JP4757501B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming equipment.

  In an image forming apparatus using a light beam scanning device, a light beam is modulated by image data, a deflecting means (hereinafter referred to as a polygon mirror) is rotated to deflect the angular velocity in the main scanning direction, and an equiangular velocity deflection is performed by an fθ lens. An image is formed by correcting the velocity deflection and scanning on an image carrier (hereinafter referred to as a photoconductor).

  However, the conventional apparatus has a problem that the image magnification varies from machine to machine due to variations in characteristics of the light beam scanning apparatus (lens). In particular, when a plastic lens is used, the shape and refractive index of the plastic lens change due to a change in environmental temperature, a change in in-machine temperature, and the like. For this reason, the scanning position on the image surface of the photosensitive member changes, a magnification error occurs in the main scanning direction, and a high-quality image may not be obtained.

  Further, in an apparatus that forms a plurality of color images using a plurality of laser beams and lenses, there is a problem that a color shift occurs due to each magnification error, and a high-quality image cannot be obtained. Therefore, it is necessary to match the image magnification of each color as much as possible.

  In order to solve the above-described problems, a means for correcting an image magnification error in the main scanning direction caused by various factors such as a change in environmental temperature and a change in machine temperature is disclosed in the image forming apparatus (for example, , See “Patent Document 1”).

JP 2000-112205 A

  In the image forming apparatus described in Patent Document 1, a magnification adjustment mark is formed for a reference color, detected, and the magnification is corrected. Then, after correcting the magnification, a misregistration detection mark is formed and detected to relatively match various misalignments.

  However, in the technique described in Patent Document 1, it is necessary to form a magnification correction mark on the conveyor belt when correcting the magnification of the reference color. Naturally, extra time is required for image writing, development, transfer, and detection. Further, the toner is consumed for the amount of pattern formation. Considering the total productivity, it is desirable to shorten the time other than actual printing (positional offset correction, process control, etc.) as much as possible. In addition, it is natural to reduce the amount of toner consumed other than actual printing.

  The present invention has been made in view of the above, and is capable of accurately correcting an image magnification error and a relative image displacement in a multicolor image while avoiding a decrease in productivity and an increase in toner consumption. It is an object of the present invention to provide an image forming apparatus that can be used.

In order to solve the above-described problems and achieve the object, the invention according to claim 1 forms a multicolor image by superimposing a single color image of the second color on a single color image of the first color. an image forming apparatus for a first color image forming means for forming a monochromatic image of the first color, the second color image forming means for forming a monochromatic image of the second color, the first color a first color image magnification correction means for correcting the image magnification in the image forming unit, a second color image magnification correction means for correcting the image magnification in the second color image forming unit, before Symbol first color image forming unit On the basis of the first color correction pattern for correcting misregistration and the second color correction pattern for correcting misregistration formed by the second color image forming means . A monochrome image of the first color formed by the one-color image forming means; And an image position shift correction means for correcting the positional deviation between the second single-color image whose serial second color image forming unit forms the image position shift correction means, the first color image magnification correction The first color correction pattern formed by the first color image forming unit after the image magnification correction is performed by the unit, and the image magnification correction performed by the second color image magnification correction unit. After correcting the positional deviation based on the second color correction pattern formed by the two-color image forming means, and after further correcting the image magnification by the first color image magnification correcting means, The first color correction pattern formed by the first color image forming unit and the second color formed by the second color image forming unit without further image magnification correction performed by the second color image magnification correcting unit. Based on correction pattern Te, further characterized in that the correction of the positional deviation.

The invention according to claim 2 is an image forming apparatus according to claim 1, wherein the first color image forming unit and the second-color image forming means, respectively, on the basis of images data, lighting And a first color image magnification correction unit and a second color image , the light source output from the light source, and a deflecting unit that deflects a light beam output from the light source in a main scanning direction by a plurality of polarization planes. The magnification correction unit measures the time difference between the light beam detection unit that detects the light beam deflected by the deflection unit at two locations on the main scanning line and the time at which the light beam detection unit detects the light beam at two locations. A time difference measuring means; and a magnification correction means for correcting an image magnification in the direction of the main scanning line based on a time difference between the two detected light beams measured by the time difference measuring means, Serial image positional deviation correcting means, the first the first color image forming unit after correcting the image magnification in the direction of the main scan lines is performed by the magnification correcting means of the first color image magnification correction means is formed The second color image forming means formed after the one color correction pattern and the magnification correction means of the second color image magnification correction means have corrected the image magnification in the direction of the main scanning line. After correcting the positional deviation based on the color correction pattern, after further correcting the image magnification in the direction of the main scanning line by the magnification correction unit of the first color image magnification correction unit. The image magnification in the direction of the main scanning line is further corrected by the first color correction pattern formed by the first color image forming unit and the magnification correction unit of the second color image magnification correction unit. The second color image forming means on the basis of the second color correction pattern formed, characterized by further corrects the positional deviation.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect , the magnification correction unit is a clock for controlling lighting of the light emitting source based on the time difference measured by the time difference measuring unit. The image magnification is corrected by changing the period of 1 pixel by pixel.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect , the magnification correction unit changes the cycle of the lighting control clock in units of one pixel at a plurality of positions. The image magnification is corrected.

The invention according to claim 5 is the image forming apparatus according to claim 4 , wherein the image magnification is changed by changing the cycle of the lighting control clock in units of one pixel at a plurality of equally spaced positions. It is characterized by correcting.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect , the magnification correction unit sets the cycle of the lighting control clock in units of one pixel at a position not adjacent in the sub-scanning direction. The image magnification is corrected by changing the image magnification.

The invention according to claim 7 is the image forming apparatus according to claim 1, wherein the first color is black.

According to the first aspect of the present invention, the image misregistration correction unit includes the first color correction pattern formed by the first color image forming unit after the image magnification correction is performed by the first color image magnification correction unit. The first color is corrected after the misregistration is corrected based on the second color correction pattern formed by the second color image forming unit after the image magnification is corrected by the second color image magnification correcting unit. The first color correction pattern formed by the first color image forming unit after the image magnification correction unit performs further image magnification correction, and the second color image magnification correction unit does not further correct the image magnification. Since the misregistration is further corrected based on the second color correction pattern formed by the two-color image forming means, it is not necessary to generate an image pattern again when correcting the image magnification. Therefore, it is possible to accurately correct an error in image magnification and a relative image position shift in a multicolor image while avoiding a decrease in productivity and an increase in toner consumption.

Further, according to the invention according to claim 2, the light emitting source of the first color image forming unit and the second color image forming unit, based on the image picture data is controlled lighting, deflecting means, an output from the light source The light beam to be deflected in the main scanning direction by a plurality of polarization planes, and the light beam detecting means of the first color image magnification correcting means and the second color image magnification correcting means performs main scanning on the light beam deflected by the deflecting means. The time difference measuring means measures the time difference when the light beam detecting means detects the light beam at the two places, and the magnification correcting means detects the two detected light beams measured by the time difference measuring means. based on the time difference, the image magnification correction in the direction of the main scanning line, the image position shift correction means, the image magnification correction in the direction of the main scanning line by the magnification correcting means of the first color image magnification correcting means The second color after the first color correction pattern formed by the first color image forming unit and the magnification correction unit of the second color image magnification correction unit correct the image magnification in the main scanning line direction. After correcting the misregistration based on the second color correction pattern formed by the image forming unit, the magnification correction unit of the first color image magnification correction unit further corrects the image magnification in the main scanning line direction. Then, the first color correction pattern formed by the first color image forming means and the magnification correction means of the second color image magnification correction means are not further corrected for the image magnification in the main scanning line direction. Since the misregistration is further corrected based on the second color correction pattern formed by the color image forming unit, it is not necessary to generate an image pattern again when correcting the image magnification. Therefore, it is possible to accurately correct an error in image magnification and a relative image position shift in a multicolor image while avoiding a decrease in productivity and an increase in toner consumption.

According to the invention of claim 3 , the magnification correction means corrects the image magnification by changing the cycle of the lighting control lighting clock of the light source in units of one pixel based on the time difference measured by the time difference measurement means. Therefore, there is an effect that the image magnification can be corrected in pixel units.

According to the invention of claim 4 , the magnification correction means corrects the image magnification by changing the cycle of the lighting control clock in units of one pixel at a plurality of positions. As a result, it is possible to avoid the occurrence of image expansion and reduction.

According to the invention of claim 5 , the magnification correction means corrects the image magnification by changing the cycle of the lighting control clock in units of one pixel at a plurality of equally spaced positions. As a result, it is possible to avoid the occurrence of image expansion and contraction.

According to the invention of claim 6 , the magnification correction means corrects the image magnification by changing the cycle of the lighting control clock in units of one pixel at a position that is not adjacent in the sub-scanning direction. It is possible to avoid the occurrence of the expansion and contraction of the image due to the change.

According to the invention of claim 7 , since the first color is black, there is an effect that the image magnification can be corrected more accurately.

With reference to the accompanying drawings, illustrating the best embodiment of an image forming equipment according to the present invention in detail.

(Embodiment 1)
FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus 1 according to the first embodiment. The image forming apparatus 1 according to the present embodiment includes four sets of light beam operation devices 10a to 10d and four sets of image forming units 20a to 20d.

  Each set of the light beam operation devices 10a to 10d and the image forming units 20a to 20d forms images of four colors of yellow (Y), magenta (M), cyan (C), and black (BK), respectively. These images are superimposed to form a color image.

  Specifically, the recording paper 40 is conveyed by the transfer belt 30. First, the first light beam operating device 10 a and the first image forming unit 20 a form a first color image on the recording paper 40. The recording paper 40 is further conveyed, and the second light beam operating device 10b and the second image forming unit 20b form a second color image on the recording paper 40. Similarly, an image of the third color is formed by the third light beam operating device 10c and the third image forming unit 20c, and further, an image of the fourth color is formed by the fourth light beam operating device 10d and the fourth image forming unit 20d. Is done. As a result, a color image in which images of four colors are superimposed on the recording paper 40 is formed. Then, the recording paper 40 is conveyed to a fixing device (not shown). Then, the image on the recording paper 40 is fixed by the fixing device.

  Each of the image forming units 20 a to 20 d includes a photoreceptor 21, a developing unit 22, a charger 23, and a transfer device 24. The developing unit 22, the charger 23 and the transfer device 24 are provided around the photoconductor 21. Further, a cleaning unit and a static eliminator (not shown) are provided around the photosensitive member 21. With these configurations, charging, exposure, development, and transfer, which are normal electrophotographic processes, are performed, and an image is formed on the recording paper 40.

  Each of the light beam operating devices 10a to 10d includes a polygon mirror 11, an fθ lens 12, and a barrel toroidal lens (BTL) 13.

  The light beam of the LD that is turned on based on the image signal is converted into a parallel beam by a collimating lens (not shown). Then, the light passes through a cylinder lens (not shown) and is deflected by a polygon mirror 11 rotated by a polygon motor. Further, the light passes through the fθ lens 12, passes through the BTL 13, is reflected by a mirror (not shown), and scans on the photosensitive member 21. The BTL 13 performs focusing in the sub-scanning direction. Specifically, the light condensing function and position correction in the sub-scanning direction (surface tilt, etc.) are performed.

  Further, a first pattern sensor 51 and a second pattern sensor 52 are provided in the vicinity of the conveyance motor 32. Both the first pattern sensor 51 and the second pattern sensor 52 are reflective optical sensors. The first pattern sensor 51 and the second pattern sensor 52 detect an image misalignment correction pattern for correcting an image misalignment. Based on the detection result, it is possible to correct the image position shift between the colors in the main scanning direction and the sub-scanning direction and the image magnification in the main scanning direction.

  FIG. 2 is a diagram showing a functional configuration of the light beam operation device 10a and the image formation control unit 60 that controls the light beam operation device 10a. The light beam operating device 10a further includes an LD unit 14, a first synchronization sensor 151, a second synchronization sensor 152, a first lens 161, a second lens 162, a first mirror 171, and a second mirror 172. have.

  The first synchronization sensor 151 and the second synchronization sensor 152 are provided at both ends of the photosensitive member 21, respectively, and detect a light beam. The light beam that has passed through the fθ lens 12 is reflected by the first mirror 171 and the second mirror 172, and is condensed by the first lens 161 and the second lens 162, respectively. The light beams collected by the first lens 161 and the second lens 162 are incident on the first synchronization sensor 151 and the second synchronization sensor 152, respectively.

  When the light beam passes through the first synchronization sensor 151, a start side synchronization detection signal XDETP is output from the first synchronization sensor 151. Similarly, when the light beam passes through the second synchronization sensor 152, the end-side synchronization detection signal XEDETP is output from the second synchronization sensor 152. The start side synchronization detection signal XDETP and the end side synchronization detection signal XEDETP are input to the image formation control unit 60.

  The image formation control unit 60 includes a magnification correction unit 602, a printer control unit 604, a pixel clock generation unit 606, a sync detection lighting control unit 608, an LD control unit 610, a writing start position control unit 612, A polygon motor control unit 614.

  The start side synchronization detection signal XDETP and the end side synchronization detection signal XEDETP are input to the magnification correction unit 602. The magnification correction unit 602 measures 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, and calculates a magnification error based on the measurement result. Then, magnification error data indicating a magnification error is created and output to the printer control unit 604. The processing for calculating the magnification error is performed at least for the reference color. In the present embodiment, the reference color is black (BK).

  FIG. 3 is a block diagram illustrating a detailed functional configuration of the magnification correction unit 602. The magnification correction unit 602 includes a time difference counting unit 6020 and a comparison control unit 6024. Further, the time difference count unit 6020 includes a counter 6021 and a latch 6022. The counter 6021 is cleared by the start side synchronization detection signal XDETP. Then, it counts up with the clock VCLK, and the count value is latched at the falling edge of the end-side synchronization detection signal XEDETP.

  The comparison control unit 6024 compares the count value (time difference: T) with a preset reference time difference T0. Then, a magnification error is calculated based on the comparison result. Then, magnification error data is sent to the printer control unit 604.

  The description returns to FIG. 2 again. The positional deviation correction pattern signals detected by the first pattern sensor 51 and the second pattern sensor 52 are sent to the printer control unit 604. The printer control unit 604 calculates a shift amount (time) of each color with respect to the reference color based on the positional shift correction pattern signal and the magnification error data input from the magnification correction unit 602. Then, correction data indicating the amount of deviation is output. More specifically, the correction data is a set value of the frequency of the reference clock signal FREF and a frequency division ratio (N).

  Here, the correction data includes main scanning direction correction data and sub-scanning direction correction data. The main scanning direction correction data is data for changing the magnification in the main scanning direction. The sub-scanning direction correction data is data for changing the magnification in the sub-scanning direction.

  The start side synchronization detection signal XDETP is also input to the pixel clock generation unit 606. The pixel clock generation unit 606 generates a pixel clock PCLK synchronized with the start side synchronization detection signal XDETP based on the correction data received from the printer control unit 604, and sends the pixel clock PCLK to the synchronization detection lighting control unit 608 and the LD control unit 610. . Thus, the frequency of the pixel clock PCLK can be changed based on the correction data. Thereby, the image magnification in the main scanning direction can be corrected.

  FIG. 4 is a block diagram illustrating a detailed functional configuration of the pixel clock generation unit 606. The pixel clock generation unit 606 includes a reference clock generation unit 6061, a VCO (Voltage Controlled Oscillator) clock generation unit 6062, and a phase synchronization clock generation unit 6067.

  FIG. 5 is a block diagram showing a detailed functional configuration of the VCO clock generator 6062. Specifically, the VCO clock generation unit 6062 is a PLL circuit (Phase Locked Loop). The VCO clock generator 6062 includes a phase comparator 6063, an LFP (low-pass filter) 6064, a VCO 6065, and a 1 / N frequency divider 6066.

  A reference clock generation unit 6061 receives correction data from the printer control unit 604 and outputs a reference clock signal FREF based on the correction data. The reference clock signal FREF is input to the phase comparator 6063 together with a signal obtained by dividing VCLK by N with a 1 / N divider. The phase comparator 6063 compares the phases of the falling edges of both signals and outputs an error component at a constant current. Further, unnecessary high frequency components and noise are removed by the LPF 6064 and sent to the VCO 6065. The VCO 6065 outputs an oscillation frequency that depends on the output of the LPF 6064.

  Since it is configured as described above, the frequency of VCLK can be changed by changing the frequency of the reference clock signal FREF and the frequency division ratio (N).

The phase-synchronized clock generation unit 6067 generates the pixel clock PCLK from VCLK set to a frequency that is eight times the pixel clock frequency. Further, a pixel clock PCLK synchronized with the synchronization detection signal XDETP is generated. If the frequency before correction is fo, the corrected frequency f ′ is calculated by (Equation 1).
f ′ = fo × T0 / T (Formula 1)

  The description returns to FIG. 2 again. The synchronization detection lighting control unit 608 first turns on the LD forced lighting signal BD to forcibly light the LD control unit 610 in order to detect the start side synchronization detection signal XDETP. Further, after detecting the start side synchronization detection signal XDETP, the LD control unit at a timing at which the start side synchronization detection signal XDETP can be reliably detected by the start side synchronization detection signal XDETP and the pixel clock PCLK to the extent that no flare light is generated. An LD compulsory lighting signal BD for lighting 610 is generated and sent to the LD control unit 610.

  The same applies to the case where the end-side synchronization detection signal XEDETP is detected. That is, the start-side synchronization detection signal XDETP and the pixel clock PCLK generate an LD forced lighting signal BD that turns on the LD control unit 610 at a timing at which the end-side synchronization detection signal XEDETP can be reliably detected without causing flare light. The data is sent to the LD control unit 610.

  FIG. 6 is a block diagram showing a functional configuration of the preceding stage of the image formation control unit 60. A line memory 61 is provided in the preceding stage. The line memory 61 captures image data from an external device such as a frame memory or a scanner at the timing of the main scanning gate signal XLGATE. Then, an image signal is output in synchronization with PCLK only during a period in which the main scanning gate signal XLGATE is 'L'. The output image signal is sent to the LD control unit 610, and the LD is turned on at that timing.

  The description returns to FIG. 2 again. The LD control unit 610 controls the lighting of the LD unit 14 according to the image signal synchronized with the synchronous detection forced lighting signal BD and the pixel clock PCLK. Then, a laser beam is emitted from the LD unit 14 under the control of the LD control unit 610, deflected by the polygon mirror 11, passes through the fθ lens 12, and scans on the photoconductor 21. The polygon motor control unit 614 controls the rotation of a polygon motor (not shown) at a specified number of rotations based on a control signal from the printer control unit 604.

  The writing start position control unit 612 receives correction data from the printer control unit 604. Based on the correction data, the timing of the main scanning gate signal XLGATE and the sub-scanning gate signal XFGATE is changed. Thereby, the writing start position of each color in the main scanning direction and the sub-scanning direction can be corrected.

  FIG. 7 is a block diagram illustrating a detailed functional configuration of the writing start position control unit 612. The writing start position control unit 612 includes a main scanning line synchronization signal generation unit 6120, a main scanning gate signal generation unit 6122, and a sub scanning gate signal generation unit 6126. Further, the main scanning gate signal generation unit 6122 includes a main scanning counter 6123, a main scanning comparator 6124, and a main scanning gate signal generation unit 6125. The sub-scanning gate signal generation unit 6126 includes a sub-scanning counter 6127, a sub-scanning comparator 6128, and a sub-scanning gate signal generation unit 6129.

  The main scanning line synchronization signal generator 6120 generates a start signal start signal XLSYNC for operating the main scanning counter 6123 and the sub scanning counter 6127. The main scanning gate signal generation unit 6122 generates a main scanning gate signal XLGATE that determines the image signal capture timing (image writing timing in the main scanning direction).

  Specifically, the main scanning counter 6123 operates with the start signal XLSYNC and the pixel clock PCLK. The main scanning comparator 6124 compares the counter value of the main scanning counter 6123 with the main scanning direction correction data from the printer control unit 604. The main scanning gate signal generation unit 6125 generates a main scanning gate signal XLGATE based on the comparison result of the main scanning comparator 6124.

  The sub-scanning gate signal generator 6126 generates a sub-scanning gate signal XFGATE that determines the image signal capture timing (image writing timing in the sub-scanning direction).

  Specifically, the sub-scanning counter 6127 operates with the start signal XLSYNC and the pixel clock PCLK from the printer control unit 604. The sub scanning comparator 6128 compares the counter value of the sub scanning counter 6127 with the sub scanning direction correction data from the printer control unit 604. The sub scanning gate signal generation unit 6129 generates the sub scanning gate signal XFGATE based on the comparison result of the sub scanning comparator 6128.

  FIG. 8 is a diagram illustrating a timing chart of the writing start position control unit 612. The counter is reset by the start signal XLSYNC and is counted up by the pixel clock PCLK. When the counter value reaches the correction data set by the printer control unit 604 (in this case, “X”), the comparison result is output from the main scanning comparator 6124, and the main scanning gate signal generation unit 6125 outputs the main scanning gate signal. XLGATE becomes 'L' (valid). The main scanning gate signal XLGATE is a signal that becomes 'L' by the image width in the main scanning direction. The same applies to the sub-scanning direction. In the sub-scanning direction, the count is incremented by the start signal XLSYNC instead of the pixel clock PCLK.

  Accordingly, the timing of the main scanning gate signal XLGATE and the sub-scanning gate signal XFGATE is changed according to the correction data value set in the comparator by the printer control unit 604. The timing of the image signal is also changed. Therefore, the image writing start position in the main scanning direction and the sub scanning direction can be changed. That is, it is possible to correct the image position shift of each color.

  In the main scanning direction, the writing start position control unit 612 can correct the writing position in units of one cycle of the pixel clock PCLK, that is, in units of one dot. In the sub-scanning direction, the writing position can be corrected in units of one cycle of the start signal XLSYNC, that is, in units of one line.

  FIG. 9 is a diagram showing an image misregistration correction pattern formed on the transfer belt 30. An image misregistration correction pattern is formed on the transfer belt 30 at a preset timing for each color. As shown in FIG. 9, the image misregistration pattern is a horizontal line and diagonal line image of each color.

  As the transfer belt 30 moves in the direction of the arrow, the first pattern sensor 51 and the second pattern sensor 52 detect image misregistration correction patterns, that is, horizontal lines and diagonal lines of each color. The detection result is sent to the printer control unit 604, and the printer control unit 604 calculates the shift amount (time) of each color with respect to BK.

  The detection timing of the oblique line image is changed by shifting the image position in the main scanning direction and the image magnification of the image. Also, the horizontal line detection timing changes due to the shift of the image position in the sub-scanning direction.

  Specifically, in the main scanning direction, the time between the timing at which the pattern BK1 is detected and the timing at which the pattern BK2 is detected is used as a reference. Then, the time TBKC12 is obtained by comparing with the time from the pattern C1 to the pattern C2.

  Further, the time from pattern BK3 to pattern BK4 is used as a reference. Then, the time TBKC 34 is obtained by comparing with the time from the pattern C 3 to the pattern C 4. The difference 'TBKC34-TBKC12' is a magnification error of the cyan image with respect to the black image. Therefore, the image magnification can be corrected by changing the frequency of the pixel clock by an amount corresponding to the amount. Then, the same pattern is formed using the corrected pixel clock.

  Similarly, TBKC12 and TBKC34 are obtained. '(TBKC34 + TBKC12) / 2' is the main scanning deviation of the black image of the cyan image. Therefore, the image magnification and the image position deviation can be corrected by changing the writing start timing by the period of the writing clock by the amount of the deviation. The same applies to magenta and yellow.

  In the sub-scanning direction, if the ideal time is Tc, the time from pattern BK1 to pattern C1 is TBKC1, and the time from pattern BK3 to pattern C3 is TBKC3, '((TBKC3 + TBKC1) / 2) -Tc' is the cyan image. A sub-scanning shift occurs with respect to the black image. Therefore, by changing the writing start timing in units of one line, the image magnification and the image position deviation can be corrected. The same applies to magenta and yellow.

  In this embodiment, the detection of the magnification error and the detection of the main scanning deviation are performed in different patterns. Instead of this, the magnification error is corrected by obtaining the time change due to the magnification error correction. The main scanning position may be corrected with the same pattern.

  FIG. 10 is a flowchart showing position correction processing in the image forming apparatus 1 according to the present embodiment. First, the polygon motor control unit 614 rotates the polygon mirror 11 at a specified number of rotations, and the LD control unit 610 turns on the LD so that the start-side synchronization detection signal XDETP is output (step S100). Next, the LD control unit 610 turns on the LD so as to also output the end-side synchronization detection signal XEDETP in order to measure the time difference between the two points. Next, the magnification correction unit 602 measures the time difference between the two points (step S102). Furthermore, it is determined whether it is necessary to correct the image magnification based on the measurement result.

  This determination is determined by the magnification correction resolution. If the measured time difference is greater than or equal to a predetermined threshold (step S104, Yes), the LD is temporarily turned off (step S106). In this embodiment, 1/2 of the correction resolution is set as a threshold value.

  Then, a set value of a frequency necessary for correcting the image magnification is calculated, set to the pixel clock generation unit 606, and a pixel clock PCLK is generated (step S108). Then, the LD is turned on again so that the start-side synchronization detection signal XDETP is output (step S110), and the image position correction operation is started (step S112).

  If the error is smaller than 1/2 of the correction resolution (No at Step S104), the image position correction operation is started without performing the correction (Step S112). After completion of the correction operation, the polygon motor is stopped and the LD is also turned off (step S114). Then, by using the generated main scanning gate signal XLGATE, sub-scanning gate signal XFGATE, and pixel clock PCLK for each color, an image in which image position shift and image magnification are corrected is output. With the above processing, magnification correction can be performed without using a pattern chart.

  FIG. 11 is a flowchart showing detailed processing in the image position correction described in FIG. First, an image misregistration correction pattern is formed on the transfer belt 30 (step S200). Next, the first pattern sensor 51 and the second pattern sensor 52 detect an image misregistration correction pattern (step S202). Next, the printer control unit 604 calculates a main scanning deviation amount, a sub-scanning deviation amount, and a main scanning magnification error amount with respect to BK (step S204).

  Next, it is determined whether or not the calculated deviation amount is equal to or greater than a predetermined threshold value. That is, it is determined whether the level is to be corrected. In the present embodiment, the correction resolution is set to one dot unit and one line unit. Accordingly, correction is performed if the deviation amount is ½ dot or more and ½ line or more.

  If the deviation amount is equal to or greater than the threshold value, that is, if it is the level to be corrected (step S206, Yes), correction data is calculated (step S208). Then, the main scanning direction correction data is set in the main scanning gate signal generation unit, the sub scanning direction correction data is set in the sub scanning gate signal generation unit 6126, and the main scanning gate signal XLGATE and the sub scanning gate signal XFGATE are generated ( Step S210).

  In the main scanning magnification error correction, it is determined whether or not the detected magnification error is at a correction level (step S212). This determination is also determined by the magnification correction resolution.

  When correcting the image magnification (step S212, Yes), a set value of a frequency necessary for correcting the image magnification is calculated. Next, the pixel clock generator 606 is set (step S214), and the pixel clock PCLK is generated (step S216).

  In the present embodiment, the magnification correction process is performed only for the reference color that is the reference in the image misalignment correction process performed after the magnification correction process. Thereby, processing time can be shortened. Further, by correcting the magnification of the reference color and then performing the image displacement correction using the reference color as a reference, the image displacement correction can be performed with high accuracy.

  Note that the magnification correction process does not necessarily have to be performed for colors other than the reference color, but as another example, the magnification correction may be performed for colors other than the reference color. As a result, even when there is an upper limit in the magnification correction range (correctable error) in the image displacement correction, the image displacement correction can be accurately performed within this range.

  As described above, the present invention has been described using the embodiment, but various changes or improvements can be added to the above embodiment.

  As such a first modification, the image position correction may be repeated twice. FIG. 12 is a flowchart illustrating image processing of the image forming apparatus 1 according to the first modification. In the image forming process according to the second embodiment, when the image position correction process (step S112) is completed, the time difference is measured again (step S102), and the subsequent processes (steps S104 to S112) are repeated.

  Thus, the correction accuracy can be improved by repeating twice. This process corresponds to performing magnification correction and main scanning position correction separately. In this example as well, the time difference measurement and the magnification correction are performed immediately before forming the image misregistration correction pattern, as in the processing according to the first embodiment.

  Further, the color for measuring and correcting the magnification is the same as in the case of the processing according to the first embodiment. However, in the magnification correction performed immediately before the second image position correction process, if the magnification is corrected by the first magnification correction and the image position correction operation, there is no large change in magnification, so only the reference color is used. Good.

  As a second modification, the process control operation may be performed after the magnification correction. The process control is a process for controlling the toner density, charging conditions, and developing conditions to be optimal in order to obtain a high-quality image.

  FIG. 13 is a flowchart illustrating image processing of the image forming apparatus 1 according to the second modification. As shown in FIG. 13, after the magnification correction processing is completed for all colors (step S110), a process control operation is performed (step S120). Thereafter, the time difference is measured again for the reference color black (step S102), and the magnification correction is performed. Then, an image position correction operation is performed.

  In the magnification correction immediately before forming the image misregistration correction pattern, if the magnification of each color is corrected before the process control operation, only the reference color may be used.

  As another example, as described in the first modification, after the process control operation, the image position correction may be further repeated twice.

  As a third modification, the image forming process described in the first embodiment may be performed, and the position correction process may be performed immediately before starting the image forming process. In the correction process at this time, it is necessary to perform magnification correction for all colors.

(Embodiment 2)
Next, the image forming apparatus 1 according to the second embodiment will be described. In the image forming apparatus 1 according to the first embodiment, the phase synchronization clock generation unit 6067 of the pixel clock generation unit 606 changes the VCLK set to a frequency eight times the pixel clock frequency to the start side synchronization detection signal XDETP. Although the synchronized pixel clock PCLK is generated, in the image forming apparatus 1 according to the second embodiment, the phase of the rising edge of the pixel clock PCLK is further set to a half cycle of VCLK based on the correction data from the printer control unit 604. Move forward or backward by minutes. In this respect, the image forming apparatus 1 according to the second embodiment is different from the image forming apparatus 1 according to the first embodiment.

  FIG. 14 is a timing chart of the pixel clock PCLK. As correction data from the printer control unit 604, “00b”, “01b”, and “10b” are acquired. '00b' indicates that no correction is performed. '01b' indicates that the phase is delayed by 1/16 PCLK. '10b' indicates that the phase is advanced by 1/16 PCLK.

  The correction data is sent in synchronization with the pixel clock PCLK and is reflected on the rising edge of the next pixel clock PCLK. When the correction data is “00b”, the pixel clock PCLK has a cycle eight times as long as VCLK. When the correction data is “01b”, the phase of the rising edge is delayed by a half period of VCLK, that is, 1/16 PCLK. In this case, after that, the original PCLK is delayed by 1/16 PCLK.

  In the timing chart of FIG. 14, the phase shift is performed three times. Therefore, the phase of the pixel clock PCLK is delayed by a total of 3 / 16PCLK. That is, the image magnification is corrected by 3 / 16PCLK.

  The printer control unit 604 calculates the number of pixels whose cycle is variable and its direction (whether it is advanced or delayed) from the magnification error data, and sends it to the phase synchronization clock generating unit 607 as correction data. The phase-synchronized clock generation unit 607 corrects the image magnification by changing the cycle of the pixel clock PCLK as shown in the timing chart of FIG.

  For example, when the reference count value (reference time difference: T0) from the start side synchronization detection signal XDETP to the end side synchronization detection signal XEDETP is set to '20000', the value measured in the correction process is assumed to be '20005'. In this case, the image is shrunk by 5 VCLK. Therefore, the phase is delayed by 1 / 16PCLK × 10 (the cycle is extended).

  FIG. 15 is a diagram for explaining a pixel whose cycle is changed. Assume that the number of dots between two points (between XDETP and XEDETP) is 32 dots, and correction is performed by 4/16 PCLK. In this case, the magnification is corrected as a whole by changing the pixel clock cycle continuously for four pixels. However, if the pixel clock cycle is continuously changed in this way, the image at the changed location locally extends (shrinks). Therefore, the variable pixel clock cycle = image width / variable pixel number = 32/4 = 8 is used to change the cycle at 8 dots. Thereby, it can correct | amend equally within an image width.

  Note that, from the viewpoint of preventing the image from locally extending (shrinking), the formula for calculating the period is not particularly limited as long as it can be evenly distributed in the image region. .

  Other configurations and processes of the image forming apparatus 1 according to the second embodiment are the same as those of the image forming apparatus 1 according to the first embodiment.

  As a first modification of the image forming apparatus 1 according to the second embodiment, in addition to changing the frequency of the pixel clock, the magnification may be further corrected. In this case, the change of the cycle in units of pixels is performed at a timing that compensates for the variable step of the pixel clock frequency. Thereby, accuracy (resolution) can be improved.

  As a second modification, in this embodiment, since the magnification correction is performed by measuring between two points, the pixels to be changed are distributed between the XDETP signal and the XEDETTP signal. In the case of magnification correction in, pixels to be changed are dispersed in the image area.

(Embodiment 3)
Next, the image forming apparatus 1 according to the third embodiment will be described. Similar to the image forming apparatus 1 according to the second embodiment, the image forming apparatus 1 according to the third embodiment disperses the pixels whose cycle is changed evenly within the image width. Further, the position is changed for each main scanning line, and the pixels whose cycle is variable are dispersed so as not to be at the same position in the sub-scanning direction. In this respect, the image forming apparatus 1 according to the third embodiment is different from the image forming apparatus 1 according to the other embodiments.

  FIG. 16 is a diagram illustrating pixels whose pixel clock cycle has been changed by the image forming apparatus 1 according to the third embodiment. The distance between the two points is 32 dots as described in the second embodiment with reference to FIG. Then, 4 pixels to be changed are inserted at a cycle of 8 dots.

  Further, the position of the pixel whose cycle is variable is determined by a counter that operates with the pixel clock PCLK. In the first line, the count is incremented from “1”, and the cycle is changed when the counter values are “8”, “16”, “24”, and “32”.

  For the second and subsequent lines, the position is varied by 3 dots for each line according to the calculation formula: variable amount of position = period of variable pixel × 3/7 = 8 × 3/7 = 3. When the variable amount exceeds the cycle of the variable pixel, the change is made with respect to the initial stage (first line) by the excess amount.

  Specifically, while counting up from '1' in the first line, it is shifted by 3 dots in the second line. The start value of the counter is set to “1 + 3 = 4”. This shifts (fastens) the position of the pixel whose cycle is changed by 3 dots. In the third line, shift by 3 dots. The start value of the counter is set to “4 + 3 = 7”. This further shifts (fastens) the position of the pixel whose cycle is changed by 3 dots. In the fourth line, “7 + 3 = 10”. However, the period of the variable pixel is over 8. Therefore, the excess “10−8 = 2” is set as the counter start value.

  As described above, the position of the pixel whose cycle is variable can be changed by changing the start value of the counter for each line. The formula for calculating the variable amount of the position is not particularly limited to this, and it is sufficient that the position can be varied randomly for each line.

  The remaining configuration and processing of the image forming apparatus 1 according to the third embodiment are the same as the configuration and processing of the image forming apparatus 1 according to the other embodiments.

(Embodiment 4)
Next, the image forming apparatus 1 according to the fourth embodiment will be described. The image forming apparatus 1 according to the fourth embodiment is a four-drum type image forming apparatus 1. FIG. 17 is a diagram illustrating an overall configuration of the image forming apparatus 1 according to the fourth embodiment. Similarly to the image forming apparatus 1 according to the other embodiments, the image forming apparatus 1 according to the fourth embodiment also forms a color image in which images of four colors (yellow, magenta, cyan, and black) are superimposed. Specifically, four sets of image forming units 80 a to 80 d and one light beam scanning device 70 are provided.

  The image forming units 80a to 80d for the respective colors are provided around the photosensitive members 81a to 81d, respectively, with developing units 82a to 82d, chargers 83a to 83d, transfer devices 84a to 83d, static eliminators 85a to 85d, and cleaning units. 86a-86d.

  An image is formed on the recording paper 40 by charging, exposure, development, and transfer, which are normal electrophotographic processes. An image of the first color is formed on the recording paper 40 conveyed in the direction of the arrow by the transfer belt 30, and then the images of the four colors are superimposed by transferring the images in the order of the second, third and fourth colors. A color image can be formed on the recording paper 40. Although not shown, the image on the recording paper 40 is fixed by the fixing device. The above processing is the same as the processing of the image forming apparatus 1 according to the other embodiments.

  Furthermore, a first pattern sensor 51 and a second pattern sensor 52 are provided for detecting an image misalignment correction pattern.

  The light beam scanning device 70 according to the fourth embodiment uses one polygon mirror 71 to deflect and scan light beams of different colors above and below the surface of the polygon mirror 71. Furthermore, by scanning the polygon mirror 71 so as to face each other, the light beams for four colors are scanned on the respective photosensitive members. The light beams of the respective colors are deflected by the polygon mirror 71 driven by the polygon motor 77, pass through the fθ lenses 72a and 72b, are folded back by the first mirrors 73a to 73d and the second mirrors 74a to 74d, and pass through the BTLs 75a to 75d. The third mirrors 76a to 76d are folded back to scan the photoreceptors 81a to 81d of the respective colors.

FIG. 18 is a view of the light beam scanning apparatus 70 shown in FIG. 17 as viewed from above. The light beams from the LD unit _Y 90a and the LD unit _BK 90d pass through CYL (cylinder lens) _Y 91a and CYL _BK 91d, respectively. Then, the light enters the lower surface of the polygon mirror 71 by the reflection mirror _Y 92a and the reflection mirror _BK 92d, respectively. Then, the polygon mirror 71 rotates to deflect the light beam, pass through the fθ lens _MY 72a and the fθ lens _BKC 72b, and is folded back by the first mirror Y73a and the first mirror BK73d.

The light beams from the LD unit _M 90b and the LD unit _C 90c pass through the CYL (cylinder lens) _M 91b and CYL _C 91b, respectively, enter the upper surface of the polygon mirror 71, and rotate as the polygon mirror 71 rotates. Deflection of the beam. Then, the light passes through the fθ lens _MY 72a and the fθ lens _BKC 72b and is folded back by the first mirror _M 83b and the first mirror C73c.

Furthermore, the first CYM (cylinder mirror) _BKC 93b, the first CMY _MY 93a, the second CYM _BKC 95b, the second CMY _MY 95a, the first synchronization sensor _BKC 92b, and the first synchronization are provided at both ends of the writing in the main scanning direction. A sensor _MY 92a, a second synchronization sensor _BKC 94b, and a second synchronization sensor _MY 94a are provided.

The light beam that has passed through the fθ lens _MY 72a is reflected and collected by the first CMY _MY 93a and is incident on the first synchronous sensor _MY 92a. Further, the light is reflected and collected by the second CMY _MY 95a and enters the second synchronization sensor _MY 94a.

On the other hand, the light beam that has passed through the fθ lens _BKC 72b is reflected and collected by the first CMY _BKC 93b and enters the first synchronization sensor _BKC 92b. Further, the light is reflected and collected by the second CMY _BKC 95b and is incident on the second synchronization sensor _BKC 94b.

The first synchronization sensor _BKC 92b and the first synchronization sensor _MY 91b are synchronization detection sensors for detecting the start side synchronization detection signal XDETP. The second synchronization sensor _BKC 94b and the second synchronization sensor _MY 84a are synchronization detection sensors for detecting the end side synchronization detection signal XEDETP.

Further, a common first CYM _BKC 93c, second CYM _BKC 95b, first synchronization sensor _BKC 92b, and second synchronization sensor _BKC 84b are used for the light beam from the LD unit _C 90c and the light beam from the LD unit _BK 90d. ing.

The same applies to the LD unit _Y 90a and the LD unit _M 90b. Two light beams are incident on the same sensor. Therefore, the incident timings are made different so that the respective light beams can be detected. As another example, a sensor may be provided for each color light beam.

  As shown in FIG. 18, yellow and magenta are scanned in the opposite direction with respect to cyan and black. Further, since the two light beams are incident on the same synchronization detection sensor, it is necessary to provide a separation circuit for separating the start-side synchronization detection signal XDETP into the respective synchronization detection signals.

  That is, the image formation control unit 60 shown in FIG. 2 sends the synchronization detection signal of each color separated by the separation circuit to the phase synchronization clock generation unit 6067, the synchronization detection lighting control unit 608, and the magnification correction unit 602 of each color. become. When a synchronization detection sensor is provided for each color light beam, each color has the same configuration as in FIG.

  In the image forming apparatus 1 according to the present embodiment, assuming that black is a reference color, for yellow and magenta whose scanning direction is opposite to black, when the image magnification changes, the image position deviation in the main scanning direction is correspondingly increased. End up. For cyan, if the change in magnification is the same, there is no misalignment. Therefore, the magnification correction accuracy directly affects the main scanning position deviation correction accuracy.

  Other configurations and processes of the image forming apparatus 1 according to the fourth embodiment are the same as those of the image forming apparatus 1 according to the other embodiments.

1 is a block diagram illustrating a configuration of an image forming apparatus 1 according to a first embodiment. It is a figure which shows the function structure of the light beam operation apparatus 10a and the image formation control part 60 which controls this. 3 is a block diagram illustrating a detailed functional configuration of a magnification correction unit 602. FIG. 3 is a block diagram illustrating a detailed functional configuration of a pixel clock generation unit 606. FIG. 5 is a block diagram showing a detailed functional configuration of a VCO clock generation unit 6062. FIG. 4 is a block diagram showing a functional configuration of a previous stage of the image formation control unit 60. FIG. It is a block diagram which shows the detailed functional structure of the writing start position control part 612. It is a figure which shows the timing chart of the writing start position control part 612. FIG. 4 is a diagram illustrating an image misregistration correction pattern formed on a transfer belt 30. 5 is a flowchart showing position correction processing in the image forming apparatus 1 according to the present embodiment. 11 is a flowchart illustrating detailed processing in the image position correction described in FIG. 10. 6 is a flowchart illustrating image processing of the image forming apparatus 1 according to a first modification of the first embodiment. 10 is a flowchart illustrating image processing of the image forming apparatus 1 according to a second modification. It is a figure which shows the timing chart of pixel clock PCLK. It is a figure for demonstrating the pixel which changes a period. FIG. 6 is a diagram illustrating pixels whose pixel clock cycle has been changed by the image forming apparatus 1 according to the third embodiment. FIG. 6 is a diagram illustrating an overall configuration of an image forming apparatus 1 according to a fourth embodiment. It is the figure which looked at the light beam scanning apparatus 70 shown in FIG. 17 from the top.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10a-10d Light beam operation apparatus 11 Polygon mirror 12 Lens 14 Unit 20a-20b Image forming part 21 Photoconductor 22 Developing unit 23 Charger 24 Transfer device 30 Transfer belt 32 Conveyance motor 40 Recording paper 51 1st pattern Sensor 52 Second pattern sensor 60 Image formation controller 61 Line memory 70 Light beam scanning device 71 Polygon mirror 72a, 72b fθ lens 73a-73d First mirror 74a-74d Second mirror 75a-75d BLT
76a to 76d Third mirror 77 Polygon motor 80a to 80d Image forming unit 81a to 81d Photoreceptor 82a to 82d Developing unit 83a to 83d Charger 84a to 84d Transfer device 85a to 85d Charger 86a to 86d Cleaning unit 90a to 90d LD unit 91a-91d CYL
92a-92d Reflective mirror 93a, 93b 1st CYM
94a, 94b second synchronization sensor 95a, 95b second CYM
151 First synchronization sensor 152 Second synchronization sensor 161 First lens 162 Second lens 171 First mirror 172 Second mirror 602 Magnification correction unit 604 Printer control unit 606 Pixel clock generation unit 606 Pixel clock generation unit 607 Phase synchronization clock generation unit 608 Synchronous detection lighting control unit 610 LD control unit 612 Write start position control unit 614 Polygon motor control unit 6020 Time difference count unit 6021 Counter 6022 Latch 6024 Comparison control unit 6061 Reference clock generation unit 6062 Clock generation unit 6063 Phase comparator 6066 1 / N frequency divider 6067 Phase synchronization clock generator 6120 Main scan line synchronization signal generator 6122 Main scan gate signal generator 6123 Main scan counter 6124 Main scan comparator 6125 Main scan gate No. generator 6126 subscanning gate signal generator 6127 subscanning counter 6128 subscanning comparator 6129 subscanning gate signal generator

Claims (7)

An image forming apparatus that forms a multicolor image by forming a single color image of a second color on top of a single color image of a first color,
First color image forming means for forming a single color image of the first color;
Second color image forming means for forming a single color image of the second color;
First color image magnification correction means for correcting image magnification in the first color image forming means;
Second color image magnification correcting means for correcting image magnification in the second color image forming means;
A first color correction pattern for correcting misregistration formed by the first color image forming means and a second color correction pattern for correcting misregistration formed by the second color image forming means. Based on the above, the positional deviation between the single color image of the first color formed by the first color image forming unit and the single color image of the second color formed by the second color image forming unit is corrected. An image misalignment correcting means,
The image positional deviation correction unit includes the first color correction pattern formed by the first color image forming unit after the image magnification correction is performed by the first color image magnification correction unit, and the second color image. After correcting the positional deviation based on the second color correction pattern formed by the second color image forming unit after the image magnification is corrected by the magnification correcting unit, the first color image is corrected. The first color correction pattern formed by the first color image forming means after the image correction is further corrected by the magnification correction means, and the image magnification is not further corrected by the second color image magnification correction means. The image forming apparatus further performs correction of the displacement based on the second color correction pattern formed by the second color image forming means. The first color image forming unit and the second color image forming unit are respectively
Based on the image data, a light emission source whose lighting is controlled,
Deflection means for deflecting the light beam output from the light source in the main scanning direction by a plurality of polarization planes,
The first color image magnification correction unit and the second color image magnification correction unit are respectively
A light beam detecting means for detecting the light beam deflected by the deflecting means at two locations on the main scanning line;
A time difference measuring means for measuring a time difference when the light beam detecting means detects the light beam at two locations;
Magnification correction means for correcting the image magnification in the direction of the main scanning line based on the time difference between the two detected light beams measured by the time difference measurement means;
The image misregistration correction unit is formed by the first color image forming unit after the magnification correction unit of the first color image magnification correction unit corrects the image magnification in the direction of the main scanning line. The second color image forming means formed after the one color correction pattern and the magnification correction means of the second color image magnification correction means have corrected the image magnification in the direction of the main scanning line. After correcting the positional deviation based on the color correction pattern, after further correcting the image magnification in the direction of the main scanning line by the magnification correction unit of the first color image magnification correction unit. The image magnification in the direction of the main scanning line is further corrected by the first color correction pattern formed by the first color image forming unit and the magnification correction unit of the second color image magnification correction unit. The second color image forming means on the basis of the second color correction pattern formed on the image forming apparatus according to claim 1, characterized in that further corrects the positional deviation.   The magnification correction unit corrects the image magnification by changing a cycle of a lighting control clock of the light emitting source in units of one pixel based on the time difference measured by the time difference measurement unit. Item 3. The image forming apparatus according to Item 2.   The image forming apparatus according to claim 3, wherein the magnification correction unit corrects the image magnification by changing a cycle of the lighting control clock in units of pixels at a plurality of positions.   The image forming apparatus according to claim 4, wherein the magnification correction unit corrects the image magnification by changing a cycle of the lighting control clock in units of one pixel at a plurality of equally spaced positions.   5. The image formation according to claim 4, wherein the magnification correction unit corrects the image magnification by changing a cycle of the lighting control clock in units of one pixel at a position that is not adjacent in the sub-scanning direction. apparatus.   The image forming apparatus according to claim 1, wherein the first color is black.

Images