JP2024055601A - Image forming device - Google Patents

Abstract

[Problem] To provide an improved mechanism for preventing degradation of image quality caused by variations in the overlap range between ends of light-emitting chips. [Solution] An image forming section of an image forming device includes an exposure head having a plurality of light-emitting chips arranged in a staggered pattern along a first direction parallel to a rotation axis of a photoconductor. Each light-emitting chip of the exposure head includes a plurality of light-emitting elements arranged parallel to the first direction. Adjacent first and second light-emitting chips are arranged such that K light-emitting elements located at a first end of the first light-emitting chip and K light-emitting elements located at a second end of the second light-emitting chip overlap in the first direction. A control section of the image forming device determines the number K using a read image of a calibration chart and controls so that the number K of light-emitting elements does not emit light. An image of the calibration chart is formed by driving a first light-emitting element group at a first current value and a second light-emitting element group at a second current value in each light-emitting chip. [Selected Figure] Figure 12

Description

The present invention relates to an image forming device.

A solid-state exposure type device is commonly known as a type of electrophotographic image forming device, which forms a latent image by exposing a photosensitive drum to light emitted by an LED (e.g., an organic EL element) rather than laser light. The exposure head of this type of device includes a light-emitting element group including multiple light-emitting elements arranged parallel to the rotation axis of the photosensitive drum, and a rod lens array that focuses the light from the light-emitting element group onto the surface of the photosensitive drum. Compared to the laser scanning type, the solid-state exposure type image forming device has the advantage that it is easy to reduce the size and cost of the device.

Patent Document 1 discloses a configuration in which, in an exposure head of a solid-state exposure type image forming device, multiple light-emitting chips, each having multiple LEDs, are arranged in a staggered pattern along a direction parallel to the rotation axis of a photosensitive drum. A 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. Patent Document 2 discloses a technology that assumes a similar staggered arrangement and reads a printed image of a test chart to measure the density difference and corrects the light amount for each light-emitting chip based on the measurement results in order to suppress uneven density caused by differences in the amount of light between adjacent light-emitting chips.

JP 2017-183436 A JP 2018-001679 A

When adopting the above-mentioned staggered arrangement of light-emitting chips, it is necessary to overlap the ends of adjacent light-emitting chips in the direction of the rotation axis so that the line parallel to the rotation axis of the photosensitive drum is covered without any gaps, and then appropriately control the light emission of the light-emitting elements in the overlapping range. However, the length of the overlapping range differs for each device due to misalignment of the light-emitting chips, or may vary even in the same device due to the influence of conditions such as temperature. If the light emission of the light-emitting elements is not appropriately controlled in accordance with such variations in the overlapping range, undesirable streaks will appear in the printed image, and the quality of the printed image will be reduced. The test chart described in Patent Document 2 did not take into account the variations in the overlapping range between the ends of adjacent light-emitting chips.

The present invention aims to provide an improved mechanism for preventing degradation of image quality caused by variations in the overlap range between the ends of light-emitting chips.

According to one aspect, a method for manufacturing a sheet-type ... The control unit causes the image forming unit to form an image of a calibration chart, and determines the number K of overlapping light-emitting elements using a read image of the calibration chart obtained by optically reading the formed image, and controls light emission by the exposure head so that the determined number K of light-emitting elements of one of the first light-emitting chip and the second light-emitting chip do not emit light. The image of the calibration chart is formed by driving a first group of light-emitting elements at a known position in the first direction among the multiple light-emitting elements of each of the multiple light-emitting chips with a first current value, and driving a second group of light-emitting elements different from the first group of light-emitting elements with a second current value different from the first current value.

The present invention makes it possible to prevent degradation of image quality caused by variations in the overlap range between the ends of the light-emitting chips.

1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment; FIG. 2 is an explanatory diagram of a configuration of a photoconductor and an exposure head according to the embodiment. FIG. 4 is an explanatory diagram of the configuration of a printed circuit board of an exposure head according to an embodiment. 3A and 3B are explanatory views of a light-emitting chip and a light-emitting element group in the light-emitting chip according to an embodiment. FIG. 1 is a plan view showing a schematic configuration of a light-emitting chip according to an embodiment. 1 is a cross-sectional view showing a schematic configuration of a light-emitting element according to an embodiment. FIG. 13 is an explanatory diagram of multiple exposure using light-emitting elements arranged in a stepped pattern. 11A and 11B are explanatory diagrams for explaining light emission control of light-emitting elements in an overlapping area between light-emitting chips. 11A and 11B are diagrams illustrating degradation of print image quality caused by fluctuations in the length of the overlapping range. FIG. 2 is a configuration diagram of a control circuit related to light emission control of the light emitting chip. FIG. 2 is a block diagram showing a configuration of a circuit related to current supply in the light-emitting chip. FIG. 4 is an explanatory diagram showing an example of an image of a calibration chart according to an embodiment. 13 is an explanatory diagram for determining an overlapping range using a read image of the calibration chart in FIG. 12 . 13 is an explanatory diagram for determining an overlapping range using a scanned image of another calibration chart. 10 is a flowchart showing an example of the flow of a calibration process that can be executed in an embodiment.

The following embodiments are 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 multiple features, not all of these multiple features are necessarily essential to the invention, and multiple 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 duplicate explanations are omitted.

1. General configuration of image forming apparatus
1 shows an example of a schematic configuration of an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 includes a reading unit 100, an image creating unit 103, a fixing unit 104, and a conveying unit 105. The reading unit 100 optically reads an original placed on a platen and generates read image data. The image creating unit 103 forms an image on a sheet based on the read image data generated by the reading unit 100, or based on print image data received from an external device via a network, for example.

The image forming unit 103 has 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 according to image data to form an electrostatic latent image on the surface of the photoconductor 102. The developer 108 develops the electrostatic latent image on the surface of the photoconductor 102 with toner 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 to a sheet in an overlapping manner, a color image containing four color components, black, yellow, magenta, and cyan, can be formed.

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 the 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 to the sheet. As described above, the toner image is transferred to the sheet while the sheet is being conveyed on the transfer belt 111. The fixing unit 104 fixes the toner image to the sheet by heating and pressurizing the sheet to which the toner image has been transferred. After the toner image is fixed, the sheet is discharged to the outside of the image forming apparatus 1 by the discharge roller 112. An optical sensor 113 is disposed at a position opposite the transfer belt 111. The optical sensor 113 is used to detect positional misalignment (color misalignment) between color components of the test image formed on the transfer belt 111 by the image forming unit 101. If color misalignment is detected, the image forming positions of the image forming units 101a, 101b, 101c, and 101d are corrected to compensate for the detected color misalignment under the control of the image controller 800 described later.

Note that, 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 disclosed herein can also be applied to an image forming apparatus that forms a monochrome image using toners of a single color.

2. Exposure head configuration example
2A and 2B show the photoconductor 102 and the exposure head 106. The exposure head 106 has a group of light-emitting elements 201, a printed circuit board 202 on which the group of light-emitting elements 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 so that its longitudinal direction is parallel to the rotation axis 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 around the rotation axis, the group of light-emitting elements 201 of the exposure head 106 emits light, and the rod lens array 203 forms an image of the light on the surface of the photoconductor 102. In this specification, the direction parallel to the rotation axis of the photoconductor 102 is also referred to as the first direction D1, and the direction perpendicular to the first direction D1 on the surface of the printed circuit board 202 (approximately parallel to the circumferential direction of the photoconductor 102) is also referred to as the second direction D2.

3(A) and 3(B) show an example of the configuration of the printed circuit board 202. Note that FIG. 3(A) shows the surface on which the connector 305 is mounted, and FIG. 3(B) shows the surface on which the light-emitting element group 201 is mounted (the surface opposite to the surface on which the connector 305 is mounted). In this embodiment, the printed circuit board 202 of the exposure head 106 includes 20 light-emitting chips 400-1 to 400-20 arranged in a staggered manner along the first direction D1. In this specification, when it is not necessary to distinguish the light-emitting chips 400-1 to 400-20 from one another, the latter branch numbers of the reference numbers are omitted, and these are collectively referred to as the light-emitting chips 400. The same applies to the branch numbers of the reference numbers of the other components. As shown in FIG. 3(B), 10 light-emitting chips 400 form one row when n is an odd number, and another 10 light-emitting chips 400 form another row when n is an even number, and the positions of these two rows in the second direction D2 are different. In the following description, the light-emitting chips 400 in the former row are also referred to as odd-numbered light-emitting chips 400, and the light-emitting chips 400 in the latter row are also referred to as even-numbered light-emitting chips 400. Each light-emitting chip 400 on the printed circuit board 202 is connected to the image controller 800 (see FIG. 10) via a connector 305. For convenience of description, the side with the smaller branch number of the light-emitting chips 400-1 to 400-20 aligned along the first direction D1 may be referred to as the "left" and the side with the larger branch number as the "right". For example, the light-emitting chip 400-1 is the leftmost light-emitting chip 400, and the light-emitting chip 400-20 is the rightmost light-emitting chip.

Figure 4 shows a schematic diagram of the light-emitting chip 400 and the arrangement of the light-emitting elements 602 in the light-emitting chip 400. Each light-emitting chip 400 includes at least a plurality of light-emitting elements 602 arranged parallel to the first direction D1. Specifically, in this embodiment, the light-emitting element array of each light-emitting chip 400 is a two-dimensional array including M rows of a plurality of light-emitting elements 602 arranged parallel to the first direction D1, and in the example of Figure 4, M = 4. The number of light-emitting elements 602 in each row may be, for example, 748. In this case, each light-emitting chip 400 has a total of 2992 (= 748 x 4) light-emitting elements 602. In the entire light-emitting element group 201 consisting of 20 light-emitting chips 400, 14960 light-emitting elements are arranged in the first direction D1. The pitch of adjacent light-emitting elements 602 in the first direction D1 may be about 21.16 μm, which corresponds to a resolution of 1200 dpi. In this case, the length of the entire light-emitting element group 201 in the first direction D1 is about 316 mm (the maximum width of the image that can be formed), and the length of each light-emitting chip 400 in the first direction D1 is about 15.8 mm. In addition, any two light-emitting elements adjacent to each other in the second direction D2 are shifted from each other in the first direction D1 by a shift amount of about 5 μm corresponding to a resolution of 4800 dpi, so that the light-emitting element array of each light-emitting chip 400 shows a stepped arrangement. The shift amount here corresponds to the pitch d3 described later (see FIG. 7). FIG. 4 shows an example in which the lower light-emitting element of the two upper and lower light-emitting elements is shifted to the left, but the lower light-emitting element may also be shifted to the right.

Furthermore, the first and second light-emitting chips 400 adjacent to each other in the first direction D1 are arranged such that K light-emitting elements located at the first end of the first light-emitting chip 400 and K light-emitting elements located at the second end of the second light-emitting chip 400 overlap in the first direction D1. Here, K is a non-negative integer. For example, when focusing on a pair of adjacent odd-numbered light-emitting chips 400 and even-numbered light-emitting chips 400, the arrangement of K light-emitting elements 602 from the right end of the former and K light-emitting elements 602 from the left end of the latter overlap in the first direction D1. In FIG. 4, the light-emitting elements 602 in the overlapping range are shown by shading, and the number K of light-emitting elements 602 of one light-emitting chip 400 in the overlapping range is K=4. Although not shown in FIG. 4, the relationship between the light-emitting elements 602 in the rightmost row of the adjacent even-numbered light-emitting chips 400 and the light-emitting elements 602 in the leftmost row of the odd-numbered light-emitting chips 400 is also similar. By overlapping the arrangement of the light-emitting element arrays in the first direction D1 in this way, even if the light-emitting chips are misaligned or the substrate expands thermally, the lines of the image along the first direction D1 can be reliably covered without gaps. The distance Ly between the light-emitting element arrays of the two rows of light-emitting chips 400 may be, for example, about 105 μm.

Note that FIG. 4 shows an example in which the number M of rows of light-emitting elements arranged in the second direction D2 in each light-emitting chip 400 is 4; however, this is not limited to this example, and M may be any integer equal to or greater than 1.

Figure 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. The light-emitting substrate 402 is also provided with a circuit section 406 for driving the light-emitting elements 602. The pads 408 are used to connect signal lines for communicating with the image controller 800, power lines for connecting to a power source, and ground lines for connecting to ground to the circuit section 406. The signal lines, power lines, and ground lines may be wires made of, for example, gold.

Figure 6 shows a part of the cross section taken along line A-A in Figure 5. A plurality of lower electrodes 504 are formed on the light-emitting substrate 402. A light-emitting layer 506 is provided on the lower electrodes 504, and an upper electrode 508 is provided on the light-emitting layer 506. The upper electrode 508 is a common electrode for the plurality of lower electrodes 504. When a voltage is applied between the lower electrode 504 and the upper electrode 508, a current flows from the lower electrode 504 to the upper electrode 508, causing the light-emitting layer 506 to emit light. Therefore, one lower electrode 504 and a partial region of the light-emitting layer 506 and upper electrode 508 corresponding to the lower electrode 504 constitute one light-emitting element 602. dx in the figure is the distance between two adjacent lower electrodes 504. dz is the distance between the lower electrode 504 and the upper electrode 508. By making dx larger than dz, it is possible to suppress leakage current between adjacent lower electrodes 504 and prevent light-emitting elements 602 that should not emit light from erroneously emitting light.

In this embodiment, each light-emitting element 602 may be configured as an organic electro-luminescence (EL) element. For example, an organic EL film may be used for the light-emitting layer 506. In other embodiments, each light-emitting element 602 may be configured as an inorganic EL element by using an inorganic EL film for the light-emitting layer 506. In general, each light-emitting element 602 may be any type of light-emitting diode (LED).

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. In the example of FIG. 6, the entire upper electrode 508 transmits the emission wavelength of the light-emitting layer 506, but the entire upper electrode 508 does not necessarily have to transmit the emission wavelength. Specifically, it is sufficient that a partial area through which light from each light-emitting element 602 passes transmits the emission wavelength.

6, one continuous light-emitting layer 506 is formed, but a plurality of light-emitting layers 506 each having a width equal to the width of the lower electrode 504 may be formed on the lower electrode 504. Also, 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 equal to the width of the lower electrode 504 may be formed corresponding to each of the lower electrodes 504. Also, 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. Even in such a configuration, one lower electrode 504 and the region of the light-emitting layer 506 and upper electrode 508 corresponding to the lower electrode 504 constitute one light-emitting element 602.

<3. Multiple Exposure>
By adopting the solid-state exposure method, it becomes easy to reduce the size and cost of the device, but the amount of light that a single light-emitting element (e.g., an organic EL element) can emit may be insufficient to form an image of a desired density. Therefore, in this embodiment, a multiple exposure technique is adopted in which each pixel area (spot area) on the photoconductor 102 is exposed in a multiple manner by sequentially emitting light from a plurality of light-emitting elements 602 arranged in the second direction.

7 is an explanatory diagram of multiple exposure by light-emitting elements arranged in a stepped pattern. R _{j _m} (j={1, 2, ..., N}, m={1, 2, 3, 4}) in the figure represents the light-emitting element 602 in the jth column from the left in the first direction and the mth row from the bottom in the second direction. W1 in the figure represents the width of the light-emitting element 602 in the first direction, and W2 represents the width of the light-emitting element 602 in the second direction. d1 represents the interval between adjacent light-emitting elements 602 in the first direction, and d2 represents the interval between adjacent light-emitting elements 602 in the second direction. d1 and d2 are the above-mentioned electrode distance dx divided into two coordinate axes, and both are determined to be wider than the interval dz between the upper electrode and the lower electrode. As described above, the minimum pitch d3 of the light-emitting elements 602 in the first direction may be about 5 μm (equivalent to 4800 dpi).

In the stepped light-emitting element array as shown in the example of FIG. 7, four light-emitting elements arranged in the second direction sequentially emit light while the photoconductor 102 is rotating, and spots corresponding to each pixel position are formed on the surface of the photoconductor 102. In the example of FIG. 7, when the pixel value at the left end of the i-th line of the input image data indicates light emission on, the light-emitting elements R _{1_1} , R _{1_2} , R _{1_3} , and R _{1_4} sequentially emit light at the timing when they face the line L _i on the surface of the photoconductor 102, respectively. As a result, the spot area at the left end of the line L _i is exposed in a multiple manner, and the corresponding spot SP ₁ is formed. Similarly, when the j-th pixel value from the left of the i-th line of the input image data indicates light emission on, the light-emitting elements R _{j_1} , R _{j_2} , R _{j_3} , and R _{j_4} sequentially emit light at the timing when they face the line L _i on the surface of the photoconductor 102, respectively. As a result, the j-th spot area from the left of the line L _i is exposed in a multiple manner, and the corresponding spot SP _j is formed. If the pitch of the light-emitting elements in the second direction is about 21.16 μm and the sheet conveying speed is 200 mm/s, the period (line period) in which each line is exposed by one light-emitting element R _{j_m} can be about 105.8 μs. In this way, the four rows of light-emitting elements of the 20 light-emitting chips 400 emit light sequentially at appropriate times, so that a smooth line of an electrostatic latent image consisting of a series of spots that have a certain spot interval and partially overlap each other can be formed on the surface of the photoconductor 102. Then, as a result of such lines being continuously formed in the circumferential direction, a two-dimensional electrostatic latent image is created.

<4. Change in the length of the overlapping range>
4, in this embodiment, any pair of two adjacent light-emitting chips 400 in the first direction are arranged such that one end of one light-emitting chip 400 of the pair overlaps one end of the other light-emitting chip 400 in the first direction. The length of the overlapping range may be the product of the number K of light-emitting elements 602 in the overlapping range and the arrangement pitch of the light-emitting elements 602.

For the sake of simplicity, FIG. 8 shows an example in which the light-emitting chip 400-1 and the light-emitting chip 400-2 have only one row of light-emitting elements 602. The light-emitting chip 400-1 includes a plurality of light-emitting elements 602-1, and the light-emitting chip 400-2 includes a plurality of light-emitting elements 602-2. The two light-emitting elements 602-1 at the right end (first end) of the light-emitting chip 400-1 overlap in the first direction with the two light-emitting elements 602-2 at the left end (second end) of the light-emitting chip 400-2. That is, the number K of light-emitting elements 602 in the overlapping range is K=2. During image formation, for example, the two light-emitting elements 602-1 at the right end of the light-emitting chip 400-1 are controlled not to emit light, and the spot of the pixel corresponding to the overlapping range is formed by the two light-emitting elements 602-2 at the left end of the light-emitting chip 400-2 emitting light. This allows a uniform image to be formed on the sheet 700 through the formation of a latent image on the photoconductor 102, development, and transfer of the toner image to the sheet.

However, the length of the overlapping range may differ from device to device due to misalignment when mounting the light-emitting chip 400 on the exposure head 106. Furthermore, the length of the overlapping range may vary even for the same device due to the influence of conditions such as temperature. Figure 9 is an explanatory diagram for explaining the deterioration in quality of the printed image caused by such variation in the length of the overlapping range.

In the example of Fig. 9A, as a result of the mounting position of the light-emitting chip 400-2 being shifted to the left (arrow Z1 in the figure), the number K of the light-emitting elements 602 in the overlapping range is K = 3. At this time, if only the two light-emitting elements 602-1 at the right end of the light-emitting chip 400-1 are controlled not to emit light as in the example of Fig. 8, the density of the pixel PX _a at the position corresponding to the left end of the light-emitting chip 400-2 becomes excessively high in the image formed on the sheet 700. If such lines are formed continuously in the second direction, high-density (e.g., black) streaks appear in the printed image.

In the example of Fig. 9B, as a result of the mounting position of the light-emitting chip 400-2 being shifted to the right (arrow Z2 in the figure), the number K of the light-emitting elements 602 in the overlapping range becomes K = 1. At this time, if the two light-emitting elements 602-1 at the right end of the light-emitting chip 400-1 are controlled not to emit light as in the example of Fig. 8, the density of the pixel _PXb at the position corresponding to the left end of the light-emitting chip 400-2 becomes excessively low in the image formed on the sheet 700. If such lines are formed continuously in the second direction, low-density (e.g., white) streaks appear in the printed image.

In this embodiment, the image controller 800 has a function of causing the image forming units 101-a to 101-d to form an image of the calibration chart in order to prevent the deterioration of the quality of the printed image described above. The image of the calibration chart is used to determine the number K of light-emitting elements 602 in the overlapping range at each boundary between the light-emitting chips 400 by reading it. The number K is determined using the read image of the calibration chart, and the light emission of the light-emitting elements 602 is appropriately controlled, thereby suppressing the appearance of streaks in the printed image.

5. Image Controller Configuration
<5-1. Basic configuration example>
10 shows an example of the configuration of a control circuit related to the light emission control of the light emitting chip 400. Note that, for the sake of simplicity, the processing for a single color component will be described here, but in reality, the same processing is performed in parallel for four color components.

The image controller 800 shown on the left of FIG. 10 is a control unit for controlling the formation of an image by the image forming unit 101. The image controller 800 is connected to each of the light-emitting chips 400 on the printed circuit board 202 via multiple signal lines 805-809. The chip select signal line 805 carries a chip select signal CS that indicates the effective range of the image data. The clock signal line 806 carries a clock signal CLK. The data signal line 807 carries image data DATA. The synchronization signal line 808 carries a line synchronization signal Lsync for identifying the line period of the image data. The communication signal line 809 carries a control signal CTL.

The image data generating unit 801 performs image processing on the image data received from the reading unit 100 or an external device to generate binary bitmap image data for controlling the on/off of the light emitting element 602 of the light emitting chip 400 on the printed circuit board 202. The image processing here may include, for example, raster conversion and halftone processing (e.g., dithering). The image data after halftone processing is a set of bits indicating whether or not to emit light from the corresponding M light emitting elements 602 for each pixel position constituting the image to be formed. When a bit at a pixel position indicates "emission", the corresponding spot area on the surface of the photoconductor 102 is multiplexedly exposed by the M light emitting elements 602. When the bit indicates "non-emission", the corresponding spot area is not exposed. The image data generating unit 801 outputs the generated image data to the chip data converting unit 802.

The chip data conversion unit 802 reads out pixel values within the corresponding readout range of the image data input from the image data generation unit 801 in each line period identified by the line synchronization signal Lsync, and sends image data indicating the readout pixel values to the data signal line 807. The image data DATA is, for example, a sequence of pixel values corresponding to the light-emitting elements 602 of the 20 light-emitting chips 400. The chip data conversion unit 802 specifies which light-emitting chip 400 should receive each portion of the image data DATA by the chip select signal CS. The chip data conversion unit 802 generates a clock signal CLK and supplies it to each light-emitting chip 400 in order to synchronize the timing of transmission and reception of individual signal values with each light-emitting chip 400.

The synchronization signal generation unit 804 determines the line divisions of the image data, generates a line synchronization signal Lsync, and supplies the generated line synchronization signal Lsync to the synchronization signal line 808.

The storage unit 810 of the printed circuit board 202 is a memory (e.g., a non-volatile memory) that stores control data for controlling light emission by each light emitting chip 400. The control data stored in the storage unit 810 may include, for example, one or more of the following:
Setting values related to the amount of drive current (for example, predetermined current values V ₁ and V ₂ described later)
A determination result of the number K for each boundary between the light-emitting chips 400 A group of known parameters used to determine the number K (for example, predetermined distances L ₁ , L ₂ , . . . and a predetermined pitch P, which will be described later)

Each light-emitting chip 400 drives each of the light-emitting elements 602 according to image data input from the chip data conversion unit 802 in each line period identified by the line synchronization signal Lsync. For example, when the chip select signal CS indicates the timing to receive data intended for the light-emitting chip, each light-emitting chip 400 receives a portion of the image data DATA intended for the chip via the data signal line 807. Then, each light-emitting chip 400 drives each light-emitting element 602 in the light-emitting element array according to the pixel value included in the received image data.

The CPU 811 controls the entire image forming apparatus 1. For example, when executing a job for normal image formation, the CPU 811 causes the image data generating unit 801 to generate the above-mentioned image data, and causes the chip data converting unit 802 to send the image data to the printed circuit board 202. Prior to executing the job, the CPU 811 reads out the latest value of the number K determined for each boundary between the light-emitting chips 400 from the storage unit 810. Then, the CPU 811 controls the generation of image data by the image data generating unit 801 so that the K light-emitting elements 602 at one end of the adjacent light-emitting chips 400 do not emit light (for example, causes a bit indicating "non-emission" to be inserted for the corresponding light-emitting element 602).

When the calibration function is called, the CPU 811 controls the printed circuit board 202 to form an image of the calibration chart. The image of the calibration chart can be formed, for example, by driving a first group of light-emitting elements of the plurality of light-emitting elements 602 of each light-emitting chip 400 with a first current value, and driving a second group of light-emitting elements different from the first group of light-emitting elements with a second current value. The second current value is a value different from the first current value, and therefore the image of the calibration chart shows a striped pattern. The number of light-emitting elements 602 included in the first group of light-emitting elements and the positions of the light-emitting elements 602 in the first direction D1 are determined in advance and are known. Therefore, by reading the image of the calibration chart formed and detecting the position of the image area formed by the first group of light-emitting elements of each light-emitting chip 400, it is possible to determine the length of the overlapping range between two adjacent light-emitting chips 400. The first current value and the second current value may both be non-zero, or one of the current values may be zero. By setting one of the current values to zero, the contrast of the image of the calibration chart becomes clear, making it easier to detect the position of a specific image area.

Figure 11 is a block diagram showing the configuration of a circuit related to the supply of current in the light-emitting chip 400. Each light-emitting chip 400 includes a digital-to-analog converter (D/A) 901, a plurality of (five in the example of Figure 11) reference current sources 902-1 to 902-5, and a plurality of light-emitting elements 602. Each light-emitting element 602 is supplied with current from one of the reference current sources 902-1 to 902-5 depending on the position of the light-emitting element 602 in the first direction. That is, in the example of Figure 11, the circuit of each light-emitting chip 400 is divided into a plurality of circuit blocks each including one reference current source 902 and a corresponding plurality of light-emitting elements 602.

The D/A 901 performs digital-to-analog conversion of the digital value of the reference current set by the CPU 811, and outputs an analog signal having a voltage according to the set value to each reference current source 902. The set value of the reference current is stored in advance in the above-mentioned storage unit 810, read by the CPU 811, and output to the D/A 901. Each of the reference current sources 902-1 to 902-5 supplies a reference current according to the voltage of the analog signal input from the D/A 901 to the light-emitting element 602. In this way, the function of being able to control the supply amount (current value) of the drive current for each circuit block in each light-emitting chip 400 is called a shading function. The above-mentioned calibration chart may be formed using this shading function. In this case, for example, the first light-emitting element group may be a collection of light-emitting elements 602 to which a current is supplied from the reference current source 902-3, and the second light-emitting element group may be a collection of light-emitting elements 602 to which a current is supplied from another reference current source 902.

The number of reference current sources 902 (i.e., the number of circuit blocks) provided in each light-emitting chip 400 is not limited to the above example, and may be any number depending on the length of the wiring within the chip or the driving capacity of the reference current sources 902.

<5-2. Examples of calibration charts and determining the number K>
FIG. 12 shows an example of an image of a calibration chart that can be formed on a sheet in this embodiment. In the example of FIG. 12, the calibration chart 610 has first image areas 611-1, 611-2, ... and second image areas 612-1, 612-2 that are alternately repeated in the first direction D1. The i-th first image area 611-i from the left is an image area formed by driving the first light-emitting element group 603-i of the i-th light-emitting chip 400-i with a first current value. In this embodiment, since there are 20 light-emitting chips 400, the calibration chart 610 has 20 first image areas 611. The position of the first light-emitting element group 603 in each light-emitting chip 400 is known, and in the example of FIG. 12, the position of the first light-emitting element group 603 is in the non-boundary portion of the light-emitting chip 400 in the first direction D1. The i-th second image area 612-i from the left is an image area formed by driving the second light-emitting element group 604-(i-1) on the right side of the i-1th light-emitting chip 400-(i-1) and the second light-emitting element group 604-i on the left side of the i-th light-emitting chip 400-i with a second current value. The calibration chart 610 has 21 second image areas 612. However, in the case of i=1, the i-1th light-emitting chip 400-(i-1) does not exist, and in the case of i=21, the i-th light-emitting chip 400-i does not exist.

As an example, the first current value may be non-zero and the second current value may be zero. In this example, the second light-emitting element group 604 driven with a current value of zero does not emit light, and the second image area 612 becomes a blank area. In this case, if there are few light-emitting elements 602 driven with the first current value, the toner image in the first image area 611 may become unclear, and the accuracy of detecting the position of the first image area 611 may decrease. Therefore, it is desirable to include a sufficient number of light-emitting elements 602 in the first light-emitting element group 603 of each light-emitting chip 400.

Figure 13 is an explanatory diagram for explaining a method for determining the number K of light-emitting elements 602 in the overlapping range using a scanned image of the calibration chart 610. Note that, here, attention is focused on the relationship between the first adjacent light-emitting chip 400-1 and the second adjacent light-emitting chip 400-2. The following explanation applies to the relationship between any two adjacent light-emitting chips 400.

For example, in response to an instruction to perform calibration being given via the user interface of the image forming device 1, the CPU 811 causes the image forming unit 101 to form an image of the calibration chart 610 on a sheet. The user or engineer sets the sheet on which the image of the calibration chart 610 has been formed in the reading unit 100 and instructs the reading of the image. The reading unit 100 optically reads the image of the calibration chart 610 and generates a read image. The CPU 811 acquires the read image of the calibration chart 610 from the reading unit 100. This read image becomes an input for determining the number K at each boundary between the light-emitting chips 400.

The CPU 811 detects the position of the first image area 611-1 formed by the first light-emitting element group 603-1 of the first light-emitting chip 400-1 in the first direction D1 in the read image of the calibration chart 610. The CPU 811 also detects the position of the first image area 611-2 formed by the first light-emitting element group 603-2 of the second light-emitting chip 400-2 in the first direction D1. The detected position of each first image area 611 may be, for example, the position of the geometric center of gravity of the image area. The CPU 811 measures the interval L _MES between the detected position of the first image area 611-1 and the detected position of the first image area 611-2 in the first direction D1. Here, the first distance L ₁ between the right end of the first light-emitting chip 400-1 and the representative position (for example, the center in the first direction D1) of the first light-emitting chip of the light-emitting chip is a known value determined by design. Similarly, the second distance _L2 between the left end of the second light-emitting chip 400-2 and the representative position of the first light-emitting element group 603-2 of the light-emitting chip is also a known value determined by design. These values are stored in advance in the storage unit 810, for example. The CPU 811 determines the number K of the light-emitting elements 602 in the overlapping range between the first light-emitting chip 400-1 and the second light-emitting chip 400-2 based on the interval L _MES measured in the read image of the calibration chart 610, as well as the first distance _L1 and the _second distance L2. For example, the CPU 811 can calculate the length L _OV of the overlapping range between the first light-emitting chip 400-1 and the second light-emitting chip 400-2 according to the following formula (1):

_LOV = ( _L1 + _L2 ) - _LME (1)

Equation (1) means that the length L _OV of the overlapping range is equal to the difference between the sum of the first distance L ₁ and the second distance L ₂ minus the interval L _MES between the detection positions. Then, the CPU 811 can calculate the number K of the light-emitting elements 602 in the overlapping range among the light-emitting elements 602 of each light-emitting chip 400 according to the following equation (2):

K = round (L _OV / P) (2)

Here, P represents the pitch of the arrangement of the light-emitting elements 602 in the first direction D1. In addition, round() is a function that rounds off the argument and returns an integer value. When the stepped light-emitting element arrangement described with reference to FIG. 7 is adopted, the pitch P may be equal to the shift amount d3. That is, the number K is determined by dividing the length L _OV of the overlapping range by the pitch P. The pitch P or the shift amount d3 is also a known value determined by design and is stored in advance in the storage unit 810. Since the first distance L ₁ , the second distance L ₂ and the pitch P are all strictly determined when each light-emitting chip 400 is designed/manufactured by a semiconductor process, if the interval L _MES can be measured with high accuracy, the number K can be calculated with high accuracy.

Depending on the characteristics of the reading unit 100 (e.g., the configuration of the image sensor), it may be possible to achieve higher reading accuracy by detecting a low-density image area rather than detecting a high-density image area. In that case, instead of the calibration chart 610 described using FIG. 12 and FIG. 13, a calibration chart 620 shown in FIG. 14 may be used. In the example of FIG. 14, the calibration chart 620 has first image areas 621-1, 621-2, ... and second image areas 622-1, 622-2 that are alternately repeated in the first direction D1. The first image area 621-i, which is the i-th image area from the left, is an image area formed by driving the first light-emitting element group of the i-th light-emitting chip 400-i with a first current value. The second image area 622-i, which is the i-th image area from the left, is an image area formed by driving the second light-emitting element group on the right side of the i-1th light-emitting chip 400-(i-1) and the second light-emitting element group on the left side of the i-th light-emitting chip 400-i with a second current value.

As an example, the second current value may be non-zero and the first current value may be zero. In this example, the first light-emitting element group driven with a current value of zero does not emit light, and the first image area 621 becomes a blank area. In this case, if there are few light-emitting elements 602 driven with the second current value, the toner image in the second image area 622 may become unclear, and the accuracy of detecting the position of the second image area 622 may decrease. Therefore, it is desirable to include a sufficient number of light-emitting elements 602 in the second light-emitting element group of each light-emitting chip 400.

Even when the calibration chart 620 is employed, the number K of light-emitting elements 602 in the overlapping range between the first and second light-emitting chips 400 can be determined through equations (1) and (2) based on the known values of the distances L ₁ , L ₂ and pitch P, as well as the measured spacing L _MES .

In the above, an example was described in which the position of the geometric center of gravity of the image area was detected as the detection position of the image area, but the position of an end point (on one of the left and right sides) may be detected instead of the center of gravity. Also, in the above, an example was described in which the shading function of each light-emitting chip 400 was used to make the drive current value different between the first light-emitting element group and the second light-emitting element group, but the light-emitting/non-light-emitting state may be switched for each light-emitting element without using the shading function. However, controlling the drive current value for each circuit block using the shading function makes it easier to miniaturize the circuit scale and is advantageous in terms of manufacturing costs.

The CPU 811 stores the value of the number K determined in this manner for each boundary between two adjacent light-emitting chips 400 in the storage unit 810. When a job for image formation is subsequently executed, as described above, the CPU 811 reads out the latest value of the number K from the storage unit 810. Then, the CPU 811 controls the light emission of the light-emitting elements 602 in the exposure head 106 so that the K light-emitting elements 602 at the end of one of the light-emitting chips 400 at each boundary do not emit light.

The rounding operation in equation (2) means that the resolution of the overlap range adjustment is limited by the pitch P. However, when the pitch P is equal to the shift amount d3 = approximately 5 μm in the stepped light-emitting element array for the above-mentioned multiple exposure, for example, the width of streaks that may appear in the printed image after the overlap range adjustment does not exceed 5 μm. It is known that streaks less than 5 μm are almost imperceptible to the human eye. Therefore, the adjustment resolution in this case is sufficient from the perspective of preventing a subjective deterioration in image quality.

Here, when a normal image forming job is executed, when the input image data expressed in the digital domain is converted into a data signal to be output to the exposure head, the K light emitting elements in the overlapping range are ignored (controlled not to emit light). In contrast, the above-mentioned calibration chart is for determining the number K of light emitting elements in the overlapping range as an unknown variable, and is therefore not suitable for converting image data into a data signal in the same manner as a normal image forming job. Therefore, in this embodiment, instead of providing the calibration chart as image data in the digital domain like the test chart described in Patent Document 2, an image of the calibration chart is formed by driving the light emitting element group of each light emitting chip 400 with a predetermined current value. This makes it possible to accurately measure the interval L _MES according to the actual physical positional relationship between the light emitting chips 400.

<6. Calibration process flow>
15 is a flowchart showing an example of the flow of a calibration process that can be executed in this embodiment. The calibration process shown in FIG. 15 is started when, for example, a user issues an instruction to execute calibration via a user interface of the image forming apparatus 1.

First, in S11, the CPU 811 of the image controller 800 causes the image forming unit 101 to form an image of the calibration chart 610. Specifically, under the control of the CPU 811, the first light-emitting element group 603 of the light-emitting elements 602 of each light-emitting chip 400 is driven with a first current value _V1 , and the second light-emitting element group 604 is driven with a second current value _V2 , and as a result, the image of the calibration chart 610 is formed on a sheet.

Next, in S12, the CPU 811 waits for an instruction to read the image of the calibration chart 610. When a reading instruction is received from the user or engineer who has placed the sheet on which the image of the calibration chart 610 is formed in the reading unit 100, the process proceeds to S13.

In S13, the CPU 811 causes the reading unit 100 to read the image of the calibration chart 610. Specifically, the reading unit 100 optically reads the sheet placed on the platen, generates a read image of the calibration chart 610, and outputs the generated read image to the CPU 811.

Next, in S14, the CPU 811 detects the position of the first image area 611 formed by the first light-emitting element group 603 of each light-emitting chip 400 in the read image of the calibration chart 610, and measures the distance L _MES between each detection position and the adjacent detection position.

Next, in S15, the CPU 811 determines the number K of light-emitting elements 602 in the overlapping range for each pair of two adjacent light-emitting chips 400 based on the spacing L _MES measured in S14 and known parameters (e.g., distances L ₁ , L ₂ , ... and pitch P).

Next, in S16, the CPU 811 stores the value of the number K determined in S15 for each pair of two adjacent light-emitting chips 400 in the storage unit 810 as control data for light emission control.

<7. Summary>
Various embodiments have been described in detail above with reference to Figs. 1 to 15. According to the above-described embodiment, the number K of light-emitting elements in the overlapping range between the light-emitting chips in the staggered arrangement of the light-emitting chips of the exposure head employing the solid-state exposure method is determined using the read image of the calibration chart. The image of the calibration chart is formed by driving a first light-emitting element group at a known position among the multiple light-emitting elements of each light-emitting chip with a first current value, and driving a second light-emitting element group different from the first light-emitting element group with a second current value different from the first current value. Therefore, even if the overlapping range fluctuates due to the influence of the mounting misalignment of the light-emitting chips or conditions such as temperature, the number K of light-emitting elements in the overlapping range after the fluctuation can be accurately determined, and the light emission by the exposure head can be controlled so that the quality of the printed image does not deteriorate.

In the above-described embodiment, the number K is determined based on the distance between the detection position of the image area corresponding to the first light-emitting element group of the first light-emitting chip and the detection position of the image area corresponding to the first light-emitting element group of the second light-emitting chip in the read image of the calibration chart. In this case, what needs to be measured in the read image is only the distance between the image areas repeated in the stripe pattern. Therefore, the above-mentioned number K can be determined quickly with a small amount of calculation for each boundary between the light-emitting chips. In particular, in the above-described embodiment, the first light-emitting element group is located in the non-boundary portion of each light-emitting chip. In this case, since there is only one boundary between the image areas corresponding to the first light-emitting element groups of two adjacent light-emitting chips, the calculation for determining the above-mentioned number K for each boundary can be further simplified.

In the above embodiment, specific numerical values are used for the purpose of 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 can be any number greater than or equal to 1. Furthermore, the size of the light-emitting element array of each light-emitting chip 400 is not limited to 4×748, and can be any other size. Furthermore, the circumferential pitch and axial pitch of the light-emitting elements are not limited to approximately 21.16 μm and approximately 5 μm, and can be any other value.

8. Other embodiments
The above-described embodiment can also be realized in the form of a process in which a program for implementing 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. Also, the embodiment can be realized by a circuit (e.g., ASIC) for implementing one or more functions.

The above embodiment includes at least the following image forming apparatus.
(Item 1)
an image forming unit that forms an image on a sheet;
A control unit that controls the formation of an image by the image forming unit;
Equipped with
The image forming unit includes:
A rotating photoconductor;
an exposure head having a plurality of light-emitting chips arranged in a staggered pattern along a first direction parallel to a rotation axis of the photosensitive member, the exposure head including a plurality of light-emitting chips each including a plurality of light-emitting elements arranged at least parallel to the first direction;
Including,
A first light emitting chip and a second light emitting chip adjacent to each other in the first direction among the plurality of light emitting chips are arranged such that K light emitting elements (K is a non-negative integer) located at a first end of the first light emitting chip and K light emitting elements located at a second end of the second light emitting chip overlap each other in the first direction,
The control unit is
forming an image of a calibration chart on the image forming unit;
determining the number K of the overlapping light-emitting elements using a read image of the calibration chart obtained by optically reading the formed image;
controlling light emission by the exposure head so that the determined number K of light emitting elements of one of the first light emitting chips and the second light emitting chips does not emit light;
the image of the calibration chart is formed by driving a first group of light-emitting elements at a known position in the first direction among the plurality of light-emitting elements of each of the plurality of light-emitting chips with a first current value, and driving a second group of light-emitting elements different from the first group of light-emitting elements with a second current value different from the first current value;
Image forming device.
(Item 2)
The control unit determines the number K of overlapping light-emitting elements based on the distance between the detection position of an image area formed by the first group of light-emitting elements of the first light-emitting chip and the detection position of an image area formed by the first group of light-emitting elements of the second light-emitting chip in the read image of the calibration chart.
(Item 3)
3. The image forming apparatus of claim 2, wherein the known positions of the first light-emitting element group are in non-boundary portions of each light-emitting chip in the first direction.
(Item 4)
The image forming apparatus described in item 3, wherein the control unit determines the number K of overlapping light-emitting elements based on a first distance between the first end of the first light-emitting chip and a representative position of the first light-emitting element group of the first light-emitting chip, a second distance between the second end of the second light-emitting chip and a representative position of the first light-emitting element group of the second light-emitting chip, and the interval between the detection positions in the read image of the calibration chart.
(Item 5)
5. The image forming apparatus according to claim 4, wherein the number K is determined by dividing the difference obtained by subtracting the interval between the detection positions from the sum of the first distance and the second distance by a predetermined pitch of the plurality of light-emitting elements.
(Item 6)
Each of the plurality of light emitting chips includes M rows (M is an integer equal to or greater than 1) of light emitting elements arranged in a second direction perpendicular to the first direction,
Any two light emitting elements adjacent to each other in the second direction are shifted from each other by a predetermined shift amount in the first direction;
The predetermined pitch is equal to the predetermined shift amount.
Item 6. The image forming apparatus according to item 5.
(Item 7)
An image forming device described in any one of items 2 to 6, wherein the detection position of the image area formed by the first light-emitting element group of each light-emitting chip in the read image of the calibration chart corresponds to the geometric center of gravity of the image area.
(Item 8)
8. The image forming apparatus according to claim 1, wherein one of the first current value and the second current value is zero.
(Item 9)
In each light emitting chip, the first light emitting element group and the second light emitting element group belong to different circuit blocks;
Each light emitting chip is configured to be able to control the drive current of the light emitting element for each circuit block.
9. The image forming apparatus according to any one of items 1 to 8.
(Item 10)
10. The image forming apparatus according to any one of items 1 to 9, wherein each of the plurality of light-emitting elements is an organic EL (Electro Luminescence) element.
(Item 11)
The image forming apparatus includes:
a reading unit that optically reads the image of the calibration chart formed by the image forming unit and generates the read image of the calibration chart;
11. The image forming apparatus according to any one of items 1 to 10, further comprising:

The invention is not limited to the above-described embodiment, and various modifications and variations are possible without departing from the spirit and scope of the invention. Therefore, the following claims are appended to disclose the scope of the invention.

1: image forming apparatus, 101 (101-a to 101-d): image forming section, 102: photoconductor, 106: exposure head, 201: light emitting element group, 202: printed circuit board, 203: rod lens array, 204: housing, 400 (400-1 to 400-20): light emitting chip, 602: light emitting element, 603 (603-1, 603-2, ...): first light emitting element group, 604 (604-1, 604-2, ...): Second light-emitting element group, 610: calibration chart, 611 (611-1, 611-2, ...): first image area, 612 (612-1, 612-2, ...): second image area, 620: calibration chart, 621 (621-1, 621-2, ...): first image area, 622 (622-1, 622-2, ...): second image area, 800: image controller (control unit), D1: first direction, D2: second direction, L ₁ : first distance, L ₂ : second distance, L _MES : interval, L _OV : length of overlapping range

Claims (11)

an image forming unit that forms an image on a sheet;
A control unit that controls the formation of an image by the image forming unit;
Equipped with
The image forming unit includes:
A rotating photoconductor;
an exposure head having a plurality of light-emitting chips arranged in a staggered pattern along a first direction parallel to a rotation axis of the photosensitive member, the exposure head including a plurality of light-emitting chips each including a plurality of light-emitting elements arranged at least parallel to the first direction;
Including,
A first light emitting chip and a second light emitting chip adjacent to each other in the first direction among the plurality of light emitting chips are arranged such that K light emitting elements (K is a non-negative integer) located at a first end of the first light emitting chip and K light emitting elements located at a second end of the second light emitting chip overlap each other in the first direction,
The control unit is
forming an image of a calibration chart on the image forming unit;
determining the number K of the overlapping light-emitting elements using a read image of the calibration chart obtained by optically reading the formed image;
controlling light emission by the exposure head so that the determined number K of light emitting elements of one of the first light emitting chips and the second light emitting chips does not emit light;
the image of the calibration chart is formed by driving a first group of light-emitting elements at a known position in the first direction among the plurality of light-emitting elements of each of the plurality of light-emitting chips with a first current value, and driving a second group of light-emitting elements different from the first group of light-emitting elements with a second current value different from the first current value;
Image forming device. The image forming device according to claim 1, wherein the control unit determines the number K of overlapping light-emitting elements based on the distance between the detection position of the image area formed by the first light-emitting element group of the first light-emitting chip and the detection position of the image area formed by the first light-emitting element group of the second light-emitting chip in the read image of the calibration chart. The image forming device according to claim 2, wherein the known positions of the first light-emitting element group are in non-border portions of each light-emitting chip in the first direction. The image forming device according to claim 3, wherein the control unit determines the number K of the overlapping light-emitting elements based on a first distance between the first end of the first light-emitting chip and a representative position of the first light-emitting element group of the first light-emitting chip, a second distance between the second end of the second light-emitting chip and a representative position of the first light-emitting element group of the second light-emitting chip, and the interval between the detection positions in the read image of the calibration chart. The image forming device according to claim 4, wherein the number K is determined by dividing the difference obtained by subtracting the interval between the detection positions from the sum of the first distance and the second distance by a predetermined pitch of the plurality of light-emitting elements. Each of the plurality of light emitting chips includes M rows (M is an integer equal to or greater than 1) of light emitting elements arranged in a second direction perpendicular to the first direction,
Any two light emitting elements adjacent to each other in the second direction are shifted from each other in the first direction by a predetermined shift amount,
The predetermined pitch is equal to the predetermined shift amount.
The image forming apparatus according to claim 5 . The image forming device according to claim 2, wherein the detection position of the image area formed by the first light-emitting element group of each light-emitting chip in the read image of the calibration chart corresponds to the geometric center of gravity of the image area. The image forming device according to claim 1, wherein one of the first current value and the second current value is zero. In each light emitting chip, the first light emitting element group and the second light emitting element group belong to different circuit blocks;
Each light emitting chip is configured to be able to control the drive current of the light emitting element for each circuit block.
The image forming apparatus according to claim 1 . The image forming device according to claim 1, wherein each of the plurality of light-emitting elements is an organic EL (Electro Luminescence) element. The image forming apparatus includes:
a reading unit that optically reads the image of the calibration chart formed by the image forming unit and generates the read image of the calibration chart;
The image forming apparatus according to any one of claims 1 to 10, further comprising:

Images