Title: Image forming apparatus with color shift sensors that are shielded from toner
Abstract: An image forming apparatus forms a toner image on a toner image bearing body and the toner image is transferred onto a recording medium. An image forming section forms the toner image on the toner image bearing body, which may be a transfer belt. A reading section optically reads the toner image formed on the image bearing body. A covering section is provided between the reading section and the toner image bearing body. The covering section can move between an opening position, where the covering section covers the reading section, and a closing position, where the covering section does not cover the reading section. A drive mechanism drives the covering section to move between the opening position and the closing position. An adjustment section adjusts the reading section when the covering section is at the closing position. The covering section includes a reflection member attached thereto.
Patent Number: 7,020,404 Issued on 03/28/2006 to Fukuda, et al.
| Inventors:
|
Fukuda; Masahiro (Tokyo, JP);
Shiobara; Toshimasa (Tokyo, JP);
Asaba; Takeshi (Tokyo, JP);
Maekawa; Masanori (Tokyo, JP)
|
| Assignee:
|
Oki Data Corporation (Tokyo, JP)
|
| Appl. No.:
|
648397 |
| Filed:
|
August 27, 2003 |
Foreign Application Priority Data
| Aug 30, 2002[JP] | 2002-253274 |
| Oct 17, 2002[JP] | 2002-302794 |
| Current U.S. Class: |
399/49; 399/74; 399/98 |
| Current Intern'l Class: |
G03G 15/00 (20060101) |
| Field of Search: |
399/49,74,98,99,298,299,301-303
|
References Cited [Referenced By]
U.S. Patent Documents
| 5517283 | May., 1996 | Hori et al.
| |
| 6219508 | Apr., 2001 | Nagatomi et al.
| |
| 6321044 | Nov., 2001 | Tanaka.
| |
| Foreign Patent Documents |
| 0 314 536 | Sep., 1988 | EP.
| |
| 05-164694 | Jun., 1993 | JP.
| |
| 2000/-081739 | Mar., 2000 | JP.
| |
| 2002/-031919 | Jan., 2002 | JP.
| |
| 2002/-131997 | May., 2002 | JP.
| |
Primary Examiner: Royer; William J.
Attorney, Agent or Firm: Rabin & Berdo, PC
Claims
What is claimed is:
1. An image forming apparatus in which a toner image is formed on an image bearing
body and the toner image is transferred onto a recording medium, comprising:
an image forming section;
a toner image bearing body;
a reading section that reads the toner image formed on said toner image bearing body;
a covering section provided between said reading section and said toner image
bearing body and movable either to a closing position where said covering section
covers said reading section or to an opening position where said covering section
does not cover said reading section;
a drive mechanism that drives said covering section to move either to the opening
position or to the closing position; and
an adjustment section that adjusts said reading section when said covering section
is at the closing position, said reading section being adjusted in such a way that
an output of said reading section changes.
2. The image forming apparatus according to claim 1, further comprising a correction
section that corrects at least one of a position on said toner image bearing body
at which a toner image is formed and a density of the toner image formed on said
toner image bearing body, the position and the density being corrected in accordance
with an output of said reading section.
3. The image forming apparatus according to claim 1, wherein said covering section
includes a reference sheet for adjusting said reading section, the reference sheet
being positioned so that when said covering section is at the closing position,
the reference sheet opposing said reading section;
wherein said adjustment section adjusts said reading section such that when said
reading section reads the reference, and the output of said reading section is
within a predetermined range.
4. The image forming apparatus according to claim 1, wherein said covering section
includes a gray reference sheet for adjusting said reading section, the gray reference
sheet being positioned so that when said covering section is at the closing position,
the reference sheet opposing said reading section.
5. An image forming apparatus in which a toner image is formed on an image bearing
body and the toner image is transferred onto a recording medium, comprising:
an image forming section;
a toner image bearing body;
a reading section that reads the toner image formed on said image bearing body;
a covering section provided between said reading section and said toner image
bearing body and movable between a closing position where said covering section
covers said reading section and an opening position where said covering section
does not cover said reading section;
a drive mechanism that drives said covering section to move between the opening
position and the closing position; and
an adjustment section that adjusts said reading section when said covering section
is at the closing position,
wherein said covering section includes a reflection member attached thereto;
wherein said reading section includes a light emitting section that emits an
amount of light to the reflection member and a light receiving section that receives
light reflected from the reflection member; and
wherein said adjustment section adjusts the amount of light in accordance with
an output of the light receiving section that detects the reflection member.
6. The image forming apparatus according to claim 5, further comprising a controller
that controls said drive mechanism to drive said covering section, the controller
controlling said drive mechanism according to a detection output of the light receiving
section that detects passage of an edge of said covering section;
wherein the reflection member has a first reflection coefficient and said toner
image bearing body has a second reflection coefficient.
7. An image forming apparatus in which a toner image is formed on an image bearing
body and the toner image is transferred onto a recording medium comprising:
an image forming section;
a toner image bearing body;
a reading section that reads the toner image formed on said image bearing body;
a covering section provided between said reading section and said toner image
bearing body and movable between a closing position where said covering section
covers said reading section and an opening position where said covering section
does not cover said reading section;
a drive mechanism that drives said covering section to move between the opening
position and the closing position;
an adjustment section that adjusts said reading section when said covering section
is at the closing position;
a fixing section in which the toner image transferred onto the recording medium
is fused into a permanent image; and
at least one of a first drive section that drives said image forming section,
a second drive section that drives said toner image bearing body, and a third drive
section that drives said fixing section;
wherein said drive mechanism is powered by one of said first drive section, said
second drive section, and said third drive section to move said covering section
between the opening position and the closing position.
8. The image forming apparatus according to claim 7, wherein said drive mechanism
drives said covering section to move straight.
9. The image forming apparatus according to claim 7, wherein said drive mechanism
includes a gear train that transmits a drive force from any one of said first drive
section, said second drive section, and said third drive section to said covering section.
10. The image forming apparatus according to claim 7, wherein said covering section
moves in a first direction to the opening position and in a second direction opposite
to the first direction to the closing position;
wherein when a rotating member of one of said first drive section, said second
drive section, and said third drive section rotates in a third direction, said
covering section moves either in the first direction or in the second direction.
11. The image forming apparatus according to claim 7, wherein said fixing section
includes a heater, and said drive mechanism is powered by said third drive section
to move said covering section to the opening position before the heater reaches
a predetermined temperature.
12. The image forming apparatus according to claim 7, wherein said fixing section
includes a motor;
wherein when the toner image is fused, the motor rotates in a forward direction; and
wherein when said covering section moves to the opening position, the motor rotates
in a reverse direction.
13. An image forming apparatus in which a toner image is formed on an image bearing
body and the toner image is transferred onto a recording medium, comprising:
an image forming section;
a toner image bearing body;
a reading section that reads the toner image formed on said image bearing body;
a covering section provided between said reading section and said toner image
bearing body and movable between a closing position where said covering section
covers said reading section and an opening position where said covering section
does not cover said reading section;
a drive mechanism that drives said covering section to move between the opening
position and the closing position;
an adjustment section that adjusts said reading section when said covering section
is at the closing position; and
a cleaning member mounted to said covering section;
wherein when said drive mechanism drives said covering section to move between
the opening position and the closing position, the cleaning member moves into contact
engagement with said reading section to remove foreign matter from said reading section.
14. An image forming apparatus in which a toner image is formed on an image bearing
body and the toner image is transferred onto a recording medium, the apparatus comprising:
an image forming section;
a toner image bearing body;
a reading section that reads the toner image formed on said toner image bearing body;
a covering section provided between said reading section and said toner image
bearing body and movable between a closing position where said covering section
covers said reading section and an opening position where said covering section
does not cover said reading section;
a drive mechanism that drives said covering section to move between the opening
position and the closing position; and
an adjustment section that adjusts said reading section when said covering section
is at the opening position, said reading section being adjusted with reference
to a surface of said toner image bearing body on which a toner image is not formed.
15. The image forming apparatus according to claim 14, further comprising a correction
section that corrects at least one of a position on said toner image bearing body
at which a toner image is formed and a density of the toner image formed on said
toner image bearing body, the position and the density being corrected in accordance
with the output of said reading section.
16. The image forming apparatus according to claim 14, wherein said adjusting
section adjusts said reading section in such a way that an output of said reading
section changes.
17. The image forming apparatus according to claim 14, wherein said adjustment
section adjusts said reading section so that an output of said reading section
is within a predetermined range.
18. An image forming apparatus in which a toner image is formed on an image bearing
body and the toner image is transferred onto a recording medium the apparatus comprising:
an image forming section;
a toner image bearing body;
a reading section that reads the toner image formed on said toner image bearing body;
a covering section provided between said reading section and said toner image
bearing body and movable between a closing position where said covering section
covers said reading section and an opening position where said covering section
does not cover said reading section;
a drive mechanism that drives said covering section to move between the opening
position and the closing position; and
an adjustment section that adjusts said reading section when said covering section
is at the opening position;
wherein said reading section includes a light emitting section that emits an
amount of light to a reflection member and a light receiving section that generates
an output in accordance with an amount of light received; and
wherein said adjustment section adjusts the amount of light emitted from the
light emitting section in accordance with the output of the light receiving section
that detects light reflected by said toner image bearing body.
19. An image forming apparatus in which a toner image is formed on an image bearing
body and the toner image is transferred onto a recording medium, the apparatus comprising:
an image forming section;
a toner image bearing body;
a reading section that reads the toner image formed on said toner image bearing body;
a covering section provided between said reading section and said toner image
bearing body and movable between a closing position where said covering section
covers said reading section and an opening position where said covering section
does not cover said reading section;
a drive mechanism that drives said covering section to move between the opening
position and the closing position;
an adjustment section that adjusts said reading section when said covering section
is at the opening position;
a fixing section in which the toner image transferred onto the recording medium
is fused into a permanent image; and
at least one of a first drive section that drives said image forming section,
a second drive section that drives said toner image bearing body, and a third drive
section that drives said fixing section;
wherein said drive mechanism is driven by one of the first drive section, second
drive section, and third drive section to open and close said covering section.
20. The image forming apparatus according to claim 19, wherein said drive mechanism
drives said covering section to move straight.
21. The image forming apparatus according to claim 19, wherein said drive mechanism
includes a gear train that transmits a drive force from any one of the first drive
section, second drive section, and third drive section to said covering section.
22. The image forming apparatus according to claim 19, wherein said covering
section moves in a first direction to the opening position and in a second direction
opposite to the first direction to the closing position;
wherein when a rotating member of one of the first drive section, the second
drive section, and the third drive section rotates in a third direction, said covering
section moves either in the first direction or in the second direction.
23. The image forming apparatus according to claim 19, wherein said fixing section
includes a heater;
said drive mechanism is powered by the third drive section to move said covering
section to the opening position before the heater reaches a predetermined temperature.
24. The image forming apparatus according to claim 19, wherein said fixing section
includes a motor;
wherein when the toner image is fused, the motor rotates in a forward direction; and
wherein when said covering section moves, the motor rotates in a reverse direction.
25. An image forming apparatus in which a toner image is formed on an image bearing
body and the toner image is transferred onto a recording medium, the apparatus comprising:
an image forming section;
a toner image bearing body;
a reading section that reads the toner image formed on said toner image bearing body;
a covering section provided between said reading section and said toner image
bearing body and movable between a closing position where said covering section
covers said reading section and an opening position where said covering section
does not cover said reading section;
a drive mechanism that drives said covering section to move between the opening
position and the closing position; and
an adjustment section that adjusts said reading section when said covering section
is at the opening position;
wherein a cleaning member is mounted to said covering section; and
wherein when said drive mechanism drives said covering section to move between
the opening position and the closing position, the cleaning member moves into contact
engagement with said reading section to remove foreign matter from said reading section.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the correction of an output of a density sensor
and a dust-proof mechanism for the density sensor and color shift sensors, which
density sensor and color shift sensors are used in a color electrophotographic
recording apparatus.
2. Description of the Related Art
A conventional color image forming apparatus incorporates image forming sections
for the respective colors and a supporting member provided below a transfer belt
that is in contact with these image forming sections. A left color shift sensor
and a right color shift sensor are disposed on the supporting member and aligned
in a direction transverse to the direction in which the transfer belt runs. The
left color shift sensor and right color shift sensor detect positional errors among
images of the respective colors at the left end and right end of a width of the
transfer belt. A density sensor is disposed midway between the left and right color
shift sensors. The sensors are located immediately below the transfer belt and
directly face the transfer belt with nothing existing between the transfer belt
and these sensors.
With such a conventional color electrophotographic recording apparatus, the
upper surfaces of the color shift sensors and the density sensor are exposed. The
upper surfaces attract dust, waste, and toner, so that toner adhering to the transfer
belt may drop from the transfer belt onto the light-receiving surfaces of the sensors
to prevent normal detection of light. Additionally, the output of the sensors varies
from sensor to sensor, so that there are variations in sensor output even when
the same object is measured.
SUMMARY OF THE INVENTION
An object of the invention is to solve the aforementioned drawbacks of the conventional apparatus.
An object of the invention is to provide an image-forming apparatus in which
for
example, reliable correction of color shift can be performed while also preventing
increases in overall size and manufacturing cost of the image-forming apparatus.
An image forming apparatus forms a toner image on an image bearing body and transfers
the toner image onto a recording medium.
The image forming apparatus includes an image forming section, a toner image
bearing body, a reading section that reads the toner image formed on the image
bearing body, a covering section, a drive mechanism, and an adjustment section.
The covering section is provided between the reading section and the toner image
bearing body and movable between a closing position where the covering section
covers the reading section and an opening position where the covering section does
not cover the reading section. The drive mechanism drives the covering section
to move between the opening position and the closing position. The adjustment section
adjusts the reading section when the covering section is at the closing position.
The covering section includes a reflection member attached thereto. The reading
section includes a light emitting section that emits an amount of light to the
reflection member and a light receiving section that receives light reflected from
the reflection member. The adjustment section adjusts the amount of light in accordance
with an output of the light receiving section that detects the reflection member.
The apparatus further includes a controller that controls the drive mechanism
to drive the covering section. The controller controls the drive mechanism according
to a detection output of the light receiving section that detects passage of an
edge of the covering section. The reflection member has a first reflection coefficient
and the image bearing body has a second reflection coefficient.
The apparatus further includes a fixing section and at least one of a first drive
section, a second drive section, and a third drive section. The fixing section
fuses the toner image transferred onto the recording medium into a permanent image.
The first drive section drives the image forming section. The second drive section
drives the toner image bearing body. The third drive section drives the fixing
section. The drive mechanism is powered by one of the first drive section, the
second drive section, and the third drive section to move the covering section
between the opening position and the closing position.
The drive mechanism drives the covering section to move straight.
The drive mechanism includes a gear train that transmits a drive force from any
one of the first drive section, the second drive section, and the third drive section
to the covering section.
The covering section moves in a first direction to the opening position and in
a second direction opposite to the first direction to the closing position. When
a rotating member of one of the first drive section, the second drive section,
and the third drive section rotates in a third direction, the covering section
moves either in the first direction or in the second direction.
The fixing section includes a heater, and the drive mechanism is powered by the
third drive section to move the covering section to the opening position before
the heater reaches a predetermined temperature.
The fixing section includes a motor. When the toner image is fused, the motor
rotates in a forward direction. When the covering section moves to the opening
position, the motor rotates in a reverse direction.
The image forming apparatus further includes a cleaning member mounted to the
covering section. When the drive mechanism drives the covering section to move
between the opening position and the closing position, the cleaning member moves
into contact engagement with the reading section to remove foreign matter from
the reading section.
The image forming apparatus further includes a correction section that corrects
at least one of a position on the image bearing body at which a toner image is
formed and a density of the toner image formed on the image bearing body, the position
and the density being corrected in accordance with an output of the reading section.
An image forming apparatus forms a toner image on an image bearing body and transfers
the toner image onto a recording medium. The apparatus includes an image forming
section, a toner image bearing body; a reading section, a covering section, a drive
mechanism, and an adjustment section. The reading section reads the toner image
formed on the toner image bearing body. The covering section is provided between
the reading section and the toner image bearing body and movable between a closing
position where the covering section covers the reading section and an opening position
where the covering section does not cover the reading section. The drive mechanism
drives the covering section to move between the opening position and the closing
position. The adjustment section adjusts the reading section when the covering
section is at the opening position.
The reading section includes a light emitting section that emits an amount of
light to the reflection member and a light receiving section that generates an
output in accordance with an amount of light received. The adjustment section adjusts
the amount of light emitted from the light emitting section in accordance with
the output of the light receiving section that detects light reflected by the toner
image bearing body.
An image forming apparatus forms a toner image on an image bearing body and transfers
the toner image onto a recording medium. The apparatus includes an image forming
section, a toner image bearing body, a reading section, a covering section, a drive
mechanism, and a cleaning member. The reading section reads the toner image formed
on the toner image bearing body. The covering section provided between the reading
section and the toner image bearing body and movable between a closing position
where the covering section covers the reading section and an opening position where
the covering section does not cover the reading section. The drive mechanism that
drives the covering section to move between the opening position and the closing
position. The cleaning member is mounted to the covering section. When the drive
mechanism drives the covering section to move between the opening position and
the closing position, the cleaning member moves into contact engagement with the
reading section to remove foreign matter from the reading section.
Further scope of applicability of the present invention will become apparent
from the detailed description given hereinafter. However, it should be understood
that the detailed description and specific examples, while indicating preferred
embodiments of the invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the invention will become
apparent to those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description
given hereinbelow and the accompanying drawings which are given by way of illustration
only, and thus are not limiting the present invention, and wherein:
FIG. 1 illustrates schematically an image-forming apparatus according to a first
embodiment of the invention;
FIG. 2 is a fragmentary perspective view as seen from a fixing unit, illustrating
a sensor unit and a belt unit;
FIG. 3 is a front view as seen from the fixing unit, illustrating a sensor unit
and a belt unit;
FIG. 4 is a top view of the sensor unit as seen from a transfer belt in a direction
shown by arrow E in FIG. 1;
FIG. 5 is a top view of the sensor unit as seen from the transfer belt in the
E direction (FIG. 1), illustrating a shutter when it is open;
FIG. 6A illustrates the direction of travel of light emitted from a density
sensor when the color calibration is performed;
FIG. 6B illustrates the direction of travel of light emitted from the density
sensor when black calibration is performed;
FIGS. 7A and 7B illustrate the relationship between the light input to the
density sensor and the output from the density sensor;
FIG. 8 illustrates a configuration of a density detecting circuit;
FIG. 9 illustrates a control block of the present invention;
FIG. 10 is a flowchart that illustrates the overall operation of the image-forming
apparatus according to the invention;
FIG. 11 is a flowchart that illustrates the procedure for calibrating the density
sensor when color toners are used;
FIG. 12 illustrates the relationship between the individual steps in the calibration
procedure and the settings of a digital-to-analog converter;
FIG. 13 is a flowchart, illustrating the procedure for calibrating the density
sensor when black toner is used;
FIG. 14 is a flowchart, illustrating the procedure for performing density correction;
FIGS. 15 and 16 are top views, illustrating a modification to the first embodiment;
FIG. 17 is a perspective view, illustrating a second embodiment;
FIG. 18 is a side view, illustrating the positional relationship between a blade
and sensor cover;
FIG. 19 is a perspective view of a pertinent portion of a third embodiment;
FIGS. 20 and 21 are a perspective view and an exploded view, respectively,
illustrating a mechanism in FIG. 1 for opening and closing a shutter according
to a fourth embodiment;
FIG. 22A is a perspective view, illustrating the mechanism for opening and closing
the shutter when the shutter is at a closing position;
FIG. 22B is a side view of FIG. 22A;
FIG. 22C illustrates the positional relationship between a first gear and a
second gear;
FIG. 23A is a perspective view, illustrating the mechanism for opening and closing
the shutter when the shutter is at an opening position;
FIG. 23B is a side view of FIG. 23A;
FIGS. 24A and 24B illustrate the operation of a gear train formed of gears;
FIG. 25 is a block diagram, illustrating a control system for the image-forming apparatus;
FIG. 26 illustrates a configuration of an image-forming apparatus according
to a fifth embodiment;
FIGS. 27-29 illustrate the mechanism (FIG. 26) for opening and closing the shutter;
FIGS. 30A and 30B illustrate a drive system for opening and closing the shutter; and
FIG. 31 illustrates the shutter and the configuration for opening and closing
the shutter according to a sixth embodiment.
DESCRIPTION OF THE INVENTION
FIRST EMBODIMENT
FIG. 1 illustrates schematically an image-forming apparatus according to a first
embodiment of the invention.
This image-forming apparatus forms color images by the use of electrophotography,
and takes the form of a tandem type image forming apparatus that includes image-forming
sections 2K, 2Y, 2M, and 2C for black, yellow, magenta,
and cyan images. The image-forming sections 2K, 2Y, 2M, and
2C are aligned in this order along the direction of travel of recording
paper P, as indicated by arrow A in FIG. 1.
The image-forming section 2K includes a photoconductive drum 20
driven in clockwise rotation by a drum motor 419K (FIG. 25). Disposed around
the photoconductive drum 20 are a charging roller 21, an LED head
22, and a developing unit 23. The developing unit 23 incorporates
a developing roller 23
a, a toner-supplying roller 23
b,
and a toner chamber 23
c therein. The toner chamber 23
c
holds black toner therein. There is provided a transfer roller 24, so
that the recording paper P is sandwiched between the photoconductive drum 20
and the transfer roller 24.
The charging roller 21 charges the surface of the photoconductive drum
20 uniformly. The LED head 22 illuminates the charged surface of
the photoconductive drum 20 selectively in accordance with image information.
The light emitted from the LED head 22 dissipates charges in areas on the
photoconductive layer of the photoconductive drum 20, leaving charges in
non-exposed areas so as to form an electrostatic latent image as a whole. The developing
unit 23 applies toner to the electrostatic latent image formed on the photoconductive
drum 20, thereby forming a toner image. The transfer roller 24 supplies
charges of an opposite polarity to the toner to the back surface of the recording
paper P, thereby transferring the toner image from the photoconductive drum 20
onto the recording paper P.
The image-forming sections 2Y, 2M, and 2C are all configured
in the same manner as the image-forming section 2K. The developing units
23 for the image-forming sections 2Y, 2M, and 2C hold
yellow, magenta, and cyan toners, respectively.
A transfer belt 116 that carries the recording paper P thereon is a so-called
endless belt entrained about rollers 25 and 26. The transfer rollers
24 for the image forming sections 2Y, 2M, and 2C are
aligned in a line between the rollers 25 and 26. The rollers 25
and 26 rotate about parallel axes that extend in a direction transverse
to the direction in which the transfer belt 116 runs. The roller 25
is a drive roller driven in rotation by a belt drive motor 417 (FIG. 25).
When the drive roller 25 rotates, the transfer belt 116 runs in a
direction shown by arrow A.
Disposed on the left of the drive roller 25 is a fixing unit 16
for pressurizing and heating the recording paper P to fuse the toner image transferred
onto the recording paper P. The fixing unit 16 includes a fixing roller
16
a that incorporates a fixing heater 415 (FIG. 25) therein,
a pressure roller 16
b, a fixing motor 416 (FIG. 25), and a
mechanism (e.g. gear train) via which the drive force of the fixing motor 416
is transmitted to the fixing roller 16
a. The fixing motor 416
generates a drive force for rotating the fixing roller 16
a. When
the fixing roller 16
a is rotated, the recording paper P is pulled
in between the fixing roller 16
a and the pressure roller 16
b.
Disposed to the left of the fixing unit 16 are discharge roller pairs 17
and 18 that advance the recording paper P to a stacker 19.
A paper cassette 10 that holds a stack of the recording paper P therein
is disposed at a lower portion of the image-forming apparatus.
Disposed to the right of the paper cassette 10 are a small-diameter
auxiliary roller 12 and a large-diameter feed roller 13 that advance
the recording paper P from the paper cassette 10. A feed motor 418
(FIG. 25) drives the auxiliary roller 12 and feed roller 13 in rotation.
There is provided an inclined plate 11 that presses the leading edge of
the top page of the stack of recording paper P against the auxiliary roller 12
and the feed roller 13. Transport roller pairs 14 and 15 are
provided along a transport path in which the recording paper P is transported from
the paper cassette 10 to the image forming section 2K.
The image-forming apparatus includes recording paper sensors 27
a-27
d
that detect the passage of the recording paper P. The recording paper sensor
27
a is disposed upstream of the transport roller pair 14 with
respect to the direction of travel of the recording paper P, and the recording
paper sensor 27
b is disposed upstream of the transport roller pair
15. The recording paper sensor 27
c is disposed upstream of
the roller 26 and the recording paper sensor 27
d is disposed
downstream of the fixing unit 16.
Color shift sensors 3
a and 3
b are provided near
the drive roller 25 and detect patterns (toner images) for optical color
shift detection, transferred onto the belt 116 by the image-forming sections
2K, 2M, 2Y, and 2C. The color shift sensors 3
a
and 3
b are disposed under the drive roller 25 and aligned
in a direction transverse to the direction in which the transfer belt 116
runs. The color shift sensors 3
a and 3
b each include
a light-emitting element and a light-receiving element. The light-emitting element
illuminates the pattern formed on the transfer belt 116. The light-receiving
element detects the light reflected from the pattern to output a voltage signal
in accordance with the intensity of the reflected light.
A density sensor 104 (FIG. 2) is provided near the drive roller 25
and optically detects patterns for density detection, the patterns being transferred
onto the transfer belt 116 by the image-forming sections 2K, 2Y,
2M, and 2C, respectively. The density sensor 104 is positioned
under the drive roller 25 to oppose the middle of the transfer belt 116
and detects the patterns for density detection on the transfer belt 116,
transferred by the image-forming sections 2K, 2Y, 2M, and
2C. The density sensor 104 includes a light-emitting element and
a light-receiving element. The light-emitting element illuminates the patterns
for density detection formed on the transfer belt 116. The light-receiving
element detects the light reflected from the patterns to output a voltage signal
in accordance with the intensity of the reflected light.
FIG. 2 is a fragmentary perspective view as seen from the fixing unit 16,
illustrating a sensor unit 114 and a belt unit 113.
FIG. 3 is a front view as seen from the fixing unit 16, illustrating
the sensor unit 114 and the belt unit 113.
The sensor unit 114 corresponds to a mechanism 30 in FIG. 1, and
is disposed immediately below the belt unit 113 to oppose the transfer belt
116. Left and right circuit boards 107 and 108 are mounted
symmetrically on the sensor unit 114, the left circuit board 107
being on the left end of the sensor unit 114 and the right circuit board
108 on the right end. The density sensor 104 is disposed in the middle
of the sensor unit 114 and detects the density of an image. Provided over
the density sensor 104 is a sheet 117 for use in the later described
calibration of a sensors.
FIG. 4 is a top view of the sensor unit 114 as seen from the transfer
belt 116 in a direction shown by arrow E in FIG. 1.
FIG. 4 illustrates a shutter 102 when it is closed. The left and right
circuit boards 107 and 108 are securely mounted on a support member
103. A color shift sensor 105 and color shift sensor 106 are
disposed on the left circuit board 107 and the right circuit board 108,
respectively, and the light-emitting and light-receiving surfaces of the color
shift sensors 105 and 106 are exposed upward. The density sensor
104 mounted on a board 110 is in the middle of the support member
103 and opposes the shutter 102. A solenoid 101 is fixed to
a permanent part, not shown, of the image-forming apparatus. One end 109
b
of a compression spring 109 is fixed to a permanent part of the image-forming
apparatus. Another end 109
a of the compression spring 109
engages a lever 101
a of the solenoid 101 to urge the shutter
102 in a direction shown by arrow F in FIG. 4. The shutter 102 is
provided between the density sensor 104 and the transfer belt 116
and engages the free end 101
b of the lever 101
a, so
that the shutter 102 is guided by a guide means, not shown, to slide in
directions shown by arrows F and G. When the solenoid 101 is energized,
the free end 101
b of the lever 101
a causes the shutter
102 to move in the G direction (FIG. 4) against the urging force of the
compression spring 109.
FIG. 5 is a top view of the sensor unit 114 as seen from the transfer
belt 116 in the E direction (FIG. 1), illustrating the shutter 102
when it is open.
When the image-forming apparatus is turned on, the belt unit 113 over
the shutter 102 is driven. A certain length of time after power-up of the
image-forming apparatus, the solenoid 101 is energized to attract the lever
101
a which in turn moves to a position shown in FIG. 5. The movement
of the lever 101
a causes the shutter 102 to move in the G
direction, so that the density sensor 104 is exposed.
The sheet 117 is attached to the surface of the shutter 102 that
opposes the density sensor 104, and used as a reference reflection member
for calibrating the density sensor 104. When the density sensor 104
detects the sheet 117, the density sensor 104 generates an output,
which in turn is used as a reference output.
FIG. 6A illustrates the direction of travel of light emitted from the density
sensor 104 when color calibration is performed.
For color calibration, the shutter 102 is closed so that the sheet 117
opposes the density sensor 104. In the embodiment, the density sensor 104
has an LED 4
d that functions as a light source. In color calibration,
the light (depicted in solid lines) emitted from the LED is reflected by the sheet
117. The density sensor 104 is mounted such that the surface 104
a
of the density sensor 104 makes an angle θ with the surface of
the sheet 117. The reflective material of the sheet 117 that operates
as a reference reflector for color calibration is Munsell color chip N6.
FIG. 6B illustrates the direction of travel of light emitted from the density
sensor 104 when black calibration is performed.
For black calibration, the shutter 102 is opened so that the density sensor
104 opposes the transfer belt 116. In this case, too, the surface
104
a of the density sensor 104 makes an angle θ with
the surface of the transfer belt 116. Thus, the light emitted from the light
source is reflected back by the surface of the transfer belt 116 into a
black sensor 104
b. The transfer belt 116 is a resin film of,
for example, polyimide and has a smooth, glossy surface.
The transfer belt 116 has a smooth, glossy surface that is difficult to
produce diffusion reflection and not suitable for color calibration. In contrast,
the sheet 117 is easy to produce diffusion reflection and therefore is employed
for color calibration.
FIGS. 7A and 7B illustrate the relationship between the light input to the
density sensor 104 and the output from the density sensor 104. When
the density sensor 104 detects the density of an image, the light emitted
from the LED is reflected back by the image formed on the transfer belt 116,
and then detected by a light-receiving element of the density sensor 104.
Thus, the output signal of the density sensor 104 is an analog signal substantially
proportional to the density of the image. The lower the density (i.e., close to
white), the larger the sensor output since the amount of reflected light is larger.
The higher the density (i.e., close to black), the smaller the sensor output. A
controller 118 (FIG. 9) receives an analog signal from the density sensor
104 and converts the received analog signal into a digital signal, thereby
acknowledging the density of the image. However, the temperature characteristic
of the output of the density sensor 104 varies from sensor to sensor. For
example, as shown in FIG. 7A, sensor A and sensor B of the same model may generate
outputs of different values even when they detect the same object image. The variations
in the output of the density sensor 104 can be attributed to, for example,
variations in the characteristics of sensor, differences in ambient temperature,
and mounting errors of the density sensor 104. In order to detect the density
of an image accurately, it is necessary to calibrate the output of the density
sensor 104.
FIG. 8 illustrates a configuration of a density detecting circuit. The LED in
the density sensor 104 radiates light and the light is reflected back by
an image formed on the transfer belt 116 into the light-receiving section
of the density sensor 104. The light-receiving section includes two systems,
one for color images and one for black images. An LSI provides a digital data DAO
to a digital-to-analog converter DAC upon clocks and loads the digital data DAO
into the DAC upon a loading signal DALD1. The current through the LED is
set in accordance with the digital data DAO. The digital-to-analog converter DAC
produces an analog signal from the input digital signal and outputs the analog
signal to the LED-driving circuit. The outputs of the density sensor 104
are read into a 10-bit ADC (channel 0) of a CPU through a low pass filter based
on an OPAMP. The digital-to-analog converter DAC produces an 8-bit digital data
DAO capable of setting the LED current in 256 different levels (0-4.5 volts). The
upper limit of the setting is 4.5 volts. The relationship between a setting and
a corresponding output voltage is such that Vout=(4.5×DAC)/256. When the output
is maximum, the setting of D/A is given by (4.5/5)×256≅230. In other
words, when the output is maximum, the setting of DAC is 230 in decimal, which
is equal to E6
H in hexadecimal.
The output of the density sensor 104 is calibrated as follows: The digital
signal output from the digital-to-analog converter DAC is changed to change the
amount of light emitted from the LED. The light emitted from the LED is reflected
back by the sheet 117 in color calibration and by the transfer belt 116
in black calibration, and then received by the density sensor 104. The density
sensor 104 in turn provides a detection signal in the form of an analog
signal to the controller 118. The output of the digital-to-analog converter
DAC is increased in increments of OA
H until the output of the density
sensor 104 increases from Vo to Vo+ΔVCAL±V
M, the Vo
being a sensor output beyond which the LED starts to light up. When the output
of the density sensor 104 reaches Vo+ΔVCAL±V
M, the
output of the digital-to-analog converter DAC is recorded. Referring to FIG. 7A,
the output Vo+Δv
cal is a substantially upper limit of the sensor
output that can change linearly, but the value of ΔV
cal may be
selected to be somewhat smaller. In this manner, the calibration operation determines
the current through the LED such that the output Vo+Δv
cal is obtained.
The controller 118 records the digital output of the digital-to-analog converter
DAC that corresponds to this LED current. When the apparatus is normally operated,
the digital output is used to energize the LED. In other words, the output of the
digital-to-analog converter DAC corresponding to Vo+ΔV
cal is used
as a reference to energize the LED so that the LED emits a reference amount of
light when the density of an image formed on the transfer belt 116 is detected.
As described above, the calibration operation determines a sensor output Vo for
a completely dark condition and a reference sensor output Vo+ΔV
cal for
the reference calibration sheet 117. Thus, when the density of an image
is detected, the density of the image can be determined as a relative value to
that of the reference calibration sheet 117. The density of the image can
be explained as follows:
Referring to FIG. 7B, we obtain Eq. (1).
ab/cb=ad/ed (1)
therefore, we obtain Eq. (2)
{(
Vo+ΔVcal)-
V1}/
Dref=(
Vi-V1)/
Di (2)
where D
ref is the density of the reference calibration sheet 117
and D
i is the density of an image. Therefore, the following relation
can be derived.
Di={(
Vi-V1)/
ΔVcal}Dref (3)
Therefore, irrespective of variations of the output characteristics such
as dark output and the slope of the graph of sensor output versus amount of light
of the density sensor 104, the linear portion of the sensor output characteristic
can be effectively used to accurately detect the density of an image.
FIG. 9 illustrates a control block of the present invention. The controller
118 in the form of, for example, a CPU, executes a program that controls
the overall operation of the image-forming apparatus. The controller 118
sends a control signal to a shutter driving section 119 so as to open and
close the shutter 102 by means of the solenoid 101 in FIGS. 4 and
5. The controller 118 receives the detection signal from the density sensor
104 in FIG. 5 and performs later described calibration and density correction.
Based on the detection signals outputted from the left and right color shift sensors
105 and 106, the controller 118 controls the driving section
120 of the image-forming section to correct left and right color shifts.
After calibration or density correction, a cleaning blade removes the toner from
the transfer belt 116 and the controller 118 sends control signals
to the image-forming sections K, Y, M, and C, respectively, to carry out a printing operation.
FIG. 10 is a flowchart that illustrates the overall operation of the image-forming
apparatus according to the invention. At step S1, the apparatus is turned
on. At step S2, the color calibration of the density sensor 104 is
performed with the shutter 102 closed, thereby eliminating the output errors
due to the variation in sensitivity among density sensors.
Then, the black calibration of the density sensor 104 is performed with
the shutter 102 open, thereby eliminating the output errors due to the variations
in sensitivity among density sensors. At step S3, the density correction
is performed with the shutter 102 open. In other words, a reference toner
image is formed on the transfer belt 116 and then the density sensor 104
detects the density of the reference toner image. With reference to the detection
output of the density sensor 104, the conditions for forming images are
changed to correct image density, thereby setting a desired image density. Likewise,
the left and right color shifts can also be corrected at step S4. In other
words, the toner images of the respective colors are formed in superposition on
the transfer belt 116 and detected by the color shift sensors 105
and 106 mounted on the opposed ends of the support member 103. The
positional errors between the respective toner images are determined by using the
detected amount of color shift. In accordance with the positional errors, the timings
at which images are formed by the image forming sections are adjusted. This completes
color shift correction. At step S5, the shutter 102 is closed and
then the program waits for a print command.
As described above, the shutter 102 on which the sheet 117 for color
calibration is attached is driven to slide above the density sensor 104
between the transfer belt 116 and the density sensor 104. Thus, when
the density correction of an image formed on the transfer belt 116 is performed,
the shutter 102 can be readily moved so that the density sensor 104
directly faces the transfer belt 116. This allows smooth and accurate density
correction of the image formed on the transfer belt 116.
FIG. 11 is a flowchart that illustrates the procedure for calibrating the density
sensor 104 when color toners are used.
FIG. 12 illustrates the relationship between the individual steps in the calibration
procedure and the settings of the digital-to-analog converter DAC.
In order to avoid adverse effects of noise, calibration is performed with the
motors stopped. The output of the density sensor 104 generates a sensor
output Vc for color toners and Vb for black toner. Color calibration is performed
using the sheet 117 in the form of Munsell color chip N6. Black calibration
is performed using the surface of the transfer belt 116 as a reference.
By way of example, color calibration will be described with reference to sensor
A in FIG. 7A. At step S1 in FIG. 11, the image-forming apparatus is tuned
on and the sheet 117 is moved to a position where the sheet 117 opposes
the density sensor 104. The sheet 117 is attached to the back surface
of the shutter 102 and therefore when the shutter 102 is closed,
the density sensor 104 can detect the density of the sheet 117. At
step S2, the controller 118 outputs a value of 00
H to
the digital-to-analog converter DAC, the value 00
H being a value at
which the LED of the density sensor 104 does not light up (dark output).
The output Vc of the density sensor 104 for the value 00
H is
recorded as V1. At steps S3 and S4, the setting of the digital-to-analog
converter DAC is increased in increments of OA
H until V
C>V
1+ΔV
CALC.
At steps S5 and S6, the setting of the digital-to-analog converter
DAC is decremented by 01
H until Vc=V
1+ΔV
CALB±V
M.
V
M is a later described calibration margin. At step S7, the setting
D
sc of the DAC when Vc becomes V1+ΔV
CALC±V
M
is stored in the EEPROM. When the density of a color image is to be measured,
the setting D
sc is output to energize the LED in the density sensor
104. Because the sheet 117 is used as a common sheet to the respective
colors, the sheet 117 should be a neutral color, e.g., gray.
By way of example, black calibration will now be described with reference to
sensor
A in FIG. 7A.
FIG. 13 is a flowchart, illustrating the procedure for calibrating the density
sensor 104 when black toner is used.
At step S1, a cleaning blade in FIG. 1 scrapes off the toner adhering to
the transfer belt 116. The shutter 102 is opened so that the density
sensor 104 opposes the surface of the transfer belt 116. The surface
of the transfer belt 116 is made of a highly reflective material to serve
as a reference for calibration. At step S2, when the value 00
H is
set to the DAC, the output Vb of the density sensor 104 is V1 and
is stored. At steps S3 and S4, the setting of the DAC is increased
in the increments of OA
H until V
b>V
1+ΔV
CALB.
ΔV
CALB is a range in which the output of the density sensor 104
changes linearly from a dark output V1 to an output just before the output
Vb is saturated. Steps S5 and S6, the setting of the digital-to-analog
converter DAC is decremented by 01
H until V
b>V
1+ΔV
CALB±V
M.
At step S7, the setting D
sb of the DAC when Vb becomes V1+ΔV
CALB±V
M
is stored in the EEPROM. When the density of a black toner is to be measured,
the setting D
sb is output to energize the LED in the density sensor 104.
The image density varies depending on the environmental conditions such as temperature
and humidity. Thus, the density correction needs to be carried out to adjust the
density of the image to a predetermined level irrespective of the environmental
conditions. For this purpose, a density-measuring pattern is printed on the transfer
belt 116 periodically and the density of this pattern is measured. If the
density of an image changes overtime or changes due to changes in environmental
operating conditions, the developing voltage and the amount of light emitted from
the LED head 22 are also changed to adjust the density of the image.
The density sensor 104 (e.g., GP2TC2, available from Sharp) used in the
embodiment incorporates an infrared LED and two photo diodes for receiving light.
As shown in FIGS. 6A and 6B, the two photo diodes are mounted at angles such that
the photo diodes can receive efficiently regular reflection (black toner) coming
from the transfer belt 116 and diffusion reflection (colored toners) coming
from the sheet 117.
FIG. 14 is a flowchart, illustrating the procedure for performing density correction.
At step S1, toner images of the respective colors are formed on the transfer
belt 116 in sequence. The black sensor 104
b detects the density
of a black toner image, and the color sensor 104
c detects the density
of a colored toner image. At step S2, based on the detected density, the
image forming conditions for the respective image-forming section is changed to
correct the density of a corresponding toner image, thereby obtaining a desired
density level. The image-forming conditions can be changed by, for example, adjusting
the developing bias and the amount of light that the LED head 22 radiates.
The amount of light can be adjusted most readily because adjustment of the amount
of light for exposure does not affect any other image-forming conditions.
FIGS. 15 and 16 are top views, illustrating a modification to the first embodiment.
The modification differs from the first embodiment in the shape of a shutter
112. The rest of the configuration of the modification is the same as the
first embodiment and thus the description thereof is omitted. In other words, when
the shutter 112 is closed, the opposed end portions 112
a and
112
b of the shutter 112 cover the left color shift sensor
105 and the right color shift sensor 106, respectively. When the
image forming apparatus is turned on, the solenoid 101 is energized to attract
the lever 101
a, thereby opening the shutter 112. Then, the
density correction and color shift correction are performed. After the density
correction and color shift correction, the solenoid 101 is de-energized
to close the shutter 112.
According to the aforementioned modification, when the shutter 112
is closed, the opposed end portions 112
a and 112
b cover
the left color shift sensor 105 and the right color shift sensor 106,
respectively, thereby preventing the toner particles adhering to the transfer belt
116 from falling onto the surfaces of the color shift sensors 105
and 106.
SECOND EMBODIMENT
FIG. 17 is a perspective view, illustrating a second embodiment.
FIG. 18 is a side view, illustrating the positional relationship between a blade
and sensor cover.
A left sensor cover 221 covers a left color shift sensor 225 and
a right sensor cover 222 covers a right color shift sensor 226. The
left sensor cover 221 and right sensor cover 222 are molded products
of transparent plastics and are fastened to a support member 227.
A shutter 228 has opposed end portions 228
a and 228
b
that face the sensor covers 221 and 222, respectively. A left
blade 223 is fixed to the end portion 228
a and extends toward
the sensor cover 221 at an angle with the end portion of the shutter 228.
The free end of the left blade 223 engages the sensor cover 221 at
an angle with the sensor cover 221 and presses the sensor cover 221
resiliently. A right blade 224 is fixed to the end portion 228
b
and extends toward the sensor cover 222 at an angle with the end portion
228
b. The end of the right blade 224 engages the sensor cover
222 at an angle with the sensor cover 222 and presses the sensor
cover 222 resiliently. When the image-forming apparatus is turned on, the
shutter 228 slides to perform color shift correction just as in the first
embodiment. Every time the shutter 228 is opened and then closed, the left
blade 223 and right blade 224 rub the surfaces of the left sensor
221 and right sensor 222, respectively. The sliding operation of
the left and right blades 223 and 224 removes toner particles deposited
on the surfaces of the color shift sensors 225 and 226.
THIRD EMBODIMENT
FIG. 19 is a perspective view of a pertinent portion of a third embodiment.
A shaft 332 is inserted rotatably into holes 331
a and 331
b
formed in a supporting member 331 and has a left gear 336 and
a right gear 337 attached to its opposed longitudinal end portions. An electromagnetic
clutch 335 is provided to one end portion of the shaft 332. The electromagnetic
clutch 335 has a gear 335
a in mesh with an idle gear 334
a,
which in turn is in mesh with gear 333
a of a motor 333.
The supporting member 331 has a left board 340 at one end portion
thereof, the left board 340 carrying a color shift sensor 342 and
a left sensor cover 344 thereon. The supporting member 331 has a
right board 341 at another end thereof, th
