Exposure device and image forming device

Abstract

To provide an improved mechanism for compensating for an error in an image forming range.SOLUTION: An image forming apparatus comprises: photoreceptors that are each driven to rotate; exposure heads that each include a plurality of light-emitting parts arranged at different positions in an axial direction of the photoreceptor, and that each form an image corresponding to the output resolution of the image forming apparatus with the plurality of light-emitting parts; and a control unit that controls the drive of the plurality of light-emitting parts based on correction data. The image includes at least first pixels and second pixels. The control unit controls the drive of the plurality of light-emitting parts based on the correction data so that a first number of light-emitting parts of the plurality of light-emitting parts form the first pixels, and a second number, which is different from the first number, of light-emitting parts of the plurality of light-emitting parts form the second pixels.SELECTED DRAWING: Figure 13D

Description

[Technical Field]

[0001] The present invention relates to an exposure apparatus having a plurality of light-emitting units. and the exposure device The present invention relates to an image forming apparatus that forms an image using a laser. [Background technology]

[0002] Electrophotographic image forming devices form an image by exposing a rotating photoreceptor to light to form an electrostatic latent image on the photoreceptor, and then developing the electrostatic latent image with toner. In particular, organic EL (Electro-Luminescence) type exposure devices that use organic EL elements for exposure have been attracting attention in recent years because they are easier to miniaturize, quieter, and less expensive than laser scanning type exposure devices that use laser light.

[0003] Patent Document 1 discloses a technique for promoting miniaturization of an organic EL type exposure device by providing an array of light emitting elements and a drive circuit on the same silicon substrate in an exposure head of the device.

[0004] Patent document 2 discloses a technique for increasing the resolution of image data used to drive a group of light-emitting elements and correcting it in order to precisely compensate for image misalignment caused by variations in the mounting position of chips on a substrate or thermal expansion of the substrate.

[0005] Patent Document 3 discloses a technology (so-called multiple exposure) in which, in a two-dimensional array of organic EL elements, the light-emitting elements in each column are arranged in a stepped manner and the light-emitting elements are caused to emit light sequentially, thereby exposing each pixel region on a photosensitive body in multiple ways. Multiple exposure makes it possible to ensure the amount of exposure necessary to form an image of sufficient density in an organic EL exposure device that uses organic EL elements that cannot emit light as strong as laser light. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-35765 [Patent Document 2] Japanese Patent Application Publication No. 2019-217653 [Patent Document 3] Japanese Patent Application Publication No. 2022-96966 Summary of the Invention [Problem to be solved by the invention]

[0007] As suggested in Patent Document 2, it is inevitable that some errors in component placement will occur during the manufacturing of exposure devices or image forming devices. Even after manufacturing, environmental factors such as temperature changes or physical forces during transportation, installation, or use can cause misalignment of components inside the device. A laser scanning exposure device that scans a photosensitive material line by line with laser light can simply adjust the scanning range to change the image formation position or expand or reduce the image formation range, but similar techniques cannot be adopted for exposure devices that use LED elements or organic EL elements for exposure. While the technology disclosed in Patent Document 2 enables high-precision compensation for misalignment, it requires relatively heavy processing, such as weighting calculations for image data resolution conversion, which tends to increase the circuit size and is not necessarily suitable for devices that require compactness and low cost.

[0008] The present invention aims to provide an improved scheme for compensating for imaging coverage errors. [Means for solving the problem]

[0009] According to one aspect, an organic EL (Electro Luminescence) type exposure device for an image forming apparatus includes an exposure head having a plurality of light-emitting elements arranged two-dimensionally to include M rows (M is an integer of 2 or more) in the circumferential direction of a photosensitive body and N columns (N is an integer of 2 or more) in the axial direction of the photosensitive body, wherein any two adjacent light-emitting elements of the M light-emitting elements in each column occupy a partially overlapping area in the axial direction; and a light-emitting control unit that controls light emission from the plurality of light-emitting elements of the exposure head so that the M light-emitting elements in the columns corresponding to each pixel position of input image data sequentially emit light while the photosensitive body is rotating, thereby forming spots corresponding to each pixel position on the surface of the photosensitive body, In the exposure head, the M light-emitting elements in each column of the plurality of light-emitting elements are arranged in a stepped pattern at a constant pitch in the axial direction, and the light-emission control unit causes the plurality of light-emitting elements to emit light based on pixel values ​​read from a readout range spanning M lines of the input image data, The light emission control unit detects a positional deviation in the axial direction of an image formed by the exposure head. When the detected positional deviation is x times the pitch (x is a natural number), The pixel value set of the input image data is shifted in a direction that cancels the detected positional deviation. The light emission control unit distributes the shift amount to each of the M lines by one pixel until the total shift amount of the pixel value set reaches x. An exposure device is provided. An image forming device including the exposure device and the photoreceptor is also provided. [Effects of the Invention]

[0010] The present invention provides an improved scheme for compensating for imaging coverage errors. [Brief explanation of the drawings]

[0011] [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. 4 is an explanatory diagram of a procedure for light emission control based on input image data. [Figure 12B] FIG. 4 is an explanatory diagram of a procedure for light emission control based on input image data. [Figure 12C] FIG. 4 is an explanatory diagram of a procedure for light emission control based on input image data. [Figure 12D] FIG. 4 is an explanatory diagram of a procedure for light emission control based on input image data. [Figure 13A] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the first scenario. [Figure 13B] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the first scenario. [Figure 13C] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the first scenario. [Figure 13D] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the first scenario. [Figure 14A] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the second scenario. [Figure 14B] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the second scenario. [Figure 14C] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the second scenario. [Figure 14D] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the second scenario. [Figure 15A] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the third scenario. [Figure 15B] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the third scenario. [Figure 15C] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the third scenario. [Figure 15D] FIG. 10 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the third scenario. [Figure 16A] FIG. 10 is an explanatory diagram of a procedure for light emission control including compensation for magnification error (insertion of pixel values). [Figure 16B] FIG. 10 is an explanatory diagram of a procedure for light emission control including compensation for magnification error (insertion of pixel values). [Figure 16C] FIG. 10 is an explanatory diagram of a procedure for light emission control including compensation for magnification error (insertion of pixel values). [Figure 16D] FIG. 10 is an explanatory diagram of a procedure for light emission control including compensation for magnification error (insertion of pixel values). [Figure 17A] 10A and 10B are explanatory diagrams of a procedure for light emission control including compensation for magnification error (thinning out pixel values). [Figure 17B] 10A and 10B are explanatory diagrams of a procedure for light emission control including compensation for magnification error (thinning out pixel values). [Figure 17C] 10A and 10B are explanatory diagrams of a procedure for light emission control including compensation for magnification error (thinning out pixel values). [Figure 17D] 10A and 10B are explanatory diagrams of a procedure for light emission control including compensation for magnification error (thinning out pixel values). [Figure 18] FIG. 10 is an explanatory diagram of a procedure for light emission control including compensation for magnification error (insertion of multiple pixel values). [Figure 19] FIG. 10 is an explanatory diagram of an implementation example of pixel value output control using an auxiliary pixel array. [Figure 20A] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in the first line cycle. [Figure 20B] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in a second line cycle. [Figure 20C]FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in a third line cycle. [Figure 20D] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in a fourth line cycle. [Figure 21] 10A and 10B are explanatory diagrams illustrating shifts in pixel values ​​in an auxiliary pixel array when a positional deviation is detected. [Figure 22A] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in the first line period in the case of misregistration compensation. [Figure 22B] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in the second line period in the case of misregistration compensation. [Figure 22C] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in the third line period in the case of misregistration compensation. [Figure 22D] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in the fourth line period in the case of misregistration compensation. [Figure 23] 10A and 10B are explanatory diagrams illustrating the insertion of pixel values ​​in an auxiliary pixel array when a magnification error is detected. [Figure 24A] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in the first line cycle in the case of magnification error compensation (error magnification<1). [Figure 24B] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in the second line cycle in the case of magnification error compensation (error magnification<1). [Figure 24C] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in the third line cycle in the case of magnification error compensation (error magnification<1). [Figure 24D] FIG. 10 is an explanatory diagram of auxiliary pixels from which pixel values ​​are read in the fourth line cycle in the case of magnification error compensation (error magnification<1). [Figure 25] 10A and 10B are explanatory diagrams illustrating thinning out of pixel values ​​in an auxiliary pixel array when a magnification error is detected. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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. Optical sensor 113 optically reads the test chart formed on transfer belt 111 by image forming unit 101. If an error in the image formation range is detected for the test chart read by optical sensor 113, image controller 700 (described later) performs control to compensate for the error when the subsequent job is executed.

[0016] 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.

[0017] 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 supports the printed circuit board 202 and the rod lens array 203. The photoconductor 102 has a cylindrical shape. The exposure head 106 is disposed 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.

[0018] 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.

[0019] 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 of the axial direction D1 may not be used to expose the photoconductor 102 unless an error in the image formation area 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.

[0020] The number J (J=N / 20) of light-emitting elements 602 arranged in each row of one light-emitting chip 400 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 748 light-emitting elements 602 in the axial direction D1 and 4 light-emitting elements 602 in the circumferential direction D2, totaling 2992 (=748×4) light-emitting elements 602. 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.

[0021] 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.

[0022] 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.

[0023] The light-emitting layer 506 may be, for example, an organic EL film. The upper electrode 508 is made 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, 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.

[0024] 6 shows that one continuous light-emitting layer 506 is formed, but multiple light-emitting layers 506 each having a width equivalent to the width W of the lower electrode 504 may be formed on the lower electrode 504. Also, in FIG. 6, the upper electrode 508 is formed as a single common electrode for the multiple lower electrodes 504, but multiple upper electrodes 508 each having a width equivalent to the width W of the lower electrode 504 may be formed corresponding to each lower electrode 504. Also, 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 a second plurality of lower electrodes 504 may be covered with a second light-emitting layer 506. Similarly, 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. 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 .

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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 (input terminals) 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.

[0031] 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 them to latch units 1004-001 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.

[0032] The kth latch unit (data holding 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.

[0033] 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.

[0034] 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.

[0035] 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, and a spot corresponding to each pixel position is formed on the surface of the photoconductor 102. Here, the spot corresponding to each pixel position also corresponds to a pixel of the image formed on the sheet. 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.

[0036] 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.

[0037] Here, the line L i The spot area on the left side of the figure is the light-emitting element R. 0_0 , R 0_1 , R 0_2 , R 0_3 In reality, the light emitting element R 0_0 , R 0_1 , R 0_2 , R 0_3 The light-emitting chips 400 may not be the leftmost light-emitting elements, but may have a row of light-emitting elements to the left of them that do not normally emit light (unless an error in the image formation range is detected). The same can be said for the right end.

[0038] Furthermore, the technology according to the present disclosure is not limited to the above-described example in which the M light-emitting elements in each column are arranged in a stepped manner so that any two adjacent light-emitting elements occupy areas that partially overlap in the axial direction. For example, the M light-emitting elements in each column may be arranged so that at least two adjacent light-emitting elements among them overlap with each other in the axial direction.

[0039] 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.

[0040] 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_3A 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.

[0041] 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_0 In 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.

[0042] 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.

[0043] 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_0 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 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 by the four light-emitting elements of each column of the light-emitting chip 400 has been performed, 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 cycle.

[0044] In this manner, in this embodiment, a drive signal based on the pixel value of each pixel position is input to four light-emitting elements in a corresponding column of the light-emitting element array. Specifically, for example, a drive signal based on a pixel value (0,0) is input to four light-emitting elements R 0_3 , R 0_2 , R 0_1 and R 0_0 When these four light-emitting elements emit light in accordance with the drive signals, a spot corresponding to the pixel value (0,0) is formed on the surface of the photoconductor 102. Similarly, a drive signal based on the pixel value (1,0) is input to the four light-emitting elements R 1_3 , R 1_2 , R 1_1 and R 1_0 When these four light emitting elements emit light in accordance with the drive signals, a spot corresponding to the pixel value (1,0) is formed on the surface of the photoconductor 102. In this way, in this embodiment, a plurality of light-emitting units (e.g., light-emitting elements) are driven by pixel values ​​(pixel data) for forming pixels of an image. For example, when forming an image with an output resolution of 1200 dpi in the axial direction, each pixel is usually arranged at a pitch P of 4800 dpi in the axial direction. A The number of light emitting units used to form one pixel may be equal to the number M of light emitting units in each column, and the pitch of the M light emitting units in the axial direction is a pitch equivalent to 1 / M of the output resolution. In other words, at least two of the M light emitting units used to form one pixel are arranged at intervals of

number

[0045] As will be understood from the explanation in this section, the light emission control unit 705 causes the multiple 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. This control of the read range is also performed in the same way when compensating for errors in the image formation range, which will be explained next.

[0046] <4. Compensation for errors in the image formation range> As described above, it is inevitable that some errors in component placement occur when manufacturing an exposure device or image forming device. Even after manufacturing, environmental factors such as temperature changes or physical forces during transportation, installation, or use can cause misalignment of components within the device. Such misalignment or misalignment of the image forming unit 101 results in an error in the imaging area. The error in the imaging area can typically include one or both of a misregistration component and a magnification error component. The misregistration component represents a displacement in the imaging area. Relative misalignment between images of multiple color components and an overall misalignment in the imaging area relative to the sheet are examples of the misregistration component. The magnification error component represents an expansion or contraction of the imaging area. The expansion of the imaging area due to thermal expansion of the exposure head 106 is an example of a magnification error component.

[0047] To determine whether such errors in the image formation range need to be compensated for, the CPU 701 of the image forming apparatus 1 performs calibration periodically, in response to a user instruction, or when a trigger condition is met. Specifically, the CPU 701 controls the image forming unit 101 to form a test chart on the transfer belt 111. The test chart here may be an image having a known pattern. The test chart is also formed by multiple exposure using the light-emitting element array of the exposure head 106. The CPU 701 also controls the optical sensor 113 to optically read the test chart formed on the transfer belt 111. The optical sensor 113 outputs read image data representing the test chart reading result to the CPU 701. The CPU 701 then compares the read image data with the known pattern to detect errors in the image formation range of the image formed through multiple exposure. Therefore, the CPU 701 according to this embodiment can function as a detection unit that detects errors (positional misalignment or magnification error) in the image formation range. If a circumferential error is detected as a result of the calibration, the CPU 701 can compensate for the circumferential error by adjusting the relative timing between the rotation of the photoconductor 102 and the light emission of the light-emitting chip 400. On the other hand, if an axial error is detected, the CPU 701 notifies the light-emitting control unit 705 of the detected axial positional deviation amount X and / or error magnification Y by outputting or transmitting correction data indicating the detected error to the light-emitting control unit 705. The positional deviation amount X can be either a positive or negative value. Regarding the error magnification Y, if Y=1, it indicates that there is no magnification error, if Y>1, it indicates that an expansion of the image formation area has been detected, and if Y<1, it indicates that a contraction of the image formation area has been detected.

[0048] <4-1. Compensation for positional deviation> When axial misalignment is detected, the light-emission control unit 705 shifts a set of pixel values ​​of the input image data corresponding to at least one row of the multiple light-emitting elements 602 of the exposure head 106 to compensate for the misalignment, in the above-described multiple-exposure light-emission control procedure. At this time, the light-emission control unit 705 may shift the set of pixel values ​​of the input image data based on the misalignment amount X and / or error magnification Y input from the CPU 701. The CPU 701 may transmit correction data for correcting the misalignment based on the misalignment amount X and / or error magnification Y to the light-emission control unit 705, and the light-emission control unit 705 may shift the set of pixel values ​​of the input image data based on the correction data. For example, if the width W0 shown in FIG. 3B indicates the normal effective image formation position in the axial direction D1, if the image misalignment is to the left, the misalignment can be canceled by shifting the image formation position to the right. Similarly, if the image misalignment is to the right, the misalignment can be canceled by shifting the image formation position to the left. In the following description, the shift direction of the image formation position (or the pixel value set) to cancel such misalignment will be referred to as the cancellation direction. Below, examples of light emission control to compensate for axial misalignment will be described for several scenarios with different misalignment amounts X.

[0049] (1) First Scenario In the first scenario, the misalignment amount X is calculated by multiplying the axial pitch P A (X=P A ). Pitch P A is the smallest unit of misalignment that can be compensated for. Here, the cancellation direction is assumed to be the right direction. Figures 13A to 13D are explanatory diagrams of the procedure for light emission control including misalignment compensation in the first scenario.

[0050] 13A, the input image data IM1 is again shown with three lines of dummy pixel values ​​added to the beginning. ATherefore, the pixel value set PG1 in the first row (the row where index i=-3) in the read range RD is selected as the pixel value set to be shifted. Then, the light emission control unit 705 shifts the selected pixel value set PG1 by one pixel in the cancellation direction, and then reads out subsets of 2992 pixel values ​​from the input image data IM1 and outputs each subset to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right in FIG. 13A, the pixel value set PG1 corresponds to the light-emitting elements in the first row of the light-emitting element array. However, as a result of the shift, the drive signal based on the pixel value (0,-3) at the left end of the pixel value set PG1 is output to the light-emitting element R 0_0 Instead, light-emitting element R 1_0 The light-emitting element R corresponding to the position that becomes blank as a result of the shift is supplied to 0_0 may be supplied with a drive signal that means turning off the light emission, and thus the light emitting element R 0_0 As shown by the dashed line in the figure, the driving signal based on the effective pixel value of the line DL0 of the input image data IM1 causes the light-emitting element R 0_3 The light is supplied to the light emitting elements in the fourth row including

[0051] Moving to FIG. 13B, in the next line period t0+1, the readout range RD for pixel values ​​from the input image data IM1 moves down by one line. The light emission control unit 705 selects the pixel value set PG2 in the first row (the row where index i=-2) in the readout range RD as the pixel value set to be shifted. Then, the light emission control unit 705 shifts the selected pixel value set PG2 by one pixel in the cancellation direction, and then outputs a subset of 2992 pixel values ​​to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right in FIG. 13B, the pixel value set PG2 corresponds to the light-emitting element in the first row of the light-emitting element array. However, as a result of the shift, the drive signal based on the pixel value (0,-2) at the left end of the pixel value set PG2 is output to the light-emitting element R 0_0 Instead, light-emitting element R 1_0 The light-emitting element R corresponding to the position that becomes blank as a result of the shift is supplied to 0_0As shown by the dashed line in the figure, the drive signal based on the effective pixel value of the line DL0 of the input image data IM1 is supplied to the light-emitting element R 0_2 The light is supplied to the light emitting elements in the third row including

[0052] Moving to FIG. 13C, in the next line period t0+2, the readout range RD for pixel values ​​from the input image data IM1 is further shifted down by one line. The light emission control unit 705 selects the pixel value set PG3 in the first row (the row where index i=-1) in the readout range RD as the pixel value set to be shifted. Then, the light emission control unit 705 shifts the selected pixel value set PG3 by one pixel in the cancellation direction, and then outputs a subset of 2992 pixel values ​​to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right in FIG. 13C, the pixel value set PG3 corresponds to the light-emitting element in the first row of the light-emitting element array. However, as a result of the shift, the drive signal based on the pixel value (0,-1) at the left end of the pixel value set PG3 is output to the light-emitting element R 0_0 Instead, light-emitting element R 1_0 The light-emitting element R corresponding to the position that becomes blank as a result of the shift is supplied to 0_0 As shown by the dashed line in the figure, the drive signal based on the effective pixel value of the line DL0 of the input image data IM1 is supplied to the light-emitting element R 0_1 The light is supplied to the light emitting elements in the second row including

[0053] Moving to FIG. 13D, in the next line period t0+3, the readout range RD for pixel values ​​from the input image data IM1 is further shifted down by one line. The light emission control unit 705 selects the pixel value set PG4 in the first row within the readout range RD as the pixel value set to be shifted. The pixel value set PG4 includes the effective pixel values ​​of line DL0 of the input image data IM1. The light emission control unit 705 then shifts the selected pixel value set PG4 by one pixel in the cancellation direction, and outputs a subset of 2992 pixel values ​​to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right of FIG. 13D, the pixel value set PG4 corresponds to the light-emitting element in the first row of the light-emitting element array. However, as a result of the shift, the drive signal based on the pixel value (0,0) at the left end of the pixel value set PG4 is output to the light-emitting element R 0_0 Instead, light-emitting element R 1_0 The light-emitting element R corresponding to the position that becomes blank as a result of the shift is supplied to 0_0 may be supplied with a drive signal that also means turning off the light emission.

[0054] As a result of the light emission control in the line periods t0 to t0+3, the effective image formation position of the line L0 on the surface of the photoconductor 102 is shifted by an axial pitch P A For example, the spot corresponding to the pixel value (0,0) at the left end of the line DL0 of the input image data IM1 is moved to the right by the amount of light emitting element R 0_3 , R 0_2 , R 0_1 , and R 1_0 However, the arrangement of the components such as the exposure head 106 is shifted to the left by a pitch P A Since the positional deviation is canceled out, the final image formation position on the photosensitive member 102, the transfer belt 111, or the sheet becomes substantially the same as in normal times.

[0055] In this scenario, in which the positional deviation of one pitch is compensated for, for example, a drive signal based on a pixel value (0,0) drives four light-emitting elements R 0_3 , R 0_2 , R 0_1 and R 1_0When these four light-emitting elements emit light in accordance with the drive signals, a spot corresponding to the pixel value (0,0) is formed at a position shifted by one pitch on the surface of the photoconductor 102. Similarly, a drive signal based on the pixel value (1,0) is input to the four light-emitting elements R 1_3 , R 1_2 , R 1_1 and R 2_0 When these four light-emitting elements emit light in accordance with the drive signal, a spot corresponding to a pixel value (1,0) is formed at a position shifted by one pitch on the surface of the photoconductor 102. Comparing this to the case without misalignment compensation described with reference to FIGS. 12A to 12D, the combination of light-emitting elements used to form a spot corresponding to the same pixel position changes when misalignment compensation is performed. For example, the combination of light-emitting elements for forming a spot corresponding to a pixel value (0,0) is (R 0_3 ,R 0_2 ,R 0_1 ,R 0_0 ), whereas in this scenario (R 0_3 ,R 0_2 ,R 0_1 ,R 1_0 ) The same applies to other pixel positions.

[0056] As can be seen from the first scenario, the light emission control unit 705 selects at least a pixel value set corresponding to a row having a light emitting element at the rear end in the cancellation direction as a pixel value set to be shifted. When the cancellation direction is to the right, the rear end is the light emitting element R. 0_0 When the cancellation direction is to the left, the light-emitting element R 0_3 The fourth row has the following: The light emission control unit 705 shifts the selected pixel value set while moving the selection position of the pixel value set in the circumferential direction in accordance with the movement of the readout range for each line period, thereby driving the plurality of light emitting elements 602. This makes it possible to maintain the effective image formation position in the axial direction displaced in the cancellation direction over multiple line periods.

[0057] (2) Second Scenario In the second scenario, the misalignment amount X is proportional to the axial pitch P A is twice as large as (X=2×P A ) Here too, the cancellation direction is assumed to be the right direction. Figures 14A to 14D are explanatory diagrams of the procedure for light emission control including positional deviation compensation in the second scenario.

[0058] 14A, the input image data IM1 is again shown with three lines of dummy pixel values ​​added to the beginning. The light emission control unit 705 calculates the positional deviation amount X=2×P A Therefore, the pixel value set PG1 in the first row and the pixel value set PG2 in the second row in the read range RD are selected as pixel value sets to be shifted. Then, the light emission control unit 705 shifts the selected pixel value sets PG1 and PG2 by one pixel in the cancellation direction, and then reads out subsets of 2992 pixel values ​​from the input image data IM1 and outputs each subset to each light emitting chip 400-n. In the light emitting chip 400-1 shown on the right in FIG. 14A, the pixel value sets PG1 and PG2 correspond to the light emitting elements in the first and second rows of the light emitting element array, respectively. However, as a result of the shift, a drive signal based on the pixel value at the left end of each pixel value set is supplied to the light emitting element in the second column from the left. The light emitting element R corresponding to the position that becomes blank as a result of the shift 0_0 and R 0_1 A drive signal that means turning off light emission can be supplied to the light-emitting element R. The drive signal based on the effective pixel value of the line DL0 of the input image data IM1 is supplied to the light-emitting element R in the same way as in the example of FIG. 0_3 The light is supplied to the light emitting elements in the fourth row including

[0059] Moving to FIG. 14B, in the next line period t0+1, the readout range RD for pixel values ​​from the input image data IM1 is shifted down by one line. The light emission control unit 705 selects the pixel value set PG2 in the first row and the pixel value set PG3 in the second row in the readout range RD as pixel value sets to be shifted. The light emission control unit 705 then shifts the selected pixel value sets PG2 and PG3 by one pixel in the cancellation direction, and outputs a subset of 2992 pixel values ​​to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right in FIG. 14B, the pixel value sets PG2 and PG3 correspond to the light-emitting elements in the first and second rows, respectively, of the light-emitting element array. However, as a result of the shift, a drive signal based on the pixel value at the left end of each pixel value set is supplied to the light-emitting element in the second column from the left. The light-emitting element R corresponding to the position that becomes blank as a result of the shift 0_0 and R 0_1 A drive signal that means turning off light emission can be supplied to the light-emitting element R. The drive signal based on the effective pixel value of the line DL0 of the input image data IM1 is supplied to the light-emitting element R in the same way as in the example of FIG. 12B. 0_2 The light is supplied to the light emitting elements in the third row including

[0060] Moving to FIG. 14C, in the next line period t0+2, the readout range RD for pixel values ​​from the input image data IM1 is further shifted down by one line. The light-emitting control unit 705 selects the pixel value set PG3 in the first row and the pixel value set PG4 in the second row within the readout range RD as pixel value sets to be shifted. The pixel value set PG4 includes the effective pixel values ​​of line DL0 of the input image data IM1. The light-emitting control unit 705 then shifts the selected pixel value sets PG3 and PG4 by one pixel in the cancellation direction, and outputs a subset of 2992 pixel values ​​to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right in FIG. 14C, the pixel value sets PG3 and PG4 correspond to the light-emitting elements in the first and second rows, respectively, of the light-emitting element array. However, as a result of the shift, the drive signal based on the pixel value at the left end of each pixel value set is supplied to the light-emitting element in the second column from the left. The light-emitting element R corresponding to the position that becomes blank as a result of the shift 0_0 and R 0_1can be supplied with a drive signal that means turning off the light emission.

[0061] Moving to FIG. 14D, in the next line period t0+3, the readout range RD for pixel values ​​from the input image data IM1 is further shifted down by one line. The light-emitting control unit 705 selects a pixel value set PG4 in the first row and a pixel value set PG5 in the second row within the readout range RD as pixel value sets to be shifted. The pixel value sets PG4 and PG5 include effective pixel values ​​of the input image data IM1. The light-emitting control unit 705 then shifts the selected pixel value sets PG4 and PG5 by one pixel in the cancellation direction, and outputs a subset of 2992 pixel values ​​to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right of FIG. 14D, the pixel value sets PG4 and PG5 correspond to the light-emitting elements in the first and second rows, respectively, of the light-emitting element array. However, as a result of the shift, drive signals based on the pixel values ​​at the left end of each pixel value set are supplied to the light-emitting elements in the second column from the left. The light-emitting element R corresponding to the position that becomes blank as a result of the shift 0_0 and R 0_1 can be supplied with a drive signal that means turning off the light emission.

[0062] As a result of the light emission control in the line periods t0 to t0+3, the effective image formation position of the line L0 on the surface of the photoconductor 102 is shifted by an axial pitch P A For example, the spot corresponding to the pixel value (0,0) at the left end of the line DL0 of the input image data IM1 is shifted to the right by twice the amount of the pixel value (0,0) of the light emitting element R 0_3 , R 0_2 , R 1_1 , and R 1_0 However, the arrangement of the components such as the exposure head 106 is 2×P A Since the positional deviation is canceled out, the final image formation position on the photosensitive member 102, the transfer belt 111, or the sheet becomes substantially the same as in normal times.

[0063] In this scenario, in which the positional deviation of two pitches is compensated for, for example, a drive signal based on a pixel value (0,0) drives four light-emitting elements R 0_3 , R 0_2 , R 1_1 and R 1_0 Similarly, a drive signal based on the pixel value (1,0) is input to the four light-emitting elements R 1_3 , R 1_2 , R 2_1 and R 2_0 , and is input to . Comparing this with the case where no misalignment compensation is performed as explained with reference to FIGS. 12A to 12D, the combination of light-emitting elements used to form a spot corresponding to the same pixel position changes depending on the amount of misalignment to be compensated when misalignment compensation is performed. For example, the combination of light-emitting elements for forming a spot corresponding to pixel value (0,0) is (R 0_3 ,R 0_2 ,R 0_1 ,R 0_0 ), whereas in this scenario (R 0_3 ,R 0_2 ,R 1_1 ,R 1_0 ) The same applies to other pixel positions.

[0064] As can be seen from the first and second scenarios, the light emission control unit 705 determines the magnitude of the positional deviation (absolute value of X) and the axial pitch P of the light emitting elements 602. A Based on the above, it is selected which of the M rows of light emitting elements 602 to shift the corresponding set of pixel values ​​for. For example, if the cancellation direction is to the right, the selected rows may be as follows: |X|=P A → 1st line |X|=2×P A → 1st line, 2nd line |X|=3×P A → 1st line, 2nd line, 3rd line |X|≧4×P A → 1st line, 2nd line, 3rd line, 4th line If the cancel direction is left, the selected rows may be: |X|=P A→ 4th line |X|=2×P A → 4th line, 3rd line |X|=3×P A → 4th line, 3rd line, 2nd line |X|≧4×P A → 4th line, 3rd line, 2nd line, 1st line

[0065] (3) Third Scenario In the third scenario, the misalignment amount X is calculated by multiplying the axial pitch P A is 5 times (X=5×P A ) Here too, the cancellation direction is assumed to be the right direction. Figures 15A to 15D are explanatory diagrams of the procedure for light emission control including positional deviation compensation in the third scenario.

[0066] 15A, the input image data IM1 is again shown with three lines of dummy pixel values ​​added to the beginning. The light emission control unit 705 calculates the positional deviation amount X=5×P A Therefore, pixel value sets PG1, PG2, PG3, and PG4 in the first, second, third, and fourth rows in the read range RD are selected as pixel value sets to be shifted. Then, the light emission control unit 705 shifts the pixel value set PG1 by two pixels to the right, and shifts the pixel value sets PG2 to PG4 by one pixel to the right. In the light-emitting chip 400-1 shown on the right in FIG. 15A, the pixel value sets PG1 to PG4 correspond to the light-emitting elements in the first to fourth rows of the light-emitting element array, respectively. However, as a result of the shift, the drive signal based on the pixel value (0, -3) at the left end of the pixel value set PG1 is driven by the light-emitting element R in the third column from the left. 2_0 The drive signals based on the pixel values ​​at the left end of the pixel value sets PG2 to PG4 are supplied to the light emitting elements in the second column from the left. 0_0 , R 0_1 , R 0_2 , R 0_3 and R 1_0 can be supplied with a drive signal that means turning off the light emission.

[0067] 15B, in the next line period t0+1, the readout range RD of pixel values ​​from the input image data IM1 is shifted down by one line. The light emission control unit 705 selects pixel value sets PG2, PG3, PG4, and PG5 in the first, second, third, and fourth rows in the readout range RD as pixel value sets to be shifted. Then, the light emission control unit 705 shifts the pixel value set PG2 by two pixels to the right, and shifts the pixel value sets PG3 to PG5 by one pixel to the right. In the light-emitting chip 400-1 shown on the right of FIG. 15B, the pixel value sets PG2 to PG5 correspond to the light-emitting elements in the first to fourth rows of the light-emitting element array, respectively. However, as a result of the shift, the drive signal based on the pixel value (0, -2) at the left end of the pixel value set PG2 is transmitted to the light-emitting element R in the third column from the left. 2_0 The drive signals based on the pixel values ​​at the left end of the pixel value sets PG3 to PG5 are supplied to the light emitting elements in the second column from the left. 0_0 , R 0_1 , R 0_2 , R 0_3 and R 1_0 can be supplied with a drive signal that means turning off the light emission.

[0068] 15C, in the next line period t0+2, the readout range RD of pixel values ​​from the input image data IM1 is further shifted down by one line. The light emission control unit 705 selects pixel value sets PG3, PG4, PG5, and PG6 in the first, second, third, and fourth rows in the readout range RD as pixel value sets to be shifted. Then, the light emission control unit 705 shifts the pixel value set PG3 by two pixels to the right, and shifts the pixel value sets PG4 to PG6 by one pixel to the right. In the light-emitting chip 400-1 shown on the right of FIG. 15C, the pixel value sets PG3 to PG6 correspond to the light-emitting elements in the first to fourth rows of the light-emitting element array, respectively. However, as a result of the shift, the drive signal based on the pixel value (0, -1) at the left end of the pixel value set PG3 is transmitted to the light-emitting element R in the third column from the left. 2_0The drive signals based on the pixel values ​​at the left end of the pixel value sets PG4 to PG6 are supplied to the light emitting elements in the second column from the left. 0_0 , R 0_1 , R 0_2 , R 0_3 and R 1_0 can be supplied with a drive signal that means turning off the light emission.

[0069] 15D, in the next line period t0+3, the readout range RD of pixel values ​​from the input image data IM1 is further shifted down by one line. The light emission control unit 705 selects pixel value sets PG4, PG5, PG6, and PG7 in the first, second, third, and fourth rows in the readout range RD as pixel value sets to be shifted. Then, the light emission control unit 705 shifts the pixel value set PG4 by two pixels to the right, and shifts the pixel value sets PG5 to PG7 by one pixel to the right. In the light-emitting chip 400-1 shown on the right of FIG. 15D, the pixel value sets PG4 to PG7 correspond to the light-emitting elements in the first to fourth rows of the light-emitting element array, respectively. However, as a result of the shift, the drive signal based on the pixel value (0,0) at the left end of the pixel value set PG4 is transmitted to the light-emitting element R in the third column from the left. 2_0 The drive signals based on the pixel values ​​at the left end of the pixel value sets PG5 to PG7 are supplied to the light emitting elements in the second column from the left. 0_0 , R 0_1 , R 0_2 , R 0_3 and R 1_0 can be supplied with a drive signal that means turning off the light emission.

[0070] As a result of the light emission control in the line periods t0 to t0+3, the effective image formation position of the line L0 on the surface of the photoconductor 102 is shifted by an axial pitch P A For example, the spot corresponding to the pixel value (0,0) at the left end of the line DL0 of the input image data IM1 is moved to the right by five times the pixel value (0,0). 1_3 , R 1_2 , R 1_1, and R 2_0 However, the arrangement of the components such as the exposure head 106 is 5×P to the left. A Since the positional deviation is canceled out, the final image formation position on the photosensitive member 102, the transfer belt 111, or the sheet becomes substantially the same as in normal times.

[0071] As can be seen from the first to third scenarios, the light emission control unit 705 determines the magnitude of the positional deviation (absolute value of X) and the axial pitch P of the light emitting elements 602. A For example, if the magnitude of the displacement |X| is greater than the axial pitch P A The shift amount is assumed to be x times (x is a natural number) of M. In this case, the light emission control unit 705 distributes the shift amount of x pixels to each row in a round-robin fashion, starting from the row having the light-emitting element at the rear end in the cancellation direction to the row having the light-emitting element at the front end. As an example, when M=4 and the cancellation direction is rightward, the rear end in the cancellation direction is located on the first row, and the front end is located on the fourth row. Therefore, the light emission control unit 705 distributes the shift amount by one pixel to the four rows in the order of first row → second row → third row → fourth row → first row → second row → ... until the total shift amount reaches x. As another example, when M=4 and the cancellation direction is leftward, the rear end in the cancellation direction is located on the fourth row, and the front end is located on the first row. Therefore, the light emission control unit 705 distributes the shift amount by one pixel to the four rows in the order of fourth row → third row → second row → first row → fourth row → third row → ... until the total shift amount reaches x. In this way, one or more pixel value sets of the input image data are shifted in the cancellation direction according to the distributed shift amount, and the plurality of light emitting elements 602 are caused to emit light, thereby correcting the axial positional deviation of the image formation position by a pitch P A This allows for flexible compensation at a granularity of

[0072] <4-2. Compensation for Magnification Error> When an axial magnification error is detected, the light emission control unit 705 selects one or more pixel positions from among the pixel positions constituting the input image data according to the error magnification Y in the above-described procedure for light emission control of multiple exposure. Then, the light emission control unit 705 inserts or thins out the pixel values ​​of each pixel position into the pixel value set of the row to which each of the selected pixel positions belongs, causing the multiple light emitting elements 602 to emit light. Whether the pixel value of each pixel position is inserted or thinned out depends on the error magnification Y; if Y<1 (i.e., in the case of a reduction in the image formation range), the pixel value is inserted, and if Y>1 (i.e., in the case of an expansion in the image formation range), the pixel value is thinned out. The light emission control unit 705 determines the error magnification Y and the axial pitch P of the light emitting elements 602. A Based on this, the number of pixel positions to be selected for pixel value insertion or thinning can be determined. Hereinafter, compensation for the reduction of the imaging range and compensation for the expansion of the imaging range will be described in detail.

[0073] <4-2-1. Compensation for reduction in image formation range> When a magnification error is detected and the error magnification Y is smaller than 1, the light emission control unit 705 inserts the pixel value of each selected pixel position into the set of pixel values ​​of the row to which that pixel position belongs. Here, inserting a pixel value into a pixel position includes shifting pixel values ​​on one side of the axial direction based on that pixel position in a direction that expands the set of pixel values, and providing a copy of the pixel value of that pixel position before the shift to that pixel position.

[0074] 16A to 16D are explanatory diagrams of the procedure for light emission control including compensation for the reduction of the image formation range. Here, it is assumed that the number of pixel positions to be selected is 1 (for example, W0×(1−Y)≒P A16A shows input image data IM2 with three lines of dummy pixel values ​​added to the beginning. Because the error magnification Y is smaller than 1, the light-emission control unit 705 selects a pixel position within the read range RD in each line period into which a pixel value should be inserted. In the example of FIG. 16A, pixel position DP0 is selected in line period t0. The selected pixel position DP0 belongs to the first row of the read range RD (the row with index i=−3). The light-emission control unit 705 inserts a pixel value into the pixel value set PG1 of this row. Specifically, the light-emission control unit 705 shifts the pixel values ​​of the subset PG1b on the right side of the axial direction by one pixel to the right based on the pixel position DP0, and assigns a copy of the pixel value (3, −3) of pixel position DP0 before the shift to pixel position DP0. The light-emission control unit 705 then reads out subsets of 2992 pixel values ​​from the input image data IM2 and outputs each subset to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right in FIG. 16A, the pixel value set PG1 corresponds to the light-emitting element in the first row of the light-emitting element array. As a result of inserting the pixel value, the driving signal based on the pixel value (3, −3) of the selected pixel position DP0 is 3_0 and light-emitting element R 4_0 , and the effective range of the light-emitting element in the first row is expanded by one light-emitting element.

[0075] 16B, in the next line period t0+1, pixel position DP0 in the readout range RD is again selected. The selected pixel position DP0 belongs to the first row of the readout range RD (the row with index i=-2). The light emission control unit 705 inserts a pixel value into the pixel value set PG2 of this row. Specifically, the light emission control unit 705 shifts the pixel values ​​of the subset PG2b on the right side of the axial direction by one pixel to the right with respect to pixel position DP0, and assigns a copy of the pixel value (3,-2) of pixel position DP0 before the shift to pixel position DP0. The light emission control unit 705 then reads out subsets of 2992 pixel values ​​from the input image data IM2 and outputs each subset to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right in FIG. 16B, the pixel value set PG2 corresponds to the light-emitting element in the first row of the light-emitting element array. As a result of the pixel value insertion, a drive signal based on the pixel value (3,-2) of the selected pixel position DP0 is applied to the light-emitting element R. 3_0 and light-emitting element R 4_0 , and here too the effective range of the light emitting element in the first row is expanded by one light emitting element.

[0076] 16C, in the next line period t0+2, pixel position DP0 in the readout range RD is selected again for the third time. The selected pixel position DP0 belongs to the first row of the readout range RD (the row with index i=-1). The light emission control unit 705 inserts a pixel value into the pixel value set PG3 of this row. Specifically, the light emission control unit 705 shifts the pixel values ​​of the subset PG3b on the right side of the axial direction by one pixel to the right with respect to pixel position DP0, and assigns a copy of the pixel value (3,-1) of pixel position DP0 before the shift to pixel position DP0. The light emission control unit 705 then reads out subsets of 2992 pixel values ​​from the input image data IM2 and outputs each subset to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right of FIG. 16C, the pixel value set PG3 corresponds to the light-emitting element in the first row of the light-emitting element array. As a result of the pixel value insertion, a drive signal based on the pixel value (3,-1) of the selected pixel position DP0 is applied to the light-emitting element R. 3_0 and light-emitting element R 4_0, and here too the effective range of the light emitting element in the first row is expanded by one light emitting element.

[0077] 16D, in the next line period t0+3, pixel position DP0 in the readout range RD is selected again for the fourth time. The selected pixel position DP0 belongs to the first row of the readout range RD (the row where index i=0). The light-emission control unit 705 inserts a pixel value into pixel value set PG4 of this row. Specifically, the light-emission control unit 705 shifts the pixel values ​​of subset PG4b on the right side of the axial direction by one pixel to the right with respect to pixel position DP0, and assigns a copy of the pixel value (3,0) of pixel position DP0 before the shift to pixel position DP0. The light-emission control unit 705 then reads out subsets of 2992 pixel values ​​from the input image data IM2 and outputs each subset to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right of FIG. 16D, pixel value set PG4 corresponds to the light-emitting element in the first row of the light-emitting element array. As a result of the pixel value insertion, a drive signal based on the pixel value (3,0) of the selected pixel position DP0 is applied to light-emitting element R. 3_0 and light-emitting element R 4_0 , and here too the effective range of the light emitting element in the first row is expanded by one light emitting element.

[0078] 16A to 16D, the drive signals based on the effective pixel values ​​of line DL0 of the input image data IM2 are supplied to the light emitting elements in the fourth, third, second, and first rows of the light emitting element array in each line period. Among these, since the pixel value set PG4 of line DL0 is expanded to the right in line period t0+3, the image formation range is expanded by the axial pitch P A However, because the exposure head 106 shrinks in the axial direction by the amount of the error magnification Y due to, for example, a temperature change, the final image formation range on the photosensitive member 102, transfer belt 111, or sheet becomes approximately the same as in normal times as a result of the magnification error being cancelled out.

[0079] In this scenario, compensation is made for the reduction of the image formation range by one pitch. For example, the drive signal based on the pixel value (3,0) is used to drive the four light-emitting elements R 3_m In addition, light-emitting element R 4_0 When these five light-emitting elements emit light in accordance with the drive signals, an enlarged spot corresponding to pixel value (3,0) is formed on the surface of photoconductor 102. Comparing this to the case without compensation for magnification error described with reference to FIGS. 12A to 12D, the number of light-emitting elements used to form a spot corresponding to the same pixel position changes when compensation for magnification error is performed. For example, the number of light-emitting elements used to form a spot corresponding to pixel value (3,0) is four in the case without compensation for magnification error, but five in this scenario. The same is true for other pixel positions.

[0080] The CPU 701 may transmit correction data for canceling the magnification error to the light emission control unit 705, and the light emission control unit 705 may control the number of light emitting units to be driven to form each pixel of the image based on the correction data. In other words, the correction data may be data for correcting the width of the image in the axial direction.

[0081] In one embodiment, the number of light-emitting units (e.g., light-emitting elements) used to form a spot corresponding to a certain pixel value (or pixel position) of the input image data may vary depending on the correction data. In other words, the number of light-emitting units driven to form a pixel of the image may vary depending on the correction data. The light-emitting control unit 705 may correct the width of the image based on the correction data by controlling the multiple light-emitting units of the exposure head as follows: -driving a first number of light emitting units to form a first pixel of an image with first pixel data; A second number of light emitting units, different from the first number, are driven to form a second pixel of the image with second pixel data.

[0082] When the width of the image is not corrected, the light-emitting control unit 705 can control the plurality of light-emitting units of the exposure head so that a first number of light-emitting units are driven to form each pixel of the image. When the width of the image is expanded, at least one pixel is formed using a second number of light-emitting units that is greater than the first number. The plurality of light-emitting units are arranged at a pitch P in the axial direction. A , they can be said to be arranged at different positions in the axial direction.

[0083] <4-2-2. Compensation for expansion of image formation area> When a magnification error is detected and the error magnification Y is greater than 1, the light emission control unit 705 thins out the pixel value of each selected pixel position from the set of pixel values ​​of the row to which that pixel position belongs. Here, thinning out the pixel value at a pixel position includes erasing the pixel value at that pixel position before thinning out, and shifting pixel values ​​on one side of that pixel position in the axial direction in a direction that reduces the set of pixel values.

[0084] 17A to 17D are explanatory diagrams of the procedure for light emission control including compensation for the expansion of the image formation range. Here, it is assumed that the number of pixel positions to be selected is 1 (for example, W0×(Y−1)≒P A17A shows input image data IM2 with three lines of dummy pixel values ​​added to the beginning. Because the error magnification Y is greater than 1, the light-emission control unit 705 selects pixel positions within the readout range RD in each line period from which pixel values ​​should be thinned. In the example of FIG. 17A, pixel position DP0 is selected in line period t0. The selected pixel position DP0 belongs to the first row of the readout range RD (the row with index i=−3). The light-emission control unit 705 thins out the pixel value of pixel position DP0 from the pixel value set PG1 of this row. Specifically, the light-emission control unit 705 deletes the pixel value (3,−3) of pixel position DP0 before the shift and shifts the pixel values ​​of subset PG1a on the left side of pixel position DP0 in the axial direction by one pixel to the right. The light-emission control unit 705 then reads out subsets of 2992 pixel values ​​from the input image data IM2 and outputs each subset to each light-emitting chip 400-n. 17A, the pixel value set PG1 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of the pixel value thinning, the drive signal based on the pixel value (3, −3) at the selected pixel position DP0 is not supplied to any of the light-emitting elements, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0085] 17B, ​​in the next line period t0+1, pixel position DP0 in readout range RD is again selected. The selected pixel position DP0 belongs to the first row of readout range RD (the row with index i=-2). The light emission control unit 705 thins out the pixel value of pixel position DP0 from pixel value set PG2 of this row. Specifically, the light emission control unit 705 deletes the pixel value (3,-2) of pixel position DP0 before the shift and shifts the pixel values ​​of subset PG2a on the left side of pixel position DP0 in the axial direction one pixel to the right. The light emission control unit 705 then reads out subsets of 2992 pixel values ​​from the input image data IM2 and outputs each subset to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right of FIG. 17B, pixel value set PG2 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of the pixel value thinning, the drive signal based on the pixel value (3,-2) of the selected pixel position DP0 is not supplied to any of the light-emitting elements, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0086] 17C, in the next line period t0+2, pixel position DP0 in readout range RD is selected again for the third time. The selected pixel position DP0 belongs to the first row of readout range RD (the row with index i=-1). The light-emission control unit 705 thins out the pixel value of pixel position DP0 from pixel value set PG3 of this row. Specifically, the light-emission control unit 705 deletes the pixel value (3,-1) of pixel position DP0 before the shift and shifts the pixel values ​​of subset PG3a on the left side of pixel position DP0 in the axial direction one pixel to the right. The light-emission control unit 705 then reads out subsets of 2992 pixel values ​​from the input image data IM2 and outputs each subset to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right of FIG. 17C, pixel value set PG3 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of the pixel value thinning, the drive signal based on the pixel value (3,-1) of the selected pixel position DP0 is not supplied to any of the light-emitting elements, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0087] Moving to FIG. 17D, in the next line period t0+3, pixel position DP0 in readout range RD is selected again for the fourth time. The selected pixel position DP0 belongs to the first row of readout range RD (the row where index i=0). The light-emission control unit 705 thins out the pixel value of pixel position DP0 from pixel value set PG4 of this row. Specifically, the light-emission control unit 705 deletes the pixel value (3,0) of pixel position DP0 before the shift and shifts the pixel values ​​of subset PG4a on the left side of pixel position DP0 in the axial direction one pixel to the right. The light-emission control unit 705 then reads out subsets of 2992 pixel values ​​from the input image data IM2 and outputs each subset to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right of FIG. 17D, pixel value set PG4 corresponds to the light-emitting elements in the first row of the light-emitting element array. As a result of the pixel value thinning, the drive signal based on the pixel value (3,0) of the selected pixel position DP0 is not supplied to any of the light-emitting elements, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0088] 17A to 17D, the drive signals based on the effective pixel values ​​of line DL0 of the input image data IM2 are supplied to the light emitting elements in the fourth, third, second, and first rows of the light emitting element array in each line period. Among these, since the pixel value set PG4 of line DL0 is reduced in line period t0+3, the image formation range is reduced by an axial pitch P A However, because the exposure head 106 expands in the axial direction by the amount of the error magnification Y due to, for example, a temperature change, the final image formation range on the photosensitive member 102, transfer belt 111, or sheet becomes approximately the same as under normal circumstances as a result of the magnification error being cancelled out.

[0089] In this scenario, compensation is made for the expansion of the image formation range by one pitch. For example, the drive signal based on the pixel value (3,0) is applied to the four light-emitting elements R 3_m Among them, light-emitting element R 3_0The signal is input to three light-emitting elements excluding the one shown in FIG. 12A. When these three light-emitting elements emit light in accordance with the drive signal, a reduced spot corresponding to the pixel value (3,0) is formed on the surface of the photoconductor 102. Comparing this to the case without compensation for magnification error described with reference to FIGS. 12A to 12D, the number of light-emitting elements used to form a spot corresponding to the same pixel position changes when compensation for magnification error is performed. For example, the number of light-emitting elements used to form a spot corresponding to pixel value (3,0) is four in the case without compensation for magnification error, but three in this scenario. The same is true for the other pixel positions.

[0090] The light emission control unit 705 can determine pixel positions at which pixel values ​​are to be inserted or at which pixel values ​​are to be thinned out based on the correction data received from the CPU 701. In other words, the light emission control unit 705 can control the image width in the axial direction of the image to be formed by inserting or thinning pixel values ​​based on the correction data. In other words, the correction data is data for correcting the image width in the axial direction.

[0091] In one embodiment, the number of light-emitting units (e.g., light-emitting elements) used to form a spot corresponding to a pixel value (or pixel position) of the input image data may vary depending on the correction data. In other words, the number of light-emitting units driven based on drive signals that are based on pixel values ​​of the image may vary depending on the correction data. When there is no magnification error to be compensated for, a first number of light-emitting units are driven to form each pixel of the image based on the corresponding pixel value of the pixel. When there is a magnification error to be compensated for, at least one pixel of the image is formed by driving a second number of light-emitting units based on the corresponding pixel value of the pixel.

[0092] When the image width is reduced, at least one pixel is formed using a second number of light emitting portions that is smaller than the first number. Since the light emitting portions are arranged at a pitch PA in the axial direction, they can be said to be arranged at different positions in the axial direction.

[0093] <4-2-3. Selection of insertion pixel position and thinning pixel position> As described above, the light emission control unit 705 determines the error magnification Y and the axial pitch P of the light emitting elements 602. A For example, the number z of pixel positions to be selected may be determined based on the error magnification Y, the pitch P, A and the width of the normal imaging range W0, can be determined according to the following formula: z=round(W0×|1-Y| / P A ) Here, round is a function that returns the rounded value of its argument.

[0094] The light emission control unit 705 may select the determined number of pixel positions randomly in the axial direction and non-randomly in the circumferential direction. By incorporating randomness into the selection of axial insertion or thinning positions, the possibility of subjective image quality degradation, such as streaks or moire, occurring as a result of compensation can be reduced. The light emission control unit 705 may also randomly select the determined number of pixel positions in pixel block units in the axial direction. For example, when selecting two pixel positions, N columns of pixels aligned in the axial direction may be divided into left-half pixel blocks and right-half pixel blocks, and one pixel position may be randomly selected from the left-half pixel block and one pixel position may be randomly selected from the right-half pixel block. This reduces the possibility of image distortion due to bias in the selected pixel positions.

[0095] The selection of the insertion position or thinning position in the circumferential direction can be performed according to the same rules as the distribution of the shift amount in the compensation for the positional shift described above. For example, when inserting z pixel values ​​and shifting the pixel value set to the right, the rear end in the shift direction is located in the first row, and the front end is located in the fourth row. Therefore, the light emission control unit 705 selects pixel positions in the circumferential direction in the order of the first row → the second row → the third row → the fourth row → the first row → the second row → ... until the number of selected pixel positions reaches z. When shifting the pixel value set to the left, the order of row selection is reversed. Figure 18 shows how the image formation range is expanded to 3×P by selecting three pixel positions and inserting pixel values. A 18 shows an example of pixel position selection when enlarging the input image data IM3 by an amount corresponding to the pixel position DP1 in the first row, the pixel position DP2 in the second row, and the pixel position DP3 in the third row within the readout range RD set for the input image data IM3. Then, the pixel values ​​to the right of the selected pixel positions DP1, DP2, and DP3 are shifted to the right. For simplicity of explanation, an example is shown in which the selected pixel positions are biased toward pixel positions corresponding to the light-emitting elements of the light-emitting chip 400-1. However, in reality, the selected pixel positions may be widely distributed throughout the entire axial direction.

[0096] <4-2-4. Compensation for magnification error accompanied by compensation for positional deviation> When the image formation range is expanded or contracted by inserting or thinning pixel values ​​as described above, the image formation position is displaced in the axial direction accordingly. The light emission control unit 705 shifts the pixel value set of each line of image data so that the compensated image formation position matches the correct position, using the same concept as for compensating for misalignment as described in the previous section. The light emission control unit 705 can shift the pixel value set to compensate for misalignment, or insert or thin out pixel values ​​to compensate for magnification error, either first, as long as the position and magnification of the image formation range are ultimately appropriate. These points also apply to the implementation example described in the next section.

[0097] <5. Implementation example using auxiliary pixel array> As described in the previous section, the light-emitting control unit 705 outputs a subset of J×M (e.g., J=748, M=4) pixel values ​​of M lines of input image data to the light-emitting chip 400-n. To control the output of such pixel values, the image controller 700 may include an image memory including an auxiliary pixel array that temporarily stores pixel values. This section describes an implementation example of the output control of pixel values ​​using such an auxiliary pixel array.

[0098] (1) Basic output control Fig. 19 is an explanatory diagram of an implementation example of pixel value output control using an auxiliary pixel array. The left side of Fig. 19 again shows a portion of the input image data IM1 that the light emission control unit 705 receives from the image data processing unit 703. Dummy pixel values ​​for three lines have been added to the input image data IM1.

[0099] The center of FIG. 19 partially illustrates an auxiliary pixel array 750 that may be included in an image memory (e.g., a frame memory). Each row of the auxiliary pixel array 750 is made up of M times the number of pixels in each row of the input image data IM1. In the example of FIG. 19, M=4. The light emission control unit 705 stores M copies of the pixel value of each pixel position in each row of the input image data in M ​​auxiliary pixels in the corresponding row of the auxiliary pixel array 750. For example, referring to FIG. 19, four copies of the pixel value (0,0) of the input image data IM1 are stored in auxiliary pixels Px1, Px2, Px3, and Px4 of the auxiliary pixel array 750, respectively.

[0100] The light emitting element array of the light emitting chip 400-1 is shown on the right side of Fig. 19. The light emission control unit 705 sequentially reads pixel values ​​from the auxiliary pixels of the corresponding auxiliary pixel set in the auxiliary pixel array 750, and outputs the read pixel values ​​to the light emitting element array, in order to cause the exposure head 106 to form spots corresponding to each pixel position of the input image data IM1. In the example of Fig. 19, the auxiliary pixels from which pixel values ​​are read in the auxiliary pixel array 750 in a certain line period are indicated by hatching. In particular, in this line period, the light emission control unit 705 reads the pixel value from auxiliary pixel Px4 out of the four auxiliary pixels in which the pixel value (0,0) is stored, and outputs the read pixel value to the light emitting element R. 0_3 Output to.

[0101] On the left side of FIGS. 20A to 20D, the auxiliary pixels from which pixel values ​​are read in the auxiliary pixel array 750 over line periods t0 to t0+3 are shown with different density shading. Focusing on the four auxiliary pixels storing the pixel value (0,0), in line period t0, the pixel value read from auxiliary pixel Px4 is used to form the spot SP in the upper left corner of the electrostatic latent image IM4 (see FIG. 20A). In line period t0+1, the pixel value read from auxiliary pixel Px3 is used to form the spot SP of the electrostatic latent image IM4 (see FIG. 20B). In line period t0+2, the pixel value read from auxiliary pixel Px2 is used to form the spot SP of the electrostatic latent image IM4 (see FIG. 20C). In line period t0+3, the pixel value read from auxiliary pixel Px1 is used to form the spot SP of the electrostatic latent image IM4 (see FIG. 20D).

[0102] The output control of pixel values ​​from the auxiliary pixel array described here is an example of basic control when no error in the image formation range is detected. In this case, each spot of the electrostatic latent image is formed as a result of light emission based on pixel values ​​read from a set of M auxiliary pixels (i.e., auxiliary pixel set) to which the same pixel value of the corresponding pixel position of the input image data is copied. For example, in the case of an auxiliary pixel set G consisting of auxiliary pixels Px1, Px2, Px3, and Px4, 0,0contributes to the formation of one spot SP of the electrostatic latent image IM4. On the other hand, if an error in the image formation range is detected, the auxiliary pixel set (the auxiliary pixels constituting the auxiliary pixel set) contributing to the formation of the corresponding spot for at least one pixel position will differ as a result of pixel value shifting, insertion, or thinning. In other words, a first auxiliary pixel set corresponding to at least one pixel position when no error in the image formation range is detected will differ from a second auxiliary pixel set corresponding to the at least one pixel position when an error in the image formation range is detected. As a result, the number of light-emitting elements corresponding to the auxiliary pixel set will change, and the number of light-emitting elements contributing to the formation of the spot corresponding to the at least one pixel position will differ. Below, we will explain in order what differences may occur in the auxiliary pixel sets when a positional deviation is detected as an error in the image formation range, when a magnification error of a magnification smaller than 1 is detected, and when a magnification error of a magnification greater than 1 is detected.

[0103] (2) Compensation for misalignment When an axial misalignment is detected as an error in the image formation range, the light emission control unit 705 shifts the pixel values ​​of at least one row of the auxiliary pixel array in a direction that cancels the detected misalignment. The amount of shift can be determined depending on the magnitude of the detected misalignment.

[0104] FIG. 21 is an explanatory diagram illustrating the shifting of pixel values ​​in the auxiliary pixel array when misalignment is detected. Similar to FIG. 19, the left side of FIG. 21 shows input image data IM1, and the center shows a partial view of the auxiliary pixel array 750. In the example of FIG. 21, it is assumed that misalignment in the axial direction (to the left in the figure) equivalent to ¼ of one pixel (e.g., 4800 dpi) has been detected. In this case, the light emission control unit 705 shifts M copies of the pixel value at each pixel position in each row of the input image data by one auxiliary pixel to the right and stores them in the M auxiliary pixels in the corresponding row of the auxiliary pixel array 750. For example, referring to FIG. 21, four copies of the pixel value (0,0) of the input image data IM1 are stored in the auxiliary pixels Px2, Px3, Px4, and Px5 of the auxiliary pixel array 750, respectively. The pixel value of the auxiliary pixel Px1 adjacent to the left of the auxiliary pixel Px2 may be set to, for example, a dummy value indicating no light emission. In the example of FIG. 21, auxiliary pixels that are set to dummy values ​​indicating no light emission due to a shift in pixel value are shown by horizontal stripes.

[0105] The light emitting element array of the light emitting chip 400-1 is shown on the right side of Fig. 21. The light emission control unit 705 sequentially reads pixel values ​​from the auxiliary pixels of the corresponding auxiliary pixel set in the auxiliary pixel array 750 and outputs the read pixel values ​​to the light emitting element array, in order to cause the exposure head 106 to form spots corresponding to each pixel position of the input image data IM1. In the example of Fig. 21, the pixel values ​​of the auxiliary pixels that have been set to dummy values ​​due to the shift in pixel values ​​are output to the light emitting element R 0_0 The result will be output to

[0106] In FIGS. 22A to 22D, the auxiliary pixels from which pixel values ​​are read within the auxiliary pixel array 750 over line periods t0 to t0+3 in the case of misregistration compensation are indicated by different density shading. However, auxiliary pixels that have been set to dummy values ​​due to pixel value shifts are indicated by horizontal stripes. Focusing on the four auxiliary pixels storing the pixel value (0,0), in line period t0, the pixel value read from auxiliary pixel Px4 is used to form the spot SP in the upper left corner of the electrostatic latent image IM4 (see FIG. 22A). In line period t0+1, the pixel value read from auxiliary pixel Px3 is used to form the spot SP of the electrostatic latent image IM4 (see FIG. 22B). In line period t0+2, the pixel value read from auxiliary pixel Px2 is used to form the spot SP of the electrostatic latent image IM4 (see FIG. 22C). In line period t0+3, the pixel value read from auxiliary pixel Px5 is used to form the spot SP of the electrostatic latent image IM4 (see FIG. 22D). The pixel value from the auxiliary pixel set to a dummy value is the pixel value of the light-emitting element R that exposes a position outside the original image formation range due to positional deviation. 0_0 However, since the dummy value indicates no light emission, the light-emitting element R 0_0 does not emit light.

[0107] 22A to 22D, the auxiliary pixel set (second auxiliary pixel set) corresponding to each spot of the electrostatic latent image when misalignment is detected includes auxiliary pixels that are not included in the corresponding auxiliary pixel set (first auxiliary pixel set) when no misalignment is detected. For example, the auxiliary pixel set G corresponding to the spot SP 0,0 When no misalignment is detected, the pixel is made up of auxiliary pixels Px1, Px2, Px3, and Px4, whereas in the examples of FIGS. 22A to 22D, the pixel is made up of auxiliary pixels Px2, Px3, Px4, and Px5.

[0108] (3) Compensation for magnification error (error magnification < 1) When an axial magnification error is detected as an error in the image formation range, and the error magnification is smaller than 1, the light emission control unit 705 inserts pixel values ​​into selected auxiliary pixel positions in at least one row of the auxiliary pixel array. The number of pixel values ​​to be inserted may be determined depending on the magnitude of the error magnification. The magnitude of the error magnification may be indicated by correction data input from the CPU 701 to the light emission control unit 705. The light emission control unit 705 may determine pixel positions into which pixel values ​​are to be inserted based on the correction data. As described above, inserting pixel values ​​may include shifting pixel values ​​on one side of the selected auxiliary pixel position in the axial direction in a direction that expands the pixel value set, and providing a copy of the pixel value of the auxiliary pixel position before the shift to the auxiliary pixel position. The light emission control unit 705 may randomly select a number of auxiliary pixel positions (insertion positions) in the axial direction determined based on the magnitude of the error magnification, or randomly in pixel block units.

[0109] FIG. 23 is an explanatory diagram illustrating the insertion of pixel values ​​into the auxiliary pixel array when a magnification error is detected. Similar to FIG. 19 , the left side of FIG. 23 shows input image data IM1, and the center shows a partial view of the auxiliary pixel array 750. In the example of FIG. 23 , since the error magnification is below 1.0 by an amount equivalent to ¼ of one pixel, the pixel value of one auxiliary pixel is inserted. Furthermore, the fourth auxiliary pixel position from the left is selected as the insertion position. In this case, the light emission control unit 705 stores M copies of pixel values ​​at each pixel position in each row of the input image data in M ​​auxiliary pixels in the corresponding row of the auxiliary pixel array 750. However, the light emission control unit 705 shifts pixel values ​​at the fourth and subsequent auxiliary pixel positions from the left by one auxiliary pixel to the right, and inserts copies of the pixel values ​​at those positions before the shift into the fourth auxiliary pixel position from the left. In the example of FIG. 23 , the auxiliary pixel at the selected insertion position is indicated by horizontal stripes. As a result of this pixel value insertion, five copies of the pixel value (0,0) of the input image data IM1 are stored in the subpixels Px1, Px2, Px3, Px4, and Px5 of the subpixel array 750, respectively.

[0110] The light emitting element array of the light emitting chip 400-1 is shown on the right side of Fig. 23. The light emission control unit 705 sequentially reads pixel values ​​from the auxiliary pixels of the corresponding auxiliary pixel set in the auxiliary pixel array 750 and outputs the read pixel values ​​to the light emitting element array, in order to cause the exposure head 106 to form spots corresponding to each pixel position of the input image data IM1. In the example of Fig. 23, the pixel value of the auxiliary pixel corresponding to the selected insertion position is 0_3 The result will be output to

[0111] In FIGS. 24A to 24D, the auxiliary pixels from which pixel values ​​are read within the auxiliary pixel array 750 over line periods t0 to t0+3 in the case of magnification error compensation (error magnification<1) are indicated by shading of different densities. However, the auxiliary pixels corresponding to the selected insertion position are indicated by horizontal stripes. Focusing on the five auxiliary pixels storing the pixel value (0,0), in line period t0, the pixel value (inserted pixel value) read from auxiliary pixel Px4 is used to form the spot SP in the upper left corner of the electrostatic latent image IM4 (see FIG. 24A). In line period t0+1, the pixel value read from auxiliary pixel Px3 is used to form the spot SP of the electrostatic latent image IM4 (see FIG. 24B). In line period t0+2, the pixel value read from auxiliary pixel Px2 is used to form the spot SP of the electrostatic latent image IM4 (see FIG. 24C). In the line period t0+3, the pixel values ​​read out from the auxiliary pixels Px1 and Px5 are used to form the spot SP of the electrostatic latent image IM4 (see FIG. 24D). In this case, the light-emitting elements corresponding to five auxiliary pixels are involved in forming the spot SP, but the size of the spot SP actually shrinks due to the magnification error. This contributes to compensating for the magnification error.

[0112] 24A to 24D, the auxiliary pixel set (second auxiliary pixel set) corresponding to at least one spot of the electrostatic latent image when a magnification error is detected includes more auxiliary pixels than the corresponding auxiliary pixel set (first auxiliary pixel set) when no magnification error is detected. For example, the auxiliary pixel set G corresponding to the spot SP 0,0When no magnification error is detected, the pixel is made up of four auxiliary pixels Px1 to Px4, whereas in the examples of FIGS. 24A to 24D, it is made up of five auxiliary pixels Px1 to Px5.

[0113] In one embodiment, the number of light-emitting units (e.g., light-emitting elements) involved in forming the spot SP changes as the number of auxiliary pixels constituting the corresponding auxiliary pixel set changes. That is, the number of light-emitting units involved in forming the spot SP is controlled based on correction data indicating the error magnification. In other words, the light-emitting control unit 705 can control the image width in the axial direction of the image to be formed by inserting or thinning pixel values ​​based on the correction data. That is, the correction data is data for correcting the image width in the axial direction.

[0114] In one embodiment, the light emission control unit 705 sequentially reads out pixel values ​​of the sub-pixel group for each pixel from the sub-pixel array 750 and outputs them to the light-emitting element array to form the corresponding spot of the pixel. That is, one pixel is formed using the same number of light-emitting elements as the number of sub-pixels corresponding to the pixel position of the pixel in the input image data. The light emission control unit 705 controls the image width in the axial direction of the image to be formed by inserting sub-pixels into the sub-pixel group at certain pixel positions based on the correction data. When several sub-pixels are inserted into the sub-pixel group, the image width increases by the number of inserted sub-pixels, and the number of light-emitting elements driven based on the pixel data associated with the sub-pixel group also increases accordingly.

[0115] (4) Compensation for magnification error (error magnification > 1) When an axial magnification error is detected as an error in the image formation range, the light emission control unit 705 thins out pixel values ​​at selected auxiliary pixel positions in at least one row of the auxiliary pixel array if the error magnification is greater than 1. The number of pixel values ​​to be thinned out may be determined depending on the magnitude of the error magnification. As described above, thinning out pixel values ​​may include deleting pixel values ​​at the selected auxiliary pixel position before thinning out, and shifting pixel values ​​on one side of the selected auxiliary pixel position in the axial direction in a direction that reduces the set of pixel values. The light emission control unit 705 may select a number of auxiliary pixel positions (thinning out positions) in the axial direction determined based on the magnitude of the error magnification, randomly or randomly in pixel block units.

[0116] FIG. 25 is an explanatory diagram illustrating the thinning of pixel values ​​in the auxiliary pixel array when a magnification error is detected. Similar to FIG. 19, the left side of FIG. 25 shows input image data IM1, and the center shows a partial view of the auxiliary pixel array 750. In the example of FIG. 25, since the error magnification exceeds 1.0 by an amount equivalent to ¼ of one pixel, pixel values ​​equivalent to one auxiliary pixel are thinned out. Furthermore, it is assumed that the fourth auxiliary pixel position from the left is selected as the thinning position. In this case, the light emission control unit 705 stores M copies of pixel values ​​at each pixel position in each row of the input image data in M ​​auxiliary pixels in the corresponding row of the auxiliary pixel array 750. However, the light emission control unit 705 erases the pixel value at the fourth auxiliary pixel position from the left and shifts the pixel values ​​at the fifth and subsequent auxiliary pixel positions from the left by one auxiliary pixel to the left. As a result of this pixel value thinning, three copies of the pixel value (0,0) of the input image data IM1 are stored in the sub-pixels Px1, Px2, and Px3 of the sub-pixel array 750, respectively.

[0117] Therefore, the sub-pixel set (second sub-pixel set) corresponding to at least one spot of the electrostatic latent image includes fewer sub-pixels than the corresponding sub-pixel set (first sub-pixel set) when no magnification error is detected. For example, when no magnification error is detected, the sub-pixel set G corresponding to the spot in the upper left corner of the electrostatic latent image includes fewer sub-pixels than the corresponding sub-pixel set G when no magnification error is detected. 0,0is composed of four auxiliary pixels Px1 to Px4, whereas in the example of FIG. 25, the auxiliary pixel set G 0,0 is composed of three auxiliary pixels Px1 to Px3. A copy of the pixel value (1,0) is stored in auxiliary pixel Px4, not a copy of the pixel value (0,0). Although only the light-emitting elements corresponding to the three auxiliary pixels are involved in forming this spot, the size of the spot actually increases due to magnification error. This contributes to compensating for the magnification error.

[0118] In one embodiment, the number of light-emitting units (e.g., light-emitting elements) involved in forming the spot SP changes as the number of auxiliary pixels constituting the corresponding auxiliary pixel set changes. That is, the number of light-emitting units involved in forming the spot SP is controlled based on correction data indicating the error magnification. In other words, the light-emitting control unit 705 can control the image width in the axial direction of the image to be formed by inserting or thinning pixel values ​​based on the correction data. That is, the correction data is data for correcting the image width in the axial direction.

[0119] In one embodiment, the light emission control unit 705 sequentially reads out pixel values ​​of the sub-pixel group for each pixel from the sub-pixel array 750 and outputs them to the light-emitting element array to form the corresponding spot of the pixel. That is, one pixel is formed using the same number of light-emitting elements as the number of sub-pixels corresponding to the pixel position of the pixel in the input image data. The light emission control unit 705 controls the image width in the axial direction of the image to be formed by thinning out sub-pixels from the sub-pixel group at a certain pixel position based on the correction data. When some sub-pixels are thinned out from the sub-pixel group, the image width is reduced by the number of thinned out sub-pixels, and the number of light-emitting elements driven based on the pixel data associated with the sub-pixel group is also reduced accordingly.

[0120] The implementation using the auxiliary pixel array described in this section makes it possible to compensate for a variety of errors in the imaging range through a relatively low-complexity algorithm that manipulates an array of discrete bits.

[0121] <6. Summary> Various embodiments have been described in detail above using FIGS. 1 to 25. According to one aspect of the above-described embodiments, in an exposure device that performs multiple exposure by sequentially emitting light from M rows of light-emitting elements arranged circumferentially around a rotating photosensitive drum, when axial image misalignment is detected, light-emission control is performed to compensate for the detected misalignment. The light-emission control includes shifting a set of pixel values ​​of input image data corresponding to at least one row of two-dimensionally arranged light-emitting elements in a direction that cancels the detected misalignment, and then supplying a drive signal based on the input image data to the light-emitting elements. A drive signal indicating that light emission is turned off can be supplied to light-emitting elements corresponding to positions that become blank as a result of the shift. This configuration allows image misalignment to be compensated for simply by controlling the read order of data that forms the basis of the drive signal, without requiring high-load processing such as resolution conversion or weighting calculation. For example, if a relative misalignment between images of multiple color components or a misalignment of an image formation position relative to a sheet is detected as a result of calibration, the effects of the misalignment can be canceled out by the above-described light-emission control, thereby maintaining good quality of the formed image. Furthermore, according to the above-described embodiment, it is possible to adjust the image formation position to compensate for misalignment without increasing the circuit scale, which can promote miniaturization and cost reduction of the exposure device. In this way, an improved mechanism for compensating for image misalignment is provided.

[0122] In the above-described embodiment, the M light-emitting elements in each column are arranged in a stepped pattern at a fixed pitch. The pixel value set corresponding to the row having at least the rearmost light-emitting element in the cancellation direction can be shifted in the cancellation direction. Therefore, the pixel value set can be appropriately selected and shifted depending on which side of the axial direction of the photoconductor the detected misalignment is.

[0123] Furthermore, in the above-described embodiment, it is possible to determine which row the pixel value set corresponding to should be shifted and how many columns the pixel value set corresponding to each row should be shifted by based on the magnitude of the detected positional misalignment and the axial pitch of the light-emitting elements. Therefore, it is possible to compensate for the positional misalignment of the image with fine granularity, with the minimum unit being the axial pitch of the light-emitting elements, which is smaller than the spot corresponding to one pixel.

[0124] In the above-described embodiment, the exposure head includes a plurality of light-emitting chips, each including a subset of a plurality of light-emitting elements. The axial range of all the light-emitting elements of the plurality of light-emitting chips is greater than the maximum width of the input image data. This configuration utilizes the portion outside the maximum width of the input image data as a margin for compensating for misalignment, thereby enabling compensation for misalignment without missing any edges of the image.

[0125] According to another aspect of the above-described embodiment, in an exposure device that performs multiple exposure by sequentially emitting light from M rows of light-emitting elements arranged circumferentially around a rotating photosensitive drum, when an axial image magnification error is detected, light emission control is performed to compensate for the detected magnification error. The light emission control includes inserting or thinning pixel values ​​for each pixel position into a set of pixel values ​​for a row to which one or more pixel positions constituting the input image data belong, selected according to the error magnification, and then supplying a drive signal based on the input image data to the light-emitting elements. This configuration enables compensation for the magnification error to be achieved simply by inserting or thinning pixel values ​​into the data underlying the drive signal, without requiring high-load processing such as resolution conversion or weighting calculation. For example, if an expansion of the image formation area due to thermal expansion of the exposure head is detected as a result of calibration, the effect of the expansion of the image formation area can be canceled out by thinning pixel values, thereby maintaining good image quality. Furthermore, the above-described embodiment enables compensation for the magnification error by adjusting the image formation area without increasing the circuit scale, thereby promoting miniaturization and cost reduction of the exposure device. In this way, an improved mechanism for compensating for image magnification error is provided.

[0126] In the above-described embodiment, when the error magnification is smaller than 1, the pixel value of each selected pixel position is inserted into the set of pixel values ​​of the row to which the selected pixel position belongs. On the other hand, when the error magnification is greater than 1, the pixel value of each selected pixel position is thinned out from the set of pixel values ​​of the row to which the selected pixel position belongs. Therefore, when the image formation range shrinks or expands due to an error in the exposure head, the effects of the shrinkage or expansion can be appropriately canceled. Inserting a pixel value includes shifting pixel values ​​on one side of the selected pixel position in the axial direction in a direction that expands the set of pixel values, and providing a copy of the pixel value of the pixel position before the shift to the selected pixel position. Thinning out pixel values ​​includes erasing the pixel value of the selected pixel position before the thinning out, and shifting pixel values ​​on one side of the selected pixel position in the axial direction in a direction that shrinks the set of pixel values. This configuration allows magnification error to be compensated for while minimizing changes in the formed image.

[0127] Furthermore, in the above-described embodiment, the number of pixel positions to be selected for pixel value insertion or thinning can be determined based on the detected error magnification and the axial pitch of the multiple light-emitting elements in the exposure head. Therefore, the magnification error can be compensated for with fine granularity, with the minimum unit being the axial pitch of the light-emitting elements, which is smaller than the spot corresponding to one pixel.

[0128] Although the present specification has primarily described the expansion of the image formation area due to thermal expansion of the exposure head 106 as an example of a magnification error component, the technology disclosed herein is not limited to this example. For example, when an image is formed on a first side of a sheet and then an image is formed on a second side (the side opposite to the first side) of the sheet, the sheet may shrink due to heating for fixing the toner image on the first side. The sheet shrinkage causes a difference in the ratio of the image size to the sheet size between the first side and the second side. Such a discrepancy in image size is also an example of a magnification error component. The error magnification Y of such a magnification error component can be detected as follows. That is, for example, the CPU 701 of the image forming apparatus 1 performs calibration in response to a user instruction. Specifically, the CPU 701 controls the image forming unit 101 to form a test chart on the first and second sides of the sheet. The test chart here may be an image having a known pattern. In forming the test chart, multiple exposure is also performed using the light-emitting element array of the exposure head 106 described above. A sheet on which a test chart is formed is placed on the platen of the reading unit 100 by the user, and the test chart is optically read by the reading unit 100. The reading unit 100 outputs read image data representing the results of reading the test chart on the first and second sides to the CPU 701. The CPU 701 then uses the read image data to calculate an error magnification Y by comparing the ratio of the image size to the sheet size on the first side with the ratio of the image size to the sheet size on the second side. The CPU 701 notifies the light emission control unit 705 of the calculated error magnification Y. Insertion or thinning of pixel values ​​based on the error magnification Y can be performed when forming an image on the second side of the sheet.

[0129] In one modified example, a reading device that optically reads an image formed on a sheet by the image forming device 1 may be connected downstream of the image forming device 1. In this embodiment, the test charts formed on the first and second sides of the sheet may be automatically read by the reading device downstream of the image forming device 1. In this case, the user does not need to place the sheet on the platen, which reduces the workload of the user.

[0130] In another variant, the above-mentioned interpolation or thinning of pixel values ​​may be performed according to a magnification factor specified via a user interface by a user who intends to enlarge or reduce the image to be formed on the sheet.

[0131] In the above embodiments, specific numerical values ​​are used for explanation purposes, but these specific numerical values ​​are merely examples, and the present invention is not limited to the specific numerical values ​​used in the embodiments. Specifically, the number of light-emitting chips provided on one printed circuit board is not limited to 20 and can be any number equal to or greater than 1. Furthermore, the size of the light-emitting element array of each light-emitting chip 400 is not limited to 4 rows and 748 columns and may be any other size. Furthermore, the circumferential pitch and axial pitch of the light-emitting elements are not limited to approximately 21.16 μm and approximately 5 μm and may be any other value.

[0132] <7. Other embodiments> The above-described embodiment can also be realized in the form of a process in which a program for realizing one or more functions is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program, or by a circuit (e.g., ASIC) that realizes one or more functions.

[0133] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0134] 1: image forming apparatus, 102: photosensitive member, 106: exposure head, 113: optical sensor, 400: light emitting chip, 602: light emitting element, 701: CPU (detection unit), 705: light emitting control unit, 750: auxiliary pixel array, IM1: input image data, P A : Axial pitch, PG1 to PG7: Pixel value set, R j_m : Light emitting element, RD: Readout range

Claims

1. In an organic EL (Electro Luminescence) type exposure device for an image forming apparatus, an exposure head having a plurality of light-emitting elements two-dimensionally arranged to include M rows (M is an integer of 2 or more) in the circumferential direction of a photosensitive member and N columns (N is an integer of 2 or more) in the axial direction of the photosensitive member, wherein any two adjacent light-emitting elements among the M light-emitting elements in each column occupy areas that partially overlap in the axial direction; a light emission control unit that controls light emission from the plurality of light emitting elements of the exposure head so that spots corresponding to each pixel position are formed on the surface of the photosensitive member by sequentially emitting light from the M light emitting elements in a row corresponding to each pixel position of the input image data while the photosensitive member is rotating; Equipped with In the exposure head, the M light-emitting elements in each row of the plurality of light-emitting elements are arranged in a stepped pattern at a constant pitch in the axial direction, the light emission control unit causes the plurality of light emitting elements to emit light based on pixel values ​​read from a read range spanning M lines of the input image data; the light emission control unit detects a positional deviation in the axial direction of the image formed by the exposure head, and when the detected positional deviation is x times (x is a natural number) the pitch, shifts a pixel value set of the input image data in a direction that cancels the detected positional deviation; the light emission control unit distributes the shift amounts to each of the M lines one pixel at a time until the total shift amount of the pixel value set reaches x; Exposure device.

2. An exposure device as described in Claim 1, wherein the light emission control unit distributes the shift amount to each of the M lines in a round robin manner.

3. The read range moves one line at a time for each line period; the pixel value set to be shifted when the positional deviation is detected moves in accordance with the movement of the readout range for each line period; 2. The exposure apparatus according to claim 1.

4. The exposure apparatus according to claim 1 , wherein the light emission control unit does not cause light emitting elements corresponding to positions that become blank as a result of the shift of the pixel value set to emit light.

5. 2. The exposure apparatus of claim 1, wherein the exposure head has a plurality of light-emitting chips, each of which includes a subset of the plurality of light-emitting elements, and the range occupied by all of the light-emitting elements of the plurality of light-emitting chips in the axial direction is wider than the range occupied by the maximum width of the input image data.

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

7. an exposure apparatus according to any one of claims 1 to 6; the photoreceptor; An image forming apparatus comprising:

8. 8. The image forming apparatus according to claim 7, further comprising a detection unit that detects the positional deviation by reading an image formed as a result of exposure by the exposure head.

9. 9. The image forming apparatus according to claim 8, wherein the positional deviation detected by the detection unit is a relative deviation between images of a plurality of color components, or a deviation in an image formation position with respect to a sheet.

Images