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 a color misregistration correction technique in an image forming apparatus. [Background technology]

[0002] Electrophotographic image forming apparatuses form toner images on a photoreceptor, which serves as an image carrier, and then transfer the image formed on the photoreceptor directly or via an intermediate transfer member to a sheet. In image forming apparatuses that use an intermediate transfer member, the amount of toner present between the photoreceptor and the intermediate transfer member fluctuates during image formation. If this fluctuation in toner amount causes a change in the frictional force between the photoreceptor and the intermediate transfer member, the relative speed between the photoreceptor and the intermediate transfer member fluctuates, which can result in color misregistration.

[0003] Patent Document 1 discloses a configuration for suppressing color misregistration caused by fluctuations in frictional force. According to Patent Document 1, fluctuations in frictional force are suppressed by supplying toner to the intermediate transfer body so that the amount of toner present between the photosensitive body and the intermediate transfer body is equal to or greater than a predetermined amount. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-164950 Summary of the Invention [Problem to be solved by the invention]

[0005] In an image forming apparatus, color misregistration can also occur due to deterioration of the image forming apparatus over time, a rise in temperature of the image forming apparatus, etc. For this reason, the image forming apparatus performs a so-called color misregistration correction process, for example, by forming an adjustment pattern including an adjustment image of each color on an intermediate transfer body and detecting the position of the adjustment image of each color to determine a correction value for the timing of forming an image of each color on a photosensitive body.

[0006] Patent Document 1 discloses a configuration for suppressing fluctuations in frictional force between a photosensitive body and an intermediate transfer body, but does not disclose a color misregistration correction process that takes into account fluctuations in frictional force between a photosensitive body and an intermediate transfer body.

[0007] The present invention provides a color misregistration correction technique that takes into account the fluctuation in frictional force between the photosensitive member and the intermediate transfer member. [Means for solving the problem]

[0008] According to one aspect of the present invention, an image forming device that forms images using toners of multiple colors includes an image forming unit that forms images using toners of different colors on each of multiple photosensitive drums that are rotated, and transfers the images formed on each of the multiple photosensitive drums to a sheet via an intermediate transfer drum that is also rotated, thereby forming a user image based on a print job on the sheet; a detection unit that detects the image formed on the intermediate transfer drum; and a control unit that controls the image forming unit to form an adjusted image of each of the multiple colors on the intermediate transfer drum, and performs a correction process that determines a correction value for the formation timing of an image of a first color of the multiple colors on the photosensitive drum based on the detection timing of the adjusted image of each of the multiple colors by the detection unit, and when forming the user image based on the print job on the sheet, the control unit varies the correction value depending on whether a first mode is selected in which a first additional image is formed on the intermediate transfer drum in addition to the user image. [Effects of the Invention]

[0009] According to the present invention, it is possible to correct color misregistration taking into consideration the fluctuation in the frictional force between the photosensitive member and the intermediate transfer member. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to some embodiments. [Figure 2] 1 is a block diagram of an image forming apparatus, according to some embodiments. [Figure 3] 5A and 5B are diagrams showing examples of images formed on the intermediate transfer body in the first mode. [Figure 4] 5A and 5B are diagrams showing examples of adjustment patterns formed on an intermediate transfer body. [Figure 5] 10 is a flowchart of a color misregistration correction process according to one embodiment. [Figure 6] FIG. 4 is an explanatory diagram of a color misregistration correction process according to an embodiment. [Figure 7] FIG. 4 is an explanatory diagram of a color misregistration correction process according to an embodiment. [Figure 8] 5A and 5B are diagrams showing examples of additional images and adjustment patterns formed on an intermediate transfer body. [Figure 9] 10 is a flowchart of a color misregistration correction process according to one embodiment. [Figure 10] 10 is a flowchart of a color misregistration correction process according to one embodiment. [Figure 11] FIG. 10 is a diagram showing an example of the relationship between an evaluation value and a correction value. [Figure 12] 1 is a flowchart of an imaging process according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0012] First Embodiment Fig. 1A is a schematic cross-sectional view of an image forming apparatus 201 according to this embodiment. In Fig. 1A, the letters Y, M, C, and K are added to the end of the reference numerals of components involved in forming images using yellow, magenta, cyan, and black toners (hereinafter, an image using toner will also be referred to as a toner image). Note that when it is not necessary to distinguish between the colors of the images formed by components, the reference numerals with the suffix omitted are used collectively.

[0013] During image formation, the photoreceptor 5 is rotated clockwise in the figure. The charging roller 7 charges the photoreceptor 5 to a predetermined potential. The exposure device 10 exposes the photoreceptor 5 to light to form an electrostatic latent image on the photoreceptor 5. The development device 8 develops the electrostatic latent image on the photoreceptor 5 with toner to form a toner image on the photoreceptor 5. The primary transfer roller 4 outputs a primary transfer voltage to transfer the toner image on the photoreceptor 5 to the intermediate transfer body 12. In the following description, the area where the toner image on the photoreceptor 5 is transferred to the intermediate transfer body 12 is referred to as the primary transfer area. A primary transfer area is defined for each of the photoreceptors 5Y, 5M, 5C, and 5K. During image formation, the intermediate transfer body 12 is rotated counterclockwise in the figure by the drive roller 11. By transferring the toner images on each photoreceptor 5 to the intermediate transfer body 12 in layers, different colors (yellow, magenta, cyan, and black) are reproduced.

[0014] The toner image transferred to the intermediate transfer body 12 is transported to a position facing the secondary transfer roller 9 by the rotation of the intermediate transfer body 12. The secondary transfer roller 9 outputs a secondary transfer voltage to transfer the toner image on the intermediate transfer body 12 to the sheet 2 transported from the cassette 1 along the transport path. In the following description, the area where the toner image on the intermediate transfer body 12 is transferred to the sheet 2 is referred to as the secondary transfer area. The fixing device 13 fixes the toner image to the sheet 2 by applying heat and pressure to the sheet 2 onto which the toner image has been transferred. After the toner image has been fixed, the sheet 2 is discharged to the tray 27 by the discharge roller 31. The sensor 50 detects the adjustment pattern formed on the intermediate transfer body 12 for correcting color misregistration.

[0015] To increase the efficiency of primary transfer, the image forming apparatus 201 can be configured so that the moving speed of the surface of the intermediate transfer body 12 is several percent faster than the moving speed of the surface of the photoreceptor 5. In this case, due to the frictional force between the intermediate transfer body 12 and the photoreceptor 5, the intermediate transfer body 12 applies a force to the photoreceptor 5 in the rotational direction of the photoreceptor 5 during image formation.

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

[0017] FIG. 2 shows the control configuration of the image forming apparatus 201. The image forming unit 260 in FIG. 2 is a collective term for the components for forming an image on the sheet 2, as described in 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 the network, it causes the engine control unit 204 to perform image formation control based on the print job. The processing unit 220 of the engine control unit 204 controls the image forming unit 260 based on the image data included in the print job to form an image on the sheet 2. In the following description, the image indicated by the image data included in the print job will be referred to as a "user image."

[0018] In this 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 body 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 body 12. The first additional image is formed to suppress fluctuations in the frictional force between the photoconductor 5 and the intermediate transfer body 12.

[0019] 3 shows a state in which a user image (letters ABC) and a first additional image are formed on the intermediate transfer body 12. Note that area 500 in FIG. 3 is an area that comes into contact with the sheet 2, i.e., an area where transfer to the sheet 2 occurs, and will be referred to as the "sheet area" below. Furthermore, an image formed in an area of ​​the surface area of ​​the intermediate transfer body 12 that is different from the sheet area 500 is not transferred to the sheet 2, and therefore, will be referred to as the "non-sheet area" below.

[0020] The hatched area in the sheet area 500 in FIG. 3 represents the first additional image. In FIG. 3, the first additional image is formed over the entire sheet area 500, but it may be formed only in the non-sheet area. Furthermore, it may be formed in both the sheet area 500 and the non-sheet area. Also, in FIG. 3, the first additional image is formed over the entire sheet area 500, but when the first additional image is formed in the sheet area 500, it may be formed only in a portion of the sheet area 500, not the entire sheet area 500. Furthermore, when the first additional image is formed in the non-sheet area, it may be formed only in a portion of the non-sheet area.

[0021] The first additional image formed in the sheet area 500 is transferred to the sheet 2. For this reason, 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 are difficult for humans to see are dispersed. For example, the first additional image can be an image in which small dots are arranged at predetermined intervals. Furthermore, when the first additional image is formed in the sheet area 500, the first additional image can be formed using yellow toner, which has the lowest human visibility of the four colors used for image formation. Because the first additional image formed in the non-sheet area is not transferred to the sheet 2, the first additional image formed in the non-sheet area can be any image of any color.

[0022] 1, the photoconductor 5Y is the one that is farthest from the primary transfer region to the secondary transfer region in the rotation direction of the intermediate transfer body 12. Therefore, when the first additional image is transferred from the photoconductor 5Y to the intermediate transfer body 12, the first additional image reaches the secondary transfer region via the primary transfer regions of the other photoconductors 5. Therefore, the toner supplied from the photoconductor 5Y to the intermediate transfer body 12 acts to suppress fluctuations in the frictional force between the other photoconductors 5 and the intermediate transfer body 12. For this reason, the first additional image can be formed on the photoconductor 5 that transfers the image to the intermediate transfer body 12 in the primary transfer region that is farthest from the secondary transfer region in the rotation direction of the intermediate transfer body 12, regardless of the formation region.

[0023] Image data of the first additional image to be formed on the intermediate transfer body 12 in the first mode is stored in advance in the engine control unit 204. Note that instead of storing image data of only one type of first additional image in the engine control unit 204, it is also possible to configure the engine control unit 204 to store image data of multiple types of first additional images. 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 depending on, for example, the content of the user image, the size of the sheet 2, etc.

[0024] When performing the color misregistration correction process, the processing unit 220 forms an adjustment pattern 60 shown in FIG. 4 on the intermediate transfer body 12. Image data of the adjustment pattern 60 is stored in advance in the engine control unit 204. The adjustment pattern 60 includes adjustment images for black, cyan, magenta, and yellow, respectively. The adjustment images are, for example, single-tone patch images. In FIG. 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. Because the reflection pattern of light on the surface of the intermediate transfer body 12 differs from the reflection pattern of light in the adjustment images, the sensor 50 can detect each adjustment image based on changes 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 the adjusted image of each color on the intermediate transfer body 12 in the rotation direction of the intermediate transfer body 12 based on the detection results of the sensor 50, i.e., the detection timing of the adjusted image of each color. Therefore, the correction unit 210 can determine the amount of color misregistration 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 misregistration detected using the adjustment pattern 60. The reference correction value for a certain color is used to correct the formation timing of the image of that color on the photoconductor 5, more specifically, the formation timing of the electrostatic latent image for the image of that color on the photoconductor 5.

[0026] 5 is a flowchart of the color misregistration correction process executed 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 results of the adjustment pattern 60 from the sensor 50, that is, the detection timing of the adjustment images of black, cyan, magenta, and yellow. In S12, the correction unit 210 determines the reference correction value for each color based on the detection results. 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 reason for using different correction values ​​in the first and second modes will be explained below. In this embodiment, the moving speed of the surface of intermediate transfer body 12 is set faster than the moving speed of the surface of photoconductor 5. As a result, intermediate transfer body 12 applies a force to photoconductor 5 in a direction that rotates photoconductor 5. This force becomes a load on drive roller 11 that rotates intermediate transfer body 12. Here, when toner is supplied between photoconductor 5 and intermediate transfer body 12 at the start of image formation, the frictional force between photoconductor 5 and intermediate transfer body 12 decreases, and therefore the load on drive roller 11 also decreases.

[0028] 6A shows an example of the change in torque of the drive roller 11 over time when image formation starts. As the transfer of the yellow toner image formed on the photoreceptor 5Y to the intermediate transfer body 12 starts, 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 5Y and the intermediate transfer body 12 reaches a predetermined amount or more.

[0029] Generally, the smaller the torque of the drive roller 11, the greater the amount of slippage of the intermediate transfer body 12 relative to the photosensitive body 5. Due to this slippage, the position on the intermediate transfer body 12 of the toner transferred from the photosensitive body 5 to the intermediate transfer body 12 moves backward in the direction of movement of the surface of the intermediate transfer body 12. The greater the amount of slippage, the greater the amount of this backward movement.

[0030] On the other hand, since the amount of toner in the adjustment patterns 60 formed on the intermediate transfer body 12 in the color misregistration correction process is small, in the color misregistration correction process, there is almost no slippage of the intermediate transfer body 12 relative to the photosensitive body 5. Therefore, the reference correction value acquired based on the detection results of the adjustment patterns 60 in the color misregistration correction process corrects color misregistration in a state where there is almost no slippage of the intermediate transfer body 12.

[0031] FIG. 6B shows the amount of yellow color misregistration when an image is formed in the second mode by correcting the timing of forming an image on the photoconductor 5, more specifically, the timing of forming an electrostatic latent image on the photoconductor 5, based on the reference correction value. In FIG. 6B and similar figures, the amount of color misregistration is indicated with a sign to indicate the direction of the color misregistration (whether it is a misregistration toward the front of the sheet in the sheet transport direction). However, since the absolute value is important for color misregistration, in the following description, unless it is clear from the context that a value with a different sign is intended, or unless otherwise specified, the "amount of color misregistration" will refer to the absolute value. The horizontal axis in FIG. 6B indicates the position along the transport direction from the leading edge of the sheet 2 in the transport direction.

[0032] When toner is supplied to the intermediate transfer body 12 at 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 slippage of the intermediate transfer body 12 increases over time, and the amount of yellow color misregistration changes along the conveyance direction of the sheet 2. Note that at the timing when transfer of the black image to the intermediate transfer body 12 starts, yellow toner has been supplied to the intermediate transfer body 12, so torque fluctuations of the intermediate transfer body 12 are small. Therefore, by performing correction based on the reference correction value, the amount of yellow color misregistration at the rear end of the sheet 2 becomes approximately zero, and the amount of color misregistration increases toward the leading end of the sheet 2.

[0033] For this reason, in this embodiment, the second adjustment value for each color is determined in advance based on the toner amount in the adjustment pattern 60 and the average toner amount used to form a user image, and is stored in the engine control unit 204. Then, the correction unit 210 calculates the second mode correction value for each color by adding the second adjustment value to the reference correction value. For example, the correction value for yellow in the second mode is the sum of the yellow reference correction value and the yellow second adjustment value.

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

[0035] 6(C), in the second mode, color misregistration remains, which varies depending on the position in the conveying direction of the sheet 2. In order to suppress this color misregistration, which varies depending on the position in the conveying direction of the sheet 2, in the first mode, the first additional image is formed on the intermediate transfer body 12, as described above.

[0036] 7A shows an example of the change over time in torque of the drive roller 11 when an image is formed in the first mode. In the first mode, the first additional image supplies toner between the photosensitive member 5 and the intermediate transfer member 12 from an early stage of image formation, improving the situation in which torque decreases over time as shown in FIG. 6A.

[0037] FIG. 7B shows the amount of color misregistration for yellow when an image is formed in the first mode after correction based on the correction value in the second mode described above. Unlike FIG. 6C, the amount of color misregistration in FIG. 7B is approximately constant regardless of the position in the conveyance direction of the sheet 2. However, a color misregistration of approximately 60 μm occurs, the same as at the leading edge of the sheet in FIG. 6C. Thus, in the first mode, if the same correction value as in the second mode is used, a steady color misregistration remains. For this reason, in this embodiment, the first adjustment value for each color is determined in advance based on the toner amount in 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. Then, the correction unit 210 calculates the first mode correction value by adding the first adjustment value to the reference correction value for each color. For example, the yellow correction value in the first mode is calculated by adding the first adjustment value to the reference correction 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 (60 μm added 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 zero regardless of the position in the sheet transport direction.

[0039] As described above, the image forming apparatus 201 of this embodiment operates in 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. The first mode is also a mode in which the amount of color misregistration can be reduced over the entire conveyance direction of the sheet, as shown in FIG. 7(C), and the second mode is also a mode in which the amount of toner consumption can be reduced.

[0040] The engine control unit 204 can determine the amount of color misregistration of the adjusted image of the first color relative to the adjusted image of the second color based on the detection timing of the adjusted image of each color in the color misregistration correction process. In this example, the second color is black, also referred to as the reference color. The first color is a color other than the second color, and in this example, it is yellow, cyan, or magenta. The engine control unit 204 then determines a correction value for the timing of forming the image of the first color on the photoconductor 5 to reduce the amount of color misregistration of the image of the first color relative to the image of the second color. Here, the engine control unit 204 differentiates the correction value in the first mode from the correction value in the second mode. With this configuration, in the first mode, the amount of color misregistration can be reduced throughout the entire sheet transport direction. In addition, in the second mode, although the amount of color misregistration varies along the sheet transport direction, the maximum value can be reduced.

[0041] 6 and 7, the absolute value of the correction value when the first mode is selected is larger than the absolute value of the correction value when the second mode is selected. More specifically, the engine control unit 204 calculates the reference correction value for the first color based on the detection timing of the adjusted image for each color. The reference correction value for the first color suppresses color misregistration that occurs in the adjusted image for the first color during color misregistration correction processing; in other words, it suppresses color misregistration when the amount of toner supplied to the intermediate transfer body 12 is small. The engine control unit 204 then determines 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 ​​for reflecting the influence of slippage of the intermediate transfer body 12 in the reference correction value, which does not reflect the influence of slippage of the intermediate transfer body 12. However, the frictional force between the intermediate transfer body 12 and the photoreceptor 5 may differ for each individual intermediate transfer body 12 and photoreceptor 5. Therefore, if the frictional force between the intermediate transfer body 12 and the photoreceptor 5 differs for each individual intermediate transfer body 12 and photoreceptor 5, the amount of residual color misregistration may be large if the first and second adjustment values ​​determined in advance are used.

[0043] For this reason, in this embodiment, the engine control unit 204 executes two processes: a second process in which only the adjustment pattern 60 shown in FIG. 4 is formed on the intermediate transfer body 12 to determine the correction value; and a first process in which a second additional image is formed on the intermediate transfer body in addition to the adjustment pattern 60 to determine the correction value. FIG. 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 an area in the width direction perpendicular to the movement direction (rotation direction) of the surface of the intermediate transfer body 12 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. Like the first additional image, the second additional image is formed on the photoconductor 5Y, which constitutes the primary transfer region and is furthest along the rotation direction of the intermediate transfer body 12 from the secondary transfer region. 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 drive torque of the drive roller 11, thereby minimizing fluctuations in the drive torque (see FIG. 6A). Image data of the second additional image is also stored in the engine control unit 204 in advance.

[0044] FIG. 9 is a flowchart of the color misregistration correction process executed 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, i.e., the detection timing of the adjustment images of black, cyan, magenta, and yellow. In S22, the correction unit 210 determines a first correction value for each color based on the detection result. The first correction value is a correction value for suppressing color misregistration that occurs in the adjustment image when the adjustment pattern 60 and the second additional image are 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, i.e., the detection timing of the adjustment images of black, cyan, magenta, and yellow. In S25, the correction unit 210 determines a second correction value based on the detection result of S24. The second correction value is a correction value for suppressing color misregistration that occurs in the adjustment image when only the adjustment pattern 60 is formed on the intermediate transfer body 12. Note that S23 to S25 correspond to the second process.

[0045] In S26, the correction unit 210 determines, for each color, a correction value to be used in the first mode and a correction value to be used in the second mode based on the first correction value and the second correction value. In the first process, the adjustment pattern 60 and the second additional image are formed, so the torque change of the drive roller 11 can be considered to be the same as during image formation in the first mode. Therefore, in this embodiment, the correction value to be 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 in the first embodiment, and because the amount of toner in the adjustment pattern 60 is small, using the second correction value in the second mode results in a large amount of color misregistration, as shown in Fig. 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 the coefficients α and β are both greater than 0 and less than 1, and furthermore, are values ​​that satisfy the condition that the sum of the coefficients α and β is 1. As an example, α=β=0.5, and in this case, the correction value in the second mode is the average value of the first correction value and the second correction value.

[0048] The values ​​of α and β are determined in advance 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, and are stored in the engine control unit 204. Alternatively, the values ​​of α and β are determined experimentally and are stored in the engine control unit 204.

[0049] As described above, in this embodiment, the correction values ​​for the first mode and the second mode are determined by performing a first process in which a second additional image is formed and the first correction value is determined, and a second process in which the second correction value is determined without forming the second additional image. This makes it possible to reduce the amount of color misregistration that remains due to individual differences in the intermediate transfer body 12. Note that in the case of an image forming apparatus that forms images only in the first mode, it is sufficient to perform only the first process.

[0050] In this embodiment, the first correction value is used as the correction value in the first mode. However, if the toner amount of an average user image is less than the total toner amount of the second additional image and the adjustment pattern 60, the correction value in the first mode can also be calculated using the first correction value, the second correction value, the coefficient α, and the coefficient β, just like the correction value in the second mode. Note that the coefficient α by which the first correction value is multiplied to calculate the correction value in the first mode is set to be larger than the coefficient α by which the first correction value is multiplied to calculate the correction value in 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 misregistration correction process separately determines the correction value for the first mode and the correction value for the second mode. In this embodiment, the color misregistration correction process generates correction information indicating the relationship between the evaluation value of the amount of toner supplied to the intermediate transfer body 12 and the correction value. Then, when a user image is formed, the correction value to be used in this image formation is determined based on the evaluation value of the amount of toner for the image to be formed on the intermediate transfer body 12 and the correction information. Note that in this embodiment as well, when a user image is formed 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 of the toner amount of an image is a value evaluating 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. As an example, the evaluation value of the toner amount of an image can be determined based on the pixel value of each pixel indicated by the image data for forming the image. The evaluation value of the toner amount of an image can also be a value obtained by dividing the amount of toner supplied to the intermediate transfer body 12 by forming the image on the intermediate transfer body 12 by a predetermined amount of toner. The predetermined amount of toner can 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 can be, for example, the area of ​​a rectangle whose 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 whose length in a 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] 10 is a flowchart of the color misregistration correction process executed 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 image combining 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 of 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 of 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. Because the amount of slippage remains unchanged whether the amount of toner on the intermediate transfer body 12 is equal to or less than a predetermined amount or equal to or greater than the predetermined amount, the correction value indicated by the correction information may be configured to have a lower limit and an upper limit. FIG. 11 shows an example of the correction information calculated by the correction unit 210 in S38. According to FIG. 11, when the evaluation value is P1, the correction value is the lower limit C1, and when the evaluation value is P2, the correction value is the upper limit C2. In the evaluation value range from P1 to P2, the correction value increases linearly as the evaluation value increases.

[0056] FIG. 12 is a flowchart of the processing executed by the processing unit 220 when forming a user image on the sheet 2. In S40, the processing unit 220 determines an evaluation value of the toner amount of the image to be transferred to the intermediate transfer body. 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 forming 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 an image based on the correction value determined in S41.

[0057] As described above, the correction value to be used in image formation is determined based on the correction information and the evaluation value of the toner amount of the image to be formed on the intermediate transfer body 12 when forming a user image. With this configuration, it is possible to determine the optimal correction value for each image formation.

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

[0059] The disclosure of this embodiment includes the following configuration. (Configuration 1) An image forming apparatus that forms an image using toner of multiple colors, an image forming unit that forms an image using toner of a different color on each of a plurality of photosensitive members that are driven to rotate, and transfers the images formed on each of the plurality of photosensitive members onto a sheet via an intermediate transfer member that is also driven to rotate, thereby forming a user image based on a print job on the sheet; a detection means for detecting an image formed on the intermediate transfer body; a control unit that performs a correction process by controlling the image forming unit to form an adjusted image of each of the plurality of colors on the intermediate transfer body, and determining a correction value for the timing of forming an image of a first color among the plurality of colors on the photosensitive body based on the detection timing of the adjusted image of each of the plurality of colors by the detection unit; 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 body in addition to the user image when the user image based on the print job is formed on the sheet. (Configuration 2) The image forming apparatus according to configuration 1, wherein the control unit makes the absolute value of the correction value when the first mode is selected larger than the absolute value of the correction value when a second mode in which the first additional image is not formed on the intermediate transfer body is selected. (Configuration 3) the control means determines a reference correction value for the formation timing to suppress color shift of the adjusted image of the first color relative to the adjusted image of the second color, based on detection timing of the adjusted image of the first color and detection timing of the adjusted image of a second color 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; 3. 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. (Configuration 4) 4. The image forming apparatus according to any one of configurations 1 to 3, wherein the control unit forms only the adjusted images of the plurality of colors on the intermediate transfer body in the correction process. (Configuration 5) 5. The image forming apparatus according to any one of configurations 1 to 4, wherein the first additional image is an image made up of dots arranged at predetermined intervals. (Configuration 6) 6. The image forming apparatus according to any one of configurations 1 to 5, wherein the first additional image is formed in a region of the intermediate transfer body where no image is transferred to the sheet. (Configuration 7) 7. The image forming apparatus according to any one of configurations 1 to 6, wherein the first additional image is formed in a region of the intermediate transfer body where an image is transferred to the sheet. (Configuration 8) 8. The image forming apparatus according to any one of configurations 1 to 7, wherein the first additional image is formed with toner of a color that is least visible to humans among the plurality of colors. (Configuration 9) the plurality of colors being yellow, cyan, magenta, and black; 9. The image forming apparatus according to any one of configurations 1 to 8, wherein the first additional image is formed with yellow toner. (Configuration 10) the first transfer regions in which the images formed on the plurality of photosensitive members are transferred to the intermediate transfer member are different from one another; the image on the intermediate transfer member is transferred to the sheet at a second transfer region; the image transferred onto the intermediate transfer body by a first photoconductor among the plurality of photoconductors is transported to the second transfer area via first transfer areas of all other photoconductors different from the first photoconductor among the plurality of photoconductors; 10. The image forming apparatus of any one of configurations 1 to 9, wherein the first additional image is formed on the first photosensitive member. (Configuration 11) The control means In the correction process, a first correction value of the formation timing is determined to suppress color misalignment of the adjusted image of the first color relative to the adjusted image of the second color among the plurality of colors by forming the adjusted image of each of the plurality of colors and a second additional image on the intermediate transfer body, and a second correction value of the formation timing is determined to suppress color misalignment of the adjusted image of the first color relative to the adjusted image of the second color by forming only the adjusted image of each of the plurality of 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. (Configuration 12) 12. The image forming apparatus according to claim 11, wherein the control unit determines the first correction value as the correction value when the first mode is selected. (Configuration 13) the control means determines the sum of the product of the first correction value and a first coefficient and the product of the second correction value and a second coefficient as the correction value when the second mode is selected; 13. The image forming apparatus according to claim 11, 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. (Configuration 14) 13. The image forming apparatus according to claim 11, wherein the control unit determines an average value of the first correction value and the second correction value as the correction value when the second mode is selected. (Configuration 15) The image forming apparatus according to any one of configurations 11 to 14, wherein the second additional image is formed in a range in a width direction perpendicular to the rotation direction of the intermediate transfer body that is different from the range in which the adjusted images of each of the plurality of colors are formed. (Configuration 16) the first transfer regions in which the images formed on the plurality of photosensitive members are transferred to the intermediate transfer member are different from one another; the image on the intermediate transfer member is transferred to the sheet at a second transfer region; the image transferred onto the intermediate transfer body by a first photoconductor among the plurality of photoconductors is transported to the second transfer area via first transfer areas of all other photoconductors different from the first photoconductor among the plurality of photoconductors; 16. The image forming apparatus of any one of configurations 11 to 15, wherein the second additional image is formed on the first photosensitive member. (Configuration 17) An image forming apparatus that forms an image using toner of multiple colors, an image forming unit that forms an image using toner of a different color on each of a plurality of photosensitive members that are driven to rotate, and transfers the images formed on each of the plurality of photosensitive members onto a sheet via an intermediate transfer member that is also driven to rotate, thereby forming a user image based on a print job on the sheet; a detection means for detecting an image formed on the intermediate transfer body; a control means for performing a correction process by controlling the image forming means to form an adjusted image of each of the plurality of colors on the intermediate transfer body, and generating correction information for determining a correction value for the timing of forming an image of a first color among the plurality of colors on the photosensitive body based on the detection timing of the adjusted image of each of the plurality of colors by the detection means; Equipped with The control means In the correction process, a first correction value of the formation timing is determined to suppress color misalignment of the adjusted image of a first color relative to the adjusted image of a second color among the plurality of colors by forming the adjusted image and the additional image for each of the plurality of colors on the intermediate transfer body, and a second correction value of the formation timing is determined to suppress color misalignment of the adjusted image of the first color relative to the adjusted image of the second color by forming only the adjusted image for each of the plurality of colors on the intermediate transfer body, an image forming apparatus that generates, as the correction information, information indicating a relationship between the evaluation value and the correction value based on a first evaluation value of the toner amount of the adjusted image and the additional image for each of the plurality of colors, a second evaluation value of the toner amount of the adjusted image for each of the plurality of colors, the first correction value, and the second correction value. (Configuration 18) The image forming apparatus of configuration 17, wherein the control means determines a third evaluation value of the amount of toner of the image to be formed on the intermediate transfer body when forming the user image based on the print job on the sheet, and determines a correction value of the formation timing to be used when forming the user image on the sheet based on the third evaluation value and the correction information. (Configuration 19) 19. The image forming apparatus according to claim 17, wherein the additional image is formed in a range in a width direction perpendicular to the rotation direction of the intermediate transfer body that is different from a range in which the adjusted images of each of the plurality of colors are formed. (Configuration 20) the first transfer regions in which the images formed on the plurality of photosensitive members are transferred to the intermediate transfer member are different from one another; the image on the intermediate transfer member is transferred to the sheet at a second transfer region; the image transferred onto the intermediate transfer body by a first photoconductor among the plurality of photoconductors is transported to the second transfer area via first transfer areas of all other photoconductors different from the first photoconductor among the plurality of photoconductors; 20. The image forming apparatus of any one of configurations 17 to 19, wherein the additional image is formed on the first photoreceptor.

[0060] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of 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 forms an image using toner of multiple colors, an image forming unit that forms an image using toner of a different color on each of a plurality of photosensitive members that are driven to rotate, and transfers the images formed on each of the plurality of photosensitive members onto a sheet via an intermediate transfer member that is also driven to rotate, thereby forming a user image based on a print job on the sheet; a detection means for detecting an image formed on the intermediate transfer body; a control unit that controls the image forming unit to form an adjusted image of each of the plurality of colors on the intermediate transfer body, and performs a correction process to determine a correction value for the timing of forming an image of a first color among the plurality of colors on the photosensitive body based on the detection timing of the adjusted image of each of the plurality of colors by the detection unit; 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 body in addition to the user image when forming the user image based on the print job on the sheet.

2. 2. The image forming apparatus according to claim 1, wherein the control means makes the absolute value of the correction value when the first mode is selected larger than the absolute value of the correction value when a second mode in which the first additional image is not formed on the intermediate transfer body is selected.

3. the control means determines a reference correction value for the formation timing to suppress color misalignment of the adjusted image of the first color relative to the adjusted image of the second color, based on detection timing of the adjusted image of the first color and detection timing of the adjusted image of a second color 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 claim 2 , wherein the absolute value of the first adjustment value is greater than the absolute value of the second adjustment value.

4. 4. The image forming apparatus according to claim 1, wherein the control unit forms only the adjusted images for each of the plurality of colors on the intermediate transfer body in the correction process.

5. 4. The image forming apparatus according to claim 1, wherein the first additional image is an image made up of dots arranged at predetermined intervals.

6. 4. The image forming apparatus according to claim 1, wherein the first additional image is formed in a region of the intermediate transfer member where no image is transferred to the sheet.

7. 4. The image forming apparatus according to claim 1, wherein the first additional image is formed in a region of the intermediate transfer member where an image is transferred to the sheet.

8. 4. The image forming apparatus according to claim 1, wherein the first additional image is formed using toner of a color that is least visible to humans among the plurality of colors.

9. the plurality of colors being yellow, cyan, magenta, and black; 4. The image forming apparatus according to claim 1, wherein the first additional image is formed with yellow toner.

10. the first transfer regions in which the images formed on the plurality of photosensitive members are transferred to the intermediate transfer member are different from one another; the image on the intermediate transfer member is transferred to the sheet at a second transfer region; the image transferred onto the intermediate transfer body by a first photoconductor among the plurality of photoconductors is transported to the second transfer area via first transfer areas of all other photoconductors different from the first photoconductor among the plurality of photoconductors; The image forming apparatus according to claim 1 , wherein the first additional image is formed on the first photosensitive member.

11. The control means In the correction process, a first correction value of the formation timing is determined to suppress color misalignment of the adjusted image of the first color relative to the adjusted image of the second color among the plurality of colors by forming the adjusted image of each of the plurality of colors and a second additional image on the intermediate transfer body, and a second correction value of the formation timing is determined to suppress color misalignment of the adjusted image of the first color relative to the adjusted image of the second color by forming only the adjusted image of each of the plurality of colors on the intermediate transfer body, 2. 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 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.

12. 12. The image forming apparatus according to claim 11, wherein the control unit determines the first correction value as the correction value when the first mode is selected.

13. the control means determines the sum of the product of the first correction value and a first coefficient and the product of the second correction value and a second coefficient as the correction value when the second mode is selected; 12. The image forming apparatus according to claim 11, 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.

14. 12. The image forming apparatus according to claim 11, wherein the control unit determines an average value of the first correction value and the second correction value as the correction value when the second mode is selected.

15. 15. The image forming apparatus according to claim 11, wherein the second additional image is formed in a range different from a range in which the adjusted images of the plurality of colors are formed in a width direction perpendicular to a rotation direction of the intermediate transfer body.

16. the first transfer regions in which the images formed on the plurality of photosensitive members are transferred to the intermediate transfer member are different from one another; the image on the intermediate transfer member is transferred to the sheet at a second transfer region; the image transferred onto the intermediate transfer body by a first photoconductor among the plurality of photoconductors is transported to the second transfer area via first transfer areas of all other photoconductors different from the first photoconductor among the plurality of photoconductors; The image forming apparatus according to claim 11 , wherein the second additional image is formed on the first photosensitive member.

17. An image forming apparatus that forms an image using toner of multiple colors, an image forming unit that forms an image using toner of a different color on each of a plurality of photosensitive members that are driven to rotate, and transfers the images formed on each of the plurality of photosensitive members onto a sheet via an intermediate transfer member that is also driven to rotate, thereby forming a user image based on a print job on the sheet; a detection means for detecting an image formed on the intermediate transfer body; a control unit that controls the image forming unit to form an adjusted image of each of the plurality of colors on the intermediate transfer body, and performs a correction process to generate correction information for determining a correction value for the timing of forming an image of a first color among the plurality of colors on the photosensitive body based on the detection timing of the adjusted image of each of the plurality of colors by the detection unit; Equipped with The control means In the correction process, a first correction value of the formation timing is determined to suppress color misalignment of the adjusted image of the first color relative to the adjusted image of the second color among the plurality of colors by forming the adjusted image and the additional image for each of the plurality of colors on the intermediate transfer body, and a second correction value of the formation timing is determined to suppress color misalignment of the adjusted image of the first color relative to the adjusted image of the second color by forming only the adjusted image for each of the plurality of colors on the intermediate transfer body, an image forming apparatus that generates, as the correction information, information indicating the relationship between the evaluation value and the correction value based on a first evaluation value of the toner amount of the adjusted image and the additional image for each of the plurality of colors, a second evaluation value of the toner amount of the adjusted image for each of the plurality of colors, the first correction value, and the second correction value.

18. 18. The image forming apparatus according to claim 17, wherein the control means determines a third evaluation value of the amount of toner of the image to be formed on the intermediate transfer body when forming the user image based on the print job on the sheet, and determines a correction value of the formation timing to be used when forming the user image on the sheet based on the third evaluation value and the correction information.

19. 19. The image forming apparatus according to claim 17, wherein the additional image is formed in a range different from a range in which the adjusted images of the plurality of colors are formed in a width direction perpendicular to a rotation direction of the intermediate transfer body.

20. the first transfer regions in which the images formed on the plurality of photosensitive members are transferred to the intermediate transfer member are different from one another; the image on the intermediate transfer member is transferred to the sheet at a second transfer region; the image transferred onto the intermediate transfer body by a first photoconductor among the plurality of photoconductors is transported to the second transfer area via first transfer areas of all other photoconductors different from the first photoconductor among the plurality of photoconductors; The image forming apparatus according to claim 17 or 18, wherein the additional image is formed on the first photosensitive member.

Images