Exposure device and image formation device

Abstract

To provide an improved mechanism for forming an image having an appropriate shape on a sheet while suppressing inclination of the image relative to the sheet.SOLUTION: An image formation device includes: a detection part for detecting a skew of a sheet in a conveyance direction; an exposure head having a light-emitting element arrangement including a plurality of light-emitting elements arranged over a first range in a main scanning direction parallel to an axial direction of a photoreceptor; and a control part for controlling light emission from the plurality of light-emitting elements according to input image data. The control part shifts the range of the light-emitting elements to be used for image formation of the respective lines of the input image data, according to the positions of the lines and the skew to be detected. When the range of the light-emitting element to be used for a line having the largest shift amount is deviated from the first range, the control part trims the images of each of the lines, in accordance with a deviation amount of the line having the largest shift amount.SELECTED DRAWING: Figure 20A

Description

[Technical field]

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

[0002] Generally, in an image forming apparatus that forms an image on a sheet while conveying the sheet in a predetermined direction, the image may be formed on the sheet in a state tilted relative to the sheet due to skew of the sheet. Patent Document 1 discloses an inkjet type image forming apparatus that, when skew of the sheet is detected, can shift the image formation range in the main scanning direction perpendicular to the conveying direction along with the conveyance of the sheet so as to suppress the tilt of the printed image.

[0003] Meanwhile, solid-state exposure type image forming apparatuses, which are a type of electrophotographic method, have been attracting attention in recent years because they are easy to miniaturize and reduce the cost of the apparatus. In solid-state exposure type image forming apparatuses, a latent image is formed on the surface of a photoreceptor by exposing the photoreceptor to light emitted by an array of multiple light-emitting elements (e.g., LEDs), and the latent image is developed with a developer, after which the developer image is transferred to a sheet. Patent Document 2 discloses a configuration in which multiple light-emitting chips, each having multiple LEDs, are arranged in a staggered pattern along the main scanning direction in an exposure head of a solid-state exposure type image forming apparatus. The configuration in which multiple light-emitting chips are arranged in a staggered pattern is advantageous in that it makes it easy to change the size of the exposure head. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-153915 A [Patent Document 2] JP 2017-183436 A Summary of the Invention [Problem to be solved by the invention]

[0005] When the method disclosed in Patent Document 1 for shifting the image formation range in accordance with the skew of the sheet is applied to a solid-state exposure type image forming apparatus, the amount of shift may deviate outside the range of the light-emitting element array of the exposure head. If the image formation range goes outside the range of the light-emitting element array, a distorted image with missing corners may be formed on the sheet.

[0006] An object of the present invention is to provide an improved mechanism capable of forming an image of a proper shape on a sheet while suppressing inclination of the image with respect to the sheet. [Means for solving the problem]

[0007] According to one aspect, there is provided an image forming apparatus for forming an image on a sheet, the image forming apparatus comprising: a skew detection unit that detects skew of the sheet with respect to a transport direction; an exposure head for exposing a photosensitive body, the exposure head having a light-emitting element array including a plurality of light-emitting elements arranged over a first range in a main scanning direction parallel to an axial direction of the photosensitive body; and a control unit that controls light emission from the plurality of light-emitting elements of the exposure head in accordance with input image data, wherein the transport direction is perpendicular to the axial direction of the photosensitive body, the control unit shifts a range of light-emitting elements of the first range to be used for forming an image of each line of the input image data in accordance with the position of the line in the input image data and the skew of the sheet detected by the skew detection unit, and when the range of light-emitting elements to be used for the line with the largest shift amount deviates from the first range, the control unit trims the image of each line of the input image data to match the deviation amount of the line with the largest shift amount. Effect of the Invention

[0008] According to the present invention, it is possible to form an image of an appropriate shape on a sheet while suppressing inclination of the image with respect to the sheet. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment; [Diagram 2] FIG. 2 is an explanatory diagram of a configuration of a photoconductor and an exposure head according to the embodiment. [Diagram 3] FIG. 4 is an explanatory diagram of 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. [Diagram 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. 4 is a circuit diagram showing a control configuration of an exposure apparatus according to an embodiment. [Figure 8] 6 is a signal chart related to access to a register of a light emitting chip according to an embodiment; [Figure 9] 11 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. 13 is an explanatory diagram of multiple exposure using light-emitting elements arranged in a stepped pattern. [Figure 12A] 5 is an explanatory diagram of a procedure for light emission control based on input image data. [Figure 12B] 5 is an explanatory diagram of a procedure for light emission control based on input image data. [Figure 12C] 5 is an explanatory diagram of a procedure for light emission control based on input image data. [Figure 12D] 5 is an explanatory diagram of a procedure for light emission control based on input image data. [Figure 13A] FIG. 11 is a diagram illustrating a procedure of light emission control including positional deviation compensation in the first scenario. [Figure 13B] FIG. 11 is a diagram illustrating a procedure of light emission control including positional deviation compensation in the first scenario. [Figure 13C]FIG. 11 is a diagram illustrating a procedure of light emission control including positional deviation compensation in the first scenario. [Figure 13D] FIG. 11 is a diagram illustrating a procedure of light emission control including positional deviation compensation in the first scenario. [Figure 14A] FIG. 11 is an explanatory diagram of a procedure of light emission control including positional deviation compensation in the second scenario. [Figure 14B] FIG. 11 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the second scenario. [Figure 14C] FIG. 11 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the second scenario. [Figure 14D] FIG. 11 is an explanatory diagram of a procedure for light emission control including positional deviation compensation in the second scenario. [Figure 15A] FIG. 13 is a diagram illustrating a procedure of light emission control including positional deviation compensation in the third scenario. [Figure 15B] FIG. 13 is a diagram illustrating a procedure of light emission control including positional deviation compensation in the third scenario. [Figure 15C] FIG. 13 is a diagram illustrating a procedure of light emission control including positional deviation compensation in the third scenario. [Figure 15D] FIG. 13 is a diagram illustrating a procedure of light emission control including positional deviation compensation in the third scenario. [Figure 16A] 11A and 11B are explanatory diagrams of a procedure for light emission control including compensation for magnification error (insertion of pixel values). [Figure 16B] 11A and 11B are explanatory diagrams of a procedure for light emission control including compensation for magnification error (insertion of pixel values). [Figure 16C] 11 is an explanatory diagram of a procedure for light emission control including compensation for magnification error (insertion of pixel values). [Figure 16D] 11A and 11B are explanatory diagrams of a procedure for light emission control including compensation for magnification error (insertion of pixel values). [Figure 17A] 5A and 5B are explanatory diagrams of a procedure for light emission control including compensation for magnification error (thinning out pixel values). [Figure 17B] 5A and 5B are explanatory diagrams of a procedure for light emission control including compensation for magnification error (thinning out pixel values). [Figure 17C] 5A to 5C are explanatory diagrams of a procedure for light emission control including compensation for magnification error (thinning out pixel values). [Figure 17D] 5A to 5C are explanatory diagrams of a procedure for light emission control including compensation for magnification error (thinning out pixel values). [Figure 18] 11 is an explanatory diagram of a procedure for light emission control including compensation for magnification error (insertion of multiple pixel values). [Figure 19A] FIG. 11 is a first explanatory diagram of the influence of a skewed sheet on a printed image. [Figure 19B] FIG. 11 is a second explanatory diagram of the effect of a skewed sheet on a printed image. [Figure 19C] FIG. 11 is a third explanatory diagram of the influence of a skewed sheet on a printed image. [Figure 19D] FIG. 4 is a fourth explanatory diagram of the influence of a skewed sheet on a printed image. [Figure 20A] FIG. 11 is a first explanatory diagram regarding trimming of image data when deviation of the shift amount occurs. [Figure 20B] FIG. 11 is a second explanatory diagram regarding trimming of image data when deviation of the shift amount occurs. [Figure 21] 10 is a flowchart showing an example of a flow of a deviation amount calculation process according to an embodiment. [Figure 22] 10 is a flowchart showing an example of the flow of image data correction processing according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0011] <1. Schematic 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.

[0012] 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 figure 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 (developer) to form a toner image. The toner image formed on the surface of the photoconductor 102 is transferred to a sheet transported on a transfer belt 111. By transferring the toner images of the four photoconductors 102 onto a sheet in an overlapping manner, a color image containing four color components, namely black, yellow, magenta, and cyan, can be formed.

[0013] The conveying unit 105 controls the feeding and conveying of the sheet. Specifically, the conveying unit 105 feeds the sheet from a designated unit among the internal storage units 109a and 109b, the external storage unit 109c, and the manual feed unit 109d to a conveying path of the image forming apparatus 1. The fed sheet is conveyed to the registration roller 110. The registration roller 110 conveys the sheet onto the transfer belt 111 at an appropriate timing so that the toner image of each photoconductor 102 is transferred onto the sheet. As described above, the toner image is transferred onto the sheet while the sheet is being conveyed on the transfer belt 111. The fixing unit 104 heats and pressurizes the sheet onto which the toner image has been transferred, thereby fixing the toner image onto the sheet. After the toner image is fixed, the sheet is discharged to the outside of the image forming apparatus 1 by the discharge roller 112.

[0014] An optical sensor 113 is disposed at a position facing the transfer belt 111. The optical sensor 113 functions as an error detection unit that detects errors in the main scanning direction of the latent image formed on the photoconductor 102 or the toner image (developer image) formed on the sheet. For example, the optical sensor 113 detects one or both of the positional deviation and magnification error of the toner image by optically reading a test chart formed on the transfer belt 111 by the image forming unit 101. These errors are caused by variations in the arrangement of light-emitting elements, which will be described later. The optical sensor 113 outputs data indicating the error detection results to the image controller 700, which will be described later.

[0015] A registration sensor 114 is disposed near the registration roller 110. The registration sensor 114 functions as a skew detection unit that detects skew of the sheet with respect to the conveying direction. The skew of the sheet can be expressed, for example, as a displacement amount (displacement ratio) in the main scanning direction perpendicular to the conveying direction per unit conveying amount of the sheet. The registration sensor 114 may further detect a positional deviation of the sheet from a reference position in the main scanning direction. The registration sensor 114 may also detect a magnification change caused by thermal expansion and contraction of the sheet. The registration sensor 114 outputs data indicating these detection results to an image controller 700 described later.

[0016] Although an example in which a toner image is directly transferred from each photoconductor 102 to a sheet on the transfer belt 111 has been described here, the toner image may be indirectly transferred from each photoconductor 102 to a sheet via an intermediate transfer body. Also, although an example in which a color image is formed using toners of multiple colors has been described here, the technology according to the present disclosure is also applicable to an image forming apparatus that forms a monochrome image using toners 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 has 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] Fig. 3(A) and Fig. 3(B) show an example of the configuration of the printed circuit board 202. 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 shows a schematic diagram of the light-emitting chip 400 and the array of the light-emitting elements 602 in the light-emitting chip 400.

[0019] As shown in the figure, the light emitting element array 201 of the exposure head 106 includes at least N columns of light emitting elements 602 arranged in the main scanning direction parallel to the axial direction D1 of the photoconductor 102. In addition, in this embodiment, the light emitting element array 201 includes M rows of light emitting elements 602 arranged in the circumferential direction D2. Therefore, the light emitting element array 201 includes M rows and N columns of light emitting elements arranged two-dimensionally, where M and N are integers of 2 or more. In the example of FIG. 3(B), the light emitting element array 201 is divided into 20 light emitting chips 400-1 to 400-20, each of which includes 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. 3(B), a first range (hereinafter also referred to as a light emitting range) W occupying all the light emitting elements of the 20 light emitting chips in the main scanning direction is 100 nm. LED is wider than the range occupied by the maximum width W0 of the input image data. In other words, the maximum width W0 of the image formed by the image forming apparatus 1 in the main scanning direction is wider than the light emitting range W LED Light emitting range W LEDmay be wider than the maximum width in the main scanning direction of a sheet of a standard size (e.g., A3 or A4) that can be used in the image forming apparatus 1. Therefore, some light-emitting elements located at both ends in the axial direction D1 may not be used to expose the photoconductor 102 unless a skew of the sheet or an error in the image forming range is detected. Each light-emitting chip 400 of the printed circuit board 202 is connected to the image controller 700 (FIG. 7) via a connector 305. In the following, 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 may be referred to 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 the 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 the light-emitting elements 602 arranged in each column of one light-emitting chip 400 may be equal to, for example, 4 (M=4). That is, in the exemplary embodiment, each light-emitting chip 400 has a total of 2992 (=748×4) light-emitting elements 602, with 748 in the axial direction D1 and 4 in the circumferential direction D2. The interval P between the center points of the light-emitting elements 602 adjacent to each other in the circumferential direction D2 is C may be, for example, about 21.16 μm, which corresponds to a resolution of 1200 dpi. The distance between the center points of adjacent light-emitting elements 602 in the axial direction D1 may also be about 21.16 μm, in which case 748 light-emitting elements 602 occupy a length of about 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 are completely arranged in a lattice in each light-emitting chip 400, but in reality, M (M=4) light-emitting elements 602 in each row are arranged in a staircase pattern. This point will be further explained later.

[0021] 5 is a plan view showing a schematic configuration of the light emitting chip 400. The 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 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 a 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 part 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 electrode 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 the 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] For example, an organic EL film can be used for the light-emitting layer 506. The upper electrode 508 is composed of a transparent electrode such as indium tin oxide (ITO) so as to transmit the emission wavelength of the light-emitting layer 506. Note that 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] In FIG. 6, one continuous light-emitting layer 506 is formed, but a plurality of 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. In FIG. 6, the upper electrode 508 is formed as one common electrode for the plurality of lower electrodes 504, but a plurality of upper electrodes 508 each having a width equivalent to the width W of the lower electrode 504 may be formed corresponding to each of the lower electrodes 504. In addition, the first plurality of lower electrodes 504 of the lower electrodes 504 of each light-emitting chip 400 may be covered by the first light-emitting layer 506, and the second plurality of lower electrodes 504 may be covered by the second light-emitting layer 506. Similarly, the first upper electrode 508 may be commonly formed corresponding to the first plurality of lower electrodes 504 of the lower electrodes 504 of each light-emitting chip 400, and the 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 a plurality of signal lines (wires). The image controller 700 has a CPU 701, a clock generating unit 702, an image data processing unit 703, a register access unit 704, a light-emitting control unit 705, and an image memory 706. The light-emitting control unit 705 is a component that configures an exposure device together with the exposure head 106. The light-emitting control unit 705 terminates a signal line between the light-emitting chip 400-n 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 for 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 generating 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. The image processing here may include, for example, raster conversion, gradation correction, color conversion, and halftone processing. The image data processing unit 703 writes the generated image data into the image memory 706 as input image data, and transfers it to the light emission control unit 705. The register access unit 704 receives control data to be written into the registers in each light emitting chip 400 from the CPU 701 and transmits it to the light emission control unit 705. The light emission control unit 705 reads out the input image data generated by the image data processing unit 703 from the image memory 706, and controls light emission from the multiple light emitting elements 602 of the exposure head 106 according to the read input image data. Particularly in this embodiment, in order to compensate for the deviation of the image formation position on the sheet, the light emission control unit 705 corrects the input image data and then controls the light emission of the exposure head 106. Such compensation will be described in detail later.

[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 circumferential speed of the photoconductor 102 is 200 mm / s and the resolution in the circumferential direction 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, since each light-emitting chip 400 has 2992 light-emitting elements 602, it is necessary to transmit image data indicating the light emission / non-light emission of each of the total 2992 light-emitting elements 602 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. It should be noted that a signal indicating non-emission of light is transmitted to the light emitting elements 602 that are not actually used for forming an image (outside the image forming range).

[0030] FIG. 10 is a functional block diagram showing a detailed configuration of one light-emitting chip 400 (n-th light-emitting chip 400-n). As also shown in FIG. 5, the light-emitting chip 400 has nine pads 408-1 to 408-9. The pads 408-1 and 408-2 are connected to a power supply voltage VCC by 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 the ground by a ground line. Each circuit of the circuit unit 406 and the upper electrode 508 are connected to the 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 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 a desired light emission intensity of the light emitting element 602, for example.

[0031] The transfer unit 1003 receives input image data including a series of pixel values ​​each indicating the emission or non-emission of one light emitting element 602 from a signal line DATAn in synchronization with a clock signal from a signal line CLK, starting from a line synchronization signal from a signal line SYNC. The transfer unit 1003 performs serial-to-parallel conversion on the series of pixel values ​​serially received from the signal line DATAn in units of M (for example, M=4) pixel values. For example, the transfer unit 1003 has four cascaded D flip-flops, and parallelizes pixel values ​​DATA-1, DATA-2, DATA-3, and DATA-4 input over four clocks, and outputs the parallelized pixel values ​​to the latch units 1004-0001 to 1004-748. The transfer unit 1003 further has four D flip-flops for delaying the line synchronization signal, and outputs a first latch signal to the latch unit 1004-001 via a signal line LAT1 at a timing delayed by four clocks from the input of the line synchronization signal.

[0032] The kth latch unit 1004-k (k is an integer from 1 to 748) holds the four pixel values ​​DATA-1, DATA-2, DATA-3, and DATA-4 input from the transfer unit 1003 at the same time as the kth latch signal is input, by using a latch circuit. In addition, except for the last-stage latch unit 1004-748, the kth latch unit 1004-k delays the kth latch signal by four clocks and outputs the (k+1)th latch signal to the latch unit 1004-(k+1) via the signal line LAT(k+1). Then, the kth latch unit 1004-k continues to output a drive signal based on the four pixel values ​​held by the latch circuit to the current drive unit 1104 during the signal period of the kth latch signal. For example, there is a delay of four clocks between the timing when the first latch signal is input to the latch unit 1004-1 and the timing when the second latch signal is input to the latch unit 1004-2. Therefore, the latch unit 1004-1 outputs drive signals based on the 1st, 2nd, 3rd and 4th pixel values ​​to the current driver 1104, whereas the latch unit 1004-2 outputs drive signals based on the 5th, 6th, 7th and 8th 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 emission driver circuits corresponding to the 2992 light emitting elements 602 each including a partial region of the light emitting layer 506. Each light emission driver circuit applies a drive voltage corresponding to the light emission 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 indicating that light emission 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 emission intensity for each light emitting element 602, may indicate one light emission intensity for each group of the light emitting elements 602, or may indicate one light emission intensity common to all the light emitting elements 602.

[0034] <3. Control of multiple exposure> FIG. 4 shows an example in which the light-emitting elements 602 are completely arranged in a lattice pattern in each light-emitting chip 400, but 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 described above, the axial spacing between two adjacent light-emitting elements among the M light-emitting elements in each row, i.e., the axial pitch P A may be approximately 5 μm, which corresponds to a resolution of 4800 dpi.

[0035] By arranging the four light-emitting elements in each row in a stepped manner in this manner, 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 row corresponding to each pixel position of the input image data sequentially emit light while the photoconductor 102 is rotating, forming spots corresponding to each pixel position on the surface of the photoconductor 102. In the example of Figure 11, when the pixel value at the left end of the i-th 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 photoconductor 102. i As a result, the line L i In the same manner, when the jth pixel value from the left of the i-th 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 photoconductor 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 a partially overlapping range 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 a partially overlapping range in the axial direction. The axial pitch P of the light-emitting elements across all 20 light-emitting chips 400 is Ais constant at 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, a smooth line of an electrostatic latent image can be formed on the surface of the photoconductor 102, which is made up of a series of spots that are partially overlapping each other with a constant spot spacing. As a result of such 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 the above description, the light is exposed to light from 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 of all the light emitting chips 400, 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 is true for the right end.

[0038] 12A to 12D are explanatory diagrams of the procedure of light emission control based on input image data. When forming an image, the light emission control unit 705 reads out input image data IM1 in a binary bitmap format from the image memory 706. On the left side of FIG. 12A, the jth pixel value from the left of 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. In the case of M=4, the range of the index i of the pixel value is {-3, -2, -1, 0, 1, 2, ...}, including the added dummy pixel values. The dummy pixel value may be, for example, zero, which means 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.

[0039] In the first line period t0 of image formation, the light-emission 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 of 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 performs serial-to-parallel conversion of 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 chip R. 0_0 , R 0_1 , R 0_2 , R 0_3 and R 1_0 In particular, as shown by the dashed line in the figure, the light emitting element R 0_3 A drive signal based on the effective pixel value of line DL0 of index i=0 of 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 according to the pixel value set of line DL0 of input image data IM1. However, at this point, multiple exposure is in progress and formation of electrostatic latent image line L0 is not completed.

[0040] FIG. 12B illustrates 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 the pixel values ​​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 element R. 0_0 , R 0_1 , R 0_2 , R 0_3 and R1_0 In the line period t0+1, the light-emitting element R 0_2 A driving signal based on the effective pixel value of the line DL0 of the input image data IM1 is supplied to the light-emitting elements in the third row including the light-emitting chip 400-1. At this time, since the photoconductor 102 is rotating in the circumferential direction, the 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, the line L0 on the surface of the photoconductor 102 is exposed again according to the pixel value set of the line DL0 of the input image data IM1.

[0041] FIG. 12C illustrates the driving of the light-emitting chip 400-1 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 the pixel values ​​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 driving signal based on the effective pixel value of the line DL0 of the input image data IM1 is supplied to the light-emitting elements of the second row including the line L0 on the surface of the photoconductor 102. At this time, the line L0 on the surface of the photoconductor 102 faces the light-emitting elements of the second row of the light-emitting chip 400-1. As a result, the line L0 on the surface of the photoconductor 102 is exposed a third time according to the pixel value set of the line DL0 of the input image data IM1.

[0042] FIG. 12D illustrates the driving of the light-emitting chip 400-1 during the next line period t0+3. In the line period t0+3, 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 (0,0) to (748,3), and outputs the pixel values ​​to the light-emitting chip 400-1 via the signal line DATA1. The light-emitting chip 400-1 supplies drive signals based on the input pixel values ​​to the 2992 light-emitting elements. In the line period t0+3, the light-emitting elements R 0_0A driving signal based on the effective pixel value of the 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, the 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, the line L0 on the surface of the photoconductor 102 is exposed four times according to the pixel value set of the 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 is performed, and the formation of the line L0 of the electrostatic latent image is completed. Lines subsequent to the line L0 of the electrostatic latent image can also be formed on the surface of the photoconductor 102 in the same manner through the repetition of such line periods.

[0043] 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 a 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.

[0044] 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 one line at a time for each line period. Such control of the read range is also performed in the dynamic control of the image formation range described next.

[0045] <4. Dynamic control of image formation range> As described above, in an image forming apparatus that forms an image on a sheet while conveying the sheet, the image may be formed on the sheet in a state inclined relative to the sheet due to skew of the sheet. In this embodiment, the registration sensor 114 detects skew of the sheet with respect to the conveying direction. The light emission control unit 705 controls the light emission possible range W LED The range of light-emitting elements to be used for forming an image of each line of the input image data among the light-emitting elements is shifted in accordance with the skew of the sheet so that a deviation of the image formation range in at least the main scanning direction is compensated for. The shift amount of each line may be an amount according to the position of the line in the input image data and the detected skew of the sheet.

[0046] In addition to the skew, it is also possible to compensate for one or both of the positional deviation and magnification error of the image in the main scanning direction. The causes of these errors are various, such as sheet misalignment or thermal expansion, or variations in the arrangement of the light-emitting elements. The skew of the sheet is a component of the amount of displacement of the image formation range in the main scanning direction that is proportional to the conveying distance of the sheet, while the positional deviation is a fixed component of the amount of displacement of the image formation range in the main scanning direction that is independent of the conveying distance of the sheet. The magnification error is a component that appears as an expansion or contraction of the image formation range. The light emission control unit 705 can determine each component of the error of the image formation range based on the sensor data input from the optical sensor 113 and the registration sensor 114.

[0047] Hereinafter, exemplary principles of compensation for misregistration, compensation for magnification error, and compensation for skew will be described in order. However, in this embodiment, compensation for misregistration and compensation for magnification error do not necessarily have to be performed.

[0048] <4-1. Compensation for position misalignment> When a misalignment in the main scanning direction is detected, the light emission control unit 705 shifts a pixel value set of the input image data corresponding to at least one row of the multiple light emitting elements 602 of the exposure head 106 in the above-mentioned procedure of light emission control of multiple exposure so as to compensate for the misalignment. For example, if the width W0 shown in FIG. 3B indicates a normal effective image formation position in the main scanning direction D1, when the image misalignment is to the left, the misalignment can be cancelled by shifting the image formation position to the right. Similarly, when the image misalignment is to the right, the misalignment can be cancelled 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) for cancelling such misalignment is referred to as the cancellation direction. Below, examples of light emission control for compensating for misalignment in the main scanning direction will be described for several scenarios with different misalignment amounts X.

[0049] (1) First Scenario In the first scenario, the positional deviation amount X is a pitch P A (X=P A ). Pitch P A is the minimum unit of positional deviation 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 of light emission control including positional deviation compensation in the first scenario.

[0050] 13A, the input image data IM1 to which three lines of dummy pixel values ​​have been added is again shown. 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 a subset 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, the light-emitting element R 1_0 The light-emitting element R corresponding to the position that will become blank as a result of the shift is supplied to the 0_0 may be supplied with a drive signal that means turning off the light emission, so that 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 is, as in the example of FIG. 12A, the light-emitting element R 0_3 The light is supplied to the light emitting elements in the fourth row including the fourth row.

[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 with 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 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. 13B, the pixel value set PG2 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,-2) at the left end of the pixel value set PG2 is output to the light-emitting element R 0_0 Instead, the light-emitting element R 1_0 The light-emitting element R corresponding to the position that will become blank as a result of the shift is supplied to the 0_0As 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 is supplied to the light-emitting element R 0_2 The light is supplied to the light emitting elements in the third row including the first row.

[0052] Moving to FIG. 13C, 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 the pixel value set PG3 in the first row (the row with 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 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. 13C, the pixel value set PG3 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,-1) at the left end of the pixel value set PG3 is output to the light-emitting element R 0_0 Instead, the light-emitting element R 1_0 The light-emitting element R corresponding to the position that will become blank as a result of the shift is supplied to the 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 is supplied to the light-emitting element R 0_1 The light is supplied to the light emitting elements in the second row including the first row.

[0053] Moving to FIG. 13D, 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 a pixel value set PG4 in the first row in the readout range RD as a pixel value set to be shifted. The pixel value set PG4 includes effective pixel values ​​of line DL0 of the input image data IM1. Then, the light emission control unit 705 shifts the selected pixel value set PG4 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 of FIG. 13D, the pixel value set PG4 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 (0,0) at the left end of the pixel value set PG4 is output to the light-emitting element R 0_0 Instead, the light-emitting element R 1_0 The light-emitting element R corresponding to the position that will become blank as a result of the shift is supplied to the 0_0 may also be supplied with a drive signal which means to turn 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 a 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 exposure head 106 and other components is shifted to the left by a pitch P A Therefore, the final image forming position on the photoconductor 102, the transfer belt 111, or the sheet becomes substantially the same as in the normal state as a result of the positional deviation being cancelled out.

[0055] In this scenario, in which the positional deviation of one pitch is compensated for, for example, a driving signal based on a pixel value (0,0) drives four light-emitting elements R 0_3 , R 0_2 , R 0_1 and R1_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 at a position shifted by one pitch on the surface of the photoconductor 102. Similarly, a drive signal based on a 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 pixel value (1,0) is formed at a position shifted by one pitch on the surface of 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 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 is true for 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 the right direction, the light emitting element R at the rear end 0_0 When the cancellation direction is the left direction, 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 multiple light emitting elements 602. This makes it possible to maintain the effective image formation position in the main scanning direction displaced in the cancellation direction over multiple line periods.

[0057] (2) Second Scenario In the second scenario, the positional deviation amount X is a pitch P A (X=2×P A 14A to 14D are explanatory diagrams of the procedure of light emission control including positional deviation compensation in the second scenario.

[0058] 14A, the input image data IM1 to which three lines of dummy pixel values ​​have been added to the beginning is again shown. 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 a subset 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, 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 the 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 manner as in the example of FIG. 0_3 The light is supplied to the light emitting elements in the fourth row including the fourth row.

[0059] Moving to FIG. 14B, 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 a pixel value set PG2 in the first row and a pixel value set PG3 in the second row in the readout range RD as pixel value sets to be shifted. Then, the light emission control unit 705 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 of 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 the 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 manner as in the example of FIG. 0_2 The light is supplied to the light emitting elements in the third row including the first row.

[0060] Moving to FIG. 14C, 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 a pixel value set PG3 in the first row and a pixel value set PG4 in the second row in the readout range RD as pixel value sets to be shifted. The pixel value set PG4 includes effective pixel values ​​of the line DL0 of the input image data IM1. Then, the light emission control unit 705 shifts the selected pixel value sets PG3 and PG4 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 side of FIG. 14C, the pixel value sets PG3 and PG4 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, 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 to turn off the light emission.

[0061] Moving to FIG. 14D, 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 a pixel value set PG4 in the first row and a pixel value set PG5 in the second row in 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. Then, the light emission control unit 705 shifts the selected pixel value sets PG4 and PG5 by one pixel in the cancellation direction, and then outputs a subset of pixel values ​​of every 2992 pixels to each light-emitting chip 400-n. In the light-emitting chip 400-1 shown on the right side of FIG. 14D, the pixel value sets PG4 and PG5 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, 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_1 can be supplied with a drive signal that means to turn 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 a 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 twice the amount of the light emitting element R 0_3 , R 0_2 , R 1_1 , and R 1_0 However, the arrangement of the exposure head 106 and other components is 2×P A Therefore, the final image formation position on the photoconductor 102, the transfer belt 111, or the sheet becomes substantially the same as in the normal state as a result of the positional deviation being cancelled out.

[0063] In this scenario, in which the positional deviation of two pitches is compensated for, for example, a driving 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 driving 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 12A to 12D, the combination of light-emitting elements used to form a spot corresponding to the same pixel position changes according to the amount of misalignment to be compensated for, 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 is true for 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 pitch P of the light emitting elements 602 in the main scanning direction. A Based on the above, it is selected which row of the M rows of light emitting elements 602 to shift the corresponding set of pixel values. 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 leftward, 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 positional deviation X is the pitch P A (X=5×P A 15A to 15D are explanatory diagrams of the procedure of light emission control including positional deviation compensation in the third scenario.

[0066] 15A, the input image data IM1 to which three lines of dummy pixel values ​​are added at the beginning is again shown. 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 readout 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 in 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 respectively supplied to the light emitting elements in the second row 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 to turn off the light emission.

[0067] Moving to FIG. 15B, in the next line period t0+1, the readout range RD of pixel values ​​from the input image data IM1 moves 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 respectively 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 to turn off the light emission.

[0068] Moving to FIG. 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 respectively supplied to the light emitting elements in the second row 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 to turn off the light emission.

[0069] Moving to FIG. 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 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 PG5 to PG7 are respectively supplied to the light emitting elements in the second row 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 to turn 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 a 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 , R1_1 , and R 2_0 However, the arrangement of the exposure head 106 and other components is 5×P A Therefore, the final image formation position on the photoconductor 102, the transfer belt 111, or the sheet becomes substantially the same as in the normal state as a result of the positional deviation being cancelled out.

[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 pitch P A For example, if the magnitude of the position shift |X| is the pitch P in the main scanning direction, the number of columns by which the pixel value set corresponding to each of the selected at least one row is shifted is determined based on the above. A It is assumed that the shift amount is x times (x is a natural number) of the pixel shift amount in the cancellation direction. In this case, the light emission control unit 705 distributes the shift amount of x pixels to each row in the order 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 in the round robin method. As an example, when M=4 and the cancellation direction is the right direction, the rear end in the cancellation direction is located in the first row, and the front end is located in the fourth row. Therefore, the light emission control unit 705 distributes the shift amount to four rows one pixel at a time, in the order of the first row → the second row → the third row → the fourth row → the first row → the second row → ..., until the total shift amount reaches x. As another example, when M=4 and the cancellation direction is the left direction, the rear end in the cancellation direction is located in the fourth row, and the front end is located in the first row. Therefore, the light emission control unit 705 distributes the shift amount to four rows one pixel at a time, in the order of the fourth row → the third row → the second row → the first row → the fourth row → the 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 positional deviation in the main scanning direction of the image formation position by a pitch P A This allows for flexible compensation with a granularity of

[0072] <4-2. Compensation for Magnification Error> When a magnification error in the main scanning direction is detected, the light emission control unit 705 selects one or more pixel positions among the pixel positions constituting the input image data according to the error magnification Y in the procedure of light emission control for multiple exposure described above. 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, and causes 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 whether the pixel value of each pixel position is inserted or thinned out based on the error magnification Y and the pitch P of the light emitting elements 602 in the main scanning direction. A Based on the above, the number of pixel positions to be selected for inserting or subtracting pixel values ​​can be determined. In the following, compensation for the reduction of the image forming range and compensation for the expansion of the image forming 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 pixel value set of the row to which that pixel position belongs. Here, inserting a pixel value into a pixel position includes shifting the pixel value on one side of the pixel position in the main scanning direction in a direction that expands the pixel value set, 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 of light emission control including compensation for the reduction of the image formation range. Here, the number of pixel positions to be selected is assumed to be 1 (for example, W0×(1−Y)≒P A16A shows input image data IM2 with three lines of dummy pixel values ​​added to the beginning. Since the error magnification Y is smaller than 1, the light emission control unit 705 selects a pixel position in which a pixel value should be inserted within the read range RD in each line period. In the example of FIG. 16A, the pixel position DP0 is selected in the line period t0. The selected pixel position DP0 belongs to the first row (the row with index i=-3) of the read range RD. 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 in the main scanning direction by one pixel to the right with respect to the pixel position DP0, and provides a copy of the pixel value (3,-3) of the pixel position DP0 before the shift to the pixel position DP0. Then, the light emission control unit 705 reads out a subset 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 the insertion of 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] Moving to FIG. 16B, in the next line period t0+1, the pixel position DP0 in the readout range RD is selected again. The selected pixel position DP0 belongs to the first row (the row with index i=-2) of the readout range RD. 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 in the main scanning direction by one pixel to the right with respect to the pixel position DP0 as a reference, and provides a copy of the pixel value (3,-2) of the pixel position DP0 before the shift to the pixel position DP0. Then, the light emission control unit 705 reads out a subset of every 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. 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 insertion of the pixel value, the driving signal based on the pixel value (3,-2) of the selected pixel position DP0 is 3_0 and light-emitting element R 4_0 , and here too the effective light-emitting element range in the first row is expanded by one light-emitting element.

[0076] Moving to FIG. 16C, in the next line period t0+2, the 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 (the row with index i=-1) of the readout range RD. 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 in the main scanning direction by one pixel to the right with respect to the pixel position DP0, and provides a copy of the pixel value (3,-1) of the pixel position DP0 before the shift to the pixel position DP0. Then, the light emission control unit 705 reads out a subset of every 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, the drive signal based on the pixel value (3,-1) of the selected pixel position DP0 is 3_0 and light-emitting element R 4_0, and here too the effective light-emitting element range in the first row is expanded by one light-emitting element.

[0077] Moving to FIG. 16D, in the next line period t0+3, the 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 (the row with index i=0) of the readout range RD. The light emission control unit 705 inserts a pixel value into the pixel value set PG4 of this row. Specifically, the light emission control unit 705 shifts the pixel values ​​of the right-side subset PG4b in the main scanning direction by one pixel to the right with respect to the pixel position DP0 as a reference, and provides a copy of the pixel value (3, 0) of the pixel position DP0 before the shift to the pixel position DP0. Then, the light emission control unit 705 reads out a subset of every 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, the 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 insertion of the pixel value, a drive signal based on the pixel value (3, 0) of the selected pixel position DP0 is input to the light-emitting element R 3_0 and light-emitting element R 4_0 , and here too the effective light-emitting element range in the first row is expanded by one light-emitting element.

[0078] 16A to 16D, the driving 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 1 / 100th of the pitch P in the main scanning direction compared to the normal state where no pixel value insertion is performed. A However, because the exposure head 106 shrinks in the main scanning direction by the amount of the error magnification Y due to, for example, a temperature change, the final image formation range on the photoconductor 102, the transfer belt 111, or the sheet becomes substantially the same as in normal times as a result of the magnification error being cancelled out.

[0079] In this scenario, which compensates for the reduction in the image formation range by one pitch, for example, the drive signal based on the pixel value (3,0) is 3_m In addition, light-emitting element R 4_0 When these five light-emitting elements emit light in accordance with the drive signal, an enlarged spot corresponding to pixel value (3,0) is formed on the surface of photoconductor 102. Comparing this to the case where there is no compensation for magnification error as described with reference to Figures 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 for forming a spot corresponding to pixel value (3,0) is four in the case where there is no compensation for magnification error, whereas in this scenario it is five. The same is true for the other pixel positions.

[0080] <4-2-2. Compensation for expansion of image formation range> 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 pixel value set of the row to which the pixel position belongs. Here, thinning out the pixel value at a pixel position includes erasing the pixel value at the pixel position before thinning out, and shifting the pixel value on one side of the pixel position in the main scanning direction in a direction that reduces the pixel value set.

[0081] 17A to 17D are explanatory diagrams of the procedure of light emission control including compensation for the expansion of the image formation range. Here, the number of pixel positions to be selected is assumed to be 1 (for example, W0×(Y−1)≒P A17A. The left side of FIG. 17A shows input image data IM2 with three lines of dummy pixel values ​​added to the beginning. Since the error magnification Y is greater than 1, the light emission control unit 705 selects a pixel position whose pixel value should be thinned out within the read range RD in each line period. In the example of FIG. 17A, the pixel position DP0 is selected in the line period t0. The selected pixel position DP0 belongs to the first row (row with index i=-3) of the read range RD. The light emission control unit 705 thins out the pixel value of the pixel position DP0 from the pixel value set PG1 of this row. Specifically, the light emission control unit 705 erases the pixel value (3,-3) of the pixel position DP0 before the shift, and shifts the pixel values ​​of the subset PG1a on the left side in the main scanning direction by one pixel to the right with respect to the pixel position DP0. Then, the light emission control unit 705 reads out a subset 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 element in the first row of the light-emitting element array. As a result of the pixel value thinning, the driving signal based on the pixel value (3, -3) of the selected pixel position DP0 is not supplied to any light-emitting element, and the effective range of the light-emitting element in the first row is reduced by one light-emitting element.

[0082] Moving to FIG. 17B, in the next line period t0+1, the pixel position DP0 in the readout range RD is selected again. The selected pixel position DP0 belongs to the first row (the row with index i=-2) of the readout range RD. The light emission control unit 705 thins out the pixel value of the pixel position DP0 from the pixel value set PG2 of this row. Specifically, the light emission control unit 705 erases the pixel value (3,-2) of the pixel position DP0 before the shift, and shifts the pixel values ​​of the subset PG2a on the left side in the main scanning direction by one pixel to the right with respect to the pixel position DP0. Then, the light emission control unit 705 reads out a subset of every 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, 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 thinning out of pixel values, a drive signal based on the pixel value (3,-2) of the selected pixel position DP0 is not supplied to any light-emitting element, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0083] Moving to FIG. 17C, in the next line period t0+2, the 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 (the row with index i=-1) of the readout range RD. The light emission control unit 705 thins out the pixel value of the pixel position DP0 from the pixel value set PG3 of this row. Specifically, the light emission control unit 705 erases the pixel value (3,-1) of the pixel position DP0 before the shift, and shifts the pixel values ​​of the subset PG3a on the left side in the main scanning direction by one pixel to the right with respect to the pixel position DP0. Then, the light emission control unit 705 reads out a subset of every 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, 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 thinning out of pixel values, a drive signal based on the pixel value (3,-1) of the selected pixel position DP0 is not supplied to any light-emitting element, and the effective range of the light-emitting elements in the first row is reduced by one light-emitting element.

[0084] Moving to FIG. 17D, in the next line period t0+3, the 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 (the row with index i=0) of the readout range RD. The light emission control unit 705 thins out the pixel value of the pixel position DP0 from the pixel value set PG4 of this row. Specifically, the light emission control unit 705 erases the pixel value (3,0) of the pixel position DP0 before the shift, and shifts the pixel values ​​of the subset PG4a on the left side in the main scanning direction by one pixel to the right with respect to the pixel position DP0. Then, the light emission control unit 705 reads out a subset 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, the 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 thinning out of pixel values, a 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.

[0085] 17A to 17D, the driving signal based on the effective pixel values ​​of line DL0 of the input image data IM2 is 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 1 / 1 the pitch P in the main scanning direction compared to the normal time when pixel values ​​are not reduced. A However, because the exposure head 106 expands in the main scanning direction by the amount of the error magnification Y due to, for example, a temperature change, the final image formation range on the photoconductor 102, the transfer belt 111, or the sheet becomes substantially the same as in normal times as a result of the magnification error being cancelled.

[0086] In this scenario, which compensates for the expansion of the image formation range by one pitch, for example, the drive signal based on the pixel value (3,0) drives the four light-emitting elements R 3_m Of these, light-emitting element R 3_0The driving signal is input to three light-emitting elements excluding the pixel value (3,0). When these three light-emitting elements emit light in accordance with the driving 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 where there is no compensation for magnification error as 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 for forming a spot corresponding to pixel value (3,0) is four in the case where there is no compensation for magnification error, whereas it is three in this scenario. The same is true for the other pixel positions.

[0087] <4-2-3. Selection of Insertion Pixel Position and Thinning-out Pixel Position> As described above, the light emission control unit 705 determines the error magnification Y and the pitch P of the light emitting elements 602 in the main scanning direction. A For example, the number of pixel positions to be selected z may be determined based on the error magnification Y, the pitch P A and the width W0 of the normal imaging range 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.

[0088] The light emission control unit 705 may select the determined number of pixel positions randomly in the main scanning direction and non-randomly in the circumferential direction. By incorporating randomness into the selection of the insertion positions or thinning positions in the main scanning direction, it is possible to reduce the possibility of subjective degradation of image quality, such as streaks or moire in the image, occurring as a result of compensation. The light emission control unit 705 may randomly select the determined number of pixel positions in pixel block units in the main scanning direction. For example, when selecting two pixel positions, N columns of pixels aligned in the main scanning 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 caused by bias in the selected pixel positions.

[0089] The selection of the insertion or thinning positions in the circumferential direction may be performed according to the same rules as the distribution of the shift amount in compensating for the above-mentioned positional misalignment. For example, when inserting z pixel values ​​to shift 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 the pixel value set is shifted to the left, the order of row selection is reversed. FIG. 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 the input image data IM3 is enlarged by 1. In the example of FIG. 18, within the read range RD set in the input image data IM3, a pixel position DP1 is selected from the first row, a pixel position DP2 is selected from the second row, and a pixel position DP3 is selected from the third row. Then, the pixel values ​​to the right of the selected pixel positions DP1, DP2, and DP3 are shifted to the right. For the sake of simplicity, an example is shown here in which the selected pixel positions are biased toward pixel positions corresponding to the light-emitting elements of the light-emitting chip 400-1, but in reality, the selected pixel positions may be widely distributed throughout the entire main scanning direction.

[0090] <4-3. Compensation for skew> As described above, compensation for the image formation range for the skew of the sheet is performed by shifting the range of the light emitting elements to be used for forming an image for each line of the input image data according to the skew of the sheet. Here, the displacement amount (also simply called the inclination) in the main scanning direction per unit conveyance amount of the sheet caused by the skew is dX, and the line L i The position of the conveyance distance Z from the reference line i Here, the reference line may be the first line read out of the input image data. Then, the line L i The component corresponding to the skew among the displacement amount in the main scanning direction of the image forming range in i The product dX Z is derived by multiplying the displacement dX by i Focusing on each line, compensation for the component corresponding to the skew of the sheet can be achieved by shifting the image formation position in the same manner as in the compensation for the misregistration described above.

[0091] By shifting the image formation range in the main scanning direction in accordance with the inclination dX as the sheet is conveyed, it is possible to suppress the inclination of the printed image caused by the skew. LED is finite, so if the shift amount is too large, the shift amount will exceed the light emission range W LED If this occurs, the image will not be formed in the deviated portion, and the printed image may end up with a distorted shape with missing corners.

[0092] 19A to 19D are explanatory diagrams of the influence of a skewed sheet on a printed image. LED and the image forming range H1. If the sheet is not skewed, the image forming range H1 does not shift as the sheet is transported, so the image forming range H1 always occupies the same range in the main scanning direction D1 regardless of the line position in the transport direction (circumferential direction) D2.

[0093] FIG. 19B shows the light emission possible range W when a relatively small skew of the sheet is detected. LED The figure shows the positional relationship between the line position L in the conveying direction D2 and the image forming range H2. When a relatively small skew is detected, the image forming range H2 is shifted in the main scanning direction D1 in accordance with the detected sheet skew as the sheet is conveyed. However, the line position L in the conveying direction D2, which shows the maximum shift amount, MAX Even in this case, the shift amount is within the light emission range W LED Do not deviate from.

[0094] FIG. 19C shows the light emitting range W when a relatively large skew of the sheet is detected. LED When a relatively large skew is detected, the shift amount calculated according to the detected sheet skew is shifted to a position halfway through the image forming range H3. LED The shift amount is the line L farthest from the reference line L0. MAX It is maximum at line L MAX may correspond to the last line read out of the input image data. As a result, as shown in FIG. 19C, the corner H3a of the image forming range H3 is within the light emitting range W LED The surface of the photoconductor corresponding to this corner H3a is not exposed. Therefore, as shown in FIG. 19D, the corner of the print image IM4 formed on the skewed sheet SH is missing, and the shape of the print image IM4 is distorted.

[0095] In this embodiment, the light emission control unit 705 performs trimming of the input image data to prevent the shape of the printed image from being distorted while suppressing the inclination of the printed image. Specifically, the light emission control unit 705 determines whether the range of light emitting elements to be used for the line with the largest shift amount is within the light emitting possible range W LED If it is determined that deviation will occur, the light emission control unit 705 trims the image of each line of the input image data to match the deviation amount of the line with the largest shift amount.

[0096] For example, the deviation amount of the line with the largest shift amount corresponds to K pixels (K is an integer equal to or greater than 1). In this case, the light emission control unit 705 may discard a partial image of K pixels at one end (deviation side) in the main scanning direction from the image of each line (typically, all lines) of the input image data. For example, the image memory 706 stores pixel values ​​of each line of the input image data. The light emission control unit 705 may discard the partial image by restricting the read range (so as not to include the partial image of K pixels) when reading out pixel values ​​to be output to the exposure head 106 from the image memory 706. The discarded partial image is not output to the light emitting element array of the exposure head 106. As a result, the pixel value is read and trimmed at the same time, so that the processing is made more efficient and the implementation cost can be suppressed. Alternatively, the light emission control unit 705 may discard the partial image by erasing pixel values ​​corresponding to the partial image of K pixels.

[0097] 20A and 20B are explanatory diagrams of the trimming of image data when deviation of the shift amount occurs. LED The positional relationship between the image forming range H3 and the reference line L0 is shown. Here, as a result of detecting a relatively large skew, the line L1 that is the furthest from the reference line L0 is detected. MAX At the right end of the image formation range H3, the light emission possible range W LED In this case, the light emission control unit 705 discards a partial image of K pixels at the right end of the input image data, and controls light emission from the light emitting element 602 of the exposure head 106 in accordance with the remaining image data. Therefore, as shown in Fig. 20B, the shape of the print image IM5 formed on the skewed sheet SH is a proper shape with no inclination on at least two sides along the transport direction D2 and no missing corners.

[0098] <5. Correction for multiple error components> As described above, factors that require a shift in the image forming range of the exposure head 106 in the main scanning direction may include, in addition to the skew of the sheet, one or both of a positional deviation and a magnification error. When the shift amounts caused by each of these factors are accumulated, the light emitting range W LED Therefore, the possibility of the image formation range deviating from the normal range increases.

[0099] Therefore, in one embodiment, the light emission control unit 705 may shift the range of light emitting elements to be used for forming an image of the first line L0 of the input image data in response to the detected positional deviation. The positional deviation here includes only a component that does not depend on the skew of the sheet. Such a shift of the fixed image formation range may be performed by offsetting (also called alignment) the writing start position in the main scanning direction (the position of the light emitting element that is the starting point of the image formation range). The light emission control unit 705 derives the shift amount for each subsequent line by calculating a component corresponding to the positional deviation and a component corresponding to the skew of the sheet. The former is a fixed component that does not depend on the line position, and the latter is a component proportional to the line position.

[0100] In addition, in one embodiment, the light emission control unit 705 may expand or reduce the range of light emitting elements to be used for forming an image of each line of the input image data in response to the detected magnification error. The expansion and reduction of the range here may be performed by inserting and thinning out pixel values ​​in the image data, respectively. The light emission control unit 705 may derive the shift amount for each line by further incorporating a component corresponding to the magnification error.

[0101] In any embodiment, the light emission control unit 705 determines the line L with the largest shift amount in the input image data based on the detection result from the sensor for one or more components to be included. MAX Here, as described above, the maximum width W0 of the image formed by the image forming apparatus 1 in the main scanning direction D1 is the light emitting range W LED (see FIG. 3B), that is, the light emission range W LEDTherefore, the light emission control unit 705 determines the light emission possible range W LED The margin of line L MAX Compare with the shift amount derived for line L MAX If the shift amount calculated for line L exceeds the margin, the light emission control unit 705 MAX In the image formation range, the light emission possible range W LED The deviation amount may correspond to the difference between the shift amount and the margin. MAX If the shift amount calculated for does not exceed the margin, the light emission control unit 705 determines that the image formation range is within the light emission possible range W LED It is judged that the light emission range W LED When the image forming range is centered with respect to the left side and the right side of the image forming range in the main scanning direction, the comparison between the shift amount and the margin may be performed respectively.

[0102] Fig. 21 is a flowchart showing an example of the flow of a deviation amount calculation process according to an embodiment. Fig. 22 is a flowchart showing an example of the flow of an image data correction process including the deviation amount calculation process of Fig. 21. The image data correction process may be performed by the light emission control unit 705 (or the CPU 701) of the image controller 700, for example, when execution of a print job is started. It is assumed that the size of the sheet used for printing (the length in the transport direction and the width in the main scanning direction) is known as a parameter of the print job.

[0103] In the deviation amount calculation process S110 in FIG. 21, first, in S111, the light emission control unit 705 calculates the left enlargement amount B L and right side expansion amount B R For example, the left side expansion amount B L and right side expansion amount B R is calculated according to the following equations (1) and (2), respectively, IN and the magnification factor B (the inverse of the error magnification factor Y) can be calculated as: B L=W IN ×(B-1) / 2 (1) B R =W IN ×(B-1) / 2 (2)

[0104] Next, in S112, the light emission control unit 705 determines the line L MAX The left shift amount S for compensating for the skew in L and right shift amount S R For example, if the right side is positive and the slope dX is negative, the left shift amount S L can be calculated according to the following formula (3): S L =|Z MAX ×dX| (3) Here, Z MAX is the line L where the shift amount is maximum MAX In this case, the right shift amount S is equal to the line position, i.e., the sheet length in the conveying direction. R may be zero. When the slope dX is positive, the right shift amount S R can be calculated according to the following formula (4): S R =Z MAX ×dX (4) In this case, the left shift amount S L may be zero.

[0105] Next, in S113, the light emission control unit 705 determines the left shift amount K L and right shift amount K R If the right side is positive, when the position deviation amount X is negative, the left shift amount K L can be calculated according to the following formula (5): K L =|X| (5) In this case, the right shift amount K R may be zero. When the position shift amount X is positive, the right shift amount K R can be calculated according to the following formula (6): K R =dX (6) In this case, the left shift amount K L may be zero.

[0106] Next, in S114, the light emission control unit 705 calculates the value B calculated in S111, S112, and S113 as shown in the following formula (7). L , S L and K L The left margin M from the left shift amount equivalent to the sum of L By subtracting L Calculate: O L =(B L +S L +K L )-M L (7) Next, in S115, the light emission control unit 705 calculates the value B calculated in S111, S112, and S113 as shown in the following formula (8). R , S R and K R The right margin M R By subtracting R Calculate: O R =(B R +S R +K R )-M R (8) In addition, the left margin M L and right margin M R may be preset according to the following equation (9): M L =M R =(W LED -W IN ) / 2 (9)

[0107] Left deviation amount O calculated in S114 LIf is greater than zero, the image formation range deviates to the left of the light emission possible range. R If is greater than zero, the imaging range deviates to the right of the light emitting possible range.

[0108] In the image data correction process of FIG. 22, first, the light emission control unit 705 executes the deviation amount calculation process S110 described above to calculate the left deviation amount O L and right deviation amount O R Calculate.

[0109] Next, in S120 and S121, the light emission control unit 705 calculates the left deviation amount O L and right deviation amount O R or the image forming range is greater than zero at either end in the main scanning direction, the light emitting range W LED For example, the amount of deviation from the left side O L If exceeds zero (S120-YES), the image formation range is within the light emission possible range W LED In this case, the process proceeds to S131. R When exceeds zero (S120-NO, S121-YES), the image formation range is within the light emission possible range W LED In this case, the process proceeds to S132. L and right deviation amount O R If neither of is greater than zero, S131 and S132 are skipped.

[0110] In S131, the light emission control unit 705 calculates the left edge of the input image by the left deviation amount O L In addition, in S132, the light emission control unit 705 trims the right edge of the input image by the number of pixels corresponding to the right deviation amount O R The trimming here is performed, for example, by trimming the read range when reading input image data from the image memory 706 by the deviation amount O L The number of pixels corresponding to the deviation amount O on the right edge RThis may be done by restricting the number of pixels corresponding to .gamma.

[0111] Next, in S133, the light emission control unit 705 offsets the signal write start position with respect to the light emitting element array so as to compensate for the positional deviation of the image forming range. The offset amount here is the left shift amount K L Or right shift amount K R , and can be applied to every line of the input image data.

[0112] Next, in S134, the light emission control unit 705 shifts the image formation range of each line according to the detected inclination and line position in accordance with the skew of the sheet. As described above, the shift amount of the i-th line is calculated by multiplying the inclination dX by the transport amount Z i When the inclination dX is positive, the image formation range is shifted in the forward direction (rightward) in the main scanning direction, and when the inclination dX is negative, the image formation range is shifted in the reverse direction (leftward).

[0113] Next, in S135, the light emission control unit 705 expands or reduces the image formation range of each line according to the detected error magnification. For example, the light emission control unit 705 can reduce the image formation range by thinning out pixel values ​​from each line, or expand the image formation range by inserting pixel values ​​into each line, according to the error magnification.

[0114] The light emission control unit 705 controls light emission from the multiple light emitting elements 602 of the exposure head 106 in accordance with the input image data corrected in this manner.

[0115] <6. Summary> Various embodiments have been described in detail above with reference to Figs. 1 to 22. According to the above-described embodiment, in an image forming apparatus for forming an image on a sheet, an exposure head for exposing a photoconductor has a light-emitting element array including a plurality of light-emitting elements arranged over a first range in a main scanning direction parallel to the axial direction of the photoconductor. A control unit of the image forming apparatus shifts a range of light-emitting elements to be used for forming an image of each line of input image data among the light-emitting elements in the first range according to the position of the line and the detected skew of the sheet. When the range of light-emitting elements to be used for the line with the largest shift amount deviates from the first range, the control unit trims the image of each line in the main scanning direction according to the deviation amount of the line with the largest shift amount. Therefore, it is possible to prevent the printed image from becoming distorted while suppressing the skew of the printed image.

[0116] In the above embodiment, when the deviation amount of the line with the largest shift amount is K pixels (K is an integer equal to or greater than 1), a partial image of K pixels at one end in the main scanning direction can be discarded from the image of each line of the input image data. Therefore, it is possible to form an image of an appropriate shape on the sheet by making maximum use of the light-emitting elements over the first range.

[0117] In one embodiment, the range of light-emitting elements to be used for forming an image of the first line may be shifted according to the misalignment of the image forming range. Then, the shift amount for each subsequent line may be derived by calculating a component according to the misalignment and a component according to the skew of the sheet. In this way, the trimming amount for each line of the input image data is determined based on the shift amount for compensating for both the misalignment and the skew, so that the printed image may be prevented from becoming distorted with missing corners even when not only the sheet is skewed but also the misalignment occurs. In another embodiment, a component according to the magnification error may also be calculated instead of (or in addition to) the component according to the misalignment. This can prevent the printed image from becoming distorted even when the image forming range needs to be expanded to compensate for the magnification error, and can avoid excessive trimming when the image forming range needs to be reduced.

[0118] In the above embodiment, the maximum width of the image formed by the image forming device in the main scanning direction is smaller than the first range. In this way, by providing a margin for the light emitting range of the exposure head with respect to the maximum width of the print image, it is possible to form a print image without partial image loss for a certain degree of skew. Also, it is easy to calculate the deviation amount of the image formation range by comparing the shift amount with the margin.

[0119] In the above embodiment, specific numerical values ​​are used for explanation, but these specific numerical values ​​are merely examples, and the present invention is not limited to the specific numerical values ​​used in the embodiment. Specifically, the number of light-emitting chips provided on one printed circuit board is not limited to 20, and may be any number equal to or greater than 1. In addition, 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. In addition, the circumferential pitch and axial pitch of the light-emitting elements are not limited to about 21.16 μm and about 5 μm, and may be any other value.

[0120] <7. Other embodiments> The above-mentioned 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. It can also be realized by a circuit (e.g., ASIC) for realizing one or more functions.

[0121] The invention is not limited to the above-described embodiments, and various modifications and variations are possible 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]

[0122] 1: image forming apparatus, 102: photoconductor, 106: exposure head, 113: optical sensor (error detection unit), 114: registration sensor (skew detection unit), 400: light emitting chip, 602: light emitting element, 701: CPU, 705: light emission control unit, 706: image memory, D1: axial direction (main scanning direction), D2: circumferential direction (transport direction), H1, H2, H3: image forming range, IM1, IM2, IM3: input image data, IM4, IM5: print image, R j_m : Light emitting element, W LED : Light emitting range (first range)

Claims

1. An image forming apparatus for forming an image on a sheet, comprising: a skew detection unit that detects skew of the sheet with respect to a conveying direction; an exposure head for exposing a photoconductor, the exposure head having a light emitting element array including a plurality of light emitting elements arranged over a first range in a main scanning direction parallel to an axial direction of the photoconductor; A control unit that controls light emission from the plurality of light-emitting elements of the exposure head in accordance with input image data; Equipped with the transport direction is perpendicular to the axial direction of the photoconductor, the control unit shifts a range of light-emitting elements to be used for forming an image of each line of the input image data among the light-emitting elements in the first range in accordance with a position of the line in the input image data and the skew of the sheet detected by the skew detection unit; When a range of light-emitting elements to be used for the line with the largest shift amount deviates from the first range, the control unit trims an image of each line of the input image data to match the deviation amount of the line with the largest shift amount. Image forming device.

2. The image forming apparatus includes: an image memory for storing pixel values ​​of each line of the input image data; Further equipped with the control unit restricts a read range when reading out pixel values ​​to be output to the exposure head from the image memory, thereby trimming an image of each line of the input image data. The image forming apparatus according to claim 1 .

3. The control unit is shifting a range of light emitting elements to be used for forming an image of a first line in response to a detected misalignment of the sheet or the light emitting element array; deriving a shift amount for each subsequent line by incorporating a component corresponding to the misalignment and a component corresponding to the skew of the sheet; The image forming apparatus according to claim 1 .

4. The control unit is Enlarging or reducing the range of light emitting elements to be used for forming each line of image in response to a magnification error detected for the sheet or the array of light emitting elements; Deriving the shift amount for each line by further calculating a component corresponding to the magnification error. The image forming apparatus according to claim 3 .

5. The control unit is Enlarging or reducing the range of light emitting elements to be used for forming each line of image in response to a magnification error detected for the sheet or the array of light emitting elements; deriving a shift amount for each line by calculating a component corresponding to the magnification error and a component corresponding to the skew of the sheet; The image forming apparatus according to claim 1 .

6. the skew of the sheet is expressed as a displacement amount in the main scanning direction per unit conveyance amount of the sheet, A component of the shift amount of each line corresponding to the skew of the sheet is derived by multiplying a transport amount from a first read line of the input image data to the line by the displacement amount. The image forming apparatus according to claim 1 .

7. 7. The image forming apparatus according to claim 6, wherein the line with the largest shift amount corresponds to a line that is read last out of the input image data.

8. 2. The image forming apparatus of claim 1, wherein when the deviation amount of the line with the largest shift amount is K pixels (K is an integer greater than or equal to 1), the control unit discards a partial image of K pixels at one end of the main scanning direction from the image of each line of the input image data, or does not output the partial image of K pixels to the exposure head.

9. The image forming apparatus according to claim 1 , wherein a maximum width in the main scanning direction of the image formed by the image forming apparatus is smaller than the first range.

10. The image forming apparatus of claim 9, wherein the control unit determines whether the range of light-emitting elements to be used for the line deviates from the first range by comparing a margin of the first range with respect to the image width in the main scanning direction of the image represented by the input image data with the shift amount derived for the line with the largest shift amount.

Images