Image forming apparatus

Abstract

The image forming apparatus is provided with an exposure head provided with a light emitting portion including a first electrode layer, a light emitting layer, and a second electrode layer, the first electrode layer including a plurality of electrodes arranged two-dimensionally in a rotation direction and a rotation axis direction of a photosensitive member, the light emitting layer being stacked on the first electrode layer, light being able to pass through the second electrode layer, and a controller capable of controlling a voltage to be applied to each of the plurality of electrodes so that one pixel is formed by control of the voltage of the plurality of electrodes arranged at different positions in the rotation direction. The plurality of electrodes are arranged so that a pitch in the rotation direction of the plurality of electrodes included in the first electrode layer is an integer multiple other than an equal multiple of a resolution in the rotation direction of an image formed by the image forming apparatus.

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] Japanese Patent Publication No. 2018-134820 does not mention the relationship between the resolution of the image formed by the image forming apparatus in the sub-scanning direction and the spacing between the light-emitting parts of the exposure head in the sub-scanning direction. Therefore, depending on the relationship between resolution and spacing, a delay circuit needs to be provided in the circuit driving the light-emitting parts during multiple exposures to offset the emission timing of adjacent light-emitting parts in the sub-scanning direction, which may increase the size of the circuit. Summary of the Invention

[0006] The purpose of this invention is to provide an image forming apparatus that can perform multiple exposures via an exposure head without using a delay circuit.

[0007] 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, the light-emitting portion including 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... A second electrode layer is disposed on a side opposite to the side where the first electrode layer is disposed and light can pass through the second electrode layer; and a 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 so that the light-emitting layer emits light, and is configured to control the voltage applied to each of the plurality of electrodes based on image data so that a pixel is formed by controlling the voltage applied to the plurality of electrodes disposed at different positions in the rotational direction, wherein the plurality of electrodes are arranged such that the spacing of the plurality of electrodes included in the first electrode layer in the rotational direction is an integer multiple of the resolution of the image formed by the image forming apparatus in the rotational direction, excluding equal multiples.

[0008] Further features of the invention will become clear from the following description of embodiments with reference to the accompanying drawings. Attached Figure Description

[0009] Figure 1 This is a schematic cross-sectional view of an image forming apparatus.

[0010] Figure 2 (a) and Figure 2 (b) is a perspective view and a cross-sectional view of the photosensitive drum and the exposure head.

[0011] Figure 3 (a) to Figure 3 (c) is a view illustrating the mounting surface of a printed circuit board included in an exposure head.

[0012] Figure 4 This is a view illustrating the positional relationship between the rod-shaped lens array and the light-emitting part.

[0013] Figure 5 This is a schematic diagram of a light-emitting element array chip.

[0014] Figure 6 This is a cross-sectional view of a light-emitting element array chip.

[0015] Figure 7 This is a schematic diagram used to illustrate the arrangement of the light-emitting parts.

[0016] Figure 8 This is a block diagram illustrating the system configuration of the image controller unit and the exposure head.

[0017] Figure 9 This is a block diagram illustrating the system configuration of the light-emitting element array chip.

[0018] Figure 10 This is the circuit diagram of the data retention section.

[0019] Figure 11 This is the operation timing diagram of the data retention section.

[0020] Figure 12 This is the circuit diagram for the analog section.

[0021] Figure 13 This is an image illustrating the exposure of a photosensitive drum.

[0022] Figure 14 This is an image illustrating the exposure of a photosensitive drum.

[0023] Figure 15 This is an image illustrating the exposure of a photosensitive drum.

[0024] Figure 16 This is a schematic diagram illustrating the configuration of the light-emitting part.

[0025] Figure 17 This is an image illustrating the exposure of a photosensitive drum.

[0026] Figure 18 This is a schematic diagram illustrating the configuration of the light-emitting part.

[0027] Figure 19 This is an image illustrating the exposure of a photosensitive drum. Detailed Implementation

[0028] (First Embodiment)

[0029] Image forming apparatus

[0030] In the following description, the general configuration of the image forming apparatus A according to a first embodiment of the present invention will be described together with reference to the accompanying drawings and the operation during image forming. 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 on 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 3 As 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.

[0044] In this embodiment, the resolution pitch 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, which enables exposure processing corresponding to an image width of approximately 316 mm (≈15.8 mm × 20 chips) in the longitudinal direction.

[0045] In the longitudinal direction 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 21.16 μm. That is, the spacing of the light-emitting portions 50 at the boundary portions of each light-emitting element array chip 40 in the longitudinal direction is a resolution spacing of 1200 dpi. Furthermore, in the transverse direction (arrow Y direction) of the light-emitting element array chip 40, the spacing L2 between the light-emitting portions 50 of adjacent light-emitting element array chips 40 is approximately 127 μm (six pixels at 1200 dpi and four pixels at 800 dpi).

[0046] 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.

[0047] Figure 4 This is a view illustrating the positional relationship between the rod-shaped lens array 23 and the light-emitting portion 50 of the light-emitting element array chip 40. (See diagram below.) Figure 4 As shown, a predetermined number of rod-shaped lens arrays 23 are arranged in the direction of arrow X, and the rod-shaped lens arrays 23 are arranged in two staggered rows in the direction of arrow Y, so as to cover the light-emitting part 50 of the light-emitting element array chip 40. In addition, the diameter of the rod-shaped lens arrays 23 is set to 290 μm, and the light emitted from the multiple light-emitting parts 50 is collected by one rod-shaped lens array 23.

[0048] <Light-emitting element array chip>

[0049] Next, the configuration of the light-emitting element array chip 40 will be described.

[0050] 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.

[0051] like Figure 5 As 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Note that when a moisture-sensitive luminescent material, such as an organic EL layer (organic light-emitting layer) or an inorganic EL layer, is used as the light-emitting layer 56, it is desirable to perform a seal to prevent moisture from entering the light-emitting 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.

[0060] 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.

[0061] 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.

[0062] 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 have deviations 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. In addition, in this embodiment, the width, shape, arrangement, etc. of the light-emitting portions 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.

[0063] 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. 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.

[0064] 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.

[0065] 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 that the light-emitting area is sufficient to obtain light intensity 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, resolution, etc. required for the exposure processing of the exposure head 6.

[0066] Furthermore, the distance between the light-emitting parts 50—that is, the distance between the lower electrodes 54—is limited based on the nominal centroid position of the lower electrodes 54. Specifically, when the lower electrodes 54 are regular polygons, the distance between them 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.

[0067] <System Configuration of Exposure Head>

[0068] 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.

[0069] 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.

[0070] Image data from the original document 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. 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 dithering processing is performed at a resolution of 2400 dpi in both the main scanning direction and the sub-scanning direction.

[0071] 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.

[0072] 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 it takes for the photosensitive drum 1 to move a distance the size of a 2400 dpi pixel (approximately 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).

[0073] 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.

[0074] 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.

[0075] <System Configuration of Light Emitting Element Array Chip>

[0076] Next, the system configuration of the light-emitting element array chip 40 will be described.

[0077] Figure 9 This is a block diagram illustrating the system configuration of the light-emitting element array chip 40. Figure 9 In this configuration, since the clock signal is input to all boxes of the digital section 80, the connections are omitted. For example... Figure 9 As shown, the circuit section 46 of the light-emitting element array chip 40 includes a digital section 80 and an analog section 86.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] Data Preservation Department

[0082] Next, the configuration of the data retention unit 85 will be described.

[0083] Figure 10 This is the circuit diagram of the data retention section 85. (For example...) Figure 10 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.

[0084] Figure 11 This is the operation timing diagram of the data retention unit 85. (For example...) Figure 11As 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.

[0085] 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.

[0086] 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.

[0087] <Simulation Department>

[0088] 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.

[0089] Figure 12 This is the circuit diagram for the analog section 86. (For example...) Figure 12 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.

[0090] 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.

[0091] 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 high and low levels; 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 for the light-emitting section 50. In this embodiment, since the drive currents for all four rows (four pixels) are output simultaneously, the light-emitting sections 50 in all four rows (four pixels) emit light simultaneously.

[0092] <Light-emitting part illumination control during image formation>

[0093] 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.

[0094] Figure 13 This is an image showing the exposure of the photosensitive drum 1. Figure 13 In the diagram, the rectangles on the photosensitive drum 1 indicate the pixels on the photosensitive drum 1, and the numbers (1-1 to 16-4) within the pixels indicate the type of image data to be written to each pixel. Although the number of pixels in the X direction is 748 pixels × 20 chips = 14960 pixels, for ease of description, ... Figure 13 Only four pixels are shown in the diagram as pixels in the direction of the arrow X.

[0095] like Figure 13 As shown, firstly, at time T1, image data from four rows is transmitted from the image controller unit 70 to the exposure head 6. As a result, the four light-emitting units 50 arranged in parallel in the direction of arrow Y emit light simultaneously, and the pixels of the four rows (1-1, 3-1, 5-1 and 7-1) are simultaneously exposed on the photosensitive drum 1.

[0096] After one clock cycle, the next four rows of image data are transmitted from the image controller unit 70 to the exposure head 6. As a result, the four light-emitting units 50 adjacent to the four light-emitting units 50 that initially emitted light emit light simultaneously, and the pixels (1-2, 3-2, 5-2 and 7-2) of the four rows adjacent to each other in the direction of arrow X are simultaneously exposed on the photosensitive drum 1.

[0097] This operation is repeated every clock cycle, and during the 52.92μs period of the row synchronization signal, 2400dpi × 4 rows of pixels are exposed on the photosensitive drum 1. Here, at time T1, image data (1-1 to 1-4) for exposing the first row of the photosensitive drum 1 is transmitted to the downstream light-emitting unit 50 located in the rotation direction of the photosensitive drum 1. On the other hand, in this embodiment, since the resolution spacing of the light-emitting element array chip 40 is 1200dpi (approximately 21.16μm) relative to the 2400dpi image resolution in the sub-scanning direction, image data spaced 2400dpi per row is transmitted to the light-emitting unit 50 located upstream of the light-emitting unit 50 for which the image data for exposing the first row is transmitted in the rotation direction of the photosensitive drum 1. For example, image data (3-1 to 3-4) for exposing the third row of the photosensitive drum 1 is transmitted to the light-emitting unit 50 located upstream of the light-emitting unit 50 for exposing the first row. Similarly, image data (5-1 to 5-4) and image data (7-1 to 7-4) are transmitted to the light-emitting unit 50 located further upstream. That is, as... Figure 1 As shown, the image formed on the photosensitive drum 1 at time T1 is spaced out in a row of 2400 dpi.

[0098] Next, at time T2, the photosensitive drum 1 rotates 2400 dpi (10.58 μm) relative to time T1 in the sub-scanning direction (arrow Y direction), and the image data of the four lines is transmitted from the image controller unit 70 to the exposure head 6 in the same manner as at time T1. Here, the image data of each line transmitted to the light-emitting unit 50 at time T2 is transmitted while being offset by one line relative to time T1.

[0099] That is, at time T2, the image data (2-1 to 2-4) for exposing the second row of the photosensitive drum 1 is transmitted to the downstream light-emitting unit 50 located in the rotational direction of the photosensitive drum 1. Furthermore, the image data (4-1 to 4-4) for exposing the fourth row of the photosensitive drum 1 at 2400 dpi intervals is transmitted to the light-emitting unit 50 located upstream of the light-emitting unit 50 to which the image data for the second row is transmitted in the rotational direction of the photosensitive drum 1. Similarly, for each row, each of the image data (6-1 to 6-4) and the image data (8-1 to 8-4) is transmitted to the adjacent light-emitting unit 50 in the rotational direction of the photosensitive drum 1.

[0100] Furthermore, at time T3, when the photosensitive drum 1 rotates 2400 dpi (10.58 μm) relative to time T2 in the sub-scanning direction (arrow Y direction), four lines of image data are transmitted from the image controller unit 70 to the exposure head 6 in the same manner as at times T1 and T2. Here, the image data of each line transmitted to the light-emitting unit 50 at time T3 is transmitted while being shifted by one line relative to time T2.

[0101] That is, at time T3, the image data (3-1 to 3-4) for exposing the third row of the photosensitive drum 1 is transmitted to the downstream light-emitting unit 50 located in the rotational direction of the photosensitive drum 1. Furthermore, the image data (5-1 to 5-4) for exposing the fifth row of the photosensitive drum 1 at 2400 dpi intervals is transmitted to the light-emitting unit 50 located upstream of the light-emitting unit 50 to which the image data for the third row is transmitted in the rotational direction of the photosensitive drum 1. Similarly, for each row, each of the image data (7-1 to 7-4) and the image data (9-1 to 9-4) is transmitted to the adjacent light-emitting unit 50 in the rotational direction of the photosensitive drum 1.

[0102] Therefore, for the third, fifth, and seventh rows of the photosensitive drum 1, the light-emitting unit 50 performs two multiple exposures at times T1 and T3. That is, a pixel is formed by multiple light-emitting units 50 performing multiple exposures. Thereafter, even after time T4, the same processing as at times T1, T2, and T3 is performed. As a result, at time T7, since exposure processing is performed for the seventh row on the photosensitive drum 1 at each of times T1 to T7, a total of four multiple exposures are performed. By repeating this operation on an image page, an electrostatic latent image undergoing four multiple exposures is formed on the entire area of ​​the photosensitive drum 1 except for the first to sixth rows.

[0103] As described above, in this embodiment, the spacing of the light-emitting portions 50 of the exposure head 6 in the sub-scanning direction is an integer multiple of the resolution spacing of the image formed by the image forming apparatus A in the sub-scanning direction (the rotation direction of the photosensitive drum 1 or the direction of arrow Y). With this configuration, multiple exposures of the photosensitive drum 1 can be performed solely by shifting the image data exposed by the light-emitting portions 50 arranged in parallel in the direction of arrow Y, without shifting the emission timing of the light-emitting portions 50 arranged in parallel in the direction of arrow Y by providing a delay circuit in the exposure head 6. Therefore, the increase in the circuit size of the exposure head 6 can be suppressed, and the manufacturing cost can be reduced.

[0104] In this embodiment, the configuration in which the photosensitive drum 1 is driven at a rotational speed of 200 mm / s has been described, but the invention is not limited thereto. Optimal image formation conditions vary depending on the type of sheet S, etc. For example, when a toner image is fixed onto thick or coated paper in the fixing apparatus 94, more heat is required compared to when the toner image is fixed onto plain paper. Therefore, it is preferable to reduce the transport speed of the sheet S to increase the fixing time. Therefore, in the following description, the case where the photosensitive drum 1 is driven at a rotational speed of 100 mm / s to reduce the transport speed of the sheet S will be considered.

[0105] With the photosensitive drum 1 driven at a rotational speed of 100 mm / s, the time required to perform an exposure at a resolution of 2400 dpi (10.58 μm) is 211.66 μs. Therefore, as Figure 14 As shown, the photosensitive drum 1 is driven at a rotational speed of 100 mm / s, and the period of the line synchronization signal is set to 105.83 μs. The emission sequence of the light-emitting part 50 of the exposure head 6 and the image data to be written for each line are similar to those in the reference above. Figure 13 The described control is used for control.

[0106] In this configuration, the rotational speed of the photosensitive drum 1 is 100 mm / s, which is for reference. Figure 13 In the described configuration, the rotational speed of the photosensitive drum 1 is half, and the exposure time at 2400 dpi (10.58 μm) is doubled. Therefore, when the light-emitting unit 50 is driven with the same driving current as in the configuration where the photosensitive drum 1 rotates at 200 mm / s, the photosensitive drum 1 is exposed with twice the intensity. Therefore, it is preferable to adjust the exposure intensity by changing the setting value of the current setting DAC 61 according to the rotational speed of the photosensitive drum 1. For example, in a configuration where the rotational speed of the photosensitive drum 1 is 100 mm / s, it is preferable that the current setting value of the DAC 61 is set to half that in the configuration where the rotational speed of the photosensitive drum 1 is 200 mm / s, and the exposure intensities are equal.

[0107] Furthermore, in a configuration where the photosensitive drum 1 is driven at a rotational speed of 100 mm / s, the following configuration can be considered as a configuration where the exposure intensity is equal to the exposure intensity in a configuration where the photosensitive drum 1 is driven at a rotational speed of 200 mm / s without changing the current setting value of the DAC 61. For example... Figure 15 As shown, firstly, the photosensitive drum 1 is driven at a rotational speed of 100 mm / s, and the period of the horizontal sync signal is set to 52.92 μs, without changing the period of the horizontal sync signal in the configuration where the photosensitive drum 1 is driven at a rotational speed of 200 mm / s.

[0108] Then, at time T1, the light-emitting part 50 passes through the reference. Figure 13The control described for the light-emitting unit 50 at time T1 is the same as that for the control of the light-emitting unit 50, and during the period of 52.92 μs, which is the period of the horizontal sync signal, pixels spaced one line apart at 2400 dpi × 4 lines are exposed on the photosensitive drum 1. Here, although the photosensitive drum 1 rotates at 100 mm / s, since the period of the horizontal sync signal is 52.92 μs corresponding to 200 mm / s, the length of the area exposed on the photosensitive drum 1 at time T1 in the direction of arrow Y is 5.29 μm, which is half of 10.58 μm.

[0109] Next, at time T2, when the photosensitive drum 1 rotates 5.29 μm relative to time T1, image data transmission from the image controller section 70 to the exposure head 6 is not performed, and exposure of the photosensitive drum 1 is not performed. Next, at time T3, when the photosensitive drum 1 rotates 10.58 μm relative to time T1 (for a line at 2400 dpi), the light-emitting section 50 is aligned with the reference... Figure 13 The light-emitting part 50 at time T2 described is controlled to emit light under the same control.

[0110] Therefore, for the seventh row of the photosensitive drum 1, the light-emitting unit 50 performs two multiple exposures at times T1 and T5. Thereafter, the same control is performed until time T13. That is, when the line synchronization signal is output twice, image data is not transmitted once (the image data is sparsified), and the light-emitting unit 50 is turned off (no light is emitted). As a result, at time T13, since exposure processing is performed for the seventh row of the photosensitive drum 1 at each of times T1, T5, T9, and T13, a total of four multiple exposures are performed. By repeating this operation, an electrostatic latent image undergoing four multiple exposures is formed over the entire area of ​​the photosensitive drum 1, excluding the first to third rows.

[0111] By implementing such control, in a configuration where the photosensitive drum 1 is driven at a rotational speed of 100 mm / s, the exposure time for each line can be made the same as in a configuration where the photosensitive drum 1 is driven at a rotational speed of 200 mm / s. Therefore, the exposure intensity can be kept equal without changing the current setting of the DAC 61. In this configuration, the length of the exposure area for each line on the photosensitive drum 1 in the sub-scanning direction (arrow Y direction) is halved. However, since the image resolution is not halved, and only the spot diameter in the sub-scanning direction is reduced, there is no adverse effect on the image, and the image sharpness is improved.

[0112] (Second Embodiment)

[0113] Next, a second embodiment of the image forming apparatus A according to the present invention will be described. Referring to the same drawings, the same parts as in the first embodiment will be indicated by the same reference numerals, and their descriptions will be omitted.

[0114] Figure 16 This is a schematic diagram illustrating the configuration of the light-emitting portion 50 of the light-emitting element array chip 40 according to this embodiment. Figure 16 As shown, in this embodiment, the light-emitting portions 50 adjacent to each other in the Y direction are arranged with a position offset by a distance d3 in the X direction. In this embodiment, the distance d3 is set to 5.29 μm (4800 dpi).

[0115] In the first embodiment, the widths W1 and W2 and the spacings d1 and d2 are W1 = W2 = 19.8 μm and d1 = d2 = 0.68 μm. That is, as in the first embodiment, the spacing of the light-emitting portions 50 in the Y-direction is set to 21.16 μm (1200 dpi). The image forming apparatus A according to this embodiment forms an image with a resolution of 2400 dpi in the sub-scanning direction, and the rotational speed of the photosensitive drum 1 is 200 mm / s. Therefore, the time taken to perform exposure at a resolution of 2400 dpi (10.58 μm) is 52.92 μs, and the period of the line synchronization signal is also 52.92 μs. Apart from the control described below, the other configurations of the image forming apparatus A in this embodiment are similar to those in the first embodiment.

[0116] Figure 17 This is an image showing the exposure of the photosensitive drum 1. Figure 17 In the diagram, the rectangles on the photosensitive drum 1 indicate the pixels on the photosensitive drum 1, and the numbers (1-1 to 16-4) within the pixels indicate the type of image data to be written to each pixel. Although the number of pixels in the X direction is 748 pixels × 20 chips = 14960 pixels, for ease of description, ... Figure 17 Only four pixels are shown in the diagram as pixels in the direction of the arrow X.

[0117] like Figure 17 As shown, firstly, at time T1, the light-emitting part 50 passes through the reference... Figure 13 The control of the light-emitting part 50 at the time T1 described is the same as that used for control, and during the period of 52.92μs, which is the period of the line synchronization signal, pixels of 2400dpi × 4 lines spaced apart by 1 line are exposed on the photosensitive drum 1.

[0118] Next, at time T2, when the photosensitive drum 1 rotates 2400 dpi (10.58 μm) relative to time T1 in the sub-scanning direction (arrow Y direction), four lines of image data are transmitted from the image controller unit 70 to the exposure head 6 in the same manner as at time T1. Here, the image data of each line transmitted to the light-emitting unit 50 at time T2 is transmitted while being offset by one line relative to time T1.

[0119] That is, at time T2, the image data (2-1 to 2-4) for exposing the second row of the photosensitive drum 1 is transmitted to the downstream light-emitting part 50 located in the rotational direction of the photosensitive drum 1. Furthermore, the image data (4-1 to 4-4) for exposing the fourth row of the photosensitive drum 1, spaced 2400 dpi apart, is transmitted to the light-emitting part 50 located upstream of the light-emitting part 50 to which the image data for the second row is transmitted in the rotational direction of the photosensitive drum 1. Similarly, image data (5-1 to 5-4) and image data (7-1 to 7-4) are transmitted to the light-emitting part 50 located further upstream. That is, as... Figure 1 As shown, the image formed on the photosensitive drum 1 at time T1 is spaced out in a row of 2400 dpi.

[0120] Furthermore, at time T3, when the photosensitive drum 1 rotates 2400 dpi (10.58 μm) relative to time T2 in the sub-scanning direction (arrow Y direction), four lines of image data are transmitted from the image controller unit 70 to the exposure head 6 in the same manner as at times T1 and T2. Here, the image data of each line transmitted to the light-emitting unit 50 at time T3 is transmitted while being shifted by one line relative to time T2.

[0121] That is, at time T3, the image data (3-1 to 3-4) for exposing the third row of the photosensitive drum 1 is transmitted to the downstream light-emitting unit 50 located in the rotational direction of the photosensitive drum 1. Furthermore, the image data (5-1 to 5-4) for exposing the fifth row of the photosensitive drum 1 at 2400 dpi intervals is transmitted to the light-emitting unit 50 located upstream of the light-emitting unit 50 to which the image data for the third row is transmitted in the rotational direction of the photosensitive drum 1. Similarly, for each row, each of the image data (7-1 to 7-4) and the image data (9-1 to 9-4) is transmitted to the adjacent light-emitting unit 50 in the rotational direction of the photosensitive drum 1.

[0122] Therefore, for the third, fifth, and seventh rows of the photosensitive drum 1, the light-emitting unit 50 performs two multiple exposures at times T1 and T3. Thereafter, even after time T4, the same process as at times T1, T2, and T3 is performed. As a result, at time T7, since exposure processing is performed for the seventh row on the photosensitive drum 1 at each of times T1 to T7, a total of four multiple exposures are performed. By repeating this operation on an image page, an electrostatic latent image undergoing four multiple exposures is formed on the entire area of ​​the photosensitive drum 1, excluding the first to sixth rows.

[0123] Similarly, in this embodiment, the spacing of the light-emitting portions 50 of the exposure head 6 in the sub-scanning direction is an integer multiple of the resolution spacing of the image formed by the image forming apparatus A in the sub-scanning direction (the rotation direction of the photosensitive drum 1 or the direction of arrow Y). Therefore, similar to the first embodiment, the photosensitive drum 1 can undergo multiple exposures without providing a delay circuit in the exposure head 6 and shifting the emission timing of the light-emitting portions 50 arranged in parallel in the direction of arrow Y. Therefore, the increase in the circuit size of the exposure head 6 can be suppressed, and the manufacturing cost can be reduced.

[0124] In this embodiment, the light-emitting portions 50 adjacent to each other in the Y-direction are arranged to be offset in position by 5.29 μm (4800 dpi) in the X-direction. Therefore, the exposure position of the light-emitting portions 50 adjacent to each other in the Y-direction on the photosensitive drum 1 is offset by 5.29 μm in the main scanning direction (X-direction), and the exposure resolution in the main scanning direction is 4800 dpi. Therefore, using the configuration of this embodiment, compared to the configuration of the first embodiment, the exposure resolution can be improved, and the image quality can be improved.

[0125] (Third Embodiment)

[0126] Next, a third embodiment of the image forming apparatus A according to the present invention will be described. Referring to the same drawings, the same parts as in the first and second embodiments will be indicated by the same reference numerals, and their descriptions will be omitted.

[0127] Figure 18 This is a schematic diagram illustrating the configuration of the light-emitting portion 50 of the light-emitting element array chip 40 according to this embodiment. Figure 18 As shown, in this embodiment, in order to increase the light intensity of the light-emitting part 50, the width W2 of the light-emitting part 50 is set to W2 = 31.07 μm, which is larger than the width W2 in the first embodiment. As in the first embodiment, the width W1 and the spacing d1 and d2 are W1 = 19.8 μm and d1 = d2 = 0.68 μm. That is, in this embodiment, the spacing of the light-emitting parts 50 in the direction of arrow Y is set to 31.75 μm (800 dpi).

[0128] The image forming apparatus A according to this embodiment forms an image with a resolution of 2400 dpi in the sub-scanning direction, and as in the first embodiment, the rotation speed of the photosensitive drum 1 is 200 mm / s. Therefore, the time taken to perform exposure at a resolution of 2400 dpi (10.58 μm) is 52.92 μs, and the period of the line synchronization signal is also 52.92 μs. Apart from the control described below, the other configurations of the image forming apparatus A in this embodiment are similar to the other configurations in the first embodiment.

[0129] Figure 19 This is an image showing the exposure of the photosensitive drum 1. Figure 17 In the diagram, the rectangles on the photosensitive drum 1 indicate the pixels on the photosensitive drum 1, and the numbers (1-1 to 7-4) within the pixels indicate the type of image data to be written to each pixel. Although the number of pixels in the X direction is 748 pixels × 20 chips = 14960 pixels, for ease of description, ... Figure 19 Only four pixels are shown in the diagram as pixels in the direction of the arrow X.

[0130] like Figure 19 As shown, firstly, at time T1, the light-emitting part 50 passes through the reference... Figure 13 The control of the light-emitting unit 50 at time T1 is the same as that described, and during the period of 52.92 μs, which is the period of the line synchronization signal, 1200 dpi × 4 lines of pixels are exposed on the photosensitive drum 1. In this embodiment, since an image with a resolution of 2400 dpi in the sub-scanning direction (arrow Y direction) is formed by the image forming apparatus A, and the interval between the light-emitting units 50 in the sub-scanning direction is 800 dpi, two lines of electrostatic latent image spaced 2400 dpi apart at time T1 are formed on the photosensitive drum 1.

[0131] Next, at time T2, when the photosensitive drum 1 rotates 2400 dpi (10.58 μm) relative to time T1 in the sub-scanning direction (arrow Y direction), four lines of image data are transmitted from the image controller unit 70 to the exposure head 6 in the same manner as at time T1. Here, the image data of each line transmitted to the light-emitting unit 50 at time T2 is transmitted while being offset by one line relative to time T1.

[0132] That is, at time T2, the image data (2-1 to 2-4) for exposing the second row of the photosensitive drum 1 is transferred to the downstream light-emitting unit 50 located in the rotational direction of the photosensitive drum 1. Furthermore, the image data (5-1 to 5-4) for exposing the fifth row of the photosensitive drum 1 is transferred to a light-emitting unit 50 located upstream of the light-emitting unit 50 to which the image data for the second row is transferred in the rotational direction of the photosensitive drum 1. Each of the image data (8-1 to 8-4) and the image data (11-1 to 11-4) is transferred to the adjacent light-emitting unit 50 in the rotational direction of the photosensitive drum 1. As described above, at time T2, each row on the photosensitive drum 1 does not undergo multiple exposures.

[0133] Next, at times T3 and T4, controls similar to those performed at times T1 and T2 are executed. Therefore, at time T4, for the fourth, seventh, and tenth rows of the photosensitive drum 1, the light-emitting unit 50 performs two multiple exposures at times T1 and T4. At times T5 and T6, controls similar to those performed at times T3 and T4 are executed. Therefore, at time T5, for the fifth, eighth, and eleventh rows of the photosensitive drum 1, the light-emitting unit 50 performs two multiple exposures at times T2 and T5. At time T6, for the sixth, ninth, and twelfth rows of the photosensitive drum 1, the light-emitting unit 50 performs two multiple exposures at times T3 and T6.

[0134] Subsequently, at time T7, in the same manner as at time T1, four lines of image data are transferred from the image controller unit 70 to the exposure head 6. Here, the image data of each line transferred to the light-emitting unit 50 at time T7 is transferred while being offset by one line relative to time T6. As a result, at time T7, since exposure processing is performed on the tenth line on the photosensitive drum 1 at each of times T1, T4, T7, and T10, a total of four multiple exposures are performed. By repeating this operation on an image page, an electrostatic latent image undergoing four multiple exposures is formed on the entire area of ​​the photosensitive drum 1 except for the first to ninth lines. Although multiple exposures are not performed on the first to third lines on the photosensitive drum 1, at least two or more multiple exposures are performed on the fourth to ninth lines.

[0135] As described above, in this embodiment, the spacing of the light-emitting portions 50 of the exposure head 6 in the sub-scanning direction is an integer multiple of the resolution in the sub-scanning direction (rotation direction of the photosensitive drum 1 or arrow Y direction) of the image formed by the image forming apparatus A. Similarly, using this configuration, multiple exposures of the photosensitive drum 1 can be performed solely by shifting the image data exposed by the light-emitting portions 50 arranged in parallel in the arrow Y direction, without shifting the emission timing of the light-emitting portions 50 arranged in parallel in the arrow Y direction by providing a delay circuit in the exposure head 6. As a result, the increase in the circuit size of the exposure head 6 can be suppressed, and the manufacturing cost can be reduced.

[0136] In the first and second embodiments, a configuration in which the image formed by the image forming apparatus A has a resolution of 2400 dpi in the sub-scanning direction (arrow Y direction) and the spacing of the light-emitting portions 50 in the sub-scanning direction (arrow Y direction) is 1200 dpi has been described. Furthermore, in the third embodiment, a configuration in which the image formed by the image forming apparatus A has a resolution of 2400 dpi in the sub-scanning direction (arrow Y direction) and the spacing of the light-emitting portions 50 in the sub-scanning direction (arrow Y direction) is 800 dpi has been described. However, the present invention is not limited thereto. That is, if the spacing of the light-emitting portions 50 of the exposure head 6 in the sub-scanning direction is an integer multiple (excluding equal multiples) of the resolution of the image formed by the image forming apparatus A in the sub-scanning direction (rotation direction of the photosensitive drum 1 and arrow Y direction), then the resolution of the image in the sub-scanning direction and the spacing of the light-emitting portions 50 in the sub-scanning direction can be freely set.

[0137] 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.

[0138] This application claims priority to Japanese Patent Application No. 2020-210270, 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, configured to expose the surface of the photosensitive member with light to form the electrostatic latent image, and includes a light-emitting element array chip, the light-emitting element array chip comprising: substrate, A first electrode layer, comprising a plurality of electrodes, is arranged two-dimensionally and spaced apart on the substrate in both the rotational direction and the rotational axis direction of the photosensitive member. Each of the plurality of electrodes corresponds to a plurality of light-emitting portions, and the plurality of electrodes includes electrodes arranged in the rotational direction. A light-emitting layer, which is stacked on the first electrode layer and configured to emit light when a voltage is applied, and A second electrode layer is disposed on the 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; and 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, so as 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, so as 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 are arranged such that the spacing between the plurality of electrodes included in the first electrode layer in the rotational direction is an integer multiple of the resolution spacing of the image formed by the image forming apparatus in the rotational direction, and the integer is greater than 1.

2. The image forming apparatus according to claim 1, wherein the controller controls the application of voltage to the electrodes arranged in parallel in the rotational direction among the plurality of electrodes included in the first electrode layer, so that the light-emitting portions arranged in parallel in the rotational direction simultaneously emit light or not emit light according to image data.

3. The image forming apparatus according to claim 1 or 2, wherein the length of the electrodes included in the first electrode layer in the rotation direction is equal to the length in the rotation axis direction.

4. The image forming apparatus according to claim 1 or 2, wherein the length of the electrode included in the first electrode layer in the rotational direction is longer than its length in the rotational axis direction.

5. The image forming apparatus according to claim 1, wherein the light-emitting layer is an organic light-emitting layer.

Images