Exposure head and image formation device including exposure head

Abstract

To solve a problem that, when image data is corrected according to a mounting position of a light emitting chip, a shape of a formed image may be affected, particularly, when image data in the entire region of the light emitting chip is corrected for the purpose of correcting deviation of an image formation position in a boundary of the chip, the shape of the formed image may be greatly affected.SOLUTION: A light emitting chip is divided in a rotational axis direction into a plurality of regions. In a region corresponding to a boundary of the plurality of light emitting chips in the plurality of regions, image data is shifted so as to reduce mounting positional deviation of the light emitting chip.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present disclosure relates to an exposure head and an image forming apparatus including the exposure head. [Background technology]

[0002] In electrophotographic printers, a method is generally known in which a photosensitive drum is exposed to light using an exposure head equipped with light-emitting elements such as LEDs or organic EL elements to form a latent image. Some of these exposure heads include a plurality of light-emitting chips, each having a plurality of light-emitting elements arranged along the rotation axis of the photosensitive drum, and the light-emitting chips are arranged in a staggered pattern on a substrate.

[0003] In the exposure head described above, there is a misalignment between the mounting position of the light-emitting chip on the substrate and the designed mounting position, which causes a misalignment in the position where the photosensitive drum is exposed, and this can affect the accuracy of image formation. In particular, in a configuration in which multiple light-emitting chips are used to expose the photosensitive drum, there are cases in which a significant misalignment in the image formation position occurs at the boundary between the chips.

[0004] Patent Document 1 discloses a configuration for reducing the deviation of the image formation position at the boundary between the above-mentioned light-emitting chips. According to Patent Document 1, correction is performed so as to interpolate image data in the region at the boundary between the chips, thereby reducing the deviation of the image formation position at the boundary between the chips. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-196342 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when image data is corrected according to the mounting position of the light-emitting chip as described above, there is a risk that the shape of the formed image may be affected. In particular, when image data for the entire area of ​​the light-emitting chip is corrected in order to correct the deviation of the image formation position at the boundary between the chips, there is a risk that the shape of the formed image may be significantly affected.

[0007] In view of the above-mentioned problems, an object of the present invention is to reduce the risk of deterioration in the quality of the formed image while reducing the deviation of the image formation position at the boundary between light-emitting chips. [Means for solving the problem]

[0008] The image forming apparatus of the present invention comprises a rotating photosensitive body, a plurality of light-emitting chips each having a plurality of light-emitting elements arranged along the rotational axis direction of the photosensitive body, a lens that focuses light emitted by the plurality of light-emitting chips onto the surface of the photosensitive body, and a control unit that outputs image data to drive the plurality of light-emitting elements, wherein the control unit divides the light-emitting chips into a plurality of regions along the rotational axis direction, and in regions among the plurality of regions corresponding to boundaries between the plurality of light-emitting chips, shifts the image data so as to reduce misalignment of the mounting position of the light-emitting chips. [Effects of the Invention]

[0009] According to the present invention, in an exposure head having a substrate on which light-emitting chips are mounted, which reduces the risk of a reduction in the quality of the formed image while reducing the deviation of the image formation position at the boundary of the light-emitting chips, it is possible to reduce the risk of a reduction in the accuracy of the mounting position of the light-emitting chips. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is an explanatory diagram of the configuration of a photosensitive member and an exposure head according to an embodiment. [Figure 3]FIG. 2 is an explanatory diagram illustrating the configuration of a printed circuit board of an exposure head according to an embodiment. [Figure 4] 1A and 1B are explanatory diagrams of a light-emitting chip and a light-emitting element array in the light-emitting chip according to an embodiment. [Figure 5] FIG. 1 is a plan view showing a schematic configuration of a light-emitting chip according to an embodiment. [Figure 6] FIG. 1 is a cross-sectional view showing a schematic configuration of a light-emitting chip according to an embodiment. [Figure 7] FIG. 2 is a circuit diagram showing the control configuration of an exposure apparatus according to an embodiment. [Figure 8] 10 is a signal chart related to access to a register of a light-emitting chip according to an embodiment; [Figure 9] 10 is a signal chart related to the transmission of image data to a light-emitting chip according to an embodiment. [Figure 10] FIG. 2 is a functional block diagram showing a detailed configuration of a light-emitting chip according to an embodiment. [Figure 11] FIG. 10 is an explanatory diagram of multiple exposure using light-emitting elements arranged in a stepped pattern. [Figure 12A] FIG. 10 is an explanatory diagram of light emission control based on input image data. [Figure 12B] FIG. 10 is an explanatory diagram of light emission control based on input image data. [Figure 12C] FIG. 10 is an explanatory diagram of light emission control based on input image data. [Figure 12D] FIG. 10 is an explanatory diagram of light emission control based on input image data. [Figure 13] 10A and 10B are diagrams showing misalignment of mounting positions of light-emitting chips according to an embodiment; [Figure 14] FIG. 10 is a diagram showing a shift amount of image data according to an embodiment. [Figure 15] FIG. 10 is a diagram showing a shift amount of image data according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. 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.

[0012] 1. General Configuration of Image Forming Apparatus 1 shows an example of a schematic configuration of an image forming apparatus 1 according to an 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 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, for example.

[0013] The image forming unit 103 includes image forming units 101a, 101b, 101c, and 101d. The image forming units 101a, 101b, 101c, and 101d form black, yellow, magenta, and cyan toner images, respectively. The image forming units 101a, 101b, 101c, and 101d have the same configuration and are collectively referred to as the image forming unit 101 below. The photoconductor 102 of the image forming unit 101 is rotated clockwise in the drawing during image formation. 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 photoreceptor 102 is transferred onto a sheet transported on a transfer belt 111. By transferring the toner images of the four photoreceptors 102 onto the sheet in an overlapping manner, a color image containing four color components, namely black, yellow, magenta, and cyan, can be formed.

[0014] The conveying unit 105 controls the feeding and transport of sheets. 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 transport path of the image forming apparatus 1. The fed sheet is transported to the registration rollers 110. The registration rollers 110 transport the sheet onto the transfer belt 111 at an appropriate timing so that the toner images on the photoconductors 102 are transferred to the sheet. As described above, the toner image is transferred to the sheet while the sheet is transported on the transfer belt 111. The fixing unit 104 fixes the toner image to the sheet by applying heat and pressure to the sheet to which the toner image has been transferred. After the toner image is fixed, the sheet is discharged to the outside of the image forming apparatus 1 by the discharge rollers 112. An optical sensor 113 is disposed opposite the transfer belt 111. The optical sensor 113 optically reads the test chart formed on the transfer belt 111 by the image forming unit 101. If a positional deviation is detected in the test chart read by the optical sensor 113, the image controller 700 (described later) performs control to compensate for the positional deviation when a subsequent job is executed.

[0015] Although an example has been described here in which a toner image is directly transferred from each photoconductor 102 to a sheet on the transfer belt 111, the toner image may also be indirectly transferred from each photoconductor 102 to a sheet via an intermediate transfer body. Also, although an example has been described here in which a color image is formed using toners of multiple colors, the technology according to the present disclosure is also applicable to an image forming apparatus that forms a monochrome image using toner of a single color.

[0016] 2. Exposure head configuration example 2(A) and 2(B) show the photoconductor 102 and the exposure head 106. The exposure head 106 includes 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 holds the rod lens array 203 and the printed circuit board 202. The photoconductor 102 has a cylindrical shape. The exposure head 106 is disposed such 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.

[0017] 3(A) and 3(B) show an example of the configuration of the printed circuit board 202. Note that Fig. 3(A) shows the surface on which the connector 305 is mounted, and Fig. 3(B) shows the surface on which the light-emitting element array 201 is mounted (the surface opposite to the surface on which the connector 305 is mounted). Fig. 4 schematically shows the light-emitting chip 400 and the arrangement of light-emitting elements 602 in the light-emitting chip 400.

[0018] In this embodiment, the light-emitting element array 201 includes a plurality of light-emitting elements arranged two-dimensionally. The light-emitting element array 201 includes, as a whole, N columns of light-emitting elements in the axial direction D1 and M rows of light-emitting elements in the circumferential direction D2 of the photoconductor, where M and N are integers equal to or greater than 2. In the example shown in FIG. 3B, the light-emitting element array 201 is divided into 20 light-emitting chips 400-1 to 400-20, each including a subset of the entire plurality of light-emitting elements, and the light-emitting chips 400-1 to 400-20 are arranged in a staggered pattern along the axial direction D1. The light-emitting chips 400-1 to 400-20 are also collectively referred to as light-emitting chips 400. As shown in FIG. 3B, the area occupied by all of the light-emitting elements of the 20 light-emitting chips in the axial direction D1 is wider than the area occupied by the maximum width W0 of the input image data. Therefore, some light-emitting elements located at both ends in the axial direction D1 may not be used to expose the photoconductor 102 unless image misalignment is detected. Each light-emitting chip 400 on the printed circuit board 202 is connected to the image controller 700 (FIG. 7) via a connector 305. For convenience of explanation, the side with the smaller branch number of the light-emitting chips 400-1 to 400-20 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 400-1 is the leftmost light-emitting chip 400, and the light-emitting chip 400-20 is the rightmost light-emitting chip.

[0019] The number J (J=N / 20) of light-emitting elements 602 arranged in each row of one light-emitting chip 400 along the rotational axis direction of the photosensitive member 102 may be equal to, for example, 748 (J=748). Meanwhile, the number M of light-emitting elements 602 arranged in each column of one light-emitting chip 400 may be equal to, for example, 4 (M=4). That is, in the exemplary embodiment, each light-emitting chip 400 has a total of 2992 (=748×4) light-emitting elements 602, with 748 in the axial direction D1 and 4 in the circumferential direction D2. The interval P between the center points of the light-emitting elements 602 adjacent to each other in the circumferential direction D2 is Cmay be, for example, approximately 21.16 μm, corresponding to a resolution of 1200 dpi. The spacing between the center points of adjacent light-emitting elements 602 in the axial direction D1 may also be approximately 21.16 μm, in which case 748 light-emitting elements 602 occupy a length of approximately 15.8 mm in the axial direction D1. Note that, for convenience of explanation, FIG. 4 shows an example in which the light-emitting elements 602 in each light-emitting chip 400 are arranged in a complete grid pattern, but in reality, M (M=4) light-emitting elements 602 in each column are arranged in a staircase pattern. This point will be explained further below.

[0020] 5 is a plan view showing a schematic configuration of the light-emitting chip 400. The plurality of light-emitting elements 602 of each light-emitting chip 400 are formed on a light-emitting substrate 402, which is, for example, a silicon substrate. A circuit unit 406 for driving the plurality of light-emitting elements 602 is provided on the light-emitting substrate 402. Signal lines for communicating with the image controller 700, power lines for connecting to a power source, and ground lines for connecting to ground are connected to the pads 408-1 to 408-9. The signal lines, power lines, and ground lines may be wires made of, for example, gold.

[0021] FIG. 6 shows a portion of the cross section taken along line AA in FIG. 5. A plurality of lower electrodes 504 are formed on the light-emitting substrate 402. A gap of length d is provided between two adjacent lower electrodes 504. A light-emitting layer 506 is provided on the lower electrodes 504, and an upper electrode 508 is provided on the light-emitting layer 506. The upper electrode 508 is a common electrode for the plurality of lower electrodes 504. When a voltage is applied between the lower electrode 504 and the upper electrode 508, a current flows from the lower electrode 504 to the upper electrode 508, causing the light-emitting layer 506 to emit light. Therefore, one lower electrode 504 and a partial region of the light-emitting layer 506 and upper electrode 508 corresponding to the lower electrode 504 constitute one light-emitting element 602. That is, in this embodiment, the light-emitting substrate 402 includes a plurality of light-emitting elements 602.

[0022] The light-emitting layer 506 may be, for example, an organic EL film. The upper electrode 508 is formed of a transparent electrode such as indium tin oxide (ITO) so as to transmit the emission wavelength of the light-emitting layer 506. In this embodiment, the entire upper electrode 508 transmits the emission wavelength of the light-emitting layer 506; however, the entire upper electrode 508 does not need to transmit the emission wavelength. Specifically, it is sufficient that a partial region through which light from each light-emitting element 602 passes transmits the emission wavelength. While FIG. 6 shows a single continuous light-emitting layer 506, multiple light-emitting layers 506 each having a width equal to the width W of the lower electrode 504 may be formed on the lower electrode 504. Furthermore, in FIG. 6, the upper electrode 508 is a single common electrode for multiple lower electrodes 504; however, multiple upper electrodes 508 each having a width equal to the width W of the lower electrode 504 may be formed corresponding to each lower electrode 504. Furthermore, among the lower electrodes 504 of each light-emitting chip 400, a first plurality of lower electrodes 504 may be covered with a first light-emitting layer 506, and the second plurality of lower electrodes 504 may be covered with a second light-emitting layer 506. Furthermore, among the lower electrodes 504 of each light-emitting chip 400, a first upper electrode 508 may be commonly formed corresponding to the first plurality of lower electrodes 504, and a second upper electrode 508 may be commonly formed corresponding to the second plurality of lower electrodes 504. Even in such a configuration, one lower electrode 504 and the region of the light-emitting layer 506 and upper electrode 508 corresponding to the lower electrode 504 constitute one light-emitting element 602.

[0023] FIG. 7 is a circuit diagram related to a control configuration for controlling the light-emitting chip 400. The image controller 700 is a control circuit that communicates with the printed circuit board 202 via multiple signal lines (wires). The image controller 700 includes a CPU 701, a clock generation unit 702, an image data processing unit 703, a register access unit 704, and a light-emitting control unit 705. The light-emitting control unit 705 is a component that constitutes an exposure device together with the exposure head 106. The light-emitting control unit 705 terminates the signal line between the image controller 700 and the printed circuit board 202. The n-th light-emitting chip 400-n (n is an integer from 1 to 20) on the printed circuit board 202 is connected to the light-emitting control unit 705 via a signal line DATAn and a signal line WRITEn. The signal line DATAn is used to transmit image data from the image controller 700 to the light-emitting chip 400-n. The signal line WRITEn is used by the image controller 700 to write control data to the register of the light-emitting chip 400-n.

[0024] One signal line CLK, one signal line SYNC, and one signal line EN are further provided between the light-emitting control unit 705 and each light-emitting chip 400. The signal line CLK is used to transmit a clock signal for transmitting data on the signal lines DATAn and WRITEn. The light-emitting control unit 705 outputs a clock signal generated based on a reference clock signal from the clock generation unit 702 to the signal line CLK. The signals transmitted to the signal lines SYNC and EN will be described later.

[0025] The CPU 701 controls the entire image forming apparatus 1. The image data processing unit 703 performs image processing on image data received from the reading unit 100 or an external device to generate binary bitmap image data for controlling the on / off of light emission of the light-emitting elements 602 of the light-emitting chips 400 on the printed circuit board 202. This image processing may include, for example, raster conversion, tone correction, color conversion, and halftone processing. The image data processing unit 703 transmits the generated image data to the light-emission control unit 705 as input image data. The register access unit 704 receives control data to be written to the registers in each light-emitting chip 400 from the CPU 701 and transmits it to the light-emission control unit 705.

[0026] FIG. 8 shows the transition of the signal level of each signal line when control data is written to the register of the light-emitting chip 400. An enable signal that is at high level during communication and indicates that communication is in progress is output to the signal line EN. The light-emitting control unit 705 transmits a start bit to the signal line WRITEn in synchronization with the rising edge of the enable signal. Next, the light-emitting control unit 705 transmits a write identification bit indicating a write operation, and then transmits the address of the register to which the control data is to be written (4 bits in this example) and the control data (8 bits in this example). When writing to the register, the light-emitting control unit 705 sets the frequency of the clock signal transmitted to the signal line CLK to, for example, 3 MHz.

[0027] FIG. 9 shows the transition of the signal level of each signal line when image data is transmitted to each light-emitting chip 400. A periodic line synchronization signal indicating the exposure timing of each line on the photoconductor 102 is output to the signal line SYNC. If the peripheral speed of the photoconductor 102 is 200 mm / s and the peripheral resolution is 1200 dpi (approximately 21.16 μm), the line synchronization signal is output at a period of approximately 105.8 μs. The light-emitting control unit 705 transmits image data to the signal lines DATA1 to DATA20 in synchronization with the rising edge of the line synchronization signal. In this embodiment, each light-emitting chip 400 has 2992 light-emitting elements 602, and therefore, image data indicating the light-emitting or non-light-emitting status of each of the total 2992 light-emitting elements 602 must be transmitted to each light-emitting chip 400 within a period of approximately 105.8 μs. Therefore, in this example, as shown in FIG. 9, when transmitting image data, the light-emitting control unit 705 sets the frequency of the clock signal transmitted to the signal line CLK to 30 MHz.

[0028] FIG. 10 is a functional block diagram showing a detailed configuration of one light-emitting chip 400 (the n-th light-emitting chip 400-n). As also shown in FIG. 5, the light-emitting chip 400 has nine pads 408-1 to 408-9. The pads 408-1 and 408-2 are connected to a power supply voltage VCC via a power supply line. Power is supplied from this power supply voltage VCC to each circuit of the circuit unit 406 of the light-emitting chip 400. The pads 408-3 and 408-4 are connected to ground via a ground line. Each circuit of the circuit unit 406 and the upper electrode 508 are connected to ground via the pads 408-3 and 408-4. The signal line CLK is connected to the transfer unit 1003, the register 1102, and the latch units 1004-001 to 1004-748 via the pad 408-5. The signal lines SYNC and DATAn are connected to the transfer unit 1003 via the pads 408-6 and 408-7. The signal lines EN and WRITEn are connected via pads 408-8 and 408-9 to a register 1102. The register 1102 stores control data indicating the desired light emission intensity of the light emitting element 602, for example.

[0029] The transfer unit 1003 receives input image data from signal line DATAn, including a series of pixel values ​​each indicating whether one light-emitting element 602 emits light or not, in synchronization with a clock signal from signal line CLK, starting from a line synchronization signal from signal line SYNC. The transfer unit 1003 performs serial-to-parallel conversion on the series of pixel values ​​serially received from signal line DATAn in units of M (e.g., M=4) pixel values. For example, the transfer unit 1003 has four cascade-connected D flip-flops, which parallelize pixel values ​​DATA-1, DATA-2, DATA-3, and DATA-4 input over four clocks and output the parallelized data to latch units 1004-0001 to 1004-748. The transfer unit 1003 also has four D flip-flops for delaying the line synchronization signal, and outputs a first latch signal to the latch unit 1004-001 via signal line LAT1 four clocks after the line synchronization signal is input.

[0030] The kth latch unit 1004-k (k is an integer from 1 to 748) holds, in a latch circuit, four pixel values ​​DATA-1, DATA-2, DATA-3, and DATA-4 input from the transfer unit 1003 simultaneously with the input of the kth latch signal. Except for the final latch unit 1004-748, the kth latch unit 1004-k delays the kth latch signal by four clocks and outputs the (k+1)th latch signal to the latch unit 1004-(k+1) via the signal line LAT(k+1). The kth latch unit 1004-k continues to output a drive signal based on the four pixel values ​​held in the latch circuit to the current drive unit 1104 during the signal period of the kth latch signal. For example, there is a four-clock delay between the timing at which the first latch signal is input to the latch unit 1004-1 and the timing at which the second latch signal is input to the latch unit 1004-2. Therefore, the latch unit 1004-1 outputs drive signals based on the first, second, third, and fourth pixel values ​​to the current driver 1104, while the latch unit 1004-2 outputs drive signals based on the fifth, sixth, seventh, and eighth pixel values ​​to the current driver 1104. Generally speaking, the latch unit 1004-k outputs drive signals based on the (4k-3), (4k-2), (4k-1), and (4k)th pixel values ​​to the current driver 1104. Therefore, in the embodiment shown in FIG. 10 , 748 latch units 1004-001 to 1004-748 output 2992 drive signals for controlling the driving of 2992 (=748×4) light-emitting elements 602 in approximately parallel to the current driver 1104. Each drive signal is a binary signal indicating a high level or a low level.

[0031] The current driver 1104 has 2992 light-emitting drive circuits corresponding to the 2992 light-emitting elements 602, each of which includes a partial region of the light-emitting layer 506. Each light-emitting drive circuit applies a drive voltage corresponding to the light-emitting intensity indicated by the control data in the register 1102 to the light-emitting layer 506 of the corresponding light-emitting element 602 while the corresponding drive signal indicates a high level, which means that light is on. This causes a current to flow through the light-emitting layer 506, causing the light-emitting element 602 to emit light. Note that the control data may indicate one individual light-emitting intensity for each light-emitting element 602, one light-emitting intensity for each group of light-emitting elements 602, or one light-emitting intensity common to all light-emitting elements 602.

[0032] 3. Controlling multiple exposures Although Fig. 4 shows an example in which the light emitting elements 602 are completely arranged in a grid pattern in each light emitting chip 400, in reality, in this embodiment, the M light emitting elements 602 in each row can be arranged in a stepped pattern at a constant pitch. Fig. 11 is an explanatory diagram of multiple exposure using light emitting elements arranged in a stepped pattern. Here, an example of the arrangement of light emitting elements in the light emitting chip 400-1 when M=4 is partially shown. R in the figure j_m (j={0,1,...,J-1}, m={0,1,2,3}) represents the light emitting element 602 in the j-th column from the left in the axial direction and in the m-th row from the top in the circumferential direction. C As mentioned above, the distance between two adjacent light-emitting elements in each row of M light-emitting elements, i.e., the axial pitch P of the light-emitting elements, A may be about 5 μm, which corresponds to a resolution of 4800 dpi.

[0033] By arranging the four light-emitting elements in each column in a stepped manner in this way, any two adjacent light-emitting elements among the four light-emitting elements occupy areas that partially overlap in the axial direction. Then, the four light-emitting elements in the column corresponding to each pixel position of the input image data sequentially emit light while the photoconductor 102 is rotating, forming spots corresponding to each pixel position on the surface of the photoconductor 102. In the example of Figure 11, when the pixel value at the left end of the ith line of the input image data indicates that light is on, the light-emitting element R 0_0 , R 0_1 , R 0_2 , R 0_3 is a line L on the surface of the photoreceptor 102. i As a result, the line L i Similarly, when the j-th pixel value from the left of the ith line of the input image data indicates that light is emitted, the light-emitting element R j_0 , R j_1 , R j_2 , R j_3 is a line L on the surface of the photoreceptor 102. i As a result, the line L i The jth spot area from the left of is multiplexed and the corresponding spot SP j is formed.

[0034] 11, in this embodiment, the light-emitting elements in two axially adjacent rows also occupy areas that partially overlap in the axial direction. Similarly, of the two axially adjacent light-emitting chips 400, the light-emitting elements in the rightmost row of the left light-emitting chip 400 and the light-emitting elements in the leftmost row of the right light-emitting chip 400 also occupy areas that partially overlap in the axial direction. The axial pitch P of the light-emitting elements across all 20 light-emitting chips 400 is Ais a constant value of about 5 μm. By sequentially emitting light at appropriate times from the four light-emitting elements in each row of these light-emitting chips 400, smooth lines of an electrostatic latent image can be formed on the surface of the photoreceptor 102, each consisting of a series of spots that are partially overlapping each other and have a constant spot spacing. As a result of these lines being continuously formed in the circumferential direction, a two-dimensional electrostatic latent image is created.

[0035] 12A to 12D are explanatory diagrams of the procedure for controlling light emission based on input image data. During image formation, the light emission control unit 705 receives input image data IM1 in a binary bitmap format from the image data processing unit 703. On the left side of FIG. 12A, the j-th pixel value from the left on the i-th line from the top of the input image data IM1, which is a two-dimensional pixel value array, is represented as (j, i) (j = {0, 1, 2, ...}, i = {0, 1, 2, ...}). The light emission control unit 705 adds dummy pixel values ​​for (M-1) lines to the beginning of the input image data IM1. When M = 4, including the added dummy pixel values, the range of pixel value index i is {-3, -2, -1, 0, 1, 2, ...}. The dummy pixel value may be, for example, zero, which indicates that light emission is off. The light emission control unit 705 may add dummy pixel values ​​to the left and right of the input image data IM1 so that the number of pixel values ​​in one line is equal to the number of light emitting elements in the axial direction, but for simplicity of explanation, only effective pixel values ​​are shown here in the axial direction.

[0036] In the first line period t0 of image formation, the light-emitting control unit 705 reads out pixel values ​​of the top four lines of the input image data IM1 and outputs a subset of 2992 (=748×4) of the read pixel values ​​to the light-emitting chip 400-n via the signal line DATAn. Focusing on the light-emitting chip 400-1 shown on the right in FIG. 12A, image data within a read range RD including pixel values ​​from (0,-3) to (748,0) is input via the signal line DATA1 during the line period t0. The light-emitting chip 400-1 serial-to-parallel converts the input image data and supplies drive signals based on these pixel values ​​to each of the 2992 light-emitting elements. For example, drive signals based on pixel values ​​(0,-3), (0,-2), (0,-1), (0,0), and (1,-3) are output to the light-emitting element R. 0_0 , R 0_1 , R 0_2 , R 0_3 and R 1_0 In particular, as shown by the broken line in the figure, the light emitting element R 0_3 A drive signal based on the effective pixel value of line DL0 of index i=0 in the input image data IM1 is supplied to the light-emitting elements in the fourth row, including line L0. As a result, line L0 on the surface of photoconductor 102 is exposed in accordance with the set of pixel values ​​of line DL0 in the input image data IM1. However, at this point, multiple exposure is still in progress, and the formation of the electrostatic latent image of line L0 is not complete.

[0037] FIG. 12B shows how the light-emitting chip 400-1 is driven during the next line period t0+1. In the line period t0+1, the light-emitting control unit 705 moves the readout range RD of the input image data IM1 down by one line, reads out pixel values ​​from (0,-2) to (748,1), and outputs them to the light-emitting chip 400-1 via the signal line DATA1. The light-emitting chip 400-1 supplies drive signals based on the input pixel values ​​to the 2992 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 R. 0_0 , R 0_1 , R 0_2 , R 0_3 and R 1_0In the line period t0+1, the light emitting element R 0_2 A drive signal based on the effective pixel values ​​of line DL0 of the input image data IM1 is supplied to the light-emitting elements in the third row, including line L0. At this time, since the photoconductor 102 is rotating in the circumferential direction, line L0 on the surface of the photoconductor 102 faces the light-emitting elements in the third row of the light-emitting chip 400-1. As a result, line L0 on the surface of the photoconductor 102 is again exposed in accordance with the set of pixel values ​​of line DL0 of the input image data IM1.

[0038] FIG. 12C shows how the light-emitting chip 400-1 is driven during the next line period t0+2. In the line period t0+2, the light-emitting control unit 705 moves the readout range RD of the input image data IM1 further down by one line, reads out pixel values ​​from (0, -1) to (748, 2), and outputs them to the light-emitting chip 400-1 via the signal line DATA1. The light-emitting chip 400-1 supplies drive signals based on the input pixel values ​​to the 2992 light-emitting elements. In the line period t0+2, the light-emitting elements R 0_1 A drive signal based on the effective pixel value of line DL0 of the input image data IM1 is supplied to the light-emitting elements of the second row including line L0 on the surface of the photoconductor 102. At this time, line L0 on the surface of the photoconductor 102 faces the light-emitting elements of the second row of light-emitting chip 400-1. As a result, line L0 on the surface of the photoconductor 102 is exposed a third time in accordance with the pixel value set of line DL0 of the input image data IM1.

[0039] FIG. 12D shows how the light-emitting chip 400-1 is driven during the next line period t0+3. In the line period t0+3, the light-emitting control unit 705 moves the read range RD of the input image data IM1 further down by one line, reads out pixel values ​​from (0,0) to (748,3), and outputs them to the light-emitting chip 400-1 via the signal line DATA1. The light-emitting chip 400-1 supplies drive signals based on the input pixel values ​​to the 2992 light-emitting elements. In the line period t0+3, the light-emitting elements R 0_0A drive signal based on the effective pixel value of line DL0 of the input image data IM1 is supplied to the light-emitting elements of the first row, including the light-emitting elements of the light-emitting chip 400-1. At this time, line L0 on the surface of the photoconductor 102 faces the light-emitting elements of the first row of the light-emitting chip 400-1. As a result, line L0 on the surface of the photoconductor 102 is exposed a fourth time according to the set of pixel values ​​of line DL0 of the input image data IM1. At this point, multiple exposure has been performed by the four light-emitting elements of each column of the light-emitting chip 400, and the formation of line L0 of the electrostatic latent image is completed. Lines subsequent to line L0 of the electrostatic latent image can also be formed on the surface of the photoconductor 102 in a similar manner through repetition of this line period. In this manner, in this embodiment, each pixel value from (0,0) to (748,3) is input to four light-emitting elements. Specifically, for example, the pixel value of (0,0) is input to four light-emitting elements R 0_0、 R 0_1 , R 0_2 , R 0_3 For example, the pixel value of (1,0) is input to the four light-emitting elements R 1_0、 R 1_1 , R 1_2 , R 1_3 That is, the spot on the photoconductor corresponding to the pixel value of (0,0) is input to the four light-emitting elements R 0_0、 R 0_1 , R 0_2 , R 0_3 The spot on the photoconductor corresponding to the pixel value of (1,0) is formed by the four light-emitting elements R 1_0、 R 1_1 , R 1_2 , R 1_3 is formed by

[0040] As can be understood from the above explanation, the light emission control unit 705 causes the plurality of light emitting elements 602 to emit light based on pixel values ​​read from a read range spanning M lines of the input image data IM1. The read range moves by one line per line period. Such control of the read range is also performed in the compensation for positional deviation, which will be described next.

[0041] In this embodiment, each of the light-emitting chips 400 is adhered to the printed circuit board 202 by an adhesive applied to the printed circuit board 202. When attaching the light-emitting chips 400 to the printed circuit board 202, it is preferable that they are mounted at ideal designed positions; however, depending on the placement accuracy during mounting, the light-emitting chips 400 may be mounted in a state deviated from the designed positions.

[0042] FIG. 9 is a diagram illustrating a state in which each light-emitting chip 400 is mounted on a printed circuit board 202 while being displaced from its design position. Factors that can cause the mounting positions of the light-emitting chips 400 to be displaced from their design positions include poor placement accuracy and thermal contraction that occurs when the adhesive that bonds the printed circuit board 202 and the light-emitting chip 400 hardens. The chip mounting position can be displaced in the longitudinal direction, lateral direction, and rotational direction of the light-emitting chip 400. FIG. 9 illustrates a case in which a displacement occurs in the rotational direction of the light-emitting chip 400. When a chip is mounted on the printed circuit board 202 rotated relative to its design position, a large displacement occurs in the relative positions of adjacent light-emitting chips 400 at the boundary between them. D1 is a value that indicates the amount of displacement from the design value of adjacent light-emitting chips 400 in the lateral direction of the board. If the amount of displacement D1 is large, a displacement occurs in the exposure position at the boundary between the light-emitting chips 400, which may affect image formation on a recording medium.

[0043] To address the above-mentioned issues, a method has been studied for reducing the deviation in the image formation position at the boundary between the light-emitting chips 400 by shifting the image data used for exposure. Fig. 10 is a diagram showing an example of a case where the image data is shifted in accordance with the deviation in the mounting position of the light-emitting chips 400. By shifting the image data as described above, it is possible to reduce the influence of the deviation in the position at the boundary between the light-emitting chips 400 in the sub-scanning direction on the image formation position.

[0044] However, while shifting the image data can reduce deviation of the image formation position at the boundary of the light-emitting chip 400, the image formation position may have a certain inclination with respect to the main scanning direction. In particular, when inclination occurs in the image formation position of a certain color, deviation occurs compared to colors without inclination, and there is a risk of deterioration in the quality of the formed image.

[0045] To address the above-mentioned issues, the present invention divides the area within the light-emitting chip 400 in the main scanning direction into multiple regions, and performs control to shift image data independently for regions corresponding to the boundaries of the light-emitting chip 400 and other regions. Figure 11 illustrates an example of dividing the area within the light-emitting chip 400. In this embodiment, the area within the light-emitting chip 400 is divided into four regions. In the divided regions corresponding to the boundaries of the light-emitting chip 400, the amount of shift of image data is determined so as to reduce the deviation of the image formation position in the sub-scanning direction. In this embodiment, the image data is shifted so that the deviation of the image formation position at the boundaries of the light-emitting chip 400 is one pixel or less in the sub-scanning direction. However, the shift amount is not limited to this, and the deviation of the image formation position may be one pixel or more. Note that, since the image forming device in this embodiment has an image formation resolution of 2400 dpi (10.5 μm) in the sub-scanning direction, the image data is shifted so that the deviation of the image formation position is 10.5 μm or less.

[0046] Among the regions into which the light-emitting chip is divided, in regions adjacent to regions corresponding to boundaries of the light-emitting chip 400, the shift amount of the image data is controlled so that the shift amount of the image data between the adjacent regions is one pixel or less. By controlling the shift amount of the image data as described above, it is possible to reduce the risk of significant deviation of the image formation position occurring in regions inside the light-emitting chip 400.

[0047] The above-described process achieves control that eliminates both streaks and color misregistration between chips. In this embodiment, a method of dividing the chip into four parts in the main scanning direction is used as an example. However, if the amount of rotation of the chip is large, the amount of shift within the chip increases. In this case, increasing the number of divisions into blocks in the main scanning direction can address streaks and color misregistration. For example, if the amount of rotation of the chip is large and the left-right positional deviation of the chip from the ideal position L is 50 μm, setting the number of divisions to 6 allows for five shifts within the chip, making it possible to correct the 50 μm deviation.

Claims

[Claim 1] A rotating photoreceptor; a plurality of light-emitting chips each having a plurality of light-emitting elements arranged along the rotation axis direction of the photosensitive member; a lens that focuses light emitted from the plurality of light-emitting chips onto a surface of the photosensitive member; a control unit that outputs image data for driving the plurality of light-emitting elements; Equipped with the control unit divides the light-emitting chip into a plurality of regions in the direction of the rotation axis, shifting the image data in a region corresponding to a boundary between the plurality of light emitting chips among the plurality of regions so as to reduce a mounting position deviation of the light emitting chips; An image forming apparatus characterized by:

Images