JP2019095676A - Image formation device and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tandem type image forming apparatus capable of ensuring correction accuracy of image misalignment even when a driving system such as an image carrier or a transfer body has a driving error. SOLUTION: The correction means for correcting the misalignment based on the data obtained by averaging the detection results of a plurality of misalignment correction patterns formed in the inter-image region from the rear end of the transferred image to the tip of the next transferred image. The pattern forming means has a detection means for detecting the length of the image in the transport direction and a storage unit for storing a specified value of the length of the image, and the pattern forming means has the detected length of the image. When the value is less than the specified value, a first pattern having at least one of the patterns is formed in the plurality of inter-image regions, and when the detected length of the image is equal to or more than the specified value, the predetermined image is formed. The length of the inter-image region in the transport direction is increased with respect to the inter-image region forming the first pattern, and the second pattern having the plurality of the patterns is provided in the predetermined inter-image region. Form. [Selection diagram] FIG. 20

Description

  The present invention relates to an image forming apparatus and an image forming method.

  In an image forming apparatus such as a color printer for printing a multicolor image, there is known one in which a single color image formed by a plurality of image carriers is superimposed on a transfer body to form a multicolor image. In such an image forming apparatus, the position of superposition of single-color images of each color is shifted due to the temperature around the apparatus and the like, and the image quality may be degraded due to a change in character color or color unevenness. is there.

  In this case, in the inter-image area from the rear end in the conveyance direction of the transferred image in which the single-color image of each color is sequentially transferred to the transfer body to the front end in the conveyance direction of the next transferred image Patent Document 1 discloses a technique for forming an image pattern and correcting the positional deviation of an image by using the pattern.

  In addition, when the length of the transferred image in the transport direction is equal to or less than a predetermined value, the length of the inter-image area in the transport direction is increased to form a correction pattern, and a technique for correcting the positional deviation of the image is disclosed. (See, for example, Patent Document 2).

  However, in the prior art, when there is a drive error in the drive system such as the image carrier or the transfer body, the formation position of the correction pattern may be displaced, and the correction accuracy of the image displacement may be lowered.

  The present invention has been made in view of the above-described problems, and it is an object of the present invention to secure the correction accuracy of the image positional deviation even when there is a driving error in a driving system such as an image carrier or a transfer body. Do.

  An image forming apparatus according to an aspect of the disclosed technique is formed on each of a plurality of image carriers on which light according to image data is irradiated to form a monochromatic latent image, and the plurality of image carriers. And a plurality of developing means for developing the latent image of the single color to obtain a single color image, and a transfer body for conveying a transfer image to which the single color image is sequentially transferred. An image forming apparatus for forming a color image, wherein in the inter-image area from the rear end of the transfer image to the front end of the next transfer image in the transport direction of the transfer image, the positional deviation of the single-color image of each color A pattern forming unit that forms a pattern for correction; a detection unit that detects the pattern; and a correction unit that corrects the positional deviation based on data obtained by averaging the outputs of the detection unit with respect to a plurality of the patterns. Previous The pattern formation includes: detection means for detecting the length of the image in the transport direction of the transferred image; and a storage unit which is referred to by the pattern formation means and stores a specified value of the length of the image. The means forms a first pattern having at least one of the patterns in the plurality of inter-image areas when the length of the detected image is less than the specified value, and the length of the detected image is If the predetermined value or more, the length of the predetermined inter-image area in the transport direction is made longer than the inter-image area forming the first pattern, and the predetermined inter-image area is Forming a second pattern having a plurality of the patterns.

  Even when there is a drive error in a drive system such as an image carrier or a transfer body, it is possible to ensure the correction accuracy of the positional deviation of the image.

FIG. 1 is a schematic view showing an example of the entire configuration of an image forming apparatus according to a first embodiment. FIG. 2 is a schematic view showing an example of the configuration of an image forming apparatus included in the image forming apparatus of the first embodiment. It is the schematic which shows an example of a structure of the light beam scanning device which the image forming apparatus of 1st Embodiment has. It is a block diagram which shows an example of the light beam scanning device which the image forming apparatus of 1st Embodiment has, and the hardware constitutions of the periphery of it. It is a block diagram showing an example of composition of a VCO clock generation device which an image forming device of a 1st embodiment has. It is a block diagram showing an example of composition of a writing start position control device which an image forming device of a 1st embodiment has. 5 is a timing chart showing an example of writing start position control in the main scanning direction in the image forming apparatus of the first embodiment. 5 is a timing chart showing an example of writing start position control in the sub scanning direction in the image forming apparatus of the first embodiment. FIG. 2 is a schematic view showing an example of a line memory which the image forming apparatus of the first embodiment has. 5 is a flowchart for explaining an example of image formation control processing in the image forming apparatus of the first embodiment. FIG. 6 is a view for explaining an example of a first correction pattern in the image forming apparatus of the first embodiment. It is a figure explaining an example of the influence of the speed fluctuation of a drive system. It is a figure explaining an example of the influence of the speed fluctuation of a drive system in case the length of a transfer image is long. It is a figure explaining an example of the influence of the speed fluctuation of a drive system when length of the field between pictures is lengthened. FIG. 6 is a view for explaining an example of a second correction pattern in the image forming apparatus of the first embodiment. FIG. 2 is a block diagram showing an example of a functional configuration of the image forming apparatus of the first embodiment. It is a figure explaining the relationship between the misregistration correction | amendment error resulting from a pattern formation error, and the length of a transfer image. It is a figure explaining an example of a position gap amendment method in case length of a transfer picture is less than a stipulated value. It is a figure explaining an example of a position gap amendment method in case length of a transfer picture is beyond a stipulated value. 5 is a flowchart illustrating an example of misalignment correction processing in the image forming apparatus according to the first embodiment.

First Embodiment
A first embodiment will be described with reference to the drawings. Hereinafter, an electrophotographic image forming apparatus having a secondary transfer mechanism called a tandem system will be described as an example. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted. The terms “image formation” and “printing” used below are synonymous. Also, except when instructed in particular, "displacement" represents "displacement of single-color images of each color", and "pattern for correction" is a "predetermined pattern formed on the intermediate transfer belt for the correction of the misalignment". "Pattern of shape" is represented.

  The image forming apparatus 100 includes an intermediate transfer unit, an image forming device 20 of each color, a light beam scanning device 21, a secondary transfer unit 22, and a fixing unit 25.

  The intermediate transfer unit has an intermediate transfer belt 10 which is an endless belt, three supporting rollers 14 to 16, and an intermediate transfer member cleaning unit 17. The intermediate transfer belt 10 is wound around supporting rollers 14 to 16 and rotates clockwise. The intermediate transfer member cleaning unit 17 is provided between the second support roller 15 and the third support roller 16 and removes residual toner remaining on the surface of the intermediate transfer belt 10 after image transfer.

  The imaging device 20 is disposed between the first support roller 14 and the second support roller 15. The image forming apparatus 20 is installed in the order of yellow (Y), magenta (M), cyan (C) and black (K) in the transport direction of the intermediate transfer belt 10. The symbols in parentheses below may indicate colors.

  The image forming apparatus 20 includes a cleaning unit, a charging unit 18, a charge removing unit, a developing unit, and a photosensitive unit 40 for each color, and performs image formation for each color. The imaging device 20 may be detachable from the image forming apparatus 100.

  The light beam scanning device 21 is provided above the imaging device 20. The light beam scanning device 21 applies a laser beam to the photosensitive drums of the photosensitive unit 40 of each color in order to form an image.

  The secondary transfer unit 22 is provided below the intermediate transfer belt 10, and includes two rollers 23 and a secondary transfer belt 24. The secondary transfer belt 24 is an endless belt. Further, the secondary transfer belt 24 is hung on the two rollers 23 and rotates. Further, the roller 23 and the secondary transfer belt 24 are installed so as to push up the intermediate transfer belt 10 and to press it against the third support roller 16.

  The secondary transfer belt 24 transfers the image formed on the intermediate transfer belt 10 to the medium. The medium is, for example, a paper or a plastic sheet.

  The fixing unit 25 is provided beside the secondary transfer unit 22. The medium on which the toner image has been transferred is sent to the fixing unit 25, and the fixing unit 25 fixes the image to the medium. The fixing unit 25 also has a fixing belt 26 and a pressure roller 27. The fixing belt 26 is an endless belt. The fixing belt 26 and the pressure roller 27 are disposed so as to press the pressure roller 27 against the fixing belt 26. Further, the fixing unit 25 performs heating.

  The sheet reversing unit 28 is provided below the secondary transfer unit 22 and the fixing unit 25. The sheet reversing unit 28 reverses the front and back of the fed medium. The sheet reversing unit 28 is used when forming an image on the back side after forming an image on the front side.

  The automatic document feeder (ADF) 400 conveys the medium onto the contact glass 32 when the start button of the operation panel is pressed and the medium is on the paper supply table 30. Do. On the other hand, when there is no medium on the paper supply table 30, the automatic sheet feeder 400 activates the image reading unit 300 to read the medium on the contact glass 32 placed by the user.

  The image reading unit 300 includes a first carriage 33, a second carriage 34, an imaging lens 35, a charge coupled device (CCD) 36, and a light source. The image reading unit 300 operates the first carriage 33 and the second carriage 34 to read the medium on the contact glass 32.

  Light is emitted from the light source of the first carriage 33 toward the contact glass 32. Next, the light from the light source of the first carriage 33 is reflected by the medium on the contact glass 32.

  The reflected light is reflected by the first mirror on the first carriage 33 toward the second carriage 34. Next, the light reflected by the second carriage 34 is imaged through the imaging lens 35 onto the CCD 36 which is a reading sensor.

  The image forming apparatus 100 creates image data of Y, M, C, and K, that is, each color, based on the data acquired from the CCD 36.

  When the start button of the operation panel is pressed, the image forming apparatus 100 receives an instruction to form an image from an external device such as a PC (Personal Computer), or receives an instruction to output a facsimile. Start rotating.

  When the rotation of the intermediate transfer belt 10 is started, the imaging device 20 starts an imaging process. The medium on which the toner image has been transferred is sent to the fixing unit 25. Next, when the fixing unit 25 performs a fixing process, an image is formed on the medium.

  The sheet feeding table 200 includes a sheet feeding roller 42, a sheet feeding unit 43, a separation roller 45, and a conveyance roller unit 48. The paper feed unit 43 has a plurality of paper feed trays 44, and the transport roller unit 48 has a transport roller 47.

  The paper feed table 200 selects one of the paper feed rollers 42. Next, the sheet feeding table 200 rotates the sheet feeding roller 42 to be selected.

  The sheet feeding unit 43 selects one sheet feeding tray among the plurality of sheet feeding trays 44 and feeds the medium from the sheet feeding tray 44. Next, the fed-out medium is separated into one sheet by the separation roller 45 and sent to the conveyance path 46. Subsequently, in the conveyance path 46, the medium is sent to the image forming apparatus 100 by the conveyance roller 47.

  The medium sent to the image forming apparatus 100 is sent to the registration roller 49 via the paper feed path 53. Next, the medium sent to the registration roller 49 is abutted against the registration roller 49 and stopped. Subsequently, the medium is sent to the secondary transfer unit 22 as the toner image enters the secondary transfer unit 22.

  The medium may be sent from the manual feed tray 51. When a medium is fed from the manual feed tray 51, the image forming apparatus 100 rotates the paper feed roller 50. Next, the paper feed roller 50 separates one sheet of medium from the plurality of media present on the manual feed tray 51. Subsequently, the sheet feeding roller 50 sends the separated medium to the sheet feeding path 53. Further, the medium sent to the paper feed path 53 is sent to the registration roller 49. Further, the processing after the medium is sent to the registration roller 49 is similar to, for example, the case where the medium is fed from the paper feed table 200.

  The medium is fixed by the fixing unit 25 and discharged. Further, the medium discharged from the fixing unit 25 is sent to the discharge roller 56 by the switching claw 55. Next, the discharge roller 56 sends the fed medium to the paper discharge tray 57 and discharges the medium.

  Further, the switching claw 55 may send the medium discharged from the fixing unit 25 to the sheet reversing unit 28. The sheet reversing unit 28 reverses the front and back of the fed medium. The reversed medium is subjected to image formation on the back side as in the front side, and is sent to the paper discharge tray 57.

  On the other hand, toner remaining on the intermediate transfer belt 10 is removed by the intermediate transfer member cleaning unit 17. When the toner remaining on the intermediate transfer belt 10 is removed, the image forming apparatus 100 prepares for the next image formation.

  Next, an example of the configuration of an image forming apparatus included in the image forming apparatus 100 according to the present embodiment will be described with reference to FIG.

  The image forming apparatus 20 includes an intermediate transfer belt 10, an intermediate transfer member cleaning unit 17, and a secondary transfer unit 22. Furthermore, the imaging device 20 has four light beam scanning devices 21 and four imaging units 20U for each color.

  The imaging device 20 forms images of a plurality of colors, that is, four colors, on the intermediate transfer belt 10 in an overlapping manner to form a color image. That is, the imaging device 20 performs an imaging process. Specifically, the process of image formation in the electrophotographic system includes five processes of charging, exposure, development, transfer and fixing, and the like. Among them, the imaging process is, for example, charging, exposure, development and transfer.

  In the imaging device 20, the light beam is incident on the photosensitive unit 40 from the light beam scanning device 21. A light beam modulated based on image data is incident on the photosensitive unit 40.

  A cleaning unit 13, a charging unit 18, a charge removing unit 19, and a developing unit 29 are respectively installed around each photosensitive unit 40.

  The charging unit 18 performs the process of charging. The charging process is a process in which the charging unit 18 charges the surface of the photosensitive unit 40.

  The charged photosensitive unit 40 is subjected to a process of exposure by a light beam. The process of exposure is a process in which an electrostatic latent image is formed on the surface of the photosensitive unit 40. The developing unit 29 carries out a process of development. The process of development is a process in which toner is attached to the electrostatic latent image formed on the photosensitive unit 40 to form a toner image. Further, toner is supplied to the developing unit 29 from a toner bottle.

  The developing unit 29 has a developing roller. The developing roller causes the toner to adhere to the photosensitive unit 40 in the process of development.

  Next, the toner image is transferred onto the intermediate transfer belt 10 by the transfer device 62. First, the single-color image of the first color is transferred onto the intermediate transfer belt 10, and then the single-color image is transferred in the order of the second, third and fourth colors. In this manner, four single-color images are sequentially superimposed on the intermediate transfer belt 10 to form one image in which four-color toners are superimposed.

  An image in which toners of four colors are superimposed is an example of a multicolor image. Further, an image in which toners of four colors are superimposed on the intermediate transfer belt 10 is an example of a transfer image.

  After the transfer, the discharging unit 19 discharges the photosensitive unit 40, and the cleaning unit 13 performs cleaning.

  When the transferred toner image is sent to the secondary transfer unit 22, the medium is sent to the secondary transfer unit 22. Thus, the toner image on the intermediate transfer belt 10 is transferred to the medium sent to the secondary transfer unit 22.

  Thereafter, the fixing unit 25 performs the fixing process. Thus, when the process up to fixing is performed, an image is formed on the medium. The intermediate transfer member cleaning unit 17 removes four color toner images after the transfer process.

  The intermediate transfer belt 10 is an example of a transfer member, and the photosensitive unit 40 is an example of an image carrier. The developing unit 29 is an example of a developing unit.

  Further, in order to perform positional deviation correction and the like, a first sensor SEN1 and a second sensor SEN2 are provided. The first sensor SEN1 and the second sensor SEN2 are, for example, reflective optical sensors or the like. Specifically, the first sensor SEN1 and the second sensor SEN2 detect a correction pattern of a predetermined shape formed on the intermediate transfer belt 10 for positional deviation correction and the like. In the detection of the correction pattern, for example, a change in the output of the reflective optical sensor according to the correction pattern is detected. Based on the detection result, positional deviation in the main scanning direction and the sub scanning direction is corrected for each color. Note that the magnification etc. in the main scanning direction may be corrected based on the detection result.

  Each of the first sensor SEN1 and the second sensor SEN2 is provided at a position after the transfer image is formed in the transfer direction of the transfer image, and detects the correction pattern for correcting the positional deviation of the single-color image It is an example of the means.

  Next, an example of the configuration of the light beam scanning device included in the image forming device of the present embodiment will be described with reference to FIG. As illustrated, the light beam scanning device 21 includes a polygon mirror 11, an fθ lens 12, a LD (Laser Diode) unit 31, a folding mirror 37, a synchronization mirror 38, a synchronization lens 39, and a cylinder lens 41. , And a synchronous sensor 54. The configuration of the light beam scanning device of each color is, for example, the same. Hereinafter, the same case will be described as an example. Therefore, duplicate explanations are omitted.

  In the illustrated example, in the light beam scanning device 21, the LD unit 31 has a light source. First, the light source of the LD unit 31 is controlled based on image data and emits light.

  A light beam emitted from the LD unit 31 passes through the cylinder lens 41 and enters the polygon mirror 11. Subsequently, the polygon mirror 11 reflects the incident light beam while being rotated by a motor or the like. The light beam is deflected by rotation of the polygon mirror 11. The light beam reflected by the polygon mirror 11 passes through the fθ lens 12, is reflected by the folding mirror 37, and is scanned on the photosensitive unit 40.

  Further, as shown in the drawing, for example, a synchronous mirror 38, a synchronous lens 39, and a synchronous sensor 54 are installed at the end where writing is performed in the main scanning direction. First, the light beam passes through the fθ lens 12, enters the synchronous mirror 38, and is reflected by the synchronous mirror 38. The light beam reflected by the synchronous mirror 38 is collected by the synchronous lens 39 and enters the synchronous sensor 54. Thus, the synchronous sensor 54 detects the timing of the start of writing in the main scanning direction from the incident light beam.

  FIG. 4 is a block diagram showing an example of a light beam scanning device 21 of the imaging device 20 of the present embodiment and a hardware configuration of the periphery thereof. The illustrated configuration example is the configuration of the light beam scanning device 21 for one color.

  Connected to the light beam scanning device 21 are a polygon motor control device 211, an LD control device 212, a synchronization detection lighting control device 213, a pixel clock generation device 214, and a writing start position control device 215. . In addition, the printer control unit 1 is connected to the polygon motor control device 211 and the like. Further, to the printer control unit 1, a first sensor SEN1, a second sensor SEN2, a storage device 2, a storage device 216, and a pixel clock generation device 214 are connected. In the storage device 216, the specified value of the length of the image is stored. Details of this specified value will be described later.

  The light beam emitted from the LD unit 31 is detected by the synchronous sensor 54 or the like. The synchronization sensor 54 outputs a synchronization detection signal XDETP when the light beam is detected. The synchronization detection signal XDETP is sent to the synchronization detection lighting control device 213, the pixel clock generation device 214, and the writing start position control device 215.

  The synchronization detection lighting control device 213 turns on the LD forced lighting signal BD to generate the synchronization detection signal XDETP. Next, when the LD forced lighting signal BD is turned ON, the LD control device 212 causes the LD unit 31 to emit a light beam. On the other hand, after the synchronization detection signal XDETP is output, the synchronization detection lighting control device 213 causes the LD unit 31 to emit a light beam based on the synchronization detection signal XDETP and the pixel clock signal PCLK. Specifically, the LD control device 212 causes the LD unit 31 to emit a light beam at such a timing that flare light is not generated and the synchronization detection signal XDETP can be generated. Furthermore, when the synchronization detection signal XDETP is detected, the synchronization detection lighting control device 213 generates an LD forced lighting signal BD that turns off the LD, and sends it to the LD control device 212.

  Further, the light quantity control timing signal APC of the LD is generated based on the synchronization detection signal XDETP and the pixel clock signal PCLK. Next, the light amount control timing signal APC is sent to the LD control device 212. Further, the processing based on the light quantity control timing signal APC is performed outside the image writing area. That is, at the timing when the light amount control timing signal APC is sent, control for adjusting the light amount is performed.

  The LD control device 212 causes the LD unit 31 to emit a light beam based on a signal indicating the LD forced lighting signal BD, the light amount control timing signal APC, and the image data DIMG synchronized with the pixel clock signal PCLK. Then, the light beam emitted by the LD unit 31 is incident on the polygon mirror 11. Next, the light beam deflected by the polygon mirror 11 passes through the fθ lens 12 and scans on the photosensitive unit 40.

  The polygon motor control device 211 controls the polygon motor to rotate at a predetermined number of rotations based on a control signal from the printer control unit 1.

  The writing start position control device 215 generates a signal for determining the writing start timing and the width of the image based on the control signal from the printer control unit 1, the synchronization detection signal XDETP, the pixel clock signal PCLK and the like. The signals for determining the write start timing and the image width are the main scanning control signal XRGATE and the sub scanning control signal XFGATE.

  When the first sensor SEN1 and the second sensor SEN2 detect the correction pattern, they send detection results to the printer control unit 1. Next, the printer control unit 1 calculates the amount of positional deviation based on the detection result. Subsequently, the printer control unit 1 generates correction data based on the positional deviation amount. Further, the printer control unit 1 sets the pixel clock generation device 214 and the writing start position control device 215 based on the correction data. Also, the printer control unit 1 stores the correction data in the storage device 2. That is, when image formation is performed, the correction data stored in the storage device 2 is read by the printer control unit 1 and settings of the pixel clock generation device 214 and the writing start position control device 215 are performed.

  The pixel clock generation device 214 includes a reference clock generation device 2141, a voltage controlled oscillator (VCO) clock generation device 2142, and a phase synchronization clock generation device 2143. The reference clock generation unit 2141 generates a reference clock signal FREF. The VCO clock generator 2142 generates a VCO clock signal VCLK.

  FIG. 5 is a block diagram showing a configuration example of the VCO clock generation device of the present embodiment. As illustrated, the VCO clock generation device 2142 includes a phase comparator 21421, a low pass filter (Low Pass Filter) 21422, a VCO 21423, and a 1 / N frequency divider 21424.

  The reference clock signal FREF from the reference clock generation device 2141 and the clock signal divided into 1 / N by the 1 / N divider 21424 are input to the phase comparator 21421. The phase comparator 21421 also compares the phases of the falling edges of the two input signals and outputs an error component at a predetermined current.

  The low pass filter 21422 removes high frequency components from the output of the phase comparator 21421 and outputs a DC voltage.

  The VCO 21423 outputs a VCO clock signal VCLK having a predetermined frequency based on the output of the low pass filter 21422.

  The 1 / N frequency divider 21424 divides the input VCO clock signal VCLK into 1 / N with the set division ratio N.

  The frequency of the reference clock signal FREF from the printer control unit 1 and the division ratio N can be set. Therefore, the frequency of the VCO clock signal VCLK is changed by setting the pixel clock generation device 214 to change the frequency of the reference clock signal FREF and the value of the division ratio N.

  Referring back to FIG. 4, the VCO clock signal VCLK input from the VCO clock generation device 2142 and the synchronization detection signal XDETP are input to the phase synchronization clock generation device 2143. Further, the phase synchronization clock generation device 2143 outputs the pixel clock signal PCLK synchronized with the synchronization detection signal XDETP to the synchronization detection lighting control device 213 or the like.

  FIG. 6 is a block diagram showing a configuration example of the writing start position control device of the present embodiment. As shown, the writing start position control device 215 has a main scanning line synchronization signal generator 2151. Also, the writing start position control device 215 has a counter 2152, a comparator 2153 and a control signal generator 2154 for main scanning and sub scanning.

  The writing start position control device 215 generates a main scanning control signal XRGATE and a sub scanning control signal XFGATE. The main scanning control signal XRGATE is generated in the main scanning direction so as to capture a signal indicating image data, that is, to indicate the write start timing of the image. On the other hand, sub-scanning control signal XFGATE is generated in the sub-scanning direction so as to indicate the acquisition of a signal indicating image data, that is, the writing start timing of the image.

  Each counter 2152 operates when the counter operation signal XLSYNC is input.

  The main scanning comparator 2153 compares the value indicated by the main scanning counter 2152 operated based on the counter operation signal XLSYNC and the pixel clock signal PCLK with the first set value SET1. The first set value SET 1 is input from the printer control unit 1. The first set value SET1 is a value determined based on the correction data.

  The control signal generator 2154 for main scanning generates a main scanning control signal XRGATE based on the comparison result output from the comparator 2153 for main scanning.

  The print start signal SRT from the printer control unit 1 is input to the sub-scanning counter 2152. The sub-scanning counter 2152 operates based on the print start signal SRT, the counter operation signal XLSYNC, and the pixel clock signal PCLK.

  The sub-scanning comparator 2153 compares the value indicated by the sub-scanning counter 2152 with the second set value SET2. The second set value SET 2 is input from the printer control unit 1. The second set value SET2 is a value determined based on the correction data.

  The control signal generator 2154 for sub scanning generates a sub scanning control signal XFGATE based on the comparison result output from the comparator 2153 for sub scanning.

  The writing start position control device 215 can correct the writing position in units of the pixel clock signal PCLK, that is, in units of one dot in the main scanning direction. On the other hand, the writing start position control device 215 can correct the writing position in units of the counter operation signal XLSYNC, that is, in units of one line, in the sub scanning direction.

  FIG. 7 is a timing chart showing an example of control of the writing start position in the main scanning direction of this embodiment. In the following description, the synchronization detection signal XDETP, the counter operation signal XLSYNC, the main scanning control signal XRGATE and the sub scanning control signal XFGATE are described as an example in which a low level is a valid signal, that is, a low active signal.

  The main scanning counter is reset by the counter operation signal XLSYNC. The main scanning counter is a counter value indicated by the main scanning counter 2152 shown in FIG.

  The main scanning counter counts up by the pixel clock signal PCLK. When the value indicated by the main scanning counter becomes the first set value SET1, the main scanning comparator 2153 outputs a signal as a comparison result. In this example, the first set value SET1 is "X". Next, when the main scanning comparator 2153 outputs a signal indicating that the first set value SET1 has been reached, the main scanning control signal generator 2154 sets the main scanning control signal XRGATE to a low level. . The main scanning control signal XRGATE is a signal that becomes low level by the image width in the main scanning direction.

  FIG. 8 is a timing chart showing an example of control of the writing start position in the sub scanning direction of the present embodiment.

  The sub-scanning counter is reset by the print start signal SRT. The sub-scanning counter is a counter value indicated by a sub-scanning counter 2152 shown in FIG.

  The sub-scanning counter counts up by the counter operation signal XLSYNC. When the value indicated by the sub-scanning counter becomes the second set value SET2, the sub-scanning comparator 2153 outputs a signal as a comparison result. In this example, the second set value SET2 is "Y". Next, when the sub-scanning comparator 2153 outputs a signal indicating that the second set value SET2 has been reached, the sub-scanning control signal generator 2154 sets the sub-scanning control signal XFGATE to the low level. Do. The sub-scanning control signal XFGATE is a signal which is at a low level by the image length in the sub-scanning direction.

  FIG. 9 is a schematic view showing an example of a line memory which the image forming apparatus 100 of the present embodiment has. The line memory LMEM shown in the figure is used, for example, at the front stage of the configuration of the image formation control apparatus 210 shown in FIG.

  The line memory LMEM stores image data fetched from a printer controller, a frame memory, a scanner or the like at a timing indicated by the sub scanning control signal XFGATE or the like. Further, it is assumed that as the image data to be stored, signals for several beams are output in synchronization with the pixel clock signal PCLK. Further, the signal output from the line memory LMEM is sent to the LD control device 212, and is controlled so that the LD lights up at the timing indicated by the signal.

  In the image forming apparatus 100 of the present embodiment, the polygon motor control device 211, the LD control device 212, the lighting control device 213 for synchronization detection, the pixel clock generation device 214, and the writing start position control device 215 are electronic circuits, for example. And other hardware. However, the present invention is not limited to this, and part or all of the processing may be realized by a CPU (Central Processing Unit) based on a program.

  On the other hand, the printer control unit 1 is realized by a CPU, a random access memory (RAM), a read only memory (ROM), an external I / F 24, and the like. However, the present invention is not limited to this, and part or all of the processing may be realized by hardware such as an electronic circuit.

  FIG. 10 is a flowchart showing an example of image formation control processing in the image forming apparatus 100.

  When the start button of the operation panel of the image forming apparatus 100 is pressed, the printer control unit 1 instructs the polygon motor control device 211 to rotate the polygon motor in step S1001. The polygon motor is a motor that rotates the polygon mirror 11 at a predetermined rotational speed. The polygon motor control device 211 controls a polygon motor.

  Subsequently, in step S1003, the printer control unit 1 transmits correction data for correcting the writing start positions of the main scanning and the sub scanning, the main scanning magnification, and the like to each control device. Correction data is set in each control unit.

  Subsequently, in step S1005, the synchronization detection lighting control device 213 instructs the LD unit 31 to turn on the LD and performs an APC (Automatic Power Control) operation to turn on the LD with a predetermined light amount.

  Subsequently, in step S1007, the control devices interlock to perform an image forming operation.

  Subsequently, in step S1009, the printer control unit 1 confirms the presence or absence of an image to be formed next.

  Next, if there is an image to be formed, the process returns to step S1007 and the image forming operation is performed again. Next, if there is no image to be formed, the printer control unit 1 instructs the LD control device 212 to turn off the LD in step S1011.

  Subsequently, in step S1013, the printer control unit 1 instructs the polygon motor control device 211 to stop the rotation of the polygon motor, and ends the image formation control process.

  Next, the correction pattern in the image forming apparatus 100 of the present embodiment and the positional deviation correction process using the correction pattern will be described in detail.

  The printer control unit 1 outputs pattern data corresponding to the correction pattern in the main scanning or sub scanning direction to the LD control device 212. Then, the LD control device 212 turns on the LD of the LD unit 31 based on the pattern data to form a latent image corresponding to the correction pattern on the photoconductor unit 40 of each color. Then, the formed latent image of each color is developed with toner, and the toner image is transferred onto the intermediate transfer belt 10. In the image forming apparatus 100, the correction pattern is thus formed on the intermediate transfer belt 10.

  FIG. 11 shows an example of the misalignment correction pattern in the image forming apparatus 100 of the first embodiment. In FIG. 11, the “belt movement direction” and the conveyance direction of the transfer image and the sub-scanning direction are mutually synonymous. Further, the “light beam scanning direction” is synonymous with the main scanning direction.

  The patterns K1, C1, M1, and Y1 are horizontal line images formed on the intermediate transfer belt 10 with K, C, M, and Y toners, respectively, and are used as correction patterns in the sub-scanning direction. The same applies to the patterns K2, C2, M2, and Y2.

  Patterns K1, C1, M1, and Y1 are formed on the left side of the intermediate transfer belt 10 in the “light beam scanning direction” in the figure, and patterns K2, C2, M2, and Y2 are formed on the right side.

  The patterns K3, C3, M3, and Y3 are formed on the rear side of the patterns K1, C1, M1, and Y1 in the "belt moving direction". These are oblique line images formed of K, C, M, and Y toners, respectively, and are used as correction patterns in the main scanning direction. Similarly, patterns K4, C4, M4, and Y4 are formed on the back side of the patterns K2, C2, M2, and Y2.

  In FIG. 11, a correction pattern in which the patterns K1, C1, M1, Y1, K3, C3, M3, and Y3 form one set is detected by the first sensor SEN1. Further, a correction pattern in which the patterns K2, C2, M2, Y2, K4, C4, M4, and Y4 form one set is detected by the second sensor SEN2. The correction pattern having the patterns K1, C1, M1, Y1, K3, C3, M3 and Y3 as one set is an example of the “first pattern”.

  The outputs of the first sensor SEN1 and the second sensor SEN2 accompanying the movement of the intermediate transfer belt 10 in the "belt moving direction" are sent to the printer control unit 1, and the amount of positional deviation of each color with respect to the K color is calculated. The unit of positional deviation is time.

  The positional deviation in the sub scanning direction changes the detection timing of the horizontal line image, and the positional deviation in the main scanning direction and the magnification error of the image change the detection timing of the oblique line image.

  The positional deviation of the C color with respect to the K color will be specifically described as an example.

  First, regarding the positional deviation in the main scanning direction, the time from the detection of the pattern K1 to the detection of the K3 is detected. Based on this, a time difference TKC13 with respect to the time from the detection of pattern C1 to the detection of C3 is calculated.

  Further, the time from the detection of pattern K2 to the detection of K4 is detected, and based on this, the time difference TKC24 with the time from the detection of pattern C2 to the detection of C4 is calculated.

  A value obtained by subtracting the time difference TKC13 from the time difference TKC24 is a magnification error in the main scanning direction of the C color with respect to the K color. The magnification in the main scanning direction refers to the imaging magnification in the scanning direction of the light of the image formed on the photosensitive unit 40 by the fθ lens 12. The magnification error in the main scanning direction is an error caused by the fluctuation of the characteristics of the fθ lens 12 such as the refractive index and the surface shape.

  By changing the frequency of the pixel clock signal PCLK by the pixel clock generation device 214 according to the calculated magnification error, the magnification error is corrected.

  Further, a value obtained by subtracting the time variation due to magnification error correction at the position of the first sensor SEN1 from the time difference TKC13 is the positional deviation amount ΔTcm of the C color with respect to the K color. The printer control unit 1 calculates the number of dots corresponding to the positional deviation amount ΔTcm as correction data, and outputs the correction data to the writing start position control device 215. The writing start position control device 215 uses the correction data to correct the timing of the XRGATE signal that determines the writing start position in the main scanning direction.

  Next, in the sub-scanning direction, a specification value of time until detection of a C-color pattern after detection of a K-color pattern with SEN1 or SEN2 is taken as Tcs. Further, the time from the detection of pattern K1 to the detection of C1 is TKC1, and the time from the detection of pattern K2 to the detection of C2 is TKC2. From these, the positional deviation amount ΔTcs of the C color with respect to the K color in the sub scanning direction is calculated from the following equation (1).

・・・・・・・（１）
プリンタ制御部１は、この位置ずれ量ΔＴｃｓに相当するライン数を補正データとして算出し、書出開始位置制御装置２１５に出力する。書出開始位置制御装置２１５は、補正データを用いて、副走査方向の書出開始位置を決定するＸＦＧＡＴＥ信号のタイミングを補正する。

・ ・ ・ ・ ・ ・ ・ ・ ・ (1)
The printer control unit 1 calculates the number of lines corresponding to the positional deviation amount ΔTcs as correction data, and outputs the correction data to the writing start position control device 215. The writing start position control device 215 uses the correction data to correct the timing of the XFGATE signal that determines the writing start position in the sub-scanning direction.

  The above description has been made taking C color as an example, but the same applies to M color and Y color for K color.

  In the present embodiment, the correction pattern is formed in an area between the rear end of each transfer image and the front end of the next transfer image in the “belt movement direction”, ie, the conveyance direction of the transfer image, ie, the inter-image area. Be done.

  In addition, the image forming apparatus 100 according to the present embodiment forms a plurality of correction patterns, and averages detection outputs of the plurality of correction patterns by the first and second sensors to calculate a positional deviation amount.

  The correction pattern is an example and is not limited to the above. For example, a diagonally inverted image may be used. Furthermore, although the locations for forming the correction pattern have been described as two locations on both sides of the intermediate transfer belt 10 in the “light beam scanning direction”, it is not limited thereto. For example, it may be formed near the center of the intermediate transfer belt 10.

  Next, in the image forming apparatus 100 according to the present embodiment, the influence of the error of the drive system on the correction of the positional deviation and the correction method of the positional deviation when the error is in the drive system will be described.

  Here, the drive system is a generic name of means for driving the photosensitive drum, the intermediate transfer belt 10 and the like which the photosensitive unit 40 of each color has. The drive system is composed of, for example, members such as a drum, a roller, a belt, and a motor.

  The error of the drive system is, for example, speed fluctuation due to eccentricity of a drum, a roller or the like, slack of a belt, or the like. The formation position of the correction pattern shifts in accordance with the speed fluctuation. The deviation of the formation position of the correction pattern due to the speed fluctuation causes an error in the correction of the positional deviation of the image caused by the temperature or the like around the device. The deviation of the formation position of the correction pattern due to the error of the drive system is hereinafter referred to as a pattern formation error.

  FIG. 12 schematically shows the time variation of the pattern formation error caused by the speed variation of the drive system. Since the pattern formation error is associated with the driving of the rotating body such as the drum and the roller, as shown in the drawing, the fluctuation has a certain periodicity. However, since a plurality of members are generated in conjunction, the amplitude and phase of the fluctuation are not necessarily reproduced, but change sequentially.

  Periods 101a, 101b, 101c, and 101d shown in FIG. 12 indicate periods in which the correction pattern is formed in the inter-image area on the intermediate transfer belt 10. Further, periods tg1 and ti1 indicated by alternate long and short dashed lines are a period corresponding to one inter-image area and a period corresponding to one transfer image area on the intermediate transfer belt 10. In the example of FIG. 12, one set of correction patterns is formed in the four inter-image areas.

  As illustrated, when the correction pattern is formed across substantially one period of the time variation of the pattern formation error, the pattern formation error in the periods 101a, 101b, 101c, and 101d in which the correction pattern is formed is Swing approximately equally on the + "side and the"-"side. Therefore, averaging the outputs of the first and second sensors in the periods 101a, 101b, 101c, and 101d cancels the influence of the pattern formation error on the positional deviation correction. And the error of position shift correction is reduced.

  On the other hand, FIG. 13 shows a case where the length of the transferred image in the transport direction is longer than that in FIG. Periods 102a and 102b indicate periods in which the correction pattern is formed in the inter-image area on the intermediate transfer belt 10, as in FIG. A period tg1 is a period corresponding to one inter-image area on the intermediate transfer belt 10. As the transfer image becomes longer, the period ti2 corresponding to the area of one transfer image is longer on the intermediate transfer belt 10.

  As the period ti2 becomes longer, the timing at which the correction pattern is formed changes from the case of FIG. 12, and the number of correction patterns formed in one cycle of the time variation of the pattern formation error becomes two. There is.

  In this case, the pattern formation errors in the periods 102 a and 102 b in which the correction pattern is formed both swing to the “+” side. Therefore, even if the outputs of the first and second sensors are respectively averaged, the influence of the pattern formation error on the positional deviation correction is not canceled. Therefore, the error of the positional deviation correction can not be reduced.

  When the length of the transferred image in the transport direction is long, as shown in FIG. 14, the image forming apparatus 100 according to the present embodiment lengthens one inter-image area and forms a long correction pattern in the transport direction. . In FIG. 14, a period 103 indicates a period in which the correction pattern is formed in the inter-image area. A period tg2 is a period corresponding to one of the increased inter-image areas. A period ti2 is a period corresponding to the area of one transfer image. In the period 103, the pattern formation error swings substantially equally to the “+” side and the “−” side.

  FIG. 15 shows an example of a correction pattern long in the transport direction formed in the case of FIG. In this pattern, 5 sets of correction patterns in which the patterns K1, C1, M1, Y1, K3, C3, M3, and Y3 shown in FIG. 11 are one set, that is, "first patterns" are continuously provided in the transport direction. It is formed.

  If the correction pattern shown in FIG. 15 is detected by the first sensor SEN1 and the second sensor SEN2 and the outputs of five sets are averaged, the influence of the pattern formation error is cancelled. Thereby, the error of position shift correction can be reduced. A pattern in which five sets of "first patterns" are continuously formed in the transport direction is an example of "second pattern".

  However, in order to lengthen one inter-image area in the correction pattern of FIG. 15, if correction using the correction pattern of FIG. 15 is always performed, the image forming speed decreases.

  Therefore, the image forming apparatus 100 according to the present embodiment detects the length of the transferred image in the transport direction, and if the length is less than the specified value, one set of correction patterns, that is, a plurality of “first patterns” is detected. In the inter-image area of On the other hand, when the length is equal to or more than the specified value, one inter-image area is lengthened, and a “second pattern” having a plurality of sets of correction patterns is formed in one inter-image area.

  An example of a functional configuration of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG.

  The image forming apparatus 100 includes an image forming unit 500, a positional deviation correction unit 501, an image length detection unit 503, and a storage unit 504. The positional deviation correction unit 501 also includes a detection unit 502.

  The image forming unit 500 forms an image based on image data. Also, using this function, the correction pattern is formed on the intermediate transfer belt 10. Therefore, the image forming unit 500 is also a pattern forming unit.

  The image forming unit 500, that is, the pattern forming unit is an example of the “pattern forming unit”. The pattern forming unit includes, for example, the printer control unit 1, the light beam scanning device 21, the photosensitive unit 40, the cleaning unit 13, the charging unit 18, the discharging unit 19, the developing unit 29, the transfer unit 62, etc. To be realized.

  The detection unit 502 detects a correction pattern. The detection unit 502 is realized by, for example, a first sensor SEN1 and a second sensor SEN2.

  The positional deviation correction unit 501 corrects the positional deviation based on the output of the detection unit 502. The positional deviation correction unit 501 is realized by, for example, the printer control unit 1, the pixel clock generation device 214, and the writing start position control device 215. Specifically, this is realized by, for example, a CPU of the printer control unit 1 and hardware such as an electronic circuit of the pixel clock generation device 214 and the writing start position control device 215. The positional deviation correction unit 501 is an example of a “correction unit that corrects positional deviation”.

  The image length detection unit 503 detects the length of the transfer image on the intermediate transfer belt 10 in the transport direction. For example, the image length detection unit 503 detects the length of the transferred image by receiving information on the size of the medium on which an image is formed from the printer control unit 1.

  Specifically, when the user of the image forming apparatus 100 selects the size of a sheet on which an image is to be formed through the operation panel, the printer control unit 1 grasps the selected sheet size, that is, the size of the medium. Alternatively, the printer control unit 1 grasps the size of the medium by reading the sheet size prepared in the image forming apparatus 100 using an optical document sensor or the like. The paper size is, for example, the finished size of the paper represented by A3 size, A4 size or the like.

  The length of the transfer image in the transport direction according to the size of the medium is obtained in advance by experiment or the like. Therefore, the image length detection unit 503 can detect the length of the transferred image by receiving the information on the size of the medium from the printer control unit 1. The image length detection unit 503 is an example of “a detection unit that detects the length of the image in the transfer direction of the transfer image”.

  The storage unit 504 stores a specified value of the length of the image in the transfer direction of the transferred image. The specified value is referred to by the pattern forming unit when determining the pattern to be formed. The storage unit 504 is realized by the storage device 216. More specifically, it is realized by an external storage device such as a ROM (Read Only Memory) of the printer control unit 1 or a USB (Universal Serial Bus).

  The above specified value is obtained in advance and stored in the storage unit 504. An example of how to obtain such a prescribed value will be described below.

  The pattern formation error is caused by, for example, the speed fluctuation of each of the photosensitive unit 40, the intermediate transfer belt 10, and the like added together. Each speed fluctuation can be predicted by giving errors to the diameter and eccentricity of the photosensitive drum of the photosensitive unit 40, the diameter and eccentricity of the support roller of the intermediate transfer belt 10, and the belt length.

  By adding these speed fluctuations by numerical operation, it is possible to predict the time fluctuation of the pattern formation error as shown in, for example, FIGS. In addition, although the time fluctuation | variation for 2 cycles was shown in FIGS. 12-14, you may estimate by increasing a period further.

  On the other hand, the period for forming the correction pattern is determined from the length of the transferred image in the transport direction and the length of the inter-image area. Therefore, it is possible to obtain a pattern formation error for each period of forming the correction pattern, and to predict a correction error caused by the pattern formation error from the average value of these.

  FIG. 17 schematically shows the relationship between the length of the transferred image in the transport direction and the correction error caused by the pattern formation error. In FIG. 17, the horizontal axis represents the length of the transferred image in the transport direction, and the vertical axis represents the correction error caused by the pattern formation error.

  Assuming that the allowable value of the correction error caused by the pattern formation error is, for example, 1/2 or less of the resolution of correction ΔC, the length A of the transferred image for which the correction error is permitted is determined. The length A of the transferred image is a specified value. The correction resolution ΔC is, for example, a value obtained by multiplying the detection time resolution of the correction pattern by the output of the first sensor SEN1 or the second sensor SEN2 by the conveyance speed of the intermediate transfer belt 10. The detection time resolution of the correction pattern is determined by the signal-to-noise ratio (SNR) of the first sensor SEN1 and the second sensor SEN2, the dynamic range of an A / D (Analog / Digital) converter, and the like.

  The conveyance speed by the intermediate transfer belt 10 is, for example, a specification value of the conveyance speed.

  When the length of the transferred image in the transport direction is equal to or more than the specified value A, the image forming apparatus 100 lengthens one inter-image area to form a plurality of correction patterns. By averaging the detection outputs of the correction pattern by the first sensor SEN1 and the second sensor SEN2, a correction error is reduced.

  When the length of the transferred image in the transport direction is equal to or more than the specified value, the length of the inter-image area to be lengthened can be determined, for example, as follows. The time variation of the pattern formation error is predicted by the method described above, and the length obtained by multiplying the variation period by the transport speed of the intermediate transfer belt 10 is determined. This length or more is taken as the length of the inter-image area set when the length of the transferred image in the transport direction is more than the specified value.

  According to this method, the length of the inter-image area set when the length of the transferred image in the transport direction is equal to or more than the specified value can be easily obtained.

  FIG. 18 shows a correction pattern formed on the intermediate transfer belt 10 when the length of the transferred image in the transport direction is less than the specified value A (mm). In FIG. 18, “pattern 1”, that is, the patterns K1, C1, M1, Y1, and K3 illustrated in FIG. 11 in the inter-image region between “image 1” and “image 2” on the first sensor SEN1 side. A correction pattern in which C 3, M 3 and Y 3 form one set is formed. Also on the second sensor SEN2 side, a correction pattern is formed in which “pattern 1”, that is, the patterns K2, C2, M2, Y2, K4, C4, M4, and Y4 shown in FIG. There is. The same applies to the inter-image areas between "image 2" and "image 3", between "image 3" and "image 4", and between "image 4" and "image 5".

  The “pattern 1” in the four inter-image areas is detected by the first sensor SEN1 and the second sensor SEN2, and their outputs are averaged to calculate the amount of positional deviation in the main scanning and sub scanning directions. Ru.

  If the length of the transferred image is less than A mm, the number of patterns formed in one inter-image area is set based on the length of the transferred image in the transport direction, the fluctuation period of the pattern formation error, and the length of the inter-image area. It may be determined in advance.

  Further, the length of the inter-image area may be determined from, for example, the number of media on which images are formed per predetermined time, that is, the number of printed sheets.

  FIG. 19 shows a correction pattern formed on the intermediate transfer belt 10 when the length of the transferred image in the transport direction is equal to or more than the specified value A (mm). In FIG. 19, for example, an inter-image area between “image 1” and “image 2” is longer in the transport direction than in the case of FIG. “Pattern 2”, that is, the patterns K1, C1, M1, Y1, K3, C3, M3, and Y3 shown in FIG. Five correction patterns are continuously formed in the transport direction. Further, on the second sensor SEN2 side, five correction patterns each including the patterns K2, C2, M2, Y2, K4, C4, M4, and Y4 as one set are continuously formed in the transport direction.

  Five sets of correction patterns in one inter-image area are detected by the first sensor SEN1 and the second sensor SEN2, their outputs are averaged, and the amount of positional deviation in the main scanning and sub scanning directions is calculated. Be done.

  Even if the correction pattern to be formed in one inter-image area when the length of the transferred image is equal to or more than the specified value is a pattern formed by repeating the correction pattern multiple times when the length of the transferred image is less than the specified value. Good. By doing this, it is possible to match the reduction effect of the correction error by the averaging to the same level in the case where the length of the transferred image is less than A mm and in the case where it is more than A mm.

  If the length of the transferred image is A mm or more, the number of patterns formed in one inter-image area is set based on the length of the transferred image in the transport direction, the fluctuation period of the pattern formation error, and the length of the inter-image area. It may be determined in advance.

  Next, an example of misalignment correction processing in the image forming apparatus 100 according to the first embodiment will be described with reference to FIG.

  First, in step S2001, the printer control unit 1 determines whether or not the positional deviation correction process is to be performed. For example, the printer control unit 1 monitors whether the number of prints by the image forming apparatus has reached a predetermined number, or monitors the temperature around the place where the image forming apparatus is installed, and detects whether or not there is a temperature change more than a specified value. Do. Based on the detection result, it is determined whether or not the positional deviation correction process is to be performed.

  When misregistration correction processing is performed, in step S2003, the image forming unit 500, that is, the pattern forming unit detects the length of the transferred image in the transport direction based on the output of the image length detection unit 503. Then, with reference to the storage unit 504, it is determined whether the length of the detected transferred image is equal to or more than the specified value A.

  In the case of A or more, in step S2005, the pattern formation unit forms “pattern 2”, that is, a second pattern in one inter-image area.

  If it is less than A, in step S2007, the pattern formation unit forms “pattern 1”, that is, the first pattern in one inter-image area. Subsequently, in step S2009, the printer control unit 1 determines whether “pattern 1” is formed in a predetermined number of inter-image areas. If the “pattern 1” is not formed in the predetermined number, the process returns to step S2003. If it is formed to a predetermined number, the process proceeds to step S2011.

  Subsequently, in step S2011, the first sensor SEN1 and the second sensor SEN2 detect the correction pattern, and output the result to the printer control unit 1. The printer control unit 1 calculates the amount of positional deviation of the sub-scanning and main scanning with respect to the K color based on the output. In the present embodiment, since a plurality of sets of patterns are formed, the amount of positional deviation is calculated from the average value of the output.

  Subsequently, in step S2013, the printer control unit 1 determines whether the data stored in the storage device 2 is to be corrected. For example, if the positional deviation amount is half or more of the correction resolution, the correction is performed.

  In the case of performing the correction, in step S2015, the printer control unit 1 calculates correction data based on the positional deviation amount.

  Subsequently, in step S2017, the printer control unit 1 updates the data of the storage device 2.

  Subsequently, in step S2019, the printer control unit 1 updates the correction data of each control device. The correction data here includes a set value of the pixel clock frequency that determines the image magnification in the main scanning direction, a set value of the XRGATE signal that determines the writing start position of the image in the main scanning direction, and an image of the image in the subscanning direction. It is a set value of the XFGATE signal that determines the writing start position.

  If the correction is not performed, the correction data is not updated.

  When the correction data is updated, an image is formed using the updated setting values thereafter.

  As described above, according to the image forming apparatus 100 of the present embodiment, even when there is a drive error in the drive system such as the image carrier or the transfer body, it is possible to ensure the correction accuracy of the positional deviation of the image.

  At the start of image formation, when the length of the transferred image is less than the specified value, the size of the medium is changed during the formation of the first pattern, and the length of the transferred image is equal to or more than the specified value. When it becomes, the image forming apparatus 100 discards the data of the first pattern acquired halfway. Then, the area between the images is lengthened to form a second pattern, and the positional deviation is corrected based on the detection output of the second pattern.

  As a result, even when the length of the transferred image is changed during the misregistration correction process, the misregistration correction process can be executed.

Second Embodiment
As another example of how to obtain the specified value of the image length in the transport direction of the transferred image, it may be obtained by the following method. That is, the time variation of the pattern formation error is predicted by the above-described method, and a length obtained by multiplying the conveyance speed by the intermediate transfer belt 10 by 1⁄2 of the variation period is set as a prescribed value.

  This is based on the fact that when the length of the transferred image in the transport direction exceeds half of the fluctuation period of the pattern formation error, the pattern formation error is often biased to either the "+" side or the "-" side. ing.

  According to this method, the prescribed value can be easily obtained.

  While examples of embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and various modifications may be made within the scope of the present invention as set forth in the claims. Modifications and changes are possible.

Reference Signs List 1 printer control unit 2, 216 storage device 10 intermediate transfer belt 11 polygon mirror 12 fθ lens 13 cleaning unit 14 to 16 support roller 17 intermediate transfer member cleaning unit 18 charging unit 19 charge removal unit 20 imaging device 21 light beam scanning device 211 polygon Motor control unit 212 LD control unit 213 Lighting control unit for synchronization detection 214 Pixel clock generation unit 215 Writing start position control unit 22 Secondary transfer unit 23 Roller 24 Secondary transfer belt 25 Fixing unit 29 Development unit 31 LD unit 40 Photoreceptor Unit 54 Synchronization sensor 62 Transfer unit 100 Image forming apparatus 101a, 101b, 101c, 101d, 102a, 102b, 103 Period of correction pattern formation 300 Image reading unit 40 Automatic feeding device 500 an image forming unit 501 positional deviation correction unit 502 detecting unit 503 image length detecting unit 504 storage unit SEN1, SEN2 first sensor, second sensor

JP 2008-073894 A JP, 2014-056118, A

Claims (7)

A plurality of image carriers on which light according to image data is irradiated to form a monochrome latent image and a latent image of the monochrome formed on each of the plurality of image carriers is developed, and a monochrome image is formed. An image forming apparatus comprising: a plurality of developing units; and a transfer body for conveying a transferred image on which the single-color image is sequentially transferred, wherein the single-color image is superimposed to form a multicolor image.
Pattern forming means for forming a pattern for correcting the positional deviation of the single-color image of each color in an inter-image area from the rear end of the transferred image to the front end of the next transferred image in the transfer direction of the transferred image; ,
Detection means for detecting the pattern;
Correction means for correcting the displacement based on data obtained by averaging the outputs of the detection means for a plurality of the patterns;
Detection means for detecting the length of the transferred image in the transport direction of the transferred image;
A storage unit in which the specified value of the length of the image is stored, which is referred to by the pattern forming unit;
The pattern forming unit forms a first pattern having at least one of the patterns in a plurality of the inter-image areas when the length of the detected image is less than the specified value, and detects the detected image When the length is equal to or more than the specified value, the length of the region in the transport direction of the predetermined inter-image region is made longer than the inter-image region forming the first pattern, and An image forming apparatus, wherein a second pattern having a plurality of the patterns is formed in an area.   The specified value is a length obtained by multiplying the half of the fluctuation period of the formation position of the pattern predicted from the speed fluctuation of the drive system that drives the image carrier and the transfer body by the conveyance speed. The image forming apparatus according to claim 1, further comprising:   The length of the second pattern in the transport direction is determined by the speed of the transport in a fluctuation cycle of the formation position of the pattern predicted from the speed fluctuation of a drive system that drives the image carrier and the transfer body. The image forming apparatus according to any one of claims 1 and 2, wherein the image forming apparatus has a length equal to or greater than a length obtained by multiplication.   The image according to any one of claims 1 to 3, wherein the second pattern is the pattern in which the first pattern is repeatedly formed a plurality of times in the transport direction. Forming device.   The correction means discards the data acquired for the first pattern when the length of the image becomes equal to or greater than a specified value during formation of the first pattern, and the second pattern The image forming apparatus according to any one of claims 1 to 4, wherein the positional deviation is corrected based on the acquired data.   The image forming apparatus according to any one of claims 1 to 5, wherein the detection unit detects the size of the medium on which the multicolor image is formed. A step of irradiating a plurality of image carriers with light according to image data to form a monochrome latent image, and developing the monochrome latent images formed on each of the plurality of image carriers. An image forming method comprising: forming a single color image; and conveying a transferred image to which the single color image is sequentially transferred, wherein the single color image is superimposed to form a multicolor image.
Forming a pattern for correcting positional deviation of the single-color image of each color in an inter-image area from the rear end of the transferred image to the front end of the next transferred image in the transport direction of the transferred image; ,
Detecting the pattern;
Correcting the positional deviation based on data obtained by averaging the outputs of the detection step for a plurality of the patterns;
Detecting the length of the transferred image in the transport direction of the transferred image;
The pattern forming step refers to a storage unit in which the specified value of the length of the image is stored, and when the detected length of the image is less than the specified value, the first inter-image area is selected. When the length of the detected inter-image area in the transport direction is the same as the inter-image area forming the first pattern, the pattern is formed and the length of the detected inter-image area is longer than the specified value. And a second pattern having a plurality of the patterns is formed in the predetermined inter-image area.

Images