JP2010277024A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus that corrects misalignment by properly determining the timing to correct the misalignment of an image. <P>SOLUTION: The color image forming apparatus 1 calculates a signal interval difference between a reference signal interval and a comparison signal interval. The reference signal interval represents a signal interval between a leading-end synchronous detection signal output from a leading-end synchronous detection sensor and a leading-end synchronous detection signal output from a non-parallel synchronous detection sensor, when consecutive printing is started in each of image forming units 30Y to 30Bk. The comparison signal interval represents a signal interval between a leading-end synchronous detection signal output from the leading-end synchronous detection sensor and a leading-end synchronous detection signal output from the non-parallel synchronous detection sensor, each time a predetermined time passes after the start of consecutive printing. Further, the color image forming apparatus 1 calculates a signal interval difference value, which is a difference between the signal interval difference of the image forming unit 30Bk and the signal interval difference of the other image forming units 30Y to 30C. Whether misalignment correction is required or not is determined based on whether the signal interval difference value exceeds a predetermined reference difference value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a color image forming apparatus, and more particularly, to a color image forming apparatus that performs misregistration correction by appropriately determining whether or not image misregistration correction is necessary.

  Conventionally, a so-called tandem type color image forming apparatus includes an image forming unit that forms images of each color such as cyan, magenta, yellow, and black along a conveyance belt or along an intermediate transfer belt. In the image forming unit for each color, the laser modulated by the image data for each color is irradiated from the writing unit to the photoconductor to form an electrostatic latent image. Each color image forming unit supplies toner of each color to the photoconductor on which the electrostatic latent image is formed, forms a toner image of each color, and is transferred onto a transfer belt or an intermediate transfer. The toner images on the photoreceptors of the respective colors are sequentially superimposed and transferred onto the belt to form a color image. In the case where the color image forming apparatus transfers to an intermediate transfer belt, the color image on the intermediate transfer belt is transferred onto a transfer sheet conveyed from a paper feeding unit by a transfer roller.

  As described above, in a color image forming apparatus including a plurality of image forming units, each image forming unit is compared with a color image forming apparatus that includes only one photoconductor called a one-drum system and forms a color image. Since color images are formed by sequentially superimposing toner images of different colors on the same surface of the same transfer paper or intermediate transfer belt, the position of the transferred image on the transfer paper or intermediate transfer belt in each image forming unit is the main. If they are shifted in the scanning direction and / or sub-scanning direction, the interval between images formed in each image forming unit may be shifted or overlapped. In the case of a color image, there will be a difference in color or color shift, and the image quality will be reduced. Getting worse.

  As this misalignment, there is an inclination in the scanning line for each color due to an assembly error inside the writing optical system, an attachment error of each unit to the color image forming apparatus main body and an attachment error of the photosensitive member to the color image forming apparatus main body. There is a tilt position shift that occurs in this way, and a parallel position shift that occurs when the position of the scanning line shifts in parallel to the reference position and the four-color image shifts in the vertical or horizontal direction as a whole. Of these misalignments, the misalignment is corrected by finely adjusting the position of the reflecting mirror of the writing unit, and the parallel misalignment is adjusted by adjusting the writing start timing in the main scanning direction or the sub scanning direction. The correction can be performed. The length of the image in the main scanning direction can be adjusted by changing the frequency of the writing pixel, that is, by adjusting the magnification error.

  And even if the color image forming apparatus is initially adjusted, such misregistration is not only caused by replacement of the image forming unit, maintenance of the color image forming apparatus, transportation of the color image forming apparatus, etc. The error also fluctuates over time due to the temperature expansion of the mechanism after forming a plurality of images.

  Therefore, conventionally, a misregistration detection pattern is formed with toner on a conveyance belt or an intermediate transfer belt that conveys transfer paper, and the misregistration detection pattern is detected. There has been proposed a technique for correcting misregistration using the correction timing when the number of sheets reaches the number of times or when the temperature changes to a predetermined temperature (see Patent Document 1).

  However, in the above prior art, since the misregistration detection pattern is formed on the transport belt or the intermediate transfer belt by the toner, the toner is consumed to form the misregistration detection pattern, and the running cost is high. There was a problem of sticking. Further, in the prior art, when the apparatus is turned on, the positional deviation correction is performed with a fixed timing such as when the number of printed sheets reaches a predetermined number of printed sheets or when the temperature changes to a predetermined temperature. For this reason, even when the positional deviation correction is not actually required, the positional deviation correction is performed and the productivity is deteriorated, or the positional deviation is not performed even though the positional deviation occurs. There was a problem that the image quality of the formed image deteriorated.

  Accordingly, the present invention provides a color image forming apparatus that determines whether or not misregistration correction is necessary at low cost and performs misregistration correction at an appropriate timing without forming a misregistration detection pattern using a developer. The purpose is to provide.

  In order to achieve the above object, according to the present invention, the leading end side synchronization detecting means disposed on the leading end side in the main scanning direction of the laser light to the latent image carrier of the plurality of image forming means detects the laser light. The leading edge side synchronization detection signal to be output and the trailing edge side synchronization detecting means arranged on the trailing edge side in the main scanning direction of the laser beam to the latent image carrier of each image forming means detect and output the laser beam. The rear end side synchronization detection signal, and the sub-scanning position deviation detection unit disposed between the front end side synchronization detection unit and the rear end side synchronization detection unit of each image forming unit in the sub scanning direction orthogonal to the main scanning direction. Based on the sub-scanning positional deviation detection signal that is detected and output at the timing corresponding to the amount of positional deviation of the laser light, the positional deviation correction means scans the laser light between the image forming means. And the correction control means And determine the necessity of the positional deviation correction based on the sub-scanning position deviation detection signal output from the scanning position deviation detecting means is characterized by controlling the execution of positional deviation correction by the positional deviation correcting means.

  Further, according to the present invention, the front end side synchronization detection means and the rear end side synchronization detection means are arranged to extend over a predetermined length in the sub-scanning direction, and the sub-scanning position deviation detection means includes: Extending over a predetermined length in a state inclined at a predetermined angle with respect to the main scanning direction or the sub-scanning direction, and synchronized with the front end according to the positional deviation of the laser light in the sub-scanning direction Detecting the laser light at a detection timing at which a time interval between the detection means and the detection timing of the laser light of the rear end side synchronous detection means changes, and outputting the sub-scanning position deviation detection signal; and the correction control means The necessity of the positional deviation correction based on the amount of change in the signal interval between at least one of the leading edge side synchronization detection signal and the trailing edge side synchronization detection signal and the sub-scanning positional deviation detection signal in each image forming unit. To judge It may be characterized.

  Further, according to the present invention, the correction control unit includes at least one of the front end side synchronization detection signal and the rear end side synchronization detection signal at a predetermined reference time in each image forming unit, and the sub-scanning position shift detection signal. The reference signal interval is the reference signal interval, and the signal interval between the leading end side synchronization detection signal and the trailing end side synchronization detection signal and the sub-scanning position shift detection signal at every predetermined elapsed time from the reference time is the comparison signal interval. A signal interval difference between the reference signal interval and the comparison signal interval is calculated, and a difference between a signal interval difference of a predetermined reference image forming unit and a signal interval difference of other image forming units among the image forming units Is calculated as a signal interval difference value, and the signal interval difference value is used as the amount of change in the signal interval, and based on whether the signal interval difference value exceeds a predetermined reference difference value, Necessity It may be characterized to determine.

  According to the present invention, it is possible to determine whether or not misregistration correction is necessary at a low cost without forming a misregistration detection pattern using a developer, and to perform misregistration correction at an appropriate timing. it can.

1 is a schematic configuration diagram of a main part of a color image forming apparatus to which a first embodiment of the present invention is applied. FIG. 3 is a block diagram of a main part of a color image forming apparatus. The figure which shows the structure and output signal of a synchronous detection part. 3 is a flowchart illustrating a shift correction control process in the color image forming apparatus according to the first embodiment. 6 is a flowchart illustrating a shift correction control process for performing shift correction after printing is completed. The flowchart which shows the deviation correction control process which controls deviation correction according to setting execution conditions. FIG. 9 is a block diagram of a main part of a color image forming apparatus according to a second embodiment. 9 is a flowchart illustrating a shift correction control process in the color image forming apparatus according to the second embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, since the Example described below is a suitable Example of this invention, various technically preferable restrictions are attached | subjected, However, The range of this invention is unduly limited by the following description. However, not all the configurations described in the present embodiment are essential constituent elements of the present invention.

  1 to 6 are diagrams showing a first embodiment of a color image forming apparatus according to the present invention. FIG. 1 shows a color image forming apparatus 1 to which the first embodiment of the color image forming apparatus according to the present invention is applied. It is a principal part schematic block diagram.

  In FIG. 1, a color image forming apparatus 1 includes a paper feed unit 10, a transport belt mechanism unit 20, and yellow (Y), magenta (M), and cyan disposed along the transport belt mechanism unit 20 in a main body casing. (C) and black (Bk) image forming units (image forming means) 30Y, 30M, 30C, 30Bk, a fixing unit 40, a system controller 50, etc. And a drive mechanism unit and an operation display unit for transmitting a drive source to each unit driven by the motor. The operation display unit includes various operation keys necessary for performing various operations of the color image forming apparatus 1 such as a numeric keypad and a start key, and also includes a display (for example, a liquid crystal display). Various command operations such as a copy operation are performed, and on the display, the content of commands input from the operation keys and various information notified from the color image forming apparatus 1 to the operator are displayed. In particular, the operation display unit (selection unit) is used to perform a selection operation as to whether or not to perform a positional deviation correction control process, which will be described later, during continuous printing. Display information.

  The paper feeding unit 10 separates the transfer paper (recording medium) P in the paper feeding cassette 11 one by one by, for example, a paper feeding roller and a separating member (not shown) and sends them to a pair of registration rollers (not shown). Then, the timing of the transfer paper P sent from the paper feed cassette 11 is adjusted, and the transfer paper P is sent to the transport belt mechanism unit 20 at a predetermined timing.

  The transport belt mechanism unit 20 includes a transport belt 21, a driving roller 22, a driven roller 23, and the like. The transport belt 21 is stretched between the driving roller 22 and the driven roller 23. The drive roller 22 is driven to rotate in a counterclockwise direction in FIG. 1 by being rotated by a drive mechanism such as a motor (not shown) under the control of the system controller 50, and the conveyor belt 21 is sent out from the paper supply unit 10. The transferred transfer paper P is sequentially conveyed to the image forming units 30Y to 30Bk for each color, and the yellow toner image, the magenta toner image, and the cyan toner are respectively transferred to the transferred transfer paper P by the image forming units 30Y to 30Bk for each color. The image and the black toner image are sequentially superimposed on the transfer paper P and transferred to form a color image.

  In the image forming units (image forming means) 30Y to 30Bk for the respective colors, photoconductors (latent image carriers) 31Y to 31Bk are arranged at predetermined intervals along the transport direction of the transport belt 21, and the photoconductors 31Y to 31Y. Around the 31Bk, charging units 32Y to 32Bk, exposure units 33Y to 33Bk, developing units 34Y to 34Bk, transfer units 35Y to 35Bk, cleaning units 36Y to 36Bk, a neutralizing unit (not shown), and the like are arranged.

  The image forming units 30Y to 30Bk uniformly charge the photosensitive members 31Y to 31Bk, which are driven to rotate clockwise in FIG. 1 by a driving mechanism (not shown), with the charging units 32Y to 32Bk, and the exposure units 33Y to 33Bk. Then, when an electrostatic latent image is formed by irradiating the photoconductors 31Y to 31Bk with lasers modulated with image data of each color, the developing units 34Y to 34B are formed on the photoconductors 31Y to 31Bk on which the electrostatic latent images are formed. At 34 Bk, yellow (Y), magenta (M), cyan (C), and black (Bk) toners (developers) are attached to form toner images (developer images) of the respective colors. When the transfer paper P is conveyed between the conveyance belt 21 and the photoconductors 31Y to 31Bk, the image forming units 30Y to 30Bk include transfer units 35Y to 35Bk disposed on the back surface of the conveyance belt 21. A transfer potential is applied, and toner images of each color of yellow (Y), magenta (M), cyan (C), and black (Bk) on the photoreceptors 31Y to 31Bk are sequentially superimposed on the transfer paper P and transferred. After the toner images have been transferred, the photoreceptors 31Y to 31Bk are cleaned by the cleaning units 36Y to 36Bk, discharged from the discharging unit, and then charged again by the charging units 32Y to 32Bk to form the next image. Perform the action.

  The transfer paper P on which a color image is formed by sequentially superimposing and transferring the toner images of each color of yellow (Y), magenta (M), cyan (C), and black (Bk) as described above is electrostatically charged. In the state of being attracted to the conveyor belt 21, the toner is further conveyed by the conveyor belt 21, separated from the conveyor belt 21, and conveyed to the fixing unit 40.

  The fixing unit 40 includes a fixing roller 41, a pressure roller 42, a pair of paper discharge rollers (not shown), and the like. The fixing roller 41 and the pressure roller 42 are pressed with a predetermined pressing force, and one of them is driven to rotate, and the other rotates. The fixing roller 41 is heated to a predetermined fixing temperature by a built-in heater. Be controlled.

  The fixing unit 40 transfers the toner of the color image or the black-and-white image to the transfer sheet P by heating and pressurizing the transfer sheet P, which has been transferred by the conveyor belt 21 after the toner image is transferred, by the fixing roller 41 and the pressure roller 42. The toner is fixed to P and discharged onto a paper discharge tray (not shown) by a pair of paper discharge rollers.

  As shown in FIG. 2, the color image forming apparatus 1 has a block configuration and includes a system controller 50, an alignment controller 51, a polygon motor control unit 52, the exposure units 33Y to 33Bk, and the like.

  The exposure units 33Y to 33Bk include an LD unit 60, a polygon mirror 61, an fθ lens 62, reflection mirrors 63a and 63b, lenses 64a and 64b, a front end synchronization detection unit 65a, a rear end synchronization detection unit 65b, and an LD (Laser Diode) control unit. 66, a sync detection lighting control unit 67, a pixel clock generation unit 68, and the like. The pixel clock generation unit 68 includes a reference clock generation unit 70, a VCO clock generation unit 71, a phase synchronization clock generation unit 72, and the like. Yes.

  The system controller (positional deviation correction means) 50 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a nonvolatile memory such as a NVRAM (Nonvolatile Random Access Memory), and the like. The ROM stores programs such as the system program of the color image forming apparatus 1 and the positional deviation correction control processing program of the present invention, and various data necessary for executing the system program and the positional deviation correction control processing program. In particular, data necessary for executing the misregistration correction control processing program, such as conditions for executing misregistration correction during continuous printing, is stored. Note that the conditions for executing this misalignment correction may be stored in the RAM. The RAM is used as a work memory or the like by the CPU of the system controller 50, stores various data, and particularly stores various data in the positional deviation correction control process.

  In the system controller 50, the CPU controls each part of the color image forming apparatus 1 while using the RAM as a work memory based on the system program in the ROM and the misregistration correction control processing program. And the misregistration correction control process during continuous printing.

  The color image forming apparatus 1 includes a ROM, an EEPROM (Electrically Erasable and Programmable Read Only Memory), an EPROM, a flash memory, a flexible disk, a CD-ROM (Compact Disc Read Only Memory), a CD-RW (Compact Disc Rewritable), Misregistration correction control for executing the misregistration correction control method of the present invention recorded on a computer-readable recording medium such as a DVD (Digital Video Disk), an SD (Secure Digital) card, or an MO (Magneto-Optical Disc). A misregistration correction that reads a processing program and introduces it into a non-volatile memory such as a ROM or a hard disk (not shown), and performs misregistration correction by determining whether or not it is necessary to correct the misregistration of images between colors at a low cost. It is constructed as a color image forming apparatus that executes a control method. The misregistration correction control processing program is a computer-executable program written in a legacy programming language such as an assembler, C, C ++, C #, Java (registered trademark), an object-oriented programming language, or the like. Can be stored and distributed.

  When a predetermined misregistration correction condition is satisfied during continuous printing, the alignment controller (correction control means) 51 uses a line synchronization signal (XDETP, XEDETP) to detect the misregistration of each color image. The correction amount of the positional deviation to be corrected is calculated, and the set values of the control signals such as the write clock and the write timing by the exposure units 33Y to 33Bk of the image forming units 30Y to 30Bk are output to the system controller 50.

  The system controller 50 changes the setting values such as the write clock and the write timing based on the set values of the control signals such as the write clock and the write timing input from the alignment controller 51, thereby shifting the position of each color. Execute correction processing.

  The polygon motor control unit 52 controls the driving of the polygon motors of the exposure units 33Y to 33Bk, and rotates the polygon mirror 61 at a specified rotational speed by the polygon motor.

  The LD control unit 66 of the exposure units 33Y to 33Bk receives the image data, the LD forced lighting signal BD from the synchronization detection lighting control unit 67, and the control signal from the system controller 50. The LD control unit 66 receives these data. The drive of the LD unit 60 is controlled based on the image data, the LD forced lighting signal BD, and the control signal.

  The LD unit 60 emits a light beam, which is driven and controlled by image data under the control of the LD control unit 66, to the polygon mirror 61 that is rotationally driven. The polygon mirror 61 receives the incident light beam. Are passed through the fθ lens 62 and irradiated onto the corresponding photoreceptors 31Y to 31Bk in the main scanning direction. At this time, the exposure units 33Y to 33Bk reflect the light beam that has passed through the fθ lens 62 by the reflection mirror 63a on the image writing (start: tip) side in the main scanning direction, and the tip synchronization detection unit via the lens 64a. When the light beam is detected, the tip synchronization detection unit 65a outputs a start side synchronization detection signal XDETP to the synchronization detection lighting control unit 67, the phase synchronization clock generation unit 72, and the alignment controller 51. Further, the exposure units 33Y to 33Bk reflect the light beam that has passed through the fθ lens 62 by the reflection mirror 63b on the image end (end: rear end) side in the main scanning direction, and detect rear end synchronization through the lens 64b. When the light beam is detected, the rear end synchronization detection unit 65 b outputs an end side synchronization detection signal (rear end side synchronization detection signal) XEDETP to the alignment controller 51.

  In the pixel clock generation unit 68, the reference clock generation unit 70 generates the reference clock FREF and outputs the reference clock FREF to the VCO clock generation unit 71. The VCO clock generation unit 71 generates the write clock VCLK from the reference clock FREF and generates the phase synchronization clock. To the unit 72 and the alignment controller 51. In the pixel clock generation unit 68, the phase synchronization clock generation unit 72 generates a clock PCLK synchronized with the start side synchronization detection signal XDETP from the clock VCLK generated by the VCO clock generation unit 71 and the start side synchronization detection signal XDETP. The data is output to the LD control unit 66 and the sync detection lighting control unit 67.

  The sync detection lighting control unit 67 first turns on the LD forced lighting signal BD to forcibly light the LD (semiconductor laser) of the LD unit 60 in order to detect the start side synchronization detection signal XDETP. After detecting the synchronization detection signal XDETP, the start-side synchronization detection signal XDETP and the clock PCLK generate an LD forced lighting signal BD that lights the LD at a timing at which the synchronization detection signal XDETP can be reliably detected without causing flare light. And output to the LD controller 66.

  The LD control unit 66 controls the lighting of the LD of the LD unit 60 according to the pulse signal width generated from the synchronization detection forced lighting signal and the image signal (image data) synchronized with the clock PCLK. The LD control unit 66 includes, for example, a PWM (Pulse Wide Modulation) signal generation unit that controls the lighting time of the LD and an LD drive unit that controls the lighting of the LD. The PWM signal generation unit includes image data. In response to the control signal from the system controller 50, the PWM signal is output to the LD driver, and the LD driver turns on the LD of the LD unit 60 for the time of the PWM signal. Further, the LD driving unit receives the LD forced lighting signal BD from the synchronization detection lighting control unit 67, and the LD driving unit outputs the LD of the LD unit 60 for the time during which the LD forced lighting signal BD is input. Light up. In the pulse phase control, the LD control unit 66 selects a phase based on a control signal (selection signal) from the system controller 50.

  The alignment controller 51 generates a synchronization detection signal XDETP, a synchronization detection signal XEDETP, and a VCO clock generator when predetermined execution conditions for performing alignment correction (positional deviation correction) are established during continuous printing. Using the write clock VCLK and the correction value calculated by the system controller 50, the skew deviation amount, main scanning registration deviation amount, main scanning magnification deviation amount, sub-scanning registration deviation amount, and correction amount are calculated, and the image forming unit 30Y. A set value of a control signal such as a write clock and a write timing by each of the exposure units 33Y to 33Bk of ˜30Bk is output to the system controller 50.

  The system controller 50 changes the setting values such as the write clock and the write timing based on the set values of the control signals such as the write clock and the write timing input from the alignment controller 51, thereby shifting the position of each color. Execute correction processing.

  The front end synchronization detection unit 65a and the rear end synchronization detection unit 65b are configured as shown in FIG. 3, and are disposed on the front end side and the rear end side with respect to the main scanning direction of the light beam.

  The tip synchronization detection unit 65a includes a tip synchronization detection plate 65aa, a tip synchronization detection sensor (tip-side synchronization detection means) 65ab, a non-parallel synchronization sensor (sub-scanning position deviation detection means) 65ac, and the like, and a tip synchronization detection plate 65aa. Includes a slit 65ad having a predetermined width in the main scanning direction of the light beam and extending a predetermined length in a direction orthogonal to the main scanning direction, and a main scanning direction having a predetermined width in the main scanning direction of the beam. And a non-parallel slit 65ae inclined at a predetermined angle with respect to the surface. In the tip synchronization detection unit 65a, the tip synchronization detection sensor 65ab receives the light beam that has passed through the slit 65ad of the tip synchronization detection plate 65aa, and as shown in FIG. 3, a tip synchronization detection signal (tip-side synchronization detection signal). XDETP is output, and the non-parallel synchronization sensor 65ac (sub-scanning position deviation detecting means) receives the light beam that has passed through the non-parallel slit 65ae, and as shown in FIG. Detection signal) XDETP is output.

  The rear end synchronization detection unit 65b includes a rear end synchronization detection plate 65ba, a rear end synchronization detection sensor (rear end side synchronization detection means) 65bb, and the like. The rear end synchronization detection plate 65ba has a light beam main scanning direction. A slit 65bc having a predetermined width and extending a predetermined length in a direction orthogonal to the main scanning direction is formed. In the rear end synchronization detection unit 65b, the rear end synchronization detection sensor 65bb receives the light beam that has passed through the slit 65bc, and outputs a rear end synchronization detection signal XEDETP as shown in FIG.

  That is, when the start-side synchronization detection signal XDETP is input from the tip synchronization detection sensor 65ab of the start-side tip synchronization detection unit 65a, the alignment controller 51 sets the main scanning time from the falling edge of the start-side synchronization detection signal XDETP. When the counting of the main scanning time counter to be timed is started and the end-side synchronization detection signal XEDETP is input from the rear-end synchronization detection sensor 65bb of the end-side rear-end synchronization detection unit 65b, the end-side synchronization detection signal XEDETP The main scanning time counter finishes counting at the falling edge, and the time from the falling edge of the start side synchronization detection signal XDETP to the falling edge of the end side synchronization detection signal XEDETP is compared with the main scanning reference count value. The main difference is that the phase of the pixel clock is shifted by the difference. Calculates the 査 correction amount, and outputs the write clock, as the set value of the control signal, such as a write timing to the system controller 50. Further, when the start-side synchronization detection signal XDETP is input from the tip synchronization detection sensor 65ab of the start-side tip synchronization detection unit 65a, the alignment controller 51 receives the sub-scanning deviation time from the falling edge of the start-side synchronization detection signal XDETP. When the end-side synchronization detection signal XEDETP is input from the rear-end synchronization detection sensor 65bb of the end-side rear-end synchronization detection unit 65b, The sub-scanning deviation time counter is counted at the falling edge of XEDETP, and the sub-scanning deviation time count value from the falling edge of the start-side synchronization detection signal XDETP to the falling edge of the end-side synchronization detection signal XEDETP is A preset reference exposure portion (in this embodiment, black Compared to the sub-scanning shift time count value of the exposure unit 33Bk), the difference only to calculate the sub-scanning position deviation correction amount, and outputs to the system controller 50 as a sub-scanning position deviation correction amount.

  The system controller 50 changes the set values such as the write clock and the write timing based on the set values of the control signals such as the write clock and the write timing input from the alignment controller 51 to perform the main scanning of each color. Each misalignment correction process such as direction misalignment correction, image magnification correction, and sub-scanning position misalignment correction is executed.

  Next, the operation of this embodiment will be described. The color image forming apparatus 1 according to the present embodiment determines whether or not misalignment correction is necessary based on the leading edge synchronization detection signal XDETP from the leading edge synchronization detection unit 65a, and performs misalignment correction processing necessary at an appropriate timing.

  That is, the color image forming apparatus 1 sequentially forms each color image on the transfer paper P by the image forming units 30Y to 30Bk for each color, and forms the color image on the transfer paper P. In the continuous printing process in which images are continuously formed, the transfer paper P is conveyed at a paper interval shorter than one circumference of the photoconductors 31Y to 31Bk, and continuous printing is performed.

  However, in the above image formation, if the image positions of the respective colors do not match in the main scanning direction, the sub-scanning direction, the magnification and the inclination, that is, if a position shift occurs, a color shift occurs and the image Quality deteriorates. In the following description, processing for correcting such misalignment is collectively referred to as misalignment correction, and misalignment correction is referred to as alignment processing according to the wording of the drawings as appropriate.

  Therefore, the color image forming apparatus 1 first checks whether the system controller 50 starts the continuous printing (step S101) as shown in FIG. In the printing of the first page, a position confirmation request is made.

  When receiving the position confirmation request from the system controller 50, the alignment controller 51 detects the tip synchronization when the light beam passes through the tip synchronization detector 65a in each of the image forming units 30Y to 30Bk as shown in FIG. The output time interval (signal interval) between the synchronization detection signal XDETP output from the sensor 65ab and the synchronization detection signal XDETP output from the tip non-parallel synchronization detection sensor 65ac is counted, and each of the counted image forming units 30Y to 30Bk is counted. The count value is stored in the internal nonvolatile memory or the like as the synchronization detection output time intervals Ysy, Ysm, Ysc, Ysk at the start of printing (step S102).

  The system controller 50 issues a position confirmation request to the alignment controller 51 at a predetermined timing if it is not at the start of printing in step S101, and when the alignment controller 51 receives the position confirmation request, as described above, In each of the image forming units 30Y to 30Bk, the synchronization detection signal XDETP output from the tip synchronization detection sensor 65ab and the synchronization detection signal output from the tip nonparallel synchronization detection sensor 65ac when the light beam passes through the tip synchronization detection unit 65a. Counts the output time interval with XDETP, obtains the current output time interval as the current synchronization detection output time interval (comparison signal interval) Ydy, Ydm, Ydc, Ydk, and starts printing previously stored in the nonvolatile memory Time synchronization detection output time interval Ysy, Ysm, Ysc, Ysk and current synchronization detection output time interval Ydy Interval differences (signal interval differences) Yddy, Yddm, Yddc, Yddk (Yddy = Ysy-Ydy, Yddm = Ysm-Ydm, Yddc = Ysc-Ydc, Yddk = Ysk-Ydk) from Ydm, Ydc, Ydk are calculated ( Step S103).

  The alignment controller 51 uses the image forming units 30Y to 30Bk as a reference from the calculated interval differences Yddy, Yddm, Yddc, and Yddk between the calculated image forming units 30Y to 30Bk (in this embodiment, the image forming unit 30Bk is used as a reference). Difference values (signal interval difference values) Yddk_y, Yddk_m, Yddk_c (Yddk_y = Yddk-Yddy, Yddk_m = Yddk-Yddk_m, Yddk_c = Yddk-Yddc) are calculated (step S104). It is checked whether at least one of the calculated difference values (signal interval change amount) Yddk_y, Yddk_m, Yddk_c exceeds a predetermined reference difference value Ydt (step S105).

  If none of the difference values Yddk_y, Yddk_m, and Yddk_c exceeds the reference difference value Ydt in step S105, the alignment controller 51 ends the misalignment correction control process as it is.

  In step S105, if any one of the difference values Yddk_y, Yddk_m, and Yddk_c exceeds the reference difference value Ydt, the alignment controller 51 transmits a misalignment correction execution request to the system controller 50 to detect misalignment correction control processing. Is finished (step S106).

  When the system controller 50 receives the misregistration correction execution request, the system controller 50 pauses continuous printing at a page break, executes the misregistration correction process as described above, and when the misregistration correction process ends, the system controller 50 continues. Resume printing.

  As described above, the color image forming apparatus 1 according to the present embodiment includes the leading edge synchronization detection sensor 65ab disposed on the leading end side in the main scanning direction of the laser light to the photoreceptors 31Y to 31Bk of the plurality of image forming units 30Y to 30Bk. Start-side synchronization detection signal XDETP that detects and outputs the laser light, and rear-end synchronization disposed on the rear-end side in the main scanning direction of the laser light to the photoreceptors 31Y to 31Bk of the image forming units 30Y to 30Bk The end-side synchronization detection signal XEDETP that the detection sensor 65bb detects and outputs the laser beam is not parallel to the front-end synchronization detection sensor 65ab and the rear-end synchronization detection sensor 65bb of each of the image forming units 30Y to 30Bk. Sub-scanning position shift that the synchronous sensor 65ac detects and outputs the laser beam at a timing according to the amount of laser beam shift in the sub-scanning direction orthogonal to the main scanning direction. Based on the tip synchronization detection signal XDETP, which is an intelligent signal, the system controller 50 corrects the laser beam scanning misalignment between the image forming units 30Y to 30Bk, and the alignment controller 51 performs non-parallel processing. Based on the start-side synchronization detection signal XDETP output from the synchronization sensor 65ac, it is determined whether or not misalignment correction is necessary, and the execution of misalignment correction by the system controller 50 is controlled.

  Therefore, it is possible to determine whether or not it is necessary to correct the misregistration at a low cost without forming a misregistration detection pattern using toner, and it is possible to correct the misregistration at an appropriate timing.

  Further, in the color image forming apparatus 1 of the present embodiment, the front end synchronization detection sensor 65ab and the rear end synchronization detection sensor 65bb are arranged to extend over a predetermined length in the sub-scanning direction, and the non-parallel synchronization sensor 65ac. Is arranged to extend over a predetermined length in a state inclined at a predetermined angle with respect to the main scanning direction or the sub-scanning direction, and according to the positional deviation of the laser light in the sub-scanning direction, the tip synchronization detection sensor 65ab and the rear end synchronization detection sensor 65bb detect the laser light at a detection timing at which the time interval with the detection timing of the laser light changes, and output a front end synchronization detection signal XDETP. At least one of the tip synchronization detection signal XDETP and the end side synchronization detection signal XEDETP in the sections 30Y to 30Bk (in this embodiment, the tip synchronization detection signal XD Based on the amount of change in signal intervals between the tip synchronization detection signal XDETP output from TP) nonparallel synchronization detecting sensor 65bb is judged whether or not to positional deviation correction.

  Therefore, it is possible to appropriately determine whether or not the position deviation correction is necessary based on only the signals output from the synchronization detection sensors 65ab, 65bb and 65ac, in particular, the tip synchronization detection signal XDETP, and the position deviation correction can be performed at an inexpensive and appropriate timing. It can be performed.

  Further, in the color image forming apparatus 1 according to the present embodiment, the alignment controller 51 detects the leading end synchronization detection signal XDETP and the non-parallel synchronization detection sensor at the start of continuous printing which is a predetermined reference time in each of the image forming units 30Y to 30Bk. The reference signal interval Ysy, Ysm, Ysc, Ysk, the signal interval from the tip synchronization detection signal XDETP output by 65bb, and the output of the tip synchronization detection signal XDETP and the non-parallel synchronization detection sensor 65bb every predetermined elapsed time from the start of continuous printing. A signal interval difference between the reference signal interval and the comparison signal interval Yddy, Yddm, Yddc, Yddk is calculated with the signal interval from the leading edge synchronization detection signal XDETP as the comparison signal intervals Ydy, Ydm, Ydc, Ydk, and each image formation is performed. Among the sections 30Y to 30Bk, the signal interval difference Yddk of the image forming section 30Bk which is a predetermined reference image forming section and the other image forming sections 30Y to 30C. Signal interval differences Yddy, Yddm, Yddc are calculated as signal interval difference values Yddk_y, Yddk_m, Yddk_c, and the signal interval difference values Yddk_y, Yddk_m, Yddk_c are used as signal interval change amounts, and the signal interval difference values are calculated. Based on whether Yddk_y, Yddk_m, and Yddk_c exceed a predetermined reference difference value Ydt, it is determined whether or not misalignment correction is necessary.

  Therefore, it is possible to more appropriately determine whether or not the positional deviation correction is necessary based on only the signals output from the synchronization detection sensors 65ab, 65bb, and 65ac, in particular, the tip synchronization detection signal XDETP. It is possible to perform misalignment correction.

  Note that when the system controller 50 receives the misalignment correction execution request, the system controller 50 immediately executes misalignment correction at the break of the next page. However, execution of misalignment correction is not limited to the above timing. For example, Alternatively, it may be executed after the continuous printing currently being executed is completed, or whether or not to perform misregistration correction may be controlled in accordance with the misregistration correction availability setting during continuous printing by the user.

  That is, when performing misregistration correction after completion of continuous printing, the system controller 50 receives a misregistration correction execution request indicating whether or not a misregistration correction execution request has been received in a memory such as a nonvolatile memory or a RAM. Information is stored, and when a misalignment correction execution request is received from the alignment controller 51 during execution of printing such as continuous printing, misalignment correction execution request reception information indicating that the misalignment correction execution request has been received is stored in a nonvolatile memory or Store in RAM or other memory.

  Then, as shown in FIG. 5, when the system controller 50 finishes printing such as continuous printing (step S201), the system controller 50 acquires correction execution request reception information from a memory such as a nonvolatile memory or a RAM (step S202). It is checked whether a positional deviation correction execution request is received based on the correction execution request reception information (step S203).

  If it is determined in step S203 that a position deviation correction execution request has not been received, the system controller 50 ends the process, and if a position deviation correction execution request has been received, the system controller 50 executes position deviation correction processing (step S204). . When the system controller 50 completes the execution of the misalignment correction process, the system controller 50 clears the misalignment correction execution request reception information in the memory and ends the misalignment correction control process (step S205).

  In this way, it can be prevented that the time until the continuous printing is completed by executing the misalignment correction during the continuous printing and the productivity of the continuous printing process is lowered, and the usability is improved. Can be improved.

  In addition, when the system controller 50 controls whether or not misalignment correction can be performed according to the setting for misalignment correction during continuous printing by the user, the system controller 50 performs continuous printing from the operation display unit of the color image forming apparatus 1. When the misalignment correction enable / disable setting is performed, the misalignment correction enable / disable setting information during continuous printing is stored in the nonvolatile memory as misalignment correction execution condition information.

  In this state, as shown in FIG. 6, when the system controller 50 receives a positional deviation correction execution request from the alignment controller 51 (step S301), the system controller 50 acquires positional deviation correction item condition information from the nonvolatile memory (step S302). ) It is checked whether the misregistration correction condition is correctable during continuous printing (step S303).

  If it is determined in step S303 that the misregistration correction condition is correctable during continuous printing, the system controller 50 temporarily stops (interrupts) continuous printing (step S304) and executes misregistration correction processing (step S305). ). When the system controller 50 completes the execution of the misregistration correction process, the system controller 50 resumes the interrupted continuous printing. When the continuous printing is completed, the system controller 50 ends the misregistration correction control process (step S306).

  In step S303, when the misregistration correction execution condition indicates that the correction during continuous printing is impossible, the system controller 50 stores the misregistration correction execution request reception information in the RAM or the non-volatile memory and performs misregistration correction control processing. The process ends (step S307).

  In this case, when the continuous printing is completed, the system controller 50 executes the misalignment correction process based on the misalignment correction execution request reception information stored in the nonvolatile memory, for example, as illustrated in FIG.

  In this way, whether or not to perform misregistration correction during continuous printing can be appropriately selected depending on whether the user attaches importance to image quality or productivity, and the usability can be further improved. .

  7 and 8 are views showing a second embodiment of the color image forming apparatus of the present invention, and FIG. 7 shows the essential parts of the color image forming apparatus to which the second embodiment of the color image forming apparatus of the present invention is applied. FIG.

  This embodiment is applied to a color image forming apparatus similar to the color image forming apparatus 1 of the first embodiment. In the description of this embodiment, the same components as those of the first embodiment are not described. The same reference numerals are attached and detailed description thereof is omitted, and even parts that are not shown will be described using the reference numerals used in the first embodiment as they are, if necessary.

  In this embodiment, the positional deviation correction is performed not only based on the leading edge synchronization detection signal XDETP from the leading edge synchronization detection unit 65a but also in consideration of the number of printed sheets and / or the temperature of the color image forming apparatus 1 as the execution condition of the positional deviation correction. It is determined whether it is time to perform correction.

  Therefore, the color image forming apparatus 1 includes a printed sheet counter 81 and a temperature sensor 82 as shown in FIG.

  The printed sheet counter 81 operates under the control of the system controller 50, counts the number of printed sheets every time one page is printed, and outputs the number of printed sheets as a count result to the alignment controller 51. That is, the system controller 50 increments the count value of the print sheet counter 81 each time the transfer sheet P is conveyed from the paper supply unit 10 and outputs the counted print sheet number to the alignment controller 51.

  The temperature sensor 82 detects the temperature in the color image forming apparatus 1 and outputs it to the alignment controller 51.

  Then, as shown in FIG. 8, the color image forming apparatus 1 takes into account not only the leading edge synchronization detection signal XDETP from the leading edge synchronization detector 65a but also the number of printed sheets and / or the temperature of the color image forming apparatus 1 and misalignment. A deviation correction control process for controlling whether or not to perform correction is performed.

  That is, in continuous printing, the color image forming apparatus 1 first checks whether the system controller 50 starts continuous printing (step S401) as shown in FIG. A request for position confirmation is made to the alignment controller 51 in printing the first page.

  When receiving the position confirmation request from the system controller 50, the alignment controller 51 outputs an output from the tip synchronization detection sensor 65ab when the light beam passes through the tip synchronization detection unit 65a in each of the image forming units 30Y to 30Bk, as described above. Output time interval between the synchronization detection signal XDETP to be output and the synchronization detection signal XDETP output from the leading end non-parallel synchronization detection sensor 65ac, and the counted count values of the image forming units 30Y to 30Bk are synchronously detected at the start of printing. The output time intervals Ysy, Ysm, Ysc, and Ysk are stored in an internal nonvolatile memory or the like, and the number of printed sheets Ps at the start of continuous printing counted by the printed sheet counter 8 is acquired and stored in the nonvolatile memory or the like. The temperature Ts at the start of continuous printing detected by the temperature sensor 82 is acquired to obtain a nonvolatile memory. To save the Li or the like (step S402).

  If it is not at the start of printing in step S401, the system controller 50 issues a position confirmation request to the alignment controller 51 at a predetermined timing (every elapsed time), and the alignment controller 51 receives the position confirmation request. Similarly to the above, in each of the image forming units 30Y to 30Bk, when the light beam passes through the tip synchronization detection unit 65a, the synchronization detection signal XDETP output from the tip synchronization detection sensor 65ab and the tip non-parallel synchronization detection sensor 65ac are output. The output time interval with the synchronization detection signal XDETP is counted, and the current output time interval is acquired as the current synchronization detection output time interval Ydy, Ydm, Ydc, Ydk, and the print start previously stored in the nonvolatile memory is started. Time synchronization detection output time interval Ysy, Ysm, Ysc, Ysk and current synchronization detection output time interval Ydy, dm, calculated Ydc, distance difference between Ydk Yddy, Yddm, Yddc, Yddk (Yddy = Ysy-Ydy, Yddm = Ysm-Ydm, Yddc = Ysc-Ydc, Yddk = Ysk-Ydk) a (step S403).

  The alignment controller 51 calculates the difference values Yddk_y, Yddk_m, Yddk_c (Yddk_y = Yddk−Yddy) between the calculated interval differences Yddy, Yddm, Yddc, Yddk of the image forming units 30Y-30Bk and the interval difference Yddk of the reference image forming unit 30Bk. Yddk_m = Yddk−Yddk_m, Yddk_c = Yddk−Yddc) is calculated (step S404), and any one of the calculated difference values Yddk_y, Yddk_m, Yddk_c exceeds a predetermined reference difference value Ydt set in advance. A check is made (step S405).

  In step S405, when any one of the difference values Yddk_y, Yddk_m, and Yddk_c does not exceed the reference difference value Ydt, the alignment controller 51 ends the misalignment correction control process as it is.

  In step S405, if any one of the difference values Yddk_y, Yddk_m, and Yddk_c exceeds the reference difference value Ydt, the alignment controller 51 acquires the current print number Pp counted by the print number counter 81, and stores the non-volatile value. The difference Ps_p from the number of printed sheets Ps at the start of continuous printing stored in the memory is calculated, and it is checked whether the difference Ps_p is equal to or larger than a preset reference number of printed sheets Pt (step S406). The reference print number Pt is set in advance from the relationship between the number of prints and the positional deviation and stored in the nonvolatile memory, but can be set as appropriate by operating the operation display unit of the color image forming apparatus 1 or the like. It may be.

  When the difference Ps_p has not reached the reference print number Pt in step S406, the alignment controller 51 ends the misalignment correction control process as it is, and in step S406, if the difference Ps_p is greater than or equal to the reference print number Pt, the temperature sensor 82, the current temperature Tp detected is calculated, and a difference Ts_p from the temperature Ts at the start of continuous printing stored in the nonvolatile memory is calculated. The difference Ts_p is equal to or higher than a preset reference temperature Tt. It is checked whether there is any (step S407). The reference temperature Tt is set in advance from the relationship between the temperature and the positional deviation and is stored in the nonvolatile memory. However, the reference temperature Tt can be appropriately set by operating the operation display unit of the color image forming apparatus 1 or the like. It may be.

  If the difference Ts_p has not reached the reference temperature Tt in step S407, the alignment controller 51 ends the correction control process as it is, and if the difference Tt is equal to or higher than the reference temperature Tt in step S407, A deviation correction execution request is transmitted, and the deviation correction control process is terminated (step S408).

  When the system controller 50 receives the misregistration correction execution request, the system controller 50 pauses continuous printing at a page break, executes misregistration correction processing, and resumes continuous printing when the misregistration correction processing ends. . Further, when the system controller 50 receives the misalignment correction execution request, as shown in FIGS. 5 and 6, the system controller 50 may execute it after completion of continuous printing currently being executed, or during continuous printing by the user. Depending on the setting of whether or not misalignment correction is possible, whether or not misalignment correction can be executed may be controlled.

  As described above, the color image forming apparatus 1 of the present embodiment includes the printed sheet counter 81 that counts the number of printed sheets and the temperature sensor 82 that detects the temperature in the color image forming apparatus 1, and the alignment controller 51. Is the amount of change in the number of printed sheets from the reference time (at the start of continuous printing or at the time of the previous misalignment correction) counted by the interval differences Yddy, Yddm, Yddc, Yddk and the number of printed sheets counter 81, which are the amount of change in the signal interval. Whether or not the misregistration correction is necessary is determined based on the amount of temperature change from the temperature at the reference time detected by the temperature sensor 82 (at the start of continuous printing or at the previous misalignment correction execution time).

  Accordingly, it is possible to more appropriately determine whether or not to perform the positional deviation correction, and it is possible to perform the positional deviation correction at a more inexpensive and more appropriate timing.

  In the above description, the tip synchronization detection signal XDETP from the tip synchronization detection sensor 65ab and the tip non-parallel synchronization detection sensor 65ac of the tip synchronization detection unit 65a satisfies the misalignment correction execution condition, and both the number of prints and the temperature. In the above description, the positional deviation correction execution request is made to the system controller 50 when the positional deviation correction execution condition is satisfied. However, the present invention is not limited to the case where both the number of printed sheets and the temperature satisfy the positional deviation correction execution condition. The positional deviation correction execution condition is that the leading edge synchronization detection signal XDETP from the leading edge synchronization detection unit 65a satisfies the positional deviation correction execution condition, and that either the number of prints or the temperature satisfies the positional deviation correction execution condition. It is good.

  Further, as a material for determining the position deviation correction execution condition, it is also possible to use only whether or not the tip synchronization detection signal XDETP from the tip synchronization detection unit 65a satisfies the position deviation correction execution condition and either the number of prints or the temperature. Good.

  Further, in the above description, the misalignment correction execution condition is used based on the leading edge synchronization detection signal XDETP, the number of printed sheets, and the temperature at the start of continuous printing. The leading edge synchronization detection signal XDETP at the start of continuous printing, the number of prints, and the temperature are not limited, and for example, the leading edge synchronization detection signal XDETP at the time of the previous misalignment correction, the number of prints, and the temperature may be used as a reference. In this case, the leading edge synchronization detection signal XDETP, the number of printed sheets, and the temperature at the time of executing the misalignment correction are acquired and stored in a nonvolatile memory or the like as the reference leading edge synchronization detecting signal XDETP, the number of printed sheets, and the temperature. Whether or not it is necessary to execute misregistration is determined based on the relationship between the detection signal XDETP, the number of printed sheets and the temperature, and the leading edge synchronization detection signal XDETP, the number of printed sheets and the temperature acquired by receiving the position confirmation request from the system controller 50.

  As described above, if the necessity of the positional deviation correction is determined based on the previous execution of the positional deviation correction as the reference time, the necessity of the positional deviation correction can be determined more appropriately.

  In the description of each of the above embodiments, the present invention is applied to an image forming method in which a color image is formed by superimposing toner images of respective colors on the transfer paper P transported by the transport belt 21 by the image forming units 30Y to 30Bk. As described above, the image forming method is not limited to the above method. For example, the color image is formed by superimposing the toner images of the respective colors on the intermediate transfer belt by the image forming units 30Y to 30Bk. The image transfer method in which the image is finally transferred onto the transfer paper P can be similarly applied.

  The invention made by the present inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to that described in the above embodiments, and various modifications can be made without departing from the scope of the invention. It goes without saying that it is possible.

  The present invention can be applied to a color image forming apparatus such as a color printer, a color composite apparatus, or the like that corrects an image position shift of each color when a color image is formed by superimposing images of each color in a plurality of image forming units. .

DESCRIPTION OF SYMBOLS 1 Color image forming apparatus 10 Paper feed part 11 Paper feed cassette 20 Conveyance belt mechanism part 21 Conveyance belt 22 Drive roller 23 Driven roller 30Y-30Bk Image formation part 31Y-31Bk Photoreceptor 32Y-32Bk Charging part 33Y-33Bk Exposure part 34Y- 34Bk Developing section 35Y to 35Bk Transfer section 36Y to 36Bk Cleaning section 40 Fixing section 41 Fixing roller 42 Pressure roller 50 System controller 51 Positioning controller 52 Polygon motor control section 60 LD unit 61 Polygon mirror 62 fθ lens 63a, 63b Reflecting mirror 64a 64b Lens 65a Tip synchronization detector 65aa Tip synchronization detection plate 65ab Tip synchronization detection sensor 65ac Non-parallel synchronization sensor 65ad Slit 65ae Non-parallel slit 65b Rear-end synchronization detection Unit 65ba trailing edge synchronization detection plate 65bb trailing edge synchronization detection sensor 65bc slit 66 LD control unit 67 lighting control unit for synchronization detection 68 pixel clock generation unit 70 reference clock generation unit 71 VCO clock generation unit 72 phase synchronization clock generation unit 81 number of printed sheets Counter 82 Temperature sensor P Transfer paper

JP 2003-149905 A

Claims (7)

A plurality of image forming units for different colors are arranged along the conveying belt or the intermediate transfer belt, and each of the image forming units receives laser light modulated by the image data for each color on the latent image carrier. An electrostatic latent image is formed by scanning in the main scanning direction, and a developer image obtained by developing the formed electrostatic latent image with a developer of a corresponding color is recorded on the conveyance belt or the recording medium When a color image is formed by sequentially superimposing and transferring on the intermediate transfer belt, and the image is transferred onto the intermediate transfer belt, the color image on the intermediate transfer belt is finally transferred to a recording medium to obtain the color image. In the color image forming apparatus to be formed,
Front-end-side synchronization detection means that is disposed on the front-end side in the main scanning direction of the laser light to the latent image carrier of each image forming means, detects the laser light, and outputs a front-end-side synchronization detection signal;
A rear-end-side synchronization detection unit that is disposed on the rear-end side in the main scanning direction of the laser beam to the latent image carrier of each image forming unit and detects the laser beam and outputs a rear-end side synchronization detection signal; ,
Sub-scanning position deviation detecting means for detecting the laser beam at a timing corresponding to the amount of positional deviation of the laser beam in the sub-scanning direction orthogonal to the main scanning direction and outputting a sub-scanning position deviation detection signal;
A position for correcting the laser beam scanning misalignment between the image forming means based on the leading edge side synchronization detection signal, the trailing edge side synchronization detection signal, and the sub-scanning position deviation detection signal in each image forming means. Deviation correction means;
A correction control unit that determines whether or not the positional deviation correction is necessary based on a sub-scanning positional deviation detection signal output from each of the sub-scanning positional deviation detection units, and controls execution of the positional deviation correction by the positional deviation correction unit;
A color image forming apparatus comprising: The leading edge side synchronization detecting means and the trailing edge side synchronization detecting means are arranged to extend over a predetermined length in the sub-scanning direction,
The sub-scanning position deviation detecting means is disposed to extend over a predetermined length in a state inclined at a predetermined angle with respect to the main scanning direction or the sub-scanning direction, and the laser beam is shifted in the sub-scanning direction. The sub-scanning position deviation detection signal is detected by detecting the laser light at a detection timing at which a time interval between the leading edge side synchronization detecting means and the trailing edge side synchronization detecting means changes with respect to the detection timing of the laser light. Output
The correction control unit is configured to change the position based on a change amount of a signal interval between at least one of the leading end side synchronization detection signal and the trailing end side synchronization detection signal and the sub-scanning position shift detection signal in each image forming unit. 2. The color image forming apparatus according to claim 1, wherein whether or not deviation correction is necessary is determined.   The correction control means uses a signal interval between at least one of the leading edge side synchronization detection signal and the trailing edge side synchronization detection signal at a predetermined reference time in each of the image forming means and the sub-scanning position shift detection signal as a reference signal. The reference signal interval is defined as a comparison signal interval between one of the leading end side synchronization detection signal and the trailing end side synchronization detection signal and the sub-scanning position shift detection signal at intervals of a predetermined elapsed time from the reference time. And a difference between a signal interval difference of a predetermined reference image forming unit and a signal interval difference of other image forming units among the image forming units as a signal interval difference value. Calculating and determining whether the positional deviation correction is necessary based on whether or not the signal interval difference value exceeds a predetermined reference difference value, using the signal interval difference value as a change amount of the signal interval. Special The color image forming apparatus according to claim 2,. The color image forming apparatus further includes a printed sheet count unit that counts the number of printed sheets,
The correction control means determines whether or not the positional deviation correction is necessary based on a change amount of the signal interval and a change amount of the number of printed sheets from the reference time counted by the number of printed sheet counting means. The color image forming apparatus according to claim 2 or 3. The color image forming apparatus further includes a temperature detecting means for detecting the temperature in the apparatus,
The correction control means determines whether or not the positional deviation correction is necessary based on a change amount of the signal interval and a temperature change amount from the temperature at the reference time detected by the temperature detection means. The color image forming apparatus according to claim 2.   The correction control means uses the start time of continuous printing or the previous execution time of the misregistration correction to sequentially form color images on the recording medium continuously conveyed at a predetermined recording medium interval as the reference time. 6. The color image forming apparatus according to claim 3, wherein it is determined whether or not misalignment correction is necessary. The color image forming apparatus determines whether or not to perform misregistration correction by the misregistration correction means during continuous printing in which a color image is sequentially formed on the recording medium continuously conveyed at a predetermined recording medium interval. A selection means for selecting,
When the correction control unit determines that the misregistration correction is necessary during the continuous printing, the misregistration correction unit temporarily interrupts the continuous printing based on a selection result by the selection unit, and 7. The color image forming apparatus according to claim 1, wherein the color image forming apparatus controls whether to perform misregistration correction or to perform the misregistration correction after the continuous printing is completed.

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