Image forming device

Abstract

To suppress deterioration in image quality caused by a mounting deviation of a light-emitting chip.SOLUTION: An image forming device includes: a photosensitive drum (102); an exposure head (106) which has a plurality of light-emitting chips (400) each including a plurality of light-emitting elements (602), and exposes the photosensitive drum (102) by the plurality of light-emitting elements (602) to form an image; an image controller (700) which transmits image data to the exposure head (106) so that the exposure head (106) forms, on the photosensitive drum (102), an image corresponding to the image data; and a storage unit (710) which stores a mounting deviation amount representing a deviation of an actual mounting position of each of the plurality of light-emitting chips (400) from a reference position. The image controller (700) divides the image data into a plurality of pieces of partial image data according to the number of the light-emitting chips (400), and transmits the partial image data to respective corresponding light-emitting chips (400) at timings based on the mounting deviation amount.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus equipped with an exposure device having a plurality of light-emitting elements. [Background technology]

[0002] Electrophotographic image forming apparatuses form images by exposing a rotating photosensitive drum to light and forming an electrostatic latent image, which is then developed with toner. Exposure devices that expose the photosensitive drum include those of a solid-state exposure type that have multiple light-emitting chips, each of which has multiple light-emitting elements arranged in a plane. Solid-state exposure exposure devices are arranged parallel to the rotation axis (drum axis) of the photosensitive drum. Patent Document 1 discloses an image forming apparatus that uses a solid-state exposure light-emitting device. In this light-emitting device, multiple light-emitting chips are arranged in a staggered pattern along the rotation axis direction of the photosensitive drum. This configuration makes it easy to change the size of the exposure device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-183436 Summary of the Invention [Problem to be solved by the invention]

[0004] Multiple light-emitting chips are mounted on the printed circuit board of the exposure device. Light-emitting chips can be mounted misaligned from their ideal positions during mounting. The amount of misalignment varies depending on the light-emitting chip. Misalignment of light-emitting chips can cause a decrease in the quality of the image formed. To prevent misalignment of each light-emitting chip, it is important to improve the mounting accuracy in the manufacturing process. However, improving the mounting accuracy in the manufacturing process increases costs. Therefore, there is a trade-off between mounting accuracy and cost.

[0005] In view of the above-mentioned problems, the present invention has as its main object to provide an image forming apparatus that suppresses degradation of image quality caused by misalignment of light-emitting chips. [Means for solving the problem]

[0006] The image forming apparatus of the present invention comprises a photosensitive body, an exposure means having a plurality of light-emitting chips each including a plurality of light-emitting elements, and exposing the photosensitive body to the plurality of light-emitting elements to form an image, a control means transmitting image data to the exposure means and forming an image on the photosensitive body according to the image data by the exposure means, and a storage means storing an amount of mounting deviation representing the deviation of the mounting position of each of the plurality of light-emitting chips from a reference position, wherein the control means divides the image data into a plurality of partial image data according to the number of light-emitting chips, and transmits the partial image data to each corresponding light-emitting chip at a timing based on the amount of mounting deviation. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress deterioration in image quality caused by misalignment of the light-emitting chips. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 2] 4A and 4B are explanatory diagrams of a photosensitive drum and an exposure head. [Figure 3] (a) and (b) are explanatory diagrams of a printed circuit board. [Figure 4] FIG. [Figure 5] FIG. [Figure 6] Cross section AA of Figure 5. [Figure 7] FIG. 3 is a diagram illustrating the configuration of an image controller. [Figure 8] 10 is a timing chart for writing control data. [Figure 9] 10 is a timing chart for transmitting print image data. [Figure 10] Detailed functional diagram of one light-emitting chip. [Figure 11] FIG. [Figure 12] FIG. [Figure 13] FIG. [Figure 14] 10A and 10B are diagrams illustrating output control of partial image data. [Figure 15] 10A and 10B are diagrams illustrating output control of partial image data. [Figure 16] FIG. 10 is an explanatory diagram of output control of partial image data. [Figure 17] FIG. 10 is an explanatory diagram of misalignment of the light-emitting chip. [Figure 18] FIG. 10 is an explanatory diagram of output control of partial image data when there is no mounting misalignment. [Figure 19] 10A to 10D are explanatory diagrams of output control of partial image data when there is no mounting misalignment. [Figure 20] 10A to 10D are explanatory diagrams of output control of partial image data when there is no mounting misalignment. [Figure 21] FIG. 10 is an explanatory diagram of output control of partial image data in a state where mounting misalignment occurs. [Figure 22] 10A to 10D are explanatory diagrams of output control of partial image data when there is mounting misalignment. [Figure 23] 10A to 10E are explanatory diagrams of output control of partial image data when there is mounting misalignment. [Figure 24] 10 is a flowchart showing an exposure control process. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the present invention will be described below 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.

[0010] (Image forming device) 1 is a diagram showing the configuration of an image forming apparatus according to this embodiment. Image forming apparatus 1 includes a reading unit 100, an image creating unit 103, a fixing unit 104, and a conveying unit 105. Reading unit 100 optically reads an original placed on a platen to generate read image data. Image creating unit 103 forms an image on a sheet based on the read image data generated by reading unit 100 or print image data acquired from an external device via a network. Such image forming apparatus 1 may be realized by, for example, a copier, a multifunction peripheral, or an MFP (Multi Function Peripheral).

[0011] The image forming unit 103 has multiple image forming units 101a, 101b, 101c, and 101d, a transfer belt 111 that transports sheets, and an optical sensor 113. The image forming units 101a, 101b, 101c, and 101d are used to form toner images of black (K), yellow (Y), magenta (M), and cyan (C), respectively. The image forming units 101a, 101b, 101c, and 101d have the same configuration, and will hereinafter be collectively referred to as image forming unit 101.

[0012] The image forming unit 101 includes a photosensitive drum 102, a charger 107, an exposure head 106, and a developing unit 108. The photosensitive drum 102 is a drum-shaped photosensitive member (image carrier) having a photosensitive layer on its surface. The photosensitive drum 102 is driven to rotate clockwise in FIG. 1 around the drum axis. The charger 107 uniformly charges the surface of the rotating photosensitive drum 102 to a predetermined potential with a predetermined polarity. The exposure head 106 is an exposure device that exposes the uniformly charged surface of the photosensitive drum 102 to light, thereby forming an electrostatic latent image on the surface of the photosensitive drum 102. As will be described in detail later, the exposure head 106 of this embodiment has a configuration in which multiple light-emitting elements are arranged in a plane.

[0013] The developing unit 108 develops the electrostatic latent image formed on the photosensitive drum 102 with a developer (e.g., toner) to form a toner image on the surface of the photosensitive drum 102. The toner images formed on the surface of the photosensitive drum 102 are sequentially transferred to a sheet transported on a transfer belt 111. The toner images of the four photosensitive drums 102 are superimposed and transferred to the sheet. As a result, a color image containing four color components, black, yellow, magenta, and cyan, is formed on the sheet. The optical sensor 113 optically reads the adjustment image formed on the transfer belt 111 by the image forming unit 101.

[0014] The conveying unit 105 controls the feeding of sheets. Sheets can be fed from the internal storage units 109a and 109b, the external storage unit 109c, and the manual feed unit 109d. The conveying unit 105 feeds a sheet from any one of the internal storage units 109a and 109b, the external storage unit 109c, and the manual feed unit 109d to the conveying path. Registration rollers 110 are provided on the conveying path. The fed sheet is conveyed to the registration rollers 110.

[0015] The registration rollers 110 correct any skew of the sheet and transport the sheet onto the transfer belt 111 at the appropriate timing so that the toner images on the photosensitive drums 102 are transferred to the predetermined positions on the sheet. As described above, the toner images are transferred onto the sheet while it is transported on the transfer belt 111. The fixing unit 104 fixes the toner images onto the sheet by applying heat and pressure to the sheet onto which the toner images have been transferred. After the toner images have been fixed, the sheet is discharged outside the image forming apparatus 1 by the discharge rollers 112.

[0016] An image controller (described later) is provided inside the image forming apparatus 1, which performs various types of image processing such as color space conversion, filtering, magnification, resolution conversion, and quantization on the scanned image data and print image data. The image controller generates print image data (hereinafter sometimes simply referred to as "image data") for image formation by the image creating unit 103 based on the scanned image data and print image data through image processing. The image controller includes an image processing module that performs the various types of image processing described above.

[0017] Although a configuration has been described here in which a toner image is directly transferred from each photosensitive drum 102 to a sheet on the transfer belt 111, the toner image may also be indirectly transferred from each photosensitive drum 102 to a sheet via an intermediate transfer body. Also, although an example in which a color image is formed using toner of multiple colors has been described here, the technology according to this embodiment is also applicable to an image forming apparatus that forms a monochrome image using toner of a single color.

[0018] (Exposure head) 2 is an explanatory diagram of the photosensitive drum 102 and the exposure head 106. Fig. 2(a) is a perspective view of the photosensitive drum 102 and the exposure head 106. Fig. 2(b) is an explanatory diagram of the exposure position. The exposure head 106 has a light emitting element array 201 having a plurality of light emitting elements, 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.

[0019] As described above, the photosensitive drum 102 has a drum shape. The exposure head 106 is disposed so that its longitudinal direction is parallel to the drum axis direction D1 of the photosensitive drum 102 and the mounting surface of the rod lens array 203 faces the surface of the photosensitive drum 102. While the photosensitive drum 102 rotates in the circumferential direction D2, the light-emitting element array 201 (light-emitting elements) of the exposure head 106 emits light, and the rod lens array 203 focuses the light on the surface of the photosensitive drum 102. The surface of the photosensitive drum 102 is uniformly charged by the charger 107, and the potential at the position where the light is focused is displaced. The position where the potential is displaced becomes an electrostatic latent image.

[0020] The light-emitting element array 201 has a plurality of light-emitting elements arranged in a plane. The light-emitting elements may be, for example, organic electroluminescence (EL) elements or light-emitting diodes (LEDs). The drum axial direction D1 is the main scanning direction, and the circumferential direction D2 is the sub-scanning direction perpendicular to the main scanning direction.

[0021] FIG. 3 is an explanatory diagram of the printed circuit board 202. A connector 305 and a light emitting element array 201 are mounted on different surfaces of the printed circuit board 202. FIG. 3(a) shows the surface of the printed circuit board 202 on which the connector 305 is mounted. FIG. 3(b) shows the surface of the printed circuit board 202 on which the light emitting element array 201 is mounted. The light emitting element array 201 includes a plurality of light emitting chips 400, each having a plurality of light emitting elements. In this embodiment, there are 20 light emitting chips 400 (light emitting chips 400-1 to 400-20). The light emitting chips 400-1 to 400-20 are arranged in a staggered pattern in the main scanning direction.

[0022] 3(b), the area occupied by all of the 20 light-emitting chips 400-1 to 400-20 in the main scanning direction is wider than the area occupied by the maximum width W0 of the image represented by the print image data. Therefore, some of the light-emitting elements located at both ends in the main scanning direction do not need to be used to expose the photosensitive drum 102 unless image misalignment is detected. Each light-emitting chip 400 on the printed circuit board 202 is connected to an image controller (described later) via a connector 305.

[0023] For ease of explanation, the side with the smaller branch number of the light-emitting chips 400-1 to 400-20 arranged in the main scanning direction 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. In FIG. 4, the two rightmost light-emitting chips 400-n and 400-n+1 are illustrated.

[0024] FIG. 4 is an explanatory diagram of the light-emitting chip 400. The light-emitting element array 201 of this embodiment includes a plurality of light-emitting elements arranged in N columns in the main scanning direction and M rows in the sub-scanning direction as a whole. M and N are integers equal to or greater than 2. The number J (J=N / 20) of light-emitting elements 602 arranged in each row (main scanning direction) of one light-emitting chip 400 is, for example, 748 (J=748). The number M of light-emitting elements 602 arranged in each column (sub-scanning direction) of one light-emitting chip 400 is, for example, 4 (M=4). That is, in this example of this embodiment, the light-emitting chip 400 has 748 light-emitting elements 602 in the main scanning direction and 4 light-emitting elements in the sub-scanning direction, for a total of 2992 (=748×4) light-emitting elements 602.

[0025] The distance PC between the center points of adjacent light-emitting elements 602 in the sub-scanning direction is approximately 21.16 μm when the resolution is 1200 dpi, for example. The distance between the center points of adjacent light-emitting elements 602 in the main scanning direction is also approximately 21.16 μm. In this case, the length of the 748 light-emitting elements 602 in the main scanning direction is approximately 15.8 mm.

[0026] For convenience, FIG. 4 shows an example in which the light-emitting elements 602 of each light-emitting chip 400 are arranged in a complete grid pattern, but in reality, M (M=4) light-emitting elements 602 in each row are arranged in a staircase pattern. This point will be described later. The light-emitting chips 400 are arranged in a staggered pattern in the main scanning direction. The distance S between the light-emitting chips 400 in the sub-scanning direction is determined by the resolution of the image in the sub-scanning direction and the rotation speed of the photosensitive drum 102. The distance S is set to, for example, 102 μm.

[0027] 5 is a plan view of the light-emitting chip 400. A plurality of light-emitting elements 602 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 mounted on the light-emitting substrate 402. The light-emitting substrate 402 is provided with pads 408-1 to 408-9 to which signal lines for communicating with an image controller, power lines for connecting to a power source, and ground lines for grounding are connected. The signal lines, power lines, and ground lines are wires made of, for example, Au.

[0028] Figure 6 is a cross-sectional view taken along the line AA in Figure 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.

[0029] When a potential difference occurs 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 that lower electrode 504 constitute one light-emitting element 602. In this way, a plurality of light-emitting elements 602 are formed on the light-emitting substrate 402.

[0030] The light-emitting layer 506 may be made of, for example, an organic EL film. The upper electrode 508 is made of, for example, a transparent electrode such as indium tin oxide (ITO) so as to transmit the wavelength of light (emission wavelength) emitted from the light-emitting layer 506. In this embodiment, the entire upper electrode 508 transmits the emission wavelength of the light-emitting layer 506, but it is not necessary for the entire upper electrode 508 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.

[0031] Although the light-emitting layer 506 of the present embodiment is formed as a single continuous light-emitting layer 506, a plurality of 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, respectively. Furthermore, a first plurality of lower electrodes 504 of the lower electrodes 504 of each light-emitting chip 400 may be covered with a first light-emitting layer 506, and a second plurality of lower electrodes 504 may be covered with a second light-emitting layer 506. Furthermore, a first upper electrode 508 may be commonly formed corresponding to the first plurality of lower electrodes 504 of the lower electrodes 504 of each light-emitting chip 400, 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.

[0032] (Image controller of exposure head 106) 7 is a configuration diagram of an image controller that controls the turning on and off of the light-emitting chip 400. The image controller 700 can communicate with the printed circuit board 202 via multiple signal lines (wires). The image controller 700 has a CPU (Central Processing Unit) 701, a clock generation unit 702, an image data processing unit 703, a register access unit 704, a light emission control unit 705, and a synchronization signal generation unit 706.

[0033] The light-emitting control unit 705, together with the exposure head 106, constitutes an exposure device. The light-emitting control unit 705 terminates the signal line between it and the printed circuit board 202. The n-th light-emitting chip 400-n on the printed circuit board 202 is connected to the light-emitting control unit 705 by a signal line DATAn and a signal line WRITEn. The signal line DATAn transmits print image data from the image controller 700 to the light-emitting chip 400-n. The signal line WRITEn is a signal line that allows the image controller 700 to write control data to a register of the light-emitting chip 400-n.

[0034] 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 transmits a clock signal for data transmission via the signal lines DATAn and WRITEn. The clock generation unit 702 generates a reference clock signal and transmits it to each unit of the image controller 700. The light-emitting control unit 705 transmits a clock signal generated based on the reference clock signal obtained from the clock generation unit 702 to each light-emitting chip 400 via the signal line CLK.

[0035] The synchronization signal generation unit 706 generates and outputs a synchronization signal synchronized with the reference clock signal obtained from the clock generation unit 702. The synchronization signal is a reference signal for the output timing of print image data from the output unit in the image data processing unit 703, and serves as a reference signal for the timing of sending print image data from the light emission control unit 705 to each light-emitting chip 400. The synchronization signal generation unit 706 outputs print image data from the light emission control unit 705 while coordinating with the image formation operation by the image creation unit 103, and generates the synchronization signal based on an image formation operation start signal (referred to as a "TOP signal" in this embodiment) from the image creation unit 103.

[0036] The CPU 701 controls the overall operation of the image forming apparatus 1. The image data processing unit 703 performs predetermined image processing on read image data and print image data acquired from the reading unit 100 or an external device. By performing image processing, the image data processing unit 703 generates binary image data (print image data) for controlling the light emission of the light emitting element 602 of the light emitting chip 400 on the printed circuit board 202.

[0037] The image processing performed by the image data processing unit 703 includes, for example, raster conversion, tone correction, color conversion, and halftone processing. The image data processing unit 703 transmits the generated binary image data (print image data) to the light emission control unit 705. The register access unit 704 receives control data to be written to the register in each light-emitting chip 400 from the CPU 701 and transmits it to the light emission control unit 705.

[0038] The print image data is data indicating whether or not each light-emitting element 602 is to emit light when exposing each line in the main scanning direction of the photosensitive drum 102. In this embodiment, as an example, the resolution of the image represented by the print image data processed by the image data processing unit 703 is set to 4800 dpi in the main scanning direction and 1200 dpi in the sub-scanning direction.

[0039] The printed circuit board 202 has a storage unit 710. The storage unit 710 is configured, for example, with a nonvolatile memory, and stores profile information indicating characteristics unique to the exposure head 106. In this embodiment, the storage unit 710 stores, as one piece of profile information, information (position information) relating to the mounting position of each of the plurality of light-emitting chips 400. The position information includes information on the mounting deviation from the ideal mounting position of each of the light-emitting chips 400 (mounting deviation amount, mounting deviation direction, etc.). The position information is generated from the actual measurement values ​​of the mounting positions of each of the plurality of light-emitting chips 400 and the ideal mounting positions when the exposure head 106 is manufactured or when the exposure head 106 is attached to the image forming apparatus 1, and is stored in the storage unit 710.

[0040] The storage unit 710 is capable of communicating with the CPU 701 of the image controller 700. The CPU 701 reads out the position information of each light-emitting chip 400 from the storage unit 710 and performs processing to suppress misalignment in mounting.

[0041] The image forming apparatus 1 has an exposure head 106 in each of the image forming units 101a to 101d. That is, in this embodiment, four printed circuit boards 202 are provided. The image controller 700 is connected to these four printed circuit boards 202, and controls the lighting of the multiple light-emitting elements 602 mounted on each of the four printed circuit boards 202.

[0042] FIG. 8 is a timing chart when control data is written to the register of each light-emitting chip 400. 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, which is at a high level during communication and indicates that communication is in progress, is transmitted 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, which indicates a write operation, to the signal line WRITEn, and then transmits the address (4 bits in this case) of the register to which the control data is to be written and the control data (8 bits in this case). When writing to the register, the light-emitting control unit 705 sets the frequency of the clock signal transmitted on the signal line CLK to, for example, 3 MHz.

[0043] 9 is a timing chart illustrating the transition of the signal level of each signal line when print image data is transmitted to each light-emitting chip 400. A periodic line synchronization signal indicating the exposure timing of each line on the photosensitive drum 102 is transmitted to the signal line SYNC. If the peripheral speed of the photosensitive drum 102 is 200 [mm / s] and the circumferential resolution is 1200 [dpi] (approximately 21.16 [μm]), the line synchronization signal is output at a period of approximately 105.8 [μs].

[0044] The light emission control unit 705 transmits print image data via signal lines DATA1 to DATA20 in synchronization with the rising edge of the line synchronization signal. Since each light emitting chip 400 in this embodiment has 2992 light emitting elements 602, it is necessary to transmit print image data to each light emitting chip 400 within a cycle of approximately 105.8 [μs] to control the light emission (illumination) of each of the 2992 light emitting elements 602. Therefore, in this embodiment, as shown in FIG. 9, when transmitting print image data, the light emission control unit 705 sets the frequency of the clock signal transmitted via the signal line CLK to 30 [MHz].

[0045] 10 is a detailed functional configuration diagram of one (n-th light-emitting chip 400-n) of the light-emitting chip 400. The circuit unit 406 includes a register 1102, a transfer unit 1103, latch units 1004-001 to 1004-748, and a current driver 1104.

[0046] As described in FIG. 5, the light-emitting chip 400 has nine pads 408-1 to 408-9. A power supply voltage VCC is applied to the pads 408-1 and 408-2 via a power supply line. The power supply voltage VCC is applied to each part of the circuit unit 406 of the light-emitting chip 400 via the pads 408-1 and 408-2. The pads 408-3 and 408-4 are grounded via a ground line. Each part of the circuit unit 406 and the upper electrode 508 are grounded via the pads 408-3 and 408-4.

[0047] The pad 408-5 is connected to a signal line CLK. The signal line CLK is connected to the transfer unit 1103, the register 1102, and the latch units 1004-001 to 1004-748 via the pad 408-5. The pad 408-6 is connected to a signal line SYNC. The pad 408-7 is connected to a signal line DATAn. The signal lines SYNC and DATAn are connected to the transfer unit 1103 via the pads 408-6 and 408-7. The pad 408-8 is connected to a signal line EN. The pad 408-9 is connected to a signal line WRITEn. The signal lines EN and WRITEn are connected to the register 1102 via the pads 408-8 and 408-9. The register 1102 stores control data indicating, for example, the light emission intensity of the light emitting element 602.

[0048] The transfer unit 1103 starts with a line synchronization signal obtained from the signal line SYNC, and synchronizes with a clock signal obtained from the signal line CLK to obtain print image data from the signal line DATAn, the print image data including a series of pixel values ​​each indicating the lighting or extinguishing of one light-emitting element 602. The transfer unit 1103 performs serial-to-parallel conversion on the series of pixel values ​​serially obtained from the signal line DATAn in units of M (for example, M=4).

[0049] For example, the transfer unit 1103 has four cascade-connected D flip-flops. The transfer unit 1103 parallelizes pixel values ​​DATA-1, DATA-2, DATA-3, and DATA-4 input over a period of four clocks and sequentially transmits them to the latch units 1004-001 to 1004-748. The transfer unit 1103 also has four D flip-flops for delaying the line synchronization signal. The transfer unit 1103 outputs a first latch signal to the latch unit 1004-001 via the signal line LAT1 with a delay of four clocks from the input of the line synchronization signal. The first latch signal is, for example, a signal obtained by delaying the line synchronization signal by four clocks.

[0050] The kth latch unit 1004-k (k is an integer from 1 to 748) latches four pixel values ​​DATA-1, DATA-2, DATA-3, and DATA-4 input from the transfer unit 1103 simultaneously with the input of the kth latch signal. Except for the last-stage 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 drive signals based on the four latched pixel values ​​to the current drive unit 1104 during the signal period of the kth latch signal.

[0051] For example, there is a delay of four clocks between the timing at which the first latch signal is input to latch unit 1004-001 and the timing at which the second latch signal is input to latch unit 1004-002. Therefore, latch unit 1004-001 outputs a drive signal based on the first to fourth pixel values ​​to current driver 1104, while latch unit 1004-002 outputs a drive signal based on the fifth to eighth pixel values ​​to current driver 1104.

[0052] Generally speaking, the latch unit 1004-k outputs drive signals based on the (4k-3)th to (4k)th pixel values ​​to the current driver 1104. Therefore, in Fig. 10, 748 latch units 1004-001 to 1004-748 output 2992 drive signals in approximately parallel to the current driver 1104 for controlling the driving of 2992 (=748 × 4) light-emitting elements 602. Each drive signal is a binary signal indicating a high or low level.

[0053] 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. While the drive signal is at a high level, which means that the light-emitting element 602 is on (lit), 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. This causes a current to flow through the light-emitting layer 506, causing the light-emitting element 602 to emit light. 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.

[0054] (Multiple exposure control) 4 shows an example in which the light-emitting elements 602 of each light-emitting chip 400 are arranged in a grid pattern, but in reality, the M light-emitting elements 602 in each row are arranged in a stepped pattern at a constant pitch. Fig. 11 is an explanatory diagram of multiple exposure using the light-emitting elements 602 arranged in a stepped pattern. Fig. 11 partially illustrates an example of the arrangement of the light-emitting elements 602 of the light-emitting chip 400-1 when M=4.

[0055] Rj_m (j = {0, 1, ..., 747}, m = {0, 1, 2, 3}) indicates the light-emitting element 602 that is in the jth column from the left in the main scanning direction and the mth row from the top in the sub-scanning direction. The pitch PC of the light-emitting elements in the sub-scanning direction is determined by the size of the light-emitting elements 602 and is, for example, approximately 21.16 μm as described above. The interval in the main scanning direction between two adjacent light-emitting elements of the M light-emitting elements in each column, i.e., the pitch PA of the light-emitting elements 602 in the main scanning direction, is, for example, approximately 5 μm in the case of a resolution of 4800 dpi.

[0056] In this way, the four light-emitting elements 602 in each column are arranged in a stepped pattern, shifted in the main scanning direction, so that any two adjacent light-emitting elements 602 of the four light-emitting elements 602 have areas that partially overlap in the main scanning direction. While the photosensitive drum 102 is rotating, the four light-emitting elements 602 in the column corresponding to each pixel position of the print image data sequentially emit light, forming spots corresponding to each pixel position on the surface of the photosensitive drum 102.

[0057] In the example of FIG. 11, when the pixel value at the left end of the ith line of the print image data indicates lighting (ON), the light-emitting elements R0_0, R0_1, R0_2, and R0_3 sequentially emit light at the timings at which they respectively face the line Li on the surface of the photosensitive drum 102. As a result, the spot area at the left end of the line Li is multiplexedly exposed to form a spot SP0. Similarly, when the jth pixel value from the left of the ith line of the print image data indicates lighting (ON), the light-emitting elements Rj_0, Rj_1, Rj_2, and Rj_3 sequentially emit light at the timings at which they respectively face the line Li on the surface of the photosensitive drum 102. As a result, the jth spot area from the left of the line Li is multiplexedly exposed to form a corresponding spot SPj.

[0058] In this manner, in this embodiment, the light-emitting elements in two rows adjacent to each other in the fast scanning direction occupy areas that partially overlap in the fast scanning direction. Similarly, of the two light-emitting chips 400 adjacent to each other in the fast scanning direction, 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 fast scanning direction (see FIG. 3(b)).

[0059] The pitch PA of the light-emitting elements 602 in the main scanning direction is constant (approximately 5 μm) across all 20 light-emitting chips 400. When the four light-emitting elements in each row of these light-emitting chips 400 emit light sequentially at appropriate timing, a smooth line of an electrostatic latent image is formed on the surface of the photosensitive drum 102, consisting of a series of spots that partially overlap each other at regular intervals. When such lines are formed continuously in the sub-scanning direction, a two-dimensional electrostatic latent image is generated on the surface of the photosensitive drum 102.

[0060] (Light Emission Control Unit) 12 is a configuration diagram of the light-emitting control unit 705. The light-emitting control unit 705 includes a data dividing unit 721, a data storage unit 723, a data output unit 724, and a memory control unit 726. The data storage unit 723 has a plurality of line memories, the number of which is the same as the number of light-emitting chips 400 mounted on the printed circuit board 202. In this embodiment, the data storage unit 723 has 20 line memories 723-1 to 723-20, corresponding to the number of light-emitting chips 400.

[0061] The data dividing unit 721 divides the print image data IM obtained from the image data processing unit 703 into K pieces of partial image data corresponding to the K light-emitting chips 400. The K pieces of partial image data are designated IM1 to IMK. In this embodiment, K=20.

[0062] FIG. 13 is an explanatory diagram of partial image data. Print image data IM represents an image for one page. The data dividing unit 721 divides the print image data IM into data units to be supplied to each light-emitting chip 400. Specifically, the data dividing unit 721 divides the print image data IM in the main scanning direction according to the number of light-emitting chips 400. If there are 20 light-emitting chips 400, the data dividing unit 721 divides the print image data IM into partial image data IM1 to IM20 corresponding to each of the 20 light-emitting chips 400. The data dividing unit 721 transmits the partial image data IM1 to IM20 to the data storage unit 723.

[0063] The data storage unit 723 provides storage areas (line memories 723-1 to 723-20) for temporarily storing a plurality of partial image data IM1 to IM20. For example, the line memories 723-1 to 723-20 are configured by SRAMs (Static Random Access Memories).

[0064] In this embodiment, 20 line memories 723-1 to 723-20 are prepared to match the number of the light-emitting chips 400. The line memories 723 are provided corresponding to the light-emitting chips 400. In this embodiment, since the number of the light-emitting chips 400 is an even number, the number of the line memories 723 is also an even number. When the number of the line memories 723 is an odd number, the storage capacity of each line memory 723 may be smaller than the storage capacity of each line memory 723 in the case where the number is even. The line memories 723-1 to 723-20 may be individual storage devices, or may be configured by dividing the storage area of ​​a single storage device.

[0065] The data output unit 724 reads out the partial image data IM1 to IM20 from each of the line memories 723-1 to 723-20 under the control of the memory control unit 726, and transmits them to the corresponding light-emitting chips 400-1 to 400-20. The memory control unit 726 controls the operations of the data output unit 724, as well as the data division unit 721 and the data storage unit 723.

[0066] (Partial image data output control) 14, 15, and 16 are explanatory diagrams of output control of partial image data. Here, output control when transmitting partial image data to the light-emitting chip 400-1 will be described. Similar read control is performed for the other light-emitting chips 400-2 to 400-20. FIGS. 14(a), 14(b), 15(a), and 15(b) each show a case where the line synchronization signal shown in FIG. 9 is received four times from the first line of the partial image data IM1. FIG. 16 shows a case where a line synchronization signal for outputting the last line of the partial image data IM1 is received. The partial image data IM1 is image data to be output to the light-emitting chip 400-1, which has been divided by the data dividing unit 721.

[0067] 14(a), 14(b), 15(a), 15(b), and the left diagram of FIG. 16, the order in which the data output unit 724 reads out the partial image data IM1 is indicated by dashed lines. Rj-m within the dashed lines indicates the partial image data to be output to the light-emitting element shown in FIG. 11. The order in which the partial image data is output is as shown in the timing chart in FIG. 9. The data output unit 724 sequentially outputs the partial image data in the order of R0-0 → R0-1 → R0-2 → R0-3 → R1-0 → R1-1.

[0068] The right diagrams of Figures 14(a), 14(b), 15(a), 15(b), and 16 show printouts produced by the data output unit 724 sending the data for the first to fourth lines of partial image data IM1 to the exposure head 106, and show the state in which the printout is printed as a valid image. The shaded areas show the state in which an image corresponding to the partial image data IM1 is actually printed. The data output unit 724 receives a synchronization signal four times, forming one line of image. This is because the resolution in the sub-scanning direction is set to 1200 dpi, which corresponds to the spacing at which the light-emitting elements 602 are arranged in the sub-scanning direction.

[0069] 14(a), 14(b), 15(a), 15(b), and 16, there are portions where there is no partial image data IM1 to be output to the light-emitting element Rj_m. When there is no partial image data IM1 corresponding to the image to be output, the data output unit 724 outputs "0" indicating "turn off."

[0070] (Light emitting chip misalignment) The following describes the mounting misalignment of the light-emitting chip 400. The light-emitting chip 400 mounted on the printed circuit board 202 may be misaligned from the ideal mounting position due to the influence of mounting accuracy. In this case, image degradation may occur on the printed image. The influence of the mounting misalignment is particularly noticeable in color printing.

[0071] Fig. 17 is an explanatory diagram of mounting misalignment of the light emitting chip 400. Fig. 17 shows a part of an enlarged view of the light emitting chips 400-1 to 400-3 mounted on the printed circuit board 202. As shown in Fig. 17, the mounting positions of the light emitting chips 400-1 to 400-3 may be displaced from their original ideal positions due to the influence of mounting accuracy. The amount of mounting misalignment differs for each of the light emitting chips 400-1 to 400-3.

[0072] The amount of mounting misalignment is detected by the following value measured after the light emitting chips 400 are mounted on the printed circuit board 202. The amount of mounting misalignment is detected by the distance from the reference position to a predetermined light emitting element of each light emitting chip 400. The reference position is a predetermined position in the sub-scanning direction, for example, the position of a predetermined light emitting element of a light emitting chip arranged at the most upstream position in the sub-scanning direction. The predetermined light emitting element is a light emitting element mounted at the most upstream position in the sub-scanning direction among the light emitting chips. In this embodiment, the position of the light emitting element at the upper left end of the light emitting chip 400-1 (broken line) is the reference position. In FIG. 17, the upstream side in the sub-scanning direction is referred to as the top, the downstream side as the bottom, the upstream side in the main scanning direction as the right, and the downstream side as the left.

[0073] 17, a distance YzureL_K from the reference position to the light-emitting element at the upper left end of each light-emitting chip 400-K and a distance YzureR_K from the reference position to the light-emitting element at the upper right end of each light-emitting chip 400-K are measured. The distance YzureL_1 is the reference position and is set to 0. The measured distances Yzure are stored in the storage unit 710 as mounting position information representing the mounting misalignment amount of each light-emitting chip 400. The CPU 701 reads out the mounting position information of each light-emitting chip 400 from the storage unit 710 and performs a process of correcting the mounting misalignment amount.

[0074] 17 is greater than the distance Yzure of the other light-emitting chips 400-1 and 400-3. This is because the light-emitting chips are arranged in a staggered pattern. The distance Yzure is measured including the distance due to the staggered arrangement. The measurement of the amount of mounting misalignment of each light-emitting element of each light-emitting chip 400 and the storage of the mounting position information of each light-emitting chip 400 in the storage unit 710 are performed when the exposure head 106 is manufactured or when the exposure head 106 is attached to the image forming apparatus.

[0075] The amount of mounting misalignment is corrected by controlling the timing at which the data output unit 724 reads out the partial image data from the data storage unit 723 and transmits it to the corresponding light-emitting chip 400. Below, the output control of the partial image data in the cases where there is no mounting misalignment and where there is a mounting misalignment will be described.

[0076] (Partial image data output control when there is no mounting misalignment) 18, 19, and 20 are explanatory diagrams of output control of partial image data when there is no mounting misalignment of the light-emitting chips 400. In the following description, the numbers assigned to each light-emitting element in the diagrams showing the on / off states of each light-emitting chip 400 correspond to Rj_m in FIG. 11, as exemplified below. 1: R0_0 in Figure 11 2: R0_1 in Figure 11 3: R0_2 in Figure 11 4: R0_3 in Figure 11 … 2989: R747_0 in Figure 11 2990: R747_1 in Figure 11 2991: R747_2 in Figure 11 2992: R747_3 in Figure 11

[0077] FIG. 18 illustrates output control of the light-emitting control unit 705 when there is no mounting misalignment of the light-emitting chips 400. FIG. 18 illustrates print image data transmitted to each light-emitting chip 400 for each line synchronization signal. The light-emitting control performed by each of the light-emitting chips 400-1 to 400-20 is the same. Here, light-emitting control of the light-emitting chip 400-1 will be described as an example. To simplify the explanation of the light-emitting state, partial image data IM1 for the light-emitting chip 400-1 indicates an image of 1000 lines, causing all light-emitting elements to emit light. 2992 pieces of image data are output to the light-emitting chip 400-1 in synchronization with one line synchronization signal. The resolution of the generated image is 4800 dpi in the main scanning direction and 1200 dpi in the sub-scanning direction. In other words, the print image data IM output by the image data processing unit 703 indicates an image of 4800 dpi in the main scanning direction and 1200 dpi in the sub-scanning direction.

[0078] As described above, the light-emitting elements 602 of this embodiment are provided in four rows in the sub-scanning direction and arranged in a stepped pattern at intervals corresponding to a resolution of 1200 dpi. To expose at a resolution of 1200 dpi in the sub-scanning direction, it is necessary to delay and input image data at 1200 dpi for each line to the light-emitting elements 602 located downstream of the four rows of light-emitting elements 602 in the rotation direction (sub-scanning direction) of the photosensitive drum 102. The delay is achieved by the data output unit 724 delaying the timing of reading the partial image data IM1 from the line memory 723-1 of the data storage unit 723 and outputting the data under the control of the memory control unit 726.

[0079] The readout operation of the partial image data IM1 for each line synchronization signal will be described. At the first line synchronization signal (1 SYNC), the data output unit 724 outputs the partial image data IM1 to the (4k-3)th (k is an integer from 1 to 748) light-emitting element to cause the light-emitting element 602 located at the most upstream of the four rows of light-emitting elements 602 in the sub-scanning direction to emit light. At this time, the data output unit 724 does not output the partial image data IM1 to the other light-emitting elements, but outputs 0 data to instruct them to be turned off. The light-emitting state of each light-emitting element of the light-emitting chip 400-1 at 1 SYNC becomes the state shown in FIG. 19(a).

[0080] 18, 19, and 20 indicate regions obtained by dividing the region in the light-emitting chip 400-1 where the light-emitting elements are mounted in the main scanning direction. In this embodiment, for each of the intra-chip divided regions 500 in the light-emitting chip 400-1, the data output unit 724 is able to change the amount of delay when reading out partial image data from the data storage unit 723 based on the control of the memory control unit 726. The intra-chip divided regions 500 will be described later. The amount of delay is determined based on, for example, the mounting misalignment amount (distances YzureL, YzureR) of the light-emitting chip.

[0081] At the second line synchronization signal (2nd SYNC), the data output unit 724 outputs partial image data IM1 to the (4k-3)th and (4k-2)th light-emitting elements in order to cause the light-emitting elements of two rows from the upstream of the four rows of light-emitting elements in the sub-scanning direction to emit light. At this time, the data output unit 724 does not output partial image data IM1 to the other light-emitting elements, but outputs 0 data to instruct them to be turned off. The light-emitting state of each light-emitting element of the light-emitting chip 400-1 at the 2nd SYNC becomes the state shown in FIG. 19(b).

[0082] At the third line synchronization signal (3rd SYNC), in order to cause the light-emitting elements of three rows from the upstream of the four rows of light-emitting elements in the sub-scanning direction to emit light, the data output unit 724 outputs partial image data IM1 to the (4k-3), (4k-2), and (4k-1)th light-emitting elements. At this time, the data output unit 724 does not output partial image data IM1 to the other light-emitting elements, but outputs 0 data to instruct them to be turned off. The light-emitting state of each light-emitting element of the light-emitting chip 400-1 at the 3rd SYNC becomes the state shown in FIG. 19(c).

[0083] At the 4th to 1000th line synchronization signals (4th to 1000th SYNC), the data output unit 724 outputs partial image data IM1 to the (4k-3), (4k-2), (4k-1), and 4kth light-emitting elements in order to cause all four columns of light to emit light. The light-emitting states of the light-emitting elements of the light-emitting chip 400-1 at the 4th to 1000th SYNC become the states shown in FIG. 19(d). At the 1000th SYNC, the output of all partial image data to the light-emitting element furthest upstream in the sub-scanning direction of the light-emitting chip 400-1 is completed.

[0084] At the 1001st line synchronization signal (1001th SYNC), the data output unit 724 outputs partial image data IM1 to the (4k-2), (4k-1), and 4kth light-emitting elements in order to cause the light-emitting elements in three rows from the downstream of the four rows of light-emitting elements in the sub-scanning direction to emit light. At this time, the data output unit 724 does not output partial image data IM1 to the other light-emitting elements, but outputs 0 data to instruct them to be turned off. The light-emitting state of each light-emitting element of the light-emitting chip 400-1 at the 1001st SYNC becomes the state shown in FIG. 20(a). At the 1001st SYNC, the output of image data to the light-emitting elements in the second row from the upstream of the four rows of light-emitting chip 400-1 in the sub-scanning direction is all completed.

[0085] At the 1002nd line synchronization signal (1002SYNC), the data output unit 724 outputs partial image data IM1 to the (4k-1), 4kth light-emitting element in order to cause light to be emitted by two rows of light-emitting elements from the downstream of the four rows of light-emitting elements in the sub-scanning direction. At this time, the data output unit 724 does not output partial image data IM1 to the other light-emitting elements, but outputs 0 data to instruct them to be turned off. The light-emitting state of each light-emitting element of the light-emitting chip 400-1 at the 1002SYNC becomes the state shown in FIG. 20(b). At the 1002SYNC, the output of image data to the light-emitting elements in the third row from the upstream of the four rows of light-emitting chip 400-1 in the sub-scanning direction is all completed.

[0086] At the 1003rd line synchronization signal (1003th SYNC), the data output unit 724 outputs partial image data IM1 to the 4kth light-emitting element to cause the light-emitting element at the most downstream of the four rows of light-emitting elements in the sub-scanning direction to emit light. At this time, the data output unit 724 does not output partial image data IM1 to the other light-emitting elements, but outputs 0 data to instruct them to be turned off. The light-emitting state of each light-emitting element of the light-emitting chip 400-1 at the 1003rd SYNC becomes the state shown in FIG. 20(c). At the 1003rd SYNC, the output of image data to the light-emitting elements at the most downstream of the four rows of light-emitting chip 400-1 in the sub-scanning direction is all completed.

[0087] At the last 1004th line synchronization signal (1004th SYNC), the data output unit 724 outputs 0 data instructing all light-emitting elements to be turned off. The light-emitting state of each light-emitting element of the light-emitting chip 400-1 at the 1004th SYNC becomes the state shown in FIG. 20(d).

[0088] In this way, the data output unit 724 reads out the partial image data IM1 from the line memory 723 and transmits it to the light-emitting chip 400-1 under the control of the memory control unit 726. The light-emitting chip 400-1 can perform exposure corresponding to an image of 1000 lines on the photosensitive drum 102. Here, the image data that causes all light-emitting elements to emit light in a 1000-line image has been described as an example. If the image data to be transmitted includes data instructing turning off, the image data of the appropriate turned-off portions is transmitted as 0 data.

[0089] (Partial image data output control when there is mounting misalignment) In this embodiment, the light-emitting chip 400 is divided into multiple regions in the main scanning direction, and the timing for outputting partial image data is set for each of the intra-chip divided regions 500 in each light-emitting chip 400 according to the amount of mounting misalignment (distances YzureL, YzureR). 21, 22, and 23 are used to explain the output control process for partial image data by the light-emitting control unit 705 when a mounting misalignment occurs in the light-emitting chip 400. The following describes an example in which distance YzureL_1 is set as the reference position (0), and YzureR_1 is shifted downstream in the sub-scanning direction by one line at 1200 [dpi] from the reference position.

[0090] 21 explains the output control of the light-emitting control unit 705 when there is a mounting misalignment of the light-emitting chips 400. FIG. 21 shows print image data transmitted to each light-emitting chip 400 for each line synchronization signal. The light-emitting control performed by each of the light-emitting chips 400-1 to 400-20 is the same. In the following explanation, the numbers assigned to each light-emitting element in the diagram showing the on / off state of each light-emitting chip 400 correspond to Rj_m in FIG. 11, as in the case of FIG. 18.

[0091] Similar to FIG. 18, FIG. 21 shows print image data transmitted to each light-emitting chip 400 for each line synchronization signal. The light emission control performed by each of the light-emitting chips 400-1 to 400-20 is the same process, with only the amount of mounting misalignment set being different. Here, the light emission control of the light-emitting chip 400-1 will be described as an example. Similar to FIG. 18, to simplify the explanation of the light emission state, partial image data IM1 for the light-emitting chip 400-1 indicates an image of 1000 lines, causing all light-emitting elements to emit light. 2992 pieces of image data are output to the light-emitting chip 400-1 in synchronization with one line synchronization signal. The resolution of the generated image is 4800 dpi in the main scanning direction and 1200 dpi in the sub-scanning direction. In other words, the print image data IM output by the image data processing unit 703 indicates an image of 4800 dpi in the main scanning direction and 1200 dpi in the sub-scanning direction.

[0092] As described above, the light-emitting elements 602 of this embodiment are provided in four rows in the sub-scanning direction and arranged in a stepped pattern at intervals corresponding to a resolution of 1200 dpi. To expose at a resolution of 1200 dpi in the sub-scanning direction, it is necessary to delay and input image data at 1200 dpi for each line to the light-emitting elements 602 located downstream of the four rows of light-emitting elements 602 in the rotation direction (sub-scanning direction) of the photosensitive drum 102. The delay is achieved by the data output unit 724 delaying the timing of reading the partial image data IM1 from the line memory 723-1 of the data storage unit 723 and outputting the data under the control of the memory control unit 726.

[0093] Here, a control example will be described in which a mounting misalignment occurs as in the case of the light-emitting chip 400-1 on the far left in Fig. 17. The left end of the light-emitting chip 400-1 is the reference position (the distance YzureL_1 is 0). The distance Yzure_R1 of the right end of the light-emitting chip 400-1 is 1. In other words, the light-emitting chip 400-1 is mounted with its right end tilted by one line at 1200 [dpi] downstream in the sub-scanning direction.

[0094] In order to correct such mounting misalignment, the light-emitting chip 400-1 is divided into two regions in the main scanning direction, with the left side being the intra-chip divided region 500-1 and the right side being the intra-chip divided region 500-2. Based on the amount of mounting misalignment, a delay amount is set when the data output unit 724 reads out partial image data for each intra-chip divided region from the data storage unit 723. Here, since the intra-chip divided region 500-1 is set as the reference position, the delay amount is set to 0, and the delay amount for the intra-chip divided region 500-2 is set to 1. The memory control unit 726 controls the reading of the partial image data IM1 for the light-emitting chip 400-1 based on these set values.

[0095] The read operation of the partial image data IM1 for each line synchronization signal will be described. The first line synchronization signal (1 SYNC) causes the light emitting element 602 located at the most upstream of the four columns of light emitting elements 602 in the intra-chip divided area 500-1 in the sub-scanning direction to emit light. To achieve this, the data output unit 724 outputs the partial image data IM1 to the (4k-3)th (k is an integer from 1 to 374) light emitting element. At this time, the data output unit 724 does not output the partial image data IM1 to the other light emitting elements, but outputs 0 data to instruct them to be turned off. The light emitting state of each light emitting element of the light emitting chip 400-1 in 1 SYNC becomes the state shown in FIG. 22(a).

[0096] The second line synchronization signal (2 SYNC) causes the light-emitting elements of two rows from the upstream of the four rows of light-emitting elements in the in-chip divided region 500-1 in the sub-scanning direction to emit light. To this end, the data output unit 724 outputs partial image data IM1 to the (4k-3)th and (4k-2)th light-emitting elements. The data output unit 724 also causes the light-emitting elements 602 located at the most upstream of the four rows of light-emitting elements 602 in the in-chip divided region 500-2 in the sub-scanning direction to emit light. To this end, the data output unit 724 outputs partial image data IM1 to the (4m-3)th (m is an integer between 375 and 748)th light-emitting element. At this time, the data output unit 724 does not output partial image data IM1 to the other light-emitting elements, but outputs 0 data to instruct them to be turned off. The light-emitting states of the light-emitting elements of the light-emitting chip 400-1 in the 2 SYNC are as shown in FIG. 22(b).

[0097] From then on, up to the 1004th line synchronization signal (1004th SYNC), control is performed such that the partial image data to be output to the intra-chip divided region 500-2 is delayed by one line synchronization signal and output to the intra-chip divided region 500-1. The light-emitting states of the light-emitting elements of the light-emitting chip 400-1 at each line synchronization signal are as shown in Figures 22(c), 22(d), and 23(a) to 23(d). Finally, at the 1005th line synchronization signal (1005th SYNC), all light-emitting elements are turned off. The light-emitting states of the light-emitting elements of the light-emitting chip 400-1 at this 1005th SYNC are as shown in Figure 23(e).

[0098] In this way, the data output unit 724 reads the partial image data IM1 from the line memory 723 and transmits it to the light-emitting chip 400-1 under the control of the memory control unit 726. The light-emitting chip 400-1 can perform exposure on the photosensitive drum 102 equivalent to an image of 1000 lines.

[0099] When there is such a mounting misalignment, the light emission control unit 705 divides the mounting area of ​​the light emitting chip 400 into multiple intra-chip divided areas 500 in the main scanning direction, and sets a delay amount when reading out the partial image data IM1 from the line memory 723 for each intra-chip divided area. This makes it possible to correct the influence of the mounting misalignment of each light emitting chip 400. The amount of mounting misalignment of each light emitting chip 400 is digitally corrected by delay control of the readout of the partial image data IM1. Therefore, an image affected by the mounting misalignment is not formed on the photosensitive drum 102. Here, the image data for a 1000-line image that causes all light emitting elements to emit light has been described as an example. When the image data to be transmitted includes data instructing turning off, the image data for the appropriate turned-off portions is transmitted as 0 data.

[0100] In the present embodiment, the mounting area of ​​the light-emitting chip 400 is divided into two in the main scanning direction, but the mounting area of ​​the light-emitting chip 400 may be divided into three or more parts. For example, the mounting area of ​​the light-emitting chip 400 may be divided into four or eight parts. The more parts are divided, the more control circuits there are, but it becomes possible to correct mounting misalignment with high precision.

[0101] (Exposure control processing) 24 is a flowchart showing the exposure control process of the exposure head 106. This process is performed by the CPU 701 and the light emission control unit 705 working together.

[0102] The CPU 701 acquires profile information including position information of the mounting positions of each of the plurality of light-emitting chips 400 from the storage unit 710 mounted on the printed circuit board 202 of the exposure head 106 (S2001). The CPU 701 transmits the acquired position information to the memory control unit 726 of the light-emitting control unit 705. The CPU 701 generates a delay amount for each of the in-chip divided regions 500 of each of the light-emitting chips 400 based on the acquired position information (S2002). The in-chip divided regions 500 of each of the light-emitting chips 400 are set in advance and are included in, for example, the profile information.

[0103] The CPU 701 waits to receive a print job instructing printing using the scanned image data generated by the reading unit 100 or print image data received from an external device via a network (S2003: N). When the print job is received (S2003: Y), the CPU 701 starts the print process. After starting the print process, the CPU 701 sets various registers in the light-emitting control unit 705 (S2004). The register setting includes setting the delay amount for each in-chip divided area 500 of each light-emitting chip 400 generated in the process of S2002 in a register in the light-emitting control unit 705. The register is provided in, for example, the memory control unit 726. The CPU 701 waits until the register setting is complete (S2005: N).

[0104] When the register setting is completed (S2005: Y), the CPU 701 acquires print image data IM using the image data processing unit 703 (S2006). The image data processing unit 703 performs image processing on the acquired print image data. The print image data that has been image processed by the image data processing unit 703 is sent to the light emission control unit 705. The following processing is performed by the light emission control unit 705 under the control of the CPU 701. The light emission control unit 705 performs the following processing under the control of the memory control unit 726, based on the control signal acquired from the CPU 701.

[0105] The data dividing unit 721 of the light emission control unit 705 divides the print image data into a plurality of partial image data corresponding to the plurality of light emitting chips 400 (S2007). Here, the print image data is divided into K pieces of partial image data corresponding to the K light emitting chips 400. The data dividing unit 721 stores the K pieces of partial image data in the corresponding line memories 723-1 to 723-K of the data storage unit 723, respectively (S2008).

[0106] The data output unit 724 sequentially reads out the partial image data that has reached its output timing from the line memory 723 under the control of the memory control unit 726, and transmits the partial image data to the corresponding light-emitting chip 400 (S2009). The memory control unit 726 determines the output timing of the partial image data based on the delay amount for each in-chip divided area 500 set in the register, and instructs the data output unit 724 to output the partial image data. As a result, the data output unit 724 shifts the read timing of the partial image data for each in-chip divided area 500 of each light-emitting chip 400 based on the mounting misalignment amount of each light-emitting chip 400, and reads out the partial image data from the line memories 723-1 to 723-K.

[0107] The CPU 701 determines whether transmission of all lines of print image data to the exposure head 106 has been completed (S2010). If transmission has not been completed (S2010: N), the CPU 701 waits until the processing of S2009 is completed. If transmission has been completed (S2010: Y), the CPU 701 ends this exposure control processing.

[0108] The specific numerical values ​​used in the above description are merely examples, and the present invention is not limited to the numerical values ​​used in the embodiments. For example, the number of light-emitting chips 400 mounted on one printed circuit board 202 is not limited to 20, as long as it is one or more. The number of light-emitting elements 602 included in each light-emitting chip 400 is also not limited to 2992. In this embodiment, one light-emitting chip 400 is configured with four sets of 748 light-emitting elements 602 arranged along the main scanning direction, but the number of sets may be one or more. The light-emitting elements 602 are arranged at a pitch of approximately 21.16 μm in the main scanning direction, corresponding to a resolution of 1200 dpi. However, the arrangement interval of the light-emitting elements 602 may be set according to the resolution and number of light-emitting elements 602. The resolution in the sub-scanning direction is not limited to 1200 dpi. The number and arrangement interval of the light-emitting elements 602 in the exposure head 106 may be determined based on the resolution and image size of the image formed by the image forming apparatus 1. The light-emitting chip 400 may have two or more divided regions 500 within the chip.

[0109] The image forming apparatus 1 equipped with the solid-state exposure exposure apparatus of this embodiment transmits divided image data at a timing based on the amount of mounting misalignment for each of the light-emitting chips 400. This makes it possible to correct the effect of image quality degradation caused by mounting misalignment through digital processing while suppressing cost increases.

Claims

1. A photoreceptor; an exposure unit having a plurality of light-emitting chips each including a plurality of light-emitting elements, and exposing the photosensitive member to the light-emitting elements to form an image; a control means for transmitting image data to the exposure means and for causing the exposure means to form an image on the photosensitive member in accordance with the image data; a storage means for storing a mounting deviation amount representing a deviation of the mounting position of each of the plurality of light emitting chips from a reference position, the control means divides the image data into a plurality of partial image data in accordance with the number of the light-emitting chips, and transmits the partial image data to the corresponding light-emitting chips at a timing based on the amount of mounting deviation. Image forming device.

2. The plurality of light-emitting elements are arranged in a first direction and a second direction perpendicular to the first direction, the mounting misalignment amount is detected using a position of a predetermined light-emitting element of a light-emitting chip arranged at the most upstream in the second direction as the reference position.

2. The image forming apparatus according to claim 1.

3. The plurality of light-emitting elements are arranged in a first direction and a second direction perpendicular to the first direction, the mounting misalignment amount is detected using a position of a most upstream light-emitting element in the second direction of the light-emitting chip arranged most upstream in the second direction as the reference position.

2. The image forming apparatus according to claim 1.

4. the control means sets timing for outputting partial image data for each of divided areas obtained by dividing an area in which light-emitting elements of the light-emitting chip are mounted into a plurality of areas in the first direction, based on the amount of mounting misalignment.

4. The image forming apparatus according to claim 3.

5. the mounting misalignment amount includes a first distance between a light-emitting element of the light-emitting chip that is most upstream in the first direction and the reference position, and a second distance between a light-emitting element of the light-emitting chip that is most downstream in the first direction and the reference position, the control means sets the timing for each of the plurality of divided areas based on the first distance and the second distance.

5. The image forming apparatus according to claim 4.

6. the photosensitive member is drum-shaped, the first direction is a drum axial direction of the photosensitive member, and the second direction is a circumferential direction of the photosensitive member.

6. The image forming apparatus according to claim 5.

7. The plurality of light emitting chips are arranged in a staggered pattern in the first direction.

7. The image forming apparatus according to claim 6.

8. The method further includes a plurality of storage means for storing the plurality of partial image data, the control means generates the plurality of partial image data from the image data corresponding to each of the plurality of light-emitting chips, and stores the generated partial image data in the corresponding storage means; The plurality of storage means are provided corresponding to the plurality of light-emitting chips.

2. The image forming apparatus according to claim 1.

9. When the number of the storage means is odd, the storage capacity of each storage means is smaller than when the number of the storage means is even.

9. The image forming apparatus according to claim 8.

10. the control means reads out the partial image data from each of the plurality of storage means and transmits the partial image data to the corresponding light-emitting chips, 9. The image forming apparatus according to claim 8.

11. The storage means is included in the exposure means.

2. The image forming apparatus according to claim 1.

Images