JP2023090135A - Image forming apparatus - Google Patents

Abstract

To prevent image position shift (color shift) on a transfer target material between images on a plurality of image carries, even if the speed ratio of the surface movement speed of the transfer target material to the surface movement speed of the plurality of image carriers is changed.SOLUTION: An image forming apparatus transfers images formed by a plurality of image carriers 5, 6, 7, 8 that make surface movement to be superimposed each other on a transfer target material (for example, intermediate transfer belt 21), and the image forming apparatus has: speed ratio changing means that changes the speed ratio of the surface movement speed of the transfer target material to the surface movement speed of the plurality of image carriers from a reference speed ratio; and transfer timing changing means (for example, control unit 100) that changes the timing to start transfer of an image on at least one image carrier of the plurality of image carriers to the transfer target material from the timing at the reference speed ratio so as to reduce image position shift on the transfer target material between the images on the plurality of image carriers that occurs due to the change of the speed ratio from the reference speed ratio.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, there is known an image forming apparatus that transfers images formed on a plurality of image bearing members that move on the surface so that they overlap each other on a transfer material.

For example, in Patent Document 1, images formed on four photoreceptors (image bearing members) are primarily transferred onto an intermediate transfer member (receiving material) so as to overlap each other, and then transferred onto a sheet (recording material). An image forming apparatus is disclosed in which secondary transfer is performed to form an image. This image forming apparatus can form images at a plurality of image forming speeds by changing the rotational speeds of the four photosensitive members and the intermediate transfer member. When operating at the first image forming speed, this image forming apparatus forms an image on each photosensitive member based on a predetermined writing timing corresponding to this operation. On the other hand, when the image forming apparatus operates at the second image forming speed, the write timing is corrected using the speed ratio of the first image forming speed to the second image forming speed. By performing image formation at this corrected start timing, even when operating at the second image forming speed, there is no image misalignment (color misalignment) on the intermediate transfer member or paper between the images of the four photoreceptors. prevented.

Conventionally, however, the speed ratio of the surface moving speed of a transfer material to the surface moving speed of a plurality of image carriers may be changed. However, there is a problem that it is not possible to suppress image position deviation on the transfer material.

In order to solve this problem, the present invention provides an image forming apparatus for transferring images formed on a plurality of image carriers moving on the surface so as to overlap each other on a transfer material, the image forming apparatus comprising: speed ratio changing means for changing a speed ratio of the surface moving speed of the transfer material to the surface moving speed of the body from a reference speed ratio; and the plurality of image carriers generated by changing the speed ratio from the reference speed ratio. The transfer start timing of the image of at least one image carrier out of the plurality of image carriers to the transfer material so that the image positional deviation on the transfer material between the images is small, and transfer timing changing means for changing from the reference speed ratio.

According to the present invention, even if the speed ratio of the surface moving speed of the transfer material to the surface moving speed of the image carriers is changed, the positional deviation of the image on the transfer material between the images of the plurality of image carriers can be prevented. (color shift) can be suppressed.

1 is a schematic configuration diagram showing main parts of a printer according to an embodiment; FIG. FIG. 10 is an explanatory view showing a state in which an image position shift (color shift) occurs on the intermediate transfer belt between the images on the photoreceptor when the speed ratio of the surface movement speed of the intermediate transfer belt to the surface movement speed of the photoreceptor is changed. FIG. 4 is an explanatory view showing the image position of each main scanning line of the photoreceptor on the intermediate transfer belt before and after changing the same speed ratio; (a) is a timing chart showing the writing start timing of each photoreceptor before correction after changing the surface moving speed of the intermediate transfer belt (after changing the speed ratio). (b) is a timing chart showing the write start timing of each photoreceptor after correction after the surface moving speed of the intermediate transfer belt is changed (after the speed ratio is changed). 4 is a flow chart showing the flow of processing for correcting the write start timing of the photoreceptor in the embodiment. FIG. 5 is an explanatory view showing an example of color matching correction patterns of respective colors formed on the intermediate transfer belt while the intermediate transfer belt is surface-moved at a reference speed;

An embodiment in which the present invention is applied to a printer as an image forming apparatus will be described below.
Note that the printer 50 according to the present embodiment is a so-called tandem-type intermediate transfer belt in which four photosensitive members, which are image bearing members, are arranged along the surface movement direction of an intermediate transfer belt, which is an intermediate transfer member serving as a transfer material. Although it is a transfer type image forming apparatus, the present invention is not limited to this. For example, a direct transfer type image forming apparatus that forms an image by directly transferring images formed on a plurality of photoreceptors (image bearing members) onto a recording material (receiving material) such as recording paper so that they overlap each other. may be

FIG. 1 is a schematic configuration diagram showing main parts of a printer 50 according to this embodiment.
This printer 50 transfers monochromatic images (monochromatic toner images) of four colors (Y, M, C, and K) respectively formed on the surfaces of four photoreceptors 5, 6, 7, and 8 onto the surface of an intermediate transfer belt 21. By superimposing them on top of each other, one page image is formed. Electrostatic latent images are formed on the surfaces of four photoreceptors 5, 6, 7 and 8 by optical writing units 1, 2, 3 and 4 as latent image forming means, respectively. The formed electrostatic latent image is conveyed to a developing area facing developing devices 9, 10, 11 and 12 as developing means as the photoreceptor rotates in the direction of arrow B in the drawing. Developing devices 9, 10, 11 and 12 supply toners of respective colors to the electrostatic latent images on the photoreceptors 5, 6, 7 and 8, respectively, so that each electrostatic latent image is formed into a toner image.

The four photoconductors 5, 6, 7, and 8 are in contact with the belt flat portion of the intermediate transfer belt 21 stretched over a plurality of support rollers, and move in the direction of surface movement (direction of arrow A in the drawing). are arranged side by side. Primary transfer rollers 13, 14, 15, and 16 are opposed to the back side of the intermediate transfer belt in the portions that come into contact with the photoreceptors. Primary transfer high voltage power sources 17 , 18 , 19 are provided to the primary transfer rollers 13 , 14 , 15 , 16 for primary transfer of the toner images on the photoreceptors 5 , 6 , 7 , 8 onto the surface of the intermediate transfer belt 21 . , 20 are connected. The respective color toner images formed on the surfaces of the photoreceptors 5, 6, 7, 8 are superimposed on the surface of the intermediate transfer belt 21 by the respective primary transfer rollers 13, 14, 15, 16, respectively. It is primarily transferred onto the surface of 21 .

The toner image primarily transferred onto the surface of the intermediate transfer belt 21 is conveyed to the secondary transfer area as the surface of the intermediate transfer belt 21 moves. In the secondary transfer area, a secondary transfer facing roller 22 as a support roller is provided on the back side of the intermediate transfer belt 21, and a secondary transfer roller 23 as a transfer member is provided on the front side of the intermediate transfer belt 21. ing. The secondary transfer roller 23 is rotationally driven by a drive motor 23a.

The secondary transfer roller 23 is configured to be able to contact and separate from the surface of the intermediate transfer belt 21 . During the image forming process, as shown in FIG. 1, the intermediate transfer belt 21 and the secondary transfer roller 23 are in contact with each other. , passes through the secondary transfer area while being sandwiched between the intermediate transfer belt 21 and the secondary transfer roller 23 . At this time, the toner image formed on the surface of the intermediate transfer belt 21 is moved by the secondary transfer roller 23 to which the secondary transfer bias is applied by the secondary transfer high-voltage power supply 24 . is secondarily transferred onto the paper 25 conveyed by the . The toner image transferred onto the paper 25 is fixed on the paper by a fixing device, and then the paper 25 as a recording material is discharged outside the machine.

In this embodiment, for example, the diameter of the driving roller 27 that drives the intermediate transfer belt 21 may change due to aging such as wear or environmental changes such as temperature. In such a case, the surface moving speed of the intermediate transfer belt 21 changes from the original surface moving speed, and the surface moving speed of the intermediate transfer belt 21 relative to the surface moving speeds of the four photoreceptors 5, 6, 7, and 8 becomes Speed ratio changes. As a result, in each primary transfer area between the photoreceptors 5, 6, 7, 8 and the intermediate transfer belt 21, the speed difference between the photoreceptor surface moving speed and the intermediate transfer belt surface moving speed changes. Each image on 21 expands and contracts (sub-scanning magnification error).

Specifically, for example, when the roller diameter of the drive roller 27 increases as the temperature rises, the surface moving speed of the intermediate transfer belt 21 increases. Therefore, the surface moving speed of the intermediate transfer belt 21 becomes relatively faster than the moving speed of each image on the photoreceptors 5, 6, 7, 8, and the intermediate transfer belt 21 moves with each image contracted in the sub-scanning direction. 21.

Since the expansion and contraction (sub-scanning magnification error) of each image on the intermediate transfer belt 21 is the same for each image, By changing the speed ratio of the surface moving speed of 21, the sub-scanning magnification error can be suppressed. The speed ratio is changed by changing the surface moving speed of the intermediate transfer belt 21, for example, by changing the number of revolutions of the drive motor 27a that drives the drive roller 27 of the intermediate transfer belt 21. FIG.

Further, for example, the diameter of the secondary transfer roller 23 may change due to aging such as wear or environmental changes such as temperature. In such a case, the transport speed of the paper 25 transported by the secondary transfer roller 23 (the surface moving speed of the paper 25) changes from the original transport speed, and the speed of the paper 25 relative to the surface moving speed of the intermediate transfer belt 21 is reduced. The speed ratio of the surface movement speed changes. As a result, in the secondary transfer area between the intermediate transfer belt 21 and the secondary transfer roller 23, the speed difference between the intermediate transfer belt surface moving speed and the paper surface moving speed changes, and the image on the paper 25 expands and contracts ( sub-scanning magnification error).

Such expansion and contraction of the image on the paper 25 (sub-scanning magnification error) can be corrected by, for example, changing the rotation speed of the drive motor 27a that drives the drive roller 27 of the intermediate transfer belt 21. It can be suppressed by changing the surface movement speed. That is, by changing the surface moving speed of the intermediate transfer belt 21, the speed ratio of the surface moving speed of the intermediate transfer belt 21 to the surface moving speed of the paper 25 changes, and the image on the paper 25 expands and contracts (sub-scanning magnification error) is suppressed. However, in this case, the speed ratio of the surface moving speed of the intermediate transfer belt 21 to the surface moving speed of the photosensitive members 5, 6, 7 and 8 is changed.

Here, as described above, when the speed ratio of the surface moving speed of the intermediate transfer belt 21 to the surface moving speed of the photoreceptors 5, 6, 7, 8 is changed, each of the photoreceptors 5, 6, 7, 8 Image positional deviation (color deviation) occurs on the intermediate transfer belt 21 between images. In the following description, it is assumed that the speed ratio is changed by changing the surface moving speed of the intermediate transfer belt 21 without changing the surface moving speed of the photoreceptors 5, 6, 7 and 8. FIG.

FIG. 2 shows intermediate transfer between images on the photoreceptors 5, 6, 7, and 8 by changing the speed ratio of the surface moving speed of the intermediate transfer belt 21 to the surface moving speed of the photoreceptors 5, 6, 7, and 8. FIG. 8 is an explanatory diagram showing a state in which an image position shift (color shift) occurs on the belt 21;
FIG. 3 shows the image positions of each main scanning line of the photoreceptors 5, 6, 7, and 8 on the intermediate transfer belt 21 before and after changing the speed ratio (images formed so as to overlap each other). FIG. 10 is an explanatory diagram showing a position (for example, the tip position of each image);

Before changing the surface moving speed of the intermediate transfer belt 21 (before changing the speed ratio), that is, when the surface moving speed of the intermediate transfer belt 21 is the reference speed, the intermediate speed shown in the lower part of FIG. As shown in the transfer belt 21, no color misregistration occurs. However, for example, when the surface moving speed of the intermediate transfer belt 21 is changed to be increased (when the speed ratio is changed to be increased), the intermediate transfer belt 21 shown in the upper side of FIG. As a result, color deviation occurs. This is because, with respect to the transfer positions Pm, Pc, and Pk of the photoreceptors 6, 7, and 8 on the downstream side, the photoreceptor 5 on the upstream side of the image leading edges Tm, Tc, and Tk on the photoreceptors 6, 7, and 8 is transferred. , 6 and 7 on the intermediate transfer belt 21 reach first.

Therefore, in the present embodiment, the image of at least one photoreceptor is transferred to the intermediate transfer belt 21 so as to reduce the amount of color misregistration caused by changing the surface moving speed of the intermediate transfer belt 21 (changing the speed ratio). Change (correct) the transfer start timing. Specifically, for example, the writing start timing of the electrostatic latent image by the optical writing units 1, 2, 3, and 4 onto the photoreceptors 5, 6, 7, and 8 (image formation start timing) is relative to the printing start timing. ) is (corrected).

FIGS. 4A and 4B show correction of the writing start timings of the photoreceptors 5, 6, 7, and 8 after changing the surface moving speed of the intermediate transfer belt 21 (after changing the speed ratio). It is a timing chart before and after.
FIG. 4A is a timing chart before correction of write start timing, and FIG. 4B is a timing chart after correction of write start timing.

The timing chart shown in FIG. 4A is before the surface moving speed of the intermediate transfer belt 21 is changed (before the speed ratio is changed), that is, when the surface moving speed of the intermediate transfer belt 21 is the reference speed (said speed ratio is the reference speed ratio). That is, in this timing chart, the write start timings for the respective photoreceptors 5, 6, 7, and 8 with respect to the print start timing are set so that color misregistration occurs when the surface moving speed of the intermediate transfer belt 21 is the reference speed. has been determined.

At this time, if the surface moving speed of the intermediate transfer belt 21 is changed from the reference speed, latent image writing on the photoreceptors 5, 6, 7 and 8 is performed at the writing start timing according to the timing chart of FIG. 4(a). When (image formation) is started, color misregistration occurs as described above. Therefore, in the present embodiment, the photoreceptors 5, 6 are arranged so as to reduce the image position shift (color shift) between the images on the photoreceptors 5, 6, 7, 8 on the intermediate transfer belt 21 caused by this change. , 7 and 8 are changed (corrected).

For example, when the surface moving speed of the intermediate transfer belt 21 is increased (the speed ratio is increased), the writing start timing to each photoreceptor 5, 6, 7, 8 with respect to the print start timing is changed (corrected) to that of the timing chart of FIG. 4(b). As a result, the transfer start timing of each image on the photoreceptors 5, 6, 7, and 8 onto the intermediate transfer belt 21 is advanced, and the transfer on the intermediate transfer belt 21 between the images on the photoreceptors 5, 6, 7, and 8 is advanced. Image misregistration (color misregistration) is reduced or eliminated.

In the present embodiment, the timing to start writing to each photoreceptor 5, 6, 7, 8 is determined based on the print start timing signal. Specifically, based on the print start timing signal, the timing to start writing to the K-color photoconductor 8 is determined, and based on the determined timing to start writing to the K-color photoconductor 8, The write start timing for each of the other photoreceptors 5, 6 and 7 is determined. The writing start timing for each of the other photoreceptors 5, 6 and 7 is the distance between the K-color photoreceptor 8 and each of the other photoreceptors 5, 6 and 7 (between the primary transfer positions of both photoreceptors). distance) can be obtained from Lky, Lkm, Lkc and the process speed (surface moving speed of the photosensitive member).

Then, when the surface moving speed of the intermediate transfer belt 21 is changed from the reference speed, the write start timing (write start timing before correction) of each of the photoreceptors 5, 6, 7, and 8 described above is changed to is multiplied by a correction coefficient corresponding to the speed of each photoreceptor to correct the write start timing of each photoreceptor. That is, the write start timings of the photoreceptors 5, 6, 7 and 8 are corrected according to the following equation (1).
Write start timing after correction=write start timing before correction×correction coefficient (1)

Note that the correction coefficient (adjustment parameter) is, for example, the surface moving speed before change (reference speed) and the surface moving speed after change (changed speed) of the intermediate transfer belt 21, as in the following equation (2). It is calculated from the ratio of
Correction coefficient = 1 ÷ (speed after change ÷ reference speed) (2)

FIG. 5 is a flow chart showing the flow of processing for correcting the writing start timings of the photoreceptors 5, 6, 7, and 8 in this embodiment.
When an image forming instruction (print job) is input, the control unit 100 drives the photoreceptors 5, 6, 7, and 8 at a predetermined surface moving speed, and controls the surface of the intermediate transfer belt 21 to move at a reference speed. Then, the drive motor 27a is controlled to start the image forming operation (S1). At this time, the writing start timings of the photoreceptors 5, 6, 7, and 8 are determined using the reference writing start timing values (timing determination parameters) stored in the storage unit of the control unit 100. FIG.

This reference write start timing value is initially a value calculated from an ideal design value so as not to cause color misregistration. This is the write start timing value corrected by the write start timing correction processing.

When the conditions for executing the reference write start timing correcting process are satisfied, the control section 100 executes the reference write start timing correcting process while the intermediate transfer belt 21 is being surface-moved at the reference speed. In the reference write start timing correction process, first, a pattern image for correcting the reference write start timing (hereinafter referred to as "color matching correction pattern") is formed on the intermediate transfer belt 21 (S2). Then, the color matching correction pattern formed on the intermediate transfer belt 21 is detected by the pattern detection sensor 26 as detection means (S3).

FIG. 6 is an explanatory diagram showing an example of color matching correction patterns TPy, TPm, TPc, and TPk formed on the intermediate transfer belt 21 while the intermediate transfer belt 21 is surface-moved at a reference speed.
The reference K color matching correction pattern TPk is formed by writing at a predetermined reference write start timing (fixed timing). On the other hand, the color matching correction patterns TPy, TPm, and TPc of other colors are arranged on the intermediate transfer belt 21 at regular intervals in the sub-scanning direction according to the value of the reference writing start timing stored in the storage section of the control section 100. is formed to open.

The transfer start timing of the color matching correction patterns TPy, TPm, and TPc of the other color photoconductors 5, 6, and 7 with respect to the color matching correction pattern TPk of the K-color photoconductor 8 serving as a reference onto the intermediate transfer belt 21 (intermediate transfer belt 21) can change over time. For example, an error in the mounting position of each photoreceptor 5, 6, 7, 8 (an error in the distance between the photoreceptors) and an error due to a change in component dimensions due to temperature change, wear, etc. may occur, and this causes a change in the transfer start timing. can. The reference write start timing correction process described above is performed to correct such changes over time.

Based on the detection result of the pattern detection sensor 26 of the color matching correction patterns TPy, TPm, TPc, and TPk formed on the intermediate transfer belt 21, the control unit 100 determines the reference patterns of the photosensitive members 5, 6, and 7 other than the K color. The write start timing value is corrected (S4). Specifically, the control unit 100 sets the intervals between the color matching correction pattern TPk of the K-color photoreceptor 8 and the color matching correction patterns TPy, TPm, and TPc of the corresponding photoreceptors 5, 6, and 7 to prescribed intervals. Calculate the pattern correction values (reference alignment parameters) that can be used. Then, the respective pattern correction values are added to the values of the reference write start timings of the photoreceptors 5, 6, and 7, and the values of the reference write start timings of the photoreceptors 5, 6, and 7 for colors other than K are calculated. make corrections. As a result, even if color misregistration occurs due to changes over time such as errors in the distance between photoreceptors, temperature changes, and errors due to component dimension changes due to wear, etc., the execution of the reference write start timing correction process can The occurrence of misalignment is suppressed.

Here, when a predetermined intermediate transfer belt speed change condition is satisfied, the control unit 100 controls the intermediate transfer belt without changing the surface moving speed of the photoreceptors 5, 6, 7, and 8 (without changing the process speed). The surface moving speed of the belt 21 is changed (Yes in S5). Examples of the predetermined intermediate transfer belt speed change condition include conditions for executing processing for correcting a sub-scanning magnification error such that the length of the formed image in the sub-scanning direction becomes longer or shorter than the original image. be done. In this case, by changing the surface moving speed of the intermediate transfer belt 21 to a speed corresponding to the magnitude of the sub-scanning magnification error, the intermediate transfer belt 21 can , the speed ratio of the surface moving speeds of , is changed, and the image expansion and contraction is corrected.

However, at this time, since the speed ratio of the surface moving speed of the intermediate transfer belt 21 to the surface moving speed of the photoreceptors 5, 6, 7, 8 is changed, as described above, the photoreceptors 5, 6, 7, 8 Image misalignment (color misalignment) occurs on the intermediate transfer belt 21 between the images. In order to suppress this color misregistration, in the present embodiment, the writing start timings of the photoreceptors 5, 6, 7, and 8 are corrected according to the changed surface moving speed of the intermediate transfer belt 21, as described above. A correction coefficient for this is calculated (S6).

After that, the control unit 100 corrects the reference write start timing using the calculated correction coefficient (S7). Then, the control unit 100 drives the photoreceptors 5, 6, 7, and 8 at a predetermined surface moving speed, and controls the drive motor 27a so that the intermediate transfer belt 21 moves at the changed speed, thereby producing an image. A forming operation is started (S8). At this time, the corrected write start timing corrected in the processing step S7 is used as the write start timing for each of the photoreceptors 5, 6, 7, and 8. FIG.

The writing start timing after correction in this embodiment is as shown in the following formula (3-1) for the K color, which is the reference.
Write start timing after correction (K color) =
K-color reference write start timing x correction coefficient (3-1)

Also, the writing start timing after correction for other colors is as shown in the following equations (3-2) to (3-4).
Write start timing after correction (color C) =
(C-color reference write start timing + pattern correction value) x correction coefficient (3-2)
Write start timing after correction (M color) =
(M-color reference write start timing + pattern correction value) x correction coefficient (3-3)
Write start timing after correction (Y color) =
(Y-color reference write start timing + pattern correction value) x correction coefficient (3-4)

In this embodiment, the writing start timing after correction by the correction coefficient is calculated for all the four photoreceptors 5, 6, 7, and 8, but only the post-correction timing for the photoreceptor used for image formation The writing start timing may be calculated. In this case, the processing load on the control unit 100 can be reduced.

What has been described above is only an example, and each of the following aspects has a unique effect.
[First aspect]
In the first mode, each image formed on a plurality of image bearing members (for example, photoreceptors 5, 6, 7, 8) moving on the surface is transferred so as to overlap each other on a transfer material (for example, intermediate transfer belt 21). In an image forming apparatus (e.g., printer 50), speed ratio changing means (e.g., controller 50) for changing the speed ratio of the surface moving speed of the transfer material to the surface moving speed of the plurality of image carriers from a reference speed ratio 100, drive motor 27a) and image position shift (color shift) on the transfer material between the images of the plurality of image carriers caused by changing the speed ratio from the reference speed ratio is reduced. At least one of the plurality of image carriers (e.g., photoreceptors 5, 6, 7, 8) is set to start transferring the image onto the transfer material at the reference speed ratio. It is characterized by having transfer timing changing means (for example, control section 100, optical writing units 1, 2, 3, and 4) for changing from 1 to 1.
Conventionally, there are cases where the speed ratio of the surface moving speed of a transfer material to the surface moving speed of a plurality of image carriers is changed from a reference speed ratio (speed ratio before change). For example, in an image forming apparatus that transfers images formed on a plurality of image bearing members that move on the surface so that they overlap each other on a transfer material, due to various factors, the direction of movement of the surface of the transfer material ( An image elongated or shrunk in the sub-scanning direction) may be formed. Such expansion and contraction of an image is called a sub-scanning magnification error. When such a sub-scanning magnification error occurs, by changing the speed ratio of the surface moving speed of the transfer material to the surface moving speed of the plurality of image carriers from the reference speed ratio, each image carrier can move to the transfer material. It is possible to cancel the sub-scanning magnification error by expanding or contracting the image when the image is transferred to the .
However, if the speed ratio of the surface moving speed of the transfer material to the surface moving speed of the plurality of image carriers is changed from the reference speed ratio in this way, the image position on the transfer material between the images of the plurality of image carriers Misalignment (color deviation) occurs. For example, if the speed ratio is changed to be larger than the reference speed ratio (the speed ratio before change), the image on the image carrier is transferred to the transfer position of the image carrier on the downstream side in the moving direction of the surface of the transfer material. The leading edge of the image transferred from the image bearing member on the upstream side in the moving direction of the surface of the transferred material reaches the leading edge earlier than the leading edge. As a result, image misalignment (color misalignment) occurs between images on a plurality of image carriers.
Therefore, in this aspect, at least one of the plurality of image carriers is arranged so as to reduce the image positional deviation on the transfer material between the images of the plurality of image carriers caused by such a change in the speed ratio. The transfer start timing of an image on one image carrier onto a transfer material is changed from that at the reference speed ratio. As a result, even if the speed ratio of the surface moving speed of the transfer material to the surface moving speed of the plurality of image carriers is changed from the reference speed ratio, the image position on the transfer material between the images of the plurality of image carriers can be maintained. Misregistration (color misregistration) can be suppressed.

[Second aspect]
A second aspect is the first aspect, wherein the speed ratio changing means adjusts the speed ratio so that the amount of expansion and contraction (sub-scanning magnification error) in the surface movement direction of the image transferred onto the transfer material is reduced. is characterized by changing
According to this aspect, even if the speed ratio is changed in order to reduce the amount of expansion and contraction (sub-scanning magnification error) in the surface movement direction of the image transferred onto the transfer material, transfer is started by the transfer timing changing means. Timing is changed to suppress color shift.

[Third aspect]
According to a third aspect, in the first or second aspect, the transfer timing changing means changes the image formation start timing (for example, writing start timing) on the at least one image bearing member to change the image. It is characterized in that the transfer start timing to the transferred material is changed.
According to this, it is possible to change the transfer start timing with a simple configuration.

[Fourth aspect]
According to a fourth aspect, in any one of the first to third aspects, when the speed ratio is a reference speed ratio, the transfer timing changing means changes the image on the transfer material between the images on the plurality of image carriers. determining the transfer start timing of the image of the at least one image carrier onto the transfer material using a reference registration parameter (for example, reference writing start timing) for matching the image positions in the When the speed ratio changing means changes the speed ratio from the reference speed ratio, the at least one image carrier is adjusted using an adjustment parameter (for example, a correction coefficient) corresponding to the surface moving speed of the transferred material after the change. It is characterized by determining the transfer start timing of the image on the transfer material.
According to this, it is possible to change the transfer start timing by simple control.

[Fifth aspect]
In a fifth aspect based on the fourth aspect, the reference registration parameter is a timing determination parameter (reference write start before correction) that determines the transfer start timing of the image of the at least one image carrier onto the transfer material. timing), and the adjustment parameter is a correction coefficient to be multiplied by the reference alignment parameter.
According to this, it is possible to change the transfer start timing by simpler control.

[Sixth aspect]
According to a sixth aspect, in the fourth or fifth aspect, the transfer timing changing means, when the speed ratio changing means changes the speed ratio from the reference speed ratio, transfers the image from the at least one image carrier. The transfer start timing is determined for an image carrier used for image formation, and the transfer start timing is not determined for an image carrier not used for image formation.
According to this, it is possible to reduce the load of processing performed by the transfer timing changing means by not determining the transfer start timing for unnecessary image carriers.

[Seventh aspect]
A seventh aspect is any one of the first to sixth aspects, wherein the at least one image carrier is a reference image carrier (for example, the K-color photoreceptor 8) among the plurality of image carriers. ) (for example, photoreceptors 5, 6 and 7 other than those for K color).
According to this, it is possible to change the transfer start timing by simpler control.

1 to 4: optical writing units 5 to 8: photoreceptors 9 to 12: developing devices 13 to 16: primary transfer rollers 17 to 20: primary transfer high voltage power supply 21: intermediate transfer belt 22: secondary transfer counter roller 23: two Secondary transfer roller 23a: Drive motor 24: Secondary transfer high-voltage power supply 25: Paper 26: Pattern detection sensor 27: Drive roller 27a: Drive motor 50: Printer 100: Controller TPy, TPm, TPc, TPk: Color matching correction pattern

JP 2017-203938 A

Claims (7)

An image forming apparatus for transferring images formed on a plurality of image carriers moving on the surface so as to overlap each other on a transfer material,
speed ratio changing means for changing a speed ratio of the surface moving speed of the transfer material to the surface moving speed of the plurality of image carriers from a reference speed ratio;
the speed ratio is changed from the reference speed ratio so that an image position shift on the transfer material between the images on the plurality of image carriers is reduced; and transfer timing changing means for changing the transfer start timing of the image on at least one image carrier onto the transfer material from that at the reference speed ratio. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the speed ratio changing means changes the speed ratio so that the amount of expansion and contraction of the image transferred onto the transfer material in the direction of surface movement is reduced. The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the transfer timing changing means changes the timing to start transferring the image onto the transfer material by changing the timing to start forming the image onto the at least one image carrier. . The image forming apparatus according to any one of claims 1 to 3,
The transfer timing changing means, when the speed ratio is the reference speed ratio, sets a reference registration parameter for matching the image positions on the transfer material between the images of the plurality of image carriers. is used to determine the transfer start timing of the image on the at least one image carrier onto the transfer material, and when the speed ratio changing means changes the speed ratio from the reference speed ratio, the transfer target after the change 1. An image forming apparatus, wherein an adjustment parameter corresponding to a surface moving speed of a transfer material is used to determine timing for starting transfer of an image on said at least one image bearing member to said transfer material. In the image forming apparatus according to claim 4,
The reference alignment parameter is an addition value to be added to a timing determination parameter for determining the timing of starting transfer of the image of the at least one image carrier onto the transfer material,
The image forming apparatus, wherein the adjustment parameter is a correction coefficient to be multiplied by the reference alignment parameter. The image forming apparatus according to claim 4 or 5,
The transfer timing changing means, when the speed ratio changing means changes the speed ratio from the reference speed ratio, changes the transfer start timing for the image carrier used for image formation among the at least one image carrier. is determined, and the transfer start timing is not determined for an image carrier that is not used for image formation. The image forming apparatus according to any one of claims 1 to 6,
The image forming apparatus, wherein the at least one image carrier is all of the plurality of image carriers except for one reference image carrier.

Images