping error Te7 appears away from SL by a distance of
Ro.multidot..theta.o1=(2.- pi.+.theta.d).multidot.Rd. Ultimately,
the final full color unit image has only the overlapping error Rte1
and the final overlapping error Te7 as illustrated in FIG. 23D.
[0395] In the exemplary embodiments of the present invention, it
has been described that the image errors mainly result from the
runouts of the OPCs 30, 40, 50, 60, which substantially transfer
the image onto the belt 70, and the runout of the driving roller
80, which drives the belt 70, without consideration of the effect
on the supporting roller 91. Thus, the effect of the supporting
roller 91 is not explained herein. It is to be understood that the
driving roller 80 and the supporting roller (driven roller) 91 are
interchangeable in the relationship.
[0396] Also, as indicated in the above equation sets, one will
understand that almost the same effect can be obtained within an
error range of .+-.0.05.
[0397] As set forth above, the roller and the roller manufacturing
method according to embodiments of the present invention are
assembled such that the positioning part of the driven coupler is
positioned at a certain angle in relation with the maximum radial
displacement of the roller body (drum body). Hence, it is possible
to control the effect on the radial displacement of the roller.
[0398] The driving unit of the image forming apparatus according to
embodiments of the present invention can control the alignment of
the OPCs based on a criterion, to thus control the effect from
radius deviations of the belt supporting roller and/or effects from
the radius deviations of the OPCs.
[0399] Furthermore, the image forming apparatus controls the
locations of the image errors occurring due to runout of the
driving roller and reduces the number of image errors in the final
overlapping image. Therefore, the image quality can be enhanced and
the reliability of the product is increased.
[0400] In particular, the frequency of image errors due to runouts
of the driving roller and/or the OPCs can be decreased even without
consideration of the radii of the OPCs and the driving roller.
[0401] The foregoing embodiments and advantages are merely
exemplary and are not to be construed as limiting the present
invention. The present teaching can be readily applied to other
types of apparatuses. Also, the description of the embodiments of
the present invention is intended to be illustrative, and not to
limit the scope of the claims, and many alternatives,
modifications, and variations will be apparent to those skilled in
the art.
* * * * *