Image forming apparatus

Abstract

The image forming apparatus includes: an exposure head comprising multiple light-emitting units, each light-emitting unit including a first electrode layer, a light-emitting layer, and a second electrode layer, the first electrode layer including multiple electrodes arranged two-dimensionally in a main scanning direction and a sub-scanning direction, the light-emitting layer being stacked on the first electrode layer, and light being able to pass through the second electrode layer; and a controller controlling the application of a voltage to each of the multiple electrodes, causing the light-emitting layer to emit light. The multiple electrodes for forming the same pixel are arranged such that some electrodes overlap each other when viewed from a rotational direction, and the centroid distance between the multiple electrodes in the rotational axis direction is equal to each other in the rotational axis direction. The width of the electrodes in the rotational axis direction is W1 [mm], the number of multiple electrodes for forming the same pixel is n, and the equal centroid distance is d3 [mm], where d3 = W1 / n (n is a natural number of 2 or greater).

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, such as an electrophotographic copier or an electrophotographic printer, which forms an image on a sheet using an electrophotographic image forming system. Background Technology

[0002] In the case of forming an image using an image forming apparatus of an electrophotographic system, firstly, an electrostatic latent image is formed on the surface of a photosensitive component by irradiating the surface with light according to image data. Then, toner is applied to the electrostatic latent image on the surface of the photosensitive component through a developing apparatus to form a toner image. The toner image is transferred to a sheet, and the toner image transferred to the sheet is heated and fixed to the sheet by a fixing apparatus to form an image.

[0003] Here, Japanese Patent Publication No. 2018-134820 discloses an image forming apparatus as a device for forming an electrostatic latent image by irradiating a photosensitive member with light. This image forming apparatus includes an exposure head, which includes a light-emitting portion using an organic EL and a lens that forms an image of the light emitted from the light-emitting portion on the surface of the photosensitive member. By using an exposure head in this manner, compared to a laser scanning system that uses a rotating polygonal mirror to perform deflection scanning of a laser to form an electrostatic latent image, the number of components can be reduced, and the size and manufacturing cost of the image forming apparatus can be decreased.

[0004] Furthermore, it cannot be said that the light intensity of a single light-emitting element in an organic EL used in an exposure head is sufficiently high. Therefore, Japanese Patent Publication No. 2018-134820 describes a configuration in which multiple light-emitting elements illuminate the same portion of the surface of a photosensitive member to supplement the light intensity used to form an electrostatic latent image on the surface of the photosensitive member. Specifically, in the exposure head, the light-emitting elements are arranged two-dimensionally in the rotational axis direction (main scanning direction) and the rotational direction (sub-scanning direction) of the photosensitive member. Then, light-emitting elements adjacent to each other in the rotational direction of the photosensitive member emit light at different timings according to the rotational speed of the photosensitive member, such that multiple light-emitting elements illuminate the same portion of the surface of the photosensitive member. Hereinafter, illuminating the same portion of the surface of the photosensitive member with light by multiple light-emitting elements in this manner is referred to as multiple exposure.

[0005] Furthermore, in the exposure head, if the mounting position of the light-emitting unit is offset when it is mounted on the substrate, there is a possibility that the exposure position on the photosensitive element will be offset, and the image position will be offset. On the other hand, Japanese Patent Publication No. 2019-217653 describes a configuration in which dithering is performed on image data having a resolution higher than the spacing between light-emitting units in the main scanning direction, the image data is offset according to the offset of the mounting position of the light-emitting units, and then the image data is converted according to the spacing of the light-emitting units in the main scanning direction. As a result, the image position offset can be corrected with a resolution higher than the spacing of the light-emitting units in the main scanning direction.

[0006] However, in the configuration of Japanese Patent Publication No. 2019-217653, the positional offset of the image can be corrected at a higher resolution than the spacing between the light-emitting parts in the main scanning direction, but the image sharpness may be reduced. This will be described below with reference to the accompanying drawings.

[0007] Figure 18 (a) is a view illustrating an example of image data when dithering is performed on image data having a resolution higher than the spacing of the light-emitting parts in the main scanning direction, and the image data is offset according to the offset of the mounting position of the light-emitting parts. Figure 18 (b) is when Figure 18 The image data shown in (a) is a view when the spacing of the light-emitting parts in the main scanning direction is transformed. As... Figure 18 As shown, in the configuration of Japanese Patent Publication No. 2019-217653, when high-resolution image data is converted according to the spacing of the light-emitting parts in the main scanning direction, the data of the edge portion of the image becomes the intermediate value, and the image clarity may be reduced. Summary of the Invention

[0008] The object of the present invention is to provide an image forming apparatus that can correct the image position in the exposure head at a resolution higher than the spacing of the light-emitting parts in the main scanning direction, while ensuring the amount of light through multiple exposures and suppressing the reduction of image sharpness.

[0009] A representative configuration of the present invention is an image forming apparatus configured to expose the surface of a photosensitive member with light to form an electrostatic latent image, and to attach a toner to the electrostatic latent image to form an image. The image forming apparatus includes: an exposure head configured to expose the surface of the photosensitive member with light to form an electrostatic latent image, and including a light-emitting portion comprising a substrate, a first electrode layer, a light-emitting layer, and a second electrode layer. The first electrode layer includes a plurality of electrodes arranged two-dimensionally and spaced apart on the substrate in the rotation direction and the rotation axis direction of the photosensitive member. The light-emitting layer is stacked on the first electrode layer and configured to emit light when a voltage is applied. The second electrode layer is disposed on a side opposite to the side of the light-emitting layer where the first electrode layer is disposed, and light can pass through the second electrode layer. A controller is configured to control the first electrode layer based on image data. The layer includes a plurality of electrodes, each of which is subjected to a voltage to cause the light-emitting layer to emit light, and is configured to control the voltage applied to each of the plurality of electrodes based on image data, such that a pixel is formed by controlling the voltage applied to the plurality of electrodes arranged at different positions in the rotational direction, wherein the plurality of electrodes for forming the same pixel are arranged such that the electrodes partially overlap each other when viewed from the rotational direction, and the centroid distance between the plurality of electrodes in the rotational axis direction is equal in the rotational axis direction, d3 = W1 / n (n is a natural number of 2 or greater), where W1 [mm] is the width of the electrode in the rotational axis direction, n is the number of electrodes for forming the same pixel, and d3 [mm] is the equal centroid distance in the rotational axis direction, and the plurality of electrodes for forming the same pixel are arranged such that the centroid positions of each electrode are positioned at intervals of d3 in the rotational axis direction.

[0010] Further features of the invention will become clear from the following description of embodiments with reference to the accompanying drawings. Attached Figure Description

[0011] Figure 1 This is a schematic cross-sectional view of an image forming apparatus.

[0012] Figure 2 (a) and Figure 2 (b) is a perspective view and a cross-sectional view of the photosensitive drum and the exposure head.

[0013] Figure 3 Figures (a) through 3(c) are views illustrating the mounting surface of a printed circuit board included in an exposure head.

[0014] Figure 4 (a) and Figure 4 (b) is a view illustrating the positional relationship between the light-emitting part to be used and the two light-emitting element array chips.

[0015] Figure 5 This is a schematic diagram of a light-emitting element array chip.

[0016] Figure 6 This is a cross-sectional view of a light-emitting element array chip.

[0017] Figure 7 This is a schematic diagram used to illustrate the arrangement of the light-emitting parts.

[0018] Figure 8 This is a block diagram illustrating the system configuration of the image controller unit and the exposure head.

[0019] Figure 9 (a) and Figure 9 (b) is an example view illustrating image data before and after high-resolution processing.

[0020] Figure 10 This is a block diagram illustrating the system configuration of the light-emitting element array chip.

[0021] Figure 11 This is the circuit diagram of the data retention section.

[0022] Figure 12 This is the operation timing diagram of the data retention section.

[0023] Figure 13 This is the circuit diagram for the analog section.

[0024] Figure 14 This is a view illustrating image data transmitted to the light-emitting part of the light-emitting element array chip.

[0025] Figure 15 This is a schematic diagram showing the position of the light on the photosensitive drum when the light-emitting part emits light.

[0026] Figure 16 This is a schematic diagram used to illustrate the arrangement of the light-emitting parts.

[0027] Figure 17 This is a schematic diagram used to illustrate the arrangement of the light-emitting parts.

[0028] Figure 18 (a) and Figure 18 (b) is an explanatory diagram used to illustrate the configuration according to the relevant technology. Detailed Implementation

[0029] Image forming apparatus

[0030] In the following description, the general configuration of the image forming apparatus A according to the invention will be described together with reference to the accompanying drawings and the operation during image formation. Note that, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, etc., of the components described below are not intended to limit the scope of the invention.

[0031] The image forming apparatus A according to this embodiment is a panchromatic image forming apparatus, wherein four color toners—yellow (Y), magenta (M), cyan (C), and black (K)—are transferred onto a sheet to form an image. In the following description, although components using each color toner are given the suffixes Y, M, C, and K, the configuration or operation of each component is substantially the same, except that the colors of the toners used are different. Therefore, the suffixes are appropriately omitted unless it is necessary to distinguish the components from each other.

[0032] Figure 1 This is a schematic cross-sectional view of image forming apparatus A. For example... Figure 1 As shown, the image forming apparatus A includes an image forming unit that forms an image. The image forming unit includes a photosensitive drum 1 (1Y, 1M, 1C, and 10K) serving as a photosensitive element, a charging device 2 (2Y, 2M, 2C, and 2K), an exposure head 6 (6Y, 6M, 6C, and 6K), a developing device 4 (4Y, 4M, 4C, and 4K), and a transfer device 5 (5Y, 5M, 5C, and 5K).

[0033] Next, the image forming operation performed by the image forming apparatus A will be described. In the case of forming an image, firstly, the sheet S contained in the sheet cassette 99a or 99b is conveyed to the alignment roller 96 via the pick-up roller 91a or 91b, the feed roller 92a or 92b, and the conveyor rollers 93a to 93c. Subsequently, the sheet S is fed to the conveyor belt 11 by the alignment roller 96 at a predetermined time.

[0034] Simultaneously, in the image forming unit, firstly, the surface of the photosensitive drum 1Y is charged by the charging device 2Y. Next, the exposure head 6Y illuminates the surface of the photosensitive drum 10Y with light based on image data read by the image reading unit 90 or image data transmitted from an external device (not shown), and an electrostatic latent image is formed on the surface of the photosensitive drum 10Y. Afterward, yellow toner is attached to the electrostatic latent image formed on the surface of the photosensitive drum 1Y by the developing device 4Y to form a yellow toner image on the surface of the photosensitive drum 1Y. When a transfer bias is applied to the transfer device 5Y, the toner image formed on the surface of the photosensitive drum 1Y is transferred to the sheet S conveyed by the conveyor belt 11.

[0035] Through a similar process, photosensitive drums 1M, 1C, and 1K are also illuminated by exposure heads 6M, 6C, and 6K to form electrostatic latent images, and magenta, cyan, and black toner images are formed by developing devices 4M, 4C, and 4K. Furthermore, when a transfer bias is applied to transfer devices 5M, 5C, and 5K, these toner images are transferred overlaid onto a yellow toner image on sheet S. As a result, a full-color toner image corresponding to the image data is formed on the surface of sheet S.

[0036] Subsequently, the sheet S carrying the toner image is conveyed to the fixing device 94 via conveyor belt 97, where it undergoes heating and pressurization. As a result, the toner image on the sheet S is fixed onto the sheet S. Then, the sheet S with the toner image fixed is discharged onto the discharge tray 95 via discharge roller 98.

[0037] <Exposure Head>

[0038] Next, the configuration of exposure head 6 will be described.

[0039] Figure 2 (a) is a perspective view of the photosensitive drum 1 and the exposure head 6. Figure 2 (b) is a cross-sectional view of the photosensitive drum 1 and the exposure head 6. Figure 3 (a) and Figure 3 (b) is a view illustrating the mounting surfaces of one side and the other side of the printed circuit board 22 included in the exposure head 6.

[0040] Figure 3 (c) is Figure 3 (b) is an enlarged view of region V shown in the figure.

[0041] like Figure 2 As shown, the exposure head 6 is fixed to the surface facing the photosensitive drum 1 by a fixing member (not shown). The exposure head 6 includes a light-emitting element array chip 40 and a printed circuit board 22 on which the light-emitting element array chip 40 is mounted. In addition, a rod lens array 23 is provided to form an image (light collection) of the light emitted from the light-emitting element array chip 40 on the photosensitive drum 1, and a housing 24 to which the rod lens array 23 and the printed circuit board 22 are fixed.

[0042] Connector 21 is mounted on the surface of printed circuit board 22 opposite to the surface on which the light-emitting element array chip 40 is mounted. Connector 21 is provided for transmission from image controller section 70 ( Figure 8 The control signals for the light-emitting element array chip 40 are transmitted and connected to the power supply line. The light-emitting element array chip 40 is driven via connector 21.

[0043] like Figure 3As shown, 20 light-emitting element array chips 40 are mounted on a printed circuit board 22 in two staggered rows. In each light-emitting element array chip 40, 748 light-emitting elements 50 are arranged at a predetermined resolution spacing in the vertical direction (arrow X direction). In each light-emitting element array chip 40, four light-emitting elements 50 are arranged at a predetermined spacing in the horizontal direction (arrow Y direction). That is, in each light-emitting element array chip 40, the light-emitting elements 50 are arranged two-dimensionally in both the arrow X and arrow Y directions. The four light-emitting elements 50 arranged in the arrow Y direction form the same pixel through multiple exposures as described below.

[0044] In this embodiment, the resolution spacing of the light-emitting element array chip 40 is 1200 dpi (approximately 21.16 μm). Furthermore, the distance from one end to the other in the longitudinal direction of the light-emitting portion 50 included in each light-emitting element array chip 40 is approximately 15.828 mm. That is, the exposure head 6 includes a total of 14,960 light-emitting portions 50 in the X-direction (arrow X), enabling exposure processing corresponding to an image width of approximately 316 mm (≈15.8 mm × 20 chips) in the longitudinal direction. Moreover, in the lateral direction (Y-direction (arrow Y) of the light-emitting element array chip 40, the spacing L1 between the light-emitting portions 50 of adjacent light-emitting element array chips 40 is approximately 105 μm (five pixels at 1200 dpi and ten pixels at 2400 dpi).

[0045] Furthermore, the light-emitting element array chips 40 adjacent to each other in the Y-direction are arranged such that the light-emitting portions 50 of each light-emitting element array chip overlap each other in the X-direction. This is done to suppress positional shifts in the mounting process of the light-emitting element array chips 40 and to prevent image stripes from forming due to shadows caused by positional shifts in the light illuminating the photosensitive drum 1 at the boundary portions between the light-emitting element array chips 40. The overlap amount is calculated based on the maximum amount of mounting variation of the mounting equipment (chip bonding machine) and is set to an amount that prevents gaps from forming between the light-emitting portions 50 of the adjacent light-emitting element array chips 40 in the Y-direction.

[0046] Furthermore, in the head information storage section 171 of the exposure head 6 ( Figure 8 In the image controller unit 70, the positional offset of the light-emitting element array chip 40 during installation is measured and stored during the manufacturing process. During image formation, the image controller unit 70... Figure 8 Based on the position offset information of the light-emitting element array chip 40 stored in the header information storage unit 171, the light-emitting unit 50 selectively emits light as described below, thereby suppressing the formation of image stripes.

[0047] Figure 4This is a view illustrating two light-emitting element array chips 40 that are adjacent to each other in the direction of arrow Y. Figure 4 In the image, the light-emitting portion 50 with a shadow line indicates the light-emitting portion 50 used during exposure, and the light-emitting portion 50 without a shadow line indicates the light-emitting portion 50 not used during exposure. Furthermore, in... Figure 4 (a) and Figure 4 In (b), the relative positions of two adjacent light-emitting element array chips 40 in the direction of arrow Y are different in the direction of arrow X.

[0048] like Figure 4 As shown, the image controller unit 70 selects the light-emitting part 50 to be used during exposure such that the distance L2 in the direction of arrow X between the light-emitting parts 50 used during exposure in two adjacent light-emitting element array chips 40 in the direction of arrow Y is closest to the interval of 4800 dpi. In this embodiment, as described below, since the exposure head 6 is configured to perform exposure at a resolution of 4800 dpi in the direction of arrow X, the distance L2 is close to the interval of 4800 dpi, but the distance L2 is set according to the resolution of the exposure performed by the exposure head 6 in the direction of arrow X.

[0049] In this embodiment, the arrow X, which represents the longitudinal direction of the light-emitting element array chip 40, is the rotation axis direction of the photosensitive drum 1 and also the main scanning direction. The arrow Y, which represents the transverse direction of the light-emitting element array chip 40, is the rotation direction of the photosensitive drum 1 and also the sub-scanning direction. The rotation direction of the photosensitive drum 1 is the tangential direction of the photosensitive drum 1 at the exposure position where light is collected by the exposure head 6. Additionally, the arrow Z represents the stacking direction of the layers of the light-emitting portion 50 with its layered structure, as described below. Note that the longitudinal direction of the light-emitting element array chip 40 can be tilted by approximately ±1° relative to the rotation axis direction of the photosensitive drum 1. The transverse direction of the light-emitting element array chip 40 can also be tilted by approximately ±1° relative to the rotation axis direction of the photosensitive drum 1.

[0050] <Light-emitting element array chip>

[0051] Next, the configuration of the light-emitting element array chip 40 will be described.

[0052] Figure 5 This is a schematic diagram of the light-emitting element array chip 40. Figure 6 It is along Figure 5 A cross-sectional view of the light-emitting element array chip 40 taken by line MM. Figure 7 This is a schematic diagram illustrating the arrangement of the light-emitting portion 50 of the light-emitting element array chip 40.

[0053] like Figure 5As shown, the light-emitting element array chip 40 includes a light-emitting substrate 42 (substrate) containing a circuit section 46 for controlling the light-emitting parts 50, a light-emitting region 44 on which a plurality of light-emitting parts 50 are regularly arranged, and wiring bonding pads 48. Signal input and output between the external components of the light-emitting element array chip 40 and the circuit section 46, as well as power supply to the circuit section 46, are performed through the wiring bonding pads 48. Note that the circuit section 46 can use analog driving circuits, digital control circuits, or circuits including both.

[0054] like Figure 6 As shown, the light-emitting part 50 includes a light-emitting substrate 42, and on the light-emitting substrate 42, there are regularly spaced elements in the X and Y directions. Figure 7 The figure shows a plurality of lower electrodes 54, light-emitting layer 56 and upper electrodes 58 arranged in two dimensions at intervals d1 and d2.

[0055] The lower electrode 54 (including a first electrode layer comprising multiple electrodes) is a plurality of electrodes formed at intervals in the form of layers on the light-emitting substrate 42, and each electrode corresponds to a pixel being provided. That is, each lower electrode 54 is provided to form a pixel.

[0056] The upper electrode 58 (second electrode layer) is stacked on the light-emitting layer 56 at a position opposite to the side of the light-emitting layer 56 where the lower electrode 54 is disposed. The upper electrode 58 is an electrode through which light of the emission wavelength of the light-emitting layer 56 can pass.

[0057] The circuit unit 46 controls the potential of the selected lower electrode 54 based on a control signal generated according to the image data, and generates a potential difference between the selected lower electrode 54 and the upper electrode 58. When a potential difference is generated between the upper electrode 58, which is the positive electrode, and the lower electrode 54, which is the negative electrode, current flows from the negative electrode into the light-emitting layer 56, and holes flow from the positive electrode into the light-emitting layer 56. Through the recombination of electrons and holes in the light-emitting layer 56, the light-emitting layer 56 emits light.

[0058] Light emitted through the light-emitting layer 56 is guided to the upper electrode 58 and emitted through the upper electrode 58. Additionally, light guided from the light-emitting layer 56 towards the lower electrode 54 is reflected from the lower electrode 54 towards the upper electrode 58, and the reflected light also passes through the upper electrode 58 and is emitted. In this way, the light-emitting part 50 emits light. Note that although there is a time difference between the emission timing of light emitted directly from the light-emitting layer 56 towards the upper electrode 58 and the emission timing of light reflected from the lower electrode 54 and emitted from the upper electrode 58, the emission timing can be considered almost identical due to the extremely small layer thickness of the light-emitting part 50.

[0059] Note that in this embodiment, the light-emitting substrate 42 is a silicon substrate. The upper electrode 58 is preferably transparent to the emission wavelength of the light-emitting layer 56. For example, by using a transparent electrode formed of indium tin oxide (ITO), the aperture ratio becomes substantially 100%, and the light emitted from the light-emitting layer 56 passes through the upper electrode 58 and is emitted as is. In this embodiment, the upper electrode 58 is a positive electrode provided for all the lower electrodes 54, but the upper electrode 58 may also be provided individually for each lower electrode 54, or one upper electrode 58 may be provided for multiple lower electrodes 54. When a transparent electrode is used as the upper electrode 58, the entire electrode is not necessarily a transparent electrode, and only the light-emitting opening can be a transparent electrode; the portion other than the opening can be an electrode other than a transparent electrode, such as a metal wire.

[0060] Organic EL films, inorganic EL layers, etc., are used as the light-emitting layer 56. When an organic EL film is used as the light-emitting layer 56, the light-emitting layer 56 can be a stacked 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. Furthermore, the light-emitting layer 56 can be formed continuously in the direction of arrow X, or it can be divided into sections with the same size as the lower electrode 54. Additionally, each lower electrode 54 can be divided into multiple groups, and a light-emitting layer 56 can be stacked on the lower electrode 54 belonging to each divided group.

[0061] Note that when a moisture-sensitive luminescent material, such as an organic or inorganic EL layer, is used as the luminescent layer 56, it is desirable to perform a seal to prevent moisture from entering the luminescent area 44. As a sealing method, for example, a single thin film of silicon oxide, silicon nitride, aluminum oxide, or a sealing film consisting of stacked films is formed. As a method for forming the sealing film, a method with excellent coverage performance, such as a stepped structure, is preferred, and, for example, atomic layer deposition (ALD) can be used. Note that the materials, configurations, and formation methods of the sealing film are merely examples and are not limited to the examples described above; appropriate selection of materials, configurations, and formation methods is sufficient.

[0062] The lower electrode 54 is preferably formed of a metal with high reflectivity relative to the emission wavelength of the light-emitting layer 56. For example, Ag, Al, or an alloy of Ag and Al are used. The lower electrode 54 is formed together with the circuit section 46 using Si integrated circuit processing technology and is directly connected to the driving section of the circuit section 46. As described above, since the lower electrode 54 is formed using Si integrated circuit processing technology with a processing rule of about 0.2 μm and high precision, the lower electrode 54 can be precisely and densely arranged. Furthermore, since the lower electrode 54 can be densely arranged, most of the light emitted by the light-emitting region 44 can be emitted, and the utilization efficiency of the light-emitting region 44 can be enhanced. The organic material of the light-emitting layer 56 fills the space between the individual lower electrodes 54, and the individual lower electrodes 54 are separated by the organic material.

[0063] Furthermore, when the voltage applied across the light-emitting section 50 becomes a predetermined value or greater, current begins to flow, and thereafter, the current value increases substantially proportionally to the voltage value. The voltage change causes the current to flow in each light-emitting section 50. Therefore, before the product is shipped from the factory, the light-emitting sections 50 of the light-emitting element array chip 40 emit light individually and sequentially, and the current flowing through the light-emitting sections 50 is adjusted so that the light collected by the rod lens array 23 has a predetermined amount of light. Note that before the product is shipped from the factory, the exposure head 6 performs not only the above-described light amount adjustment but also focus adjustment to adjust the spacing between the light-emitting element array chip 40 and the rod lens array 23.

[0064] like Figure 7 As shown, the light-emitting portions 50 are arranged in a matrix at predetermined intervals in the light-emitting region 44 along the X and Y directions of the arrow. In this embodiment, the width W1 of the light-emitting portions 50 in the X direction is 19.80 μm, and the interval d1 between adjacent light-emitting portions 50 in the X direction is 0.68 μm. That is, the light-emitting portions 50 are arranged at a spacing of 21.16 μm (1200 dpi) in the X direction. Note that the spacing of the light-emitting portions 50 in the X direction may deviate within tolerance. The tolerance of the spacing of the light-emitting portions 50 in the X direction is ±1% relative to the design nominal spacing of the light-emitting portions 50 in the X direction. That is, the tolerance of the spacing of the light-emitting portions 50 in the X direction according to this embodiment is ±0.21 μm.

[0065] Similar to width W1, the width W2 of the light-emitting part 50 in the direction of arrow Y is also 19.80 μm. That is, the light-emitting part 50 in this embodiment has a square shape with one side measuring 19.80 μm. Note that although the light-emitting part 50 has a square shape because widths W1 and W2 are equal, widths W1 and W2 can deviate within tolerance ranges. In this embodiment, the tolerance for both widths W1 and W2 is ±0.2 μm.

[0066] Furthermore, similar to the interval d1, the interval d2 between adjacent light-emitting portions 50 in the arrow Y direction is also 0.68 μm, and the light-emitting portions 50 are also arranged at a spacing of 21.16 μm (1200 dpi) in the arrow Y direction. Note that the spacing of the light-emitting portions 50 in the arrow Y direction can have deviations within tolerance. The tolerance of the spacing of the light-emitting portions 50 in the arrow Y direction is ±1% relative to the design nominal spacing of the light-emitting portions 50 in the arrow Y direction. That is, the tolerance of the spacing of the light-emitting portions 50 in the arrow Y direction according to this embodiment is ±0.21 μm. Here, the intervals d1 and d2 between the light-emitting portions 50 are set to be greater than the interval dz between the upper electrode 58 and the lower electrode 54. Figure 6 With this configuration, leakage current between the lower electrodes 54 that are adjacent to each other in the X and Y directions can be suppressed, and erroneous emission of the light-emitting part 50 can be suppressed.

[0067] Here, in this embodiment, the width, shape, and arrangement of the light-emitting portion 50 are basically determined by the width, shape, and arrangement of the lower electrode 54, and therefore can also be referred to as the width, shape, and arrangement of the lower electrode 54. Furthermore, in this embodiment, the distance between the light-emitting portions 50—that is, the distance between the lower electrodes 54—means the distance between the centroids defined based on the nominal centroid position of the lower electrode 54.

[0068] The light-emitting portions 50 adjacent to each other in the Y-direction are arranged such that their positions are offset by a distance d3 in the X-direction. In this embodiment, the distance d3 is set to 5.29 μm (4800 dpi). Regarding all the light-emitting portions 50, the four light-emitting portions 50 arranged in parallel in the Y-direction are arranged such that they are offset from each other by an integer multiple of the distance d3 in the X-direction. In other words, the four lower electrodes 54 provided in the Y-direction to form the same pixel are arranged such that they partially overlap each other when viewed from the Y-direction and that the centroid distance between the lower electrodes 54 in the X-direction is equal.

[0069] Here, in this embodiment, the interval d3 is determined as follows. That is, the resolution of the image formed by the image forming apparatus A in the main scanning direction (arrow X direction) is m [dpi], the number of light-emitting parts 50 arranged in parallel in the arrow Y direction is n, and the reference value for the offset of the position of the light-emitting parts 50 arranged in parallel in the arrow Y direction in the arrow X direction is the interval d3 [mm] (reference value). In this case, the interval d3 is obtained from d3 = 25.4 / m × 1 / n, and the light-emitting parts 50 arranged in parallel in the arrow Y direction are arranged such that their positions are offset from each other by an integer multiple of the interval d3. That is, in this embodiment, since m = 1200 and n = 4, d3 = 25.4 / 1200 × 1 / 4 = 0.00529 [mm] = 5.29 [μm].

[0070] Furthermore, even when the interval d3 is determined as follows, the same result as the calculation result of the interval d3 above is obtained. That is, the distance between the multiple light-emitting parts 50 having the same position in the arrow Y direction and the distance in the arrow X direction is q [mm], the number of light-emitting parts 50 arranged in parallel in the arrow Y direction is n, and the reference value for the offset of the position of the light-emitting parts 50 arranged in parallel in the arrow Y direction in the arrow X direction is the interval d3 [mm] (reference value). In this case, the interval d3 is obtained from d3 = q / n, and the light-emitting parts 50 arranged in parallel in the arrow Y direction are arranged such that their positions are offset from each other by an integer multiple of the interval d3. That is, in this embodiment, since q = 0.02116 and n = 4, therefore d3 = 0.02116 / 4 = 0.00529 [mm] = 5.29 [μm].

[0071] Furthermore, instead of the above determination method, the interval d3 can be determined as follows. That is, when light-emitting parts 50 are arranged at different positions in the Y direction of arrow to form the same pixel, the number of light-emitting parts 50 is n, and the width of the light-emitting parts 50 in the X direction of arrow is W1 [mm]. In this case, the interval d3 is obtained from d3 = W1 / n (n is a natural number of 2 or greater). The light-emitting parts 50 arranged at different positions in the Y direction of arrow to form the same pixel are arranged such that the centroid of the light-emitting parts 50 is positioned at an interval d3 in the X direction of arrow. That is, in order to form the same pixel through the following multiple exposure, the light-emitting parts 50 are arranged such that the equal centroid distance between the four light-emitting parts 50 arranged at different positions in the Y direction of arrow is d3 in the X direction of arrow. In this embodiment, W1 = 19.80 [μm] = 0.01980 [mm] and n = 4. Therefore, d3 = 0.01980 / 4 = 0.00495 [mm] = 4.95 [μm]. By setting the interval d3 in this way, the overlap of the four light-emitting parts 50 arranged at different positions in the Y direction in order to form the same pixel becomes uniform in the X direction, so that in the multiple exposure described below, the amount of light in each pixel becomes uniform and the density of each pixel becomes uniform.

[0072] In this invention, the shape of the light-emitting portion 50 is not limited to a square, and can be a polygon, circle, ellipse, etc., with more sides than a quadrilateral, as long as light is emitted with an exposure area size corresponding to the output resolution of the image forming apparatus A and the image quality of the output image meets the design specifications of the image forming apparatus A. However, since the light intensity of organic light-emitting materials is less than that of LEDs, it is preferable to reduce the distance between adjacent light-emitting portions 50 with square shapes, because this ensures the light-emitting area sufficient to change the potential of the photosensitive drum 1. Furthermore, as long as two or more light-emitting portions 50 are provided, the number of light-emitting portions 50 arranged in parallel in the direction of arrow Y is not limited to four, and is determined based on the light intensity required for the exposure processing of the exposure head 6, the resolution of the image formed by the image forming apparatus A, etc.

[0073] As described above, the distance between the light-emitting parts 50—that is, the distance between the lower electrodes 54—is defined based on the nominal centroid position of the lower electrodes 54. Specifically, when the lower electrodes 54 are regular polygons, the distance between their centroids is set based on the intersection of their diagonals; when the lower electrodes 54 are circles, the distance is set based on the center of the circle; and when the lower electrodes 54 are ellipses, the distance is set based on the intersection of their major and minor axes. When the lower electrodes 54 are regular polygons, the corners do not need to be perfect angles and can be rounded.

[0074] <System Configuration of Exposure Head>

[0075] Next, the configuration of the exposure head 6 and the image controller unit 70 (controller) that controls the exposure head 6 will be described. The image controller unit 70 is provided on the main body side of the image forming apparatus A. Although the control performed when processing one image data (monochrome) will be described below, similar processing is performed in parallel for four image data corresponding to yellow, magenta, cyan, and black when the image forming operation is performed.

[0076] Figure 8 This is a block diagram illustrating the system configuration of the image controller unit 70 and the exposure head 6. (See diagram for example.) Figure 8 As shown, the image controller unit 70 includes an image data generation unit 71, a chip data conversion unit 72, a CPU 73, and a synchronization signal generation unit 74. The image controller unit 70 performs image data processing and image formation timing processing through these components, and transmits control signals for controlling the exposure head 6 to the printed circuit board 22 of the exposure head 6.

[0077] Image data from the original image read by the image reading unit 90 and image data transmitted from an external device via a network are input to the image data generation unit 71 (image processing unit). The image data generation unit 71 performs dithering processing on the input image data at a resolution indicated by the CPU 73, and generates image data for outputting the image. In this embodiment, the image data generation unit 71 performs dithering processing at a resolution of 1200 dpi and using binary grayscale, and then generates data with binary grayscale, a main scanning direction of 4800 dpi, and a sub-scanning direction of 2400 dpi through resolution enhancement processing. In the resolution enhancement processing, the 1200 dpi data is simply copied.

[0078] Figure 9 (a) is a view of an example of image data D1 (first image data) before high-resolution processing in the illustrated image data generation unit 71. Figure 9 (b) is a view illustrating image data D2 (second image data) obtained by performing resolution enhancement processing on image data D1 by the image data generation unit 71. Figure 9 As shown, image data D2, corresponding to the exposure resolution of the light-emitting element array chip 40, is generated through resolution enhancement processing. At this time, by generating binary data, the image data generation unit 71 can achieve high-resolution image formation without sacrificing image clarity.

[0079] In this embodiment, since the resolution of the dithering process in the image data generation unit 71 is 1200 dpi, the image data after dithering is generated in units of four light-emitting units 50 arranged in parallel in the X direction on the photosensitive drum 1. In the rows of the four light-emitting units 50 extending in the X direction and arranged in parallel in the Y direction, the distances of the light-emitting units 50 in the first row and the second row from the center of the rod lens array 23 are different, therefore the amount of light illuminating the photosensitive drum 1 differs between rows. This also applies to the light-emitting units 50 in the third and fourth rows. Therefore, by performing dithering processing in units of four light-emitting units 50 arranged in parallel in the X direction to generate image data, the occurrence of moiré patterns and banding caused by the density difference of the generated points can be suppressed. Furthermore, by shifting the image data in a manner that corrects the image position of the dithered image data at a resolution of 4800 dpi, the image position can be corrected at a high resolution of 4800 dpi, while simultaneously suppressing moiré patterns and banding.

[0080] The synchronization signal generation unit 74 periodically generates a horizontal synchronization signal (control signal) indicating the start of image data taking-in, and transmits the horizontal synchronization signal to the chip data conversion unit 72. The CPU 73 sets the period of the surface of the photosensitive drum 1 moving by the size of pixels in the rotation direction at a preset rotation speed of the photosensitive drum 1 according to the resolution of the image formed by the image forming apparatus A in the sub-scanning direction, and indicates the time interval of the signal period to the synchronization signal generation unit 74.

[0081] In this embodiment, the image formed by the image forming apparatus A has a resolution of 2400 dpi in the sub-scanning direction, and the photosensitive drum 1 rotates at 200 mm / s. Therefore, the time taken for the photosensitive drum 1 to move a distance of 2400 dpi (10.58 μm) is 52.92 μs, and the period of the horizontal sync signal is 52.92 μs. Note that the rotational speed of the photosensitive drum 1 is calculated by the CPU 73 based on the setting value stored in the storage unit (not shown).

[0082] The chip data conversion unit 72, in sync with the horizontal synchronization signal generated and input by the synchronization signal generation unit 74, divides the image data of one line × four rows (the number of light-emitting parts 50 in the Y direction of arrow) into each light-emitting element array chip 40. Then, the chip data conversion unit 72 transmits the image data along with the clock signal and the horizontal synchronization signal to each light-emitting element array chip 40 via the horizontal synchronization signal line 75, the clock signal line 76, and the image data signal line 77. Note that there are four image data signal lines 77, which is the same as the number of light-emitting parts 50 in the Y direction of arrow.

[0083] The head information storage unit 171, included in the exposure head 6, is connected to the CPU 73 via a communication signal line 79. The head information storage unit 171 stores the emission amount and mounting position information of each light-emitting element array chip 40 as head information. The light-emitting element array chip 40 emits light from its light-emitting section 50 based on the setting values ​​of each of the signals input from the image controller unit 70. Additionally, the light-emitting element array chip 40 generates a line synchronization signal to be used in another light-emitting element array chip 40 connected via a line synchronization signal line 75.

[0084] <System Configuration of Light Emitting Element Array Chip>

[0085] Next, the system configuration of the light-emitting element array chip 40 will be described.

[0086] Figure 10 This is a block diagram illustrating the system configuration of the light-emitting element array chip 40. Figure 10 In this configuration, since the clock signal is input to all boxes of the digital section 80, the connections are omitted. For example... Figure 10 As shown, the circuit section 46 of the light-emitting element array chip 40 includes a digital section 80 and an analog section 86.

[0087] The digital unit 80 includes a communication IF unit 81, a register unit 82, a receive signal generation unit 83, a line synchronization signal generation unit 84, and a data holding unit 85. Based on preset values, image data signals, and line synchronization signals synchronized with a clock signal, the digital unit 80 generates pulse signals to cause the light-emitting units 50 to emit light, and transmits these pulse signals to the analog unit 86. Note that 748 light-emitting units 50 are provided as the data holding unit 85; 748 (85-001 to 85-748) is the number of light-emitting units 50 included in a light-emitting element array chip 40 in the direction of arrow X.

[0088] The horizontal synchronization signal generation unit 84 delays the input horizontal synchronization signal by a predetermined time and generates a horizontal synchronization signal to be used in another light-emitting element array chip 40 connected via the horizontal synchronization signal line 75. The receiving signal generation unit 83 outputs a data latch signal we001 to the data holding unit 85-001 at a time when the input horizontal synchronization signal is delayed by a predetermined setting time input from the register unit 82.

[0089] The register section 82 stores information about the delay time of the received signal generation section 83 and the setting information of the drive current set by the analog section 86. The communication IF section 81 controls the writing of setting values ​​to the register section 82 and the reading of setting values ​​from the register section 82 based on the communication signal input from the CPU 73.

[0090] Data Preservation Department

[0091] Next, the configuration of the data retention unit 85 will be described.

[0092] Figure 11 This is the circuit diagram of the data retention unit 85. (For example...) Figure 11 As shown, four lines of image data (image data 1 to 4), a clock signal, and data latch signals wen (n = 1 to 748) are input to the data holding unit 85. Each data holding unit 85 includes four flip-flop circuits and four gate circuits for latching the four lines of image data input simultaneously with the timing of the data latch signal input. Each data holding unit 85 includes a flip-flop circuit for delaying by one clock cycle and outputting the data latch signal.

[0093] Figure 12 This is the operation timing diagram for the data retention unit 85. (For example...) Figure 12 As shown, four lines of image data (D1[1] to D1[4]) are simultaneously input to the data holding unit 85-001. The data holding unit 85-001 latches the image data at the timing of the data latch signal we001 input from the receiving signal generation unit 83, and generates drive signals (P001[1] to P001[4]). In addition, the data holding unit 85-001 delays the input data latch signal we001 by one clock cycle and transmits the delayed data latch signal as the data latch signal we002 to the next data holding unit 85-002.

[0094] Four lines of image data (D2[1] to D2[4]) are simultaneously input to the data holding unit 85-002. The data holding unit 85-002 latches the image data at the timing of the data latch signal we002 input from the data holding unit 85-001, and generates drive signals (P002[1] to P002[4]). In addition, the data holding unit 85-002 delays the data latch signal we002 by one clock cycle and transmits the delayed data latch signal as the data latch signal we003 to the data holding unit 85-003.

[0095] In this manner, the data holding units 85 (-001 to 748) sequentially latch image data while simultaneously transmitting data latch signals up to the 748th data holding unit 85. Then, once the image data is latched, the data holding units 85 (-001 to 748) transmit the latched signal as a drive signal to the analog unit 86. In this embodiment, since four rows of image data are latched by one data latch signal, the drive signals for all four rows (four pixels) are output simultaneously.

[0096] <Simulation Department>

[0097] Next, the configuration of the analog unit 86 will be described. The analog unit 86 includes a drive circuit connected one-to-one to each light-emitting unit 50. For ease of description, one drive circuit will be described below, but it is assumed that the number of drive circuits is the same as the number of light-emitting units 50 - that is, 2992 drive circuits (748 × 4 rows) exist.

[0098] Figure 13 This is the circuit diagram for the analog section 86. (For example...) Figure 13 As shown, the analog section 86 includes a current setting DAC 61, a current control MOSFET 62, and a switching MOSFET 63. The DAC 61 receives the setting value of the current flowing from the register section 82 of the digital section 80 to the light-emitting section 50 as a digital value, converts the current setting value into an analog voltage, and outputs an analog voltage.

[0099] The current-controlled MOSFET 62 is a Pch MOSFET with a source terminal connected to the supply voltage VDD and a gate terminal connected to the output of DAC 61. Furthermore, the current flowing from the source to the drain increases with the analog voltage input to DAC 61.

[0100] The switching MOSFET 63 is a Pch MOSFET, having a source terminal connected to the drain terminal of the current-control MOSFET 62, and a gate terminal into which a drive signal output from the data holding section 85 is input. The drive signal is a binary signal indicating a high or low level, and when a high level is input, MOSFET 63 is turned on, and the current controlled by the current-control MOSFET 62 flows from the source to the drain. Since the drain terminal is connected to the anode terminal of the light-emitting section 50, the current becomes the drive current of the light-emitting section 50.

[0101] <Light-emitting part illumination control during image formation>

[0102] Next, the illumination control of the light-emitting unit 50 during image formation will be described. In the following description, the emitting of the light-emitting unit 50 means that the light-emitting unit 50 emits light in an amount sufficient to change the charging potential of the photosensitive drum 1 to the point where the toner image is developed. That is, the emitting of the light-emitting unit 50 does not include the case where the light-emitting unit 50 emits light in an amount sufficient to change the charging potential of the photosensitive drum 1 to the point where the toner image is not developed into a visible image.

[0103] Figure 14 This is a view illustrating the image data transmitted to the light-emitting portion 50 of the light-emitting element array chip 40 during the formation of a line of images extending in the main scanning direction (arrow X direction). For example... Figure 14As shown, when forming the aforementioned line image, firstly, the uppermost of the four light-emitting units 50 arranged in parallel along the rotation direction (arrow Y direction) of the photosensitive drum 1 emits light. Next, with a timing delay of 2400 dpi for two lines, the light-emitting unit 50 immediately downstream of the initially emitted light-emitting unit 50 emits light. During the delay operation, the image data readout position is set such that image data at the corresponding position is read relative to a shared line synchronization signal. As a result, the exposure position (irradiation position) of the light emitted from the uppermost light-emitting unit 50 in the rotation direction of the photosensitive drum 1 in the sub-scanning direction and the exposure position of the light emitted from the light-emitting unit 50 immediately downstream of the initially emitted light-emitting unit 50 in the sub-scanning direction on the photosensitive drum 1 can be aligned.

[0104] Next, the three light-emitting units 50 positioned downstream of the uppermost light-emitting unit 50 in the rotational direction of the photosensitive drum 1 emit light at a timing delay of 2400 dpi for four rows from the timing delay of the light-emitting unit 50 positioned upstream in the rotational direction of the photosensitive drum 1. Similarly, the four light-emitting units 50 positioned downstream of the uppermost light-emitting unit 50 in the rotational direction of the photosensitive drum 1 emit light at a timing delay of 2400 dpi for six rows from the timing delay of the light-emitting unit 50 positioned upstream in the rotational direction of the photosensitive drum 1. As a result, the light emitted from the four light-emitting units 50 arranged in parallel in the rotational direction of the photosensitive drum 1 can be aligned at all exposure positions in the sub-scanning direction on the photosensitive drum 1.

[0105] Figure 15 This is a schematic diagram illustrating the light illumination position on the photosensitive drum 1 when the four light-emitting units 50 arranged in parallel in the direction of arrow Y emit light through the above control. Figure 15 As shown, when four light-emitting units 50 arranged in parallel in the direction of arrow Y emit light at the aforementioned timing, the photosensitive drum 1 is illuminated with light H1 to H4 emitted from the four light-emitting units 50 at the same position in the direction of arrow Y and at a position offset by a distance d3 in the direction of arrow X. Here, since the distance d3 is set to d3 = 25.4 / m × 1 / n, at least two overlapping portions of light H1 to H4 are formed on the photosensitive drum 1, thereby forming a pixel. Therefore, the amount of light can be compensated when multiple exposures are performed on the photosensitive drum 1 to form an electrostatic latent image.

[0106] In this embodiment, the light-emitting units 50 arranged in parallel along the Y direction are offset from each other by 5.29 μm (=d3) along the X direction (corresponding to 4800 dpi). Therefore, exposure processing can be performed on the photosensitive drum 1 at a resolution of 4800 dpi without setting the data of the edge portions of the image to intermediate values. Thus, the image position can be corrected at a resolution higher than the spacing of the light-emitting units 50 in the main scanning direction, while suppressing the reduction in image sharpness. Even in the case of a configuration where the interval d3 obtained from d3 = W1 / n (n is a natural number of 2 or greater) is 4.95 [μm], the effect of performing exposure processing on the photosensitive drum 1 at a resolution higher than the spacing of the light-emitting units 50 in the main scanning direction can still be obtained. In this case, the image data generation unit 71 performs resolution enhancement processing based on the value of the interval d3 calculated from d3 = W1 / n (n is a natural number of 2 or greater).

[0107] Furthermore, when the width W1 of the light-emitting portion 50 in the X-direction is small, the overlap of light H1 to H4 between the parallel light-emitting portions 50 arranged in the Y-direction becomes smaller. This may result in poor performance of multiple exposures or the formation of gaps between light H1 to H4, leading to image stripes. Therefore, the width W1 is set to at least two or more times the spacing d3. As a result, light emitted not only from light-emitting portions 50 adjacent in the Y-direction but also from light-emitting portions 50 next to adjacent light-emitting portions 50 in the Y-direction can overlap on the photosensitive drum 1, enabling high-precision multiple exposures and suppressing the formation of image stripes.

[0108] Furthermore, as mentioned above, in Figure 3 In (c), the distance L1 (shortest distance) between the light-emitting portions 50 included in two adjacent light-emitting element array chips 40 in the direction of arrow Y is set to ten rows of 2400 dpi. Therefore, with respect to the rotation direction of the photosensitive drum 1, a light emission timing delay of 12 rows is achieved between the downstream light-emitting portion 50 of the first light-emitting element array chip 40 and the upstream light-emitting portion 50 of the second light-emitting element array chip 40, which is located downstream of the first light-emitting element array chip 40. This 12-row delay is obtained by adding two rows corresponding to the light-emitting area of ​​the pixel to the distance L1. Using this configuration, the exposure positions in the sub-scanning direction on the photosensitive drum 1 can be aligned between the light-emitting portions 50 included in the staggered light-emitting element array chips 40.

[0109] In this embodiment, for all the light-emitting portions 50 of the light-emitting element array chip 40, the configuration in which the light-emitting portions 50 arranged in parallel in the Y direction of arrow are arranged such that their positions are offset from each other by an integer multiple of the distance d3 in the X direction of arrow has been described. However, the present invention is not limited thereto. That is, if the plurality of light-emitting portions 50 included in the light-emitting element array chip 40 includes a group (electrode group) of light-emitting portions arranged in parallel in the Y direction of arrow such that their positions are offset from each other by an integer multiple of the distance d3 in the X direction of arrow, the same effect as described above can be obtained.

[0110] Furthermore, in this embodiment, the arrangement of light-emitting portions 50 adjacent to each other in the arrow Y direction in the light-emitting element array chip 40 such that they are offset by a positional distance d3 in the arrow X direction has been described, but the present invention is not limited thereto. That is, for example, as Figure 16 As shown, if the offset in the X direction between multiple light-emitting parts 50 arranged in parallel in the Y direction is an integer multiple of the interval d3, then the offset between adjacent light-emitting parts 50 in the Y direction does not need to be the interval d3. Figure 17 As shown, the multiple light-emitting parts 50 arranged in parallel in the direction of arrow Y can be partially included in the light-emitting parts 50 at the same positions in the direction of arrow X. Similarly, using... Figure 16 or Figure 17 The configuration shown allows for exposures similar to the one described above to be performed by adjusting the image data transmitted to the light-emitting unit 50.

[0111] Although the invention has been described with reference to exemplary embodiments, the invention is not limited to the disclosed exemplary embodiments. The appended claims are to be given the broadest interpretation to cover all modifications, equivalent structures, and functions.

[0112] This application claims priority to Japanese Patent Application No. 2020-210271, filed on December 18, 2020, the entire contents of which are incorporated herein by reference.

Claims

1. An image forming apparatus configured to expose the surface of a photosensitive member with light to form an electrostatic latent image, and to attach a toner to the electrostatic latent image to form an image, the image forming apparatus comprising: An exposure head is configured to expose the surface of the photosensitive member with light to form the electrostatic latent image, and includes a light-emitting portion comprising a substrate, a first electrode layer, a light-emitting layer, and a second electrode layer. The first electrode layer includes a plurality of electrodes arranged two-dimensionally and spaced apart on the substrate in the rotation direction of the photosensitive member and in the rotation axis direction of the photosensitive member. The light-emitting layer is stacked on the first electrode layer and configured to emit light when a voltage is applied. The second electrode layer is arranged on a side opposite to the side where the first electrode layer is disposed relative to the light-emitting layer, and light can pass through the second electrode layer. as well as The controller is configured to control the application of voltage to each of the plurality of electrodes included in the first electrode layer based on image data to cause the light-emitting layer to emit light, and is configured to control the voltage applied to each of the plurality of electrodes based on the image data to form a pixel by controlling the voltage applied to the plurality of electrodes arranged at different positions in the rotational direction. The plurality of electrodes used to form the same pixel are arranged such that, when viewed from the rotation direction, the electrodes partially overlap each other, and the centroid distance between the plurality of electrodes in the rotation axis direction is equal in the rotation axis direction. d3 = q / n, where n is a natural number of 2 or greater, and where q is the spacing between the electrodes in the direction of the rotation axis, n is the number of electrodes used to form the same pixel, and d3 is the equal centroid distance in the direction of the rotation axis, and the plurality of electrodes used to form the same pixel are arranged such that the centroid positions of each electrode are positioned at intervals of d3 in the direction of the rotation axis.

2. The image forming apparatus according to claim 1, wherein in the electrode group, the plurality of electrodes arranged in parallel in the rotation direction are arranged such that adjacent electrodes are arranged such that they are offset by d3 in position in the rotation axis direction.

3. The image forming apparatus according to claim 1 or 2, wherein the width of each of the plurality of electrodes in the direction of the rotation axis is two or more times d3.

4. The image forming apparatus according to claim 1, wherein the controller includes an image processing unit configured to process the image data, and The image processing unit generates first image data, and then converts the first image data according to the arrangement of the plurality of electrodes included in the first electrode layer to generate second image data with a higher resolution than the first image data, and corrects the second image data according to the image position.

5. The image forming apparatus of claim 1, wherein the controller controls the voltage applied to each of the plurality of electrodes included in the first electrode layer based on binary image data.

Images