U.S. patent number RE48,108 [Application Number 15/263,064] was granted by the patent office on 2020-07-21 for image forming apparatus, image forming method, and computer program product for causing a computer to execute the method.
This patent grant is currently assigned to RICOH COMPANY, LTD.. The grantee listed for this patent is RICOH COMPANY, LTD.. Invention is credited to Keigo Nakamura, Reki Nakamura, Yasuhiko Ogino, Takahiro Seki, Emiko Shiraishi.
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United States Patent |
RE48,108 |
Shiraishi , et al. |
July 21, 2020 |
Image forming apparatus, image forming method, and computer program
product for causing a computer to execute the method
Abstract
An image forming apparatus includes: an image carrier; a toner
image forming unit that forms a toner image on the image carrier; a
transfer unit that transfers the toner image on the image carrier
to a transfer target having ridges and valleys on a surface
thereof; an adjusting unit that adjusts a ratio of A/B, where A is
a transfer ratio [%] from the image carrier to a valley portion of
the transfer target while B is a transfer ratio [%] from the image
carrier to a ridge portion of the transfer target, based on an
adjustment input by a user; and a control unit that controls a
transfer condition of the transfer unit based on the ratio of A/B
adjusted by the adjusting unit.
Inventors: |
Shiraishi; Emiko (Tokyo,
JP), Ogino; Yasuhiko (Kanagawa, JP),
Nakamura; Reki (Kanagawa, JP), Nakamura; Keigo
(Kanagawa, JP), Seki; Takahiro (Kanagawa,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
RICOH COMPANY, LTD. |
Tokyo |
N/A |
JP |
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|
Assignee: |
RICOH COMPANY, LTD. (Tokyo,
JP)
|
Family
ID: |
1000004625666 |
Appl.
No.: |
15/263,064 |
Filed: |
September 12, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13042635 |
Dec 3, 2013 |
8600247 |
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Reissue of: |
14068557 |
Oct 31, 2013 |
8837969 |
Sep 16, 2014 |
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Foreign Application Priority Data
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Mar 16, 2010 [JP] |
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2010-058660 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03G
13/16 (20130101); G03G 13/16 (20130101); G03G
15/1605 (20130101); G03G 15/1605 (20130101); G03G
15/1675 (20130101); G03G 15/1675 (20130101); G03G
15/6594 (20130101); G03G 15/6594 (20130101); G03G
2215/00738 (20130101); G03G 2215/00738 (20130101); G03G
2215/00476 (20130101); G03G 2215/00476 (20130101) |
Current International
Class: |
G03G
15/16 (20060101); G03G 15/00 (20060101); G03G
13/16 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2002-156839 |
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May 2002 |
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JP |
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2006-267486 |
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Oct 2006 |
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JP |
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2006267486 |
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Oct 2006 |
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JP |
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4031923 |
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Oct 2007 |
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JP |
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Other References
Matsumoto et al. (JP02006267486A Translation). cited by examiner
.
Matsumoto et al. (JP02006267486A Official Translation). cited by
examiner.
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Primary Examiner: Andujar; Leonardo
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application .Iadd.is a reissue application of U.S. Pat. No.
8,837,969 issued Sep. 16, 2014, from U.S. application Ser. No.
14/068,557, which .Iaddend.is a continuation of U.S. application
Ser. No. 13/042,635, filed Mar. 8, 2011, .Iadd.and that issued as
U.S. Pat. No. 8,600,247 on Dec. 3, 2013, .Iaddend.and is based upon
and claims the benefit of priority from prior Japanese Patent
Application No. 2010-058660, filed Mar. 16, 2010, .Iadd.and
.Iaddend.the entire contents of .[.both of which.]. .Iadd.each of
the above applications .Iaddend.are incorporated herein by
reference.
Claims
What is claimed is:
1. An image forming apparatus, comprising: an image carrier; a
transfer .[.unit.]. .Iadd.roller .Iaddend.that transfers a toner
image on the image carrier to a sheet; a .[.transfer bias
application unit.]. .Iadd.power source .Iaddend.that applies, to
the transfer .[.unit.]. .Iadd.roller.Iaddend., a transfer bias in
which an alternating-current component is superimposed on a
direct-current component; .[.an adjusting unit.]. .Iadd.input
device hardware .Iaddend.that .[.adjusts a level of the
alternating-current component and a level of the direct-current
component.]. .Iadd.a user operates only when a predetermined kind
of the sheet having ridges and valleys on a surface thereof is
selected to input a ratio between a selectable image density in a
valley portion of the sheet and a selectable image density in a
ridge portion of the sheet.Iaddend.; and .[.a.]. .Iadd.processing
circuitry configured to adjust a level of the alternating-current
component and a level of the direct-current component based on the
ratio between the selectable image density in the valley portion of
the sheet and the selectable image density in the ridge portion of
the sheet that is input by the input device hardware, and to
.Iaddend.control .[.unit that controls.]. the .[.transfer bias
application unit.]. .Iadd.power source .Iaddend.to apply the
transfer bias .[.based on.]. .Iadd.according to .Iaddend.the level
of the alternating-current component and the level of the
direct-current component .Iadd.that is .Iaddend.adjusted
.Iadd.based on the ratio between the selectable image density in
the valley portion of the sheet and the selectable image density in
the ridge portion of the sheet that is input .Iaddend.by the
.[.adjusting unit.]. .Iadd.input device hardware, wherein a value
of the level of the alternating-current component increases and a
value of the level of the direct-current component decreases as the
ratio between the selectable image density in the valley portion of
the sheet and the selectable image density in the ridge portion of
the sheet that is input by the input device hardware increases, the
value of the level of the alternating-current component being
greater than zero when the ratio between the selectable image
density in the valley portion of the sheet and the selectable image
density in the ridge portion of the sheet that is input by the
input device hardware is greater than or equal to 1.Iaddend..
2. The image forming apparatus according to claim 1, .[.further
comprising a selection unit that selects a.]. .Iadd.wherein the
input device hardware allows selection of the predetermined
.Iaddend.kind of the sheet, .[.wherein the adjusting unit allows to
adjust the level of the alternating-current component and the level
of the direct-current component.]. .Iadd.and the input device
hardware allows input of the ratio .Iaddend.only when the sheet
selected by the .[.selection unit.]. .Iadd.input device hardware
.Iaddend.is a predetermined sheet.
.[.3. The image forming apparatus according to claim 2, wherein the
predetermined sheet is a sheet having ridges and valleys on a
surface thereof..].
4. The image forming apparatus according to claim 2, wherein, when
the sheet selected by the .[.selection unit.]. .Iadd.input device
hardware .Iaddend.is a sheet other than the predetermined sheet,
the .[.control unit controls.]. .Iadd.processing circuitry is
configured to control .Iaddend.the .[.transfer bias application
unit.]. .Iadd.power source .Iaddend.to apply the transfer bias
having only the direct-current component.
5. The image forming apparatus according to claim 2, wherein the
.[.selection unit.]. .Iadd.input device hardware .Iaddend.includes
an operation panel.
6. The image forming apparatus according to claim 1, wherein the
.[.adjusting unit.]. .Iadd.input device hardware .Iaddend.includes
an operation panel.
7. The image forming apparatus according to claim 1, wherein the
image carrier is an intermediate transfer belt.
8. The image forming apparatus according to claim 1, .[.wherein the
transfer unit includes.]. .Iadd.further comprising .Iaddend.a
transfer .[.member configured.]. .Iadd.conveyor .Iaddend.to contact
with the image carrier via the sheet .Iadd.so that the transfer
roller transfers the toner image on the image carrier to the
sheet.Iaddend..
9. The image forming apparatus according to claim 8, wherein the
transfer .[.member.]. .Iadd.conveyor .Iaddend.is a transfer
conveying belt.
10. An image forming apparatus, comprising: an image carrier; a
transfer .[.unit.]. .Iadd.roller .Iaddend.that transfers a toner
image on the image carrier to a sheet having ridges and valleys on
a surface thereof; a .[.transfer bias application unit.].
.Iadd.power source .Iaddend.that applies, to the transfer
.[.unit.]. .Iadd.roller.Iaddend., a transfer bias in which an
alternating-current component is superimposed on a direct-current
component; .[.an adjusting unit.]. .Iadd.input device hardware
.Iaddend.that .[.adjusts a level of the alternating-current
component and a level of the direct-current component.]. .Iadd.a
user operates only when a predetermined kind of the sheet having
ridges and valleys on a surface thereof is selected to input a
ratio between a selectable image density in a valley portion of the
sheet and a selectable image density in a ridge portion of the
sheet.Iaddend.; and .[.a.]. .Iadd.processing circuitry configured
to adjust a level of the alternating-current component and a level
of the direct-current component based on the ratio between the
selectable image density in the valley portion of the sheet and the
selectable image density in the ridge portion of the sheet that is
input by the input device hardware, and to .Iaddend.control .[.unit
that controls.]. the transfer bias applied to the transfer .[.unit
based on.]. .Iadd.roller according to .Iaddend.the level of the
alternating-current component and the level of the direct-current
component .Iadd.that is .Iaddend.adjusted .Iadd.based on the ratio
between the selectable image density in the valley portion of the
sheet and the selectable image density in the ridge portion of the
sheet that is input .Iaddend.by the .[.adjusting unit.].
.Iadd.input device hardware, wherein a value of the level of the
alternating-current component increases and a value of the level of
the direct-current component decreases as the ratio between the
selectable image density in the valley portion of the sheet and the
selectable image density in the ridge portion of the sheet that is
input by the input device hardware increases, the value of the
level of the alternating-current component being greater than zero
when the ratio between the selectable image density in the valley
portion of the sheet and the selectable image density in the ridge
portion of the sheet that is input by the input device hardware is
greater than or equal to 1.Iaddend..
11. An image forming apparatus, comprising: an image carrier; a
transfer .[.unit.]. .Iadd.roller .Iaddend.that transfers a toner
image on the image carrier to a sheet; a .[.transfer bias
application unit.]. .Iadd.power source .Iaddend.that applies a
transfer bias to the transfer .[.unit.]. .Iadd.roller.Iaddend.;
.[.a selecting unit.]. .Iadd.input device hardware that a user
operates only when a predetermined kind of the sheet having ridges
and valleys on a surface thereof is selected .Iaddend.to .[.select
the transfer bias from any one of a first direct-current voltage
and a superimposed voltage in which an alternating-current voltage
is superimposed on a second direct-current voltage.]. .Iadd.input a
a ratio between a selectable image density in a valley portion of
the sheet and a selectable image density in a ridge portion of the
sheet.Iaddend.; and .[.a.]. .Iadd.processing circuitry configured
to select the transfer bias from any one of a first direct-current
voltage and a superimposed voltage in which an alternating-current
voltage is superimposed on a second direct-current voltage based on
the ratio between the selectable image density in the valley
portion of the sheet and the selectable image density in the ridge
portion of the sheet that is input by the input device hardware,
and to .Iaddend.control .[.unit that controls.]. the transfer bias
applied to the transfer .[.unit.]. .Iadd.roller according to the
transfer bias that is selected .Iaddend.based on .[.a selection
result of.]. the .[.selecting unit.]. .Iadd.ratio between the
selectable image density in the valley portion of the sheet and the
selectable image density in the ridge portion of the sheet that is
input by the input device hardware.Iaddend., wherein a level of the
first direct-current voltage is greater than a level of the second
direct-current voltage.Iadd., and wherein a value of the level of
the alternating-current voltage increases and a value of the level
of the direct-current voltage decreases as the ratio between the
selectable image density in the valley portion of the sheet and the
selectable image density in the ridge portion of the sheet that is
input by the input device hardware increases, the value of the
level of the alternating-current voltage being greater than zero
when the ratio between the selectable image density in the valley
portion of the sheet and the selectable image density in the ridge
portion of the sheet that is input by the input device hardware is
greater than or equal to 1.Iaddend..
12. The image forming apparatus according to claim 11, .[.wherein
the transfer unit includes.]. .Iadd.further comprising .Iaddend.a
transfer .[.member.]. .Iadd.conveyor .Iaddend.that forms a transfer
nip between the image carrier and the transfer .[.member.].
.Iadd.conveyor.Iaddend., and wherein the toner image on the image
carrier is transferred to the sheet at the transfer nip.
13. The image forming apparatus according to claim 12, wherein the
transfer .[.member.]. .Iadd.conveyor .Iaddend.is a transfer
conveying belt.
14. The image forming apparatus according to claim 11, wherein the
image carrier is an intermediate transfer belt.
15. An image forming apparatus, comprising: an image carrier; a
transfer .[.unit.]. .Iadd.roller .Iaddend.that transfers a toner
image on the image carrier to a sheet; a .[.transfer bias
application unit.]. .Iadd.power source .Iaddend.that applies a
transfer bias to the transfer .[.unit.]. .Iadd.roller.Iaddend.;
.[.a selecting unit to select the transfer bias from any one of a
first direct current and a superimposed current in which an
alternating current is superimposed on a second direct-current
voltage.]. .Iadd.input device hardware that a user operates only
when a predetermined kind of the sheet having ridges and valleys on
a surface thereof is selected to input a ratio between a selectable
image density in a valley portion of the sheet and a selectable
image density in a ridge portion of the sheet.Iaddend.; and .[.a.].
.Iadd.processing circuitry configured to select the transfer bias
from any one of a first direct current and a superimposed current
in which an alternating current is superimposed on a second direct
current based on the ratio between the selectable image density in
the valley portion of the sheet and the selectable image density in
the ridge portion of the sheet that is input by the input device
hardware, and to .Iaddend.control .[.unit that controls.]. the
transfer bias applied to the transfer .[.unit.]. .Iadd.roller
according to the transfer bias that is selected .Iaddend.based on
.[.a selection result of.]. the .[.selecting unit.]. .Iadd.ratio
between the selectable image density in the valley portion of the
sheet and the selectable image density in the ridge portion of the
sheet that is input by the input device hardware.Iaddend., wherein
a level of the first direct current is greater than a level of the
second direct current.Iadd., and wherein a value of a level of the
alternating current increases and a value of a level of the direct
current decreases as the ratio between the selectable image density
in the valley portion of the sheet and the selectable image density
in the ridge portion of the sheet that is input by the input device
hardware increases, the value of the level of the alternating
current being greater than zero when the ratio between the
selectable image density in the valley portion of the sheet and the
selectable image density in the ridge portion of the sheet that is
input by the input device hardware is greater than or equal to
1.Iaddend..
16. The image forming apparatus according to claim 15, .[.wherein
the transfer unit includes.]. .Iadd.further comprising .Iaddend.a
transfer .[.member.]. .Iadd.conveyor .Iaddend.that forms a transfer
nip between the image carrier and the transfer .[.member.].
.Iadd.conveyor.Iaddend., and wherein the toner image on the image
carrier is transferred to the sheet at the transfer nip.
17. The image forming apparatus according to claim 16, wherein the
transfer .[.member.]. .Iadd.conveyor .Iaddend.is a transfer
conveying belt.
18. The image forming apparatus according to claim 15, wherein the
image carrier is an intermediate transfer belt.
.Iadd.19. An image transferring apparatus, comprising: a
belt-shaped image carrier including an elastic layer; a transfer
roller to transfer a toner image on the image carrier to a sheet; a
power source to apply, to the transfer roller, a transfer bias in
which an alternating-current component is superimposed on a
direct-current component; and input device hardware that a user
operates only when a predetermined kind of the sheet having ridges
and valleys on a surface thereof is selected to input a selection
of a ratio between a selectable image density in a valley portion
of the sheet and a selectable image density in a ridge portion of
the sheet, and the transfer bias is adjusted based on the ratio
between the selectable image density in the valley portion of the
sheet and the selectable image density in the ridge portion of the
sheet that is input by the input device hardware, wherein a value
of a level of the alternating-current component increases and a
value of a level of the direct-current component decreases as the
ratio between the selectable image density in the valley portion of
the sheet and the selectable image density in the ridge portion of
the sheet that is input by the input device hardware increases, the
value of the level of the alternating-current component being
greater than zero when the ratio between the selectable image
density in the valley portion of the sheet and the selectable image
density in the ridge portion of the sheet that is input by the
input device hardware is greater than or equal to 1..Iaddend.
.Iadd.20. The image transferring apparatus according to claim 19,
wherein the image carrier includes a resin layer on which the
elastic layer is formed..Iaddend.
.Iadd.21. The image transferring apparatus according to claim 20,
wherein the image carrier includes a coated layer formed on the
elastic layer..Iaddend.
.Iadd.22. The image transferring apparatus according to claim 21,
wherein the coated layer contains fluorine components..Iaddend.
.Iadd.23. The image transferring apparatus according to claim 19,
further comprising: processing circuitry configured to adjust the
transfer bias based on the ratio between the selectable image
density in the valley portion of the sheet and the selectable image
density in the ridge portion of the sheet that is input by the
input device hardware, and to control the power source to apply the
transfer bias according to the transfer bias that is adjusted based
on the ratio between the selectable image density in the valley
portion of the sheet and the selectable image density in the ridge
portion of the sheet that is input by the input device hardware,
wherein the processing circuitry is configured to adjust a level of
the direct-current component..Iaddend.
.Iadd.24. The image transferring apparatus according to claim 23,
wherein the processing circuitry is configured to adjust the
transfer bias such that a level of the alternating-current
component increases as the level of the direct-current component
decreases..Iaddend.
.Iadd.25. The image transferring apparatus according to claim 23,
wherein the input device hardware includes an operation
panel..Iaddend.
.Iadd.26. The image transferring apparatus according to claim 19,
wherein the input device hardware allows selection of the
predetermined kind of the sheet, and when the sheet selected by the
input device hardware is a sheet other than the predetermined
sheet, the power source applies the transfer bias having only the
direct-current component..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotography image
forming apparatus, such as a copying machine, a facsimile, and a
printer; an image forming method used therein; and a computer
program product for causing a computer to execute the method.
2. Description of the Related Art
Electrophotography image forming apparatuses have been widely used
in high speed mass printing field typified by newspapers, posters,
books, and direct mail with recent progress in high speed operation
and colorization technology for the apparatuses. In such field,
various kinds of printing media are used. There are increasing
demands for printing on a transfer target having low surface
smoothness such as embossed paper. However, when the
electrophotography image forming apparatuses are used for such
medium, a problem arises in that toner is not sufficiently
transferred to a valley portion compared with a ridge portion of a
transfer target; because a transfer electric field at the valley
portion is smaller than that at the ridge portion. As a result,
white spots occur in an image formed on a transfer target having
low surface smoothness. In order to address this problem, image
forming apparatuses employing transfer methods for solving the
problem have been proposed. Refer to Japanese Patent Application
Laid-open No. 2002-156839, Japanese Patent Application Laid-open
No. 2002-202638, and Japanese Patent Application Laid-open No.
2006-267486. For example, Japanese Patent Application Laid-open No.
2006-267486 discloses an image forming apparatus employing a
transfer method in which an alternating voltage is superimposed on
transfer bias. In the image forming apparatus, the superimposing of
the alternating voltage on the transfer bias causes toner to be
reciprocated between an image carrier and a transfer target so as
to increase frequency of toner contacting with a valley portion of
a recording medium, thereby reducing failures of toner transfer to
a valley portion on a surface of the recording medium. This image
forming apparatus is suitable for printing characters on rough
surface paper, such as in a case of newspaper printing, because the
reduction of failures of toner transfer to a valley portion
enhances character visibility.
In most cases where embossed paper having ridges and valleys that
are intentionally provided to give premium accents is used as a
transfer target, images having higher design property rather than
characters are printed. In such cases, printing that utilizes
texture of the transfer target is desired. For example, when
texture of an image drawn with colored pencils or printed by block
print is desired, a toner adhesion amount on a valley portion is
reduced; while when texture of an image drawn with paints is
desired, a toner adhesion amount on a valley portion is set to be
larger than that on a ridge portion. In this way, various kinds of
texture can be made by intentionally differentiating the toner
adhesion amounts between ridge and valley portions. The prior art
image forming apparatuses, however, cannot adjust the toner
adhesion amount between ridge and valley portions. As a result, a
problem arises in that texture of a transfer target is lost and not
utilized.
SUMMARY OF THE INVENTION
It is an object of the present invention to at least partially
solve the problems in the conventional technology.
According to an aspect of the present invention, there is provided
an image forming apparatus, including: an image carrier; a toner
image forming unit that forms a toner image on the image carrier; a
transfer unit that transfers the toner image on the image carrier
to a transfer target having ridges and valleys on a surface
thereof; an adjusting unit that adjusts a ratio of A/B, where A is
a transfer ratio [%] from the image carrier to a valley portion of
the transfer target while B is a transfer ratio [%] from the image
carrier to a ridge portion of the transfer target, based on an
adjustment input by a user; and a control unit that controls a
transfer condition of the transfer unit based on the ratio of A/B
adjusted by the adjusting unit.
According to another aspect of the present invention, there is
provided an image forming method for an image forming apparatus
that includes: an image carrier; a toner image forming unit that
forms a toner image on the image carrier; and a transfer unit that
transfers the toner image on the image carrier to a transfer target
having ridges and valleys on a surface thereof, the method
including: adjusting a ratio of A/B, where A is a transfer ratio
[%] from the image carrier to a valley portion of the transfer
target while B is a transfer ratio [%] from the image carrier to a
ridge portion of the transfer target, based on an adjustment input
by a user by an adjusting unit; and controlling a transfer
condition of the transfer unit based on the ratio of A/B adjusted
at the adjusting by a controlling unit.
According to still another aspect of the present invention, there
is provided a computer program product including a non-transitory
computer-usable medium having computer-readable program codes
embodied in the medium for image forming in an image forming
apparatus that includes: an image carrier; a toner image forming
unit that forms a toner image on the image carrier; and a transfer
unit that transfers the toner image on the image carrier to a
transfer target having ridges and valleys on a surface thereof, the
program codes when executed causing a computer to execute:
adjusting a ratio of A/B, where A is a transfer ratio [%] from the
image carrier to a valley portion of the transfer target while B is
a transfer ratio [%] from the image carrier to a ridge portion of
the transfer target, based on an adjustment input by a user by an
adjusting unit; and controlling a transfer condition of the
transfer unit based on the ratio of A/B adjusted at the adjusting
by a controlling unit.
The above and other objects, features, advantages and technical and
industrial significance of this invention will be better understood
by reading the following detailed description of presently
preferred embodiments of the invention, when considered in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustrating an overall structure of an image
forming apparatus according to an embodiment;
FIG. 2 is a schematic illustrating a structure of an image forming
section of the image forming apparatus;
FIG. 3 is a schematic to describe more detail structures of the
image forming units for respective colors of the image forming
section;
FIG. 4 is an explanatory view illustrating an example of a basic
setting screen of a print setting screen of the image forming
apparatus;
FIG. 5 is an explanatory view illustrating a result when a solid
image is printed on Leathac paper by controlling a condition of
secondary transfer bias applied to a secondary transfer bias
roller;
FIG. 6 is a graph illustrating luminance values measured on a
valley portion and a ridge portion of an image printed on a white
sheet in each of five levels of FIG. 5; and
FIG. 7 is a flowchart illustrating an example of secondary transfer
bias control when a detection unit is provided.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment is described below in which the present invention is
applied to an image forming apparatus 10 that employs
electrophotography and is capable of forming color images. FIG. 1
is a schematic illustrating an overall structure of the image
forming apparatus 10 according to the embodiment. The image forming
apparatus 10 includes an image scanning section 11, an image
writing section 12, an image forming section 13, and a paper
feeding unit 14, for forming color images by electrophotography.
FIG. 2 is a schematic illustrating a structure of only the image
forming section 13 of the image forming apparatus 10.
The schematic structure and operation of the image forming 10 is
described below. In FIGS. 1 and 2, an image signal is produced
based on image data of an original image scanned by the image
scanning section 11 or image data sent from a host computer serving
as an external information processing apparatus (a user terminal
apparatus). The produced image signal is converted into color
signals of yellow (Y), magenta (M), cyan (C), and black (Bk) for
image forming, and the color signals are transmitted to the image
writing section 12. The image writing section 12 is structured with
a laser scanning optical system including a laser light source, a
deflector such as a rotating polygon mirror, a scanning imaging
optical system, and a mirror group, as exemplarily illustrated in
FIG. 1. The image writing section 12 may he structured with a light
emitting diode (LED) writing system composed of an LED array in
which a plurality of LEDs serving as optical elements are arrayed
in a one-dimension or a two-dimension, and an imaging optical
system. The image writing section 12 further includes four writing
optical paths 12Y, 12M, 12C, and 12Bk each corresponding to one of
the color signals. As illustrated in FIG. 2, the image writing
section 12 writes images corresponding to the color signals into
respective photosensitive elements 21Y, 21M, 21C, and 21Bk serving
as image carriers each included in one of four image forming units
provided to the image forming section 13, through the respective
writing optical paths 12Y, 12M, 12C, and 12Bk.
FIG. 3 is a schematic to describe more detailed structures of the
image forming units for the respective colors of the image forming
section 13. Generally, an organic photoconductor (OPC)
photosensitive element is used for the photosensitive elements 21Y
for yellow (Y), 21M for magenta (M), 21C for cyan (C), and 21Bk for
black (Bk), each included in the respective image forming units
provided in the image forming section 13. As illustrated in FIGS. 2
and 3, a charging unit, an exposing unit using a laser beam from
the image writing section 12, a developing unit, a primary transfer
bias roller serving as a primary transfer unit, and a cleaning
device are disposed around each of the photosensitive elements 21Y,
21M, 21C, and 21Bk. The charging units for the four photosensitive
elements are charging units 16Y, 16M, 16C, and 16Bk. The developing
units for the four photosensitive elements are developing units
20Y, 20M, 20C, and 20Bk. The primary transfer bias rollers for the
four photosensitive elements are primary transfer bias rollers 23Y,
23M, 23C, and 23Bk. The cleaning devices for the four
photosensitive elements are cleaning devices 30Y, 30M, 30C, and
30Bk.
In the embodiment, a developing unit employing a two-component
magnetic brush developing method is used for each of the developing
units 20Y, 20M, 20C, and 20Bk. However, other developing units
employing other methods may be used. An intermediate transfer belt
22 that serves as an intermediate transfer body and an image
carrier is provided so as to extend between each of the
photosensitive elements 21Y, 21M, 21C, and 21Bk and corresponding
one of the primary transfer bias rollers 23Y, 23M, 23C, and 23Bk.
Each color toner image formed on the respective photosensitive
elements is sequentially transferred onto the intermediate transfer
belt 22 so as to overlap with each other.
A sheet (transfer sheet) P serving as a transfer target is fed from
the paper feeding unit 14 or a paper feeding bank 18 (refer to FIG.
1) of the image forming apparatus 10. Thereafter, the sheet P is
fed via a pair of registration rollers 17 illustrated in FIG. 2,
and then is carried by a transfer conveying belt 50 serving as a
transfer conveying member. The toner images transferred on the
intermediate transfer belt 22 are secondarily transferred
(collective transfer) on the sheet P with a secondary transfer bias
roller 60 serving as a secondary transfer unit at a point where the
intermediate transfer belt 22 and the transfer conveying belt 50
are made contact with each other. As a result, a color image is
formed on the sheet P. Secondary transfer bias having a
predetermined transfer voltage is applied to the secondary transfer
bias roller 60 from a secondary transfer bias power source (not
illustrated) serving as a transfer bias application unit. In the
embodiment, secondary transfer bias is applied that has a transfer
voltage in which an alternating voltage is superimposed on a
direct-current voltage.
The sheet P having the color image formed thereon is conveyed on
the transfer conveying belt 50 to a fixing unit 15. The image
transferred on the sheet P is fixed by the fixing unit 15, and
thereafter the sheet P is externally discharged from the main body
of the image forming apparatus.
Toner that has not been transferred onto the sheet P in the
secondary transfer and remains on the intermediate transfer belt 22
is removed from the intermediate transfer belt 22 by a belt
cleaning device 25 serving as an intermediate transfer body
cleaning unit. A lubricant coating device 26 is disposed downstream
from the belt cleaning device 25. The lubricant coating device 26
includes solid lubricant 26a, a conductive brush 26b that coats the
solid lubricant 26a on the intermediate transfer belt 22 by sliding
on the intermediate transfer belt 22. The conductive brush 26b
constantly makes contact with the intermediate transfer belt 22 so
as to coat the solid lubricant 26a onto the intermediate transfer
belt 22. The solid lubricant 26a acts to enhance cleaning property
of the intermediate transfer belt 22 so as to prevent an occurrence
of toner filming, thereby increasing durability of the intermediate
transfer belt 22.
Each surface of the photosensitive elements 21Y, 21M, 21C, and 21Bk
is charged with a predetermined potential (e.g., about -700 V) by
the respective charging units 16Y, 16M, 16C, and 16Bk each disposed
upstream of the respective writing optical paths 12Y, 12M, 12C, and
12Bk, before image writing. In the embodiment, the charging units
16Y, 16M, 16C, and 16Bk use a conductive rubber roller. Each
conductive rubber roller of the charging units 16Y, 16M, 16C, and
16Bk is disposed so as not to make contact with and charge the
respective photosensitive elements 21Y, 21M, 21C, and 21Bk with a
distance of about 50 .mu.m from the photosensitive element. In
addition, an alternating-current voltage having predetermined
frequency and peak-to-peak voltage (e.g., a frequency of about 1
kHz, and a peak-to-peak voltage of 2 kV) is applied to each
conductive rubber roller. The center value of the
alternating-current voltage is set to a predetermined potential
(e.g., about -800 V). Accordingly, each surface of the
photosensitive elements 21Y, 21M, 21C, and 21Bk is uniformly
charged with a predetermined potential (e.g., about -700 V).
The charging means that charges each surface of the photosensitive
elements 21Y, 21M, 21C, and 21Bk is not limited to the non-contact
charging employed by the charging units as described above, but the
following methods also can be used: contact charging in which the
conductive rubber roller is disposed so as to make contact with and
charge each of the photosensitive elements 21Y, 21M, 21C, and 21Bk;
a combination of alternating-current (AC) charging and
direct-current (DC) charging; DC bias roller charging in which each
of the photosensitive elements is charged with DC bias of about
-1400 V without applying AC bias; conventionally well-used corona
charging using a corotron or scorotron system; and conventionally
well-used brush charging.
After each surface of the photosensitive elements 21Y, 21M, 21C,
and 21Bk is charged, the image writing section 12 writes images on
each surface of the photosensitive elements 21Y, 21M, 21C, and
21Bk. As a result, static latent images each corresponding to one
of color images of yellow, magenta, cyan, and black are
respectively formed on the surfaces of the photosensitive elements
21Y for yellow, 21M for magenta, 21C for cyan, and 21Bk for black.
These static latent images are developed by the developing units
20Y for yellow, 20M for magenta, 20C for cyan, and 20Bk for
black.
As illustrated in FIG. 3, each of the developing units 20Y, 20M,
20C, and 20Bk includes a developing roller 201 serving as a
developer carrier, a doctor blade 202 serving as a developer amount
regulating member, two screws 203 and 204 serving as a developer
agitation carriage unit, a toner density sensor 205 serving as a
toner density detection unit, and a development case 206. The
screws 203 and 204 are disposed so as to be positioned in
diagonally lower direction from the developing roller 201. The two
screws 203 and 204 are disposed in a horizontal direction in
parallel with each other. The development case 206 has a partition
206a that partitions the development case 206 into two chambers so
as to separate the two screws 203 and 204 from each other. The
partition 206a has two cutouts, one at the front side and the other
at the rear side in FIG. 3, so that developer in each chamber of
the development case 206 is circulated and carried by the two
screws 203 and 204.
The development case 206 has an opening portion 206b formed at a
part facing the photosensitive element so as to expose part of the
developing roller 201 out of the opening portion 206b. In addition,
the developing roller 201, the screws 203 and 204, and the doctor
blade 202 are disposed as illustrated in FIG. 3 so as to provide a
relatively slightly large space above the screw 204 inside the
development case 206. The development cases 206 of the developing
units 20Y, 20M, 20C, and 20Bk respectively house developer of
colors of yellow, magenta, cyan, and black for developing static
latent images each corresponding to one of color images. In the
embodiment, two-component developer in which non-magnetic toner and
magnetic carriers are dispersed and mixed is used as the
developer.
Each developer of the developing units 20Y, 20M, 20C, and 20Bk is
agitated and carried by the two screws 203 and 204 rotating in the
opposite direction from each other, so that the developer
constantly circulates in each chamber of the development case 206
by passing through the cutouts provided at the front and rear sides
of the partition 206a. The developer is supplied toward the
developing roller 201 by a screw 204 that circulates, agitates, and
carries the developer. The developing roller 201 is composed of a
magnetic roller 201a serving as a magnetic field generation unit
and a developing sleeve 201b that is nonmagnetic and rotatably
mounted on the magnetic roller 201a so as to cover the outer
circumference of the magnetic roller 201a.
The developer supplied to the developing roller 201 is carried on a
surface of the developing sleeve 201b by a magnetic force of the
magnetic roller 201a and the rotation of the developing sleeve 201b
so as to be held in a magnetic brush-like shape. The developer held
in the magnetic brush-like shape on the surface of the developing
sleeve 201b is carried toward the opening portion 206b of the
development case 206 while co-rotating with the rotation of the
developing sleeve 201b. The developer is cut by the doctor blade
202 with a fixed length so as to be measured with a proper amount
before entering the opening portion 206b. Thereafter, the developer
is moved into a developing region formed between the surface of the
developing roller 201 exposed out of the opening portion 206b and
the surface of the photosensitive element.
The developer cut off by the doctor blade 202 does not move into
the developing region, but moves along the outer circumference of
the developer held in a magnetic brush-like shape on the surface of
the developing sleeve 201b and drops onto the screw 204 by own
weight so as to return to a circulation carriage path of the
development case 206. The developer returned to the circulation
carriage path is agitated and carried again by the two screws 203
and 204, and thereafter supplied to the developing roller 201 again
by the screw 204.
On the other hand, the developer having moved into the developing
region forms a toner image on the photosensitive element by
transferring toner on a static latent image formed on the
photosensitive element so as to visualize the static latent image.
Developing bias is applied on the developing sleeve 201b with a
predetermined voltage (e.g., -500 V). A potential difference
between a photosensitive element potential (e.g., about -150 V)
that is an potential of an exposure region on the photosensitive
element and the developing bias causes toner in the developer held
on the developing sleeve 201b to transfer on the static latent
image formed on the photosensitive element.
Excessive developer including toner and carriers that have not been
consumed in visualizing the static latent image is moved so as to
be returned inside the development case 206 while being held on the
developing sleeve 201b. The excessive developer leaves from the
developing sleeve 201b and drops onto the screw 204 by own weight
when the developer is moved into an area on which a magnetic force
of the magnetic roller 201a doses not act of the surface of the
developing sleeve 201b. As a result, the excessive developer is
collected into the circulation carriage path of the development
case 206. The collected excessive developer is then agitated and
carried again by the two screws 203 and 204, and thereafter
supplied to the developing roller 201 again by the screw 204.
As described above, the developer is repeatedly supplied to and
collected from the developing sleeve 201b while circulating inside
the development case 206 by being agitated and carried by the two
screws 203 and 204. As toner in developer is consumed by repeatedly
carrying out developing processing for visualizing static latent
images on the photosensitive element, a toner density in developer
housed in the development case 206 gradually lowers. In each of the
developing units 20Y, 20M, 20C, and 20Bk, the toner density sensor
205 detects a toner density of developer housed in the development
case 206. Based on a detection result of the toner density sensor
205, a toner replenishing unit (not illustrated) timely replenishes
new supplemental toner in the development case 206 so as to
constantly maintain a toner density of developer in the development
case 206 at a fixed toner density.
The color toner images formed on the photosensitive elements 21Y,
21M, 21C, and 21Bk are primarily transferred and sequentially,
color by color, overlapped on a surface of an intermediate transfer
belt 22 that rotates while making contact with the surfaces of the
photosensitive elements, by the primary transfer bias rollers 23Y,
23M, 23C, and 23Bk disposed so as to be opposite to the
photosensitive elements 21Y, 21M, 21C, and 21Bk, respectively. In
other word, the primary transfer bias rollers 23Y, 23M, 23C, and
23Bk, which are disposed to face the respective photosensitive
elements with the intermediate transfer belt 22 interposed
therebetween, cause a transfer electric field to be generated in a
primary transfer region between the intermediate transfer belt 22
and the photosensitive elements having a predetermined
photosensitive element potential on their surfaces (e.g., about
-150 V). The toner images on the photosensitive elements are
statistically transferred on the intermediate transfer belt 22 with
the transfer electric field.
A conductive sponge roller is generally used as the primary
transfer bias rollers 23Y, 23M, 23C, and 23Bk. There are two
methods to provide conductivity to the roller: one is a method in
which an ion conductive agent is mixed into rubber material, and
the other one is a method in which an electron conductive agent
such as carbon is mixed into rubber material. A roller using an
electron conductive agent, however, generally has markedly uneven
resistivity. Thus, the roller is unsuitable for good transfer.
Therefore, in the embodiment, the primary transfer bias roller is
made of ion conductive foamed nitrile butadiene rubber (NBR) having
a hardness of Asker C 40 degrees and a resistance value of
10.sup.7.OMEGA.. Transfer bias is applied to the primary transfer
roller so as to generate a transfer electric field.
Various kinds of material can be used for the intermediate transfer
belt 22. The following belts are preferably used: a belt made of
polyimide having excellent durability and high Young's modulus; a
belt made of polyvinylidene fluoride (PVDF) having excellent
surface smoothness; and a multi-layered belt composed of a
polyurethane resin layer, a polyurethane rubber layer formed on the
polyurethane resin layer, and a coating layer that contains
fluorine components, and is formed on the polyurethane rubber layer
so as to serve as an elastic surface layer. The manufacturing
method and material of the intermediate transfer belt are not
limited to any specific ones. In the embodiment, a polyimide resin
was used as the material because the resin is most suitable from a
strength point of view. The belt made of the polyimide resin had a
surface resistivity of 1.times.10.sup.11.OMEGA./.quadrature. and a
volume resistivity of 1.times.10.sup.9 .OMEGA.cm.
The polyimide intermediate transfer belt was formed by a general
method as follows: a polymer solution including carbon black
dispersed therein was injected into a cylindrical metal mold; and
an endless film was formed by centrifugal molding, i.e., the
cylindrical metal mold was rotated while being heated at 100 to
200.degree. C. The film thus formed was removed from the mold with
a semi-hardened state, and overlaid on an iron spindle so as to be
hardened by progressing the imidization reaction at 300 to
450.degree. C. As a result, the intermediate transfer belt was
made. In this process, characteristics of the belt can be
controlled by changing a carbon amount, a firing temperature, and a
hardening speed, for example. This method also can control the
volume resistivity and the surface resistivity. The volume
resistivity and the surface resistivity were measured with High
Rester-UP (MCP-HT450) high resistance meter and URS probe
(MCP-HTP14) both of which are manufactured by Mitsubishi Chemical
Co., Ltd.
As described above, each color toner image formed on the
photosensitive elements 21Y, 21M, 21C, and 21Bk is sequentially
overlapped on the surface of the intermediate transfer belt 22 by
primary transfer, whereby a full-color toner image composed of four
color toner images is formed on the intermediate transfer belt 22.
The full-color toner image formed on the intermediate transfer belt
22 is secondarily transferred (collective transfer) on the sheet P
carried by the transfer conveying belt 50 after being fed by the
registration roller 17, by the secondary transfer bias roller 60 to
which predetermined secondary transfer bias is applied. User
adjustment on a secondary transfer condition (secondary transfer
bias application condition) is described later in detail.
The sheet P on which the full-color image has been formed by the
secondary transfer is carried to the fixing unit 15 by the transfer
conveying belt 50. The secondarily transferred full-color image is
fixed by the fixing unit 15, and thereafter the sheet P is
externally discharged out from the main body of the image forming
apparatus. Remaining toner that remains on the intermediate
transfer belt 22 after the secondary transfer is removed from the
intermediate transfer belt 22 by the belt cleaning device 25. Then,
a subsequent image is formed by the image forming units for the
respective colors of the image forming section 13.
Toner remaining on each of the photosensitive elements 21Y, 21M,
21C, and 21Bk after the primary transfer is removed by the
respective cleaning devices 30Y, 30M, 30C, and 30Bk as the
following manner. As illustrated in FIG. 3, the cleaning device of
the embodiment employs a combine use of a cleaning blade 301 that
serves as a cleaning member and is made of a polyurethane rubber
having elasticity, and a fur brush 302 having conductivity. An
electric field roller 303 made of metal is disposed so as to make
contact with the fur brush 302. A scraper 304 is disposed so as to
make contact with the electric field roller 303.
In FIG. 3, toner remaining on each of the photosensitive elements
21Y, 21M, 21C, and 21Bk is scraped and dropped off from the
photosensitive element by the fur brush 302 rotating in an opposite
direction (a counter direction) from the rotating direction of the
photosensitive element. Toner stuck to the fur brush 302 is removed
by the electric field roller 303 rotating in the opposite direction
from the rotating direction of the fur brush 302 and sticks to the
electric field roller 303. The toner stuck to the electric field
roller 303 is scraped by the scraper 304 and drops into a cleaning
case 305 for being collected therein. Cleaning bias is applied to
the electric field roller 303. Remaining toner on the
photosensitive element is moved from the fur brush 302 to the
electric field roller 303 by a static electric force caused by the
cleaning bias, and thereafter is scraped off from the electric
field roller 303 by the scraper 304.
The toner thus collected in the cleaning case 305 is moved by a
collecting screw 306 to a waste toner bottle (not illustrated) or
the developing unit of the image forming unit provided with the
cleaning device. In a printer of the embodiment, toner collected
from the cleaning case 305 by the collecting screw 306 is returned
to the corresponding developing unit so as to reuse it.
Each cleaning device of the image forming units is disposed in such
a manner that a part where the collecting screw 306 in one certain
cleaning device is provided to overlap a part of the development
case 206 located above the screw 203 of the developing unit of the
image forming unit that is adjacent downstream to the one certain
cleaning device, as illustrated in FIG. 2. This arrangement enables
the image forming units to be closely disposed with each other, and
the main body of the image forming apparatus to be reduced in
size.
User adjustment on the secondary transfer condition of the image
forming apparatus having the structure described above is described
below.
First, the description is made when no detection unit that detects
surface smoothness of the sheet P as a transfer target is
provided.
FIG. 4 illustrates an example of a basic setting screen of a print
setting screen used when an image forming condition is set for the
image forming apparatus 10 of the embodiment. This print setting
screen is displayed on a display section (e.g., a liquid crystal
display) provided on an operation panel of the image forming
apparatus 10, or a display section (e.g., a liquid crystal display)
of a host computer that serves as an external information
processing apparatus (a user terminal apparatus) and in which a
printer driver compatible with the image forming apparatus 10 is
installed.
In a basic setting screen 900 of the print setting screen
illustrated in FIG. 4, a density selection section 900b is
displayed only when "heavy paper" having ridges and valleys on its
surface, "colored paper", or "special paper" is selected from a
sheet-kind selection column in a sheet-kind selection section 900a.
The density selection section 900b is for selecting a "valley
portion image density/ridge portion image density". In the density
selection section 900b, the "valley portion image density"
corresponds to a transfer rate A [%] from the intermediate transfer
belt 22 to a valley portion of the sheet P while the "ridge portion
image density" corresponds to a transfer rate B [%] from the
intermediate transfer belt 22 to a ridge portion of the sheet P.
The "valley portion image density/ridge portion image density"
corresponds to a ratio of A/B. In a five-level grayscale display
extending in the traverse direction of the density selection
section 900b, the valley portion image density is relatively lower
than the ridge portion image density in a light area located on the
left side; and as the area closes to the right side, the valley
portion image density becomes relatively higher than the ridge
portion image density.
A user can select and set any one of the five levels indicating the
"valley portion image density/ridge portion image density" in the
density selection section 900b by operating the operation panel
serving as an adjusting unit of the image forming apparatus 10, or
operating an operation section (e.g., a keyboard or a mouse)
serving as the adjusting unit of the host computer. Based on the
selection result of the "valley portion image density/ridge portion
image density", a control unit controls a condition of secondary
transfer bias applied to the secondary transfer bias roller 60. As
for the control unit, for example, a main control section in a
control system included in the image forming apparatus 10 can be
used. The main control section includes a CPU and memories.
The relations between the five levels of the "valley portion image
density/ridge portion image density" (ratio of A/B) that a user can
select and set, and the secondary transfer condition are
exemplarily listed as follows.
(1) When a user sets the "valley portion image density/ridge
portion image density" to the lowest ratio, secondary transfer bias
having a direct-current component (hereinafter referred to as a "DC
component") that is set to -3000 V, and an alternating-current
component (hereinafter referred to as a "AC component") whose
amplitude is set to 0 V is applied to the secondary transfer bias
roller 60. In other words, the secondary transfer bias is a
direct-current voltage. This bias application condition is the same
as that in normal image forming. (2) When a user sets the "valley
portion image density/ridge portion image density" to the second
lowest ratio, secondary transfer bias having the DC component that
is set to -600 V, and the AC component with a sine wave having a
frequency of 1 kHz whose amplitude is set to 2000 V is applied to
the secondary transfer bias roller 60. (3) When a user sets the
"valley portion image density/ridge portion image density" to the
third lowest ratio, secondary transfer bias having the DC component
that is set to -300 V, and the AC component with a sine wave having
a frequency of 1 kHz whose amplitude is set to 4000 V is applied to
the secondary transfer bias roller 60. (4) When a user sets the
"valley portion image density/ridge portion image density" to the
fourth lowest ratio, secondary transfer bias having the DC
component that is set to -100 V, and the AC component with a sine
wave having a frequency of 1 kHz whose amplitude is set to 4000 V
is applied to the secondary transfer bias roller 60. (5) When a
user sets the "valley portion image density/ridge portion image
density" to the highest ratio, secondary transfer bias having the
DC component that is set to 0 V, and the AC component with a sine
wave having a frequency of 1 kHz whose amplitude is set to 4000 V
is applied to the secondary transfer bias roller 60.
FIG. 5 illustrates the results in which a solid image is printed
onto Leathac paper by controlling the secondary transfer bias
application condition to the secondary transfer bias roller 60 in
each of the five levels (1) to (5) described above. Each of the
five levels (1) to (5) in FIG. 5, a magnitude relation between the
transfer rate A for valley portions and the transfer rate B for
ridge portions can be estimated as follows. The term "transfer
rate" is defined as follows: a toner adhesion amount on a sheet
after transfer [mg/cm.sup.2]/a toner adhesion amount on the
intermediate transfer belt 22 before transfer [mg/cm.sup.2].
Accordingly, the magnitude relation between the transfer rates A
and B is determined by "a relation between a toner adhesion amount
on a valley portion of a sheet" and "a toner adhesion amount on a
ridge portion of the sheet", when "the toner adhesion amount before
transfer" is constant regardless of locations on a sheet such as a
case of the printed solid image illustrated in FIG. 5. As for a
sheet, such as a white sheet, having higher luminance than that of
toner on its exposed surface, it is known that a toner adhesion
amount on the sheet monotonically decreases with respect to
luminance of a toner image imaged by a charge coupled device (CCD)
camera serving as an image capturing unit. Consequently, the
following relations can be determined: when luminance of a toner
image is higher in a ridge portion than that in a valley portion,
A/B>1; when luminance of a toner image is lower in the ridge
portion than that in the valley portion, A/B<1; and when
luminance of a toner image in the ridge portion equals to that in
the valley portion, A/B=1.
In contrast, a toner adhesion amount monotonically increases with
respect to luminance of a toner image imaged by a CCD camera in a
case of a sheet having lower luminance than that of toner on its
exposed surface. Consequently, in this case, the following
relations can be determined: when luminance of a toner image is
higher in a ridge portion than that in a valley portion, A/B<1;
when luminance of a toner image is lower in the ridge portion than
that in the valley portion, A/B>1; and when luminance of a toner
image in the ridge portion equals to that in the valley portion,
A/B=1.
FIG. 6 is a graph illustrating the results in which luminance is
measured on valley and ridge portions of an image printed on a
white sheet in each of the five levels (1) to (5) in FIG. 5. FIG. 6
also illustrates photographs of each measurement points in the
image of the five levels (1) to (5) together with the luminance
measurement results. The graph is made by averaging measurement
values on a plurality of points as illustrated in the photographs
because luminance values vary depending on the points of the valley
and ridge portions even in the same image. As can be seen from the
graph of FIG. 6, images of level (1) to (3) show the relation of
A/B<1 because the luminance of the toner image in a ridge
portion is lower than that in a valley portion. The image of level
(4) shows the relation of A/B=1 because the luminance of the toner
image in the valley portion nearly equals to that in the ridge
portion. The image of level (5) shows the relation of A/B>1
because the luminance of the toner image in the ridge portion is
higher than that in the valley portion.
From the results illustrated in FIG. 6, it can be determined that
decreasing of the DC component of the secondary transfer bias has
an effect of decreasing the transfer rate B for ridge portions;
while an increase in the amplitude of the AC component of the
secondary transfer bias has an effect of increasing the transfer
rate A for valley portions. Based on the results, the secondary
transfer bias application condition is controlled in such a manner
that the larger a user adjusts the "valley portion image
density/ridge portion image density" (corresponds to a ratio of
A/B), the smaller the DC component of the secondary transfer bias
and the larger the amplitude of the AC component of the secondary
transfer bias. This control allowed forming an image having the
relation of A/B>1 as well as an image having the relation of
A/B<1 and an image having the relation of A/B=1.
In addition, the same effect as describe above was achieved when
the secondary transfer bias roller 60 was constant-current
controlled as described in the following cases (1) to (5). In order
to handle various kinds of sheets, constant-current control is
preferable than constant-voltage control.
(1) When a user sets the "valley portion image density/ridge
portion image density" to the lowest ratio, secondary transfer bias
having the DC component that is set to -30 .mu.A, and the AC
component that is set to 0 .mu.A, i.e., the secondary transfer bias
is a direct-current, is applied to the secondary transfer bias
roller 60. (2) When a user sets the "valley portion image
density/ridge portion image density" to the second lowest ratio,
secondary transfer bias having the DC component that is set to -6
.mu.A, and the AC component that is a sine wave having a frequency
of 1 kHz and set to 20 .mu.A is applied to the secondary transfer
bias roller 60. (3) When a user sets the "valley portion image
density/ridge portion image density" to the third lowest ratio,
secondary transfer bias having the DC component that is set to -3
.mu.A, and the AC component that is a sine wave having a frequency
of 1 kHz and set to 40 .mu.A is applied to the secondary transfer
bias roller 60. (4) When a user sets the "valley portion image
density/ridge portion image density" to the fourth lowest ratio,
secondary transfer bias having the DC component that is set to -1
.mu.A, and the AC component that is a sine wave having a frequency
of 1 kHz and set to 40 .mu.A is applied to the secondary transfer
bias roller 60. (5) When a user sets the "valley portion image
density/ridge portion image density" to the highest ratio,
secondary transfer bias having the DC component that is set to 0
.mu.A, and the AC component that is a sine wave having a frequency
of 1 kHz and set to 40 .mu.A is applied to the secondary transfer
bias roller 60.
When a sheet excluding the sheets described above (heavy paper,
colored paper, and special paper), such as regular paper, recycled
paper, and coated paper, were selected, the selection of the
"valley portion image density" was disabled because such selected
paper has few ridges and valleys. Secondary transfer bias having
the DC component that was set to -3000 V (in constant-current
control, the DC component is set to -30 .mu.A) was applied as
usual.
Next, the description is made when a detection unit that detects
surface smoothness of a sheet is provided. The detection unit that
detects the smoothness can include, for example, a light emitting
sensor that emits light toward a transfer target surface of the
sheet P, and a light receiving sensor that receives light that is
emitted from the light emitting sensor and reflected by the
transfer target surface of the sheet P. In the detection unit thus
structured, it can be determined that when a received light amount
is small, smoothness is low; while when a received light amount is
large, smoothness is high. A detection unit 70, an example of the
detection unit, can be disposed upstream in a sheet carrying
direction of the secondary transfer bias roller 60 as exemplarily
illustrated in FIG. 2.
When the detection unit 70 is provided, a user can select,
regardless of the kind of the sheet, any of the five levels
indicating the "valley portion image density/ridge portion image
density" corresponding to a ratio of A/B in the basic setting
screen of the print setting screen displayed on the display section
provided on the operation panel of the image forming apparatus 10,
or the display section of the host computer.
FIG. 7 is a flowchart illustrating an example of secondary transfer
bias control when the detection unit 70 is provided. Upon starting
of a print job, a selection result of the five levels indicating
the "valley portion image density/ridge portion image density" is
determined (S1). If the lowest (the lightest) level of the "valley
portion image density/ridge portion image density" is selected, the
control unit controls in such a manner that secondary transfer bias
having the DC component set to -3000 V, i.e., the secondary
transfer bias is a direct-current voltage, is applied to the
secondary transfer bias roller 60 (S2). If the second to fourth
lower levels, and the highest level of the "valley portion image
density/ridge portion image density" are set, the detection unit 70
detects smoothness of a sheet (S3 to S6).
If the smoothness detected by the detection unit 70 of the sheet is
equal to or higher than a predetermined value (No at each of S7 to
S10), it is not necessary to add the AC component for saving a
toner adhesion amount because the sheet has few ridges and valleys
on the surface. Accordingly, the control unit controls in such a
manner that secondary transfer bias having the DC component set to
-3000 V, i.e., meaning the secondary transfer bias being a
direct-current voltage, is applied to the secondary transfer bias
roller 60 (S2) in the same manner as the case when the lowest (the
lightest) level of the "valley portion image density/ridge portion
image density" is selected. As a result, toner can be prevented
from being scattered during the secondary transfer, whereby image
quality can be improved.
If the smoothness detected by the detection unit 70 of the sheet is
equal to or lower than the predetermined value (Yes at each of S7
to S10), the control unit controls in such a manner that secondary
transfer bias determined according to the user selected level of
the "valley portion image density/ridge portion image density" is
applied to the secondary transfer bias roller 60 in the same manner
as the cases (2) to (5) (S11 to S14). S1 to S14 are repeated until
a job-end step at which the print job ends (S15).
The controlling of the secondary transfer bias, applied to the
secondary transfer bias roller 60 by detecting a surface property
(smoothness) of the sheet P as illustrated in the flowchart of FIG.
7, saved selecting the kind of sheets piece by piece and also
increased productivity.
The constant-current control is also preferable for handling
various kinds of sheets in the case when the detection unit 70 is
provided, as the same in the case when no detection unit is
provided.
According to the embodiment described above, a user can adjust a
ratio of A/B according to texture that the user intends to obtain,
where A is defined as a transfer rate [%] from the intermediate
transfer belt 22 serving as an image carrier to a valley portion of
the sheet P serving as a transfer target; while B is defined as a
transfer rate [%] from the intermediate transfer belt 22 to a ridge
portion of the sheet P. Once a user adjusts the ratio of A/B
according to the user's intention, a transfer condition of the
transfer unit, including the secondary transfer bias roller 60 that
transfers a toner image to the sheet P from the intermediate
transfer belt 22, is controlled based on the adjusted ratio of A/B.
The control of the transfer condition enables the toner image on
the intermediate transfer belt 22 to be transferred on the sheet P
by changing the ratio of the transfer rates of the valley and ridge
portions of the sheet P so as to achieve texture that the user
intends to obtain. Consequently, images can be formed on the sheet
P having low surface smoothness without loosing texture that the
user intends to obtain.
In addition, according to the embodiment, the image forming
apparatus further includes a transfer bias application unit
(secondary transfer bias power source) that applies transfer bias,
in which an AC component (alternating-current component)
superimposed with a DC component (direct-current component) is
applied onto the secondary transfer bias roller 60. The transfer
bias application unit is controlled in such a manner that the
larger the ratio of A/B set by a user is, the smaller the
direct-current component of the transfer bias and the larger the
amplitude of the alternating-current component of the transfer
bias. The control of the DC component and the AC component of the
transfer bias enables transfer rates of the valley and ridge
portions of the sheet to be individually and properly controlled.
As a result, images can be reliably formed on the sheet P having
low surface smoothness according to the ratio of A/B adjusted by a
user.
In addition, according to the embodiment, the ratio of A/B can be
adjusted to a plurality of levels including at least one range
satisfying A/B>1, a range satisfying A/B=1, and at least one
range satisfying A/B<1, whereby a user can easily adjust the
ratio of A/B.
Furthermore, according to the embodiment including the detection
unit 70 that detects surface smoothness of the sheet P, the kinds
of sheets having different surface smoothness (degree of ridges and
valleys) can be determined based on the detection result of the
detection unit 70. Accordingly, a user does not need to select the
kinds of sheets; and a transfer condition (secondary transfer bias)
can be properly controlled according to surface smoothness of a
sheet. In addition, a user can save selecting the kinds of sheets
piece by piece, whereby productivity can be increased.
Furthermore, according to the embodiment, when the surface
smoothness detected by the detection unit 70 of the sheet P is
equal to or greater than a predetermined value, it is not necessary
to add the AC component for saving a toner adhesion amount because
the sheet has few ridges and valleys on the surface. In this case,
the control unit controls in such a manner that transfer bias
having only a direct-current component is applied to the secondary
transfer bias roller 60 regardless of a ratio of A/B adjusted by a
user. As a result, toner can be prevented from being scattered
during the secondary transfer, whereby image quality can be
improved.
In the embodiment, the "valley portion image density/ridge portion
image density" corresponding to a ratio of A/B can be adjusted
(selected and set) to five levels. However, the number of
adjustable levels of the "valley portion image density/ridge
portion image density" is not limited to five. For example, the
present invention can be applied to a case of three adjustable
levels (selected and set to three levels): a range satisfying
A/B>1; a range satisfying A/B=1; and a range satisfying A/B<1
in the same manner as the case of the five levels.
In the embodiment, a control target is the transfer bias (the
secondary transfer bias). However, besides the transfer bias (the
secondary transfer bias), the present invention can be applied to
other transfer conditions that are controlled according to the
"valley portion image density/ridge portion image density"
corresponding to a ratio of A/B adjusted by a user in the same
manner as the case of the transfer bias. Any control targets may be
applicable as long as they can change individually the transfer
rates of the valley and ridge portions of a sheet.
In the embodiment, the transfer condition when a toner image is
transferred to a sheet from the intermediate transfer belt 22 is
controlled. However, the present invention can be applied, in the
same manner of the embodiment, to a case of controlling a transfer
condition when a toner image is directly transferred to the sheet P
from the photosensitive element 21 without being transferred to the
intermediate transfer belt 22.
According to the present invention, a user can adjust a ratio of
A/B according to texture that the user intends to obtain, where A
is defined as a transfer rate [%] from an image carrier to a valley
portion of a transfer target; while B is defined as a transfer rate
[%] from the image carrier to a ridge portion of the transfer
target. For example, when a user intends to obtain texture of an
image drawn with colored pencils or printed by block print, the
user adjust the ratio of A/B to small so as to reduce a toner
adhesion amount on the valley portion. For another example, when a
user intends to reduce an effect of texture of a transfer target
for printing characters and the like with high visibility, the user
adjusts the ratio of A/B so as to equalize the toner adhesion
amount on the ridge portion and the valley portion. Once a user
adjusts the ratio of A/B according to the user's intention, a
transfer condition of a transfer unit that transfers a toner image
to the transfer target from the image carrier is controlled based
on the adjusted ratio of A/B. The control of the transfer condition
enables the toner image on the image carrier to be transferred on
the transfer target by changing the ratio of the transfer rates of
the valley and ridge portions of the transfer target so as to
achieve texture that the user intends to obtain. Consequently, the
present invention exhibits an effect of forming images on a
transfer target having low surface smoothness without loosing
texture that a user intends to obtain.
Although the invention has been described with respect to specific
embodiments for a complete and clear disclosure, the appended
claims are not to be thus limited but are to be construed as
embodying all modifications and alternative constructions that may
occur to one skilled in the art that fairly fall within the basic
teaching herein set forth.
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