Image forming apparatus and image forming method

Abstract

To detect a driving state of a driving system including photoreceptors and an intermediate transfer belt, and when erroneous image position deviation correction is performed, notify a user of the situation to prevent inconvenience that image quality is reduced due to the erroneous image position deviation correction.SOLUTION: An image forming apparatus forms a pattern for detecting image position deviation formed of a plurality of colors on a transfer belt, and corrects image position deviation of images in respective colors on the basis of a result of detection of the pattern for detecting image position deviation. In this case, a determination unit detects an amount of difference between a pattern interval in the pattern for detecting image position deviation on the transfer belt and a pattern interval to be a reference for every color, and the amount of difference is equal to or more than a predetermined threshold, determines occurrence of abnormality in a driving state of the driving system that drives the transfer belt. When abnormality in the driving state of the driving system is determined on the basis of the amount of a difference in any color, a notification unit notifies a user of the occurrence of image position deviation.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and an image forming method. [Background technology]

[0002] 2. Description of the Related Art Color image forming apparatuses are known today that form an image by irradiating an image carrier with image light according to image data, forming a latent image, developing it in a developing unit, and transferring it onto recording paper.

[0003] In addition, in such color image forming apparatuses, a technology is known in which an image misalignment detection pattern transferred onto a belt is detected, the amount of image misalignment of each color relative to a reference color is calculated, and the image position is corrected based on the calculation result.

[0004] For example, Patent Document 1 (JP 2007-293047 A) discloses a color image forming apparatus that can detect the amount of misalignment of registration marks in the shortest time possible, excluding speed fluctuation factors such as the photosensitive drum or intermediate transfer belt, and that also aims to improve the accuracy of color registration correction. This color image forming apparatus calculates the average speed of the registration marks for each color, calculates the difference from the average speed of a reference color, and multiplies the result by the detected amount of misalignment to calculate the actual amount of misalignment. Summary of the Invention [Problem to be solved by the invention]

[0005] In the conventional color image forming apparatus, image position correction control is possible if a pattern for detecting image position deviation formed on an intermediate transfer belt can be detected.

[0006] However, there are cases where the image misalignment detection patterns are not accurately detected due to the driving state of the drive system, such as the photosensitive drum and transfer belt, etc. If image misalignment detection patterns are not accurately detected and image misalignment correction is performed based on the detection results of the image misalignment detection patterns, the image misalignment correction will be erroneous, resulting in a decrease in image quality.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an image forming apparatus and an image forming method that detect the driving status of the drive system, such as the photosensitive member and transfer belt, and notify the user if incorrect image position deviation correction is being performed, thereby preventing the inconvenience of image quality being reduced due to incorrect image position deviation correction. [Means for solving the problem]

[0008] In order to solve the above problems and achieve the object, the present invention provides a multi-color of a forming unit for forming an image misalignment detection pattern on a transfer belt; and a transfer unit for forming an image misalignment detection pattern formed on the transfer belt. By color a correction unit that corrects image position deviation of each image of each color based on the detection result of the image position deviation detection pattern by the detection unit; For each color The device has a judgment unit that detects the difference between the pattern spacing and a reference pattern spacing for each color, and if the difference is equal to or greater than a predetermined threshold, judges that an abnormality has occurred in the driving state of at least the drive system that drives the transfer belt, and a notification unit that notifies of the occurrence of image position deviation if the judgment unit judges that an abnormality has occurred in the driving state of the drive system based on the difference between any of the colors. [Effects of the Invention]

[0009] According to the present invention, the driving status of the driving system such as the photosensitive member and transfer belt is detected, and an alert is issued if an incorrect image position shift correction is being performed, thereby preventing the inconvenience of image quality being reduced due to incorrect image position shift correction. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of a color image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing the configuration of an image forming device of the color image forming apparatus according to the embodiment. [Figure 3] FIG. 3 is a top view showing the light beam scanning device as viewed from above. [Figure 4] FIG. 4 is a block diagram of an image formation control unit that drives the light beam scanning device. [Figure 5] FIG. 5 is a block diagram showing the configuration of the VCO clock generating section of the pixel clock generating section. [Figure 6] FIG. 6 is a block diagram of the writing start position control unit. [Figure 7] FIG. 7 is a timing chart of the writing start position control in the main scanning direction in the writing start position control unit. [Figure 8] FIG. 8 is a timing chart of the writing start position control in the sub-scanning direction in the writing start position control unit. [Figure 9] FIG. 9 is a block diagram showing the configuration of the front stage of the LD control unit. [Figure 10] FIG. 10 is a flowchart showing the flow of the print control operation of the color image forming apparatus according to the first embodiment. [Figure 11] FIG. 11 is a functional block diagram of each function realized by the printer control unit executing the image position deviation correction program stored in the storage unit. [Figure 12] FIG. 12 is a flowchart showing the flow of image position deviation correction processing executed based on each function of the printer control unit. [Figure 13] FIG. 13 is a diagram for explaining the detection error of the image positional deviation detection pattern. [Figure 14] FIG. 14 is a diagram showing an example of an image positional deviation detection pattern. [Figure 15]FIG. 15 is a flowchart showing the flow of print control after image positional deviation correction in the color image forming apparatus according to the first embodiment. [Figure 16] FIG. 16 is a flowchart illustrating a second modified example of the first embodiment. [Figure 17] FIG. 17 is a diagram illustrating an example of an image positional deviation detection pattern according to the third embodiment. [Figure 18] FIG. 18 is a flowchart showing the flow of image position deviation correction processing executed based on each function of the printer control unit according to the third embodiment. [Figure 19] FIG. 19 is a diagram showing an example of an image positional deviation detection pattern according to a modified example of the third embodiment. [Figure 20] FIG. 20 is a diagram showing the configuration of an image forming device of a color image forming apparatus according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] A color image forming apparatus (one example of an image forming apparatus) according to an embodiment will be described below with reference to the accompanying drawings.

[0012] [First embodiment] (Overall composition) FIG. 1 is a cross-sectional view of a color image forming apparatus 1 according to a first embodiment. As shown in FIG. 1, the color image forming apparatus 1 has an intermediate transfer unit at its center. This intermediate transfer unit is provided with an intermediate transfer belt 10, which is an endless belt. The intermediate transfer belt 10 is wound around three support rollers 14-16 that are rotated by a motor or the like, and is driven to rotate clockwise. An intermediate transfer member cleaning unit 17 is provided to the right of the second support roller 15 to remove residual toner remaining on the intermediate transfer belt 10 after image transfer.

[0013] An image forming device 20 including photoconductors 40 for each of the colors yellow (Y), magenta (M), cyan (C), and black (K), a charger 18, a developing unit 8, and a cleaning unit 9 is provided along the direction of movement of the intermediate transfer belt 10 between the first support roller 14 and the second support roller 15. The image forming device 20, which is an example of a toner developing section, is detachable from the main body of the color image forming apparatus 1. In addition, a toner bottle for supplying toner to the developing unit 8 is provided for each color.

[0014] Above the image forming device 20, there is provided a light beam scanning device 21 (an example of an optical writing unit) that irradiates each photoconductor 40 of each color photoconductor unit with a laser beam for image formation. Also, below the intermediate transfer belt 10, there is provided a secondary transfer unit 22. The secondary transfer unit 22 is arranged so that a secondary transfer belt 24, which is an endless belt, is stretched between two rollers 23 and pushes up the intermediate transfer belt 10 and presses it against a third support roller 16. This secondary transfer belt 24 transfers the image on the intermediate transfer belt 10 onto paper.

[0015] A fixing unit 25 that fixes the transferred image on the paper is provided next to the secondary transfer unit 22, and the paper with the transferred toner image is transported. The fixing unit 25 has a heating and pressure roller 27 pressed against a fixing belt 26, which is an endless belt. Below the secondary transfer unit 22 and the fixing unit 25, a sheet reversing unit 28 is provided that reverses the paper immediately after an image has been formed on its front side so that an image can also be recorded on its back side and transports it.

[0016] When a start switch on the operation unit is operated, if a document is set on the document feed tray 30 of the automatic document feeder (ADF) 400, the document is transported onto the contact glass 32. If no document is set on the ADF 400, the scanner of the image reading unit 300 is driven to read and scan the first carriage 33 and the second carriage 34 in order to read a document manually placed on the contact glass 32. Then, light is irradiated onto the contact glass from a light source on the first carriage 33, and light reflected from the document surface is reflected by a first mirror on the first carriage 33 and directed toward the second carriage 34, and then reflected by a mirror on the second carriage 34 to form an image on the CCD 36, which is a reading sensor, through an imaging lens 35. Recording data for each of the colors Y, M, C, and K is generated based on the image signal obtained by the CCD 36.

[0017] Furthermore, when a start switch is operated, when an instruction to output an image is given from a personal computer or the like, or when an instruction to output an image received via facsimile communication is given, the rotational driving of the intermediate transfer belt 10 is started, and each unit of the image forming device 20 starts preparation for image formation. Then, the image forming sequence for each color starts, an exposure laser modulated based on each color recording data is projected onto the photosensitive drum for each color, and each color toner image is transferred onto the intermediate transfer belt 10 as a single image, superimposed thereon, by each color image forming process.

[0018] The paper is transported to secondary transfer unit 22 at the same time that the leading edge of the toner image enters secondary transfer unit 22, thereby transferring the toner image from intermediate transfer belt 10 to the paper. The paper with the toner image transferred to it is transported to fixing unit 25, where the toner image is fixed to the paper.

[0019] By selectively rotating one of the paper feed rollers 42 of the paper feed table 200, the paper is fed from one of the paper feed trays 44 provided in the paper feed unit 43, and only one sheet is separated by a separation roller 45 and conveyed to a conveying roller unit 46. The paper is then conveyed by a conveying roller 47 to a conveying roller unit 48 in the printer 100, and after coming into contact with a registration roller 49 of the conveying roller unit 48 and temporarily stopping, is conveyed to the secondary transfer unit 22 at the timing described above.

[0020] It is also possible to feed paper by inserting it into manual feed tray 51. When the user inserts paper into manual feed tray 51, printer 100 rotates paper feed roller 50 to separate one of the sheets on manual feed tray 51 and pull it into manual feed path 53. This pulled-in paper comes into contact with registration roller 49 in the same manner as described above and is temporarily stopped.

[0021] The paper that has been subjected to fixing processing by fixing unit 25 and is discharged is guided by switching claw 55 to discharge rollers 56 and stacked on paper discharge tray 57. Alternatively, the paper is guided by switching claw 55 to sheet reversing unit 28, where it is reversed and guided again to the transfer position, and after an image is recorded on the back side as well, it is discharged by discharge rollers 56 onto paper discharge tray 57.

[0022] On the other hand, after the image transfer, residual toner is removed from the intermediate transfer belt 10 by the intermediate transfer body cleaning unit 17. This makes it possible to form images again.

[0023] (Configuration of the imaging device) Fig. 2 is a diagram showing the configuration of the imaging device 20. As shown in Fig. 2, the imaging device 20 is equipped with four sets of image forming units and four sets of light beam scanning devices 21 to form a color image by superimposing images of four colors (yellow, magenta, cyan, and black). Each photoconductor 40 is rotated by a motor or the like.

[0024] 3, the light beam scanning device 21 is equipped with an LD control board that selectively emits a light beam by being driven and modulated in accordance with image data. The emitted light beam is deflected by a polygon mirror rotated by a polygon motor, reflected by a folding mirror via an fθ lens, and scans the photosensitive member 40, which is rotated and driven.

[0025] For each color, a charger 18, a developing unit 8, a transfer unit 7, a cleaning unit 9, and a static eliminator 19 are provided around the photoconductor 40. A first-color image is formed on the intermediate transfer belt 10 through the typical electrophotographic process of charging, exposing, developing, and transferring. Images of the second, third, and fourth colors are then transferred in this order, forming a color image in which four color images are superimposed. Furthermore, a secondary transfer unit 22 transfers the image formed on the intermediate transfer belt 10 onto the transported paper. This allows a color image in which four color images are superimposed to be formed on the paper. The color image formed on the paper is fixed to the paper by a fixing device. Residual toner on the intermediate transfer belt 10 is removed by an intermediate transfer body cleaning unit 17.

[0026] As will be described later, the imaging device 20 is also provided with a first sensor 61 and a second sensor 62 for detecting image misregistration detection patterns formed on the intermediate transfer belt 10. The first and second sensors 61 and 62 are reflective optical sensors that detect the image misregistration detection patterns formed on the intermediate transfer belt 10. The color image forming apparatus 1 of the first embodiment corrects image misregistrations between colors in the main scanning direction and the sub-scanning direction and the image magnification in the main scanning direction based on the detection results of the image misregistration detection patterns by the first and second sensors 61 and 62. The color image forming apparatus 1 also detects speed fluctuations of a drive system 60 (see FIG. 4 ) for the photoconductor 40, the intermediate transfer belt 10, etc., based on the detection results. Here, the drive system 60 refers to a member that rotates the photoconductor 40, the intermediate transfer belt 10, etc. For example, the three support rollers 14 to 16 that rotate the intermediate transfer belt 10, the motor that drives the support rollers 14 to 16, and the motor that rotates the photosensitive member 40 are included.

[0027] (Configuration of the optical beam scanning device) FIG. 3 is a top view showing the light beam scanning device 21 as seen from above. The light beam scanning devices for each color have a common configuration shown in FIG. 3. In FIG. 3, a light beam from an LD unit 71 passes through a CYL (cylinder lens) 72 and is incident on a polygon mirror 73. The polygon mirror 73 deflects the light beam by rotating. The deflected light beam passes through an fθ lens 74 and a second lens 75 that corrects the beam position in the sub-scanning direction, and is then irradiated onto the photosensitive member 40 by a folding mirror 76. In this way, the photosensitive member 40 is scanned with the light beam.

[0028] At the writing start end in the main scanning direction, there are provided a synchronization mirror 77, a synchronization lens 78, and a synchronization sensor 79. The light beam that has passed through the fθ lens 74 is reflected by the synchronization mirror 77, condensed by the synchronization lens 78, and incident on the synchronization sensor 79. The synchronization sensor 79 functions as a synchronization detection sensor for detecting a synchronization detection signal that determines the writing start timing of the main scanning.

[0029] (Configuration of image formation control unit) Fig. 4 is a block diagram of an image formation control unit that drives such a light beam scanning device 21. Fig. 4 shows an image formation control unit and light beam scanning device for one color, but an image formation control unit and light beam scanning device are provided for each color except for a printer control unit 87, a storage unit 88, a first sensor 61, and a second sensor 62. The printer control unit 87 controls the entire color image forming apparatus 1. The printer control unit 87 controls the drive system 60 to rotate the photosensitive member 40, the intermediate transfer belt 10, etc.

[0030] A synchronous sensor 79 for detecting the light beam is provided on the image writing side of the end in the main scanning direction of the light beam scanning device 21. The light beam that has passed through the fθ lens 74 is reflected by a synchronous mirror 77, condensed by a synchronous lens 78, and then incident on the synchronous sensor 79.

[0031] When the light beam passes over the synchronization sensor 79, a synchronization detection signal XDETP is output from the synchronization sensor 79 and supplied to a phase synchronization clock generation unit 84 of the pixel clock generation unit 130, a synchronization detection lighting control unit 83, and a write start position control unit 81. The phase synchronization clock generation unit 84 of the pixel clock generation unit 130 generates a pixel clock PCLK synchronized with the synchronization detection signal XDETP and supplies it to the write start position control unit 81, the LD control unit 82, and the synchronization detection lighting control unit 83.

[0032] In order to first detect the synchronous detection signal XDETP, the synchronous detection lighting control unit 83 forcibly lights up the LD unit 71 by turning on the LD forced lighting signal BD. In response to this, after detecting the synchronous detection signal XDETP, the synchronous detection lighting control unit 83 uses the synchronous detection signal XDETP and the pixel clock PCLK to control the lighting of the LD unit 71 at a timing that allows the synchronous detection signal XDETP to be detected reliably without causing flare light. Then, when the synchronous detection lighting control unit 83 detects the synchronous detection signal XDETP in this way, it generates an LD forced lighting signal BD for controlling the turning off of the LD unit 71 and supplies this to the LD control unit 82.

[0033] Furthermore, the synchronous detection lighting control unit 83 generates a light intensity control timing signal APC for each LD using the synchronous detection signal XDETP and the pixel clock PCLK, and supplies it to the LD control unit 82. The generation of this light intensity control timing signal APC is executed by controlling the light intensity to a predetermined light intensity at a timing outside the image writing area.

[0034] The LD control unit 82 controls the lighting of the LD unit 71 in accordance with the synchronous detection forced lighting signal BD, the light amount control timing signal APC, and image data synchronized with the pixel clock PCLK. The light beam emitted from the LD unit 71 is deflected by the polygon mirror 73, passes through the fθ lens 74 and the second lens 75, and is scanned onto the photosensitive member 40 by the folding mirror 76.

[0035] The polygon motor control unit 80 controls the polygon motor to rotate at a specified number of rotations based on a control signal from the printer control unit 87. The writing start position control unit 81 generates a main scanning control signal XLGATE and a sub scanning control signal XFGATE that determine the image writing start timing and image width based on the synchronization detection signal XDETP, the pixel clock PCLK, and the control signal from the printer control unit 87.

[0036] The first and second sensors 61, 62 that detect the image misalignment detection patterns supply the detected image pattern information to the printer control unit 87. The printer control unit 87 calculates the amount of misalignment of each image misalignment detection pattern and generates correction data for correcting this misalignment. This correction data is set in the writing start position control unit 81 and the pixel clock generation unit 130, and is also stored in the memory unit 88. The correction data stored in the memory unit 88 is read by the printer control unit 87, which is an example of a correction unit, when an image formation operation is performed, and is set in the writing start position control unit 81 and the pixel clock generation unit 130.

[0037] The printer control unit 87 also calculates the speed fluctuations of the photosensitive member 40 and the intermediate transfer belt 10 from the pattern intervals of the image misalignment detection patterns detected by the first and second sensors 61 and 62, and displays the information on an operation panel (not shown) or the like. This will be described in more detail later.

[0038] (Configuration of VCO clock generation section) 5 is a block diagram showing the configuration of VCO clock generation unit 85 of pixel clock generation unit 130. As shown in this Fig. 5, VCO clock generation unit 85 inputs to phase comparator 91 a reference clock signal FREF from reference clock generation unit 86 and a signal obtained by dividing the VCLK output signal, which is the output signal of VCO clock generation unit 85, by N using 1 / N divider 94.

[0039] A phase comparator 91 compares the phases of the reference clock signal FREF and the VCLK output signal at the timing of the falling edges, and outputs an error component signal as a constant current. This error component signal is passed through an LPF (low-pass filter) 92 to remove unnecessary high-frequency components and noise, and is then supplied to a VCO (voltage-controlled oscillator) 93.

[0040] The VCO 93 oscillates a signal with an oscillation frequency that depends on the output of the LPF 92. Therefore, the frequency of the VCLK output signal can be varied by varying the frequency and division ratio "N" of the reference clock signal FREF from the reference clock generating unit 86 using the printer control unit 87. Changing the frequency of the VCLK output signal also changes the frequency of the pixel clock PCLK.

[0041] (Configuration of writing start position control unit) Fig. 6 is a block diagram of the writing start position control unit 81 shown in Fig. 4. As shown in Fig. 6, the writing start position control unit 81 has a main scanning line synchronization signal generating unit 96, a main scanning gate signal generating unit 98, and a sub-scanning gate signal generating unit 97.

[0042] The main-scan line synchronization signal generator 96 generates an XLSYNC signal for operating a main-scan counter 103 in a main-scan gate signal generator 98 and a sub-scan counter 99 in a sub-scan gate signal generator 97. The main-scan gate signal generator 98 generates an XLGATE signal for determining the timing of image signal capture (image writing start timing in the main-scan direction). The sub-scan gate signal generator 97 generates an XFGATE signal for determining the timing of image signal capture (image writing start timing in the sub-scan direction).

[0043] The main scanning gate signal generating unit 98 has a comparator 104 that compares the counter value of a main scanning counter 103 that operates on the XLSYNC signal and the pixel clock PCLK with a first set value (correction data) from the printer control unit 87. The main scanning gate signal generating unit 98 also has a gate signal generating unit 105 that generates an XLGATE signal based on the comparison result from the comparator 104.

[0044] The sub-scanning gate signal generating unit 97 has a sub-scanning counter 99 that operates with a control signal (print start signal), an XLSYNC signal, and a pixel clock PCLK from the printer control unit 87, and a comparator 101 that compares the counter value with a second set value (correction data) from the printer control unit 87. The sub-scanning gate signal generating unit 97 also has a gate signal generating unit 102 that generates an XFGATE signal from the comparison result from the comparator 101.

[0045] The writing start position control unit 81 corrects the writing position in the main scanning direction in units of one cycle of the pixel clock PCLK, that is, in units of one dot, based on the correction data stored in the memory unit 88. The writing start position control unit 81 also corrects the writing position in the sub-scanning direction in units of one cycle of the XLSYNC signal, that is, in units of one line, based on the correction data stored in the memory unit 88.

[0046] FIG. 7 is a timing chart of the writing start position control in the main scanning direction in the writing start position control unit 81. Of these, FIG. 7(a) shows the timing of the pixel clock PCLK. FIG. 7(b) shows the timing of the synchronization detection signal XDETP output from the synchronization sensor 79 when the light beam passes over it. FIG. 7(c) shows the timing of the XLSYNC signal generated by the main scanning line synchronization signal generator 96. FIG. 7(d) shows the timing of the XFGATE signal generated by the gate signal generator 102. FIG. 7(e) shows the counter value of the main scanning counter 103. FIG. 7(f) shows the timing of the XLGATE signal generated by the gate signal generator 105. FIG. 7(g) shows the timing of the image signal.

[0047] In the timing chart of Fig. 7, the main scanning counter 103 starts counting the pixel clock PCLK shown in Fig. 7(a) after its counter value is reset by the XLSYNC signal shown in Fig. 7(c). As a result, each time the main scanning counter 103 counts the pixel clock PCLK, the counter value counts up by one, as shown in Fig. 7(e). When this counter value reaches a first set value set by the printer control unit 87 (in this case, the counter value of "X" shown in Fig. 7(e)), the comparator 104 outputs the comparison result, and the XLGATE signal generated by the gate signal generation unit 105 goes low (enabled), as shown in Fig. 7(f). The XLGATE signal is a signal that goes low for the width of the image in the main scanning direction.

[0048] FIG. 8 is a timing chart of the writing start position control in the sub-scanning direction in the writing start position control unit 81. Of these, FIG. 8(a) shows the timing of the print start signal. FIG. 8(b) shows the timing of the XLSYNC signal generated by the main scan line synchronization signal generation unit 96. FIG. 8(c) shows the counter value of the sub-scanning counter 99. FIG. 8(d) shows the timing of the XFGATE signal generated by the gate signal generation unit 102. FIG. 8(e) shows the timing of the image signal.

[0049] In the timing chart of FIG. 8, after the counter value of the sub-scanning counter 99 shown in FIG. 8(c) is reset by the print start signal from the printer control unit 87 shown in FIG. 8(a), the sub-scanning counter 99 starts counting the XLSYNC signal shown in FIG. 8(b) generated by the main scan line synchronization signal generator 96. As a result, each time the sub-scanning counter 99 counts the XLSYNC signal, the counter value counts up by one as shown in FIG. 8(c). When this counter value reaches a second set value set by the printer control unit 87 (in this case, the counter value of "Y" shown in FIG. 8(c)), the comparator 101 outputs the comparison result, and the XFGATE signal generated by the gate signal generator 102 goes low (enabled) as shown in FIG. 8(d). The XFGATE signal is a signal that remains low for the length of the image in the sub-scanning direction.

[0050] (LD control unit configuration) 9 is a block diagram showing the configuration of the front stage of the LD control unit 82. As shown in FIG. 9, a line memory 106 is provided in the front stage of the LD control unit 82. The LD control unit 82 acquires image data from, for example, a printer controller, a frame memory, or a scanner using this line memory 106 in accordance with the timing of the XFGATE signal and the XLGATE signal. The image data captured in the line memory 106 is output in synchronization with the pixel clock PCLK and supplied to the LD unit 71. This causes the LD unit 71 to emit a light beam.

[0051] (Print control operation) Fig. 10 is a flowchart showing the flow of the print control operation of color image forming apparatus 1 of the first embodiment. In the flowchart of Fig. 10, when the start key on the operation panel is operated, printer control unit 87 controls polygon motor control unit 80 to rotate the polygon motor at a specified rotation speed based on the printing conditions (step S1).

[0052] Next, the printer control unit 87 sets the correction data (setting values ​​of the writing start positions in the main scanning direction and sub-scanning direction and the magnification) stored in the memory unit 88 to the writing start position control unit 81, the LD control unit 82, the synchronous detection lighting control unit 83, and the pixel clock generation unit 130 (step S2). As a result, the LDs are turned on to output the synchronous detection signal, and each LD is enabled to light up at the specified light intensity (APC operation: step S3).

[0053] Thereafter, the printer control unit 87 starts the image forming operation (step S4), and if there is no next image (step S5: No), it controls each LD to be turned off (step S6) via the LD control unit 82. Then, the printer control unit 87 controls the polygon motor to be stopped via the polygon motor control unit 80 (step S7), and ends the print control process shown in the flowchart of FIG.

[0054] (Image position correction function) Here, the color image forming apparatus 1 of the first embodiment performs an image misalignment correction process at a predetermined timing. This image misalignment correction process is executed by the printer control unit 87 based on an image misalignment correction program stored in the storage unit 88.

[0055] 11 is a functional block diagram of each function realized by printer control unit 87 executing the image position deviation correction program stored in memory unit 88. As shown in Fig. 11, printer control unit 87 realizes each function of correction data setting unit 110, pattern formation control unit 111, pattern detection unit 112, deviation amount calculation unit 113, determination unit 114, correction data calculation unit 115, memory control unit 116, image formation control unit 117, speed fluctuation amount calculation unit 118, and display control unit 119 by executing the image position deviation correction program.

[0056] A correction data setting unit 110 sets the correction data stored in the memory unit 88 to the writing start position control unit 81, the LD control unit 82, the synchronization detection lighting control unit 83, and the pixel clock generation unit 130. A pattern formation control unit 111, which is an example of a forming unit, forms a pattern for correcting image position misalignment. A pattern detection unit 112, which is an example of a detection unit, detects the pattern for correcting image position misalignment formed on the intermediate transfer belt 10 based on the sensor outputs of the first and second sensors 61 and 62.

[0057] The deviation amount calculation unit 113 calculates the amount of deviation (color deviation) of each color relative to the reference color based on the image deviation correction pattern detected by the pattern detection unit 112. The determination unit 114 determines whether or not to perform image deviation correction based on the calculated amount of deviation of each color relative to the reference color. The correction data calculation unit 115 calculates correction data when image deviation correction is to be performed. The memory control unit 116 updates the correction data stored in the memory unit 88 with the calculated correction data.

[0058] Based on the calculated correction data, the image formation control unit 117 performs the printing process described using the flowchart in Fig. 10. The speed fluctuation calculation unit 118 calculates the driving state (speed fluctuation) of the driving system 60, including the photoconductor 40 on which the image misalignment detection pattern is formed and the intermediate transfer belt 10. The display control unit 119, which is an example of a notification unit, controls the display unit to display an error message indicating the occurrence of an abnormality when the calculated speed fluctuation of the driving system 60 is equal to or greater than a predetermined value.

[0059] In this example, the correction data setting unit 110 to the display control unit 119 are realized by software using an image position deviation correction program, but all or part of these may be realized by hardware such as an IC (Integrated Circuit).

[0060] The image misalignment correction program may be provided by being recorded in the form of file information in an installable or executable format on a computer-readable recording medium such as a CD-ROM or a flexible disk (FD).The image misalignment correction program may be provided by being recorded on a computer-readable recording medium such as a CD-R, a DVD (Digital Versatile Disk), a Blu-ray (registered trademark) disk, or a semiconductor memory.The image misalignment correction program may be provided by being installed via a network such as the Internet.The image misalignment correction program may be provided by being pre-installed in a ROM or the like within the device.

[0061] (Image position deviation correction processing) 12 is a flowchart showing the flow of the image misalignment correction process executed based on each function of the printer control unit 87. The timing of the image misalignment correction process described below is controlled by the printer control unit 87. For example, the image misalignment correction process is executed immediately after the power is turned on, immediately before printing, when a specified number of prints is reached, or when the monitored temperature exceeds a specified value (when a specified temperature change occurs), etc.

[0062] In the flowchart of FIG. 12, in step S11, the correction data setting unit 110 sets the correction data stored in the memory unit 88 to the writing start position control unit 81, the LD control unit 82, the synchronization detection lighting control unit 83, and the pixel clock generation unit 130. In step S12, the pattern formation control unit 111 forms an image misalignment correction pattern. In step S13, the pattern detection unit 112 detects the image misalignment correction pattern formed on the intermediate transfer belt 10 based on the sensor outputs of the first and second sensors 61 and 62. Then, in step S14, the deviation amount calculation unit 113 calculates the deviation amount (color deviation amount) of each color relative to the reference color based on the image misalignment correction pattern detected by the pattern detection unit 112. Note that if multiple sets of image misalignment detection patterns are formed, the deviation amount calculation unit 113 calculates the average deviation amount of each color to reduce errors.

[0063] In step S15, the determination unit 114 determines whether or not to perform image position shift correction based on the calculated shift amount of each color relative to the reference color. The determination unit 114 determines that correction should be performed if the shift amount is equal to or greater than half the correction resolution, for example. If the calculated shift amount of each color is less than half the correction resolution, correction is not necessary (step S15: No), and the process of the flowchart in FIG. 12 ends.

[0064] On the other hand, if the calculated deviation amount for each color is equal to or greater than half the correction resolution, correction is necessary (step S15: Yes), and the correction data calculation unit 115 calculates correction data (step S16). Note that the "correction data" refers to the setting value of the pixel clock frequency that determines the image magnification in the main scanning direction, the setting value of the XLGATE signal that determines the image position in the main scanning direction, and the setting value of the XFGATE signal that determines the image position in the sub-scanning direction.

[0065] In step S17, the storage control unit 116 updates the correction data stored in the storage unit 88 with the calculated correction data. As a result, the updated correction data is newly set in the writing start position control unit 81, the LD control unit 82, the synchronization detection lighting control unit 83, and the pixel clock generation unit 130 (step S18), and the printing process described with reference to FIG.

[0066] (Warning based on fluctuations in the drivetrain) On the other hand, in the color image forming apparatus 1 of the first embodiment, when the image misalignment detection pattern is detected in step S13, the amount of misalignment for each color is calculated in step S14, and in step S19, the speed fluctuation amount calculation unit 118 calculates the amount of speed fluctuation of the drive system 60, such as the photosensitive element 40 on which the image misalignment detection pattern is formed and the intermediate transfer belt 10.

[0067] In step S20, the speed fluctuation amount calculation unit 118 determines whether the fluctuation amount of the drivetrain 60 is equal to or greater than a predetermined amount. If the fluctuation amount of the drivetrain 60 is less than the predetermined amount (step S20: No), the process shown in the flowchart in FIG. 12 ends.

[0068] On the other hand, if the fluctuation amount of the drive system 60 is greater than or equal to a predetermined amount (step S20: Yes), the display control unit 119, which is an example of a notification unit, displays an error message (warning) on ​​a display unit such as an operation panel, indicating that there is a possibility that image position shift has occurred (step S21).

[0069] As an example, the display control unit 119 displays an error message on the display unit, such as "Image position deviation may have occurred." This allows the user to recognize that image position deviation has occurred due to a malfunction of the drive system 60. Upon seeing this error message, the user will inspect the drive system 60, adjust the image position deviation to a predetermined deviation or less, and then resume printing.

[0070] In this example, an error message indicating that image misalignment has occurred is displayed, but the error message indicating that image misalignment has occurred may be output as audio, or an electronic sound may be output to indicate that image misalignment has occurred. Alternatively, a light-emitting diode or the like may be controlled to emit light to indicate that image misalignment has occurred.

[0071] (Example of detection error) Fig. 13 is a diagram for explaining detection errors of the image misalignment detection patterns. That is, Fig. 13 shows an example of detection errors of the image misalignment detection patterns when there is a speed fluctuation in the drive system 60, including the photosensitive member 40 and the intermediate transfer belt 10. When the periodic fluctuation of the image misalignment detection patterns detected by the first and second sensors 61 and 62 is the periodic fluctuation shown in Fig. 13, it may be possible to reduce the detection error by increasing the number of image misalignment detection patterns to detect multiple patterns and averaging the detection outputs.

[0072] However, if the amplitude (detection error) fluctuates and if the period of the fluctuation is long compared to the time during which the image position deviation detection pattern is formed, it becomes difficult to reduce the detection error. For this reason, as explained in steps S20 and S21, it becomes necessary to detect the amount of fluctuation in the drive system 60 and notify the user of an abnormality.

[0073] (Details of the operation for calculating the amount of image positional deviation) Fig. 14 is a diagram showing an example of an image misalignment detection pattern. The pattern formation control unit 111 shown in Fig. 11 forms an image misalignment detection pattern during a period when no image to be printed is being formed (between sheets, etc.). Note that the image misalignment detection pattern may be formed before printing starts or when printing ends.

[0074] The photoreceptor 40 forms horizontal line patterns (K11C11M11Y11, K21C21M21Y21, K12C12M12Y12, K22C22M22Y22...) and diagonal line patterns (K31C31M31Y31, K41C41M41Y41, K32C32M32Y32, K42C42M42Y42...) for each color on the intermediate transfer belt 10.

[0075] 14 (sub-scanning direction), which is the direction in which the intermediate transfer belt 10 moves and the direction intersecting the moving direction, and is the direction in which the image misalignment detection patterns are formed, horizontal line patterns and diagonal line patterns of each color are detected sequentially by the first sensor 61 or the second sensor 62. The detection outputs of each pattern are supplied from the sensors 61 and 62 to the misalignment amount calculation unit 113 and the speed fluctuation amount calculation unit 118 of the printer control unit 87.

[0076] (Details of calculation of drivetrain fluctuation amount) Next, such an image position deviation detection pattern can be used not only to calculate the correction value for the image position deviation amount, but also to determine the state of the drive system 60 based on a change in the pattern position.

[0077] That is, the intervals between the multiple patterns are formed on the intermediate transfer belt 10 so as to be a predetermined distance, and therefore the intervals between patterns of the same color are constant. However, if there is a fluctuation in the speed of the photosensitive member 40 that scans the light beam and the intermediate transfer belt 10 on which the image misalignment detection patterns are formed, the pattern intervals will fluctuate accordingly. For this reason, the speed fluctuation amount calculation unit 118 calculates the amount of fluctuation relative to a predetermined distance, making it possible to determine the state of the drive system 60.

[0078] Specifically, the speed fluctuation amount calculation unit 118 defines the specified value as one calculated from a preset value, and calculates "ΔL_K11", which is the difference (absolute value) between "L_K11", the interval between horizontal line pattern K11 and horizontal line pattern K12, and the specified value "A", for the black horizontal line pattern detected by the first sensor 61. Similarly, the speed fluctuation amount calculation unit 118 calculates "ΔL_K1(n-1)", which is the difference (absolute value) between each of the sets of patterns K12 to K13 and the set K1n-1 to K1n, and the specified value "A", which is an example of a reference value.

[0079] Then, the speed fluctuation calculation unit 118 compares each of the (n-1) calculation results with a judgment value "X," which is an example of a predetermined threshold, and determines whether or not there is an abnormality in the drive system 60 based on, for example, the following first and second conditions, and notifies the display control unit 119. Note that the judgment value "X" is a value determined in advance based on the degree of influence on image position deviation.

[0080] First condition: If the (n-1) maximum value is less than X, the speed fluctuation amount calculation unit 118 determines that the fluctuation is within the expected range and notifies the display control unit 119 that there is no abnormality (normal).

[0081] Second condition: If the (n-1) largest value is equal to or greater than X, the speed fluctuation amount calculation unit 118 determines that the fluctuation is unexpected, and notifies the display control unit 119 that "anomaly has occurred."

[0082] The speed fluctuation amount calculation unit 118 detects an abnormality in the drive system 60 in the same manner as described above using a diagonal line pattern in addition to the horizontal line pattern described above, and notifies the display control unit 119 of the abnormality.

[0083] The speed fluctuation amount calculation unit 118 also uses the image position deviation detection pattern detected by the second sensor 62 to detect an abnormality in the drive system 60 in the same manner as described above, and notifies the display control unit 119 of the abnormality.

[0084] The speed fluctuation amount calculation unit 118 also uses the image misalignment detection patterns of cyan, magenta, and yellow, which are colors other than black, to detect an abnormality in the drive system 60 in the same manner as described above, and notifies the display control unit 119. The speed fluctuation amount calculation unit 118 performs the above-mentioned abnormality detection of the drive system 60 based on the image misalignment detection patterns of each of the colors black, cyan, magenta, and yellow, and when an abnormality in the drive system 60 is detected based on the image misalignment detection patterns of any one color or multiple colors, it notifies the display control unit 119 that an abnormality has occurred in the drive system 60 for any one of the colors.

[0085] (Color-specific abnormality notification) The speed fluctuation amount calculation unit 118 detects abnormalities in the drive system 60 described above based on the image position shift detection patterns for each of the colors black, cyan, magenta, and yellow, and if an abnormality in the drive system 60 is detected, it notifies the display control unit 119 of the color in which the abnormality was detected and that an abnormality has occurred in the drive system 60.

[0086] For example, if an abnormality occurs in black, it is possible that all colors will be affected because black is the reference color for image misalignment correction, but if repairs are required, it is easier to identify the cause of the abnormality if the color in which the abnormality occurred can be identified. For this reason, by notifying both the occurrence of image misalignment and the color in which the abnormality was detected, such as black, it is possible to easily identify the location of the abnormality.

[0087] (Notification of abnormal occurrence with specified pattern location) The speed fluctuation calculation unit 118 detects abnormalities in the drive system 60 described above for each group pattern, such as the group K11-Y11, the group K21-Y21, the group K12-Y12, the group K22-Y22, etc., and notifies the user that an abnormality has occurred in the drive system 60, along with the position of the pattern in which the abnormality was detected.

[0088] As described above, image position deviation correction is performed by averaging the detection values ​​of the sensors 61 and 62 to calculate the amount of deviation, but image position deviation may occur even if an abnormality is detected by either one of the sensors 61 or 62. For this reason, by notifying both the occurrence of image position deviation and the position of the pattern where the abnormality was detected, it is possible to easily identify the location of the abnormality and facilitate repairs, etc.

[0089] (First Modification) Anomaly detection may be performed for each color or for each pattern position (for example, the front side or the back side). In addition, if the presence or absence of an anomaly varies depending on the positions of the sensors 61 and 62, notification may be made by specifying the position, for example, the front side or the back side.

[0090] (Print control after image misalignment correction) 15 is a flowchart showing the flow of print control after image positional deviation correction in color image forming apparatus 1 of the first embodiment. In the flowchart of Fig. 15, when the start key on the operation panel is operated, printer control unit 87 controls polygon motor control unit 80 to rotate the polygon motor at a specified rotation speed based on the printing conditions (step S31).

[0091] Next, the printer control unit 87 sets the correction data (the write start positions in the main scanning direction and sub-scanning direction, and the magnification setting value) calculated as described above and updated in the storage unit 88 to the write start position control unit 81, the LD control unit 82, the synchronous detection lighting control unit 83, and the pixel clock generation unit 130 (step S32). As a result, the LDs are turned on to output the synchronous detection signal, and each LD is enabled to light up at the specified light intensity (APC operation: step S33).

[0092] Thereafter, the printer control unit 87 starts the image forming operation (step S34), and if there is no next image (step S35: No), it controls each LD to be turned off (step S36) via the LD control unit 82. Then, the printer control unit 87 controls the polygon motor to stop via the polygon motor control unit 80 (step S37).

[0093] Next, when printing is performed in this manner, it is possible to visually check whether or not image position misalignment has actually occurred based on the printed matter. Therefore, the display control unit 119 controls the display unit to hide the message (cancel the notification) when printing is completed (step S38). This ends the processing of the flowchart in FIG. 15.

[0094] If the occurrence of image misalignment is visually confirmed based on the printed matter, the printer control unit 87 executes the image misalignment correction operation described above again after printing is completed, and performs the image misalignment correction process.

[0095] (Second Modification) Here, the color image forming apparatus 1 of the first embodiment is capable of identifying and notifying the color in which an abnormality has been detected as described above. In this case, the display control unit 119 controls the display unit to display an error message such as "An abnormality may have occurred in the cyan color."

[0096] However, if the printed image does not contain cyan, it is difficult for the user to determine from the printed matter whether or not there is truly an abnormality. For this reason, as shown in the flowchart of FIG. 16, in step S50 after printing is completed, the display control unit 119 determines whether or not the printed matter contains the color for which an abnormality has been detected. If the printed matter contains the color for which an abnormality has been detected (step S50: Yes), the user can determine the presence or absence of an abnormality based on the printed matter, and the display control unit 119 hides the above-mentioned error message in step S38 and ends the processing of the flowchart of FIG. 16. Note that the processing of steps S31 to S37 of the flowchart of FIG. 16 is the same as the processing of the same step numbers in the flowchart of FIG. 15.

[0097] On the other hand, if the printed matter does not contain the color for which the abnormality was detected (step S50: No), it is difficult for the user to determine whether or not there is an abnormality based on the printed matter, so the display control unit 119 leaves the error message displayed on the display unit and ends the processing of the flowchart in Figure 16. In this case, image position misalignment correction processing is performed after printing is completed, and the image position misalignment is corrected. The error message after correction may be hidden, or the error message may continue to be displayed until a printed matter containing the color for which the abnormality was detected is printed.

[0098] (Effects of the first embodiment) As is clear from the above description, the color image forming apparatus 1 of the first embodiment forms multiple sets of image misalignment detection patterns. These image misalignment detection patterns are generated to have a predetermined interval (distance), so the interval between image misalignment detection patterns of the same color should be constant. However, if there is a fluctuation in the speed of the photosensitive member that scans the beam or the transfer belt that transfers the image misalignment detection patterns, this influence causes the interval between the image misalignment detection patterns to fluctuate. Therefore, the color image forming apparatus 1 of the embodiment detects the amount of fluctuation in the interval between the image misalignment detection patterns relative to the predetermined interval (distance), thereby determining the state of the drive system 60 and notifying the user. This prevents the inconvenience of erroneous image misalignment correction being performed when there is a fluctuation in the drive system 60, resulting in a decrease in image quality.

[0099] [Second embodiment] Next, a color image forming apparatus according to a second embodiment will be described. In the color image forming apparatus 1 according to the first embodiment described above, the speed fluctuation amount calculation unit 118 determines whether or not there is an abnormality in the driving state of the drive system 60 based on the following first and second conditions, and notifies the user.

[0100] First condition: If the (n-1) maximum value is less than X, the speed fluctuation amount calculation unit 118 determines that the fluctuation is within the expected range and notifies the display control unit 119 that there is no abnormality (normal).

[0101] Second condition: If the (n-1) largest value is equal to or greater than X, the speed fluctuation amount calculation unit 118 determines that the fluctuation is unexpected, and notifies the display control unit 119 that "anomaly has occurred."

[0102] In contrast, the color image forming apparatus of the second embodiment is an example in which the presence or absence of an abnormality in the driving state of the drive system 60 is determined and notified based on the third to sixth conditions described below, in addition to the first and second conditions described above. Note that this is the only point that differs between the first embodiment described above and the second embodiment described below. Therefore, only the differences between the two will be described below, and redundant explanations will be omitted.

[0103] That is, in the case of the color image forming apparatus of the second embodiment, the speed fluctuation amount calculation unit 118 calculates (n-1) sum values ​​along with (n-1) maximum values. Then, based on these maximum values ​​and sum values, the presence or absence of an abnormality in the driving state of the drive system 60 is determined and notified based on the following third to sixth conditions. The maximum value "X" and sum value "Y" used in this determination are predetermined values ​​based on the degree of influence on image position deviation. This sum value is zero if the amount of fluctuation is the same on the positive and negative sides. However, if one of the positive and negative sides is greater, the sum value becomes large, indicating that the fluctuation is not periodic. Therefore, the speed fluctuation amount calculation unit 118 determines the presence or absence of an abnormality in the drive system 60 based on the (n-1) maximum values ​​along with the (n-1) sum values ​​as follows:

[0104] Third condition: If the maximum value is less than X and the added value is less than Y, it is determined that the fluctuation is within the expected range and a "No abnormality (normal)" notification is sent.

[0105] Fourth condition: If the maximum value is equal to or greater than X and the added value is less than Y, it is determined to be an unexpected fluctuation and a notification of "abnormality" is sent.

[0106] Fifth condition: If the maximum value is less than X and the added value is greater than or equal to Y, the fluctuation is determined to be within the expected range and a "No abnormalities (normal)" notification is sent.

[0107] 6th condition: If the maximum value is greater than or equal to X and the added value is greater than or equal to Y, it is determined to be an unexpected fluctuation and a notification of "abnormality" is sent.

[0108] The speed fluctuation calculation unit 118 makes such a judgment based on the diagonal line pattern as well as the detection output of the pattern of the second sensor 62, and also makes the same judgment for patterns of colors other than black, such as cyan, magenta, and yellow.

[0109] This allows the driving state of the drive train 60 to be determined in more detail and an abnormality to be notified, and also provides the same effects as those of the first embodiment described above.

[0110] [Third embodiment] Next, a color image forming apparatus according to a third embodiment will be described. The color image forming apparatus according to the third embodiment is an example in which three rows of patterns for detecting image misalignment are formed on the intermediate transfer belt 10. Note that the third embodiment described below differs from the first or second embodiment described above in this respect. Therefore, only the differences between the two will be described below, and redundant explanations will be omitted.

[0111] 17 and 18 are diagrams showing a third embodiment.

[0112] 17 is a diagram showing an example of an image position deviation detection pattern according to the third embodiment. While there are two sensors in FIG. 14, there are three sensors in the third embodiment.

[0113] Here, the third sensor 63 at the center in the third embodiment is installed to correct the difference between the main scanning magnification on the front side (left half shown in FIG. 17) and the main scanning magnification on the rear side (right half shown in FIG. 17). Also, since the amount of misalignment is calculated as the average value of the first, second, and third sensors 61, 62, and 63, the third sensor 63 is installed to improve the accuracy of correcting sub-scanning misalignment. Therefore, during periods when images to be printed are not being formed (such as between sheets of paper), three rows of patterns for detecting image misalignment are formed, and in addition to the detection states of the first and second sensors 61 and 62, the detection state of the third sensor 63 is also calculated for misalignment correction.

[0114] The pattern formation control unit 111 shown in Fig. 11 forms the image misalignment detection pattern shown in Fig. 17 during a period when no image to be printed is being formed (between sheets, etc.). Note that the image misalignment detection pattern may be formed before printing starts, when printing ends, or when image formation is interrupted during continuous printing.

[0115] The photosensitive member 40 forms horizontal line patterns (K11C11M11Y11, K21C21M21Y21, K51C51M51Y51, K12C12M12Y12, K22C22M22Y22, K52C52M52Y52...) and diagonal line patterns (K31C31M31Y31, K41C41M41Y41, K61C61M61Y61, K32C32M32Y32, K42C42M42Y42, K62C62M62Y62...) for each color on the intermediate transfer belt 10.

[0116] 17, which is the direction in which the intermediate transfer belt 10 moves and the direction intersecting the moving direction, and which is the direction in which the image misalignment detection patterns are formed, horizontal line patterns and diagonal line patterns of each color are detected sequentially by a first sensor 61, a second sensor 62, and a third sensor 63. The detection outputs of each pattern are supplied from the sensors 61, 62, and 63 to a misalignment amount calculation unit 113 and a speed fluctuation amount calculation unit 118 of the printer control unit 87.

[0117] (Details of calculation of drivetrain fluctuation amount) Next, such an image position deviation detection pattern can be used not only to calculate the correction value for the image position deviation amount, but also to determine the state of the drive system 60 based on a change in the pattern position.

[0118] That is, the intervals between the multiple patterns are formed on the intermediate transfer belt 10 so as to be a predetermined distance, and therefore the intervals between patterns of the same color are constant. However, if there is a fluctuation in the speed of the photosensitive member 40 that scans the light beam and the intermediate transfer belt 10 on which the image misalignment detection patterns are formed, the pattern intervals will fluctuate accordingly. For this reason, the speed fluctuation amount calculation unit 118 calculates the amount of fluctuation relative to a predetermined distance, making it possible to determine the state of the drive system 60.

[0119] Specifically, the speed fluctuation amount calculation unit 118 defines the specified value as one calculated from a preset value, and calculates "ΔL_K11", which is the difference (absolute value) between "L_K11", the interval between horizontal line pattern K11 and horizontal line pattern K12, and the specified value "A", for the black horizontal line pattern detected by the first sensor 61. Similarly, the speed fluctuation amount calculation unit 118 calculates "ΔL_K1(n-1)", which is the difference (absolute value) between each of the sets of patterns K12 to K13 and the set K1n-1 to K1n, and the specified value "A", which is an example of a reference value.

[0120] Then, the speed fluctuation amount calculation unit 118 compares the (n-1) calculation results with a judgment value "X" and a judgment value "Z," which are examples of predetermined thresholds, and determines whether or not there is an abnormality in the drive system 60 based on, for example, the following first, second, and third conditions, and notifies the display control unit 119. Note that the judgment value "X" and the judgment value "Z" are values ​​determined in advance based on the degree of influence on image position deviation.

[0121] First condition: If the (n-1) maximum value is equal to or greater than Z, the speed fluctuation amount calculation unit 118 determines that the fluctuation is unexpected, and notifies the display control unit 119 of "correction stopped."

[0122] Second condition: If the (n-1) maximum value is less than X, the speed fluctuation amount calculation unit 118 determines that the fluctuation is within the expected range and notifies the display control unit 119 that there is no abnormality (normal).

[0123] Third condition: If the (n-1) largest value is equal to or greater than X, the speed fluctuation amount calculation unit 118 determines that the fluctuation is unexpected, and notifies the display control unit 119 that "anomaly has occurred."

[0124] The speed fluctuation amount calculation unit 118 calculates (n-1) maximum values ​​and (n-1) additional values. Then, based on these maximum values ​​and additional values, it determines whether or not there is an abnormality in the driving state of the drive system 60, and notifies the user of the abnormality, based on the following fourth to seventh conditions. The maximum value "X" and additional value "Y" used in this determination are predetermined values ​​based on the degree of influence on image position deviation. This additional value is zero if the amount of fluctuation is the same on the positive and negative sides. However, if one of the positive and negative sides is larger, the additional value becomes large, indicating that the fluctuation is not periodic. Therefore, the speed fluctuation amount calculation unit 118 determines whether or not there is an abnormality in the drive system 60, as follows, based on the (n-1) maximum values ​​and (n-1) additional values.

[0125] Fourth condition: If the maximum value is less than X and the added value is less than Y, it is determined that the fluctuation is within the expected range and a "No abnormality (normal)" notification is sent.

[0126] Fifth condition: If the maximum value is equal to or greater than X and the added value is less than Y, it is determined to be an unexpected fluctuation and a notification of "abnormality" is sent.

[0127] Sixth condition: If the maximum value is less than X and the added value is greater than or equal to Y, the fluctuation is determined to be within the expected range and a "No abnormalities (normal)" notification is sent.

[0128] Seventh condition: If the maximum value is greater than or equal to X and the added value is greater than or equal to Y, it is determined to be an unexpected fluctuation and a notification of "abnormality" is sent.

[0129] The judgment value "Z" is determined based on the fourth to seventh conditions described above ("X" is replaced with "Z" and detailed explanations are omitted) to determine whether or not there is an abnormality in the driving state of the drivetrain 60, and notification is provided.

[0130] The speed fluctuation calculation unit 118 makes such a judgment based on the diagonal line pattern as well as on the detection output of the patterns of the second sensor 62 and the second sensor 63, and also on patterns of colors other than black, such as cyan, magenta, and yellow.

[0131] This allows the driving state of the drive train 60 to be determined in more detail and an abnormality to be notified, and also provides the same effects as those of the first embodiment described above.

[0132] Anomaly detection may be performed for each color and for each pattern position (front side, center, back side, etc.). If the presence or absence of an anomaly varies depending on the position of the sensors 61, 62, and 63, notification may be made by specifying the position, for example, the front side, center, back side, etc.

[0133] Furthermore, regarding the color specification, if an abnormality occurs in black, it is possible that all colors will be affected because it is the reference color for image misalignment correction. However, if repair is required, for example, specifying the color makes it easier to determine the cause. Therefore, it is preferable to notify both the occurrence of image misalignment and the black abnormality. Regarding the position specification, the image misalignment correction control calculates the amount of misalignment by averaging the detection values ​​of each sensor, so even an abnormality in just one location can cause image misalignment. However, if repair is required, specifying the position makes it easier to determine the cause, so it is preferable to notify both the occurrence of image misalignment and the location of the abnormality.

[0134] (Image position deviation correction processing) FIG. 18 is a flowchart showing the flow of the image position deviation correction process when the image position deviation detection pattern shown in FIG. 17 is used.

[0135] In step S11, the correction data setting unit 110 sets the correction data stored in the memory unit 88 to the write start position control unit 81, the LD control unit 82, the synchronization detection lighting control unit 83, and the pixel clock generation unit 130. In step S12, the pattern formation control unit 111 forms a pattern for correcting image position misalignment. In step S13, the pattern detection unit 112 detects the pattern for correcting image position misalignment formed on the intermediate transfer belt 10 based on the sensor outputs of the first, second, and third sensors 61, 62, and 63.

[0136] When the image misalignment detection pattern is detected, in step S60, the speed fluctuation calculation unit 118 calculates the speed fluctuation of the drive system 60, including the photosensitive member 40 on which the image misalignment detection pattern is formed and the intermediate transfer belt 10.

[0137] In step S61, if the amount of variation is equal to or greater than the aforementioned judgment value "Z," the correction may actually increase the amount of deviation, which may prevent the image position deviation correction from being performed properly. Therefore, a message indicating that the correction is to be stopped is displayed on the operation panel or the like (step S65), and the process ends.

[0138] In step S61, if the amount of fluctuation is less than the above-mentioned determination value "Z", the speed fluctuation calculation unit 118 determines whether the amount of fluctuation is greater than a determination value "X" that is smaller than the determination value "Z" (step S62).

[0139] In step S62, if the amount of variation is equal to or greater than the aforementioned judgment value "X", a message indicating that image position shift may occur after correction is displayed on the operation panel or the like (step S63), thereby informing the user that there is a possibility of an abnormality.

[0140] In step S62, if the amount of variation is less than the above-mentioned judgment value "X", the judgment unit 114 calculates the amount of deviation of each color from the reference color (step S64), and determines whether or not to perform image position deviation correction based on the calculated amount of deviation of each color from the reference color (step S15).

[0141] The determination unit 114 determines that correction should be performed if the amount of misalignment is, for example, equal to or greater than half the correction resolution. If the calculated amount of misalignment for each color is less than half the correction resolution, correction is not necessary (step S15: No), and the process of the flowchart in FIG. 18 ends.

[0142] On the other hand, if the calculated deviation amount for each color is equal to or greater than half the correction resolution, correction is necessary (step S15: Yes), and the correction data calculation unit 115 calculates correction data (step S16). Note that the "correction data" refers to the setting value of the pixel clock frequency that determines the image magnification in the main scanning direction, the setting value of the XLGATE signal that determines the image position in the main scanning direction, and the setting value of the XFGATE signal that determines the image position in the sub-scanning direction.

[0143] In step S17, the storage control unit 116 updates the correction data stored in the storage unit 88 with the calculated correction data. As a result, the updated correction data is newly set in the writing start position control unit 81, the LD control unit 82, the synchronization detection lighting control unit 83, and the pixel clock generation unit 130 (step S18), and the printing process described with reference to FIG.

[0144] [Modification of the third embodiment] In the third embodiment, three rows of patterns for detecting image positional deviation are formed on the intermediate transfer belt 10, but in this modified example, different patterns are formed depending on the conditions.

[0145] Fig. 19 is a diagram showing an example of an image misalignment detection pattern according to a modified example of the third embodiment. The pattern formation control unit 111 shown in Fig. 11 forms the image misalignment detection pattern shown in Fig. 19 during a period when no image to be printed is being formed (such as between sheets of paper).

[0146] On the other hand, before printing starts, when printing ends, or when image formation is interrupted during continuous printing, the image position deviation detection pattern shown in FIG. 17 is formed.

[0147] In this way, by varying the number of rows for forming the image misalignment detection pattern depending on the printing state, the amount of toner consumed can be reduced.

[0148] [Fourth embodiment] Next, a color image forming apparatus according to a fourth embodiment will be described.

[0149] 20 is a diagram showing the configuration of an imaging device of a color image forming apparatus according to a fourth embodiment. In the first embodiment, a first sensor 61 and a second sensor 62 detect the image misregistration detection patterns formed on the intermediate transfer belt 10, but in the fourth embodiment, a fourth sensor 65 and a fifth sensor 66 detect the image misregistration detection patterns formed on the secondary transfer belt. Note that components similar to those in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0150] The intermediate transfer belt 10 according to the fourth embodiment transfers the image misalignment detection pattern formed on the intermediate transfer belt 10 to the secondary transfer belt 24. Fourth and fifth sensors 65 and 66, which are reflective optical sensors, detect the image misalignment detection pattern formed on the secondary transfer belt. The fourth and fifth sensors 65 and 66 supply the detected image pattern information to a printer control unit 87. As in the above-described embodiments, the printer control unit 87 calculates the amount of misalignment of the image misalignment detection pattern (which in this embodiment is formed on the secondary transfer belt 24) and generates correction data to correct this misalignment. This correction data is set in the writing start position control unit 81 and the pixel clock generation unit 130 and is also stored in a memory unit 88. The correction data stored in the memory unit 88 is read by the printer control unit 87, which is an example of a correction unit, during image formation and set in the writing start position control unit 81 and the pixel clock generation unit 130.

[0151] The printer control unit 87 corrects the image position shift between each color in the main scanning direction and the sub-scanning direction and the image magnification in the main scanning direction based on the detection results of the image position shift detection patterns by the fourth sensor 65 and the fifth sensor 66. The printer control unit 87 then calculates the speed fluctuations of the photosensitive member 40, the intermediate transfer belt 10, and the secondary transfer belt 24 from the pattern spacing of the image position shift detection patterns detected by the fourth sensor 65 and the fifth sensor 66, and displays this information on an operation panel (not shown) or the like.

[0152] The image position deviation detection patterns that have passed through the fourth sensor 65 and the fifth sensor 66 are removed by the secondary transfer belt cleaning unit 70.

[0153] Here, the description of the image misalignment detection pattern will be omitted by replacing the intermediate transfer belt 10 in FIGS. 14 and 17 with the secondary transfer belt 24. The fourth sensor 65 and the fifth sensor 66 can be configured as shown in FIGS. 14 and 17. The description of the flowcharts in FIGS. 12 and 18 will also be omitted by replacing the intermediate transfer belt 10 on which the image misalignment detection pattern is formed with the secondary transfer belt 24. In this embodiment, the forming unit corresponds to the pattern detection unit 112 and the intermediate transfer belt 10, and forms (transfers) the image misalignment detection pattern on the intermediate transfer belt 10 onto the secondary transfer belt 24.

[0154] In the fourth embodiment as well, it is possible to prevent the inconvenience of image quality being reduced when erroneous image position deviation correction is performed in a state where fluctuations occur in the drive system 60.

[0155] Finally, the above-described embodiments are presented by way of example only and are not intended to limit the scope of the present invention. These novel embodiments may be embodied in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. Such embodiments and modifications are intended to be included within the scope and spirit of the invention, as well as within the scope of the claims and their equivalents. [Explanation of symbols]

[0156] 1. Color image forming device 10 Intermediate transfer belt 21 Optical beam scanning device 24 Secondary transfer belt 40 Photoreceptor 60 Drivetrain 61 First Sensor 62 Second Sensor 63 Third Sensor 65 The Fourth Sensor 66 The Fifth Sensor 73 Polygon Mirror 80 Polygon motor control unit 81 Writing start position control section 82 LD control section 83 Synchronous detection lighting control unit 84 Phase-synchronized clock generator 85 VCO clock generation section 86 Reference clock generation unit 87 Printer control unit 88 Memory section 110 Correction data setting section 111 Pattern formation control section 112 Pattern detection unit 113 Deviation amount calculation unit 114 Judgment Department 115 Correction data calculation unit 116 Memory control unit 117 Image formation control unit 118 Speed ​​fluctuation calculation unit 119 Display control unit 130 Pixel clock generation unit [Prior art documents] [Patent documents]

[0157] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-293047

Claims

1. a forming unit that forms a pattern for detecting image misregistration of a plurality of colors on a transfer belt; a detection unit that detects the image misalignment detection patterns formed on the transfer belt for each color; a correction unit that corrects image position shift of each image of each color based on the detection result of the image position shift detection pattern by the detection unit; a determining unit that detects, for each color, a difference between a pattern interval for each color of the image misalignment detection pattern formed on the transfer belt and a pattern interval serving as a reference value, and determines, when the difference is equal to or greater than a predetermined threshold value, that an abnormality has occurred in the driving state of at least a drive system that drives the transfer belt; a notification unit that notifies the occurrence of the image position deviation when the determination unit determines that the driving state of the drive system is abnormal based on the difference amount of any of the colors; and An image forming apparatus having the same.

2. A forming unit that forms an image misalignment detection pattern formed in multiple colors on a transfer belt; a detection unit that detects the image misalignment detection pattern formed on the transfer belt; a correction unit that corrects image position shift of each image of each color based on the detection result of the image position shift detection pattern by the detection unit; a determining unit that detects a difference between a pattern interval of the image misalignment detection pattern formed on the transfer belt and a pattern interval serving as a reference value for each of the colors, and determines that an abnormality has occurred in the driving state of at least a drive system that drives the transfer belt when the difference is equal to or greater than a predetermined threshold value; a notification unit that notifies the occurrence of the image position deviation when the determination unit determines that the driving state of the drive system is abnormal based on the difference amount of any of the colors; and and The notification unit notifies the color for which it has been determined that an abnormality has occurred in the driving state of the driving system together with the notification of the occurrence of the image position deviation. An image forming apparatus comprising:

3. A forming unit that forms an image misalignment detection pattern formed in multiple colors on a transfer belt; a detection unit that detects the image misalignment detection pattern formed on the transfer belt; a correction unit that corrects image position shift of each image of each color based on the detection result of the image position shift detection pattern by the detection unit; a determining unit that detects a difference between a pattern interval of the image misalignment detection pattern formed on the transfer belt and a pattern interval serving as a reference value for each of the colors, and determines that an abnormality has occurred in the driving state of at least a drive system that drives the transfer belt when the difference is equal to or greater than a predetermined threshold value; a notification unit that notifies the occurrence of the image position deviation when the determination unit determines that the driving state of the drive system is abnormal based on the difference amount of any of the colors; and and The notification unit notifies the position of the image position deviation detection pattern where it has been determined that an abnormality has occurred in the driving state of the driving system, together with notifying the occurrence of the image position deviation. An image forming apparatus comprising:

4. the forming unit forms the image misalignment detection patterns in at least two rows along the moving direction of the transfer belt; the detection unit detects each of the two rows of the image position shift detection patterns, The determining unit determines whether or not an abnormality has occurred in the driving state of the drive system based on the detection outputs of the image misalignment detection patterns detected by the detecting unit, using both a pattern interval of the image misalignment detection patterns corresponding to a main scanning direction that is a direction perpendicular to the moving direction of the transfer belt and a pattern interval of the image misalignment detection patterns corresponding to a sub-scanning direction that is the moving direction of the transfer belt.

4. The image forming apparatus according to claim 1, wherein:

5. The detecting units are located at three positions intersecting the moving direction of the transfer belt and detect the image position deviation detecting patterns.

5. The image forming apparatus according to claim 1, wherein:

6. The forming unit forms the image misalignment detection patterns in two or three rows along the moving direction of the transfer belt and intersecting with the moving direction of the transfer belt.

6. The image forming apparatus according to claim 5,

7. the transfer belt includes a first transfer belt and a second transfer belt in contact with the first transfer belt; the forming unit forms the image misregistration detection pattern on the first transfer belt and transfers the image misregistration detection pattern on the first transfer belt to the second transfer belt; The detection unit detects the image misalignment detection pattern on the second transfer belt.

7. The image forming apparatus according to claim 1, wherein:

8. The notification unit displays a message corresponding to the notification on a display unit.

8. The image forming apparatus according to claim 1, wherein:

9. The notification unit cancels the notification after printing the printed matter.

9. The image forming apparatus according to claim 1, wherein:

10. A forming unit that forms an image misalignment detection pattern formed in multiple colors on a transfer belt; a detection unit that detects the image misalignment detection pattern formed on the transfer belt; a correction unit that corrects image position shift of each image of each color based on the detection result of the image position shift detection pattern by the detection unit; a determining unit that detects a difference between a pattern interval of the image misalignment detection pattern formed on the transfer belt and a pattern interval serving as a reference value for each of the colors, and determines that an abnormality has occurred in the driving state of at least a drive system that drives the transfer belt when the difference is equal to or greater than a predetermined threshold value; a notification unit that notifies the occurrence of the image position deviation when the determination unit determines that the driving state of the drive system is abnormal based on the difference amount of any of the colors; and and The notification unit cancels the notification after printing the printed matter. An image forming apparatus comprising:

11. If the printed matter does not include a color in which an abnormality in the driving state of the drive system has been detected, the notification unit continues to issue the notification even after printing of the printed matter has been completed.

11. The image forming apparatus according to claim 9, wherein:

12. a forming step in which a forming unit forms an image misregistration detection pattern formed in a plurality of colors on a transfer belt; a detecting step in which a detecting unit detects the image misalignment detection pattern formed on the transfer belt; a correcting step in which a correcting unit corrects image position shifts of the images of each of the colors based on a detection result of the image position shift detection pattern by the detecting unit; a determining step in which a determining unit detects a difference between a pattern interval of the image misalignment detection pattern formed on the transfer belt and a pattern interval serving as a reference value for each of the colors, and determines that an abnormality has occurred in the driving state of at least a drive system that drives the transfer belt when the difference is equal to or greater than a predetermined threshold value; a notification step in which, when the determination unit determines that the driving state of the drive system is abnormal based on the difference amount of any of the colors, a notification unit notifies that the image position deviation has occurred; and The notification step notifies the color for which it has been determined that an abnormality has occurred in the driving state of the driving system together with the notification of the occurrence of the image position deviation. An image forming method comprising:

Images