Image forming apparatus, color shift correction method, and control program

Abstract

To perform appropriate color shift adjustment even when executing a plurality of types of printing modes different in the number of colors or the combination of colors.SOLUTION: An image forming apparatus 1 comprises: a crimp release mechanism 15 that moves at least one primary transfer unit 21, of a plurality of primary transfer units 21 provided opposite to a plurality of photoreceptor drums 31, respectively, to switch between a crimp position where transfer nips are formed and a release position where the photoreceptor drums 31 and an intermediate transfer belt 22 are separated from each other; and a control unit 11 that performs color shift adjustment when the combination of imaging units used for image formation is changed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, a color shift correction method, and a control program.

Background Art

[0002] In an electrophotographic full-color image forming apparatus, color images are superimposed on an intermediate body such as an intermediate transfer belt to form a color image. If the image formation positions of each color do not match with high precision, color shift occurs. As a technique for adjusting color shift, there is a technique in which registration wave lines of each color are formed on an intermediate transfer body, and the image formation positions of each color are calculated by detecting these positions with an optical sensor to perform color shift correction. For example, in the image forming apparatus disclosed in Patent Document 1, when the pressing force of the secondary transfer unit is changed according to the type of paper, the problem is that the positions of the toner images of each color on the intermediate transfer belt are shifted. To solve this problem, under conditions of the pressing forces of a plurality of different secondary transfer units, a resist pattern is formed on the intermediate transfer belt and detected by a detection unit, thereby generating color shift correction data corresponding to the plurality of pressing forces.

[0003] Generally, an image forming apparatus can execute a plurality of types of print modes in which the number of colors of toner used or the combination of colors is different. In each print mode, in an image forming unit that is not used (configured by a photosensitive drum, a developing device, etc.), the drive is stopped to suppress deterioration of the apparatus due to wear or the like. At this time, in order to prevent problems such as scratches due to unnecessary rubbing between the unused and stopped photosensitive drum and the moving and rotating intermediate transfer belt, the intermediate transfer belt is separated from the photosensitive drum by retreating the primary transfer roller from the crimping position to the release position. In Patent Document 2, different print modes such as a monochrome mode and a multicolor mode can be executed, and when performing calibration for correcting the amount of color shift and density, the timing of executing the calibration is varied depending on the difference in the print mode.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-133544 [Patent Document 2] Japanese Patent Publication No. 2006-201457 [Overview of the project] [Problems that the invention aims to solve]

[0005] The intermediate transfer belt is tensioned by multiple rollers, including drive rollers, tension rollers, and primary transfer rollers, which are positioned on its inner circumference. Depending on the printing mode, the pressure / release state of the primary transfer rollers that are in contact with the intermediate transfer belt is switched, which changes the tension of the intermediate transfer belt and consequently changes the amount of color misalignment.

[0006] The technology described in Patent Document 2 changes the timing of calibration execution depending on the print mode, but does not consider calibration for each different print mode, and therefore cannot handle multiple types of print modes with different numbers of colors or color combinations. The technology described in Patent Document 1 generates color misalignment correction data that corresponds to changes in the pressing force of the secondary transfer section, enabling appropriate color misalignment adjustment in response to changes in pressing force, but similarly cannot handle multiple types of print modes with different numbers of colors or color combinations.

[0007] The present invention has been made in view of the above circumstances, and aims to provide an image forming apparatus, a color misalignment correction method, and a control program that can perform appropriate color misalignment adjustment even when executing multiple types of printing modes with different numbers of colors or color combinations. [Means for solving the problem]

[0008] The above objectives of the present invention are achieved by the following means.

[0009] (1) Multiple imaging units, each including an image carrier, which are used by a developer to form toner images of different colors on the image carrier, An intermediate transfer belt onto which the toner image on the image carrier is transferred, Multiple primary transfer sections are provided opposite to each of the multiple image carriers, and a transfer nip is formed by biasing the intermediate transfer belt from the inner circumferential surface towards the image carrier, A crimping release mechanism that, depending on the combination of imaging units used for image formation, moves at least one of the primary transfer sections to switch between a crimping position where the transfer nip is formed and a release position where the intermediate transfer belt and the image carrier are separated, An image forming apparatus comprising: a control unit that performs color shift adjustment when the combination of the imaging units used in image formation is changed.

[0010] (2) A sensor is provided to detect a color shift correction pattern formed by the toner image transferred onto the intermediate transfer belt, The image forming apparatus according to (1) above, wherein the control unit performs the color shift adjustment by detecting the color shift correction pattern.

[0011] (3) The image forming apparatus according to (2) above, wherein the control unit, in the color shift adjustment, detects the position of the pattern formed by the plurality of image forming units using the sensor, and, when one of the plurality of toners is used as the reference color, determines the amount of color shift correction during image formation based on the image formation positions of the toners of the other colors relative to the image formation positions of the toner of the reference color.

[0012] (4) The image forming apparatus according to (3) above, wherein the control unit corrects the image forming position in at least one of the plurality of image forming units by the amount of color shift correction.

[0013] (5) The image forming apparatus according to (4) above, further comprising a storage unit that stores the amount of color shift correction determined by the color shift adjustment for each combination of the image forming units in which the primary transfer unit is set to the pressing position and used for image formation.

[0014] (6) The image forming apparatus according to (5) above, wherein the control unit performs color shift correction using the color shift correction amount stored in the storage unit for each combination of the image forming units used.

[0015] (7) The storage unit stores the color shift correction amount along with the device status information of the image forming apparatus at the time of color shift adjustment, The control unit, when either primary transfer unit is switched from the crimping position to the release position or vice versa by the crimping release mechanism, The device status information linked to the color shift correction amount that matches the combination of imaging units used is compared with the current device status information of the image forming apparatus. If the change exceeds a predetermined value, perform the color shift correction using the newly obtained color shift correction amount obtained by performing the color shift adjustment. The image forming apparatus according to (5) or (6) above, wherein if the change is less than a predetermined amount, the color shift correction is performed using the color shift correction amount stored in the storage unit without performing the color shift adjustment.

[0016] (8) The image forming apparatus is an image forming apparatus that forms an image on continuous paper, An image forming apparatus according to any one of (1) to (6) above, comprising a secondary transfer unit for transferring the toner image on the intermediate transfer belt to the continuous paper.

[0017] (9) The image forming apparatus according to (8) above, wherein the pressing of the secondary transfer portion to the intermediate transfer belt is released during the color misalignment adjustment.

[0018] (10) The control unit stores a preset shift value or correction coefficient for the amount of color shift correction when the secondary transfer unit is in the pressed state and the released state. The image forming apparatus according to (9) above, wherein the color shift correction amount is set to a value obtained by adding the shift value to the color shift amount detected by the sensor, or by multiplying it by the correction coefficient.

[0019] (11) The plurality of image forming units includes four image forming units that form toner images of Y, M, C, and K colors. The combinations of the plurality of image forming units include a first group composed of the four image forming units that form toner images of Y, M, C, and K colors respectively, and a second group composed of a combination of colors different from those of the first group. When the control unit is changed from the first group to the second group or vice versa according to the setting in the print job, the image forming apparatus according to any one of (1) to (6) above executes the color shift adjustment.

[0020] (12) The plurality of image forming units further includes an image forming unit that forms a special color toner image other than Y, M, C, and K colors. The image forming apparatus according to (11) above, wherein the second group includes a combination of the five image forming units that form toner images of Y, M, C, K colors, and a special color toner image.

[0021] (13) A color shift correction method executed by an image forming apparatus including an image carrier, a plurality of image forming units that form toner images of different colors on the image carrier by a developing device, an intermediate transfer belt onto which the toner image on the image carrier is transferred, a plurality of primary transfer units provided opposite to the plurality of image carriers respectively, and forming a transfer nip by urging toward the image carrier from the inner peripheral surface side of the intermediate transfer belt, and a pressure release mechanism that switches between a pressure bonding position where the transfer nip is formed and a release position where the intermediate transfer belt and the image carrier are separated by moving at least one of the primary transfer units according to the combination of the image forming units used for image formation. The method includes a step (a) of performing color shift adjustment when the combination of the image forming units used for image formation is changed. A color shift correction method that executes a process including a step (a) of performing color shift adjustment when the combination of the image forming units used for image formation is changed.

[0022] (14) A control program for controlling an image forming apparatus comprising: a plurality of image forming units including an image carrier, each of which a developer forms a toner image of a different color on the image carrier; an intermediate transfer belt onto which the toner image on the image carrier is transferred; a plurality of primary transfer units provided opposite to each of the plurality of image carriers, which form a transfer nip by biasing the intermediate transfer belt toward the image carrier from the inner circumferential surface side; and a crimping release mechanism that moves at least one of the primary transfer units according to the combination of image forming units used for image forming, thereby switching between a crimping position where the transfer nip is formed and a release position where the intermediate transfer belt and the image carrier are separated, the control program for controlling an image forming apparatus, A control program for causing a computer to perform a process including (a) adjusting for color shift when the combination of imaging units used in image formation is changed. [Effects of the Invention]

[0023] The image forming apparatus according to the present invention includes a pressure release mechanism that switches between a pressure position in which the transfer nip is formed and a release position in which the intermediate transfer belt and the image carrier are separated, by moving at least one of the primary transfer units according to the combination of image forming units used for image formation, and a control unit that performs color misalignment adjustment when the combination of image forming units used for image formation is changed. This enables appropriate color misalignment adjustment even when executing multiple types of printing modes with different numbers of colors or color combinations. [Brief explanation of the drawing]

[0024] [Figure 1] This figure shows a schematic configuration of the image forming apparatus according to this embodiment. [Figure 2] This is a block diagram of an image forming apparatus. [Figure 3] This is a schematic diagram showing the pressure / release state of the primary transfer area in various printing modes (Group 1, Group 2-1, Group 2-2). [Figure 4] This figure shows an example of the amount of color shift correction. [Figure 5] This is a perspective view illustrating the resist sensor and resist pattern. [Figure 6] This is a flowchart showing the color shift correction process in the first embodiment, which is performed in an image forming apparatus. [Figure 7] This is a subroutine flowchart showing the color shift adjustment in step S05. [Figure 8] This is a flowchart showing the color shift correction process in the second embodiment, which is performed in an image forming apparatus. [Figure 9] This figure shows an example of the color shift correction amount linked to the device state used in the second embodiment. [Modes for carrying out the invention]

[0025] Embodiments of the present invention will be described below with reference to the attached drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios. The recording material includes long or roll-shaped continuous paper and cut (sheet-fed) paper. The continuous paper also includes long label paper in which adhesive-coated labels are laminated onto long release paper.

[0026] Figure 1 is a diagram showing the schematic configuration of the image forming apparatus 1 according to this embodiment. Figure 2 is a block diagram showing the hardware configuration of the image forming apparatus 1. Figure 3 is a schematic diagram showing the pressing / releasing state of the primary transfer unit 21 in various printing modes (groups 1-2-1 and 2-2). As shown in Figures 1 and 2, the image forming apparatus 1 includes an image forming apparatus body 10, a supply device 50, and a winding device 60 that are mechanically and electrically connected to each other.

[0027] (Feeding device 50, winding device 60) The supply device 50 includes a folder 51 to which the main reel 90 of the continuous paper 91 (also called a roll sheet or roll paper) is detachably attached. The winding device 60 includes a folder 61 for winding up the continuous paper 91 fed from the main reel 90. The supply device 50 and the winding device 60 also include a control unit, a storage unit, a paper transport unit, and a communication unit (some components are not shown). These components have the same functions as the components of the image forming apparatus main body 10 with corresponding names, which will be described later. The supply device 50 feeds the continuous paper 91 from the main reel 90 attached to the folder 51 to the downstream side of the transport path. The image forming apparatus main body 10 performs image formation on the fed-out continuous paper 91. The continuous paper 91, on which the image has been formed in the image forming apparatus main body 10, is transported to the downstream winding device 60, where it is wound up and held in the folder 61.

[0028] The image forming apparatus main unit 10 comprises a control unit 11, a storage unit 12, an operation display unit 13, a paper transport unit 14, a first pressure release mechanism 15, a second pressure release mechanism 16, an image forming unit 20, a resist sensor 17, an environmental sensor 18, and a communication unit 19, all of which are interconnected via signal lines. The image forming apparatus main unit 10 executes multiple types of printing modes with different numbers of colors or color combinations. As shown in Figure 3, the printing modes include a four-color mode using basic colors (yellow (Y), magenta (M), cyan (C), and black (K)) (hereinafter also referred to as the first group), a five-color mode adding a spot color (S) to these (hereinafter also referred to as the second group (2-1 group)), and a two-color spot color mode using K and S (hereinafter also referred to as the second group (2-3 group)). The four-color mode corresponds to the standard full-color mode. Special (S) toners include, for example, white toner and colorless transparent toner (clear toner) that improves the visibility of the paper.

[0029] (Control Unit 11) The control unit 11 is a CPU that controls each part of the device and performs various calculations according to the program. The control unit 11 also functions as a color shift adjustment unit 111 and an image processing unit 112.

[0030] The color misalignment adjustment unit 111 performs color misalignment adjustment (also called a resist pattern and resist adjustment, respectively) using a color misalignment correction pattern when the tension state of the intermediate transfer belt 22 changes due to the first pressure release mechanism 15 switching one of the primary transfer units 21 of the image forming unit 20 from the pressure position to the release position, or vice versa, in conjunction with a change in the printing mode. The color misalignment adjustment unit 111 also determines the amount of color misalignment correction for each color through color misalignment adjustment. Figure 4 shows an example of the color misalignment correction amount set by the color misalignment adjustment unit 111. The color misalignment correction amount is set for each printing mode, or more specifically, for each number of colors or color combination used in the printing mode. Some color misalignment correction amounts are set based on the amount of color misalignment from a predetermined color among the colors used in each printing mode, with the reference color being used as the reference color. In the example in Figure 4, the color misalignment correction amounts for the main scan position and sub scan position are set with K as the reference color (the same applies to the example in Figure 9). Figure 4 shows examples of print modes for three color combinations (groups 1, 2-1, and 2-2) where the color shift correction amount stored in the memory unit 12 is limited to these. If other color combinations are available for print modes, the color shift correction amount for those other combinations may also be set and stored.

[0031] The image processing unit 112 performs rasterization on the print data (image data) included in the print job. The image processing unit 112 also performs image processing on the rasterized raster image data, including gamma correction, screen correction, and density balance. Furthermore, the image processing unit 112 uses the color shift correction amount to perform image processing related to two-dimensional position correction, including the position of the main / sub scan, the magnification of the main / sub scan, tilt correction, and curvature correction.

[0032] (Storage unit 12) The memory unit 12 consists of a ROM for pre-storing various programs and data, a RAM for temporarily storing programs and data as a working area, and a hard disk for storing various programs and data. The memory unit 12 also stores the color shift correction amount (see Figure 4 below). The memory unit 12 also stores the total number of prints performed by the image forming apparatus 1, starting from the time the apparatus was installed. The total number of prints is incremented by the control unit 11 each time a print is made.

[0033] (Operation display section 13) The operation display unit 13 is equipped with a touch panel, numeric keypad, start button, stop button, etc., and is used for inputting various settings and instructions.

[0034] (Paper transport unit 14) The paper transport unit 14 is equipped with a transport path with multiple transport rollers and transports continuous paper 91 in cooperation with the paper transport units of the supply device 50 and the winding device 60.

[0035] (Image forming unit 20) The image forming unit 20 forms an image, for example, by an electrophotographic method. The image forming unit 20 includes writing units (not shown) corresponding to basic colors (Y, M, C, K) and spot colors (S), image forming units 30Y, 30M, 30C, 30K, 30S (hereinafter, these are collectively referred to as the image forming unit 30, and the same applies to the primary transfer unit 21 below), and primary transfer units 21Y, 21M, 21C, 21K, 21S (see Figure 3). The image forming unit 20 also includes an intermediate transfer belt 22, a secondary transfer unit 23, and a fixing unit 24.

[0036] The image-forming unit 30Y includes a photoreceptor drum 31Y, a developer 32Y, a charger (not shown), a cleaning unit (not shown), etc. The photoreceptor drum 31Y functions as an image carrier on which a toner image is formed by the developer. The other image-forming units 30M, 30C, 30K, and 30S have the same configuration as the image-forming unit 30Y, except that the toner color inside the developer 32 is different. Note that in Figure 1, the reference numerals for the photoreceptor drum 31 and developer 32 are omitted except for the Y color.

[0037] As shown in Figure 3, each primary transfer section 21 is composed of a biasing member such as a spring and transfer rollers r6 to r10. The intermediate transfer belt 22 is an endless belt, for example, a semiconductor belt with a thickness of 80 μm made of polyimide and set to a volume resistivity of 8 to 11 LOGΩ·cm. The intermediate transfer belt 22 is stretched by a plurality of rollers r1 to r5 arranged inside, and one of the transfer rollers r6 to r10 (see Figure 3) of the primary transfer section 21. Rollers r1 and / or r2 are drive rollers, and the driving force from the drive source is transmitted to them. Roller r4 is a tension roller, and while applying an outward biasing force to the intermediate transfer belt 22, it moves in an inward / outward direction (radial direction) within a predetermined range. The plurality of primary transfer sections 21 are each positioned inside the intermediate transfer belt 22, facing the photoreceptor drum 31 (image carrier). As shown in Figure 3(a), in the 5-color mode, all primary transfer units 21 are positioned at the crimping position. At the crimping position, the primary transfer units 21 are biased with a predetermined load from the inner circumferential surface side of the intermediate transfer belt 22 toward the photoreceptor drum 31, and contact with the intermediate transfer belt 22 to form a primary transfer nip N1. The secondary transfer units 23 are biased with a predetermined load toward the opposing roller r2 positioned on the inner circumferential surface of the intermediate transfer belt 22, and contact with the intermediate transfer belt 22 to form a secondary transfer nip N2.

[0038] In the image forming unit 20, the toner images formed on the photoreceptor drums 31 of each color image forming unit 30 are transferred to the intermediate transfer belt 22 by the primary transfer unit 21 and sequentially stacked to form a full-color toner image of four colors or five colors including spot colors. The full-color toner image is transferred to the continuous paper 91 by the secondary transfer unit 23. After transfer, the toner image is heated and pressurized by the downstream fixing unit 24 and fixed to the continuous paper 91. Any remaining toner on the intermediate transfer belt 22 is removed by a cleaning unit (not shown) positioned opposite the roller r3.

[0039] (First crimp release mechanism 15) The first crimp release mechanisms 15a and 15b (hereinafter collectively referred to as the first crimp release mechanism 15) are each equipped with a drive source such as a drive motor, a cam, an arm, etc., and switch between a crimped position and a released position by moving the primary transfer section 21 in the radial direction of the intermediate transfer belt 22 (hereinafter also referred to as crimp / release switching). The first crimp release mechanism 15a switches the crimp / release of the three primary transfer sections 21Y, 21M, and 21C together. The first crimp release mechanism 15b switches the crimp / release of the primary transfer section 21S individually. However, the first crimp release mechanism 15 is not limited to this and may be configured to allow the crimp / release switching of at least one of the multiple primary transfer sections 21Y, 21M, 21C, 21K, and 21S. Furthermore, the first pressure release mechanism 15 may be configured to allow individual pressure / release switching for each of the primary transfer sections 21Y, 21M, and 21C. Alternatively, it may be configured to allow pressure / release switching for the primary transfer section 21K for the K color. In this way, multi-color printing other than the three printing modes shown in Figure 3 (for example, combinations of 2 to 4 of Y, M, C, K, and S) can be performed.

[0040] In the "pressure position," as shown in Figure 3(a), the primary transfer section 21Y (roller r6) is biased with a predetermined load and comes into contact with the photoreceptor drum 31Y via the intermediate transfer belt 22, thereby forming a primary transfer nip N1. In the "release position," as shown in Figure 3(c), the primary transfer section 21Y retracts inward, causing the intermediate transfer belt 22 and the photoreceptor drum 31Y to be separated. In this release position, the primary transfer section 21Y (roller r6) moves inward, resulting in non-contact with the intermediate transfer belt 22 (state shown in Figure 3(c)) or slight contact (not shown), changing the tension state of the intermediate transfer belt 22 at rollers r1 to r10. In the 5-color mode shown in Figure 3(a), all five primary transfer sections 21Y, 21M, 21C, 21K, and 21S are in the pressure position, and the intermediate transfer belt 22 is tensioned by 10 rollers r1 to r10.

[0041] When the printing mode is switched from the 5-color mode shown in Figure 3(a) to the 4-color mode shown in Figure 3(b), the primary transfer unit 21S is switched from the pressed position to the released position by the first pressure release mechanism 15b (indicated by an arrow in Figure 3(b)). In this case, the intermediate transfer belt 22 becomes non-contact with the photoreceptor drum 31S and the primary transfer unit 21S, and the intermediate transfer belt 22 is tensioned by nine rollers r1 to r9. The slack in the tension state (change in path) of the intermediate transfer belt 22 due to the movement of the primary transfer unit 21S is mitigated by the tension roller r4 moving upward (outward) (indicated by an arrow in Figure 3(b)). Similarly, when switching from the spot color mode shown in Figure 3(a) to the spot color mode shown in Figure 3(c), the primary transfer units 21Y, 21M, and 21C are switched from the pressed position to the released position by the first pressure release mechanism 15a. In Figure 3(c), the intermediate transfer belt 22 is stretched by seven rollers, r1 to r5, r9, and r10. In this application, the inventors have found that when the printing mode is changed, the color used changes, and the combination of primary transfer sections 21 being pressed changes, the amount of color misalignment changes. Therefore, appropriate color misalignment adjustment is made possible by performing color misalignment correction as described later.

[0042] (Second crimp release mechanism 16) The second crimping release mechanism 16 includes a drive source such as a drive motor, a cam, an arm, etc., and switches between crimping and releasing the secondary transfer section 23. As shown in Figure 3(a), in the crimping position, the secondary transfer section 23 is biased toward the opposing roller r2 with a predetermined load and forms a secondary transfer nip N2 by contacting the continuous paper 91 and the intermediate transfer belt 22. In the release position (not shown), the secondary transfer section 23 retracts downward and becomes non-contact with the intermediate transfer belt 22. At this time, the continuous paper 91 also moves downward due to its own weight and becomes non-contact with the intermediate transfer belt 22.

[0043] (Resist Sensor 17) Figure 5 is a perspective view illustrating the resist sensor 17 and the resist pattern. The resist sensors 17a, 17b, and 17c (hereinafter collectively referred to as resist sensor 17) are reflective optical sensors incorporating, for example, light-emitting elements such as light-emitting diodes and light-receiving elements such as photodiodes. The resist sensors 17 are positioned opposite the roller r1 at three locations: both ends and the center in the axial direction (main scanning direction). Furthermore, when using a special color toner employing transparent toner, the resist sensors 17 may be selected to have detection sensitivity even for the transparent toner.

[0044] The resist sensor 17 detects a resist pattern for color misalignment correction for each color formed on the outer surface of the intermediate transfer belt 22 in order to obtain the amount of color misalignment correction for correcting the color misalignment of each color on the paper when performing color misalignment correction (also called color resist). The resist pattern consists of a straight line along the main scanning direction and a diagonal straight line intersecting it (V-shaped or U-shaped). The position in the main scanning direction is detected from the detection result of the positional relationship between the two straight lines of the resist pattern or the detection interval, and the amount of positional misalignment in the sub-scanning direction perpendicular to the main scanning direction can be detected from the detection timing of the straight line along the main scanning direction. This amount of positional misalignment is the amount of positional misalignment with respect to a reference color (in most cases, the K color), with one of the colors used being the reference color. Based on the amount of positional misalignment, the amount of color misalignment correction for the main and sub-scanning positions of each color (other than the reference color) is determined as shown in Figure 4 above. In addition, the main scanning magnification, sub-scanning magnification, slope, and curvature can be obtained from the combination of the results of the three resist sensors 17a, 17b, and 17c arranged in the main scanning direction, or from their respective detection timings. The number of resist sensors 17 should be sufficient to detect the resist pattern across the entire width of the intermediate transfer belt 22 so as to detect the positional displacement of the curvature component of the intermediate transfer belt 22. Four or more resist sensors may be arranged. Alternatively, a single line sensor with multiple image sensors arranged in a line may be used.

[0045] (Environmental sensor 18) The environmental sensor 18 detects the temperature and humidity inside the image forming apparatus body 10. In particular, the environmental sensor 18 is positioned near the intermediate transfer belt 22 and measures the temperature of the intermediate transfer belt 22.

[0046] (Communications Section 19) The communication unit 19 is an interface for communicating with other devices such as the supply device 50 and the winding device 60. The communication unit 19 also serves as an interface for network connection with external devices such as a PC.

[0047] (Color shift correction process in the first embodiment) Figure 6 is a flowchart showing the color shift correction process in the first embodiment performed by the image forming apparatus 1.

[0048] (Step S01) When the image forming apparatus 1 receives a print job from a user via the operation display unit 13 or a PC, it starts the print job. The print job data includes print data and a job ticket. The job ticket describes the print mode to be executed.

[0049] (Step S02) The control unit 11 determines whether the combination of image-making units 30 used has changed compared to the print mode of the previous print job, based on the print mode of the print job to be executed. More specifically, it determines whether it is necessary to switch the press-fit / release position of any of the primary transfer units 21. If the print mode switches between (1) 5-color mode, (2) 4-color mode, and (3) spot color mode, any of the primary transfer units 21 will be switched from the press-fit position to the release position, or vice versa. If a press-fit / release switch of any of the primary transfer units 21 is required (step S02: YES), the process proceeds to step S04. On the other hand, if there is no change in the image-making units 30 used and no switching is required (step S02: NO), the process proceeds to step S03. Note that the types of print modes are not limited to the three types (1) to (3), and other combinations may also be included. For example, it may include a combination of two, three, or four multicolor (e.g., Y and K) from among Y, M, C, K, and S.

[0050] (Step S03) Here, the image processing unit 112 of the control unit 11 performs image processing using the current color shift correction amount for the print job, and the image forming unit 20 then forms an image on the continuous paper 91 using the image data after this image processing, and the process ends (end).

[0051] (Step S04) The control unit 11 controls the first crimp release mechanism 15 to switch one or more primary transfer sections 21 between crimping and release. For example, if the previous setting was the four-color mode shown in Figure 3(b) and it is to change to the special color mode shown in Figure 3(c), the first crimp release mechanism 15a switches the primary transfer sections 21Y, 21M, and 21C from the crimped position to the release position, and conversely, the first crimp release mechanism 15b switches the primary transfer section 21S from the release position to the crimped position.

[0052] (Step S05) Here, the color shift adjustment unit 111 performs color shift adjustment. Figure 7 is a subroutine flowchart showing the color shift adjustment process in step S05.

[0053] (Step S501) The control unit 11 moves the secondary transfer unit 23 to the release position using the second pressure release mechanism 16, separating it from the opposing roller r2. At this time, the control unit may also stop the continuous paper 91 if it is being transported, turn off the heater of the fixing unit 24, and move the fixing roller to the separated position.

[0054] (Steps S502~S504) The color shift adjustment unit 111 uses the image-forming unit 30 to form resist patterns of each color on the intermediate transfer belt 22 and detects the resist patterns with the resist sensor 17. The color shift adjustment unit 111 also calculates the position of the resist pattern in the main scanning direction and the position (detection timing) in the sub-scanning direction based on the detection signals from each resist sensor 17, and determines various color shift correction amounts as shown in Figure 4.

[0055] (Step S505) The control unit 11 moves the secondary transfer section 23 to the crimping position using the second crimping release mechanism 16, returning it to the crimped state that forms the transfer nip N2. This completes the process shown in Figure 7, and the process returns to step S06 and onward in Figure 6.

[0056] (Step S06) Here, the image processing unit 112 of the control unit 11 performs image processing using the color shift correction amount obtained in step S05, and the image forming unit 20 then forms an image on the continuous paper 91 using the image data after this image processing, and the process ends (end).

[0057] As described above, the control unit of the image forming apparatus according to this embodiment moves at least one of the primary transfer units according to the combination of image forming units used for image formation, thereby switching between a pressing position where the transfer nip is formed and a release position where the intermediate transfer belt and the image carrier are separated. When the combination of image forming units used for image formation is changed, color misalignment adjustment is performed using a pattern for color misalignment correction. This enables appropriate color misalignment adjustment even when executing multiple types of printing modes with different numbers of colors or color combinations.

[0058] (Color shift correction process in the second embodiment) Next, the color shift correction process in the second embodiment will be described with reference to Figures 8 and 9. Figure 8 is a flowchart showing the color shift correction process in the second embodiment performed by the image forming apparatus 1, and Figure 9 is an example of the color shift correction amount stored in the storage unit 12. As shown in Figure 9, in the second embodiment, the color shift correction amount stored for each print mode is associated with the state information of the image forming apparatus 1 at the time of color shift adjustment when the color shift correction amount was determined. The items of the apparatus state information include the total number of prints and the ambient temperature, as shown in Figure 9. The total number of prints is the current total number of prints information that is updated sequentially and stored in the storage unit 12. Note that the total number of prints may be replaced with an indicator of the usage time, operating time, or number of printed images of the image forming apparatus 1. The ambient temperature is the internal temperature at the time of the previous color shift adjustment, as detected by the ambient sensor 18. Note that the apparatus state information only needs to include at least one of these two items. In the second embodiment, as described below, if the change in the device state is less than a predetermined amount, the color shift correction amount from the previous color shift adjustment is applied as is, and a new color shift adjustment is omitted.

[0059] (Steps S21-S24) The processing here is the same as the processing in steps S01 to S04 shown in Figure 6, so the explanation is omitted.

[0060] (Step S25) The control unit 11 reads the color shift correction amount for the same number and type of colors used in a print mode from the storage unit 12. For example, if the print mode is changed from another print mode to a 5-color mode, the control unit 11 reads the color shift correction amount for the matching 5-color mode. This color shift correction amount is associated with the device status information at the time of color shift adjustment when this color shift correction amount was determined (as shown in Figure 9 by the update process in step S30 described later).

[0061] (Step S26) The control unit 11 acquires current device status information. For example, it acquires temperature information from the environmental sensor 18, or reads the total number of prints from the storage unit 12.

[0062] (Step S27) The control unit 11 compares the device status information for the color shift correction amount read in step S25 with the current device status information acquired in step S26. If the change in the device status information is less than a predetermined value (YES), the process proceeds to step S28. On the other hand, if the change in status is greater than or equal to a predetermined value (NO), the process proceeds to step S29. For example, if the difference in ambient temperature is less than 3°C, or if the difference in the total number of prints is less than 1500 prints, the process proceeds to step S28. Note that either of these two items may be used as the device status, or they may be combined so that if the difference in either item is less than a predetermined value, it is determined to be YES and the process proceeds to step S28.

[0063] (Step S28) Here, the image forming apparatus 1 executes the print job by applying the color shift correction amount stored in the storage unit 12, which was read in step S25, without performing any new color shift adjustment by the color shift adjustment unit 111. Specifically, the image processing unit 112 of the control unit 11 performs image processing using the color shift correction amount from the previous print job read in step S25, and the image forming unit 20 uses this processed image data to form an image on the continuous paper 91, and then the process ends (end).

[0064] (Step S29) Here, the color misalignment adjustment unit 111 performs color misalignment adjustment. This process is the same as step S05 (subroutine flowchart in Figure 7), so the explanation is omitted.

[0065] (Step S30) The control unit 11 updates the data in the storage unit 12 with the color shift correction amount (hereinafter referred to as the new color shift correction amount) determined by the color shift adjustment in step S29. During this update, the color combination information of the image-making unit 30 and the current device status information acquired in step S26 are linked and stored.

[0066] (Step S31) Here, the image forming apparatus 1 applies the new color shift correction amount obtained in step S29 and executes the print job. Specifically, the image processing unit 112 of the control unit 11 performs image processing using the new color shift correction amount, and the image forming unit 20 uses this processed image data to form an image on the continuous paper 91, and the process ends (end).

[0067] In this second embodiment, the same effects as in the first embodiment are obtained, and furthermore, the device status information of the image forming apparatus is compared with the device status information of the current image forming apparatus, and if the change is greater than a predetermined value, color shift correction is performed using the newly obtained color shift correction amount obtained by performing color shift adjustment. On the other hand, if the change is less than a predetermined value, color shift correction is performed using the previous (past) color shift correction amount stored in the memory unit without performing color shift adjustment. In this way, when the previous color shift correction amount can be used, color shift adjustment can be omitted, and a decrease in productivity can be suppressed.

[0068] The configuration of the image forming apparatus described above is intended to illustrate the main components in order to explain the features of the above embodiment, and is not limited to the above configuration; various modifications can be made within the scope of the claims. Furthermore, it does not preclude configurations that are generally found in image forming apparatuses.

[0069] (modified version) For example, although the image forming apparatus 1 of the above embodiment shows an example using continuous paper, an image forming apparatus 1 using cut paper may also be used. Furthermore, when using continuous paper, the pressure of the secondary transfer unit 23 was released to adjust the color misalignment, but when executing a print job, the secondary transfer unit 23 is pressure-pressed, so the state is different between the time of color misalignment adjustment and the time of printing. In some cases, the color misalignment may be affected between different pressure states of the secondary transfer unit 23. In such cases, the amount or rate of change of color misalignment in the pressure / release state of the secondary transfer unit 23 may be determined in advance, stored in the storage unit 12, and used to perform a predictive correction. For example, the amount of color misalignment calculated from the detection of the resist sensor 17 by the processing in Figures 6 and 7 is used to obtain a value obtained by adding a shift value corresponding to the amount or rate of change of color misalignment or multiplying it by a correction coefficient, and this value is applied as the corrected color misalignment correction amount.

[0070] Furthermore, the means and methods for performing various processing in the image forming apparatus according to the above embodiment can be implemented by either a dedicated hardware circuit or a programmed computer. The program may be provided, for example, on a computer-readable recording medium such as a USB memory stick or a DVD (Digital Versatile Disc)-ROM, or it may be provided online via a network such as the Internet. In this case, the program recorded on the computer-readable recording medium is usually transferred to and stored in a storage unit such as a hard disk. The program may also be provided as a standalone application software, or it may be incorporated into the software of the apparatus as a function of the apparatus. [Explanation of symbols]

[0071] 1. Image forming apparatus 10 Image forming apparatus main unit 11 Control Unit 111 Color shift adjustment section 112 Image Processing Unit 12 Storage section 13 Operation display section 14. Paper transport section 15, 15a, 15b First crimp release mechanism 16. Second crimp release mechanism 17, 17a, 17b, 17c Resist Sensor 18 Environmental Sensors 19 Communications Department 20 Image forming unit 21, 21Y, 21M, 21C, 21K, 21S Primary Transfer Section r6~r10 Transfer Roller 22 Intermediate transfer belt 23 Secondary transfer section 24 Fixing section 30, 30Y, 30M, 30C, 30K, 30S Image Production Unit 31 Photoconductor Drum 32 Developer 50 Feeding device 60 Winding device

Claims

1. A plurality of image-forming units, each including an image carrier, which use a developer to form toner images of different colors on the image carrier, An intermediate transfer belt onto which the toner image on the image carrier is transferred, A plurality of primary transfer sections are provided opposite each of the plurality of image carriers and form transfer nips by biasing the intermediate transfer belt toward the image carrier from the inner circumferential surface side, A secondary transfer unit transfers the toner image on the intermediate transfer belt to continuous paper, A crimping release mechanism that, depending on the combination of imaging units used for image formation, moves at least one of the primary transfer sections to switch between a crimping position where the transfer nip is formed and a release position where the intermediate transfer belt and the image carrier are separated, An image forming apparatus comprising: a control unit that performs color shift adjustment when the combination of the imaging units used in image formation is changed, When performing the color misalignment adjustment, the control unit releases the pressure of the secondary transfer section on the intermediate transfer belt. An image forming apparatus in which the amount of color shift correction during image formation is set to a value obtained by adding a preset shift value of the color shift correction amount when the secondary transfer section is in a pressed state and when it is released, to the amount of color shift detected by the sensor, or by multiplying it by a correction coefficient.

2. The image forming apparatus according to claim 1, wherein the sensor detects a color shift correction pattern formed by the toner image transferred onto the intermediate transfer belt.

3. The image forming apparatus according to claim 2, wherein the control unit performs the color shift adjustment by detecting the color shift correction pattern using the sensor.

4. The image forming apparatus according to claim 2, wherein the control unit, in the color shift adjustment, detects the position of the pattern formed by the plurality of image forming units using the sensor, and, when one of the plurality of toners is used as the reference color, determines the amount of color shift correction during image formation based on the image formation positions of the toners of the other colors relative to the image formation positions of the toner of the reference color.

5. The image forming apparatus according to claim 4, wherein the control unit corrects the image forming position in at least one of the plurality of image forming units by the amount of color shift correction.

6. The image forming apparatus according to claim 5, further comprising a storage unit that stores the amount of color shift correction determined by the color shift adjustment for each combination of the image forming units from the plurality of image forming units in which the primary transfer unit is set to the pressing position and used for image forming.

7. The image forming apparatus according to claim 6, wherein the control unit performs color shift correction using the color shift correction amount stored in the storage unit for each combination of the image forming units used.

8. The storage unit stores the color shift correction amount along with the device status information of the image forming apparatus at the time of color shift adjustment. The control unit, when either primary transfer unit is switched from the crimping position to the release position or vice versa by the crimping release mechanism, The device status information linked to the color shift correction amount that matches the combination of imaging units used is compared with the current device status information of the image forming apparatus. If the change exceeds a predetermined value, perform color shift correction using the newly obtained color shift correction amount obtained by performing the color shift adjustment. The image forming apparatus according to claim 6 or claim 7, wherein if the change is less than a predetermined amount, the color shift correction is performed using the color shift correction amount stored in the storage unit without performing the color shift adjustment.

9. The image forming apparatus according to claim 1, wherein the control unit stores a preset shift value or correction coefficient for the amount of color shift correction when the secondary transfer unit is in a pressed state and a released state.

10. The aforementioned plurality of image-forming units include four image-forming units that form toner images of Y, M, C, and K colors. The combination of multiple image-forming units includes a first group consisting of four image-forming units that form toner images for each of the Y, M, C, and K colors, and a second group consisting of a different color combination than that of the first group. The image forming apparatus according to any one of claims 1 to 7, wherein the control unit performs the color misalignment adjustment when the print job is changed from the first group to the second group or vice versa according to the settings.

11. The aforementioned plurality of image-forming units further include image-forming units that form toner images of special colors other than Y, M, C, and K. The image forming apparatus according to claim 10, wherein the second group includes a combination of five imaging units that form toner images of Y, M, C, K, and spot colors.

12. A color shift correction method performed in an image forming apparatus comprising: an image carrier including a plurality of image forming units that each form a toner image of a different color on the image carrier by a developer; an intermediate transfer belt onto which the toner image on the image carrier is transferred; a plurality of primary transfer units provided opposite each of the plurality of image carriers and forming a transfer nip by biasing the intermediate transfer belt toward the image carrier from the inner circumferential surface side; a secondary transfer unit that transfers the toner image on the intermediate transfer belt to continuous paper; and a pressure release mechanism that moves at least one of the primary transfer units according to the combination of image forming units used for image formation to switch between a pressure position where the transfer nip is formed and a release position where the intermediate transfer belt and the image carrier are separated. When the combination of the image-forming units used for image formation is changed, a process including step (a) of performing color shift adjustment is performed, When performing the color misalignment adjustment in step (a) above, the pressure on the secondary transfer portion to the intermediate transfer belt is released, A color shift correction method in which the amount of color shift correction during image formation adjusted in step (a) is set to a value obtained by adding a preset shift value of the color shift correction amount when the secondary transfer section is pressed and when it is released, to the amount of color shift detected by the sensor, or by multiplying it by a correction coefficient.

13. A control program for controlling an image forming apparatus comprising: an image carrier, a plurality of image forming units that each form a toner image of a different color on the image carrier by a developer; an intermediate transfer belt onto which the toner image on the image carrier is transferred; a plurality of primary transfer units provided opposite each of the plurality of image carriers and forming a transfer nip by biasing the intermediate transfer belt toward the image carrier from the inner circumferential surface side; a secondary transfer unit that transfers the toner image on the intermediate transfer belt toward continuous paper; and a pressure release mechanism that moves at least one of the primary transfer units according to the combination of image forming units used for image formation, thereby switching between a pressure position where the transfer nip is formed and a release position where the intermediate transfer belt and the image carrier are separated. A process including a step (a) of performing color shift adjustment when the combination of imaging units used for image formation is changed, When performing the color misalignment adjustment in step (a) above, the pressure on the secondary transfer portion to the intermediate transfer belt is released, A control program for causing a computer to execute a process, wherein the amount of color shift correction during image formation adjusted in step (a) is set to a value obtained by adding a preset shift value of the color shift correction amount when the secondary transfer section is in a pressed state and when it is released, to the amount of color shift detected by the sensor, or by multiplying it by a correction coefficient.

Images