JP2005224947A - Optical scanner and multicolor image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly correct misregistration (color shift) of a beam spot between colors all over a scanning area, even on the occurrence of a variation with time, such as a variation in temperature. <P>SOLUTION: A pixel clock control circuit 23 makes transition timing of a pixel clock variable, in accordance with the result of a comparison between phase data 21 for providing instructions on the transition timing, and a high-frequency clock generated by a high-frequency clock generating circuit 20; and a signal, which shifts a phase of the pixel clock, is inputted into a light source 24, so that a beam spot position can be corrected. The scanning area 27 is split into a plurality of sections, and the density of the beam spot positions is corrected in each split section. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning device used in a digital copying machine, a laser printer, and the like, and a multicolor image forming apparatus using the optical scanning device.

  In general, an optical scanning device widely known in relation to a laser printer or the like generally deflects a light beam from a light source side by an optical deflector and collects the light beam toward a surface to be scanned by a scanning imaging optical system such as an fθ lens. Thus, a light spot is formed on the surface to be scanned, and the surface to be scanned is optically scanned (main scan) with this light spot. What constitutes the surface to be scanned is a photosensitive surface of a photosensitive medium such as a photoconductive photosensitive member.

  As the optical deflector, a polygon scanner whose deflecting surface rotates at a constant angular velocity is generally used, and a light source such as a semiconductor laser is modulated at a certain frequency. When an optical scanning device is configured using such a light source and an optical deflector, and the surface to be scanned such as a photoconductor is optically scanned, the beam spot positions are not arranged at equal intervals, and the scanning speed is not constant. For this reason, in order to perform optical scanning with the beam spot positions arranged at equal intervals and with a constant scanning speed, correction is performed using a scanning imaging optical system such as an fθ lens, and so on. Speed light scanning becomes possible. However, there is a limit to the correction of the scanning speed using an fθ lens or the like, and the scanning speed cannot be made completely constant, resulting in “scanning speed unevenness”. Furthermore, the scanning speed unevenness increases due to manufacturing error of the fθ lens, variation with time, and the like.

  When unevenness in scanning speed occurs, the image is distorted and the image quality is degraded. In the case of a color image forming apparatus, since a plurality of fθ lenses are used, scanning speed unevenness varies depending on colors due to the influence of manufacturing errors and installation errors of the fθ lenses, resulting in color misregistration. .

  As a technique for correcting the scanning speed unevenness, for example, a method of correcting the beam spot position along the scanning line by basically changing the frequency of the pixel clock is known (for example, Patent Documents 1 and 2). See).

  As another method of correcting the scanning speed unevenness, a method of correcting the beam spot position along the scanning line by dividing the scanning region into a plurality of sections and changing the phase of the pixel clock for each divided section. Has been proposed by the present applicant (see, for example, Patent Documents 3 and 4).

  By using the beam spot position correction method described in the above application, color misregistration correction is possible in the initial stage (at the time of shipment from the factory). However, in the above application, the color misregistration correction method at the time variation is described. Not.

  A color image forming apparatus generally uses a plurality of fθ lenses, and the fθ lenses are installed at spatially different locations. If the installation locations are spatially different, the optical characteristics of the fθ lens will differ between colors due to the temperature difference between the installation locations, and color misregistration correction is performed at the initial stage (factory shipment) using the beam spot position correction method. Even if this occurs, color misregistration occurs.

  Further, generally, an optical deflector such as a polygon scanner is used in the optical scanning device, and the polygon scanner rotates at a high speed, and therefore becomes a large heat source. Due to the influence of the heat source, a temperature distribution is generated in the fθ lens, and the temperature distribution is not the same among the plurality of fθ lenses.

  Furthermore, a temperature distribution is generated in the fθ lens due to the influence of the airflow generated by the rotation of the polygon scanner, which leads to color misregistration.

  As described above, even when there is no color misregistration at the time of initial printing in the continuous printing of a large number of sheets, color misregistration occurs at the end of continuous printing.

  In recent years, in order to improve the accuracy of the scanning speed correction, it has become common to use a special surface typified by an aspherical shape for an optical element such as an fθ lens. Often used is a low-cost resin whose surface can be easily manufactured. Such an optical element made of resin and adopting a special surface can achieve both high-precision optical scanning and cost reduction.

  However, the resin has a larger coefficient of thermal expansion than that of glass. Therefore, a shape change and a refractive index change are likely to occur due to temperature fluctuation (temperature distribution). Therefore, when a resin is used for an optical element such as an fθ lens, the color shift caused by the influence of the temperature fluctuation as described above is large.

  As a method of correcting color misregistration due to temperature fluctuation as described above, there is a method of correcting color misregistration by changing the frequency of the pixel clock by detecting the scanning time from the scanning start end to the scanning end end (for example, , See Patent Document 5).

  However, this method can correct color misregistration at the scanning start end and end end, but cannot correct it at the center.

  As shown in FIG. 1, in the method of distributing a light beam in both directions using a single polygon scanner, the air flow of the polygon scanner with respect to the fθ lens is generated in the opposite direction depending on the direction of distributing the light beam. As a result, the temperature distribution caused by the influence of the air current generated by the polygon scanner is reversed depending on the direction in which the light beam is distributed, and a large color shift occurs.

  In order to alleviate the above problem, a method is known in which all light beams are deflected in the same direction using a single polygon scanner, and a scanning lens closest to the polygon scanner is shared by all light beams (for example, (See Patent Documents 6 and 7).

Japanese Patent Laid-Open No. 11-167081 JP 2001-228415 A JP 2003-98465 A JP 2003-103830 A Japanese Patent Laid-Open No. 9-58053 JP-A-2-250020 Japanese Patent Laid-Open No. 7-43627

  If the above-described method is used, the influence of the temperature distribution due to the air flow of the polygon scanner is reduced. However, since the scanning lens closest to the polygon scanner shares all the light beams, the scanning lens becomes higher in the sub-scanning direction, and the temperature distribution is generated differently depending on the position in the sub-scanning direction, resulting in color shift. End up.

  An object of the present invention is to provide an optical scanning device and a multicolor image forming apparatus that can satisfactorily correct a beam spot position shift (color shift) between colors over the entire scanning region even when there is a temporal variation such as a temperature variation. There is.

Specifically, first, in claims 1 to 9, a change in optical scanning characteristics at the time of fluctuation such as temperature fluctuation is detected, and a fluctuation in temperature is detected by correcting a fluctuation in beam spot position based on the detection result. The purpose is to realize an optical scanning device capable of maintaining good scanning characteristics even when the time variation of
According to a tenth aspect of the present invention, there is provided an image forming apparatus having the optical scanning device, and an object of the present invention is to obtain a good image even at the time of fluctuation such as temperature fluctuation.
It is an object of the present invention to obtain an image with little color misregistration even when there is a temporal variation such as a temperature variation by realizing a multicolor image forming apparatus having a plurality of the optical scanning devices.

  According to the present invention (Claim 1), an optical scanning device that scans a light beam from a light source with an optical deflector and focuses the light beam on a surface to be scanned by a scanning imaging optical system in the main scanning direction on the surface to be scanned. Beam spot position correcting means capable of correcting the density of beam spot position intervals along the path, storage means for storing information for correcting the density of the beam spot position intervals, and detecting or predicting fluctuations in the beam spot position And rewriting the information stored in the storage means based on the result obtained by the means for detecting or predicting the variation in the beam spot position. The method is characterized in that the fluctuation of the beam spot position is corrected.

  According to the present invention (Claim 2), in the optical scanning device according to Claim 1, the beam spot position correcting unit divides the scanning region into a plurality of sections, and corrects the density of the beam spot position intervals for each divided section. It is characterized by doing.

  According to the present invention (Claim 3), in the optical scanning device according to Claim 2, the division section is set by dividing a scanning region at different intervals.

  According to a fourth aspect of the present invention, in the optical scanning device according to the first aspect, the beam spot position correcting unit varies the period of the pixel clock based on the phase data indicating the transition timing of the pixel clock. In addition, the density of the beam spot position interval is corrected, and at least the phase data is stored in the storage means.

  According to the present invention (Claim 5), in the optical scanning device according to Claim 1, the means for detecting or predicting the fluctuation of the beam spot position is at least along the main scanning direction for detecting the light beam from the light source. Two photodetecting means are provided, and scanning is performed by detecting a scanning time between the photodetecting means.

  According to the present invention (Claim 6), in the optical scanning device according to Claim 5, the light detection means is shared by a plurality of light beams deflected in the same direction by at least an optical deflector. .

  According to the present invention (Claim 7), in the optical scanning apparatus according to Claim 1, the means for detecting or predicting the fluctuation of the beam spot position is provided with a temperature detection means, and detects the temperature in the optical scanning apparatus. It is characterized by performing by.

  In the optical scanning device according to the first aspect of the present invention, the means for detecting or predicting the fluctuation of the beam spot position includes means for measuring the driving time of the optical deflector, and driving the optical deflector. This is performed by detecting time.

  According to the present invention (Claim 9), in the optical scanning device according to Claim 1, the correction of the beam spot position is performed in an ineffective area during continuous printing or between a print job and a print job. And

  The present invention (Claim 10) includes the optical scanning device according to any one of Claims 1 to 9, a developing unit that visualizes the electrostatic image with toner, and a transfer that forms a visualized image. And rewriting the information stored in the storage means based on the result obtained by the means for detecting or predicting the fluctuation of the beam spot position, and correcting the fluctuation of the beam spot position. It is characterized by that.

  The present invention (invention 11) includes a plurality of optical scanning devices according to any one of claims 1 to 9, and developing means for visualizing the electrostatic image with toner of each color, and each of the visualized colors In a multicolor image forming apparatus having a transfer means for forming a color image by superimposing images, the storage means stores the result based on the result obtained by the means for detecting or predicting the variation in the beam spot position. The information is rewritten, and the deviation of the beam spot position of each color image relative to the reference color image is corrected.

  The multicolor image forming apparatus according to claim 11 of the present invention has at least one light detection means for detecting light beams from the plurality of light sources, and the plurality of light beams are light detection means. The deviation of the relative beam spot position between each color is corrected by the time difference detected by the above.

  According to the present invention (Claim 13), in the multicolor image forming apparatus according to Claim 12, the light detecting means is shared by a plurality of light beams deflected in the same direction by at least an optical deflector. And

  According to the present invention (Claim 14), in the multicolor image forming apparatus according to Claim 11, the means for substantially matching the image writing position between the colors and the image writing end position between the colors are substantially the same. And means for substantially adjusting the image width.

  According to the present invention (Claim 15), in the multi-color image forming apparatus according to Claim 11, there is provided means for substantially matching the image writing position between the respective colors, and the relative beam spot position deviation between the respective colors is determined. And correcting the beam spot position correction amount at each image height and setting the information stored in the storage means so that the fluctuation of the image width or the deviation of the image width between colors is corrected. Features.

  According to the present invention (Claim 16), in the multicolor image forming apparatus according to Claim 11, the direction toward one end of the output image is defined as positive, and the direction toward the other is defined as negative, and correction of beam spot position deviation is performed. The sign of the direction is inverted near the center image height, and the correction amount is adjusted so that the beam spot position correction amount at each image height is substantially symmetrical about the center image height, and stored in the storage means. It is characterized by setting information.

  According to the present invention (Claim 17), in the multicolor image forming apparatus according to Claim 11, the direction toward one end of the output image is defined as positive, and the direction toward the other is defined as negative. The beam spot position correction amount at each image height is adjusted so that the direction is the same direction over the entire image height, and the correction amount is the largest near the center image height and decreases as the peripheral image height increases, The information stored in the storage means is set.

  By using the present invention (Claim 1), even when a beam spot position shift occurs during a time-dependent change such as a temperature change, the beam spot position shift can be favorably corrected. Thus, it is possible to obtain an optical scanning device that can maintain good optical scanning characteristics even when it varies with time.

  By using the present invention (claims 2 and 4), the density of the beam spot position interval can be corrected with high accuracy. Furthermore, since the linearity correction can be relaxed in the design of the scanning imaging lens, the scanning imaging lens can be made thin and uniform, and as a result, the scanning imaging lens has a highly accurate surface shape at low cost. Can be obtained.

  By using the present invention (Claim 3), it is possible to achieve both cost reduction by reducing the number of divisions and high accuracy of beam spot position correction.

  By using the present invention (Claims 5, 7, and 8), it is possible to predict well the beam spot position fluctuation at the time of fluctuation such as temperature fluctuation. Spot position fluctuation can be corrected.

  By using the present invention (Claims 6 and 13), the number of light detection means can be reduced, and the cost can be reduced. Furthermore, since a detection error due to variations in characteristics between elements of a light detection means such as a photodiode can be eliminated, highly accurate time detection is possible.

  By using the present invention (claim 9), it is possible to obtain a highly accurate image with little color shift and color density change even during continuous printing.

  By using the present invention (claim 10), a high-quality image free from image distortion and the like can be obtained even when the temperature fluctuates. Further, it is possible to reduce the toner consumption during the beam spot position correction.

  By using the present invention (claim 11), a high-quality image with little color shift and color density change can be obtained even when the temperature fluctuates. Further, it is possible to reduce the toner consumption during the beam spot position correction.

  By using the present invention (Claim 12), it is possible to predict well the beam spot position fluctuation at the time of fluctuation such as temperature fluctuation. Based on the prediction result, the beam spot position fluctuation can be favorably performed. A high-accuracy image that can be corrected and has little color shift or change in color density is obtained.

  By using the present invention (Claim 14), it is possible to improve the correction accuracy at the intermediate image height by making the image writing position and the writing end position coincide with each other well, and over the entire image area. A high-quality image with little color shift can be obtained.

  By using the present invention (Claim 15), it is possible to simplify the correction algorithm, reduce expensive photodetection means such as an expensive photodiode, and reduce the beam spot position deviation between the respective colors. And a high-quality image with little color misregistration can be obtained.

  By using the present invention (Claims 16 and 17), it is possible to satisfactorily correct relative positional deviation between colors over the entire image height, and high accuracy with little color deviation and change in color density. Images can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an embodiment in which the optical scanning device of the present invention is applied to a 4-drum tandem color image forming apparatus. FIG. 1A shows a state where the optical arrangement of the optical scanning device is viewed from the sub-scanning direction, and FIG. 1B shows a state viewed from the main scanning direction. For simplification of illustration, the optical path from the deflecting means to the surface to be scanned is linearly developed.

  In the following description, Y, M, C, and K indicate yellow, magenta, cyan, and black colors.

  In FIG. 1A, laser light sources 1Y to 1K are semiconductor lasers, which are yellow (Y), magenta (M), cyan (C), and black (K), respectively. A light beam for writing an “electro-latent image” is emitted. 2Y to 2K are coupling lenses, and 3Y to 3K are cylindrical lenses.

  The light beam emitted from the laser light source 1K (1Y) is converted into a parallel light beam by a coupling lens 2K (2Y), shaped by an aperture (not shown), and then sub-scanned (perpendicular to the drawing) by a cylindrical lens 3K (3Y). And is focused as a line image long in the main scanning direction at the position of the deflecting reflection surface of the polygon mirror 4.

  Similarly, the light beam emitted from the laser light source 1M (1C) is converted into a parallel light beam by the coupling lens 2M (2C), shaped by an aperture (not shown), and then shaped by the cylindrical lens 3M (3C) in the sub-scanning direction ( The light beam is focused only in the direction orthogonal to the drawing and is formed as a line image long in the main scanning direction at the position of the deflecting reflection surface of the polygon mirror 4.

  The incident position of the light beam emitted from the laser light source 1K (1Y) on the polygon mirror and the incident position of the light beam emitted from the laser light source 1M (1C) on the polygon mirror are planes including the rotation axis of the polygon mirror. In contrast, the positional relationship is almost symmetrical.

  In FIG. 1, yellow (Y) and black (K) are scanned in the same direction, and cyan (C) and magenta (M) are scanned in the same direction, but this combination may be changed.

  The polygon mirror 4 has six deflecting reflecting surfaces. In FIG. 1, “each deflecting reflecting surface is a single reflecting surface in the rotation axis direction”, but between the light beams not used as the deflecting reflecting surface. A portion in which a groove is formed so as to be “a little smaller than the inscribed circle of the polygon mirror 4” may be used.

  The four light beams from the laser light source side are simultaneously deflected at a constant angular velocity as the polygon mirror 4 rotates at a constant speed. The four light beams to be deflected are guided to the scanned surfaces 7Y to 7K by the scanning imaging lenses 5Y to 5K and the scanning imaging lenses 6Y to 6K, respectively, and as light spots on the scanned surfaces 7Y to 7K, respectively. The light is condensed and optical scanning of the scanned surface is performed.

  As shown in FIGS. 1A and 1B, the scanning imaging lenses 5Y to 5K and 6Y to 6K constitute “imaging means”. The scanning imaging lens 5Y and the scanning imaging lens 6Y constitute a “scanning imaging optical system” that forms a light spot for optically scanning the surface to be scanned 7Y. Similarly, the scanning imaging lens 5K and the scanning imaging lens 6K are a “scanning imaging optical system” that forms a light spot for optically scanning the surface to be scanned 7K, and the scanning imaging lens 5C and the scanning imaging lens 6C. Constitutes a “scanning imaging optical system” that forms a light spot for optically scanning the scanned surface 7C, and the scanning imaging lens 5M and the scanning imaging lens 6M are light beams for optically scanning the scanned surface 7M. A “scanning imaging optical system” for forming spots is formed.

  That is, the “imaging means” is composed of the four sets of scanning imaging optical systems, and more specifically, is composed of eight scanning imaging lenses 5Y to 5K and 6Y to 6K.

  The scanned surfaces 7Y to 7K are actually “image carriers”. That is, the optical scanning device shown in FIG. 1 uses different image carriers 7Y for the light beams emitted from the plurality of laser light sources 1Y to 1K via the deflecting unit 4 and the imaging units 5Y to 5K and 6Y to 6K. An optical scanning device that guides light to ˜7K and performs optical scanning, and is configured to optically scan each light beam emitted from the plurality of laser light sources 1Y to 1K by using a common deflecting means 4, and forms an image The means includes a plurality of scanning imaging lenses 5Y to 5K and 6Y to 6K.

  Corresponding light beams are condensed as light spots on the image carriers 7Y to 7K, respectively, and light scanning is performed by these light spots, and “an electrostatic latent image to be visualized by yellow toner” is displayed on the image carrier 7Y. Are formed, and “electrostatic latent images to be visualized by magenta toner, cyan toner, and black toner” are formed on the image carriers 7M, 7C, and 7K, respectively.

  These electrostatic latent images are visualized by corresponding color toners, transferred onto the same sheet-like recording medium and overlapped with each other, as will be described later, to form a color image. Then, this color image is fixed on the sheet-like recording medium.

  In addition, in the embodiment described above, the light beam from each laser light source is converted into a parallel light beam by a coupling lens, but the light beam after passing through the coupling lens is referred to as a “weak convergent light beam or a weak divergent light beam”. Thus, the optical scanning optical system can be configured.

  Further, the present invention includes a beam spot position correcting unit capable of correcting the density of the beam spot position interval and a unit for detecting or predicting a variation in the beam spot position interval. The detection or prediction means detects or predicts the fluctuation of the beam spot position interval, and the beam spot position correction means corrects the fluctuation of the beam spot position interval based on the detection or prediction result. By adopting such a configuration, even when the beam spot position is shifted due to a change over time such as a temperature change, it is possible to return to the beam spot position before the change, so that it does not depend on a change over time such as a temperature change. High-precision optical scanning is possible.

  A method of dividing the scanning region into a plurality of sections and correcting the density of the beam spot position intervals for each divided section will be described with reference to FIGS.

  In the embodiment of FIG. 5, the beam spot position is corrected by changing the transition timing by the phase data 21 instructing the transition timing and the high frequency clock 20 and inputting a signal obtained by shifting the phase of the pixel clock 23 to the light source 24. doing. Hereinafter, a pixel corresponding to a clock for shifting the phase is referred to as a “phase shift pixel”.

  FIG. 6 shows how the density of the beam spot position interval can be corrected. For simplification of description, it is assumed that the phase shift pixels are arranged at equal intervals. The number of pixels in the direction in which the phase of the pixel clock is delayed is represented by-.

  6A shows a state in which the pixel clock is uniform (before correction), and FIG. 6B shows a state in which the phase of the pixel clock is advanced by 1/16 PCLK (PCLK means the pixel clock) every two pixels. FIG. 6C shows a state in which the phase of the pixel clock is delayed by 1/16 PCLK every two pixels (the number of phase shift pixels is −6). ). In FIG. 6B, the pixels are generally denser than in FIG. 6A, and in FIG. 6C, the pixels are generally sparse relative to FIG. 6A. (Accurately, only the interval between the phase shift pixel and the adjacent pixel changes, but on average, it can be regarded as sparse or dense as a whole). If the number of phase shift pixels is changed, naturally the degree of density (sparseness) of the pixels can be changed.

  By dividing the effective scanning region into a plurality of sections and changing the number of phase shift pixels in each section, that is, by combining the states of FIG. 6B and FIG. 6C, the number of phase shift pixels is adjusted. By adjusting the degree of pixel density (sparseness), it is possible to satisfactorily correct the density of the main scanning beam spot position interval in the effective scanning region.

  When the scanning area is divided into a plurality of sections as described above, it is preferable to divide the scanning area with different widths (hereinafter, dividing with different widths is referred to as “partial division”). Since the width of the divided section can be varied depending on the density of the beam spot position interval, the density of the beam spot position interval can be effectively corrected. This means that high-precision correction can be performed with a smaller number of divisions, and it is possible to achieve both cost reduction and higher correction accuracy by reducing memory by reducing the number of divisions.

  FIGS. 2, 3 and 4 are diagrams showing the principle of changing the cycle of the pixel clock based on the phase data indicating the transition timing of the pixel clock.

  In FIG. 2, the pixel clock generation circuit 10 includes a high frequency clock generation circuit 11, a counter 12, a comparison circuit 13, and a pixel clock control circuit 14. The high frequency clock generation circuit 11 generates a high frequency clock VCLK serving as a reference for the pixel clock PCLK. The counter 12 is a counter that operates at the rising edge of the high frequency clock VCKL and counts the VCKL. The comparison circuit 12 compares the counter value with a preset value and phase data indicating the phase shift amount as the transition timing of the pixel clock given from the outside, and outputs the control signal a and the control signal b based on the comparison result To do. The pixel clock control circuit 13 controls the transition timing of the pixel clock PCLK based on the control signal a and the control signal b.

  Here, the phase data is used to correct the scanning unevenness caused by the characteristics of the scanning lens, to correct the dot positional deviation due to the rotational irregularity of the polygon mirror, and to correct the dot positional deviation caused by the chromatic aberration of the laser beam. Data for indicating the amount of phase shift, and is generally given as a digital value of several bits.

  The operation of the pixel clock generation circuit of FIG. 2 will be described with reference to the timing chart of FIG. Here, the pixel clock PCLK is divided by 8 of the high-frequency clock VCLK, and the duty ratio is 50% as a standard. FIG. 3A shows how a standard pixel clock PCLK with a duty ratio of 50% corresponding to VCLK divided by 8 is generated, and FIG. 3B shows only 1/8 clock with respect to VCLK divided by 8 clock. FIG. 3C shows a state in which the PCLK with the advanced phase is generated, and FIG. 3C shows a state in which the PCLK clock whose phase is delayed by 1/8 clock with respect to the VCLK divided by 8 is generated.

  First, FIG. 3A will be described. Here, a value of “7” is given as the phase data. In the comparison circuit 13, “3” is set in advance. The counter 12 operates and counts at the rising edge of the high frequency clock VCLK. The comparison circuit 13 first outputs the control signal a when the value of the counter 12 reaches “3”. Since the control signal a is “H”, the pixel clock control circuit 13 changes the pixel clock PCLK from “H” to “L” at the clock timing of the circled number 1. Next, the comparison circuit 13 compares the given phase data with the counter value, and outputs a control signal b if they match. In FIG. 3A, when the value of the counter 12 reaches “7”, the comparison circuit 13 outputs the control signal b. Since the control signal b is “H”, the pixel clock control circuit 14 changes the pixel clock PCLK from “L” to “H” at the timing of the clock with the number 2 with a circle. At this time, the comparison circuit 13 simultaneously resets the counter 12 and starts counting from 0 again. Thereby, as shown in FIG. 3A, the pixel clock PCLK having a duty ratio of 50% corresponding to the frequency division of the high frequency clock VCLK by 8 can be generated. If the set value of the comparison circuit 13 is changed, the duty ratio changes.

  Next, FIG. 3B will be described. Here, it is assumed that “8” is given as the phase data. The counter 12 counts the high frequency clock VCLK. The comparison circuit 13 first outputs the control signal a when the value of the counter 12 reaches “3”. Since the control signal a is “H”, the pixel clock control circuit 14 changes the pixel clock PCLK from “H” to “L” at the timing of the clock with the circled number 1. Next, the comparison circuit 13 outputs the control signal b when the value of the counter 12 coincides with the given phase data (here, 8). Since the control signal b is “H”, the pixel clock control circuit 14 changes the pixel clock PCLK from “L” to “H” at the timing of the clock with the number 2 with a circle. At this time, the comparison circuit 13 simultaneously resets the counter 12 and starts counting from 0 again. Thereby, as shown in FIG. 3B, it is possible to generate the pixel clock PCLK in which the phase is advanced by 1/8 clock with respect to the frequency-divided clock of the high frequency clock VCLK by 8.

  Next, FIG. 3C will be described. Here, “6” is given as the phase data. The counter 12 counts the pixel clock VCLK. The comparison circuit 13 first outputs the control signal a when the value of the counter 12 reaches “3”. Since the control signal a is “H”, the pixel clock control circuit 14 changes the pixel clock PCLK from “H” to “L” at the timing of the clock with the circled number 1. Next, the comparison circuit 13 outputs the control signal b when the value of the counter 12 coincides with the given phase data (here, 6). Since the control signal b is “H”, the pixel clock control circuit 14 changes the pixel clock PCLK from “L” to “H” at the timing of the clock with the number 2 with a circle. At this time, the counter 12 is reset at the same time to start counting from 0 again. Thereby, as shown in FIG. 3C, it is possible to generate the pixel clock PCLK whose phase is delayed by 1/8 clock with respect to the divide-by-8 clock of the high-frequency clock VCLK.

  For example, by providing the phase data in synchronization with the rising edge of the pixel clock PCLK, the phase of the pixel clock PCLK can be changed every clock. FIG. 4 is a timing diagram showing this.

  As described above, the phase of the pixel clock PCLK can be controlled in the ± direction in units of the clock width of the high-frequency clock VCLK with a simple configuration.

  As described above, since the phase of the pixel clock PCLK can be changed every clock, high-definition correction is possible. However, if the phase is changed every clock, the phase is changed every clock. Since it is necessary to have data in the memory, a considerable amount of memory is required, resulting in an increase in cost.

  Therefore, as shown in FIG. 6 described above, phase shift pixels may be arranged at fixed pixel intervals, which can greatly reduce the memory. The “phase data” in the present invention includes not only data indicating the phase shift amount as described above, but also information on how many pixels the phase shift is performed. By adopting the above method, it is possible to correct the density of the beam spot position interval. In addition, by storing at least the phase data in the storage unit and making it rewritable, even if the beam spot position fluctuates due to temporal changes such as temperature fluctuations, the phase data stored in the storage unit is rewritten, By changing the correction state of the beam spot position, the fluctuation of the beam spot position can be corrected.

  When rewriting the information stored in the storage means, it is possible to correct the beam spot position deviation with higher accuracy if both the division position and phase data are rewritten. However, if both are rewritten, the correction algorithm becomes complicated. There is a problem. Further, if only the phase data is rewritten, the correction accuracy is slightly lowered, but the correction algorithm can be simplified. Therefore, even if the correction algorithm is complex, it is better to set both the division position and phase data to be rewritable when high-accuracy correction is required, and it is necessary to simplify the correction algorithm even if the correction accuracy drops slightly. Sometimes it is desirable to set only the phase data to be rewritable.

  Further, the scanning imaging lens in the optical scanning device is normally corrected so that the main scanning beam spot position changes linearly with respect to the rotation of the optical deflecting device (linearity correction). The above correction can be relaxed, and the performance of other optical characteristics can be improved, and the thickness and thickness can be reduced (the difference between the center thickness and the peripheral thickness is small). This thin and uniform scanning lens is very advantageous for processing, and a scanning lens with high surface accuracy can be manufactured at a low cost. Therefore, the merit of weakening the linearity correction is very great.

  According to the present invention, by providing at least two light detection means along the main scanning direction and measuring the scanning time between the two light detection means, the fluctuation amount of the beam spot position or the relative relationship between the color images. Since the beam spot position deviation can be predicted, the beam spot position can be corrected. This will be described with reference to FIG.

  PDs 1 to 4 in FIG. 1 indicate light detection means. In this embodiment, photodiodes (PD) are used as the light detection means. It is assumed that the optical characteristics change due to temporal changes such as temperature fluctuations, and the light rays reaching PD1 to PD4 change from solid lines to dotted lines. If it changes so, the scanning time between PD1 and PD2 will be observed longer than the scanning time in an initial state. The scanning time between PD3 and PD4 is observed to be shorter than the scanning time in the initial state.

  For example, if the beam spot position interval expands or contracts by the same interval over the entire scanning area, just make corrections so that the writing position and writing end position match before and after the optical characteristics change (beam spot position interval). Without correcting the distortion of the beam spot, it is possible to correct the beam spot position fluctuation with a certain degree of accuracy even at the intermediate image height. However, normally, when the optical characteristics change, the beam spot position interval does not expand or contract by the same interval over the entire scanning region, but changes with distortion (dense / dense) at a specific location. Therefore, it is necessary to correct the beam spot position variation not only at the writing position and the writing end position but also at the intermediate image height, that is, a correction method capable of correcting the density of the beam spot position is essential.

  The location of the beam spot position distortion that occurs when the temperature fluctuates as described above varies depending on the layout in the optical scanning device, the installation location of the optical scanning device in the image forming apparatus, and the like. If the layout, the installation location of the optical scanning device in the image forming apparatus, and the like are determined, the location of the distortion of the beam spot position that occurs when the temperature fluctuates is almost determined, and the amount of distortion generated is the above PD1. There is almost a correlation with the scanning time between PD2 (PD3 and PD4).

  Therefore, by measuring the scanning time between the above PD1 and PD2 (PD3 and PD4) and detecting the amount of fluctuation from the initial stage, the fluctuation of the beam spot position that occurs at the time of fluctuation such as temperature fluctuation can be accurately detected. Can be corrected. Further, by comparing the scanning time between PD1 and PD2 and the scanning time between PD3 and PD4, it is possible to correct a relative beam spot position shift between the respective colors at the time of variation such as temperature variation.

  By devising the layout in the optical scanning device such as an optical element, it is possible to share the light detection means at least among a plurality of light beams deflected in the same direction by the optical deflector. By sharing the light detection means among a plurality of light beams, it is possible to reduce the number of light detection means and reduce costs, for example, detection by variation in characteristics between elements of the light detection means such as a photodiode. Since errors can be eliminated, highly accurate time detection is possible.

  By detecting temperature fluctuations in the optical scanning device, it is also possible to predict fluctuations in the beam spot position that occur when there are temporal fluctuations such as temperature fluctuations.

  During continuous printing, the polygon mirror keeps rotating and the polygon mirror generates heat. Due to the heat of the polygon mirror, which is a large heat generation source, and the influence of the airflow caused by the rotation of the polygon mirror, the refractive index and the surface shape of the scanning imaging lens change, thereby changing the beam spot position deviation. Therefore, even if the beam spot position deviation does not occur at the beginning of continuous printing, it gradually occurs between continuous printing, and of course, a large beam spot position deviation occurs when the number of continuous printing is large. To do. Further, the scanning imaging lens close to the polygon mirror often has a strong power, and therefore, the beam spot position shift fluctuation caused by the refractive index and the surface shape change due to the influence of heat is large.

  As described above, the primary cause of the fluctuation of the beam spot position that occurs at the time of fluctuation such as temperature fluctuation is heat generation of the polygon mirror. Therefore, it is very useful to provide a temperature detection means, and it is good to detect the heat generation amount of the polygon mirror, the temperature of the scanning imaging lens closest to the polygon mirror, and the scanning imaging lens with the highest power, It is preferable to correct the variation of the beam spot position based on the detection result. Further, a relative beam spot position shift between the respective colors may be corrected based on the temperature detection result.

  Since the heat generation of the polygon mirror becomes larger as the driving time becomes longer, the driving time may be detected instead of the temperature.

  Although the polygon mirror has been described as an example of the optical deflector, the same applies when an optical deflector such as a galvano mirror is used. Further, a relative beam spot position shift between the colors may be corrected based on the driving time detection result.

  As described above, even if the beam spot position shift does not occur at the beginning of continuous printing, the beam spot position shift gradually occurs between continuous prints due to the influence of the heat and air flow of the polygon mirror. However, a large beam spot position deviation occurs when the number of continuous prints is large.

Therefore, the correction of the beam spot position deviation is preferably performed at “invalid area at the time of continuous printing”, for example, between papers at the time of continuous printing. It may also be performed between print jobs.
Next, an image forming apparatus provided with the optical scanning device will be described. An example of the image forming apparatus will be described using a laser printer shown in FIG.

  The laser printer 100 has a “cylindrical photoconductive photosensitive member” as the latent image carrier 111. Around the latent image carrier 111, a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are provided. A “corona charger” can also be used as the charging means. Further, an optical scanning device 117 that performs optical scanning with the laser beam LB is provided, and “exposure by optical writing” is performed between the charging roller 112 and the developing device 113. The light source (not shown) in the optical scanning device 117 has means for changing the cycle of the pixel clock as described above.

  In FIG. 7, 116 is a fixing device, 118 is a cassette, 119 is a registration roller pair, 120 is a paper feed roller, 121 is a conveyance path, 122 is a paper discharge roller pair, 123 is a tray, and P is a transfer sheet as a recording medium. Show.

  When forming an image, the image carrier 111, which is a photoconductive photosensitive member, is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 112, and the optical beam of the laser beam LB of the optical scanning device 117 is written. An electrostatic latent image is formed upon exposure to the image. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. This electrostatic latent image is reversely developed by the developing device 113, and a toner image is formed on the image carrier 111.

  The cassette 118 storing the transfer paper P is detachable from the main body of the image forming apparatus 100. When the transfer paper P is mounted as shown in the drawing, the uppermost sheet of the stored transfer paper P is fed by the paper supply roller 120. The leading edge of the fed transfer paper P is caught by the registration roller pair 119. The registration roller pair 119 feeds the transfer paper P to the transfer unit at the timing when the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114. The transfer paper P to which the toner image is transferred is sent to the fixing device 116, where the toner image is fixed by the fixing device 116, passes through the conveyance path 121, and is discharged onto the tray 123 by the discharge roller pair 122. The surface of the image carrier 111 after the toner image has been transferred is cleaned by a cleaning device 115 to remove residual toner, paper dust, and the like.

  5. An image forming apparatus that forms a latent image on the latent image carrier 111 by optical scanning and visualizes the latent image to obtain a desired recorded image, and is an optical scanning device that optically scans the latent image carrier 111. The latent image carrier 111 is a photoconductive photosensitive member, and an electrostatic latent image is formed by uniform charging and optical scanning, and the formed electrostatic latent image is used. Is visualized as a toner image.

  The optical scanning device of the image forming apparatus is the optical scanning device of the present invention, and each optical scanning device detects or predicts a variation in beam spot position deviation that occurs when a temporal variation such as a temperature variation occurs, and based on the detection or prediction result. Thus, the fluctuation of the beam spot position deviation is corrected. With such a configuration, a high-quality image without image distortion or the like can be obtained even when the temperature changes or the like changes with time.

  In the present invention, it is also possible to correct fluctuations in the beam spot position deviation by drawing a toner pattern and detecting it. However, as the number of times of toner pattern drawing increases, the amount of toner consumption increases accordingly, which adversely affects the environment. Therefore, it is desirable to reduce the amount of toner consumption by using the beam spot position deviation predicting means at the time of fluctuation with time.

  Hereinafter, a color image forming apparatus including a plurality of the optical scanning devices will be described. FIG. 11 shows a tandem type full color laser printer to which the present invention is applied.

  A conveying belt 2 is provided on the lower side of the apparatus so as to convey transfer paper (not shown) fed from the sheet feeding cassette 1 in the horizontal direction. On the conveying belt 2, a photosensitive body 3Y for yellow Y, a photosensitive body 3M for magenta M, a photosensitive body 3C for cyan C, and a photosensitive body 3K for black K are sequentially arranged at equal intervals from the upstream side. Yes. In the following, the subscripts Y, M, C, and K are appropriately added for distinction. These photoreceptors 3Y, 3M, 3C, and 3K are all formed to have the same diameter, and process members are sequentially disposed around the photoreceptors in accordance with an electrophotographic process. Taking the photoconductor 3Y as an example, a charging charger 4Y, an optical scanning optical system 5Y, a developing device 6Y, a transfer charger 7Y, a cleaning device 8Y, and the like are sequentially arranged. The same applies to the other photoconductors 3M, 3C, 3K. That is, in the present embodiment, the photoconductors 3Y, 3M, 3C, and 3K are irradiated surfaces set for the respective colors, and one optical scanning optical system 5Y, 5M, 5C, and 5K is provided for each. They are provided in a one-to-one correspondence.

  In addition, a registration roller 9 and a belt charging charger 10 are provided around the transport belt 2 on the upstream side of the photoconductor 5Y, and a belt separation charger 11 is provided on the downstream side of the photoconductor 5K. A static elimination charger 12, a cleaning device 13, and the like are provided in this order. Further, a fixing device 14 is provided on the downstream side of the belt separating charger 11 in the transport direction, and is connected to a paper discharge tray 15 by a paper discharge roller 16.

  In such a schematic configuration, for example, in the case of the full color mode (multiple color mode), each of the photoreceptors 3Y, 3M, 3C, and 3K is based on the image signals of the colors Y, M, C, and K, respectively. An electrostatic latent image is formed by optical scanning of the light beam by the optical scanning devices 5Y, 5M, 5C, and 5K. These electrostatic latent images are developed with the corresponding color toners to form toner images, which are superposed by being sequentially transferred onto transfer paper that is electrostatically attracted onto the transport belt 2 and transported. After being fixed as an image, it is discharged.

  An image in which high-quality image reproducibility can be secured without color misregistration by using the optical scanning device provided with the optical scanning optical systems 5Y, 5M, 5C, and 5K of the image forming device as the optical scanning device of the present invention. A forming apparatus can be realized.

  An optical scanning device in this image forming apparatus includes a beam spot position correcting unit capable of correcting the density of beam spot position intervals, and a unit for detecting or predicting a relative beam spot position deviation of each color image with respect to a reference color image have. By detecting or predicting the relative beam spot position deviation of each color image with respect to the reference color image, the relative beam spot position deviation of each color image with respect to the reference color is detected or predicted, and based on the detection or prediction result, It is possible to correct a relative beam spot position shift of each color image with respect to the reference color image. By adopting such a configuration, it is possible to correct a relative beam spot position deviation between colors even when temperature changes and the like with time, and even in situations where temperature fluctuations occur during continuous printing or the like. An image forming apparatus capable of obtaining a high-quality image with little color misregistration can be provided.

  In the present invention, it is also possible to correct relative beam spot position deviation by drawing a toner pattern and detecting it. However, as the number of times of toner pattern drawing increases, the amount of toner consumption increases accordingly, which adversely affects the environment. Therefore, it is desirable to reduce the toner consumption amount by using the beam spot position deviation predicting means at the time of fluctuation with time.

  As an alternative means for predicting the relative beam spot position deviation between each color at the time of fluctuation such as temperature fluctuation, at least one light detection means is provided, and the detection result by the light detection means is obtained between each color. By comparing, it is possible to correct a relative beam spot position shift between the colors. This will be described with reference to FIG.

  As an example, let us consider correcting the relative displacement between the beam spot position on the image carrier developed with magenta and the beam spot position on the image carrier developed with cyan. PDM is a photodiode for detecting a light beam guided on an image carrier to be developed with magenta, and PDC is a photodiode for detecting a light beam guided on an image carrier to be developed with cyan.

  Initially, the light beams detected by the PDM and the PDC are both solid lines, but the scanning characteristics vary depending on the colors due to temporal changes such as temperature fluctuations. The light beams detected by the PDM are dotted lines and PDCs. It is assumed that the light beam represented by 変 化 changes like a one-dot chain line. At this time, even if the writing position is adjusted between the colors by adjusting the writing position of the image, the density of the beam spot position occurs at the center image height, and the amount of the generated density and the generation position are between the colors (for example, Different between cyan and magenta). Therefore, a correction method that can correct the density of the beam spot position interval is essential.

  Here, the time difference between the signals detected by the PDM and the PDC was initially a certain time difference t0, but after the time change such as the temperature change, the time difference between the signals detected by the PDM and the PDC changes from the time t0. . Therefore, when there is a difference in the change in optical characteristics between cyan and magenta, the time difference between the signals detected by the PDM and PDC changes from the initial time difference t0.

  As described above, if the relationship between the time difference between the colors of the signal detected by the photodiode and the relative fluctuation amount between the colors of the beam spot positions between the colors is examined in advance, the temporal change of the temperature fluctuation or the like can be obtained. It is possible to correct a relative beam spot position shift between the colors at the time of change.

  When a relative beam spot position shift occurs between the colors due to temporal fluctuations such as temperature fluctuations, the image writing is first performed by adjusting the time of the scanning start timing signal input to each LD corresponding to each color. Adjust the position so that the colors are almost the same. Thereafter, the image width is corrected between the respective colors by means for substantially matching the image width so that the image writing end positions are approximately the same between the respective colors. This correction may be performed by changing the frequency of the pixel clock, or the image width may be corrected by applying the correction described in FIGS. 5B and 5C to the entire effective scanning region. These two methods may be used in combination.

  After the writing position and the writing end position coincide, the density of the beam spot positions may be corrected at the intermediate image height so that there is no relative beam spot position shift between the colors. However, when correcting the density of the beam spot position interval at the intermediate image height, it is necessary to set correction data so that the writing end position does not change.

  By using such a method, it is possible to make the start position and end position of the image coincide with each other with very high accuracy, so that it is easy to perform relative beam spot position correction even at intermediate image heights, and high accuracy correction. Is possible. Furthermore, if the image writing position and the writing end position coincide with each other with high accuracy, the relative beam spot position shift amount to be corrected with the intermediate image height can be small, so even with the intermediate image height with high accuracy. As a result, it is possible to obtain a high-quality image with little color shift over the entire image.

  When a relative beam spot position shift occurs between the colors due to temporal fluctuations such as temperature fluctuations, the image writing is first performed by adjusting the time of the scanning start timing signal input to each LD corresponding to each color. The positions are adjusted so that the colors substantially coincide with each other, and then the density of the beam spot positions is corrected for each color so that the beam spot position shift between the colors is reduced at the intermediate image height. At that time, the variation of the image width or the shift of the image width between the colors can be corrected by devising the setting of the phase data so that the change of the image width or the shift of the image width between the colors is corrected. As information for correcting the density of the beam spot position interval, it is preferable to obtain correction data from the prediction result by the above-described prediction means.

  Such a correction method can be executed with a simple algorithm, can reduce expensive photodetection means such as expensive photodiodes, and can reduce the beam spot position deviation between the colors. A high-quality image with little deviation can be obtained.

  In the output image, the direction toward one end is defined as positive, and the direction toward the other end is defined as negative. When light beams from a plurality of light sources are deflected in the same direction by the optical deflector, a temperature distribution difference as shown in FIG. 9A is generated above and below the sub-scanning direction of the scanning lens closest to the optical deflector. Cheap. When such a temperature distribution difference occurs, when the image writing position and writing end position are aligned, the vicinity of the center image height is not easily affected, but the image heights on both sides cause beam spot position shifts that are opposite to each other. Also, the positional deviation amount tends to be symmetric with respect to the vicinity of the center image height. In such a case, the beam spot position is corrected so that the correction direction is reversed at the image heights on both sides centered around the center image height, and the correction amount is set to be approximately symmetrical with respect to the center. It is good to do it (FIG. 9B).

  In the output image, the direction toward one end is defined as positive, and the direction toward the other end is defined as negative. As shown in FIG. 1, when deflecting light beams from a plurality of light sources in directions opposite to each other with respect to the optical deflector, in the scanning lens closest to the optical deflector, as shown in FIG. Temperature distribution is likely to occur. When such a temperature distribution occurs, when the image writing position and the image writing end position are aligned, the beam spot position deviation amount is the largest near the center image height, and the beam spot position deviation direction extends over the entire image height. It tends to occur in the same direction (same code). In such a case, it is preferable that the beam spot position correction direction is the same over the entire image height, and that the correction amount is maximized in the vicinity of the center image height (FIG. 10B). ).

An embodiment in which the optical scanning device of the present invention is applied to a 4-drum tandem color image forming apparatus will be described. 1 shows a configuration of a pixel clock generation circuit. FIG. 3 is a timing chart for explaining the operation of FIG. 2. FIG. 3 is another timing diagram for explaining the operation of FIG. 2. It is a figure explaining the method which divides | segments a scanning area | region into a some area and corrects the density of the beam spot position interval for every division | segmentation area. This shows how the density of the beam spot position interval can be corrected. 1 shows a laser printer equipped with an optical scanning device. It is a figure explaining the correction | amendment of the relative beam spot position shift between each color. An example of beam spot position correction will be described. Another example of beam spot position deviation correction will be described. 1 shows a tandem type full color laser printer to which the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Coupling lens 3 Cylindrical lens 4 Polygon mirror 5, 6 Scan imaging lens 7 Scanning surface

Claims (17)

  In an optical scanning apparatus that scans a light beam from a light source with an optical deflector and focuses it on a scanned surface by a scanning imaging optical system, the density of beam spot positions along the main scanning direction on the scanned surface is reduced. Beam spot position correcting means capable of correcting, storage means for storing information for correcting the density of the beam spot position intervals, means for detecting or predicting fluctuations in the beam spot position, and The storage means can be rewritten, and the information stored in the storage means is rewritten based on the result obtained by the means for detecting or predicting the fluctuation of the beam spot position, thereby correcting the fluctuation of the beam spot position. An optical scanning device.   2. The optical scanning device according to claim 1, wherein the beam spot position correcting unit divides the scanning region into a plurality of sections and corrects the density of the beam spot position intervals for each of the divided sections. .   3. The optical scanning device according to claim 2, wherein the divided section is set by dividing a scanning region at different intervals.   The optical scanning device according to claim 1, wherein the beam spot position correcting unit corrects the density of the beam spot position interval by changing the period of the pixel clock based on phase data indicating the transition timing of the pixel clock. And at least the phase data is stored in the storage means.   2. The optical scanning device according to claim 1, wherein the means for detecting or predicting the fluctuation of the beam spot position includes at least two light detection means along a main scanning direction for detecting a light beam from the light source, An optical scanning device characterized in that the scanning is performed by detecting a scanning time between the light detection means.   6. The optical scanning device according to claim 5, wherein the light detection means is shared among a plurality of light beams deflected in the same direction by at least an optical deflector.   2. The optical scanning device according to claim 1, wherein the means for detecting or predicting the fluctuation of the beam spot position is provided with a temperature detecting means and detecting the temperature in the optical scanning device. apparatus.   2. The optical scanning device according to claim 1, wherein the means for detecting or predicting the fluctuation of the beam spot position includes means for measuring the driving time of the optical deflector and detecting the driving time of the optical deflector. An optical scanning device.   2. The optical scanning device according to claim 1, wherein the correction of the beam spot position is performed in an ineffective area during continuous printing or between a print job and a print job.   An image forming apparatus comprising: the optical scanning device according to claim 1; a developing unit that visualizes an electrostatic image with toner; and a transfer unit that forms a visualized image. An image forming apparatus characterized in that, based on a result obtained by the means for detecting or predicting the fluctuation of the beam spot position, the information stored in the storage means is rewritten to correct the fluctuation of the beam spot position. .   A plurality of optical scanning devices according to any one of claims 1 to 9, wherein a developing unit that visualizes an electrostatic image with toner of each color and a color image obtained by superimposing the visualized color images In a multicolor image forming apparatus having a transfer means for forming, a reference color image is rewritten based on the result obtained by the means for detecting or predicting the fluctuation of the beam spot position, and the information stored in the storage means is rewritten. A multi-color image forming apparatus for correcting a shift of a relative beam spot position of each color image with respect to.   The multicolor image forming apparatus according to claim 11, further comprising at least one light detection unit that detects light beams from the plurality of light sources, and a time difference at which the plurality of light beams are detected by the light detection unit, A multicolor image forming apparatus for correcting a shift of a relative beam spot position between colors.   13. The multicolor image forming apparatus according to claim 12, wherein the light detection means is shared by a plurality of light beams deflected in the same direction by at least an optical deflector.   12. The multicolor image forming apparatus according to claim 11, wherein means for substantially matching an image writing position between each color and means for substantially matching an image width so that an image writing end position between each color substantially matches. A multicolor image forming apparatus comprising:   12. The multicolor image forming apparatus according to claim 11, further comprising means for roughly aligning an image writing position between each color, correcting a relative beam spot position deviation between each color, A multicolor image forming apparatus characterized in that a beam spot position correction amount at each image height is adjusted and information stored in the storage means is set so that an image width shift between colors is corrected.   12. The multicolor image forming apparatus according to claim 11, wherein a direction toward one end of the output image is defined as positive, and a direction toward the other is defined as negative, and a sign of a beam spot position correction direction is defined near the center image height. Inverting and adjusting the beam spot position correction amount at each image height so that the correction amount is substantially symmetrical around the center image height, and setting the information stored in the storage means Multicolor image forming apparatus.   12. The multicolor image forming apparatus according to claim 11, wherein a direction toward one end in the output image is defined as positive, and a direction toward the other is defined as negative, and a beam spot position correction direction is over the entire image height. The information stored in the storage means is set by adjusting the beam spot position correction amount at each image height so that the correction amount is the same direction and the correction amount is the largest in the vicinity of the central image height and decreases as the peripheral image height increases. A multicolor image forming apparatus.

Images