JP5621448B2 - Optical writing apparatus, image forming apparatus, and control method of optical writing apparatus - Google Patents

Description

  The present invention relates to an optical writing apparatus, an image forming apparatus, and an optical writing apparatus control method, and more particularly to correction of image skew.

  In recent years, there has been a tendency to digitize information, and image processing apparatuses such as printers and facsimiles used for outputting digitized information and scanners used for digitizing documents have become indispensable devices. Such an image processing apparatus is often configured as a multifunction machine that can be used as a printer, a facsimile, a scanner, or a copier by providing an imaging function, an image forming function, a communication function, and the like.

  Among such image processing apparatuses, electrophotographic image forming apparatuses are widely used in image forming apparatuses used for outputting digitized documents. In an electrophotographic image forming apparatus, an electrostatic latent image is formed by exposing a photoreceptor, and the electrostatic latent image is developed using a developer such as toner to form a toner image. Paper output is performed by transferring the toner image onto paper.

  As one of the methods for performing full-color printing in an electrophotographic image forming apparatus, in a tandem image forming apparatus, photosensitive drums of respective colors arranged on a conveyed body such as a sheet to be conveyed and an intermediate transfer belt Images are transferred in order. For this reason, it is important to align the images transferred by the photosensitive drums of the respective colors.

  In an electrophotographic image forming apparatus, in the case of an LD (Laser Diode) raster optical system, an optical writing apparatus that exposes a photosensitive member is a light source that irradiates a beam that exposes the photosensitive member, and deflects the irradiated beam to sensitize the light. It includes a deflector such as a polygon scanner for scanning the entire body. In such an optical writing device using an LD raster optical system, there are errors due to distortion, displacement, etc. of the fθ lens and reflecting mirror, and such errors appear as skew in the formed image.

  Here, in the LD raster optical system, the beam is scanned on the rotating photosensitive drum. Therefore, when the beam is scanned in a direction perpendicular to the conveyance direction of the drum surface, the photosensitive drum rotates while the beam is scanned. The skew does not occur in the direction perpendicular to the surface conveyance direction.

  In order to cope with this, in the image forming apparatus of the LD raster optical system, when the surface of the photosensitive drum is scanned when the rotation of the photosensitive drum is at a predetermined speed, the beam arrival point on the surface of the photosensitive drum is determined. The optical system is adjusted so that the locus is in a direction perpendicular to the transport direction.

  On the other hand, in a color image forming apparatus, the PPM (Page Per Minute) may be changed depending on the characteristics of the paper to be conveyed and the printing resolution. For example, paper jams can be prevented by transporting plain paper at a normal transport speed and transporting thick paper used for postcards at a half speed. Further, in an apparatus capable of printing with a resolution of 600 dpi (dots per inch) at a normal transport speed, if the transport speed is set to 1/2 speed, printing at 1200 dpi is possible in the sub-scanning direction.

  However, as described above, since the optical system is adjusted according to the rotation of the photosensitive drum and the rotation of the polygon scanner, the surface of the photosensitive drum is changed when the PPM is changed depending on the characteristics of the paper to be conveyed and the printing resolution. The trajectory of the beam arrival point is not perpendicular to the transport direction, and skew occurs.

  As described above, as a method of correcting the skew generated due to various factors, a suitable image can be finally obtained by mechanically correcting the image to be output and by deforming the image to be output by image processing according to the skew amount. There is a method to make it form.

  In the mechanical correction method, correction is realized by providing an adjustment mechanism that displaces the mirror and head mounting positions inside the writing unit. However, an actuator such as a motor is required to perform this adjustment automatically. As a result, the cost of the entire apparatus increases.

  On the other hand, in the correction by image processing, the skew is corrected by shifting the pixels constituting the image in the sub-scanning direction at a certain position in the main scanning direction. As a method of shifting the pixels in the sub-scanning direction, the pixels constituting the image are stored in the line memory for each main scanning line, and the image is sub-scanned by switching the line memory for reading out the pixels according to the writing position in the main scanning direction. There are a method of shifting in the direction and a method of storing the pixel in a state where it is shifted in the sub-scanning direction at a certain position in the main scanning direction when the pixel is stored in the line memory. In this case, it is only necessary to add a line memory to the image processing unit in accordance with the correction range. Therefore, mechanical correction can be realized at a relatively low cost, and automatic correction can be performed. This is effective as a skew correction method.

  However, in the case of the method of correcting by image processing, a change occurs in the dither pattern at the image shift position. Due to the change in the dither pattern, the adjacent relationship of the pixels in the main scanning direction changes, for example, white pixels become black pixels, and the toner adhesion area at the time of output changes. In an image expressed by a pseudo gradation process such as a dither method, the variation in the toner adhesion area frequently occurs continuously or periodically in the sub-scanning direction, and the sub-scanning is performed on the image formed on the printing paper. It becomes a streak-like noise in the direction.

  In order to cope with such a problem, a method for preventing the occurrence of the streak-like noise by performing image shift at a position where the image pattern of the dither matrix does not exist has been proposed (for example, see Patent Document 1).

  In the LD raster optical system, the beam irradiated to each photosensitive drum may be irradiated from both sides to the rotating polygon scanner. In such a case, when skew occurs, an image drawn and formed by a beam irradiated from one side (hereinafter referred to as a first image) is drawn and formed by a beam irradiated from the other side. The skew direction is opposite to the skew of the image (hereinafter referred to as the second image). When tilts occur in opposite directions as described above, the shift amount between the first image and the second image increases as the end of the image is approached, and appears as a color shift.

  When using the technique disclosed in Patent Document 1, in order to perform image shift while avoiding the dither matrix range, the image shift cycle must be at least equal to or greater than the dither matrix range, and the number of correctable lines is limited. is there. Further, it cannot be used for an image in which a dither pattern is developed on the entire page.

  The present invention has been made in consideration of the above circumstances, and an object of the present invention is to prevent image quality deterioration due to dither pattern changes while suppressing an increase in cost with a simple configuration in skew correction in an optical writing apparatus.

In order to solve the above problems, according to one embodiment of the present invention, an electrostatic latent image is formed on a rotating photosensitive member by reflecting the irradiated light beam by a rotating reflecting mirror, guiding the light beam onto the photosensitive member, and scanning. An optical writing device to be formed, the light source device including at least two light sources that respectively irradiate the light beam from different directions with respect to the reflecting mirror, and the rotating reflecting mirror that irradiates from one of the two light sources The scanned light beam moves on the photosensitive member so as to move from one end side to the opposite side in the main scanning direction, and the light beam emitted from the other of the two light sources scans on the photosensitive member. A scanning unit that scans so as to move from the other end side in the direction toward the opposite side, an image information acquisition unit that acquires image information that is information of an image to be formed as the electrostatic latent image, and the acquired Image information A light emission control unit for controlling the light source device to irradiate the light beam, and information stored in each main scanning line based on the acquired image information, which is information on pixels constituting the image. The timing adjustment unit that adjusts the timing and inputs it to the light emission control unit, and the electrostatic latent image formed by the light beam emitted by the other of the two light sources is the same direction as the shift direction by the timing adjustment unit And an image forming position adjusting unit that shifts by half a pixel , and the scanning unit is configured to detect the reflected light beam when the ratio of the scanning speed of the light beam to the rotation speed of the photosensitive member is in the first state. the locus of arrival point on the photosensitive member is provided such that the direction of rotation perpendicular to said line of the photosensitive member, wherein the timing adjusting section, the light with respect to the rotation speed of the photosensitive member The ratio of the scanning speed of over arm is the locus of the arrival point in the photosensitive member on the fold and was in the light beam of the first state is inclined with respect to the rotational direction and the direction perpendicular of the photosensitive member In the second state, the pixel information input to one of the two light sources is shifted by one pixel in the sub-scanning direction at one position of the main scanning line.

  According to the present invention, in skew correction in an optical writing device, it is possible to prevent deterioration in image quality due to a change in dither pattern while suppressing an increase in cost with a simple configuration.

1 is a block diagram illustrating a hardware configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a functional configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of a print engine according to an embodiment of the present invention. It is a figure which shows typically the structure of the optical writing apparatus which concerns on embodiment of this invention. It is a figure which shows typically the structure of the optical writing apparatus which concerns on embodiment of this invention. It is a block diagram which shows the control part of the optical writing apparatus which concerns on embodiment of this invention. It is a figure which shows the concept of the skew correction which concerns on embodiment of this invention. It is a figure which shows the concept of the skew correction which concerns on embodiment of this invention. It is a figure which shows the concept of the skew correction which concerns on embodiment of this invention. It is a figure which shows the subject solved by the skew correction which concerns on embodiment of this invention. It is a figure which shows the locus | trajectory of the beam irradiated from the optical writing apparatus which concerns on embodiment of this invention, and the state after transcription | transfer. It is a figure which shows the aspect of the skew correction which concerns on embodiment of this invention. It is a figure which shows the other aspect of the skew correction which concerns on embodiment of this invention. It is a figure which shows the other aspect of the skew correction which concerns on embodiment of this invention. It is a figure which shows the principle of image quality degradation reduction in the skew correction which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, a multi function peripheral (MFP) as an image forming apparatus will be described as an example. The image forming apparatus according to the present embodiment is an electrophotographic multifunction machine using an LD (Laser Diode) raster optical system, and can perform image formation by 600 dpi (dots per inch) with a normal PPM (Page Per Minute). Thus, image formation at 1200 dpi is realized by reducing the PPM to ½.

  In such an image forming apparatus, the aspect of correcting the skew generated when the timing of the rotation of the polygon scanner and the rotation of the photosensitive drum is shifted due to the change of the PPM is the gist of the present embodiment. Note that the image forming apparatus need not be a multifunction machine, and may be, for example, a copying machine, a printer, a facsimile machine, or the like.

  FIG. 1 is a block diagram illustrating a hardware configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes an engine that executes image formation in addition to the same configuration as an information processing terminal such as a general server or a PC (Personal Computer). That is, the image forming apparatus 1 according to the present embodiment includes a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 11, a ROM (Read Only Memory) 12, an engine 13, an HDD (Hard Disk Drive) 14, and an I / O. F15 is connected via the bus 18. Further, an LCD (Liquid Crystal Display) 16 and an operation unit 17 are connected to the I / F 15.

  The CPU 10 is a calculation unit and controls the operation of the entire image forming apparatus 1. The RAM 11 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 10 processes information. The ROM 12 is a read-only nonvolatile storage medium, and stores programs such as firmware. The engine 13 is configured to actually execute image formation in the image forming apparatus 1.

  The HDD 14 is a nonvolatile storage medium capable of reading and writing information, and stores an OS (Operating System), various control programs, application programs, and the like. The I / F 15 connects and controls the bus 18 and various hardware and networks. The LCD 16 is a visual user interface for the user to check the state of the image forming apparatus 1. The operation unit 17 is a user interface such as a keyboard and a mouse for the user to input information to the image forming apparatus 1.

  In such a hardware configuration, a program stored in a recording medium such as the ROM 12, the HDD 14, or an optical disk (not shown) is read into the RAM 11 and operates according to the control of the CPU 10, thereby configuring a software control unit. A functional block that realizes the functions of the image forming apparatus 1 according to the present embodiment is configured by a combination of the software control unit configured as described above and hardware.

  Next, the functional configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus 1 according to the present embodiment. As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment includes a controller 20, an ADF (Auto Document Feeder) 21, a scanner unit 22, a paper discharge tray 23, a display panel 24, and a paper feed table. 25, a print engine 26, a paper discharge tray 27, and a network I / F 28.

  The controller 20 includes a main control unit 30, an engine control unit 31, an input / output control unit 32, an image processing unit 33, and an operation display control unit 34. As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment is configured as a multifunction machine having a scanner unit 22 and a print engine 26. In FIG. 2, the electrical connection is indicated by solid arrows, and the flow of paper is indicated by broken arrows.

  The display panel 24 is an output interface that visually displays the state of the image forming apparatus 1 and is an input when the user directly operates the image forming apparatus 1 or inputs information to the image forming apparatus 1 as a touch panel. It is also an interface (operation unit). The network I / F 28 is an interface for the image forming apparatus 1 to communicate with other devices via the network, and uses an Ethernet (registered trademark) or a USB (Universal Serial Bus) interface.

  The controller 20 is configured by a combination of software and hardware. Specifically, a control program such as firmware stored in a nonvolatile recording medium such as the ROM 12 and the nonvolatile memory and the HDD 14 and the optical disk is loaded into a volatile memory (hereinafter referred to as a memory) such as the RAM 11 to control the CPU 10. The controller 20 is configured by a software control unit configured according to the above and hardware such as an integrated circuit. The controller 20 functions as a control unit that controls the entire image forming apparatus 1.

  The main control unit 30 plays a role of controlling each unit included in the controller 20 and gives a command to each unit of the controller 20. The engine control unit 31 serves as a drive unit that controls or drives the print engine 26, the scanner unit 22, and the like. The input / output control unit 32 inputs a signal or a command input via the network I / F 28 to the main control unit 30. The main control unit 30 controls the input / output control unit 32 and accesses other devices via the network I / F 28.

  The image processing unit 33 generates drawing information based on the print information included in the input print job under the control of the main control unit 30. The drawing information is information for drawing an image to be formed in the image forming operation by the print engine 26 as an image forming unit. The print information included in the print job is image information converted into a format that can be recognized by the image forming apparatus 1 by a printer driver installed in an information processing apparatus such as a PC. The operation display control unit 34 displays information on the display panel 24 or notifies the main control unit 30 of information input via the display panel 24.

  When the image forming apparatus 1 operates as a printer, first, the input / output control unit 32 receives a print job via the network I / F 28. The input / output control unit 32 transfers the received print job to the main control unit 30. When receiving the print job, the main control unit 30 controls the image processing unit 33 to generate drawing information based on the print information included in the print job.

  When drawing information is generated by the image processing unit 33, the engine control unit 31 performs image formation on the paper conveyed from the paper feed table 25 based on the generated drawing information. That is, the print engine 26 functions as an image forming unit. The paper on which image formation has been performed by the print engine 26 is discharged to a paper discharge tray 27.

  Further, when the image forming apparatus 1 operates as a copying machine, the image processing unit 33 generates drawing information based on the imaging information received by the engine control unit 31 from the scanner unit 22 or the image information generated by the image processing unit 33. To do. Based on the drawing information, the engine control unit 31 drives the print engine 26 as in the case of the printer operation.

  Next, the configuration of the print engine 26 according to the present embodiment will be described with reference to FIG. As shown in FIG. 3, the print engine 26 according to the present embodiment includes a configuration in which image forming units 106 of respective colors are arranged along a conveyor belt 105 that is an endless moving unit, which is a so-called tandem type. It is what is said. That is, along the conveying belt 105 that conveys a sheet (an example of a recording medium) 104 that is separated and fed from the sheet feeding tray 101 by the sheet feeding roller 102 and the separation roller 103, the upstream side in the conveying direction of the conveying belt 105. A plurality of image forming units (electrophotographic process units) 106BK, 106M, 106C, and 106Y are arranged in this order.

  The plurality of image forming units 106BK, 106M, 106C, and 106Y have the same internal configuration except that the colors of the toner images to be formed are different. The image forming unit 106BK forms a black image, the image forming unit 106M forms a magenta image, the image forming unit 106C forms a cyan image, and the image forming unit 106Y forms a yellow image. In the following description, the image forming unit 106BK will be described in detail. However, since the other image forming units 106M, 106C, and 106Y are the same as the image forming unit 106BK, the image forming units 106M, 106C, and 106Y are similar to the image forming unit 106BK. As for each of the components, only the symbols distinguished by M, C, and Y are displayed in the drawing in place of the BK attached to each component of the image forming unit 106BK, and the description thereof is omitted.

  The conveying belt 105 is an endless belt, that is, an endless belt that is stretched between a driving roller 107 and a driven roller 108 that are rotationally driven. The drive roller 107 is driven to rotate by a drive motor (not shown), and the drive motor, the drive roller 107, and the driven roller 108 function as a drive unit that moves the conveyance belt 105 that is an endless moving unit. .

  At the time of image formation, the paper 104 stored in the paper feed tray 101 is sent out in order from the top, and the first image forming unit 106BK is conveyed by the conveyance belt 105 that is attracted to and rotated by the conveyance belt 105 by electrostatic adsorption action. Where the black toner image is transferred. That is, the conveyance belt 105 functions as a conveyance body that conveys a sheet that is an image transfer target.

  The image forming unit 106BK includes a photoconductor drum 109BK as a photoconductor, a charger 110BK arranged around the photoconductor drum 109BK, an optical writing device 111, a developing device 112BK, a photoconductor cleaner (not shown), and a static eliminator. 113BK and the like. The optical writing device 111 is configured to form an electrostatic latent image by exposing the respective photosensitive drums 109BK, 109M, 109C, and 109Y (hereinafter collectively referred to as the photosensitive drum 109).

  At the time of image formation, the outer peripheral surface of the photosensitive drum 109BK is uniformly charged by the charger 110BK in the dark, and then writing is performed by irradiation light corresponding to the black image from the optical writing device 111. An image is formed. The developing device 112BK visualizes the electrostatic latent image with black toner, thereby forming a black toner image on the photosensitive drum 109BK.

  This toner image is transferred onto the sheet 104 by the action of the transfer unit 115BK at a position (transfer position) where the photosensitive drum 109BK and the sheet 104 on the conveying belt 105 contact each other. By this transfer, an image of black toner is formed on the paper 104. After the transfer of the toner image is completed, unnecessary toner remaining on the outer peripheral surface of the photosensitive drum 109BK is wiped off by the photosensitive cleaner, and then the charge is removed by the charge eliminator 113BK, and waits for the next image formation.

  As described above, the sheet 104 on which the black toner image is transferred by the image forming unit 106BK is transported to the next image forming unit 106M by the transport belt 105. In the image forming unit 106M, a magenta toner image is formed on the photosensitive drum 109M by a process similar to the image forming process in the image forming unit 106BK, and the toner image is superimposed on the black image formed on the paper 104. And is transcribed.

  The sheet 104 is further conveyed to the next image forming units 106C and 106Y, and a cyan toner image formed on the photoconductive drum 109C and a yellow toner image formed on the photoconductive drum 109Y by the same operation. Are superimposed on the sheet 104 and transferred. In this way, a full color image is formed on the sheet 104. The sheet 104 on which the full-color superimposed image is formed is peeled off from the conveying belt 105 and the image is fixed by the fixing device 116, and then discharged to the outside of the image forming apparatus.

  Next, the optical writing device 111 according to the present embodiment will be described. FIG. 4 is a view of the optical writing device 111 according to the present embodiment as viewed from above. FIG. 5 is a cross-sectional view of the optical writing device according to the present embodiment as viewed from the side. As shown in FIGS. 4 and 5, the laser beams for writing on the photosensitive drums 109BK, 109M, 109C, and 109Y of the respective colors are light source devices 281BK, 281M, 281C, and 281Y as light sources (hereinafter collectively referred to as “light source device 281”). ). Note that the light source device 281 according to the present embodiment includes a semiconductor laser, a collimator lens, a slit, a prism, a cylinder lens, and the like.

  The laser beam emitted from the light source device 281 is reflected by the reflecting mirror 280. Each laser beam is guided to mirrors 282BK, 282M, 282C, and 282Y (hereinafter collectively referred to as “mirror 282”) by an optical system such as an fθ lens (not shown), and further, the photosensitive drums 109BK and 109M are further guided by the optical system ahead. , 109C, 109Y. That is, the reflecting mirror 280, the mirror 282, and other optical systems function as a scanning unit.

  The reflecting mirror 280 is a hexahedral polygon mirror, and by rotating, the laser beam for one line in the main scanning direction can be scanned per polygon mirror surface. The optical writing device 111 according to this embodiment divides the four light source devices into light source devices of two colors of 281BK, 281M, and 281C, 281Y, and performs scanning using different reflecting surfaces of the reflecting mirror 280. It is possible to write on four different photosensitive drums at the same time with a more compact configuration than the scanning method using only one reflecting surface.

  In addition, a horizontal synchronization detection sensor 283 is provided in the vicinity of the scanning start position in the range where the laser beam is scanned by the reflecting mirror 280. When the laser beam emitted from the light source device 281 enters the horizontal synchronization detection sensor 283, the timing of the scanning start position of the main scanning line is detected, and the control device that controls the light source device 281 and the reflecting mirror 280 are synchronized. Be taken.

  Next, a control block of the optical writing device 111 according to the present embodiment will be described with reference to FIG. FIG. 6 is a diagram illustrating a functional configuration of the optical writing device control unit 120 that controls the optical writing device 111 according to the present embodiment and a connection relationship with the light source device 281. As illustrated in FIG. 6, the optical writing device control unit 120 according to the present embodiment includes a light emission control unit 121, a line memory 122, an image information acquisition unit 123, and a delay control unit 124.

  Note that the optical writing device 111 according to the present embodiment includes an information processing mechanism such as the CPU 10, the RAM 11, and the ROM 12 as described in FIG. 1. The optical writing device control unit 120 as shown in FIG. Similar to the controller 20 of the image forming apparatus 1, a control program stored in a storage medium such as the ROM 12 is loaded into the RAM 11, and a software control unit configured by the CPU 10 performing calculations according to the program, hardware, Consists of a combination of

  The light emission control unit 121 is a light source control unit that controls the issuance of the light source device 281 based on the pixel information. The light emission control unit 121 controls turning on / off of the light source device 281 for each pixel according to a clock indicating one pixel in the main scanning direction, that is, a pixel clock.

  The line memory 122 is a storage medium that stores pixel information for each main scanning line of an image in accordance with image information input from the engine control unit 31. The pixel information stored in the line memory 122 is input to the light emission control unit 121, so that the light emission control unit 121 controls turning on / off of the light source device 281.

  FIG. 7 is a diagram illustrating a relationship between the order of pixel data input to the light emission control unit 121 and an actually rendered image. 7 shows the order of pixel data input to the light emission control unit 121. The first line is 1a, 1b, 1c,..., The second line is 2a, 2b, 2c,. Pixel data is input to the light emission control unit 121 such as 3a, 3b, 3c,. The lower part of FIG. 7 is a diagram illustrating an example of an image drawn based on pixel data input to the light emission control unit 121, and pixels drawn corresponding to each pixel data are indicated by circles. .

  The image information acquisition unit 123 acquires image information input from the controller 20 and stores information on pixels constituting the image in the line memory 122 for each main scanning line. In addition, the image information acquisition unit 123 inputs pixel information that does not need to be stored in the line memory to the light emission control unit 121. The delay control unit 124 controls input of pixel data from the line memory 122 to the light emission control unit 121. The processing by the delay control unit 124 is one of the gist according to the present embodiment, and the delay control unit 124 adjusts the timing and inputs the pixel information stored in the line memory 122 to the light emission control unit 121. . That is, the line memory 122 and the delay control unit 124 function as a timing adjustment unit.

  In the optical writing device 111 according to the present embodiment, each component is adjusted so that no skew is generated in the PPM mode corresponding to 600 dpi, and the delay control unit 124 is configured to be in the PPM mode corresponding to 1200 dpi. 2, the skew generated by the change in the PPM is adjusted by controlling the timing of inputting the pixel data from the line memory 122 to the light emission controller 121. The basic concept of skew correction will be described with reference to FIGS.

  FIG. 8 is a diagram illustrating the relationship between the pixel data input to the light emission control unit 121 and the actually rendered image, as in FIG. 7, and illustrates a state in which a skew has occurred. In the example of FIG. 8, the image is raised to the left in the figure due to the skew of the light beam. FIG. 9 is a diagram showing a state in which the generated skew is corrected as shown in FIG. In the example of FIG. 9, pixel data input to the light emission control unit 121 is shifted in the sub-scanning direction every six pixels as shown in the upper part. As a result, as shown in the lower part of FIG. 9, the overall shift amount due to the skew is reduced.

  Next, an adverse effect of the skew correction shown in FIG. 9 will be described with reference to FIGS. 10 (a) and 10 (b). FIGS. 10A and 10B are diagrams illustrating an example in which shift correction is performed on an image that has been dithered by one pixel interval in the main scanning direction and the sub-scanning direction. Is before correction, and FIG. 10B shows after correction. In FIG. 10B, the image is shifted at a position indicated by a bold dotted line.

  As shown in FIG. 10B, when the same correction as that in FIG. 9 is performed, the dither pattern has a one-pixel interval, so that the lit pixel (( Colored pixels) and unlit pixels (plain pixels) are connected, and the image density changes at that position. As a result, it appears as streak noise in the sub-scanning direction at the position where the image is shifted. Reducing such noise is one of the gist according to the present embodiment.

  Next, the problem of color misregistration regarding skew that occurs when the PPM changes will be described with reference to FIGS. FIG. 11A shows the locus of the arrival point on the photosensitive drum 109 of the light beam emitted from the light source devices 281BK and 281C and the post-transfer in the PPM corresponding to 600 dpi in the image forming apparatus 1 according to the present embodiment. It is a figure which shows the state of.

  As described above, the image forming apparatus 1 according to the present embodiment has a beam irradiated from the light source device 281BK as shown in FIG. 11A because the optical system is adjusted in the PPM corresponding to 600 dpi. And the trajectory of the beam emitted from the light source device 281C are lines parallel to the main scanning direction. However, as shown in FIG. 11, since the light source device 281BK and the light source device 281C irradiate the reflecting mirror 280 with beams from opposite sides, the directions in which the respective beams scan the photosensitive drum 109 are reversed. Become.

  That is, the beam irradiated from the light source device 281BK scans on the photosensitive drum 109BK from one end side to the opposite side in the main scanning direction, and the beam irradiated from the light source device 281V moves on the photosensitive drum 109C. Scan from the other end side in the main scanning direction toward the opposite side. Note that, on the right side of FIG. 11A, for clarity of illustration, the images transferred from the photosensitive drum 109BK and the photosensitive drum 109C are shifted from each other, but actually overlap.

  On the other hand, FIG. 11B is a diagram showing the locus of the arrival point on the photosensitive drum 109 of the light beam emitted from the light source devices 281BK and 281C and the state after transfer in the PPM corresponding to 1200 dpi. is there. In a PPM that supports 1200 dpi, the speed of rotation of the photosensitive drum 109 is halved. On the other hand, since the number of rotations of the reflecting mirror 280 does not change, the trajectory of the beam emitted from the light source device 281BK and the trajectory of the beam emitted from the light source device 281C are respectively shown in FIG. Causes skew.

  Since the light source device 281BK and the light source device 281C each irradiate a beam from the opposite side to the reflecting mirror 280, the traveling direction of the beam arrival point on the photosensitive drum 109 is opposite. As a result, as shown on the right side of FIG. 11B, the skew direction between the image transferred from the photosensitive drum 109BK and the image transferred from the photosensitive drum 109C is reversed.

  In the case of FIG. 11B, the edge of the image, that is, the portion where the trajectory of the beam emitted from the light source device 281BK and the trajectory of the beam emitted from the light source device 281C are farthest in the sub-scanning direction. The shift width is one dot of 1200 dpi, which is about 21 (μm). That is, a color shift of one dot occurs between the image transferred from the photosensitive drum 109BK and the image transferred from the photosensitive drum 109C.

  Although illustration is omitted in FIGS. 11A and 11B, such a problem is similarly caused when the light source device is arranged on the opposite side of the reflecting mirror 280. Arise. That is, in the optical writing device according to the present embodiment, as shown in FIG. 4, the same occurs in the combination of the light source device 281BK and the light source device 281Y, and the combination of the light source device 281M and the light source device 18C or the light source device 281Y. Thus, the gist of the present embodiment is to correct the color misregistration caused by the skew caused by changing the PPM.

  Next, an aspect of color misregistration correction according to the present embodiment will be described with reference to FIG. FIG. 12 is a diagram showing a mode of color misregistration correction according to the present embodiment, and a mode of color misregistration correction when skew is generated as shown in FIG. 11B, that is, in the case of PPM corresponding to 1200 dpi. FIG.

  In the locus of the arrival point of the light beam on the photosensitive drum 109 and the state after transfer shown in FIG. 12, the locus of the corresponding main scanning line is indicated by a broken line, and the locus of the other main scanning line is indicated by a one-dot chain line. Yes. As shown in FIG. 12, in the color misregistration correction according to the present embodiment, among the light source device 28BK and the light source device 281C that irradiate the beam from the opposite side to the reflecting mirror 280, the beam irradiated from the light source device 281C is used. The pixel shift as described with reference to FIG. 9 is performed at one point in the main scanning direction.

  The pixel shift as shown in FIG. 12 is realized by the delay control unit 124. That is, until halfway through one main scanning line, the image information acquisition unit 123 directly inputs pixel data to the light emission control unit 121, and the light emission control unit 121 is based on the pixel data input from the image information acquisition unit 123. The light source device 281C is caused to emit light.

  When the pixel data input to the light emission control unit 121 reaches a pixel at a certain point on the main scanning line, the delay control unit 124 controls the line memory 122 to store the main line one line before the line memory 122 stored. The pixel data of the scanning line is input to the light emission control unit 121. As a result, the light emission control unit 121 performs light emission control of the light source device 281C based on the pixel data of the main scanning line one line before from the middle of the main scanning line, so that an image to be formed is in the middle of the main scanning line. Shift in the sub-scanning direction.

  It should be noted that the position on the main scanning line where the pixel is shifted is within a predetermined pixel range from the approximate center on the main scanning line, that is, the center on the main scanning line, as shown in FIG. In the example shown in FIG. 12, the beam irradiated from the light source device 281BK is shifted by half a pixel in the sub-scanning direction as a whole. As a result, as shown in FIG. 11B, the displacement of the image, which was about 21 (μm) at the maximum, becomes 10.5 (μm) at the maximum as shown in FIG. 12, and the amount of displacement is halved. Has been reduced.

  Various methods can be used as a method of shifting the image as a whole in the sub-scanning direction by half a pixel. For example, it can be realized by mechanically moving the mirror 282BK. Further, in the optical system between the light source device 281BK and the photosensitive drum 109BK, it can also be realized by inserting a lens, a mirror or the like to change the optical path. In these cases, the configuration in which the mirror 282BK is mechanically moved and the inserted lens and mirror function as an image forming position adjusting unit.

  Further, the PPM for image formation is further reduced to ½, and an image of one main scanning line at 1200 dpi is drawn by scanning for two rotations of the reflecting mirror 280 with the same pixel data, that is, drawing for every half pixel. This can also be realized by shifting the pixel data input to the light source device 281BK by half a pixel. In this case, a line memory that stores pixel data and a control unit that controls reading of pixels from the line memory function as an image forming position adjustment unit.

  In the example of FIG. 12, the light source device 281BK and the light source device 281C are described as examples. However, the light source device 281M and the light source device 281Y are also light source devices in the same direction with respect to the reflecting mirror 280, respectively. It is the same. That is, the light source device 281M draws an image shifted by half a pixel in the sub-scanning direction, similarly to the light source device 281BK, and the light source device 281Y draws an image shifted in the main scanning direction in the same way as the light source device 281C. To do.

  As shown in FIG. 12, when the image is shifted by one line at one place on the main scanning line, it is sufficient that the pixel data of the main scanning line one line before can be referred to. One line may be provided for each of the light source device 281C and the light source device 281Y to be performed, and an increase in cost can be suppressed.

  As shown in FIG. 12, in the positional deviation correction method according to the present embodiment, the light source device 281BK that draws a black image does not shift the pixel data that is the basis of the light emission control, and does not shift the pixel data. Thus, pixel data serving as a basis for light emission control is shifted for the light source device 281C and the light source device 281Y arranged on the opposite side of the light source device 281BK.

  As described with reference to FIG. 10, there is a case where the dither pattern is lost and the image quality is deteriorated by performing the image shift. However, in the present embodiment, the black image is not shifted and cyan and The image is shifted only for the yellow image. Since cyan and yellow images have lower densities than black images, even if the dither pattern breaks down, it is difficult to perceive image quality degradation. For this reason, in the misalignment correction according to the present embodiment, it is possible to reduce image quality degradation.

  As described above, in the optical writing device 111 included in the image forming apparatus 1 according to the present embodiment, the trajectory of the light beam scanned on the surface of the photosensitive drum by changing the PPM is perpendicular to the paper transport direction. Pixel data input to the light source device that irradiates the beam from one side of the reflecting mirror when shifted relative to the direction is shifted by half a pixel as a whole and pixel data that is input to the light source device that irradiates the beam from the opposite side Are shifted in the middle of the main scanning direction. As a result, the color misregistration amount of the image can be reduced, and deterioration of the image quality due to the change of the dither pattern can be prevented while suppressing an increase in cost with a simple configuration.

  In the above embodiment, the case where the image drawn by the light source device 281BK and the light source device 281M is shifted by half a pixel in the sub-scanning direction has been described as an example. However, the image drawn by the light source device 281BK and the light source device 281M may be left as it is. Such an embodiment is shown in FIG.

  13, as in FIG. 12, pixel data input to the light source device 281 </ b> C is shifted in the main scanning direction, and an image drawn by the light source device 281 </ b> BK is the same as in FIG. 11B. It is a figure which shows the example made into the state.

  In the case of the example of FIG. 13, the maximum value of the color misregistration amount is 21 (μm), which is not different from FIG. However, as shown in FIG. 13, the direction of color misregistration can be unified. In the case of FIG. 11 (b), one side of the image in the main scanning direction has a color shift of cyan on the upper side and black on the lower side, but on the other side, the tentative plan is shifted on the lower side and black on the upper side. Yes.

  On the other hand, in the example of FIG. 13, in the entire range in the main scanning direction of the image, cyan is shifted upward and black is shifted downward, and the direction of the color shift is unified. Accordingly, it is possible to reduce the degradation of the image quality recognized by the user, compared to the case of FIG.

  Further, by continuously forming images in the image forming apparatus 1, when the temperature of the reflecting mirror 280 rises, the reflecting surface of the reflecting mirror 280 is distorted, and the exposure position on the surface of the photosensitive drum 109 changes. As a result, color misregistration occurs in each image drawn by the light beams irradiated from the opposite sides to the reflecting mirror 280, and the state shown in FIG. 13 may be changed to the state shown in FIG. Such an embodiment is shown in FIG.

  FIG. 14 is a diagram illustrating changes in the transferred image in accordance with changes in the temperature of the reflecting mirror 280. FIG. 14A shows a state where the temperature of the reflecting mirror 280 has not yet risen, and is the same state as FIG. When the temperature of the reflecting mirror 280 rises from the state (a) and the irradiation position of the light beam on the surface of the photosensitive drum 109 is shifted, the state shown in (b) at the center of FIG.

  The state of (b) in the center of FIG. 14 is the same as the state of FIG. 12, and is the state where the amount of color misregistration is reduced most. When the temperature of the reflecting mirror 280 further rises from the state (b), the irradiation position of the light beam on the surface of the photosensitive drum 109 is further shifted to a state shown in (c) on the right side of FIG. In the state of (c), the color misregistration amount is the same as the state of FIG. 13, and the color misregistration direction is the opposite direction to that of FIG.

  The state of the image after the transfer transitions between the states (a) to (c) of FIG. 14 with the temperature change of the reflecting mirror 280. That is, the color misregistration amount changes according to the temperature change of the reflecting mirror 280 with the state where the color misregistration amount is reduced most. Therefore, as in the example shown in FIG. 13, the image drawn by the light source device 281BK and the light source device 281M is not subjected to the process of shifting by half a pixel in the sub-scanning direction. It may be reduced.

  In the above embodiment, the case where the photosensitive drum 109 is changed from the 600 dpi mode to the 1200 dpi mode by halving the rotational speed of the photosensitive drum 109 has been described as an example. The same effect can be obtained by doubling the number of rotations of the reflecting mirror 280 without changing the speed of the above.

  Further, in the above-described embodiment, the example in which the present embodiment is applied has been described on the assumption that the mode is changed from the 600 dpi mode to the 1200 dpi mode. However, the present invention is not limited to this, and the trajectory of the light beam on the surface of the photosensitive drum 109 is shown in FIG. In the case of the state as shown in b), it is possible to obtain the effect of color misregistration correction by applying the same.

  In order to further reduce the deterioration of image quality, it is preferable to shift the image in a region where the image density is as high or low as possible in the region in the main scanning direction. Such an embodiment is shown in FIGS. 15 (a) and 15 (b). FIG. 15A is a diagram illustrating the pixel arrangement before the shift is performed, and FIG. 15B is a diagram illustrating the pixel arrangement after the shift is performed.

  As described above, degradation in image quality occurs due to the collapse of the dither pattern, but the region with a high image density, that is, a region of an image close to a solid image, is shifted at L2 shown in FIG. Shows the case. On the other hand, the region having a low image density is a region of an image close to a solid color, and indicates a case where a shift is performed at L1 shown in FIG.

  It can be seen that there is no region in which the image density is changed as compared with the state shown in FIG. 15A even when the shift is performed in either L1 or L2 shown in FIG. That is, a region having a high image density and a region having a low image density are regions where there is no dithering that leads to deterioration of image quality due to pixel shift, and shifting in such a region causes deterioration in image quality. Can be prevented.

  Such processing can be realized, for example, when the delay control unit 124 acquires information indicating a high density area or a low density area of the image from the controller 20 and determines an image shift position based on the information. . That is, the delay control unit 124 functions as a shift position information acquisition unit that acquires shift position information indicating the shift position. In addition, when a plurality of lines are provided as the line memory 1222, it is possible to determine the image density based on the pixel data stored in the line memory 122. The delay control unit 124 may make a determination based on the processed image information.

  Further, as described above, the pixel shift position in the embodiment is within a predetermined pixel range from the center on the main scanning line. Accordingly, in the determination of the pixel shift position based on the image density as described above, the highest or lowest position of the image density is employed within the pixel range.

  In the above embodiment, the case where the PPM is halved in order to double the resolution from 600 dpi to 1200 dpi, that is, the amount of skew generated thereby is maximum with respect to the entire range in the main scanning direction. The amount of shift in the middle of the main scanning line is one pixel, that is, only one location. In addition, if the generated skew amount is 2 dots, there are 2 shift locations, and if the generated skew amount is 3 dots, there are 3 shift locations.

1 Image forming apparatus 10 CPU
11 RAM
12 ROM
13 Engine 14 HDD
15 I / F
16 LCD
17 Operation unit 18 Bus 20 Controller 21 ADF
22 Scanner unit 23 Paper discharge tray 24 Display panel 25 Paper feed table 26 Print engine 27 Paper discharge tray 28 Network I / F
30 Main control unit 31 Engine control unit 32 Input / output control unit 33 Image processing unit 34 Operation display control unit 101 Paper feed tray 102 Paper feed roller 103 Separating roller 104 Paper 105 Conveying belts 106BK, 106C, 106M, 106Y Image forming unit 107 Drive Roller 108 Followed roller 109BK, 109C, 109M, 109Y Photoconductor drum 110BK Charger 111 Optical writing device 112BK, 112C, 112M, 112Y Developer 113BK, 113C, 113M, 113Y Charger 115BK, 115C, 115M, 115Y Transfer device 116 Fixing 120 Optical writing device control unit 121 Light emission control unit 122 Line memory 123 Image information acquisition unit 124 Delay control unit 280 Reflectors 281, 281BK, 281Y, 281M, 281C LEDA
282, 282BK, 282Y, 282M, 282C Mirror 283 Horizontal synchronization detection sensor

JP 2009-27683 A

Claims (9)

An optical writing device that forms an electrostatic latent image on a rotating photosensitive member by reflecting an irradiated light beam by a rotating reflecting mirror, scanning the light beam on the photosensitive member, and scanning the photosensitive member,
A light source device including at least two light sources that respectively irradiate the light beam from different directions with respect to the reflecting mirror ;
The rotating reflecting mirror scans the photosensitive member so that the light beam emitted from one of the two light sources moves from one end to the opposite side in the main scanning direction, and A scanning unit that scans so that the light beam emitted from the other side moves on the photosensitive member from the other end side in the main scanning direction toward the opposite side ;
An image information acquisition unit that acquires image information that is information of an image to be formed as the electrostatic latent image;
A light emission control unit for controlling the light source device based on the acquired image information to irradiate the light beam;
A timing adjustment unit that adjusts the timing and inputs the information stored for each main scanning line based on the acquired image information to the light emission control unit, which is information on pixels constituting the image ;
An image forming position adjustment unit that shifts the electrostatic latent image formed by the light beam emitted by the other of the two light sources by a half pixel in the same direction as the shift direction by the timing adjustment unit ;
In the scanning unit, when the ratio of the scanning speed of the light beam to the rotational speed of the photosensitive member is in the first state, the locus of the arrival point of the reflected light beam on the photosensitive member is It is provided to be a line perpendicular to the rotation direction,
The timing adjustment unit is configured such that the ratio of the scanning speed of the light beam to the rotational speed of the photoconductor is twice that of the first state, and the locus of the arrival point of the light beam on the photoconductor is the photoconductor. When the second state is inclined with respect to the direction perpendicular to the rotation direction of the pixel, the pixel information input to one of the two light sources is one pixel in the sub-scanning direction at one position of the main scanning line. An optical writing device characterized by being shifted by a minute . The timing adjustment unit shifts information of the pixels input to a light source that emits a light beam for forming an image other than black among the two light sources in the sub-scanning direction in the middle of the main scanning line. The optical writing device according to claim 1. The timing adjustment unit stores information of pixels constituting the image for one main scanning line based on the acquired image information, and based on the acquired image information until the middle of the main scanning line. the image information of the pixels constituting is input to the light emission control unit, characterized that you enter information of pixels the storage from the middle of the main scanning line on the light emission control unit Te claim 1 or 2 The optical writing device according to 1. The timing adjustment unit acquires shift position information indicating a position on a main scanning line for shifting the pixel information in the sub-scanning direction, thereby substituting the pixel information at the position indicated by the acquired shift position information. Shift in the scanning direction,
The position on the main scanning line for shifting the pixel information in the sub-scanning direction is determined based on the density of the image to be formed. Optical writing device. Position on the main scanning line shifting information of the pixels in the sub-scanning direction, the optical writing device according to claim 4, characterized in der Rukoto within a predetermined range of pixels from the center on the main scanning line. 6. The position on the main scanning line where the pixel information is shifted in the sub-scanning direction is a position where the density of the image to be formed is the highest in the predetermined pixel range. Optical writing device. 6. The position on the main scanning line where the pixel information is shifted in the sub-scanning direction is a position where the density of the image to be formed is the lowest within the predetermined pixel range. Optical writing device. An image forming apparatus comprising the optical writing device according to claim 1.   A scanning unit that reflects a light beam for forming an electrostatic latent image on a rotating photosensitive member by a rotating reflecting mirror, guides the light beam onto the photosensitive member, and scans the light from different directions with respect to the reflecting mirror. A method of controlling an optical writing device including a light source device including at least two light sources for irradiating a beam,
  The scanning unit scans so that the light beam emitted from one of the two light sources moves on the photosensitive member from one end side to the opposite side in the main scanning direction, and from the other of the two light sources. The irradiated light beam is scanned so as to move on the photosensitive member from the other end side in the main scanning direction to the opposite side, and the ratio of the scanning speed of the light beam to the rotational speed of the photosensitive member is the first. In the state, the locus of the arrival point of the reflected light beam on the photoconductor is provided so as to be a line perpendicular to the rotation direction of the photoconductor,
  Obtaining image information which is information of an image to be formed as the electrostatic latent image;
  Controlling the light source device based on the acquired image information to irradiate the light beam;
  The ratio of the scanning speed of the light beam to the rotational speed of the photoconductor is twice that of the first state, and the locus of the arrival point of the light beam on the photoconductor is perpendicular to the rotation direction of the photoconductor. When the second state is inclined with respect to the direction, the timing of the information of the pixels constituting the image and stored for each main scanning line based on the acquired image information is adjusted. Then, by inputting to the light emission control unit, the pixel information input to one of the two light sources is shifted by one pixel in the sub-scanning direction at one place on the main scanning line,
  A method for controlling an optical writing apparatus, comprising: shifting an electrostatic latent image formed by a light beam emitted from the other of the two light sources by half a pixel in the same direction as the shift direction.