JP2015063135A - Optical writing device, image forming apparatus, method for controlling optical writing device, program for controlling optical writing device, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical writing device capable of realizing gradation expression in an optical writing device using a binary head with a simple structure.SOLUTION: An optical writing device forming an electrostatic latent image on a photosensitive element with an LEDA 281 capable of controlling two states which are a switch on state and a switch off state includes: a pixel information acquiring unit 123 that acquires multilevel pixel information in which one pixel is expressed in multilevel scales, the multilevel pixel information being information of each pixel for constituting an image to be formed; a line memory 122 that stores the acquired multilevel pixel information for each main scanning line; and a light emission control unit 121 that performs exposure for one pixel in original resolution with N times exposure by emitting the LEDA 281 with a period corresponding to N-fold resolution of sub scanning direction resolution of the stored multilevel pixel information.

Description

  The present invention relates to an optical writing apparatus, an image forming apparatus, an optical writing apparatus control method, an optical writing apparatus control program, and a recording medium, and in particular, an image forming output based on image data in which one pixel is expressed by multi-value data. The present invention relates to control of an optical writing device capable of performing the above.

  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.

  In an electrophotographic image forming apparatus, an optical writing device that exposes a photosensitive member includes an LD (Laser Diode) raster optical system and an LEDA (Light Emitting Diode Array) head. In the LEDA, the photosensitive member is exposed for each main scanning line by the LED light source chips arranged in a line. As the type of the LED light source, a binary control light source (hereinafter referred to as a binary head) is used. And a light source capable of expressing gradation by changing the light emission intensity (hereinafter referred to as a multi-value head).

  However, due to problems such as manufacturing tolerances, in the multi-value control light source, the emission intensity varies among different light sources. The variation in the light emission intensity of the light source results in a variation in the exposure intensity of the photosensitive member, resulting in a variation in image density. Therefore, at present, a binary head is often used as the light source of the optical writing apparatus.

  In an optical writing device using an LED light source, as a method for enabling gradation expression, a main scanning line for one pixel is divided into a plurality of sublines, different exposure energies are set for each subline, and the level of each pixel is set. A method of selecting a subline to be turned on according to a tone value has been proposed (for example, see Patent Document 1).

  Even in the case of using a binary head in an optical writing device using an LED light source, it is necessary to cope with an image forming output of an image including gradation expression such as gray scale. When configuring a controller of an image forming apparatus corresponding to an optical writing device, a function enabling gradation expression using a binary head can be installed on the controller side, and a special configuration is provided on the optical writing device side. There is no need to provide.

  On the other hand, when the controller of the image forming apparatus and the optical writing apparatus are designed independently, in order to provide an optical writing apparatus that can support various controllers, it is necessary to provide the above-described functions on the optical writing apparatus side. is there. On the other hand, for example, when using the method disclosed in Patent Document 1, it is necessary to provide a line memory for each subline, and it is necessary to adjust the exposure intensity for each subline, which complicates the control system. Circuit scale and production cost increase.

  The present invention has been made in view of the above circumstances, and an object thereof is to realize gradation expression with a simple configuration in an optical writing apparatus using a binary head.

  In order to solve the above-described problems, one embodiment of the present invention is an optical writing device that forms an electrostatic latent image on a photosensitive member by a binary light source capable of controlling two states of lighting and extinguishing. A pixel information acquisition unit that acquires information on each pixel constituting an image to be formed as an electrostatic latent image, wherein one pixel is expressed by multi-level gradation, and the acquired multi-value A line pixel information storage unit that stores pixel information for each main scanning line; and a light emission control unit that controls the binary light source based on the stored multi-value pixel information to expose the photoconductor, The light emission control unit exposes the photosensitive member to the binary light source at a cycle corresponding to a resolution of N times that is a positive integer multiple of the resolution in the sub-scanning direction of the stored multi-value pixel information. One pixel of exposure at the original resolution in a single exposure In the control of the binary light source N times in each pixel, the lighting and extinguishing of the binary light source are controlled based on the lighting ratio conversion information for converting the multi-level gradation into the lighting ratio in the N times. In this case, the lighting ratio information is referred to based on the skew correction amount specified by the resolution of N times the pixel shift amount in the sub-scanning direction according to the position on the main scanning line. .

  Another aspect of the present invention is an image forming apparatus including the optical writing device.

  According to still another aspect of the present invention, there is provided a control method for an optical writing apparatus that forms an electrostatic latent image on a photosensitive member by a binary light source capable of controlling two states of lighting and extinguishing. Information of each pixel constituting an image to be formed as a latent image, wherein multi-value pixel information in which one pixel is expressed by multi-level gradation is acquired and stored in a storage medium for each main scanning line, By exposing the photosensitive member to the binary light source at a cycle corresponding to a resolution of N times that is a positive integer multiple of the resolution in the sub-scanning direction of the stored multi-value pixel information, the original is obtained in N exposures. In the control of the binary light source N times in each pixel, exposure is performed for one pixel in the resolution, and the two-stage gradation is converted into the lighting ratio in the N times, based on the lighting ratio conversion information. For controlling on / off of value light source When the control value is acquired, the lighting ratio information is referred to based on the skew correction amount specified by the N-times resolution in the sub-scanning direction in accordance with the position on the main scanning line. It is characterized by.

  According to still another aspect of the present invention, there is provided a control program for an optical writing device for forming an electrostatic latent image on a photosensitive member by a binary light source capable of controlling two states of lighting and extinguishing, Acquiring information on each pixel constituting an image to be formed as a latent image, wherein each pixel is expressed by multi-level gradation, and storing it in a storage medium for each main scanning line; and By exposing the photosensitive member to the binary light source at a cycle corresponding to a resolution N times that is a positive integer multiple of the resolution in the sub-scanning direction of the stored multi-value pixel information, the exposure is performed N times. In the step of performing exposure for one pixel at the original resolution and the control of the binary light source N times in each pixel, the lighting ratio conversion information for converting the multi-level gradation into the lighting ratio in the N times Based on the binary light source When acquiring control values for controlling lighting and extinction, the pixel shift amount in the sub-scanning direction according to the position on the main scanning line is based on the skew correction amount specified with the N times resolution. And causing the information processing apparatus to execute a step of referring to the lighting ratio information.

  Yet another aspect of the present invention is a recording medium, wherein the control program is recorded in a format readable by an information processing apparatus.

  According to the present invention, gradation expression can be realized with a simple configuration in an optical writing apparatus using a binary head.

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 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 pixel information stored in the line memory which concerns on embodiment of this invention, and each pixel output. It is a figure which shows the example of the information memorize | stored in the gamma conversion information storage part which concerns on embodiment of this invention. It is a figure which shows operation | movement of the optical writing device control part concerning embodiment of this invention. It is a figure which shows the example of the image actually drawn by 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 other embodiment of this invention. It is a figure which shows the example of the information memorize | stored in the skew correction information storage part which concerns on other embodiment of this invention. It is a figure which shows the concept of the skew correction which concerns on other embodiment of this invention. It is a figure which shows the concept of the skew correction which concerns on other embodiment of this invention. It is a figure which shows the subject solved by the skew correction which concerns on other embodiment of this invention. It is a figure which shows the subject solved by the skew correction which concerns on other embodiment of this invention. 6 is a flowchart illustrating a pixel data read operation according to another embodiment of the present invention. It is a flowchart which shows the acquisition operation of the control value from the gamma conversion table which concerns on other embodiment of this invention. It is a figure which shows the aspect of the skew correction which concerns on other embodiment of this invention. It is a figure which shows the pixel information stored in the line memory which concerns on other embodiment of this invention, and each pixel output.

Embodiment 1 FIG.
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, and its gist is an aspect of skew correction in an optical writing apparatus for forming an electrostatic latent image on a photoreceptor. 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 a mechanism that actually executes 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 the CPU 10 performs calculations according to those programs, thereby configuring a software control unit. The 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.

  When the image forming apparatus 1 operates as a scanner, the operation display control unit 34 or the input / output unit is operated in accordance with a user operation on the display panel 24 or a scan execution instruction input from an external PC or the like via the network I / F 28. The control unit 32 transfers a scan execution signal to the main control unit 30. The main control unit 30 controls the engine control unit 31 based on the received scan execution signal.

  The engine control unit 31 drives the ADF 21 and conveys the document to be imaged set on the ADF 21 to the scanner unit 22. Further, the engine control unit 31 drives the scanner unit 22 and images a document conveyed from the ADF 21. If no original is set on the ADF 21 and the original is directly set on the scanner unit 22, the scanner unit 22 takes an image of the set original under the control of the engine control unit 31. That is, the scanner unit 22 operates as an imaging unit.

  In the imaging operation, an imaging element such as a CCD included in the scanner unit 22 optically scans the document, and imaging information generated based on the optical information is generated. The engine control unit 31 transfers the imaging information generated by the scanner unit 22 to the image processing unit 33. The image processing unit 33 generates image information based on the imaging information received from the engine control unit 31 according to the control of the main control unit 30. Image information generated by the image processing unit 33 is stored in a storage medium attached to the image forming apparatus 1 such as the HDD 40. That is, the scanner unit 22, the engine control unit 31, and the image processing unit 33 work together to function as a document reading unit.

  The image information generated by the image processing unit 33 is stored in the HDD 40 or the like as it is according to a user instruction or transmitted to an external device via the input / output control unit 32 and the network I / F 28. That is, the ADF 21 and the engine control unit 31 function as an image input unit.

  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 diagram showing an arrangement relationship between the optical writing device 111 and the photosensitive drum 109 according to the present embodiment. As shown in FIG. 4, the irradiation light irradiated to the photosensitive drums 109BK, 109M, 109C, and 109Y of the respective colors is LEDA (LED Array) 281BK, 281M, 281C, and 281Y as light sources (hereinafter collectively referred to as LEDA281). ).

  The LEDA 281 is configured by arranging LEDs as light emitting elements in the main scanning direction of the photosensitive drum 109. The control unit included in the optical writing device 111 controls the on / off state of each LED arranged in the main scanning direction for each main scanning line based on the image data to be output, so that the photoconductor The surface of the drum 109 is selectively exposed to form an electrostatic latent image. That is, the LEDA 281 forms an electrostatic latent image for one line in the main scanning direction of an image to be output by one turn-on / off control. The LEDA 281 according to the present embodiment is a binary light source that can be controlled only to turn on / off.

  Next, a control block of the optical writing device 111 according to the present embodiment will be described with reference to FIG. FIG. 5 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 LEDA 281. As illustrated in FIG. 5, 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 γ conversion information storage unit 124.

  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, and the optical writing device control unit 120 as shown in FIG. Similar to the controller 20 of the image forming apparatus 1, a software control unit configured by loading a control program stored in a storage medium such as the ROM 12 into the RAM 11 and the CPU 10 performing calculations according to the program, It is comprised by the combination.

  The light emission control unit 121 is a light source control unit that controls the light emission of the LEDA 281 based on pixel information stored in the line memory 122 based on image information input from the engine control unit 31 of the controller 20. The light emission control unit 121 controls turning on / off of the light emission control unit 121 for each scanning line according to the clock in the sub-scanning direction.

  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. That is, the line memory 122 functions as a line pixel information storage unit. The light emission control unit 121 reads pixel information stored in the line memory 122 for each line, and controls lighting / extinguishing of the LEDA 281.

  FIG. 6 is a diagram showing the relationship between the reading order of the pixel data stored in the line memory 122 and the image actually drawn. 6 shows the readout order of the pixel data stored in the line memory 122. The first line is “0a”, “0b”, “0c”... The second line is “1a”. The pixel data stored in the line memory 122 is read out as “1b”, “1c”,..., “2a”, “2b”, “2c”,. The lower part of FIG. 6 is a diagram illustrating an example of an image drawn based on the pixel data read from the line memory 122, and the pixels drawn corresponding to the respective pixel data are indicated by circles. .

  Here, as shown in FIG. 6, in the present embodiment, the pixel data of one main scanning line is drawn by being divided into four lines. In other words, the light emission control unit 121 controls the lighting / extinguishing of the LEDA 281 at a cycle corresponding to a resolution four times the resolution of the image data input to the optical writing device control unit 120 in the sub-scanning direction.

  As shown in FIG. 6, when the light emission control unit 121 reads out pixel data of one main scanning line, the light emission control unit 121 divides the range of one pixel in the sub scanning direction into four sub lines, and turns on / off the LEDA 281 for each sub line. To draw sub-pixels. The respective sublines and subpixels are identified by subaddresses “0” to “3” as indicated by “0a — 0”, “0a — 1”, “0a — 2”, and “0a — 3”. The light emission control unit 121 controls lighting / extinguishing of the LEDA 281 while counting the sub-lines in drawing one main scanning line. That is, the light emission control unit 121 stores the count value of the subline.

  In FIG. 6, for ease of illustration, one pixel composed of four subpixels such as “1a — 0” to “1a — 3” is displayed long in the sub-scanning direction. The ratio of the main scanning direction to the sub-scanning direction is 1: 1.

  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 the present embodiment, the image information acquired by the image information acquisition unit 123 is image information in which each pixel is expressed with multiple gradation densities, and the pixel information that the image information acquisition unit 123 stores in the line memory 122 is: This is multi-value pixel information having density information of a plurality of gradations.

  The γ conversion information storage unit 124 stores information of a γ conversion table for converting the multi-value pixel information into binary information, that is, information indicating lighting / extinguishing of the light source corresponding to each pixel. FIG. 7 shows information of the γ conversion table according to the present embodiment. As shown in FIG. 7, in the γ conversion table according to the present embodiment, the gradation values in the multi-value pixel information described above and the sub-address described in FIG. 6 are arranged in a matrix, and for each combination. Information indicating lighting / extinguishing is stored.

  In other words, the γ conversion table is for each combination of a sequence of exposure for a plurality of times (in this embodiment, four times) for drawing one main scanning line and one pixel, and multi-level gradation in multi-value pixel information. In addition, the control value for controlling the turning on / off of the LEDA 281 that is a binary light source is stored information.

  For example, when the value indicating the gradation in a certain pixel is “3”, in the drawing of the pixel corresponding to the multi-value pixel information, the light emission control unit 121 sets the LED A 281 to the subaddress “0” to “2”. The sub address “3” turns off the LEDA 281. Thereby, the density corresponding to the gradation value of “3” is expressed by the ratio of lighting / extinguishing in the four sub-pixels.

  Next, the operation of the issuance control unit 121 according to this embodiment will be described. FIG. 8 is a flowchart showing the operation of the issuance control unit 121 according to the present embodiment. When image data is input from the controller 20 of the image forming apparatus 1 to the optical writing device control unit 120 and multi-value pixel information is stored in the line memory 122 in the image forming output, the light emission control unit 121 sets the subline count to “0”. The pixel data is read out from the line memory 122 (S802).

  When the pixel data is read from the line memory 122, the light emission control unit 121 refers to the γ conversion table stored in the γ conversion information storage unit 124, and for each pixel on the main scanning line, the gradation of the multi-value pixel information. A control value for turning on / off determined by the data and the subline count value is acquired (S803). Then, the light emission control unit 121 controls the light emission of the LEDA 281 based on the acquired control value (S804).

  Further, the light emission control unit 121 confirms the subline count value (S805), and if the subline count value is “3” (S805 / YES), that is, when drawing of all sublines for one main scanning line is completed, It is confirmed whether or not the output of the image to be output has been completed (S806). If the output of the image to be output has been completed (S806 / YES), the process ends. If not completed (S806 / NO), the processes from S801 are repeated.

  On the other hand, if the subline count value is not “3” (S805 / NO), the light emission control unit 121 increments the subline count value (S807), and repeats the processing from S803, whereby in the next S803, Then, the control values of the different sublines are read and the light emission control is executed. With such processing, the light emission control of the LEDA 281 by the light emission control unit 121 according to the present embodiment is executed.

  Next, an example of an image rendered as a result of the processing as shown in FIG. 8 will be described with reference to FIGS. FIG. 9A is a diagram illustrating an image represented by multi-value pixel information. As shown in FIG. 9A, when a gradation image by pixels with gradation values “4” to “0” is rendered by the optical writing device 120 according to the present embodiment, the image is shown in FIG. 9B. As described above, an image in which light and shade, that is, gradation is expressed by binary sub-pixels is drawn.

  As described above, in the optical writing device 111 according to the present embodiment, when multi-value pixel information is input from the controller 20 of the image forming apparatus 1, the resolution in the sub-scanning direction is quadrupled and four sublines and sub A pixel is defined, and shades of five gradations are expressed by the ratio of lighting / extinguishing in drawing of the four sub-pixels. At this time, in order to realize the four sublines, the line memory is not quadrupled, but when drawing the four sublines, each subfield is determined according to the original multi-value pixel information, the γ conversion table, and the count value of the subline count. Judgment of pixel on / off.

  Therefore, an increase in cost due to an increase in line memory can be avoided, and gradation expression can be realized in an optical writing apparatus using a binary head with a simple configuration.

  In the above-described embodiment, the case where the modification in the sub-scanning direction is quadrupled has been described as an example. However, it is applicable if it is a positive integer multiple, such as three times or less, five times or more. It is possible to obtain the same effect as described above.

Embodiment 2. FIG.
In the present embodiment, a case where skew correction is performed in addition to the processing described in the first embodiment will be described. In addition, about the structure which attaches | subjects the code | symbol similar to Embodiment 1, it shall show the part which is the same as that of Embodiment 1, or an equivalent part, and abbreviate | omits detailed description.

  In the optical writing apparatus as described in the first embodiment, a so-called skew is generated in which a tilted image is formed due to an attachment error of the LEDA 281 or an attachment error of the LED chip in the LEDA 281. Specifically, since the electrostatic latent image is formed on the photosensitive drum 109 by exposure from the LEDA 281, the direction in which the LEDs are arranged in the LEDA 281 is different from the main scanning direction of the photosensitive drum 109. When it is tilted or when the LEDA itself is tilted, the electrostatic latent image is tilted corresponding to the tilt. The electrostatic latent image is developed to form an inclined image. The gist of the present embodiment is to perform correction so that this skew does not occur.

  FIG. 10 is a block diagram illustrating a functional configuration of the light emission control unit 121 according to the present embodiment. As illustrated in FIG. 10, the light emission control unit 121 according to the present embodiment includes a skew correction information storage unit 125 in addition to the configuration illustrated in FIG. 5. As shown in FIG. 11, the skew correction information storage unit 125 stores information on the skew correction amount, that is, the shift amount in the sub-scanning direction over the entire main scanning line. In FIG. 11, “a”, “b”, “c”,... Correspond to “a”, “b”, “c”,.

  In the present embodiment, when the light emission control unit 121 reads out pixel information from the line memory 122, the pixel is shifted in the sub-scanning direction and read out based on the information stored in the skew correction information storage unit 125. Correction is performed. The basic concept of skew correction will be described with reference to FIGS.

  FIG. 12 is a diagram illustrating the relationship between the pixel data read from the line memory 122 and the actually drawn image, as in FIG. 7, and illustrates a state in which a skew has occurred. In the example of FIG. 12, the image is raised to the left in the figure due to the skew of the light beam. FIG. 13 is a diagram illustrating a state in which the generated skew is corrected as illustrated in FIG. In the example of FIG. 13, pixel data read from the line memory 122 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. 13, the total shift amount due to the skew is reduced. In the examples of FIGS. 12 and 13, for ease of explanation, one circle is shown for one pixel data.

  Next, an adverse effect of the skew correction shown in FIG. 13 will be described with reference to FIGS. 14 (a) and 14 (b). FIGS. 14A and 14B 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. 14B shows after correction. In FIG. 14B, the image is shifted at a position indicated by a bold dotted line.

  As shown in FIG. 14B, when the same correction as that in FIG. 13 is performed, the dither pattern has a one-pixel interval. Therefore, as shown by the dotted circle in the figure, 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.

  15 (a) and 15 (b), in order to reduce the noise described in FIG. 14 (b), the resolution in the sub-scanning direction is doubled and the shift amount when shifting the image is half that of the original pixel. It is a figure which shows the example at the time of setting it as the pixel part. In this case, as shown in FIG. 15A, in order to double the resolution in the sub-scanning direction of the image, the clock frequency for controlling the turning on / off of the LEDA 281 is doubled and the light emission control unit 121 is used. However, when reading out the pixel data from the line memory 122, the pixel data of one main scanning line is read out twice in succession. That is, one main scanning line at the original resolution is drawn in two steps.

  Then, as shown in FIG. 15B, a single shift amount when shifting the image in the sub-scanning direction is set to a half pixel, and a shift amount corresponding to one pixel is obtained in total to indicate a shift amount for one pixel. Thus, the number of shifts is set to 2 times. As a result, as shown by the dotted circle in the figure, the area of the lit pixel and the unlit pixel that are connected at the position where the image is shifted is halved, thereby suppressing the visual influence that is recognized as noise. it can.

  Next, the operation of the light emission control unit 121 according to this embodiment will be described. In principle, the light emission control unit 121 according to the present embodiment also performs the same process as in the flowchart of FIG. However, in S802 and S803 in FIG. 8, processing corresponding to the skew correction amount is performed. First, the details of the processing of S802 in the present embodiment will be described with reference to FIG.

  As shown in FIG. 16, the light emission control unit 121 selects addresses in the main scanning direction in order in the main scanning line direction when reading image data (S1601). The addresses in the main scanning direction are “a”, “b”, “c”... Shown in FIG. When an address in the main scanning direction is selected, the light emission control unit 121 acquires a skew correction amount corresponding to the address in the main scanning direction from the skew correction information storage unit 125, and subtracts the skew correction amount from the current subline count value. A value is obtained (S1602).

  If the value obtained by subtracting the skew correction amount from the subline count value is not a negative value (S1602 / YES), the light emission control unit 121 reads the pixel data in order from the line memory 122 (S1603). On the other hand, when the value obtained by subtracting the skew correction amount from the subline count value is a negative value (S1602 / NO), the pixel data of the main scanning line one line before is read from the line memory 122 (S1604).

  When the processing of S1603 and S1604 is completed, the light emission control unit 121 checks whether the processing is completed over the entire range of the main scanning line (S1605), and if not completed (S1605 / NO), the processing from S1601 is repeated. If completed (S1605 / YES), the process is terminated. As described above, the light emission control unit 121 according to the present embodiment switches the main scanning line of the pixel data to be read according to the skew correction amount.

  Next, details of the processing of S803 in the present embodiment will be described with reference to FIG. As shown in FIG. 17, the light emission control unit 121 obtains a value obtained by subtracting the skew correction amount from the current subline count value when acquiring the control value from the γ conversion table (S1701). If the value obtained by subtracting the skew correction amount from the subline count value is not a negative value (S1701 / YES), the light emission control unit 121 uses the value as it is as a subaddress (S1702).

  When the value obtained by subtracting the skew correction amount from the subline count value is a negative value (S1701 / NO), the light emission control unit 121 sets the value obtained by adding 4 to the subaddress (S1703). When the processes of S1702 and S1703 are completed, the light emission control unit 121 acquires a control value from the γ conversion table based on the determined sub address and the pixel data read by the process of FIG. 16 (S1704), and ends the process.

  Next, FIG. 18 shows an example of an image drawn through the processing of FIGS. 16 and 17. FIG. 18 is a diagram illustrating a result of applying the skew correction amount illustrated in FIG. 11 to the image information illustrated in FIG. 9A according to the first embodiment. As shown in FIG. 18, the pixels are shifted in the sub-scanning direction according to the skew correction amount shown in FIG.

  As described above, in the present embodiment, even when skew correction is performed, the same function as that of the first embodiment can be realized. It is possible to realize gradation expression in an optical writing device using a value head.

  In all the embodiments and the present embodiment, the resolution in the sub-scanning direction is quadrupled in order to enable gradation expression with a binary head, but as described in FIGS. 14 and 15, the sub-scanning direction When performing the skew correction by the image shift, the image quality degradation due to the skew correction can be reduced by multiplying the resolution of the image in the sub-scanning direction by an integral multiple. Therefore, in this embodiment, the process of multiplying the resolution in the sub-scanning direction by a plurality of times contributes to the two purposes of realizing gradation expression and reducing image quality degradation by skew correction. It becomes possible.

  In the above embodiment, the case where the lighting / extinguishing pattern of each sub-address corresponding to the gradation data of each pixel is constant based on the γ conversion table as shown in FIG. 7 has been described as an example. However, in order to reduce the deterioration of image quality due to the change in image density as described with reference to FIGS. 14 and 15, the lighting / extinguishing pattern of each subaddress according to the gradation data of each pixel may be variable.

  In such a mode, for example, the γ-conversion information storage unit 124 turns on / off each subaddress so that there is little change in density when the pixel is shifted for each combination of gradation values of adjacent pixels. Is stored. Then, the light emission control unit 121 can be realized by switching the γ conversion table to be referred to according to the combination of gradation values of adjacent pixels.

  It should be noted that the aspect in which the lighting / extinguishing pattern of each subaddress is made variable in this way is worth applying even when skew correction is not performed as in the first embodiment. For example, when an image as shown in FIG. 9B is formed, the colored / colorless pattern for each pixel is constant, so that moire may occur in addition to the gradation as shown in FIG. 9A. is there. On the other hand, moire can be prevented by making the lighting / extinguishing pattern of each sub-address variable so that a certain pattern does not occur.

  In the first and second embodiments, when pixel data is read in S802 of FIG. 8, it is basically read in the order input to the line memory 122. If the value obtained by subtracting the skew correction amount from the subline count value is negative. The case where pixel data of the previous main scanning line is read has been described as an example. In addition to the main address for each main scanning line, a continuous address counted for each subline is set, and the continuous address is divided by a multiple of the resolution in the subscanning direction (4 in this embodiment). The main address can also be determined based on the integer part. Such an example is shown in FIG.

  FIG. 19 is a diagram illustrating a correspondence relationship between a continuous address counted for each sub-line and a main address indicating the original main scan line in an aspect in which each main scan line is drawn by being divided into sub-lines. is there. As shown in FIG. 19, the continuous address increases by one for each subline. Here, when each continuous address is divided by “4”, which is a multiple of the resolution in the sub-scanning direction, and the integer part of the quotient is taken, it can be seen that each main address is the main address.

  That is, in the operation of FIG. 8, the light emission control unit 121 counts consecutive addresses for each drawing of each subline, and when reading pixel data, the count value of the continuous addresses is a multiple of the resolution in the sub-scanning direction. Pixel data is read from the main address corresponding to the integer part of the quotient divided by. Further, as in the second embodiment, when the skew correction amount is considered, the value obtained by subtracting the skew correction amount from the count value of the continuous address is divided by the resolution in the sub-scanning direction, and the same processing is performed. Even in such an embodiment, the same effect as described above can be obtained.

  In such a case, it is preferable to set the multiple N of the resolution in the sub-scanning direction to the nth power of 2 (where n is a positive integer). As a result, the process of taking the integer part of the quotient divided by N is the same as the process of truncating the lower N / 2 bits when the original numerical value is expressed in binary, and can simplify the process. it can.

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 Static eliminator 115BK, 115C, 115M, 115Y Transfer device 116 Fixing Device 117 pattern detection sensor 120 optical writing device control unit 121 light emission control unit 122, 122a, 122b line memory 123 image information acquisition unit 124 gamma conversion information storage unit 125 skew correction information acquisition unit 28 1,281BK, 281Y, 281M, 281C LEDA

JP 2007-245537 A

Claims (9)

An optical writing device that forms an electrostatic latent image on a photosensitive member by a binary light source that can control two states of turning on and off,
A pixel information acquisition unit that acquires information of each pixel constituting an image to be formed as the electrostatic latent image, and that acquires multi-value pixel information in which one pixel is expressed by multiple levels of gradation,
A line pixel information storage unit for storing the acquired multi-value pixel information for each main scanning line;
A light emission control unit that controls the binary light source based on the stored multi-value pixel information to expose the photoconductor,
The light emission control unit exposes the photosensitive member to the binary light source at a cycle corresponding to a resolution of N times that is a positive integer multiple of the resolution in the sub-scanning direction of the stored multi-value pixel information. Lighting ratio conversion for performing exposure for one pixel at the original resolution in N exposures, and converting the multi-level gradation into the lighting ratio in the N times in the control of the binary light source N times in each pixel. When controlling the turning on and off of the binary light source based on the information, the amount of pixel shift in the sub-scanning direction according to the position on the main scanning line is set to the skew correction amount specified with the N times resolution. An optical writing apparatus characterized in that the lighting ratio information is referred to based on the lighting ratio information. The lighting ratio information includes the binary light source for each combination of the order in the N exposures and the multi-stage gradation in order to convert the multi-stage gradation into the N-time lighting ratio. Control information for controlling turning on and off is information stored,
Based on the lighting ratio conversion information, the light emission control unit acquires a control value corresponding to a combination of an order in the N exposures and a gradation indicated by the multi-value pixel information, and turns on and off the binary light source The optical writing apparatus according to claim 1, wherein the optical writing device is obtained by controlling the turn-on or turn-off designation by correcting the order of the N exposures based on the skew correction amount. The pixel information storage unit stores the multi-value pixel information with numerical values in the order obtained for each main scanning line,
The light emission control unit counts the number of exposures of the photoconductor with a period corresponding to a resolution N times the resolution in the sub-scanning direction of the stored multi-value pixel information, and divides the count value by the N. 3. The optical writing device according to claim 1, wherein the multi-value pixel information stored in the pixel information storage unit is read out in accordance with a numerical value of an integer part of the quotient.   The light emission control unit acquires a control value for controlling turning on and off of the binary light source from the lighting ratio information that is different for each combination of gradation values of adjacent pixels in the multi-value pixel information. The optical writing device according to any one of claims 1 to 3.   4. The optical writing device according to claim 3, wherein the N is a positive integer power of 2.   An image forming apparatus comprising the optical writing device according to claim 1. A method of controlling an optical writing device that forms an electrostatic latent image on a photosensitive member by a binary light source capable of controlling two states of lighting and extinguishing,
Information on each pixel constituting the image to be formed as the electrostatic latent image, which is obtained by storing multi-value pixel information in which one pixel is expressed by multi-level gradation and storing it in a storage medium for each main scanning line And
The binary light source is exposed to the binary light source at a cycle corresponding to a resolution of N times that is a positive integer multiple of the resolution in the sub-scanning direction of the stored multi-value pixel information. One pixel exposure at a resolution of
In controlling the binary light source N times in each pixel, to control lighting and extinction of the binary light source based on lighting ratio conversion information for converting the multi-stage gradation into the lighting ratio in N times. When the control value is acquired, the lighting ratio information is referred to based on the skew correction amount in which the pixel shift amount in the sub-scanning direction according to the position on the main scan line is designated with the N times resolution. A method of controlling an optical writing device. A control program for an optical writing device that forms an electrostatic latent image on a photosensitive member by a binary light source capable of controlling two states of turning on and off,
Information on each pixel constituting the image to be formed as the electrostatic latent image, which is obtained by storing multi-value pixel information in which one pixel is expressed by multi-level gradation and storing it in a storage medium for each main scanning line And steps to
The binary light source is exposed to the binary light source at a cycle corresponding to a resolution of N times that is a positive integer multiple of the resolution in the sub-scanning direction of the stored multi-value pixel information. Exposing one pixel at a resolution of
In controlling the binary light source N times in each pixel, to control lighting and extinction of the binary light source based on lighting ratio conversion information for converting the multi-stage gradation into the lighting ratio in N times. When the control value is acquired, the lighting ratio information is referred to based on the skew correction amount in which the pixel shift amount in the sub-scanning direction according to the position on the main scan line is designated with the N times resolution. And a step of causing the information processing apparatus to execute the step.   A recording medium in which the control program according to claim 8 is recorded in a format readable by an information processing apparatus.