JP2018001679A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of density unevenness at the time when performing exposure by a head in which a plurality of chips where a plurality of light-emitting elements are arranged are arrayed.SOLUTION: A scan unit 14 reads a test chart formed in a recording medium by an image formation unit 13. A control unit 11 acquires an image of the test chart read by the scan unit 14. The control unit 11 identifies the density of an end of a region corresponding to a chip of an LPH (LED Print Head) of an exposure device 33 in the acquired image for each chip. The control unit 11 identifies the correction amount of the light amount of light emitted by the chip adjacent in the main-scanning direction to the selected chip so that the difference between the density of the end of the region corresponding to the selected chip and the density of the end of the region corresponding to the chip adjacent in the main-scanning direction to the selected chip becomes small. The control unit 11 corrects the light amount of the light emitted by the chip according to the identified correction amount.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

  Patent Document 1 discloses an image forming apparatus that forms an electrostatic latent image on a photoreceptor using LPH (LED Print Head). This image forming apparatus reads the output test pattern, and based on the read result, the density ratio of each pixel (obtained by dividing the density of each pixel by the average value of the density of all pixels) is a predetermined value. As described above, the light intensity of each LED provided in the LPH is adjusted to suppress the occurrence of density unevenness.

Japanese Patent No. 4403744

  Some LPHs have a plurality of chips in which a plurality of LEDs are arranged in the main scanning direction. When the LPH is configured by arranging a plurality of chips in the main scanning direction, between adjacent chips, the light quantity of the LED at the end of the other chip side in one chip and the one chip side in the other chip If there is a difference in the amount of light of the LED at the end of the light, density unevenness occurs in the portion where there is a difference.

  The present invention has been made under the above-described background, and an object of the present invention is to provide a technique for suppressing the occurrence of density unevenness when performing exposure with a head in which a plurality of chips each having a plurality of light emitting elements are arranged. To do.

  In the image forming apparatus according to claim 1 of the present invention, a plurality of chips having a plurality of light emitting elements are arranged in the main scanning direction, the image holding body is exposed by the light emitting elements, and the image holding body is formed by the exposure. An image forming unit that develops the electrostatic latent image to form an image on a recording medium, a fixing unit that fixes the image formed on the recording medium, and a reading that reads an image fixed on the recording medium by the fixing unit And a density specifying unit for specifying the density of the edge in the main scanning direction of the region corresponding to the chip for each of the plurality of chips in the image read by the reading unit, and the chip are sequentially selected and selected The correction amount of the amount of light emitted from the second chip adjacent to the first chip in the main scanning direction is the density specified by the density specifying unit and the density of the end of the region corresponding to the first chip; Above The correction amount specifying unit specified by the difference between the density specified by the degree specifying unit and the density of the end of the region corresponding to the second chip, and the correction amount specifying unit specifying the amount of light emitted by the chip And a correction unit that performs correction according to the corrected amount.

  In the image forming apparatus according to claim 2 of the present invention, the correction amount specifying unit includes a density of an end portion of an area corresponding to the first chip, and a density of an end portion of the area corresponding to the second chip. If the difference is equal to or greater than a predetermined threshold, the correction amount is specified.

  In the image forming apparatus according to claim 3 of the present invention, when the correction amount specifying unit specifies the correction amount for one chip, the correction amount is sequentially specified for all unselected chips.

According to the image forming apparatus of the first aspect of the present invention, it is possible to suppress density unevenness when performing exposure with a head in which a plurality of chips each having a plurality of light emitting elements are arranged.
According to the image forming apparatus of the second aspect of the present invention, it is possible to specify the correction amount for the chip having a large difference in the light amount at the end portion between the adjacent chips, and suppress the occurrence of density unevenness.
According to the image forming apparatus of the third aspect of the present invention, it is possible to suppress the difference in density between the chips from being opened.

1 is a diagram illustrating a hardware configuration of an image forming apparatus 1 according to an embodiment of the present invention. The figure which showed an example of the arrangement | sequence of the chip | tip in LPH. The functional block diagram of the control part 11. FIG. The flowchart which showed the flow of the process which the control part 11 performs. FIG. 3 is a diagram illustrating an example of a test chart that the image forming apparatus 1 forms on a sheet. The figure for demonstrating the area | region corresponding to chip | tip C1-Cm in a test image. The figure which showed an example of the data expand | deployed by RAM. The figure for demonstrating the operation | movement of correction | amendment. The flowchart which showed the flow of the process which the control part 11 performs. The figure which showed an example of the table which stored light quantity sensitivity. The flowchart which showed the flow of the process which the control part 11 which concerns on a modified example performs.

[Embodiment]
FIG. 1 is a diagram illustrating a hardware configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 has a copying function, a facsimile function, a scanning function, and an image forming function for forming an image represented by image data acquired from an external computer device on a sheet.

  The control unit 11 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls each unit of the image forming apparatus 1 by executing a program stored in the ROM. The operation unit 15 includes a touch panel and a plurality of buttons for operating the image forming apparatus 1. The storage unit 17 stores image data and various data used to control the image forming apparatus 1.

The communication unit 16 is connected to a communication line, and performs data communication with other devices connected to the communication line. Examples of the communication line include a telephone line and a LAN (local area network). The communication unit 16 acquires image data indicating an image to be formed on a sheet from another device.
The scanning unit 14 optically reads a document and generates image data representing an image of the read document. The scanning unit 14 outputs the generated image data to the control unit 11. In the present embodiment, the image data is in a bitmap format, and each pixel has density information based on the RGB color system. The scanning unit 14 is an example of a reading unit that reads an image formed on a recording medium.

  The image processing unit 12 performs various types of image processing on the image data supplied from the control unit 11. The image processing unit 12 performs image processing such as color correction and gradation correction on the image represented by the supplied image data, and yellow (Y), magenta (M), and cyan (C) from the image subjected to the image processing. , Black (K) image data of each color is generated and output to the image forming unit 13.

The image forming unit 13 is an example of an image forming unit that forms an image on a sheet (recording medium) by an electrophotographic method in accordance with supplied YMCK image data. The image forming unit 13 includes image forming engines 21Y, 21M, 21C, and 21K, an intermediate transfer belt 22, a secondary transfer roller 23, and a fixing device 24. Each of the image forming engines 21Y, 21M, 21C, and 21K includes a photosensitive drum 31, a charger 32, an exposure device 33, a developing device 34, and a primary transfer roller 35. The image forming engine 21Y forms a yellow toner image according to the supplied yellow image data, and the image forming engine 21M forms a magenta toner image according to the supplied magenta image data. 21C forms a cyan toner image according to the supplied cyan image data, and the image forming engine 21K forms a black toner image according to the supplied black image data.
When the photosensitive drum 31, the charger 32, the exposure device 33, the developing device 34, and the primary transfer roller 35 of each image forming engine are distinguished, the end of the code of the image forming engine is given to each. For example, when describing the exposure device 33 of the image forming engine 21Y, it will be referred to as the exposure device 33Y.

A photosensitive drum 31 as an example of an image holding member has a photosensitive layer formed on the surface thereof, and rotates about an axis. The charger 32 charges the surface of the photosensitive drum 31 to a predetermined potential.
The exposure apparatus 33 includes an LPH and a drive circuit 330 that drives a light emitting element included in the LPH. The LPH according to the present invention includes a plurality of chips each having a plurality of light emitting elements (LEDs in the present embodiment) arranged in a line. The LPH also includes a lens array for imaging light emitted from the light emitting element on the photosensitive drum 31. In the LPH, a plurality of chips are arranged so that the light emitting elements are arranged in the main scanning direction.

  FIG. 2 is a diagram for explaining the arrangement of chips in the LPH. In the LPH, m chips C1 to Cm are arranged in a direction (main scanning direction) horizontal to the axial direction of the photosensitive drum 31. In each of the chips C1 to Cm, n light emitting elements L1 to Ln that irradiate the photosensitive drum 31 with light are arranged in the axial direction (main scanning direction) of the photosensitive drum 31. In the following description, when it is not necessary to distinguish each of the chips C1 to Cm, these will be referred to as “chip C” for convenience of description. Similarly, when it is not necessary to distinguish each of the light emitting elements L1 to Ln, these will be referred to as “light emitting element L” for convenience of explanation. Further, even-numbered chips C counted from the origin in the main scanning direction are referred to as even-numbered chips, and odd-numbered chips C counted from the origin in the main scanning direction are referred to as odd-numbered chips.

  The exposure device 33 irradiates the charged photosensitive drum 31 with light from the light emitting element L according to the supplied image data, thereby exposing the surface of the photosensitive drum 31 to electrostatically charge the photosensitive drum 31. A latent image is formed. The developing device 34 develops the electrostatic latent image formed on the photoconductive drum 31 with toner to form a toner image. The primary transfer roller 35 transfers the toner image formed on the photosensitive drum 31 to the intermediate transfer belt 22.

  The intermediate transfer belt 22 is supported by a driving roller 22a and a backup roller 22b, and is rotated in the direction of arrow A in the figure by the driving roller 22a. The intermediate transfer belt 22 conveys the toner image transferred from the photosensitive drum 31 of the image forming engines 21Y, 21M, 21C, and 21K to the secondary transfer roller 23. The secondary transfer roller 23 transfers the toner image formed on the intermediate transfer belt 22 to a recording medium such as paper. The recording medium to which the toner image is transferred is conveyed to the fixing device 24. The fixing device 24 fixes the toner image on the recording medium by heating and pressing. The fixing device 24 is an example of a fixing unit that fixes an image on a recording medium. The recording medium on which the toner image is fixed is discharged from the image forming apparatus 1.

  FIG. 3 is a functional block diagram of functions realized by the CPU of the control unit 11 executing a program. The density specifying unit 111 specifies the density of the region corresponding to the chips C1 to Cm for each of the chips C1 to Cm in the image represented by the image data generated by the scanning unit 14. The correction amount specifying unit 112 specifies the correction amount of the amount of light emitted from the chips C1 to Cm according to the density specified by the density specifying unit 111 and the state of the image forming unit 13. The correction unit 113 controls the drive circuit in accordance with the correction amount specified by the correction amount specifying unit 112, and corrects the amount of light emitted from the chips C1 to Cm.

(Operation example of embodiment)
FIG. 4 is a flowchart showing a flow of processing performed by the control unit 11 in order to suppress uneven density of an image formed on a sheet. An example of the operation performed by the image forming apparatus 1 in order to suppress the density unevenness of the image formed on the paper will be described with reference to FIG.

  First, when the user of the image forming apparatus 1 performs an operation for instructing correction of toner image density unevenness in the operation unit 15, the control unit 11 controls each unit to form an image of a test chart on a sheet (step). SA1). Specifically, the control unit 11 supplies image data of a predetermined test chart to the image processing unit 12. The image processing unit 12 generates image data of each color of Y, M, C, and K according to the supplied image data. The image processing unit 12 supplies Y image data to the image forming engine 21Y, and supplies M image data to the image forming engine 21M. Further, the image processing unit 12 supplies the C image data to the image forming engine 21C, and supplies the K image data to the image forming engine 21K. When image data is supplied to the image forming engine 21Y, the image forming engine 21M, the image forming engine 21C, and the image forming engine 21K, the image forming unit 13 transfers a toner image corresponding to the supplied image onto a sheet, and The image is fixed on the paper, and the paper on which the toner image is fixed is discharged from the image forming apparatus 1.

  FIG. 5 is a diagram illustrating an example of a test chart that the image forming apparatus 1 forms on a sheet. The test chart includes a test image CY, a test image CM, a test image CC, and a test image CK. The test image CY is an image formed only with yellow toner, and the test image CM is an image formed only with magenta toner. The test image CC is an image formed only with cyan toner, and the test image CK is an image formed only with black toner.

  Each test image includes a rectangular image G1 formed based on a predetermined first density and a rectangular image G2 formed based on a predetermined second density along the main scanning direction. Have. In the present embodiment, the first concentration is higher than the second concentration. Each test image has a plurality of lines LE. A distance D between adjacent lines LE represents the width of an image obtained by exposure of one chip C. For example, the distance between the line LE at the left end in the main scanning direction in FIG. 5 and the line LE adjacent to the line LE at the left end in the main scanning direction in FIG. 5 corresponds to the width of the image obtained by the exposure of the chip C1. ing.

  When the test chart is discharged from the image forming apparatus 1, the user of the image forming apparatus 1 sets the discharged test chart in the scan unit 14 and performs an operation for instructing reading of the test chart on the operation unit 15. When this operation is performed, the control unit 11 controls the scanning unit 14 to read the test chart, and acquires the density of the test chart in units of chip C (step SA2).

  Specifically, when the scanning unit 14 reads the test chart, image data representing the read test chart is supplied to the control unit 11. This image data is in a bitmap format, and each pixel has density information based on the RGB color system. The image data supplied to the control unit 11 is stored in the storage unit 17. Here, as shown in FIG. 6, the areas A1 to An indicated by dotted lines are images obtained by exposure of the chips C1 to Cm. When the image data is supplied, the control unit 11 (density specifying unit 111) calculates the density of each test image in units of chip C. For example, for the test image CY, the control unit 11 calculates the average value of the R (red) density, the average value of the G (green) density, and the average value of the B (blue) density of the area A1 corresponding to the chip C1. calculate. The control unit 11 also calculates an average density value for each RGB color for the regions A2 to Am of the test image CY. The control unit 11 also calculates an average density value for each of the RGB colors for the regions A1 to Am for the test image CM, the test image CC, and the test image CK.

  Next, the control unit 11 (density specifying unit 111) develops data used for suppressing density unevenness of the image formed on the sheet in the RAM (step SA3). FIG. 7 is a diagram showing an example of data expanded in the RAM by the process of step SA3. Specifically, the control unit 11 calculates the average density of B (blue) in the areas A1 to Am among the average densities of RGB colors obtained from the areas A1 to Am of the test image CY to the average density Y_B [1] to Y_B [1]. [M] is expanded in the RAM. Further, the control unit 11 calculates the average density of G (green) in the areas A1 to Am among the average densities of RGB colors obtained from the areas A1 to Am of the test image CM as the average density M_G [1] to [m]. To RAM. Further, the control unit 11 calculates the average density of R (red) in the areas A1 to Am among the average densities of RGB colors obtained from the areas A1 to Am of the test image CC as the average density C_R [1] to [m]. To RAM. Further, the control unit 11 calculates the average density of green (G) in the areas A1 to Am among the average densities of RGB colors obtained from the areas A1 to Am of the test image CK as the average density K_G [1] to [m]. To RAM.

  When the process of step SA3 is completed, the control unit 11 (density specifying unit 111) determines whether there is a value outside the predetermined range in the average density developed in the RAM (step SA4). For example, when dust adheres to the read test chart or when dust adheres to the scan unit 14, the image data generated by the scan unit 14 includes a dust image. In such a case, the density of the portion where the dust image is present differs from the other portions, and the average density is outside the predetermined range. When there is a value outside the predetermined range in the average density developed in the RAM (YES in step SA4), the control unit 11 displays an error screen for notifying that the scan result of the test chart is abnormal. The operation unit 15 is controlled to be displayed on the touch panel 15 (step SA6).

  On the other hand, when there is no value outside the predetermined range in the average density developed in the RAM (NO in step SA4), the control unit 11 (density specifying unit 111) sets the average density value to L * a * b. The value is converted to a color system value of * (step SA5). Here, the control unit 11 converts the values of the average densities Y_B [1] to [m] into b * values, and stores the obtained b * values as Y_b * [1] to [m]. Further, the control unit 11 converts the values of the average densities M_G [1] to [m] into L * values, and stores the obtained L * values as M_L * [1] to [m]. In addition, the control unit 11 converts the values of the average densities C_R [1] to [m] into L * values, and stores the obtained L * values as C_L * [1] to [m]. In addition, the control unit 11 converts the average density values K_G [1] to [m] into L * values, and stores the obtained L * values as K_L * [1] to [m]. As a method for converting the average density value into the L * a * b * color system value, for example, the RGB color system density value is converted into the L * a * b * color system value. A conversion table is stored in the storage unit 17, and values are converted using this conversion table.

When finishing the process of step SA5, the control unit 11 (correction amount specifying unit 112) corrects the values of Y_b *, M_L *, C_L *, and K_L * related to the even chip (step SA7). Specifically, first, Y_b * [1] to [m], M_L * [1] to [m], C_L [1] to [m] *, and K_L * [1] to [m] related to the chips C1 to Cm. m], Y_b * [1] to [m] before correction, M_L * [1] to [m] before correction, C_L * [1] to [m] before correction, and K_L * [1] to before correction. Copy to RAM as [m]. Next, the control unit 11 corrects the values of Y_b *, M_L *, C_L *, and K_L * related to the even-numbered chips using the following equations (1) to (4).
Y_b * [i] = (Y_b * [i + 1] −Y_b * [i−1]) ÷ 2 + Y_b * [i−1] (1)
M_L * [i] = (M_L * [i + 1] −M_L * [i−1]) ÷ 2 + M_L * [i−1] (2)
C_L * [i] = (C_L * [i + 1] −C_L * [i−1]) ÷ 2 + C_L * [i−1] (3)
K_L * [i] = (K_L * [i + 1] −K_L * [i−1]) ÷ 2 + K_L * [i−1] (4)

  In step SA7, the control unit 11 sets the initial value of i to 2 and increases the value of i by two. When the value of i exceeds m−2, the correction for the even-numbered chip is terminated. FIG. 8 is a diagram for explaining the correction operation in step SA7. For example, when the value of Y_b * [2] related to the chip C2 is related to Y_b * [1] related to the chip C1 and Y_b * [3] related to the chip C3 as shown on the left side of FIG. ), The value of Y_b * [2] related to the chip C2 is corrected, as shown on the right side of FIG. 8, the Y_b * [2] of the chip C2 becomes Y_b * [1] of the chip C1 and the chip C3. Is corrected to an average value with Y_b * [3].

When finishing the process of step SA7, the control unit 11 (correction amount specifying unit 112) corrects the values of Y_b *, M_L *, C_L *, and K_L * related to the odd-numbered chip (step SA8). Specifically, in the above formulas (1) to (4), when the initial value of i is set to 3, the value of i is incremented by two, and the value of i exceeds the number m of chips C. Then, the correction related to the odd-numbered chip is finished.
When the processes of step SA7 and step SA8 are completed, the values of Y_b *, M_L *, C_L *, and K_L * for each chip C are Y_b *, M_L *, C_L * and the chip C adjacent to each other in the main scanning direction. The state is corrected so that the difference is small with respect to the value of K_L *.

  Next, the control unit 11 corrects the values of Y_b *, M_L *, C_L *, and K_L * related to each chip C based on the densities of the end portions of the regions A1 to Am (step SA9). FIG. 9 is a flowchart showing the flow of processing performed by the control unit 11 in step SA9. First, the control unit 11 (the density specifying unit 111) analyzes the image data of the test chart stored in the storage unit 17 in step SA2, and each of the areas A1 to Am for each of the image CY, the image CM, the image CC, and the image CK. The density of R (red), G (green), and B (blue) at both ends is specified (step SB1). Next, the control unit 11 selects an image to be used for correction from the image CY, the image CM, the image CC, and the image CK (step SB2), and initializes the value of the variable i that becomes a counter for repeated processing. 1 (step SB3).

  After step SB3, the controller 11 determines that the difference between the density of the edge of the area Ai of the selected image and the density of the edge of the area Ai + 1 adjacent to the area Ai on the area Ai side is greater than or equal to a predetermined threshold. It is determined whether or not there is (step SB4). This threshold value is a value at which, for example, the difference in density is visible to the human eye. When it is determined NO in step SB4, the control unit 11 determines whether i = m−1, that is, whether the value of i is the number of chips C−1 (step SB6). When the value of i is not m−1 (NO in step SB6), the control unit 11 increments the value of i (step SB7), and returns the process flow to step SB4.

  On the other hand, when the control unit 11 determines YES in Step SB4, the control unit 11 calculates the average density corrected in Steps SA7 and SA8 in the area Ai + 1 adjacent to the area Ai + 1 and the density at the end of the area Ai on the area Ai + 1 side. Correction is performed based on the difference from the density of the end of the area on the area Ai side (step SB5).

  For example, the control unit 11 determines that the image selected in step SB2 is the image CY, i = 2, and the density at the end of the region A2 side of the region A2 of the image CY and the region A2 side of the region A3 of the image CY If the difference in the density at the end is greater than or equal to the threshold value, YES is determined in step SB4. Then, the control unit 11 determines the blue density (first density) at the end on the area A3 side of the area A2 of the image CY and the blue density (second density) at the end on the area A2 side of the area A3 of the image CY. It converts into the value of b *, and calculates the difference between the first density and the second density. When the second density is −a with respect to the first density, the control unit 11 adds the calculated absolute value of Y_b * [3] to the second density with respect to the first density. Is + a, the calculated difference is subtracted from Y_b * [3].

  For example, the control unit 11 determines that the image selected in step SB2 is the image CM, i = 2, and the density at the end of the region A2 side of the region A2 of the image CM and the region of the region A3 of the image CM. If the density difference at the end on the A2 side is greater than or equal to the threshold value, YES is determined in step SB4. Then, the control unit 11 determines the green density (first density) at the end of the area A2 of the image CM in the area A3 and the green density (second density) at the end of the area A3 of the image CM in the area A2. It converts into the value of L *, and calculates the difference between the first density and the second density. When the second density is −b with respect to the first density, the control unit 11 adds the absolute value of the calculated difference to M_L * [3], and the second density with respect to the first density. Is + b, the calculated difference is subtracted from M_L * [3].

  For example, the control unit 11 determines that the image selected in step SB2 is the image CC, i = 2, and the density at the end of the region A2 of the region A2 of the image CC and the region A3 of the image CC. If the density difference at the end on the A2 side is greater than or equal to the threshold value, YES is determined in step SB4. Then, the control unit 11 sets the red density (first density) at the end of the area A3 of the image CC on the area A3 side and the red density (second density) of the end of the area A3 on the area A2 of the image CC. It converts into the value of L *, and calculates the difference between the first density and the second density. When the second density is −c with respect to the first density, the control unit 11 adds the absolute value of the calculated difference to C_L * [3], and the second density with respect to the first density. Is + c, the calculated difference is subtracted from C_L * [3].

  In addition, for example, the control unit 11 determines that the image selected in step SB2 is the image CK, i = 2, the density at the end of the region A3 side of the region A2 of the image CK, and the region of the region A3 of the image CK If the density difference at the end on the A2 side is greater than or equal to the threshold value, YES is determined in step SB4. Then, the control unit 11 determines the green density (first density) at the end of the area A3 in the area A2 of the image CK and the green density (second density) at the end of the area A3 in the area A3 of the image CK. It converts into the value of L *, and calculates the difference between the first density and the second density. When the second density is −d with respect to the first density, the control unit 11 adds the calculated absolute value of K_L * [3] to the second density with respect to the first density. Is + d, the calculated difference is subtracted from K_L * [3].

  When the process of step SB5 is completed, the control unit 11 determines whether i = m−1 (step SB6). When the value of i is not m−1 (NO in step SB6), the control unit 11 increments the value of i (step SB7), and returns the process flow to step SB4. When the value of i is m−1 (YES in Step SB6), the control unit 11 determines whether all of the image CY, the image CM, the image CC, and the image CK have been selected (Step SB8). When it is determined NO in step SB8, the control unit 11 returns the process flow to step SB2 and selects an image that is not used for correction. When the control unit 11 finishes selecting all of the image CY, the image CM, the image CC, and the image CK (YES in step B8), the control unit 11 ends the process of FIG. 9 and moves the process flow to step SA10.

  When finishing the process of step SA9, the control unit 11 (correction amount specifying unit 112) corrects Y_b * [1] to [m], M_L * [1] to [m], and C_L * [1 after step SA9. ] To [m] and K_L * [1] to [m], Y_b * [1] to [m] before correction, M_L * [1] to [m] before correction, C_L * [1] before correction The difference between ~ [m] and the values of K_L * [1] to [m] before correction is calculated (step SA10). Specifically, the control unit 11 obtains a difference between Y_b * [1] to [m] after correction and Y_b * [1] to [m] before correction, and the obtained difference is ΔY_b * [1] to [Y]. [M] is stored in the RAM. Moreover, the control part 11 calculates | requires the difference of M_L * [1]-[m] after correction | amendment, and M_L * [1]-[m] before correction | amendment, and calculates | requires the calculated | required difference (DELTA) M_L * [1]-[m]. Is stored in the RAM. Moreover, the control part 11 calculates | requires the difference of C_L * [1]-[m] after correction | amendment, and C_L * [1]-[m] before correction | amendment, and calculates | requires the calculated difference to (DELTA) C_L * [1]-[m]. Is stored in the RAM. Moreover, the control part 11 calculates | requires the difference of K_L * [1]-[m] after correction | amendment, and K_L * [1]-[m] before correction | amendment, and calculates | requires the calculated | required difference (DELTA) K_L * [1]-[m]. Is stored in the RAM. For example, the control unit 11 stores the difference between Y_b * [1] after correction and Y_b * [1] before correction in the RAM as ΔY_b * [1].

When the control unit 11 (correction amount specifying unit 112) finishes the process of step SA10, the control unit 11 (correction amount specifying unit 112) calculates the correction amount of the light amount output from the chips C1 to Cm of the exposure apparatus 33 (step SA11).
Specifically, Y_Δ light amounts [1] to [m] representing the correction amounts of the light amounts output from the chips C1 to Cm of the exposure apparatus 33Y are calculated using the equation (5).
Y_Δ light quantity [i] = (ΔY_b * [i] ÷ Y_light quantity sensitivity) × (Y_light quantity gain ÷ 100) (5)
The control unit 11 sets the initial value of i to 1 and increases the value of i one by one. When the value of i exceeds m, the calculation of Y_Δ light quantity [i] is terminated.

Here, the Y_light quantity gain is a coefficient predetermined for the exposure apparatus 33Y and is stored in the storage unit 17. The Y_light quantity sensitivity is a coefficient corresponding to the photosensitivity of the photosensitive drum 31 </ b> Y and is stored in the storage unit 17. The Y_light quantity sensitivity represents how much the b * value of yellow changes when the quantity of light is changed by a predetermined amount (for example, 1% of the quantity of light that can be output). The photosensitivity of the photosensitive drum 31 varies depending on the film thickness of the photosensitive drum 31. For this reason, in the present embodiment, as shown in FIG. 10, a table storing Y_light quantity sensitivity corresponding to the film thickness of the photosensitive drum 31Y is stored in the storage unit 17, and the controller 11 Y_light quantity sensitivity corresponding to the film thickness of the body drum 31Y is acquired from the table, and Y_Δ light quantity [i] is calculated.
In other words, the control unit 11 includes a plurality of methods for specifying the Y_Δ light quantity [i] corresponding to the film thickness (image forming process state) of the photosensitive drum 31Y, and corresponds to the film thickness state. The selected method is selected, and Y_Δ light quantity [i] is specified by the selected method.

Further, the control unit 11 calculates M_Δ light amounts [1] to [m] representing the correction amounts of the light amounts output from the chips C1 to Cm of the exposure apparatus 33M using the formula (6).
M_Δlight quantity [i] = (ΔM_L * [i] ÷ M_light quantity sensitivity) × (M_light quantity gain ÷ 100) (6)
The control unit 11 sets the initial value of i to 1 and increases the value of i one by one. When the value of i exceeds m, the calculation of the M_Δ light quantity [i] ends.

Here, the M_light quantity gain is a coefficient predetermined for the exposure apparatus 33M, and is stored in the storage unit 17. The M_light quantity sensitivity is a coefficient corresponding to the photosensitivity of the photosensitive drum 31 </ b> M and is stored in the storage unit 17. The M_light quantity sensitivity represents how much the value of L * of magenta changes when the quantity of light is changed by a predetermined amount (for example, 1% of the quantity of light that can be output). As shown in FIG. 10, the M_light quantity sensitivity is also stored in a table in accordance with the film thickness of the photosensitive drum 31M, as with the Y_light quantity sensitivity, and the control unit 11 determines the film thickness of the photosensitive drum 31M. M_light quantity sensitivity corresponding to is obtained from the table and M_Δ light quantity [i] is calculated.
In other words, the control unit 11 includes a plurality of methods for specifying the M_Δ light quantity [i] corresponding to the film thickness (image forming process state) of the photosensitive drum 31M, and corresponds to the film thickness state. The selected method is selected, and the M_Δ light quantity [i] is specified by the selected method.

Further, the control unit 11 calculates C_Δ light amounts [1] to [m] representing the correction amount of the light amount output from the chips C1 to Cm of the exposure apparatus 33C using the formula (7).
C_Δ light quantity [i] = (ΔC_L * [i] ÷ C_light quantity sensitivity) × (C_light quantity gain ÷ 100) (7)
The control unit 11 sets the initial value of i to 1, increases the value of i one by one, and ends the calculation of the C_Δ light quantity [i] when the value of i exceeds m.

Here, the C_light quantity gain is a coefficient predetermined for the exposure apparatus 33 </ b> C, and is stored in the storage unit 17. The C_light quantity sensitivity is a coefficient corresponding to the photosensitivity of the photosensitive drum 31 </ b> C and is stored in the storage unit 17. C_light quantity sensitivity represents how much the L * value of cyan changes when the light quantity is changed by a predetermined amount (for example, 1%). As shown in FIG. 10, the C_light quantity sensitivity is also stored in the table in accordance with the film thickness of the photosensitive drum 31C in the same manner as the Y_light quantity sensitivity, and the control unit 11 determines the film thickness of the photosensitive drum 31C. C_light quantity sensitivity corresponding to is obtained from the table and C_Δ light quantity [i] is calculated.
In other words, the control unit 11 includes a plurality of methods for specifying the C_Δ light quantity [i] corresponding to the film thickness (image forming process state) of the photosensitive drum 31C, and corresponds to the film thickness state. The selected method is selected, and C_Δ light quantity [i] is specified by the selected method.

Further, the control unit 11 calculates K_Δ light amounts [1] to [m] representing the correction amounts of the light amounts output from the chips C1 to Cm of the exposure apparatus 33K using the equation (8).
K_Δlight quantity [i] = (ΔK_L * [i] ÷ K_light quantity sensitivity) × (K_light quantity gain ÷ 100) (8)
The control unit 11 sets the initial value of i to 1, increases the value of i one by one, and ends the calculation of the K_Δ light quantity [i] when the value of i exceeds m.

Here, the K_light quantity gain is a coefficient predetermined for the exposure apparatus 33 </ b> K, and is stored in the storage unit 17. The K_light quantity sensitivity is a coefficient corresponding to the photosensitivity of the photosensitive drum 31 </ b> K and is stored in the storage unit 17. The K_light quantity sensitivity represents how much the value of black L * changes when the quantity of light is changed by a predetermined amount (for example, 1% of the quantity of light that can be output). As shown in FIG. 10, the K_light quantity sensitivity is stored in the table in accordance with the film thickness of the photosensitive drum 31 </ b> K similarly to the Y_light quantity sensitivity, and the control unit 11 determines the film thickness of the photosensitive drum 31 </ b> K. K_light quantity sensitivity corresponding to is obtained from the table and K_Δ light quantity [i] is calculated.
In other words, the control unit 11 includes a plurality of methods for specifying the K_Δ light amount [i] corresponding to the film thickness (image forming process state) of the photosensitive drum 31K, and corresponds to the film thickness state. The selected method is selected, and the K_Δ light quantity [i] is specified by the selected method.

When the control unit 11 (correction unit 113) finishes the process of step SA11, the control unit 11 (correction unit 113) acquires data to be supplied to the drive circuit 330 in order to change the light amount of the chips C1 to Cm by the correction amount calculated in step SA11 ( Step SA12).
Specifically, the storage unit 17 stores a table in which a correction amount of light amount is associated with data supplied to the drive circuit 330 in order to change the light amount by the correction amount. The control unit 11 acquires the corresponding data from the table for each calculated Y_Δ light quantity [1] to [m] and sets it as correction data Ydata [1] to [m]. Further, the control unit 11 obtains corresponding data from the table for each of the calculated M_Δ light amounts [1] to [m] and sets them as correction data Mdata [1] to [m]. Further, the control unit 11 obtains corresponding data from the table for each calculated C_Δ light quantity [1] to [m] and sets it as correction data Cdata [1] to [m]. In addition, the control unit 11 acquires corresponding data from the table for each calculated K_Δ light amount [1] to [m], and sets the data as correction data Kdata [1] to [m]. That is, the control unit 11 acquires correction data for correcting the light amount for each of the chips C1 to Cm of the exposure apparatus 33Y, the exposure apparatus 33M, the exposure apparatus 33C, and the exposure apparatus 33K.

  When the process of step SA12 is completed, the control unit 11 (correction unit 113) supplies the correction data acquired in step SA11 to the drive circuit 330 of the exposure apparatus 33 (step SA13). Specifically, the control unit 11 supplies the correction data Ydata [1] to [m] to the drive circuit 330Y, and supplies the correction data Mdata [1] to [m] to the drive circuit 330M. Further, the control unit 11 supplies the correction data Cdata [1] to [m] to the drive circuit 330C, and supplies the correction data Kdata [1] to [m] to the drive circuit 330K. Each drive circuit 330 drives the chips C1 to Cm in accordance with the supplied correction data, and controls the amount of light output from the chips C1 to Cm. For example, the drive circuit 330Y controls the chip C2 based on the correction data Ydata [2]. Thereby, the light quantity of the chip C2 changes by the amount of Y_Δ light quantity [2].

  According to the present embodiment, by the processing of FIG. 10, between adjacent chips, the light quantity of the LED at the other chip side end in one chip C and the LED at the one chip side end in the other chip Since the light amount is corrected so as to reduce the difference from the light amount, the occurrence of uneven density can be suppressed.

[Modification]
As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above, It can implement with another various form. For example, the present invention may be implemented by modifying the above-described embodiment as follows. In addition, you may combine each of embodiment mentioned above and the following modifications.

  In the embodiment described above, after step SA8, the values of Y_b *, M_L *, C_L *, and K_L * related to each chip C are corrected based on the densities of the end portions of the areas A1 to Am. The timing for performing the process of step SA9 is not limited to the timing of the embodiment. For example, in the modified example, in the process of FIG. 4, after step SA8, the process of step SA10 to step SA13 is performed without performing the process of step SA9. Next, the control unit 11 performs the processing shown in FIG. Note that the processing in step SC1 to step SC6 in FIG. 11 is the same as the processing in step SA1 to step SA6 described above, and a description thereof will be omitted.

  Next, the control unit 11 performs Y_b * [1] to [m], M_L * [1] to [m], C_L [1] to [m] *, and K_L * related to the chips C1 to Cm stored in Step SC5. The values of [1] to [m] are set to Y_b * [1] to [m] before correction, M_L * [1] to [m] before correction, C_L * [1] to [m] before correction, and K_L before correction. * Copy to RAM as [1] to [m] (step SC7).

Next, the control unit 11 corrects the values of Y_b *, M_L *, C_L *, and K_L * related to each chip C based on the densities of the end portions of the regions A1 to Am (step SC8). The process of step SC8 is the same as the process of step SA9, and here, the control unit 11 executes the process shown in FIG. When the process of step SC8 is completed, control unit 11 performs the processes of steps SC9 to SC12. In addition, since the process of step SC9-step SC12 is the same as the process of step SA10-step SA13 mentioned above, the description is abbreviate | omitted.
Also in this modification, as in the above-described embodiment, the difference between the light amount of the LED at the other chip side end in one chip C and the light amount of the LED at the one chip side end in the other chip. Since the amount of light is corrected so as to reduce the density, the occurrence of uneven density can be suppressed.

  In the process of FIG. 9, the control unit 11 returns the process flow to step SB4 after step SB7. However, instead of returning to step SB4, the control unit 11 may return to step SB5.

  In the above-described embodiment, after correcting Y_b *, M_L *, C_L *, and K_L * values for even chips, correction of Y_b *, M_L *, C_L *, and K_L * values for odd chips is performed. However, after correcting the Y_b *, M_L *, C_L * and K_L * values related to the odd-numbered chips, the Y_b *, M_L *, C_L * and K_L * values related to the even-numbered chips are corrected. It is good also as a structure to perform.

In the embodiment described above, when correcting the values of Y_b *, M_L *, C_L *, and K_L * related to the chip C in step SA7 and step SA8, the Y_b *, M_L *, C_L *, and the adjacent chip C are corrected. The value is corrected based on the value of K_L *, but based on the values of Y_b *, M_L *, C_L * and K_L * of the chip C within a predetermined range from the chip of interest as a chip to be corrected. For example, the values of Y_b *, M_L *, C_L *, and K_L * may be corrected by the following equations (9) to (12).
Y_b * [i] = (Y_b * [i + 2] −Y_b * [i−2]) ÷ 2 + Y_b * [i−2] (9)
M_L * [i] = (M_L * [i + 2] −M_L * [i−2]) ÷ 2 + M_L * [i−2] (10)
C_L * [i] = (C_L * [i + 2] −C_L * [i−2]) ÷ 2 + C_L * [i−2] (11)
K_L * [i] = (K_L * [i + 2] −K_L * [i−2]) ÷ 2 + K_L * [i−2] (12)

  In the above-described embodiment, the values of Y_b *, M_L *, C_L *, and K_L * are corrected by linear approximation using the equations (1) to (4), but Y_b *, M_L *, C_L *, and The method for correcting the value of K_L * is not limited to linear approximation. For example, the values of Y_b *, M_L *, C_L *, and K_L * may be corrected by polynomial approximation.

  In the above-described embodiment, the image forming apparatus 1 is configured to use dry toner, but may be configured to use liquid toner, that is, to perform liquid development. In the above-described embodiment, the image forming apparatus 1 is an apparatus that forms an image on a sheet by an electrophotographic method, but is not limited to the electrophotographic method. For example, in a single-pass inkjet printer having a plurality of print heads, the correction amount of the density of the image formed by the odd-numbered print heads in the main scanning direction and the even-numbered ink jets according to the result of reading the test chart. The correction amount of the density of the image formed by the print head may be obtained, and the drive of the print head may be controlled according to the obtained correction amount.

In the above-described embodiment, in step SA10, the Y_light quantity sensitivity, M_light quantity sensitivity, C_light quantity sensitivity, and K_light quantity sensitivity are set in accordance with the film thickness of the photosensitive drum 31. However, the present invention is not limited to this configuration. Absent.
For example, instead of changing the values of Y_light quantity sensitivity, M_light quantity sensitivity, C_light quantity sensitivity, and K_light quantity sensitivity according to the film thickness, a predetermined fixed value may be used.
In the present invention, a plurality of reference light amounts (reference light amounts) are set, and the reference light amount is selected and selected according to the state of the image forming unit 13 (for example, the temperature in the image forming unit 13). A configuration in which the light amount is corrected around the light amount may be employed. In this case, the values of Y_light quantity sensitivity, M_light quantity sensitivity, C_light quantity sensitivity, and K_light quantity sensitivity may be changed according to the selected light quantity.
Alternatively, the Y_light quantity sensitivity, M_light quantity sensitivity, C_light quantity sensitivity, and K_light quantity sensitivity values may be changed according to the light potential or dark potential of the photosensitive drum 31 and the bias voltage of the developing device 34.
Further, the Y_light quantity sensitivity, M_light quantity sensitivity, C_light quantity sensitivity, and K_light quantity sensitivity values are changed in accordance with the state of toner in the developing unit 34 (how much toner is contained in the developing unit 34). Also good.

In the above-described embodiment, values of Y_light quantity sensitivity, M_light quantity sensitivity, C_light quantity sensitivity, and K_light quantity sensitivity are acquired using a table, but the present invention is not limited to this configuration. For example, in the configuration in which the values of Y_light quantity sensitivity, M_light quantity sensitivity, C_light quantity sensitivity, and K_light quantity sensitivity are changed according to the film thickness of the photosensitive drum 31, a coefficient corresponding to the film thickness with respect to a predetermined initial value. The values of Y_light quantity sensitivity, M_light quantity sensitivity, C_light quantity sensitivity, and K_light quantity sensitivity may be acquired by multiplying.
Further, in the present invention, image formation such as the reference light quantity of light output from the chips C1 to Cm, the light and dark potentials of the photosensitive drum 31, the bias voltage of the developing device 34, the ratio of toner in the developing device 34, and the like. According to the state of the unit 13, formulas for obtaining values of Y_light quantity sensitivity, M_light quantity sensitivity, C_light quantity sensitivity, and K_light quantity sensitivity are set, and formulas corresponding to the parameters are selected and Y_light quantity sensitivity, M_light quantity sensitivity, C_ You may make it acquire the value of light quantity sensitivity and K_light quantity sensitivity.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 ... Control part, 12 ... Image processing part, 13 ... Image forming part, 14 ... Scan part, 15 ... Operation part, 16 ... Communication part, 17 ... Memory | storage part, 21K, 21C, 21M, 21Y DESCRIPTION OF SYMBOLS Image forming engine 31 ... Photoconductor drum 33 ... Exposure device 111 ... Density specifying unit 112 ... Correction amount specifying unit 113 ... Correction unit 330 ... Driving circuit C1-Cm ... Chip, CY, CM, CC CK: Test image L1-Ln: Light emitting element

Claims (3)

A plurality of chips having a plurality of light emitting elements are arranged in the main scanning direction, the image holding member is exposed by the light emitting elements, and the electrostatic latent image formed on the image holding member by the exposure is developed to form an image on a recording medium. An image forming unit for forming
A fixing unit for fixing an image formed on the recording medium;
A reading unit for reading an image fixed on the recording medium by the fixing unit;
In the image read by the reading unit, a density specifying unit that specifies the density of the end in the main scanning direction of the region corresponding to the chip for each of the plurality of chips;
The chips are sequentially selected, and the correction amount of the amount of light emitted from the second chip adjacent to the selected first chip in the main scanning direction is the density specified by the density specifying unit and corresponds to the first chip. A correction amount specifying unit that is specified by the difference between the density at the end of the region and the density at the end of the region corresponding to the second chip, the density specified by the density specifying unit;
An image forming apparatus comprising: a correction unit that corrects the amount of light emitted from the chip according to the correction amount specified by the correction amount specifying unit. When the difference between the density of the edge of the area corresponding to the first chip and the density of the edge of the area corresponding to the second chip is equal to or greater than a predetermined threshold, The image forming apparatus according to claim 1, wherein a correction amount is specified. The image forming apparatus according to claim 1, wherein the correction amount specifying unit sequentially specifies the correction amounts for all unselected chips when the correction amount is specified for one of the chips.

Images