JP2005234510A - Optical scanner, image forming method, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an optical scanner in which the pixel shift in a vertical scanning direction in an image forming apparatus is corrected with a high degree of accuracy. <P>SOLUTION: Light beams from a plurality of light sources 2 on a surface emitting laser 1 are used for scanning along adjacent scanning lines on a plane to be scanned. Two light sources corresponding to two adjacent scanning lines form a pair, and one of the pair of light sources is used as a main light source and the other is used as a sublight source, the pixel shift in the vertical scanning direction is corrected with a high degree of accuracy by varying the light quantity distribution in the vertical scanning direction on the plane to be scanned with the light beams from a set of the light sources by varying the light quantity ratio of the main light source and the sublight source without varying the total light quantity of the pair of light sources and without making the light quantity of the sublight source exceed the light quantity of the main light source. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a laser printer or a digital copying machine, and an optical scanning apparatus applied thereto.

  FIG. 14 schematically shows a general configuration of an image forming apparatus using an electrophotographic process such as a laser printer or a digital copying machine. In FIG. 14, a laser beam output from a semiconductor laser unit 1001 that is a light source is scanned by a rotating polygon mirror 1002 (deflector) and passes through a scanning lens 1003 on a photoconductor 1004 that is a medium to be scanned. And exposing the photoreceptor 1004 to form an electrostatic latent image. For each line, the photodetector 1005 detects the scanning beam. The phase synchronization circuit 1009 receives the clock from the clock generation circuit 1008 and generates an image clock (pixel clock) that is phase-synchronized for each line based on the output signal of the photodetector 1005. The image processing unit 1006 supplies the image clock and the image data synchronized therewith to the laser driving circuit 1007. The laser driving circuit 1007 controls the formation of an electrostatic latent image on the photoconductor 1004 by controlling the light emission time of the semiconductor laser unit 1001 according to the image data and the image clock.

  In recent years, the demand for higher printing speed (image formation speed) and higher image quality has increased, and in response to this, the polygon motor, which is a deflector, and the pixel clock, which is the reference clock for laser modulation, have been increased. However, the speed limit of either method is approaching.

  Therefore, the use of multi-beam optical scanning using a plurality of light sources has been used to cope with higher speeds. In the multi-beam optical scanning method, the number of light beams that can be scanned simultaneously by the deflection of the deflector increases, so that the rotation speed of the polygon motor, which is a deflector, can be reduced, and the pixel clock frequency can be lowered. Thus, it is possible to perform optical scanning and image formation.

  As a light source constituting a multi-beam, a method using a combination of a plurality of single beam laser chips or a method using an LD array in which a plurality of light emitting elements are incorporated on one laser chip is used.

  Semiconductor lasers such as LD arrays constituting the multi-beam are extremely small and can be modulated directly and at high speed by a drive current, so that they have been widely used as light sources for laser printers and the like in recent years. However, since the relationship between the drive current of the semiconductor laser and the optical output has a characteristic that changes with temperature, in the case of a surface emitting laser in which a plurality of light sources are configured on the same chip, the distance between the light sources is short. The effects of temperature change and temperature crosstalk due to the temperature are prominent, and this tends to cause fluctuations in the amount of light. For example, Patent Documents 1 and 3 are known documents relating to techniques for improving such a problem of thermal crosstalk, and Patent Document 2 is a known document relating to control of light emission intensity and light emission time in pixel units. .

JP 2001-272615 A JP 2003-72135 A JP 2001-350111 A

  The present invention relates to an optical scanning device that performs optical scanning using a plurality of light sources including surface-emitting lasers and the like, and an image forming apparatus that uses the optical scanning device, and its purpose is a factor such as color misregistration during color image recording. Effectively corrects the dot position deviation in the sub-scanning direction, equalizes the progress of characteristic deterioration of multiple light sources, extends the life of the light source, and reduces the amount of light due to uneven characteristic deterioration of the multiple light sources. For example, image density unevenness due to variations is reduced.

  The invention of claim 1 has a plurality of light sources for generating a light beam for scanning the surface to be scanned, and a light source driving means for driving them. Two light sources corresponding to one scanning line are set as one set, and one of the set of light sources is set as a main light source and the other is set as a sub light source. By changing the light quantity ratio between the main light source and the sub light source without causing the light quantity of the light source to exceed the light quantity of the main light source, the light quantity in the sub scanning direction on the surface to be scanned of the light beam generated from one set of light sources An optical scanning device characterized by controlling distribution.

  The invention of claim 2 has a plurality of light sources for generating a light beam for scanning the surface to be scanned, and a light source driving means for driving them, and the light source driving means includes three adjacent light sources on the surface to be scanned. Three light sources corresponding to one scanning line are set as one set, and among the one set of light sources, a light source corresponding to the center scanning line is a main light source, and the remaining two light sources are sub-light sources, respectively. Generated from a set of light sources by changing the light intensity ratio between the main light source and each sub light source without changing the total light amount of the light source and without exceeding the light amount of each sub light source. An optical scanning device that controls a light amount distribution in the sub-scanning direction of a light beam to be scanned on a surface to be scanned.

  The invention of claim 3 has a plurality of light sources for generating a light beam for scanning the surface to be scanned and light source driving means for driving them, and the light source driving means are adjacent to each other on the surface to be scanned. Two light sources corresponding to one scanning line are made into one set, and the ratio of the light quantity between the light sources is changed without changing the total light quantity of the one light source, thereby scanning the light beam generated from the one set of light sources. An optical scanning device characterized by controlling a light amount distribution in a sub-scanning direction on a surface.

  According to a fourth aspect of the present invention, in the optical scanning device according to the first or second aspect of the present invention, the light source driving means includes means for switching between a light source driven as a main light source and a light source driven as a sub light source. Device.

  According to a fifth aspect of the invention, in the optical scanning device according to the first or second aspect of the invention, when the interval between the scanning lines corresponding to the main light source on the surface to be scanned is ΔX, the scanning line corresponding to the main light source on the surface to be scanned is And an interval between the main light source and the scanning line corresponding to the sub-light source is ΔX / 2 or less.

  According to a sixth aspect of the present invention, in the optical scanning device according to any one of the first to fifth aspects, a surface emitting laser in which a plurality of light sources are arranged in a grid on the same chip is provided as the plurality of light sources. This is a featured optical scanning device.

  According to a seventh aspect of the present invention, there is provided an image forming method for forming an electrostatic latent image on a scanned medium by using the surface of the scanned medium as a scanned surface and scanning the scanned surface with a light beam. A set of two light beams that scan adjacent scanning lines is formed to form an electrostatic latent image of the pixel array by one set of light beams, and the total light quantity of one set of light beams is changed without changing the total amount of light beams. The image forming method is characterized in that the barycentric position of the pixel in the sub-scanning direction is controlled by changing the light quantity ratio.

  According to an eighth aspect of the present invention, there is provided an image forming method for forming an electrostatic latent image on a scanned medium by using the surface of the scanned medium as a scanned surface and scanning the scanned surface with a light beam. A set of three light beams that scan the adjacent scanning lines is formed to form an electrostatic latent image of the pixel array by one set of light beams, and the central light beam of the one set of light beams is used as the main beam. The remaining two light beams are sub-beams, and the barycentric position of the pixel in the sub-scanning direction is obtained by changing the light amount ratio between the main beam and each sub-beam without changing the total light amount of one set of light beams. Is an image forming method.

  According to a ninth aspect of the present invention, there is provided an image forming apparatus that includes a medium to be scanned and an optical scanning device that scans the surface with a light beam using a light beam, and forms an electrostatic latent image on the medium to be scanned. The scanning apparatus is an image forming apparatus comprising the optical scanning apparatus according to any one of claims 1 to 6.

  The invention of claim 10 includes a plurality of color-measuring scanned media and an optical scanning device that scans with a light beam using the surface as a surface to be scanned. In the image forming apparatus for forming a latent image, the optical scanning device comprises the optical scanning device according to any one of claims 1 to 6.

  According to the first to sixth aspects of the present invention, since the light amount distribution in the sub-scanning direction of the light beam from the one set of light sources is controlled, the pixel array is recorded when the pixel row is recorded by the light beams from the one set of light sources. It is possible to control the position of the center of gravity in the sub-scanning direction, and therefore it is possible to correct the positional deviation of the recorded pixels in the sub-scanning direction with high accuracy. According to the third aspect of the present invention, it is possible to perform correction of positional deviation of pixels in the sub-scanning direction in a wider range in both directions. According to the fourth aspect of the present invention, the progress of the characteristic deterioration of the plurality of light sources can be equalized. According to the fifth aspect of the present invention, it is difficult to cause overlapping of light distribution by adjacent sets of light sources, that is, overlapping of adjacent pixel columns. According to the sixth aspect of the invention, the structure related to the light source can be simplified, and the positional relationship between the plurality of light sources can be defined with high accuracy. According to the seventh and eighth aspects of the invention, it is possible to correct the positional deviation in the sub-scanning direction of the recorded pixel row with high accuracy. According to the ninth and tenth aspects of the invention, it is possible to form a high-quality image in which the positional deviation of the pixel in the sub-scanning direction is corrected. In particular, according to the tenth aspect of the invention, the position of the pixel in the sub-scanning direction is possible. For example, it is possible to form an image with little color misregistration due to misregistration.

  In a typical embodiment of the present invention, one or a plurality of surface emitting lasers in which a plurality of light sources are arranged on the same chip are used as means for generating a light beam for scanning a surface to be scanned. The scanned surface is simultaneously scanned by a plurality of light beams. Then, with two or more light sources as one set, two or more adjacent scanning lines on the surface to be scanned are scanned by two or more light beams from each set of light sources, thereby recording a pixel row. The That is, a plurality of light sources are used for recording the same pixel. At the time of recording, the barycentric position of the recorded pixels in the sub-scanning direction is controlled by changing the ratio of the amount of light between the plurality of light sources in each group.

  The light quantity control method of the light source includes a method (1) for controlling the light quantity by using one of the light sources as a main light source and the remaining light source as a sub light source, and a light quantity by using two light sources as a main light source. It can be divided into the method (2) for controlling. The difference is as follows.

  In the case of the former method (2), the light quantity of the sub light source is always smaller than the light quantity of the main light source, and the total light quantity of the main light source and the sub light source is kept constant, and the ratio of the light quantity of each light source is changed. The position of the center of gravity of the recorded pixel in the sub-scanning direction is controlled with reference to the scanning line by the light beam of the main light source. In the case of the latter method (2), there is no restriction on the magnitude relationship between the light amounts of the main light source and the sub light source, and the ratio of the light amounts of the main light sources is changed while keeping the total light amount of the two main light sources constant. Thus, the barycentric position of the recorded pixel in the sub-scanning direction is controlled with reference to the intermediate position of the two scanning lines by the light beams of the two main light sources.

  A plurality of light beams from a plurality of light sources are guided to a polarizer such as a polygon mirror via an optical system including an optical lens, for example, and the light beams deflected by the polarizer are optical lenses including an optical lens. A light spot is formed on the scanned surface by being guided to the scanned surface through the system. In the case of an electrophotographic image forming apparatus, the surface to be scanned is the surface of a photoconductor, and an electrostatic latent image is formed by exposing the surface of the photoconductor uniformly charged in advance with a light spot. It is visualized by developing. In the case of a color image forming apparatus, formation of an electrostatic latent image and toner development are performed for each color plate.

  Hereinafter, embodiments of the present invention will be specifically described.

  In this embodiment, as a means for generating a plurality of light beams for image formation, for example, a surface in which a plurality of light sources (light emitting points) 2 are arranged in a grid pattern on the same chip as shown in FIG. A light emitting laser 1 is used. In the following description, the symbols P1A to P4C as shown in the figure are appropriately used for specifying the individual light sources 2. The number of light sources arranged on the chip can be increased or decreased as appropriate.

  A light beam emitted from each light source 2 of such a surface emitting laser 1 is used to scan a surface to be scanned through an optical system including a polarizer (here, a polygon mirror). As schematically shown in FIGS. 1 to 3, the column direction of the array grating of the light sources 2 is at a predetermined angle with respect to the sub-scanning direction so that the scanning lines by the plurality of light beams are arranged at predetermined intervals in the sub-scanning direction. The relative angle between the surface emitting laser 1 and the reflecting surface of the polygon mirror is set so as to form θ. Such an angular relationship is described in Patent Documents 1 and 3 and the like. Thus, the scanning lines of the light beams from the light sources P1A, P2A, P3A, P4A, P1B, P2B, P3B, P4B, P1C, P2C, P3C, and P4C are sequentially adjacent.

  As in the example described in Patent Document 3, instead of tilting the surface emitting laser 1, the column direction of the array grating of the light sources on the surface emitting laser 1 can be tilted by a predetermined angle in advance. Such an embodiment is also included in this embodiment. Also, a plurality of surface emitting lasers can be used in combination. For example, as schematically illustrated in FIG. 5, two surface emitting lasers 1a and 1b may be used. Three or more can be combined. Thus, an embodiment in which a plurality of surface emitting lasers are used in combination is also included in this embodiment.

  A plurality of light sources for generating light beams for scanning adjacent scanning lines on the surface to be scanned are set as one set, and a plurality of light beams from each set of light sources are used for forming one line of an image. The above-described two methods are used as a method of controlling the light amount of each set of light sources.

  2 and 3 schematically show an example of the method (1). FIG. 2 shows a pair of two light sources 2 for generating two light beams for scanning two adjacent scanning lines, one light source of each set being a main light source and the other light source being a sub light source. The case where it uses as a light source is shown. In this example, of the pair of light sources P1A and P2A, the light source P1A is used as the main light source and the light source P2A is used as the sub light source, and the light source P3A is used as the main light source and the light source P4A is used as the sub light source among the pair of the light sources P3A and P4A. Of the pair of light sources P1B and P2B, the light source P1B is used as the main light source and the light source P2B is used as the sub-light source. Similarly, the light source P3B is used as the main light source, the light source P4B as the sub light source, the light source 1C as the main light source, the light source P2C as the sub light source, the light source 3C as the main light source, and the light source P4C as the sub light source.

  FIG. 3 shows a set of three light sources 2 for generating three light beams for scanning three adjacent scanning lines, and the light source corresponding to the central scanning line is the main light source among the light sources of each set. The case where a light source and the remaining two light sources are used as sub-light sources is shown. In this example, the light sources P2A, P3A, and P4A are set as one set, and the light source P3A is used as the main light source and the light sources P2A and P4A are used as the sub light sources. Similarly, the light sources P1B, P2B, and P3B are set as one set, the light source P2B is used as the main light source, the remaining light sources P1B and 3B are used as the sub-light sources, and the light sources P4B, P1C, and P2C are set as one set. Of these, the light source P1C is used as a main light source, and the remaining light sources P4B and P3C are used as sub-light sources.

  FIG. 4 schematically shows an example of the method (2). In this example, both light sources P1A and P2A, light sources P3A and P4A, light sources P1B and P2B, light sources P3B and P4B, light sources P1C and P2C, and light sources P3C and P4C Are used as main light sources.

  FIG. 7 shows how the light amount distribution (scanned light amount distribution) in the sub-scanning direction on the surface to be scanned of the light beam from one set of light sources is changed by changing the light amount ratio between the light sources. It shows schematically how it changes. In the figure, the upper part shows the light emission signals of the light sources A and B, and the lower part shows the scanning light amount distribution on the surface to be scanned by the light beams from the light sources A and B. Here, it is assumed that the amount of light is controlled by changing the light emission time of the light source.

  In the example of FIG. 2, the main light source P1A is the light source A, and the sub-light source P2A is the light source B. As in the pixel 7, when the light amount of the light source A is 100% and the light amount of the light source B is 0%, the center of the scanning light amount distribution of the light beams of these two light sources coincides with the center of the light beam of the light source A. The barycentric position in the sub-scanning direction of the pixels recorded by the light beams of these two light sources coincides with the scanning line by the light beam of the light source A. If the light amount of the light source A is decreased and the light amount of the light source B is increased as in the pixel 6, the center of the scanning light amount distribution is shifted downward, so that the barycentric position of the recorded pixel is the light of the light source B. It approaches the scanning line side by the beam. When the light amount of the light source A is further reduced and the light amount of the light source B is further increased as in the pixel 5, the center of gravity of the recording pixel further moves. However, since the total light amount of the light sources A and B is kept constant, the recording density of the pixels is constant. In the method of using one of the two light sources as the main light source and the other as the sub light source, the light amount ratio is controlled so that the light amount of the sub light source does not exceed the light amount of the main light source. , 6 and 7, and a scanning light amount distribution are used.

  When a set of a main light source and two sub light sources is used as in the example of FIG. 3, the main light source is the light source A and each sub light source is the light source B, and the scanning light amount distribution is sub-scanned by controlling the same light amount ratio. The position of the center of gravity of the recorded pixel in the sub-scanning direction is set in both directions from the scanning line by the main light source to the scanning line side by one sub-light source or to the scanning line side by the other sub-light source. Obviously, it can be moved.

  In the example of FIG. 4, the main light source P1A is the light source A, and the other main light source P2A is the light source B. In this case, if the light amounts of the light sources A and B are 50%, the center of gravity of the recorded image is located at the boundary between the scanning lines of the light sources A and B as in the pixel 5. When the light amount ratio of the light source A is increased, the center of gravity of the recording pixel moves toward the scanning line side of the light source A. Conversely, when the light amount ratio of the light source B is increased, the center of gravity of the recording pixel moves toward the scanning line side of the light source B. That is, in this method, by changing the light quantity ratio between the light sources A and B, all the scanning light quantity distributions such as the pixels 1 to 7 can be used. Since the total light amount is kept constant, the recording density of the pixels is constant.

  In the above description, the light quantity is controlled by changing the light emission time (pulse width of the light emission signal) of the light source. Similar light quantity control can be performed by changing the light emission intensity, that is, the level of the light emission signal, as shown in FIG.

  When the light amount ratio control as in the example of FIG. 2 or FIG. 3 is performed, as illustrated in FIG. 8 or FIG. 9, for example, the light amount ratio data of the main and sub light sources corresponding to the pixel positions in the main scanning direction is stored in advance. Prepare and read out the light amount ratio corresponding to the pixel position from the table and adjust the pulse width or level of the light emission signal of each light source at the time of recording scanning, thereby controlling the light amount ratio as described above. By controlling the barycentric position of the pixel in the sub-scanning direction, it is possible to correct the positional deviation of each line of the image in the sub-scanning direction with high accuracy. Control of the light quantity ratio of the two main light sources as in the example of FIG. 3 is also possible by the same method.

  Note that when the interval between the scanning lines by the light beam (main beam) of the main light source is Δx, the interval between the scanning line by the main beam and the scanning line by the light beam (sub beam) of the sub light source is Δx / 2. The following is preferable. In this way, it is possible to prevent the overlapping of the scanning light amount distributions of the light beams of the light sources of each set, that is, the overlapping of the pixels in the adjacent lines in the sub-scanning direction.

  When controlling the combined light amount ratio of the main light source and the sub light source, the main light source generally has a larger light emission amount and light emission time, and therefore the main light source is more likely to deteriorate in characteristics than the sub light source. That is, the lifetime of the main light source is likely to be shorter than that of the auxiliary light source. If the progress of deterioration of the characteristics of the light source is uneven, it is not preferable in terms of uneven recording density and maintenance. In order to avoid such inconvenience, it is effective to switch between the main light source and the sub light source. This switching can be performed, for example, every line scan, every page scan, or the like. In this embodiment, when the control method as shown in FIG. 2 or FIG. 3 is used, such switching between the main light source and the sub light source is performed.

  FIG. 10 is a block diagram illustrating a configuration example of a light source driving system in the present embodiment. In FIG. 10, an LD driving circuit 14 is a means for generating a light emission signal for driving the light sources P1A to P4C by the method described with reference to FIGS. The main scanning counter 11 is means for detecting a horizontal scanning position by counting a pixel clock synchronized with the horizontal scanning of each line. The light quantity ratio generation circuit 12 includes a look-up table (LUT) that stores data on the light quantity ratio corresponding to the horizontal scanning position, and the LD driving circuit sets the light quantity ratio corresponding to the horizontal scanning position indicated by the main scanning counter 11. 14 is a means for supplying to. The switching counter 13 is means for counting the number of scanning lines in response to the output of the main scanning counter 11 and supplying a signal for switching the main light source and the sub light source to the LD driving circuit 14 every predetermined number of lines. The LD drive circuit 14 generates a light emission signal for each set of light sources according to the image data. At this time, the pulse width or level of the light emission signal for each set of light sources according to the light amount ratio given from the light amount ratio generation circuit 12. To control. Further, the main light source and the sub light source are switched according to the signal from the switching counter 13.

  FIG. 11 is a schematic perspective view illustrating a configuration example of the optical scanning device according to the present embodiment. In FIG. 11, reference numeral 801 denotes an optical unit, which includes one or more surface emitting lasers on which a plurality of light sources are arranged, and a printed circuit board 802 on which a drive system circuit as described in FIG. Is installed. The optical unit 801 is pressed against the wall surface of the optical housing perpendicular to the optical axis by a spring, and the inclination of the optical unit 801 is adjusted and held by an adjusting screw 803. The adjustment screw 803 is screwed into a protrusion formed on the wall surface of the housing. Inside the optical housing, a cylinder lens 805, a polygon mirror 808 and its driving motor, an fθ lens 806, a folding mirror 807, and a toroidal lens 812 are positioned and attached. Reference numeral 813 denotes a mirror for horizontal synchronization detection, and a printed circuit board 809 on which a synchronization detection sensor for detecting a light beam reflected by the mirror 813 is mounted is mounted on the wall surface of the housing. The upper portion of the optical housing is sealed with a cover 811 and is fixed to the frame member of the image forming apparatus main body with screws by a plurality of mounting portions 810 protruding from the wall surface.

  The light source of the surface emitting laser of the optical unit 810 is driven as described above to generate a plurality of light beams. This light beam is guided to the polygon mirror 808 via the cylinder lens 805. The light beam deflected by the polygon mirror 808 goes to the scanning surface (not shown) via the fθ lens 806, the mirror 807, and the toroidal lens 812, and scans the scanning surface.

  FIG. 12 is a schematic cross-sectional view illustrating a configuration example of the image forming apparatus according to the present embodiment. In FIG. 12, 900 is the optical scanning device shown in FIG. Reference numeral 901 denotes a photosensitive drum, and the surface of the photosensitive drum 901 is scanned by the optical scanning device 900. Around the photosensitive drum 901, a charging device 902 for charging the surface thereof at a high voltage, a developing roller 903 and a toner cartridge 904 for supplying toner to the developing roller 903, and a toner image on the photosensitive drum 901. A transfer charger 906 for transferring the toner onto the recording paper and a cleaning case 905 for scraping and storing residual toner on the photosensitive drum 901 are disposed. The recording paper is supplied from the paper supply tray 906 by the paper supply roller 907, is sent out by the registration roller pair 908 in accordance with the recording start timing in the sub-scanning direction, passes between the photosensitive drum 901 and the transfer charger 906, and At this time, the toner image is transferred. The recording sheet is discharged onto the discharge tray 910 by the discharge roller 912 after fixing the toner image by the fixing roller 909. The recording operation is well known, and the surface of the photosensitive drum 901 charged by the charger 902 is scanned with the light beam from the optical scanning device 900. The electrostatic latent image formed by this scanning is developed with toner when passing through the developing device, and the toner image is transferred onto the recording paper when passing through the transfer charger 906.

  According to the optical scanning device 900, as described with reference to FIGS. 2 to 10, it is possible to correct the positional deviation of the pixels in the sub-scanning direction with high accuracy. Therefore, this image forming apparatus is capable of high-quality image recording in which the positional deviation of the pixels in the sub-scanning direction is corrected with high accuracy. In addition, since the optical scanning device 900 can simultaneously perform recording scanning of a plurality of lines, high-speed image recording is possible.

  The present invention can be similarly applied to a tandem color image forming apparatus. An outline of such an embodiment will be described with reference to FIG.

  The color image forming apparatus according to the present embodiment uses separate photoconductors 2509a, 2509b, 2509c, and 2509d for forming images of each color of cyan, magenta, yellow, and black. In such a tandem apparatus, the photoconductor in each color station is scanned by a light beam that has passed through a separate optical path, so that the dot position deviation in the sub-scanning direction that occurs on the photoconductor has different characteristics for each station. . Therefore, good image quality, particularly good color reproducibility cannot be obtained unless dot position correction in the sub-scanning direction is performed accurately for each color station.

  In FIG. 13, reference numeral 2505 denotes a polygon mirror having a two-stage configuration. Although not shown in FIG. 13, a plurality of light beams are output from the surface emitting lasers prepared for each color station and related to FIGS. 1 to 9, which are not shown in the figure. Are simultaneously incident on different reflecting surfaces of the polygon mirror 2505.

  The station including the photoreceptor 2509a will be described. The light beam deflected by the polygon mirror 2505 passes through the first scanning lens 2506a, the mirror 2513a, the second scanning lens 2507a, the mirrors 2514a and 2515a, and the beam splitter 2508a. The photoconductor 2509a is scanned to form an electrostatic latent image. A part of the laser light beam reflected by the half mirror surface of the beam splitter 2508a is detected by a photodetector 2510a for horizontal synchronization detection. Since it is clear from the drawings that the scanning systems of the other color stations have the same configuration, the description will not be repeated.

  Although not shown, a light source driving system as shown in FIG. 10 is provided for each station, and pixel clocks synchronized with horizontal synchronizing signals from the photodetectors 2501a, 2510b, 2510c, and 2510d for detecting horizontal synchronization are supplied to each station. Each light source driving system drives each light source of the surface emitting laser. The driving method is as described with reference to FIGS.

  Around the photoconductors 2509a, 2509b, 2509c, and 2509d of each station, there are means for uniformly charging the surface of the photoconductor, means for developing the electrostatic latent image on the photoconductor into a corresponding color toner image, Means for transferring the developed toner image to the intermediate transfer member 2516, means for removing and collecting the toner that has not been transferred to the surface of the photosensitive member, and means for superimposing the color toner images on the intermediate transfer member 2516 onto a sheet. There are means for fixing the toner image on the paper, which are not shown.

  The image forming apparatus of this embodiment can obtain a high-quality image with a small sub-scanning dot position shift because the dot-position shift in the sub-scanning direction at each color station is corrected with high accuracy. In particular, since color misregistration caused by sub-scanning dot position misalignment between stations can be effectively reduced, an image with good color reproducibility can be obtained.

It is a figure which shows the light source arrangement | sequence on a surface emitting laser. It is explanatory drawing of the recording scan by the group of the main light source and one sublight source. It is explanatory drawing of the recording scanning by the group of a main light source and two sub light sources. It is explanatory drawing of the recording scan by the group of two main light sources. It is a figure which shows the example using two surface emitting lasers. It is explanatory drawing of the light quantity ratio and scanning light quantity distribution in the case of using the group of two light sources. It is a figure which shows the example which controls the light quantity ratio in the case of using the group of two light sources by changing the level of a light emission signal. It is a figure which shows the example of the light quantity ratio data in the case of using the group of a main light source and a sublight source. It is a figure which shows the example of the light quantity ratio data in the case of using the group of a main light source and two sub light sources. It is a block diagram which shows the example of the light source drive system which concerns on this invention. It is a perspective view which shows an example of the optical scanning device concerning this invention. 1 is a cross-sectional view illustrating an example of an image forming apparatus according to the present invention. 1 is a schematic diagram illustrating an example of a tandem color image forming apparatus according to the present invention. 1 is an explanatory diagram of a general configuration of an electrophotographic image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface emitting laser 2 Light source 11 Main scanning counter 12 Light quantity ratio production | generation circuit 13 Switching counter 14 LD drive circuit 801 Light source unit 805 Cylinder lens 806 f (theta) lens 807 Folding mirror 808 Polygon mirror 812 Toroidal lens 900 Optical scanning device 901 Photosensitive drum

Claims (10)

A plurality of light sources for generating a light beam for scanning the surface to be scanned, and light source driving means for driving them,
The light source driving means includes two light sources corresponding to two adjacent scanning lines on the scanning surface as one set, one of the light sources as a main light source, and the other as a sub light source. It is generated from a set of light sources by changing the light amount ratio between the main light source and the sub light source without changing the total light amount of the light source and without exceeding the light amount of the main light source. An optical scanning device characterized by controlling a light amount distribution in a sub-scanning direction on a surface to be scanned of a light beam. A plurality of light sources for generating a light beam for scanning the surface to be scanned, and light source driving means for driving them,
The light source driving means sets three light sources corresponding to three adjacent scanning lines on the surface to be scanned as one set, and among the one set of light sources, the light source corresponding to the central scanning line is the main light source and the remaining light sources Each of the two light sources is a sub-light source, and the amount of light between the main light source and each sub-light source is not changed without changing the total light amount of one set of light sources and without exceeding the light amount of each sub-light source. An optical scanning apparatus characterized by controlling a light amount distribution in a sub-scanning direction on a surface to be scanned of a light beam generated from a set of light sources by changing a ratio. A plurality of light sources for generating a light beam for scanning the surface to be scanned, and light source driving means for driving them,
The light source driving means sets two light sources corresponding to two adjacent scanning lines on the scanned surface as one set, and changes the light amount ratio between the light sources without changing the total light amount of the one light source. An optical scanning device characterized by controlling a light amount distribution in a sub-scanning direction on a surface to be scanned of a light beam generated from a set of light sources. The optical scanning device according to claim 1 or 2,
The light source driving means includes means for switching between a light source driven as a main light source and a light source driven as a sub light source. The optical scanning device according to claim 1 or 2,
When the interval between the scanning lines corresponding to the main light source on the surface to be scanned is ΔX,
An optical scanning device characterized in that an interval between a scanning line corresponding to a main light source on a surface to be scanned and a scanning line corresponding to a sub-light source with respect to the main light source is ΔX / 2 or less. The optical scanning device according to any one of claims 1 to 5,
An optical scanning device comprising a surface emitting laser in which a plurality of light sources are arranged in a grid on the same chip as the plurality of light sources. In an image forming method for forming an electrostatic latent image on a scanned medium by scanning the scanned surface with a light beam using the surface of the scanned medium as a scanned surface,
A set of two light beams that scan adjacent scanning lines on the surface to be scanned is formed as a set, and an electrostatic latent image of a pixel row is formed by the set of light beams, and the total amount of light of the set of light beams is changed. An image forming method comprising controlling a barycentric position of a pixel in a sub-scanning direction by changing a light amount ratio between light beams without any change. In an image forming method for forming an electrostatic latent image on a scanned medium by scanning the scanned surface with a light beam using the surface of the scanned medium as a scanned surface,
A set of three light beams that scan adjacent scanning lines on the surface to be scanned is formed, and an electrostatic latent image of a pixel row is formed by one set of light beams, and the center light of the one set of light beams is formed. The beam is a main beam and the remaining two light beams are sub-beams, and the light quantity ratio between the main beam and each sub-beam is changed without changing the total light quantity of one set of light beams. An image forming method comprising controlling a barycentric position of a pixel. In an image forming apparatus that has a scanned medium and an optical scanning device that scans with a light beam using the surface as a scanned surface, and forms an electrostatic latent image on the scanned medium,
An image forming apparatus comprising the optical scanning device according to claim 1. Image forming that has a plurality of scanned media for different colors and an optical scanning device that scans with a light beam using those surfaces as scanned surfaces, and forms electrostatic latent images for different colors on the scanned media In the device
An image forming apparatus comprising the optical scanning device according to claim 1.

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