JP2009066832A - Image forming device and image forming program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the nonuniformness of density of an image under various conditions in an image forming device though the structure is simple. <P>SOLUTION: Multiple types of correction value tables in which multiple types of conditions (such as gradation width of image) under which the nonuniformness of image occurs in an image correspond to correction values for correcting the nonuniformness of density are stored in a storage part (RAM 52) for each multiple LEDs. The selection part of a CPU 50 selects a proper correction value table from the correction value tables stored in the storage part according to the conditions (density value of image) in image formation. Since a calculation circuit for calculating the correction values as in conventional examples is not required, the structure is simple. Also, the nonuniformness of density of the image can be suppressed under various conditions by selecting a proper correction value table from the correction value tables adaptable to various conditions. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus and an image forming program, and more particularly, to an image forming apparatus and an image forming program in which a light emitting diode array in which a plurality of light emitting diode elements are arranged is used as a light source of exposure means. is there.

  Conventionally, in an electrophotographic image forming apparatus, a light emitted from a laser diode is scanned using a polygon mirror as an exposure device for exposing a charged image carrier (photosensitive member) (hereinafter referred to as “laser beam type”). And those of a type using a light emitting diode array in which a plurality of light emitting diode elements are arranged (hereinafter referred to as “LED array type”) are mainly provided.

  In an image forming apparatus using an LED array type exposure device, a light emitting diode array cannot be manufactured so that the light emitting characteristics of a plurality of light emitting diode elements (hereinafter abbreviated as LED elements) are all uniform. Even if an equal amount of current is supplied to the elements, the amount of light differs for each LED element, resulting in variations in the amount of exposure by the LED array, resulting in uneven density in the formed image. .

For this reason, various image forming apparatuses have been proposed that correct variations in light emission characteristics for each of a plurality of LED elements constituting an LED array (see, for example, Patent Documents 1 to 3). For example, in the conventional example described in Patent Document 1, a correction value for each LED element is obtained by calculation from parameters measured in advance for each LED array. In the conventional example described in Patent Document 3, an LED array in which a plurality of blocks including a plurality of LED elements whose light amounts are unified by sorting is provided, and a correction value table storing correction values for each block The density unevenness is corrected by adjusting the current flowing through the LED elements of each block with the correction value read from the correction value table.
JP 2004-188846 A JP 2004-188849 A Japanese Patent No. 2849244

  However, in the former conventional example, an arithmetic circuit for calculating a correction value from a parameter is required, so that the configuration becomes complicated and large-scale. In the latter conventional example, there is only one type of correction value table, so there is a problem that the conditions that can be corrected are limited.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image forming apparatus and an image forming program capable of suppressing unevenness in image density under various conditions with a simple configuration. There is.

  In order to achieve the above object, the invention according to claim 1 is an exposure means using a light-emitting diode array in which a plurality of light-emitting diode elements are arranged as a light source, and an electrostatic formed by exposure by the exposure means. An image carrier that carries the latent image, a developing unit that develops and visualizes the electrostatic latent image carried by the image carrier with a developer, a transfer unit that transfers the visualized developer image to the transfer member, and an image In accordance with a formation request, in an image forming apparatus provided with a control unit that executes at least an exposure unit, a development unit, and a transfer unit to execute an image forming process, the control unit sets the static electricity unit for each of a plurality of light emitting diode elements. A storage unit that stores a plurality of types of correction value tables in which a plurality of types of conditions that cause density unevenness of the electrostatic latent image and correction values for correcting the density unevenness are associated with each other, and the conditions at the time of image formation Therefore, a selection unit that selects an appropriate correction value table from among a plurality of types of correction value tables stored in the storage unit, and each light emitting diode element for each light-emitting diode element with reference to the correction value table selected by the selection unit A correction value instructing unit for instructing the exposure unit with a correction value, and the exposure unit adjusts the light amount of each light emitting diode element in accordance with the correction value instructed from the correction value instructing unit.

  According to a second aspect of the present invention, in the first aspect of the present invention, the condition is a gradation width of an image included in the image formation request, and the plurality of gradations set for each stage obtained by dividing the entire gradation range into a plurality of stages. A type of correction value table is stored in the storage unit.

  According to a third aspect of the present invention, in the first aspect, the condition is a gradation of an image included in an image formation request, and each stage obtained by dividing a sum of gradations of neighboring pixels with respect to an arbitrary pixel into a plurality of stages. The plurality of types of correction value tables set for each are stored in a storage unit.

  According to a fourth aspect of the present invention, in the first aspect of the invention, there is provided a housing for storing the exposure unit, the image carrier, the developing unit, the transfer unit, and the control unit, and the condition is an internal environment of the casing. It is characterized by being.

  According to a fifth aspect of the present invention, in the first aspect of the invention, there is provided a housing for storing the exposure unit, the image carrier, the developing unit, the transfer unit, and the control unit, and the condition is determined by an external environment of the casing. It is characterized by being.

  According to a sixth aspect of the present invention, in the first aspect of the present invention, the temperature detecting means for detecting the temperature of the exposure means is provided, the condition is the temperature of the exposure means, and the selection unit is at the time of image formation detected by the temperature detecting means. The correction value table is selected according to the temperature.

  The invention according to claim 7 is the invention according to claim 1, wherein the condition is a manufacturer of the image carrier, and the selection unit selects a correction value table according to the manufacturer of the image carrier at the time of image formation. To do.

  The invention according to an eighth aspect is the invention according to the first aspect, wherein the condition is a type of the image carrier, and the selection unit selects a correction value table according to the type of the image carrier at the time of image formation. To do.

  The invention according to claim 9 is the invention according to claim 1, wherein the condition is a manufacturing lot of the image carrier, and the selection unit selects the correction value table according to the manufacturing lot of the image carrier at the time of image formation. Features.

  According to a tenth aspect of the present invention, in the first aspect, the condition is the degree of use of the image carrier, and the selection unit selects the correction value table according to the degree of use of the image carrier during image formation. Features.

  According to an eleventh aspect of the present invention, in the first aspect, the condition is a degree of deterioration for each light emitting diode element, and the selection unit selects a correction value table according to the degree of deterioration of each light emitting diode element during image formation. It is characterized by that.

  According to a twelfth aspect of the present invention, in the first aspect of the invention, for each of the plurality of light emitting diode elements, a plurality of types of conditions that cause density unevenness of the electrostatic latent image and a correction value for correcting the density unevenness are respectively provided. The exposure unit includes a second storage unit that stores a plurality of associated correction value tables, and the plurality of types of correction value tables are transferred from the second storage unit to the storage unit included in the control unit. Features.

  According to a thirteenth aspect of the present invention, in the first aspect of the invention, the upper limit and the lower limit of the condition are stored in a second storage unit, and the selection unit selects the correction value table in consideration of the upper limit and the lower limit. Features.

  According to a fourteenth aspect of the invention, in the first aspect of the invention, the upper limit and the lower limit of the condition are stored in a storage unit of the control means, and the selection unit selects the correction value table in consideration of the upper limit and the lower limit. Features.

  According to a fifteenth aspect of the present invention, there is provided an image forming program for use in the image forming apparatus according to any one of the first to fourteenth aspects, in order to achieve the above object. Processing for selecting an appropriate correction value table from a plurality of types of correction value tables stored in the storage unit, and referring to the selected correction value table, the correction value for each light emitting diode element is stored in the exposure unit. Instructing processing is performed.

  According to the first and fifteenth aspects of the present invention, for each of the plurality of light emitting diode elements, a plurality of types of conditions that cause the density unevenness of the electrostatic latent image are associated with correction values for correcting the density unevenness. A plurality of types of correction value tables are stored in the storage unit, and the selection unit selects an appropriate correction value table from among a plurality of types of correction value tables stored in the storage unit based on the conditions at the time of image formation. Therefore, unlike the conventional example, an arithmetic circuit for calculating a correction value is not required, so the configuration is simple, and an appropriate correction value table is selected from a plurality of types of correction value tables corresponding to various conditions. By doing so, it is possible to suppress the density unevenness of the image under various conditions.

  According to the invention of claim 2, since the density unevenness of the image does not necessarily change linearly from the low density to the high density, the gradation range of the image included in the image formation request is used as a condition. By storing the plurality of types of correction value tables set for each stage obtained by dividing the above into a plurality of stages, the density unevenness can be appropriately corrected regardless of the density level.

  According to the invention of claim 3, the condition is the gradation of the image included in the image formation request, and is set for each stage obtained by dividing the sum of the gradations of neighboring pixels with respect to an arbitrary pixel into a plurality of stages. Since the plurality of types of correction value tables are stored in the storage unit, halftone density unevenness can be corrected appropriately.

  According to the fourth aspect of the present invention, a plurality of types of correction value tables are stored in the storage unit under the condition of the internal environment of the housing that houses the exposure unit, the image carrier, the development unit, the transfer unit, and the control unit. Therefore, for example, the density unevenness can be corrected by selecting an appropriate correction table according to the temperature and humidity in the housing.

  According to the invention of claim 5, a plurality of types of correction value tables are stored in the storage unit on the condition of the external environment of the housing that houses the exposure means, the image carrier, the development means, the transfer means, and the control means. Therefore, for example, the density unevenness can be corrected by selecting an appropriate correction table according to the ambient temperature and humidity outside the housing.

  According to a sixth aspect of the present invention, the temperature detecting means for detecting the temperature of the exposure means is provided, the condition is the temperature of the exposure means, and the selection unit corrects according to the temperature at the time of image formation detected by the temperature detecting means. Since the value table is selected, the density unevenness caused by the temperature variation of the light emitting diode element can be corrected appropriately.

  According to the invention of claim 7, the condition is the manufacturer of the image carrier, and the selection unit selects the correction value table according to the manufacturer of the image carrier at the time of image formation. The density unevenness can be corrected appropriately.

  According to the invention of claim 8, the condition is the type of the image carrier, and the selection unit selects the correction value table according to the type of the image carrier at the time of image formation. The density unevenness can be corrected appropriately.

  According to the invention of claim 9, the condition is a production lot of the image carrier, and the selection unit selects the correction value table according to the production lot of the image carrier at the time of image formation. The density unevenness can be appropriately corrected for each lot.

  According to the invention of claim 10, the condition is the degree of use of the image carrier, and the selection unit selects the correction value table according to the degree of use of the image carrier during image formation. The density unevenness according to the degree can be corrected appropriately.

  According to the invention of claim 11, the condition is the degree of deterioration for each light emitting diode element, and the selection unit selects the correction value table according to the degree of deterioration of each light emitting diode element during image formation. The density unevenness according to the degree of deterioration can be corrected appropriately.

  According to the twelfth aspect of the present invention, for each of the plurality of light emitting diode elements, a plurality of types in which a plurality of types of conditions causing uneven density of the electrostatic latent image and correction values for correcting the density unevenness are associated with each other. The second storage unit that stores the correction value table is provided in the exposure unit, and a plurality of types of correction value tables are transferred from the second storage unit to the storage unit provided in the control unit. In the case of replacement, the new exposure means correction value table after the replacement is automatically transferred to the storage section of the control means, which improves usability.

  According to the invention of claim 13, the upper limit and the lower limit of the condition are stored in the second storage unit, and the selection unit selects the correction value table in consideration of the upper limit and the lower limit. Since the range of conditions (upper limit and lower limit) is stored for each exposure means, it is possible to save the trouble of changing the range when the exposure means is replaced.

  In the invention of claim 14, in the invention of claim 1, the upper limit and the lower limit of the condition are stored in the storage unit of the control means, and the selection unit selects the correction value table in consideration of the upper limit and the lower limit. The range of conditions (upper limit and lower limit) serving as a selection criterion can be freely changed.

  Hereinafter, embodiments in which the technical idea of the present invention is applied to a tandem type color printer will be described in detail with reference to the drawings. However, the image forming apparatus to which the technical idea of the present invention can be applied is not limited to the tandem type color printer, and the present invention can be applied to all image forming apparatuses employing an electrophotographic system such as a monochrome printer, a copying machine, and a facsimile. The technical idea can be applied.

  First, the structure of a color printer common to each embodiment will be briefly described with reference to FIG. In this color printer, a paper feed tray 13 is detachably attached to the lower part of the housing 12, and the transfer paper P stored in the paper feed tray 13 is fed by a paper feed roller 14. Also, a waste toner box 15 for storing waste toner generated by cleaning the photosensitive drum 21 and the intermediate transfer belt 16 as described later is attached to and detached from the front side of the upper portion of the paper feed tray 13 in the housing 12. A waste toner full detection sensor 17 is provided on the side surface of the waste toner box 15 to detect that the amount of waste toner stored has reached a predetermined upper limit.

  An intermediate transfer belt 16 composed of an endless belt wound around a tension roller 18 and a driving roller 19 is stretched substantially horizontally in the depth direction in the center of the housing 12 in the depth direction. As a result, the drive roller 19 is driven and rotated counterclockwise, whereby the intermediate transfer belt 16 rotates in the direction indicated by the arrow. Above the intermediate transfer belt 16 in the housing 12, toners (developers) of black, magenta, cyan, and yellow are used, and toner images (developer images) of the respective colors are formed by a known image forming process. The four image forming units 20K, 20M, 20C, and 20Y are sequentially arranged at intervals from the upstream side in the rotational direction of the intermediate transfer belt 16 toward the downstream side (leftward in FIG. 2).

  These four image forming cartridges 20K, 20M, 20C, and 20Y have exactly the same structure except for the color of the toner to be used. Therefore, only the configuration of the image forming cartridge 20K for black toner will be described in detail. The description of the image forming cartridges 20M, 20C, and 20Y for the other color toners is omitted. However, the constituent elements of the image forming cartridges 20M, 20C, and 20Y for the respective colors of magenta, cyan, and yellow are replaced with “K” symbols attached to the respective constituent elements of the black image forming cartridge 20K. A distinction is made by attaching the symbols “M”, “C”, and “Y”.

  The image forming cartridge 20K includes a photosensitive drum 21K that rotates clockwise in FIG. 2, a cleaning unit 24K that includes a charging roller 22K, a developing unit 23K, an exposure unit 30K, a cleaner blade 241K, and a waste toner collection roller 242K around the photosensitive drum 21K. Etc. are provided integrally. The developing unit 23K includes a toner tank 231K having a paddle 235K for stirring the toner, a developing roller 232K provided near the lower end of the toner tank 231K, a supply roller 233K, a developing blade 234K, and the like. The black toner is supplied to the developing roller 232K by the supply roller 233K, and the amount fed to the photosensitive drum 21K by the developing blade 234K is regulated to be constant.

  The exposure device 30K is configured by housing an LED array (not shown) in which a plurality (for example, about 5,000) of LED elements are arranged in one or more rows in a housing, and the light emitting surface of the LED array is photosensitive. The photosensitive drum 21K is arranged so that the axial direction of the photosensitive drum 21K and the arrangement direction of the LED elements (longitudinal direction of the exposure device 30K) coincide with the outer peripheral surface of the photosensitive drum 21K (surface on which the photosensitive member is formed). Then, the outer peripheral surface (photosensitive member surface) of the photosensitive drum 21K is exposed by irradiating the outer peripheral surface of the photosensitive drum 21K uniformly charged by the charging roller 22K with light emitted from the LED array of the exposure device 30K. An electrostatic latent image is formed. Note that the light emission control of the LED elements is performed by adjusting the current supply to each LED element by the exposure device controllers 54K, 54M, 54C, and 54Y, as will be described later.

  A primary transfer roller 25K is disposed below the photosensitive drum 21K so as to face the outer peripheral surface of each photosensitive drum 21K with the intermediate transfer belt 16 interposed therebetween. The primary transfer roller 25K is rotatably provided by a rotation mechanism (not shown) and is movable between a position in contact with the intermediate transfer belt 16 and a position not in contact with a movement mechanism (not shown).

  Further, a secondary transfer roller 32 is provided so as to face the drive roller 19 with the intermediate transfer belt 16 and the transfer paper conveyance path 41 interposed therebetween and to rotate in contact with the intermediate transfer belt 16, and drive the intermediate transfer belt 16. A transfer belt cleaner 40 is provided above the end portion on the roller 19 side. In the transfer paper conveyance path 41, a registration roller 33 and a registration sensor 34 are disposed on the upstream side of the secondary transfer roller 32, and a fixing device 35, a paper discharge sensor 36, and a paper discharge roller 37 are disposed on the downstream side. Has been. Reference numeral 42 denotes a double-sided conveyance path branched from the transfer paper conveyance path 41, which is provided with a double-sided conveyance roller 38 and a double-sided sensor 39, and is used when images are formed on both sides of the transfer paper.

  In the image formation, first, the outer peripheral surface of the photosensitive drum 219K in the black image forming cartridge 20K is uniformly charged by the charging roller 22K in the dark, and then exposed to light irradiated from the exposure device 30K to be electrostatically charged. A latent image is formed. The electrostatic latent image is visualized by the developing device 23K with black toner, and a black toner image is formed on the outer peripheral surface of the photosensitive drum 219K.

  This toner image is transferred onto the intermediate transfer belt 16 by the action of the primary transfer roller 25K at the position where the photosensitive drum 21K and the intermediate transfer belt 16 are in contact (primary transfer position). As a result, the toner image is transferred onto the intermediate transfer belt 16. An image with black toner is formed. After the transfer of the toner image is completed, the photosensitive drum 21K waits for the next image formation after unnecessary toner remaining on the outer peripheral surface is wiped off by the cleaner blade 241K of the cleaning unit 24K. The toner wiped off by the cleaner blade 241K is collected by a waste toner collecting roller 242K and sent to the waste toner box 15 through a duct (not shown).

  In this way, the intermediate transfer belt 16 onto which the black toner image has been transferred by the image forming cartridge 20K is then conveyed to the position of the magenta image forming cartridge 20M. In the magenta image forming cartridge 20M, a magenta toner image is formed on the outer peripheral surface of the photosensitive drum 21M by the same process as the image forming process by the black image forming cartridge 20K described above, and the toner image is primarily transferred. By the action of the roller 25M, the black image formed on the intermediate transfer belt 16 is transferred onto the black image.

  The intermediate transfer belt 16 is further sequentially conveyed to the positions of the cyan and yellow image forming cartridges 20C and 20Y, and the cyan toner image formed on the photosensitive drum 21C and the photosensitive drum 21Y are moved by the same operation. The yellow toner image formed on the toner image is sequentially transferred to the toner image on the intermediate transfer belt 16. Thus, a full-color toner image is formed on the intermediate transfer belt 16. The area of the intermediate transfer belt 16 on which the full-color toner image is formed passes through the tension roller 18 and is conveyed to a position where it contacts the secondary transfer roller 32. When printing only black toner during image formation, the primary transfer rollers 25M, 25C, and 25Y are retracted to positions away from the photosensitive drums 21M, 21C, and 21Y, respectively, and the above-described image forming process is performed. Only with the black image forming cartridge 20K, a black and white toner image is created and transferred onto the intermediate transfer belt 16.

  On the other hand, the transfer paper P stored in the paper feed tray 13 is sequentially fed out from the uppermost transfer paper P as the paper feed roller 2 rotates counterclockwise, and after the leading edge is detected by the registration sensor 34, It waits at a position that reaches the registration roller 3. The registration roller 3 starts to be driven by the nip portion between the intermediate transfer belt 16 and the secondary transfer roller 32 immediately before the toner image transferred onto the intermediate transfer belt 16 contacts the secondary transfer roller 32. The toner image on the intermediate transfer belt 16 is transferred (secondary transfer) onto the transfer paper P.

  The transfer paper P onto which the toner image on the intermediate transfer belt 16 has been transferred is transported to the fixing device 35, and the transferred toner image is fixed by heat and pressure. The paper is discharged onto a paper discharge unit 12 a formed on the top surface of the paper 12. The intermediate transfer belt 16 that has finished the secondary transfer of the toner image is rotated toward the image forming cartridge 20K in order to transfer a new toner image again after the toner remaining on the surface is removed by the transfer belt cleaner 40. Moved.

  When performing double-sided printing, when the transfer paper P passes the paper discharge roller 37 and the passage of the rear end thereof is detected by the paper discharge sensor 36, the rotation of the paper discharge roller 34 is reversed, and the transfer paper P Is fed into the double-sided conveyance path 42. The transfer paper P sent to the double-sided conveyance path 42 is conveyed by the double-sided conveyance roller 38, detected by the double-sided sensor 39, and conveyed until the leading edge reaches the registration roller 33 again. Thereafter, the registration roller 33 is started at a predetermined timing, the transfer paper P is re-fed to the secondary transfer position by the secondary transfer roller 32, and a toner image is formed on the surface of the transfer paper P opposite to the previous time. The transferred toner image is fixed on the transfer paper by heat and pressure in the fixing device 33, and the transfer paper is discharged onto the paper discharge unit 12 a by the paper discharge roller 37.

  FIG. 1 is a block diagram showing a configuration of a control unit CN that controls the entire image forming apparatus. The CPU 50 executes the image forming process described above by executing the image forming program stored in the ROM 51. The CPU 50 controls the image data processing unit 53 for processing image data for printing received from an external computer device and the exposure devices 30K, 30M, 30C, and 30Y for each color in addition to the memories of the ROM 51 and the RAM 52. Exposure unit controllers 54K, 54M, 54C, 54Y, a drive motor controller 55 for controlling various drive motors, a paper transport controller 56 for controlling the transport of the transfer paper P through the transfer paper transport path 41 and the double-sided transport path 42, Various sensors such as a high voltage power source controller 57 for controlling the supply of high voltage for operation from the high voltage power source 58 to the charging rollers 22K, 22M, 22C, 22Y, the fixing device 35, etc., the registration sensor 34, the waste toner full detection sensor 17, etc. A sensor detection unit 59 that detects output and a temperature / humidity sensor 60 that detects the ambient temperature and humidity in the housing 12 are connected. To have. Here, the ROM 51 stores a plurality of types of correction value tables related to the gist of the present invention. However, a rewritable nonvolatile memory (EEPROM) or a static power backed up by a backup power source is used as a storage unit for the correction value table. A RAM may be provided separately.

  The image data processing unit performs a conventionally known conversion process for converting image data for printing received from an external computer device into a form suitable for image formation, for example, rearrangement of the order of pixels in the image data, etc. Processing to output to the exposure device controllers 54K, 54M, 54C, 54Y is performed.

  Here, by executing the image forming program according to the present invention by the CPU 50, an appropriate correction is selected from among a plurality of types of correction value tables stored in the storage unit (ROM 51) based on various conditions at the time of image formation. A function for selecting a value table and a function for instructing the exposure unit controllers 54K, 54M, 54C, and 54Y to specify a correction value for each LED element with reference to the selected correction value table, that is, the invention specification described in the claims The “selection unit” and the “correction value instruction unit” which are matters are realized. Therefore, hereinafter, the “selection unit” and the “correction value instruction unit” will be described as the main body of each function.

(Embodiment 1)
The present embodiment is characterized in that the gradation of each pixel of the image data is used as a condition for causing uneven density. That is, if the density of each pixel of the image data received from the outside is quantized with 8 bits, it has 256 gradations from 0 to 255, but the density unevenness of the image is not necessarily limited. It does not always change linearly from low concentration to high concentration.

  Therefore, in the present embodiment, 256 gradation levels are divided into three ranges, for example, a density value range of 0 to 85 (low density range), a density value range of 86 to 171 (intermediate density range), and a density value. Is divided into ranges of 172 to 255 (high concentration range), and correction values for each LED element constituting the LED array in each range are obtained in advance to create three types of correction value tables, and the created 3 Types of correction value tables (first correction value table, second correction value table, and third correction value table) are stored in the storage unit (ROM 51). Here, since an image for one pixel in the image data is formed by light emitted from one LED element, the density of the pixel corresponding to each LED element can be adjusted by adjusting the light emission amount for each LED element. It can be increased or decreased.

  3A and 3B show specific examples of the correction value table. In the illustrated example, the number of LED elements constituting the LED array (the number of pixels in one line) is 4992, and numbers 1 to 4992 are assigned to the respective pixels (LED elements). The correction value data corresponding to each number is composed of 4 bits, and 16 types of correction values are assigned to each bit example as shown in FIG. In the illustrated example, correction ratios (%) in increments of 0.5 from -4.0 to +4.5 are assigned to each bit string as correction values. This correction ratio is, for example, the ratio of density values when 256 gradations are taken as 100%.

  Next, the operation of this embodiment will be described with reference to the flowchart of FIG. However, in this embodiment, monochrome printing in which an image is formed using only black toner will be described. However, color printing in which an image is formed using magenta, cyan, and yellow toners other than black may also be used. Since it is the same process, description is abbreviate | omitted.

  The control unit CN waits until a print activation trigger is applied from the outside (S1), and when the print activation is activated and image data is input from the outside to the I / O unit of the CPU 50 via the image data processing unit 53. The CPU 50 transfers the input image data to a buffer in the RAM 52 (S2). Subsequently, the CPU 50 initializes a variable m corresponding to one line of image data (pixel array exposed simultaneously by the LED array) to zero (S3), and the number of pixels in one line (LEDs simultaneously emitting light in the LED array). A variable n corresponding to the number of elements) is initialized to zero (S4).

  The selection unit of the CPU 50 determines which of the three ranges (low density range, intermediate density range, and high density range) the density value of the nth bit (pixel) in the mth line of the image data belongs to. (S5, S6), and the most appropriate correction value table is selected based on the determination result. Then, the correction value instruction unit of the CPU 50 program-transfers correction value data corresponding to the density value of the nth bit in the correction value table selected by the selection unit to the RAM 52 (S7, S8, or S9). The nth bit image data (density value) stored in the buffer of the RAM 52 and the correction value data transferred from the correction value table are transferred to the I / O unit of the CPU 50 by DMA transfer, and further, the correction value instruction unit However, the correction value data and the image data are sent from the I / O unit to the exposure device control unit 54K by using various correction value data transmission signals and image data transmission signals, such as a clock and an enable signal generated by the CPU 50 ( S10). Thereafter, the CPU 50 increments the variable n (S11), repeats the processing from S5 to S11 until the variable n reaches the number of pixels in one line, and when the variable n reaches the number of pixels in one line (S12), the variable m Is incremented (S13), and the processes from S4 to S13 are repeated until the variable m reaches the total number of lines of the image data. When the variable m reaches the total number of lines of the image data (S14), the process ends.

  The exposure unit controller 54K controls the exposure unit 30K based on the correction value data and the image data instructed from the correction value instruction unit of the CPU 50, thereby adjusting the current supply to the corresponding LED element to emit light. The variation in the amount can be corrected, and as a result, the density unevenness of the image can be suppressed.

  As described above, according to the present embodiment, for each of a plurality of LED elements, a plurality of types of conditions (for example, gradation width of an image) that cause uneven density of an image (electrostatic latent image) and the uneven density are corrected. Are stored in the storage unit (ROM 51), and a plurality of types stored in the storage unit based on the condition (pixel density value) at the time of image formation. Since the selection unit selects an appropriate correction value table from among the correction value tables, the arithmetic circuit for calculating the correction value is not required as in the conventional example, and the configuration is simple, and various conditions are met. By selecting an appropriate correction value table from a plurality of corresponding correction value tables, it is possible to suppress image density unevenness under various conditions. In addition, since the density unevenness of the image does not always change linearly from the low density to the high density, the gradation width of the image included in the image formation request (image data) as in this embodiment is used as a condition. By storing the plurality of types of correction value tables set for each stage obtained by dividing the gradation range into a plurality of stages, the density unevenness can be appropriately corrected regardless of the density value. . In the present embodiment, the selection unit and the correction value instruction unit are realized by causing the CPU 50 to execute the image forming program. However, the selection unit and the correction value instruction unit may be configured by dedicated hardware.

(Embodiment 2)
In the first embodiment, the correction value table is selected based on only the density value of each pixel. However, in this embodiment, in order to improve the gradation reproducibility at an intermediate density value, the vicinity of an arbitrary pixel is selected. The feature is that the sum of the gradations of pixels is divided into a plurality of stages, and an optimum correction value table is selected from a plurality of types of correction value tables set for each stage.

  Specifically, as shown in FIG. 5, when the sum of density values of pixels near 8 of the target pixel A is calculated, the total range (0 to 2040) that the sum can take is divided into three ranges, for example, density Each LED element that divides the value sum into a range of 0 to 680, a sum of density values of 681 to 1359, and a sum of density values of 1360 to 2040 and constitutes an LED array in each range Three types of correction value tables (first correction value table, second correction value table, and third correction value table) are created as well as three types of correction value tables are obtained by obtaining correction values for each of them in advance. It is stored in the storage unit (ROM 51).

  Then, the selection unit of the CPU 50 calculates the sum of the density values of the eight neighboring pixels for each pixel of the image data, and determines which of the above three ranges the sum is the most appropriate correction value. Select a table. Further, the correction value instruction unit of the CPU 50 sends (instructs) the correction value data and the image data (the density value of the target pixel A) determined by referring to the correction value table selected by the selection unit to the exposure device control unit 30K. Thus, it is possible to suppress the density unevenness of the image and improve the gradation reproducibility at an intermediate density value.

  In the present embodiment, an example is described in which calculation is performed using the sum of the densities of eight neighboring pixels with respect to an arbitrary pixel. However, for example, the sum of upper, lower, left, and right pixels or the sum of both adjacent pixels may be used.

(Embodiment 3)
In the present embodiment, the most appropriate correction value table is selected from a plurality of types of correction value tables based on the temperature and humidity detected by the temperature / humidity sensor 60 installed inside or outside the housing 12. There is a feature in the point.

  The correction value table is, for example, a correction value table (first correction value table) that is appropriate when the internal or external temperature of the housing 12 is 30 degrees or higher or the humidity is 80% or higher. A correction value table (second correction value table) that is appropriate when the internal or external temperature is 5 degrees or less or the humidity is 10% or less, and the internal or external temperature of the housing 12 is higher than 5 degrees and Three types of correction value tables (third correction value table) that are appropriate when the range is less than 30 degrees or when the humidity is higher than 10% and lower than 80% are stored in the storage unit (ROM 51). Has been.

  Then, the selection unit of the CPU 50 selects the most appropriate correction value table based on the temperature and humidity values inside or outside the housing 12 detected by the temperature / humidity sensor 60 when actually performing printing (image formation). The correction value instruction unit of the CPU 50 determines correction value data with reference to the correction value table selected by the selection unit, and sends (instructs) the determined correction value data and image data to the exposure device control unit 30K. Therefore, the density unevenness of the image can be suppressed corresponding to the change in the temperature and humidity environment inside or outside the housing 12.

(Embodiment 4)
In the present embodiment, the most appropriate correction value table is selected from a plurality of types of correction value tables based on the temperature and humidity detected by the temperature / humidity sensors installed in the LED arrays of the exposure devices 30K, 30M, 30C, and 30Y. It is characterized by

  The correction value table is, for example, a correction value table (first correction value table) that is appropriate when the temperature of the LED array is 80 degrees or higher or the humidity is 80% or higher, the temperature of the LED array is 20 degrees or lower, or A correction value table (second correction value table) that is appropriate when the humidity is 10% or less, a range where the temperature of the LED array is higher than 20 degrees and lower than 80 degrees, or the humidity is higher than 10% and 80% Three types of correction value tables (third correction value table) that are appropriate when the range is less than the range are stored in the storage unit (ROM 51).

  The selection unit of the CPU 50 selects the most appropriate correction value table based on the temperature and humidity values of the LED array detected by the temperature / humidity sensor when actually performing printing (image formation), and the selection unit selects the correction value table. With reference to the correction value table, the correction value instruction unit of the CPU 50 determines correction value data, and sends (instructs) the determined correction value data and image data to the exposure device control unit 30K. The density unevenness of the image can be suppressed corresponding to the change of the temperature and humidity environment of the devices 30K, 30M, 30C, 30Y).

(Embodiment 5)
In the present embodiment, the most appropriate correction value table is selected from a plurality of types of correction value tables based on conditions related to the photosensitive drum (manufacturing company, material forming the photosensitive member, and manufacturing lot of the photosensitive member manufactured by the same manufacturing company). It is characterized in that a correction value table is selected.

  For example, when the photosensitive drums 21K, 21M, 21C, and 21Y are manufactured by any one of the A company, the B company, and the C company, they are appropriate when the photosensitive drum manufactured by the A company is used. Correction value table (first correction value table), correction value table (second correction value table) that is appropriate when a photosensitive drum manufactured by company B is used, photosensitive sensor manufactured by company C Three types of correction value tables (third correction value table) that are appropriate when the body drum is used are stored in the storage unit (ROM 51).

  In addition, when the photosensitive member in the photosensitive drums 21K, 21M, 21C, and 21Y is formed of any of the three types of materials A, B, and C, the photosensitive drum of the material A is used. Correction value table (first correction value table) that is appropriate in this case, correction value table (second correction value table) that is appropriate when the photosensitive drum of material B is used, and material C Three types of correction value tables (third correction value table) that are appropriate when the photosensitive drum is used are stored in the storage unit (ROM 51).

  Alternatively, when the photosensitive drums 21K, 21M, 21C, and 21Y are any of three manufacturing lots A, B, and C manufactured by the same manufacturing company, the photosensitive drums of the manufacturing lot A are used. Correction value table (first correction value table) that is appropriate when the photosensitive drum is in use, a correction value table (second correction value table) that is appropriate when the photosensitive drum of the production lot B is used, and manufacturing Three types of correction value tables (third correction value table) that are appropriate when the photosensitive drum of lot C is used are stored in the storage unit (ROM 51).

  Here, as a means for holding the information, the photosensitive drum is mounted with a semiconductor memory or an RFID tag in which a readout terminal is exposed, and information (manufacturer or photoconductor) held in the holding means. The CPU 50 can read out the material forming the material or the production lot of the photoconductor manufactured by the same manufacturing company. However, a specific configuration for reading information from a semiconductor memory or an RFID tag can be realized by a conventionally known technique, and thus detailed description thereof is omitted.

  Then, when actually performing printing (image formation), the selection unit of the CPU 50 selects the most appropriate correction value table based on the information read from the photosensitive drums 21K, 21M, 21C, and 21Y, and is selected by the selection unit. Referring to the correction value table, the correction value instruction unit of the CPU 50 determines the correction value data, and sends (instructs) the determined correction value data and image data to the exposure device control unit 30K. It is possible to suppress unevenness in image density according to the difference in various conditions relating to 21M, 21C, and 21Y (manufacturing company or a material forming the photoconductor or a manufacturing lot of the photoconductor manufactured by the same manufacturing company). Instead of holding the information such as the manufacturing company, the material forming the photoconductor, the production lot of the photoconductor manufactured by the same manufacturing company, the unique identification code assigned to the photoconductor drum. (ID) is held, and the CPU 50 may acquire information on a manufacturing company, a material forming the photoconductor, a manufacturing lot of the photoconductor manufactured by the same manufacturing company, and the like based on the identification code. .

(Embodiment 6)
The present embodiment is characterized in that the most appropriate correction value table is selected from a plurality of types of correction value tables based on the usage level of the photosensitive drum 21 or the deterioration level of the exposure device 30 (LED array).

  Specifically, if the CPU 50 counts the number of printed sheets for each of the photosensitive drums 21K, 21M, 21C, and 21Y or the number of printed sheets for each of the exposure devices 30K, 30M, 30C, and 30Y as a count, the photosensitive member is determined by the number of printed sheets. The degree of use of the drums 21K, 21M, 21C, and 21Y and the degree of deterioration of the exposure devices 30K, 30M, 30C, and 30Y (LED array) can be determined. However, when the photosensitive drums 21K, 21M, 21C, and 21Y and the exposure devices 30K, 30M, 30C, and 30Y are replaced, it is necessary to initialize the count of the number of printed sheets.

  Regarding the usage of the photosensitive drum 21, for example, a correction value table (first correction value table) that is appropriate when a photosensitive drum having a number of printed sheets in the range of 0 to 10,000 is used, A correction value table (second correction value table) that is appropriate when a photosensitive drum having a printed number in the range of 10,000 to 20,000 is used, and a photosensitive drum with a printed number of 20,000 or more. Three types of correction value tables (third correction value table) that are appropriate when using are stored in the storage unit (ROM 51).

  On the other hand, with respect to the degree of deterioration of the exposure device 30, for example, a correction value table (first correction value table) that is appropriate when using an exposure device with a number of printed sheets in the range of 0 to 100,000 sheets, A correction value table (second correction value table) that is appropriate when using an exposure device with a printed number in the range of 100,000 to 200,000, and an exposure device with a printed number of 200,000 or more In this case, three types of correction value tables (third correction value table) that are appropriate in the case of being stored are stored in the storage unit (ROM 51).

  When actually performing printing (image formation), the selection unit of the CPU 50 determines the usage of the photosensitive drum 21 and the degree of deterioration of the exposure device 30 from the number of printed sheets at that time, and based on the degree of use or the degree of deterioration. The correction value table of the CPU 50 determines the correction value data with reference to the correction value table selected by the selection unit, and determines the correction value data and the image data. Since the image is sent (instructed) to the control unit 30K, unevenness in image density can be suppressed according to the usage of the photosensitive drum 21 and the degree of deterioration of the exposure device 30.

(Embodiment 7)
By the way, there is an exposure device 30 configured to be exchangeable by housing in a housing a drive circuit that drives the LED array by driving a current to each LED element of the LED array, and is generally called an LED print head. It is. In this embodiment, when the exposure devices 30K, 30M, 30C, and 30M are configured as LED print heads, a storage unit (ROM, EEPROM, etc.) storing a plurality of types of correction value tables is provided in the housing together with a drive circuit and the like. A feature is that a plurality of types of correction value tables stored and stored in the storage unit are transferred to a RAM 52 provided in the control unit CN or a rewritable nonvolatile memory (not shown) such as an EEPROM.

  The CPU 50 of the control unit CN transfers the correction value table from the storage unit of the exposure unit 30 to the RAM 52 or a non-illustrated non-volatile memory every time the power is turned on or when the power is turned on for the first time after the exposure unit 30 is replaced. As described above, the selection unit selects the most appropriate correction value table based on various conditions from among a plurality of types of correction value tables stored in the RAM 52 or a non-volatile memory (not shown), and the other Similar to the embodiment, the density unevenness of the image can be suppressed. In addition, since the correction value table is stored in the storage unit of the exposure unit 30 and transferred from the storage unit to the storage unit of the control unit CN, the storage of the control unit CN is performed when the exposure unit 30 is replaced. There is an advantage that the trouble of updating the correction value table stored in the section can be saved.

  Further, the upper and lower limits that define the gradation width of the first embodiment, the temperature / humidity range of the third and fourth embodiments, or the range of use or deterioration of the sixth embodiment are stored in the storage unit of the exposure unit 30 together with the correction value table. If transferred to the control unit CN, there is an advantage that it is possible to save the trouble of changing these ranges when the exposure device 30 is replaced. On the other hand, if the upper limit and the lower limit that define these ranges are stored in the storage unit of the control unit CN, there is an advantage that the ranges (upper limit and lower limit) can be freely changed.

It is a block diagram which shows the structure of the control part in embodiment. It is a whole block diagram same as the above. It is a figure which shows the specific example of the correction value table in Embodiment 1. FIG. It is a flowchart for operation | movement description same as the above. FIG. 9 is an operation explanatory diagram of the second embodiment.

Explanation of symbols

30K, 30M, 30C, 30Y Exposure unit CN control unit 50 CPU
51 ROM
52 RAM
53 Image data processing unit 54K, 54M, 54C, 54Y Exposure unit control unit

Claims (15)

An exposure unit using a light emitting diode array in which a plurality of light emitting diode elements are arranged as a light source, an image carrier that carries an electrostatic latent image formed by exposure by the exposure unit, and an image carrier A developing unit that develops and visualizes the electrostatic latent image to be developed with a developer, a transfer unit that transfers the visualized developer image to a transfer body, and at least an exposure unit, a developing unit, and a transfer unit according to an image formation request And an image forming apparatus including a control unit that executes an image forming process by controlling
The control means includes, for each of the plurality of light emitting diode elements, a plurality of types of correction value tables in which a plurality of types of conditions causing uneven density of the electrostatic latent image and correction values for correcting the density unevenness are associated with each other. A storage unit for storing, a selection unit for selecting an appropriate correction value table from among a plurality of types of correction value tables stored in the storage unit based on the conditions at the time of image formation, and the selection unit selected by the selection unit A correction value instructing unit for instructing the exposure unit of the correction value for each light-emitting diode element with reference to the correction value table,
An exposure unit adjusts the light quantity of each light emitting diode element according to a correction value instructed from a correction value instructing unit.   The condition is a gradation width of an image included in the image formation request, and the plurality of types of correction value tables set for each stage obtained by dividing the entire gradation range into a plurality of stages are stored in a storage unit. The image forming apparatus according to claim 1.   The condition is the gradation of the image included in the image formation request, and stores the plurality of types of correction value tables set for each stage obtained by dividing the sum of the gradations of neighboring pixels for an arbitrary pixel into a plurality of stages. The image forming apparatus according to claim 1, wherein the image forming apparatus is stored in a unit.   2. The image forming apparatus according to claim 1, further comprising a housing for storing each of the exposure unit, the image carrier, the developing unit, the transfer unit, and the control unit, wherein the condition is an internal environment of the housing. .   2. The image forming apparatus according to claim 1, further comprising a housing for storing each of the exposure unit, the image carrier, the developing unit, the transfer unit, and the control unit, wherein the condition is an external environment of the casing. .   A temperature detection unit for detecting a temperature of the exposure unit, wherein the condition is the temperature of the exposure unit, and the selection unit selects a correction value table according to the temperature at the time of image formation detected by the temperature detection unit. The image forming apparatus according to claim 1.   2. The image forming apparatus according to claim 1, wherein the condition is a manufacturer of the image carrier, and the selection unit selects a correction value table according to the manufacturer of the image carrier at the time of image formation.   2. The image forming apparatus according to claim 1, wherein the condition is a type of the image carrier, and the selection unit selects a correction value table according to the type of the image carrier at the time of image formation.   2. The image forming apparatus according to claim 1, wherein the condition is a production lot of the image carrier, and the selection unit selects a correction value table according to the production lot of the image carrier at the time of image formation.   The image forming apparatus according to claim 1, wherein the condition is a degree of use of the image carrier, and the selection unit selects a correction value table according to the degree of use of the image carrier during image formation.   The image forming apparatus according to claim 1, wherein the condition is a degree of deterioration for each light emitting diode element, and the selection unit selects a correction value table according to the degree of deterioration of each light emitting diode element during image formation.   A second type of correction value table is stored in which a plurality of types of conditions that cause density unevenness of the electrostatic latent image and correction values for correcting the density unevenness are associated with each other for each of the plurality of light emitting diode elements. 2. The image forming apparatus according to claim 1, wherein the storage unit is provided in the exposure unit, and a plurality of types of correction value tables are transferred from the second storage unit to the storage unit provided in the control unit.   The image forming apparatus according to claim 1, wherein an upper limit and a lower limit of the condition are stored in a second storage unit, and the selection unit selects a correction value table in consideration of the upper limit and the lower limit.   The image forming apparatus according to claim 1, wherein an upper limit and a lower limit of the condition are stored in a storage unit of a control unit, and the selection unit selects a correction value table in consideration of the upper limit and the lower limit.   15. An image forming program for use in the image forming apparatus according to claim 1, wherein the computer includes a plurality of types of correction value tables stored in a storage unit based on the conditions at the time of image formation. An image forming program for performing a process of selecting an appropriate correction value table from the above and a process of instructing an exposure unit of a correction value for each light-emitting diode element with reference to the selected correction value table .

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