JP2006251407A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for ensuring high image quality by correcting a detection time of a main scanning synchronous signal and suppressing color shift due to shift of an image formation start position of a sub-scanning direction generated between colors and between pages. <P>SOLUTION: The image forming apparatus is provided with a detecting means for detecting a detected means being an image formation start reference of each color provided on an intermediate transfer body at a prescribed position. The image forming apparatus detects an image formation start signal of the sub-scanning direction generated when detecting the detected means, then, receives a laser beam deflected at a deflection reflection face of a rotary multi-face mirror to an image carrier moved in the sub-scanning direction by a light receiving element, starts image formation in a main scanning direction on the basis of the detected main scanning synchronous signal, and forms a color image. The image forming apparatus detects the image formation start signal of the sub-scanning direction, then, corrects a detecting time of the main scanning synchronous signal when delaying to the detecting time detected more than the previously obtained light receiving element by the detecting time of the main scanning synchronous signal, and starts the image formation on the basis of the corrected detecting time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and an image forming method for performing timing control for starting image formation in a copying machine, a printer, or the like.

In an electrophotographic multicolor image forming apparatus, toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (K) are formed on an intermediate transfer member, and this is formed. A full color image is printed by transferring the toner image onto a recording medium. If the writing position of each color is deviated when printing this full-color image, when the superimposed toner image is transferred onto the recording medium, color misregistration occurs and the image quality deteriorates. Therefore, it is necessary to control the alignment of the image writing start position.
2. Description of the Related Art Conventionally, in an image forming apparatus that forms an image by transferring a toner image onto an intermediate transfer member, a reference mark for alignment is provided on the intermediate transfer member, and this reference mark is detected by a sensor and a detection signal is sent to the CPU. The image writing in the sub-scanning direction is started with reference to this timing. Further, a main scanning synchronization signal is detected for each scanning line, this detection signal is taken into a CPU, and an image in the main scanning direction is written on the basis of the taking timing.

  Japanese Patent Application Laid-Open No. 2004-228561 detects a main scanning synchronization signal and fetches it into a CPU, and controls the position of the intermediate transfer belt based on this detection signal, and the deviation between the intermediate transfer belt position detection signal and the main scanning synchronization detection signal. A method for controlling the image transfer start time is described.

In Patent Document 2, a light source used for recording of the first first line is selected from a plurality of light sources in accordance with a time difference between an image formation start signal for determining an image formation start position in the sub-scanning direction and a main scanning synchronization signal. There has been proposed a multi-beam laser recording apparatus including a light source selection unit that delays the start of image formation of the first line in accordance with the time difference and an image formation start delay unit.
JP 2002-123056 A Japanese Patent Laid-Open No. 11-212009

  In monochromatic laser scanning writing type image formation, an image formation start signal generated by detecting a mark provided on the intermediate transfer member by a mark detection means, and a main scanning synchronization signal generated by rotation of a rotary polygon mirror Are asynchronous, the timing relationship between the image formation start signal and the main scanning synchronization signal differs every time between colors and between pages. Since the image formation start timing is determined by the timing of the image formation start signal and the main scanning synchronization signal for each color, the image formation position differs depending on this time difference, and color misregistration occurs. For example, a color shift of about one scan occurs between when the image formation start signal is generated immediately before the main scan synchronization signal and when the image formation start signal is generated immediately after the main scan synchronization signal. To do.

  In the CPU processing, if other interrupt processing is being performed at the time of interruption of the main scanning synchronization signal, the temporary processing is suspended, and therefore the timing when the CPU accepts the processing is delayed with respect to the actual sensor detection timing. When the image formation start position is controlled by controlling the image formation start timing based on the relationship between the mark detection timing and the main scanning synchronization signal detection timing, the amount of color misregistration may increase due to the delay of this timing.

  In Patent Document 2, scanning delay and beam selection at the start of image formation are performed based on the timing of the image formation start signal and main scanning synchronization signal for each color, and this color shift is reduced to 1/2 scan or less. The formation start timing is determined for each color based on the relationship between the image formation start signal and the main scanning synchronization signal, and the timing relationship between the colors is not taken into consideration. Color misregistration occurs and color misregistration cannot be suppressed.

  The present invention corrects the detection time of the main scanning synchronization signal without using an expensive CPU or dedicated hardware circuit capable of high-speed processing, and generates an image formation start position in the sub-scanning direction that occurs between colors and between pages. An object of the present invention is to provide an image forming apparatus and an image forming method capable of suppressing color misregistration due to misregistration, thereby enabling high-quality image formation.

  An image forming apparatus according to a first aspect of the present invention includes: a detection unit that serves as an image formation start reference for each color provided on an intermediate transfer member; and a detection unit that detects the detection unit at a predetermined position. After the detection means detects the image forming start signal in the sub-scanning direction generated when the detected means is detected, the image carrying member moving in the sub-scanning direction is deflected by the deflecting reflecting surface of the rotary polygon mirror. An electrostatic latent image formed on the image carrier by starting image formation by performing scanning according to image recording information in the main scanning direction based on a main scanning synchronization signal detected by receiving a laser beam received by a light receiving element A toner image is generated by the developing means, and the process of transferring the toner image onto the intermediate transfer member is repeated a plurality of times for each color, and the toner images are sequentially superimposed for each color to form a color image, Image in the sub-scanning direction After the detection start signal is detected, when the detection time of the main scanning synchronization signal is delayed with respect to the detection time detected by the light receiving element obtained in advance, the detection time of the main scanning synchronization signal is corrected and the correction is performed. Image formation is started based on the detected time.

  According to a second aspect of the present invention, there is provided an image forming apparatus comprising: a main scanning synchronization signal detecting means for detecting a main scanning synchronization signal by receiving a laser beam deflected by a deflection reflection surface of the rotary polygon mirror; Main scanning synchronization signal number counting means for measuring the number of scanning synchronization signals; main scanning synchronization signal detection time acquisition means for acquiring detection time of the main scanning synchronization signal; and storage means for storing the main scanning synchronization signal detection time. Calculating means for determining the time interval of the main scanning synchronization signal from the detection time of the storage means, determination means for determining the presence or absence of a delay in the main scanning synchronization signal detection time, and main scanning synchronization based on the result of the determination means Compensation means for correcting the signal detection time is provided, which is obtained from the count value of the time interval of the main scanning synchronization signal obtained in advance before the start of image formation and the main scanning synchronization signal detection time detected at the time of image formation. When the time interval count value of the main scanning synchronization signal is compared and it is determined that there is a delay in the detection time of the main scanning synchronization signal, image formation is performed based on the detection time of the main scanning synchronization signal in which the delay is corrected by the correction means. It is characterized by starting.

  According to a third aspect of the present invention, in the apparatus according to the second aspect, acquisition of a detection time of a main scanning synchronization signal detected by receiving a laser beam deflected by a deflecting reflection surface of the rotary polygon mirror with a light receiving element; From the detection time, the time interval of the main scanning synchronization signal corresponding to each surface of the rotary polygon mirror is counted for each sequence before the start of image formation, the time interval count value of the main scanning synchronization signal, and the image When the time interval count value of the main scanning synchronization signal obtained from the main scanning synchronization signal detection time detected at the time of formation is compared and it is determined that there is a delay in the detection time of the main scanning synchronization signal, the correction means delays The image formation is started based on the detection time of the main scanning synchronization signal in which the correction is corrected.

  According to a fourth aspect of the present invention, in the apparatus according to the second aspect, acquisition of a detection time of a main scanning synchronization signal detected by receiving a laser beam deflected by a deflecting reflection surface of the rotary polygon mirror with a light receiving element; The time interval of the main scanning synchronization signal corresponding to each surface of the rotary polygon mirror is counted in advance from the detection time, the count value is stored as a lookup table, and the time interval of the stored main scanning synchronization signal is stored. Is compared with the time interval count value of the main scanning synchronization signal obtained from the main scanning synchronization signal detection time detected during image formation, and it is determined that there is a delay in the detection time of the main scanning synchronization signal The image forming is started based on the detection time of the main scanning synchronization signal whose delay is corrected by the correcting means.

  According to a fifth aspect of the present invention, in the apparatus according to the third or fourth aspect, the detection time of the main scanning synchronization signal detected by receiving the laser beam deflected by the deflection reflection surface of the rotary polygon mirror with the light receiving element Obtaining and counting the time interval of the main scanning synchronization signal corresponding to each surface of the rotary polygon mirror from the detection time, and the difference between the maximum value and the minimum value of the time interval is set to an arbitrary value set in advance. When the difference value is smaller than the difference value, the average value of the count values is controlled as the count value of the time interval of the main scanning synchronization signal.

  According to a sixth aspect of the present invention, in the apparatus according to any one of the first to fifth aspects, the storage means for storing the main scanning synchronization signal detection time is a main scanning synchronization signal detection time detected at the time of image formation. Is capable of storing and storing at least (number of surfaces + 1) of the rotary polygon mirror, and means for determining the order of the stored time series and replacing the most recently detected time with the previously stored detection time. Storage means, and counting the time interval of the main scanning synchronization signal corresponding to each surface of the rotary polygon mirror from the stored detection time.

  According to a seventh aspect of the present invention, in the apparatus according to the first or second aspect of the present invention, the apparatus has scanning type writing means having a plurality of beams arranged in the sub-scanning direction, and starts image formation in response to an image formation start signal for the second color. The second color image formation is started by delaying the writing start timing or beam selection so that the difference between the time and the image formation start time with respect to the first color image formation start signal is minimized. In the subsequent image formation of the nth color (an integer of n ≧ 3), the maximum image formation start time of each color with respect to the image formation start signal of each color from the first color to the (n−1) th color already formed The average start time tm between the value and the minimum value is obtained, and the write start timing is set so that the time difference between the image formation start time with respect to the image formation start signal for the nth color and the average start time tm is minimized. Characterized in that so as to start the extension or beam selection.

  According to an eighth aspect of the present invention, in the apparatus according to the seventh aspect, in the image formation for the third and subsequent colors, the write timing is delayed or beam selection control is performed so that the time difference from the average start time tm is minimized. When the image formation start time deviates from the amplitude of the image formation start time of each color with respect to the image formation start signal of each color from the first color to the (n-1) th color that has already been formed, the maximum value or the minimum value of the amplitude Assuming an image formation start time for advancing or delaying a predetermined amount of beam in the sub-scanning direction from the deviation from the value and the image formation start time obtained by the delay of the writing timing or beam selection control, the maximum value of the amplitude at that time Alternatively, the deviation from the minimum value is compared, and image formation is started at an image formation start time at which the deviation becomes small.

  According to a ninth aspect of the present invention, in the apparatus according to any one of the first to eighth aspects, the image forming unit includes a plurality of image forming units arranged to face the moving surface of the intermediate transfer member. The means selectively selects one image carrier, one writing means, at least two developing means for developing an electrostatic latent image formed on the image carrier by the writing means, and the developing means. And switching means for driving.

  According to a tenth aspect of the present invention, an image forming start signal in the sub-scanning direction generated by detecting an image forming start reference for each color provided on the intermediate transfer member is detected, and the image forming start signal is detected in the sub-scanning direction. The moving image carrier receives a laser beam deflected by the deflecting and reflecting surface of the rotary polygon mirror, detects a main scanning synchronization signal, and performs scanning according to image recording information based on the main scanning synchronization signal. A plurality of processes for each color are carried out for each color by starting image formation on the image carrier, generating a toner image from the electrostatic latent image formed on the image carrier, and transferring the toner image to the intermediate transfer member. A light-receiving element obtained by detecting in advance the detection time of the main-scanning synchronization signal after detecting the image-forming start signal in the sub-scanning direction by a method of repeatedly forming the color image by sequentially superimposing the toner images for each color Detected by When you are delayed with respect detection time, the main scanning to correct the detection time of synchronizing signals, characterized in that image formation is started on the basis of the corrected detection time.

  According to an eleventh aspect of the present invention, in the method according to the tenth aspect, acquisition of a detection time of a main scanning synchronization signal detected by receiving a laser beam deflected by the deflection reflection surface of the rotary polygon mirror with a light receiving element; From the detection time, the time interval of the main scanning synchronization signal corresponding to each surface of the rotary polygon mirror is counted for each sequence before the start of image formation, the time interval count value of the main scanning synchronization signal, and the image When the time interval count value of the main scanning synchronization signal obtained from the main scanning synchronization signal detection time detected at the time of formation is compared and it is determined that there is a delay in the detection time of the main scanning synchronization signal, the correction means delays The image formation is started based on the detection time of the main scanning synchronization signal in which the correction is corrected.

  According to a twelfth aspect of the present invention, in the method of the tenth aspect, acquisition of a detection time of a main scanning synchronization signal detected by receiving a laser beam deflected by the deflecting and reflecting surface of the rotary polygon mirror with a light receiving element; The time interval of the main scanning synchronization signal corresponding to each surface of the rotary polygon mirror is counted in advance from the detection time, the count value is stored as a lookup table, and the time interval of the stored main scanning synchronization signal is stored. When comparing the count value with the time interval count value of the main scanning synchronization signal obtained from the main scanning synchronization signal detection time detected at the time of image formation, and determining that there is a delay in the detection time of the main scanning synchronization signal, Image formation is started based on the detection time of the main scanning synchronization signal whose delay is corrected by the correcting means.

  According to a thirteenth aspect of the present invention, in the method according to the eleventh or twelfth aspect, the detection time of the main scanning synchronization signal detected by the light receiving element receiving the laser beam deflected by the deflection reflection surface of the rotary polygon mirror Obtaining and counting the time interval of the main scanning synchronization signal corresponding to each surface of the rotary polygon mirror from the detection time, and the difference between the maximum value and the minimum value of the time interval count is an arbitrary value set in advance. When the difference value is smaller than the difference value, the average value of the count values is controlled as the count value of the time interval of the main scanning synchronization signal.

  According to a fourteenth aspect of the present invention, in the method according to the tenth aspect of the present invention, the image forming start time with respect to the second color image formation start signal has scanning writing means having a plurality of beams arranged in the sub-scanning direction. The second color image formation is started by delaying the write start timing or beam selection so that the difference between the first color image formation start signal and the image formation start time is minimized. In the image formation of the nth color (an integer of n ≧ 3), the maximum value of the image formation start time of each color with respect to the image formation start signal of each color from the first color to the (n−1) th color already formed The average start time tm of the minimum value is obtained, and the write start timing is delayed so that the time difference between the image formation start time with respect to the image formation start signal of the nth color and the average start time tm is minimized. Other is characterized in that so as to start the beam selection.

  According to a fifteenth aspect of the present invention, in the method of the fourteenth aspect, in the image formation for the third and subsequent colors, the write timing delay or the beam selection control is performed so that a time difference from the average start time tm is minimized. The maximum value of the amplitude when the image formation start time obtained by the above method deviates from the amplitude of the image formation start time of each color with respect to the image formation start signal of each color from the first color to the (n-1) th color already formed Alternatively, from the deviation from the minimum value and the delay of the writing timing or the image formation start time obtained by the beam selection control, an image formation start time for advancing or delaying a predetermined beam amount in the sub-scanning direction is assumed, and the amplitude at that time The deviation from the maximum value or the minimum value is compared, and image formation is started at the image formation start time when the deviation is small. The features.

  According to the present invention, after detecting the image formation start signal in the sub-scanning direction, the main scanning synchronization is detected when the detection time of the main scanning synchronization signal is delayed with respect to the detection time detected by the light receiving element obtained in advance. Since the signal detection time is corrected and image formation is started based on the corrected detection time, it is possible to reduce the leading position deviation of the superimposed image generated based on the mark detection on the intermediate transfer member.

  Hereinafter, the present invention will be specifically described with reference to embodiments shown in the drawings.

  FIG. 1 shows an image forming apparatus 30 using a multi-beam laser scanning optical system 34 according to an embodiment of the present invention. The image forming unit 31 includes an image carrier 32 driven in a direction orthogonal to laser scanning by the multi-beam laser scanning optical system 34, a charging unit 33, a writing unit 34, and a developing unit arranged around the image carrier 32. (Developer) 35, a primary transfer unit 36, and a cleaning unit 37.

  The multi-beam laser scanning optical system 34 includes a multi-beam light source composed of a plurality of light sources, and laser beams from the plurality of light sources modulated in accordance with image information are collimated by a collimating lens, and then are rotated polygon mirrors. The image spot 32 is scanned and exposed by the laser spot scanned by the deflecting and reflecting surface of the rotary polygonal mirror 22 as scanning means rotated by the motor for use and narrowed down by the imaging lens. The image carrier 32 is exposed and recorded two-dimensionally by being driven in the direction orthogonal to the laser scanning by the image carrier drive means. The light receiving element is disposed outside the image range recording within the scanning range of the laser scanning, receives and detects at least one of the plurality of laser beams, and determines a recording start position in the main scanning direction.

  Below the image carrier 32, an intermediate transfer body 40 for transferring a toner image formed on the image carrier 32, a mark 41 provided on the intermediate transfer body 40 as a reference for starting image formation, and the mark Mark detecting means 42 for detecting, and transferring means 43 for transferring the toner image transferred onto the intermediate transfer body 40 to the recording medium 44 are arranged.

  The image forming apparatus shown in FIG. 1 includes a rotation switching type developing device 35 including a developing unit that performs development with toners of four colors of yellow (Y), magenta (M), cyan (C), and black (K). The image unit 31 is a one-drum type multi-color recording multi-beam laser recording apparatus that performs four exposure recordings on one image carrier 32 while switching each color developing unit of the developing unit 35. In this case, the developing means 35 in the image forming unit 31 adds four colors to the three primary colors to form four colors. Therefore, these colors are assigned to each developing device, and are sequentially switched and developed to form a full-color image. be able to.

  The image carrier 32 rotates in the direction indicated by the arrow, and its surface is uniformly charged by the charging means 33. When the mark 41 provided on the intermediate transfer body 40 is detected by the mark detection means 42, the writing means 34 starts exposure of the first color based on the image data, and the electrostatic latent image on the image carrier 32. Form an image. The developing means 35 switches to the first developing color Y, develops the electrostatic latent image, and forms the first color toner image. At the contact point with the intermediate transfer body 40, the primary transferring means 36 performs the intermediate transfer. It is transferred to the body 40.

  When the intermediate transfer body 40 rotates once and the mark 41 provided on the intermediate transfer body 40 is detected again by the mark detection means 42, the writing means 34 starts exposure of the second color based on the image data. Then, an electrostatic latent image is formed on the image carrier 32. The developing means 35 switches to the second developing color M, develops the electrostatic latent image, and forms the second color toner image. At the contact point with the intermediate transfer body 40, the primary transferring means 36 The toner image is transferred to the intermediate transfer body 40 so as to overlap the toner image of the first color. Similarly, the third color C color toner and the fourth color K color toner image are sequentially transferred to the intermediate transfer member 40 so as to overlap, and a full-color toner image is formed on the intermediate transfer member 40. By transferring this full-color toner image to the recording medium 44, a full-color image can be obtained on the recording medium 44. The toner image on the recording medium 44 is fixed by fixing means (not shown), and a full color image can be obtained on the recording medium 40.

  Below the image forming unit 31, a paper feeding device (not shown) that feeds the stacked recording media 44 one by one is arranged. One sheet of the recording medium 44 sent out from the paper feeding device is fed to the transfer means 43 by a paper feeding roller (not shown) and a registration roller (not shown). A fixing device (not shown) including a heating roller (not shown) and a pressure roller (not shown) that rotates in pressure contact with the heating roller is disposed on the downstream side of the transfer unit 43.

  The toner image is transferred by the transfer unit 43 to a recording medium sent from a paper supply unit (not shown) when a color image of Y, M, C, and K is finally formed on the intermediate transfer body 40 by the above procedure. Then, it is fixed by fixing means (not shown). The intermediate transfer member 40 that has finished transferring the toner image is subjected to removal of residual toner by the cleaning means 37.

  In this embodiment, a plurality of developing devices 35 are rotated and switched, a toner image for each color is formed on one image carrier 32, and a toner image for each color is sequentially superimposed on the intermediate transfer member 40. The image forming apparatus 30 that performs batch transfer onto the recording medium 44 after the transfer has been described, but image units that form one or more color images are arranged at regular intervals along the same moving surface of the intermediate transfer member. The present invention can also be applied to an image recording apparatus in which images of one color or a plurality of colors are sequentially superimposed and transferred onto an intermediate transfer member and then transferred to a recording medium at a time.

  FIG. 2 shows an optical writing apparatus using a laser scanning optical system. The optical writing device includes a light source 21. The light source 21 corresponds to image information of each color of black (K), cyan (C), magenta (M), and yellow (Y) by a modulation unit (not shown). Then, a laser beam is emitted as a light beam that is modulated in succession and sequentially modulated with image information of each color of black, cyan, magenta, and yellow.

  The laser beam from the light source 21 is collimated by the collimator lens 25 and then deflected by the deflecting / reflecting surface by the rotary polygon mirror 22 as scanning means. The rotary polygon mirror 22 is repeatedly driven in the main scanning direction by being rotationally driven by a driving unit (not shown). The laser beam from the rotary polygon mirror 22 is narrowed down by the imaging lens 23 and imaged on the photosensitive member 27 as a laser spot. Here, the photoreceptor 27 corresponds to the image carrier 32 in FIG. The laser spot is rotated and driven by a driving means (not shown), and the laser spot is repeatedly scanned in the main scanning direction to form an electrostatic latent image on the photoreceptor 27.

  Here, the light receiving element 24 as the main scanning synchronization signal generating means is disposed outside the image range within the laser beam scanning range, receives the laser beam from the rotary polygon mirror 22 and detects this, and detects it in the main scanning direction. A main scanning synchronization signal for determining a recording start position (horizontal registration) is generated. On the other hand, the image formation start signal in the sub-scanning direction, which determines the image formation start position in the sub-scanning direction, is the mark 41 provided on the intermediate transfer member 40 shown in FIG. Detection by the mark detection means 42 generates an image formation start signal in the sub-scanning direction.

  The main scanning synchronization signal from the light receiving element 24 and the image formation start signal in the sub-scanning direction from the mark detection means 42 are sent to a CPU (Central Processing Unit), which detects the main scanning synchronization signal and the mark from the light receiving element 24. In accordance with an image formation start signal from the means 42 in the sub-scanning direction, optical writing to the photoconductor 27 is performed on the optical writing device.

  FIG. 3 shows the relationship between each detection signal and each processing timing. In FIG. 3, an image formation start signal in the sub-scanning direction obtained by detecting the mark 41 provided on the intermediate transfer member 40 shown in FIG. The figure shows the relationship between the main scanning synchronization signal obtained by receiving the laser beam and the timing at which the main scanning synchronization signal is received and processed by the CPU interrupt processing.

  Normally, the time for receiving the main scanning synchronization signal obtained by detecting the laser beam with the light receiving element 24 in the interrupt process of the CPU and starting the processing with respect to the time for detecting the laser beam with the light receiving element 24 is equal to the time for the CPU processing time. Only the process is started with a delay. This delay is a very short time with respect to the scanning cycle, and the processing time is almost constant, so that it can be ignored in controlling the start timing of image formation. However, when the main scanning synchronization signal is detected, other interrupt processing is accepted first and is being executed. 1) In the control mode in which interrupt processing is performed in the order accepted, 2) the first accepted interrupt. In the case of a control mode in which processing has a higher priority and priority is given to interrupt processing with higher priority, the main scanning synchronization signal interrupt processing is temporarily suspended. Is received and the timer value at that time is acquired, the time recognized by the CPU is delayed with respect to the time detected by the light receiving element 24.

  Accordingly, the first line in the sub-scanning direction is determined according to the time difference from the detection time of the image formation start signal in the sub-scanning direction as shown in JP-A-11-212009 to the main scanning synchronization signal detected immediately thereafter. When the light source used for the image recording is selected from a plurality of light sources and the control for delaying the scanning of the start of image formation on the first line is performed, the CPU recognizes the time detected by the light receiving element 24. If the time is delayed, the image formation is originally started without performing the scanning delay, and the one-line scanning delay is performed. As a result, a deviation for one scanning occurs or the light source is selected. When the formation of an image is started without selecting a light source, there is a case where one line shift occurs.

  On the other hand, at the timing shown in FIG. 3, the start time of the main scanning synchronization CPU interruption process is delayed with respect to the main scanning synchronization detection signal immediately after the image formation start signal in the sub-scanning direction is detected. This is because other interrupt processing (not shown) is preferentially executed at this timing, so that the main scanning synchronization signal interrupt processing is suspended until the processing ends, and the start time of the main scanning synchronization signal interrupt processing is delayed. Because. When this interrupt process is started, the timer value at this point is acquired. Therefore, a delay occurs with respect to the time detected by the light receiving element 24. This delay is stored in advance by means such as measurement, and compared with the timer value at the time of interruption, the time detected by the light receiving element 24 is predicted and corrected, and the sub-scan is performed based on the corrected time. The image formation start time is controlled based on the time difference from the detection time of the direction image formation start signal.

  FIG. 4 shows the configuration of the main scanning synchronization signal delay presence / absence determination means and correction means. When the main scanning synchronization signal obtained by receiving the laser beam from the rotary polygon mirror 22 by the light receiving element 24 (main scanning synchronization signal detection means) shown in FIG. The count value of the internal timer is stored in the detection time storage means 101. Further, every time the main scanning synchronization signal is detected by the main scanning synchronization signal number counting means 102, the count value for counting the number of times of detection is incremented, and the count value is given to the detection time, and the detection time storage means 101 is countered. As data. Thereby, the relationship corresponding to each surface of the rotary polygon mirror 22 can be grasped.

  When an image formation start signal in the sub-scanning direction is detected, the count value of the internal timer stored in the detection time storage means 101 and the count value of the number of detections are read, and main scanning before and after the image formation start signal is detected in the sub-scanning direction. The time interval of the synchronization signal is calculated by the time interval calculation calculation means 103. This time interval is compared with a preset reference value (measured value 106) to determine whether there is a delay in the detection time. When it is determined that there is a delay in the detection time (detection time period delay determination means), the detection time correction means 104 corrects the detection time to be predicted in advance. The detection time determined to have a delay is replaced with the corrected detection time and stored in the detection time storage unit 101.

  FIG. 5 shows the control system. In FIG. 5, the CPU is connected to a ROM for storing programs, initial values, etc., a RAM for storing various data, a TIMER for measuring time based on a clock, an interrupt controller for controlling interrupts, etc., via an address bus and a data bus. Has been.

  The clock generation means (not shown) uses an internal clock of the CPU or a clock generator externally connected to the CPU. The interrupt controller detects an interrupt to the CPU by an interrupt detection signal, sets an interrupt mode, sets an interrupt priority order, and controls interrupt permission / prohibition.

  FIG. 6 shows a flowchart of control. When system power is turned on or the system is reset, interrupts are disabled, bus controller settings, interrupt control mode settings, communication settings, various initialization processes and checks, and variables with initial values are transferred from ROM to RAM Etc. are set as initial settings. When the initial setting is completed, the state is returned to the interrupt enabled state, and the process proceeds to the main routine process. In the main routine process, process 1 and process 2 are sequentially performed. Usually, the main routine is composed of an infinite loop, and repeated processing is executed.

  If the interrupt request signal is input to the interrupt controller when the main routine processing is being executed, the interrupt controller issues an interrupt request to the CPU unless the interrupt enabled state or other interrupt processing is being executed. Suspends the processing being executed and prioritizes interrupt processing. When the interrupt process ends, the process returns to the process being executed, and the process is resumed.

  Here, the processing procedure of the interrupt processing differs depending on the setting of the interrupt control mode and the interrupt priority order. For example, when interrupt processing occurs in duplicate, a method of processing interrupt processing sequentially in the order of acceptance, when interrupt processing with high priority occurs while executing interrupt processing with low priority, interrupt processing with high priority There is a method of preferentially processing.

  FIG. 7 shows a flowchart of main scanning synchronization signal interrupt processing. When the laser beam from the rotary polygon mirror 22 is received by the light receiving element 24 (main scanning synchronization signal detecting means) shown in FIG. 2, an interrupt request is issued to the interrupt controller as a main scanning synchronization signal. When this interrupt is accepted, the main scanning synchronization signal detection interrupt processing is performed. At this time, the time at the time of interruption is acquired as the count value of the timer and stored in the detection time storage means. Each time a main scanning synchronization signal is detected, the detection time is stored in the detection time storage means.

  When a main scanning synchronization signal is detected immediately after the mark 41 provided on the intermediate transfer member 40 shown in FIG. 1 is detected by the mark detection means 42, the timer counts when the stored main scanning synchronization signal is detected. The value is read and the time interval (timer count value) of the main scanning synchronization signal is calculated. Next, a preset reference value or a pre-measured measurement value is read and compared with the calculated time interval of the main scanning synchronization signal to determine whether there is a delay in the detection time of the main scanning synchronization signal before and after the mark detection.

  When it is determined that there is a delay in the detection time of the main scanning synchronization signal, the detection time of the correct main scanning synchronization signal to be predicted is calculated from the previous and subsequent detection times and the preset reference value or the measured value, The calculated detection time is replaced and stored. Based on this corrected detection time, the start of image formation is controlled.

  By performing such control, it is possible to reduce the misalignment of the head position of the superimposed image generated based on the mark detection on the intermediate transfer body 40.

  The light receiving element 24 shown in FIG. 2 receives the laser beam from the rotary polygon mirror 22, makes an interrupt request to the CPU as a main scanning synchronization signal, and obtains a timer value at that time to detect a detection time interval between the main scanning synchronization signals. When the print sequence is being executed, there is a possibility that the timer value processed by the CPU may be delayed due to the interrupt processing being overlapped by a plurality of other interrupt processing. Therefore, in addition to the print sequence, the control is executed so that only the interrupt processing of the image forming signal in the main scanning direction is executed in a state where no other interrupt processing is generated in advance, and the time of the accurate main scanning synchronization signal is The interval is measured and stored. This measurement is preferably performed for each sequence before the start of image formation. However, a method of performing periodically, performing every fixed number of prints, or performing each time the power is turned on may be used.

  By comparing the time interval measured by this method with the time interval acquired during execution of the print sequence, the presence or absence of delay can be determined. Moreover, this measurement can be omitted by storing and holding the time interval measured in advance by the above-described method or the like as a lookup.

  The rotating polygon mirror 22 has some variation in scanning time due to variations in the surface and the like. When it is determined that the variation in the detection time interval of the main scanning synchronization signal corresponding to each surface is small, thereafter, the average detection time interval is calculated from the detection time measured for a certain time without considering the surface, The calculated time interval is used as the time interval of the main scanning synchronization signal, and is applied to delay correction of the detection time.

  Also by performing the control as described above, it is possible to reduce the misalignment of the head position of the superimposed image generated based on the mark detection on the intermediate transfer member.

  FIG. 8 shows the rotating polygon mirror 22. If the number of surfaces of the rotary polygon mirror 22 is 6, the detection times of the main scanning synchronization signals scanned from the 1st surface to the 6th surface are sequentially stored and held. Next, the detection time of the main scanning synchronization signal scanned on one surface is stored and held again. Thus, if at least one detection time greater than the number of faces can be stored, the time interval from 1 to 2 faces, the time interval from 2 faces to 3 faces, ... the time interval from 5 faces to 6 faces, and 6 One time interval from the surface can be stored and held at a time. Therefore, the time interval corresponding to each surface can be calculated.

  The oldest detection time is erased from the oldest stored time, and the latest detection time is stored. The stored spaces are sequentially shifted and stored in the storage area. Alternatively, the latest detection time may be sequentially overwritten and stored in the oldest detection time stored, and when calculating the time interval, the detection time may be read in time series to calculate each time interval. With such a configuration, the storage unit can be configured with a small capacity.

  FIG. 9 shows an image formation start signal (a) in the sub-scanning direction generated by detecting a mark on the intermediate transfer member 40 shown in FIG. 1 and a main scanning synchronization signal (vertical line shown in FIG. 9). Show the relationship.

  The time difference between the image formation start signal (a) and the main scanning synchronization signal is shifted by the period T of the main scanning synchronization signal at the maximum as shown in (b) and (c). If the first color image formation start is performed with the main scanning synchronization signal p1 at the timing (b) shown in FIG. 9, the image formation start timing for the second color and thereafter cannot be corrected, and the timing (c) is assumed. When the main scanning synchronization signal is generated, the main scanning synchronization signal p2 is started, and a deviation of one scanning occurs at the maximum.

  In contrast, in this embodiment, first, the image formation of the first color is started from the main scanning synchronization signal after a certain time has elapsed after the detection of the image formation start signal. FIG. 10 shows image formation start dot positions under control when the number of beams is two in the multi-beam laser recording apparatus. Black dots shown in FIG. 10 are dots on the image formation start side in the sub-scanning direction.

  When image formation of the first color is generated after detection of an image formation start signal in the sub-scanning direction and the main scanning synchronization signal has elapsed after 3T / 4 or more, image formation is started at the timing of the main scanning synchronization signal. In this example, image formation is started in synchronization with the first main scanning synchronization signal. In the second color, after the image formation start signal is detected, when the main scanning synchronization signal p1 is generated at time t2, the main scan is delayed by one scan so that the difference Δt from the image formation start time of the first color is minimized. Image formation is started by the synchronization signal p2. The image formation start time from the image formation start signal at this time is t2 + T. Here, the average start time tm1 (average synchronization 1) of the image formation start times of the first color and the second color is (t1 + (t2 + T)) / 2.

  For the third color, image formation is started by selecting a beam (white beam: L1) so that the time difference Δt between the average start time tm1 of the first color and the second color and the image formation start time of the third color is minimized. To do. Assuming a pseudo synchronization signal (a dotted line between the black beam (Du) and the white beam (L1) shown in FIG. 10) for the selected white beam L1, the image formation start time for the third color is set. Therefore, the image formation start time for the third color image formation start signal is t3 + T / 2. Here, the average start time tm2 of the maximum value and the minimum value of the image formation start time from the first color to the third color already formed is obtained. Since the maximum value of the image formation start time is t2 + T of the second color and the minimum value is t3 + T / 2 of the third color, the maximum value and the minimum value of the image formation start time from the first color to the third color. The average start time tm2 is ((t2 + T) + (t3 + T / 2)) / 2.

  For the fourth color, the time difference Δt between the time t4 from the image formation start signal to the main scanning synchronization signal and the maximum value of the image formation start time from the first color to the third color and the average start time tm2 of the minimum value is Since it becomes smaller than the time delay when scanning delay or beam is selected, image formation is started at time t4 from the image formation start signal to the main scanning synchronization signal.

  The criteria for determining the image formation start time for the second and subsequent colors shown in FIG. 10 are as follows according to the time difference Δt.

  When Δt <T / 4, image formation is started in the time from the image formation start signal to the next main scanning synchronization signal. When T / 4 ≦ Δt <3T / 4, after the time from the image formation start signal to the next main scanning synchronization signal has elapsed, beam selection is performed and image formation is started. When Δt ≧ 3T / 4, after the time from the image formation start signal to the next main scanning synchronization signal has elapsed, image formation is started with a further delay of one scan.

  FIG. 11 shows a block diagram for performing control. A mark detection unit 51 that detects the reference mark 41 on the intermediate transfer member 40 shown in FIG. 1 and generates an image formation start signal in the sub-scanning direction, and an image formation start signal in the sub-scanning direction when the first color image is formed. After the detection, a measuring unit 52 that measures an elapsed time until the main scanning synchronization signal that is generated first, a first storage unit 53 that stores and holds the measurement time of the measuring unit 52, and a preset first reference value 54, the first storage means 53 and the first reference value 54 are compared, the first determination means 55 for determining the magnitude, and the first storage means 53 based on the result of the first determination means 55. The first addition means 56 for adding and updating the first value obtained in advance, and the elapsed time from the detection of the image forming start signal in the sub-scanning direction during the image formation of the second color to the first main scanning synchronization signal The measurement time of the measuring means 52 for measuring Second storage means 63, calculation means 60 for obtaining a difference between the values stored in the first storage means 53 and the second storage means 63, a first reference value 54 and a second reference value set in advance. Based on the result of the 2nd determination means 65 and the 2nd determination means 65 which determines the magnitude of the difference calculated | required by the reference value 64 and the calculating means 60, and the 1st value calculated | required beforehand by the 2nd memory | storage means 63 Alternatively, the second addition means 66 for adding and updating the second value, and the first average storage means 67 for obtaining and storing the average value of the values stored in the first storage means 53 and the second storage means 63; The third storage means for storing and holding the measurement time of the measurement means 52 for measuring the elapsed time from the detection of the image formation start signal in the sub-scanning direction when the third color image is formed to the first main scanning synchronization signal. 73, first storage means 53, second storage means 63, and third storage hand The second average storage means 77 for obtaining and storing the average value of the maximum value and the minimum value stored in the memory 73, and the first occurrence after detecting the image formation start signal in the sub-scanning direction during the fourth color image formation. Image formation based on the results of the fourth storage means 83 for storing and holding the measurement time of the measurement means 52 for measuring the elapsed time until the main scanning synchronization signal and the first determination means 55 or the second determination means 65 The timing delay means 80 for delaying the start time and the data selection output control means 90 for selecting or switching the output of image data input from the outside based on the result of the second determination means 65 and the timing delay means 80. It is configured.

  The operation of FIG. 11 is shown below. When the first color image is formed, the elapsed time from the image formation start signal to the generation of the main scanning synchronization signal is determined by the first determination means 55, and when 3T / 4 or more has elapsed, the main scanning synchronization signal Image formation is started at the timing, and when the time has not elapsed, the image formation start time is controlled by the timing delay means 80 so as to be delayed by one scan from the main scanning synchronization signal. The first reference value is 3T / 4.

  When the scanning is delayed by one scan, the first adding means 56 adds and updates the first time T obtained in advance to the first storage means 53. When the second color image is formed, the second storage unit 63 stores the elapsed time from the image formation start signal to the generation of the main scanning synchronization signal, and the first addition unit 56 adds and updates the first addition unit 56 as necessary. The difference between the values stored in the storage means 53 is obtained by the computing means 60 and judged by the second judging means 65. When the time difference at this time is less than T / 4, image formation is started at the timing of the main scanning synchronization signal, and when it is T / 4 or more and less than 3T / 4, the subsequent timing is started at the timing of the main scanning synchronization signal. The image formation start time is controlled by the timing delay means 80 so that the image formation is started by selecting one of the beams, and when it is 3T / 4 or more, it is delayed by one scanning from the main scanning synchronization signal. At this time, when the beam is selected, the data selection / output control means 90 selects or switches the output of the image data input from the outside so that the subsequent beam forms the data of the first line of the image. Here, the second reference value 64 is T / 4. Further, the second adding means 66 stores the first time T obtained in advance in the second storage means 63 when the beam is selected and the second time T / 2 obtained in advance when the beam is selected. Add and update.

  The first average storage means 67 obtains and stores the average value of the values stored in the first storage means 53 and the second storage means 63 that are added and updated as necessary.

  When the third color image is formed, the difference between the value stored in the first storage means 67 and the value stored in the first storage means 67 is calculated from the value stored in the third storage means 73 that stores the elapsed time from the image formation start signal to the generation of the main scanning synchronization signal. Obtained by means 60 and judged by second judging means 65.

  In accordance with the determination result, the image forming start time is controlled by the timing delay means 80, and the image selection / output switching is performed by the data selection output control means 90, as in the second color, and image formation is started. Similarly, the second addition means 66 adds and updates the value in the third storage means 73. Further, the second average storage unit 77 obtains an average value of the values stored in the first storage unit 53, the second storage unit 63, and the third storage unit 73, which are added and updated as necessary. Remember.

  At the time of image formation of the fourth color, the difference between the value stored in the fourth storage means 83 and the value stored in the second average storage means 77 is calculated from the elapsed time from the image formation start signal to the generation of the main scanning synchronization signal. Obtained by means 60 and judged by second judging means 65. According to the determination result, similarly to the second color and the third color, the timing delay unit 80 controls the image formation start time, the data selection output control unit 90 selects or switches the image data, and starts image formation. .

  In such control, since the main scanning synchronization signal and the image recording start signal in the sub-scanning direction are asynchronous, it is possible to reduce color misregistration occurring between colors.

  FIG. 12 shows the operation of this embodiment. The left side (A) in the figure shows the positional relationship of the image formation start dots according to the control method of this embodiment, and the right side (B) shows the positional relationship of the image formation start dots according to the control method of Japanese Patent Laid-Open No. 11-212009. Note that FIG. 12 shows only one dot at the start of writing in which writing is performed with a beam for starting image formation of each color. The horizontal axis indicates time, the long vertical line on the left indicates the image formation start signal, the vertical short solid line indicates the synchronization signal, and the vertical short dotted line indicates the timing when the beam is selected. The value on the left is the time to the first main scanning synchronization signal for the image formation start signal of each color when the main scanning synchronization signal period T is 100. The numerical value on the right side of the dot is the time until the start of image formation for the image formation start signal of each color. The time from the first Y color to the fourth K color is shown in order from the top.

  First, an example of the control method of this embodiment shown in FIG. When the mark 41 on the intermediate transfer body 40 shown in FIG. 1 is detected by the mark detection means 42, an image formation start signal is generated. In the first color Y, the time t1 from the detected image formation start signal to the next main scanning synchronization signal is 56. Since the time t1 is smaller than 3T / 4, image formation is started at a time delayed by one scanning, that is, at a time 156 synchronized with the second main scanning synchronization signal after the mark detection.

  For the second color M, the time t2 from the image formation start signal to the next main scanning synchronization signal is 22. The time difference between the time t2 and the first color image formation start time 156 is 134. Since this time difference is larger than 3T / 4, one scan is delayed. Next, the time difference between this one-scan delayed time 122 and the first color image formation start time 156 is 34. Since this time difference is larger than T / 4, further beam selection is performed and writing is started from the succeeding beam. That is, the second color image formation start time is 172. Here, the average start time of the first color and the second color is 164 because it is the average time of the image formation start time 156 of the first color and the image formation start time 172 of the second color.

  In the third color C, the time t3 from the image formation start signal to the next main scanning synchronization signal is 64. The time difference between the time t3 and the average start time 164 of the first color and the second color is 100. Since this time difference is larger than 3T / 4, one scan is delayed. Next, the time difference between the time 164 delayed by one scan and the average start time 164 of the first color and the second color is zero. Since this time difference is smaller than T / 4, image formation is started at time 164 delayed by one scan. Here, the average start time of the maximum value and the minimum value of the image formation start time from the first color to the third color already formed is calculated. Since the maximum value is 172 for the second color and the minimum value is 156 for the first color, the average start time is 164.

  In the fourth color K, the time t4 from the image formation start signal to the next main scanning synchronization signal is 78. The time difference between the time t4 and the average start time 164 of the maximum value and the minimum value of the image formation start time from the first color to the third color is 86. Since this time difference is larger than 3T / 4, one scan is delayed. Next, the time difference between the time 178 delayed by one scan and the maximum value of the image formation start time from the first color to the third color and the average start time 164 of the minimum value is 14. Since this time difference is smaller than T / 4, image formation is started at time 178 delayed by one scan.

  Accordingly, the amount of color misregistration is the time 156 for the first color Y when image formation is started at the earliest timing, and the time 178 for the fourth color K when image formation is started at the latest timing. The time difference 22 is

  FIG. 13 shows a control method of still another embodiment. In addition, the content of the notation of the same figure is the same as what was demonstrated using FIG.

  In FIG. 13, (A) on the left side is a control method according to another embodiment, and (B) on the right side is a control method for minimizing the amount of color misregistration after the third color obtained by changing the control method in FIG. 12. Shows the positional relationship of the image formation start dots.

  When the mark 41 on the intermediate transfer body 40 is detected by the mark detection means 42, an image formation start signal is generated. For the first color Y, the time t1 from the detected image formation start signal to the next main scanning synchronization signal is 74. Since the time t1 is smaller than 3T / 4, image formation is started at a time delayed by one scan, that is, at a time 174 synchronized with the second main scanning synchronization signal after the mark detection.

  For the second color M, the time t2 from the image formation start signal to the next main scanning synchronization signal is 86. The time difference between the time t2 and the first color image formation start time 174 is 88. Since this time difference is larger than 3T / 4, one scan is delayed. Next, the time difference between the one-scan delayed time 186 and the first color image formation start time 174 is 12. Since this time difference is smaller than T / 4, image formation is started at a time 186 delayed by one scan. Here, the average start time of the first color and the second color is 180 because it is the average start time of the first color image formation start time 174 and the second color image formation start time 186.

  In the third color C, the time t3 from the image formation start signal to the next main scanning synchronization signal is 54. The time difference between this time t3 and the average start time 180 of the first color and the second color is 126. Since this time difference is larger than 3T / 4, one scan is delayed. Next, the time difference between the time 154 delayed by one scan and the average start time 180 of the first color and the second color is 26. Since this time difference is larger than T / 4, further beam selection is performed and image formation is started from the succeeding beam. That is, the image formation start time for the third color is 204. At this time, the amount of color misregistration from the first color to the third color is 30.

  The image formation start time 204 for the third color is out of the amplitude of the image formation start time 174 for the first color and the image formation start time 186 for the second color that have already been formed. Consider a case where image formation is started at a timing advanced by T / 2 periods, that is, by beam selection. At this time, a case is considered where beam selection is not performed and image formation is started at the timing of the second main scanning synchronization signal from the image formation start signal, that is, at time 154. At this time, the amount of color misregistration from the first color to the third color is 32.

  Accordingly, the amount of color misregistration is smaller when one scan is delayed from the image formation start signal and the beam selection is performed and image formation is started from the succeeding beam. Therefore, the third color forms an image at this timing. The image formation start time is 204. Here, the average start time of the maximum value and the minimum value of the image formation start time from the first color to the third color already formed is calculated. Since the maximum value is 204 for the third color and the minimum value is 174 for the first color, the average start time is 189.

  In the fourth color K, the time t4 from the image formation start signal to the next main scanning synchronization signal is 10. The time difference between the time t4 and the average start time 189 of the maximum and minimum image formation start times from the first color to the third color is 179. Since this time difference is larger than 3T / 4, one scan is delayed. Next, the time difference between the time 110 delayed by one scan and the maximum value of the image formation start time from the first color to the third color and the average start time 189 of the minimum value is 79. Since this time difference is larger than T / 4, further beam selection is performed and writing is started from the succeeding beam. That is, the image formation start time for the fourth color is 160. At this time, the amount of color shift from the first color to the fourth color is 44.

  The image formation start time 160 for the fourth color is out of the amplitude of the maximum value 204 (third color) and the minimum value 174 (first color) of the image formation start time that has already been formed. Consider a case where image formation is started at a timing when the start time 160 is delayed by T / 2 periods, that is, by beam selection. At this time, the beam selection is changed so as not to be performed, and the timing of the third main scanning synchronization signal from the image formation start signal delayed by one scan, that is, the time when image formation is started at time 210 is considered. At this time, the amount of color misregistration from the first color to the fourth color is 36.

  Accordingly, when the image formation is delayed by two scans from the image formation start signal, the color misregistration amount becomes smaller. Therefore, the fourth color starts image formation at this timing, and the image formation start time is 210. To do.

  FIG. 14 shows another embodiment of the image forming apparatus, in which two sets of image forming units are arranged at regular intervals along the same moving surface of the intermediate transfer body 40 in the apparatus of the above-described embodiment. Yes.

  The image forming apparatus 1 shown in FIG. 14 uses drum-like photoreceptors 14 and 14 ′ as image carriers, and charging means 15 and 15 ′ and writing means 16 and 16 ′ are provided around the photoreceptors 14 and 14 ′. The first and second image forming units 20 and 20 ′ are configured by arranging image forming means such as developing means 13 and 13 ′ and cleaning means, and such image forming units 20 and 20 ′ are intermediately transferred. It arrange | positions along the same movement surface of the body 2 at fixed intervals. The developing means 13 includes an A color developing device 12 and a C color developing device 11. The developing device 11 and the developing device 12 can be switched and driven alternatively by a predetermined switching means.

  If attention is paid to one image forming unit, the image forming process is in accordance with a general electrostatic recording system, and writing means 16 is formed on the photoconductors 14 and 14 'uniformly charged by a charger in the dark. , 16 ′, an electrostatic latent image of a certain color is written, and the electrostatic latent image is visualized by the developing means 13, 13 ′ and transferred to the intermediate transfer body 2.

  While the same image forming area of the intermediate transfer body 2 sequentially passes through the two image forming units 20 and 20 ′, each image forming unit 20 and 20 ′ transfers a toner image one color at a time. While the two-color superimposed image area on the transfer belt 2 passes through the two image forming units 20 and 20 'again in sequence, the toner images of different colors from the image forming units 20 and 20' are used. When the same image forming area passes through each of the image forming units 20 and 20 ′ twice, the full color toner image is superimposed and transferred. If this full-color toner image is transferred to a recording medium, a full-color image can be obtained on the recording medium. The toner image on the recording medium can be fixed by a fixing means (not shown) to obtain a full color image on the recording medium. After the transfer of the color image, the intermediate transfer member 2 is subjected to removal of residual toner by a cleaning device (not shown).

  By detecting the mark M1 or the mark M2 provided on the intermediate transfer body 2 by the mark detection means 5, generating an image formation start signal, and applying the image formation control method of the present invention, there is little color misregistration. A high-quality full-color image can be formed.

It is sectional drawing which shows the internal structure which concerns on one Embodiment of this invention. It is a top view which shows the scanning means which concerns on one Embodiment of this invention. It is a timing chart concerning one embodiment of the present invention. It is a block diagram which shows the structure which concerns on one Embodiment of this invention. It is a block diagram which shows the structure which concerns on one Embodiment of this invention. It is a flowchart concerning one embodiment of the present invention. It is a flowchart concerning one embodiment of the present invention. It is explanatory drawing which concerns on one Embodiment of this invention. It is a timing chart concerning one embodiment of the present invention. It is a timing chart concerning one embodiment of the present invention. It is a block diagram concerning one embodiment of the present invention. It is a timing chart concerning one embodiment of the present invention. It is a timing chart concerning one embodiment of the present invention. It is a side view concerning one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 22 Rotating polygon mirror 32 Image carrier 33 Charging means 34 Writing means 35 Developer 40 Intermediate transfer body 41 Mark 42 Mark detection means 43 Transfer means

Claims (15)

To-be-detected means provided as an image formation start reference for each color provided on the intermediate transfer member;
Detecting means for detecting the detected means at a predetermined position;
After the detection means detects the image forming start signal in the sub-scanning direction generated when the detected means is detected, the image carrying member moving in the sub-scanning direction is deflected by the deflecting reflecting surface of the rotary polygon mirror. An electrostatic latent image formed on the image carrier by starting image formation by performing scanning according to image recording information in the main scanning direction based on a main scanning synchronization signal detected by receiving a laser beam received by a light receiving element A toner image is generated by the developing means, and the process of transferring the toner image onto the intermediate transfer member is repeated a plurality of times for each color, and the toner images are sequentially superimposed for each color to form a color image,
After detecting the image formation start signal in the sub-scanning direction, when the detection time of the main scanning synchronization signal is delayed with respect to the detection time detected by the light receiving element obtained in advance, the detection time of the main scanning synchronization signal , And image formation is started based on the corrected detection time. Main scanning synchronization signal detecting means for detecting a main scanning synchronization signal by receiving a laser beam deflected by the deflection reflection surface of the rotary polygon mirror;
Main scanning synchronization signal number counting means for measuring the number of detected main scanning synchronization signals;
Main scanning synchronization signal detection time acquisition means for acquiring the detection time of the main scanning synchronization signal;
Storage means for storing the main scanning synchronization signal detection time;
A calculation means for obtaining a time interval of the main scanning synchronization signal from the detection time of the storage means;
Determination means for determining presence or absence of a delay in the main scanning synchronization signal detection time;
Correction means for correcting the main scanning synchronization signal detection time based on the result of the determination means;
The time interval count value of the main scanning synchronization signal obtained in advance before the start of image formation is compared with the time interval count value of the main scanning synchronization signal obtained from the main scanning synchronization signal detection time detected at the time of image formation. When it is determined that there is a delay in the detection time of the main scanning synchronization signal, the image forming apparatus starts image formation based on the detection time of the main scanning synchronization signal whose delay is corrected by the correction means.   Acquiring the detection time of the main scanning synchronization signal detected by receiving the laser beam deflected by the deflecting and reflecting surface of the rotating polygon mirror with the light receiving element, and corresponding to each surface of the rotating polygon mirror from the detection time The main scanning synchronization signal time interval is counted for each sequence before starting image formation, and the main scanning synchronization signal is obtained from the time interval count value of the main scanning synchronization signal and the main scanning synchronization signal detection time detected during image formation. When the time interval count value of the synchronization signal is compared and it is determined that there is a delay in the detection time of the main scanning synchronization signal, image formation is started based on the detection time of the main scanning synchronization signal whose delay is corrected by the correction means The image forming apparatus according to claim 2, wherein:   Acquiring the detection time of the main scanning synchronization signal detected by receiving the laser beam deflected by the deflecting and reflecting surface of the rotating polygon mirror with the light receiving element, and corresponding to each surface of the rotating polygon mirror from the detection time The time interval of the main scanning synchronization signal is counted in advance, the count value is stored as a lookup table, and the stored time interval count value of the main scanning synchronization signal and the main scanning synchronization signal detection detected at the time of image formation The time interval count value of the main scanning synchronization signal obtained from the time is compared, and when it is determined that there is a delay in the detection time of the main scanning synchronization signal, the detection time of the main scanning synchronization signal in which the delay is corrected by the correction means The image forming apparatus according to claim 2, wherein image formation is started based on   Acquiring the detection time of the main scanning synchronization signal detected by receiving the laser beam deflected by the deflecting and reflecting surface of the rotating polygon mirror with the light receiving element, and corresponding to each surface of the rotating polygon mirror from the detection time The time interval of the main scanning synchronization signal is counted, and when the difference between the maximum value and the minimum value of the time interval is smaller than an arbitrary difference value set in advance, the average value of the count values is calculated as the main scanning synchronization signal. 5. The image forming apparatus according to claim 3, wherein the image forming apparatus is controlled as a count value of a time interval. The storage means for storing the main scanning synchronization signal detection time is capable of storing and holding at least (the number of surfaces + 1) of the rotary polygon mirror as the main scanning synchronization signal detection time detected at the time of image formation,
Means for determining the order of the stored time series, and means for replacing the most recently detected time with the most recently stored detection time and storing it,
6. The image forming apparatus according to claim 1, wherein a time interval of a main scanning synchronization signal corresponding to each surface of the rotary polygon mirror is counted from the stored detection time. Scanning-type writing means having a plurality of beams arranged in the sub-scanning direction;
The write start timing is delayed or the beam is selected so that the difference between the image formation start time for the second color image formation start signal and the image formation start time for the first color image formation start signal is minimized. In the image formation of the nth color (n ≧ 3) after the third color is started, the image of each color from the first color to the (n−1) th color already formed is started. An average start time tm of the maximum and minimum image formation start times of each color with respect to the formation start signal is obtained, and a time difference between the image formation start time with respect to the image formation start signal of the nth color and the average start time tm is minimum. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is started by delaying writing start timing or selecting a beam.   In the image formation for the third and subsequent colors, the image formation start time obtained by delaying the write timing or beam selection control so as to minimize the time difference from the average start time tm to the first color from the first color already formed. (N-1) When deviation from the image formation start time of each color with respect to the image formation start signal of each color up to the color, the deviation from the maximum or minimum value of the amplitude and the write timing delay or beam selection control Assuming an image formation start time for advancing or delaying a predetermined amount of beam in the sub-scanning direction from the image formation start time, comparing the deviation from the maximum or minimum value of the amplitude at that time, an image with a small deviation 8. The image forming apparatus according to claim 7, wherein image formation is started at the formation start time. It has a plurality of image forming means arranged facing the moving surface of the intermediate transfer member,
The image forming means alternatively comprises one image carrier, one writing means, at least two developing means for developing an electrostatic latent image formed on the image carrier by the writing means, and the developing means. The image forming apparatus according to claim 1, further comprising a switching unit that selectively drives the image forming apparatus. An image forming start signal in the sub-scanning direction generated by detecting an image forming start reference for each color provided on the intermediate transfer member is detected, and the rotating polygon mirror is applied to the image carrier that moves in the sub-scanning direction. The main scanning synchronization signal is detected by receiving the laser beam deflected by the deflecting and reflecting surface, and the image carrier is scanned based on the main scanning synchronization signal to form an image. Starting, generating a toner image from the electrostatic latent image formed on the image carrier, and transferring the toner image to the intermediate transfer member a plurality of times for each color, and sequentially superimposing the toner images for each color. In this method, a color image is formed.
After detecting the image formation start signal in the sub-scanning direction, when the detection time of the main scanning synchronization signal is delayed with respect to the detection time detected by the light receiving element obtained in advance, the detection time of the main scanning synchronization signal And forming an image based on the corrected detection time.   Acquiring the detection time of the main scanning synchronization signal detected by receiving the laser beam deflected by the deflecting and reflecting surface of the rotating polygon mirror with the light receiving element, and corresponding to each surface of the rotating polygon mirror from the detection time The main scanning synchronization signal time interval is counted for each sequence before starting image formation, and the main scanning synchronization signal is obtained from the time interval count value of the main scanning synchronization signal and the main scanning synchronization signal detection time detected during image formation. When the time interval count value of the synchronization signal is compared and it is determined that there is a delay in the detection time of the main scanning synchronization signal, image formation is started based on the detection time of the main scanning synchronization signal whose delay is corrected by the correction means The image forming method according to claim 10.   Acquisition of the detection time of the main scanning synchronization signal detected by receiving the laser beam deflected by the deflecting and reflecting surface of the rotary polygon mirror with the light receiving element, and the main time corresponding to each surface of the rotary polygon mirror from the detection time The time interval of the scanning synchronization signal is counted in advance, the count value is stored as a lookup table, and the stored time interval count value of the main scanning synchronization signal and the main scanning synchronization signal detection time detected at the time of image formation The time interval count value of the main scanning synchronization signal obtained from the above is compared, and when it is determined that there is a delay in the detection time of the main scanning synchronization signal, the detection time of the main scanning synchronization signal in which the delay is corrected by the correction means The image forming method according to claim 10, wherein the image formation is started based on the image formation.   Acquiring the detection time of the main scanning synchronization signal detected by receiving the laser beam deflected by the deflecting and reflecting surface of the rotating polygon mirror with the light receiving element, and corresponding to each surface of the rotating polygon mirror from the detection time The time interval of the main scanning synchronization signal is counted, and when the difference between the maximum value and the minimum value of the time interval is smaller than an arbitrary difference value set in advance, the average value of the count values is calculated as the main scanning synchronization signal. The image forming method according to claim 11, wherein the image forming method is controlled as a count value of a time interval. Scanning-type writing means having a plurality of beams arranged in the sub-scanning direction;
The write start timing is delayed or the beam is selected so that the difference between the image formation start time for the second color image formation start signal and the image formation start time for the first color image formation start signal is minimized. In the image formation of the nth color (n ≧ 3) after the third color is started, the image of each color from the first color to the (n−1) th color already formed is started. An average start time tm of the maximum and minimum image formation start times of each color with respect to the formation start signal is obtained, and a time difference between the image formation start time with respect to the image formation start signal of the nth color and the average start time tm is minimum. 11. The image forming method according to claim 10, wherein the image forming method is started by delaying the writing start timing or selecting a beam.   In the image formation for the third and subsequent colors, the first color for which the image formation start time obtained by the delay of the write timing or the beam selection control is already formed so as to minimize the time difference from the average start time tm. To the (n-1) th color image formation start signal, when the deviation from the amplitude of the image formation start time of each color with respect to the image formation start signal of each color, the deviation from the maximum or minimum value of the amplitude and the delay of the write timing or the beam selection Assuming an image formation start time for advancing or delaying a predetermined amount of beam in the sub-scanning direction from the image formation start time obtained by control, the deviation from the maximum value or minimum value of the amplitude at that time is compared. 15. The image forming method according to claim 14, wherein image formation is started at a smaller image formation start time.

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