JP2005231090A - Method for correcting beam spot position, optical scanner, and multicolor image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct the density of beam spot positions with high degree of accuracy by using a simple algorithm. <P>SOLUTION: A case (a) indicates the beam spot positions before correction, which are deviated from positions of dotted lines (drawn at regular intervals). A case (b) indicates a case wherein intervals among the beam spot positions are made shorter so as to be regular intervals. The interval between the beam spot positions at both ends of a section is made shorter, so that the spot beam positions can be wholly made denser. A case (c) indicates a case wherein the intervals among the beam spot positions are made longer so as to be regular intervals. The widths of the sections are made greater at regular intervals, so that the spot beam positions can be wholly made sparser. This makes the density of the beam spot positions corrected with high degree of accuracy. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a beam spot position correcting method for a digital copying machine, a laser printer, a laser facsimile, and the like, and an optical scanning device and a multicolor image forming apparatus using the beam spot position correcting method.

  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, the scanning speed cannot be made completely constant, and “scanning speed unevenness” occurs, and it is desirable that the beam spot position interval is preferably equal. Density occurs. Furthermore, the density of the beam spot position interval increases due to manufacturing errors of the fθ lens.

  When the density of the beam spot positions is uneven, the image is distorted and the image quality is deteriorated. Further, in the case of a color image forming apparatus, since a plurality of fθ lenses are used, due to the influence of manufacturing errors of the fθ lens and the like, the density of beam spot position intervals that differ depending on colors occurs, resulting in color shift. Arise.

  As a technique for correcting the density of the beam spot position interval, 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). 1-3).

Japanese Patent Laid-Open No. 11-167081 JP 2001-228415 A JP 2003-98465 A

  However, the conventional method (frequency modulation method) that changes the frequency of the pixel clock generally has a complicated configuration of the pixel clock control unit, and increases as the frequency modulation width becomes minute, so fine control cannot be performed. Therefore, there is a problem that the beam spot position cannot be corrected with high accuracy. In addition, there is a problem that an algorithm for obtaining correction data necessary for correction is very complicated.

  An object of the present invention is to provide a beam spot position correction method capable of correcting the density of beam spot position intervals with a simple algorithm and with high accuracy.

  Another object of the present invention is to provide an optical scanning device capable of high-precision optical scanning.

  Another object of the present invention is to provide a multicolor image forming apparatus capable of providing a high-quality color image with little color misregistration.

  The present invention relates to a beam spot position correction method in an optical scanning apparatus that scans a surface to be scanned with a light beam from a light source, and divides the scanning area on the surface to be scanned into a plurality of sections and supports both ends of each section. The most important thing is to adjust the light beam emission timing for each of the sections so that the interval between the beam spot positions of the pixels to be changed changes by a predetermined amount, and to correct the density of the beam spot positions in the entire scanning region. Features.

  By using the present invention (claim 1), the density of the beam spot position interval on the non-scanning surface can be realized by a highly accurate and simple algorithm, and further, the complexity of the circuit can be prevented.

  By using the present invention (Claim 2), it is possible to prevent the circuit from becoming complicated and to achieve both simplification of the correction algorithm and correction accuracy.

  By using the present invention (Claim 3), it is possible to realize highly accurate beam spot position deviation correction not only at both ends of the section but also at the center of the section.

  By using the present invention (Claim 4), it is possible to improve the beam spot position deviation correction accuracy.

  By using the present invention (Claim 5), the density of the beam spot position interval on the non-scanning surface can be realized by a highly accurate and simple algorithm, and further, the complexity of the circuit can be prevented.

  By using the present invention (Claim 6), the amount of memory can be reduced, and the cost can be significantly reduced.

  By using the present invention (Claim 7), it is possible to reduce costs while preventing a reduction in correction accuracy.

  By using the present invention (claim 8), it is possible to provide an optical scanning device capable of performing high-precision optical scanning.

  By using the present invention (claim 9), it is possible to provide a multi-color image forming apparatus for high-quality color images with little color misregistration.

  By using the present invention (claim 10), correction can be performed specifically for color shift reduction, so that a high-quality color image with little color shift can be provided.

  By using the present invention (claim 11), the adjustment process can be simplified, and a high-quality color image with little color shift can be provided at low cost.

  By using the present invention (claim 12), even when a large density occurs in the interval between the beam spot positions corresponding to the reference color due to the influence of a manufacturing error or the like, the color misregistration correction can be performed with high accuracy. This makes it possible to provide a high-quality color image with little color misregistration.

  By using the present invention (Claim 13), it is possible to perform color misregistration correction with high accuracy even when a large density occurs in the interval between the beam spot positions due to the influence of manufacturing errors and the like, and there is little color misregistration. A high-quality color image can be provided.

  By using the present invention (claim 14), the adjustment process can be simplified while preventing a reduction in correction accuracy, and the cost can be reduced.

  By using the present invention (Claim 15), the number of divisions can be minimized, and high-precision beam spot position shift correction can be performed at low cost, and a high-quality color image with little color shift is provided. be able to.

  By using the present invention (claims 16 and 17), it is possible to effectively correct the beam spot position deviation, and it is possible to provide a high-quality color image with little color deviation.

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

  The present invention will be described with reference to FIG. First, consider one section. FIG. 1A shows the beam spot position before correction. The intervals between the dotted lines are equal, and the beam spot position is preferably located on this dotted line. However, the beam spot position is not usually on the dotted line due to the reasons described above. In FIG. 1A, the beam spot position is drawn so as to be on the dotted line, but this is for simplification of the description. Originally, the beam spot position before correction is not on the dotted line. It is necessary to correct the deviation from the dotted line. FIG. 1B is a diagram illustrating a case where the beam spot position interval is reduced at equal intervals. It can be seen that the width of the section defined by the beam spot position interval at both ends of the section is reduced (they are dense as a whole). FIG. 1C is a diagram showing a case where the beam spot position interval is enlarged at equal intervals. It can be seen that the width of the section is enlarged at equal intervals (sparse as a whole). FIGS. 1 (d) and 1 (e) schematically show displacements from the dotted line, respectively FIG. 1 (b) and FIG. 1 (c). Here, the position shift shifted to the right side on the paper surface is positive, and the position shift shifted to the left side is negative. The inclination of each straight line is determined by the amount by which the beam spot position interval is reduced (enlarged). When the beam spot position interval is greatly reduced (enlarged), the inclination of the straight line becomes steep.

  Next, consider a combination of a plurality of sections. The solid line in FIG. 2 indicates the beam spot position deviation before correction. Sections 1 and 3 are close to the state of FIG. 1C and are generally sparse areas, and sections 2 and 4 are close to the state of FIG. 1B and are generally dense areas. By combining the states of FIG. 1B and FIG. 1C and appropriately changing the amount of reduction (enlargement) of the beam spot position interval, it is possible to perform correction as shown by a one-dot chain line in FIG. The state before correction indicated by the solid line can be corrected like the state indicated by the dotted line. That is, by using the present invention, the density of the beam spot position interval can be corrected with high accuracy.

  Furthermore, since the present invention performs correction separately for each section, there is an advantage that correction data can be easily created and a correction algorithm is simple. The fact that correction data is easy to create means that errors are less likely to occur when generating correction data, so that it is possible to correct the density of beam spot position intervals with higher accuracy.

  In FIGS. 1B and 1C, the beam spot position interval is changed so as to be quadratic, cubic, etc. on the graph instead of being reduced (enlarged) at equal intervals. It is possible to correct with higher accuracy. However, there are disadvantages such that the correction algorithm becomes complicated, the circuit becomes complicated, and it takes time to create correction data at the time of factory shipment, resulting in an increase in cost. In order to improve the correction accuracy, it is also possible to implement a method of taking a section finely. Therefore, within the section, the beam spot position interval is reduced or expanded at an interval that can be regarded as an equal interval, so that high accuracy and low cost are achieved. It is better to make the correction and simplification of the correction algorithm compatible.

  Further, as shown in FIG. 7, a method of changing the beam spot position interval at regular intervals may be adopted (FIG. 7 shows the case where the beam spot position interval is changed every other pixel. The distance between the neighbors has changed). In such a case, when expressed in a graph, what changed linearly in FIG. 2 changes in a staircase pattern in FIG. However, since it can be regarded as a straight line when viewed macroscopically, it can be regarded as being enlarged or reduced at an interval that can be regarded as an equal interval. Therefore, the beam spot position interval may be changed at regular intervals as shown in FIG. And are included in the scope of the present invention. Further, the places where the beam spot position interval is changed are included in the scope of the present invention even when they are arranged randomly rather than at regular intervals.

  By making the beam spot position deviation with respect to the target substantially zero at both ends of each section, the beam spot position can be brought close to the target even in the middle of the section, and high-precision correction is possible.

  As described above, when the scanning area is divided into a plurality of sections, it is preferable to divide the scanning area with different widths. For example, when a beam spot position shift as shown by a solid line in FIG. 3 occurs, the interval between the beam spot positions is such that a section is widened in a region close to a straight line and a section is narrowed in a region where a curve is bent. Since the width of the divided section can be made variable depending on the density generation state, the density of the beam spot position interval can be effectively corrected, and the correction accuracy can be improved even with the same number of divisions.

  FIGS. 4, 5 and 6 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. 4, 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. 4 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. 5A shows how a standard pixel clock PCLK with a duty ratio of 50% corresponding to VCLK divided by 8 is generated, and FIG. 5B shows only 1/8 clock with respect to VCLK divided by 8 clock. FIG. 5C shows a state in which the phase-advanced PCLK is generated, and FIG. 5C shows a state in which a PCLK clock whose phase is delayed by 1/8 clock with respect to the VCLK divided by 8 is generated.

  First, FIG. 5A 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. 5A, 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. 5A, 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. 5B 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. As a result, as shown in FIG. 5B, 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. 5C 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. 5C, it is possible to generate the pixel clock PCLK whose phase is delayed by 1/8 clock with respect to the divided frequency 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. 6 is a timing chart 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, that is, the beam spot position can be corrected.

  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.

  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, it is preferable to perform phase shifts at regular intervals, which can greatly reduce the memory.

  Note that 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.

  As the number of divisions is increased, the correction accuracy is improved. However, if the number of divisions is increased, the amount of memory increases as the number of divisions is increased, resulting in an increase in cost. Even if the number of divisions is increased beyond a certain level, the correction accuracy is hardly improved, and in any case, if it is 15 divisions, it can be corrected to an allowable amount. Therefore, the number of divisions should be set to 15 divisions or less, and the cost can be reduced by reducing the memory amount while preventing the correction accuracy from being lowered.

  FIG. 8 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. 8A shows a state where the optical arrangement of the optical scanning device is viewed from the sub-scanning direction, and FIG. 8B 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. 8A, laser light sources 1Y to 1K are “semiconductor lasers” and are visualized with “color toners of yellow (Y), magenta (M), cyan (C), and black (K), respectively. A light beam is emitted to write an “electrostatic latent image”. 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. Although FIG. 8 shows a diagram in which yellow (Y) and black (K) are scanned in the same direction and cyan (C) and magenta (M) are scanned in the same direction, this combination may be changed.

  The polygon mirror 4 has six deflection reflection surfaces. In FIG. 8, it is drawn as “each deflection reflection surface is a single reflection surface in the rotation axis direction”. A portion in which a groove is formed so as to be “slightly smaller in diameter than the inscribed circle of the polygon mirror 4” may be used in the portion between the light beams that is not 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. 8A and 8B, 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. 8 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 above-described embodiment, the light beam from each laser light source is converted into a parallel light beam by the coupling lens. Thus, the optical scanning optical system can also be configured. Furthermore, the present invention is provided with a beam spot position correcting means capable of correcting the density of the beam spot position interval, and by the above-described beam spot position correction method, the density of the beam spot position interval can be determined with high accuracy and a simple algorithm. It can be corrected.

  Hereinafter, a color image forming apparatus including a plurality of the optical scanning devices will be described. FIG. 9 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.

  The optical scanning device in this image forming apparatus includes a beam spot position correcting unit capable of correcting the density of the beam spot position interval, and the above-described beam spot position correction method can accurately and accurately adjust the beam spot position interval. It can be corrected with a simple algorithm. Accordingly, it is possible to correct the color misregistration with high accuracy, and a high-quality image can be obtained.

  Furthermore, if the color misregistration is suppressed at the initial stage (at the time of shipment from the factory) by the beam spot position correcting means capable of correcting the density of the beam spot position interval, the color generated due to the influence of temporal variation such as temperature variation. Since the deviation can also be suppressed, the number of times of beam spot position correction by detecting the toner patch can be reduced. Therefore, the toner consumption can be reduced.

  In recent years, the required quality for color images has increased. In a color image, an important factor that affects quality is the absolute position of the beam spot (= corresponding to distortion of the image) and the relative position (= corresponding to color shift) between each color of the beam spot position. Of these two factors, the absolute position accuracy of the beam spot is low, except for some uses such as CAD drawing output. However, the relative position between each color of the beam spot position, that is, the color misregistration requires very high accuracy, and even a slight color misregistration is recognized. Therefore, it is very important to make corrections specifically for the relative positions (= corresponding to color shifts) between the colors of the beam spot positions in order to improve the quality of the color image.

  It is possible to correct both the absolute position of the beam spot and the relative position between each color by correcting the beam spot positions corresponding to each color so that they are aligned at equal intervals. In general, the amount of correction increases, and the density of the beam spot position interval becomes complicated, so that effective color misregistration is reduced from the viewpoint of color misregistration reduction. It's hard to say. In order to perform effective color misregistration correction, the main scanning beam spot position intervals of each color are not corrected at equal intervals, but the main scanning beam spot position corresponding to a certain color is used as a reference, It is preferable to correct the main scanning beam spot position corresponding to the color. Effective correction is possible by reducing the amount to be corrected by using the main scanning beam spot position corresponding to a certain color as a reference instead of making the main scanning beam spot position interval completely equal. As a result, color misregistration can be effectively reduced.

  It is desirable not to correct the above-mentioned main scanning beam spot position deviation corresponding to the color used as a reference for correction. By doing so, the adjustment process can be simplified and the cost can be reduced.

  However, as described above, if the main scanning beam spot position deviation corresponding to the reference color is not corrected, a large manufacturing error occurs in the optical scanning device or image forming apparatus corresponding to the reference color. Sometimes, color misregistration cannot be effectively reduced. In such a case, it is preferable to correct the main scanning beam spot position for the reference color. When correcting the main scanning beam spot position corresponding to the reference color, if the correction is performed so that the beam spot position interval is equal, the main scanning beam spot position corresponding to the color other than the reference is set to the reference. When the correction is performed, the correction amount becomes large and the density condition to be corrected becomes complicated, so that effective correction cannot be performed and color misregistration cannot be reduced effectively. Therefore, when correcting the main scanning beam spot position corresponding to the reference color, the correction is made not to make the beam spot position interval equal, but to leave a certain amount of density. Good to do. By doing so, when the beam spot position corresponding to a color other than the reference is corrected with respect to the reference, the correction amount can be reduced and the density of the beam spot position can be made relatively simple. Therefore, more effective correction can be performed, and color misregistration can be effectively reduced.

  As to what kind of density is corrected so as to remain, for example, it is preferable to set the density of the beam spot position interval already in design, the density of the beam spot position interval that is likely to occur in manufacturing, etc. .

As the order of correcting the beam spot position deviation, the color deviation can be effectively corrected by taking the following method. 1. Correction is performed so that the beam spot position corresponding to each pixel of the reference color becomes a preset target value.
2. Differences are corrected using the beam spot positions corresponding to the pixels of other colors as the target values of the beam spot positions of the reference color after the correction.

  In the formation of the scanning imaging lens, a similar manufacturing error often occurs. When the manufacturing error of the scanning imaging lens greatly contributes to the beam spot position deviation, the main scanning beam spot position deviation tends to be similar between the colors (FIG. 10). In such a case, even if the division position is set to be the same for all colors, substantially the same correction accuracy can be obtained as compared with the case where the division position is optimized and set for each color, and the adjustment process is simplified. The cost can be reduced.

  When correcting the beam spot position corresponding to each pixel with respect to the target or reference beam spot position, the difference from the target or reference beam spot position after performing the beam spot position correction as described above. Is defined as the beam spot position correction residual, it is preferable that the correction residual remains in the same level in each section.

As described above, when correcting the beam spot position corresponding to each pixel with respect to the target or reference beam spot position, it is desirable to perform correction by setting the division position so as to satisfy the following expression.
a1, a2, ....., an <Average (a1, a2, ....., an) × 2
However, a1, a2, ....., an represent the maximum value of correction residual in each interval (assumed to be absolute), and Average (a1, a2, ....., an) is a1, Indicates the average value of a2, ....., an.

  By satisfying the above formula, the correction residual in each section can be made equivalent in all sections. As a result, the number of divisions can be minimized, and a good beam spot position deviation can be achieved at low cost. Correction is possible. 13 and 14 show an embodiment in which the beam spot position deviation is corrected according to the present invention.

  In the characteristics of the beam spot position deviation defined by the difference between the beam spot position corresponding to each pixel and the target value or reference beam spot position with respect to the image height, extreme values (the beam spot position interval is sparse to dense). (Corresponding to changing places) is greatly related to the correction accuracy.

  If the number of extreme values and the number of divisions are about the same number, the beam spot position deviation with respect to the reference can be corrected most effectively by setting the division position near the image height where at least one of the extreme values is ( 11), it is possible to provide a high-quality color image with little color misregistration. The division position set near the extreme image height is desirably set within about ± 8 mm from the extreme image height. By setting the division position, it is possible to suppress the color shift to an allowable level. This makes it possible to provide a high-quality color image.

  FIG. 13 shows a first example in which the beam spot position deviation is corrected according to the present invention. The beam spot position deviation with respect to the target was 71 μm before the correction, but was reduced to 14 μm after the correction, thereby providing a high-quality image.

  In addition, when the number of divisions is set to be larger than the number of extreme values, the image height including the extreme image height and slightly shifted to both sides from the extreme image height is at both ends of the section. At least one section corresponding to is provided (FIG. 12). By setting the section in such a manner, the beam spot position shift can be effectively corrected.

  When setting the image height slightly shifted on both sides from the extreme image height at both ends of the section, it is preferable to set both ends of the section within ± 15 mm from the extreme image height. By doing so, it is possible to suppress the color shift to an acceptable level, and it is possible to provide a high-quality color image.

  FIG. 14 shows a second example in which the beam spot position deviation is corrected according to the present invention. The beam spot position deviation with respect to the target was 78 μm before the correction, but was reduced to 10 μm after the correction, thereby providing a high-quality image.

It is a figure explaining the correction method of the beam spot position (one section) of the present invention. It is a figure explaining the correction method of the beam spot position (a plurality of sections) of the present invention. It is a figure explaining other correction methods of a beam spot position (a plurality of sections) of the present invention. 1 shows a configuration of a pixel clock generation circuit. FIG. 5 is a timing chart for explaining the operation of FIG. 4. FIG. 5 is another timing chart for explaining the operation of FIG. 4. A method of changing the beam spot position interval at regular intervals according to the present invention will be described. 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 tandem type full color laser printer to which the present invention is applied. A tendency of positional deviation of the main scanning beam spot between the colors is shown. An example of correcting the beam spot position deviation with respect to the reference will be shown. Another example of correcting the beam spot position deviation with respect to the reference will be shown. An example of beam spot position deviation before and after correction is shown. Another example of beam spot position deviation before and after correction is shown.

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 a beam spot position correction method in an optical scanning device that scans a surface to be scanned with a light beam from a light source, a scanning region on the surface to be scanned is divided into a plurality of sections, and a beam of pixels corresponding to both ends of each section The beam spot position is characterized by adjusting the light emission timing of the light beam for each of the sections so that the spot position interval changes by a predetermined amount and correcting the density of the beam spot position interval in the entire scanning region. Correction method.   2. The beam spot position correcting method according to claim 1, wherein an interval between beam spot positions corresponding to each pixel in the section is reduced or enlarged at an interval that can be regarded as an equal interval or an approximately equal interval. Position correction method.   2. The beam spot position correcting method according to claim 1, wherein correction is performed so that a deviation of a beam spot position corresponding to pixels at both ends of each section with respect to a preset target value is substantially zero. Beam spot position correction method.   2. The beam spot position correcting method according to claim 1, wherein the scanning area is divided into different widths.   2. The beam spot position correction method according to claim 1, wherein the light emission timing of the light beam is adjusted by shifting a phase of a pixel clock signal based on phase data indicating a transition timing of the pixel clock. The beam spot position correction method.   6. The beam spot position correction method according to claim 5, wherein intervals between pixels for shifting the phase in the section are set to be substantially equal.   2. The beam spot position correcting method according to claim 1, wherein the number of divisions in the effective scanning region is 15 or less.   A light source, an optical deflector that scans the light beam from the light source, a scanning imaging optical system that collects the light beam, and a beam spot position correction capable of correcting the density of the beam spot position on the scanned surface 8. An optical scanning device comprising: a beam spot position correcting method according to claim 1 as the beam spot position correcting unit.   9. A plurality of optical scanning devices according to claim 8, comprising at least developing means for visualizing an electrostatic image with toner of each color and transfer means for forming a color image by superimposing the visualized color images. A multicolor image forming apparatus.   10. The multicolor image forming apparatus according to claim 9, wherein a beam spot position corresponding to each pixel of a reference color is set as a target value, and beam spot positions corresponding to other colors are corrected. Color image forming apparatus.   11. The multicolor image forming apparatus according to claim 10, wherein the beam spot position corresponding to the reference color does not correct the beam spot position.   11. The multicolor image forming apparatus according to claim 10, wherein a target value is determined for a beam spot position corresponding to the reference color so that a certain amount of density is maintained at an interval between the beam spot positions corresponding to each pixel. A multicolor image forming apparatus that performs correction. 13. The multicolor image forming apparatus according to claim 12, wherein the beam spot position is corrected in the following order.
1. Correction is performed so that the beam spot position corresponding to each pixel of the reference color becomes a preset target value.
2. Differences are corrected using the beam spot positions corresponding to the pixels of other colors as the target values of the beam spot positions of the reference color after the correction.   14. The multicolor image forming apparatus according to claim 9, wherein the division positions are the same in a plurality of colors. 14. The multi-color image forming apparatus according to claim 9, wherein a maximum value of a beam spot position correction residual in each section when correcting a target or reference beam spot position. A multicolor image forming apparatus satisfying the following relationship when a1, a2,..., An (absolute value) are satisfied.
a1, a2, ....., an <Average (a1, a2, ....., an) × 2
However, Average (a1, a2, ....., an) represents the average value of a1, a2, ....., an.   14. The multicolor image forming apparatus according to claim 9, wherein a beam spot position deviation defined by a difference between a beam spot position corresponding to each pixel and a target or reference beam spot position is determined. A multicolor image forming apparatus characterized in that at least one portion is divided in the vicinity of an image height that is an extreme value in the characteristics with respect to the image height.   14. The multicolor image forming apparatus according to claim 9, wherein a beam spot position deviation defined by a difference between a beam spot position corresponding to each pixel and a target or reference beam spot position is determined. A multicolor image characterized by providing at least one section that includes an image height that is an extreme value and has an image height slightly deviated on both sides of the image height that is an extreme value in characteristics with respect to the image height. Forming equipment.

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