JP2008191181A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which correction values for many test positions can be obtained while the number of test images to be formed is reduced. <P>SOLUTION: Since correspondence relationship of a second color is acquired for a patch forming position 510 where patches are thinned based on the patch density of a first color for the patch forming position and paper printing density, a correction table of each color for adjusting image density is generated also for a patch forming position 510 where any color patches are thinned, and then the correction table of each color is generated for each patch forming position. Consequently, the correction table for each patch forming position is generated while reducing the number of patches to be formed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that can reduce the number of test images to be formed and obtain correction values for a large number of test positions.

  Conventionally, in an image forming apparatus, calibration processing for maintaining the quality of a printed image has been performed. This calibration process is a process for correcting the density and hue of the printed image that has changed due to aging of the device, etc., and the density of the test image formed for each color and predetermined density is measured with a sensor or measuring instrument. The correction value for the print image is determined from the correspondence between the input value and the density of the test image (see, for example, Patent Document 1).

An example of calibration processing executed in such an image forming apparatus will be described. First, in the image forming apparatus, a reference position of a transfer belt for forming a plurality of patches (test images) is stored based on test image data, and a plurality of patches having the same density in each printing color are sequentially arranged from the reference position. It is formed at a location (for example, 40 times if there are 10 types of density in 4 colors of CMYK). Next, the patch is printed on a recording sheet, the patch of the printed recording sheet is measured with a measuring instrument or the like, and the measured value is input to the image forming apparatus. By performing such an operation, even if the density is the same as the position of the patch formed on the transfer belt, the correspondence with density unevenness having different densities depending on the transfer belt formation location is stored. A correction value can be obtained. When a print image is formed on a transfer bell, by using this correction value, it is possible to correct the density unevenness of the print image, and a highly accurate image in which the density unevenness is suppressed can be obtained. Can be printed.
JP 2000-301811 A

  However, when patches are formed for each density of each print color at a large number of positions, there is a problem that consumables such as toner are easily consumed.

  On the other hand, if the number of patches is simply reduced, an appropriate correction value can be obtained at a position where the patch is formed, but an appropriate correction value cannot be obtained at a position where the patch is not formed. .

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of obtaining correction values for a large number of test positions while reducing the number of test images to be formed.

  In order to achieve this object, an image forming apparatus according to claim 1 is provided for each of a plurality of colors, and is formed by a developing unit that develops an electrostatic latent image to form a toner image, and the developing unit. An image carrier that carries the toner image and an image formed on the recording medium by transferring the toner image carried on the image carrier to the recording medium. First color test image forming means for forming a first color test image to be formed at a plurality of test positions on the image carrier, and a plurality of second color test images including a second color toner image. The second color test image forming means formed at any one of the test positions, the density of the test image formed by the first color test image forming means or the second color test image forming means, and the test image is a recording medium. Test mark formed by being transferred to Correspondence relation acquisition means for acquiring the correspondence relation with the density of the image for each of the plurality of test positions for each color, correspondence relation storage means for storing the correspondence relation acquired by the correspondence relation acquisition means, Correction value determining means for determining, for each color, a correction value for adjusting the density of an image formed on the recording medium using the correspondence relationship stored by the correspondence relationship storage means, for each of the test positions; When the correspondence relationship of the first color and the correspondence relationship of the second color are already stored in the correspondence relationship storage unit, the correspondence relationship of the first color and the second color already stored in the correspondence relationship storage unit Approximate judging means for judging whether each of the plurality of test positions is approximate, and the second color test image forming means is the first color corresponding relation as a result of the approximation judging means. And second For the test position determined to be approximate to the corresponding relationship of the second color, the second color test image is thinned out, and the correspondence acquisition unit is configured to determine the test position from which the second color test image is thinned. The second color correspondence relationship is acquired based on the test image density of the first color and the test print image density for the test position.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the correspondence relationship storage unit determines whether the correspondence relationship of the first color and the correspondence relationship of the second color are already stored. When the correspondence relationship presence / absence determination means and the correspondence relationship presence / absence determination means determine that the correspondence relationship of the first color and the correspondence relationship of the second color have already been stored, the first color test image forming means A first color test image composed of a first color toner image is formed at a plurality of test positions on the image carrier, and the density of the formed first color test image and the test image are recorded on the recording medium. New density acquisition means for acquiring the density of a test print image formed by being transferred to the image, and the correspondence acquisition means is configured to acquire the new density for a test position where a second color test image is thinned out. 1st color text acquired by means Based on the bets image density and the test print image density, and acquires a second color corresponding relationship.

  The image forming apparatus according to claim 3, wherein the approximate determination unit includes a first color test image density and a second color test image corresponding to each test image density. When the difference from the density is within a predetermined range, it is determined that the correspondence relationship between the first color and the correspondence relationship between the second color is approximate.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the approximate determination means includes a second value within a predetermined range within ± 5% of the test image density of the first color. When the color test image density is included, it is determined that the correspondence relationship between the first color and the correspondence relationship between the second color is approximate.

  5. The image forming apparatus according to claim 1, further comprising position detection means for detecting a predetermined position on the image carrier, wherein the first color test image forming means is the image forming apparatus according to any one of claims 1 to 4. The second color test image forming means forms a test image at the test position based on the predetermined position detected by the position detecting means.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the image forming apparatus further includes a first color determining unit that determines a color having the maximum remaining amount of toner as the first color. And

  The image forming apparatus according to claim 7 is the image forming apparatus according to any one of claims 1 to 5, wherein the developing unit is provided for each of three or more colors, and each of the three or more colors is provided. Of these, first color determination means for determining any one color as the first color, and second color determination means for determining colors other than the first color determined by the first color determination means as the second colors, respectively. The correspondence relationship acquisition means acquires the correspondence relationship of each color determined as the second color by the second color determination means.

  The image forming apparatus according to claim 8 is the image forming apparatus according to claim 7, wherein the developing unit is provided for each of at least three colors including yellow, and the first color determining unit is other than yellow. Among the colors, the color having the maximum remaining toner amount is determined as the first color.

  An image forming apparatus according to a ninth aspect is the image forming apparatus according to any one of the first to eighth aspects, wherein the correspondence relationship storage unit stores the correspondence relationship between the first color and the correspondence relationship between the second color. The correspondence relationship presence / absence determination means for determining whether or not the correspondence relationship is present and the correspondence relationship between the first color and the correspondence relationship of the second color are not stored in the correspondence relationship storage means. If determined, a test image of each color is formed at each of the test positions where the first color test image is formed by the first color test image forming means, and the test image density and the test image are recorded on the recording medium. And a new correspondence acquisition unit that acquires a correspondence relationship with the density of the test print image formed by being transferred to the correspondence relationship storage unit.

  The image forming apparatus according to claim 10 is the image forming apparatus according to any one of claims 1 to 9, wherein the test position at which the first color test image is arranged by the first color test image forming unit is an image. The carrier is provided with a plurality of rows in the main scanning direction, and the image carrier is provided with a plurality of rows in a direction perpendicular to the main scanning direction.

  The image forming apparatus according to claim 11 is the image forming apparatus according to any one of claims 1 to 9, wherein the first color test image forming unit includes a first color test image. Test position changing means for changing a test position where an image is formed according to a user instruction is provided.

  According to the image forming apparatus of claim 1, the first color test image forming unit forms the first color test image including the first color toner image at a plurality of test positions on the image carrier. The second color test image forming means forms a second color test image composed of the second color toner image at any one of a plurality of test positions. The correspondence between the density of the test image formed by the first color test image forming means or the second color test image forming means and the density of the test print image formed by transferring the test image to the recording medium However, the correspondence relationship acquisition means acquires each of the plurality of test positions for each color, and the correspondence relationship acquired by the correspondence relationship acquisition means is stored in the correspondence relationship storage means. Then, the correction value for adjusting the density of the image formed on the recording medium by the correction value determining unit using the corresponding relationship stored in the corresponding relationship storing unit is set for each of the test positions for each color. Determined about.

  Here, when the correspondence relationship of the first color and the correspondence relationship of the second color are already stored in the correspondence relationship storage means, the correspondence relationship of the first color already stored in the correspondence relationship storage means and the second relationship are stored. Whether the color correspondence is approximated is determined for each of the plurality of test positions by the approximation determining unit, and the second color test image forming unit determines the first color correspondence and the first color as a result of the approximation determining unit. The test image of the second color is thinned out for the test position determined to be close to the correspondence relationship between the two colors. Then, the correspondence relationship acquisition means, for the test position where the test image of the second color is thinned out, corresponds to the second color based on the test image density of the first color and the test print image density for the test position. The relationship is acquired by the correspondence relationship acquisition means.

  If the correspondence relationship of the first color and the correspondence relationship of the second color already stored in the correspondence relationship storage means are approximate, the correspondence relationship of the first color and the second color are also formed at the next test image formation. It is expected that the correspondence relationship of Therefore, for the test position where the test image of the second color is thinned out, the correspondence relationship of the second color is acquired based on the test image density of the first color and the test print image density at the test position. . Therefore, the correction value of the second color can be determined also for the test position where the test image of the second color is thinned out. As a result, it is possible to obtain appropriate correction values for a large number of test positions while reducing the number of test images to be formed.

  According to the image forming apparatus of the second aspect, in addition to the effect produced by the image forming apparatus according to the first aspect, the correspondence relationship storage means stores the correspondence relationship between the first color and the second color in the correspondence relationship storage means. If it is determined whether the correspondence relationship is already stored, and the correspondence relationship presence / absence determining means determines that the correspondence relationship of the first color and the correspondence relationship of the second color are already stored, the first color A first color test image composed of a first color toner image is formed at a plurality of test positions on the image carrier by the test image forming means, the density of the formed first color test image, and the test The density of the test print image formed by transferring the image to the recording medium is acquired. Then, the correspondence relationship acquisition means, for the test position where the second color test image is thinned out, is based on the first color test image density and the test print image density acquired by the new density acquisition means. Since the color correspondence is acquired, there is an effect that an appropriate correction value reflecting the latest environment can be obtained even for the test position where the test image of the second color is thinned out.

  According to the image forming apparatus of the third aspect, in addition to the effect produced by the image forming apparatus according to the first or second aspect, the approximate determination means includes the first color test image density and the first color corresponding to each test image density. If the difference between the test image densities of the two colors is within a predetermined range, it is determined that the correspondence relationship between the first color and the correspondence relationship between the second color is approximate. Therefore, the correspondence relationship between the first color and the second color When the correspondence is reliably approximated, the second color test image is thinned out. Therefore, there is an effect that an appropriate correction value can be determined for the second color.

  According to the image forming apparatus of the fourth aspect, in addition to the effect produced by the image forming apparatus according to the first or second aspect, the approximation determining means is a predetermined value within ± 5% of the test image density of the first color. When the test image density of the second color is included in the range, it is determined that the correspondence relationship of the first color and the correspondence relationship of the second color are approximate, so the correspondence relationship of the first color and the correspondence of the second color When the relationship is sufficiently close, the second color test image is thinned out. Therefore, there is an effect that an appropriate correction value can be determined for the second color.

  According to the image forming apparatus of the fifth aspect, in addition to the effect produced by the image forming apparatus according to any one of the first to fourth aspects, the predetermined position on the image carrier is detected by the position detecting unit, and the first color is detected. Since the test image forming means and the second color test image forming means form a test image at the test position based on the predetermined position detected by the position detecting means, based on the predetermined position detected by the position detecting means. Based on each determined test position and the correction value for each test position, it is possible to compensate for the difference in characteristics for each position of the image carrier and to perform high-accuracy correction.

  According to the image forming apparatus of the sixth aspect, in addition to the effect produced by the image forming apparatus according to any one of the first to fifth aspects, the color having the maximum remaining amount of toner is determined as the first color. The color having a relatively small remaining amount is determined as the second color, and the test image is thinned out, so that the amount of toner used can be saved.

  According to the image forming apparatus of the seventh aspect, in addition to the effect produced by the image forming apparatus according to any one of the first to fifth aspects, among the three or more colors, colors other than the first color are respectively Since the colors are determined as two colors, the test image is thinned out for each color other than the color determined as the first color, and the amount of toner used can be saved.

  According to the image forming apparatus of the eighth aspect, in addition to the effect produced by the image forming apparatus of the seventh aspect, the color having the maximum remaining amount of toner is determined as the first color. The small number of colors is determined as the second color, the test image is thinned out, and the amount of toner used can be saved. In addition, since colors other than yellow are determined as the first color, there is an effect that more test images can be thinned out. That is, the test image density of yellow is different from that of other colors. For example, when the color is light, it is possible to thin out more test images when the other color is the first color than when the yellow color is the first color. Is obtained.

  According to the image forming apparatus of the ninth aspect, in addition to the effect produced by the image forming apparatus according to any one of the first to eighth aspects, the correspondence relationship storage unit stores the correspondence relationship between the first color and the second color. If the relationship is already stored, and it is determined that the correspondence relationship of the first color and the correspondence relationship of the second color are not stored in the correspondence relationship storage means, the new correspondence relationship acquisition means A test image of each color is formed at each test position where the first color test image forming unit forms the first color test image, and the test image density and the test image are transferred to the recording medium. The correspondence relationship with the density of the test print image formed by the above is acquired and stored in the correspondence storage means. Therefore, when the test image is formed after the next time, the second color test image can be thinned to save the amount of toner used.

  According to the image forming apparatus of the tenth aspect, in addition to the effect produced by the image forming apparatus according to any one of the first to ninth aspects, the test positions are provided in a plurality of rows in the main scanning direction on the image carrier, and Since a plurality of rows are provided in a direction perpendicular to the main scanning direction, the difference in characteristics of each position of the image carrier is finely corrected based on the correction value determined for each test position. There is an effect that accuracy can be corrected.

  According to the image forming apparatus of the eleventh aspect, in addition to the effect produced by the image forming apparatus according to any one of the first to ninth aspects, the first color test image forming means is configured by the first color toner image. Since the test position where the first color test image is formed is changed by the test position changing means according to the user instruction, the test image is not formed at a position unnecessary for the user, and the amount of toner used is saved. There is an effect that can be done.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic sectional view of a main part of a laser printer 1 as an image forming apparatus according to the present embodiment. The laser printer 1 shown in FIG. 1 is configured as a four-cycle laser printer, and has a main body casing 3 for feeding a paper 5 and a predetermined image on the fed paper 5. And an image forming unit 9 for forming the image.

  The paper feed unit 7 includes a paper feed tray 11 in which the papers 5 are stacked and stored, a paper feed roller 13 that contacts the paper 5 at the top of the paper feed tray 11 and picks up the paper 5 one by one by rotation, A conveyance roller 15 and a registration roller 17 are provided for conveying the paper 5 to the image forming position. This image forming position is a transfer position for transferring a toner image on an intermediate transfer belt 51, which will be described later, to the paper 5. In this embodiment, the image forming position is a contact position between the intermediate transfer belt 51 and a transfer roller 27, which will be described later. .

  The image forming unit 9 includes a scanner unit 21, a process unit 23, an intermediate transfer belt mechanism unit 25, a transfer roller 27, a fixing unit 29, and the like. In the laser printer 1, the scanning direction of the laser beam by the scanner unit 21 (the vertical direction in FIG. 1) is referred to as the main scanning direction.

  The process unit 23 includes a plurality (four) of developing cartridges 35, a belt photoreceptor mechanism unit 31, and the like. The four developing cartridges 35 (an example of a developing unit) include, for each color, a yellow developing cartridge 35Y that stores yellow toner, a magenta developing cartridge 35M that stores magenta toner, and a cyan developing that stores cyan toner. Each of the cartridge 35 </ b> C and the black developing cartridge 35 </ b> K containing black toner is sequentially arranged in parallel from the bottom to the top at a predetermined interval in the vertical direction on the front side in the main body casing 3. .

  Each developing cartridge 35 includes a developing roller 37 (a yellow developing roller 37Y, a magenta developing roller 37M, a cyan developing roller 37C, and a black developing roller 37K), a layer thickness regulating blade (not shown), a supply roller, a toner container, and the like. In order to bring each developing roller 37 into contact with or separate from the surface of the belt photosensitive member 33, a separation solenoid 38 (yellow separation solenoid 38Y, magenta separation solenoid 38M, cyan separation solenoid 38C, black separation solenoid 38K, respectively). ) Is configured to be movable in the horizontal direction.

  The belt photoreceptor mechanism 31 includes a first belt photoreceptor roller 39, a second belt photoreceptor roller 41, a third belt photoreceptor roller 43, and these first belt photoreceptor roller 39, second belt photoreceptor roller 41, And a belt photoconductor 33 wound around the third belt photoconductor roller 43, a belt photoconductor charger 45, a potential adder 47, and a potential gradient controller 49.

  The intermediate transfer belt mechanism unit 25 is disposed on the rear side of the belt photoconductor mechanism unit 31, and a belt photoconductor 33 and an intermediate transfer belt (ITB: Inter Transfer Belt) 51 to be described later are attached to the second belt photoconductor roller 41. A first intermediate transfer belt roller 53 disposed substantially opposite thereto, a second intermediate transfer belt roller 55 disposed obliquely below and below the first intermediate transfer belt roller 53, and a rear side of the second intermediate transfer belt roller 55. The third intermediate transfer belt roller 57 and the first intermediate transfer belt roller 53 through the third intermediate transfer belt roller 57 are wound around the outer periphery of a third intermediate transfer belt roller 57 and a first intermediate transfer belt roller 53 or a third intermediate transfer belt roller 57 which are arranged opposite to each other with a transfer roller 27, which will be described later, interposed therebetween. The intermediate transfer belt 51 is provided.

  Further, a density detection sensor 71 for detecting the density of each color on the intermediate transfer belt 51 is provided. The density detection sensor 71 includes a light source that emits light in the infrared region, a lens that irradiates the light source onto the intermediate transfer belt 51, and a phototransistor that receives the reflected light.

  Further, a marker detection sensor 99 for detecting a marker 511 (see FIG. 3) on the intermediate transfer belt 51 is provided. The marker detection sensor 99 includes a detection coil that generates a high-frequency magnetic field, and is a proximity sensor that detects a marker 511 provided at a predetermined position on the intermediate transfer belt 51 in a non-contact manner.

  The transfer roller 27 is disposed so as to face the third intermediate transfer belt roller 57 of the intermediate transfer belt mechanism unit 25 with the intermediate transfer belt 51 interposed therebetween, and a metal roller shaft is covered with a roller made of a conductive rubber material. And is rotatably supported.

  The transfer roller 27 is positioned at the standby position while the visible images for each color are sequentially transferred to the intermediate transfer belt 51 during printing, and all the visible images are transferred from the belt photoreceptor 33 to the intermediate transfer belt. When the color image is formed on the intermediate transfer belt 51 after being transferred to the intermediate transfer belt 51, it is located at a transferable position.

  The fixing unit 29 is disposed behind the intermediate transfer belt mechanism unit 25, and includes a heating roller 61, a pressing roller 63 that presses the heating roller 61, and a pair of downstream units that are provided on the downstream side of the heating roller 61 and the pressing roller 63. A conveyance roller 65.

  FIG. 2 is a block diagram schematically showing the main electrical configuration of the laser printer 1. As shown in FIG. 2, the laser printer 1 is provided with a control device 90 that controls each component by a CPU 91, a ROM 92, a RAM 93, a flash memory 94, and an ASIC 100 (Application Specific Integrated Circuit). Further, a main motor 96, a scanner motor 97, an operation panel 98 including input keys and a liquid crystal display device, a density detection sensor 71, a marker detection sensor 99, and the like are provided in a form electrically connected to the ASIC 100. Thus, a control system is configured.

  The CPU 91 controls each component via the ASIC 100 while storing the processing result in the RAM 93 or the flash memory 94 according to the processing procedure stored in the ROM 92.

  The ROM 92 is a non-rewritable memory that stores various control programs executed by the CPU 91 and data necessary for the CPU 91 to execute these control programs. A program for executing the processing shown in the flowcharts of FIGS. 5 to 7 and FIGS. 9, 10, 13, and 14 is stored in the ROM 92.

  The RAM 93 is a memory for temporarily storing data and programs necessary for various processes executed by the CPU 91. The RAM 93 includes a C patch formation position memory 931, an M patch formation position memory 932, a Y patch formation position memory 933, and a K patch formation position memory 934, which are used in a calibration process (see FIG. 5) described later. A C measurement result memory 935, an M measurement result memory 936, a Y measurement result memory 937, and a K measurement result memory 938 are provided.

  With reference to FIG. 3 and FIG. 4, an outline of the calibration process and each memory in the RAM 93 used in the calibration process will be described. The calibration process is a test patch applied to the intermediate transfer belt 51 at each predetermined timing such as when a user command is given at the time of factory shipment or when the number of sheets 5 on which an image is formed exceeds a predetermined number. Then, a test image is formed on the paper 5 by transferring the patch, and the density of the patch and the density of the test image (hereinafter referred to as paper printing density) are measured, and the correction table (see FIG. 8). Is the process of creating.

  FIG. 3A shows a density formed opposite to the intermediate transfer belt 51 in order to measure the patch formation position 510 provided on the intermediate transfer belt 51 and the patch formed on the intermediate transfer belt 51 in the calibration process. It is a figure which shows the detection sensor 71 typically. The intermediate transfer belt 51 is wound around a first intermediate transfer belt roller 53 to a third intermediate transfer belt roller 57 arranged in a triangular shape as shown in FIG. In FIG. 3A, the intermediate transfer belt 51 is illustrated in a plan view for easy understanding of the drawing.

  As shown in FIG. 3A, the intermediate transfer belt 51 is provided with a marker for indicating the position in the sub-scanning direction, that is, the circumferential direction of the intermediate transfer belt 51 (the direction of arrow B shown in FIG. 3A). 511 is provided. The marker 511 is made of metal, and is detected by the marker detection sensor 99 (see FIG. 1), thereby determining the position of the intermediate transfer belt 51 in the circumferential direction. Further, the leading S of the patch forming position 510 can also be detected with the marker detection sensor 99 as a reference.

  In FIG. 3A, an area used for transfer onto the paper 5 is referred to as a transfer area 512 and is indicated by a two-dot chain line. That is, the transfer area 512 is an area where a toner image to be transferred to the paper 5 is formed.

  In FIG. 3A, the patch forming positions 510 are provided, for example, in five rows in the main scanning direction (the direction of arrow A shown in FIG. 3A) in the transfer region 512 of the intermediate transfer belt 51, and in the sub-scanning direction. That is, for example, the case where eight rows are provided in the circumferential direction of the intermediate transfer belt 51 (the direction of the arrow B shown in FIG. 3B) is shown as an example. Thus, by providing a large number of patch formation positions 510 in a matrix in the transfer region 512, fine correction according to the position can be performed in the subsequent image data correction processing (see FIG. 14).

  As shown in FIG. 3A, when five patch formation positions 510 are provided in the main scanning direction, for example, five density detection sensors 71 are provided in the main scanning direction. Alternatively, only one may be provided, and a configuration such as a mechanism that slides in the main scanning direction may be provided, or a line sensor may be provided. Accordingly, the density of the patch formed at each patch forming position 510 can be detected as the intermediate transfer belt 51 rotates.

  FIG. 3B is an image diagram showing patches of the same density formed at each patch forming position 510 of the intermediate transfer belt 51. In FIG. 3B, the variation in the density of each patch is emphasized, and the thickness of the actually formed patch is not accurately illustrated. As shown in FIG. 3B, it can be seen that even if patches having the same density are formed at each position, density unevenness occurs depending on the formed position. Further, when a patch having such density unevenness is transferred to the paper 5, uneven density also occurs in the image (test image) transferred to the paper 5. In the calibration process (see FIG. 5), a correction table (see FIG. 8) for correcting the density unevenness generated at each patch forming position 510 is created.

  Next, the configuration of each memory of the RAM 93 used in the calibration process will be described with reference to FIG.

  FIG. 4A is a diagram schematically showing a configuration of the C patch formation position memory 931 in which whether or not cyan patches are formed at respective positions is stored. In the following description, the intermediate transfer belt 51 is described as being provided with N patch forming positions 510. Each of the N patch forming positions 510 will be described with the first to Nth numbers.

  When a cyan patch is formed on the intermediate transfer belt 51, the value of the C patch formation position memory 931 is read, and a patch is formed on the intermediate transfer belt 51 according to this value. That is, a cyan patch is formed at the patch formation position 510 in which ON is stored, but a cyan patch is thinned out (not formed) at the patch formation position 510 in which OFF is stored. Become.

  Although illustration and detailed description are omitted, in the laser printer 1 of this embodiment, an M patch formation position memory 932 for storing whether or not to form a magenta patch, whether or not to form a yellow patch. Y patch formation position memory 933 for storing and a K patch formation position memory 934 for storing whether or not to form a black patch. These have the same configuration as the C patch formation position memory 931, and for each of the first to Nth patch formation positions 510, it is stored whether the patch of each color is formed or thinned out.

  FIG. 4B is a diagram schematically illustrating the configuration of the C measurement result memory 935. As shown in FIG. 4B, the C measurement result memory 935 stores the density value given to the image forming unit 9 to form each patch and the cyan patch formed with the density value, as a density detection sensor. This is a memory for storing the patch density obtained as a result of measurement at 71 and the paper print density which is the density of the test image formed by transferring the patch to the paper 5. Here, in the present embodiment, the paper print density is described as being input from a known colorimeter connected to the laser printer 1. This colorimeter irradiates the paper 5 with light and detects the reflected light. From this detection result, each color of cyan, magenta, yellow and black is measured and automatically input to the laser printer 1. Is something that can be done. It may be manually input.

  In the laser printer 1 of this embodiment, a patch is formed for each color for each predetermined density value. For example, a cyan patch having a density value of 12.5% is first formed at each patch forming position 510 of the intermediate transfer belt 51, and the patch density is measured and transferred to the paper 5. When a paper print density is input from a colorimeter (not shown), the same processing is performed for each of magenta, yellow, and black at a density value of 12.5%. Next, a cyan patch is formed on the intermediate transfer belt 51 with a density value of 25%, the patch density is measured and transferred to the paper 5, and the paper print density is acquired. That is, the patch formation and the transfer process to the paper 5 are repeated as many times as the number of types of density values multiplied by the number of colors (in this embodiment, 8 types × 4 colors = 32 times). The patch density and paper print density measured during the repetition of the process are all stored in the measurement result memories 935, 936, 937, and 938.

  Although illustration and detailed description are omitted, the M measurement result memory 936, the Y measurement result memory 937, and the K measurement result memory 938 have the same configuration, and patch density and paper printing for each density value. The concentration is stored.

  Returning to FIG. The flash memory 94 is a rewritable nonvolatile memory, and a correction table memory 941 in which correction tables for the first to Nth patch formation positions 510 are stored, and cyan, magenta, yellow, and black colors. A toner remaining amount memory 942 is provided for the remaining amount of toner. The correction table memory 941 stores a correction table (see FIG. 8) for each of the first to Nth patch formation positions 510. As will be described later, the correction table stored in the correction table memory 941 is a table in which the correspondence between the patch density and the paper printing density is stored. When the intermediate transfer belt 51 is replaced, there is a possibility of fluctuation. Therefore, in this embodiment, when any one of the belt photoreceptor 33, the developing cartridge 35, and the intermediate transfer belt 51 is replaced, all the correction tables stored in the correction table memory 941 are cleared.

  The main motor 96 is a motor that rotates the second belt photosensitive roller 41, the first intermediate transfer belt roller 53, and the like described above in synchronization. The scanner motor 97 is a motor that rotates the driving device in the scanner unit 21. The CPU 91 performs drive control of the main motor 96 and the scanner motor 97 based on a program stored in the ROM 92 in advance.

  The control device 90 is provided with a network interface (network I / F) 95 for connecting to an external device such as a personal computer. The network interface 95 is connected to the computer 150. The CPU 91 performs a process of forming an image based on the image data input from the computer 150 via the network interface 95 on the recording surface of the paper 5 by performing drive control of each unit as described above.

  Next, a calibration process executed in the laser printer 1 configured as described above will be described with reference to a flowchart.

  FIG. 5 is a flowchart of the calibration process executed in the laser printer 1. As described above, this calibration processing is performed at a predetermined timing, such as when the execution instruction is received from the user at the time of shipment from the factory, or when the number of sheets 5 on which the image has been formed exceeds a predetermined number. It is a process executed in

  First, it is determined whether a correction table for each color for each patch formation position 510 has already been stored in the correction table memory 941 (S2). When the correction table is not stored (S2: No), all patch calibration processing is executed (S4). Note that the case where the correction table is not stored specifically refers to the case where calibration is performed for the first time in the factory of the laser printer 1 or from the previous calibration process after the purchase of the laser printer 1. This is a case where any one of the belt photosensitive member 33, the developing cartridge 35, and the intermediate transfer belt 51 is replaced and the correction table memory 941 is cleared before the calibration process.

  The all patch calibration process will be described with reference to FIGS. 6 and 7 are flowcharts showing the all patch correction table creation processing (S4). This all patch correction table creation process (S4) forms cyan, magenta, yellow, and black color patches for each of the first to Nth patch formation positions 510 (see FIG. 3A). This is a process of creating a correction table for each color for each of the first to Nth patch formation positions 510 by measuring the density.

  First, for each of the C patch formation position memory 931, the M patch formation position memory 932, the Y patch formation position memory 933, and the K patch formation position memory 934, all the values from the first to the Nth patch formation position 510 are turned on. (S402).

  Next, one color is set as a processing contrast color (S404). At this time, it is preferable to select at random. Here, for example, cyan is the processing target color. Then, the intermediate transfer belt 51 is driven by the main motor 96 to detect the leading S (see FIG. 4A) of the patch forming position 510 (S406). Specifically, the marker provided on the intermediate transfer belt 51 is read by the marker detection sensor 99 (see FIG. 1), and the number of driving pulses of the main motor 96 (the main motor 96 is stepped with reference to the marker reading position). By counting the number of rotation pulses (when the main motor 96 is a DC motor and equipped with a rotary encoder), the leading S of the predetermined patch formation position 510 can be detected. .

  Next, patches having the same density value are formed in the processing contrast color at each of the first to Nth patch forming positions 510 on the intermediate transfer belt 51 (S408). When the density of each patch formed on the intermediate transfer belt 51 is input from the density detection sensor 71 (see FIG. 1), the patch density is stored in the C measurement result memory 935 for the processing contrast color (S410). ).

  Next, the formed patch is transferred to the paper 5 to form a test image (S412). Then, using a colorimeter (not shown), the density (paper printing density) of the test image formed on the paper 5 is measured, and when input to the laser printer 1 (S414: Yes), the paper printing density is processed. The contrast color C measurement result memory 935 is stored (S416). It is determined whether such processing has been performed for each density value (S418). If there is an unprocessed density value (S418: No), the process returns to S406, and a patch of the processed contrast color is formed with the next density value.

  If processing is performed for all density values of the processing contrast color while the processing is repeated in this manner (S418: Yes), it is next determined whether or not processing has been performed for each color of magenta, yellow, and black ( S420). If there is an unprocessed color (S420: No), the process returns to S404, and the process after S406 is repeated with the unprocessed color as the next process contrast color (S404).

  When the processing for all colors is completed while the processing is repeated (S420: Yes), that is, when the patch density and the paper printing density are acquired for all the colors and all the density values, the process proceeds to S422 shown in FIG. Transition to processing.

  FIG. 7 is a flowchart showing the all-patch correction table creation process, and shows steps subsequent to the steps shown in FIG. First, one color is set as a processing target color (S422). Here, cyan extracted at random is used. Next, the variable j is set to “1” (S424). The variable j is used as a variable indicating the target patch formation position 510.

  Next, the patch density and paper print density of the processing contrast color at the jth patch formation position 510 are read from the C measurement result memory 935 (see FIG. 2) (S426). Since the measurement result memories 935, 936, 937, and 938 store the patch density and the paper print density for all the density values by the steps S402 to S420 described with reference to FIG. They are all read out.

  Next, based on the read patch density and the paper print density, a correspondence between the patch density of the processing contrast color at the jth patch formation position 510 and the paper print density is created (S428). A correction table for the processing contrast color at the j-th patch formation position 510 is created and stored in the correction table memory (S430).

  The correction table will be described with reference to FIG. FIG. 8 is an image diagram schematically showing the correction table. As shown in FIG. 8, the correction table includes an I region, a II region, and a III region. Note that the correction table shown in FIG. 8 is assumed to be a correction table created for cyan at the j-th patch formation position 510.

  The I area is an area in which the correspondence between the target value that is the correction target pixel value and the paper print density is stored. In order to eliminate the density unevenness, it is desirable that the target value and the paper printing density have a linear relationship, and therefore, a correspondence relationship in which the target value = paper printing density × α is stored in the first area. . Here, α is a proportionality constant at which the paper print density becomes the maximum value when the target value is 100%.

  The second area is an area in which the correspondence between the paper print density and the patch density is stored. In this second region, the correspondence between the paper print density and the patch density obtained by the measurement is plotted. In the present embodiment, patches are formed for eight types of density values, and the relationship between the patch density and the paper printing density is acquired. As shown in FIG. Plotted.

  The third area is an area in which the correspondence between the measured patch density and the density value is stored. That is, when patches are formed with eight types of density values, the correspondence between each density value and the patch density obtained from the density value is stored.

  An overview of processing for obtaining a density value corresponding to a target value from the target value will be described with reference to the correction table thus created. For example, as shown in FIG. 8, a case where an image having a target value “60%” is to be formed at a position on the paper 5 corresponding to the j-th patch forming position 510 will be described. Here, it is assumed that the paper print density corresponding to the target value “60%” is “1.2”. When an image with the target value “60%” is to be formed at the j-th patch forming position 510, the paper print density “1.2” is determined from the relationship of the I area based on the target value “60%”. The As indicated by the relationship in the second region, the patch density corresponding to the paper printing density “1.2” is “49.5%”. The density value “50.5%” corresponding to% is uniquely determined.

  By inputting “50.5%” as the correction value determined in this way, an image having the same density as the target value of 60% is formed at the j-th patch forming position 510. In FIG. 8, the correspondence between the paper printing density and the patch density and the correspondence between the density value and the patch density are estimated from eight points plotted based on the measurement results in order to make it easier to visually understand. However, the values stored in the second and third areas of the correction table may be discrete values. In that case, the patch density and the density value corresponding to the target value may be obtained by mathematical formulas such as linear interpolation using the discrete values.

  Returning to FIG. Next, it is determined whether or not the variable j is N (S432). If the variable j is less than N (S432: No), “1” is added to the variable j (S434), and the process of S426 is performed. Returning, the next patch forming position 510 is processed. On the other hand, when the variable j becomes N (S432: Yes), it is then determined whether or not the processing has been completed for all colors (S436), and there are unprocessed colors, here magenta, yellow, and black ( S436: No), the process returns to S422, and the process is repeated from S424 with one unprocessed color as the process target color.

  When the process is completed for all colors in this way (S436: Yes), the all patch correction table creation process (S4) is terminated. According to the all patch correction table creation processing, a correction table is created for each color for the first to Nth patch formation positions 510 and stored in the correction table memory 741 (see FIG. 2).

  Returning to FIG. The case where it is determined that the correction table has been stored in the process of S2 as a result of the creation of the correction table as a result of the all patch correction table creation process (S4) (S2: Yes) will be described. In this case, the second and subsequent calibration patch formation processing (S6) and the second and subsequent correction table creation processing (S8) are executed.

  With reference to FIGS. 9 and 10, the second and subsequent calibration patch formation processing (S6) will be described. 9 and 10 are flowcharts showing the calibration patch forming process (S6) for the second and subsequent times. In the all patch correction table creation process (S4) described with reference to FIG. 6, patches are formed for each color at all the first to Nth patch formation positions 510. On the other hand, in the second and subsequent calibration patch formation processes (S6), the correction table is created using the patch density of other colors and the paper print density among the first to Nth patch formation positions 510. The patch forming position 510 that can be created is a process of thinning out patches.

  First, a color other than yellow, that is, one of cyan, magenta, and black in the present embodiment, is determined as the first color (S62). Here, it is assumed that cyan is determined as the first color. In addition, about the color which was not determined as a 1st color, it will be determined and processed as a 2nd color one by one in order at a later step.

  Next, in the patch formation position memory for the first color, the values are turned on for all of the first to Nth patch formation positions 510 (S64). As a result, in the subsequent step, patches are formed at all patch formation positions 510 for the first color (here cyan). The reason why yellow is not the first color will be described later with reference to FIG.

  Next, one color other than the first color is determined as the second color (S66). Here, it is assumed that magenta is determined as the second color. Then, the variable i is set to 1 (S68), and the correction table for the first color (here cyan) and the second color (here magenta) among the correction tables at the i-th patch formation position 510 is read from the correction table memory 941. Read (S70). Then, it is determined whether or not the correspondence relationship of the first color and the correspondence relationship of the second color in the read region II of the correction table are close to each other (S72).

  With reference to FIG. 11, a case where the correspondence relationship between the first color and the correspondence relationship between the second color approximate each other in the region II will be described. FIG. 11 is a diagram schematically showing a correction table at the i-th patch formation position 510. In order to easily show the correspondence between cyan (C) and the correspondence between magenta (M), the correspondence between cyan is shown. The correspondence relationship between the second region of magenta and the second region of the correction table illustrated with a solid line is shown in a dashed line. As shown in FIG. 11, at the i-th patch formation position 510, it can be seen that the correspondence relationship of cyan as the first color and the correspondence relationship of magenta as the second color are approximated.

  More specifically, in this embodiment, for each patch density, a difference Δx between cyan paper printing density and magenta paper printing density is calculated, and the difference Δx is within a predetermined range (for example, cyan paper printing density). In the case where the print density is within a range of ± 5%, it is determined that the correspondence relationship between the first color and the correspondence relationship between the second color is approximate. In other words, when the test image density of the second color is included within a range of ± 5% of the test image density of the first color, the correspondence relation of the first color and the correspondence relation of the second color are approximated. I decided to judge.

  As described above, when discrete values are stored in the second region of the correction table, that is, when the measured values of the patch density and the paper print density are stored as they are, the patch density of the first color is In some cases, the patch density of the second color is slightly different. In that case, for the second color, the paper print density at the same patch density as the patch density of the first color is calculated by linear interpolation, and both are approximated based on the difference Δx of the paper print density with respect to the same patch density. It may be determined whether or not. In the second area of the correction table, when the correspondence between the patch density and the paper print density is stored as a function estimated from each measurement value, the function of the first color and the function of the second color are stored. For example, when the difference between the coefficients of the functions is determined to be within a predetermined range, it may be determined that the first color correspondence and the second color correspondence are approximate.

  FIG. 12 is a diagram schematically showing a correction table for the i-th patch formation position 510. Similarly to FIG. 11, in order to show the correspondence relationship for each color in an easy-to-understand manner, the region II includes cyan (C). The correspondence relationship of magenta (M) is indicated by a one-dot chain line, the correspondence relationship of black (K) is indicated by a two-dot chain line, and the correspondence relationship of yellow (Y) is indicated by a wavy line. ing.

  As is apparent from FIG. 12, when the correspondence relationship created in the region II is compared for each color, the curves indicating the correspondence relationship between cyan, magenta, and black are similar to each other. There are many cases where the paper printing density becomes lighter than the color. Therefore, when one of cyan, magenta, and black other than yellow is used as the first color, it is easier to approximate the other colors, more patches can be thinned out, and the toner saving effect is enhanced. Therefore, in this embodiment, colors other than yellow are determined as the first color.

  Returning to FIG. When it is determined that the correspondence relationship between the first color and the correspondence relationship between the second color are approximate to each other in the second region of the correction table at the i-th patch formation position 510 (S72: Yes), the patch formation position of the second color The value of the i-th patch formation position 510 in the memory (here, the M patch formation position memory 932) is turned off (S74). Therefore, when the patch is formed in the subsequent step, the second color patch is not formed (thinned out) at the i-th patch forming position 510.

  On the other hand, when it is determined that the correspondence relationship of the first color and the correspondence relationship of the second color are not close to each other in the II region of the correction table at the i-th patch formation position 510 (S72: No), The value of the i-th patch formation position 510 in the patch formation position memory (here, the M patch formation position memory 932) is turned on (S76). Accordingly, when the patch is formed in the subsequent step, the second color patch is formed at the i-th patch formation position 510.

  Next, it is determined whether or not the variable i is N (S78). If the variable i is not yet N (S78: No), “1” is added to the variable i (S80), and S70. Returning to the process, the correction table for the next patch formation position 510 is read from the correction table memory 941 (S70), and the process is repeated.

  In this way, when the processing is completed for all patch formation positions 510, the variable i becomes N (S78: Yes), so whether all the colors have been processed, that is, all colors other than the first color are displayed. It is determined whether or not the second color has been processed (S82). If there is an unprocessed color (S82: No), the unprocessed color is set as the second color (S83), the process returns to S68, and the process is repeated for the color from the first patch formation position 510.

  As described above, when the processing for all the colors is completed while the color other than the first color is determined as the second color and the processing is repeated (S82: Yes), that is, the C patch formation position memory 931, When an ON or OFF value is stored in each of the first to Nth patch forming positions 510 in the M patch forming position memory 932, the Y patch forming position memory 933, and the K patch forming position memory 934, next, FIG. The process proceeds to S84 shown in FIG.

  FIG. 10 is a flowchart showing the calibration patch forming process for the second and subsequent times, and shows the steps after S84, which is the next step after S82 shown in FIG. As shown in FIG. 10, in the process of S84, one color is set as a process contrast color (S84). Here, description will be given assuming that cyan is determined as the processing contrast color. Next, the intermediate transfer belt 51 is driven by the main motor 96 to detect the leading S (see FIG. 4A) of the patch forming position 510 (S86).

  Next, according to the value of the processing contrast color patch formation position memory (here, the value of the C patch formation position memory 931), the processing contrast color patch having the same density value is formed on the intermediate transfer belt 51 (S88). In this process, a patch is formed for the patch formation position 510 where ON is stored, and a patch is thinned out for the patch formation position 510 where OFF is stored. For the color, patches of that color are formed at all of the first to Nth patch formation positions 510, while for the color determined as the second color, only the patch formation positions 510 in which ON is stored are stored. Patches are thinned out at patch forming positions 510 where patches are formed and OFF is stored.

  Next, the density of each patch input from the density detection sensor 71 (see FIG. 4A) is stored in the measurement result memory of the processing contrast color (S90). For example, if a cyan patch is formed, the patch density of the cyan patch is stored in the C measurement result memory 935. Here, “0” is input as the patch density for the patch formation position 510 where the patches are thinned out, and stored in the measurement result memories 935, 936, 937, and 938 for the corresponding colors.

  Next, the formed patch is transferred to the paper 5 to form a test image (S92). Then, using a colorimeter (not shown), the density of the test image (paper printing density) formed on the paper 5 is measured and waits until the paper printing density is input (S94). When the paper print density is input (S94: Yes), the paper print density is stored in the measurement result memory (S96). It is determined whether or not such processing has been performed for each density value of the processing contrast color (S98). If there is an unprocessed density value (S98: No), the process returns to S86, and a patch of the processed contrast color is formed at the next density value according to the value of the patch formation position memory of the processed contrast color.

  When the processing for each density value of the processing contrast color is completed while the processing is repeated in this way (S98: Yes), it is then determined whether or not such processing has been performed for all colors (S100). When there is an unprocessed color (S100: No), the unprocessed color is set as a process target color (S102), and the process returns to S86.

  When the patch formation, transfer, and measurement are completed for all colors and each density value while the process is repeated, the calibration patch formation process (S6) for the second and subsequent times is completed. According to the second and subsequent calibration patch formation processing (S6), the first color patch is formed at all the first to Nth patch formation positions 510, and the relationship between the patch density and the paper print density is determined. To be acquired. On the other hand, since the patch of the second color is thinned out at the patch formation position 510 determined that the correspondence of the first color and the correspondence of the second color are approximate, the number of patches to be formed can be reduced, The amount of toner used can be saved.

  Next, the second and subsequent correction table creation processing (S8) for creating a correction table using the patch density and the paper print density acquired in the second and subsequent calibration patch formation processing (S6) is executed.

  FIG. 13 is a flowchart showing the second and subsequent correction table creation processing (S8). This second and subsequent correction table creation processing is processing for creating a correction table for each color for each of the first to Nth patch formation positions 510 and storing it in the correction table memory 941 (see FIG. 2).

  In the second and subsequent correction table creation processing, first, the variable k is set to 1 (S122), and one color is set as a processing contrast color (S124). Next, it is determined whether or not the processing contrast color is the first color (S126). Here, description will be given first assuming that the processing contrast color is cyan, which is the first color.

  Here, in the second and subsequent calibration patch formation processing (S6) executed before the second and subsequent correction table creation processing (S8), the first to Nth patch formation is performed for the first color. Patches were formed for all of the positions 510. Therefore, for the first color, the patch density and the paper print density are measured for all of the first to Nth patch formation positions 510 and stored in the measurement result memories 935, 936, 937, and 938. Therefore, for the first color, a correction table can be created using the patch density and paper print density of the first color acquired in the calibration patch forming process (S6) from the second most recent time.

  Specifically, when the processing contrast color is the first color (S126: Yes), the patch density and the paper print density of the first color at the k-th patch forming position 510 are read, and the processing at the k-th patch forming position 510 is performed. A correspondence relationship between the patch density of the contrast color (first color) and the paper printing density is created and stored in the second area of the correction table (S128).

  Next, a relationship between the patch density and the density value of the first color at the k-th patch formation position 510 is created and stored in the region III of the correction table, whereby the color to be processed (the first color at the k-th patch formation position 510). A correction table for one color is created (S130). Then, the created correction table for the k-th patch formation position 510 is stored in the correction table memory 941 (S131).

  Next, it is determined whether or not the variable k is N (S132). When the variable k is less than N (S132: No), “1” is added to the variable k (S134), and the process returns to S126. By repeating the process in this way, a correction table is created for all of the first to Nth patch formation positions 510 for the first color and stored in the correction table memory 941.

  If the variable k becomes N while repeating the processing for the first color in this way (S132: Yes), it is next determined whether or not processing has been performed for all colors (S136). When there is an unprocessed color (S136: No), the unprocessed color is set as a process target color (S137), and the process returns to S126.

  Next, a case will be described in which a color other than the first color, that is, the second color in the second and subsequent calibration patch formation processing (S6) is the processing contrast color. When the processing contrast color is not the first color (S126: No), it is determined whether or not the patch density at the k-th patch forming position 510 is “0” (S138). When the patch density at the k-th patch formation position 510 is not “0”, that is, when the patch of the processing contrast color is formed at the k-th patch formation position 510 (S138: No), the k-th patch formation position 510 is reached. The patch density and the paper print density of the color to be processed in are read out, the correspondence between the patch density of the process contrast color and the paper print density at the k-th patch formation position 510 is created, and stored in the second area of the correction table. (S140).

  Next, the relationship between the patch density and the density value of the processing contrast color at the k-th patch forming position 510 is created and stored in the third area of the correction table, thereby correcting the processing target color at the k-th patch forming position 510. A table is created (S142). Then, the created correction table is stored in the correction table memory 941 (S131), and the process proceeds to S132. That is, a correction table is created using the patch density and paper print density of the color to be processed acquired in the calibration patch forming process (S6) from the second time onward.

  On the other hand, when the patch density at the k-th patch formation position 510 is “0”, that is, when the patch of the processing contrast color is thinned out at the k-th patch formation position 510 (S138: Yes), the k-th patch formation position 510 is obtained. The patch density and the paper print density of the first color at the patch forming position 510 are read out, and the patch density and the paper print density of the first color are used as the patch density and the paper print density of the process contrast color, and the correspondence of the process contrast color The relationship is created and stored in the second area of the correction table (S128). Next, the relationship between the patch density and the density value of the first color at the k-th patch formation position 510 is created as the relationship between the patch density and the density value of the processing contrast color, and stored in the area III of the correction table. Thus, a correction table for the processing target color at the k-th patch formation position 510 is created (S130), and the created correction table is stored in the correction table memory 941 (S131). That is, since the processing contrast color patches have been thinned out at the k-th patch forming position 510, the first color patch density and the paper print density acquired in the calibration patch forming process (S6) from the second time onward are used. Use it to create a correction table.

  As the processing is repeated in this manner, a correction table for each color is created for the first to Nth patch formation positions 510, and when the processing is completed for all colors (S136: Yes), the second and subsequent corrections are made. The table creation process (S8) is terminated.

  According to the second and subsequent correction table creation processing (S8), the patch formation position 510 where the patches are thinned out is determined based on the patch density of the first color and the paper print density at the patch formation position 510. Since the correspondence relationship between the two colors is acquired, a correction table for each color for adjusting the image density can be created for the patch formation position 510 where patches of any color are thinned out. A correction table for each color is created for each forming position 510. Therefore, it is possible to create a correction table for each patch forming position 510 while reducing the number of patches to be formed. Further, the patch density and the paper print density of the first color used for creating the correspondence relationship of the second color are values acquired in the second and subsequent calibration patch formation processes (S6). is there. That is, since the value reflects the latest environment, a correction table that reflects changes over time since the previous calibration process can be created, and an appropriate correction value can be obtained in an image data correction process (see FIG. 14) described later. Can be determined.

  On the other hand, for the patch formation position 510 where the patch is formed for the second color, a correction table is created using the measurement result of the second color, so the correspondence between the first color and the correspondence between the second color For patch formation positions 510 that are not approximated, a correction table reflecting changes over time is created, and an appropriate correction value can be determined in an image data correction process (see FIG. 14) described later.

  The image data correction process using the correction table created as described above will be described with reference to FIG. FIG. 14 is a flowchart showing image data correction processing. This image data correction process is activated when image data is input to the laser printer 1 from a PC or the like, and the density of the image formed on the paper 5 is determined using the correction table created as described above. This is a process for determining a correction value for adjustment for each color for each patch formation position 510 and reflecting the correction value in the image data at the time of image formation.

  First, the target value of the correction target pixel is read from the image data (S1301). This target value is a value indicating the target density for each color of cyan, magenta, yellow, and black. Next, the four nearest patch formation positions 510 are selected as the correction target pixel formation positions (S1302).

  With reference to FIG. 15, the four patch formation positions 510 selected in the process of S1302 will be described. FIG. 15A is a diagram showing a patch formation position 510 provided on the intermediate transfer belt 51 and a correction target pixel formation position P. FIG. In FIG. 15A, the four patch formation positions 510 closest to the correction target pixel formation position are colored. As described above, since the transfer area 512 is an area corresponding to the paper 5 for one page, the correction target pixel formation position P in the transfer area 512 can be specified in accordance with the position information of the correction target pixel. Since each patch formation position 510 in the transfer area 512 is determined in advance, the four patch formation positions 510 closest to the correction target pixel can be selected based on the correction target pixel formation position in the transfer area 512. It can be done.

  Returning to FIG. Next, the correction table created for the four selected patch formation positions 510 is read (S1304). In the present embodiment, four color correction tables are stored for each patch formation position 510, so that a total of 16 correction tables are read out.

  Next, for each read correction table, each correction value (density value) for the read target value of the correction target pixel is obtained (S1306). Then, using the correction value obtained for each correction table, the correction value of the correction target pixel is obtained for each color. This can be obtained, for example, by area interpolation based on the distance from the correction target pixel to the four selected patch formation positions 510 (S1308).

  The area interpolation will be described with reference to FIG. FIG. 15B is an image diagram showing the concept of area interpolation performed in the process of S1308. As shown in FIG. 15B, a square 102 having apexes at the centers of the four selected patch forming positions 510 is created, and two auxiliary lines 103 that intersect perpendicularly at the correction pixel forming position P, At 104, the square is divided into four rectangles 106, 107, 108 and 109. Then, the correction value obtained from each patch forming position 510 is weighted according to the area of the rectangle to which each vertex belongs, and the correction value of the correction target pixel is determined. In this way, an appropriate correction value corresponding to the position can be determined for the correction target pixel formed at a position other than the patch formation position 510.

  Returning to FIG. Next, it is determined whether or not the processing for all the pixels has been completed (S1310). If the processing for all the pixels has not yet been completed (S1310: No), the processing returns to S1301, and the uncorrected pixels are corrected next. The process is repeated as the target pixel.

  When the process for all the pixels is completed while the process is repeated in this manner (S1310: Yes), the image data correction process is terminated. Since the processing after the correction processing is a known processing, detailed description thereof is omitted, but the laser printer 1 adjusts the pulse width of the laser beam and develops each development based on the correction value obtained by the image data correction processing. Since the voltage applied to the roller 37 and the belt photoreceptor charger 45 is adjusted, the density of each color printed on the paper 5 is appropriately corrected, and the density unevenness in one page is corrected on the paper 5. Can be formed.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications and changes can be easily made without departing from the spirit of the present invention. Can be inferred.

  For example, in the above embodiment, the first to Nth patch formation positions 510 used in the calibration process are determined in advance, and the first color is patched to all of the first to Nth patch formation positions 510. Was forming. Alternatively, the patch formation position 510 used in the calibration process may be changed according to a user instruction.

  With reference to FIG. 16, the patch formation position 510 determined according to a user instruction will be described. FIG. 16A is a diagram showing only the patch formation position 510 determined according to the user instruction among the patch formation positions 510 described in the above-described embodiment, and FIG. FIG. 6 is a diagram showing an example of a calibration position designation screen displayed on an operation panel 98 (see FIG. 2) of the laser printer 1.

  The user forms a large number of patches in a range in which the user desires a reliable calibration process in the transfer area 512, and does not form a patch in a range where the accuracy of the calibration process is not so required. I want to save toner usage. Here, in this modified example, as shown in FIG. 16A, the transfer area 512 is divided into a left area 513, a central area 514, and a right area 515, and calibration is required in each of the areas 513, 514, and 515. The number of patches corresponding to the degree was formed in each of the regions 513, 514, and 515.

  Therefore, when the calibration designation screen as shown in FIG. 16B is displayed on the display screen of the operation panel 98, the user operates the operation panel 98 to thereby operate the left range, the center range, and the right range. For each of these, input the necessity of calibration.

  FIG. 17 is a flowchart illustrating a modification of the all-patch correction table creation process. 17, the same process as the all patch correction table creating process of the embodiment described with reference to FIG. 6 is denoted by the same reference numeral, and the description thereof is omitted. Only the different processing will be described.

  First, a calibration position designation screen (see FIG. 16B) is displayed on the operation panel 98 (S4001). When the user performs an operation on the display, each of the C patch forming position memory, the M patch forming position memory, the Y patch forming position memory, and the K patch forming position memory is operated according to the user operation. The stored value is stored (S4002). Specifically, the number of patch formations is determined for each of the regions 513, 514, and 515 according to the degree of necessity input from the user, and the patch formation position is determined according to the number. Then, “invalid” is stored as a value for the patch forming position where the patch is not formed, and “on” is stored as a value for the patch forming position where the patch is formed.

  In the subsequent processing, no patch is formed for the first color or the second color at the patch formation position in which “invalid” is stored as the value. As described above, by changing the patch forming position 510 where the patch is formed in accordance with the user operation, the patch is not formed at a position unnecessary for the user, and the amount of toner used can be saved.

  Further, according to the second and subsequent correction table creation processing (S8) of the above-described embodiment, when the patch density of the second color is “0” (S138: Yes), the first color at the k-th patch formation position 510 is obtained. The patch density and the paper print density are read out, and the correspondence between the second color patch density and the paper print density is created. Instead, if the relationship between the patch density of the first color and the paper print density is stored as a function, for example, the function is obtained as it is as the correspondence relationship of the second color. Also good.

  Further, according to the calibration processing of the above-described embodiment, the patch forming position 510 is provided only in the transfer region 512 corresponding to the sheet 5 of one page of the intermediate transfer belt 51, but the patch is formed on the entire circumference of the intermediate transfer belt 51. A position 510 may be provided.

  Further, according to the calibration processing of the above-described embodiment, the patch forming position 510 is provided on the intermediate transfer belt 51 and the density of the patch is measured on the intermediate transfer belt 51. A patch may be formed and the density of the patch on the belt photoreceptor 33 may be measured.

  The laser printer 1 according to the above-described embodiment is a so-called transfer belt type laser printer that transfers a toner image formed on a photosensitive member to a transfer belt and forms an image on a sheet 5 using the transfer belt. For example, a laser printer that transfers a toner image from a photoreceptor to a transfer drum and forms an image on the sheet 5 from the transfer drum, or a laser that forms a toner image formed on the photoreceptor directly on the sheet 5. The present invention can also be applied to a printer. In that case, the photoconductor and the transfer drum may correspond to the image carrier described in the claims.

1 is a schematic cross-sectional view of a main part of a laser printer as an image forming apparatus according to an embodiment. FIG. 2 is a block diagram conceptually showing an electrical configuration of the laser printer shown in FIG. 1. FIG. 6A is a diagram schematically illustrating a patch formation position provided on the intermediate transfer belt and a density detection sensor disposed opposite to the intermediate transfer belt in order to measure a patch formed on the intermediate transfer belt. FIGS. 7A and 7B are image diagrams that emphasize the level of density of patches formed at each patch forming position of the intermediate transfer belt. FIGS. (A) is a figure which shows typically the structure of C patch formation position memory, (b) is a figure which shows the structure of C measurement result memory 935 typically. It is a flowchart of the calibration process performed in a laser printer. It is a flowchart which shows all the patch correction table creation processes. It is a flowchart which shows all the patch correction table creation processes. It is a figure which shows a correction table typically. The second and subsequent calibration patch formation processes will be described. The second and subsequent calibration patch formation processes will be described. It is a figure which shows typically the correction table of the i-th patch formation position. It is a figure which shows typically the correction table of the i-th patch formation position. It is a flowchart which shows the correction table creation process after the 2nd time. It is a flowchart which shows an image data correction process. (A) is a figure which shows the patch formation position provided in an intermediate transfer belt, and the formation position of a correction object pixel, (b) is an image figure which shows the concept of area interpolation. (A) is a figure which attaches and shows only the patch formation position determined according to the user instruction among the patch formation positions described in the embodiment, and (b) is displayed on the operation panel of the laser printer. It is the figure which showed an example of the screen displayed. It is a flowchart which shows the modification of all the patch correction table creation processes.

Explanation of symbols

1 Laser printer (image forming device)
5 paper (recording medium)
21 Scanner unit (exposure means)
35 Developing cartridge (developing means)
51 Intermediate transfer belt (image carrier)
99 Marker detection means (position detection means)
941 Correction table memory (correspondence storage means)
S2 Correspondence relation presence / absence judgment means S4 New correspondence relation acquisition means S6 New density acquisition means S8 Correspondence relation acquisition means S62 First color determination means S66, S83 Second color determination means S72 Approximation judgment means S88 First color test image forming means, first Two-color test image forming means S1300 Correction value determining means S4002 Test position changing means

Claims (11)

A developing unit that is provided for each of a plurality of colors and that develops an electrostatic latent image to form a toner image;
An image carrier for carrying a toner image formed by the developing means;
In an image forming apparatus for forming an image on a recording medium by transferring the toner image carried on the image bearing member to the recording medium,
First color test image forming means for forming a first color test image composed of a first color toner image at a plurality of test positions on the image carrier;
Second color test image forming means for forming a second color test image composed of a second color toner image at any of the plurality of test positions;
A correspondence relationship between the density of the test image formed by the first color test image forming unit or the second color test image forming unit and the density of the test print image formed by transferring the test image to the recording medium, Correspondence acquisition means for acquiring each of the plurality of test positions for each color;
Correspondence storage means for storing the correspondence acquired by the correspondence acquisition means;
Correction value determining means for determining, for each color, a correction value for adjusting the density of an image formed on the recording medium, for each color, using the correspondence stored by the correspondence storage means; ,
When the correspondence relationship of the first color and the correspondence relationship of the second color are already stored in the correspondence relationship storage unit, the correspondence relationship of the first color and the second color already stored in the correspondence relationship storage unit Approximation determination means for determining whether each of the plurality of test positions approximates the correspondence relationship of
The second color test image forming means thins out the second color test image at the test position determined as a result of the approximation judgment means that the correspondence relation between the first color and the correspondence relation between the second color is approximate. And
For the test position where the test image of the second color is thinned out, the correspondence relationship acquisition means corresponds to the second color based on the test image density of the first color and the test print image density for the test position. An image forming apparatus characterized by acquiring a relationship. A correspondence presence / absence judging means for judging whether the correspondence relation of the first color and the correspondence relation of the second color are already stored in the correspondence relation storage means;
When the correspondence relationship presence / absence determining means determines that the correspondence relationship between the first color and the correspondence relationship between the second color has already been stored, the toner image of the first color is determined by the first color test image forming means. Are formed at a plurality of test positions on the image carrier, and the density of the formed first color test image and the test image are transferred to a recording medium. New density acquisition means for acquiring the density of the test print image,
The correspondence relationship acquisition unit is configured to determine, based on the first color test image density and the test print image density acquired by the new density acquisition unit, the test position where the second color test image is thinned out. The image forming apparatus according to claim 1, wherein a correspondence relationship between colors is acquired.   When the difference between the test image density of the first color and the test image density of the second color corresponding to each test image density is within a predetermined range, the approximation determining unit determines the correspondence between the first color and the second color. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus determines that the correspondence relationship is approximate.   The approximate determination means, when the test image density of the second color is included in a predetermined range within ± 5% of the test image density of the first color, the correspondence relationship between the first color and the correspondence between the second color The image forming apparatus according to claim 1, wherein the relationship is determined to be approximate. A position detecting means for detecting a predetermined position in the image carrier,
5. The first color test image forming unit and the second color test image forming unit form a test image at a test position based on a predetermined position detected by the position detecting unit. The image forming apparatus according to any one of the above.   The image forming apparatus according to claim 1, further comprising a first color determining unit that determines a color having the maximum amount of toner as the first color. The developing means is provided for each of three or more colors,
First color determining means for determining any one of the three or more colors as the first color;
A second color determining means for determining each color other than the first color determined by the first color determining means as a second color;
The image forming apparatus according to claim 1, wherein the correspondence relationship acquisition unit acquires a correspondence relationship of each color determined as the second color by the second color determination unit. The developing means is provided for each of three or more colors including at least yellow,
The image forming apparatus according to claim 7, wherein the first color determining unit determines a color having the maximum remaining amount of toner out of colors other than yellow as the first color. A correspondence presence / absence judging means for judging whether the correspondence relation of the first color and the correspondence relation of the second color are already stored in the correspondence relation storage means;
When the correspondence relationship presence / absence determining means determines that the correspondence relationship between the first color and the correspondence relationship between the second color is not stored in the correspondence relationship storage means, a test image of each color is stored in the first color image. The test color image is formed for each test position where the first color test image is formed by the one color test image forming means, and the test image density and the test print image formed by transferring the test image to the recording medium. 9. The image forming apparatus according to claim 1, further comprising a new correspondence acquisition unit that acquires a correspondence relationship with the density and stores the correspondence relationship in the correspondence relationship storage unit.   The test positions where the first color test image forming means is arranged by the first color test image forming means are provided in a plurality of rows in the main scanning direction on the image carrier and are perpendicular to the main scanning direction on the image carrier. The image forming apparatus according to claim 1, wherein a plurality of rows are provided in the direction.   Test position changing means for changing a test position at which a first color test image composed of a first color toner image is formed by the first color test image forming means in accordance with a user instruction. The image forming apparatus according to claim 1.

Images