JP2011007980A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem, wherein although conventionally, a domain is divided into a main scanning direction for determining a correction amount of sub-scanning, especially, a low cost model has weak pixel-based gradation reproduction, and depending on the phase of the sub-scanning, blurs are generated at, for example, a fine line.SOLUTION: In digital register correction that corrects a polygon face tangle error by image processing, there is less blurs of the fine line, and color shift can be suppressed to the minimum. By noticing the amount of color shift, interpolation width is varied.

Description

  The present invention relates to an image processing apparatus that overlaps colors using a plurality of photosensitive drums and a beam scanning system in an electrophotographic system or the like to obtain a color image.

  Conventionally, in digital composite copying machines, especially in low-end products, space saving tends to be more important. As an optical system means for realizing space saving, there is an oblique incidence method. As shown in FIG. 4, a light emitting element for a latent image, a photosensitive drum for holding the latent image, and a polygon mirror for beam scanning are arranged at different height positions so as to be inclined with respect to the beam scanning plane. Incident. In this method, there are different distances a and b from the center position at the center and end of the polygon surface. Due to the difference in the center position, the position irradiated on the photosensitive drum varies in the height direction.

  A dotted line in FIG. 3 indicates an ideal scanning path, and a solid line indicates a scanning path that is affected by the height variation. In the oblique incidence method, in order to cancel this height variation, a correction lens is placed on the beam path, and the rate of refraction in the height direction is changed according to the scanning position to cancel the variation and achieve high image quality. Is realized. However, it takes time to process the correction lens, ensure accuracy, and the adjustment process for realizing the desired state of the optical system, all affecting the manufacturing cost. Further, even in a system that makes incidence perpendicular to the rotation axis of the polygon other than oblique incidence, fluctuation in the height direction can occur.

  FIG. 7A shows an ideal optical system that irradiates the photosensitive surface at a certain height regardless of the distance from the rotation axis to the surface.

  FIG. 7B shows a state in which an attachment error is included in the rotating shaft, although it is extremely shown for easy understanding.

  In this case, as in the case of oblique incidence, height variation occurs on the photosensitive surface depending on the scanning position, which has an effect on image quality.

  Especially in high-end models, these errors are also a problem.

  A digital correction method has been devised as a technique corresponding to the above scanning curvature. In the photosensitive drum of FIG. 5, the dotted line is an ideal scanning trajectory, and the actual scanning trajectory in which the solid lines in (A), (B), and (C) pass within ± 0.5 lines of the ideal scanning trajectory. Indicates. Both ends are closest to (A), and (C) is close to the center.

  Therefore, in accordance with the scanning area, the image data is transferred in the order of (A) .fwdarw. (B) .fwdarw. (C) .fwdarw. (B) .fwdarw. (A) to output image data to be printed on an ideal scanning line.

  As previously suggested, include Patent Documents 1 to 3.

  Further, the deviation within ± 0.5 lines is corrected by using the interpolation in the sub-scanning direction perpendicular to the scanning orbit.

  Patent document 4 is mentioned as a proposal which combined optical correction | amendment and the correction | amendment of the subscanning direction.

  However, in the method using interpolation in the sub-scanning direction, shifting the phase by interpolation is a highly difficult technique due to the characteristics of electrophotography.

  Particularly in low-cost products, the uniformity of thin line thickness tends to be easily lost due to poor gradation reproduction of fine dots.

  FIG. 6 shows this state, in which a square indicates one dot by PWM (Pulse Width Modulation), and (a) is an ideal thin line with a width of 1 dot.

  (B) is a correction without interpolation processing, but as a detrimental effect of the part where lines are changed, jaggy is a conspicuous thin line.

  (C) corrects the curvature of scanning, and the thickness of the correction portion by the center interpolation is difficult to reproduce uniformly.

  For this reason, as shown in (d), a technique has been proposed that achieves an image quality with no jaggies and uniform thin lines by setting the correction range by interpolation to a minimum interval.

Japanese Patent Laid-Open No. 02-050176 JP 2005-304011 A JP 2003-276235 A JP 2003-182146 A

  If the correction method shown in the background technology section is conceptually represented by a graph, it is as shown in FIG.

  (A) shows the curve to be corrected and the relationship corrected in line units.

  (B) is the difference between the line unit correction and the correction curve, and is an error component that needs to be handled by interpolation processing.

  (C) shows a partial correction curve only in the vicinity of the line transfer.

  The partial correction prevents unevenness of the thickness of the thin line, while the error shown in (d) occurs in a portion away from the change point.

  For example, even if there are no harmful effects in reproducing Y (Yellow), M (Maganda), C (Cyan), and K (Black), which are basic colors for forming a color space for electrophotography, R (Red), G ( When color reproduction by superposition such as Green) and B (Blue) is necessary, the amount of color misregistration becomes a problem.

  Suppose (a) to (d) indicate ColorA, and ColorB has a correction curve (e).

  In the first half of the graph, Color A and Color B have the same slope, but the latter half has the opposite slope.

  At this time, as shown in (f), the amount of misregistration due to partial correction also has the same amount of color misregistration between the two colors in the first half. It does not occur, and the latter half is generated twice as much as the color shift is emphasized.

  An object of the present invention is to suppress the occurrence of color unevenness and secondary colors due to the effect of partial correction due to a large amount of color misregistration due to the relationship between correction curves between two colors.

  According to the present invention, the first scanning unit that scans in one direction to form an image of at least one line and the second scanning unit that obtains a scanning effect in the vertical direction with the first scanning unit for forming a two-dimensional image. Characteristic storage means for storing at least the vertical error characteristics of the scanning means of the first scanning means and the ideal scanning of the first scanning means, image storage means for storing images of a plurality of lines, and image storage within one scanning period First scanning means having line selection means for switching lines read from the means and interpolation means for interpolating the output of the line selection means, controlling parameters of the line selection means and the interpolation means according to the characteristic storage means In an image forming apparatus that reduces an error from an ideal scan, a color image is obtained by superimposing a plurality of colors, and color misregistration characteristic storage means for storing color misregistration information by error correction is provided. Reducing the amount of color shift by varying the correction width of the correction processing according to the storage means.

  Further, the correction method performs interpolation by calculation such as linear interpolation.

  The first scanning means uses a polygon mirror, and the scanning error is corrected including the error due to the inclination of the polygon rotation axis.

  The second scanning means obtains a scanning effect by rotating the photosensitive drum in the electrophotographic system.

  High image quality is achieved by all or any combination of the above methods.

  According to the first aspect of the present invention, since the correction of the scanning curve is performed by changing the partial correction range in consideration of the amount of color misregistration, the color misregistration is performed in order to perform the correction range within the necessary and sufficient range. good image quality is obtained reduced.

  According to the second aspect of the invention, since the sub-scan interpolation process is linearly interpolated, the interpolation process can be realized with simpler hardware.

  According to the third aspect of the present invention, by applying the system to a system using a polygon mirror, the cost for adjusting the inclination of the polygon attachment can be reduced or zero.

  Further, according to the invention described in claim 4, the present invention can be applied to an electrophotographic system.

Block diagram of a first embodiment of the present invention System configuration of an embodiment of the present invention It shows the trajectory of the main scanning on the photoreceptor Diagram showing the optical path of the laser Diagram showing the relationship between the correction of the scanning track and the photoreceptor It shows a correction accuracy of within one pixel by interpolation processing Diagram illustrating an optical path due to the error in the rotation axis of the polygon Graph showing the relationship between the correction curve and error Block diagram of a digital circuit system according to an embodiment of the present invention Diagram showing the relationship between interpolation coefficients and color shift of the present invention Configuration of the laser scanning system embodiment of the present invention Block diagram of a second embodiment of the present invention

  A first embodiment in which the embodiment of the present invention is applied to a four-drum color copying machine in which four photoconductors are arranged in tandem will be described.

  FIG. 2 is a schematic configuration diagram of the entire color copying apparatus according to the first embodiment.

  First, an outline of a color image reading apparatus (hereinafter referred to as “color scanner”) 1 and a color image recording apparatus (hereinafter referred to as “color printer”) 2 constituting the color copying apparatus will be described with reference to FIG.

  The color scanner 1 forms an image of the document 13 on the color sensor 17 through the illumination lamp 14, the mirror groups 15A, B, and C and the lens 16, and converts the color image information of the document into, for example, blue (Blue, This is read for each color separation light of B (hereinafter referred to as “B”), green (hereinafter referred to as “G”), and red (hereinafter referred to as “R”) and converted into an electrical image signal. Then, based on the color separation image signal intensity levels of B, G, and R obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and black (hereinafter referred to as Bk), cyan (Cyan, hereinafter referred to as C), magenta (hereinafter referred to as Magenta), and yellow (hereinafter referred to as Y) color image data are obtained.

  Next, an outline of the color image recording apparatus 2 of FIG. 2 will be described. In the color printer 2, the writing optical units 28M (for magenta), 28Y (for yellow), 28C (for cyan), and 28K (for black) provided for each color toner are supplied from the color scanner 1. The color image data is converted into an optical signal, optical writing corresponding to the original image is performed, and the photosensitive members 21M (for magenta), 21Y (for yellow), 21C (for cyan), 21K (for black) provided for each color. ) To form an electrostatic latent image. These photoreceptors 21M, 21Y, 21C, and 21K rotate counterclockwise as indicated by arrows, and around the chargers 27M (for magenta), 27Y (for yellow), and 27C (for cyan) provided for each color, respectively. ), 27K (for black), and around the photosensitive members 21M, 21Y, 21C, and 21K of the respective colors, the M developing unit 213M, the C developing unit 213C, the Y developing unit 213Y, and the Bk developing unit 213K are the photosensitive member 21M, The developing devices are arranged so as to contact 21Y, 21C, and 21K. Also, an intermediate transfer belt 22 as an intermediate transfer member and a first transfer bias blade 217M (for magenta), 217Y (for yellow), 217C (for cyan), 217K (for black) as first transfer means for each color, It is stretched between a drive roller 220 that drives the intermediate transfer belt 22 by a drive motor (not shown) and driven roller groups 219 and 237.

  Each developing unit in each of the image forming systems described above rotates to bring the developer head into contact with the surface of the photoreceptor to develop the electrostatic latent image, and rotates to pump up and stir the developer. It is configured by a developer paddle.

  The second transfer bias roller 221 is disposed at a position facing the driven roller 219 of the intermediate transfer belt 22, and is provided with a contact / separation mechanism that drives the intermediate transfer belt 22 so as to be able to contact and disconnect.

  Further, a belt cleaning unit 222 is provided at a predetermined position facing the driven roller 237 on the surface of the intermediate transfer belt 22. The contact / separation operation timing of the belt cleaning unit 222 is separated from the belt surface from the start of printing until the belt transfer of the rear end portion of the final color image is completed, and at the predetermined timing thereafter, the contact / separation mechanism Cleaning is performed by contacting the belt surface (not shown).

  In the color printer unit, first, image formation is started from magenta. Thereafter, cyan image formation is started at a timing delayed from the rotational speed of the intermediate transfer belt 22 by the difference between the positions of the photoconductors 21M and 21C. The yellow image formation is started at a timing delayed by the displacement of the positions of the photoreceptor 21C and the photoreceptor 21CY, and then delayed by the displacement of the positions of the photoreceptor 21Y and the photoreceptor 21K with respect to the rotational speed of the intermediate transfer belt 22. imaging of black is started at timing.

  Each color is processed by the image processing unit, and the image stored in the recording means is read out. Based on this image data from a predetermined timing, the respective color chargers 27M, 27Y, 27C, 27K of the apparatus sequentially and uniformly. Optical writing with laser light is performed on the charged photoconductors 21M, 21Y, 21C, and 21K by the laser scanner units 28M, 28Y, 28C, and 28K for each color, and latent image formation starts sequentially. Hereinafter, magenta image formation will be described as a representative example of four drums. When exposure of the laser to the photoconductor 21M is started, the developing sleeve of the M developing unit 213M rotates and a developing bias is applied so that development can be performed from the leading end portion of the M latent image. Thereafter, the developing operation of the M latent image is continued, and when the trailing end of the latent image has passed the M developing position, the development inoperative state is set. The toner image of the first magenta image formed on the photosensitive member 21 is transferred to the intermediate transfer belt 22 by the first transfer bias blade 217M and held on the intermediate transfer belt.

  A series of these operations is sequentially performed in the other units of yellow, cyan, and black, and a full-color toner image formed by the first image of each color is formed on the intermediate transfer belt 22.

  Here, a configuration diagram of the laser scanner unit 28 according to the first embodiment will be described with reference to FIG.

  The light emitting element array 281 has four light emitting elements, and simultaneously irradiates four lines. (M = N = 4) The light emitting element array 281 is coupled to the polygon motor 283 through the lens 282 to irradiate the surface of the rotating six-sided polygon mirror.

  The polygon motor 283 is polarized so that the laser light of the light emitting element array 281 is scanned six times per rotation.

  The polarized laser light is detected by a BeamDetect (hereinafter referred to as BD) detection element 286 at the beginning of scanning, and generates a BD signal that triggers the start of exposure for each main scan.

  On the other hand, a signal of an HP sensor (not shown) provided on the intermediate transfer member is received, phase control is performed so that the polygon motor 283 is synchronized with the BD signal at the rising edge or falling edge of the signal, and the rising edge of the HP sensor signal. Alternatively, the exposure start timing in the sub-scanning direction is obtained by the falling edge. Further, the scanning speed of the edge is corrected by the fθ lens 284, and the light is polarized by the flat mirror 285 and irradiated to the photosensitive drum 21 disposed below.

  When a full-color toner image is formed on the intermediate transfer belt 22, the second transfer bias roller 221 moves to a position in contact with the intermediate transfer belt by a separation / contact mechanism. The recording medium to be output before the full-color toner image is formed on the intermediate transfer belt 22 is made to wait by the registration roller 225 from the cassette 223 via the paper feed roller 224 and the transport rollers 226, 227, and 228. deep. When the second transfer bias roller 221 contacts the intermediate transfer belt 22, the registration roller 225 is turned on so that the toner image on the intermediate transfer belt 22 is transferred to a predetermined position on the recording medium, and the recording medium is moved to the second transfer bias. Feed to roller 221. In the second transfer bias roller, a predetermined transfer bias is applied in order to transfer the toner image on the intermediate transfer belt to the recording medium, whereby the toner image is collectively transferred to the recording medium.

  The recording medium transferred as described above is conveyed to the fixing device 25, and the toner image is melted and fixed by the upper and lower fixing rollers controlled to a predetermined temperature to obtain a high-resolution full-color copy.

  The surface of the intermediate transfer belt 22 after being transferred to the recording medium is cleaned by the cleaning unit 222, and the copying operation is completed.

  Next, the configuration of the system of the present invention will be described with reference to FIG. The image signal read from the color scanner 1 is subjected to image processing such as shading correction depending on the reading device by the reading system image processing unit 91 and passed to the central image processing unit 95. The central image processing unit 95 stores the image in the image memory 94 and passes the image signal to the output system image processing 96 to 99 at an appropriate timing reflecting the distance between the drums. The central image processing unit 95 transmits and receives external input data such as a telephone line and a network via the external interface 93.

  When the received data is PDL (Page Description Language), the PDL processing unit 92 develops the image information. The output system image processes 96 to 99 perform image processing on Y, M, C, and K colors, respectively, and perform processing optimal for laser output and correction processing.

  Figure 1 shows an internal block diagram of the 96 to 99. In this embodiment, the line shift width is 20 lines at the maximum including manufacturing variations, and the line buffer 101 includes the number of lines corresponding to the assumed maximum deviation width and the lines to be used for the subsequent interpolation processing calculation. Hold. Each time one line is transferred, the line buffer 101 replaces the first transferred line data and holds the latest 20 + 1 lines. The line selector 102 receives all the line data held in the line buffer, selects them according to the correction amount calculation 104, and outputs them.

  In this embodiment, since the interpolation operation 103 is linear interpolation, the line selector 102 outputs two lines near the interpolation position. Further, the correction amount calculation 104 reads the next correction position and the correction amount from the bending characteristic memory 106 in advance. Further, the color misregistration amount in the vicinity of the next correction position is read in advance from the color misregistration amount memory 107. Then, the position in the line is grasped by the output of the main scanning counter 105, and the correction amount at each pixel position is output from the correction range determined by the distance from the correction position, the correction amount, and the color shift amount. The unit of the correction amount is a line, and the correction amount is determined so that the remaining error is in the range of 0 to less than 1 line, and passed to the line selector 101. The remaining error is passed to the interpolation operation 103 as a system value for linear interpolation.

  The operation of the correction amount calculation 104 will be described in more detail with reference to FIG.

  FIG. 10 is a timing chart simulating the operation. In both (a), (b), and (c), pixel IDs 1, 2, 3,. . . And count.

  (A) and (b) show the data of Color A and Color B, respectively, and the ideal correction amount is a numerical value corresponding to the scanning curve read from the bending characteristic memory for each color, and is ideal. It matches the correction value. The integer part of the value of the ideal correction amount indicates the sub-scanning position in the line image read from one select line 1 of the output of the line selector 102. The position of the image of the line read from the select line 2 is a value obtained by adding 1 to the value of the select line 1. The decimal part of the numerical value of the ideal correction amount indicates an interpolation coefficient.

  In this embodiment, a plurality of interpolation coefficient patterns can be selected. The interpolation coefficient (entire area) is interpolated with an ideal interpolation coefficient. The interpolation coefficient (-n to + n) performs an interpolating process between lines in the range of 2n + 1 pixels.

  In the diagrams (a) and (b), interpolation coefficients n = 1, 2, and 3 are shown.

  The amount of deviation from the ideal interpolation is shown in the lower stage of the interpolation coefficient.

  In (c), the color misregistration is obtained from the difference between the misregistration amounts of (a) and (b). The color shift is obtained between the interpolations in the entire area and the shift amount of the interpolation coefficient having the same interpolation range. Further, in the lower stage, an absolute value is taken as a value indicating the degree of the color shift.

  The center position of the interpolation is the target pixel for measuring the degree of color misregistration, centering on the pixel whose interpolation coefficient is close to 0.5 and up to the line switching position. Further, in the lower stage, the total amount of partial color misregistration is obtained in this way. The left half has the same correction slope between colors, so no color misregistration occurs. In addition, since the right half has different correction inclinations between colors, it can be seen that the larger the correction range, the smaller the total color shift amount.

  For example, if the partial cumulative amount of color misregistration is set within 1.5, n = 1 is selected for pixel ID6 and n = 3 is selected for pixel ID16. The range in which interpolation processing is performed at each interpolation position is determined in advance and stored in the color misregistration amount memory 107.

  In the interpolation calculation 104, when the interpolation coefficient is α, the calculation is performed using the following equation.

Output = Line 1 × (1−α) + Line 2 × α
As described above, according to the embodiment of the present invention, the amount of color misregistration can be reduced while maintaining the uniformity of the thickness of the fine line, and a good image quality can be obtained.

  The basic processing of the second embodiment of the present invention is the same as that of the first embodiment, but the operations of the PDL processing unit 92 and the image memory 94 and the configuration of the output system image processing are different.

  The reading operation of the PDL processing unit 92 and the image memory 94 is developed into a two-dimensional image by emulating the operations of the line buffer 101 and the line selector 102 of the first embodiment in software.

  Therefore, as shown in the select line 1 in FIGS. 10A and 10B, the joint lines are combined in one line and transferred to the output system image processing 96 to 99. The output system image processing 96 to 99 is the same as the interpolation operation 103 in the first embodiment by holding one line and outputting two lines simultaneously in the input line buffer 121 shown in the block diagram of FIG. data, the image data is transferred at the timing.

  As described above, according to the second embodiment of the present invention, since line selection is performed at the time of software development, it is not necessary to have a large amount of line buffers, and a low-cost system can be realized.

  In the embodiment of the present invention, the algorithm for determining the correction range has been described as a method for determining the correction range at a time between two colors. For example, the amount of color misregistration is calculated based on one color, and the same color is interpolated. It is also possible to set an appropriate interpolation coefficient by reflecting the update of the processing width, updating this for other colors and other portions, and repeating the update.

  In the embodiment of the present invention, the interpolation process is performed by linear interpolation, but an interpolation process having bicubic or other good filter characteristics may be selected within a range where the hardware scale is allowed.

  In this embodiment, the polygon mirror is used as the scanning means of the optical system, but it is easy to generate the same phenomenon even if other scanning means such as a galvano mirror or EO (electro-optic element) is used. I can imagine.

  Therefore, the present invention may be applied to other scanning systems.

  In the present invention, the information on the amount of color misregistration and the information on the bending characteristic are stored separately in the memory. However, the same memory may be used, and color misregistration information is included as a correction range and a correction coefficient for each part. Even if they are stored in the memory in the form, they may be conceptually the same.

  In addition, although information at the time of shipment is stored using a nonvolatile memory in the embodiment of the present invention, it can also be realized by a combination of a hard disk and a volatile memory.

1 Color scanner 2 Color printer

Claims (5)

First scanning means for scanning in one direction to form an image of at least one line;
A second scanning means for obtaining a scanning effect perpendicular to the first scanning means for two-dimensional image formation;
A characteristic storage means for storing at least a vertical error characteristic with respect to an ideal scan of the first scanning means;
Image storage means for storing images of a plurality of lines;
Line selection means for switching lines read from the image storage means within one scanning period;
Interpolation means for interpolating the output of the line selection means,
According to the characteristic storage means, control the parameters of the line selection means and the interpolation means,
In an image forming apparatus that reduces an error from an ideal scan of a first scanning unit,
While obtaining a color image by superimposing multiple colors,
Color misregistration characteristic storage means for storing color misregistration information by error correction,
An image forming apparatus, wherein the amount of color misregistration is reduced by varying a correction width of correction processing according to a color misregistration characteristic storage unit.   2. The image forming apparatus according to claim 1, wherein the correction method is linear interpolation. The image forming apparatus according to claim 1.
The first scanning means uses a polygon mirror,
An image forming apparatus, wherein the scanning error includes an error due to a tilt of a polygon rotation axis. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 2, wherein the second scanning means is rotation of a photosensitive drum in an electrophotographic system. The image forming apparatus according to claim 1.
An image forming apparatus characterized in that the scanning characteristic storage means and the color misregistration characteristic storage means are collected in at least one storage means as information of correction ranges for interpolation at a plurality of locations in one line.

Images