U.S. patent application number 12/762838 was filed with the patent office on 2010-10-21 for sheet feeding apparatus and image forming apparatus.
This patent application is currently assigned to KONICA MINOLTA BUSINESS TECHNOLOGIES, INC.. Invention is credited to Akira KOSUGI, Tomoo SUZUKI, Daisuke UEDA.
Application Number | 20100264577 12/762838 |
Document ID | / |
Family ID | 42980385 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100264577 |
Kind Code |
A1 |
SUZUKI; Tomoo ; et
al. |
October 21, 2010 |
SHEET FEEDING APPARATUS AND IMAGE FORMING APPARATUS
Abstract
A sheet feeding apparatus which includes a sheet loading tray
for stacking sheets; a suction and conveyance section which is
placed above stacked sheets on the sheet loading tray and sucks and
conveys a sheet in the sheet conveying direction; an air blowing
section which blows air at the stacked sheets on the sheet loading
tray and causes the sheet to float up; and a skew correction
section which corrects a skew of the sheet conveyed by the suction
and conveyance section.
Inventors: |
SUZUKI; Tomoo; (Tokyo,
JP) ; KOSUGI; Akira; (Tokyo, JP) ; UEDA;
Daisuke; (Tokyo, JP) |
Correspondence
Address: |
CANTOR COLBURN, LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
KONICA MINOLTA BUSINESS
TECHNOLOGIES, INC.
Tokyo
JP
|
Family ID: |
42980385 |
Appl. No.: |
12/762838 |
Filed: |
April 19, 2010 |
Current U.S.
Class: |
271/11 |
Current CPC
Class: |
B65H 9/002 20130101;
B65H 2511/242 20130101; B65H 9/006 20130101; B65H 2511/216
20130101; B65H 3/128 20130101; B65H 2511/242 20130101; B65H 2220/11
20130101; B65H 2220/02 20130101; B65H 2404/2693 20130101; B65H
2301/331 20130101; B65H 2220/01 20130101; B65H 2511/216 20130101;
B65H 2801/06 20130101 |
Class at
Publication: |
271/11 |
International
Class: |
B65H 7/06 20060101
B65H007/06; B65H 3/08 20060101 B65H003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2009 |
JP |
2009-101733 |
Claims
1. A sheet feeding apparatus comprising: a sheet loading tray for
stacking sheets; a suction and conveyance section which is placed
above stacked sheets on the sheet loading tray and sucks and
conveys a sheet in the sheet conveying direction; an air blowing
section which blows air at the stacked sheets on the sheet loading
tray and causes the sheet to float up; and a skew correction
section which corrects a skew of the sheet conveyed by the suction
and conveyance section.
2. The sheet feeding apparatus of claim 1, further comprising a
pair of conveying rollers provided on a downstream side in the
sheet conveying direction relative to the suction and conveyance
section and along the width direction perpendicular to the sheet
conveying direction, to convey the sheet conveyed from the suction
and conveyance section towards the downstream side in the sheet
conveying direction, wherein the skew correction section is a
section which controls the pair of conveyance rollers to stop, and
during the period when the pair of conveyance rollers is stopped,
controls at least the pair of conveyance rollers so that a leading
edge of the sheet is made to abut against the pair of conveyance
rollers.
3. The sheet feeding apparatus of claim 1, further comprising: a
skew detection section which detects a skew amount of the sheet
conveyed by the suction and conveyance section, wherein the suction
and conveyance section comprises a plurality of sheet conveying
sections, each of the plurality of sheet conveying sections being
arranged along the width direction and being capable of conveying
the sheet with independent conveying speed to each other, wherein
the skew correction section is configured to control the conveying
speeds of the plurality of sheet conveying sections respectively,
according to the skew amount of the sheet detected by the skew
detection section.
4. The sheet feeding apparatus of claim 1, further comprising: a
skew detection section which detects a skew amount of the sheet
conveyed by the suction and conveyance section; and a displacing
section which displaces the suction and conveyance section with
respect to the sheet conveying direction, wherein the skew
correction section is configured to control the displacing section
to change an angle of the suction and conveyance section with
respect to the sheet conveying direction according to the skew
amount of the sheet detected by the skew detection section.
5. The sheet feeding apparatus of claim 3, further comprising: a
sheet detection sensor which detects a leading edge of the sheet
fed out by the suction and conveyance section; and a pair of
conveying rollers provided on a downstream side in the sheet
conveying direction relative to the sheet detection sensor and
along the width direction perpendicular to the sheet conveying
direction, to convey the sheet conveyed from the suction and
conveyance section towards the downstream side in the sheet
conveying direction, wherein the skew correction section completes
a skew correction before the leading edge of the sheet conveyed by
the suction and conveyance section arrives at the pair of conveying
rollers.
6. The sheet feeding apparatus of claim 4, further comprising: a
sheet detection sensor which detects a leading edge of the sheet
fed out by the suction and conveyance section; and a pair of
conveying rollers provided on a downstream side in the sheet
conveying direction relative to the sheet detection sensor and
along the width direction perpendicular to the sheet conveying
direction, to convey the sheet conveyed from the suction and
conveyance section towards the downstream side in the sheet
conveying direction, wherein the skew correction section completes
a skew correction before the leading edge of the sheet conveyed by
the suction and conveyance section arrives at the pair of conveying
rollers.
7. The sheet feeding apparatus of claim 3, further comprising: a
sheet detection sensor which detects a leading edge of the sheet
fed out by the suction and conveyance section; and a sheet
separation section which blows air to separate sheets conveyed by
the suction and conveyance section, the sheet separation section
being provided on an upstream side relative to the sheet detection
sensor, wherein, the skew detection section detects the skew amount
of the sheet based on a signal from the sheet detection sensor, and
the skew correction section stops the operation of the sheet
separating section at least when the sheet detecting section is
detecting the leading edge of the sheet.
8. The sheet feeding apparatus of claim 4, further comprising: a
sheet detection sensor which detects a leading edge of the sheet
fed out by the suction and conveyance section; and a sheet
separation section which blows air to separate sheets conveyed by
the suction and conveyance section, the sheet separation section
being provided on an upstream side relative to the sheet detection
sensor, wherein, the skew detection section detects the skew amount
of the sheet based on a signal from the sheet detection sensor, and
the skew correction section stops the operation of the sheet
separating section at least when the sheet detecting section is
detecting the leading edge of the sheet.
9. An image forming system comprising: a sheet feeding apparatus of
claim 1; and an image forming apparatus which forms an image on a
sheet conveyed by the sheet feeding apparatus.
10. The image forming system of claim 9, further comprising another
skew correction section which corrects a skew of the sheet conveyed
from the sheet feeding apparatus before forming the image on the
sheet.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application is based on Japanese Patent
Application No. 2009-101733 filed with Japanese Patent Office on
Apr. 20, 2009, the entire content of which is hereby incorporated
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to a sheet feeding apparatus
that separates and feeds one sheet at a time from a stack of sheets
placed on a table for sheets, and to image forming apparatuses.
[0004] 2. Background Technology
[0005] In recent years, air sheet feeding apparatuses that can feed
a large quantity of sheets are being used in image forming
apparatuses such as copying machines, printers, etc. An air sheet
feeding apparatus is one in which a sheet is made to float up by
blowing air on to the side surface of a stack of sheets, a sheet is
made to get sucked on to the suction surface of a belt, etc., in
which are formed air suction holes that suck in air, and the sheet
is conveyed by driving the belt in a rotating manner.
[0006] Conventionally, this kind of sheet feeding apparatus was one
that fed large quantities of sheets of the same size or of the same
type. However, in recent years, due to the progress in digital
information technology, a printing method called print on demand
has come into widespread use in which the data prepared by a
computer, etc., is printed out directly without going through an
intermediate step of preparing offset printing films or plates, and
sheet feeding apparatuses have become necessary that can feed
sheets of various types and sizes that are being used in the
printing industry.
[0007] In Examined Japanese Patent Application Publication No.
3855512 (Patent Document 1), an air sheet feeding apparatus has
been disclosed wherein, nozzles (sheet raising means) that jet out
air on the front surface of a stack of sheets for causing a sheet
to float up, and nozzles (sheet separating means) for blowing air
for separating other sheets from a single sheet that is made to be
sucked and attached to the conveying belt are provided on the front
side of the stack of sheets in the direction of feeding the
sheet.
[0008] According to Patent Document 1, sheet feeding is made
possible without feeding several sheets simultaneously by
selectively switching the air from the sheet raising means and the
sheet separating means according to the timing of sheet feeding by
the conveying belt.
[0009] In Examined Japanese Patent Application Publication No.
3891405 (Patent Document 2), an air sheet feeding apparatus has
been disclosed wherein, a sheet at the topmost surface of a stack
of sheets is fed while being sucked by a suction and conveyance
means because the sheet is floated up by a first air blowing means
that blows air on the front surface of a stack of sheets from the
front side of the direction of sheet feeding, and a second air
blowing means that blows air on the side surface of the stack of
sheets.
[0010] According to Patent Document 2, a positioning member is
provided that restricts the height on the side surface of a sheet
or in its neighborhood, a constant sheet separation is obtained at
all times by selecting the air blow from a second air blowing means
in accordance with the size of the sheet.
[0011] However, in an air sheet feeding apparatus described in
Patent Document 1 or Patent Document 2, in order to separate
definitely the topmost sheet that is sucked by the sucking and
conveying section from the other sheets, a certain amount of space
is required in the up-down direction between the topmost surface of
the stack of sheets and the suction and conveyance section.
[0012] In this kind of configuration, in the floating process of
transiting from the stacked state to the state of getting sucked by
the sucking and conveying section, since the raised sheet can take
various types of postures (such as flexure or distortion) depending
on the condition of the air getting into the stack of sheets,
conditions can arise in which the leading edge of the sheet is
sucked by the suction and conveyance section at an angle to the
conveying direction. If a sheet is sucked and conveyed in this
condition, the suction area moves towards the trailing edge so as
to maintain the position of the leading edge of the sheet that is
inclined. In other words, the sheet gets skewed.
[0013] As described above, an air sheet feeding apparatus has the
problem that the fluctuations in the sheet skewing are large, and
improvement of sheet skewing is desired. In particular, the demand
is very strict about the positional accuracy of the image formed on
a sheet and the sheet (image registration) in the field of print on
demand, and improvement of sheet skewing is strongly desired in the
case of air sheet feeding apparatuses used in this field.
[0014] In an image forming apparatus, although a skewing correction
mechanism (paper registration mechanism) is provided at a position
just before image transfer, particularly in the case of sheets of
large sizes, since the part of the sheet on the upstream side is
nipped by a plurality of conveying rollers, even if an attempt is
made to correct a large skewing at this point of time, due to the
pulling of the sheet between the registration mechanism and the
conveying rollers, a large stress is applied on the sheet, problems
occur such as buckling or wrinkling, etc.
[0015] An object of the present invention is to solve the problem
that the fluctuations in sheet skewing are large, and to provide an
air sheet feeding apparatus having excellent sheet feeding
performance that is demanded in the print on demand field.
SUMMARY OF THE INVENTION
[0016] A sheet feeding apparatus and a system reflecting the
aspects of the present invention for solving the above problems are
the following: [0017] 1. A sheet feeding apparatus including a
sheet loading tray for stacking sheets; a suction and conveyance
section which is placed above stacked sheets on the sheet loading
tray and sucks and conveys a sheet in the sheet conveying
direction; an air blowing section which blows air at the stacked
sheets on the sheet loading tray and causes the sheet to float up;
and a skew correction section which corrects a skew of the sheet
conveyed by the suction and conveyance section. [0018] 2. The sheet
feeding apparatus of above item 1, further including a pair of
conveying rollers provided on a downstream side in the sheet
conveying direction relative to the suction and conveyance section
and along the width direction perpendicular to the sheet conveying
direction, to convey the sheet conveyed from the suction and
conveyance section towards the downstream side in the sheet
conveying direction,
[0019] wherein the skew correction section is a section which
controls the pair of conveyance rollers to stop, and during the
period when the pair of conveyance rollers is stopped, controls at
least the pair of conveyance rollers so that a leading edge of the
sheet is made to abut against the pair of conveyance rollers.
[0020] 3. The sheet feeding apparatus of above item 1, further
including a skew detection section which detects a skew amount of
the sheet conveyed by the suction and conveyance section,
[0021] wherein the suction and conveyance section comprises a
plurality of sheet conveying sections, each of the plurality of
sheet conveying sections being arranged along the width direction
and being capable of conveying the sheet with independent conveying
speed to each other,
[0022] wherein the skew correction section is configured to control
the conveying speeds of the plurality of sheet conveying sections
respectively, according to the skew amount of the sheet detected by
the skew detection section. [0023] 4. The sheet feeding apparatus
of above item 1, further including a skew detection section which
detects a skew amount of the sheet conveyed by the suction and
conveyance section; and a displacing section which displaces the
suction and conveyance section with respect to the sheet conveying
direction,
[0024] wherein the skew correction section is configured to control
the displacing section to change an angle of the suction and
conveyance section with respect to the sheet conveying direction
according to the skew amount of the sheet detected by the skew
detection section. [0025] 5. The sheet feeding apparatus of above
item 3 or 4, further including a sheet detection sensor which
detects a leading edge of the sheet fed out by the suction and
conveyance section; and a pair of conveying rollers provided on a
downstream side in the sheet conveying direction relative to the
sheet detection sensor and along the width direction perpendicular
to the sheet conveying direction, to convey the sheet conveyed from
the suction and conveyance section towards the downstream side in
the sheet conveying direction,
[0026] wherein the skew correction section completes a skew
correction before the leading edge of the sheet conveyed by the
suction and conveyance section arrives at the pair of conveying
rollers.
[0027] 6. The sheet feeding apparatus of above item 3 or 4, further
including a sheet detection sensor which detects a leading edge of
the sheet fed out by the suction and conveyance section; and a
sheet separation section which blows air to separate sheets
conveyed by the suction and conveyance section, the sheet
separation section being provided on an upstream side relative to
the sheet detection sensor,
[0028] wherein, the skew detection section detects the skew amount
of the sheet based on a signal from the sheet detection sensor, and
the skew correction section stops the operation of the sheet
separating section at least when the sheet detecting section is
detecting the leading edge of the sheet. [0029] 7. An image forming
system including a sheet feeding apparatus of any one of above
items 1 to 6, and an image forming apparatus which forms an image
on a sheet conveyed by the sheet feeding apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] These and other objects, advantages and features of the
invention will become apparent from the following description
thereof taken in conjunction with the accompanying drawings in
which:
[0031] FIG. 1 is an overall configuration diagram of an image
forming apparatus having an image forming apparatus, an image
reading apparatus, an automatic document feeding apparatus, and a
large quantity sheet feeding apparatus;
[0032] FIG. 2 is a perspective view of the important parts of a
large quantity sheet feeding apparatus according to the present
invention;
[0033] FIG. 3 is a front middle cross-sectional view diagram
showing the main unit of a sheet feeding apparatus;
[0034] FIG. 4 is a side view diagram showing the main unit of a
sheet feeding apparatus;
[0035] FIG. 5 is a plan view diagram showing the main unit of a
sheet feeding apparatus;
[0036] FIG. 6 is a block diagram showing the control system related
to the control section 100 that also functions as a skew correction
section that corrects the skew of a sheet according to the present
invention;
[0037] FIGS. 7a-7c are schematic diagrams showing the operation of
the conveying roller pair and the process of sheet correction;
[0038] FIG. 8 is an operation timing chart showing the sheet
conveying control related to a first preferred embodiment;
[0039] FIG. 9 is a time chart showing the sheet conveying control
carried out by the control section 100 as a skew correction section
according to a second preferred embodiment of the present
invention;
[0040] FIG. 10 is schematic diagram showing an angle varying
section 69 that varies the angle of the suction and conveyance
section 60.
[0041] FIG. 11 is a schematic cross-sectional diagram in which the
angle varying section 69 has been cut horizontally at the top
surface of the top supporting member 81; and
[0042] FIG. 12 is a flow chart showing the sheet conveying control
carried out by the control section 100 functioning as a skew
correction section according to a third preferred embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] While some preferred embodiments of the present invention
are described below with reference to the drawings, the present
invention shall not be construed to be limited to the preferred
embodiments described below.
[0044] Some preferred embodiments of the present invention are
described below with reference to the drawings.
[0045] Image Forming Apparatus:
[0046] FIG. 1 is an overall configuration diagram of an image
forming apparatus having an image forming apparatus A, an image
reading apparatus SC, an automatic document feeding apparatus DF,
and a large quantity sheet feeding apparatus LT.
[0047] The image forming apparatus A shown in the figure is
configured from an image forming section having a photoreceptor
(image carrier) 1, a charging unit 2, an image exposure unit 3, a
developing unit 4, a transfer unit 5, and a cleaning unit 6, etc.,
a fixing unit 7, and a sheet conveying system.
[0048] The sheet conveying system is configured to have a sheet
feeding cassette 10, a first sheet feeding section 11, a second
sheet feeding section 12, a sheet discharging section 14, a
conveying path switching section 15, a reentrant sheet re-feeding
section 16, and an inverting sheet discharging section 17.
[0049] A document d placed on the document table of the automatic
document feeding apparatus DF is conveyed by a sheet feeding
section, the images on one side or both sides of the document are
read out by the optical system of the image reading apparatus SC,
and read by an image sensor CCD. After the analog signal obtained
by photoelectric conversion by the image sensor CCD is subjected
to, in the image processing section 20, analog processing, A/D
conversion, shading correction, image compression processing, etc.,
the image signal is sent to the image exposure unit 3.
[0050] In the image forming section, the processes of charging,
exposure, developing, transfer, separation, cleaning, etc., are
carried out.
[0051] In the image forming section, electric charge (negative
electric charge in the present preferred embodiment) is put by the
charging unit 2 on the photoreceptor 1, an electrostatic latent
image is formed by laser light emission from the image exposure
unit 3, and the electrostatic latent image is converted into an
apparent image by the developing unit 4 and becomes a toner image
(the toner image has negative electric charge in the present
preferred embodiment). Next, a sheet P stored in the sheet feeding
cassette 10 is conveyed from a first sheet feeding section 1. On
the other hand, the toner remaining on the photoreceptor 1 after
transferring is cleaned by the cleaning unit 6.
[0052] The sheet P is conveyed in synchronization with the toner
image by the second sheet feeding section 12 made of a registration
roller. At this time, the skew during conveying is corrected by the
sheet P abutting against the second sheet feeding section. In other
words, the second sheet feeding section 12 is not only a
registration section that synchronizes the toner image and the
sheet P, but also a skew correction section that corrects the skew
of the sheet during conveying. After that, the sheet P has the
toner image transferred onto it by the transfer section after which
it is fixed by the fixing unit 7. The sheet P after fixing is
discharged to outside the apparatus by the sheet discharging
section 14.
[0053] Further, in the case of double sided copying, the sheet P
with image formed on its first surface is fed to the reentrant
sheet re-feeding section 16 and is turned upside down, and, after
image formation is made on its second surface again in the image
forming section, it is discharged to outside the apparatus by the
sheet discharging section 14. In the case of inverting sheet
discharge, after the sheet P that has been branched from the normal
sheet discharge path is turned upside down by being switched back
in the inverting sheet discharging section 17, it is discharged to
outside the apparatus by the sheet discharging section 14.
[0054] Further, in the present preferred embodiment, the sheet
feeding cassette 10 inside the image forming apparatus A can also
have a sheet feeding apparatus according to the present invention
to be described later, that is, it can have a suction and
conveyance section, an air blowing section, and a skew correction
section.
[0055] Sheet Feeding Apparatus:
[0056] The large quantity sheet feeding apparatus LT according to
the present invention and connected to the image forming apparatus
A has a sheet feeding apparatus main unit 30, a first air blowing
section 40 and a second air blowing section 50 as air blowing
sections, a suction and conveyance section 60, etc., stores a large
quantity of sheets P, and feeds one sheet Pat a time to the image
forming apparatus A.
[0057] The sheet feeding apparatus main unit 30 has sheet loading
trays 31, a sheet leading edge restricting member 32, a sheet
trailing edge restricting member 33, and guide rails 34. There are
three sheet loading trays 31, and the construction is such that
each sheet loading tray 31 can be drawn out from the large quantity
sheet feeding apparatus LT due to the guide rails 34. For example,
in the large quantity sheet feeding apparatus LT, 1300 sheets can
be loaded in the first tray, and 1850 sheets each can be stored in
the second and third trays, so that in total it is possible to
store about 6000 sheets.
[0058] FIG. 2 is a perspective view of the important parts of the
sheet feeding apparatus main unit 30 according to the present
invention, FIG. 3 is a front cross-sectional view diagram of the
sheet feeding apparatus main unit 30, FIG. 4 is a side view diagram
of the sheet feeding apparatus main unit 30, and FIG. 5 is a plan
view diagram of the sheet feeding apparatus main unit 30.
[0059] The suction and conveyance section 60 of FIG. 2 has been
shown in an assumed position that has been shifted horizontally
towards the downstream side of the sheet conveying direction by the
extent indicated by the arrow b from its actual position when
installed in the sheet feeding apparatus main unit 30.
[0060] As is shown in FIG. 2, a sheet stack Ps and the topmost
sheet P1 are placed on the sheet loading tray 31, and are stored so
that they can be raised or lowered along with the sheet loading
tray by a mechanism not shown in the figure.
[0061] A pair of sheet side edge restricting sections 70 restrict
the sheet stack Ps in the width direction that is at right angles
to the sheet conveying direction, and have on the inside the sheet
side edge restricting members 71 in close contact with the side
edges of the sheet stack Ps. The relative distance along the width
direction of the sheets of the sheet side edge restricting section
70 can be changed freely, and restricts the position of the sheet
stack Ps along the width direction according to the size of the
sheet.
[0062] The sheet side edge restricting section 70 has a box type
structure with a large strength of rigidity and is sufficiently
long in the sheet feeding direction, and it has been made possible
to maintain the gap between the sheet side edge restricting member
71 and the side edge of the sheet stack Ps even at the topmost part
of the sheet stack Ps to within the prescribed values for a wide
range of sheet sizes.
[0063] The sheet leading edge restricting member 32 restricts the
leading edge of the sheet stack Ps in the sheet loading tray 31,
and is fixed to the sheet feeding apparatus main unit 30.
[0064] The sheet trailing edge restricting member 33 can be moved
freely along the length direction of the sheet P, restricts the
position of the trailing edge of the sheet P in the sheet feeding
direction, and is being supported by the sheet feeding apparatus
main unit 30 so that it can be displaced along the sheet feeding
direction. The sheet side edge restricting members 71 and the sheet
trailing edge restricting member 33 are provided with a height and
shape so that the sheet P can be restricted at all times even when
the sheet P is made to float up by blowing air as described
later.
[0065] Further, as is shown in FIG. 3, in the sheet trailing edge
restricting member 33 is placed a height sensor PS3 that detects
the height of the topmost part of the sheet stack loaded in the
sheet loading tray.
[0066] The topmost position of the of the sheet stack Ps loaded in
the sheet loading tray 31 is maintained by a control section to be
described later, based on the signal of the height sensor PS3, so
as to be at the most optimum height for receiving the air blow. In
other words, based on the result of detection by the height sensor
PS3 shown in FIG. 3, the bottom plate 34 of the sheet loading tray
31 is raised by driving a raising and lowering motor not shown in
the figure, and control is carried out so that the topmost part of
the stack of sheets Ps is at all times maintained to be at the
prescribed height.
[0067] Mechanism of Sheet Separation Using Air Blow:
[0068] As is shown in FIG. 2, air is being blown from the sheet
conveying direction and from the sheet width directions on the
topmost part of the sheet stack Ps. The air blow in the sheet width
direction is along the two directions of the arrows A2 and A2, and
even in the sheet conveying direction, the air blow is as indicated
by the arrows B1 and B2.
[0069] First Air Blowing Sections:
[0070] As is shown in FIG. 2 and FIG. 3, the first air blowing
sections 40 that blow air on to the top of the sheet stack Ps from
the width directions are placed on both sides of the sheet loading
tray 31. The first air blowing sections 40 are provided in the
sheet side edge restricting section 70. A first air blowing section
40 is made of an air blowing fan 41, guide plates 42, etc. The air
blow indicated by the arrows A1 and A2 is blowing air above the top
part of the sheet stack Ps from the first air blow outlet 72 placed
in the sheet side edge restricting member 71 of the sheet side edge
restricting section 70. As is shown in FIG. 4, the air blowing fan
41 has been installed on the sheet side edge restricting section 70
with its air outlet facing upward. The air that is discharged
upwards has its direction changed by 90.degree. by the guide plate
42 and is blown horizontally from the first air blow outlet 72 of
the sheet side edge restricting member 71.
[0071] Further, the first air blow outlet 72 and the first air blow
section 40 are provided in the sheet side edge restricting section
70, can be moved integrally with the sheet side edge restricting
member 71, and it has been made possible to have a constant
positional relationship with the sheet stack Ps at all times while
corresponding to changes in the sheet size.
[0072] As is shown in FIG. 3, relative to the first air blow outlet
72, there are several air exhaust outlets 73 provided on the side
surface of the sheet side edge restricting member 71 positioned on
the upstream side in the direction of sheet conveying, and it has
been ensured that there is no large distortion in the shape of the
sheet that has floated up.
[0073] Second Air Blowing Section:
[0074] Next, the second air blowing section 50 placed on the
downstream side of the sheet loading tray 31 in the sheet conveying
direction and acting as a sheet separation section and as a sheet
floating up section is described based on FIG. 2 and FIG. 3.
[0075] The second air blowing section 50 is constituted from an
electric fan 51 and an air flow guide 52 connected to the electric
fan 51. The second air blowing section 50 blows air towards the
leading edge and topmost part of the sheet stack loaded in the
sheet loading tray from the second air blow outlet 53A of the air
flow guide 52. The electric fan 51 has been installed inside the
air flow guide 52. In the top part of the air flow guide 52, there
is a second air blow outlet 53A facing towards the downstream side
of the sheet conveying direction. The air ejected from the second
air blow outlet 53A is facing horizontally towards the downstream
side of the sheet conveying direction as shown by the arrow B1 in
FIG. 2.
[0076] The air blow from the second air blow outlet 53A is the air
blow for making the sheet P at the topmost part of the sheet stack
Ps separate and float up, and is being blown at the top part of the
leading edge of the sheet stack Ps. At this time, the second air
blowing section 50 operates as a floating up section that makes the
sheet float up.
[0077] Further, in the top part of the air flow guide 52, there is
a third air blow outlet 53B on the downstream side of the second
air blow outlet 53A, and the third air blow outlet 53B has been cut
open so as to face upwards. The air flow from the third air blow
outlet 53B, as is shown in the arrow B2 in FIG. 2, is pointing
towards an obliquely upward direction at a sheet that is conveyed
towards the upstream side relative to the detection position of the
two sheet detecting sensors PS2A (PS2B) which are explained in
detail later.
[0078] The air blown in the direction B2 from the third air blow
outlet 53B is the air blow for making only one sheet get sucked and
conveyed by the suction and conveyance section 60, and is being
blown in the direction of the suction belt 63 of the suction and
conveyance section 60.
[0079] The air flow guide 52, as is shown in FIG. 3, links the
second air blow outlet 53A and the electric fan 51, or is formed to
have a duct structure that links the third air blow outlet 53B and
the electric fan 51. The duct is branched into a first duct 54A and
a second duct 54B. Further, there is a shutter 55 at the branching
point, and this shutter 55 makes it possible to switch the air flow
rate through the first duct 54A and the second duct 54B.
[0080] The second air blowing section 50, according to the
selection by the shutter 55, functions as a sheet flowing up
section that ejects air from the second air blow outlet 53A which
is at the end of the first duct 54A, or as the sheet separation
section that ejects air from the third air blow outlet 53B which is
a the end of the second duct 54B.
[0081] By making the shutter 55 operate as an air flow switching
section as shown in FIG. 3 by a solenoid not shown in the figure,
the function as a sheet separation section is put in the operating
state or the stopped state, or else, the function as a sheet
floating up section is put in the stopped state or the operating
state. In other words, the second air blowing section 50 has two
switchable functions. It is both the sheet floating up section that
makes a sheet P float up and the sheet separation section that
separates the sheet P. As is shown in FIG. 3, when the shutter is
in the state indicated by continuous lines, the sheet separation
section is in the operating state, and when it is in the state
indicated by broken lines, the sheet separation section is in the
stopped state.
[0082] Suction and Conveyance Section:
[0083] As is shown in FIG. 3, the suction and conveyance section 60
is positioned above the sheet stack Ps loaded in the sheet loading
tray and is placed on the downstream side of the sheet conveying
direction, and is fixed to the top supporting member of the large
quantity sheet feeding apparatus LT.
[0084] As is shown in FIG. 2 and FIG. 4, the suction and conveyance
section 60 has the first sheet conveying section 60A and the second
sheet conveying section 60B along the width direction at right
angles to the sheet conveying direction. Each sheet conveying
section has a supporting member 68, a large diameter roller 61, two
small diameter rollers 62, and a suction belt 63 that is wound
around and rotates over the large diameter roller 61 and the small
diameter rollers 62.
[0085] Each supporting member 68 is fixed to the top supporting
member 81, and respectively supports one large diameter roller 61
and two small diameter rollers 62 in a free to rotate manner.
[0086] The axes of the two large diameter rollers 61 are
respectively coupled to two suction and conveyance motors (having a
first suction and conveyance motor M2A and a second suction and
conveyance motor M2B) which are fixed to each of the supporting
members 68. Further, two suction belts 63 can be rotated
independently of each other by the two suction and conveyance
motors.
[0087] The suction belts 63 have a plurality of penetrating holes
of small diameter pierced in them as is shown in the figure. On the
inside of each suction belt 63 is a suction duct 64A of the suction
section 64 and are fixed to the supporting member 68.
[0088] The suction section 64 is made of a suction duct 64A and a
suction fan 64B coupled thereto. At the bottom of the suction duct,
there are openings 64C (FIG. 3) opposing respectively the suction
belt 63. The openings 64C determine the air suction position of the
suction and conveyance section 60. The sucked air is exhausted to
the back of the large quantity sheet feeding apparatus LT via the
suction duct 64A.
[0089] Further, it is also possible to have a configuration in
which a suction fan 64B is provided in a fixed manner at the deep
end of the sheet feeding apparatus main unit 30, and connect it to
the suction and conveyance section 60 by a suction duct.
[0090] The suction fan 64B is operating all the time, and the
suction and conveyance section 60 adheres by sucking to the suction
belt 63 the topmost sheet P that has floated up due to air blowing
by the sheet separation mechanism which is described later. Next,
due to the operation of the first suction and conveyance motor M2A
and the second suction and conveyance motor M2B, the suction belt
63 rotates whereby the sheet P is conveyed in the sheet conveying
direction (arrow a), and fed to the image forming apparatus A. It
is possible to carry out control of varying independently the
speeds of the first suction and conveyance motor M2A and the second
suction and conveyance motor M2B, and these two operate under
operating conditions that have been adjusted in advance so that the
sheet P is conveyed in the sheet conveying direction.
[0091] As is shown in FIG. 3, in the neighborhood of the opening
64C of the suction duct 64A, a sheet suction and adhesion sensor
PS1 has been placed that detects whether or not the topmost sheet P
has been sucked by and adhered to the suction belt.
[0092] Further, on the outlet side of the large quantity sheet
feeding apparatus LT is placed a conveying roller pair 39 made of a
master and a slave conveying rollers that definitely convey the
sheet P conveyed by the suction belt to the image forming apparatus
A.
[0093] Sheet Detection Sensor:
[0094] In addition, between the suction and conveyance section 60
and the conveying roller pair 39 in the sheet conveying direction,
and also in the neighborhood of the suction belt 63, a first sheet
detection sensor PS2A and a second sheet detecting section PS2B
that detect the leading edge of the sheet P that is passing through
are placed along the width direction.
[0095] FIG. 5 is a plan view diagram of the sheet feeding apparatus
main unit, and shows that a first sheet detection sensor PS2A and a
second sheet detecting section PS2B are placed on the downstream
side in the sheet conveying direction (the direction of the arrow
a) from the suction and conveyance section 60 while being separated
by W (mm) along the width direction. In addition, a conveying
roller pair 39 has been placed on the downstream side at a
separation of D (mm) from the detection positions of the two sheet
detection sensors. A clutch CL1 is present between the shaft of the
conveying roller pair 39 and the driving shaft 38 that rotates
because of being coupled to conveying roller driving motor M1.
[0096] The clutch CL1 is a drive transmission selection section
that switches the transmission of drive to the shaft of the
conveying roller pair 39 from the driving shaft 38.
[0097] Control Section:
[0098] FIG. 6 is a block diagram of the control system related to
the control section 100 that also functions as a skew correction
section that corrects the skew of sheets according to the present
invention.
[0099] The control section 100 has a computation and control
section 101 made of a CPU and that rules the sheet conveying
control and the main part of the skew correction section, a ROM 102
that stores the programs, a RAM 103 that is used in the calculation
control carried out by the computation and control section 101,
drive circuits 104 that drive the motors and solenoids, etc., based
on the instructions (signals) from the control section 100, and a
bus 105.
[0100] The sheet suction sensor PS1, the first sheet detection
sensor PS2A, and the second sheet detecting section PS2B are
connected to the control section 100 via an input interface that is
not shown in the figure.
[0101] The drive circuits 104 are the circuits that drive the
solenoid SL1 that actuates the shutter 55 of FIG. 3, the clutch CL1
of FIG. 5, and the motors M1, M2A, and M2B shown in FIG. 2, FIG. 4,
and FIG. 5, and the motor M3 to be described later.
[0102] The computation and control section 101, based on the
signals from the first sheet detection sensor PS2A and the second
sheet detecting section PS2B, and according to the control program,
appropriately outputs to the drive circuits 104 the commands
(signals) for driving the conveying roller driving motor M1, the
first suction and conveyance motor M2A, and the second suction and
conveyance motor M2B, so that sheets are conveyed one at a time to
the image forming apparatus A.
[0103] Sheet Skew Detection Section:
[0104] The first sheet detection sensor PS2A and the second sheet
detecting section PS2B detect the presence or absence of a passing
sheet P, the timing th of the passing of the leading edge of a
sheet is detected based on the timing at which the detection signal
changes from the sheet absent level to the sheet present level.
Also, the timing tr of the passing of the trailing edge of a sheet
is detected based on the timing at which the detection signal
changes from the sheet present level to the sheet absent level.
Further, the sheet present or absent signal, the sheet leading edge
detection signal, and the sheet trailing edge detection signal are
output to the computation and control section 101.
[0105] The computation and control section 101 detects the time tha
of the leading edge detection signal of the first sheet detection
sensor PS2A and the time thb of the leading edge detection signal
of the second sheet detection sensor PS2B, and based on their time
difference (tha-thb), computes the amount (angle) and direction of
skew of the sheet P.
[0106] If the linear speed of the suction and conveyance belt 63
that is driven rotationally by the first suction and conveyance
motor M2A and the second suction and conveyance motor M2B is taken
as Vb (mm/sec), and the skew angle of the sheet P is taken as S,
then the relationship of Equation 1 will be satisfied.
.theta.=arc tan {Vb(tha-thb)/W} Eqn. 1
[0107] As is shown in FIG. 5, .theta. is the skew angle of the
leading edge of the sheet P, W is the distance between the
detection position of the first sheet detection sensor PS2A and the
detection position of the second sheet detection sensor PS2B.
[0108] The computation and control section 101 is calculating the
sheet skew angle .theta. (.degree.) based on Eqn. 1. In addition,
the direction of the skew is being judged depending on whether the
difference (tha-thb) is negative or positive. When this difference
is negative, the sheet P is judged to be skewed to the right, and
to the left if the difference is positive.
[0109] Further, the amount of skew of the sheet P can also be the
time difference (tha-thb) of leading edge detection, or it can also
be the distance d indicated in FIG. 5.
[0110] The present invention shall not be limited to the sheet
detection sensors shown here, but can also be on that detects the
trailing edge of the sheet P.
[0111] The sheet skew detection section can also be one that
detects the above time difference (tha-thb) itself as the amount of
skew. Further, it is also possible to store in advance a
correspondence table between the time difference (tha-thb) and the
skew angle .theta., and to detect the skew angle .theta. by
referring to this table.
[0112] Skew Correction Section of the First Preferred
Embodiment:
[0113] FIG. 5 is an outline diagram showing the conveying roller
pair used in the skew correction section of the first preferred
embodiment of the present invention.
[0114] The skew correction section of the first preferred
embodiment is one that controls at least the rotational drive of
the conveying roller pair 39, by temporarily stopping the rotating
conveying roller pair 39, so that the leading edge of the sheet P
abuts against the conveying roller pair 39 during the period that
the conveying roller pair 39 has stopped. The operation of the
clutch CL1 is controlled so that the rotation of the conveying
roller pair 39 is started again when a prescribed time period has
elapsed after the leading edge of a sheet P is detected from the
signal of a sheet detection sensor (PS2A or PS2B). Therefore,
correcting sheet skew has been made possible using a paper
registration mechanism of carrying out control so that the
conveying roller pair 39 that was conventionally being rotated
continuously is made to stop temporarily at a prescribed timing,
and again made to start rotating again at another prescribed
timing. The role undertaken by the loop forming roller in a
conventional paper registration mechanism is being played by the
suction belt 63.
[0115] FIGS. 7a-7c are schematic diagrams showing the operation of
the conveying roller pair and the process of sheet correction.
[0116] FIG. 7a shows a sheet P at the point of time when a sheet P
skewed to the right has arrived at the nip of the left side
conveying roller pair 39. The broken line indicates the leading
edge of the sheet P at the point of time when the leading edge of
sheet P is passing through the first sheet detection sensor PS2A.
At this point of time, the clutch CL1 has stopped transmitting
drive power, and the conveying roller pair 39 has stopped. It is
very important that the clutch CL1 should have stopped before the
leading edge of the sheet P has arrived at the nip.
[0117] The angle .theta. shown in the figure is the angle of skew
of the sheet P.
[0118] FIG. 7b shows the condition in which the leading edge of a
sheet P has penetrated into the entire area of the nip of the
conveying roller pair 39 by the conveying force of the suction and
conveyance section 60. The skew of the leading edge of the sheet P
has been eliminated. The single dot and dash line at the left of
the sheet P indicates the area in which the curling of the sheet P
has become large. Corresponding to the sheet skew angle .theta.
shown in FIG. 4, the looping of the left part of the leading edge
of the sheet P is larger than the right part of the leading edge.
At this point, the state of the clutch CL1 is continuing to be the
off state of power transmission. Of course, an appropriate amount
of looping is formed even at the right part of the leading edge of
the sheet (the area D in FIG. 5).
[0119] FIG. 7c is the point of time after the state of FIG. 7b has
been passed, the state of the clutch CL1 has switched to the ON
state of power transmission, and a certain additional time period
has elapsed. As is shown in the figure, the skew of the sheet P has
been corrected from the leading edge side due to the conveying
force of the conveying roller pair 39 and sheet P is being conveyed
normally in the sheet conveying direction.
[0120] The loop formed in the sheet P in FIG. 7b, gradually moves
toward the rear part of the sheet while maintaining its size, and
gets eliminated when sheet P progresses and its trailing edge side
is near the position where it is released from the suction and
conveyance section 60.
[0121] The leading edge of the sheet P, which is floated up by the
flow of air and is conveyed while being sucked by the suction belt
63 of the suction and conveyance section 60 with a skew angle of
.theta., has its progress stopped at the nip of the conveying
roller pair 39 in the stopped condition. On the other hand, since
the sheet next to the sheet P is conveyed at a prescribed interval
by the suction and conveyance section 60 in the leading edge
prevented condition, a loop with a prescribed range is formed in
the sheet in the region D shown in FIG. 5.
[0122] However, formation of a loop is only in the case of sheets
which are easily buckled such as thin sheets, etc., and in the case
of sheets which are not easily buckled such as thick sheets, etc.,
when the leading edge of the sheet arrives at the nip of the
conveying roller 39 that is in the stopped state, because slipping
occurs between the suction belt 63 and the sheet, the leading edge
of the sheet abuts uniformly.
[0123] After a prescribed period has elapsed, the state of the
clutch CL1 is switched to the ON state of power transmission, the
conveying roller pair 39 starts rotating, and the sheet P is
discharged towards the image forming apparatus A after its skew is
corrected.
[0124] As has been shown above, the sheet P, has no problems of
sheet folding or wrinkling, and is conveyed to the downstream side
with its skew corrected from the leading edge part.
[0125] FIG. 8 is a timing chart of the operations of the sheet
conveying control related to the first preferred embodiment.
[0126] FIG. 8 shows the operation timings related to the sheet
suction section PS1 and the first sheet detection sensor PS2A (the
second sheet detection sensor PS2B), the clutch CL1 that carries
out drive power transmission to the conveying roller pair 39, the
first suction and conveyance motor M2A and the second suction and
conveyance motor M2B that rotate the suction belt 63, and the
solenoid SL1 that actuates the shutter of the second air blowing
section.
[0127] The operation timings of the conveying roller drive motor M1
and the air blowing fan 41 of the first air blowing section that
floats up the sheet P, and of the motor fan 51 of the second air
blowing section are the period from the start of sheet feeding
until end of sheet feeding, during which period these are
operating, which has been omitted from the descriptions.
[0128] FIG. 8 shows the timing chart for the period from the
beginning of sheet feeding in continuous sheet feeding to near the
starting feeding the third sheet. The timing of sheet conveying is
broadly divided into the first sheet suction Ta and first sheet
feeding Tb, second sheet feeding Tc, and third sheet feeding Td.
The operation timings of the different sections are determined by
t3 to t7 set in advance for the sheet feeding starting timings Tb,
Tc, and Td of the different sheets, the sheet leading edge
detection timings, and for the sheet trailing edge detection
timings.
[0129] The timings of the sheet leading edge detection and the
sheet trailing edge detection are judged based on the detection
signals of the sheet detection sensors PS2A and PS2B, and differ
for each sheet feeding.
[0130] The operation of the clutch CL1 that switches the drive of
the conveying roller pair 39 that is carried out by the skew
correction section of the first preferred embodiment according to
the present invention is described below according to FIG. 8.
[0131] The computation and control section 101 puts the clutch CL1
in the power transmission OFF state when a sheet feeding is
started. Next, a timer is started when the leading edge of a first
sheet P is detected from the detection signal of the sheet
detection sensor, and the clutch CL1 is switched to the power
transmission ON state after a prescribed time duration t3 has
elapsed.
[0132] The prescribed time period t3 is selected within a range so
that it satisfies the following Eqn. 2, and also so that sheet
folding, wrinkling, etc., due to excessive looping of the sheet P
does not occur. D in Eqn. 2 is the distance (in mm) shown in FIG.
4, and Vb is the conveying speed of the sheet P by the suction belt
63. Further, tm is the looping time determined for forming loops of
less than a prescribed range.
t3=D/Vb+tm Eqn. 2
[0133] The control section 100 starts a timer when the trailing
edge of the first sheet P is detected from the detection signal of
the sheet detection sensor, and the clutch CL1 is switched to the
power transmission OFF state after a prescribed time duration t5
has elapsed, and stops the conveying roller pair 39 in advance in
order to correct the skew of the second sheet.
[0134] The control section 100 carries out controls such as the
above even for the second and succeeding sheets, and the skew of
the sheet that occurs at the time that a sheet is sucked by the
suction and conveyance section is corrected.
[0135] However, although the looping time has been set here as tm,
it is also possible to use a loop detection section that detects
the amount of loop of the sheet.
[0136] Skew Correction Section of a Second Preferred
Embodiment:
[0137] FIG. 9 is a time chart showing the operations of the
different parts of the sheet feeding apparatus main unit 30 related
to the sheet conveying control carried out by the control section
100 as a skew correction section according to the second preferred
embodiment of the present invention.
[0138] The computation and control section 101 according to the
second preferred embodiment of the present invention calculates the
difference (tha-thb) between the sheet left and right leading edge
timings based on the signals of the first sheet detection sensor
PS2A and the second sheet detection sensor PS2B, and in addition,
calculates the skew angle .theta. of the sheet and the skew
direction data SD according to the above Eqn. 1. Next, the speed
profile corresponding to the skew angle .theta. is determined by
referring to a table that is not shown in the figure but that is
stored in the ROM 102, and outputs the determined speed profile to
the drive circuit 104 of FIG. 6. The drive circuit 104 drives the
first suction and conveyance motor M2A and the second suction and
conveyance motor M2B in accordance with the received profile.
[0139] These two suction and conveyance motors are both stepping
motors, and drive the large diameter roller 61 in a rotating manner
by a prescribed angle per each unit pulse signal. In addition, the
sheet P can be conveyed at mutually independent conveying speeds,
and the orientation of the sheet conveyed by the suction and
conveyance section 60 can be changed freely by the speed profiles
of the first suction and conveyance motor M2A and the second
suction and conveyance motor M2B.
[0140] In the time chart of FIG. 9, the speed profiles of the two
suction and conveyance motors are shown as VPn, VPr+, and VPl+.
[0141] VPn is the reference speed profile. VPr+ is the speed
profile for correcting right skew with respect to the reference
speed profile. VPl+ is the speed profile for correcting left skew
with respect to the reference speed profile.
[0142] FIG. 9 is only an example, and the amount of skew of the
first sheet P is within the prescribed range, and is the case in
which sheet skew correction is judged to be not required. The
computation and control section 101 determines the speed profiles
of both the suction and conveyance motors to be the reference speed
profile VPn.
[0143] On the other hand, the amount of sheet skew of the second
sheet P is more than the prescribed range, and also the skew is
towards the right, and this is the case in which sheet skew
correction is judged to be required. The computation and control
section 101 determines the speed profile of the first suction and
conveyance motor M2A as the speed profile VPr+ according to the
detected amount of skew in this case and determines the speed
profile of the second suction and conveyance motor M2B as the
reference speed profile VPn.
[0144] Further, the amount of sheet skew of the third sheet P is
more than the prescribed range, and also the skew is towards the
left, and this is the case in which sheet skew correction is judged
to be required. The computation and control section 101 determines
the speed profile of the second suction and conveyance motor M2B as
the speed profile VPl+ according to the detected amount of skew in
this case and determines the speed profile of the first suction and
conveyance motor M2A as the reference speed profile VPn.
[0145] Further, the integrated area (speed.times.time) of the speed
profile corresponds to the distance that the leading edge of the
sheet P has progressed beyond leading edge detection. In the
example shown in the second sheet in FIG. 9, the integrated area of
the VPr+ speed profile is larger by the area of the projection
shape H in the figure relative to the integrated area of the speed
profile VPn. Therefore, the right part of the sheet progresses well
in the sheet conveying direction by the distance corresponding to
this area, and the sheet P rotates to the left relatively. As a
result, the right part of the sheet progresses corresponding to the
amount of skew d towards the right shown in FIG. 4 and the skew of
the sheet is completely corrected.
[0146] Further, as a condition of making the correction of the
sheet P complete, it is necessary to complete the correction of the
skew of the sheet before the leading edge of the sheet arrives at
the nip of the conveying roller pair 39.
[0147] As is shown in the timing chart of FIG. 9, the projection
shape H has been set to within the time period t9 (t9=t8-.alpha.)
shown in the figure considering the fluctuations in the conveying
speed, etc., of the suction belt 63. Here, t8 is the time period
from the detection of the leading edge until the leading edge of
the sheet arrives at the nip of the conveying roller pair 39, and
.alpha. is a constant considering the above fluctuations.
[0148] Further, the computation and control section 101 determines
the above speed profile VPr+ or VPl+ by referring to the table not
shown in the figure so that the area of the projection shape H
shown in FIG. 9 changes according to the amount of skew or the skew
angle, and outputs the speed profile VPn and the determined VPr+ or
VPl+ to the drive circuit 104.
[0149] The drive circuit 104 drives the first suction and
conveyance motor M2A or the second suction and conveyance motor M2B
in accordance with the speed profile VPn or VPr+ or VPl+ input by
the computation and control section 101.
[0150] In the above manner, in the skew correction section of the
second preferred embodiment, the amount of skew of the sheet P is
detected, after the orientation of the sheet P sucked by the
suction and conveyance section 60 is changed with respect to the
suction and conveyance section 60 according to the detected amount
of skew thereby correcting the skew of the entire sheet including
the leading edge, the sheet is sheet is conveyed to the nip of the
conveying roller 39 with the same speeds at left and right at all
times during the period from t9 to t8 shown in FIG. 9, this is a
method that does not require the formation of a loop as in the
first preferred embodiment, this method is superior in stable
conveying of the sheet, and can convey smoothly. However, since
this is a method in which high performance is required in the time
resolution of the sheet skew detection section as the conveying
speed of the apparatus becomes faster, it is necessary to take care
such as selecting the sensors considering sufficiently the
conveying speed at the time of design, etc.
[0151] Skew Correction Section of a Third Preferred Embodiment:
[0152] The skew correction section of a third preferred embodiment
of the present invention is a control section 100 that controls the
angle varying section as a displacement section described below so
that the angle of the suction and conveyance section 60 with
respect to the sheet conveying direction is changed according to
the skew angle of the leading edge of the sheet P.
[0153] FIG. 10 shows an angle varying section 69 that varies the
angle of the suction and conveyance section 60. As is shown in the
figure, the two conveying belts 63 are rotated together by driving
the first suction and conveyance motor M2A.
[0154] The supporting member 68 of the suction and conveyance
section 60 is supported below the top supporting member 81 of the
sheet feeding apparatus main unit 30 by one reference supporting
shaft 693 and tow sliding supporting shafts 694.
[0155] On the right end of the supporting member 68 is provided a
flat gear wheel 695 drawing and ellipse with a radius R1 centering
on the reference supporting shaft 693. On the other hand, above the
top supporting member 81 of the sheet feeding main unit 30 is fixed
a motor supporting member 691 that supports the angle varying motor
M3, and a gear wheel 692 fixed to the shaft of the angle varying
motor M3 engages with the flat gear wheel 693.
[0156] FIG. 11 is a cross-sectional view schematic diagram cutting
the angle varying section 69 horizontally at the top surface of the
tops supporting member 81, and shows the relationship between the
top supporting member 81 and the supporting member 68 that is
displaced with respect to the top supporting member 81.
[0157] The supporting member 68 that determines the orientation of
the suction and conveyance section 60 can rotate horizontally with
the reference hole 81C opened in the top supporting member 81 as
the pivot. The top supporting member 81 has two holes 81B forming
an inside ellipse R2, so that the sliding supporting shaft 694 can
slide. In addition, a hole 81A is provided at the position of the
radius R1 in which the gear wheel 692 fixed to the shaft of the
angle varying motor M3 passes through.
[0158] The angle varying section 69 is one in which, when the gear
wheel 692 of the angle varying motor M3 is rotated by an angle
.phi. in the direction of the arrow b, the flat gear wheel 695
moves in the direction of the arrow c, the suction and conveyance
section 60 moves in the direction of the arrow d, and rotates by an
angle .theta. with respect to the sheet conveying direction.
[0159] The angle varying motor M3 is one that can accurately rotate
the gear wheel 692 in the desired direction by the desired angle,
and although a stepping motor is suitable and is used, it is not
necessary to restrict to this.
[0160] FIG. 12 is a flow chart related to the sheet conveying
control carried out by the control section 100 as a sheet skew
correction section of the third preferred embodiment according to
the present invention.
[0161] The Steps S01 to S05 are controlled by the computation and
control section 101, and the Step S06 is controlled by the drive
circuit 104.
[0162] The Step S01 is a step of judging whether or not the leading
edge of the sheet P is detected by the first sheet detection
section PS2A and the second sheet detection sensor PS2B. The
operation progresses to Step S02 when the judgment is YES in this
step.
[0163] The Step S02 is a step of detecting the timings th1 and th2
of the leading edge of the sheet P from the signals of the first
sheet detection sensor PS2A and the second sheet detection sensor
PS2B, and the operation proceeds to Step S03.
[0164] The Step S03 is a step of calculating the direction of skew
of the sheet P based on the timings th1 and th2 of the leading edge
of the sheet P and calculating the sheet skew angle .theta. based
on Eqn. 1. The operation proceeds next to Step S04.
[0165] The Step S04 is a step of referring to the table
corresponding to the direction of skew and the angle .theta. of the
sheet skew obtained in Step S03 and obtaining the operating
conditions of the angle varying motor (number of pulse steps and
direction of rotation).
[0166] The Step S05 is a step of outputting the operation
conditions obtained in Step S04 to the drive circuit 104.
[0167] The Step S06 is controlled by the drive circuit 104, and is
a step in which the drive of the angle varying section 69 is
controlled according to the operation conditions obtained from the
computation and control section 101. For example, as is shown in
FIG. 11, the motor shaft M3 is rotated in the counterclockwise
direction by an angle .phi., and the suction and conveyance section
60 rotates (in the direction of the arrow a) by an angle .theta.
with respect to the sheet conveying direction. As a result, the
sheet skew is corrected by an angle .theta. in the direction of
left skew.
[0168] Further, the skew correction section 60 of the third
preferred embodiment is, similar to the second preferred
embodiment, one that carries out control so that the operation of
the drive circuit 104 for correcting the skew of the sheet P is
completed before the sheet P arrives at the nip of the conveying
roller pair 39.
[0169] Further, in the skew correction sections of the second and
third preferred embodiments, there are cases in which it is
demanded that the timing of the leading edge of the sheet is
detected accurately and that the amount of skew of the sheet P is
detected with a high accuracy. In such situations, control is
carried out so that air flow for separation by blowing air from the
second air blowing section 50 shown in FIG. 3 is stopped before
detecting the timing of the leading edge of the sheet, thereby
increasing the sheet skew detection accuracy, and making it
possible to prevent wrong detection of sheet skew. Explanation is
given based on the timing chart of FIG. 10.
[0170] The time period t6 shows the time period from the timing of
the start of feeding of each sheet P to the timing of switching the
state of the solenoid SL1 from the separation state to the floating
up state by operating the shutter of the second air blowing
section. The time period tx is the time period from starting the
sheet feeding until the time when the leading edge of the sheet is
expected to be detected. As is shown in the figure, t6 is set to be
sufficiently smaller than tx so that the second air blowing section
as a sheet separation section stops with sufficient margin before
the timing at which the leading edge of the sheet P is detected. As
a consequence, the second air blowing section as a sheet separation
section is being controlled by the control section 100 as a skew
correction section so that there is no problem caused to skew
detection.
[0171] According to a sheet feeding apparatus of the present
invention, by providing a skew correction section that corrects the
skew of a sheet conveyed by the suction and conveyance section, it
is possible to solve the problem of the skew of a sheet before it
is sent to the conveying path on the downstream side from the air
sheet feeding apparatus.
* * * * *