Exposure device and image formation device

Abstract

To provide a technique advantageous for suppressing deterioration of image quality.SOLUTION: An exposure device includes a light-emitting chip including a plurality of light-emitting elements, and a light-emitting control part, wherein the plurality of light-emitting elements is divided into a plurality of blocks in a row direction, and is driven by a driving circuit arranged corresponding to a belonging block, the light-emitting control part controls the light-emitting elements so as to form an electrostatic latent image constituted of a plurality of spots in a photoreceptor, each of the plurality of spots is formed of a predetermined number of light-emitting elements, the number of light-emitting elements forming at least the one spot among the plurality of spots is changed from the predetermined number of light-emitting elements, according to correction data for correcting the width in the axial direction of an image, the position of the spot of the other part is shifted, and at least the one spot is formed using the light-emitting elements excluding the light-emitting elements arranged on rows at both ends in the row direction of each of the blocks.SELECTED DRAWING: Figure 10A

Description

[Technical Field]

[0001] The present invention relates to an exposure device and an image forming apparatus. [Background technology]

[0002] An electrophotographic image forming apparatus forms an image by exposing a rotating photoreceptor to light to form an electrostatic latent image on the photoreceptor, and then developing the formed electrostatic latent image with toner. Patent Document 1 discloses an image forming apparatus equipped with an exposure device using organic electroluminescence (EL) elements. Patent Document 1 also discloses a technology for compensating for image misalignment caused by variations in the mounting position of light-emitting chips on the substrate of the exposure head of the exposure device and thermal expansion of the substrate. Patent Document 2 discloses a light-emitting chip equipped with multiple groups, each group consisting of multiple light-emitting elements and a drive circuit that drives them. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-031853 [Patent Document 2] Japanese Patent Publication No. 2022-162410 Summary of the Invention [Problem to be solved by the invention]

[0004] In light-emitting chips that make up a group such as that shown in Patent Document 2, when data is inserted or thinned out to compensate for magnification errors, unevenness caused by compensation for magnification errors may be visible depending on the position where the data is inserted or thinned out.

[0005] An object of the present invention is to provide a technique that is advantageous in suppressing degradation of image quality. [Means for solving the problem]

[0006] In view of the above problems, an exposure device according to an embodiment of the present invention is an exposure device comprising: a light-emitting chip having a plurality of light-emitting elements arranged in a plurality of rows and a plurality of columns, with the row direction aligned along the axial direction of a photosensitive body; and a light-emitting control unit for controlling the light-emitting chip; wherein the light-emitting region in which the plurality of light-emitting elements are arranged is divided into a plurality of blocks aligned along the row direction, and each light-emitting element is driven by a drive circuit arranged corresponding to the block to which it belongs; the light-emitting control unit controls the plurality of light-emitting elements so that an electrostatic latent image for forming an image, consisting of a plurality of spots, is formed on the photosensitive body while the photosensitive body rotates; each of the plurality of spots is formed by a predetermined number of light-emitting elements among the plurality of light-emitting elements; the number of light-emitting elements forming at least one of the plurality of spots is changed from the predetermined number according to correction data for correcting the axial width of the image; and the positions of some of the other spots are shifted according to the change in the number of light-emitting elements forming the at least one spot; and the at least one spot is formed using light-emitting elements among the plurality of light-emitting elements excluding the light-emitting elements arranged in the columns at both ends of the row direction of each block. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a technique that is advantageous in suppressing degradation of image quality. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an image forming apparatus using an exposure apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of a photosensitive member and an exposure head according to the present embodiment. [Figure 3] FIG. 2 is a diagram showing an example of the configuration of a printed circuit board of an exposure head according to the present embodiment. [Figure 4] 1A and 1B are diagrams showing a configuration example of a light-emitting chip according to an embodiment of the present invention; [Figure 5] FIG. 2 is a circuit diagram showing an example of a configuration for controlling the light-emitting chip of the present embodiment. [Figure 6] FIG. 2 is a block diagram showing a configuration example of the light-emitting chip according to the embodiment. [Figure 7] FIG. 2 is a circuit diagram showing a configuration example of a drive circuit for the light-emitting chip according to the embodiment. [Figure 8] 1A to 1C are diagrams illustrating multiple exposure using the light-emitting chip of the present embodiment. [Figure 9A] 5A to 5C are diagrams for explaining light emission control based on image data of the exposure apparatus of the present embodiment. [Figure 9B] 5A to 5C are diagrams for explaining light emission control based on image data of the exposure apparatus of the present embodiment. [Figure 9C] 5A to 5C are diagrams for explaining light emission control based on image data of the exposure apparatus of the present embodiment. [Figure 9D] 5A to 5C are diagrams for explaining light emission control based on image data of the exposure apparatus of the present embodiment. [Figure 10A] 5A and 5B are diagrams for explaining compensation (data insertion) for magnification errors in the exposure apparatus of the present embodiment. [Figure 10B] 5A and 5B are diagrams for explaining compensation (data insertion) for magnification errors in the exposure apparatus of the present embodiment. [Figure 10C] 5A and 5B are diagrams for explaining compensation (data insertion) for magnification errors in the exposure apparatus of the present embodiment. [Figure 10D] 5A and 5B are diagrams for explaining compensation (data insertion) for magnification errors in the exposure apparatus of the present embodiment. [Figure 11A] 5A and 5B are diagrams for explaining compensation (data thinning) of magnification errors in the exposure apparatus of the present embodiment. [Figure 11B] 5A and 5B are diagrams for explaining compensation (data thinning) of magnification errors in the exposure apparatus of the present embodiment. [Figure 11C] 5A and 5B are diagrams for explaining compensation (data thinning) of magnification errors in the exposure apparatus of the present embodiment. [Figure 11D] 5A and 5B are diagrams for explaining compensation (data thinning) of magnification errors in the exposure apparatus of the present embodiment. [Figure 12] 5A to 5C are diagrams for explaining compensation of magnification errors in the exposure apparatus of the present embodiment. [Figure 13] FIG. 2 is a layout diagram showing a configuration example of the light-emitting device of the present embodiment. [Figure 14] FIG. 2 is a layout diagram showing an example of an exposure head using the light-emitting device of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0010] An exposure device according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 12. FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus 1 including an exposure device according to this embodiment. The image forming apparatus 1 includes a reading unit 100, an image creating unit 103, a fixing unit 104, and a conveying unit 105. The reading unit 100 optically reads an original placed on a platen and generates read image data. The image creating unit 103 forms an image on a sheet, for example, based on the read image data generated by the reading unit 100 or based on print image data received from an external device via a network. The image creating unit 103 includes image forming units 101a to 101d. The image forming units 101a to 101d can form black, yellow, magenta, and cyan toner images, respectively. The image forming units 101a to 101d can have similar configurations. Therefore, hereinafter, unless a specific image forming unit among the image forming units 101a to 101d is being referred to, the image forming unit 101 may simply be referred to as the image forming unit 101. The photoconductor 102 of the image forming unit 101 is rotated clockwise in FIG. 1 when forming an image. The charger 107 charges the photoconductor 102. The exposure head 106 exposes the photoconductor 102 to light to form an electrostatic latent image on the surface of the photoconductor 102. The developer 108 develops the electrostatic latent image on the photoconductor 102 with toner to form a toner image. The toner image formed on the surface of the photoconductor 102 is transferred to a sheet transported on a transfer belt 111. By transferring the toner images of the four photoconductors 102 onto the sheet in an overlapping manner, a color image containing four color components: black, yellow, magenta, and cyan can be formed. The transport unit 105 controls the feeding and transport of the sheet. More specifically, the conveying unit 105 feeds a sheet from a designated unit among the internal storage units 109a and 109b, the external storage unit 109c, and the manual feed unit 109d to a conveying path of the image forming apparatus 1. The fed sheet is conveyed to the registration rollers 110. The registration rollers 110 convey the sheet onto the transfer belt 111 at an appropriate timing so that the toner images on the photoconductors 102 are transferred onto the sheet. As described above, the toner images are transferred onto the sheet while the sheet is being conveyed on the transfer belt 111.The fixing unit 104 fixes the toner image to the sheet by applying heat and pressure to the sheet onto which the toner image has been transferred. After the toner image has been fixed, the sheet is discharged to the outside of the image forming apparatus 1 by a discharge roller 112. An optical sensor 113 is disposed opposite the transfer belt 111. The optical sensor 113 optically reads a test chart formed on the transfer belt 111 by the image forming unit 101. If an error in the image formation range of the test chart read by the optical sensor 113 is detected, the image controller 500 (described later) performs control to compensate for the error when executing a subsequent job. The above description has been given of an example in which a toner image is directly transferred from each photoconductor 102 to a sheet on the transfer belt 111. However, this is not limited thereto, and the toner image may be indirectly transferred from each photoconductor 102 to a sheet via an intermediate transfer body. Furthermore, while the above description has been given of an example in which a color image is formed using toners of multiple colors, the technology disclosed herein can also be applied to an image forming apparatus that forms a monochrome image using toner of a single color.

[0011] 2(a) and 2(b) are diagrams illustrating the configuration of the exposure head of this embodiment. The exposure head 106 may include a light-emitting element array 201, a printed circuit board 202 on which the light-emitting element array 201 is mounted, a rod lens array 203, and a housing 204 that supports the printed circuit board 202 and the rod lens array 203. The photoconductor 102 has a cylindrical shape. The exposure head 106 is disposed so that its longitudinal direction is parallel to the axial direction D1 of the photoconductor 102 and the surface on which the rod lens array 203 is attached faces the surface of the photoconductor 102. While the photoconductor 102 rotates in the circumferential direction D2, the light-emitting element array 201 of the exposure head 106 emits light, and the rod lens array 203 focuses the light on the surface of the photoconductor 102.

[0012] FIG. 3 is a diagram illustrating the configuration of a printed circuit board of an exposure head according to this embodiment. In this embodiment, the light-emitting element array 201 is divided into 17 light-emitting chips 300-1 to 300-17. The light-emitting chips 300-1 to 300-17 are arranged in a staggered pattern along the axial direction D1 of the photoconductor 102. Hereinafter, unless a specific light-emitting chip among the light-emitting chips 300-1 to 300-17 is indicated, it may be simply referred to as the light-emitting chip 300. The area occupied by all of the light-emitting elements of the 17 light-emitting chips 300 in the axial direction D1 of the photoconductor 102 may be wider than the area occupied by the maximum width W0 of the input image data. Therefore, some light-emitting elements located at both ends of the photoconductor 102 along the axial direction D1 may not be used to expose the photoconductor 102 unless an error in the image formation area is detected. For convenience of explanation, the side with the smaller branch number of the light-emitting chips 300-1 to 300-17 arranged along the axial direction D1 may be referred to as the "left" and the side with the larger branch number as the "right." For example, the light-emitting chip 300-1 is the "leftmost" light-emitting chip 300, and the light-emitting chip 300-17 is the "rightmost" light-emitting chip.

[0013] FIG. 4 is a diagram illustrating a light-emitting chip according to this embodiment and an arrangement of light-emitting elements within the light-emitting chip. FIG. 4 schematically illustrates a light-emitting chip 300 and an arrangement of light-emitting elements 402 arranged in the light-emitting chip 300. In this embodiment, the light-emitting element array 201 includes a plurality of light-emitting elements 402 arranged two-dimensionally to form a plurality of rows and a plurality of columns. The light-emitting element array 201 as a whole includes N columns of light-emitting elements 402 along the axial direction D1 of the photoconductor 102 and M rows of light-emitting elements 402 along the circumferential direction D2 of the photoconductor 102. Here, M and N are integers equal to or greater than 2. In each light-emitting chip 300, the light-emitting elements 402 are arranged in an array to form a plurality of rows and a plurality of columns. The number J (J=N / 17) of light-emitting elements 402 arranged in each row of one light-emitting chip 300 may be, for example, 872 (J=872). Meanwhile, the number M of light-emitting elements 402 arranged in each column of one light-emitting chip 300 may be, for example, 4 (M=4). That is, in an exemplary embodiment, each light-emitting chip 300 includes 872 light-emitting elements 402 arranged in rows along the axial direction D1 of the photoconductor 102 and four light-emitting elements 402 arranged in columns along the circumferential direction D2 of the photoconductor 102, for a total of 3,488 (=872 × 4) light-emitting elements 402. The spacing Pc between the centers of adjacent light-emitting elements 402 in the column direction may be approximately 21.16 μm, corresponding to a resolution of 1,200 dpi, for example. The spacing Pc between the centers of adjacent light-emitting elements 402 in the row direction may also be approximately 21.16 μm, in which case the 872 light-emitting elements 402 occupy a length of approximately 18.5 mm in the row direction. For ease of explanation, FIG. 4 illustrates an example in which the light-emitting elements 402 in each light-emitting chip 300 are arranged in a complete grid pattern. However, in reality, the M (M = 4) light-emitting elements 402 in each column are arranged in a stepped pattern at a fixed pitch in the row direction, with some offsetting. This point will be explained further below.

[0014] 5 is a block diagram of a configuration for controlling the light-emitting chip 300. The image controller 500 is a control circuit that communicates with the printed circuit board 202 via multiple signal lines. The image controller 500 may include a CPU 501, a clock generation unit 502, an image data processing unit 503, a register access unit 504, and a light-emitting control unit 505. The light-emitting control unit 505 is a component that configures an exposure device together with the exposure head 106 provided in the light-emitting chip 300. The light-emitting control unit 505 can also be said to be a control circuit for controlling the light-emitting chip 300.

[0015] The n-th light-emitting chip 300-n (in this embodiment, n is an integer from 1 to 17) on the printed circuit board 202 is connected to the light-emitting control unit 505 via a signal line DATAn and a signal line WRITEn. The signal line DATAn is used to transmit image data from the image controller 500 to the light-emitting chip 300-n. The signal line WRITEn is used by the image controller 500 to write control data to the register of the light-emitting chip 300-n. The CPU 501 controls the entire image forming apparatus 1. The image data processing unit 503 performs image processing on image data received from the reading unit 100 or an external device, and generates binary bitmap image data for controlling the light-emitting elements 402 of the light-emitting chip 300 on the printed circuit board 202 to emit or not emit light. The image data processing unit 503 transmits the generated image data to the light-emitting control unit 505 as input image data. The register access unit 504 receives control data to be written to the register in each light-emitting chip 300 from the CPU 501 and transmits the control data to the light-emitting control unit 505.

[0016] Next, the configuration of the light-emitting chip 300 will be described. FIG. 6 is a circuit block diagram of the light-emitting chip 300 according to this embodiment. The light-emitting chip 300 may include an interface circuit 600, a register 601, a reference current generating circuit 610, a programmable current source 611, a bias current source 612, a current control circuit 613, a drive transistor 614, a data holding circuit 615, and a shift register 616. The interface circuit 600 receives mode information and information related to image data from the light-emission control unit 505 and outputs data signals to the register 601 and the shift register 616. The programmable current source 611 uses the output current of the reference current generating circuit 610 as a reference and outputs an analog current corresponding to a digital value supplied from the register 601 to the bias current source 612. The drive current of the drive transistor 614 is controlled by the setting value of the register 601. The bias current source 612 supplies an output current corresponding to the setting value set in the register 601 to the current control circuit 613. The current control circuit 613 generates a bias voltage for the drive transistor 614. The shift register 616 controls the timing of light emission or non-emission of the light emitting element 402 based on the data signal from the interface circuit 600. The data holding circuit 615 holds information corresponding to each light emitting element 402 and determines whether the light emitting element 402 emits light or not. The drive transistor 614 is connected to the light emitting element 402, and the drive current is determined by the bias voltage supplied from the current control circuit 613, and the light emission or non-emission of the light emitting element is controlled by the signal supplied from the data holding circuit 615.

[0017] FIG. 7 is a circuit diagram focusing on the driving transistor 614 of the light-emitting chip 300 according to this embodiment. Adjustment of the light-emitting current and light-emitting control of the light-emitting element 402 will be described. The bias current source 612 is composed of transistors M0 to Mi. The current control circuit 613 is composed of transistors M1a to Mia and buffers B1 to Bi connected between the gate terminals and drain terminals of the transistors M1a to Mia. The driving transistor 614 is composed of first transistors M11 to Mik and second transistors M111 to Mi1k. The second transistors M111 to Mi1k are connected in series to the light-emitting elements O11 to Oik, respectively. Here, the light-emitting elements O11 to Oik correspond to the above-mentioned light-emitting elements 402.

[0018] In this embodiment, the light-emitting region of the light-emitting chip 300, in which a plurality of light-emitting elements 402 are arranged, is divided into a plurality of blocks 701 arranged in the row direction, and each light-emitting element 402 is driven by a drive circuit arranged corresponding to the block 701 to which it belongs. Of the blocks 701, attention is focused on block 701-1. Block 701-1 includes a transistor M1a of the current control circuit 613, first transistors M11 to M1k and second transistors M111 to M11k of the drive transistor 614, and light-emitting elements O11 to O1k. It can also be said that the light-emitting elements O11 to O1k (light-emitting elements 402) are driven by a drive circuit including the transistor M1a of the current control circuit 613, the first transistors M11 to M1k and second transistors M111 to M11k of the drive transistor 614. Similarly, block 701-i includes transistor Mia of current control circuit 613, first transistors Mi1-Mik of drive transistor 614, second transistor group i11-Mi1k, and light-emitting elements Oi1-Oik. It can also be said that light-emitting elements Oi1-Oik (light-emitting elements 402) are driven by a drive circuit including transistor Mia of current control circuit 613, first transistors Mi1-Mik of drive transistor 614, and second transistors Mi11-Mi1k.

[0019] The output current I of the programmable current source 611out is connected to the drain terminal of the transistor M0 of the bias current source 612. The transistor M0 is diode-connected, and the current I out A bias voltage determined by is commonly applied to the gates of the transistors M0 to Mi.

[0020] In a block 701, for example, block 701-1, the drain terminal of the transistor M1a and the drain terminal of the transistor M1, which constitute the current control circuit 613, are connected in series. The gate terminal of the transistor M1a is connected to the drain terminal of the transistor M1a via a buffer B1. A voltage determined by the current I1 is commonly applied to the gates of the first transistors M11 to M1k. The voltage between the gate and source of the first transistors M11 to M1k is the same, allowing equal drive currents to be supplied to the light-emitting elements O11 to O1k. Although not explicitly shown in FIG. 7, a drive voltage is applied from the data retention circuit 615 to the gates of the second transistors M111 to M11k. This controls whether or not current is supplied to the light-emitting elements O11 to O1k. In other words, the second transistors M111 to M11k function as switches. The light-emitting elements O11 to O1k are driven by the first transistors M11 to M1k and the second transistors M111 to M11k to emit light.

[0021] 4 above shows an example in which the light-emitting elements 402 in each light-emitting chip 300 are completely arranged in a lattice pattern, but in this embodiment, the M light-emitting elements 402 in each column are arranged in a stepped pattern at a constant pitch, with partial offset in the row direction. For example, among the multiple light-emitting elements 402 arranged in each column, at least one light-emitting element 402 may be arranged with partial offset in the row direction. FIG. 8 is a diagram illustrating multiple exposure using the light-emitting elements 402 arranged in a stepped pattern in this embodiment.

[0022] 8 partially illustrates an example of the arrangement of the light-emitting elements 402 in the light-emitting chip 300 when M=4. Rj_m (j={0, 1,..., J-1} (J=872), m={0, 1, 2, 3}) in the figure represents the light-emitting element 402 that is in the j-th column from the left in the row direction of the light-emitting chip 300 along the axial direction D1 of the photoconductor 102 and in the m-th row from the top in the column direction intersecting the row direction. Hereinafter, when referring to a specific light-emitting element 402 that is arranged in the j-th and m-th rows among the light-emitting elements 402, it may be referred to as "light-emitting element Rj_m."

[0023] As described above, the pitch Pc of the light-emitting elements 402 in the column direction may be approximately 21.16 μm. The offset distance in the row direction between two adjacent light-emitting elements 402 among the M light-emitting elements 402 in each column, i.e., the pitch Pa of the light-emitting elements 402 in the row direction, may be approximately 5 μm, corresponding to a resolution of 4800 dpi. By arranging the four light-emitting elements 402 in each column in a stepped manner, any two adjacent light-emitting elements 402 among the four light-emitting elements 402 occupy areas that partially overlap in the row direction. The four light-emitting elements 402 in the column corresponding to each pixel position of the image data sequentially emit light while the photoconductor 102 is rotating, thereby forming spots SP corresponding to each pixel position on the surface of the photoconductor 102. Here, the spots SP corresponding to each pixel position correspond to pixels of the image to be formed on the sheet. The light-emission control unit 505 controls the multiple light-emitting elements 402 so that an electrostatic latent image for forming an image, composed of the multiple spots SP, is formed on the photoconductor 102 while the photoconductor 102 is rotating. It can also be said that each of the plurality of spots SP is formed by a predetermined number (for example, four) of the plurality of light-emitting elements 402.

[0024] In the example shown in FIG. 8, when the pixel value data at the left end of the ith row of the image data indicates that light emission is on, the light-emitting elements R0_0, R0_1, R0_2, and R0_3 sequentially emit light at the timing when they respectively face the line Li on the surface of the photoconductor 102. As a result, the spot area at the left end of the line Li is exposed in a multiplicity manner, and the corresponding spot SP0 is formed. Similarly, when the pixel value data at the jth pixel from the left of the ith row of the input image data indicates that light emission is on, the light-emitting elements Rj_0, Rj_1, Rj_2, and Rj_3 sequentially emit light at the timing when they respectively face the line Li on the surface of the photoconductor 102. As a result, the spot area at the jth pixel from the left of the line Li is exposed in a multiplicity manner, and the corresponding spot SP0 is formed. j In addition, the technology according to the present disclosure is not limited to the example in which the M light-emitting elements in each column are arranged in a stepped pattern so that any two adjacent light-emitting elements 402 partially overlap in the row direction. For example, one light-emitting element among the M light-emitting elements in each column may be arranged shifted in the row direction.

[0025] Next, a procedure for emission control based on image formation data will be described. FIGS. 9A to 9D are diagrams for explaining a procedure for emission control based on image formation data (hereinafter sometimes referred to as image data). At the time of image formation, the emission control unit 505 receives binary bitmap format image data IM1 from the image data processing unit 503. On the left side of FIG. 9A, the pixel value at the j-th pixel from the left in the i-th row of the image data IM1, which is a two-dimensional pixel value array, is denoted as (j, i) (j = {0, 1, 2,...}, i = {0, 1, 2,...}). The emission control unit 505 adds (M - 1) rows of dummy data (pixel values) to the head of the image data IM1. When M = 4, including the added dummy pixel values, the range of the index i of the pixel values becomes {-3, -2, -1, 0, 1, 2,...}. The dummy pixel value may be, for example, a value (e.g., zero) that means emission off. The emission control unit 505 can also add dummy pixel values to the left and right of the image data IM1 so that the number of pixel values in one line is equal to the number of light emitting elements 402 in the row direction. As described above, the range occupied by all the light emitting elements 402 of the 17 light emitting chips 300 in the axial direction D1 of the photoreceptor 102 is wider than the range occupied by the maximum width W0 of the image data IM1 (the number of light emitting elements corresponding to W0 < N (= 17 × J)). However, for simplicity of explanation, only effective pixel values are shown in the figures and the following description.

[0026] Also, in FIGS. 9A to 11D below, the block 701 described using FIG. 7 is also shown with respect to the row direction in which the light emitting elements 402 are arranged. In FIG. 9A, the light emitting elements 402 arranged in the columns of j = 0 to k - 1 belong to the block 701-1. Similarly, the light emitting elements 402 arranged in the columns of j = k to 2k - 1 belong to the block 701-2, and the light emitting elements 402 arranged in the columns of j = 2k to 3k - 1 belong to the block 701-3. Also, the boundary of each block 701 is defined as the block boundary 901.

[0027] During the first line period t0 of image formation (electrostatic latent image formation), the light-emitting control unit 505 reads pixel value data for the top four lines of image data IM1 and outputs data for every 3488 (=872×4) of the read pixel values ​​to the light-emitting chip 300 via signal line DATAn. Focusing on the light-emitting chip 300-1 shown on the right side of FIG. 9A, image data within a read range RD including pixel value data from (0, −3) to (872, 0) is input via signal line DATA1 during the line period t0. The light-emitting chip 300-1 serial-to-parallel converts the input image data and supplies drive signals based on the pixel value data to each of the 3488 light-emitting elements 402. For example, drive signals based on pixel values ​​(0, −3), (0, −2), (0, −1), (0, 0), and (1, −3) are supplied to the light-emitting elements R0_0, R0_1, R0_2, R0_3, and R1_0. A drive signal based on the effective pixel value data of line DL0 of index i=0 in image data IM1 is supplied to the light-emitting elements in the fourth row, including light-emitting element R0_3, which is surrounded by a dashed line in the figure. As a result, line L0 on the surface of photoconductor 102 is exposed in accordance with the pixel value set (data string) of line DL0 in image data IM1. However, at this point, multiple exposure is still in progress, and formation of the electrostatic latent image of line L0 is not complete.

[0028] FIG. 9B illustrates the driving of the light-emitting chip 300-1 during the line period t0+1 following the line period t0. In the line period t0+1, the light-emitting control unit 505 moves the readout range RD of the image data IM1 down one line, reads pixel value data from (0, −2) to (872, 1), and outputs the data to the light-emitting chip 300-1 via the signal line DATA1. The light-emitting chip 300-1 supplies drive signals based on the input pixel value data to the 3,488 light-emitting elements. For example, drive signals based on pixel values ​​(0, −2), (0, −1), (0, 0), (0, 1), and (1, −2) are supplied to the light-emitting elements R0_0, R0_1, R0_2, R0_3, and R1_0. In the line period t0+1, a drive signal based on the effective pixel value data of the line DL0 of the image data IM1 is supplied to the light-emitting elements in the third row, including the light-emitting element R0_2. At this time, since the photoconductor 102 is rotating in the circumferential direction D2, the line L0 on the surface of the photoconductor 102 faces the light-emitting elements in the third row of the light-emitting chip 300-1. As a result, the line L0 on the surface of the photoconductor 102 is again exposed in accordance with the data string of the line DL0 of the image data IM1.

[0029] FIG. 9C illustrates the driving of the light-emitting chip 300-1 during the line period t0+2 following the line period t0+1. In the line period t0+2, the light-emitting control unit 505 moves the readout range RD of the image data IM1 down one line, reads pixel value data from (0, -1) to (871, 2), and outputs the data to the light-emitting chip 300-1 via the signal line DATA1. The light-emitting chip 300-1 supplies drive signals based on the input pixel value data to the 3,488 light-emitting elements. In the line period t0+2, a drive signal based on the effective pixel value data of the line DL0 of the image data IM1 is supplied to the light-emitting elements in the second row, including the light-emitting element R0_1. At this time, the line L0 on the surface of the photoconductor 102 faces the light-emitting elements in the second row of the light-emitting chip 300-1. As a result, the line L0 on the surface of the photoconductor 102 is exposed in accordance with the data sequence of the line DL0 of the third image data IM1.

[0030] FIG. 9D illustrates the driving of the light-emitting chip 300-1 during the line period t0+3 following the line period t0+2. In the line period t0+3, the light-emitting control unit 505 moves the readout range RD of the image data IM1 down one line, reads pixel value data from (0,0) to (872,3), and outputs the data to the light-emitting chip 300-1 via the signal line DATA1. The light-emitting chip 300-1 supplies drive signals based on the input pixel value data to the 3,488 light-emitting elements. In the line period t0+3, a drive signal based on the effective pixel value data of the line DL0 of the input image data IM1 is supplied to the light-emitting elements in the first row, including the light-emitting element R0_0. At this time, the line L0 on the surface of the photoconductor 102 faces the light-emitting elements in the first row of the light-emitting chip 300-1. As a result, the line L0 on the surface of the photoconductor 102 is exposed in accordance with the data sequence of the line DL0 of the fourth image data IM1. At this point, multiple exposure has been performed by the four light-emitting elements in each row of the light-emitting chip 300, completing the formation of line L0 of the electrostatic latent image. Lines subsequent to line L0 of the electrostatic latent image are also formed on the surface of the photoconductor 102 in a similar manner through repetition of this line cycle.

[0031] In this embodiment, a drive signal based on the pixel value of each pixel position is input to four light-emitting elements in a corresponding column of the light-emitting element array. Specifically, for example, a drive signal based on a pixel value (0,0) is input to four light-emitting elements R0_3, R0_2, R0_1, and R0_0. When these four light-emitting elements R0_3, R0_2, R0_1, and R0_0 emit light in accordance with the drive signal, a spot corresponding to the pixel value (0,0) is formed on the surface of the photoconductor 102. Similarly, a drive signal based on a pixel value (1,0) is input to four light-emitting elements R1_3, R1_2, R1_1, and R1_0. When these four light-emitting elements R1_3, R1_2, R1_1, and R1_0 emit light in accordance with the drive signal, a spot corresponding to the pixel value (1,0) is formed on the surface of the photoconductor 102.

[0032] Here, we consider errors that occur in the image forming apparatus 1 and the exposure device (the exposure device includes the light-emitting chip 300 with the exposure head 106 and the light-emission control unit 505, as described above) included in the image forming apparatus 1. When manufacturing the exposure device or the image forming apparatus 1 including the exposure device, it is inevitable that some errors will occur in the placement of components. Even after the image forming apparatus 1 is manufactured, environmental factors such as temperature changes, transport and installation of the image forming apparatus 1, and physical forces during use of the image forming apparatus 1 can cause misalignment of components within the apparatus. For example, placement errors or misalignments in the image forming unit 101 result in errors in the image formation area. Errors in the image formation area can typically include one or both of a positional misalignment component and a magnification error component. The positional misalignment component represents a displacement of the image formation position. Examples of positional misalignment components include a relative misalignment between images of multiple color components and an overall misalignment of the image formation position relative to the sheet. The magnification error component represents an expansion or contraction of the image formation area. An expansion of the image formation area due to thermal expansion of the exposure head 106 is an example of a magnification error component.

[0033] Next, a case where magnification correction is performed to compensate for the magnification error component will be described. The CPU 501 of the image forming apparatus 1 performs calibration periodically, in response to a user instruction, or when a trigger condition is met to determine whether or not compensation for the error in the image formation area is necessary. Specifically, the CPU 501 controls the image forming unit 101 to form a test chart on the transfer belt 111. The test chart here may be an image having a known pattern. The test chart is also formed by multiple exposure using the light-emitting element array of the exposure head 106 described above. The CPU 501 also controls the optical sensor 113 to optically read the test chart formed on the transfer belt 111. The optical sensor 113 outputs read image data representing the test chart reading result to the CPU 501. The CPU 501 then compares the read image data with the known pattern to detect an error in the image formation area of ​​the image formed through the multiple exposure. Therefore, the CPU 501 according to this embodiment can function as a detection unit that detects errors (misalignment or magnification error) in the image formation area. If an error in the axial direction D1 of the photoconductor 102 is detected as a result of the calibration, the CPU 501 outputs correction data indicating the detected error to the light-emission control unit 505. As a result, the error magnification Y of the detected image in the axial direction D1 of the photoconductor 102 is notified to the light-emission control unit 505. Hereinafter, the error magnification Y in the correction data is defined as follows: when Y=1, there is no magnification error; when Y>1, an expansion of the image formation range has been detected; and when Y<1, a reduction of the image formation range has been detected.

[0034] As described above, the light-emitting control unit 505 controls the plurality of light-emitting elements 402 based on the data sequence of image data for forming an image. When a magnification error along the axial direction D1 of the photoconductor 102 is detected in the obtained image, the light-emitting control unit 505 selects at least one piece of data included in the data sequence constituting the image data according to the error magnification Y in the above-described multiple exposure light-emitting control procedure. Then, the light-emitting control unit 505 performs a process of inserting or thinning at least one piece of data into a data sequence corresponding to at least one row of the plurality of light-emitting elements 402 according to the correction data (error magnification Y) for correcting the width of the image in the axial direction D1 of the photoconductor 102. The light-emitting control unit 505 causes the plurality of light-emitting elements 402 to emit light using the processed data sequence. At this time, the light-emitting control unit 505 has block division information for the blocks 701 of the light-emitting chip 300. The block division information may be stored, for example, in a memory within the light-emitting control unit 505. The data insertion or thinning process is performed on data corresponding to the plurality of light-emitting elements 402, excluding the light-emitting elements 402 arranged in the columns at both ends of the row direction (along the axial direction D1 of the photosensitive element 102) of each block 701.

[0035] The data insertion or thinning process is performed based on the error magnification Y of the correction data. If the error magnification Y<1 (if a reduction in the image formation area is detected), data insertion is performed. Correction data with an error magnification Y<1 can be considered correction data that indicates an expansion of the image formation area. Furthermore, if the error magnification Y>1 (if an expansion of the image formation area is detected), data thinning is performed. Correction data with an error magnification Y<1 can be considered correction data that indicates a reduction in the image formation area. The light emission control unit 505 can determine the number of data items to insert or thin based on the error magnification Y included in the correction data and the pitch Pa in the row direction of the light emitting elements 402. Below, compensation for when a reduction in the image formation area is detected (Y<1) and compensation for when an expansion of the image formation area is detected (Y>1) will be described in detail.

[0036] First, compensation when a reduction in the image formation area is detected, in other words, compensation for expanding the image formation area, will be described. When a magnification error is detected and the error magnification Y is smaller than 1, the light-emitting control unit 505 inserts data at a predetermined position in a data string corresponding to one row of the light-emitting elements 402 selected for data insertion among the plurality of light-emitting elements 402. As described above, the predetermined position is a data position corresponding to the light-emitting elements 402 among the plurality of light-emitting elements 402 excluding the light-emitting elements 402 arranged in the columns at both ends in the row direction of each block 701. Here, inserting data at a certain position includes shifting data on one side in the row direction based on that position in a direction that expands the data string, and providing a copy of the data (pixel value) at that position before the shift.

[0037] 10A to 10D are diagrams illustrating a procedure for light emission control including compensation for magnification error (data insertion). Here, a case where one piece of data is inserted will be described. The left side of FIG. 10A shows image data IM2 with three rows of dummy pixel values ​​added to the beginning. Since the error magnification Y is smaller than 1, the light emission control unit 505 selects a position DP0 within the read range RD in each line cycle to insert data. In the example of FIG. 10A, position DP0 is selected in line cycle t0. In this embodiment, position DP0 is shown as being within block 701-2. When setting pixel position DP0 in block 701-2, the light emission control unit 505 does not select data corresponding to light emitting elements 402 adjacent to the block boundary 901 with the adjacent blocks 701-1 and 701-3. The light emission control unit 505 selects position DP0 for data corresponding to light emitting elements 402 that are at least one pixel to the right or left of the block boundary 901 in block 701-2. The position DP0 belongs to the first row of the readout range RD (the row with index i=−3). The light-emission control unit 505 inserts data (pixel values) into the data string PG1 of this row. Specifically, the light-emission control unit 505 shifts the data (pixel values) of the subset PG1b of the data string PG1 corresponding to the right side of the row direction of the light-emitting element 402 by one position to the right, using the position DP0 as a reference, and provides a copy of the pixel value (k+1,−3) before the shift at the position DP0 to the position DP0. Next, the light-emission control unit 505 reads out data of every 3488 pixel values ​​from the image data IM2 and outputs it to the light-emitting chip 300 via the signal line DATAn. In the light-emitting chip 300-1 shown on the right side of FIG. 10A, the data string PG1 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of inserting the data (pixel value), a drive signal based on the pixel value (k+1, -3) of the selected position DP0 is supplied to the light-emitting elements Rk+1_0 and Rk+2_0, and the effective range of the light-emitting elements in the first row is expanded by one light-emitting element.

[0038] In the present embodiment, data insertion is performed on data corresponding to the light-emitting elements 402 among the plurality of light-emitting elements 402, excluding the light-emitting elements 402 arranged in columns at both ends of each block 701 in the row direction. However, this is not limited thereto, and data insertion may also be performed on data corresponding to the light-emitting element 402 among the plurality of light-emitting elements 402 arranged in the center of each block 701 in the row direction. Here, the light-emitting element 402 arranged in the center of the block 701 may refer to, for example, the light-emitting element 402 arranged in one central region when the light-emitting elements 402 in the block 701 are divided into three equal parts in the row direction. Furthermore, for example, the light-emitting element 402 arranged in the center of the block 701 may refer to the light-emitting element 402 arranged in the two central regions when the light-emitting elements 402 in the block 701 are divided into four equal parts in the row direction. Furthermore, for example, the light-emitting element 402 arranged in the center of the block 701 may refer to the light-emitting element 402 arranged in the three central regions when the light-emitting elements 402 in the block 701 are divided into five equal parts in the row direction.

[0039] 10B, in the line period t0+1 following the line period t0, the position DP0 in the readout range RD is again selected. The selected position DP0 belongs to the first row of the readout range RD (the row with index i=-2). The light-emission control unit 505 inserts data (pixel values) into the data string PG2 of this row. Specifically, the light-emission control unit 505 shifts the data (pixel values) of the subset PG2b of the data string PG2 on the right side in the row direction relative to the position DP0 to the right by one position, and provides a copy of the pixel value (k+1,-2) of the position DP0 before the shift to the position DP0. Next, the light-emission control unit 505 reads out data of every 3,488 pixel values ​​from the image data IM2 and outputs it to the light-emitting chip 300 via the signal line DATAn. In the light-emitting chip 300-1 shown on the right side of FIG. 10B, the data string PG2 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of inserting the data (pixel value), a drive signal based on the pixel value (k+1, -2) of the selected position DP0 is supplied to the light-emitting elements Rk+1_0 and Rk+2_0, and here too, the effective range of the light-emitting elements in the first row is expanded by one light-emitting element.

[0040] 10C, in the line period t0+2 following the line period t0+1, the position DP0 in the readout range RD is selected three times. The selected position DP0 belongs to the first row of the readout range RD (the row with index i=-1). The light-emission control unit 505 inserts data (pixel values) into the data string PG3 of this row. Specifically, the light-emission control unit 505 shifts the data (pixel values) of the subset PG3b of the data string PG3 on the right side in the row direction relative to the position DP0 to the right by one position, and assigns a copy of the pixel value (k+1,-1) of the position DP0 before the shift to the position DP0. Next, the light-emission control unit 505 reads data of every 3,488 pixel values ​​from the image data IM2 and outputs it to each light-emitting chip 300 via the signal line DATAn. In the light-emitting chip 300-1 shown on the right side of FIG. 10C, the data string PG3 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of inserting the data (pixel value), a drive signal based on the pixel value (k+1,-1) of the selected position DP0 is supplied to the light-emitting elements Rk+1_0 and Rk+2_0, and here too, the range of the effective light-emitting elements in the first row is expanded by one light-emitting element.

[0041] 10D, in the line period t0+3 following the line period t0+2, the position DP0 in the readout range RD is selected four times. The selected position DP0 belongs to the first row of the readout range RD (the row where index i=0). The light-emission control unit 505 inserts data (pixel values) into the data string PG4 of this row. Specifically, the light-emission control unit 505 shifts the data (pixel values) of the subset PG4b of the data string PG4 on the right side of the row direction relative to the position DP0 to the right by one position, and assigns a copy of the pixel value (k+1, 0) of the position DP0 before the shift to the position DP0. Next, the light-emission control unit 505 reads data of every 3,488 pixel values ​​from the image data IM2 and outputs it to each light-emitting chip 300 via the signal line DATAn. In the light-emitting chip 300-1 shown on the right side of FIG. 10D, the data string PG4 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of inserting the data (pixel value), a drive signal based on the pixel value (k+1,0) of the selected position DP0 is supplied to the light-emitting elements Rk+1_0 and Rk+2_0, and here too the effective range of the light-emitting elements in the first row is expanded by one light-emitting element.

[0042] 10A to 10D, compensation is performed for the detection of a reduction in the image formation range by one pitch. In this operation, for example, a drive signal based on pixel value (k+1, 0) is supplied to light-emitting element Rk+2_0 in addition to four light-emitting elements Rk+1_m (m=0 to 3) with index j=k+1. When these five light-emitting elements Rk+1_m (m=0 to 3) and Rk+2_0 emit light in accordance with the drive signal, an enlarged spot SP0 corresponding to pixel value (k+1, 0) is formed on the surface of photoconductor 102, as shown in FIG. 12(a). Compared with the case where magnification error is not compensated (Y=0) described using FIGS. 9A to 9D, the number of light-emitting elements 402 used to form spots SP corresponding to the same pixel positions of the formed image changes when magnification error compensation is performed. For example, the number of light-emitting elements for forming a spot corresponding to pixel value (k+1,0) is four when the magnification error Y is not compensated (Y=0), whereas it is five in the operations shown in FIGS. 10A-10D. The same applies to other pixel positions. Thus, the light-emission control unit 505 changes (increases if Y<1) the number of light-emitting elements 402 forming at least one spot SP from the predetermined number when the magnification error is not compensated, in accordance with the correction data for correcting the width in the axial direction D1 of the image. In this case, the light-emission control unit 505 shifts the positions of some of the spots SP (corresponding to data to the right of position DP0) in accordance with the change (increase if Y<1) in the number of light-emitting elements forming at least one spot SP. This results in the image formation range being expanded in the axial direction of the photoconductor 102.

[0043] Next, compensation when an expansion of the image formation area is detected, in other words, compensation for reducing the image formation area, will be described. When a magnification error is detected and the error magnification Y is greater than 1, the light emission control unit 505 thins out data at a predetermined position in a data column corresponding to light emitting elements in one row selected for data thinning among the plurality of light emitting elements 402. As described above, the predetermined position is a position of data corresponding to light emitting elements 402 among the plurality of light emitting elements 402 excluding the light emitting elements 402 arranged in columns at both ends in the row direction of each block 701. Here, thinning out data at a certain position includes erasing the data (pixel values) at that position before thinning out and shifting the data on one side of that position in the axial direction in a direction that reduces the data column.

[0044] 11A to 11D are diagrams illustrating a procedure for light emission control including compensation for magnification error (data thinning). Here, a case where one piece of data is thinned out will be described. On the left side of FIG. 11A, image data IM2 with three rows of dummy pixel values ​​added to the beginning is shown. Since the error magnification Y is greater than 1, the light emission control unit 505 selects a position DP0 within the read range RD in each line cycle where data is thinned out. In the example of FIG. 11A, position DP0 is selected in line cycle t0. In this embodiment, position DP0 is shown as being within block 701-2. When setting pixel position DP0 in block 701-2, the light emission control unit 505 does not select data corresponding to light emitting elements 402 that border the block boundary 901 with the adjacent blocks 701-1 and 701-3. In block 701-2, the light emission control unit 505 selects position DP0 for data corresponding to light emitting elements 402 that are at least one pixel to the right or left of the block boundary 901. The position DP0 belongs to the first row of the readout range RD (the row with index i=−3). The light-emission control unit 505 thins out the data (pixel value) of the position DP0 from the data string PG1 of this row. Specifically, the light-emission control unit 505 deletes the pixel value (k+1,−3) of the position DP0 before the shift, and shifts the data (pixel values) of the subset PG1a of the data string PG1 on the left side of the row direction by one pixel to the right, using the position DP0 as a reference. Next, the light-emission control unit 505 reads out data of every 3,488 pixel values ​​from the image data IM2 and outputs them to the light-emitting chip 300 via the signal line DATAn. In the light-emitting chip 300-1 shown on the right side of FIG. 11A, the data string PG1 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of thinning out the data (pixel value), a drive signal based on the pixel value (k+1,−3) of the selected position DP0 is not supplied to any light-emitting elements, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0045] In the present embodiment, data thinning is performed on data corresponding to the light-emitting elements 402, excluding the light-emitting elements 402 arranged in columns at both ends of each block 701 in the row direction. However, this is not limited to this, and data thinning may be performed on data corresponding to the light-emitting elements 402 arranged in the center of each block 701 in the row direction. Here, the light-emitting elements 402 arranged in the center of the block 701 may refer to, for example, the light-emitting elements 402 arranged in one central region when the light-emitting elements 402 in the block 701 are divided into three equal parts in the row direction. Furthermore, for example, the light-emitting elements 402 arranged in the center of the block 701 may refer to the light-emitting elements 402 arranged in the two central regions when the light-emitting elements 402 in the block 701 are divided into four equal parts in the row direction. Furthermore, for example, the light-emitting elements 402 arranged in the center of the block 701 may refer to the light-emitting elements 402 arranged in the three central regions when the light-emitting elements 402 in the block 701 are divided into five equal parts in the row direction.

[0046] 11B, in the line period t0+1 following the line period t0, the position DP0 in the readout range RD is again selected. The selected position DP0 belongs to the first row of the readout range RD (the row with index i=-2). The light-emission control unit 505 thins out the data (pixel values) at the position DP0 from the data string PG2 of this row. Specifically, the light-emission control unit 505 deletes the pixel value (k+1,-2) before the shift of the position DP0, and shifts the data (pixel values) of the subset PG2a of the data string PG2 on the left side of the row direction relative to the position DP0 to the right by one pixel. Next, the light-emission control unit 505 reads out data of every 3,488 pixel values ​​from the image data IM2 and outputs the data to the light-emitting chip 300 via the signal line DATAn. In the light-emitting chip 300-1 shown on the right side of FIG. 11B, the data string PG2 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of thinning out the data (pixel values), the drive signal based on the pixel value (k+1,-2) at the selected position DP0 is not supplied to any of the light-emitting elements, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0047] 11C, in the line period t0+2 following the line period t0+1, the position DP0 in the readout range RD is selected three times. The selected position DP0 belongs to the first row of the readout range RD (the row where index i=-1). The light-emission control unit 505 thins out the data (pixel values) at position DP0 from the data string PG3 of this row. Specifically, the light-emission control unit 505 deletes the pixel value (k+1,-1) before the shift of position DP0, and shifts the data (pixel values) of subset PG3a of data string PG3 on the left side of the row direction relative to position DP0 to the right by one pixel. Next, the light-emission control unit 505 reads out data of every 3,488 pixel values ​​from the image data IM2 and outputs the data to the light-emitting chip 300 via the signal line DATAn. In the light-emitting chip 300-1 shown on the right side of FIG. 11C, the data string PG3 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of thinning out the data (pixel values), the drive signal based on the pixel value (k+1,-1) at the selected position DP0 is not supplied to any of the light-emitting elements, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0048] 11D, in the line period t0+3 following the line period t0+2, the position DP0 in the readout range RD is selected four times. The selected position DP0 belongs to the first row of the readout range RD (the row where index i=0). The light-emission control unit 505 thins out the data (pixel values) at position DP0 from the data string PG4 of this row. Specifically, the light-emission control unit 505 deletes the pixel value (k+1, 0) before the shift of position DP0 and shifts the data (pixel values) of subset PG4a of data string PG4 on the left side of the row direction relative to position DP0 to the right by one pixel. Next, the light-emission control unit 505 reads out data of every 3,488 pixel values ​​from the image data IM2 and outputs the data to the light-emitting chip 300 via the signal line DATAn. In the light-emitting chip 300-1 shown on the right side of FIG. 11D, the data string PG4 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of thinning out the data (pixel values), the drive signal based on the pixel value (k+1,0) at the selected position DP0 is not supplied to any of the light-emitting elements, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0049] 11A to 11D, compensation is performed for the detection of an expansion of the image formation range by one pitch. In this operation, for example, a drive signal based on a pixel value (k+1, 0) is supplied to three light-emitting elements Rk+1_m (m=1 to 3) excluding the light-emitting element Rk+1_0 out of four light-emitting elements Rk+1_m (m=0 to 3) with index j=k+1. When these three light-emitting elements Rk+1_m (m=1 to 3) emit light in accordance with the drive signal, a reduced spot SP corresponding to the pixel value (k+1, 0) is generated as shown in FIG. 12(b). j are formed on the surface of the photoconductor 102. Compared with the case without magnification error compensation (Y=0) described using FIGS. 9A to 9D, the number of light-emitting elements used to form spots SP corresponding to the same pixel positions of the formed image changes when magnification error compensation is performed. For example, the number of light-emitting elements for forming spots corresponding to pixel value (0, 3) is four when magnification error compensation is not performed (Y=0), whereas it is three in the operation shown in FIGS. 11A to 11D. The same applies to other pixel positions. In this way, the light-emitting control unit 505 changes (decreases if Y>1) the number of light-emitting elements 402 forming at least one spot SP from the predetermined number when magnification error compensation is not performed, in accordance with the correction data for correcting the width in the axial direction D1 of the image. In this case, the light-emitting control unit 505 shifts the positions of some of the spots SP (corresponding to data to the left of position DP0) in accordance with the change (decreases if Y>1) in the number of light-emitting elements forming at least one spot SP. This results in the image formation area being reduced in the axial direction of the photoconductor 102.

[0050] The light-emission control unit 505 determines a predetermined position at which to insert or thin out data (pixel values) based on the correction data supplied from the CPU 501. In other words, the light-emission control unit 505 can control the image width of the formed image along the axial direction D1 of the photoconductor 102 by inserting or thinning out data (pixel values) based on the correction data. In other words, the above-mentioned correction data is data for correcting the image width along the axial direction of the photoconductor 102.

[0051] The light-emitting elements 402 on the light-emitting chip 300 are divided into multiple blocks 701 as described above, and each block is driven by a different driving circuit. For example, the light-emitting elements O11 to O1k arranged in block 701-1 are driven by a driving circuit including a transistor M1a of the current control circuit 613, first transistors M11 to M1k of the driving transistor 614, and second transistors M111 to M11k. Furthermore, for example, the light-emitting elements Oi1 to Oik arranged in block 701-i are driven by a driving circuit including a transistor Mia of the current control circuit 613, and first transistors Mi1 to Mik of the driving transistor 614, and second transistors Mi11 to Mi1k. Relative variations in the driving circuits between the blocks 701 may cause variations in the light intensity between the light-emitting elements 402 belonging to block 701-1 and the light-emitting elements 402 belonging to block 701-2. This variation in the amount of light is caused by, for example, manufacturing variations in transistors included in the drive circuit, and is visually recognized as unevenness (brightness and darkness) in the image formed in the image forming apparatus 1. Therefore, a design is made to suppress the variation between blocks 701 so that the variation in the amount of light is not recognized as unevenness in the image.

[0052] Meanwhile, when compensating for magnification error as described above, the number of light-emitting elements 402 that form spots SP corresponding to pixels of the image to be formed is adjusted according to the magnification at which correction is performed. For example, when no correction is performed, spots SP are formed using four light-emitting elements 402. On the other hand, when correction is performed to expand the image formation range, spots SP are formed using five light-emitting elements 402 for some of the spots SP. Furthermore, when correction is performed to reduce the image formation range, spots SP are formed using three light-emitting elements 402 for some of the spots SP.

[0053] Applying magnification error compensation to a light-emitting chip 300 in which light-emitting elements 402 are driven by different drive circuits for each block 701 can result in significant variations in light intensity at the block boundary 901 between the blocks 701, potentially affecting print quality. For example, let the light intensity of one light-emitting element 402 driven in block 701-1 be L1, and the light intensity of one light-emitting element 402 driven in block 701-2 be L1 + ΔL. The light intensity for forming spots SP without correction is 4×L1 in block 701-1 and 4×L1 + 4×ΔL in block 701-2. On the other hand, the light intensity for forming spots SP with correction to expand the image formation area is 5×L1 in block 701-1 and 5×L1 + 5×ΔL in block 701-2. Furthermore, the light intensity for forming spots SP with correction to reduce the image formation area is 3×L1 in block 701-1 and 3×L1 + 3×ΔL in block 701-2. In block 701-1, when a spot SP formed using four light-emitting elements 402 and a spot SP formed using five light-emitting elements 402 due to magnification error compensation are adjacent to each other, the difference in light intensity between the adjacent spots SP is L1. On the other hand, when a spot formed using four light-emitting elements 402 in block 701-1 and a spot formed using five light-emitting elements 402 in block 701-2 are adjacent to each other, the difference in light intensity between the adjacent spots SP is L1 + 5 × ΔL. In other words, when data insertion or thinning is performed at the boundary of blocks 701 to compensate for magnification error, the difference in light intensity between adjacent spots SP increases due to two factors: variation between blocks 701 and the number of light-emitting elements 402 that form the spots SP, which may affect print image quality.

[0054] In this embodiment, the light-emitting control unit 505 performs a process of inserting or thinning at least one data item into a data column corresponding to at least one row of the plurality of light-emitting elements 402 based on the correction data supplied from the CPU 501. The data insertion or thinning is performed on data corresponding to the plurality of light-emitting elements 402, excluding the light-emitting elements 402 arranged in the columns at both ends of each block 701 in the row direction. As a result, the spot SP, in which the number of light-emitting elements 402 used to form the electrostatic latent image changes from that without correction (compensation), is formed using the plurality of light-emitting elements 402, excluding the light-emitting elements 402 arranged in the columns at both ends of each block 701 in the row direction. This suppresses the effects of uneven light emission intensity due to variations in the light emission intensity between blocks 701, thereby suppressing image unevenness. Here, the block 701 in one light-emitting chip 300 has been described. However, this is not limited to this. As shown in FIG. 3, the light-emitting element array 201 may include a plurality of light-emitting chips 300 arranged along the axial direction D1 of the photoconductor 102. Therefore, data insertion or thinning may be performed on data corresponding to the light-emitting elements 402, excluding the light-emitting elements 402 arranged in columns at both ends in the row direction of the light-emitting chip 300, among the plurality of light-emitting elements 402. As a result, the spot SP, in which the number of light-emitting elements 402 used to form an electrostatic latent image changes from that in the absence of correction (compensation), is formed using the light-emitting elements 402, excluding the light-emitting elements 402 arranged in columns at both ends in the row direction of the light-emitting chip 300, among the plurality of light-emitting elements 402. The light-emitting elements 402 arranged at both ends in the row direction of the light-emitting chip 300 may be the light-emitting elements 402 arranged at one end of the block 701 in the row direction.

[0055] 13 is a schematic diagram showing one form of the light-emitting chip 300 according to this embodiment. The light-emitting chip 300 according to this embodiment can be used, for example, as a light source for an image forming device. The light-emitting chip 300 according to this embodiment has a rectangular shape with long sides parallel to a first direction and short sides parallel to a direction intersecting the first direction. For example, the first direction may be a direction along the rotation axis direction (axial direction D1) of the photosensitive member 102 of the image forming device 1.

[0056] The substrate 1701 has a polygonal shape, and an example of a rectangular substrate 1701 will be described here. In this specification, the direction of the long sides of the rectangular substrate 1701 is referred to as a first direction, and the direction of the short sides perpendicular to the long side is referred to as a second direction. In addition, the polygon in this specification also includes shapes with rounded corners. A moisture-resistant ring 1700 is disposed on the rectangular substrate 1701, and serves to suppress and prevent moisture from penetrating into the light-emitting chip 300. The moisture-resistant ring 1700 can be, for example, a guard ring formed of a wiring layer.

[0057] A light-emitting region 1702, a contact region 1703, pads 1704, and a circuit 1706 are arranged inside the moisture-resistant ring 1700. The circuit 1706 is a part of the circuit for driving each light-emitting chip, and specific examples thereof include, but are not limited to, an input protection circuit, an input circuit to which driving data is input, and a logic circuit for processing data. The light-emitting elements EL are arranged in a matrix within the light-emitting region 1702. The contact region 1703 is an area where wiring electrically connected to a common electrode of the light-emitting elements EL is arranged. The pads 1704 electrically connect the contact region 1703, the circuit 1706, etc. to external elements.

[0058] The outer periphery of the moisture-resistant ring 1700 may include a plurality of recessed portions, which can be used as contact areas for contacting ribs that are part of a mask for vapor deposition in a film-forming process, for example.

[0059] Each of the plurality of light-emitting elements EL arranged in a matrix in the light-emitting region 1702 is composed of a light-emitting layer and a first electrode and a second electrode that sandwich the light-emitting layer. In this embodiment, the first electrode may be an independent electrode provided for each light-emitting element EL, and the second electrode may be a common electrode provided for all the light-emitting elements EL.

[0060] For example, in the case where light-emitting region 1702 has four rows of light-emitting elements EL, the initial positions of the light-emitting elements EL in the first row and the first positions of the light-emitting elements EL in the second row may be shifted in the first direction by ¼ of the X-direction dimension of the light-emitting elements EL, as illustrated in Fig. 13. In the case of n rows, where n is an integer of 2 or greater, the initial positions of the light-emitting elements EL in the first row and the first positions of the light-emitting elements EL in the second row may be shifted in the X direction by 1 / n of the X-direction dimension of the light-emitting elements EL. Such a configuration is advantageous for improving resolution.

[0061] The contact region 1703 is an area adjacent to the light emitting region 1702 of the substrate 1701, and is disposed inside the moisture-resistant ring 1700. At least one of the contact region 1703, the pad 1704, and the circuit 1706, together with the recess of the moisture-resistant ring 1700, may be disposed between the light emitting region 1702 and one long side end of the substrate 1701, and may be disposed in series in the long side direction (first direction).

[0062] In this way, by arranging the contact region 1703, the pad 1704, the circuit 1706, etc. in the same position in the short side direction, the length of the light emitting chip 300 in the short side direction (second direction) can be reduced, and the light emitting chip 300 can be made smaller.

[0063] The light-emitting chip 300 of this embodiment has multiple contact regions 1703 between the common electrode of the light-emitting element EL and the power supply wiring along the long side edge of the light-emitting chip. If the common electrode is made of, for example, a transparent electrode material with relatively high electrical resistance, the amount of voltage drop in the long side direction may be large. Therefore, the voltage applied to each OLED varies depending on the distance from the contact region to which the potential is supplied. This may result in differences in actual emission brightness between OLEDs to which a voltage is applied to emit light with the same brightness, resulting in shading and other problems. By having multiple contact regions 1703 along the long side as in this embodiment, the voltage drop of the common electrode along the long side direction can be suppressed, thereby preventing shading and other problems.

[0064] In this embodiment, an example in which the light-emitting chip 300 is used in a head substrate 1800 of an exposure head, which is a light-emitting module provided in an image forming apparatus, will be described with reference to Figures 14(a) to 14(c). Figure 14(a) is a schematic perspective view of the head substrate 1800. Figure 14(b) shows an arrangement of a plurality of light-emitting elements EL provided on the head substrate 1800, and Figure 14(c) shows an enlarged view of a portion of Figure 14(b).

[0065] An LED chip 1803 is mounted on the head substrate 1800. As the LED chip 1803, for example, the above-described light-emitting chip 300 can be used.

[0066] 14(a), an LED chip 1803 is provided on one surface of a head substrate 1800, and a long flexible flat cable (FFC) connector 1807 is provided on the other surface. The one surface of the head substrate 1800 here refers to the surface (upper surface, front surface) on which the LED chip 1803 is provided. The other surface of the substrate refers to the surface (lower surface, back surface) opposite to the side on which the LED chip 1803 is provided.

[0067] The FFC connector 1807 is attached to the other surface (bottom surface, back surface) of the head substrate 1800 so that its longitudinal direction follows the longitudinal direction of the head substrate 1800. The long FFC connector 1807 is provided to input a control signal (drive signal) from a control circuit section of the main body of the image forming apparatus, and the control signal is transferred to each LED chip 1803. The LED chips 1803 are driven (to emit light or turn off) by the control signal input to the head substrate 1800.

[0068] The LED chips 1803 mounted on the head substrate 1800 will now be described. As shown in Fig. 14(b) and Fig. 14(c), a plurality of light-emitting elements EL are arranged on one surface of the head substrate 1800. For example, a plurality of LED chips 1803-1 to 1803-17 (17 chips) are arranged. Fig. 14(b) illustrates LED chips 1803_1, 1803_7, 1803_8, 1803_9, 1803_10, and 1803_17. Each of the LED chips 1803_1 to 1803_17 has a plurality of light-emitting elements EL arranged in its longitudinal direction, and for example, 516 light-emitting elements EL are arranged.

[0069] In the longitudinal direction of the LED chip 1803, the center-to-center distance k2 between adjacent light-emitting elements EL corresponds to the resolution of the image forming device. For example, when the resolution of the image forming device in this embodiment is 1200 dpi, the light-emitting elements EL are arranged so that the center-to-center distance k2 between adjacent light-emitting elements EL is 21.16 μm in the longitudinal direction of the LED chips 1803_1 to 1803_17. Therefore, the exposure range of the exposure head in this embodiment is approximately 314 mm.

[0070] The photosensitive layer of the photosensitive drum is formed with a width of 314 mm or more. Since the long side of A4 size recording paper and the short side of A3 size recording paper are 297 mm, the exposure head of this embodiment has an exposure range that can form images on A4 size recording paper and A3 size recording paper. While Figure 14(c) shows an example in which multiple light-emitting elements EL are arranged in the longitudinal direction, light-emitting elements EL may be arranged in the lateral direction as well as the longitudinal direction.

[0071] A plurality of LED chips 1803_1 to 1803_17 are arranged in the axial direction of the photosensitive drum. Specifically, the LED chips 1803_1 to 1803_17 are alternately arranged in two rows along the axial direction of the photosensitive drum. That is, as shown in FIG. 14(b), counting from the left, the odd-numbered LED chips 1803_1, 1803_3, ..., 1803_17 are mounted in a row in the longitudinal direction of the head substrate 1800. Also, counting from the left, the even-numbered LED chips 1803_2, 1803_4, ..., 1803_16 are mounted in a row in the longitudinal direction of the head substrate 1800. The LED chips 1803 are arranged in this manner. As a result, as shown in FIG. 14(c), the center-to-center distance k1 of the light-emitting elements EL can be made equal to the center-to-center distance k2 of the light-emitting elements EL in the longitudinal direction of the LED chip 1803. Here, the center-to-center distance k1 of the light-emitting elements EL indicates the center-to-center distance between the light-emitting elements EL arranged at one end of the LED chip 1803_7 and the other end of the LED chip 1803_8. Also, the center-to-center distance k2 of the light-emitting elements EL indicates the center-to-center distance k2 between adjacent light-emitting elements EL in the LED chip 1803_8.

[0072] In other words, the center-to-center distance k1 between adjacent light-emitting elements EL arranged on one end of an LED chip 1803 and the other end of another LED chip 1803 can be made equal to the center-to-center distance k2 between adjacent light-emitting elements EL on one LED chip 1803.

[0073] In this embodiment, the light-emitting element EL is an organic light-emitting element that is a current-driven light-emitting element. The organic light-emitting elements are arranged in a line on a TFT substrate along the main scanning direction (axial direction D1 of the photosensitive element 102), for example, and are electrically connected in parallel by power supply wiring that is also provided along the main scanning direction.

[0074] When the light-emitting device is used in an exposure head, linear exposure is performed, and therefore the ratio of the longitudinal direction (first direction) to the lateral direction (second direction) of the shape of the light-emitting region 1702 is larger than when the light-emitting device is used in a display device, etc. The ratio of the longitudinal direction (first direction) to the lateral direction (second direction) of the shape of the LED chip substrate is also larger.

[0075] Specifically, for example, the length of the long side of LED chip 1803 (or light-emitting region 1702) is at least five times the length of the short side of LED chip 1803 (or light-emitting region 1702), and may be at least ten times the length. For example, the length of the long side of LED chip 1803 (or light-emitting region 1702) can be at least 20 times the length of the short side of LED chip 1803 (or light-emitting region 1702).

[0076] The length of the long side of the LED chip 1803 is determined by the axial length of the photosensitive drum, the number of LED chips arranged in the axial direction, and the arrangement of the LED chips 1803. The length of the short side of the LED chip 1803 is determined by whether the light-emitting element EL is arranged in the light-emitting region 1702 in the direction perpendicular to the axis of the photosensitive drum, and the arrangement of the pad 1704 and the contact region 1703.

[0077] Furthermore, the organic layer may be configured to have a red-emitting layer, taking into account the wavelength dependency of the photosensitive drum's photosensitivity. The LED chip 1803 may have a color filter. By including a color filter, the amount of normal light incident on the photosensitive drum is not reduced, and stray light from unintended directions can be absorbed, improving print quality.

[0078] The disclosure of this specification includes the following exposure apparatus and image forming apparatus.

[0079] (Item 1) An exposure device comprising: a light-emitting chip having a plurality of light-emitting elements arranged in a plurality of rows and a plurality of columns, the row direction of which is aligned with an axial direction of a photosensitive body; and a light-emitting control unit for controlling the light-emitting chip, a light-emitting region in which the plurality of light-emitting elements are arranged is divided into a plurality of blocks arranged along the row direction, and each light-emitting element is driven by a drive circuit arranged corresponding to the block to which it belongs; The light emission control unit controlling the plurality of light-emitting elements so that an electrostatic latent image for forming an image, which is composed of a plurality of spots, is formed on the photosensitive member while the photosensitive member is rotating, and each of the plurality of spots is formed by a predetermined number of light-emitting elements among the plurality of light-emitting elements; changing the number of light-emitting elements forming at least one of the plurality of spots from the predetermined number in accordance with correction data for correcting the width in the axial direction of the image, and shifting positions of some of the other spots in accordance with the change in the number of light-emitting elements forming the at least one spot; an exposure apparatus, wherein the at least one spot is formed using light-emitting elements among the plurality of light-emitting elements, excluding light-emitting elements arranged in columns at both ends of each block in the row direction;

[0080] (Item 2) 2. The exposure apparatus according to item 1, wherein the at least one spot is formed using a light-emitting element, among the plurality of light-emitting elements, that is arranged at the center of each block in the row direction.

[0081] (Item 3) 3. The exposure apparatus according to item 1 or 2, characterized in that the light emission control unit increases the number of light-emitting elements for forming the at least one spot from the predetermined number when the correction data indicates that the image formation range is to be expanded, and decreases the number of light-emitting elements for forming the at least one spot from the predetermined number when the correction data indicates that the image formation range is to be reduced.

[0082] (Item 4) the exposure device includes a plurality of light-emitting chips including the light-emitting chip arranged along the axial direction; 4. The exposure apparatus according to any one of items 1 to 3, wherein the at least one spot is not formed by light-emitting elements arranged in columns at both ends in the row direction in each light-emitting chip.

[0083] (Item 5) 5. The exposure apparatus according to item 4, wherein the plurality of light-emitting chips are arranged in a staggered pattern.

[0084] (Item 6) 6. The exposure apparatus according to any one of items 1 to 5, wherein at least one of the light-emitting elements arranged in each column among the plurality of light-emitting elements is arranged to be partially shifted in the row direction.

[0085] (Item 7) An exposure device described in any one of items 1 to 6, characterized in that the light-emitting elements arranged in each column among the plurality of light-emitting elements are arranged in a stepped manner at a constant pitch in the row direction, with partial offsets.

[0086] (Item 8) The light emission control unit controlling the plurality of light emitting elements based on an image formation data string for forming an image; 8. The exposure apparatus according to any one of items 1 to 7, characterized in that, depending on the correction data, data corresponding to the at least one spot is inserted or thinned out in the data column corresponding to at least one row of the plurality of light-emitting elements.

[0087] (Item 9) An exposure device comprising: a light-emitting chip having a plurality of light-emitting elements arranged in a plurality of rows and a plurality of columns, the row direction of which is aligned with an axial direction of a photosensitive body; and a light-emitting control unit for controlling the light-emitting chip, a light-emitting region in which the plurality of light-emitting elements are arranged is divided into a plurality of blocks arranged along the row direction, and each light-emitting element is driven by a drive circuit arranged corresponding to the block to which it belongs; Among the plurality of light-emitting elements, at least one light-emitting element arranged in each column is arranged to be partially shifted in the row direction, The light emission control unit controlling the plurality of light emitting elements based on an image formation data string for forming an image; performing a process of inserting or thinning at least one piece of data in the data column corresponding to at least one row of the plurality of light-emitting elements according to correction data for correcting the width of the image in the axial direction; The exposure apparatus is characterized in that the processing is performed on data corresponding to light-emitting elements among the plurality of light-emitting elements, excluding light-emitting elements arranged in columns at both ends in the row direction of each block.

[0088] (Item 10) An exposure apparatus according to any one of items 1 to 9, the photoreceptor; An image forming apparatus comprising:

[0089] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0090] 102: photosensitive member, 300: light emitting chip, 402: light emitting element, 505: light emission control unit, 701: block, D1: axial direction, SP: spot

Claims

1. An exposure device comprising: a light-emitting chip having a plurality of light-emitting elements arranged in a plurality of rows and a plurality of columns, the row direction of which is aligned with an axial direction of a photosensitive body; and a light-emitting control unit for controlling the light-emitting chip, a light-emitting region in which the plurality of light-emitting elements are arranged is divided into a plurality of blocks arranged along the row direction, and each light-emitting element is driven by a drive circuit arranged corresponding to the block to which it belongs; The light emission control unit controlling the plurality of light-emitting elements so that an electrostatic latent image for forming an image, which is composed of a plurality of spots, is formed on the photosensitive member while the photosensitive member is rotating, and each of the plurality of spots is formed by a predetermined number of light-emitting elements among the plurality of light-emitting elements; changing the number of light-emitting elements forming at least one of the plurality of spots from the predetermined number in accordance with correction data for correcting the width in the axial direction of the image, and shifting positions of some of the other spots in accordance with the change in the number of light-emitting elements forming the at least one spot; an exposure apparatus, wherein the at least one spot is formed using light-emitting elements of the plurality of light-emitting elements excluding light-emitting elements arranged in columns at both ends of each block in the row direction;

2. 2. The exposure apparatus according to claim 1, wherein the at least one spot is formed using a light-emitting element, among the plurality of light-emitting elements, that is arranged at the center of each block in the row direction.

3. 2. The exposure apparatus according to claim 1, wherein the light emission control unit increases the number of light-emitting elements for forming the at least one spot from the predetermined number when the correction data indicates that the image formation range is to be expanded, and decreases the number of light-emitting elements for forming the at least one spot from the predetermined number when the correction data indicates that the image formation range is to be reduced.

4. the exposure device includes a plurality of light-emitting chips including the light-emitting chip arranged along the axial direction; 2. The exposure apparatus according to claim 1, wherein the at least one spot is not formed by light-emitting elements arranged in columns at both ends in the row direction in each light-emitting chip.

5. 5. The exposure apparatus according to claim 4, wherein the plurality of light-emitting chips are arranged in a staggered pattern.

6. 2. The exposure apparatus according to claim 1, wherein at least one of the light-emitting elements arranged in each column among the plurality of light-emitting elements is arranged to be partially shifted in the row direction.

7. 2. The exposure apparatus according to claim 1, wherein the light emitting elements arranged in each column among the plurality of light emitting elements are arranged in a stepped manner at a constant pitch in the row direction so as to be partially shifted.

8. The light emission control unit controlling the plurality of light emitting elements based on an image formation data string for forming an image; 2. The exposure apparatus according to claim 1, wherein data corresponding to the at least one spot is inserted or thinned out in the data column corresponding to at least one row of the plurality of light-emitting elements according to the correction data.

9. An exposure device comprising: a light-emitting chip having a plurality of light-emitting elements arranged in a plurality of rows and a plurality of columns, the row direction of which is aligned with an axial direction of a photosensitive body; and a light-emitting control unit for controlling the light-emitting chip, a light-emitting region in which the plurality of light-emitting elements are arranged is divided into a plurality of blocks arranged along the row direction, and each light-emitting element is driven by a drive circuit arranged corresponding to the block to which it belongs; The light emission control unit controlling the plurality of light emitting elements based on an image formation data string for forming an image; performing a process of inserting or thinning at least one piece of data in the data column corresponding to at least one row of the plurality of light-emitting elements according to correction data for correcting the width of the image in the axial direction; The exposure apparatus is characterized in that the processing is performed on data corresponding to light-emitting elements among the plurality of light-emitting elements, excluding light-emitting elements arranged in columns at both ends in the row direction of each block.

10. An exposure apparatus according to any one of claims 1 to 9; the photoreceptor; An image forming apparatus comprising:

Images