Image forming apparatus

Abstract

This system accurately determines the amount of DC color shift while minimizing the effects of AC color shift. [Solution] The image forming apparatus forms a detection pattern on an image carrier by forming a first image and a second image on each of a plurality of photoreceptors and transferring them to an image carrier, thereby forming a detection pattern on the image carrier that includes a first image group including a plurality of first images of different colors and a second image group including a plurality of second images of different colors. The apparatus is equipped with control means that determines the amount of color shift in the rotation direction of the image carrier and the amount of color shift in the width direction perpendicular to the rotation direction based on the detection result of the detection pattern. The first image is a linear image in a first direction, and the second image is a linear image in a second direction different from the first direction. The detection pattern includes a plurality of basic patterns arranged at a first interval in the rotation direction, and each of the plurality of basic patterns includes a first image group and a second image group arranged at a second interval in the rotation direction, and a first image group and a second image group arranged at a third interval different from the second interval.

Description

Technical Field

[0001] The present invention relates to color shift correction technology in an image forming apparatus.

Background Art

[0002] In an image forming apparatus that forms images of different colors on a plurality of photoreceptors and transfers the images formed on each photoreceptor onto a transfer belt to form a color image, color shift may occur due to mechanical factors or environmental factors. Color shift includes a steady color shift (hereinafter referred to as DC color shift) that does not depend on the position in the rotation direction of the transfer belt, and an unsteady color shift (hereinafter referred to as AC color shift) that changes depending on the position in the rotation direction of the transfer belt, and the AC color shift is caused by factors such as eccentricity of rotating bodies such as photoreceptors and transfer belts, eccentricity of drive members such as motors that drive the rotating bodies, and unevenness in the thickness of the transfer belt.

[0003] To suppress DC color shift, the image forming apparatus performs color shift correction processing. Specifically, the image forming apparatus forms a detection pattern including images of each color on the transfer belt, and detects the relative positional relationship of the images of each color included in the detection pattern. Then, the image forming apparatus determines the amount of color shift of the images of other colors with respect to the image of the reference color based on the detection result of the detection pattern. The image forming apparatus generates correction parameters for suppressing the color shift of each color based on the determined amount of color shift. By performing image formation based on the correction parameters, DC color shift can be suppressed. Here, if AC color shift occurs in the color shift correction processing, depending on the arrangement of each image of the detection pattern on the transfer belt, an error occurs in the amount of color shift of the DC color shift determined in the color shift correction processing due to the influence of the AC color shift, and the DC color shift remains.

[0004] Patent Document 1 discloses a detection pattern for performing color shift correction processing that suppresses the influence of AC color shift. According to Patent Document 1, a first image group and a second image group that are inclined in opposite directions with respect to the conveyance direction (moving direction) of the surface of the transfer belt are arranged alternately at equal intervals along the conveyance direction.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-203964 [Overview of the project] [Problems that the invention aims to solve]

[0006] AC color shift occurs not only over a period of one rotation of the rotating body or the motor driving it, but also over a period of 1 / M rotations, where M is an integer greater than or equal to 2. In the following explanation, AC color shift over a period of one rotation of the rotating body or the motor driving it will be referred to as "basic AC color shift." AC color shift over a period of 1 / M rotations will be referred to as "Mth-order AC color shift."

[0007] When the first and second image groups are arranged alternately at equal intervals along the transport direction of the transfer belt, it may not be possible to suppress the effects of M-order AC color shift. In this case, the effects of M-order AC color shift will result in residual errors in the amount of DC color shift determined by the color shift correction process.

[0008] This invention provides a technology for accurately determining the amount of DC color shift while suppressing the influence of AC color shift. [Means for solving the problem]

[0009] According to one aspect of the present invention, an image forming apparatus includes a plurality of photoreceptors that are driven to rotate and on which images of different colors are formed, an image carrier that is driven to rotate and on which the images formed on the plurality of photoreceptors are transferred, a detection means for detecting the images transferred to the image carrier, and a detection pattern formed on the image carrier by forming a first image and a second image on each of the plurality of photoreceptors and transferring them to the image carrier, thereby forming a first image group including a plurality of first images of different colors and a second image group including a plurality of second images of different colors, and based on the detection result of the detection pattern by the detection means, the color shift in the rotational direction of the image carrier is detected. The system includes a control means for determining a quantity and a color shift amount in the width direction perpendicular to the rotation direction, wherein the first image is a linear image in a first direction different from the rotation direction, the second image is a linear image in a second direction different from the rotation direction and the first direction, the detection pattern includes a plurality of basic patterns arranged at a first interval in the rotation direction, each of the plurality of basic patterns includes a first group of images and a second group of images arranged at a second interval in the rotation direction, and a first group of images and a second group of images arranged at a third interval different from the second interval in the rotation direction. [Effects of the Invention]

[0010] According to the present invention, it is possible to accurately determine the amount of DC color shift while suppressing the influence of AC color shift. [Brief explanation of the drawing]

[0011] [Figure 1] Control configuration diagrams of image forming apparatus according to several embodiments. [Figure 2] Configuration diagrams of a printer engine according to several embodiments. [Figure 3] Diagrams illustrating the configuration of the mechanism according to several embodiments. [Figure 4] Diagrams illustrating the sensor in several embodiments. [Figure 5] A diagram showing pairs of images according to several embodiments. [Figure 6]An explanatory diagram of how images are detected using a sensor. [Figure 7] An explanatory diagram of the principle for determining the amount of color shift in the width direction. [Figure 8] A diagram showing examples of the arrangement of the basic pattern according to several embodiments. [Figure 9] A diagram showing a basic pattern according to one embodiment. [Figure 10] Flowcharts of color shift correction processing according to several embodiments. [Figure 11] An explanatory diagram of the phase difference between the first and second image groups for third-order AC color shift. [Figure 12] A diagram showing a basic pattern according to one embodiment. [Modes for carrying out the invention]

[0012] 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.

[0013] <First Embodiment> Figure 1 is a diagram showing the configuration of an image forming system including an image forming apparatus 102 according to this embodiment. When the video controller 103 of the image forming apparatus 102 receives an instruction to form an image from the host computer 101, it performs various image processing such as color conversion and halftone processing on the image data received along with the instruction, and transmits the processed image data to the printer engine 104. The printer engine 104 forms an image on a sheet based on the image data from the video controller 103.

[0014] FIG. 2 is a schematic configuration diagram of the printer engine 104. The central processing unit (CPU) 303 of the engine control unit 301 executes a control program stored in the nonvolatile memory 306 to control the mechanism unit 302 to form an image on a sheet. At that time, the CPU 303 uses the RAM 305 as a main memory and a work area. The application specific integrated circuit (ASIC) 304 also controls the mechanism unit 302 for image formation on the sheet under the control of the CPU 303. The engine interface (IF) 307 is a communication unit with the video controller 103. Each functional block of the engine control unit 301 is configured to be able to communicate with each other via the system bus 312.

[0015] Note that a configuration may be adopted in which part or all of the functions described as being executed by the CPU 303 are executed by the ASIC 304. Also, a configuration may be adopted in which part or all of the functions described as being executed by the ASIC 304 are executed by the CPU 303. Further, additional dedicated hardware not shown may be provided, and a configuration may be adopted in which part or all of the functions described as being executed by the CPU 303 or the ASIC 304 are executed by the hardware.

[0016] Figure 3 is a cross-sectional view of the mechanism unit 302 shown in Figure 2. In Figure 3, the characters Y, M, C, and K at the end of the reference numerals indicate that the colors of the images related to the members indicated by the reference numerals are yellow, magenta, cyan, and black, respectively. In the following description, when there is no need to distinguish the colors of the images related to the members, the reference numerals excluding the characters at the end are used generically. The photoreceptor 22 is rotationally driven in the counterclockwise direction in the figure during image formation. The charging unit 23 charges the surface of the photoreceptor 22 to a uniform potential. The optical scanning unit 24 forms an electrostatic latent image on the photoreceptor 22 by scanning the rotationally driven photoreceptor 22 with light based on image data. The rotational axis direction of the photoreceptor 22 is referred to as the main scanning direction. Also, the rotational direction of the photoreceptor 22 is referred to as the sub-scanning direction. The main scanning direction and the sub-scanning direction are orthogonal to each other. The developing unit 26 forms an image (toner image) on the photoreceptor 22 by developing the electrostatic latent image formed on the photoreceptor 22 with toner. The image formed on the photoreceptor 22 is transferred to the transfer belt 27, which is an image carrier. Note that by overlapping and transferring the images of each photoreceptor 22 onto the transfer belt 27, a full-color image is formed on the transfer belt 27.

[0017] The transfer belt 27 is rotationally driven in the clockwise direction in the figure by the drive roller 25 during image formation. As a result, the image on the transfer belt 27 is conveyed to the opposing position of the transfer roller 28. On the other hand, the sheet 11 stored in the cassette 21 is conveyed to the opposing position of the transfer roller 28 in accordance with the timing when the image on the transfer belt 27 is conveyed to the opposing position of the transfer roller 28. The transfer roller 28 transfers the image on the transfer belt 27 to the sheet 11. After the transfer of the image, the sheet 11 is conveyed to the fixing unit 30. The fixing unit 30 fixes the image to the sheet 11 by heating and pressing the sheet 11. After the fixing of the image, the sheet 11 is discharged to the outside of the image forming apparatus 102. The sensor 6 is provided at the opposing position of the transfer belt 27 and detects the detection pattern formed on the transfer belt 27 in the color shift correction process.

[0018] Figure 4 is an explanatory diagram of the sensor 6 according to this embodiment. As shown in Figure 4(A), the sensor 6 is a collective term for sensors 6L and 6R, which are provided at different positions in the width direction perpendicular to the transport direction on the surface of the transfer belt 27. The transport direction corresponds to the sub-scanning direction of the photoreceptor 22, and the width direction corresponds to the main scanning direction of the photoreceptor 22. The transport direction is also the rotation direction of the transfer belt 27. Figure 4(B) is a configuration diagram of the sensor 6. The light-emitting unit 61 is, for example, a light-emitting diode (LED), which irradiates light toward the area of ​​the transfer belt 27 including the irradiation position 63. The light-receiving unit 62 is, for example, a phototransistor, which receives the reflected light irradiated by the light-emitting unit 61 from the surface of the transfer belt 27 and the detection pattern formed thereon. As shown in Figure 4(B), the light-emitting unit 61 and the light-receiving unit 62 are arranged such that the angle A of the straight line connecting the light-emitting unit 61 and the irradiation position 63, with respect to the normal direction of the transfer belt 27, is different from the angle B of the straight line connecting the light-receiving unit 62 and the irradiation position 63. As a result, the light-receiving unit 62 receives diffusely reflected light from the transfer belt 27 and the detection pattern. The light-receiving unit 62 transmits a detection signal indicating the light-receiving level (light-receiving intensity or amount of light-receiving) to the engine control unit 301. Alternatively, a separate light-receiving unit that mainly detects specularly reflected light may be provided.

[0019] Sensor 6 irradiates light toward the region including the irradiation position 63 and detects a detection pattern based on the reflected light. Therefore, the region irradiated by light from sensor 6, including the irradiation position 63, becomes the detection region of the detection pattern by sensor 6. The line 701L in Figure 4(A) connects the light irradiation positions 63 by sensor 6L, which change with the rotation of the transfer belt 27, and the straight line 701R in Figure 4(B) connects the light irradiation positions 63 by sensor 6R, which change with the rotation of the transfer belt 27. In order for sensor 6L to detect a detection pattern, the detection pattern must be formed on the straight line 701L, and in order for sensor 6R to detect a detection pattern, the detection pattern must be formed on the straight line 701R. In the following explanation, the position on the straight line 701L will also be referred to as the detectable position 701L of sensor 6L, and the position on the straight line 701R will also be referred to as the detectable position 701R of sensor 6R. Furthermore, if sensors 6L and 6R are not distinguished, the detectable positions 701L and 701R are collectively referred to as detectable position 701.

[0020] Next, we will describe the image group pairs that constitute the detection pattern formed on the transfer belt 27 during the color shift correction process. In the following description, unless otherwise stated in the context, expressions related to direction and order such as "front side" and "rear side" will be based on the transport direction of the transfer belt 27. Figure 5 shows the image group pair. The image group pair includes a first image group and a second image group. The first image group includes linear images Y1, B1, M1, and C1 tilted at 45 degrees with respect to the transport direction. Image Y1 is a yellow image, image B1 is a black image, image M1 is a magenta image, and image C1 is a cyan image. In this embodiment, image B1 is formed on top of image Y1. As shown in Figure 5, image Y1 is divided by image B1 into a front part (hereinafter referred to as front image Y1) and a rear part (hereinafter referred to as rear image Y1). The reason for creating image B1 on top of image Y1 will be explained later.

[0021] The second image group includes images Y2, B2, M2, and C2, which correspond to images Y1, B1, M1, and C1, respectively. In this embodiment, each image in the second image group is an inverted version of the corresponding image in the first image group, with respect to the transport direction. In other words, in this embodiment, the first and second image groups are symmetrical with respect to the transport direction. Since the first and second image groups are symmetrical with respect to the transport direction, the first image group will be described below, and the description of the second image group will be omitted.

[0022] As shown in Figure 5, non-image-forming regions are provided between image M1 and image C1, and between the rear image Y1 and image M1, with the length of these regions in the transport direction (hereinafter referred to as non-image-forming length) being s. Furthermore, the lengths of the front image Y1, image B1, rear image Y1, image M1, and image C1 in the transport direction (hereinafter referred to as image length) are w. In addition, the length of the front image Y1, image B1, rear image Y1, image M1, and image C1 in the width direction (hereinafter referred to as image width) is h.

[0023] As described above, in this embodiment, the sensor 6 receives diffusely reflected light from each image of the transfer belt 27 and the detection pattern. Here, the light emitted by the sensor 6 is mainly specularly reflected from the surface of the transfer belt 27, and the light emitted by the sensor 6 is mainly diffusely reflected from the yellow, cyan, and magenta images. Therefore, when the yellow, cyan, and magenta images are within the detection area of ​​the sensor 6, the light reception level (received light intensity or amount of light) of the sensor 6 is greater than when the surface of the transfer belt 27 (unformed area) is within the detection area of ​​the sensor 6.

[0024] Figure 6 shows the detection signal when image M1 passes through the detection area of ​​sensor 6. As described above, because the light reflection patterns of image M1 and the surface of the transfer belt 27 are different, when image M1 passes through the detection area of ​​sensor 6, the detection signal initially increases and then decreases. The engine control unit 301 uses the timing te0, when the detection signal exceeds a threshold, as the detection timing for the front edge of image M1, and the timing te1, when the detection signal falls below the threshold, as the detection timing for the rear edge of image M1. The engine control unit 301 then uses the average of the two detection timings te0 and te1 as the detection timing for image M1. The average of the two detection timings te0 and te1 can be considered as the detection timing approximately at the center of the transport direction of image M1. The same applies to image C1.

[0025] Next, we will explain the reason for forming image B1 on top of image Y1. In a black image, the amount of light that is specularly and diffusely reflected due to light absorption is small. For this reason, the light reception level of sensor 6 does not change significantly when the black image is within the detection area of ​​sensor 6 and when the surface of the transfer belt 27 (non-formed area) is within the detection area of ​​sensor 6. Therefore, even if image B1 is formed with non-formed areas on both the front and back sides, as in image M1 and image C1, image B1 cannot be detected. For this reason, in this embodiment, image B1 is formed in a part of the area of ​​image Y1.

[0026] As the front image Y1, image B1, and rear image Y1 pass sequentially through the detection area of ​​sensor 6, the light reception level of sensor 6 changes in a manner that inverts the detection signal level shown in Figure 6. Therefore, the engine control unit 301 determines the detection timing of image B1 by setting the timing te0, when the detection signal falls below a threshold, as the detection timing for the front edge of image B1, and the timing te1, when the detection signal exceeds a threshold, as the detection timing for the rear edge of image B1. Since the light reception level of sensor 6 is low when image B1 is in the detection area, the rear image Y1 (or front image Y1) can be detected as explained in Figure 6. Note that the threshold used to determine the edge detection timing can be different for each color of the image.

[0027] In this manner, image B1 is formed on top of image Y1 in order to detect images of each color using the light-receiving unit 62, which receives diffusely reflected light from the transfer belt 27 and the detection pattern. In this embodiment, image B1 is formed on top of image Y1, but it is also possible to form image B1 on top of images M1 or C1. Furthermore, if the sensor 6 is equipped with a light-receiving unit that receives specularly reflected light from the transfer belt 27 and the detection pattern, it is not necessary to form image B1 on top of images of other colors. In this case, the first image group can be formed by providing non-formed regions between each of images Y1, B1, M1, and C1.

[0028] In the following explanation, as shown in Figure 5, g is defined as the shortest distance of the unformed region between the last image C1 of the first image group and the first image Y2 of the second image group. Furthermore, the distance between the transport direction center position of the front image Y1 and the transport direction center position of the front image Y2 on a straight line 500 passing through the widthwise center of each image is denoted as the image group interval La. The image group interval La is also the distance between the transport direction center position of a certain image in the first image group and the transport direction center position of the corresponding image in the second image group. The image group pairs are formed such that the straight line 500 coincides with the detectable position 701 of the sensor 6.

[0029] Next, we will explain how to determine the amount of color shift in the transport direction and width direction from the detection results of the image group pair shown in Figure 5 by the sensor 6. In the following explanation, black will be used as the reference color. Therefore, the engine control unit 301 will determine the amount of color shift of the yellow, magenta, and cyan images relative to the black image. Since the principle for determining the amount of color shift is the same for each color, only the method for determining the amount of color shift of cyan will be explained below. Note that the reference color is not limited to black and may be any other color.

[0030] First, let's explain the amount of color misalignment in the transport direction. If there is no color misalignment in the transport direction, the distance between image B1 and image C1 in the transport direction, and the distance between image B2 and image C2 in the transport direction are both 2s + 3w. The engine control unit 301 calculates BC#1, the first distance in the transport direction between image B1 and image C1, by multiplying the difference between the detection timing of image B1 and the detection timing of image C1 by the moving speed of the surface of the transfer belt 27. Similarly, the engine control unit 301 calculates BC#2, the second distance in the transport direction between image B2 and image C2, by multiplying the difference between the detection timings of image B2 and image C2 by the moving speed of the surface of the transfer belt 27. Then, the engine control unit 301 determines the amount of color misalignment in the transport direction by subtracting the ideal distance (2s + 3w) from the average value of the first distance BC#1 and the second distance BC#2. A positive value for the color shift indicates that the cyan image is shifted behind its ideal position, while a negative value indicates that the cyan image is shifted in front of its ideal position.

[0031] Next, we will explain the amount of color shift in the width direction. Figure 7 shows a state where the cyan image is shifted to the left by a value of E in the transport direction. Since each image is at a 45-degree angle with respect to the transport direction, the first distance BC#1 in the transport direction between image B1 and image C1 is longer by a value of E than the ideal distance (2s + 3w). On the other hand, the second distance BC#2 in the transport direction between image B2 and image C2 is shorter by a value of E than the ideal distance (2s + 3w). As is clear from Figure 7, subtracting the second distance BC#2 from the first distance BC#1 gives a value of 2E, which is twice the amount of color shift. Therefore, the engine control unit 301 determines that half the value obtained by subtracting BC#2 from BC#1 is the amount of color shift in the width direction. Note that a positive value for the amount of color shift indicates that the cyan image is shifted to the left in the transport direction, and a negative value for the amount of color shift indicates that the cyan image is shifted to the right in the transport direction.

[0032] Next, the detection pattern formed on the transfer belt 27 during the color shift correction process will be explained. It is assumed that the circumference Ly of the transfer belt 27 is 760 [mm], and the image forming apparatus 102 is configured such that the amount of surface movement of the transfer belt 27 during one rotation of the photoreceptor 22 is Lx = 108 [mm]. Figures 8 and 9 are explanatory diagrams of the detection pattern for suppressing the effects of the "basic AC color shift," "secondary AC color shift," and "tertiary AC color shift" of the photoreceptor 22, as well as the "basic AC color shift" of the transfer belt 27.

[0033] As described above, the basic AC color shift of the photoreceptor 22 is the AC color shift with a period of one rotation of the photoreceptor 22 as one cycle. This is also the AC color shift that occurs on the surface of the transfer belt 27 with a period of interval Lx. The secondary AC color shift of the photoreceptor 22 is the AC color shift with a period of one half rotation of the photoreceptor 22 as one cycle. This is also the AC color shift that occurs on the surface of the transfer belt 27 with a period of interval Lx / 2. The tertiary AC color shift of the photoreceptor 22 is the AC color shift with a period of one-third rotation of the photoreceptor 22 as one cycle. This is also the AC color shift that occurs on the surface of the transfer belt 27 with a period of interval Lx / 3. Similarly, the basic AC color shift of the transfer belt 27 is the AC color shift that occurs with a period of one rotation of the transfer belt 27, that is, with a period of interval Ly on the surface of the transfer belt 27.

[0034] The detection pattern in this example, as shown in Figure 8, consists of three basic patterns #1 to #3 arranged with a pattern interval Lb = {2 + (1 / 3)}Lx = 252 [mm]. The pattern interval Lb is the distance between the same position in the same image of two consecutive basic patterns. The pattern interval Lb is also referred to as the first interval. In this example, since the circumference Ly of the transfer belt 27 is 760 [mm], the pattern interval Lb is approximately equal to 1 / 3 of the circumference Ly of the transfer belt 27. Each basic pattern includes two image group pairs, #1 and #2, as shown in Figure 9. The image group interval La of image group pair #1 (see Figure 5) is Lx / 2 = 54 [mm], and the image group interval La of image group pair #2 is Lx = 108 [mm]. The image group interval La of image group pair #1 is also referred to as the second interval, and the image group interval La of image group pair #2 is also referred to as the third interval.

[0035] The image group spacing La can be calculated as 5w + 2s + g + h. Therefore, as an example, if we set g = 24 [mm] for image group pair #1 and g = 78 [mm] for image group pair #2, and set w = 2 [mm], s = 4 [mm], and h = 12 [mm], the above image group spacing La can be obtained.

[0036] Next, a method for determining the amount of color shift based on the detection pattern described in Figures 8 and 9 will be explained. The detection pattern in this embodiment includes three image group pair #1 and three image group pair #2. The reason will be explained later, but in this embodiment, three image group pair #1 is used to determine the amount of color shift in the transport direction, and three image group pair #2 is used to determine the amount of color shift in the width direction. More specifically, the average of the three amount of color shift in the transport direction obtained based on the detection results of each of the three image group pair #1 is taken as the amount of color shift in the transport direction detected by the detection pattern. Similarly, the average of the three amount of color shift in the width direction obtained based on the detection results of each of the three image group pair #2 is taken as the amount of color shift in the width direction detected by the detection pattern.

[0037] As shown in Figure 4, the engine control unit 301 forms detection patterns on the transfer belt 27, one detected by sensor 6R and the other by sensor 6L. In the following description, the detection pattern detected by sensor 6R will be referred to as detection pattern R, and the detection pattern detected by sensor 6L will be referred to as detection pattern L. The engine control unit 301 uses the average of the amount of color misalignment in the transport direction detected by detection pattern R and the amount of color misalignment in the transport direction detected by detection pattern L as the final amount of color misalignment in the transport direction in the color misalignment correction process. Similarly, the engine control unit 301 uses the average of the amount of color misalignment in the width direction detected by detection pattern R and the amount of color misalignment in the width direction detected by detection pattern L as the final amount of color misalignment in the width direction in the color misalignment correction process.

[0038] Furthermore, the engine control unit 301 can determine the amount of image scaling in the width direction based on the difference between the amount of color shift in the width direction detected by detection pattern R and the amount of color shift in the width direction detected by detection pattern L. Furthermore, the engine control unit 301 can determine the amount of image tilt based on the difference between the amount of color shift in the transport direction detected by detection pattern R and the amount of color shift in the transport direction detected by detection pattern L.

[0039] Figure 10 is a flowchart of the color shift correction process according to this embodiment. The image forming apparatus starts the color shift correction process when predetermined conditions are met. These predetermined conditions may be met, for example, when the power is turned on. They may also be met when a predetermined number of prints have been made since the last color shift correction process, or when a predetermined amount of time has elapsed since the last color shift correction process. Furthermore, they may be met when the internal temperature of the image forming apparatus fluctuates by more than a predetermined value. The image forming apparatus may also start the color shift correction process in response to user instructions.

[0040] In S10, the engine control unit 301 forms detection pattern L and detection pattern R on the transfer belt 27. In S11, the engine control unit 301 obtains the detection result of detection pattern L from sensor 6L and the detection result of detection pattern R from sensor 6R. In S12, as described above, the engine control unit 301 determines the amount of color shift in the width direction, the amount of color shift in the transport direction, the amount of expansion / contraction in the width direction, and the amount of image tilt. In S13, based on the determination results in S12, the engine control unit 301 determines and saves correction parameters to reduce the amount of color shift in the width direction, the amount of color shift in the transport direction, the amount of expansion / contraction in the width direction, and the amount of image tilt. In subsequent image formation, the engine control unit 301 uses these correction parameters to perform image formation.

[0041] Next, we will explain why we use three image group pair #1 to determine the amount of color shift in the transport direction, and three image group pair #2 to determine the amount of color shift in the width direction. The basic patterns are arranged with a pattern interval Lb = {2 + (1 / 3)}Lx, as shown in Figure 8. In other words, the three basic patterns are arranged with a phase difference of 2π / 3 in the basic AC color shift where the length of one period (=2π) is Lx on the transfer belt 27. For example, if we take the phase of the placement position of basic pattern #1 as the reference, i.e., 0, then the phases of the placement positions of basic pattern #2 and basic pattern #3 are 2π / 3 and 4π / 3, respectively. In this way, since the three basic patterns are arranged with the same phase difference over one period of the basic AC color shift, by averaging the detection results of each of the three detection patterns, it is possible to suppress the error due to the influence of the basic AC color shift included in the amount of color shift determined by each basic pattern.

[0042] In the case of secondary AC color shift, where half a rotation of the photoreceptor 22 equals one period = 2π, the length of one period in the transfer belt 27 is Lx / 2. In this case, the phase of the placement positions of basic patterns #1, #2, and #3 is twice that of the basic AC color shift. That is, in the case of secondary AC color shift, the phases of the placement positions of basic patterns #1, #2, and #3 are 2×0=0, 2×2π / 3=4π / 3, and 2×4π / 3=2π / 3. Thus, even with secondary AC color shift, the three basic patterns are arranged with the same phase difference over one period. Therefore, by averaging the detection results of each of the three detection patterns, it is possible to suppress the error due to the influence of secondary AC color shift included in the amount of color shift determined for each basic pattern.

[0043] On the other hand, in the case of tertiary AC color shift, where 1 / 3 rotation of the photoreceptor 22 equals 1 period = 2π, the length of one period in the transfer belt 27 is Lx / 3. In this case, the phase of the placement positions of basic patterns #1, #2, and #3 is three times that of the basic AC color shift. That is, in the case of tertiary AC color shift, the phases of the placement positions of basic patterns #1, #2, and #3 are 3×0=0, 3×2π / 3=0, and 3×4π / 3=0, respectively. Thus, in the case of tertiary AC color shift, the phases of the placement positions of basic patterns #1, #2, and #3 are the same. Therefore, in the case of tertiary AC color shift, the influence cannot be suppressed by calculating the average of the three detection patterns, as can be done with basic AC color shift and tertiary AC color shift. Therefore, for tertiary AC color shift, it is necessary to suppress its influence in the amount of color shift determined based on the detection results of each of the three detection patterns.

[0044] As explained in Figure 5, the amount of color shift in the transport direction is calculated based on the average of the first distance in the transport direction measured in the first image group and the second distance in the transport direction measured in the second image group, that is, the sum of the first and second distances. On the other hand, the amount of color shift in the width direction is calculated based on the difference between the first and second distances.

[0045] As described above, one period of the third-order AC color shift is a distance of Lx / 3 on the transfer belt 27. Also, in image group pair #1, the distance in the transport direction between the first image group and the second image group is Lx / 2. Therefore, if the phase of the first image group is 0, the phase of the second image group is (Lx / 2) / (Lx / 3)=1.5, which is π. Thus, in the third-order AC color shift, the phase difference between the first image group and the second image group of image group pair #1 is π, meaning that the first image group and the second image group of image group pair #1 are in opposite phase. On the other hand, in image group pair #2, the distance in the transport direction between the first image group and the second image group is Lx. Therefore, if the phase of the first image group is 0, the phase of the second image group is (Lx) / (Lx / 3)=3, which is 0. Therefore, in a third-order AC color shift, the phase difference between the first and second image groups of image group pair #2 is 0, meaning that the first and second image groups of image group pair #2 are in phase.

[0046] This is shown in Figure 11. In Figure 11, reference numeral 600 indicates the first image group of image group pair #1 and image group pair #2, with a phase of 0. Reference numeral 601 indicates the second image group of image group pair #1, and reference numeral 602 indicates the second image group of image group pair #2. The sine wave in Figure 11 shows the color shift due to third-order AC color shift. As is clear from Figure 11, the phase of the second image group of image group pair #1 is out of phase with that of the first image group of image group pair #1, and the phase of the second image group of image group pair #2 is in phase with that of the first image group of image group pair #1.

[0047] Therefore, when the amount of color shift in the transport direction is determined using image pair #1, the error due to third-order AC color shift included in the first distance and the error due to third-order AC color shift included in the second distance are added in opposite phases and cancel each other out. On the other hand, when the amount of color shift in the width direction is determined using image pair #1, the error due to third-order AC color shift included in the first distance and the error due to third-order AC color shift included in the second distance are added in phase and remain.

[0048] Similarly, when calculating the widthwise color shift using image pair #2, the error due to third-order AC color shift in the first distance and the error due to third-order AC color shift in the second distance are added in opposite phases and cancel each other out. However, when calculating the transport direction color shift using image pair #2, the error due to third-order AC color shift in the first distance and the error due to third-order AC color shift in the second distance are added in phase and remain.

[0049] For example, suppose a basic pattern is formed as shown in Figure 8, containing only one of the image group pair #1 and image group pair #2 shown in Figure 9. Even in this case, for basic AC color shift and secondary AC color shift, the phases of the three basic patterns differ by 2π / 3, so the effect of AC color shift can be suppressed by averaging the amount of color shift obtained for each of the three basic patterns. However, as described above, for tertiary AC color shift, where the arrangement of the three basic patterns is in phase, the effect of AC color shift cannot be suppressed by averaging the amount of color shift obtained for each of the three basic patterns. Therefore, for tertiary AC color shift, it is necessary to suppress the effect of AC color shift for each amount of color shift obtained for each image group pair. However, with image group pair #1 alone, the effect of tertiary AC color shift remains in the amount of color shift in the width direction, and with image group pair #2 alone, the effect of tertiary AC color shift remains in the amount of color shift in the transport direction. Therefore, in this embodiment, the basic pattern is provided with two pairs of image groups with different image group spacings La. The amount of color shift in the transport direction is determined using one pair of image groups, and the amount of color shift in the width direction is determined using the other pair of image groups.

[0050] Furthermore, as described above, the distance between two adjacent basic patterns in the three basic patterns is approximately 1 / 3 of the circumference of the transfer belt 27. Therefore, by averaging the amount of color shift obtained from the three basic patterns, the influence of the basic AC color shift of the transfer belt 27 can also be suppressed.

[0051] In the above embodiment, the pattern spacing of the three basic patterns was set to Lb = {2 + (1 / 3)}Lx. As a result, the three basic patterns were arranged so that their phases differed by 2π / 3 in the basic AC color shift. Here, the "2" in {2 + (1 / 3)} is the distance the transfer belt 27 moves while the photoreceptor 22 rotates only twice, and it is clear that even if the value is an integer other than 2, the phase of the arrangement positions of the three basic patterns will differ by 2π / 3. In other words, the "2" in Lb = {2 + (1 / 3)}Lx used in the embodiment is just an example and can be any integer greater than or equal to 0. On the other hand, the "1 / 3" in {2 + (1 / 3)} indicates that the phases of the three basic patterns are arranged so that they differ by 1 / 3 of 2π.

[0052] Therefore, more generally, the pattern interval Lb of a detection pattern containing N basic patterns (where N is an integer greater than or equal to 2) can be given by Lb = {S + (1 / N)}Lx, where S is any integer greater than or equal to 0. As a result, on the transfer belt 27, the N basic patterns are positioned at positions with a phase difference of 2π / N. In the example in Figure 8, N is 3. Furthermore, in the above example, the length of one detection pattern containing three basic patterns was the same as the circumference of the transfer belt 27. However, if the circumference of the transfer belt 27 is long, it is also possible to form multiple detection patterns and determine the correction parameter by averaging the amount of color shift obtained for each detection pattern.

[0053] Furthermore, in the example in Figure 9, the image group interval La for image group pair #1 was set to Lx / 2 = 3Lx / 6. However, as is clear from Figure 11, whether the image group interval La is Lx / 6 or 5Lx / 6, the phase difference between the first and second image groups of image group pair #1 is π. Therefore, the image group interval La for image group pair #1 can be an odd multiple of Lx / 6 when N=3. More generally, for a detection pattern containing N basic patterns, the image group interval La for image group pair #1 can be an odd multiple of Lx × (1 / 2N).

[0054] Similarly, in the example in Figure 9, the image group interval La for image group pair #2 was set to Lx = 6Lx / 6. However, as is clear from Figure 11, the phase difference between the first and second image groups of image group pair #2 is 0 whether the image group interval La is 2Lx / 6 or 4Lx / 6. Therefore, the image group interval La for image group pair #2 can be an even multiple of Lx / 6 when N=3. More generally, for a detection pattern containing N basic patterns, the image group interval La for image group pair #2 can be an even multiple of Lx × (1 / 2N).

[0055] Furthermore, in the above example, Lx was defined as the distance the surface of the transfer belt 27 moves during the period of one rotation of the photoreceptor 22, that is, during the rotation period of the photoreceptor 22. However, if a basic AC color shift occurs due to eccentricity of the motor driving the photoreceptor 22, Lx can be defined as the distance the surface of the transfer belt 27 moves during the rotation period of the motor. Moreover, the AC color shift with the longest period caused by the photoreceptor 22 or the driving member of the photoreceptor 22 can be defined as the basic AC color shift of the photoreceptor 22, and Lx can be defined as the distance the surface of the transfer belt 27 moves during this longest period. Furthermore, in Figure 9, the first and second image groups of image group pair #1 are formed adjacently on the transfer belt 27, and then the first and second image groups of image group pair #2 are formed adjacently on the transfer belt 27. However, the formation order of the four image groups is not limited to that shown in Figure 9; for example, the first image group of image group pair #1, the first image group of image group pair #2, the second image group of image group pair #1, and the second image group of image group pair #2 may be formed in that order.

[0056] Furthermore, as shown in Figure 5, in this example, the direction of each linear image in the first image group was -45 degrees relative to the transport direction, assuming clockwise direction is positive, and the direction of each linear image in the second image group was +45 degrees relative to the transport direction. In this case, the amount of change from the ideal values ​​of the first and second distances is the same as the amount of color shift in the width direction. However, if at least one of the first and second distances changes from the ideal value according to the amount of color shift in the width direction, and the amount of change of the first and second distances is different, the amount of color shift in the width direction can be determined.

[0057] Therefore, if the first angle of the linear images in the first image group with respect to the transport direction is not 0, and the second angle of the linear images in the second image group with respect to the transport direction is not 0, and the first and second angles are different, then the amount of color shift in the width direction can be determined. Therefore, the first and second image groups are not limited to those shown in Figure 5.

[0058] With the above configuration, the influence of AC color shift caused by the rotation of the photoreceptor 22 or the motor driving the photoreceptor 22 can be suppressed, and the amount of DC color shift can be accurately determined. Furthermore, depending on the pattern spacing Lb, which is the distance between basic patterns, and the circumference of the transfer belt 27, the influence of AC color shift caused by the rotation of the transfer belt 27 or the drive roller 25 that drives the transfer belt 27 can also be suppressed.

[0059] <Second Embodiment> Next, the second embodiment will be described, focusing on the differences from the first embodiment. Figure 12 shows the basic pattern according to this embodiment. The basic pattern is arranged as shown in Figure 8. The detection patterns shown in Figures 8 and 11 also suppress the effects of the "basic AC color shift," "secondary AC color shift," and "tertiary AC color shift" of the photoreceptor 22, as well as the "basic AC color shift" of the transfer belt 27.

[0060] The basic pattern of the first embodiment included image group pair #1 and image group pair #2, with each of image group pair #1 and image group pair #2 containing a first image group and a second image group. The basic pattern of this embodiment is a common first image group for image group pair #1 and image group pair #2 in the first embodiment. Therefore, the image group spacing La between the first image group and one of the second image groups is Lx / 2, and the image group spacing La between the first image group and the other of the second image groups is Lx.

[0061] In this embodiment, the number of first image groups included in the basic pattern can be reduced compared to the first embodiment, and therefore the length of the basic pattern in the transport direction can be shortened compared to the first embodiment. Consequently, the region between the basic patterns can be used, for example, to form a detection pattern for density correction, and calibration can be performed efficiently, such as by performing color shift correction processing and density correction processing in parallel. In addition, the amount of toner consumed in color shift correction processing can be reduced.

[0062] [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.

[0063] This embodiment includes the following configuration. (Composition 1) Multiple photoreceptors that are driven to rotate and form images of different colors, An image carrier that is driven to rotate and onto which images formed on the plurality of photoreceptors are transferred, A detection means for detecting the image transferred to the image carrier, A detection pattern is formed on the image carrier by forming a first image and a second image on each of the plurality of photoreceptors and transferring them to the image carrier, thereby forming a first image group including a plurality of first images of different colors and a second image group including a plurality of second images of different colors. A control means determines the amount of color shift in the rotational direction of the image carrier and the amount of color shift in the width direction perpendicular to the rotational direction based on the detection result of the detection pattern by the detection means. Equipped with, The first image is a linear image in a first direction different from the rotation direction, The second image is a linear image in a second direction different from the rotation direction and the first direction. The detection pattern includes a plurality of basic patterns arranged at a first interval in the rotational direction, An image forming apparatus in which each of the plurality of basic patterns includes a first image group and a second image group arranged at a second interval in the rotational direction, and a first image group and a second image group arranged at a third interval different from the second interval in the rotational direction. (Configuration 2) The image forming apparatus according to configuration 1, wherein the control means uses the detection results of the first image group and the second image group arranged at the second interval to determine the amount of color shift in the rotational direction, and uses the detection results of the first image group and the second image group arranged at the third interval to determine the amount of color shift in the width direction. (Composition 3) The image forming apparatus according to claim 1 or 2, wherein the first image group among the first and second image groups arranged at the second interval is the same as the first image group among the first and second image groups arranged at the third interval. (Composition 4) The image forming apparatus according to configuration 1 or 2, wherein the first image group and the second image group arranged at the second interval are different from the first image group and the second image group arranged at the third interval. (Composition 5) The aforementioned multiple basic patterns are N basic patterns that are integers greater than or equal to 2. The image forming apparatus according to any one of configurations 1 to 4, wherein the first interval, the second interval, and the third interval are intervals based on N. (Composition 6) The image forming apparatus according to configuration 5, wherein the first interval corresponds to the distance the surface of the image carrier moves during a period of {S + (1 / N)} times the rotation period of the plurality of photoreceptors or the motor driving the plurality of photoreceptors, and S is an integer greater than or equal to 0. (Composition 7) The second interval corresponds to the distance the surface of the image carrier moves during a period obtained by multiplying the rotation period of the plurality of photoreceptors or the motor driving the plurality of photoreceptors by an odd number, The image forming apparatus according to configuration 5 or 6, wherein the third interval corresponds to the distance the surface of the image carrier moves during a period obtained by multiplying (1 / 2N) times the rotation period by an even number. (Composition 8) The image forming apparatus according to configuration 5, wherein the first interval is an interval corresponding to a phase difference of 2π / N, when the distance the surface of the image carrier moves during the period in which the plurality of photoreceptors or the motor driving the plurality of photoreceptors rotates is defined as one period. (Composition 9) The second interval is the interval in which the first image group and the second image group are in opposite phase, when one period is defined as the distance the surface of the image carrier moves during one rotation of the plurality of photoreceptors or the motor driving the plurality of photoreceptors. The image forming apparatus according to configuration 5 or 6, wherein the third interval is the interval at which the first image group and the second image group are in phase, when the distance the surface of the image carrier moves during the period of one rotation of the plurality of photoreceptors or the motor driving the plurality of photoreceptors is defined as one period.

[0064] 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]

[0065] 22Y, 22M, 22C, 22K: Photoreceptor, 27: Transfer belt, 6: Sensor, 301: Engine control unit

Claims

1. Multiple photoreceptors that are driven to rotate and form images of different colors, An image carrier that is driven to rotate and onto which images formed on the plurality of photoreceptors are transferred, A detection means for detecting the image transferred to the image carrier, A detection pattern is formed on the image carrier by forming a first image and a second image on each of the plurality of photoreceptors and transferring them to the image carrier, thereby forming a first image group including a plurality of first images of different colors and a second image group including a plurality of second images of different colors. A control means determines the amount of color shift in the rotational direction of the image carrier and the amount of color shift in the width direction perpendicular to the rotational direction based on the detection result of the detection pattern by the detection means. Equipped with, The first image is a linear image in a first direction different from the rotation direction, The second image is a linear image in a second direction different from the rotation direction and the first direction. The detection pattern includes a plurality of basic patterns arranged at a first interval in the rotational direction, An image forming apparatus in which each of the plurality of basic patterns includes a first group of images and a second group of images arranged at a second interval in the rotational direction, and a first group of images and a second group of images arranged at a third interval different from the second interval in the rotational direction.

2. The image forming apparatus according to claim 1, wherein the control means uses the detection results of the first image group and the second image group arranged at the second interval to determine the amount of color shift in the rotational direction, and uses the detection results of the first image group and the second image group arranged at the third interval to determine the amount of color shift in the width direction.

3. The image forming apparatus according to claim 1, wherein the first image group among the first and second image groups arranged at the second interval is the same as the first image group among the first and second image groups arranged at the third interval.

4. The image forming apparatus according to claim 1, wherein the first image group and the second image group arranged at the second interval are different from the first image group and the second image group arranged at the third interval.

5. The aforementioned multiple basic patterns are N basic patterns that are integers greater than or equal to 2. The image forming apparatus according to any one of claims 1 to 4, wherein the first interval, the second interval, and the third interval are intervals based on N.

6. The image forming apparatus according to claim 5, wherein the first interval corresponds to the distance the surface of the image carrier moves during a period of {S + (1 / N)} times the rotation period of the plurality of photoreceptors or the motor driving the plurality of photoreceptors, and S is an integer of 0 or more.

7. The second interval corresponds to the distance the surface of the image carrier moves during a period obtained by multiplying the rotation period of the plurality of photoreceptors or the motor driving the plurality of photoreceptors by an odd number, The image forming apparatus according to claim 5, wherein the third interval corresponds to the distance the surface of the image carrier moves during a period obtained by multiplying (1 / 2N) times the rotation period by an even number.

8. The image forming apparatus according to claim 5, wherein the first interval is an interval corresponding to a phase difference of 2π / N, when the distance the surface of the image carrier moves during the period in which the plurality of photoreceptors or the motor driving the plurality of photoreceptors rotates once is defined as one period.

9. The second interval is the interval in which the first image group and the second image group are in opposite phases, when one period is defined as the distance the surface of the image carrier moves during one rotation of the plurality of photoreceptors or the motor driving the plurality of photoreceptors. The image forming apparatus according to claim 5, wherein the third interval is the interval at which the first image group and the second image group are in phase, when the distance the surface of the image carrier moves during the period of one rotation of the plurality of photoreceptors or the motor driving the plurality of photoreceptors is defined as one period.

Images