Information processing apparatus, image forming apparatus, control method, and program

Abstract

To solve such a problem that correction accuracy of a light amount in an image forming apparatus is insufficient.SOLUTION: An information processing device generates correction data for correcting a light amount of an image forming apparatus having an exposure head including a plurality of light-emitting element array chips each having a plurality of light-emitting elements. The information processing device comprises: first correction means that generates first correction data for correcting a light amount difference at boundaries between adjacent light-emitting element array chips; and second correction means that generates second correction data for correcting a light amount distribution of the exposure head corrected by the first correction data.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to an information processing apparatus, an image forming apparatus, a control method, and a program.

Background Art

[0002] An image forming apparatus having an exposure head and a photoreceptor rod and printing an image is known. The exposure head has a plurality of light emitting element array chips each having a plurality of light emitting elements. In such an image forming apparatus, an image is printed on a recording medium such as paper by irradiating light from the light emitting elements of the exposure head onto the photoreceptor rod.

[0003] In such an image forming apparatus, since there is a difference in light amount between the light emitting elements, a technique for correcting the light amount is known.

[0004] For example, in Patent Document 1, based on the variation in density obtained by reading a printed chart with a scanner or the like, the difference in the average value of the light amount of each of the light emitting element array chips is obtained and corrected, and then the light amounts at the ends of the light emitting element array chips are corrected. A technique is disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the technique of Patent Document 1, since the light amount is corrected in a state where there is a steep light amount difference at the boundary between the light emitting element array chips, the accuracy of the light amount correction is not sufficient.

[0007] Therefore, the present invention provides an information processing device, an image forming apparatus, a control method, and a program that can improve the accuracy of light intensity correction in an image forming apparatus. [Means for solving the problem]

[0008] To solve this problem, for example, the information processing apparatus of the present invention has the following configuration. That is, An information processing device that generates correction data for correcting the light intensity of an image forming apparatus having an exposure head having multiple light-emitting array chips each having multiple light-emitting elements, A first correction means for generating first correction data to correct the difference in light intensity at the boundary between adjacent light-emitting element array chips, A second correction means for generating second correction data to correct the light intensity distribution of the exposure head corrected by the first correction data, Equipped with 、 The first correction means calculates the difference in light intensity and generates the first correction data based on the light intensity data obtained by scanning the first correction image. . [Effects of the Invention]

[0009] According to the present invention, the accuracy of light intensity correction in an image forming apparatus can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] A diagram showing the overall configuration of the image forming apparatus according to the embodiment. [Figure 2] A diagram illustrating the exposure head and photoreceptor drum of an embodiment. [Figure 3] A plan view of a printed circuit board in which the group of light-emitting elements and connectors of the embodiment are arranged. [Figure 4] A plan view showing a schematic configuration of the light-emitting element array chip of the embodiment. [Figure 5] A cross-sectional view of a portion of the light-emitting section of the embodiment. [Figure 6] A plan view illustrating the overlap of the light-emitting elements in the embodiment. [Figure 7] A block diagram illustrating the control system of the image forming apparatus according to the embodiment. [Figure 8] Block diagram of the internal circuit of the light-emitting element array chip of the embodiment. [Figure 9] Block diagram for explaining the configuration of the light amount correction unit of the embodiment. [Figure 10] Diagram for explaining the process of correcting an image of the embodiment. [Figure 11] Diagram of the light amount correction chart printed to obtain light amount variations. [Figure 12] Diagram of the flowchart of the correction process for generating correction data for correcting the light amount. [Figure 13] Diagram of the light amount distribution of the exposure head before correction in the longitudinal direction of the light-emitting element array chip. [Figure 14] Diagram of the light amount distribution of the exposure head after correction in the longitudinal direction of the light-emitting element array chip. [ [Figure 15] Diagram of the light amount distribution before correction within the light-emitting element array chip. [Figure 16] Diagram for explaining the sampling area and dot influence for each light-emitting element array chip of the embodiment. [Figure 17] Diagram showing the light amount distribution of 18 sample area columns corresponding to one light-emitting element array chip. [Figure 18] Diagram showing the light amount distribution in the case where vertical streaks occur in the image. [Figure 19] Plan view showing the state in which the light-emitting element array chips are arranged. [Figure 20] Block diagram for explaining the hardware configuration of the control system of the image forming apparatus of the embodiment.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant explanations are omitted.

[0012] <Embodiment> (Overall configuration of the image forming apparatus) A brief description will be given of the electrophotographic image forming apparatus 10 in this embodiment. Figure 1 shows the overall configuration of the image forming apparatus 10. The image forming apparatus 10 comprises a scanner unit 100, an image forming unit 103, a fixing unit 104, a paper feeding / transporting unit 105, an optical sensor 113, and a printer control unit (not shown) that controls these. In the following description, the term "image" may include "image data".

[0013] The scanner unit 100 illuminates the document placed on the document glass with light to optically read the image of the document. The scanner unit 100 converts the light from the scanned image of the document into an electrical signal to create image data and output it.

[0014] The image forming unit 103 has four sets of image forming units 101a, 101b, 101c, and 101d. When it is not necessary to distinguish between the image forming units 101a, 101b, 101c, and 101d, they are referred to as image forming unit 101. The number of sets of image forming units 101 is not limited to four and may be changed as appropriate. This embodiment has four sets of image forming units 101a, 101b, 101c, and 101d corresponding to four colors: cyan (C), magenta (M), yellow (Y), and black (K). The four sets of image forming units 101 are arranged in the order of cyan (C), magenta (M), yellow (Y), and black (K). The image forming unit 101 performs a series of electrophotographic processes (charging, exposure, development, and transfer) on a recording medium such as paper that is being transported. The four-unit image forming unit 101 sequentially performs magenta, yellow, and black image formation operations after a predetermined time has elapsed since the start of image formation at the cyan station. In this way, the four-unit image forming unit 101 sequentially prints images of the corresponding colors, forming a full-color image on paper.

[0015] Each of the image forming units 101 includes a photoreceptor drum 102, an exposure head 106, a charger 107, and a developer 108. The photoreceptor drum 102 is driven to rotate. The charger 107 charges the rotating photoreceptor drum 102. The exposure head 106 irradiates the photoreceptor drum 102 with light according to the image data to form an electrostatic latent image. The developer 108 generates a toner image by developing toner onto the electrostatic latent image formed on the photoreceptor drum 102. The toner image is transferred to paper being transported on the transfer belt 111.

[0016] The paper feeding / transportation unit 105 includes an internal paper feeding unit 109a, an internal paper feeding unit 109b, an external paper feeding unit 109c, a manual feed unit 109d, a register roller 110, and a transfer belt 111. In the paper feeding / transportation unit 105, the paper feeding unit designated in advance from among the internal paper feeding unit 109a, internal paper feeding unit 109b, external paper feeding unit 109c, and manual feed unit 109d feeds the paper. The fed paper is transported to the register roller 110. The register roller 110 transports the paper onto the transfer belt 111 at the timing when the toner image formed in the image-making unit 103 described above is transferred onto the paper. An optical sensor 113 is positioned opposite the transfer belt 111. The optical sensor 113 detects the position of a test chart printed on the transfer belt 111 in order to derive the amount of color misalignment between each station. The resulting color shift is communicated to the image controller unit (described later), and the image position of each color is corrected. This control ensures that a full-color toner image without color shift is transferred to the paper.

[0017] The fuser unit 104 has multiple opposing rollers and heat sources such as halogen heaters. In the fuser unit 104, the toner on the paper, which has been transferred with a toner image and transported from the transfer belt 111, is melted by the heat from the heat sources and the pressure from the rollers, and fixed to the paper. The fuser unit 104 then discharges the paper with the toner image fixed to it to the outside of the image forming apparatus 10 using the paper discharge roller 112.

[0018] The printer control unit (not shown) communicates with the overall control unit (not shown), which controls the entire image forming apparatus 10, and executes control such as image forming in accordance with its instructions. It also manages the status of each of the aforementioned parts, such as the scanner, image formation, fixing, and paper feeding / transport, to control the entire system so that it can operate smoothly in harmony.

[0019] (Exposure head configuration) The exposure head 106 that exposes the photoreceptor drum 102 will now be described. Figure 2 is a diagram illustrating the exposure head and the photoreceptor drum. Figure 2(a) shows the arrangement of the exposure head 106 relative to the photoreceptor drum 102. Figure 2(b) shows how the light emitted from the light-emitting element group 201 is focused onto the photoreceptor drum 102 by the rod lens array 203.

[0020] The exposure head 106 and the photoreceptor drum 102 are each attached to the image forming apparatus 10 by mounting members (not shown). The exposure head 106 has a light-emitting element group 201, a printed circuit board 202, a rod lens array 203, and a housing 204. The light-emitting element group 201 has a plurality of arranged light-emitting elements. The light-emitting elements are, for example, LEDs (Light Emitting Diodes) such as semiconductor light-emitting elements and organic EL (Electro Luminescence) elements. The light-emitting element group 201 is mounted on the printed circuit board 202. The rod lens array 203 is arranged on the optical path of the light emitted from the light-emitting element group 201. The rod lens array 203 has a plurality of arranged rod lenses. The housing 204 holds the light-emitting element group 201, the printed circuit board 202, and the rod lens array 203.

[0021] In image printing, the exposure head 106 causes the light-emitting elements on the chip surface of the light-emitting element group 201 to emit light according to the image data. The rod lens array 203 focuses the light emitted by the light-emitting element group 201 onto the photoreceptor drum 102. As a result, an electrostatic latent image is formed on the photoreceptor drum 102.

[0022] In the factory, the exposure head 106 is adjusted individually. During the adjustment process, focus adjustment and light intensity adjustment are performed to adjust the spot at the light-gathering position of the exposure head 106 to a predetermined size. Here, the distance between the photoreceptor drum 102 and the rod lens array 203, and the distance between the rod lens array 203 and the light-emitting element group 201 are arranged to be a predetermined interval, so that the light emitted from the light-emitting element group 201 is imaged onto the photoreceptor drum 102. For this reason, during focus adjustment, the mounting position of the rod lens array 203 is adjusted so that the distance between the rod lens array 203 and the light-emitting element group 201 is a desired value. Also, during light intensity adjustment, each light-emitting element is made to emit light individually and sequentially, and the drive current of each light-emitting element is adjusted so that the light gathered through the rod lens array 203 is of a predetermined light intensity.

[0023] (Circuit board configuration) Figure 3 is a plan view of the printed circuit board 202 on which the light-emitting element group 201 and the connector 305 are arranged. Figure 3(a) is a plan view of the side opposite to the side on which the light-emitting element group 201 is mounted (hereinafter referred to as the side without light-emitting element mounting). Figure 3(b) is a plan view of the side on which the light-emitting element group 201 is mounted (hereinafter referred to as the side with light-emitting element mounting).

[0024] The light-emitting element group 201 consists of 17 light-emitting element array chips 400-1 to 400-17 arranged in a staggered pattern on a printed circuit board 202. When it is not necessary to distinguish between the light-emitting element array chips 400-1 to 400-17, they are referred to simply as light-emitting element array chip 400. The direction in which the light-emitting element array chips 400 are arranged is just one example of the arrangement direction. Since the light-emitting element group 201 has multiple light-emitting element array chips 400 arranged on the surface of the printed circuit board 202, it can be considered a surface-emitting device. Each light-emitting element array chip 400 has 748 light-emitting elements that function as light-emitting points, arranged along the longitudinal direction at a predetermined pitch corresponding to the chip's resolution. In this embodiment, the pitch of adjacent light-emitting elements in the longitudinal direction of the chip is a pitch corresponding to a resolution of 1200 dpi (approximately 21.16 μm), and the distance from end to end of the 748 light-emitting elements within the light-emitting element array chip 400 is approximately 15.8 mm. Seventeen light-emitting element array chips 400 are arranged in the light-emitting element group 201. As a result, the number of light-emitting elements that can be exposed by the light-emitting element group 201 becomes 12,716, enabling image formation corresponding to an image width of approximately 267 mm. The light-emitting element array chips 400-1 to 400-17 are arranged in two rows in a staggered pattern. Each row of the light-emitting element array chips 400 is arranged along the longitudinal direction of the printed circuit board 202.

[0025] Figure 3(c) is an enlarged plan view of the boundary between the light-emitting element array chips. As mentioned above, in the light-emitting element array chip 400, the light-emitting elements 602 are arranged at intervals of 1200 dpi. Four rows of light-emitting elements 602 are arranged in the short direction. Each row of light-emitting elements 602 is offset by approximately 5 μm (equivalent to 4800 dpi) in the longitudinal direction. The light-emitting elements 602 are arranged such that the spacing Ly of the light-emitting points (light-emitting elements 602) in the short direction of the exposure head 106 of the staggered two rows of light-emitting element array chips 400 is approximately 105 μm (equivalent to 5 pixels at 1200 dpi, or 10 pixels at 2400 dpi). In addition, in the longitudinal direction of the exposure head 106, the light-emitting elements 602 are arranged to overlap between the light-emitting element array chips 400. In this embodiment, the four light-emitting elements 602 at the ends overlap. The amount of overlap is not limited to four light-emitting elements 602. For example, the overlap amount can be determined based on the maximum amount of mounting variation in the mounting equipment (die bonder) so that no gaps are created between the light-emitting elements 602 of adjacent light-emitting element array chips 400.

[0026] A connector 305 is located on the non-mounted side of the printed circuit board 202. The connector 305 receives control signals output from the image controller unit to control the light-emitting element array chip 400 and connects the power line to the light-emitting element array chip 400. Each light-emitting element array chip 400 is driven via the connector 305.

[0027] (Configuration of the light-emitting element array chip) Figure 4 is a plan view showing a schematic configuration of the light-emitting element array chip 400. The light-emitting element array chip 400 has a light-emitting substrate 402, a light-emitting section 404, a circuit section 406, and a plurality of WB pads 408.

[0028] The light-emitting substrate 402 may be a silicon substrate. Process technology for forming integrated circuits on silicon substrates has also advanced, and silicon is already used as a substrate for various integrated circuits. This offers advantages such as the ability to form high-speed and high-performance circuits at high density, and the availability of large-diameter silicon wafers, making it inexpensive to obtain.

[0029] The light-emitting section 404 includes a plurality of light-emitting elements 602 provided on the light-emitting substrate 402.

[0030] The circuit unit 406 is built into the light-emitting substrate 402. The circuit unit 406 controls the light-emitting unit 404. The circuit unit 406 may be an analog drive circuit, a digital control circuit, or a configuration including both. In this embodiment, the circuit unit 406 has a drive unit for driving the light-emitting element, a data transfer unit for generating a light-emitting signal, and a light-emitting signal generation unit. By forming the circuit unit 406 on a Si substrate, it becomes a circuit capable of handling high speeds.

[0031] The WB pad 408 is an abbreviation for wire bonding pad and is provided on the light-emitting substrate 402. Power supply to the circuit section 406 and input / output of signals from outside the light-emitting element array chip 400 are performed via the WB pad 408.

[0032] (Light-emitting section configuration) Figure 5 is a cross-sectional view of a portion of the light-emitting section 404 along line AA in Figure 4. The configuration of the light-emitting section 404 will be explained using Figure 5.

[0033] The light-emitting section 404 has a plurality of lower electrodes 504, a light-emitting layer 506, and an upper electrode 508. The plurality of lower electrodes 504, the light-emitting layer 506, and the upper electrode 508 are stacked on a light-emitting substrate 402. The lower electrodes 504 are independent electrodes provided for each light-emitting element (pixel). The light-emitting layer 506 is provided in common for the plurality of light-emitting elements and is a layer that emits light when, for example, an electric current flows through it. The upper electrode 508 is a common electrode provided in common for the plurality of light-emitting elements. The plurality of lower electrodes 504 have a width W in the X direction in the figure and are formed with a predetermined gap dx between adjacent lower electrodes 504 in the X direction. When a voltage is applied between the lower electrodes 504 and the upper electrode 508, an electric current flows from the lower electrodes 504 to the upper electrode 508. As a result, the light-emitting layer 506 between the lower electrodes 504 and the upper electrode 508 emits light. By increasing the electrode spacing dx relative to the spacing dz between the lower electrode 504 and the upper electrode 508, leakage current between adjacent lower electrodes 504 can be eliminated, preventing false light emission from adjacent pixels.

[0034] In the manufacturing process of the light-emitting section 404, the light-emitting layer 506 is formed on the lower electrode 504 after the lower electrode 504 has been formed. In the figure, the light-emitting layer 506 is formed continuously over the entire surface, but it is not limited to this. For example, the light-emitting layer 506 may be divided into sections of approximately the same size as the lower electrode 504. The light-emitting layer 506 may be, for example, an organic EL film. When an organic EL film is used as the light-emitting layer 506, the light-emitting layer 506 may be a laminated structure that includes functional layers such as an electron transport layer, a hole transport layer, an electron injection layer, a hole injection layer, an electron blocking layer, and a hole blocking layer as needed. In addition, the light-emitting layer 506 may be an inorganic EL layer or the like, instead of an organic EL layer.

[0035] The upper electrode 508 is formed on the light-emitting layer 506 after the lower electrode 504 has been formed on the light-emitting layer 506. The upper electrode 508 is transparent to the emission wavelength of the light-emitting layer 506. Therefore, the upper electrode 508 is a transparent electrode, such as indium tin oxide (ITO). In this embodiment, a configuration in which the entire upper electrode 508 is formed of a transparent electrode (ITO) will be described as an example. Note that the transparent electrode of the upper electrode 508 only needs to be formed at the opening that emits light, and does not necessarily need to cover the entire light-emitting element array chip 400. For example, a transparent electrode may be formed only at the opening, and the area outside the opening may be wired with an electrode other than a transparent electrode (such as metal wiring).

[0036] (Light-emitting element arrangement (high-resolution overlapping arrangement)) Figure 6 is a plan view illustrating the overlap of the light-emitting elements. The light-emitting section 404 has multiple light-emitting elements 602-11 to 602-mn. m and n are positive integers. When it is not necessary to distinguish between the multiple light-emitting elements 602-11 to 602-mn, they are referred to as light-emitting element 602.

[0037] Figure 6(a) is a plan view illustrating the arrangement of multiple light-emitting elements 602 of the light-emitting unit 404. The multiple light-emitting elements 602 are arranged in rows along the X direction in the figure at predetermined intervals, for example, at a pitch of 21.16 μm in the case of 1200 dpi. The rows of light-emitting elements 602 along the X direction are denoted as light-emitting element row 604-1 to light-emitting element row 604-2. When it is not necessary to distinguish between light-emitting element row 604-1 to light-emitting element row 604-2, they are referred to as light-emitting element row 604. The multiple light-emitting elements 602 are also arranged in the Y direction at predetermined pitches. The light-emitting elements 602 are arranged in a matrix with n elements in the row direction (X direction in the figure) and m elements in a direction different from the row direction (Y direction in the figure). In this embodiment, four rows of light-emitting elements 602 are arranged in the Y direction, but it is sufficient for the light-emitting elements 602 to be arranged in two or more rows.

[0038] In the figure, width W1 is the width of the light-emitting element 602 in the X direction. The width W2 of the light-emitting element 602 in the Y direction may be the same as width W1, but is not limited to being the same width. Spacing d1 is the spacing between adjacent light-emitting elements 602 in the X direction. Spacing d2 is the spacing between adjacent light-emitting elements 602 in the Y direction. Here, spacings d1 and d2 are the distance dx between electrodes mentioned above, expressed in two-dimensional coordinates. Spacings d1 and d2 are determined to be wider than the spacing dz between the upper electrode 508 and the lower electrode 504. Light-emitting element rows 604-1 to 604-4 are arranged with a positional offset in the X direction. In this embodiment, the positional offset d3 of the light-emitting element row 604 is 5 μm (equivalent to 4800 dpi).

[0039] As shown above, each light-emitting element row 604 is arranged in the Y direction. By each light-emitting element row 604 emitting light at different emission timings, an image can be formed on the same line on the photoreceptor drum 102. Figure 6(b) shows the light spots 606 of the light-emitting element row 604 when the emission timing of each light-emitting element row 604 is shifted and the same line on the photoreceptor drum 102 is exposed. The actual width of the light spot 606 will be larger than the width W1 of the light-emitting element 602 due to the effects of lens focus shifts, etc., but in this example, for the sake of simplicity, we will explain it as if the width of the light spot 606 is approximately equal to the width W1. The latent image potential formed on the photoreceptor drum 102 by the light spot 606 of each light-emitting element 602 is smooth because the adjacent light-emitting elements 602 overlap with each other, eliminating abrupt potential fluctuations between the light-emitting elements 602. If the width W1 of the light-emitting element 602 is small, the overlap of the light spots 606 decreases, creating gaps between the light spots 606 and causing image defects such as image streaks. In this embodiment, the width W1 is at least twice the positional displacement d3 of the light-emitting element row 604. As a result, the light spot 606 of the light-emitting element 602 overlaps not only with the light spot 606 of the adjacent light-emitting element 602, but also with the light spot 606 of the light-emitting element 602 two positions away. Consequently, this embodiment can increase resistance to image streaks.

[0040] (Control block) Figure 7 is a block diagram illustrating the control system of the image forming apparatus 10. The image forming apparatus 10 further includes an image controller unit 800 electrically connected to the printed circuit board 202. In this embodiment, for the sake of simplicity, the processing of a single color will be described, but the same processing may be performed in parallel with four colors simultaneously.

[0041] The image controller unit 800 transmits signals for controlling the printed circuit board 202. The signals transmitted by the image controller unit 800 include a chip select signal representing the effective range of the image data, a clock signal, image data, a line synchronization signal representing the delimiter of each line of image data, and a communication signal with the CPU 811 of the processing unit 820. Each signal is transmitted to the light-emitting element array chip 400 in the printed circuit board 202 via one of the chip select signal line 805, clock signal line 806, image data signal line 807, line synchronization signal line 808, or communication signal line 809.

[0042] The image controller unit 800 performs processing on image data and processing on printing timing. The image controller unit 800 has a processing unit 820 which includes an image data generation unit 801, a light intensity correction unit 802, a chip data conversion unit 803, a synchronization signal generation unit 804, and a CPU 811. The processing unit 820 is an example of an information processing unit. Some or all of the functions of the image data generation unit 801, the light intensity correction unit 802, the chip data conversion unit 803, and the synchronization signal generation unit 804 may be implemented by one or more circuits such as an ASIC (Application Specific Integrated Circuit) and a PLD (Programmable Logic Device) including an FPGA (Field Programmable Gate Array).

[0043] The image data generation unit 801 performs dithering on image data acquired from the scanner unit 100 or from outside the image forming apparatus 10 at a resolution instructed by the CPU 811. This allows the image data generation unit 801 to generate image data for printing. In this embodiment, the image data generation unit 801 performs dithering at a resolution of 1200 dpi in the sub-scanning direction and 4800 dpi in the main scanning direction.

[0044] The light intensity correction unit 802 performs light intensity correction on the dithered image data based on the light intensity correction value obtained from the CPU 811. The light intensity correction unit 802 inserts and removes image data for each main scan position within the chip to correct variations in light intensity within the chip.

[0045] The synchronization signal generation unit 804 determines the line boundaries of the image data, generates a line synchronization signal, and supplies it to the line synchronization signal line 808.

[0046] The chip data conversion unit 803 divides the image data for one line into individual light-emitting element array chips 400 in synchronization with the line synchronization signal generated by the synchronization signal generation unit 804, and sends it to the printed circuit board 202 along with a clock signal and a chip select signal indicating which part of the image data will be received by which light-emitting element array chip 400.

[0047] CPU811 stands for Central Processing Unit and performs various arithmetic operations. CPU811 is an example of a first correction means and a second correction means. CPU811 generates light intensity correction data from image reading values ​​input from the scanner unit 100 and outputs the generated light intensity correction data to the light intensity correction unit 802 and the light-emitting element array chip 400. For example, CPU811 generates correction data (first correction data) that corrects the light intensity difference at the boundary between adjacent light-emitting element array chips 400. CPU811 generates correction data (second correction data) that corrects the light intensity distribution of the exposure head whose boundary light intensity difference has been corrected by the said correction data. The light-emitting element array chip 400 sets the setting current of its built-in reference current source according to instructions from CPU811 and controls the overall light intensity of the light-emitting element array chip 400.

[0048] The CPU 811 instructs the synchronization signal generation unit 804 on the time interval of the signal period, using a predetermined rotational speed of the photoreceptor drum 102, where one line period is defined as the period during which the surface of the photoreceptor drum 102 moves by a pixel size of 1200 dpi (approximately 21.2 μm) in the rotational direction. For example, when printing at a speed of 200 mm / s in the paper transport direction, the CPU 811 instructs the synchronization signal generation unit 804 on a time interval of 105.8 μs (decimal places omitted). The CPU 811 calculates the speed in the paper transport direction using the printing speed setting value (fixed value) set in the speed control unit (not shown) of the photoreceptor drum 102.

[0049] Next, the configuration of the printed circuit board 202 will be described. The printed circuit board 202 further includes a head information storage unit 810.

[0050] The head information storage unit 810 is a storage device that stores head information such as the amount of light emitted by each light-emitting element array chip 400 and the position information of the mounted element. The head information storage unit 810 is connected to the CPU 811 via a communication signal line 809.

[0051] The clock signal line 806, image data signal line 807, line synchronization signal line 808, and communication signal line 809 are connected to all light-emitting element array chips 400. The chip select signal line 805 is a bus signal with 17 lines, and it transmits signals in a one-to-one correspondence to each of the light-emitting element array chips 400-1 to 400-17. The chip data conversion unit transfers image data to the light-emitting element array chips 400 line by line based on the line synchronization signal. The 17 light-emitting element array chips 400 become capable of data writing when the chip select signal transmitted from the chip data conversion unit 803 transitions from Low to High. The chip data conversion unit 803 sequentially sets the chip select signal to High for each light-emitting element array chip 400 and transfers the image data corresponding to each light-emitting element array chip 400, thereby transferring image data line by line. After receiving the image data, the light-emitting element array chip 400 performs a light emission operation according to the image data at the timing of the next line synchronization signal input.

[0052] Figure 8 is a block diagram of the internal circuitry of the light-emitting element array chip 400. The internal circuitry of the light-emitting element array chip 400 includes a D / A 901 and reference current sources 902-1 to 902-5. When it is not necessary to distinguish between reference current sources 902-1 to 902-5, they are referred to simply as reference current source 902. The D / A 901 is a DA converter that generates an analog voltage based on data instructed by the CPU 811. The light-emitting element array chip 400 is divided into multiple blocks in the longitudinal direction, and the analog voltage generated by the D / A 901 is distributed to the reference current sources 902-1 to 902-5 of each block. Each reference current source 902 of each block generates a reference current based on the analog voltage and supplies it to the light-emitting elements 903 of the light-emitting element array chip 400. That is, the current of each light-emitting element 903 is determined by the reference current source 902 of each block. In this embodiment, an example was given in which the chip is divided into five blocks and the reference current source 902 is used. However, the number of blocks may be changed depending on the longitudinal wiring distance of the chip and the driving capability of the reference current source 902.

[0053] (Light intensity correction unit 802) Figure 9 is a block diagram illustrating the configuration of the light intensity correction unit 802. The light intensity correction unit 802 generates image data to correct density variations caused by the light intensity correction value AmA, the light intensity correction value AmB, and the spot correction value AmC. The light intensity correction value AmA corresponds to the current variation caused by variations in the circuit of each block of the light-emitting element array chip 400. The light intensity correction value AmB corresponds to the light intensity variation caused by variations in the luminous efficiency of the lens in the longitudinal direction. The spot correction value AmC corresponds to the density variation caused by variations in the longitudinal direction of the spot. The light intensity correction value AmA, the light intensity correction value AmB, and the spot correction value AmC are set and output by, for example, the CPU 811.

[0054] The light intensity correction unit 802 includes a gradation data unit 1105, a gradation-by-gradation correction unit 1106, a subtraction data unit 1107, an addition data unit 1108, and an image correction unit 1109.

[0055] The gradation data unit 1105 acquires image data that has been dithered by the image data generation unit 801. The gradation data unit 1105 reads the gradation values ​​from the acquired image data and outputs the gradation data to the gradation correction unit 1106.

[0056] The tone correction unit 1106 acquires the tone data, spot correction value AmC, and tone intensity correction table Tb output by the tone data unit 1105. The spot correction value AmC is a value used to process cases where the spot partially enlarges in the main scanning direction and the amount of density variation differs for each tone. In the tone intensity correction table Tb, a pre-set light intensity correction value AmD is associated with the spot correction value AmC and the tone data of the image data. The tone correction unit 1106 refers to the tone intensity correction table Tb and extracts the light intensity correction value AmD associated with the acquired spot correction value AmC and tone data. If the light intensity is to be increased, the tone correction unit 1106 outputs the extracted light intensity correction value AmD to the summing data unit 1108. When the gradation correction unit 1106 reduces the light intensity, it outputs the extracted light intensity correction value AmD to the subtraction data unit 1107.

[0057] The subtraction data unit 1107 calculates subtraction data to reduce the light intensity from the light intensity correction values ​​AmA, AmB, and AmD, and outputs it to the image correction unit 1109. The subtraction data unit 1107 may, for example, calculate the total value of the subtractions from the light intensity correction values ​​AmA, AmB, and AmD as the subtraction data.

[0058] The addition data unit 1108 outputs the acquired addition data to the image correction unit 1109.

[0059] The image correction unit 1109 acquires subtraction data calculated by the subtraction data unit 1107, addition data output by the addition data unit 1108, and image data that has been dithered by the image data generation unit 801. The image correction unit 1109 corrects the image using the subtraction data, addition data, and image data to generate a corrected image (hereinafter also referred to as the corrected image).

[0060] Figure 10 is a diagram illustrating the image correction process. Figure 10(a) shows an example of the image before correction (hereinafter referred to as the uncorrected image 1001). The uncorrected image 1001 shown in Figure 10(a) may be a part of the image to be corrected. Figure 10(b) is the image for correction (hereinafter referred to as the correction image 1002). Figure 10(c) is the corrected image 1003.

[0061] The image correction unit 1109 acquires an uncorrected image 1001 of a predetermined image size. The image correction unit 1109 generates a corrected image 1002 with positive and negative signs using subtraction data and addition data. Furthermore, the image correction unit 1109 processes the corrected image 1002 for the predetermined image size. For example, the image correction unit 1109 calculates the light intensity correction ratio per unit area according to either the acquired subtraction data or addition data, and selects pixels to add or subtract for the predetermined image size. Specifically, when subtracting light intensity by 4%, the image correction unit 1109 selects 4 pixels out of 10 × 10 pixels (100 pixels in total) as subtraction data, as shown in the figure. Based on the 4 selected pixels, the image correction unit 1109 performs a subtraction process on the light-emitting pixels of the uncorrected image 1001 to generate a corrected image 1003.

[0062] As an example of a method for generating a correction image shown in Figure 10(b), the image correction unit 1109 may use a threshold matrix table to determine the number and position of correction pixels for a given correction amount. In the generally known blue noise mask method, image data is generated using a threshold matrix table with high-frequency spatial frequency characteristics. In this embodiment, the image correction unit 1109 uses the blue noise mask method to generate a spatially high-frequency correction image 1002 and adds or subtracts it from the pre-correction image 1001. The image correction unit 1109 selects the pixels to be corrected by determining the correction position according to the correction amount using the threshold matrix table. In this embodiment, the threshold matrix table is 10 × 10 pixel in size and stores ON and OFF threshold data for the correction amount. If the correction amount at each pixel position exceeds the threshold of the corresponding pixel in the threshold matrix table, the image correction unit 1109 determines that the pixel is corrected ON. The image correction unit 1109 corrects the light intensity across the entire longitudinal direction by repeatedly processing the 10 × 10 pixel units described above in the longitudinal direction. The threshold matrix table used will be the same setting used repeatedly, and the image correction unit 1109 will set different correction amounts depending on the position in the longitudinal direction. Through the above operation, the image correction unit 1109 corrects the amount of light with an arbitrary correction amount for a predetermined position in the longitudinal direction.

[0063] The image correction unit 1109 can achieve high-precision light intensity correction by setting the correction resolution sufficiently fine with respect to the dot size of the uncorrected image 1001. In this embodiment, the image correction unit 1109 performs addition and subtraction on the image at 4800 dpi in the main scanning direction and 2400 dpi in the sub-scanning direction. The image unit to be processed is described as an example of 10 × 10 pixels, but the image correction unit 1109 may specify insertion and removal locations for larger images. When using the blue noise mask method, it is desirable to process with a size of 128 × 128 pixels or 256 × 256 pixels. By increasing the processing image size, it becomes possible to randomly scatter the spatial frequencies of the insertion and removal locations, which prevents the occurrence of interference moiré between the original image and the insertion and removal pixel period. In addition, the processing of the light intensity correction unit 802 is performed before that of the chip data conversion unit 803. Since the chip data conversion unit 803 divides the image data in the main scanning direction for each light-emitting element array chip 400, the light intensity correction unit 802 is better positioned upstream of the chip data conversion unit 803 in order to perform continuous processing in the main scanning direction.

[0064] (Method for generating light intensity correction data using optical measurement) In this embodiment, light intensity correction is performed by adjusting the current for each chip to compensate for variations in light intensity in the longitudinal direction, and light intensity adjustment is performed using image data for light intensity changes finer than those at the chip level. The data for correction can be obtained by measuring it during the assembly and adjustment process of the exposure head 106, or by obtaining the data within the image forming apparatus 10. The light intensity data measured during the assembly and adjustment process is stored in the head information storage unit 810 in the printed circuit board 202. The CPU 811 reads the light intensity data from the head information storage unit 810.

[0065] The CPU 811 sets the correction value for each light-emitting element array chip, calculated based on the read light intensity data, to the D / A 901. The CPU 811 sets the light intensity correction value AmA for light intensity variations finer than the width of the light-emitting element array chip to the light intensity correction unit 802. The CPU 811 may also set the light intensity correction value AmB and spot correction value AmC for current variations to the light intensity correction unit 802. As a result, the image correction unit 1109 of the light intensity correction unit 802 corrects the image.

[0066] Of the correction values ​​set by the CPU 811 in the light intensity correction unit 802, the spot correction value AmC is a component where the image spot changes locally. Therefore, under conditions where all light-emitting elements are lit, the spot correction value AmC is not measured as a component of light intensity variation. Accordingly, the CPU 811 does not use the component where the image spot changes locally in the process of calculating the setting value of D / A901. Under conditions where all light-emitting elements 602 are lit, the CPU 811 measures the light intensity value of each light-emitting element array chip and adjusts the value of D / A901 so that the light-emitting element 602 with the lowest light intensity in the light-emitting element array chip 400 reaches a predetermined target light intensity. The subtraction data unit 1107 of the light intensity correction unit 802 determines the light intensity value to be subtracted as subtraction data. If the correction amount of the image data value is large, image defects such as distortion of the dot shape will occur, so the CPU 811 determines the subtraction data to be small, for example, to the minimum value. The CPU 811 adjusts the value of the D / A 901 so that the light-emitting element 602 with the lowest light intensity within the light-emitting element array chip 400 reaches a predetermined target light intensity. As a result, the D / A 901 roughly adjusts the light intensity, and the light intensity correction unit 802 corrects only the component of light intensity variation within the plane of the light-emitting element array chip 400.

[0067] Furthermore, for components of the imaging spot that change locally, the amount of variation can be read by discretely emitting light from the light-emitting element 602. For example, the imaging spot is measured by emitting light from one light-emitting point and reading the imaging spot at the imaging position of the exposure head with a CCD (Charge Coupled Device) camera. In this embodiment, the imaging spot is measured during the assembly process, and the amount of change in the local imaging spot and its location are stored in the head information storage unit 810.

[0068] As mentioned above, light intensity can be made uniform by performing light measurements during the assembly and adjustment process. However, within the image forming apparatus 10, light intensity can also be adjusted by having the scanner unit 100 read a printed light intensity correction chart. The following describes the method of adjusting light intensity using the scanner unit 100. In the method of adjusting light intensity using the scanner unit 100, the setting value of the D / A901 is adjusted based on the result of reading the image with the scanner unit 100 and the result of detecting the density difference between the light-emitting element array chips 400. After adjusting the density difference between the light-emitting element array chips 400, the density variation across the entire longitudinal direction of the image is measured, and the CPU 811 sets the density variation as the light intensity correction value AmB, thereby making the density of the image uniform in the longitudinal direction.

[0069] (Method for generating light intensity correction data using a light intensity correction chart) <1. Correction chart, light intensity conversion method, and how to check for focus clipping> Next, we will describe how to acquire correction data within the image forming apparatus 10.

[0070] Figure 11 shows a light intensity correction chart that is printed to acquire light intensity variations. The light intensity correction chart is printed when a correction process to adjust light intensity variations is instructed via the user interface. The user reads the printed light intensity correction chart with the scanner unit 100, and light intensity correction data is generated inside the image forming apparatus 10.

[0071] The light intensity correction chart includes strip-shaped images 2101 to 2104 corresponding to four colors Y (yellow), M (magenta), C (cyan), and K (black) arranged in a strip along the longitudinal direction, and reference marks 2121 to 2124. Reference marks 2121 to 2124 are positioned corresponding to each of the images 2101 to 2104. Reference marks 2121 to 2124 are marks for identifying the position of the light-emitting element array chip 400. Each reference mark 2121 to 2124 is printed by the emission of light from the edge pixels of the light-emitting element array chip 400. In this embodiment, since 17 light-emitting element array chips 400 are arranged, reference marks 2121 to 2124 are printed corresponding to 16 locations at the boundaries of each light-emitting element array chip 400. The CPU 811 calculates the center of gravity of the reference marks 2121 to 2124 read by the scanner unit 100, thereby calculating the boundary position of each light-emitting element array chip 400. This allows for accurate calculation of the position of the light-emitting element array chip 400 relative to the image, even if there is a misalignment of the light intensity correction chart relative to the paper.

[0072] The CPU 811 converts the sensor signal (luminance signal of the CCD sensor) read by the scanner unit 100 into density information using a predetermined conversion coefficient, and then converts this density information into light intensity information. This conversion process is also called density-light intensity conversion processing. When converting from density information to light intensity information, the CPU 811 may use a conversion coefficient that has been experimentally determined in advance. The relationship between density and light intensity may change depending on the temperature and humidity conditions around the image forming apparatus 10. Therefore, the image forming apparatus 10 in this embodiment stores different conversion coefficients in advance according to the temperature and humidity conditions. This makes it possible for the image forming apparatus 10 to obtain light intensity information with high accuracy by using a conversion coefficient that corresponds to the temperature and humidity conditions. In that case, the image forming apparatus 10 also has a temperature sensor and a humidity sensor, and detects temperature information and humidity information when outputting the light intensity correction chart and uses them for correction.

[0073] If the distance between the exposure head 106 and the photosensitive drum 102 deviates from a predetermined distance, the focus of the light collected by the exposure head 106 will shift, which may cause density abnormalities. In particular, if the distance between the exposure head 106 and the photosensitive drum 102 differs at both ends of the exposure head 106, a large density difference will occur at both ends of the exposure head 106. Since the amount of density fluctuation caused by the focus shift varies depending on the image gradation and the size of the dots to be printed, it may not be possible to fully correct it with light intensity correction. In this embodiment, focus detection marks 2111 to 2118 are printed to detect the focus shift. The light intensity correction chart has focus detection marks 2111 to 2114 corresponding to colors Y, M, C, and K at the left end. The light intensity correction chart has focus detection marks 2115 to 2118 corresponding to colors Y, M, C, and K at the right end. The focus detection marks 2111 to 2118 are images where two lines extending diagonally intersect. The diagonal lines are sensitive to fluctuations in the light spot size in the main scanning direction and sub-scanning direction, and the lines disappear when the light spot becomes larger. In addition, the intersection points of the lines are printed darker than the areas outside the intersection points. By comparing the image density at the edges of focus detection marks 2115 to 2118 with the image density at the intersection points, the degree to which the light spot has enlarged can be detected. In this embodiment, the CPU 811 may determine whether the amount of light spot enlargement is within an acceptable range based on the results of reading focus detection marks 2115 to 2118 by the scanner unit 100, and if it is outside the acceptable range, it may terminate the series of light intensity adjustment operations and notify the user of the abnormal state by image or sound.

[0074] <2. Explanation of the correction process: After correcting the difference in light intensity between chips, long-period variations are corrected.> Figure 12 is a flowchart of the correction process that generates correction data to correct the light intensity. When the user instructs the CPU 811 to start the density variation correction process via a user interface such as a touch panel, the CPU 811 starts the correction process.

[0075] In S2201, CPU811 prints and outputs the light intensity correction chart shown in Figure 11, and then proceeds to S2202.

[0076] In S2202, the CPU 811 receives a scan start command and determines whether or not to start scanning. For example, a user places the outputted light intensity correction chart into the scanner unit 100 and commands to start scanning via the user interface. When the CPU 811 receives the scan start command from the user, it determines that scanning should start and proceeds to S2203. The CPU 811 remains in standby mode until it determines that scanning should start.

[0077] In S2203, CPU811 performs a scan on the light intensity correction chart, obtains light intensity information from the reading results of the light intensity correction chart, and calculates the light intensity. Proceed to S2204. The light intensity information may be light intensity or density information for calculating light intensity. The specific calculation of light intensity will be described later.

[0078] In S2204, the CPU 811 calculates the difference in light intensity at the boundaries between the light-emitting element array chips 400, calculates correction data (an example of first correction data) to correct the difference in light intensity, and corrects the difference in light intensity between the light-emitting element array chips 400 by setting the D / A 901 that supplies the drive current to each light-emitting element array chip 400.

[0079] Figure 13 shows the light intensity distribution of the exposure head 106 in the longitudinal direction of the light-emitting element array chip 400 before correction. Figure 14 shows the light intensity distribution of the exposure head 106 in the longitudinal direction of the light-emitting element array chip 400 after correction. The vertical axis in Figures 13 and 14 represents the light intensity of the light-emitting element array chip 400. The horizontal axis in Figures 13 and 14 represents the position of the light-emitting element array chip 400 in the longitudinal direction. Therefore, Figures 13 and 14 show the light intensity distribution at each position of the light-emitting element array chip 400. The dashed lines in Figures 13 and 14 indicate the boundaries between adjacent light-emitting element array chips 400. Therefore, the area between the dashed lines represents a single light-emitting element array chip 400. Note that the correction referred to in Figures 13 and 14 is the correction of the light intensity difference at the boundaries of the light-emitting element array chip 400.

[0080] In this embodiment, since there are 17 light-emitting element array chips 400 in the exposure head 106, the light intensity distribution for 17 chips is obtained. However, to simplify the diagram, Figure 13 shows the light intensity distribution for the central 7 chips. In the light intensity distribution before correction shown in Figure 13, a steep difference in light intensity occurs at the boundaries of the light-emitting element array chips 400, indicated by the dashed lines. In S2204, the CPU 811 generates correction data to reduce the difference in light intensity between the light-emitting element array chips 400 and corrects the light intensity. As a result, in the corrected light intensity distribution shown in Figure 14, the steep difference in light intensity at the boundaries of the light-emitting element array chips 400, indicated by the dashed lines, is corrected, reducing the step at the boundary and making the boundary smoother.

[0081] The following steps, S2205-S2207, involve the same processing as S2201-S2203, so we will explain them in a simplified manner.

[0082] In S2205, the CPU 811 prints the light intensity correction chart shown in Figure 11 and proceeds to S2206. Here, the CPU 811 corrects the light intensity of the light-emitting element array chip 400 using the correction data calculated in S2204, and prints the light intensity correction chart with the boundary light intensity difference reduced.

[0083] In S2206, CPU811 waits until it receives a command from the user to start the scan. Once CPU811 receives the command from the user to start the scan, it decides to start the scan and proceeds to S2207.

[0084] In S2207, the CPU 811 performs a scan on the light intensity correction chart, obtains light intensity information from the reading results of the light intensity correction chart, and proceeds to S2208. Here, the CPU 811 scans the printed light intensity correction chart, which has been corrected based on the correction data generated in S2204, to obtain light intensity information. Therefore, the light intensity information obtained by the CPU 811 is a smooth light intensity distribution without any steps at the boundaries of the light-emitting element array chip 400, as shown in Figure 14.

[0085] In S2208, the CPU 811 calculates and sets correction data (an example of second correction data) to correct the light intensity distribution of multiple predetermined sample areas within the light-emitting element array chip 400 based on the light intensity information. The light intensity distribution to be corrected is the light intensity distribution spanning multiple light-emitting element array chips 400. Here, the light intensity distribution to be corrected is the light intensity distribution spanning all light-emitting element array chips 400, in other words, the overall light intensity distribution of the exposure head 106. The CPU 811 sets this correction data for the light intensity distribution as the correction data for the light intensity correction value AmB, which corrects for light intensity variation.

[0086] As described above, in this embodiment correct the difference in light quantity at the boundaries between the light-emitting element array chips 400, and then correct the overall light quantity distribution of the exposure head 106 based on the light quantity correction chart printed based on this correction. The CPU 811 corrects gentle fluctuations by correcting the overall light quantity distribution of the exposure head 106, making the light quantity distribution closer to flat. For example, the CPU 811 generates correction data approximating the overall light quantity distribution of the exposure head 106 with a quadratic function or the like. The quadratic function mentioned here is, for example, a function showing the relationship between the position in the longitudinal direction of the exposure head 106 and the light quantity at that position. In this embodiment, first, by correcting the sharp difference in light quantity at the boundaries between the light-emitting element array chips 400, the approximation accuracy when approximating the light quantity distribution can be improved.

[0087] <Method of Averaging in Sub-Scanning Direction for Obtaining Intra-Chip Light Quantity Information in S2203> FIG. 15 is a diagram of the light quantity distribution before correction within the light-emitting element array chip 400 acquired in S2203. In this embodiment, the scanner unit 100 scans a light quantity correction chart that is a two-dimensional strip-shaped image, and the CPU 811 calculates one-dimensional light quantity information corresponding to the position in the longitudinal direction within the exposure head 106 from the two-dimensional light quantity correction chart.

[0088] FIG. 16 is a diagram for explaining the sample area and dot influence for each light-emitting element array chip 400. FIG. 16(a) is a diagram of two-dimensional image information corresponding to one acquired light-emitting element array chip 400 by the scanner unit 100. In this embodiment, the image area corresponding to one light-emitting element array chip 400 is divided in two directions: the longitudinal direction of the exposure head 106 and the direction (hereinafter referred to as the orthogonal direction) intersecting (here, perpendicular) with the longitudinal direction of the exposure head 106. As a result, the image area is divided into sample areas arranged two-dimensionally. Specifically, the image area is divided into 18 sample areas in the longitudinal direction of the exposure head 106 and 12 sample areas in the orthogonal direction. The orthogonal direction is an example of an intersecting direction. When the average density of each sample area is detected, the CPU 811 converts the light quantity for each sample area from the average density by the above-described density-light quantity conversion process.

[0089] Through the following process, the CPU 811 calculates the light amounts of the columns of 18 sample areas arranged in the longitudinal direction of the exposure head 106. The sample area columns are columns extending in the orthogonal direction. The CPU 811 deletes at least the sample areas of the maximum value and the minimum value (here, the values of the light amount or density) among the 12 sample areas arranged in the orthogonal direction. In the present embodiment, the CPU 811 deletes the sample areas having the first and second largest values and the first and second smallest values of the light amount or density among the 12 sample areas arranged in the orthogonal direction. The CPU 811 calculates the average value of the light amount of each of the 18 sample areas in the longitudinal direction as the light amount of the sample areas in the longitudinal direction based on the remaining 8 sample areas in the orthogonal direction that were not excluded among the 12 sample areas arranged in the orthogonal direction of the exposure head 106. For example, the CPU 811 performs an averaging process on the data of 8 sample areas excluding the two with the largest magnitudes and the two with the smallest magnitudes among the data of the light amounts of the 12 sample areas p1-1 to p1-12, and calculates the average value as the light amount of the sample areas of the sample area column p1. Note that the CPU 811 may calculate the average of the density and then calculate the light amount instead of the light amount.

[0090] FIG. 16(b) shows a state in which dots Dt are printed unintentionally due to factors such as dirt on the light amount correction chart. In cases where extra dots Dt are printed on the chart and cases where the image is white and missing, an error occurs in the calculation result of the light amount. Therefore, as described above, the CPU 811 excludes the top two and bottom two in terms of the magnitude of the light amount (or density) in the sample area column in the orthogonal direction including 12 sample areas, so that even if unintentional dots Dt are printed, the occurrence of a detection error in the light amount can be suppressed.

[0091] <S2204 First inter-chip light amount difference calculation method Measures for density variation and streaks> Figure 17 shows the light intensity distribution of 18 sample area rows corresponding to one light-emitting element array chip 400. Here, a sample area row is a row of sample areas extending in an orthogonal direction. For example, sample area row p1 is a row of sample areas including sample areas p1-1 to p1-12.

[0092] The CPU 811 calculates the light intensity at the left and right edges of each of the 18 sample area rows p1 to p18 within the light-emitting element array chip 400, which were calculated in S2203. Since the outermost sample area rows p1 and p18 may detect the density of the image printed by the adjacent light-emitting element array chip 400, the CPU 811 excludes sample area rows p1 and p18 from the calculation of their light intensity. In other words, the CPU 811 uses the second and subsequent sample area rows p2, p3, etc., or sample area rows p17, p16, etc., to calculate the light intensity of the left and right edge sample area rows p1 and p18, respectively. Here, the CPU 811 uses the three sample area rows at the left and right edges, excluding the outermost left and right sample area rows p1 and p18, to calculate the light intensity of the left and right edge sample area rows p1 and p18, respectively. Specifically, the CPU 811 calculates the light intensity of the leftmost sample area column p1 using the three leftmost sample area columns p2 to p4, excluding sample area column p1 of the light-emitting element array chip 400. The CPU 811 calculates the light intensity of the rightmost sample area column p18 using the data from the rightmost sample area columns p17 to p15, excluding sample area column p18 of the light-emitting element array chip 400. As a calculation method, the CPU 811 may perform an approximate calculation using the three sample area columns, such as the least squares method, to calculate the light intensity of the sample area columns at both the left and right ends of the light-emitting element array chip 400. By using a linear or quadratic function as the approximation formula, the CPU 811 can accurately determine the light intensity at both ends, even if there is a concentration difference within the light-emitting element array chip 400 due to long-period concentration variations.

[0093] Here, the image printed by the image forming apparatus 10 may include vertical streaks due to various factors within the apparatus. FIG. 18 is a diagram showing the light quantity distribution in a case where vertical streaks occur in the image. In this example, the sample area columns p15 and p16 obtain a higher light quantity than the surrounding sample area columns. When the CPU 811 calculates the light quantity at the right end portion of the light emitting element array chip 400 using the sample area columns p15 and p16, the error in the light quantity becomes large. Therefore, in such a case, the CPU 811 derives an approximation formula from the sample area columns p17, p14, and p13, excluding the sample area columns p15 and p16, among the sample area columns starting from the second column after the end portion. As a method of exclusion, the CPU 811 calculates an approximation formula by the least squares method for the light quantities of the sample area columns p2 to p17, and excludes the sample area columns with a light quantity exceeding a predetermined allowable range of ±δA (the range of limit1 and limit2 in the figure). Further, the CPU 811 newly sets the same number of sample area columns as the excluded sample area columns in the central direction of the light emitting element array chip 400 from the excluded sample area columns (sample area columns p13 and p14 in FIG. 18). Therefore, the CPU 811 extracts the sample area columns with a light quantity within the allowable range of ±δA among the sample area columns starting from the second column after the end portion (here, the right end portion) in the order close to the end portion, and calculates the light quantity of the sample area column p18 at the end portion.

[0094] A <S2204 Second method for calculating the light quantity difference between chips Align the left and right while keeping the center of the exposure head constant> In this embodiment, the CPU 811 uses the light intensity at both ends of each light-emitting element array chip 400 calculated by the process described above to determine the drive current value for each light-emitting element array chip 400 so as to minimize the difference in light intensity between each light-emitting element array chip 400. If the adjustment amount of the drive current between each light-emitting element array chip 400 becomes too large, the density of the entire image may fluctuate (become too dark or too light). Therefore, in order to minimize the adjustment amount of the drive current, the CPU 811 determines the light intensity correction value for each light-emitting element array chip 400 so as to correct the difference in light intensity between the left and right light-emitting chips, using the central chip of the exposure head 106 as a reference.

[0095] Figure 19 is a plan view showing the arrangement of the light-emitting element array chips 400. Referring to Figure 19, the correction of the light intensity at the boundaries of adjacent light-emitting element array chips 400 will be explained. Figure 19(a) shows the area for calculating the light intensity of the seven central light-emitting element array chips 400. First, the CPU 811 derives the light intensity at the left and right edges of the central light-emitting element array chip 400 from the light intensity (or density) of area D9_L and area D9_R. The CPU 811 may determine the method for calculating the light intensity by the calculation of the 18 sample area columns of the light-emitting element array chip 400 as described above.

[0096] The CPU 811 corrects the set light intensity of the light-emitting element array chip 400-8 based on the difference between the light intensity of area D9_L at the left end of the light-emitting element array chip 400-9 and the light intensity of area D8_R at the right end of the light-emitting element array chip 400-8. For example, the CPU 811 may add or subtract this difference from the set light intensity of the light-emitting element array chip 400-8 to obtain the corrected set light intensity. Here, the relationship between light intensity and drive current is assumed to be converted using a predetermined conversion coefficient. As described above, the CPU 811 overwrites the set value of the D / A901 of the light-emitting chip 8 with the calculated drive current in order to control the light intensity.

[0097] Similarly, CPU811 calculates the light intensity of the light-emitting element array chip 400-10 by adding or subtracting the difference between the light intensity of area D9_R at the right edge of the light-emitting element array chip 400-9 and the light intensity of area D10_L at the left edge of the light-emitting element array chip 400-10 to the set light intensity of the light-emitting element array chip 400-10 before correction.

[0098] Figure 19(b) is a diagram illustrating the light intensity of the light-emitting element array chips 400 other than those on either side of the central light-emitting element array chip 400-9. Areas D7_R, D8_L, D10_R, and D11_L are areas for calculating the difference in light intensity to correct the light intensity of light-emitting element array chips 400-7 and 400-11.

[0099] The CPU 811 sequentially calculates the light intensity of the light-emitting element array chips 400-8 and 400-10 by starting from the difference in light intensity at the edges. The CPU 811 corrects the light intensity of the light-emitting element array chip 400-7 based on the difference in light intensity between area D7_R and area D8_L. The CPU 811 corrects the light intensity of the light-emitting element array chip 400-11 based on the difference in light intensity between area D10_R and area D11_L. The CPU 811 performs a similar process, and using the light-emitting element array chip 400-9 in the center of the exposure head 106, it sequentially calculates the light intensity of the light-emitting element array chips 400 along the left-right direction and corrects the light intensity of light-emitting element array chips 400-1 to 400-17.

[0100] Figure 20 is a block diagram showing the hardware configuration of the processing unit 820. The processing unit 820 is, for example, a computer. The processing unit 820 has a processor 2001, memory 2002, storage 2003, communication IF 2004, input IF 2005, output IF 2006, and bus 2007. The processor 2001, memory 2002, storage 2003, communication IF 2004, input IF 2005, and output IF 2006 are connected to each other via bus 2007 so that data can be input and output.

[0101] Processor 2001 includes a CPU 811. Processing unit 820 may have other processors such as an MPU (Micro Processing Unit), a GPU (Graphics Processing Unit), and a QPU (Quantum Processing Unit) in place of or in addition to the CPU 811. Processor 2001 may function as a first correction means and a second correction means by executing a program.

[0102] Some or all of the functions of the image data generation unit 801, the light intensity correction unit 802, the chip data conversion unit 803, and the synchronization signal generation unit 804 may be implemented by one or more processors 2001, including the CPU 811, reading a program stored in the storage 2003, expanding it into the memory 2002, and executing it.

[0103] Memory 2002 is a high-speed read-and-write storage device. Memory 2002 may be, for example, RAM (Random Access Memory). Memory 2002 functions as a work area when the processor 2001 executes a program.

[0104] Storage 2003 is a non-volatile, high-capacity storage device. Storage 2003 may be, for example, ROM (Read Only Memory), HDD (Hard Disk Drive), or SSD (Solid State Drive). Storage 2003 stores programs such as correction processes executed by processor 2001, parameters necessary for program execution, and image data to be processed by the programs.

[0105] Communication IF2004 is an interface for connecting to an external network. Communication IF2004 may be an interface for wireless communication or an interface for wired communication, and is not particularly limited to these.

[0106] Input IF2005 is an interface connected to an input device. Input IF2005 is connected to input devices such as a user interface, mouse, keyboard, touchpad, or scanner unit 100. Input IF2005 outputs user instructions and other information received from the input device to processor 2001.

[0107] Output IF2006 is an interface connected to an output device. Output IF2006 is connected to an output device such as an image display device, such as a display. Output IF2006 outputs data such as image data acquired from the CPU 811 of processor 2001 to the output device.

[0108] As described above, the image forming apparatus 10 of this embodiment generates correction data to correct the steep light intensity difference at the boundary between adjacent light-emitting element array chips 400, and corrects the light intensity distribution of the exposure head 106, which has been corrected for the boundary light intensity difference (light intensity step) using this correction data. As a result, this embodiment can improve the accuracy of the correction and improve the image quality after correction compared to the case in which the light intensity distribution of the exposure head 106 is corrected while leaving the steep light intensity difference at the boundary.

[0109] In this embodiment, when calculating the light intensity of a sample area row, the average value of the light intensity of the sample area row, excluding at least the maximum and minimum values, is calculated as the light intensity of the sample area row. As a result, this embodiment can remove outliers in the light intensity due to noise, etc., and thus improve the accuracy of calculating the light intensity of the sample area row.

[0110] In this embodiment, the light intensity of the sample area rows at the edge of the light-emitting element array chip 400 is calculated based on the light intensity of the sample area rows from the second row onward from the edge. This makes it possible to improve the accuracy of calculating the light intensity of the sample area rows at the edge, which are susceptible to the influence of adjacent light-emitting element array chips 400.

[0111] In this embodiment, the light intensity at the edge of the light-emitting element array chip 400 is calculated based on the light intensity of the sample area rows from the second row onward at the edge, where the light intensity is within a predetermined tolerance range. As a result, this embodiment can remove outliers in light intensity due to noise, etc., thereby improving the accuracy of calculating the light intensity of the sample area rows at the edge.

[0112] In this embodiment, the light intensity is corrected sequentially from the central light-emitting element array chip 400 to the end light-emitting element array chip 400 in the direction in which the multiple light-emitting element array chips 400 are arranged. As a result, this embodiment can reduce the difference in light intensity before and after correction compared to correcting from the end light-emitting element array chip 400, and thus reduce the difference in image before and after correction.

[0113] In this embodiment, a quadratic function is generated as correction data that makes the overall light intensity distribution, according to the position of the exposure head 106, closer to flat, thereby reducing the size of the correction data.

[0114] In this embodiment, correction data is generated by scanning a light intensity correction chart printed with the same image data, for both boundary correction and overall correction of the light intensity distribution of the exposure head 106. This allows this embodiment to reduce the size of the image data.

[0115] (Other embodiments) The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. Furthermore, the present invention can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0116] The disclosures herein include the following information processing devices, image forming apparatuses, control methods, and programs. (Item 1) An information processing device that generates correction data for correcting the light intensity of an image forming apparatus having an exposure head having multiple light-emitting array chips each having multiple light-emitting elements, A first correction means for generating first correction data to correct the difference in light intensity at the boundary between adjacent light-emitting element array chips, A second correction means for generating second correction data to correct the light intensity distribution of the exposure head corrected by the first correction data, An information processing device characterized by comprising: (Item 2) The first correction means generates the first correction data such that the difference in light intensity at the boundaries between adjacent light-emitting element array chips among the plurality of light-emitting element array chips becomes smaller. The information processing device described in item 1, characterized by the features described herein. (Item 3) The first correction means calculates the difference in light intensity and generates the first correction data based on the light intensity data obtained by scanning the first correction image. An information processing device as described in item 1 or item 2. (Item 4) The first correction means is, The light intensity of multiple sample areas is calculated by dividing the image area of ​​the multiple light-emitting element array chips into two dimensions along multiple rows along the direction in which the multiple light-emitting element array chips are arranged, and along multiple columns intersecting the rows. The average value of the light intensity, excluding at least the maximum and minimum values ​​of each row in the sample area, is calculated as the light intensity of the rows in the multiple sample areas. The first correction data is calculated based on the amount of light. An information processing device according to any one of items 1 to 3, characterized by the above. (Item 5) The first correction means calculates the light intensity of a column containing the plurality of sample areas at the end facing the boundary of the light-emitting element array chip based on the light intensity of the columns containing the plurality of sample areas from the second column onward from that end. The information processing device described in item 4, characterized by the features described herein. (Item 6) The first correction means calculates the light intensity of the sample area column at the end based on the light intensity of the sample area column from the second column onward from the end, where the light intensity is within a predetermined tolerance range. The information processing device described in item 5, characterized by the features described herein. (Item 7) The first correction means corrects the light intensity in the direction in which the plurality of light-emitting element array chips are arranged, starting from the central light-emitting element array chip and progressing to the end light-emitting element array chips. An information processing device according to any one of items 1 to 6, characterized by the above. (Item 8) The second correction means generates the second correction data so as to make the overall light intensity distribution, according to the position in the exposure head, as flat as possible. An information processing device according to any one of items 1 to 7, characterized by the above. (Item 9) The second correction means generates a quadratic function as the second correction data that makes the light intensity distribution closer to flat. The information processing device described in item 8, characterized by the features described herein. (Item 10) The second correction means generates the second correction data based on the amount of light obtained by scanning a second image, which is printed using the same image data as the first image based on the first correction data. The information processing device described in item 3, characterized by the features described herein. (Item 11) The information processing device described in item 1, The exposure head controlled by the information processing device, A photoreceptor drum in which an electrostatic latent image is formed by the exposure head, An image forming apparatus having (Item 12) A control method for generating correction data to correct the light intensity of an image forming apparatus having an exposure head having multiple light-emitting array chips each having multiple light-emitting elements, A first correction step generates first correction data to correct the difference in light intensity at the boundary between adjacent light-emitting element array chips, A second correction step is to generate second correction data for correcting the light intensity distribution of the exposure head corrected by the first correction data, A control method characterized by comprising: (Item 13) A program to cause a computer to function as one of the means of an information processing device described in any one of items 1 through 10.

[0117] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of Symbols]

[0118] 10...Image forming apparatus, 102...Photoreceptor drum, 106...Exposure head, 400...Light-emitting element array chip, 602, 903...Light-emitting elements, 604...Light-emitting element row, 606...Light spot, 800...Image controller unit, 820...Processing device, 811...CPU, 1...Processor, 2101, 2104...Image, p1-p18...Sample area row.

Claims

1. An information processing device that generates correction data for correcting the light intensity of an image forming apparatus having an exposure head having multiple light-emitting array chips each having multiple light-emitting elements, A first correction means for generating first correction data to correct the difference in light intensity at the boundary between adjacent light-emitting element array chips, A second correction means for generating second correction data to correct the light intensity distribution of the exposure head corrected by the first correction data, Equipped with, The first correction means calculates the difference in light intensity and generates the first correction data based on the light intensity data obtained by scanning the first correction image. An information processing device characterized by the following:

2. The first correction means generates the first correction data such that the difference in light intensity at the boundaries between adjacent light-emitting element array chips among the plurality of light-emitting element array chips becomes smaller. The information processing apparatus according to feature 1.

3. The first correction means is, The light intensity of multiple sample areas obtained by dividing the image area of ​​the multiple light-emitting element array chips into two dimensions along multiple rows along the direction in which the multiple light-emitting element array chips are arranged, and along multiple columns intersecting the rows, is calculated. The average value of the light intensity, excluding at least the maximum and minimum values ​​of each row in the sample area, is calculated as the light intensity of the rows in the multiple sample areas. The first correction data is calculated based on the amount of light. The information processing apparatus according to feature 1.

4. The first correction means calculates the light intensity of a column containing the plurality of sample areas at the end facing the boundary of the light-emitting element array chip based on the light intensity of the columns containing the plurality of sample areas from the second column onward from that end. The information processing apparatus according to claim 3.

5. The first correction means calculates the light intensity of the sample area column at the end based on the light intensity of the sample area column from the second column onward from the end, where the light intensity is within a predetermined tolerance range. The information processing apparatus according to feature 4.

6. The first correction means corrects the light intensity in the direction in which the plurality of light-emitting element array chips are arranged, starting from the central light-emitting element array chip and progressing to the end light-emitting element array chips. The information processing apparatus according to feature 1.

7. The second correction means generates the second correction data so as to make the overall light intensity distribution, according to the position in the exposure head, as flat as possible. The information processing apparatus according to feature 1.

8. The second correction means generates a quadratic function as the second correction data that makes the light intensity distribution closer to flat. The information processing apparatus according to feature 7.

9. The second correction means generates the second correction data based on the amount of light obtained by scanning a second image, which is printed using the same image data as the first image based on the first correction data. The information processing apparatus according to feature 1.

10. The information processing apparatus according to claim 1, The exposure head controlled by the information processing device, A photoreceptor drum in which an electrostatic latent image is formed by the exposure head, An image forming apparatus having

11. A control method for generating correction data to correct the light intensity of an image forming apparatus having an exposure head having multiple light-emitting array chips each having multiple light-emitting elements, A first correction step generates first correction data to correct the difference in light intensity at the boundary between adjacent light-emitting element array chips, A second correction step is to generate second correction data for correcting the light intensity distribution of the exposure head corrected by the first correction data, Equipped with, The first correction step generates the first correction data by calculating the difference in light intensity based on the light intensity data obtained by scanning the first correction image. A control method characterized by the following:

12. A program for causing a computer to function as one of the means of an information processing device described in any one of claims 1 to 9.

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