JP2010152093A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing irregularity generated on a contour of a toner image. <P>SOLUTION: Laser diodes LDa1 to LDc1 are a plurality of light sources arranged to be spaced in a subscanning direction Z, and radiate beams to the same pixel on a photoreceptor drum as an object to be irradiated. A CPU is a controller which adjusts a position of the center of gravity in the subscanning direction Z of each of the plurality of beams by changing a ratio of energy of the beam radiated by each of the plurality of laser diodes LDa1 to LDc1, and adjusts total sum of the energy of the beams radiated to the pixel P1 being the object to be irradiated in accordance with states of the pixels located around the pixel of the object to be irradiated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an electrostatic latent image by irradiating a scanned surface with a beam.

  As a conventional image forming apparatus, for example, an image forming apparatus described in Patent Document 1 is known. In the image forming apparatus, the light source unit includes light sources arranged so as to be arranged in the sub-scanning direction at a density that is an integer multiple of 2 or more with respect to the density of the pixels on the surface to be scanned. Then, when the pixel position is shifted in the sub-scanning direction, the exposure energy amounts of the plurality of light sources forming one pixel are adjusted. At this time, the total exposure energy amount of a plurality of light sources forming one pixel is kept constant. As a result, pixel shift in the sub-scanning direction can be corrected with high accuracy.

  However, the image forming apparatus described in Patent Document 1 has a problem that unevenness occurs in the contour of the toner image as described below. FIG. 17 is a diagram illustrating the intensity distribution of the beam irradiated to one pixel in the image forming apparatus described in Patent Document 1. In FIG. The horizontal axis indicates the amount of light, and the vertical axis indicates the position in the sub-scanning direction. In FIG. 17, it is assumed that the light source unit has two light sources.

  In FIG. 17A, only the light source arranged on the lower side in the sub-scanning direction irradiates the beam B1, and the light source arranged on the upper side in the sub-scanning direction does not irradiate the beam B2. In this case, the position of the center of gravity of the beam B12 (that is, the beam B1) obtained by combining the beam B1 and the beam B2 is a point A1, as shown in FIG. On the other hand, in FIG. 17B, the light source arranged on the lower side in the sub-scanning direction and the light source arranged on the upper side in the sub-scanning direction are beams B1 and B2 having light amounts half that of the light source in FIG. Is being irradiated. In this case, the position of the center of gravity of the beam B12 is a point A2 above the point A1. As described above, the position of the center of gravity of the beam B12 in the sub-scanning direction can be adjusted by adjusting the light amounts of the beams B1 and B2 irradiated by the two light sources.

By the way, the toner image is formed by the positively charged toner being attached to the pixels on the scanned surface under the influence of the electric field generated by the electrostatic latent image formed on the scanned surface. Specifically, toner adheres to pixels on the scanned surface whose potential is lower than the threshold value, and toner does not adhere to pixels on the scanned surface whose potential is equal to or higher than the threshold value. Whether the pixel potential is lower than the threshold value or more than the threshold value depends on whether or not the light amount of the beam B12 irradiated to the pixel is more than the threshold value. For example, in the pixel shown in FIG. 17A, the area where the toner adheres is an area having a width r1 where the intensity of the beam B12 is larger than the threshold value S. Similarly, in the pixel shown in FIG. 17B, the area where the toner adheres is an area having a width r2 where the intensity of the beam B12 is larger than the threshold value S. Here, as is apparent from FIG. 17, the width r1 is smaller than the width r2. Therefore, in the pixel shown in FIG. 17A, the area where the toner adheres is circular, whereas in the pixel shown in FIG. 17B, the area where the toner adheres is a long axis in the sub-scanning direction. It becomes the ellipse shape which has. As a result, in the pixels shown in FIG. 17A and FIG. 17B, the width in the sub-scanning direction of the area where the toner adheres in the pixels is different although the total amount of exposure energy is the same. End up. Therefore, when the pixels shown in FIGS. 17A and 17B are mixed and arranged in the main scanning direction in the contour of the toner image, the contour of the toner image is uneven.
JP 2007-160508 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can suppress unevenness generated in the contour of a toner image.

  An image forming apparatus according to an aspect of the present invention is a plurality of light sources arranged at intervals in a sub-scanning direction with a surface to be scanned, and the same pixel on the surface to be scanned is irradiated as a beam to be irradiated. A control unit that adjusts the position of the center of gravity in the sub-scanning direction of the plurality of beams by changing the ratio of energy of the plurality of light sources to be irradiated and the energy of the beams irradiated by each of the plurality of light sources. A control unit that adjusts the sum of the energy of the beam irradiated to the irradiation target pixel in accordance with the state of the pixels positioned around the pixel and the number of the beams irradiated to the irradiation target pixel It is characterized by comprising.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus)
First, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an image forming apparatus 100 according to an embodiment of the present invention.

  This image forming apparatus is an electrophotographic color printer and is configured to form an image of four colors (Y: yellow, M: magenta, C: cyan, K: black) by a so-called tandem method. is there. An image is formed at each image forming station 101 and is combined on the intermediate transfer belt 112. In each figure, the letters Y, M, C, and K attached to the reference numerals mean members for yellow, magenta, cyan, and black, respectively.

  The outline of the image forming station 101 (101Y, 101M, 101C, 101K) will be described. The photosensitive drum 102 (102Y, 102M, 102C, 102K), the laser scanning optical unit 1 (1Y, 1M, 1C, 1K), Developing unit 104 (104Y, 104M, 104C, 104K) and the like are included.

  Beams BY, BM, BC, and BK emitted from each laser scanning optical unit 1 irradiate each photosensitive drum 102 to form an image of each color. On the other hand, an intermediate transfer belt 112 is stretched endlessly by rollers 113, 114, 115 immediately below the image forming station 101, is driven to rotate in the direction of arrow A, and is a portion where the roller 113 is installed. A secondary transfer roller 116 is disposed at a portion (secondary transfer portion) that faces 112. In addition, a paper feeding unit 130 that feeds the stacked transfer materials one by one is installed in the lower part of the image forming apparatus.

  Image data is transmitted as image data for each YMCK from an image reading device (scanner) or a computer (not shown) to the storage unit 12 (see FIG. 3), and each laser scanning optical unit 1 is driven based on these image data, A toner image is formed on each photosensitive drum 102. Such an electrophotographic process is well known and will not be described.

  The toner images formed on the respective photosensitive drums 102 are sequentially primary-transferred onto the intermediate transfer belt 112 that is rotationally driven in the direction of arrow A, and four color images are combined. On the other hand, the transfer material is fed upward from the paper feeding unit 130 one by one, and the composite image is secondarily transferred from the intermediate transfer belt 112 by the electric field applied from the secondary transfer roller 116 in the secondary transfer unit. Thereafter, the transfer material is conveyed to a fixing device (not shown), and the toner is heated and fixed, and is discharged to the upper surface of the image forming apparatus.

  A TOD sensor 106 for detecting the fed paper is installed immediately before the secondary transfer unit, and the transfer material and the image on the intermediate transfer belt 112 are synchronized. In addition, a registration sensor 105 for detecting a registration correction image formed on the intermediate transfer belt 112 is provided. A registration correction image is formed on the intermediate transfer belt 112 for each image forming station 101, and the correction image is detected by the registration sensor 105, thereby adjusting the light emission timing of each laser beam BY, BM, BC, BK. , YMCK images are accurately combined on the intermediate transfer belt 112.

(Laser scanning optical unit)
Next, each laser scanning optical unit 1 will be described with reference to the drawings. FIG. 2 is a plan view of the laser scanning optical unit 1. FIG. 3 is a block diagram of the image forming apparatus. FIG. 4 is a diagram illustrating a configuration of the light source unit 2. As shown in FIG. 2, the traveling direction of the beam is defined as traveling direction X, the main scanning direction is defined as main scanning direction Y, and the sub-scanning direction is defined as sub-scanning direction Z.

  Each laser scanning optical unit 1 includes a light source unit 2, a collimator lens 3, and a scanning unit. The light source unit 2 includes a plurality of laser diodes. The scanning unit includes a polygon mirror 4, an SOS sensor 5, scanning lenses 6 a and 6 b, and a folding mirror 7. The polygon mirror 4 is rotationally driven at a predetermined speed based on a drive signal input to the drive unit 22 (see FIG. 3). The SOS sensor 5 outputs a main scanning synchronization signal (hereinafter also referred to as an SOS signal).

  As shown in FIG. 4, the light source unit 2 is a surface emitting laser constituted by a chip 30 and laser diodes LDa1 to LDa4, LDb1 to LDb4, LDc1 to LDc4 (hereinafter collectively referred to as laser diode LD). It is. The laser diodes LD are arranged in a matrix on the rectangular chips 30. By arranging the chip 30 so that the long side of the rectangular chip 30 is inclined with respect to the sub-scanning direction Z, the laser diodes LD are arranged in the sub-scanning direction Z with an interval d / 3. The laser diodes LDa1, LDb1, and LDc1 irradiate beams A1, B1, and C1 on the same pixel P1 on the photosensitive drum 102 as an irradiation target. The laser diodes LDa2, LDb2, and LDc2 irradiate the same pixels P2 on the photosensitive drum 102 with the beams A2, B2, and C2, respectively. The laser diodes LDa3, LDb3, and LDc3 irradiate the same pixel P3 on the photosensitive drum 102 with the beams A3, B3, and C3. The laser diodes LDa4, LDb4, and LDc4 irradiate the same pixel P4 on the photosensitive drum 102 with the beams A4, B4, and C4.

  The beams A1 to C4 radiated from the laser diode LD are converted into substantially parallel light by the collimator lens 3, deflected in the main scanning direction Y at a uniform angular velocity on each reflecting surface of the polygon mirror 4, and transmitted through the scanning lenses 6a and 6b. Then, the light is reflected by the folding mirror 7 to form an image on the photosensitive drum 102 and scan in the main scanning direction Y. A two-dimensional electrostatic latent image is formed on the photosensitive drum 102 by the main scanning and the sub scanning by the rotation of the photosensitive drum 102.

  The scanning lenses 6 a and 6 b have an fθ characteristic that corrects the beam deflected at a constant angular velocity by the polygon mirror 4 to a uniform velocity in the main scanning direction Y, and an imaging property that forms an image of the beam on the photosensitive drum 102. is doing.

  The SOS sensor 5 is disposed outside the image area, and a beam that has passed through the scanning lenses 6a and 6b and reflected by the folding mirror 7 is incident thereon. The SOS sensor 5 is used for detecting the scanning speed of the polygon mirror 4 and synchronizing the main scanning direction Y of each beam.

  The laser scanning optical unit 1 is controlled by a control unit shown in FIG. In FIG. 3, the light source unit 2, polygon mirror 4, SOS sensor 5, CPU 10, storage unit 12, pixel clock generation circuit 14, crystal oscillator 16, image processing unit 18, laser drive circuit 20, drive unit 22, and registration sensor 105 Is described.

  The registration sensor 105 detects a registration correction image formed on the intermediate transfer belt 112 and outputs the detection result to the CPU 10. Based on the detection result from the registration sensor 105 and the information stored in the storage unit, the CPU 10 generates the positional deviation information by calculating the pitch deviation in the main scanning direction and the sub-scanning direction of the registration correction image. . The CPU 10 generates correction information for correcting the pitch deviation in the main scanning direction and the sub-scanning direction based on the positional deviation information and the image data, and outputs the correction information to the image processing unit 18.

  The crystal oscillator 16 outputs a signal having a predetermined frequency to the pixel clock generation circuit 14. The pixel clock generation circuit 14 generates a pixel clock based on a signal from the crystal oscillator 16 and outputs the pixel clock to the image processing unit 18. Further, image data is supplied to the image processing unit 18. Then, the image processing unit 18 generates a modulation signal for forming an image in which the pitch deviation in the main scanning direction and the sub scanning direction is corrected based on the pixel clock, the image data, and the correction information, and the laser driving circuit 20. Output to. The laser drive circuit 20 drives the light source unit 2 based on the modulation signal. Thereby, the light source part 2 irradiates beam A1-C4.

  Further, the laser driving circuit 20 is individually driven by a control signal from the CPU 10 so as to be driven only in the horizontal and vertical effective periods. A signal indicating the light amount of the beam from the light source unit 2 is fed back to the laser drive circuit 20, and the drive of each laser diode LD of the light source unit 2 is controlled so that the light amount is constant.

  As described above, the beam output from the light source unit 2 is deflected by the polygon mirror 4 and scans on the photosensitive drum 102. Drawing by scanning on one surface of the polygon mirror 4 is referred to as one scanning. The writing position of the deflected beam in the main scanning direction Y is controlled based on the SOS signal detected by the SOS sensor 5 disposed on the tip side of the scanning region. That is, the SOS signal of the SOS sensor 5 is supplied to the pixel clock generation circuit 14 and the image writing timing by each laser diode LD of the light source unit 2 is controlled.

(Correction of pitch deviation in the sub-scanning direction)
Hereinafter, correction of pitch deviation in the sub-scanning direction Z will be described with reference to the drawings. The correction of the pitch deviation in the main scanning direction Y is performed by adjusting the light emission timing of the laser diode LD as in the case of a general image forming apparatus, and thus the description thereof is omitted.

  In the image forming apparatus 100, a pitch shift in the sub-scanning direction Z occurs due to various causes. Therefore, in the image forming apparatus 100, as shown in FIG. 4, three laser diodes LD are arranged so that one pixel P can be irradiated with a beam. Hereinafter, the laser diodes LDa1, LDb1, and LDc1 of FIG. 4 will be described as an example. When there is no pitch shift in the sub-scanning direction Z, only the laser diode LDb1 arranged at the center in the sub-scanning direction Z outputs the beam B1. On the other hand, when a pitch shift occurs on the positive direction side in the sub-scanning direction Z, the laser diodes LDa1 and LDb1 output beams A1 and B1. As a result, the center of gravity of the combined beam A1, B1 is shifted to the positive direction side in the sub-scanning direction Z. Similarly, when a pitch shift occurs on the negative direction side in the sub-scanning direction Z, the laser diodes LDb1 and LDc1 output beams B1 and C1. As a result, the center of gravity of the beam obtained by combining the beams B1 and C1 is shifted to the negative direction side in the sub-scanning direction Z. Hereinafter, correction of pitch deviation in the sub-scanning direction Z will be described in more detail with reference to the drawings.

  FIG. 5 is a graph showing light emission patterns of the laser diodes LDa1, LDb1, and LDc1. 100% in FIG. 5 means the amount of light when only the laser diode LDb1 outputs the beam B1. FIG. 6 is a graph showing the intensity distribution of the beams A1, B1, and C1 in the light emission pattern shown in FIG. In FIG. 6, the vertical axis indicates the sub-scanning direction Z, and the horizontal axis indicates the amount of light.

  In the image forming apparatus 100 according to the present embodiment, there are light emission patterns of patterns 1 to 9 as shown in FIG. When there is no pitch shift in the sub-scanning direction Z, the pattern 5 irradiates the pixel P1 with the beam B1. At this time, as shown in the pattern 5 in FIG. 6, the center of gravity of the beam B <b> 1 indicated by the alternate long and short dash line is located in the approximate center in the sub-scanning direction Z.

  On the other hand, when a pitch shift has occurred on the positive direction side in the sub-scanning direction Z, the beam A1 and the beam B1 are emitted to the pixel P1. At this time, the ratio between the light amount of the beam A1 and the light amount of the beam B1 is changed in a state where the sum of the light amount of the beam A1 and the light amount of the beam B1 is kept constant (that is, the sum is 100%). As a result, the position of the center of gravity in the sub-scanning direction Z of the combined beam A1, B1 is adjusted. For example, in the pattern 7, the light amount of the beam A1 is 50%, and the light amount of the beam B1 is 50%. Thereby, as shown in the pattern 7 in FIG. 6, the center of gravity of the combined beam A1, B1 indicated by the one-dot chain line is closer to the positive direction side in the sub-scanning direction Z than the position of the center of gravity in the pattern 5. Moving. Further, in the pattern 8, the light amount of the beam A1 is 75%, and the light amount of the beam B1 is 25%. As described above, by increasing the light amount of the beam A1, the center of gravity of the beam obtained by combining the beams A1 and B1 indicated by the alternate long and short dash line is compared with the position of the center of gravity in the pattern 7, as shown in the pattern 8 of FIG. In addition, it moves to the positive direction side in the sub-scanning direction Z.

  In addition, when a pitch shift occurs on the negative direction side in the sub-scanning direction Z, the beam B1 and the beam C1 are emitted to the pixel P1. At this time, the ratio between the light amount of the beam B1 and the light amount of the beam C1 is changed in a state where the sum of the light amount of the beam B1 and the light amount of the beam C1 is kept constant (that is, the sum is 100%). Thereby, the position of the center of gravity in the sub-scanning direction Z of the beam obtained by combining the beams B1 and C1 is adjusted. For example, in the pattern 3, the light amount of the beam B1 is 50%, and the light amount of the beam C1 is 50%. Thereby, as shown in the pattern 3 of FIG. 6, the center of gravity of the beam obtained by combining the beams B <b> 1 and C <b> 1 indicated by the one-dot chain line is closer to the negative direction side in the sub-scanning direction Z than the position of the center of gravity in the pattern 5. Moving. Further, in the pattern 2, the light amount of the beam C1 is 75%, and the light amount of the beam B1 is 25%. In this way, by increasing the light amount of the beam C1, the center of gravity of the beam obtained by combining the beams B1 and C1 indicated by the alternate long and short dash line is compared with the position of the center of gravity in the pattern 3 as shown in the pattern 2 of FIG. In addition, it moves further to the negative direction side in the sub-scanning direction Z.

  By the way, in the above-described correction method for pitch deviation in the sub-scanning direction Z, as in the image forming apparatus described in Patent Document 1, irregularities are generated in the contour of the toner image. For example, in the pattern 5, the beam B1 is irradiated with a light amount of 100%. This is the state shown in FIG. 17A, and the region where the toner adheres is within the region of width r1. On the other hand, in the pattern 7, the beams A1 and B1 are each irradiated with a light amount of 50%. This is the state shown in FIG. 17B, and the region where the toner adheres is in the region of the width r2 larger than the width r1. Therefore, the area of the area where the toner adheres in the pixel P1 differs between the pattern 5 and the pattern 7. As a result, when the pixel to which the toner is adhered according to the pattern 5 and the pixel to which the toner is adhered according to the pattern 7 are arranged in the main scanning direction Y in the contour of the toner image, the contour of the toner image is uneven.

  Therefore, the image forming apparatus 100 determines the state of the pixels located around the pixel P1 that is the irradiation target of the beam and the number of the beams A1, B1, and C1 irradiated to the irradiation target pixel P1. The total light amount of the beams A1, B1, and C1 irradiated to the pixel P1 to be irradiated is adjusted. Hereinafter, it will be described in detail with reference to the drawings. FIG. 7 is a diagram illustrating an example of a toner image. In FIG. 7A, a straight line extending in the main scanning direction Y is drawn. In FIGS. 7B and 7C, a straight line having a thickness twice that of FIG. 7A is drawn. It is. FIG. 8 is a graph showing light emission patterns of the laser diodes LDa1, LDb1, and LDc1. FIG. 9 is a graph showing the intensity distribution of the beams A1, B1, and C1 in the light emission pattern shown in FIG. In FIG. 9, the vertical axis indicates the sub-scanning direction Z, and the horizontal axis indicates the amount of light. The dotted lines in FIGS. 8 and 9 indicate the light amounts in FIGS.

  As shown in FIGS. 7A to 7C, in the image forming apparatus 100, at least one of the pixels adjacent in the sub-scanning direction Z of the pixel P1 that irradiates the beam is a pixel to which toner does not adhere ( That is, when the pixel P1 is irradiated with one beam, the total energy when the pixel P1 is irradiated with a plurality of beams is larger than the total energy when the pixel P1 is irradiated with one beam. Adjust smaller. This will be described in more detail below.

  When at least one of the pixels adjacent to the pixel P1 in the sub-scanning direction Z is a pixel to which toner does not adhere, the beam is irradiated with the light emission patterns of patterns 10 to 18 shown in FIG. Specifically, when no pitch shift in the sub-scanning direction Z occurs, the pattern 14 irradiates the pixel P1 with one beam B1. At this time, as shown in the pattern 14 of FIG. 9, the center of gravity of the beam B <b> 1 indicated by the alternate long and short dash line is located substantially in the center in the sub-scanning direction Z. The light amount of the beam B1 in the pattern 14 is 100%, which is the same as the light amount of the beam B1 of the pattern 5.

  On the other hand, when a pitch shift has occurred on the positive direction side in the sub-scanning direction Z, the beam A1 and the beam B1 are emitted to the pixel P1. At this time, the ratio between the light amount of the beam A1 and the light amount of the beam B1 is changed in a state where the sum of the light amount of the beam A1 and the light amount of the beam B1 is smaller than the light amount (100%) of the beam B1 in the pattern 14. As a result, the position of the center of gravity in the sub-scanning direction Z of the combined beam A1, B1 is adjusted. For example, in the pattern 16, the light amount of the beam A1 is 30%, and the light amount of the beam B1 is 30%. As a result, as shown in the pattern 16 of FIG. 9, the center of gravity of the beam obtained by combining the beams A1 and B1 indicated by the alternate long and short dash line is closer to the positive side in the sub-scanning direction Z than the position of the center of gravity in the pattern 14. Moving. Further, the light amount of the beam obtained by combining the beams A1 and B1 in the pattern 16 is 60% of the light amount of the beam B1 in the pattern 14. Therefore, in the pattern 16, the width in the sub-scanning direction Z of the region where the light amount of the combined beam A 1, B 1 exceeds the threshold value is smaller than the width in the pattern 7 and approaches the width in the pattern 14.

  In addition, when a pitch shift occurs on the negative direction side in the sub-scanning direction Z, the beam B1 and the beam C1 are emitted to the pixel P1. At this time, the ratio between the light amount of the beam B1 and the light amount of the beam C1 is changed in a state where the sum of the light amount of the beam B1 and the light amount of the beam C1 is smaller than the light amount (100%) of the beam B1 in the pattern 14. Thereby, the position of the center of gravity in the sub-scanning direction Z of the beam obtained by combining the beams B1 and C1 is adjusted. For example, in the pattern 12, the light amount of the beam B1 is 30%, and the light amount of the beam C1 is 30%. As a result, as shown in the pattern 12 of FIG. 9, the center of gravity of the beam obtained by combining the beams B1 and C1 indicated by the alternate long and short dash line is closer to the negative direction side in the sub-scanning direction Z than the position of the center of gravity in the pattern 14. Moving. Further, the light amount of the beam obtained by combining the beams B1 and C1 in the pattern 12 is 60% of the light amount of the beam B1 in the pattern 14. Therefore, in the pattern 12, the width in the sub-scanning direction Z of the region where the light amount of the combined beam B1, C1 exceeds the threshold is smaller than the width in the pattern 3, and approaches the width in the pattern 14.

  In order to realize the above control, the image forming apparatus 100 stores the table 1 shown in Table 1 and the table 2 shown in Table 2 in the storage unit 12 shown in FIG. Table 1 is a table in which the light emission patterns of patterns 1 to 9 in FIGS. 5 and 6 are recorded, and Table 2 is a table in which the light emission patterns of patterns 10 to 18 in FIGS. 8 and 9 are recorded. is there.

(Operation of image forming apparatus)
The operation of the image forming apparatus 100 will be described below with reference to the drawings. FIG. 10 is a flowchart illustrating an operation performed by the CPU 10 of the image forming apparatus 100.

  First, based on the detection result from the registration sensor 105 and information stored in the storage unit 12, the CPU 10 calculates the pitch deviation in the main scanning direction and the sub-scanning direction of the registration correction image to calculate the positional deviation information. Is generated (step S1). Next, the CPU 10 acquires image data of an image to be printed from a connected device (not shown) such as a scanner (step S2).

  Next, the CPU 10 reads the first pixel data from the acquired image data (step S3). The pixel data is data indicating whether or not toner is applied to the pixel. Specifically, the pixel data is “1” when the toner is applied and “0” when the toner is not applied. is there. Therefore, the CPU 10 determines whether or not the pixel data is “1” (step S4). When the pixel data is not “1”, the pixel is not irradiated with the beam. Therefore, the process proceeds to step S11. On the other hand, when the pixel data is “1”, the pixel is irradiated with a beam. Therefore, the process proceeds to step S5.

  When the pixel data is “1”, the CPU 10 determines whether or not both of the pixel data of the pixels adjacent to the pixel corresponding to the pixel data in the sub-scanning direction Z are “1” (Step 1). S5). In step S5, the CPU 10 determines whether or not at least one of the pixels adjacent to the pixel corresponding to the pixel data in the sub-scanning direction Z is a pixel to which toner does not adhere. When both of the pixel data are “1”, the CPU 10 determines that both of the pixels adjacent to the pixel corresponding to the pixel data in the sub-scanning direction Z are pixels to which the toner adheres. Thereafter, the process proceeds to step S6. On the other hand, when both of the pixel data are not “1”, the CPU 10 determines that at least one of the pixels adjacent to the pixel corresponding to the pixel data in the sub-scanning direction Z is a pixel to which toner does not adhere. . Thereafter, the process proceeds to step S8.

  When both the pixel data are “1”, the CPU 10 reads Table 1 shown in Table 1 (Step S6). Then, the CPU 10 generates correction information corresponding to the pixel data based on the positional deviation information generated in step S1 (step S7). Specifically, the CPU 10 acquires a pitch shift in the sub-scanning direction Z from the position shift information, and selects a light emission pattern (Pattern 1 to Pattern 9) corresponding to the magnitude of the pitch shift from the table 1. Then, the CPU 10 outputs the selected light emission pattern to the image processing unit 18 as correction information. Then, the image processing unit 18 generates a modulation signal based on the pixel data and the correction information, and outputs the modulation signal to the laser driving circuit 20. The laser drive circuit 20 drives the light source unit 2 based on the modulation signal. Thereby, the light source part 2 irradiates beams A1-C1. The beams A1 to C1 are irradiated for a certain time. Thereafter, the process proceeds to step S10.

  When both of the pixel data are not “1”, the CPU 10 reads Table 2 shown in Table 2 (Step S8). And CPU10 produces | generates the correction information corresponding to pixel data based on the positional offset information produced | generated in step S1 (step S9). Specifically, the CPU 10 acquires a pitch shift in the sub-scanning direction Z from the position shift information, and selects a light emission pattern (pattern 10 to pattern 18) corresponding to the magnitude of the pitch shift from the table 2. Then, the CPU 10 outputs the selected light emission pattern to the image processing unit 18 as correction information. Then, the image processing unit 18 generates a modulation signal based on the pixel data and the correction information, and outputs the modulation signal to the laser driving circuit 20. The laser drive circuit 20 drives the light source unit 2 based on the modulation signal. Thereby, the light source part 2 irradiates beams A1-C1. The beams A1 to C1 are irradiated for a certain time. Thereafter, the process proceeds to step S10.

  In step S10, the CPU 10 determines whether or not reading of all pixel data has been completed (step S10). When the reading of all pixel data is completed, this process ends. If reading of all pixel data has not been completed, the process proceeds to step S11.

  In step S11, the CPU 10 reads the next pixel data (step S11). Thereafter, the process proceeds to step S4, and the processes of steps S4 to S10 are performed for the next pixel data. This is the end of the description of the operation of the image forming apparatus 100. In the description of the operation of the image forming apparatus 100 using FIG. 10, the irradiation of the beams A1 to C1 has been described. However, in practice, in order to simultaneously write a plurality of lines of latent images, the beams A2 to C2, A3 to C3, and A4 to C4 are also irradiated simultaneously with the beams A1 to C1.

(effect)
According to the image forming apparatus 100, as described below, it is possible to suppress the occurrence of unevenness in the contour of the toner image. More specifically, in the image forming apparatus 100, when at least one of the pixels adjacent in the sub-scanning direction Z of the pixel P <b> 1 that irradiates the beam is a pixel to which toner does not adhere, the CPU 10 When a plurality of beams are irradiated to the pixel P1 (the pattern 10 to the pattern 13 and the pattern 15 to the pattern 18 in FIG. 8) rather than the total light amount when the single beam is irradiated (the pattern 14 in FIG. 8). The total amount of light is reduced. Thus, when the beam is irradiated with the patterns 10 to 13 and the patterns 15 to 18, the width in the sub-scanning direction Z of the region where the toner adheres to the pixel P <b> 1 is the pixel when the beam is irradiated with the pattern 14. It approaches the width in the sub-scanning direction Z of the area where the toner adheres to P1. As a result, even if the pixels irradiated with the beams from the patterns 10 to 18 are mixedly arranged in the main scanning direction Y in the outline of the toner image, the occurrence of unevenness in the outline of the toner image is suppressed. The image forming apparatus 100 is particularly suitable for accurately forming a fine line toner image extending in the main scanning direction Y.

(Other embodiments)
The image forming apparatus according to the present invention is not limited to the one shown in the above embodiment, and can be modified within the range of the paper.

  Here, in the image forming apparatus 100, whether or not the toner adheres to the pixel depends more specifically on the energy of the beam applied to the pixel. Therefore, the CPU 10 is supposed to adjust the total light amount of the beam, but actually adjusts the total energy of the beam. The beam energy is obtained by multiplying the light amount of the beam by the irradiation time of the beam. In the embodiment, since the beam irradiation time is constant, the CPU 10 is equivalent to adjusting the beam energy if the light amount of the beam is adjusted.

  However, the beam energy may not be adjusted by adjusting the light amount of the beam. The adjustment of the beam energy may be performed by adjusting the irradiation time of the beam. FIG. 11 is a diagram illustrating the relationship between the light amount of the beam and the irradiation time of the beam in the light emission patterns of patterns 10 to 18. In FIG. 11, dotted lines correspond to patterns 1 to 9.

  In FIG. 11, the energy of the beams A1, B1, and C1 is adjusted by adjusting the irradiation time of the beam, and the position of the combined beam A1, B1, and C1 in the sub-scanning direction Z is adjusted. . Further, the total irradiation time of the beams A1, B1, and C1 in the patterns 10 to 13 and the patterns 15 to 18 is shorter than the total irradiation time of the beams A1, B1, and C1 in the pattern 14. In this way, by adjusting the total beam irradiation time, the total beam energy in the pattern 14 may be made different from the total patterns 10 to 13 and 15 to 18. In the patterns 1 to 18, it is assumed that the beams A1, B1, and C1 all have the same amount of light.

  As shown in FIG. 7B, the toner adheres to the pixel on the positive direction side in the sub-scanning direction Z of the pixel P1, and the toner does not adhere to the pixel on the negative direction side in the sub-scanning direction Z of the pixel P1. Alternatively, the beams A1, B1, and C1 may be irradiated with a light emission pattern as shown in FIG. FIG. 12 is a diagram showing a light emission pattern when the beams A1, B1, and C1 are irradiated to the pixel P1 in FIG. 7B.

  In FIG. 7B, toner adheres to the pixel on the positive direction side in the sub-scanning direction Z of the pixel P1, and toner does not adhere to the pixel on the negative direction side in the sub-scanning direction Z of the pixel P1. Therefore, in the pixel P1, the width of the region to which the toner adheres does not have to increase even in the negative direction side of the sub-scanning direction Z. Therefore, as shown in FIG. 12, in the patterns 11 to 13, it is only necessary to reduce the light amount of the beam C1 on the negative direction side in the sub-scanning direction Z. Similarly, in the patterns 15 to 17, it is sufficient that the light amount of the beam B1 on the negative direction side in the sub-scanning direction Z is reduced.

  In FIG. 12, in the patterns 11 to 13, the light amount of the beam C1 on the negative direction side in the sub-scanning direction Z is reduced, and the light amount of the beam B1 on the positive direction side in the sub-scanning direction Z is not reduced. However, as shown in FIG. 13, the amount of decrease in the light amount of the beam C1 on the negative direction side in the sub-scanning direction Z may be made larger than the amount of decrease in the beam B1 on the positive direction side in the sub-scanning direction Z. Good. Similarly, in the patterns 15 to 17, the light amount of the beam B1 on the negative direction side in the sub-scanning direction Z is reduced, and the light amount of the beam A1 on the positive direction side in the sub-scanning direction Z is not reduced. However, as shown in FIG. 13, the amount of decrease in the light amount of the beam B1 on the negative direction side in the sub-scanning direction Z may be made larger than the amount of decrease in the beam A1 on the positive direction side in the sub-scanning direction Z. Good.

  Further, as shown in FIG. 7C, the toner adheres to the pixel on the negative side in the sub scanning direction Z of the pixel P1, and the toner adheres to the pixel on the positive direction side in the sub scanning direction Z of the pixel P1. If not, the beams A1, B1, and C1 may be irradiated with a light emission pattern as shown in FIG. FIG. 14 is a diagram showing a light emission pattern when the beams A1, B1, and C1 are irradiated to the pixel P1 in FIG. 7C.

  In FIG. 7C, toner adheres to the pixel on the negative direction side in the sub-scanning direction Z of the pixel P1, and toner does not adhere to the pixel on the positive direction side in the sub-scanning direction Z of the pixel P1. Therefore, in the pixel P1, the width of the region to which the toner adheres does not have to increase even in the positive direction side of the sub-scanning direction Z. Therefore, as shown in FIG. 14, in the patterns 11 to 13, the light amount of the beam B <b> 1 on the positive direction side in the sub-scanning direction Z may be reduced. Similarly, in the patterns 15 to 17, it is only necessary to reduce the light amount of the beam A1 on the positive direction side in the sub-scanning direction Z.

  In FIG. 14, in the patterns 11 to 13, the light amount of the beam B1 on the positive direction side in the sub-scanning direction Z is reduced, and the light amount of the beam C1 on the negative direction side in the sub-scanning direction Z is not reduced. However, as shown in FIG. 15, the reduction amount of the beam B1 on the positive side in the sub-scanning direction Z may be made larger than the reduction amount of the beam C1 on the negative side in the sub-scanning direction Z. Good. Similarly, in the patterns 15 to 17, the light amount of the beam A1 on the positive direction side in the sub-scanning direction Z is reduced, and the light amount of the beam B1 on the negative direction side in the sub-scanning direction Z is not reduced. However, as shown in FIG. 15, the reduction amount of the beam A1 on the positive side in the sub-scanning direction Z may be made larger than the reduction amount of the beam B1 on the negative side in the sub-scanning direction Z. Good.

  As shown in FIG. 16, when a diagonal toner image is formed, the width of the region to which the toner of the pixel P1 adheres may be widened in the sub-scanning direction Z. The oblique line toner image means that the pixel P1 and the pixels adjacent to the pixel P1 are arranged in a straight line in the oblique direction of the sub-scanning direction Z in a state where the beam is irradiated, and are adjacent to the sub-scanning direction Z of the pixel P1. It means that at least one of the pixels is a pixel that is not irradiated with a beam. In this case, the total energy when one beam is irradiated onto the pixel P1 may be equal to the total energy when a plurality of beams are irradiated onto the pixel P1. That is, the beam may be irradiated to the pixel P1 with the light emission patterns of the patterns 1 to 9.

  In the image forming apparatus 100, each pixel data has only binary information indicating whether toner is attached or not. However, there are cases where it is desired to express multi-tone density changes in the image forming apparatus 100. In such a case, one pixel may be a subpixel, and for example, one pixel may be constituted by eight subpixels (pixels). Thereby, it is possible to express a change in density of 8 gradations with one pixel.

  Note that in the image forming apparatus 100, a multi-tone density change may be expressed by one pixel.

  In the image forming apparatus 100, the total light amount of the patterns 10 to 18 is uniformly reduced by 40% with respect to the total light amount of the patterns 1 to 9, but this reduction amount is 40%. Not exclusively. Further, the amount of decrease may not be uniform.

  In the image forming apparatus 100, the interval between the pixels on the photosensitive drum 102 in the sub-scanning direction Z is three times the interval between the beams A1, B1, and C1, as shown in FIG. It may be an integer multiple of B1 and C1.

1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is the figure which planarly viewed the laser scanning optical unit. 1 is a block diagram of an image forming apparatus. It is the figure which showed the structure of the light source part. It is the graph which showed the light emission pattern of the laser diode. 6 is a graph showing a beam intensity distribution in the light emission pattern shown in FIG. 5. FIG. 6 is a diagram illustrating an example of a toner image. It is the graph which showed the light emission pattern of the laser diode. It is the graph which showed the intensity distribution of the beam in the light emission pattern shown in FIG. 3 is a flowchart illustrating an operation performed by a CPU of the image forming apparatus. It is the figure which showed the relationship between the light quantity of the beam in the light emission pattern of the pattern 10-pattern 18, and the irradiation time of a beam. It is the figure which showed the light emission pattern when irradiating a beam with respect to the pixel of FIG.7 (b). It is the figure which showed the light emission pattern when irradiating a beam with respect to the pixel of FIG.7 (b). It is the figure which showed the light emission pattern when irradiating a beam with respect to the pixel of FIG.7 (c). It is the figure which showed the light emission pattern when irradiating a beam with respect to the pixel of FIG.7 (c). FIG. 6 is a diagram illustrating an example of a toner image. 6 is a diagram illustrating an intensity distribution of a beam irradiated to one pixel in the image forming apparatus described in Patent Document 1. FIG.

Explanation of symbols

A1 to A4, B1 to B4, C1 to C4 beams LDa1 to LDa4, LDb1 to LDb4, LDc1 to LDc4 Laser diodes P1 to P4 Pixel 10 CPU
12 Storage unit

Claims (5)

A scanned surface;
A plurality of light sources arranged in the sub-scanning direction at intervals, and a plurality of light sources for irradiating a beam with the same pixel on the scanned surface as an irradiation target;
A control unit that adjusts the position of the center of gravity in the sub-scanning direction of the plurality of beams by changing the ratio of the energy of the beam emitted by each of the plurality of light sources, and is located around the pixel to be irradiated A control unit that adjusts the sum of the energy of the beams irradiated to the irradiation target pixels according to the state of the pixels and the number of the beams irradiated to the irradiation target pixels;
Having
An image forming apparatus. When at least one of the pixels adjacent to the irradiation target pixel in the sub-scanning direction is a pixel that is not irradiated with the beam, the control unit applies one beam to the irradiation target pixel. Reducing the total energy when the plurality of beams are irradiated to the pixel to be irradiated, than the total energy when
The image forming apparatus according to claim 1. The control unit is configured such that the irradiation target pixel and a pixel adjacent to the irradiation target pixel are arranged in a straight line in an oblique direction of the sub-scanning direction in a state where the beam is irradiated, and When at least one of the pixels adjacent in the scanning direction is a pixel that is not irradiated with the beam, the sum of the energy when one of the irradiation target pixels is irradiated with the beam, and the irradiation target The sum of the energy when the plurality of beams are irradiated to the pixels of
The image forming apparatus according to claim 2. An interval in the sub-scanning direction of the pixels on the scanned surface is an integer multiple of an interval in the sub-scanning direction of the plurality of beams;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The plurality of light sources are surface-emitting lasers in which a plurality of lasers are arranged in a matrix on the same chip;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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