JP2005202249A - Color image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming apparatus capable of reducing a positional shift gradually shifted.
A writing unit 5, developing devices 6a, 6b, 6c and 6d, a photoreceptor belt 1, an intermediate transfer belt 10, a transfer unit 14 for transferring a toner image on the intermediate transfer belt 10 onto a transfer sheet 17a, and the photoreceptor. In an image forming apparatus having a photosensitive belt drive unit 2 for driving the belt 1 and an intermediate transfer belt drive unit 11 for driving the intermediate transfer belt 10, a load fluctuation is applied to the intermediate transfer belt 10 during image formation of two or more colors. When the load is applied to the intermediate transfer belt 10, the linear speed of the intermediate transfer belt 10 is increased at the timing during which the toner image on the photosensitive belt 1 is primarily transferred to the intermediate transfer belt 10. .
[Selection] Figure 1

Description

  The present invention relates to a technique for preventing color misregistration of a color image forming apparatus that transfers images from a photosensitive member to an intermediate transfer belt by superimposing four colors.

In recent years, in the color image forming apparatus, with the increase in the number of images that can be output, the load fluctuations of the cleaning unit and the secondary transfer unit cannot be removed from the image forming timing.
FIG. 4 is a timing chart showing the color image formation timing of the four colors. A Bk latent image is written at a writing position A on the photosensitive member, a Bk toner image is formed on the photosensitive member by the Bk developing unit, and is primarily transferred to the intermediate transfer belt at the primary transfer position B.
This operation is repeated M, C, and Y, and the flow from the transfer of the fourth color Y to the transfer paper, the second transfer to the transfer paper, and the cleaning of the transfer residual toner by the belt cleaning device is shown. Referring to the first image formation in FIG. 4, the belt cleaning device is in contact with the intermediate transfer belt during the primary transfer of Bk, and the belt cleaning device is separated in M, C, and Y.
When the belt cleaning device is in contact with the intermediate transfer belt, the linear speed of the intermediate transfer belt is slower than when the belt cleaning device is separated. This is caused by the belt being stretched by the contact load of the belt cleaning device or the elastic layer of the intermediate transfer driving roller that drives the intermediate transfer belt being crushed.
Further, the diameter of the intermediate transfer driving roller is reduced, and a slight slip occurs between the intermediate transfer driving roller and the intermediate transfer belt, and the torque of the drive system for driving the intermediate transfer belt is insufficient.
Bk intermediate transfer belt with belt cleaning device contact load during primary transfer compared to M, C, Y intermediate transfer belt linear speed without belt cleaning device contact load during primary transfer Due to the slow linear velocity, Bk causes a positional shift with respect to M, C, and Y on the intermediate transfer belt.
For ease of explanation, assuming that the linear velocity of the intermediate transfer belt 10 of Bk during the primary transfer is V1, and the linear velocity of the intermediate transfer belt 10 of M, C, Y during the primary transfer is V2, V1 <V2.
FIG. 5 is a schematic diagram showing a toner image (tentatively a caterpillar image) on the intermediate transfer belt that is primarily transferred from the photosensitive belt when the speeds of V1 and V2 are constant. If the length interval is L and a toner image written with M, C, and Y at 4L intervals, and Bk is written at 3L intervals, the positional deviation on the Bk basis is the trailing edge of the image. As the distance increases, the amount of deviation gradually increases.
In FIG. 5, since the four colors match at the tip, the amount of misalignment increases toward the rear end, but conversely, if the rear end matches, the amount of misalignment at the tip increases. .
As described above, it is difficult to adjust the positional shift for a phenomenon in which the amount of positional shift is not constant and gradually shifts, and it is impossible to match each color exactly.

For example, if the cleaning unit is in contact with the intermediate transfer belt while the first color is transferred from the photosensitive member to the intermediate transfer belt and the cleaning unit is separated from the second color and thereafter in the four color overlap, the contact load of the cleaning unit As a result, the linear velocity of the intermediate transfer belt for the first color is slower than the linear velocity for the second and subsequent colors.
As a result, if the linear velocity after the second color is considered to be constant, the first color appears as a phenomenon that gradually shifts from the front end to the rear end with respect to the image after the second color. It becomes an unpreferable state.
In other words, if the load fluctuation is performed at the timing between non-image formation, it is only shifted in parallel with the other colors. Therefore, the color overlap can be performed only by shifting the writing timing so that the shifted color matches the other color. Accuracy can be improved relatively easily.
However, if the color is gradually shifted by one color, the trailing edge is shifted even if the leading edge of the paper is aligned, and the leading edge is shifted even if the trailing edge is aligned. Further, particularly in the case of an image such as a halftone image, there is a drawback in that the amount of color misregistration is different even in one image, so that the positional misalignment is noticeable and the color changes.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a color image forming apparatus that makes it possible to reduce such a position shift that gradually shifts in consideration of the above-described actual situation.

In order to solve the above problems, the invention described in claim 1 includes a writing unit, a developing device, a photoreceptor belt, an intermediate transfer belt, a transfer unit for transferring a toner image on the intermediate transfer belt to a transfer paper, and the photoreceptor. In a color image forming apparatus having a photosensitive belt driving unit for driving a belt and an intermediate transfer belt driving unit for driving the intermediate transfer belt, when load fluctuation occurs in the intermediate transfer belt during image formation of two or more colors, A color image forming apparatus that increases a linear speed of the intermediate transfer belt at a timing during which a toner image on the photosensitive belt is primarily transferred to the intermediate transfer belt when a load is input to the intermediate transfer belt. .
According to a second aspect of the present invention, there is provided the color image forming apparatus according to the first aspect, wherein a linear velocity of the intermediate transfer belt is changed in accordance with a load applied to the intermediate transfer belt.
According to a third aspect of the present invention, there is provided measuring means for measuring the linear velocity of the intermediate transfer belt that changes according to a load, and the measurement result is fed back to optimally adjust the linear velocity of the intermediate transfer belt. The color image forming apparatus according to claim 1 or 2, further comprising an adjusting unit.

  According to the present invention, since the linear speed of the intermediate transfer belt is the same when the intermediate transfer belt is loaded and when there is no load, it is possible to reduce misalignment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of an embodiment of a color image forming apparatus according to the present invention. In FIG. 1, a photosensitive member that carries an electrostatic latent image formed by laser writing and a developed toner image is a photosensitive belt 1 as a flexible belt-like image carrier in this apparatus.
The photosensitive belt 1 is installed between rotating rollers 2, 3 a, 3 b and is rotated (sub-scanned) in the direction of arrow A (clockwise) in the figure by the rotational driving of the rotating roller 2, and the belt surface is The image forming surface is configured.
As means for forming an electrostatic latent image and a toner image on the photoreceptor belt 1, a charging charger 4 for uniformly charging the surface of the photoreceptor belt 1, a laser writing unit 5, color developing devices 6a and 6b, 6c, 6d.
The color developing devices 6a, 6b, 6c, and 6d include developing units for magenta (M), cyan (C), yellow (Y), and black (Bk), which are color constituent colors. The developing unit used here includes means for developing with a one-component developer (toner).
In this embodiment, since the image on the photosensitive belt 1 is formed on the transfer paper via the intermediate transfer member, the intermediate transfer belt 10 is provided. The intermediate transfer belt 10 is installed between the rotation rollers 11 and 12, and is rotated in the direction of arrow B (counterclockwise) in the drawing by the rotation driving of the rotation roller 11.
The photosensitive belt 1 and the intermediate transfer belt 10 are in contact with each other at a portion where the rotating roller 3b of the photosensitive belt 1 is provided. On the intermediate transfer belt 10 side of the contact portion, a conductive bias roller 13 is in contact with the back surface of the intermediate transfer belt 10 under predetermined conditions.
A mark 22 for alignment with the intermediate transfer belt 10 is provided on the back surface of the intermediate transfer belt 10, and a detection unit 21 that detects the mark 22 is provided. The write signal is controlled by this mark detection.
Constituent elements related to transfer paper processing include a paper feed table (paper feed cassette) 17, paper feed roller 18, transport roller pair 19 a and 19 b, registration roller pair 20 a and 20 b, and intermediate transfer belt 10. An intermediate transfer roller 14 for transferring the image, a fixing device 23, a pair of paper discharge rollers 24 a and 24 b, and a paper discharge stack unit 25.

Here, an image forming operation of the color image forming apparatus of the embodiment shown in FIG. 1 will be described. In FIG. 1, a photosensitive belt 1 as a flexible belt-like image carrier is uniformly charged by a charger 4 and then laser light is controlled by a laser writing unit 5 based on image information. As a result of the scanning exposure, an electrostatic latent image is formed on the surface.
Image information used in one step of scanning exposure while rotating the photosensitive belt 1 to form an electrostatic latent image is monochromatic image information obtained by separating a desired full-color image into magenta, cyan, yellow, and black color information. It is.
Based on this information, the light emission of the semiconductor laser is controlled. The generated laser beam is scanned and optical path adjusted by an optical device and output as writing beam light L.
The writing timing of each color is controlled by a signal obtained by detecting the mark 22 provided on the intermediate transfer belt 10, and the electrostatic latent images formed based on single-color image information are handled by the color developing devices 6a, 6b, 6c, and 6d. The magenta (M), cyan (C), yellow (Y), and black (Bk) toners are each developed in a single color, and the respective color images are sequentially formed on the photosensitive belt 1.
Each monochrome image of M, C, Y, Bk formed on the photosensitive belt 1 rotating in the direction of arrow A in FIG. 1 is biased on the intermediate transfer belt 10 rotating in the direction of arrow B in FIG. The images are sequentially superimposed and transferred by the action of a predetermined transfer bias applied to the roller 13.
The images of M, C, Y, and Bk superimposed on the intermediate transfer belt 10 pass from the paper feed table (paper feed cassette) 17 through the paper feed roller 18, transport roller pairs 19a and 19b, and resist roller pairs 20a and 20b. The intermediate transfer roller 14 collectively transfers the transfer paper 17a conveyed to the transfer unit.
After the transfer is completed, the transfer paper 17a is fixed by the fixing device 23 to complete a full-color image, and the print image is discharged to the paper discharge stack unit 25 through the paper discharge roller pair 24a and 24b.
Note that the toner on the photosensitive belt 1 is cleaned as the final step of image formation on the photosensitive belt 1 in FIG. For this purpose, a cleaning blade 15 that is always in contact with the photosensitive belt 1 is provided. Similarly, the intermediate transfer belt 10 is also provided with a cleaning unit 16.
The cleaning brush 16a of the cleaning unit 16 is held at a position separated from the surface of the intermediate transfer belt 10 during the image forming operation, and after the formed image is transferred onto the transfer paper 17a, it is brought into contact with the surface of the intermediate transfer belt 10. . Further, the photosensitive belt 1, the charging charger 4, the intermediate transfer belt 10, the cleaning blade 15, and the cleaning unit 16 can be integrated, and can be configured to be detachable from the main body as a process cartridge.

FIG. 2 is a block diagram showing an example of a control system of the color image forming apparatus shown in FIG. Next, the control system of the color image forming apparatus shown in FIG. 1 will be described. As shown in FIG. 2, the control system includes a main control unit 27 and a plurality of peripheral control units.
The main control unit 27 supervises the entire operation related to the image formation outlined above, a CPU 28 as a constituent element, a ROM 29 storing a control program and various data, and a RAM 30 temporarily storing various data as a work area. And NVRAM 35 which is a nonvolatile memory for storing parameters for determining the operating conditions of the apparatus and information necessary for managing the apparatus.
The main control unit 27 connects the laser optical system control unit 32, the developing bias control unit 33, the toner adhesion amount sensor 26, the photoconductor / transfer belt drive control unit 34, and the like via the I / O interface 31.
The laser optical system control unit 32 controls the laser writing unit 5, and the development bias control unit 33 controls the development bias applied to each of the color developing devices 6 a, 6 b, 6 c, 6 d, and the photoreceptor / transfer belt drive control unit 34. Controls the rotation of the photosensitive belt 1 and the intermediate transfer belt 10.
All of these control operations are performed according to commands from the CPU 28. The toner adhesion amount sensor 26 detects the adhesion amount of the toner formed on the photosensitive belt 1 under predetermined conditions, and the CPU 28 that receives the detection data obtains an adjustment value of a developing bias described later from the toner adhesion amount, It is set in the developing bias controller 33 to control the toner density.
As described in relation to the prior art, the belt cleaning device does not have a contact load during the primary transfer, and the belt cleaning during the primary transfer is faster than the M, C, Y intermediate transfer belt linear speed. As the linear transfer belt linear speed of Bk having the apparatus contact load is slowed, Bk is misaligned with respect to M, C, and Y on the intermediate transfer belt.

The photoreceptor belt 1 is driven by a photoreceptor drive roller 2, and the intermediate transfer belt 10 is driven by an intermediate transfer belt drive roller 12. The rotation roller (photosensitive belt driving roller) 2 and the intermediate transfer belt driving roller 12 are provided with independent driving systems arranged on the main body side.
The drive system, the photosensitive belt drive roller 2 and the intermediate transfer belt drive roller 12 are coupled by a joint to transmit power (not shown). Here, the timing of image formation will be described with reference to the timing chart of the first image formation of FIG. 4 described in relation to the prior art. During the primary transfer of Bk to the intermediate transfer belt 10, the belt cleaning device contact load There is.
The linear velocity of the intermediate transfer belt 10 during the primary transfer of Bk to the intermediate transfer belt 10 is VBk. Further, there is no belt cleaning device contact load while M, C, and Y are primarily transferred to the intermediate transfer belt 10. The linear velocities of the intermediate transfer belt 10 during the primary transfer of M, C, and Y to the intermediate transfer belt are VM, VC, and VY, respectively.
The drive system for driving the intermediate transfer belt 10 is controlled so as to satisfy the following conditional expression.
(VM-VBk) / VM <0.02%
(VC-VBk) / VC <0.02%
(VY-VBk) / VY <0.02%
In the above description, the belt cleaning device contact load is Bk. However, the belt cleaning device contact load is the same even when the order of image formation is different or in the two-color mode in which only two colors are developed. It is necessary to reduce the change in the linear velocity of the intermediate transfer belt 10 due to the presence or absence of.
Therefore, when the intermediate transfer belt 10 has a belt cleaning device load, the linear speed of the intermediate transfer belt 10 of the image forming color to be primarily transferred is Vα, and when the intermediate transfer belt has no belt cleaning device load, the primary transfer is performed. Let VΒ be the linear velocity of the intermediate transfer belt of the image forming color.
According to this assumption, the control of the drive system that drives the intermediate transfer belt 10 satisfies the following conditional expression.
(VΒ−Vα) / VΒ <0.02%

Looking at the second image forming timing in FIG. 4, in addition to the belt cleaning device contact load, the load of the secondary transfer roller 14 is applied to the intermediate transfer belt 10 during the secondary transfer. As described above, when the contact load on the intermediate transfer belt 10 is different between the first image formation and the second image formation (second and subsequent images), the linear velocity of the intermediate transfer belt 10 with respect to each load condition. Need to control.
In the image forming color (Bk in FIG. 5) that is primarily transferred when the belt cleaning device is in contact, the intermediate transfer belt linear velocity is expressed as Vγ while the secondary transfer contact load is applied between the primary transfers. The intermediate transfer belt linear velocity when only the belt cleaning device is loaded between the transfers is Vδ, and the intermediate transfer belt linear velocity when there is no load is VΒ.
According to this assumption, the drive system for driving the intermediate transfer belt 10 is controlled so as to satisfy the following conditional expression.
(VΒ−Vα) / VΒ <0.02%
(VΒ−Vδ) / VΒ <0.02%
The mark detection unit 21 detects the mark 22 of the intermediate transfer belt 10 and performs writing timing control. Depending on the mark counted by the mark detection unit 21, the linear speed of the intermediate transfer belt 10 or the intermediate transfer belt is controlled. The time for one round is calculated.

FIG. 3 is a flowchart for explaining the intermediate transfer belt linear velocity correction. When each conditional expression shown above is not satisfied, the drive system control for driving the intermediate transfer belt 10 is corrected so as to satisfy the conditional expression.
That is, first, the intermediate transfer belt mark 22 is detected (S1). Next, the linear velocity of the intermediate transfer belt 10 is calculated (S2). Here, the conditional expression is satisfied (S3). If not satisfied, the intermediate transfer belt drive system is controlled (S4). The conditional expression is satisfied by the control result (S3), and the intermediate transfer belt drive system control correction is not performed (S5).
The load on the intermediate transfer belt 10 is independent even if the load conditions are different, such as the load on the first sheet is only the load on the cleaning unit and the second and subsequent sheets are on both the cleaning unit and the secondary transfer unit. In addition, since the linear velocity of the intermediate transfer belt 10 is controlled, it is possible to reduce the positional deviation that gradually shifts similarly in the first and second sheets.
The load on the intermediate transfer belt 10 changes due to various effects. For example, when the brush of the cleaning unit 16 is tilted, worn, or has a blade, the load decreases due to wear of the tip, the elongation rate of the intermediate transfer belt 10 changes with time, lubricant such as Mars is used as an intermediate transfer belt. Is applied to the intermediate transfer belt 10 due to various factors such as a change in μ on the intermediate transfer belt 10 due to the degree of application of the lubricant.
For this reason, when a load is applied to the intermediate transfer belt 10 at a certain timing (process control mode), the linear speed when the intermediate transfer belt 10 is not present is measured, and the linear speed of the intermediate transfer belt 10 is adjusted so that both are the same linear speed. Have means.
As a result, it is possible to reduce a positional shift that gradually shifts with respect to a change with time. Furthermore, if this correction is performed for each image formation, an accurate adjustment can be performed.

1 is a schematic diagram showing an overall configuration of an embodiment of a color image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating an example of a control system of the color image forming apparatus illustrated in FIG. 1. 6 is a flowchart for explaining intermediate transfer belt linear velocity correction. It is a timing chart which shows the color image formation timing of 4 colors. FIG. 5 is a schematic diagram showing a toner image (tentatively a caterpillar image) on an intermediate transfer belt that is primarily transferred from a photosensitive belt when the speeds of V1 and V2 are constant.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Photoconductor belt, 2 Rotating roller (Photoconductor belt drive roller, photoconductor belt drive unit), 5 Laser writing unit, 6a Color developing device, 6b Color developing device, 6c Color developing device, 6d Color developing device, 10 Intermediate Transfer belt, 11 rotation roller (intermediate transfer belt drive unit), 14 intermediate transfer roller (transfer unit), 17a transfer paper, 23 fixing device, 21 mark detection means (intermediate transfer belt mark sensor, measurement means), 22 intermediate transfer Belt mark, 27 main control unit, 28 CPU (adjustment means)

Claims (3)

  Writing unit, developing device, photosensitive belt, intermediate transfer belt, transfer unit for transferring the toner image on the intermediate transfer belt to transfer paper, photosensitive belt driving unit for driving the photosensitive belt, and driving the intermediate transfer belt In the color image forming apparatus having the intermediate transfer belt driving unit, when load fluctuation occurs in the intermediate transfer belt during image formation of two or more colors, the toner on the photosensitive belt is applied when the load is input to the intermediate transfer belt. A color image forming apparatus, wherein a linear speed of the intermediate transfer belt is increased at a timing during which an image is primarily transferred to the intermediate transfer belt.   2. The color image forming apparatus according to claim 1, wherein a linear velocity of the intermediate transfer belt is changed in accordance with a load applied to the intermediate transfer belt.   The apparatus includes a measuring unit that measures a linear speed of the intermediate transfer belt that changes depending on a load, and an adjusting unit that optimally adjusts the linear speed of the intermediate transfer belt by feeding back the measurement result. 3. A color image forming apparatus according to 1 or 2.

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