Image forming apparatus

Abstract

To provide a color shift correction technique in consideration of variation in frictional force between a photoreceptor and an intermediate transfer body.SOLUTION: The image forming apparatus includes an image forming unit configured to form an image based on a print job on a sheet by forming images with toners of different colors on a plurality of photoconductors that are rotationally driven, respectively, and transferring the images formed on the plurality of photoconductors to the sheet via an intermediate transfer member that is rotationally driven, a detection unit configured to detect the image formed on the intermediate transfer member, and a control unit configured to control the image forming unit to form adjustment images of the plurality of colors on the intermediate transfer member. And a control unit configured to perform correction processing of determining a correction value of a formation timing of an image of a first color among the plurality of colors on the photosensitive member based on a detection timing of the adjustment image of each of the plurality of colors by the detection unit, wherein the control unit changes the correction value depending on whether a first mode of forming a first additional image on the intermediate transfer member in addition to a user image is selected when the user image based on a print job is formed on a sheet.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to color misregistration correction technology for image forming apparatuses. [Background Art]

[0002] An electrophotographic image forming apparatus forms a toner image on a photoconductor that serves as an image bearing member, and transfers the image formed on the photoconductor onto a sheet directly or via an intermediate transfer member. In an image forming apparatus using an intermediate transfer member, the amount of toner present between the photoconductor and the intermediate transfer member fluctuates during image formation. If the frictional force between the photoconductor and the intermediate transfer member fluctuates due to this fluctuation in the toner amount, the relative speed between the photoconductor and the intermediate transfer member fluctuates, which may cause color misregistration.

[0003] Patent Document 1 discloses a configuration that suppresses color misregistration caused by this fluctuation in frictional force. According to Patent Document 1, fluctuation in frictional force is suppressed by supplying toner to the intermediate transfer member to keep the amount of toner present between the photoconductor and the intermediate transfer member at or above a predetermined amount. [Prior Art Literature] [Patent Literature]

[0004] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2008-164950 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] In an image forming apparatus, color misregistration may also occur due to aged deterioration of the image forming apparatus, temperature rise of the image forming apparatus, and the like. For this reason, the image forming apparatus performs so-called color misregistration correction processing, in which, for example, an adjustment pattern including adjustment images of each color is formed on the intermediate transfer member, and the position of each color adjustment image is detected to determine a correction value for the timing of forming each color image on the photoconductor.

[0006] Patent Document 1 discloses a configuration that suppresses fluctuations in frictional force between a photoreceptor and an intermediate transfer material, but it does not disclose a color shift correction process that takes into account fluctuations in frictional force between the photoreceptor and the intermediate transfer material.

[0007] This invention provides a color shift correction technique that takes into account fluctuations in the frictional force between the photoreceptor and the intermediate transfer material. [Means for solving the problem]

[0008] According to one aspect of the present invention, an image forming apparatus that forms an image using toners of multiple colors, comprising: an image forming means for forming an image with toners of different colors on each of a plurality of rotationally driven photoreceptors, and transferring the images formed on each of the plurality of photoreceptors to a sheet via a rotationally driven intermediate transfer body to form a user image based on a print job on the sheet; a detection means for detecting the image formed on the intermediate transfer body; and a control means for controlling the image forming means to form adjustment images of each of the plurality of colors on the intermediate transfer body, and for performing a correction process to determine a correction value for the timing of forming the image of the first color among the plurality of colors on the photoreceptor based on the detection timing of the adjustment images of each of the plurality of colors by the detection means, wherein the control means, when forming the user image based on the print job on the sheet, in addition to the user image to suppress fluctuations in frictional force between the plurality of photoreceptors and the intermediate transfer body A first mode is selected in which a first additional image is formed on the intermediate transfer body. The absolute value of the correction value in this case is made greater than the absolute value of the correction value when the second mode is selected in which the first additional image is not formed on the intermediate transfer body. . [Effects of the Invention]

[0009] According to the present invention, color shift correction can be performed while taking into account fluctuations in the frictional force between the photoreceptor and the intermediate transfer material. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic diagram of an image forming apparatus according to several embodiments. [Figure 2] Block diagrams of image forming apparatus according to several embodiments. [Figure 3]This figure shows an example of an image formed on an intermediate transfer medium in the first mode. [Figure 4] A diagram showing an example of a modification pattern formed in the intermediate transfer. [Figure 5] A flowchart of a color shift correction process according to one embodiment. [Figure 6] An explanatory diagram of a color shift correction process according to one embodiment. [Figure 7] An explanatory diagram of a color shift correction process according to one embodiment. [Figure 8] A figure showing examples of additional images and adjustment patterns formed on an intermediate transfer medium. [Figure 9] A flowchart of a color shift correction process according to one embodiment. [Figure 10] A flowchart of a color shift correction process according to one embodiment. [Figure 11] A diagram illustrating an example of the relationship between evaluation values ​​and correction values. [Figure 12] A flowchart of an image formation process according to one embodiment. [Modes for carrying out the invention]

[0011] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0012] <First Embodiment> Figure 1(A) is a schematic cross-sectional view of the image forming apparatus 201 according to this embodiment. In Figure 1(A), the reference numerals of the components involved in the formation of images using yellow, magenta, cyan, and black toners (hereinafter, images using toners will also be referred to as toner images) are suffixed with the letters Y, M, C, and K. However, if it is not necessary to distinguish the colors of the images that the components are involved in forming, the reference numerals are used generically with the suffix omitted.

[0013] During image formation, the photoconductor 5 is rotationally driven in the clockwise direction shown in the figure. The charging roller 7 charges the photoconductor 5 to a predetermined potential. The exposure device 10 exposes the photoconductor 5 to form an electrostatic latent image on the photoconductor 5. The developing device 8 develops the electrostatic latent image on the photoconductor 5 with toner to form a toner image on the photoconductor 5. The primary transfer roller 4 transfers the toner image from the photoconductor 5 onto the intermediate transfer member 12 by outputting a primary transfer voltage. In the following description, the region where the toner image on the photoconductor 5 is transferred onto the intermediate transfer member 12 is referred to as a primary transfer region. The primary transfer region is defined for each of the photoconductors 5Y, 5M, 5C and 5K. During image formation, the intermediate transfer member 12 is rotationally driven in the counterclockwise direction shown in the figure by the driving roller 11. By overlapping and transferring the toner images from each photoconductor 5 onto the intermediate transfer member 12, colors different from yellow, magenta, cyan and black can be reproduced.

[0014] The toner image transferred onto the intermediate transfer member 12 is conveyed to a position facing the secondary transfer roller 9 by the rotation of the intermediate transfer member 12. The secondary transfer roller 9 transfers the toner image from the intermediate transfer member 12 onto the sheet 2 conveyed along the conveyance path from the cassette 1 by outputting a secondary transfer voltage. In the following description, the region where the toner image on the intermediate transfer member 12 is transferred onto the sheet 2 is referred to as a secondary transfer region. The fixing device 13 heats and pressurizes the sheet 2 onto which the toner image has been transferred, thereby fixing the toner image onto the sheet 2. After the toner image is fixed, the sheet 2 is discharged onto the tray 27 by the discharge roller 31. The sensor 50 detects an adjustment pattern for color misregistration correction formed on the intermediate transfer member 12.

[0015] In order to increase primary transfer efficiency, the image forming apparatus 201 may be configured such that the moving speed of the surface of the intermediate transfer member 12 is higher than the moving speed of the surface of the photoconductor 5 by about several percent. In this case, due to the frictional force between the intermediate transfer member 12 and the photoconductor 5, the intermediate transfer member 12 applies a force in the rotational direction of the photoconductor 5 to the photoconductor 5 during image formation.

[0016] FIG. 1B shows a configuration example of the sensor 50. The light-emitting element 51 irradiates light toward the intermediate transfer member 12. The light-emitting element 51 is, for example, a light-emitting diode (LED). The light-receiving element 52a and the light-receiving element 52b receive reflected light emitted by the light-emitting element 51 and reflected by the intermediate transfer member 12 or the toner 61 thereon. The light-receiving elements 52a and 52b are, for example, photodiodes. The light-receiving element 52a is arranged so as to mainly receive reflected light that is specularly reflected by the intermediate transfer member 12 or the toner 61. The light-receiving element 52b is arranged so as not to receive the reflected light that is specularly reflected by the intermediate transfer member 12 or the toner 61, and to receive diffusely reflected light.

[0017] FIG. 2 shows a control configuration of the image forming apparatus 201. The image forming section 260 in FIG. 2 is a general term for members for forming an image on a sheet 2 described with reference to FIG. 1. The controller 202 controls the entire image forming apparatus 201. When the controller 202 receives a print job from the host computer 200 via a network, it causes an engine control section 204 to perform image formation control based on the print job. A processing section 220 of the engine control section 204 controls the image forming section 260 based on image data included in the print job to form an image on the sheet 2. In the following description, an image indicated by the image data included in the print job is referred to as a "user image".

[0018] In the present embodiment, the image forming apparatus 201 operates in a first mode or a second mode. The first mode is a mode in which a "first additional image" described later is formed on the intermediate transfer member 12 together with a user image based on a print job. The second mode is a mode in which only a user image based on a print job is formed on the intermediate transfer member 12. The first additional image is formed to suppress fluctuation in frictional force between the photoconductor 5 and the intermediate transfer member 12.

[0019] Figure 3 shows the state in which a user image (letters A, B, C) and a first additional image have been formed on the intermediate transfer body 12. The region 500 in Figure 3 is the region that comes into contact with the sheet 2, that is, the region where the transfer to the sheet 2 takes place, and will be referred to as the "sheet region" below. Images formed in regions of the surface area of ​​the intermediate transfer body 12 that are different from the sheet region 500 are not transferred to the sheet 2, and will therefore be referred to as the "non-sheet region" below.

[0020] The shading within the sheet region 500 in Figure 3 represents the first additional image. In Figure 3, the first additional image is formed over the entire sheet region 500, but it may also be configured to form the first additional image only in the non-sheet region. Furthermore, it may also be configured to form the first additional image in both the sheet region 500 and the non-sheet region. In addition, although the first additional image is formed over the entire sheet region 500 in Figure 3, when the first additional image is formed within the sheet region 500, it may also be configured to form the first additional image only in a portion of the sheet region 500, rather than over the entire sheet region 500. Furthermore, when the first additional image is formed in the non-sheet region, it may also be configured to form the first additional image only in a portion of the non-sheet region.

[0021] The first additional image formed within the sheet area 500 is transferred to sheet 2. Therefore, the first additional image formed in the sheet area 500 can be a dot image (a dot image) in which small dots of a color that is difficult for humans to see are dispersed. For example, the first additional image may be an image in which small dots are arranged at predetermined intervals. Also, when forming the first additional image within the sheet area 500, the first additional image can be formed using yellow toner, which has the lowest human visibility among the four colors used for image formation. Since the first additional image formed in the non-sheet area is not transferred to sheet 2, the first additional image formed in the non-sheet area can be any image of any color.

[0022] Furthermore, as shown in Figure 1, in the rotational direction of the intermediate transfer body 12, the photoreceptor 5Y has the greatest distance from the primary transfer region to the secondary transfer region. Therefore, when the first additional image is transferred from the photoreceptor 5Y to the intermediate transfer body 12, the first additional image reaches the secondary transfer region via the primary transfer regions of each of the other photoreceptors 5. Consequently, the toner supplied from the photoreceptor 5Y to the intermediate transfer body 12 works to suppress fluctuations in frictional force between the other photoreceptors 5 and the intermediate transfer body 12. For this reason, regardless of its formation region, the first additional image can be formed on the photoreceptor 5 that transfers the image to the intermediate transfer body 12 in the primary transfer region that has the greatest distance to the secondary transfer region in the rotational direction of the intermediate transfer body 12.

[0023] In the first mode, the image data of the first additional image to be formed on the intermediate transfer body 12 is stored in the engine control unit 204 in advance. It is also possible to store multiple types of image data of the first additional image in the engine control unit 204, rather than storing only one type of image data. When operating in the first mode, the engine control unit 204 can select the type of first additional image to be formed on the intermediate transfer body 12, for example, according to the content of the user image or the size of the sheet 2.

[0024] When performing color shift correction processing, the processing unit 220 forms the adjustment pattern 60 shown in Figure 4 on the intermediate transfer body 12. The image data of the adjustment pattern 60 is stored in the engine control unit 204 in advance. The adjustment pattern 60 includes adjustment images for black, cyan, magenta, and yellow. The adjustment images are, for example, single-tone patch images. In Figure 4, the letters K, C, M, and Y written below the patch images (adjustment images) indicate that the colors of the adjustment images are black, cyan, magenta, and yellow. Since the way light is reflected on the surface of the intermediate transfer body 12 and the way light is reflected in the adjustment images are different, the sensor 50 can detect each adjustment image based on the change in the amount of light received by the light receiving element 52a or 52b.

[0025] The correction unit 210 can determine the formation position of each color adjustment image on the intermediate transfer body 12 in the rotational direction of the intermediate transfer body 12, based on the detection results of the sensor 50, that is, the detection timing of the adjustment images of each color. Therefore, the correction unit 210 can determine the amount of color shift of the cyan, magenta, and yellow images relative to the black image, which is the reference color in this example. The correction unit 210 can determine a reference correction value for each of cyan, magenta, and yellow to reduce the color shift detected in the adjustment pattern 60. The reference correction value for a certain color is used to correct the formation timing of forming the image of that color on the photoreceptor 5, or more specifically, the formation timing of forming the electrostatic latent image for that color on the photoreceptor 5.

[0026] Figure 5 is a flowchart of the color shift correction process performed by the engine control unit 204. In S10, the processing unit 220 forms the adjustment pattern 60 on the intermediate transfer body 12. In S11, the correction unit 210 obtains the detection result of the adjustment pattern 60 from the sensor 50, that is, the detection timing of the adjustment images for black, cyan, magenta, and yellow. In S12, the correction unit 210 determines the reference correction value for each color based on the detection result. In S13, the correction unit 210 determines and saves the correction value for each color in the first mode and the correction value for each color in the second mode based on the reference correction value.

[0027] The following explains why different correction values ​​are used in the first and second modes. In this embodiment, the moving speed of the surface of the intermediate transfer body 12 is faster than the moving speed of the surface of the photoreceptor 5, and as a result, the intermediate transfer body 12 exerts a force on the photoreceptor 5 in a direction that rotates the photoreceptor 5. This force becomes a load on the drive roller 11 that rotates the intermediate transfer body 12. Here, when toner is supplied between the photoreceptor 5 and the intermediate transfer body 12 at the start of image formation, the frictional force between the photoreceptor 5 and the intermediate transfer body 12 decreases, and therefore the load on the drive roller 11 also decreases.

[0028] Figure 6(A) shows an example of the time change in the torque of the drive roller 11 when image formation begins. As the transfer of the yellow toner image formed on the photoreceptor 5Y to the intermediate transfer body 12 begins, the load on the drive roller 11 decreases over time, and therefore the torque of the drive roller 11 also decreases over time. This decrease in torque continues until the amount of toner between the photoreceptor 5 and the intermediate transfer body 12 exceeds a predetermined amount.

[0029] Generally, the smaller the torque of the drive roller 11, the greater the amount of slip of the intermediate transfer body 12 relative to the photoreceptor 5. Due to this slip, the position of the toner transferred from the photoreceptor 5 to the intermediate transfer body 12 moves backward in the direction of movement of the surface of the intermediate transfer body 12. This backward movement increases as the amount of slip increases.

[0030] On the other hand, since the amount of toner in the adjustment pattern 60 formed on the intermediate transfer body 12 during the color shift correction process is small, there is almost no slippage of the intermediate transfer body 12 relative to the photoreceptor 5 during the color shift correction process. Therefore, the reference correction value obtained based on the detection result of the adjustment pattern 60 during the color shift correction process corrects the color shift in a state where there is almost no slippage of the intermediate transfer body 12.

[0031] Figure 6(B) shows the amount of yellow color shift when the timing of image formation on the photoreceptor 5, or more specifically, the timing of electrostatic latent image formation on the photoreceptor 5, is corrected based on a reference correction value and the image is formed in the second mode. In Figure 6(B) and similar figures, the amount of color shift is indicated with a sign to show the direction of the color shift (whether or not it is a shift towards the front with respect to the sheet transport direction). However, since the absolute value of the color shift is important, in the following explanation, unless it is clear from the context that a value with a distinguished sign is intended, or unless otherwise specified, "amount of color shift" will mean its absolute value. The horizontal axis in Figure 6(B) shows the position along the transport direction from the leading edge of the sheet 2 in the transport direction.

[0032] As toner is supplied to the intermediate transfer body 12 upon the start of image formation, the torque of the drive roller 11 decreases over time, as shown in Figure 6(A). As a result, the amount of slip of the intermediate transfer body 12 increases over time, and the amount of yellow color shift changes along the transport direction of the sheet 2. At the timing when the transfer of the black image to the intermediate transfer body 12 begins, the torque fluctuation of the intermediate transfer body 12 is small because yellow toner is being supplied to the intermediate transfer body 12. Therefore, by performing correction based on the reference correction value, the amount of yellow color shift at the rear end of the sheet 2 becomes approximately 0, and the amount of color shift increases towards the front end of the sheet 2.

[0033] Therefore, in this embodiment, the second adjustment value for each color is predetermined and stored in the engine control unit 204 based on the toner amount of the adjustment pattern 60 and the average toner amount used to form the user image. The correction unit 210 then uses the second adjustment value added to the reference correction value for each color as the correction value for the second mode. For example, the correction value for yellow in the second mode is the reference correction value for yellow plus the second adjustment value for yellow.

[0034] Figure 6(C) shows the amount of yellow color shift when an image is formed in second mode, based on a correction value obtained by setting the second adjustment value for yellow to 30 μm. The graph in Figure 6(C) corresponds to the graph in Figure 6(B) shifted upward by 30 μm, which is the second adjustment value. When color shift correction is performed using only the reference correction value, the maximum value of the color shift was approximately 90 μm, whereas by correcting the reference correction value based on the second adjustment value, the maximum value of the color shift is reduced to approximately 60 μm.

[0035] Here, as shown in Figure 6(C), in the second mode, a color shift remains that changes depending on the position of the sheet 2 in the transport direction. In order to suppress this color shift that changes depending on the position of the sheet 2 in the transport direction, in the first mode, as described above, the first additional image is formed on the intermediate transfer body 12.

[0036] Figure 7(A) shows an example of the time change of the torque of the drive roller 11 when an image is formed in the first mode. In the first mode, toner is supplied between the photoreceptor 5 and the intermediate transfer body 12 from an early stage of image formation by the first additional image, so the situation in which the torque decreases over time, as shown in Figure 6(A), is improved.

[0037] Figure 7(B) shows the amount of yellow color shift when an image is formed in the first mode after correction based on the correction values ​​for the second mode described above. In Figure 7(B), unlike Figure 6(C), the amount of color shift is approximately constant regardless of the position in the transport direction of the sheet 2. However, a color shift of approximately 60 μm occurs, the same as at the leading edge of the sheet in Figure 6(C). Thus, if the same correction values ​​as in the second mode are used in the first mode, a steady-state color shift remains. For this reason, in this embodiment, the first adjustment value for each color is determined in advance based on the toner amount of the adjustment pattern 60 and the average toner amount used to form the user image and the first additional image, and stored in the engine control unit 204. The correction unit 210 then uses the first adjustment value added to the reference correction value for each color as the correction value for the first mode. For example, the correction value for yellow in the first mode is the reference correction value for yellow plus the first adjustment value for yellow.

[0038] Figure 7(C) shows the amount of yellow color shift when an image is formed in the first mode, based on a correction value obtained by setting the first adjustment value for yellow to 90 μm (adding 60 μm to the second adjustment value of 30 μm). The graph in Figure 7(C) corresponds to the graph in Figure 7(B) shifted upward by 60 μm, which is the difference between the first and second adjustment values. In Figure 7(C), the amount of yellow color shift is approximately 0 regardless of the position in the sheet transport direction.

[0039] As described above, the image forming apparatus 201 of this embodiment operates in either a first mode or a second mode based on user settings. The first mode is a mode in which, when forming an image based on a print job, a first additional image is formed on the intermediate transfer body 12 in addition to the user image, and the second mode is a mode in which the first additional image is not formed on the intermediate transfer body 12. As shown in Figure 7(C), the first mode is also a mode that can suppress the amount of color misalignment over the entire sheet transport direction, and the second mode is also a mode that can suppress toner consumption.

[0040] The engine control unit 204 can determine the amount of color shift of the first color adjustment image relative to the second color adjustment image based on the detection timing of the adjustment images for each color in the color shift correction process. In this example, the second color is black and is also called the reference color. The first color is a color other than the second color, and in this example, it is yellow, cyan, and magenta. The engine control unit 204 then determines a correction value for the formation timing of the first color image on the photoreceptor 5 in order to reduce the amount of color shift of the first color image relative to the second color image. Here, the engine control unit 204 makes the correction value in the first mode different from the correction value in the second mode. With this configuration, in the first mode, the amount of color shift can be reduced over the entire sheet transport direction. In the second mode, although the amount of color shift changes along the sheet transport direction, its maximum value can be reduced.

[0041] As explained in Figures 6 and 7, the absolute value of the correction value when the first mode is selected is greater than the absolute value of the correction value when the second mode is selected. More specifically, the engine control unit 204 determines the reference correction value for the first color based on the detection timing of the adjustment images for each color. The reference correction value for the first color suppresses the color misalignment that occurred in the adjustment image of the first color during the color misalignment correction process; in other words, it suppresses the color misalignment when the amount of toner supplied to the intermediate transfer body 12 is small. The engine control unit 204 then uses the value obtained by adding the first adjustment value to the reference correction value as the correction value when the first mode is selected, and the value obtained by adding the second adjustment value to the reference correction value as the correction value when the second mode is selected.

[0042] <Second Embodiment> Next, the second embodiment will be described, focusing on the differences from the first embodiment. In the first embodiment, the first and second adjustment values ​​were determined in advance. Here, the first and second adjustment values ​​were values ​​used to reflect the effect of slippage of the intermediate transfer body 12 in the standard correction value, which did not reflect the effect of slippage of the intermediate transfer body 12. However, the frictional force between the intermediate transfer body 12 and the photoreceptor 5 may differ from one intermediate transfer body 12 to another. Therefore, if the frictional force between the intermediate transfer body 12 and the photoreceptor 5 differs from one individual to another, the amount of residual color shift may be large with the first and second adjustment values ​​determined in advance.

[0043] Therefore, in this embodiment, the engine control unit 204 performs a second process of forming only the adjustment pattern 60 shown in Figure 4 on the intermediate transfer body 12 and determining the correction value, and a first process of forming a second additional image on the intermediate transfer body in addition to the adjustment pattern 60 and determining the correction value. Figure 8 shows the state in which the adjustment pattern 60 and the second additional image are formed on the intermediate transfer body 12 in the first process. The second additional image is formed in the width direction perpendicular to the movement direction (rotation direction) of the surface of the intermediate transfer body 12, in a range where the adjustment pattern 60 is not formed. This is to prevent a decrease in the detection accuracy of the adjustment pattern 60 by the sensor 50. The second additional image is formed on the photoreceptor 5Y that constitutes the primary transfer region, which is the furthest distance along the rotation direction of the intermediate transfer body 12 to the secondary transfer region, similar to the first additional image. The pattern of the second additional image is determined so that the toner supplied to the intermediate transfer body 12 by the second additional image quickly reduces the driving torque of the drive roller 11, thereby reducing fluctuations in the driving torque (see Figure 6(A)). The image data of the second additional image is also stored in the engine control unit 204 in advance.

[0044] Figure 9 is a flowchart of the color shift correction process performed by the engine control unit 204. In S20, the processing unit 220 forms the adjustment pattern 60 and the second additional image on the intermediate transfer body 12. In S21, the correction unit 210 obtains the detection result of the adjustment pattern 60 from the sensor 50, that is, the detection timing of the adjustment images for black, cyan, magenta, and yellow. In S22, the correction unit 210 determines the first correction value for each color based on the detection result. The first correction value is a correction value to suppress the color shift that occurred in the adjustment image when the adjustment pattern 60 and the second additional image were formed on the intermediate transfer body 12. Note that S20 to S22 correspond to the first process. In S23, the correction unit 210 forms only the adjustment pattern 60 on the intermediate transfer body 12. In S24, the correction unit 210 obtains the detection result of the adjustment pattern 60 from the sensor 50, that is, the detection timing of the adjustment images for black, cyan, magenta, and yellow. In S25, the correction unit 210 determines a second correction value based on the detection result in S24. The second correction value is a correction value to suppress the color shift that occurred in the adjustment image when only the adjustment pattern 60 was formed on the intermediate transfer body 12. Note that S23 to S25 correspond to the second processing.

[0045] In S26, the correction unit 210 determines the correction values ​​to be used in the first mode and the correction values ​​to be used in the second mode for each color, based on the first correction value and the second correction value. Since the adjustment pattern 60 and the second additional image are formed in the first processing, the torque change of the drive roller 11 can be considered to be the same as when the image is formed in the first mode. Therefore, in this embodiment, the correction value used in the first mode is the first correction value or a value based on the first correction value.

[0046] Furthermore, the second correction value is the reference correction value of the first embodiment, and because the amount of toner in adjustment pattern 60 is small, using the second correction value in the second mode results in a large amount of color shift, as shown in Figure 6(B). For this reason, in this embodiment, the correction value used in the second mode is set to a value between the first correction value and the second correction value.

[0047] Specifically, the correction value used in the second mode is the sum of the value obtained by multiplying the first correction value by the coefficient α and the value obtained by multiplying the second correction value by the coefficient β. Note that both coefficients α and β are greater than 0 and less than 1, and their sum is 1. For example, if α = β = 0.5, then the correction value in the second mode will be the average of the first and second correction values.

[0048] The values ​​of α and β are predetermined and stored in the engine control unit 204 based on, for example, the toner amount of the adjustment pattern 60, the toner amount of the second additional image formed in S20, and the average toner amount of the user image. Alternatively, the values ​​of α and β are determined experimentally and stored in the engine control unit 204.

[0049] In this embodiment, the correction values ​​for the first and second modes are determined by performing a first process of forming a second additional image and determining the first correction value, and a second process of determining the second correction value without forming a second additional image. This makes it possible to suppress the amount of color shift remaining due to individual differences in the intermediate transfer body 12. In the case of an image forming apparatus that performs image formation only in the first mode, only the first process needs to be performed.

[0050] Furthermore, in this embodiment, the first correction value was used as the correction value in the first mode. However, if the average amount of toner in the user image is less than the total amount of toner in the second additional image and the adjustment pattern 60, the correction value for the first mode can also be determined in the same way as the correction value for the second mode, using the first correction value, the second correction value, coefficient α, and coefficient β. Note that the coefficient α multiplied by the first correction value to determine the correction value for the first mode is made larger than the coefficient α multiplied by the first correction value to determine the correction value for the second mode.

[0051] <Third Embodiment> Next, the third embodiment will be described, focusing on the differences from the first and second embodiments. In the first and second embodiments, the color shift correction process determined the correction value for the first mode and the correction value for the second mode individually. In this embodiment, the color shift correction process generates correction information showing the relationship between the evaluated value of the amount of toner supplied to the intermediate transfer body 12 and the correction value. Then, when forming the user image, the correction value to be used in image formation is determined based on the evaluated value of the amount of toner of the image to be formed on the intermediate transfer body 12 and the correction information. In this embodiment as well, when forming the user image on the sheet 2, a first additional image can be formed on the intermediate transfer body 12 in addition to the user image.

[0052] The evaluation value for the toner amount of the image is a value that evaluates the total amount of toner of each color supplied to the intermediate transfer body 12 by forming the image on the intermediate transfer body 12. For example, the evaluation value for the toner amount of the image can be determined based on the pixel value of each pixel shown in the image data used to form the image. Alternatively, the evaluation value for the toner amount of the image can be the amount of toner supplied to the intermediate transfer body 12 by forming the image on the intermediate transfer body 12 divided by a predetermined toner amount. The predetermined toner amount may be, for example, the amount of toner supplied to the intermediate transfer body 12 by forming a solid image of a predetermined area on the intermediate transfer body 12. The predetermined area may be, for example, the area of ​​a rectangle where the length in the direction of movement of the surface of the intermediate transfer body 12 is the same as the length of the sheet, and the length in the direction perpendicular to the direction of movement of the surface of the intermediate transfer body 12 is the same as the length of the intermediate transfer body 12 in that direction.

[0053] Figure 10 is a flowchart of the color shift correction process performed by the engine control unit 204. In S30, the processing unit 220 forms the adjustment pattern 60 and the second additional image on the intermediate transfer body 12. In S31, the engine control unit 204 determines a first evaluation value, which is an evaluation value of the toner amount of the combined image of the adjustment pattern 60 and the second additional image. In S32, the correction unit 210 obtains the detection result of the adjustment pattern 60 from the sensor 50, that is, the detection timing of the adjustment images for black, cyan, magenta, and yellow. In S33, the correction unit 210 determines a first correction value based on the detection result in S32. The first correction value is the same as in the second embodiment.

[0054] In S34, the processing unit 220 forms only the adjustment pattern 60 on the intermediate transfer body 12. In S35, the engine control unit 204 determines a second evaluation value, which is an evaluation value of the toner amount of the adjustment pattern 60. In S36, the correction unit 210 obtains the detection result of the adjustment pattern 60 from the sensor 50, that is, the detection timing of the adjustment images for black, cyan, magenta, and yellow. In S37, the correction unit 210 determines a second correction value based on the detection result in S36. The second correction value is the same as in the second embodiment.

[0055] In S38, the correction unit 210 determines the relationship between the evaluation value and the correction value based on the first evaluation value and the first correction value, and the second evaluation value and the second correction value, and generates correction information. Note that the amount of slip does not change whether the amount of toner in the intermediate transfer body 12 falls below a predetermined amount or exceeds a predetermined amount, so the correction value indicated by the correction information may be configured to have a lower limit and an upper limit. Figure 11 shows an example of the correction information obtained by the correction unit 210 in S38. According to Figure 11, the correction value when the evaluation value is P1 is the lower limit C1, the correction value when the evaluation value is P2 is the upper limit C2, and in the range of evaluation values ​​from P1 to P2, the correction value increases linearly with increasing evaluation value.

[0056] Figure 12 is a flowchart of the processes executed by the processing unit 220 when a user image is formed on sheet 2. In S40, the processing unit 220 determines the evaluation value of the toner amount of the image to be transferred to the intermediate transfer medium. If the first additional image is not formed, the processing unit 220 determines the evaluation value based on the image data of the user image. If the first additional image is formed, the processing unit 220 determines the evaluation value based on the image data that forms both the user image and the first additional image. In S41, the processing unit 220 determines a correction value by referring to correction information based on the evaluation value determined in S40. In S42, the processing unit 220 forms the image based on the correction value determined in S41.

[0057] Based on the correction information and the evaluation value of the toner amount of the image formed on the intermediate transfer body 12 when forming the user image, the correction value to be used in image formation is determined. With this configuration, the optimal correction value can be determined for each image formation.

[0058] [Other embodiments] The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0059] This embodiment includes the following configuration. (Composition 1) An image forming apparatus that performs image formation using multiple colors of toner, Image forming means for forming images on a sheet based on a print job by forming images with different colored toners on each of a plurality of rotating photoreceptors, and transferring the images formed on each of the plurality of photoreceptors to a sheet via a rotating intermediate transfer body, A detection means for detecting an image formed on the intermediate transfer medium, Control means for controlling the image forming means to form adjustment images for each of the multiple colors on the intermediate transfer medium, and for performing a correction process to determine a correction value for the timing of forming the image of the first color among the multiple colors on the photoreceptor based on the detection timing of each of the multiple color adjustment images by the detection means, Equipped with, The control means varies the correction value depending on whether a first mode is selected in which a first additional image is formed on the intermediate transfer medium in addition to the user image when forming the user image on the sheet based on the print job. (Configuration 2) The image forming apparatus according to configuration 1, wherein the control means makes the absolute value of the correction value when the first mode is selected greater than the absolute value of the correction value when the second mode is selected in which the first additional image is not formed on the intermediate transfer body. (Composition 3) The control means determines a reference correction value for the formation timing to suppress the color shift of the first color adjustment image relative to the second color adjustment image, based on the detection timing of the first color adjustment image and the detection timing of the second color adjustment image, which is different from the first color among the plurality of colors, determines the correction value when the first mode is selected by adding a first adjustment value to the reference correction value, and determines the correction value when the second mode is selected by adding a second adjustment value to the reference correction value. The image forming apparatus according to configuration 2, wherein the absolute value of the first adjustment value is greater than the absolute value of the second adjustment value. (Composition 4) The image forming apparatus according to any one of configurations 1 to 3, wherein the control means forms only the adjustment images for each of the plurality of colors on the intermediate transfer medium during the correction process. (Composition 5) The image forming apparatus according to any one of configurations 1 to 4, wherein the first additional image is an image composed of dots arranged at predetermined intervals. (Composition 6) The image forming apparatus according to any one of configurations 1 to 5, wherein the first additional image is formed in the region of the intermediate transfer body where no image transfer to the sheet is performed. (Composition 7) The image forming apparatus according to any one of configurations 1 to 6, wherein the first additional image is formed in the region of the intermediate transfer body where the image is transferred to the sheet. (Composition 8) The image forming apparatus according to any one of configurations 1 to 7, wherein the first additional image is formed with toner of the color least visible to humans among the plurality of colors. (Composition 9) The aforementioned multiple colors are yellow, cyan, magenta, and black. The first additional image is formed with yellow toner, as described in any one of configurations 1 to 8 of the image forming apparatus. (Composition 10) The first transfer regions on which the images formed on the plurality of photoreceptors are transferred to the intermediate transfer medium are different from each other. The image of the intermediate transfer body is transferred to the sheet in the second transfer region. The image transferred to the intermediate transfer medium by the first photoreceptor among the plurality of photoreceptors is transported to the second transfer medium via the first transfer region of each of the other photoreceptors among the plurality of photoreceptors, which are different from the first photoreceptor. The first additional image is formed on the first photoreceptor, as described in any one of the configurations 1 to 9 of the image forming apparatus. (Composition 11) The control means is In the correction process, a first correction value for the formation timing is determined to suppress the color shift of the first color adjustment image relative to the second color adjustment image among the multiple colors by forming adjustment images for each of the multiple colors and a second additional image on the intermediate transfer body, and a second correction value for the formation timing is determined to suppress the color shift of the first color adjustment image relative to the second color adjustment image by forming only the adjustment images for each of the multiple colors on the intermediate transfer body. The image forming apparatus according to configuration 1, wherein the correction value when the first mode is selected is determined based on the first correction value, and the correction value when the second mode in which the first additional image is not formed on the intermediate transfer body is selected is determined based on both the first correction value and the second correction value. (Composition 12) The image forming apparatus according to configuration 11, wherein the control means determines the first correction value to be the correction value when the first mode is selected. (Composition 13) The control means determines that the sum of the product of the first correction value and the first coefficient and the product of the second correction value and the second coefficient is the correction value when the second mode is selected. The image forming apparatus according to configuration 11 or 12, wherein the first coefficient and the second coefficient are greater than 0 and less than 1, and the sum of the first coefficient and the second coefficient is 1. (Composition 14) The image forming apparatus according to configuration 11 or 12, wherein the control means determines the average value of the first correction value and the second correction value to be the correction value when the second mode is selected. (Composition 15) The image forming apparatus according to any one of configurations 11 to 14, wherein the second additional image is formed in a width direction perpendicular to the rotation direction of the intermediate transfer body, in a range different from the range in which the adjustment images for each of the plurality of colors are formed. (Composition 16) The first transfer regions on which the images formed on the plurality of photoreceptors are transferred to the intermediate transfer medium are different from each other. The image of the intermediate transfer body is transferred to the sheet in the second transfer region. The image transferred to the intermediate transfer medium by the first photoreceptor among the plurality of photoreceptors is transported to the second transfer medium via the first transfer region of each of the other photoreceptors among the plurality of photoreceptors, which are different from the first photoreceptor. The second additional image is formed on the first photoreceptor, as described in the image forming apparatus according to any one of configurations 11 to 15. (Composition 17) An image forming apparatus that performs image formation using multiple colors of toner, Image forming means for forming images on a sheet based on a print job by forming images with different colored toners on each of a plurality of rotating photoreceptors, and transferring the images formed on each of the plurality of photoreceptors to a sheet via a rotating intermediate transfer body, A detection means for detecting an image formed on the intermediate transfer medium, Control means for controlling the image forming means to form adjustment images for each of the multiple colors on the intermediate transfer medium, and for performing correction processing to generate correction information for determining a correction value for the timing of forming the image of the first color among the multiple colors on the photoreceptor based on the detection timing of each of the multiple color adjustment images by the detection means, Equipped with, The control means is In the correction process, a first correction value for the formation timing is determined to suppress the color shift of the first color adjustment image relative to the second color adjustment image among the multiple colors by forming adjustment images and additional images for each of the multiple colors on the intermediate transfer body, and a second correction value for the formation timing is determined to suppress the color shift of the first color adjustment image relative to the second color adjustment image by forming only the adjustment images for each of the multiple colors on the intermediate transfer body. An image forming apparatus that generates information indicating the relationship between evaluation values ​​and correction values ​​as correction information, based on a first evaluation value of the toner amount of each of the multiple color adjustment images and the additional image, a second evaluation value of the toner amount of each of the multiple color adjustment images, the first correction value, and the second correction value. (Composition 18) The image forming apparatus according to configuration 17, wherein the control means determines a third evaluation value for the amount of toner of the image to be formed on the intermediate transfer body when forming the user image on the sheet based on the print job, and determines a correction value for the formation timing to be used when forming the user image on the sheet based on the third evaluation value and the correction information. (Composition 19) The image forming apparatus according to configuration 17 or 18, wherein the additional image is formed in a width direction perpendicular to the rotation direction of the intermediate transfer body, in a range different from the range in which the adjustment images for each of the plurality of colors are formed. (Composition 20) The first transfer regions on which the images formed on the plurality of photoreceptors are transferred to the intermediate transfer medium are different from each other. The image of the intermediate transfer body is transferred to the sheet in the second transfer region. The image transferred to the intermediate transfer medium by the first photoreceptor among the plurality of photoreceptors is transported to the second transfer medium via the first transfer region of each of the other photoreceptors among the plurality of photoreceptors, which are different from the first photoreceptor. The additional image is formed on the first photoreceptor, as described in any one of the configurations 17 to 19 of the image forming apparatus.

[0060] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of Symbols]

[0061] 260: Image forming unit, 50: Sensor, 204: Engine control unit

Claims

1. An image forming apparatus that performs image formation using multiple colors of toner, Image forming means for forming images on a sheet based on a print job by forming images with different colored toners on each of a plurality of rotating photoreceptors, and transferring the images formed on each of the plurality of photoreceptors to a sheet via a rotating intermediate transfer body, A detection means for detecting an image formed on the intermediate transfer medium, Control means for controlling the image forming means to form adjustment images of each of the multiple colors on the intermediate transfer medium, and for performing a correction process to determine a correction value for the timing of forming the image of the first color among the multiple colors on the photoreceptor based on the detection timing of each of the multiple color adjustment images by the detection means, Equipped with, Image forming apparatus, wherein the control means, when forming the user image on the sheet based on the print job, makes the absolute value of the correction value greater than the absolute value of the correction value when a first mode is selected in which a first additional image is formed on the intermediate transfer body in addition to the user image, for suppressing fluctuations in frictional force between the plurality of photoreceptors and the intermediate transfer body, when a second mode is selected in which the first additional image is not formed on the intermediate transfer body.

2. The control means determines a reference correction value for the formation timing to suppress the color shift of the first color adjustment image relative to the second color adjustment image, based on the detection timing of the first color adjustment image and the detection timing of the second color adjustment image, which is different from the first color among the plurality of colors, determines the correction value when the first mode is selected by adding the first adjustment value to the reference correction value, and determines the correction value when the second mode is selected by adding the second adjustment value to the reference correction value. The image forming apparatus according to claim 1, wherein the absolute value of the first adjustment value is greater than the absolute value of the second adjustment value.

3. The image forming apparatus according to claim 1 or 2, wherein the control means, in the correction process, forms only the adjustment images for each of the plurality of colors on the intermediate transfer body.

4. The image forming apparatus according to claim 1 or 2, wherein the first additional image is an image composed of dots arranged at predetermined intervals.

5. The image forming apparatus according to claim 1 or 2, wherein the first additional image is formed in a region of the intermediate transfer body where no image transfer to the sheet is performed.

6. The image forming apparatus according to claim 1 or 2, wherein the first additional image is formed in the region of the intermediate transfer body where the image is transferred to the sheet.

7. The image forming apparatus according to claim 1 or 2, wherein the first additional image is formed with toner of the color among the plurality of colors that is least visible to humans.

8. The aforementioned multiple colors are yellow, cyan, magenta, and black. The image forming apparatus according to claim 1 or 2, wherein the first additional image is formed with yellow toner.

9. The first transfer regions on which the images formed on the plurality of photoreceptors are transferred to the intermediate transfer medium are different from each other. The image of the intermediate transfer body is transferred to the sheet in the second transfer region. The image transferred to the intermediate transfer medium by the first photoreceptor among the plurality of photoreceptors is transported to the second transfer medium via the first transfer region of each of the other photoreceptors among the plurality of photoreceptors, which are different from the first photoreceptor. The image forming apparatus according to claim 1 or 2, wherein the first additional image is formed on the first photoreceptor.

10. The control means is In the correction process, the first correction value for the formation timing is determined to suppress the color shift of the adjustment image of the first color relative to the adjustment image of the second color relative to the adjustment image of the second color relative to the adjustment image of the second color relative to the adjustment image of the second color relative to the adjustment image of the second color relative to the adjustment image of the second color relative to the adjustment image of the second color relative to the adjustment image of the first first color relative to the adjustment image of the second color relative to the adjustment image of the first color relative to the adjustment image of the first color relative to the adjustment image of the first color relative to the adjustment image of the second color relative to the adjustment image of the first color relative to The image forming apparatus according to claim 1, wherein the correction value when the first mode is selected is determined based on the first correction value, and the correction value when the second mode is selected is determined based on both the first correction value and the second correction value.

11. The image forming apparatus according to claim 10, wherein the control means determines the first correction value to be the correction value when the first mode is selected.

12. The control means determines that the sum of the product of the first correction value and the first coefficient and the product of the second correction value and the second coefficient is the correction value when the second mode is selected. The image forming apparatus according to claim 10, wherein the first coefficient and the second coefficient are greater than 0 and less than 1, and the sum of the first coefficient and the second coefficient is 1.

13. The image forming apparatus according to claim 10, wherein the control means determines the average value of the first correction value and the second correction value to be the correction value when the second mode is selected.

14. The image forming apparatus according to any one of claims 10 to 13, wherein the second additional image is formed in a width direction perpendicular to the rotation direction of the intermediate transfer body, in a range different from the range in which the adjustment images for each of the plurality of colors are formed.

15. The first transfer regions on which the images formed on the plurality of photoreceptors are transferred to the intermediate transfer medium are different from each other. The image of the intermediate transfer body is transferred to the sheet in the second transfer region. The image transferred to the intermediate transfer medium by the first photoreceptor among the plurality of photoreceptors is transported to the second transfer medium via the first transfer region of each of the other photoreceptors among the plurality of photoreceptors, which are different from the first photoreceptor. The image forming apparatus according to any one of claims 10 to 13, wherein the second additional image is formed on the first photoreceptor.

Images