JP2001215770A - Image forming device and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact image forming device and an image forming method by which a high-quality image is formed in high throughput. SOLUTION: An intermediate transfer belt 41 is basically driven to be rotated at the same reference driving speed V0 in synchronization with a photoreceptor 21. Therefore, registration deviation is zero until timing t1 when a cleaner blade 491 abuts on the belt 41. In such timing t1, the belt 41 is temporarily driven to be rotated at 1st driving speed V1 higher than the driving speed V0 of the photoreceptor 21, so that the belt 41 is fed to a positive side in a subscanning direction too much, and the registration deviation to a negative side caused by the abutting of the blade 491 on the belt 41 is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for transferring a toner image formed on a photoreceptor to a transfer medium rotated in a sub-scanning direction for a plurality of different toner colors. The present invention relates to an image forming apparatus and an image forming method for forming a color image by superimposing toner images.

[0002]

2. Description of the Related Art An example of this type of image forming apparatus is shown in FIG. This image forming apparatus forms a full-color image by superimposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K). When an image signal is given to a control unit (not shown), each part of the engine unit E is controlled in accordance with a command from the control unit to correspond to an image signal on a sheet member S such as a transfer sheet, a copy sheet or an OHP sheet. To form an image.

In the engine section E, a toner image can be formed on the photosensitive member 21 of the image carrier unit 2. That is, the image carrier unit 2 includes a photoreceptor 21 rotatable in the direction of the arrow in FIG. 16, and further includes a charging roller 22 as a charging unit, a developing unit around the photoreceptor 21 along the rotation direction. Developing units 23Y, 23C, 2
3M, 23K, and a photoreceptor cleaner blade 24 are disposed, respectively.

In this apparatus, the charging roller 22 is connected to the photosensitive member 2
After the outer peripheral surface of the photoreceptor 21 is uniformly charged by contacting the outer peripheral surface of the photoconductor 1, the laser light L is emitted from the exposure unit 3 toward the outer peripheral surface of the photoconductor 21. As shown in FIG. 1, the exposure unit 3 includes a light emitting element 31 such as a semiconductor laser that is modulated and driven in accordance with an image signal, and a laser beam L from the light emitting element 31 is rotated by a high-speed motor 32. Incident on a polygon mirror 33 to be formed. The laser light L reflected by the polygon mirror 33 is transmitted to the lens 34 and the mirror 3
5, the photosensitive drum 21 is scanned in the main scanning direction (a direction perpendicular to the plane of the drawing) to form an electrostatic latent image corresponding to an image signal. Reference numeral 36 denotes a horizontal synchronization reading sensor for obtaining a synchronization signal in the main scanning direction, that is, a horizontal synchronization signal HSYNC.

The electrostatic latent image formed in this way is
Is developed with toner. That is, in this embodiment, as the developing unit 23, a developing unit 23Y for yellow, a developing unit 23C for cyan, a developing unit 23M for magenta, and a developing unit 23K for black are arranged along the photoconductor 21 in this order. Have been. These developing units 23Y and 23
Each of C, 23M, and 23K is configured to be able to freely contact and separate from the photoconductor 21, and the four developing units 23Y, 23M, 23C, and 23 according to instructions from the control unit.
B selectively contacts the photoconductor 21 and applies a high voltage to apply a toner of a selected color to the surface of the photoconductor 21 to apply electrostatic latent on the photoconductor 21. Reveals an image.

[0006] The toner image developed by the developing unit 23 is transferred onto the intermediate transfer belt 41 of the transfer unit 4 in a primary transfer region R1 located between the black developing device 23K and the photosensitive member cleaner blade 24. Transcribed. A cleaner blade 24 for the photoconductor is disposed at a position in the circumferential direction (the direction indicated by the arrow in FIG. 16) from the primary transfer region R1, and remains on the outer peripheral surface of the photoconductor 21 after the primary transfer. Scrape off the toner.

Next, the configuration of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 includes a roller 4
2 to 47; an intermediate transfer belt 41 stretched over the rollers 42 to 47; a secondary transfer roller 48 for secondary transferring the intermediate toner image transferred to the intermediate transfer belt 41 to the sheet member S; A belt driving unit (not shown) for rotating and driving the intermediate transfer belt 41 in synchronization with the photoconductor 21 is provided. When the color image is to be transferred to the sheet member S, the color images are formed by superimposing the toner images of the respective colors formed on the photoreceptor 21 on the intermediate transfer belt 41. The sheet member S is taken out from the cassette 61, the manual feed tray 62 or an additional cassette (not shown) by the sheet feeding unit 63, and is conveyed to the secondary transfer area R2. Further, a full-color image is obtained by secondarily transferring the color image to the sheet member S.

After the secondary transfer, toner remaining on the outer peripheral surface of the intermediate transfer belt 41 is removed by a cleaner blade 491 provided on a belt cleaner 49. That is, the belt cleaner 49
Is disposed opposite to the roller 46 with the intermediate transfer belt 41 interposed therebetween. At an appropriate timing, the cleaner blade 491 comes into contact with the intermediate transfer belt 41 to scrape toner remaining on the outer peripheral surface thereof. Drop.

A sensor 40 for detecting a reference position of the intermediate transfer belt 41 is disposed near the roller 43, and a synchronization signal in a sub-scanning direction substantially orthogonal to the main scanning direction, that is, a vertical synchronization signal. It functions as a vertical synchronization reading sensor for obtaining VSYNC.

The sheet member S on which the toner image has been transferred by the transfer unit 4 as described above is secondarily transferred along a predetermined feeding path (two-dot chain line) by the feeding section 63 of the feeding / discharging unit 6. The toner image is conveyed to the fixing unit 5 disposed downstream of the region R2, and the conveyed toner image on the sheet member S is fixed on the sheet member S. Then, the sheet member S is further conveyed to the paper discharge section 64 along the paper supply path, and then discharged to the standard paper discharge tray.

[0011]

In the image forming apparatus constructed as described above, in order to superimpose a plurality of color toner images while registering each other, the vertical synchronizing reading sensor 40 outputs a vertical synchronizing read sensor 40. The synchronization signal VSYNC is used. That is, each time the vertical synchronization signal VSYNC is output, a toner image is formed on the photoconductor 21 at a predetermined timing, and then the toner image is formed on the intermediate transfer belt 41 that rotates at a constant transport speed in synchronization with the photoconductor 21. Is primarily transferred, and by controlling the registration in this way, toner images of a plurality of colors are accurately superimposed. Therefore, the intermediate transfer belt 41 needs to be rotated and conveyed at a constant speed in synchronization with the photosensitive member 21 during the period from the output of the vertical synchronization signal VSYNC to the completion of the primary transfer.

However, as described above, the secondary transfer roller 48 is attached to the intermediate transfer belt 41 at an appropriate timing.
And the cleaner blade 491 temporarily abuts. Therefore, the rotation of the intermediate transfer belt 41 is hindered by the contact, the intermediate transfer belt 41 is elastically extended, and a load is applied to a belt driving unit (not shown) that rotationally drives the intermediate transfer belt 41. As a result, the intermediate transfer belt 41 cannot be rotated and conveyed at a constant speed. If the secondary transfer roller 48 or the cleaner blade 491 comes into contact with the intermediate transfer belt 41 during the period from the output of the vertical synchronization signal VSYNC to the completion of the primary transfer, the toner image is Deviate from each other, that is, a registration shift occurs, which causes a deterioration in image quality.

Here, for example, from the output of the vertical synchronization signal VSYNC to the completion of the primary transfer, the secondary transfer roller 4
8 and the cleaner blade 491
The above-mentioned problem can be solved by setting an operation sequence so as not to come in contact with or to perform the secondary transfer process and the cleaning process after the primary transfer is completed. When the image forming process is performed in the above, the total processing time becomes longer, and the number of processed sheets per unit time, that is, the throughput is greatly reduced. In particular, in order to efficiently carry the toner image on the intermediate transfer belt 41, for example, when the maximum size toner image is set to be carried on almost the entirety of the intermediate transfer belt 41, the primary transfer is completed. In order to perform the secondary transfer process and the cleaning process later, the intermediate transfer belt 41 is idled at least once more than the four primary transfer processes, and the secondary transfer process and the belt cleaning are performed during the idle rotation process. It is necessary to perform processing and the like, and as a result, the throughput is greatly reduced.

If the entire circumference of the intermediate transfer belt 41 is set to be sufficiently longer than the maximum image size, idling of the intermediate transfer belt 41 can be avoided. In this case, the utilization efficiency of the intermediate transfer belt 41 is reduced. And the throughput decreases accordingly. Moreover, the intermediate transfer belt 4
The size of the device is increased by an amount corresponding to the length of 1.

The present invention has been made in view of the above problems, and has as its object to provide a compact image forming apparatus and an image forming method capable of forming a high-quality image with high throughput.

[0016]

According to the present invention, a transfer process for transferring a toner image formed on a photoreceptor to a transfer medium which is driven to rotate in the sub-scanning direction is repeated for a plurality of different toner colors. The present invention relates to an image forming apparatus and an image forming method for forming a color image by superimposing toner images of toner colors, and in order to achieve the above object,
It is configured as follows.

In the present invention, the separation and contact of the contacting means with the transfer medium is performed during the repetition of the transfer process. Therefore, after the primary transfer is completed, the secondary transfer process and the cleaning process are performed. It has excellent processing efficiency and high throughput as compared with the prior art. Further, the transfer medium does not need to be set longer than necessary as in the related art, and the size of the apparatus can be reduced.

In this case, as described above, registration deviation occurs when the contact means comes into contact with the transfer medium. In the present invention, the registration deviation is corrected as follows.

In one embodiment of the present invention, while the transfer medium is basically controlled in synchronization with the photosensitive member, the contact means temporarily comes into contact with the transfer medium when the transfer processing is repeated. In response to the above, the transfer medium is driven to rotate at a higher driving speed than the photoconductor, so that the contact means corrects the registration deviation of the toner image on the transfer medium due to the contact with the transfer medium. Make up.

In the invention having such a configuration, when the abutting means abuts on the transfer medium, a transfer load acts on the transfer medium due to the abutting operation, and a registration shift occurs on the minus side in the sub-scanning direction. However, the transfer medium is rotated at a drive speed higher than that of the photoconductor in response to the contact of the transfer unit with the transfer medium as described above, and the registration deviation is suppressed. Therefore, a high quality color image can be obtained by suppressing the registration deviation.

In another aspect of the present invention, while the transfer medium is basically driven and controlled in synchronization with the photosensitive member, the transfer medium is temporarily brought into contact with the transfer medium when the transfer processing is repeated. The transfer medium is rotated at a drive speed lower than that of the photoconductor in accordance with the separation of the transfer medium from the transfer medium, and the transfer is performed when the contact means that has been in contact with the transfer medium separates from the transfer medium. The configuration is such that registration deviation of the toner image on the medium is corrected.

According to the invention having such a configuration, when the contacting means which has been in contact with the transfer medium is separated from the transfer medium, the load applied to the transfer medium is released, contrary to the contact. A registration shift occurs on the plus side in the sub-scanning direction. However, as described above, the transfer medium is rotated at a drive speed lower than that of the photoconductor corresponding to the separation of the contact means from the transfer medium. Is suppressed. Therefore, a high quality color image can be obtained by suppressing the registration deviation.

Further, in another aspect of the present invention, the transfer medium is caused to be brought into temporary contact with the transfer medium while the transfer processing is repeated while the transfer medium is constantly rotated and driven in synchronization with the photosensitive member. A temporal change in the relative amount of registration deviation of the toner image on the transfer medium is obtained, and a drive control pattern of the transfer medium is set based on the temporal change in the amount of registration deviation. By controlling the drive of the transfer medium in accordance with the drive control pattern, the drive of the transfer medium is basically controlled in synchronization with the photoconductor, but the transfer medium is executed when the transfer process is repeated. The transfer medium is accelerated / decelerated with respect to the photoconductor in accordance with the separation / contact of the contact means, thereby correcting the registration deviation accompanying the separation / contact of the contact means.

In the present invention, the drive control pattern of the transfer medium is determined in advance based on the temporal change of the amount of registration error, and the drive of the transfer medium is controlled by the drive control pattern. When the contact means comes into contact with the transfer medium, a transfer load acts on the transfer medium due to the contact operation, and a registration shift occurs on the minus side in the sub-scanning direction. Then, the transfer medium is rotated at a drive speed higher than that of the photoconductor in accordance with the contact of the transfer medium with the transfer medium, and the registration deviation is suppressed. On the other hand, when the contact means is separated from the transfer medium, the load applied to the transfer medium is released, contrary to the time of contact,
Although registration deviation occurs on the plus side in the sub-scanning direction, when the drive of the transfer medium is controlled based on the drive control pattern,
The transfer medium is rotated at a drive speed lower than that of the photoconductor in accordance with the separation of the contact means from the transfer medium, and the registration deviation is suppressed. Therefore, a high quality color image can be obtained by suppressing the registration deviation.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention utilizes the basic principle first discovered by the present inventor, and the following describes the basic principle of the present invention.
The present embodiment using the basic principle will be described in detail.

A. Basic Principle of the Invention Conventionally, when primary transfer processing is repeated and a contact means such as a secondary transfer roller or a cleaner blade is brought into contact with an intermediate transfer belt, registration deviation occurs and image quality deteriorates. The phenomenon itself was known. However, it has not been analyzed in detail what kind of technical matter it is based on, or the relationship between the separation / contact of the contact means and the amount of registration deviation. Therefore, FIG.
The operation of the image forming apparatus of No. 6 in the operation sequence shown in FIG. 1 is required to examine in detail the state of occurrence of registration deviation, and to correct the registration deviation based on the examination result to improve image quality. The resist control amount was determined.
Hereinafter, this will be described in detail with reference to FIGS.

FIG. 1 is a timing chart showing an example of an operation sequence in the image forming apparatus of FIG.
As shown in the figure, when the apparatus power is turned on or when the sleep mode of the image forming apparatus is released, the intermediate transfer belt 41 synchronizes with the photoconductor 21 to a predetermined driving speed V0.
The vertical synchronization signal VSYNC is intermittently output from the vertical synchronization reading sensor 40 by being rotationally driven (FIGS. 3 to 6). Then, the vertical synchronization signal VSYNC is output at timings VT1 to VT7,
.., The yellow electrostatic latent image, the cyan electrostatic latent image, the magenta electrostatic latent image, and the black electrostatic latent image are repeatedly formed on the photoreceptor 21 in this order after a certain period of time. . After the electrostatic latent image is formed, the developing units 23Y and 23
One of the developing devices M, 23C and 23B selectively comes into contact with the photoconductor 21 to make an electrostatic latent image on the photoconductor 21 visible,
The toner image is primarily transferred onto the intermediate transfer belt 41.
Accordingly, all the toner images of each color are formed at a predetermined position on the photoconductor 21, that is, a reference latent image forming position, and the intermediate transfer belt 41 that rotates in synchronization with the photoconductor 21 is formed.
Is primarily transferred at the same position (primary transfer processing for each toner color).

When the primary transfer process is repeated for four colors, the four color toner images are superimposed on the intermediate transfer belt 41 to form a color image. When a color image is obtained in this way, the secondary transfer roller 48 abuts on the intermediate transfer belt 41 with the sheet member S interposed therebetween, and secondary-transfers the color image onto the sheet member S. At the same time, the cleaner blade 491 is turned on according to the CB signal. The toner remaining in contact with the intermediate transfer belt 41 on the belt surface is removed. The sheet member S on which the color image is formed by repeating such an operation is sequentially discharged to the standard discharge tray.

This is the outline of the operation of the image forming apparatus in accordance with the operation sequence shown in FIG. 1. The relationship between such an operation and the amount of registration deviation in the sub-scanning direction is examined. Gave different results. Such a difference is caused by the difference in the operation sequence. Hereinafter, the operation sequence for forming the first sheet (hereinafter, referred to as “first print sequence”) and the image formation for the second and subsequent sheets will be described. The operation sequence (hereinafter, referred to as “second printing sequence”) will be described separately. Also, in this type of apparatus, since there is a third print sequence associated with the idling process, this will also be described.

A-1. First Printing Sequence First, when the apparatus power is turned on (or the sleep mode of the image forming apparatus is released), the intermediate transfer belt 41
Are rotated and conveyed, and the vertical synchronization signal VSYNC is sequentially output from the vertical synchronization reading sensor 40 at timings VT1 to VT3. The yellow toner image Y1 is transferred to the intermediate transfer belt 41 as described above corresponding to the first timing VT1. One on top
Next, the cyan toner image C1 is primary-transferred onto the intermediate transfer belt 41 so as to overlap the yellow toner image Y1 at the timing VT2, and the magenta toner image M1 is further converted into the yellow toner image Y1 at the timing VT3.
And an intermediate transfer belt 41 superimposed on the cyan toner image C1.
The primary transfer is performed thereon. During this time, the cleaning process and the secondary transfer process of the intermediate transfer belt 41 are not performed, and the abutting means (the secondary transfer roller 48 and the cleaner blade 49) are not used.
1) is separated from the intermediate transfer belt 41. Therefore, these three toner images Y1, C1, and M1 are all superimposed at the same position on the intermediate transfer belt 41, and are accurately registered in the sub-scanning direction. That is, FIG.
As shown in FIG. 3, these three toner images Y1, C1, M1
All of the transfer start positions coincide with the reference transfer start position, and their post-transfer end positions also coincide with the reference transfer post-end position. FIG. 1 (and FIG. 1 described later)
The dashed line in (0) indicates the primary transfer position where each toner image is transferred. In the actual primary transfer process, the toner images are sequentially superimposed at this dashed line portion. For convenience of description, each toner image is illustrated as being vertically separated.

Next, at timing VT4, the vertical synchronizing signal VS
When the YNC is output, as shown in FIG.
Thereafter, a VIDEO signal is supplied to the exposure unit 3 to form an electrostatic latent image corresponding to the black toner image K1 at a predetermined reference latent image forming position in the same manner as other toner colors. I do. Then, the primary transfer process is started from a point in time when a predetermined time T20 has elapsed from the output of the vertical synchronization signal VSYNC (timing VT4). At this point, the yellow toner image Y1 and the cyan toner image C
1 and the magenta toner image M1, the cleaner blade 491 is separated from the intermediate transfer belt 41, and as a result, as shown in FIG.
The transfer start position of No. 1 also coincides with the reference transfer start position similarly to the other toner images Y1, C1, M1. Then, while the separation is continued, the black toner image K1 is superimposed while being accurately registered with the other toner images Y1, C1, and M1 that have already been primary-transferred.

However, 1 of the black toner image K1
At a certain point when the second half of the next transfer is reached, that is, at the timing t
At 1, the CB signal for controlling the operation of the cleaner blade 491 rises from the L level to the H level, the cleaner blade 491 contacts the intermediate transfer belt 41, and the black toner image K1 is compared with the other toner images Y1, C1, and M1. In the sub-scanning direction. That is, the timing t
At 1, the cleaner blade 491 contacts the intermediate transfer belt 41, and the intermediate transfer belt 41 is rotated at the same drive speed V0 in synchronization with the photosensitive member 21, but the cleaner blade 491 (contact means). Is the intermediate transfer belt 4
The intermediate transfer belt 41 acts instantaneously in the sub-scanning direction, causing an extension A27 in the sub-scanning direction. as a result,
On the negative side in the sub-scanning direction, a resist displacement occurs by a resist displacement amount A27.

Further, after the timing t1, the cleaner blade 491 is kept in contact with the intermediate transfer belt 41 to execute the cleaning process of the intermediate transfer belt 41 until the CB signal next rises again from the L level to the H level. However, the primary transfer processing of the black toner image K1 is continued in the contact state until timing t2. As a result, the registration deviation is further increased, and the final registration deviation amount of the black toner image K1 in the sub-scanning direction is A32 = A27 + A6, and as shown in FIG. It is shifted from the rear end position of the transfer by the shift amount A32 in the (-) direction. However, the symbol A6 corresponds to the belt elongation caused by the cleaner blade 491 continuing to contact the intermediate transfer belt 41 from the timing t1 to the timing t2 (that is, the time A7). Also, in the same figure (and a diagram showing a temporal change in the amount of registration deviation described later), a thick solid line indicates the registration deviation of the toner image of the corresponding toner color, while a thick broken line indicates the understanding of the state of occurrence of the registration deviation. It is an auxiliary line to help.

As described above, for the first color image, as shown in FIG.
Only 1 deviates from the other toner images Y1, C1 and M1, and in particular, at the rear end of the color image, deviates by the registration deviation amount A32. Incidentally, before the cleaner blade 491 abuts, the secondary transfer roller 48 also abuts on the intermediate transfer belt 41 and a similar registration shift occurs. The corresponding registration shift amount is smaller than that of the cleaner blade 491. , To make it easier to understand the basic principles of the invention,
Here, the secondary transfer roller 4 with respect to the intermediate transfer belt 41
The description will be made while ignoring the registration deviation due to the separation and contact of No. 8.

A-2. Second printing sequence Such a registration error does not occur only on the first sheet, but also appears on the second color image. That is, in order to form the second yellow toner image Y2,
As shown in FIG. 4, at timing VT5, the vertical synchronizing signal VS
After a predetermined time T10 has elapsed from the output of YNC, a VIDEO signal for forming the yellow toner image Y2 is given to the exposure unit 3. Then, while an electrostatic latent image corresponding to the yellow toner image Y2 is formed on the photoreceptor 21, toner development is performed by the yellow developing unit 23Y.
Output of the vertical synchronization signal VSYNC (timing VT5)
After a lapse of a predetermined time T20 from the time t3
Then, the primary transfer process is started.

However, some time after the output timing VT5 of the vertical synchronizing signal VSYNC, the cleaner blade 491 comes into contact with the intermediate transfer belt 41 as described above, and the intermediate transfer belt 41 instantaneously expands in the sub-scanning direction. Moreover, the contact state is changed to C as described later.
Since the B signal continues until it rises to the H level, the elongation in the sub-scanning direction increases as time elapses. And
At the primary transfer start timing t3, the registration deviation amount A30 in the sub-scanning direction is A30 = A27 + A9. However, the symbol A9 corresponds to belt elongation caused by the cleaner blade 491 continuing to contact the intermediate transfer belt 41 from the timing t1 to the timing t3 (that is, the time A10).

When the intermediate transfer belt 41 has passed through the belt cleaner 49 for about one revolution, the entire belt is cleaned and the cleaning process is completed. At a timing t4, the CB signal rises again from the L level to the H level. The cleaner blade 491 is used for the intermediate transfer belt 41
Separate from. During the period from the start of the primary transfer (timing t3) to the separation of the cleaner blade 491 (timing t4), the cleaner blade 491 keeps contacting the intermediate transfer belt 41. During that time, the intermediate transfer belt 41 is moved to A12 (= t4−t3). Is extended by the extension amount A11 in the sub-scanning direction, and the registration deviation further increases, and the registration deviation amount immediately before the timing t4 becomes the deviation amount A35 in the (-) direction.

On the other hand, at this timing t4, the cleaner blade 491 separates from the intermediate transfer belt 41. Accordingly, the load applied to the intermediate transfer belt 41 is released contrary to the time of the contact.
Is reduced by the contraction amount A26, and the registration deviation amount in the sub-scanning direction is reduced by A26. As described above, for the second color image, the transfer start position of the yellow toner image Y2 is greatly shifted from the reference transfer start position. Moreover,
As the primary transfer progresses, the amount of registration deviation increases,
When the cleaner blade 491 separates at the timing t4 during the next transfer, the amount of registration deviation decreases in reverse. Thus, the image quality is degraded.

The transfer start position of the cyan toner image C2, which is primarily transferred after the yellow toner image Y2, is shifted from the reference transfer start position under the influence of the separation and contact of the cleaner blade 491. This phenomenon will be described with reference to FIG.

In order to form the second cyan toner image C2, a VIDEO signal for forming the cyan toner image C2 is transmitted to the exposure unit after a lapse of a predetermined time T10 from the output of the vertical synchronization signal VSYNC at timing VT6. 3
Given to. Then, while forming an electrostatic latent image corresponding to the cyan toner image C2 on the photoconductor 21, the toner is developed by the cyan developing unit 23C. Further, the primary transfer process is started at a time when a predetermined time T20 has elapsed from the output of the vertical synchronization signal VSYNC (timing VT6), that is, at timing t5.

Here, at the output timing VT6 of the vertical synchronizing signal VSYNC, the cleaner blade 491 is in contact with the intermediate transfer belt 41 as described above, and the timing t4 (the CB signal rises again from the L level to the H level). This contact state is maintained until the time A14. Therefore, the intermediate transfer belt 41 extends by A13 between the timing VT6 and the timing t4.
On the other hand, when the cleaner blade 491 separates from the intermediate transfer belt 41 at the timing t4, the load applied to the intermediate transfer belt 41 is released and the Shrinks by A26. Thereafter, the separated state is maintained until the CB signal next rises from the L level to the H level again. As a result, at the start of the primary transfer of the cyan toner image C2 (timing t5), the registration deviation amount A34 in the sub-scanning direction is A34 = A26-A13. This leads to a decrease in image quality.

As described above, 1 of the cyan toner image C2
When the next transfer is completed, the toner image formation of the magenta toner image M2 and the primary transfer process are performed next. During the process, the cleaner blade 491 rotates the intermediate transfer belt 41.
In the same manner as in the first sheet, no registration deviation occurs in the sub-scanning direction, and the registration deviation amount becomes zero. For this reason, in the image forming apparatus that forms an image in the operation sequence shown in FIG. 1, the magenta toner image is used as the reference toner image, and the transfer start position and the transfer end position thereof are referred to as “reference transfer start position” and “reference transfer position”, respectively. Transfer end position ".

When the primary transfer of the magenta toner image M2 is completed, the image formation of the third black toner image and the primary transfer process are performed. In this case, the primary transfer is performed similarly to the second sheet. On the way, the cleaner blade 491 abuts on the intermediate transfer belt 41 to extend the intermediate transfer belt 41 by A32, and a registration shift occurs in the (-) direction in the sub-scanning direction. Note that the profile (hereinafter, simply referred to as “profile”) indicating the temporal change in the amount of registration deviation is the same as that in FIG. 3, and the image quality is degraded.

Further, following the third color image, 4
In the case of successively forming color images on the second and subsequent sheets, the same registration deviation as in the above-described second sheet occurs.

A-3. Third printing sequence Further, in this type of image forming apparatus, the intermediate transfer belt 4
1 may run idle. For example, if the interval between image data from an external device such as a host computer is longer than a certain value, the intermediate transfer belt 41 is idled.
At this time, the cleaner blade 491 is
1 is in a contact state. When a new image formation is started, the intermediate transfer belt 41 is driven to rotate to start image formation. However, when the first yellow toner image is primarily transferred, the second and subsequent sheets shown in FIG. The same registration deviation as in the case of the cyan toner image occurs.

That is, as shown in FIG. 6, when image formation is restarted and the intermediate transfer belt 41 is driven to rotate at the same driving speed V0 as the photosensitive member 21, the vertical synchronization reading sensor 40 outputs a vertical synchronization signal VSYNC. Is output at a timing VT01. After the cleaner blade 491 separates from the intermediate transfer belt 41 after a predetermined time A14 from the timing VT01, the primary transfer of the yellow toner image is started. For this reason, the transfer start position is shifted in the (+) direction by the shift amount A34 for the same reason as in the case of the cyan toner image C2 in the above “A-2. Second print sequence”.

Since the subsequent primary transfer of the cyan and magenta toner images is always performed with the cleaner blade 491 being separated from the intermediate transfer belt 41, no registration deviation occurs. 1 as in the case of the first and second print sequences.
During the next transfer, the cleaner blades 491 and 2
When the next transfer roller 48 comes into contact with the intermediate transfer belt 41, a registration shift of the shift amount A32 occurs in the (-) direction.

As described above, when the contact means such as the cleaner blade 491 comes into contact with the intermediate transfer belt 41 while the primary transfer process is being repeated, a predetermined amount of registration deviation is set according to the contact / contact timing. Occurs. The profile itself is unique depending on the device configuration and operating conditions, and the profile itself does not change unless the device configuration or operation sequence is changed. On the other hand, by accelerating and decelerating the intermediate transfer belt 41, registration deviation from the reference toner image can be reduced to zero or suppressed. For example, as for the cyan toner image C2, as shown in FIG. 5, the transfer start position of the cyan toner image C2 has a shift amount A34 in the (+) direction with respect to the reference transfer start position. The intermediate transfer belt 41 is rotated at a drive speed lower than that of the photoconductor 21 at the same time as or before or after the contact unit is separated from the intermediate transfer belt 41, so that the intermediate transfer belt 41 is not changed. By performing control so as to delay to the minus side in the sub-scanning direction by a distance corresponding to the registration deviation amount A26, the registration deviation amount can be made zero.

Therefore, prior to the actual image forming process, the same analysis as described above is performed in advance from the apparatus configuration and the operation sequence to derive a profile of the registration deviation, and the profile (time-dependent change of the registration deviation amount) The drive control pattern of the intermediate transfer belt 41 is determined in advance based on the above, and in the actual image forming process, the drive control of the intermediate transfer belt 41 is performed in accordance with the drive control pattern, thereby suppressing registration deviation and achieving high quality. An image can be formed. Hereinafter, specific embodiments will be sequentially described.

B. First Embodiment Image forming apparatuses according to the first embodiment and other embodiments use the above-described "basic principle of the invention", and have the same mechanical configuration as that of FIG. On the other hand, it has remarkable features not found in the prior art in its electric configuration and image forming method. Therefore, in the following, the description of the mechanical configuration is omitted, and the electrical configuration and the image forming method will be mainly described in detail.

B-1. Electrical Configuration FIG. 7 is an electrical configuration diagram showing an embodiment of an image forming apparatus according to the present invention, and has a configuration common to all embodiments described below. This image forming apparatus includes:
When an image signal is provided from an external device such as a host computer to the main controller 11 of the control unit 1,
In response to a command from the CPU 111 of the main controller 11, the engine controller 12 controls each part of the engine unit E configured as shown in FIG. 16 to form an image corresponding to the image signal on the sheet member S.

This engine controller 12 is a CPU 1
And a horizontal synchronization signal HSYNC from the horizontal synchronization reading sensor 36 as an input signal from the engine unit E.
Also, the vertical synchronization signal VSYNC is output from the vertical synchronization read sensor 40.
Has been received respectively. Further, based on these input signals and various kinds of information, the CPU 121 causes the photoconductor driving unit 2 to operate.
A drive command signal for controlling the driving of the photoconductor 1a is supplied to the photoconductor drive control circuit 127, and the photoconductor drive control circuit 127 controls the photoconductor drive unit 21a to drive the photoconductor 21 at a constant speed V0. ing.

The CPU 121 includes a belt driving unit 41a.
Is supplied to the belt drive control circuit 122, and the belt drive control circuit 122 controls the belt drive unit 41a. In the present embodiment, the intermediate transfer belt 41 is basically driven to rotate in synchronization with the photoconductor 21 by the belt driving unit 41a, and also in accordance with the separation / contact timing of the contact unit as described later. Thus, the intermediate transfer belt 41 is temporarily driven at a drive speed different from the drive speed V0 of the photoconductor 21.

Further, the CPU 121 executes a process for establishing and storing a resist profile (a temporal change in the amount of registration deviation), a process for determining a drive control pattern of the intermediate transfer belt 41, and the like, which will be described later. That is, the CPU 121 functions as a “drive control pattern determination unit” of the present invention.

The engine controller 12 includes, as a dedicated control circuit for controlling the transfer unit 4, a transfer roller separation / contact control circuit 123 and a belt cleaner other than the belt drive control circuit 122 and the photosensitive member drive control circuit 127. A separation / contact control circuit 124 is further provided. The transfer roller separation / contact control circuit 123 controls the secondary transfer roller driving unit 48 a based on a command signal from the CPU 121 to separate and contact the secondary transfer roller 48 with the intermediate transfer belt 41 at an appropriate timing. On the other hand, the belt cleaner separation / contact control circuit 124 controls the belt cleaner drive unit 49a by giving the CB signal to the belt cleaner drive unit 49a based on the command signal from the CPU 121, and transfers the cleaner blade 491 to the intermediate transfer at an appropriate timing. The belt 41 is brought into contact with and separated from the belt 41.

Reference numeral 113 in the figure is an image memory provided in the main controller 11 for storing an image provided from an external device such as a host computer via the interface 112, and reference numeral 125 is an engine unit E. Is a RAM for temporarily storing control data for controlling the operation, calculation results in the CPU 121, and the like, and a reference numeral 126 is a ROM for storing a calculation program executed by the CPU 121 and the like.

B-2. Next, the operation of the image forming apparatus according to this embodiment will be described. In this embodiment, the image quality is improved by correcting the registration deviation of the black toner image. Hereinafter, the operation of the first embodiment will be described in detail with reference to FIGS.

FIG. 8 is a flowchart showing the operation of the image forming apparatus according to the first embodiment. In this image forming apparatus, when the apparatus power is turned on, prior to the actual image forming process, a profile setting step of registration deviation (step S1) is executed to transfer the intermediate transfer belt 41 to the photosensitive member 2.
On the intermediate transfer belt 41 generated by bringing the cleaner blade 491 into and out of contact with the intermediate transfer belt 41 at a preset separation and abutment timing while rotating and driving at the same drive speed V0 always in synchronization with the intermediate transfer belt 41 Of the relative registration shift amount of the toner image of FIG. In this embodiment, since the correction target of the registration shift is limited to the black toner image, the registration shift amount A27 of the black toner image at the contact timing t1 at which the cleaner blade 491 contacts the intermediate transfer belt 41 (FIG. 3). Is enacted. The details of the operation for automatically setting the registration deviation amount A27 (step S1) will be described later in the section "F. Registration registration profile establishment processing".

In this manner, the profile of the registration deviation, that is, the temporal change of the registration deviation amount is established (step S
When 1) is completed, the process waits for a print request from an external device such as a host computer (step S2). When there is a print request, it is determined whether the print mode is monochrome printing or color printing (step S3). If it is determined that the printing mode is monochrome printing, normal image forming processing is performed without registration control. Execute and return to step S2. On the other hand, if it is determined in step S3 that the printing is color printing, the process proceeds to step S4, where a belt drive control pattern based on the profile of registration deviation is obtained.

As already described with reference to FIG.
When the black toner image transfer process is performed while the intermediate transfer belt 41 is constantly driven to rotate at the same drive speed V0 in synchronization with the photoconductor 21, the toner image is transferred to the intermediate transfer belt 4.
At the time t1, the cleaner blade (contact means) 491 abuts on the intermediate transfer belt 41 during the transfer to the intermediate transfer belt 41, and this acts as a transport load of the intermediate transfer belt 41. An elongation A27 occurs in the sub-scanning direction, and as a result, a resist displacement occurs in the (−) direction by a resist displacement amount A27. Therefore, in this embodiment, as shown in the lowermost graph of FIG. 9, at the same time when the cleaner blade 491 contacts the intermediate transfer belt 41,
A drive control pattern for temporarily rotating the intermediate transfer belt 41 at a first drive speed V1 higher than the drive speed V0 of the photoconductor 21 is determined.

Then, in the next step S5, the drive of the intermediate transfer belt 41 is controlled according to this drive control pattern. That is, the intermediate transfer belt 41 is basically driven to rotate at the same reference drive speed V0 in synchronization with the photosensitive member 21, and the cleaner blade 491
Until the timing t1 when it comes into contact with 1, the amount of registration deviation is zero. At the timing t1, the intermediate transfer belt 41 is temporarily driven to rotate at the first drive speed V1 higher than the drive speed V0 of the photoconductor 21, so that the intermediate transfer belt 41 is additionally moved to the plus side in the sub-scanning direction. Feeding, cleaner blade 491 to intermediate transfer belt 41
The misregistration to the minus side due to the contact of is corrected.

Here, as described above, the timing t1
When the intermediate transfer belt 41 is temporarily driven at the first drive speed V1, the distance Δ1 proportional to the speed difference (V1−V0) is compared with the case where the intermediate transfer belt 41 is driven at the same drive speed V0 as the photosensitive member 21. However, the intermediate transfer belt 41 is additionally fed to the plus side, but it is desirable to set the acceleration / deceleration pattern of the driving speed at the timing t1 so that this distance Δ1 substantially matches the registration deviation amount A27. As shown in the middle part (registration deviation profile) of the figure, the amount of registration deviation at the timing t1 can be made substantially zero.

In this embodiment, the CPU 12
The DC motor is controlled by a so-called external clock system in which the clock signal supplied from 1 to the belt drive control circuit 122 is changed to perform acceleration / deceleration control of the DC motor serving as the drive source of the belt drive unit 41a. Therefore, the DC motor can be controlled with excellent controllability. Moreover, when the external clock method is adopted, the DC motor can be controlled with an arbitrary control waveform (acceleration / deceleration pattern) by changing the clock signal given from the CPU 121. Therefore, in this embodiment, as shown in FIG. 9, a rectangular acceleration / deceleration pattern is employed, but the driving speed of the intermediate transfer belt 41 is controlled by various acceleration / deceleration patterns such as a trapezoidal shape and a triangular shape. The registration may be corrected with higher accuracy. In this regard, the same applies to the following embodiments.

Further, in this embodiment, the intermediate transfer belt 41 is driven at the drive speed V0 of the photosensitive member 21 during the acceleration / deceleration possible period.
Acceleration / deceleration control. Here, the “acceleration / deceleration possible period” refers to a period during which the VIDEO signal is at the H level and the exposure processing is stopped, that is, a non-exposure timing. If a difference occurs in the drive speed between the photoconductor 21 and the intermediate transfer belt 41 during the exposure process (exposure timing), an external force may act on the photoconductor 21 to disturb the latent image. is there. On the other hand, if the acceleration and deceleration of the intermediate transfer belt 41 is controlled only during the acceleration / deceleration possible period (non-exposure timing) as in this embodiment, such disturbance of the latent image can be prevented.

In this embodiment, at the timing t1
After the driving speed of the intermediate transfer belt 41 is temporarily increased to the first driving speed V1, the driving speed is returned to the same driving speed V0 as that of the photoconductor 21, so that the transfer process of the black toner image is completed until timing t2. During that time, the resist displacement amount A6 occurs.

As a result, in this embodiment, when the first color image is formed, as shown in FIG. 10, the black toner image K1 is transferred to the other toner images Y1, C1, and M1 at the rear end of the transfer. A slight amount of registration deviation A6 in the (-) direction
In the case where the resist control is not performed simply by shifting
3), the maximum deviation of the black toner image can be greatly reduced.

When the formation of the first color image is completed while suppressing the registration deviation based on the profile of the registration deviation in this way, it is determined in step S6 whether or not the printing is completed, and it is determined that the printing is completed. If so, the process returns to step S2 and waits for the next print request. On the other hand, if it is determined that printing has not been completed, the process returns to step S3, and the same processing as described above is repeated. Therefore, when the second color image is formed after the formation of the first color image as described above, the process proceeds from step S3 to step S4, and the registration shift of the black toner image is performed in the same manner as described above. It is possible to form a high-quality image with suppression.

C. Second Embodiment In the first embodiment, since the driving speed of the intermediate transfer belt 41 is temporarily increased to the first driving speed V1 at the timing t1, and then returned to the driving speed V0 of the photosensitive member 21, the black speed is reduced. Registration deviation has occurred on the rear end side of the toner image.
In order to eliminate the registration error, the following configuration may be used.

First, in step S1, in addition to the instantaneous registration deviation amount A27 at the timing t1, the registration deviation amount A6 generated between the timing t1 and the timing t2 is further obtained. The details of the operation for automatically setting the registration deviation amount A6 (step S1) will be described later in the section "F. Registration registration profile establishment processing".

Then, in step S4, the instantaneous registration deviation amount A27 at the timing t1 and the timing t1 to t2
1 based on the amount of registration deviation A6 gradually increasing between
As shown in the lowermost graph of FIG.
Not only temporarily rotates the intermediate transfer belt 41 at a first drive speed V1 higher than the drive speed V0 of the photoconductor 21, but also subsequently rotates the second drive speed V2 ( Timing t at V0 <V2 <V1)
A driving control pattern (the lowermost graph in FIG. 11) for rotating the intermediate transfer belt 41 in accordance with the driving control pattern is obtained in advance, so that the registration deviation of the black toner image can be more accurately performed. Can be corrected.

In this case, the intermediate transfer belt 41 is basically rotated at the same reference drive speed V 0 in synchronization with the photosensitive member 21, and the registration is performed until the timing t 1 at which the cleaner blade 491 contacts the intermediate transfer belt 41. The shift amount is zero. Then, at the timing t1, the intermediate transfer belt 41 is temporarily driven to rotate at the first drive speed V1 higher than the drive speed V0 of the photoconductor 21 as in the first embodiment. An instantaneous registration shift to the negative side due to the contact of the contact 491 is corrected.

Since the cleaner blade 491 keeps contacting the intermediate transfer belt 41 following the instantaneous registration correction, the load becomes a load and a registration shift to the minus side occurs. During this time, the intermediate transfer belt 41 is continuously driven at the drive speed V0 of the photoconductor 21.
It is rotationally driven at a higher second driving speed V2. As a result, the intermediate transfer belt 41 is extraly fed to the plus side in the sub-scanning direction, and registration deviation to the minus side due to the contact of the cleaner blade 491 with the intermediate transfer belt 41 is corrected.

Here, at the second drive speed V2, the timing t2
When the intermediate transfer belt 41 is driven continuously up to the distance 22, which is proportional to the speed difference (V2−V0), as compared with the case where the intermediate transfer belt 41 is driven at the same drive speed V0 as the photosensitive member 21.
However, the intermediate transfer belt 41 is additionally fed to the plus side, but it is desirable to set the second drive speed V2 so that this distance Δ2 substantially matches the registration deviation amount A6. As shown in the section (registration deviation profile), the registration deviation can be made zero over the entire black toner image. As a result, a higher quality image can be formed as compared with the first embodiment.

D. Third Embodiment The first and second embodiments are different from the first embodiment in that the cleaner blade 49 is used.
In order to correct the registration deviation caused by the contact means such as 1 contacting the intermediate transfer belt 41, the contact means contacting the intermediate transfer belt 41 is used as described above. Even when it is separated from 41, a registration shift occurs. Therefore, the registration error can be corrected by configuring the image forming apparatus as described below, and a higher quality image can be formed.

FIG. 12 is an operation explanatory diagram of the third embodiment of the image forming apparatus according to the present invention. In the third embodiment, similarly to the first embodiment, when the apparatus power is turned on in step S1, prior to the actual image forming processing, a registration deviation profile establishing step (step S1) is performed to execute an intermediate process. The transfer belt 41 is rotated and driven at the same drive speed V0 constantly in synchronization with the photoconductor 21 and the cleaner blade 491 is separated from and brought into contact with the intermediate transfer belt 41 at a preset separation and contact timing. The temporal change in the relative amount of registration deviation of the toner image on the intermediate transfer belt 41 is obtained. In this embodiment, since the correction target of the registration shift is limited to the cyan toner image, the registration shift amount A13 (see FIG. 7) generated by the cleaner blade 491 being continuously in contact with the intermediate transfer belt 41 until timing t4. 5), and the registration deviation amount A26 (FIG. 5) of the cyan toner image at the timing t4 at which the cyan toner image is separated from the intermediate transfer belt 41 is established. The details of the operation for automatically setting the registration deviation amounts A13 and A26 (step S1) will be described later in the section "F. Registration registration profile establishment processing".

In this way, the profile of the registration deviation, that is, the temporal change of the registration deviation amount is established (step S
When 1) is completed, the process waits for a print request from an external device such as a host computer (step S2). When there is a print request, it is determined whether the print mode is monochrome printing or color printing (step S3). If it is determined that the printing mode is monochrome printing, normal image forming processing is performed without registration control. Execute and return to step S2. On the other hand, if it is determined in step S3 that the printing is color printing, the process proceeds to step S4, where a belt drive control pattern based on the profile of registration deviation is obtained.

As already described with reference to FIG.
When the transfer process of the cyan toner image is executed while the intermediate transfer belt 41 is constantly rotated and driven at the same drive speed V0 in synchronization with the photoconductor 21, the transfer start position of the toner image is shifted by the registration deviation amount A34 (= A26− A13) is shifted to the plus side in the sub-scanning direction. Therefore, in this embodiment, FIG.
As shown in the lowermost graph, the cleaner blade 491 is separated from the intermediate transfer belt 41 and, at the same time, the intermediate transfer belt 41 is temporarily rotated at a third drive speed V3 lower than the drive speed V0 of the photoconductor 21. I want a drive control pattern.

Then, in the next step S5, the drive of the intermediate transfer belt 41 is controlled in accordance with this drive control pattern. That is, the intermediate transfer belt 41 is basically driven to rotate at the same reference drive speed V0 in synchronization with the photosensitive member 21, and the cleaner blade 491
The registration deviation amount gradually increases to the negative side until the timing t4, which is away from 1, and becomes the registration deviation amount A13 immediately before the timing t4. Next, at the timing t4, the cleaner blade 491 separates from the intermediate transfer belt 41, The instantaneous contraction A26 of the intermediate transfer belt 41 occurs, and the total amount of registration shift becomes the amount of shift A34 on the plus side in the sub-scanning direction.

At the timing t4, the intermediate transfer belt 41 is temporarily driven to rotate at the third drive speed V3 lower than the drive speed V0 of the photoconductor 21, thereby moving the intermediate transfer belt 41 to the minus side in the sub-scanning direction. Pulling back excessively, cleaner blade 491 from intermediate transfer belt 41
The registration deviation to the plus side due to the separation of is corrected.

Here, as described above, the timing t4
When the intermediate transfer belt 41 is temporarily driven at the third drive speed V3, the distance .DELTA.3 proportional to the speed difference (V0-V3) as compared with the case where the intermediate transfer belt 41 is driven at the same drive speed V0 as the photosensitive member 21. However, the intermediate transfer belt 41 is excessively pulled back to the minus side. However, it is desirable to set the driving speed acceleration / deceleration pattern at the timing t4 so that the distance Δ3 substantially matches the registration deviation amount A34. In the middle of the same figure (registration profile)
As shown in (5), the amount of registration deviation at the timing t4 can be made substantially zero. The transfer start position of the cyan toner image can be corrected to the reference transfer start position. As a result, the cyan toner image can be transferred onto the intermediate transfer belt 41 without registration deviation.

When the formation of the color image is completed while suppressing the registration deviation based on the profile of the registration deviation in this way, it is determined in step S6 whether or not the printing has been completed. , Step S
Return to step 2 and wait for the next print request. On the other hand, if it is determined that printing has not been completed, the process returns to step S3, and the same processing as described above is repeated. Therefore, when forming the next color image following the above-described color image formation,
From step S3, the process further proceeds to step S4, and a high-quality image can be formed by suppressing the registration deviation of the cyan toner image as described above.

In the third embodiment, the driving speed of the intermediate transfer belt 41 is changed at the same time when the cleaner blade 491 separates from the intermediate transfer belt 41 (timing t4), but the vertical synchronization signal VT6 is output. Since 1
The drive speed may be changed at an arbitrary timing until the next transfer is started, that is, during the time T20.

E. Fourth Embodiment In the first and second embodiments, the cleaner blade 49 is used.
In the third embodiment, a contact means such as a cleaner blade 491 separates the contact means such as a cleaner blade 491 from the intermediate transfer belt 41. The correction is performed only for the registration deviation caused by the correction, but it may be desirable to correct both of them. This is because the transfer of the toner image of a certain toner color to the intermediate transfer belt 41 may be affected both by the contact of the cleaner blade 491 and by the separation of the cleaner blade 491. For example, the case where the yellow toner image shown in FIG. Also in such a case, by configuring as follows, it is possible to correct the registration deviation caused by the contacting means such as the cleaner blade 491 coming into contact with and separating from the intermediate transfer belt 41 to form an image with good quality. it can.

FIG. 13 is an operation explanatory view of the fourth embodiment of the image forming apparatus according to the present invention. In the fourth embodiment, as in the first embodiment, when the apparatus power is turned on in step S1, prior to the actual image forming processing, a registration deviation profile establishing step (step S1) is executed to execute an intermediate process. The transfer belt 41 is rotated and driven at the same drive speed V0 constantly in synchronization with the photoconductor 21 and the cleaner blade 491 is separated from and brought into contact with the intermediate transfer belt 41 at a preset separation and contact timing. The temporal change in the relative amount of registration deviation of the toner image on the intermediate transfer belt 41 is obtained. In this embodiment, since the correction target of the registration deviation is limited to the yellow toner image, the cleaning blade 491
A27, A9,
A11 (FIG. 4) and the registration deviation amount A caused by the separation of the cleaner blade 491 from the intermediate transfer belt 41.
26 (Figure 4) is enacted. Note that these registration deviation amounts A27, A9, A11, and A26 are automatically established (step S10).
The details of 1) will be described later in the section “F.

In this manner, the profile of the registration deviation, that is, the temporal change of the registration deviation amount is established (step S
When 1) is completed, the process waits for a print request from an external device such as a host computer (step S2). When there is a print request, it is determined whether the print mode is monochrome printing or color printing (step S3). If it is determined that the printing mode is monochrome printing, normal image forming processing is performed without registration control. Execute and return to step S2. On the other hand, if it is determined in step S3 that the printing is color printing, the process proceeds to step S4, where a belt drive control pattern based on the profile of registration deviation is obtained.

As already described with reference to FIG.
When the transfer process of the yellow toner image is performed while the intermediate transfer belt 41 is constantly rotated and driven at the same drive speed V0 in synchronization with the photosensitive member 21, the transfer of the cleaner blade 491 to and from the intermediate transfer belt 41 is performed according to the separation / contact. Change. Therefore, in this embodiment, a drive control pattern corresponding to the separation / contact of the cleaner blade 491 is obtained as shown in the lowermost graph of FIG. Since the drive control pattern is a combination of the drive control patterns of the first to third embodiments, a detailed description thereof will be omitted here.

In the next step S5, the drive of the intermediate transfer belt 41 is controlled in accordance with this drive control pattern, whereby the cleaner blade 491 abuts on the intermediate transfer belt 41, so that the transfer start position of the yellow toner image becomes the reference. The deviation from the transfer start position is corrected, and the cleaner blade 4 is moved during the transfer of the yellow toner image.
The registration shift caused by the separation of the intermediate transfer belt 91 from the intermediate transfer belt 41 can be corrected, and a good yellow toner image without registration shift can be transferred to the intermediate transfer belt 41.

Note that the drive control pattern is not limited to this, and the contact means such as the cleaner blade 491 can be used while the intermediate transfer belt 41 is basically driven at the same drive speed V0 as the photosensitive member 21. The drive speed of the intermediate transfer belt 41 may be accelerated or decelerated with respect to the reference drive speed V0 at an appropriate timing in accordance with the separation / contact of.

F. FIG. 14 is a flowchart showing a process of automatically establishing a profile of a registration error. First, the following initial setting conditions are set in advance based on the apparatus configuration and operation sequence of the image forming apparatus according to the above-described embodiment.
It is stored in the OM 126. Then, as shown in FIG. 15, based on the VSYNC signal, (1) the cleaner blade 491 and the secondary transfer roller 48
(2) Period T2 in which the cleaner blade 491 and the secondary transfer roller 48 keep contacting with the intermediate transfer belt 41, (3) Period in which the cleaner blade 491 and the secondary transfer roller 48 separate from the intermediate transfer belt 41. Period T
(3) and (4) The profile establishment job (step S11) in which the cycle T4 in which the cleaner blade 491 and the secondary transfer roller 48 keep separating from the intermediate transfer belt 41 as one job is repeated a predetermined number of times, for example, 20 times (step S11) S12).

The initial conditions are: A2: process speed (peripheral speed of the intermediate transfer belt 41), A7: time from contact of the cleaner blade 491 to completion of the primary transfer of the black toner image (see FIG. 3), A8 A: Time required for the intermediate transfer belt 41 to make one rotation A10: One of the yellow toner images from the contact of the cleaner blade
Time until the next transfer starts (see FIG. 4), A12: Time from the transfer start position of the yellow toner image to separation of the cleaner blade (see FIG. 4), A14: Time from VSYNC signal to separation of the cleaner blade (see FIG. 5) A17: A time interval from the VSYNC signal in the cycle T1 to the contact with the cleaner blade (see FIG. 15), and A18: a time interval from the VSYNC signal in the cycle T3 to the separation of the cleaner blade (see FIG. 15).

In this embodiment, the charging bias and the primary transfer bias are always set to ON while the profile establishment job (step S11) is repeatedly executed. Although not shown in FIG. 16, a static elimination lamp is provided between the primary transfer region R1 and the photoreceptor cleaner blade 24.
This static elimination lamp is always set to the ON state. Further, while the secondary transfer roller 48 is in contact with the intermediate transfer belt 41, a secondary transfer bias is applied to obtain a profile of registration deviation in a state close to actual printing.

When 20 actual measured values are obtained for each of the periods T1 to T4, the average value T1 is obtained.
(av) to T4 (av) are calculated (step S1)
3). Further, deviation amounts A27, A6, A9, A11, and A26 for specifying the profile of the registration deviation, that is, the registration deviation amounts generated due to the separation and contact of the contacting means are obtained by calculation based on the following equations (step S14). .
The reason will be described separately.

<Registration Amounts A6 and A27> As shown in FIG. 3, during the primary transfer of the black toner image K1 to the intermediate transfer belt 41, the cleaning blade 4
The contact of the cleaner blade 491 is continued even when the contact of the cleaner blade 491 is started and, for example, the primary transfer of the black toner image K1 of A3 size is completed, so that the registration deviation amount A32 in the sub-scanning direction occurs. . The resist displacement A32 is the sum of the two elongations A6 and A27.
That is, A32 = A6 + A27.

Here, the contact elongation A6 is the contact elongation generated when the intermediate transfer belt 41 is rotated and conveyed while the cleaner blade 491 is in contact, and the elongation A27 is
This is the instantaneous elongation (elasticity + slippage) when the cleaner blade 491 contacts the intermediate transfer belt 41.

First, the elongation A6 will be examined. The periodic difference A1 is generated by the contact of the cleaner blade 491, and the periodic difference A1 can be obtained by the following equation: A1 = (T2 (av) -T4 (av)) × A2 × 1000 . Then, the black toner image K1
During the primary transfer, the cleaner blade 491 is in contact only for a predetermined time A7, so that the contact elongation A6 is A6 = A1 × A7 / A8.

On the other hand, the instantaneous elongation A27 can be obtained by comparing the periods T1 and T4. That is, the instantaneous elongation A27 can be obtained by the following equation: A27 = (T1 (av) -T4 (av)) * A2 * 1000-A15. However, as shown in FIG. 15, the elongation A15 does not increase during the period T1.
Numeral 1 is the elongation due to the contact for a predetermined time A17, and this elongation A15 can be obtained by A15 = A1 × (A8−A17) / A8.

<Registration A9, A11, A26> As shown in FIG. 4, following the primary transfer of the black toner image K1, the yellow toner image Y2 is transferred to the intermediate transfer belt 41.
When the primary transfer is performed, the extension A30 (= A27 + A9) occurs in the sub-scanning direction during the time A10 from the contact of the cleaner blade to the start of the primary transfer of the yellow toner image. Further, even after the primary transfer is started, the cleaner blade 491 is also required.
Is in contact with the intermediate transfer belt 41, so that the elongation A11 occurs. On the other hand, immediately before the primary transfer is completed, the cleaner blade 491 separates from the intermediate transfer belt 41, and contraction A26 occurs.

Here, the elongation at the start of the primary transfer A30
As described above, A30 = A27 + A9, where the elongation A9 is the elongation caused by the intermediate transfer belt 41 being rotated and conveyed only for the time A10 while the cleaner blade 491 is in contact with the following equation. A9 = A1 × A10 / A8

The elongation A11 is an elongation caused by the cleaner blade 491 being in contact with the intermediate transfer belt 41 even after the primary transfer is started, and is obtained by the following equation: A11 = A1 × A12 / A8 Can be.

Further, the shrinkage A26 is caused by the cleaner blade 4
The reference numeral 91 indicates the separation from the intermediate transfer belt 41, which can be obtained by comparing the periods T3 and T4. That is, it can be obtained based on the following equation: A26 = A25− (T3 (av) −T4 (av)) × A2 × 1000. A25 in the formula is
As shown in FIG. 15, this is the elongation in the cycle T3, which can be obtained by the following equation: A25 = A1 × A18 / A8.

<Registration A13> As shown in FIG. 5, when the cyan toner image is primary-transferred onto the intermediate transfer belt 41 following the primary transfer of the yellow toner image, it becomes a reference for the primary transfer. When the VSYNC signal VT6 is output, the cleaner blade 491 is in contact with the intermediate transfer belt 41, and then remains in contact for a time A14 before the primary transfer of the cyan toner image is started. Since the intermediate transfer belt 41 is rotated and conveyed, elongation A13 occurs. That is, the elongation A13 is A13 = A1 × A14 / A8.

As described above, in the process of establishing the profile of the registration shift, the secondary transfer bias is applied while the secondary transfer roller 48 is in contact with the intermediate transfer belt 41. This is not an essential requirement for establishing a profile, and a secondary transfer bias may not be applied, or a bias having a polarity opposite to that of the secondary transfer bias may be applied. In each case, the following effects are obtained. Can be That is, when the secondary transfer bias is not applied, the setting process can be simplified. When a secondary transfer bias is applied, the load applied to the intermediate transfer belt 41 and the belt driving unit 41a by the secondary transfer roller 48 approaches an actual printing state,
The profile of the registration error can be accurately obtained. Further, when a bias having a reverse polarity is applied, the toner adhering to the secondary transfer roller 48 is transferred to the intermediate transfer belt 41.
Then, the secondary transfer roller 48 is cleaned to prevent the back surface of the sheet member from being stained by the secondary transfer roller 48, and a good printing result can be obtained.

Also, in the above-described establishing process, since the primary transfer bias is applied to the intermediate transfer belt 41 to obtain the profile of the registration deviation in a state close to the actual printing, the profile of the registration deviation (time variation of the registration deviation amount) ) Can be determined accurately.

Further, in the establishment processing, the profile establishment job (step S11) is repeated 20 times from the start of driving (step S12), and 20 measured values of the periods T1 to T4 are measured respectively, and based on these measured values, The resist control amount is required. However, immediately after the start of the driving, the rotation and conveyance of the intermediate transfer belt 41 may not be stable, and the period T1 to T1 measured in such a state may not be stable.
If the registration control amount is obtained based on T4, the accuracy of the registration control amount may be reduced. Therefore,
In order to solve such a problem, the intermediate transfer belt 41 is rotated and conveyed a predetermined number of times from the start of driving, and after its operation is stabilized, each period T1 to T4 is actually measured, and the registration is performed based on the measured values. The amount of deviation may be obtained, and in this manner, the profile of the resist deviation can be obtained with high accuracy.

G. Others The present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. For example, in the above embodiment, a DC motor is employed as a drive source for rotationally driving the intermediate transfer belt 41, and registration control is performed by controlling the acceleration and deceleration of the DC motor. Using a motor,
The registration control may be performed by pulse driving control based on the registration control amount.

In the above embodiment, the profile of the resist deviation is obtained by executing the step of establishing the profile of the resist deviation during the operation of the apparatus. However, instead of the step of establishing the profile of the resist deviation, the profile of the resist deviation is determined in advance. May be obtained in advance, and various registration deviation amounts specifying the profile may be stored in the ROM 126. For example, a storage unit is incorporated in the transfer unit 4, and at the stage of assembling the transfer unit 4, only the transfer unit 4 is driven alone to determine a profile of the registration shift, and various registration shift amounts for specifying the profile are provided. May be stored in the storage unit of the transfer unit 4. In this case, the profile of the registration deviation can be obtained at the time of manufacturing and assembling the transfer unit 4, and the profile of the registration deviation can be obtained without waiting for completion of other units, for example, the image carrier unit 2 and the exposure unit 3. Can be
It is possible to improve the efficiency of assembling the entire device.

Further, a profile of registration deviation may be obtained at the stage when the entire image forming apparatus is assembled, and various registration deviation amounts for specifying the profile may be stored in the ROM 126. By doing so, a result reflecting the effect of the units other than the transfer unit 4 on the profile of the resist misalignment is obtained, and the profile of the misregistration with higher accuracy than when the profile of the misregistration is obtained by the transfer unit 4 alone is obtained. can get.

In the above embodiment, the registration deviation is corrected only for a specific toner image. However, the embodiments may be combined to correct the registration deviation for a plurality of different toner images. Good.

The image forming apparatus according to the above embodiment prints an image given from an external device such as a host computer via the interface 112 on a sheet member such as copy paper, transfer paper, paper, and a transparent sheet for OHP. However, the present invention can be applied to an electrophotographic color image forming apparatus such as a copying machine or a facsimile apparatus, that is, an image forming apparatus that forms a color image by superimposing a plurality of color toners.

Further, in the above embodiment, the transfer step of transferring the toner image formed on the photoreceptor 21 onto the intermediate transfer belt 41 is executed for each toner color to form a color image on the intermediate transfer belt 41. However, the toner image is transferred to a transfer medium other than the intermediate transfer belt (a transfer drum, a transfer belt, a transfer sheet, an intermediate transfer drum, an intermediate transfer sheet, a reflective recording sheet, a transparent storage sheet, etc.), and a color image is formed. The present invention can also be applied to an image forming apparatus that forms the image.

[0111]

As described above, according to the present invention, the separation / contact of the contact means with the transfer medium is performed during the repetition of the transfer process, so that the secondary transfer is completed after the primary transfer is completed. Compared to the conventional technology that performed the transfer process and the cleaning process, it has excellent processing efficiency, can perform image formation with high throughput, and requires the transfer medium to be set longer than necessary as in the conventional technology. In addition, the size of the device can be reduced. In addition, registration misalignment occurs when the contact means comes into contact with and separates from the transfer medium. However, since the registration misalignment is corrected as described below, the registration misalignment is suppressed to obtain a high-quality color image. be able to.

In one embodiment of the present invention, while the transfer medium is basically driven and controlled in synchronization with the photosensitive member, the contact means temporarily comes into contact with the transfer medium when the transfer processing is repeated. In response to this, the transfer medium is driven to rotate at a higher driving speed than the photoreceptor, thereby correcting the registration deviation of the toner image on the transfer medium due to the contact means coming into contact with the transfer medium. .

In another aspect of the present invention, while the transfer medium is basically driven and controlled in synchronization with the photosensitive member, the transfer medium is temporarily brought into contact with the transfer medium when the transfer processing is repeated. The transfer medium is rotated at a drive speed lower than that of the photoconductor in accordance with the separation of the transfer medium from the transfer medium, and the transfer is performed when the contact means that has been in contact with the transfer medium separates from the transfer medium. The registration error of the toner image on the medium is corrected.

Further, according to another aspect of the present invention, when the transfer process is repeated while the transfer medium is constantly driven to rotate in synchronization with the photosensitive member, the contact means temporarily comes into contact with the transfer medium. A temporal change in the relative amount of registration deviation of the toner image on the transfer medium is obtained, and a drive control pattern of the transfer medium is set based on the temporal change in the amount of registration deviation. By controlling the drive of the transfer medium in accordance with the drive control pattern, the drive of the transfer medium is basically controlled in synchronization with the photoconductor, but the transfer medium is executed when the transfer process is repeated. The transfer medium is accelerated / decelerated with respect to the photoconductor in accordance with the separation / contact of the contact means, thereby correcting the registration deviation accompanying the separation / contact of the contact means.

[Brief description of the drawings]

FIG. 1 is a timing chart showing an example of operation timing in an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram schematically illustrating a registration state of each toner image when a primary transfer process is performed at the operation timing of FIG. 1 without performing registration control.

FIG. 3 is a diagram illustrating a temporal change in a registration deviation amount when a black toner image is transferred without performing registration control.

FIG. 4 is a diagram illustrating a temporal change of a registration deviation amount when a yellow toner image is transferred without performing registration control.

FIG. 5 is a diagram illustrating a temporal change of a registration shift amount when a cyan toner image is transferred without performing registration control.

FIG. 6 is a diagram illustrating a temporal change in a registration deviation amount when a yellow toner image is transferred without performing registration control.

FIG. 7 is an electrical configuration diagram showing an embodiment of the image forming apparatus according to the present invention.

FIG. 8 is a flowchart illustrating an operation of the image forming apparatus according to the first embodiment.

FIG. 9 is an operation explanatory diagram of the first embodiment of the image forming apparatus according to the present invention;

FIG. 10 is a diagram schematically illustrating a registration state of each toner image when a primary transfer process is performed at the operation timing of FIG. 1 while performing registration control.

FIG. 11 is an operation explanatory view of a second embodiment of the image forming apparatus according to the present invention.

FIG. 12 is an operation explanatory diagram of a third embodiment of the image forming apparatus according to the present invention.

FIG. 13 is an operation explanatory view of a fourth embodiment of the image forming apparatus according to the present invention.

FIG. 14 is a flowchart illustrating processing for automatically establishing a profile of registration deviation.

FIG. 15 is a timing chart showing the contents of a profile establishment job.

FIG. 16 is a diagram showing a configuration of an image forming apparatus as a background art of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Control unit (control means) 3 ... Exposure unit (exposure means) 4 ... Transfer unit 12 ... Engine controller (control means) 21 ... Photoconductor 21a ... Photoconductor drive part 41 ... Intermediate transfer belt (transfer medium) 41a ... Belt Drive unit (transfer medium driving unit) 121 CPU (control unit, drive control pattern determination unit) 122 belt drive control circuit (drive control unit) 126 ROM (storage unit) 127 photoconductor drive control circuit 491 cleaner Blade (contact means) V0: (reference) drive speed V1: first drive speed V2: second drive speed V3: third drive speed C1, C2: cyan toner image E: engine unit K1, K2: black toner image M1 , M2: magenta toner image T1 to T4: cycle Y1, Y2: yellow toner image

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] September 27, 2000 (2009.2)
7)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

The electrostatic latent image formed in this way is
Is developed with toner. That is, in this embodiment, as the developing unit 23, a developing unit 23Y for yellow, a developing unit 23C for cyan, a developing unit 23M for magenta, and a developing unit 23K for black are arranged along the photoconductor 21 in this order. Have been. These developing units 23Y and 23
C, 23M, and 23K are configured to be freely movable toward and away from the photoreceptor 21, respectively, and in response to a command from the control unit, the four developing units 23Y , 23C, 23M, and 23.
One of the developing devices of K selectively contacts the photosensitive member 21, and a high voltage is applied to apply the toner of the selected color to the surface of the photosensitive member 21, and the electrostatic latent on the photosensitive member 21 is applied. Reveals an image.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

However, as described above, the secondary transfer roller 48 is attached to the intermediate transfer belt 41 at an appropriate timing.
And the cleaner blade 491 temporarily abuts. Therefore, the rotation of the intermediate transfer belt 41 is hindered by the contact, the intermediate transfer belt 41 is elastically extended, and a load is applied to a belt driving unit (not shown) that rotationally drives the intermediate transfer belt 41. As a result, the intermediate transfer belt 41 cannot be rotated and conveyed at a constant speed. As a result, the intermediate transfer belt 41
To the secondary transfer roller 48 or the cleaner blade 491
When the toner images come into contact with each other, the toner image
They are shifted from each other, that is, a registration error occurs.
In some cases, the image quality is degraded.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Deleted

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Deleted

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus and an image forming method capable of forming a high-quality image .

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

According to the present invention, the separation and contact of the contact means with the transfer medium is performed during the repetition of the transfer processing . This place
In this case, as described above, the contact means may contact the transfer medium.
The resist misalignment occurs with this, but in the present invention,
To correct the registration deviation.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Deleted

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

FIG. 1 is a timing chart showing an example of an operation sequence in the image forming apparatus of FIG.
As shown in the figure, when the apparatus power is turned on or when the sleep mode of the image forming apparatus is released, the intermediate transfer belt 41 synchronizes with the photoconductor 21 to a predetermined driving speed V0.
The vertical synchronization signal VSYNC is intermittently output from the vertical synchronization reading sensor 40 by being rotationally driven (FIGS. 3 to 6). Then, the vertical synchronization signal VSYNC is output at timings VT1 to VT7,
.., The yellow electrostatic latent image, the cyan electrostatic latent image, the magenta electrostatic latent image, and the black electrostatic latent image are repeatedly formed on the photoreceptor 21 in this order after a certain period of time. . After the electrostatic latent image is formed, the developing devices 23Y and 23Y
One of the developing devices C, 23M, and 23K selectively comes into contact with the photoconductor 21 to make the electrostatic latent image on the photoconductor 21 visible,
The toner image is primarily transferred onto the intermediate transfer belt 41.
Accordingly, all the toner images of each color are formed at a predetermined position on the photoconductor 21, that is, a reference latent image forming position, and the intermediate transfer belt 41 that rotates in synchronization with the photoconductor 21 is formed.
Is primarily transferred at the same position (primary transfer processing for each toner color).

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0111

[Correction method] Change

[Correction contents]

As described above, according to the present invention, during the repetition of the transfer process, the contact means is separated from and brought into contact with the transfer medium. The contact causes a registration error . However, Regis
Since the deviation is corrected as follows,
High quality color images can be obtained by suppressing the displacement
You.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 EB04 EC20 ED02 ED24 ED27 EE03 EE04 EE07 EF09 2H030 AA01 AD03 AD16 BB23 BB42 BB53 2H032 AA05 BA09 BA19 CA01 CA13

Claims (11)

[Claims] 1. A transfer process for transferring a toner image formed on a photoconductor to a transfer medium that is driven to rotate in a sub-scanning direction.
In an image forming apparatus that repeatedly forms a color image by superimposing toner images of respective toner colors on a plurality of toner colors different from each other, it is possible to temporarily contact the transfer medium when the transfer process is repeated. Contact means, basically, while controlling the drive of the transfer medium in synchronization with the photoconductor, at a drive speed higher than that of the photoconductor corresponding to the contact of the transfer means with the transfer medium. Image forming apparatus comprising: a control unit configured to rotationally drive the transfer medium and to correct registration deviation of a toner image on the transfer medium caused by the contact unit abutting on the transfer medium. apparatus. 2. The control device according to claim 1, wherein the contact unit contacts the transfer medium while the toner image on the photosensitive member is being transferred to the transfer medium. 2. The image forming apparatus according to claim 1, wherein the transfer medium is temporarily rotated at a first driving speed higher than that of the photoconductor, and an instantaneous registration error of the toner image caused by the contact of the transfer medium with the transfer medium is corrected. Image forming apparatus. 3. The control unit corrects an instantaneous registration deviation of the toner image, and thereafter, while the transfer of the toner image continues while the contact unit is in contact with the transfer medium, the control unit corrects the toner image. 3. The image forming apparatus according to claim 2, wherein the transfer medium is rotated at a second driving speed that is faster than the first driving speed, and the transfer error is corrected during the continuous transfer. 4. A transfer process for transferring a toner image formed on a photoconductor to a transfer medium that is driven to rotate in a sub-scanning direction.
In an image forming apparatus that repeatedly forms a color image by superimposing toner images of respective toner colors on a plurality of toner colors different from each other, it is possible to temporarily contact the transfer medium when the transfer process is repeated. Contact means, basically, while controlling the drive of the transfer medium in synchronization with the photoreceptor, the contact means, which has been in contact with the transfer medium, is separated from the transfer medium, The transfer medium is rotated at a drive speed lower than that of the photoreceptor, and a registration shift of the toner image on the transfer medium is caused by the separation of the contact unit that has been in contact with the transfer medium from the transfer medium. An image forming apparatus comprising: a control unit that corrects an image. 5. The control device according to claim 1, wherein the contact unit is separated from the transfer medium while the toner image on the photosensitive member is being transferred to the transfer medium. The transfer medium is temporarily driven to rotate at a third drive speed lower than the body, and the instantaneous registration shift of the toner image due to the contact means contacting the transfer medium being separated from the transfer medium. The image forming apparatus according to claim 4, wherein the correction is performed. 6. A transfer process for transferring a toner image formed on a photoconductor to a transfer medium that is driven to rotate in a sub-scanning direction.
In an image forming apparatus that repeatedly forms a color image by superimposing toner images of respective toner colors on a plurality of toner colors different from each other, it is possible to temporarily contact the transfer medium when the transfer process is repeated. Contact means, basically, while controlling the drive of the transfer medium in synchronization with the photoconductor, transferring the transfer medium to the photoconductor in accordance with the separation / contact of the contact means with respect to the transfer medium. An image forming apparatus comprising: a control unit that accelerates and decelerates and corrects a registration shift due to separation and contact of the contact unit. 7. A transfer medium driving means for rotating and driving the transfer medium independently of the photoreceptor, wherein the control means drives the transfer medium to rotate constantly in synchronization with the photoreceptor. A drive control pattern determining unit that determines a drive control pattern of the transfer medium driving unit based on a temporal change in the amount of registration deviation that occurs when the transfer control unit controls the transfer medium drive unit based on the drive control pattern. The image forming apparatus according to claim 6, further comprising: a drive control unit configured to control a drive speed of the transfer medium. 8. An exposure device for exposing an electrostatic latent image corresponding to the toner image onto the photoreceptor, wherein the control device controls the transfer medium at a non-exposure timing other than an exposure timing by the exposure device. The image forming apparatus according to claim 1, wherein the image forming apparatus is temporarily driven to rotate at a driving speed different from that of the photoconductor. 9. A transfer process for transferring a toner image formed on a photoconductor to a transfer medium that is driven to rotate in a sub-scanning direction.
In an image forming method of repeatedly forming a color image by superimposing toner images of respective toner colors on a plurality of different toner colors, while basically controlling the drive of the transfer medium in synchronization with the photoconductor, In response to the contact unit temporarily contacting the transfer medium, the transfer medium is rotated at a drive speed higher than that of the photoconductor, and the contact unit comes into contact with the transfer medium. An image forming method, comprising correcting registration deviation of a toner image on the transfer medium. 10. A transfer process for transferring a toner image formed on a photoreceptor to a transfer medium that is rotated in a sub-scanning direction is repeated for a plurality of different toner colors so that toner images of respective toner colors are superimposed. In the image forming method of forming a color image by using the transfer medium, while the drive of the transfer medium is basically controlled in synchronization with the photoconductor, the contact unit that has been in contact with the transfer medium is separated from the transfer medium. Accordingly, the transfer medium is rotationally driven at a drive speed lower than that of the photoconductor, so that the contact unit that has contacted the transfer medium separates from the transfer medium. An image forming method for correcting a registration error of the toner image. 11. A transfer process for transferring a toner image formed on a photoreceptor to a transfer medium that is rotationally driven in a sub-scanning direction is repeated for a plurality of different toner colors so that toner images of respective toner colors are superimposed. An image forming method for forming a color image, wherein the abutting unit temporarily abuts on the transfer medium when the transfer process is repeated while the transfer medium is constantly driven to rotate in synchronization with the photoconductor. A profile setting step for determining a temporal change in a relative registration shift amount of the toner image on the transfer medium caused by the transfer control pattern, and a drive control pattern for setting a drive control pattern of the transfer medium based on the temporal change in the registration shift amount Setting and controlling the drive of the transfer medium in accordance with the drive control pattern so that the transfer medium is basically the same as the photoconductor. While controlling the driving of the transfer medium, the transfer medium is accelerated or decelerated with respect to the photoconductor in accordance with the separation / contact of the contact means with the transfer medium, and the registration shift accompanying the separation / contact of the contact means is performed. And a correction step for correcting the image quality.