JP4582782B2 - Multicolor image forming apparatus and color misregistration correction method - Google Patents

Description

  The present invention relates to a multicolor image forming apparatus used in a digital copying machine, a laser printer, a laser facsimile, and the like, and more particularly, to a color misregistration correction method in a multicolor image forming apparatus.

  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 an optical deflector, a polygon scanner whose deflection surface rotates at an equal angular velocity, a galvano mirror whose polarization plane vibrates, and the like are generally used. When a light source such as a semiconductor laser is modulated at a certain frequency and an optical scanning device is configured using the above optical deflector, and the surface to be scanned such as a photoconductor is optically scanned, the beam spot positions are equally spaced. The scanning speed is not constant. Therefore, in order to perform optical scanning with the beam spot positions arranged at equal intervals and with a constant scanning speed, the scanning speed is corrected by using a scanning imaging optical system such as an fθ lens. Can be scanned at a constant speed. However, there is a limit to the correction of the scanning speed using an fθ lens or the like, and the beam spot position interval cannot be made completely equal on the surface to be scanned, and the density of the beam spot position interval remains.

  If the density remains in the beam spot position interval, the image is distorted and the image quality is deteriorated. 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 correction method capable of adjusting the density of the beam spot positions, for example, as described in Patent Documents 1 and 2, a method of correcting the beam spot position along the scanning line by basically changing the frequency of the pixel clock. It has been known. Further, as another correction method capable of increasing or decreasing the beam spot position interval, as described in Patent Documents 3 and 4, beam spot position correction for correcting the main scanning beam spot position deviation by changing the phase of the pixel clock. The method is known. By forming an image using these beam spot position correction methods, a color image can be obtained in which the density of beam spot position intervals is small and there is almost no color shift.

  Furthermore, as described in Patent Document 5, there is a method of correcting color misregistration by specifying the correction mode to correct the density of the beam spot position interval.

Japanese Patent Laid-Open No. 11-167081 JP 2001-228415 A JP 2003-98465 A JP 2004-98590 A JP 2004-098591 A

  However, even if the color misregistration correction by the above-mentioned density correction of the beam spot position interval is performed at the time of shipment from the factory, the color misregistration occurs due to a change in the installation environment, an unexpected impact, or the like. Also, when replacing the optical scanning device, it is necessary to perform density correction of the beam spot position interval different from that before the replacement. Occurrence of the density of the beam spot position interval is complicated and shows different occurrences depending on the environment and impact. Therefore, in the method of specifying the correction mode described in Patent Document 5, it is almost impossible to perform color misregistration correction in every scene, such as environmental change, impact, and replacement of an optical scanning device. Limited to some.

  An object of the present invention is to provide a multicolor image forming apparatus capable of effectively performing color misregistration correction for occurrence of color misregistration in every scene such as change in installation environment, unexpected impact, replacement of optical scanning device, and the like, and The object is to provide a color misregistration correction method.

The present invention relates to a light source, a plurality of optical scanning devices that scan a light beam from the light source and form an image on the image carrier, and an electrostatic image formed on the image carrier by the optical scanning device to each color toner. A multi-color image forming unit that has a developing unit that visualizes the image and a transfer unit that superimposes each color image visualized on the image carrier and transfers the image to a medium such as paper. In the apparatus, a color spot correction mode that includes beam spot position correction means for correcting the density of the beam spot position interval on the image carrier, and capable of correcting a color shift of any color with respect to at least a reference color, and the color A color misregistration measurement pattern output means for outputting a predetermined color misregistration measurement pattern in the misregistration correction mode, and measuring the color misregistration amount by visually measuring the output color misregistration measurement pattern, and A color misregistration correction amount input unit that inputs color misregistration correction information measured by a misregistration measurement pattern, and performs the color misregistration correction by the beam spot position correcting unit based on the color misregistration correction information. The color patterns are arranged so as to overlap in the color misregistration measurement direction for the reference color and the color for color misregistration correction, and are arranged at a plurality of locations in the color misregistration measurement direction. The main feature is that the color is different from the color to be subjected to color misregistration correction , one is equally spaced and the other is not equally spaced .

By using the present invention (Claim 1 ), it is possible to improve the recognition accuracy of the presence / absence of color misregistration and the direction of color misregistration, and to estimate the amount of color misregistration. Furthermore, the setting of the color misregistration correction amount can be optimized in accordance with the tendency of color misregistration.

By using the present invention (claim 2 ), not only can the color misregistration amount be estimated, but also the ease of reading the color misregistration correction amount can be improved.

By using the present invention (Claim 3 ), it is possible to recognize the presence / absence of color misregistration, the direction of color misregistration, and the color misregistration amount at a time.

By using the present invention (Claim 4 ), it is possible to reduce time and labor required for color misregistration correction, or to achieve high accuracy of color misregistration correction.

By using the present invention (Claim 5 ), it is possible to perform color misregistration correction independently only in a part of the region.

By using the present invention (Claim 6 ), clock jitter or the like hardly occurs at the joints of the sections, and independent color misregistration correction can be performed only in a part of the area at low cost.

By using the present invention (Claim 7 ), it is possible to perform color misregistration correction independently only in a part of the region.

By using the present invention (claim 8 ), the time and labor required for color misregistration correction can be simplified.

By using the present invention (claim 9 ), it is possible to simplify the time and labor required for color misregistration correction and save resources such as toner and paper.

By using the present invention (claim 10 ), the time and labor required for color misregistration correction can be simplified.

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

  FIG. 1 shows an optical scanning device developed in a full-color image forming apparatus. In the embodiment shown in FIG. 1, four stations are scanned in one direction. Further, in FIG. 1, only one station is shown for the sake of simplicity. FIG. 2 is a sectional view thereof.

  In the image forming apparatus for forming a color image by arranging four photosensitive drums 101, 102, 103, and 104 along the moving direction of the transfer belt 105 and sequentially transferring toner images of different colors, each optical scanning device Are integrally formed, and all light beams are scanned on the same surface of a single polygon mirror 213.

  In the embodiment, a pair of semiconductor lasers is provided for each photosensitive member, and scanning is performed by shifting one line pitch in the sub-scanning direction in accordance with the recording density so that two lines are simultaneously scanned. . The beam 201 from each light source unit has an emission position that is different in the sub-scanning direction for each of a plurality of light source units (only one light source unit is shown), and the emission direction is a polygon mirror in the main scanning direction. The optical path lengths from the light emission point to the deflection point of the polygon mirror are set to be the same.

  The cylinder lens 209 has one surface having a common curvature in the plane and the other in the sub-scanning direction, and each light beam is converged so as to be linear in the sub-scanning direction on the deflection surface. Is a conjugate in the sub-scanning direction to form a surface tilt correction optical system in combination with a toroidal lens described later.

  Each beam is emitted from each semiconductor laser at equal intervals so as to be parallel to the sub-scanning direction, in the embodiment, L = 5 mm. The polygon mirror reflection surface is also incident perpendicularly to the reflection surface while maintaining this interval L. Therefore, it is difficult to physically overlap the semiconductor laser and the light source means for holding the coupling lens vertically (in the sub-scanning direction), and they are arranged so as to be shifted in the main scanning direction.

  The polygon mirror 213 is formed thick, and in the embodiment, it is a six-sided mirror, and a groove is provided in a portion between the beams not used for deflection so that the diameter is slightly smaller than the inscribed circle of the polygon mirror, thereby further reducing windage loss. The thickness of one layer is about 2 mm.

  The fθ lens 218 is common to each beam, is formed thick like a polygon mirror, and has no convergence in the sub-scanning direction. The main scanning direction has a non-circular arc shape that gives power so that the beam moves at a constant speed on the surface of each photoconductor as the polygon mirror rotates. Each beam is formed in a spot shape on the surface of the photosensitive member by the toroidal lens 220 having a correction function, and optical scanning means for simultaneously recording four latent images is configured.

  In each optical scanning means, a plurality of folding mirrors are used so that the optical path lengths from the polygon mirror to the surface of the photoconductor coincide with each other, and the incident positions and incident angles with respect to the photoconductor drums arranged at equal intervals are equal. Is placed.

  Explaining the optical path for each optical scanning means, the beam 201 from the light source unit 250 is deflected by the polygon mirror 213, passes through the fθ lens 218, is reflected by the folding mirror 224, enters the toroidal lens 220, and Reflected by the folding mirror 227 and guided to the photosensitive drum 102, for example, a yellow image is formed as the first optical scanning unit.

  Further, the present invention has a beam spot position correcting means capable of correcting the density of the beam spot position interval. By this beam spot position correcting means, the color misregistration can be corrected by correcting the density of the beam spot position interval, and a color image with little color misregistration can be provided.

  The beam spot position correcting means capable of correcting the density of the beam spot position interval will be described below. When the light source is driven with a clock with a fixed period, as described above, due to the influence of the manufacturing error, installation error, etc. of the fθ lens, the density of the beam spot position is sparse. In order to correct the density of the beam spot position interval, the light source may be driven by modulating the clock instead of a fixed period so as to correct the influence of the manufacturing error and installation error of the fθ lens.

  FIG. 1 shows a block diagram of driving a light source by modulating a clock. First, the high-frequency clock generator 1 generates a clock signal having a constant period. The signal is input to the beam spot position interval density correction circuit 2. The beam spot position interval density correction circuit 2 generates a modulated pixel clock whose period is not constant by frequency modulation, phase modulation, or the like. The signal is input to the write control unit 3, and the write control unit 3 generates modulation data by allocating the image data read by the image processing unit 4 to each pixel based on the pixel clock PCLK. Drive 5. By the above method, it is possible to correct the density of the beam spot position interval.

  Note that the configuration of the pixel clock generation circuit is not limited to that shown in FIG. 1, and includes a configuration of a circuit having the same effect as described above.

  However, as described above, even if color misregistration correction is performed at the time of shipment from the factory by adjusting the density of the beam spot position interval, a color image in which color misregistration is conspicuous is output due to a change in the installation environment or an unexpected impact. There is a risk that. Also, when replacing the optical scanning device, the density of the beam spot position interval must be set differently from that before the replacement because the optical scanning device before and after the replacement is different in the density of the beam spot position interval. In this case, an increase in color misregistration is caused. Therefore, it is preferable to provide a color misregistration correction mode, which allows the user or service person to perform color misregistration correction.

  In the color misregistration correction mode, a color misregistration measurement pattern is output, and the color misregistration measurement is performed using the color misregistration measurement pattern. Based on the color misregistration measurement result, the beam spot position correction unit determines the beam spot position interval. It is better to correct the density and correct the color shift.

  As a method for measuring the color shift from the output image information, in the case of an MFP equipped with a scanner function, it is preferable to measure the color shift using a scanner. In the case of a printer not equipped with a scanner function, it is necessary to measure by visual observation or loupe.

  Usually, it is very difficult to visually distinguish color misregistration using a color misregistration measurement pattern. Therefore, it is necessary to devise a color misregistration measurement pattern. FIG. 3A shows an example of a color misregistration measurement pattern. In FIG. 3A, the reference color and the color for which color misregistration correction is performed are output in the direction perpendicular to the color misregistration measurement direction. By superimposing in this way, color misregistration can be easily recognized. FIG. 3B illustrates a case where the reference color and the color for which color misregistration correction is not performed are overlapped with each other in the color misregistration measurement direction, and FIG. In FIGS. 3B and 3C, the color misregistration amounts are drawn to be the same. As can be seen by comparing FIG. 3B and FIG. 3C, it is much easier to recognize the overlapping with respect to the color misregistration measurement direction as shown in FIG.

  Further, as shown in FIG. 3 (a), the color misregistration is near the position where the color misregistration measurement is performed, as compared with the case where the color misregistration measurement pattern exists alone as shown in FIGS. 3 (b) and 3 (c). It is easier to recognize the color misregistration and the color misregistration direction when there are a plurality of measurement patterns in the color misregistration measurement direction. Thus, it is easier to recognize color misregistration when the color misregistration is viewed at a plurality of spatially separated positions than when the color misregistration is measured at a single spatial location. Therefore, it is preferable to arrange a plurality of color misregistration measurement patterns in the vicinity where color misregistration measurement is performed.

  In FIG. 3A, the color misregistration measurement pattern is drawn so as to be interrupted in the direction orthogonal to the color misregistration measurement direction, but this may be connected (FIG. 3D).

  Further, it is preferable to have a color misregistration correction amount input means that can input (select) the direction of color misregistration (to which the color to be measured deviates from the reference color) and the correction amount in a stepwise manner. The correction amount that can be input (selected) may be one level (when only the direction of color misregistration is input and the color misregistration correction amount is determined in advance in the apparatus). It is better to repeat the correction. However, it is better to be able to input (select) the correction amount in multiple stages rather than one stage, and it is preferable to be able to select the correction amount at intervals of about 100 μm at most. If the interval for selecting the correction amount is reduced, fine color misregistration correction can be performed. However, if a certain color misregistration correction range (for example, 210 μm) is to be secured, the value to be selected becomes too large, and the user selects It can be confusing and cumbersome to service personnel. Conversely, if the interval is too large, the color misregistration correction accuracy will deteriorate. Further, although the recognizable color shift varies depending on the situation and the individual, it is about 50 μm, so it is not necessary to take a finer than that, and it is best to set the interval between the correction amounts at around 50 μm. The range of the correction amount interval (from 20 μm to 100 μm at most) is a range in which both the color misregistration correction accuracy and the color misregistration correction range can be achieved. By doing as described above, it is possible to correct the color misregistration to such an extent that it cannot be recognized by human eyes, and it becomes very easy to input the correction amount.

  At this time, the visibility of the color misregistration is further enhanced when the interval p (mm) in the color misregistration measurement direction of the color misregistration measurement pattern is somewhat high. Specifically, it is preferable to set 1 mm ≦ p ≦ 30 mm. If the interval p is larger than 30 mm, there is almost no difference from the case where the color misregistration measurement pattern exists alone, and when it is arranged at a high density of 1 mm or less, the density is too high and reverse. Color misregistration is difficult to recognize.

  The embodiment of FIG. 3 is an embodiment in which the color misregistration measurement pattern has the same interval in the color misregistration measurement direction for the reference color and the color for which color misregistration correction is performed. The pattern can sufficiently recognize the color shift and the direction of the color shift, but it is difficult to recognize the amount of the color shift. For further highly accurate color misregistration correction, it is necessary to visually recognize the amount of color misregistration. Therefore, it is necessary to devise a color misregistration measurement pattern.

FIG. 4 shows an example of a color misregistration measurement pattern that can visually recognize the amount of color misregistration. In FIG. 4, the color misregistration measurement pattern has a slightly different interval in the color misregistration measurement direction between the reference color and the color for which color misregistration correction is performed. In FIG. 4, the interval in the reference color is 3 mm, and the interval in the color for which color misregistration correction is performed is 3.1 mm. In FIG. 4, for the reference color and the color for which color misregistration measurement is performed, the color misregistration measurement pattern is drawn while being shifted in the direction perpendicular to the color misregistration measurement direction. Actually, it overlaps in the direction perpendicular to the color misregistration measurement direction as in FIG.
In FIG. 4, seven misregistration measurement patterns are shown in the vicinity of the position where the color misregistration correction is performed, and the color for which the misregistration correction is performed with respect to the reference color is (a) color. When there is no shift, (b) +100 μm shift, (c) −200 μm shift. As shown in FIG. 4, the color misregistration direction is positive when it is shifted to the right side of the drawing. In (a), assuming that the color misregistration measurement pattern is set so as to match at the center of the seven color misregistration measurement patterns, in the case of (b), the third color misregistration measurement pattern is the same from the left. In the case of (c), the second color misalignment measurement pattern from the right matches. As described above, the color of the color for which the color misregistration correction is performed with respect to the reference color simply by looking at which position in the color misregistration measurement pattern the color misregistration measurement pattern matches or is closest to. The direction and amount of deviation can be estimated. Although it is very difficult to visually measure the absolute amount of color misregistration, it is sufficiently possible to find a color misregistration measurement pattern with the least color misregistration. Since the amount of color misregistration can be estimated visually, it is most suitable for the present invention.

  Even when the color misregistration measurement pattern is different between the reference color and the color for which color misregistration correction is performed, the interval a (mm) of the color misregistration measurement pattern in the color misregistration measurement direction satisfies 1 ≦ a ≦ 30 as described above. It is preferable to satisfy this condition, so that both the visibility of the color misregistration measurement pattern and the color misregistration correction accuracy can be achieved. If a is smaller than 1 mm, the color misregistration measurement patterns are too dense and the visibility of the color misregistration measurement pattern is deteriorated, and it is difficult to recognize the color misregistration measurement pattern that minimizes the color misregistration. turn into. On the other hand, when a is larger than 30 mm, when a plurality of color misregistration measurement patterns are drawn in the vicinity of the color misregistration measurement, the color misregistration measurement pattern is located far from the position where the color misregistration measurement is performed. Therefore, when the color misregistration is estimated by such a color misregistration measurement pattern, the error becomes too large to effectively perform the color misregistration correction.

The difference b (μm) in the color misregistration measurement direction that is different between the reference color and the color for which color misregistration correction is performed corresponds to the resolution of the color misregistration measurement, and therefore, the following equation should be satisfied.
20 ≦ b ≦ 100
In the above formula, when b is smaller than 20 μm, the resolution of the color misregistration measurement is improved, but the measurement range of the color misregistration amount becomes small (if the number of color misregistration measurement patterns does not change), and the measurement range should be expanded. Then, it is necessary to draw a large number of color misregistration measurement patterns, and it becomes difficult to select a color misregistration measurement pattern with the least color misregistration. For example, assuming that b = 10 μm and obtaining a color misregistration amount measurement range of ± 200 μm, 400 ÷ 10 + 1 = 41 color misregistration measurement patterns are required. Selecting a color misregistration measurement pattern with little color misregistration is a very complicated operation.

  If b is larger than 100 μm, the resolution of the color misregistration measurement deteriorates and the color misregistration cannot be effectively corrected. Therefore, b is preferably set to around 50 μm. As described above, the color misregistration perceived by the human eye is about 50 μm, depending on the situation and the individual. Further, the generated color misregistration is usually about ± 200 μm at most. Therefore, when b = 50 μm, it is best to form 400 ÷ 50 + 1 = 9 color misregistration measurement patterns at intervals of about 5 mm in the vicinity of the position where the color misregistration measurement is performed, and the color misregistration measurement that minimizes the color misregistration. Therefore, it is possible to achieve both ease of selecting a pattern for use and resolution of color misregistration measurement.

  The color misregistration measurement pattern is preferably a figure having a component perpendicular or nearly perpendicular to the color misregistration measurement direction. The example shown in FIG. 3 is an example, and is a figure having only a vertical component with respect to the color misregistration measurement direction. By doing so, the visibility of the color misregistration measurement pattern is improved.

  The above-described color misregistration measurement pattern should be equally spaced for both the reference color and the color for which color misregistration correction is performed. If both are equally spaced, the color misregistration correction amounts are also aligned at equal intervals (for example, when b = 50 μm). The color misregistration correction amount is 50 μm, 100 μm, 150 μm,...), And it is easy to select the color misregistration correction amount.

  In FIG. 4, the color misregistration measurement pattern is set to be equally spaced in both the reference color and the color for which color misregistration correction is performed, but when b = 50 μm and nine color misregistration measurement patterns are drawn, ± When a color shift of 200, ± 150, ± 100, ± 50, 0 (μm) has occurred, the color shift of the reference color and the color shift measurement pattern for correcting the color shift is 0 (the pattern is Overlap).

  Here, when the tendency of the generation amount of the color misregistration measurement pattern is known in advance, and when it is desired to finely set the resolution (for example, ± 200, ± 120, ± 80, ± 50) in a part of the color misregistration region. As shown in FIG. 5, the interval of either the reference color or the color for which color misregistration correction is performed is not equal, but the interval may be modulated depending on the location. FIG. 5 modulates the interval of the color misregistration measurement pattern for the color for which color misregistration correction is performed, and when the color for which color misregistration correction is performed with respect to the reference color is ± 120, ± 80, ± 50, This is an example when setting is made such that a portion where a reference color and a color misregistration measurement pattern for color misregistration correction overlap is generated. Similarly to FIG. 4, FIG. 5 shows the color misregistration measurement patterns arranged in the direction perpendicular to the color misregistration measurement direction for the sake of easy viewing, but actually overlaps. FIG. 5A shows the case where the color misregistration is 0, and the central color misregistration measurement patterns overlap among the seven color misregistration measurement patterns. (B) is when +80 μm is shifted, and the second from the left of the color shift measurement pattern is overlapped. (C) is when −120 μm is shifted, and the rightmost color misregistration measurement pattern overlaps.

  As described above, the color misalignment measurement pattern is optimized according to the tendency of color misregistration by modulating the interval of either the reference color or the color for color misregistration correction according to the location instead of equal intervals. (That is, the interval between correction amounts that can be selected can be optimized), and effective color misregistration correction can be performed.

  Similar to FIGS. 4 and 5, a plurality of color misregistration detection patterns are arranged in a direction orthogonal to the color misregistration measurement direction, and a plurality of color misregistration measurement patterns are arranged according to the position in the direction orthogonal to the color misregistration measurement direction. This can be realized by changing the interval. Hereinafter, a description will be given with reference to FIG.

  In FIG. 6, the interval of the color misregistration measurement pattern for the reference color is 3.0 mm for the first, second, and third rows, and the interval of the color misregistration measurement pattern for the color to be corrected for color misregistration is one row. The eye is 3.1 mm, the second line is 3.2 mm, and the third line is 3.3 mm. When the color misregistration for color misregistration correction with respect to the reference color does not have the color misalignment in FIG. 6A, the center pattern of the three color misregistration measurement patterns overlaps, but (b) When there is a deviation of +100 μm (the deviation in the right direction on the paper is defined as +), the patterns overlap in the leftmost pattern of the first row. (C) When shifted by −200 μm, the patterns overlap in the rightmost pattern in the second row. That is, in the color misregistration measurement pattern as shown in FIG. 6, when the color for color misregistration correction with respect to the reference color has a deviation of 100 μm, the patterns overlap in the first row, and when the deviation of 200 μm has occurred. When a shift of 300 μm occurs in the second row, pattern overlap occurs in the third row, and it is possible to estimate the color shift amount and direction. Further, since the color misregistration measurement pattern has a one-to-one correspondence between the position in the direction orthogonal to the color misregistration measurement direction and the color misregistration correction amount, the color misregistration correction amount can be easily read.

  As shown in FIG. 7, by outputting color misregistration measurement patterns of a plurality of colors at different positions orthogonal to the color misregistration measurement direction, color misregistration correction of a plurality of colors can be performed with one output. Therefore, it is possible to save output media such as paper. Furthermore, since the number of output times of the color misregistration measurement pattern can be reduced, the color misregistration correction procedure can be simplified, and the burden on the user and service personnel can be reduced. FIG. 7 shows an example in which black is set as the reference color, and cyan is output in the first row, magenta in the second row, and yellow in the third row as the color for color misregistration correction. Both the reference color and the color for which color misregistration correction is performed are a pattern for measuring color misregistration at equal intervals, the interval for the reference color is 3.0 mm, and the color for which color misregistration correction is performed is 3.1 mm. From the embodiment of FIG. 7, it can be estimated that cyan is offset by +100 μm, magenta is +200 μm, and yellow is shifted by −200 μm.

  The above method is most suitable for the present invention because the presence / absence, the color misregistration direction and the color misregistration amount of a plurality of colors can be recognized from a single color misregistration measurement pattern output.

  Further, the pattern for measuring the color misregistration between each color and the reference color may be a color misregistration measurement pattern as shown in FIGS. 4 and 5, or a color misregistration measurement pattern as shown in FIG. Also good.

  There is not always a color shift in all other colors with respect to the reference color. Therefore, it is preferable that the correction circuit 2 includes a color misregistration correction color selection unit that can select a color for color misregistration correction. By doing so, color misregistration correction is performed only for the color in which the color misregistration has occurred with respect to the reference color, thereby reducing the time and labor required for the color misregistration correction by the user or service person.

  As the density correction of the main scanning beam spot position interval, the most suitable method for the present invention is a method in which the effective scanning area is divided into a plurality of sections and the correction is performed for each section. The reason is as follows. When correcting the color misregistration by correcting the density of the beam spot position interval using the output color misregistration measurement pattern, "If a part is corrected, a new color misregistration will occur in the other part" If this happens, correction will be very time-consuming. If a method of dividing the effective scanning area into a plurality of sections and correcting each section is used, correction can be performed independently for each section. It is possible to perform a correction such that “the color misregistration correction is not performed in some other regions”. Therefore, it is possible to independently correct only the portion where the color misregistration occurs, and the color misregistration correction becomes very simple.

  A method of correcting the density of the beam spot position intervals by dividing the effective scanning area into a plurality of sections and correcting the beam spot positions for each section will be described below.

  First, consider one section. FIG. 8A is a diagram showing the beam spot position in one section before correction, and it is assumed that the optical scanning is performed from left to right on the paper surface. The dotted lines are written at equal intervals, and it is desirable that the beam spot position be on this dotted line. However, for the reasons described above, the beam spot position is usually not on the dotted line. In FIG. 8A, the beam spot position is drawn so as to be on the dotted line, but this is for the sake of simplification. In actuality, the beam spot position before correction is located at a position shifted from the dotted line. It is necessary to correct this deviation from the dotted line. FIG. 8B is a diagram illustrating a case where the beam spot position interval is reduced at equal intervals. At this time, if the positional deviation from the dotted line is taken on the vertical axis and the beam spot position in the optical scanning direction is taken on the horizontal axis, the graph will fall to the right. FIG. 8C is a diagram showing a case where the beam spot position interval is enlarged at equal intervals. At this time, if the positional deviation from the dotted line is taken on the vertical axis and the beam spot position in the optical scanning direction is taken on the horizontal axis, the graph will fall to the right. Here, the position shift shifted to the right side of the dotted line 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 multiple sections. The solid line shown in FIG. 9 is the beam spot position deviation before correction, and shows the position deviation from the dotted lines in FIG. In the sections 1 and 3, the beam spot position interval is a sparse region as a whole, which is close to the state shown in FIG. In the sections 2 and 4, the beam spot position interval is an overall dense region, which is close to the state shown in FIG. Therefore, in the sections 1 and 3, the correction for reducing the beam spot position interval as a whole, that is, the correction shown in FIG. 8B may be performed. In the sections 2 and 4, the correction for expanding the beam spot position interval as a whole, The correction shown in FIG. 8C may be performed. As described above, the correction states shown in FIG. 8B and FIG. 8C are combined, and the correction as shown by the one-dot chain line in FIG. 9 is performed by appropriately changing the amount of reduction (enlargement) of the beam spot position interval. It is possible to correct the state before correction indicated by the solid line as in 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.

  In each section, it is preferable to correct the density of the beam spot position by adjusting the emission timing of the light beam by shifting the phase of the signal of the pixel clock.

  FIGS. 10, 11 and 12 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. 10, 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 13 compares the counter value with a preset value and the 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 14 controls the transition timing of the pixel clock PCLK based on the control signals a and 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. 10 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. 11A shows how a standard pixel clock PCLK with a duty ratio of 50% corresponding to VCLK divided by 8 is generated, and FIG. 11B shows only 1/8 clock with respect to VCLK divided by 8 clock. FIG. 11C shows a state in which the PCLK with the advanced phase is generated, and FIG. 11C 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. 11A 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 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 compares the given phase data with the counter value, and outputs a control signal b if they match. In FIG. 11A, 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. 11A, 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. 11B 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 matches 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. 11B, it is possible to generate the pixel clock PCLK whose phase is advanced by 1/8 clock with respect to the frequency-divided clock of the high frequency clock VCLK by 8.

  Next, FIG. 11C 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. As a result, as shown in FIG. 11C, it is possible to generate the pixel clock PCLK whose phase is delayed by 1/8 clock with respect to the frequency divided 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. 12 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.

  As described above, since the phase of the pixel clock PCLK can be changed every clock (that is, every dot), high-definition correction is possible.

  If the phase is changed every clock, it is necessary to store the phase data in the memory every clock, so that a considerable amount of memory is required, resulting in an increase in cost. In order to reduce costs, the effective scanning area is divided into a plurality of sections, the pixel clock is phase-shifted at regular intervals within one section, and the number of pixels to be phase-shifted is changed for each section. Anyway. By doing so, the memory can be greatly reduced.

  As an example of the above, FIG. 13 shows an example in which the phase of the pixel clock is shifted every two pixels. As shown in FIG. 13, when the phase of the pixel clock is shifted every two pixels, the beam spot position changes in a staircase pattern before correction, but the amount of phase shift of the pixel clock is small (for example, 1/16 pixel). Clock) and can be regarded as a linear approximation. Also, the slope of the straight line can be changed by changing the interval for shifting the phase. For example, if the phase is shifted every other pixel, the slope of the straight line becomes steeper (the correction amount increases). If the phase is shifted every other pixel, the slope of the straight line becomes gentler (the correction amount becomes smaller). As described above, by changing the phase of the pixel clock at regular intervals and changing the interval of the pixel clock to be phase-shifted for each section, the correction as shown in FIG. 9 can be made approximately.

  The phase shift amount is preferably a constant amount (for example, ± 1/16 pixel clock) from the viewpoint of simplification of the algorithm. In addition, it is not always necessary to shift the phase at regular intervals within the section, and the intervals of pixels to be phase shifted may be arranged so as to be sparse and dense in accordance with the state of beam spot position deviation to be corrected. By doing so, high-precision optical scanning becomes possible.

  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 a method of correcting the density of the beam spot position interval, a method of shifting the pixel clock phase is most desirable. Since the method of shifting the phase can be realized with a relatively simple electric circuit, it is advantageous not only in terms of low power consumption and cost, but also in that it is difficult to generate clock jitter at the joints of sections. It is.

  Further, correction of the beam spot position in each section can be realized by changing the frequency of the pixel clock for each section. This will be described with reference to FIG. In order to correct the beam spot position deviation as indicated by the solid line in FIG. 14B, the frequency may be changed stepwise as shown in FIG. 14A. If the frequency of the pixel clock is changed stepwise for each section, the beam spot position can be corrected in a linear function in each section, and the slope of the linear function is changed according to the amount of change in the pixel clock. Can do. Here, shifting to the image height on the scanning end side is defined as a positive positional shift. FIG. 14A shows the amount of change from the frequency before correction. In section 1 in FIG. 14, referring to FIGS. 8 and 9, the beam spot position interval is sparse as a whole, so that it can be corrected by making the frequency higher than before correction. In section 2, since the beam spot position interval is generally dense, the frequency can be corrected by making it lower than before correction. If the same thing is done in the sections 3 and 4, the beam spot position deviation can be corrected well in all sections.

  Here, the change in the frequency of the pixel clock is not limited to a staircase shape, and may be changed in a linear function, a quadratic function, or the like, and the correction is performed closer to the actual beam spot position deviation. Therefore, it is possible to correct the beam spot position deviation with high accuracy.

  Locations where color misregistration tends to occur tend to be determined by the multicolor image forming apparatus, and usually the largest color misregistration tends to occur around the middle of the edge of the image area and the center of the image area. Therefore, if the color misregistration correction is performed only in the vicinity where the color misregistration is most likely to occur, the color misregistration correction can be satisfactorily performed in the entire image region. Therefore, it is preferable to determine a position where color misregistration correction is performed in advance in the apparatus, and output a color misregistration measurement pattern in the vicinity of the position to perform color misregistration correction. It is possible to reduce labor and time for correcting the deviation.

  Also, in normal use of the device, there are few color shifts in all other colors with respect to the reference color, so it is efficient to output a color shift measurement pattern for all colors. However, the time and labor required for color misregistration correction increase, and the load on the user and serviceman increases. Furthermore, it leads to waste of resources such as output media such as toner and paper. Therefore, it is preferable to select a color for which color misregistration correction is performed, and to output a color misregistration measurement pattern for only the selected color and the reference color, and to perform color misregistration correction. It can be effectively corrected only for colors.

  When the optical scanning device is replaced or when there is a large environmental change or impact due to a change in the installation location of the device, it is necessary to perform color misregistration correction for all colors. In such a case, as described above, a color to be corrected is selected, and a color misregistration measurement pattern is output only for the color and the reference color. When the color misregistration correction is performed on the reference color, the output of the color misregistration measurement pattern and the input of the color misregistration correction information are repeated, which gives a user and a service person a complicated feeling. Therefore, it is preferable to first perform color misregistration correction by selecting a color to be subjected to color misregistration correction after collectively outputting the color misregistration measurement patterns for all colors with respect to the reference color.

  As described above, “Select a color for color misregistration correction, output a color misregistration measurement pattern for only that color, and perform color misregistration correction” and “Color misregistration measurement pattern for all colors” The two color misregistration correction methods of “color misregistration correction method for selecting color for color misregistration correction after performing color misregistration correction after output collectively” for normal use, optical scanning device replacement and device Therefore, a multicolor image forming apparatus capable of either correction method is desirable.

1 shows a pixel clock generation circuit and an optical scanning device of the present invention. It is sectional drawing of an optical scanning device. The pattern for color misregistration measurement (Example 1) is shown. The pattern for color misregistration measurement (Example 2) is shown. A color misregistration measurement pattern (Example 3) is shown. A color misregistration measurement pattern (Example 4) is shown. A color misregistration measurement pattern (Example 5) is shown. It is a figure explaining the method of correct | amending the density of the beam spot position space | interval. It is a figure explaining the method of correct | amending the density of the beam spot position space | interval. 1 shows a configuration of a pixel clock generation circuit. FIG. 11 is a timing chart for explaining the operation of FIG. 10. FIG. 11 is another timing chart for explaining the operation of FIG. 10. An example in which the phase of the pixel clock is shifted every two pixels is shown. An example in which the beam spot position in each section is corrected by changing the frequency of the pixel clock for each section will be described.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High frequency clock generation part 2 Beam spot position space | interval density correction circuit 3 Write control part 4 Image processing part 5 Light source drive part

Claims (10)

A light source, a plurality of optical scanning devices that scan a light beam from the light source and form an image on the image carrier, and an electrostatic image formed on the image carrier by the optical scanning device is visualized with each color toner A multi-color image forming apparatus that outputs a color image, and a developing unit that superimposes each color image visualized on the image carrier and transfers the image to a medium such as paper. A color spot correction mode including beam spot position correction means for correcting the density of beam spot position intervals on the image carrier, and capable of correcting a color shift of an arbitrary color with respect to at least a reference color, and the color shift correction mode Color misregistration measurement pattern output means for outputting a predetermined color misregistration measurement pattern, and measuring the color misregistration amount by visually measuring the output color misregistration measurement pattern, and measuring the color misregistration. A color misregistration correction amount input unit that inputs color misregistration correction information measured by a pattern, performs color misregistration correction by the beam spot position correcting unit based on the color misregistration correction information, and the color misregistration measurement pattern is The reference color and the color to be subjected to color misregistration correction are arranged so as to overlap in the color misregistration measurement direction, and are arranged at a plurality of locations in the color misregistration measurement direction. A multicolor image forming apparatus characterized in that the color to be subjected to misregistration correction is different , one is equally spaced and the other is not equally spaced . The multicolor image forming apparatus according to claim 1 , wherein a plurality of the color misregistration measurement patterns of the reference color and the color for which color misregistration correction is performed are output at different positions orthogonal to the color misregistration measurement direction, and the reference color and A multicolor image forming apparatus, wherein an interval between the color misregistration measurement patterns is changed in accordance with a position in a direction orthogonal to the color misregistration measurement direction in at least one of the colors subjected to color misregistration correction. 3. The multicolor image forming apparatus according to claim 1, wherein a plurality of the color misregistration measurement patterns are output at different positions in the direction orthogonal to the color misregistration measurement direction, and according to the position in the direction orthogonal to the color misregistration measurement direction. A multicolor image forming apparatus characterized in that the color for outputting the color misregistration measurement pattern is different. 4. The multicolor image forming apparatus according to claim 1 , further comprising color misregistration correction color selection means for selecting a color for color misregistration correction. 2. The multicolor image forming apparatus according to claim 1 , wherein the beam spot position correcting means divides the scanning area into a plurality of sections and performs beam spot position correction for each section. . 6. A multi-color image forming apparatus according to claim 5 , wherein said beam spot position correcting means is performed by shifting a phase of a pixel clock. 6. The multi-color image forming apparatus according to claim 5 , wherein said beam spot position correcting means is performed by modulating a frequency of a pixel clock. A color shift correcting method using a multi-color image forming apparatus according to any one of claims 1 to 7, wherein the color shift measurement pattern position for a preset color shift correction of the color shift measurement direction A color misregistration correction method, wherein the color misregistration correction is performed at a position where the color misregistration measurement pattern is output, while outputting only in the vicinity. A color shift correcting method using a multi-color image forming apparatus according to any one of claims 4-7, to select the color for color shift correction, the color shift only for the selected color and the reference color A color misregistration correction method, wherein a color misregistration correction is performed by outputting a measurement pattern. A color misregistration correction method using the multicolor image forming apparatus according to any one of claims 1 to 7 , wherein the color misregistration measurement pattern is output for all colors, and a color is determined based on the output result. A color misregistration correction method comprising selecting a color to be misregistration correction and performing color misregistration correction.

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