Image forming device

Abstract

To reduce noise without deteriorating the image quality.SOLUTION: An exposure head 106 includes a plurality of plane light emitting element array chips 400-1 to 20 which are provided on the surface of a printed circuit board 202, in which a plurality of light emitting elements 602 emitting light are arrayed in the main-scanning direction, and are arrayed in two lines of a first line and a second line in the sub-scanning direction orthogonal to the main-scanning direction. The plane light emitting element array chips 400-2, ..., 20 in the first line and the plane light emitting element array chips 400-1, ..., 19 in the second line are arranged in the zigzag shape along the main-scanning direction. The intervals between the plane light emitting element array chips 400-2, ..., 20 in the first line and the plane light emitting element array chips 400-1, ..., 19 in the second are set to be the integral multiplication of the image resolution pitch in the sub-scanning direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an exposure head that exposes a photosensitive drum. Do The present invention relates to an image forming apparatus equipped with the same. [Background technology]

[0002] Conventionally, electrophotographic printers have been commonly known that expose a photosensitive drum to light using an exposure head that uses light-emitting elements such as LEDs or organic electroluminescent elements to form a latent image on the photosensitive drum. Such an exposure head is composed of a row of light-emitting elements arranged in the longitudinal direction of the photosensitive drum and a rod lens array that focuses light from the row of light-emitting elements on the photosensitive drum. The LEDs or organic electroluminescent elements are surface-emitting light-emitting element arrays in which the direction of light emitted from the light-emitting surface is parallel to the optical axis of the rod lens array.

[0003] In the exposure head, the length of the light-emitting element array is determined by the width of the image formation area on the photosensitive drum, and the spacing between the light-emitting elements is determined by the image resolution of the printer. For example, in a 1200 dpi printer, the pixel spacing is 21.16 μm (omitted from the third decimal point), so the spacing between the light-emitting elements is also 21.16 μm. Printers using such exposure heads use fewer parts than laser scanning printers that deflect and scan a laser beam using a polygon motor, making it easier to make the device smaller and less expensive.

[0004] In this situation, conventionally, there is known an exposure head in which a TFT circuit and an organic EL are provided on a long transparent glass substrate (for example, Patent Document 1). Also, conventionally, there is known an exposure head formed using an LED / driver IC composite chip in which an integrated circuit thin film and a light-emitting layer thin film are attached to a long substrate (for example, Patent Document 2). Furthermore, conventionally, there is known an exposure head in which a compound semiconductor chip in which a self-scanning light-emitting element is formed on a long substrate (for example, Patent Document 3). [Prior art documents] [Patent documents]

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2015-112856 Patent Document 2 Japanese Patent Application Laid-Open No. 2009-296003 Patent Document 3 Japanese Patent Application Laid-Open No. 2017-183436 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] However, in Patent Documents 1 to 3, since the substrate has an elongated shape and can be regarded as an antenna electrically, there is a problem that it is easy to radiate electrical noise. For example, an exposure head corresponding to an image width of 300 mm and an image resolution of 1200 dpi requires 14,000 or more light-emitting elements in the main scanning direction and is equipped with a large number of light-emitting elements. When a large number of light-emitting elements are lit in such an exposure head, there is a problem that noise increases and it is easy to radiate noise in combination with the shape of the substrate.

[0007] On the other hand, a method of reducing noise by shifting the light emission timing of the light-emitting elements is conceivable. However, when the light emission timing is shifted, there is a concern that the position of the formed image in the sub-scanning direction is shifted and image quality deteriorates.

[0008] An object of the present invention is to provide an image forming apparatus capable of reducing noise without deteriorating image quality. Ru picture and an image forming apparatus. MEANS FOR SOLVING THE PROBLEMS

[0009] An image forming apparatus according to the present invention is an image forming apparatus that forms an image on a recording medium, and includes a rotating photosensitive drum and ,before arranged along the main scanning direction parallel to the rotation axis of the photosensitive drum a first semiconductor chip having a first row of light emitting elements; at a position different from that of the first semiconductor chip in the sub-scanning direction orthogonal to the main scanning direction Established a second semiconductor chip thus obtained an exposure head including a second semiconductor chip having a second light-emitting element row arranged along the main scanning direction; and a control unit that outputs a first light-emitting signal that controls the light-emitting timing of a first light-emitting element included in the first light-emitting element row, and a second light-emitting signal that controls the light-emitting timing of a second light-emitting element included in the second light-emitting element row, wherein, when a distance between the first light-emitting element row and the second light-emitting element row in the sub-scanning direction is S, S is different from an integer multiple of the resolution pitch in the sub-scanning direction of the image formed on the recording medium the law of nature , the control unit outputs the second light-emitting signal with a delay of S / Ps relative to the first light-emitting signal, where Ps is a rotation speed of the surface of the photosensitive drum. characterized by this. [Effect of the Invention]

[0010] According to the present invention, noise can be reduced without degrading the image quality. [Brief Description of the Drawings]

[0011] [Figure 1] It is a schematic diagram of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 2] It is a schematic diagram of an exposure head and a photosensitive drum according to Embodiment 1 of the present invention. [Figure 3] It is a schematic diagram showing the configuration of an exposure head according to Embodiment 1 of the present invention. [Figure 4] It is a schematic diagram of a surface light emitting element array chip of an exposure head according to Embodiment 1 of the present invention. [Figure 5] It is a cross-sectional view taken along line A-A of FIG. 4. [Figure 6] It is a schematic diagram showing the arrangement of light emitting elements of a surface light emitting element array chip of an exposure head according to Embodiment 1 of the present invention. [Figure 7] It is a timing chart of an exposure head according to Embodiment 1 of the present invention. [Figure 8] It is a timing chart of an exposure head according to Embodiment 1 of the present invention. [Figure 9] It is a schematic diagram showing the configuration of an exposure head according to Embodiment 2 of the present invention. [Embodiments for Carrying Out the Invention]

[0012] Hereinafter, embodiments will be described in detail with reference to the drawings.

[0013] (Embodiment 1) [Configuration of Image Forming Apparatus] The configuration of the image forming apparatus 1 according to Embodiment 1 of the present invention will be described in detail with reference to FIG. 1.

[0014] The image forming apparatus 1 includes a scanner unit 100, an image forming unit 103, a fixing unit 104, a paper feeding / conveying unit 105, and a registration roller 110.

[0015] The scanner unit 100 irradiates illumination onto a document placed on the document table, optically reads the image of the document, converts the read image into an electrical signal, and creates image data. The scanner unit 100 outputs the created image data to a printer control unit (not shown).

[0016] The image forming unit 103 operates under the control of the printer control unit, forms an image on a sheet conveyed from the registration roller 110, and conveys the sheet on which the image has been formed to the fixing unit 104. The image forming unit 103 has four image forming units that perform a series of electrophotographic processes of charging, exposure, development, and transfer. The image forming unit 103 forms a full-color image on the sheet by four image forming units arranged in the order of cyan (C), magenta (M), yellow (Y), and black (K). Each of the four image forming units sequentially executes the image forming operations of magenta, yellow, and black after a predetermined time has elapsed since the start of cyan image formation.

[0017] Specifically, the image forming unit 103 includes a photosensitive drum 102, an exposure head 106, a charger 107, a developer 108, a transfer belt 111, and an optical sensor 113.

[0018] The photosensitive drum 102 as an image carrier is attached to the image forming apparatus 1 by an attachment member (not shown) and is rotationally driven.

[0019] The exposure head 106 is attached to the image forming apparatus 1 by an attachment member (not shown). The exposure head 106 is composed of four exposure heads 106a, 106b, 106c, and 106d corresponding to the four imaging units. The exposure head 106 forms a latent image (electrostatic latent image) on the photosensitive drum 102 by concentrating and exposing the photosensitive drum 102 with light emitted in accordance with image data. The configuration of the exposure head 106 will be described in detail later.

[0020] The charger 107 charges the photosensitive drum 102 .

[0021] The developing device 108 supplies toner to the latent image formed on the photosensitive drum 102 to develop it, thereby forming a toner image (developer image) on the photosensitive drum 102.

[0022] The transfer belt 111 transports the sheet transported by the registration rollers 110 to the fixing unit 104. A toner image developed by the developing unit 108 is transferred onto the sheet transported by the transfer belt 111.

[0023] An optical sensor 113 is provided opposite the transfer belt 111 and detects the position of a test chart printed on the transfer belt 111 in order to derive the amount of color misregistration between each of the image-forming units. The optical sensor 113 outputs the detection result of the test chart position to an image controller (not shown). Based on the detection result of the test chart position input from the optical sensor 113, the image controller derives the amount of color misregistration between each of the image-forming units of the image-forming unit 103 and performs control to correct the image position of each color. This control allows a full-color toner image without color misregistration to be transferred onto the sheet.

[0024] Fixing unit 104 is made up of a combination of rollers and has a built-in heat source such as a halogen heater (not shown). Fixing unit 104 melts and fixes the toner on the sheet onto which the toner image has been transferred by imaging unit 103 using heat and pressure, and discharges the sheet with the fixed toner outside image forming apparatus 1 using paper discharge rollers 112.

[0025] The paper feeding / conveying unit 105 includes an in-body paper feeding unit 109a, an in-body paper feeding unit 109b, an external paper feeding unit 109c, and a manual paper feeding unit 109d, and feeds a sheet from a pre-instructed paper feeding unit and conveys it to the registration roller 110.

[0026] The registration roller 110 conveys the sheet conveyed from the paper feeding / conveying unit 105 to the transfer belt 111 at the timing of transferring the toner image formed in the image forming unit 103 onto the sheet.

[0027] The printer control unit controls the operations of the scanner unit 100, the image forming unit 103, the fixing unit 104, and the paper feeding / conveying unit 105. The printer control unit communicates with the MFP control unit that controls the entire MFP (the entire image forming apparatus 1), and controls the operations while managing the states of the scanner unit 100, the image forming unit 103, the fixing unit 104, and the paper feeding / conveying unit 105 in accordance with the instructions of the MFP control unit.

[0028] <Configuration of the exposure head> The configuration of the exposure head 106 according to Embodiment 1 of the present invention will be described in detail with reference to FIGS. 2 and 3.

[0029] FIG. 2(a) shows the arrangement state of the exposure head 106 with respect to the photosensitive drum 102, and FIG. 2(b) shows the state where the light emitted from the light emitting element group 201 is condensed on the photosensitive drum 102 by the rod lens array 203.

[0030] FIG. 3(a) shows the surface opposite to the surface on which the light emitting element group 201 of the printed circuit board 202 is mounted (hereinafter referred to as the "non-light emitting element mounting surface"), and FIG. 3(b) shows the surface on which the light emitting element group 201 is mounted (hereinafter referred to as the "light emitting element mounting surface"). Further, FIG. 3(c) shows the state of the boundary portion between the chips of the surface light emitting element array chips 400-1 to 400-20.

[0031] The exposure head 106 includes a group of light-emitting elements 201 , a printed circuit board 202 , a rod lens array 203 , and a housing 204 .

[0032] The light emitting element group 201 is mounted on the light emitting element mounting surface of the printed circuit board 202 and is composed of 20 surface light emitting element array chips 400-1 to 400-20 as semiconductor chips. As shown in Fig. 3(b), the surface light emitting element array chips 400-1 to 400-20 are arranged in two rows, row A as the first row and row B as the second row, in the Y direction which is the sub-scanning direction orthogonal to the X direction which is the main scanning direction. The surface light emitting element array chips 400-2, 4, 6, ..., 20 in row A and the surface light emitting element array chips 400-1, 3, 5, ..., 19 in row B are arranged in a staggered pattern along the X direction.

[0033] The interval S between the surface light emitting element array chips 400-2, 4, 6, ..., 20 in row A and the surface light emitting element array chips 400-1, 3, 5, ..., 19 in row B is set so as not to be an integer multiple of the minimum distance in the Y direction of the latent image formed on the photosensitive drum 102. Specifically, the interval S is set so as to satisfy the following formula (1):

[0034] S = (α + β) × Ly (1) where α is a positive integer β is a real number, 0<β<1, Ly is the minimum distance in the Y direction of the latent image formed on the photosensitive drum 102.

[0035] Ly in equation (1) is the same as the image resolution pitch (pixel spacing) in the Y direction, and is approximately 21.16 μm when the image resolution pitch in the Y direction is 1200 dpi, for example.

[0036] In this embodiment, Ly=21.16 μm, α=14, and β=0.5 are substituted into equation (1) and rounded off to the first decimal place to obtain S=307 μm. This allows the exposure head 106 to reduce noise without degrading image quality.

[0037] In each of the surface light emitting element array chips 400-1 to 400-20, 748 light emitting elements 602 are arranged at a predetermined image resolution pitch in the X direction, which is the longitudinal direction. Here, the image resolution pitch is exemplified by 1200 dpi (approximately 21.16 μm). Also, the distance from end to end of the 748 light emitting elements 602 in each of the surface light emitting element array chips 400-1 to 400-20 is exemplified by approximately 15.8 mm here.

[0038] In this exemplary case, the image resolution pitch between the light emitting element 602-n and the light emitting element 602-1 located at the boundary of the surface light emitting element array chips 400-1 to 400-20 shown in FIG. 3(c) is also 1200 dpi (approximately 21.16 μm). Note that the light emitting elements 602 located at the boundary of the surface light emitting element array chips 400-1 to 400-20 may be arranged so as to overlap by several pixels in consideration of the mounting accuracy of the surface light emitting element array chips 400-1 to 400-20.

[0039] The surface light emitting element array chips 400-1 to 400-20 are fixed to the printed circuit board 202 by, for example, an ultraviolet curable adhesive, a thermosetting adhesive, or a conductive adhesive. The surface light emitting element array chips 400-1 to 400-20 are driven by a control signal input from a driver IC (not shown) via a connector 305. The details of the configuration of the surface light emitting element array chips 400-1 to 400-20 will be described later.

[0040] When the number of light emitting elements 602 that can be exposed is 14,960 elements, the exposure head 106 enables image formation corresponding to an image width of approximately 316 mm.

[0041] As shown in FIG. 3(a), the printed circuit board 202 as a substrate is provided with a connector 305 and a driver IC (not shown) for driving the light emitting element group 201 on the non-light emitting element mounting surface. As shown in FIG. 3(b), the light emitting element group 201 is mounted on the light emitting element mounting surface as the surface of the printed circuit board 202.

[0042] The connector 305 is connected to a driver IC (not shown) and a power supply provided on the non-light-emitting element mounting surface of the printed circuit board 202 via signal lines (not shown), and is also connected to the light-emitting element group 201.

[0043] The rod lens array 203 is arranged such that the distance between the rod lens array 203 and the light-emitting element group 201 is a predetermined distance, and the distance between the rod lens array 203 and the photosensitive drum 102 is a predetermined distance, so that the light emitted from the light-emitting element group 201 is imaged on the photosensitive drum 102.

[0044] The rod lens array 203 and the printed circuit board 202 are attached to the housing 204.

[0045] The exposure head 106 having the above configuration is assembled as a single unit in a factory, and focus adjustment and light amount adjustment for adjusting the spot at the focusing position to a predetermined size are performed. Here, in the focus adjustment, the attachment position of the rod lens array 203 is adjusted so that the distance between the rod lens array 203 and the light-emitting element group 201 becomes a desired distance. In the light amount adjustment, each light-emitting element 602 of the light-emitting element group 201 is caused to emit light sequentially one by one, and the drive current of each light-emitting element 602 is adjusted so that the light condensed on the photosensitive drum 102 via the rod lens array 203 becomes a predetermined light amount.

[0046] <Configuration of surface-emitting element array chip> The configuration of the surface-emitting element array chips 400-1 to 400-20 of the exposure head 106 according to Embodiment 1 of the present invention will be described in detail with reference to FIG. 4.

[0047] The surface-emitting element array chip 400 is a chip configured by providing light-emitting elements 602 on an Si substrate, and includes a light-emitting substrate 402, a light-emitting portion 404, a circuit portion 406, and wire bonding pads (WB pads) 408.

[0048] The light emitting substrate 402 is a Si substrate, and is provided with a light emitting section 404, a circuit section 406, and wire bonding pads 408. Here, Si substrates have been developed with advanced processing technology for forming integrated circuits, and are already used as substrates for various integrated circuits, so they have the advantage of being able to form high-speed, highly functional circuits at high density, and also being inexpensive because large-diameter wafers are readily available.

[0049] The light emitting section 404 includes a light emitting element 602. The configuration of the light emitting section 404 will be described in detail later.

[0050] The circuit section 406 has a circuit configuration including an analog drive circuit, a digital control circuit, or both an analog drive circuit and a digital drive circuit, and controls the light emitting section 404 .

[0051] The wire bonding pads 408 supply power to the circuit section 406 and input and output signals between the surface light emitting element array chip 400 and the outside.

[0052] The light emitting portion 404 may be a compound semiconductor thin film such as AlGaAs formed by a transfer method or the like on a Si substrate or the like on which a driving circuit or the like has been formed in advance.

[0053] <Configuration of the light-emitting unit> The configuration of the light emitting section 404 of the surface light emitting element array chips 400-1 to 400-20 of the exposure head 106 according to the first embodiment of the present invention will be described in detail with reference to FIG.

[0054] The light-emitting section 404 is the portion where the light-emitting substrate 402 and the upper electrode 508 face each other, and the light-emitting layer 506 in the facing portion, and is configured by stacking multiple lower electrodes 504, light-emitting layers 506, and upper electrodes 508 in this order on the light-emitting substrate 402.

[0055] The lower electrode 504 is an independent electrode and is formed on the light-emitting substrate 402. The lower electrode 504 has a width W in the X direction, and a plurality of lower electrodes 504 are formed with a predetermined interval d provided between adjacent lower electrodes 504 in the X direction. The lower electrode 504 is formed using Si integrated circuit processing technology with a processing rule of about 0.2 μm in high precision along with the formation of the circuit portion 406, and is connected to a driving portion (not shown) of the circuit portion 406. Thereby, the lower electrodes 504 can be arranged with high density and high precision. Also, since the light-emitting locations of the light-emitting elements 602 are substantially the same as the lower electrodes 504, it becomes possible to arrange the light-emitting elements 602 with high density.

[0056] The lower electrode 504 is preferably formed of a metal having a high reflectivity with respect to the light-emitting wavelength of the light-emitting layer 506, and is formed of silver (Ag), aluminum (Al), or an alloy of silver and aluminum, etc.

[0057] The light-emitting layer 506 is formed on the lower electrode 504 and is, for example, an organic EL film or an inorganic EL film, etc. When the light-emitting layer 506 is an organic EL film, it is a laminated structure including 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 required.

[0058] When the light-emitting layer 506 is formed of a material vulnerable to moisture such as an organic EL layer or an inorganic EL layer, etc., it is desirable that it is sealed to prevent the intrusion of moisture into the light-emitting portion 404. The light-emitting layer 506 prevents the intrusion of moisture into the light-emitting portion 404 by, for example, a single film of a thin film such as silicon oxide, silicon nitride, or aluminum oxide, or a sealing film formed by laminating thin films such as silicon oxide, silicon nitride, and aluminum oxide. As a method for forming the sealing film, a method excellent in the coating performance of a structure such as a step is preferable, and for example, an atomic layer deposition method (ALD method) can be used.

[0059] The light-emitting layer 506 may be formed continuously or may be divided into pieces of approximately the same size as the lower electrode 504. The material, configuration, and formation method of the sealing film described above are merely examples, and are not limited to the above examples, and any suitable material may be selected as appropriate.

[0060] The upper electrode 508 is a common electrode and is formed on the light-emitting layer 506. The upper electrode 508 is preferably transparent to the emission wavelength of the light-emitting layer 506, and a transparent electrode such as indium tin oxide (ITO) can be used.

[0061] The light-emitting unit 404 having the above configuration applies a current to the light-emitting layer 506 through a selected lower electrode 504 from the plurality of lower electrodes 504 and the upper electrode 508, thereby causing the light-emitting layer 506 to emit light at a location corresponding to the selected lower electrode 504. As a result, the light-emitting unit 404 emits light through the upper electrode 508 on the side of the light-emitting layer 506 opposite the light-emitting substrate 402.

[0062] By using a transparent electrode such as indium tin oxide for the upper electrode 508, the aperture ratio can be made substantially 100%, and light emitted from the light-emitting layer 506 can be used as emitted light as is. Furthermore, by forming the lower electrodes 504 using high-precision Si integrated circuit processing technology, the lower electrodes 504 can be arranged at high density, which allows almost the entire area of the light-emitting portion 404 to emit light, thereby improving the utilization efficiency of the light-emitting portion 404. Here, the area of the light-emitting portion 404 is the total area of the plurality of lower electrodes 504 and the total area of the plurality of intervals d.

[0063] <Arrangement of light-emitting elements in the light-emitting section> The arrangement of the light emitting elements 602 of the light emitting section 404 of the exposure head 106 according to the first embodiment of the present invention will be described in detail with reference to FIG.

[0064] 6A is a plan view of the light emitting element row 604, FIG. 6B is a cross-sectional view of the light emitting element row 604, and FIG. 6C is a modified example of the light emitting element row 604. In FIG.

[0065] 6(a) and 6(b), W1 is the width of the light-emitting element 602 in the X direction, and d1 is the distance between adjacent light-emitting elements 602 in the X direction. Also, in Fig. 6(c), W2 is the width of the light-emitting element 602 in the Y direction, and d2 is the distance between adjacent light-emitting elements 602 in the Y direction.

[0066] In FIG. 6(b), for example, the light emitting element 602-3 is the part surrounded by the dashed line.

[0067] The light emitting element row 604 is configured by arranging a plurality of light emitting elements 602 at a predetermined interval (pitch) along the X direction. For example, the predetermined interval is 21.16 μm when the image resolution in the Y direction is 1200 dpi. In addition, W1 is exemplified as 20.9 μm, and d1 is exemplified as 0.26 μm.

[0068] Here, if the light-emitting layer 506 is sufficiently thin, the light-emitting location of the light-emitting element 602 is substantially the same as the lower electrode 504, and W1 can be regarded as W in FIG. 5, and d1 as d in FIG.

[0069] The light emitting element row 604 is not limited to a single row in which the light emitting elements 602 are arranged in the X direction as shown in Fig. 6(a), but may also be multiple rows in which the light emitting elements 602 are arranged in the Y direction as shown in Fig. 6(c). In Fig. 6(c), the light emitting element row 604 is configured by arranging m rows of the light emitting elements 602 in the Y direction. When the light intensity of the light emitting elements 602 is low, for example, the light intensity required for the light emitting elements 602 can be reduced to 1 / m by performing multiple exposure using light emitting element rows 604-1, 604-2, ..., 604-m as shown in Fig. 6(c).

[0070] The light emitting element rows 604-1 to 604-m are configured by arranging a plurality of light emitting element rows 604 at a predetermined interval (pitch) along the Y direction. The predetermined interval is, for example, 21.16 μm when the image resolution in the Y direction is 1200 dpi. In addition, W2 is exemplified as 20.9 μm, and d2 is exemplified as 0.26 μm.

[0071] Here, a light-emitting element 602 having a light-emitting layer 506 which is an organic EL layer is called an organic EL element, and a light-emitting element 602 having a light-emitting layer 506 which is an inorganic EL layer is called an inorganic EL element.

[0072] <Operation of exposure head> The operation of the exposure head 106 according to Embodiment 1 of the present invention will be described in detail with reference to FIGS. 7 and 8.

[0073] In FIG. 7, FIG. 7(a) shows a part of the light-emitting elements 602-A of the surface-emitting element array chips 400-2, 4, ···, 20 arranged in a staggered pattern in column A, and a part of the light-emitting elements 602-B of the surface-emitting element array chips 400-1, 3, ···, 19 arranged in a staggered pattern in column B. Further, FIG. 7(b) shows the light-emitting timings of the light-emitting elements 602 of the surface-emitting element array chips 400-2, 4, ···, 20 in column A and the light-emitting elements 602 of the surface-emitting element array chips 400-1, 3, ···, 19 in column B. Further, FIG. 7(c) shows the latent image formed on the photosensitive drum 102 according to the light-emitting timing shown in FIG. 7(b).

[0074] In FIG. 8, FIG. 8(a) shows a part of the light-emitting elements 602-A of the surface-emitting element array chips 400-2, 4, ···, 20 arranged in a staggered pattern in column A, and a part of the light-emitting elements 602-B of the surface-emitting element array chips 400-1, 3, ···, 19 arranged in a staggered pattern in column B. Further, FIG. 8(b) shows the light-emitting timings of the light-emitting elements 602 of the surface-emitting element array chips 400-2, 4, ···, 20 in column A and the light-emitting elements 602 of the surface-emitting element array chips 400-1, 3, ···, 19 in column B. Further, FIG. 8(c) shows the latent image formed on the photosensitive drum 102 according to the light-emitting timing shown in FIG. 8(b).

[0075] In FIGS. 7(a) and 8(a), the light-emitting element 602-A is the light-emitting element 602 of the surface-emitting element array chips 400-2, ···, 20 in column A, and the light-emitting element 602-B is the light-emitting element 602 of the surface-emitting element array chips 400-1, ···, 19 in column B.

[0076] Figs. 7 and 8 show, as an example, the case where the light-emitting element arrays 604 are arranged in 7 columns (lines) in the Y direction (when m = 7 in Fig. 6(c)).

[0077] When the time required for the latent image formed on the photosensitive drum 102 to move by the minimum distance Ly in the Y direction is T0 and the process speed (conveying speed) is Ps, the relationship among Ly, T0, and Ps is as shown in Equation (2).

[0078] T0 = Ly / Ps (2)

[0079] As shown in Fig. 7(a), the light-emitting element 602-A and the light-emitting element 602-B are separated by a distance S in the Y direction. At this time, in order for the light-emitting element 602-A and the light-emitting element 602-B to be exposed at the same position in the Y direction of the photosensitive drum 102, it is necessary to delay the light emission start timing of the light-emitting element 602-B by S / Ps from the light emission start timing of the light-emitting element 602-A. When the delay time at this time is Td, Td is as shown in Equation (3) from Equations (1) and (2).

[0080] Td = S / Ps = (α + β) × T0 (3)

[0081] In Fig. 7(b), 1A, 2A, ···, 7A indicate the light emission signals of the first line, the second line, ···, the seventh line of the light-emitting element 602-A. Also, in Fig. 7(b), 1B, 2B, ···, 7B indicate the light emission signals of the first line, the second line, ···, the seventh line of the light-emitting element 602-B. Note that Fig. 7(b) illustrates the case where α = 2 and β = 0.5.

[0082] At this time, as described above, the light emission start time Tb(1) of the light emission signal 1B of the light-emitting element 602-B is delayed by (α + β) × T0 from the light emission start time Ta(1) of the light emission signal 1A of the light-emitting element 602-A. Also, when the time between the light emission start time Ta(3) of the light emission signal 3A and the light emission start time Tb(1) of the light emission signal 1B is ΔT, ΔT = (α + β)T0 - αT0 = βT0.

[0083] As a result, the emission start times of light-emitting signals 1A, 2A, ... and light-emitting signals 1B, 2B, ... will overlap when ΔT is 0 or an integer, but because β is a decimal, ΔT is not 0 or an integer and they do not overlap. Therefore, the noise generated when light-emitting element 602-A starts to emit light and the noise generated when light-emitting element 602-B starts to emit light do not overlap in terms of time. This makes it possible to reduce increases in noise intensity.

[0084] In FIG. 7(c), 1a, 2a, . . . , 7a indicate latent images formed by the light-emitting element 602-A, and 1b, 2b, . . . , 7b indicate latent images formed by the light-emitting element 602-B.

[0085] 7(c), the latent image formed by the light-emitting element 602-A and the latent image formed by the light-emitting element 602-B are at the same position in the Y direction on the photosensitive drum 102, and no positional deviation occurs. In this way, by determining the interval S using equation (1), it is possible to prevent the interval S between the light-emitting points from becoming an integer multiple of the image resolution pitch in the Y direction.

[0086] Furthermore, the light emission timings of the light emitting elements 602-A and 602-B are set so that the latent image formed by the light emitting element 602-A and the latent image formed by the light emitting element 602-B are formed at the same position in the Y direction on the photosensitive drum 102. This ensures a shift of ΔT between the light emission timing of the light emitting element 602-A and the light emission timing of the light emitting element 602-B, making it possible to reduce an increase in noise intensity.

[0087] Next, as a comparison with the present embodiment, the case where the distance S between the light-emitting element 602-A and the light-emitting element 602-B is an integer multiple of the minimum distance in the Y direction of the latent image formed on the photosensitive drum 102 (β=0) will be described with reference to FIG. 8.

[0088] In Fig. 8, the distance S between the light-emitting element 602-A and the light-emitting element 602-B was set to 2Ly. In this case, in order to form the latent images by the light-emitting element 602-A and the light-emitting element 602-B at the same position in the Y direction on the photosensitive drum 102, it is necessary to delay the light emission timing of the light-emitting element 602-B by 2T0 from the light emission timing of the light-emitting element 602-A. As a result, for example, as shown in Fig. 8(b), the light emission start time Ta(3) of the light emission signal 3A of the third line of the light-emitting element 602-A and the light emission start time Tb(1) of the light emission signal 1B of the first line of the light-emitting element 602-B overlap, and the intensity of the noise increases.

[0089] On the other hand, in order to avoid an increase in the intensity of the noise, it is conceivable to delay the light emission start time Tb(1) by, for example, 2.5T0 from the light emission start time Ta(3) so that the light emission start time Ta(3) and the light emission start time Tb(1) do not overlap. However, in this case, as shown in Fig. 8(c), a positional shift occurs in the Y direction between the latent image formed by the light-emitting element 602-A and the latent image formed by the light-emitting element 602-B on the photosensitive drum 102.

[0090] Thus, the distance S between the surface-emitting element array chips 400-2, ···, 20 in the A column and the surface-emitting element array chips 400-1, ···, 19 in the B column is set by the formula (1). Thereby, when forming the exposure head 106 by arranging a plurality of surface-emitting element array chips 400-1 to 400-20 in a staggered manner, an increase in noise intensity can be reduced without image quality degradation.

[0091] In the present embodiment, the surface-emitting element array chips 400-2, 4, 6, ···, 20 in the A column and the surface-emitting element array chips 400-1, 3, 5, ···, 19 in the B column are arranged in a staggered manner along the main scanning direction. Further, the distance S between the surface-emitting element array chips 400-2, 4, 6, ···, 20 in the A column and the surface-emitting element array chips 400-1, 3, 5, ···, 19 in the B column is set so as not to be an integer multiple of the image resolution pitch in the sub-scanning direction. Thereby, noise can be reduced without degrading the image quality.

[0092] (Embodiment 2) The configuration of the image forming apparatus according to the second embodiment of the present invention is the same as that of the image forming apparatus 1 shown in Fig. 1, and therefore a description thereof will be omitted. Also, the configuration of the exposure head according to this embodiment is the same as that of the exposure head 106 shown in Figs. 3 to 6, and therefore a description thereof will be omitted.

[0093] <Exposure head operation> The operation of the exposure head according to the second embodiment of the present invention will be described in detail with reference to FIG.

[0094] In this embodiment, the surface light emitting element array chips 400-1 to 400-20 are characterized as being self-scanning light emitting chips in which self-scanning light emitting devices (SLEDs: Self Scanning Light Emitting Devices) are formed on a compound semiconductor substrate.

[0095] 9, the surface light emitting element array chips 400-1 to 400-20 are chips in which self-scanning light emitting devices are formed in a staggered pattern on a compound semiconductor substrate. The surface light emitting element array chips 400-1 to 400-20 cannot all be turned on at the same time, and a predetermined number of light emitting elements 602 are turned on and scanned along the X direction to expose the photosensitive drum 102. In addition to the light emitting elements 602, each of the surface light emitting element array chips 400-1 to 400-20 has a self-transfer circuit formed of a transfer thyristor, a coupling diode, or the like.

[0096] 9, the surface light emitting element array chips 400-1 to 400-20 scan by turning on the light emitting elements 602 in mutually opposing directions. Note that the surface light emitting element array chips 400-1 to 400-20 are not limited to scanning by turning on the light emitting elements 602 in mutually opposing directions, and may also scan by turning on the light emitting elements 602 in the same direction.

[0097] The interval S between the surface light emitting element array chips 400-2, 4, 6, ..., 20 in row A and the surface light emitting element array chips 400-1, 3, 5, ..., 19 in row B is set to satisfy formula (1). Then, the light emission timing of the light emitting elements 602 is controlled according to the interval S in the Y direction between the surface light emitting element array chips 400-2, 4, 6, ..., 20 in row A and the surface light emitting element array chips 400-1, 3, 5, ..., 19 in row B. Specifically, the light emission timing is controlled so that the exposure position by the surface light emitting element array chips 400-2, ..., 20 in row A and the exposure position by the surface light emitting element array chips 400-1, ..., 19 in row B are the same in the Y direction on the photosensitive drum 102.

[0098] In this embodiment, the image resolution in the Y direction is set to 2400 dpi, and in equation (1), Ly = 10.6 μm, α = 14, and β = 0.5, and S = 153 μm after rounding to the first decimal place. In this way, the surface light emitting element array chips 400-1 to 400-20 are arranged to satisfy equation (1). This allows the light emission timing of the surface light emitting element array chips 400-2, ..., 20 in row A and the surface light emitting element array chips 400-1, ..., 19 in row B to be shifted even when exposed to the same position in the Y direction of the photosensitive drum 102. Therefore, an increase in noise intensity can be reduced.

[0099] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0100] 1. Image forming device 102 Photosensitive drum 103 Image creation section 104 Fixing section 105 Conveyor 106 Exposure head 107 Charger 108 Developer 110 Register Roller 111 Transfer belt 112 Paper ejection roller 113 Optical Sensor 201 Light emitting element group 202 Printed Circuit Board 203 Rod Lens Array 204 Housing 305 Connector 400-1 to 400-20 Surface-emitting element array chip 402 Light-emitting substrate 404 Light-emitting part 406 Circuit section 408 Wire bonding pad 504 Lower electrode 506 Light-emitting layer 508 Upper electrode 602 Light-emitting element 604 Light-emitting element array

Claims

1. An image forming apparatus for forming an image on a recording medium, comprising: a rotating photosensitive drum; a first semiconductor chip having a first light emitting element array arranged along a main scanning direction parallel to the rotation axis of the photosensitive drum, and a second semiconductor chip provided at a position different from that of the first semiconductor chip in a sub-scanning direction orthogonal to the main scanning direction, the second semiconductor chip having a second light emitting element array arranged along the main scanning direction; and an exposure head having the second semiconductor chip; a control unit that outputs a first light emission signal for controlling the light emission timing of the first light emitting elements included in the first light emitting element array and a second light emission signal for controlling the light emission timing of the second light emitting elements included in the second light emitting element array; wherein in the sub-scanning direction, when the distance between the first light emitting element array and the second light emitting element array is S, S is different from an integer multiple of the resolution pitch in the sub-scanning direction of the image formed on the recording medium; when the rotation speed of the surface of the photosensitive drum is Ps, the control unit outputs the second light emission signal with a delay of S / Ps with respect to the first light emission signal. An image forming apparatus characterized by the above.

2. When the first semiconductor chip and the second semiconductor chip are such that the resolution pitch of the image in the sub-scanning direction is Ly, α is a positive integer, and β is a real number with 0 < β < 1, S = (α + β) × Ly The image forming apparatus according to claim 1, wherein the image forming apparatus is arranged to satisfy the above condition. An image forming apparatus according to claim 1, characterized by the above.

3. The first light emitting element array and the second light emitting element array emit light such that their positions in the sub-scanning direction on the surface of the photosensitive drum are the same. An image forming apparatus according to claim 1, characterized by the above.

4. The first light emitting element array and the second light emitting element array emit light at a timing such that the position of the electrostatic latent image formed by the first light emitting element array on the surface of the photosensitive drum and the position of the electrostatic latent image formed by the second light emitting element array on the surface of the photosensitive drum are the same in the sub-scanning direction. An image forming apparatus according to claim 1, characterized by the above.

5. The first light emitting element and the second light emitting element are an organic EL element or an inorganic EL element. An image forming apparatus according to any one of claims 1 to 4, characterized by the above.

Images