Exposure device and image forming apparatus

Abstract

The invention relates to an exposure apparatus and an image forming apparatus. The exposure apparatus includes: a chip having light emitting elements arranged along an axial direction of a photosensitive member; a generation unit that generates a first synchronization signal synchronized with a second synchronization signal corresponding to a rotational speed of the photosensitive member; and a transmission unit that transmits the data signal to the chip during the row period. The second synchronization signal indicates a first period or a second period according to the rotational speed. The second period is N times the first period. The first synchronization signal indicates a first period independent of the rotational speed. Transmitting a row of data signals to the chip during one row period of N row periods when the photosensitive member rotates at a slower second rotation speed; and transmitting the non-emission signal during the remaining (one or more) of the N row periods.

Description

Technical Field

[0001] The present invention relates to an exposure device and an image forming device. Background Art

[0002] An electrophotographic image forming apparatus forms an image by optically exposing a rotatably driven photosensitive member to form an electrostatic latent image thereon and developing the electrostatic latent image with toner. Among them, compared with a laser scanning type exposure device, a solid-state exposure type exposure device that images light from a light-emitting element array onto the surface of a photosensitive member using a rod lens array has attracted attention because it is easy to miniaturize, enhance quietness, and reduce costs.

[0003] Japanese Patent Laid-Open No. 2022-96965 discloses an example of a solid-state exposure type exposure device. The image controller of the exposure device in Japanese Patent Laid-Open No. 2022-96965 outputs a series of data signals for light emission control to a plurality of light-emitting chips during each line period indicated by a line synchronization signal, and each light-emitting chip has a light-emitting element array. Each light-emitting chip drives a plurality of light-emitting elements in the light-emitting element array according to a series of data signals input from the image controller. Summary of the Invention

[0004] Generally, in the case of an image forming apparatus using an electrophotographic method, the heat required to fix a toner image to a sheet varies depending on the basis weight of the sheet. For example, the heat required to sufficiently adhere toner to thick paper is greater than the heat required to adhere toner to plain paper. Therefore, when printing on thick paper, the processing speed is usually made slower than when printing on plain paper, so as to ensure sufficient time for applying heat to the thick paper at the fixing unit.

[0005] However, when the light-emitting elements are maintained in the light-emitting state within one line period, as in the case of the exposure device in Japanese Patent Laid-Open No. 2022-96965, if the processing speed is set to be slow, the line period is correspondingly extended, which causes the photosensitive member to be exposed for a longer time than necessary. By making the light-emitting elements emit light only during a part of the line period, such overexposure can be prevented, but changing the synchronization control method in response to the setting of the processing speed leads to circuit complexity and cost increase.

[0006] In view of the above problems, the present invention aims to provide a mechanism that can prevent overexposure of the photosensitive member while avoiding circuit configuration complexity.

[0007] According to a first aspect, an exposure apparatus is provided, including: at least one light-emitting chip having a plurality of light-emitting elements arranged in rows parallel to an axial direction of a photosensitive member configured to rotate; a synchronization signal generation unit configured to generate a first synchronization signal synchronized with a second synchronization signal corresponding to a rotation speed of the photosensitive member, the first synchronization signal being for controlling transmission of data signals for each row to the at least one light-emitting chip; and a transmission unit configured to transmit, during a row period indicated by the first synchronization signal, data signals for one row for light emission control of the plurality of light-emitting elements to the at least one light-emitting chip. When the photosensitive member rotates at a first rotation speed, the second synchronization signal indicates a first row period, and when the photosensitive member rotates at a second rotation speed which is 1 / N (N is an integer, 1 < N) of the first rotation speed, it indicates a second row period which is N times the first row period. The synchronization signal generation unit is configured to generate the first synchronization signal indicating the first row period regardless of the rotation speed of the photosensitive member, and when the photosensitive member rotates at the second rotation speed, the transmission unit is configured to: transmit, during one row period among N row periods indicated by the first synchronization signal, data signals for one row to the at least one light-emitting chip; and transmit, during the remaining one or more row periods among the N row periods, non-light emission signals for preventing the plurality of light-emitting elements from emitting light to the at least one light-emitting chip.

[0008] According to a second aspect, an image forming apparatus is provided, including: the exposure apparatus of the first aspect; a photosensitive member; a developing device configured to develop a latent image formed as a result of the exposure apparatus exposing the photosensitive member and form a toner image on a surface of the photosensitive member; a fixing unit configured to fix the toner image transferred from the photosensitive member to a sheet onto the sheet; and a setting unit configured to set a rotation speed of the photosensitive member according to a type of the sheet.

[0009] Further features of the present invention will become clear from the following description of exemplary embodiments (with reference to the accompanying drawings). Description of the Drawings

[0010] Figure 1 is a configuration diagram showing a schematic configuration of an image forming apparatus according to an embodiment.

[0011] Figure 2A is a first explanatory diagram of a configuration of a photosensitive member and an exposure head according to an embodiment.

[0012] Figure 2B is a second explanatory diagram of a configuration of a photosensitive member and an exposure head according to an embodiment.

[0013] Figure 3AIt is a first illustrative diagram of the structure of a printed circuit board of an exposure head according to an embodiment.

[0014] Figure 3B It is a second illustrative diagram of the structure of a printed circuit board of an exposure head according to an embodiment.

[0015] Figure 4 It is a plan view of a schematic structure of a light-emitting chip according to an embodiment.

[0016] Figure 5 It is a cross-sectional view showing an example of the structure of a light-emitting element according to an embodiment.

[0017] Figure 6 It is a block diagram showing an example of a control configuration of an exposure apparatus according to an embodiment.

[0018] Figure 7 It is a signal diagram related to writing control data to a light-emitting chip according to an embodiment.

[0019] Figure 8 It is a signal diagram related to transmitting image data to a light-emitting chip according to an embodiment.

[0020] Figure 9 It is a block diagram showing an example of a detailed circuit structure of a light-emitting chip according to an embodiment.

[0021] Figure 10 It is a circuit diagram showing a partial structure of a current driving unit corresponding to one light-emitting element.

[0022] Figure 11 It is a signal diagram related to the timing of outputting a driving signal from each latch unit to the current driving unit.

[0023] Figure 12 It is a signal diagram for illustrating problems related to an embodiment.

[0024] Figure 13 It is a block diagram showing an example of a detailed structure of a data communication unit according to an embodiment.

[0025] Figure 14 It is a signal diagram showing an example of the timing of processing image data when the processing speed is set to a normal value.

[0026] Figure 15 It is a signal diagram showing an example of the timing of processing image data when the processing speed is set to 1 / 2 of the normal value.

[0027] Figure 16 is related to Figure 15 the timing of outputting a driving signal to the current driving unit in the example shown in

[0028] Figure 17 It is a signal diagram showing an example of the timing for processing image data when the processing speed is set to 1 / 3 of the normal value.

[0029] Figure 18 is related to Figure 17 the signal diagram related to the timing of outputting a drive signal to the current drive unit in the example shown in Detailed Description of the Invention

[0030] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but the invention is not limited to the invention that requires all such features, and multiple such features can be appropriately combined. In addition, in the drawings, the same or similar configurations are given the same reference numerals, and their repeated descriptions are omitted.

[0031] <1. Schematic Configuration of the Image Forming Apparatus>

[0032] Figure 1 An example of the schematic configuration of an image forming apparatus 1 according to an embodiment is shown. The image forming apparatus 1 includes a reading unit 100, an image forming unit 103, a fixing unit 104, and a transport unit 105. The reading unit 100 optically reads an original placed on the platen and generates read image data. The image forming unit 103 forms an image on a sheet based on the read image data generated by the reading unit 100 or based on, for example, print image data received from an external device via a network.

[0033] The image forming unit 103 includes image forming units 101a, 101b, 101c, and 101d that respectively form toner images of black, yellow, magenta, and cyan. The image forming units 101a, 101b, 101c, and 101d have the same configuration, and are hereinafter also collectively referred to as the image forming unit 101. The photosensitive member 102 of the image forming unit 101 is driven to rotate in the clockwise direction in the figure during image formation. The charger 107 charges the photosensitive member 102. The exposure head 106 exposes the photosensitive member 102 with light to form an electrostatic latent image on the surface of the photosensitive member 102. The developing device 108 develops the electrostatic latent image on the photosensitive member 102 with toner to form a toner image. The toner image formed on the surface of the photosensitive member 102 is transferred to a sheet being transported on the transfer belt 111. By transferring the toner images of the four photosensitive members 102 in a superimposed manner onto the sheet, a color image including four color components (i.e., black, yellow, magenta, and cyan) can be formed.

[0034] The transport unit 105 controls the feeding and transportation of the sheet. Specifically, the transport unit 105 feeds the sheet from the unit specified among the internal storage units 109a and 109b, the external storage unit 109c, and the manual feeding unit 109d into the transport path in the image forming apparatus 1. The fed sheet is transported to the registration roller 110. The registration roller 110 transports the sheet to the transfer belt 111 at an appropriate timing so that the toner image of each photosensitive member 102 is transferred to the sheet. As mentioned above, when the sheet is transported on the transfer belt 111, the toner image is transferred to the sheet. The fixing unit 104 fixes the toner image to the sheet by heating and pressing the sheet onto which the toner image has been transferred. After the toner image is fixed, the sheet is discharged to the outside of the image forming apparatus 1 by the discharge roller 112. The optical sensor 113 is located at a position facing the transfer belt 111. The optical sensor 113 optically reads the test pattern formed by the image forming unit 101 on the transfer belt 111. In the case where an error in the image forming range is detected for the test pattern read by the optical sensor 113, the image controller 710 described below performs control for compensating the error when performing subsequent operations.

[0035] Although an example in which the toner image is directly transferred from each photosensitive member 102 to the sheet on the transfer belt 111 has been described here, the toner image may alternatively be indirectly transferred from each photosensitive member 102 to the sheet via an intermediate transfer member. In addition, although an example in which a color image is formed using toners of multiple colors has been described here, the technology according to the present disclosure is also applicable to an image forming apparatus that forms a monochromatic image using a toner of a single color.

[0036] <Example of the structure of the exposure head>

[0037] Figure 2A and Figure 2B The photosensitive member 102 and the exposure head 106 are shown. The exposure head 106 includes a light emitting element array 201, a printed circuit board 202 on which the light emitting element array 201 is mounted, a rod lens array 203, and a housing 204 that supports the printed circuit board 202 and the rod lens array 203. The photosensitive member 102 has a cylindrical shape. The exposure head 106 is arranged such that its longitudinal direction is parallel to the axial direction D1 of the photosensitive member 102, and the surface of the exposure head 106 to which the rod lens array 203 is attached faces the surface of the photosensitive member 102. When the photosensitive member 102 rotates in the circumferential direction D2, the light emitting element array 201 of the exposure head 106 emits light, and the rod lens array 203 images the light onto the surface of the photosensitive member 102.

[0038] Figure 3A and Figure 3B An example of the structure of the printed circuit board 202 is shown. Note thatFigure 3A shows the surface on which the connector 305 is mounted, while Figure 3B shows the surface on which the light-emitting element array 201 is mounted (the surface on the opposite side of the surface on which the connector 305 is mounted).

[0039] In the present embodiment, the light-emitting element array 201 has a plurality of light-emitting elements arranged two-dimensionally. The light-emitting element array 201 as a whole includes N columns and M rows of light-emitting elements in the axial direction D1 of the photosensitive member, where M and N are integers not less than two. In Figure 3B the example, the light-emitting element array 201 is composed of twenty individual light-emitting chips 400-1 to 400-20, and each light-emitting chip includes a subset of all the plurality of light-emitting elements. The light-emitting chips 400-1 to 400-20 are arranged in a staggered manner along a reference line 310 parallel to the axial direction D1. The light-emitting chips 400-1 to 400-20 are also collectively referred to as the light-emitting chip 400. As Figure 3B shown, the range occupied by all the light-emitting elements of the twenty light-emitting chips in the axial direction D1 is wider than the range occupied by the maximum width W0 of the input image data. Thus, unless an error in the image formation range is detected, some of the light-emitting elements located at both ends in the axial direction D1 may not be used for exposing the photosensitive member 102. Each light-emitting chip 400 on the printed circuit board 202 is connected to the image controller 710 via the connector 305( Figure 6 ). Hereinafter, for the sake of convenience of description, the side with a smaller branch number among the light-emitting chips 400-1 to 400-20 arranged in the axial direction D1 is sometimes referred to as "left" and the side with a larger branch number is referred to as "right". For example, the light-emitting chip 400-1 is the left-end light-emitting chip 400, and the light-emitting chip 400-20 is the right-end light-emitting chip.

[0040] Figure 4 is a plan view of a schematic configuration of a light-emitting chip 400. The plurality of light-emitting elements 602 of each light-emitting chip 400 are formed on a light-emitting substrate 402, which is, for example, a silicon substrate. The light-emitting substrate 402 has a circuit section 406 for driving the plurality of light-emitting elements 602. The pads 408-1 to 408-9 are connected to signal lines for communicating with the image controller 710, power lines for connecting to a power source, and ground lines for connecting to ground. The signal lines, power lines, and ground lines can be, for example, gold wires.

[0041] The number J (J = N / 20) of the light-emitting elements 602 arranged in each row of a light-emitting chip 400 can be, for example, equal to 748 (J = 748). At the same time, the number M of the light-emitting elements 602 arranged in each column of a light-emitting chip 400 can be, for example, equal to 4 (M = 4). That is, in the exemplary embodiment, each light-emitting chip 400 has a total of 2992 (= 748 × 4) light-emitting elements 602, with 748 elements in the axial direction D1 and 4 elements in the circumferential direction D2. The interval between the center points of the adjacent light-emitting elements 602 in the circumferential direction D2 can be, for example, approximately 21.16 μm, corresponding to a resolution of 1200 dpi. The interval between the center points of the adjacent light-emitting elements 602 in the axial direction D1 can also be approximately 21.16 μm, and in this case, the 748 light-emitting elements 602 occupy a length of approximately 15.8 mm in the axial direction D1. It should be noted that, for ease of description, Figure 4 An example is shown in which the light-emitting elements 602 are arranged in a completely grid pattern in each light-emitting chip 400. However, the M (M = 4) light-emitting elements 602 in each column can be arranged in a stepped pattern or a partially stepped pattern. The arrangement of the light-emitting elements 602 in the stepped pattern will be further described below.

[0042] Figure 5 FIG. is a cross-sectional view showing an example of the structure of the light-emitting element 602. A plurality of lower electrodes 504 are formed on a light-emitting substrate 402 which is a silicon substrate. A gap with a length of d is provided between two adjacent lower electrodes 504. A light-emitting layer 506 is provided on the lower electrodes 504, and an upper electrode 508 is provided on the light-emitting layer 506. The upper electrode 508 is a common electrode for the plurality of lower electrodes 504. When a voltage is applied between the lower electrode 504 and the upper electrode 508, as a result of current flowing from the lower electrode 504 to the upper electrode 508, the light-emitting layer 506 emits light. Therefore, a partial area of one lower electrode 504 and the corresponding light-emitting layer 506 and upper electrode 508 constitutes one light-emitting element 602. That is, in the present embodiment, the light-emitting substrate 402 includes a plurality of light-emitting elements 602.

[0043] An organic EL film is used as the light-emitting layer 506. That is, the light-emitting element 602 is an organic EL element. The upper electrode 508 is composed of a transparent electrode made of, for example, indium tin oxide (ITO) or the like to allow the light-emitting wavelength of the light-emitting layer 506 to pass through. Note that, in the present embodiment, the entire upper electrode 508 allows the light-emitting wavelength of the light-emitting layer 506 to pass through, but the entire upper electrode 508 does not have to allow the light-emitting wavelength to pass through. Specifically, it is sufficient that a partial area through which the light from each light-emitting element 602 passes allows the light-emitting wavelength to pass through.

[0044] Note that, inFigure 5 In this case, a continuous light-emitting layer 506 is formed, but alternatively, a plurality of light-emitting layers 506 may be formed on the corresponding lower electrodes 504, and each light-emitting layer 506 has a width equal to the width W of the corresponding lower electrode 504. Additionally, in Figure 5 In this case, the upper electrode 508 is formed as a common electrode for the plurality of lower electrodes 504; however, alternatively, a plurality of upper electrodes 508 may be formed corresponding to the respective lower electrodes 504, and each upper electrode 508 has a width equal to the width W of the corresponding lower electrode 504. Additionally, the first plurality of lower electrodes 504 among the lower electrodes 504 of each light-emitting chip 400 may be covered by the first light-emitting layer 506, and the second plurality of lower electrodes 504 may be covered by the second light-emitting layer 506. Similarly, a first upper electrode 508 may be commonly formed for the first plurality of lower electrodes 504 among the lower electrodes 504 of each light-emitting chip 400, and a second upper electrode 508 may be commonly formed for the second plurality of lower electrodes 504. With such a configuration, the region of one lower electrode 504 and the corresponding light-emitting layer 506 and upper electrode 508 also constitutes a light-emitting element 602.

[0045] Figure 6 is a block diagram showing an example of a control configuration for controlling the light-emitting chip 400. The image controller 710 is a control circuit that communicates with the printed circuit board 202 via a plurality of signal lines (wires). The image controller 710 includes a first CPU 711, an image data generation unit 713, a register access unit 714, and a data communication unit 715. The data communication unit 715 terminates the signal lines connected to the printed circuit board 202. The nth light-emitting chip 400-n (n is an integer from 1 to 20) on the printed circuit board 202 is connected to the data communication unit 715 via a pair of data signal lines and control signal lines. The data signal lines carry the image data DATAn for the light-emitting chip 400-n. The control signal lines carry the control data WRITEn to be written into the register of the light-emitting chip 400-n.

[0046] Additionally, a clock signal line, a synchronization signal line, and an enable signal line are provided between the data communication unit 715 and each light-emitting chip 400-n. The clock signal line carries a clock signal CLK for identifying the timing of each bit of the image data DATAn and the control data WRITEn. The data communication unit 715 generates the clock signal CLK based on the reference clock signal R_CLK generated by the clock generation unit 701 and outputs the generated clock signal CLK to the clock signal line. The synchronization signal line carries a first synchronization signal SYNC described below. The enable signal line carries an enable signal EN described below.

[0047] The page storage unit 702 is a storage device that temporarily stores page by page the page description language (PDL) data representing each page of the input image of a print job received from the reading unit 100 or an external device. The page storage unit 702 can be, for example, a mass storage or a hard disk drive (HDD).

[0048] The first CPU 711 is a control unit that controls image processing in the image controller 710 and communication with the printed circuit board 202. The second CPU 720 is a control unit that controls the image forming operation in the image forming unit 101. The image data generation unit 713 performs image processing on the PDL data on each page stored in the page storage unit 702 to generate image data in binary bitmap format for controlling the light emission of a plurality of light emitting elements 602 of the light emitting chip 400 on the printed circuit board 202. The image processing here can include, for example, raster conversion, gray scale correction, color conversion, and halftoning. The image data generation unit 713 outputs the generated image data as input image data to the data communication unit 715. The register access unit 714 obtains control data to be written to the registers in each light emitting chip 400 from the first CPU 711 and outputs the obtained control data to the data communication unit 715.

[0049] The image forming apparatus 1 further includes a main processor (e.g., a CPU) 700 that controls the overall operation of the image forming apparatus 1. When starting to execute a print job, the main processor 700 outputs a first trigger signal TOP indicating the operation start timing to the image production unit 103, the fixing unit 104, and the transport unit 105. The fixing unit 104 starts controlling the temperature of the fixing roller in response to the input of the first trigger signal TOP. The transport unit 105 starts feeding and transporting the sheet in response to the input of the first trigger signal TOP.

[0050] The data communication unit 715 starts operating in response to the input of the first trigger signal TOP and outputs a second trigger signal P_TOP indicating the timing to start transmitting the input image data for each page and a second synchronization signal P_SYNC indicating the synchronization timing for each row to the second CPU 720. The second CPU 720 causes the corresponding part of the image forming unit 101 to start operating in response to the input of the second trigger signal P_TOP. For example, the second CPU 720 synchronously controls the rotation of the photosensitive member 102 and the transport of the sheet using the transfer belt 111 based on the second synchronization signal P_SYNC so that the toner image on the surface of the photosensitive member 102 is transferred to the designated image forming position on the sheet.

[0051] Figure 7It is a signal diagram related to writing control data into the register of the light-emitting chip 400. When transmitting control data, the enable signal EN is at a high level on the enable signal line. The data communication unit 715 transmits a start bit to the control signal line synchronously with the rising edge of the enable signal. Next, the data communication unit 715 transmits a write identification bit indicating a write operation, and then transmits the address (four bits in this example) of the register to which the control data is to be written and the control data (eight bits in this example). The data communication unit 715 sets the frequency of the clock signal CLK to, for example, 3 MHz when writing to the register.

[0052] Figure 8 It is a signal diagram related to transmitting image data to each light-emitting chip 400. The data communication unit 715 transmits a periodic first synchronization signal SYNC to the synchronization signal line, and the first synchronization signal SYNC indicates the timing of exposing the photosensitive member 102 to the image data for each row. When the circumferential speed of the photosensitive member 102 is 200 mm / s and the resolution in the circumferential direction is 1200 dpi (approximately 21.16 μm), the first synchronization signal SYNC is a pulse signal that switches to a high level at a period of approximately 105.8 μs. The data communication unit 715 transmits image data DATA1 to DATA20 in parallel to twenty data signal lines synchronously with the rising edge of the first synchronization signal SYNC. Since each light-emitting chip 400 in this embodiment has 2992 light-emitting elements 602, it is necessary to transmit bits indicating whether to cause the 2992 light-emitting elements 602 to emit light to the light-emitting chip 400 at a period of approximately 105.8 μs. Therefore, in this example, the data communication unit 715 sets the frequency of the clock signal CLK to 30 MHz when transmitting image data, as Figure 8 shown. Note that, as used herein, the image data transmitted to the i-th row of the light-emitting chip 400-n is represented as Li-D n , and when referring to each bit in the image data, the index (i.e., the light-emitting element number) of the bit is also represented in square brackets. However, in Figure 8 , the row number Li is omitted in the box of each bit.

[0053] Figure 9It is a block diagram showing an example of the detailed circuit configuration of a light-emitting chip 400 (the nth light-emitting chip 400-n). The light-emitting chip 400 has nine pads 408-1 to 408-9, a circuit section 406, and a light-emitting element array 410. The pads 408-1 and 408-2 are connected to the power supply voltage VCC through a power supply line. The power from the power supply voltage VCC is supplied to each circuit in the circuit section 406 of the light-emitting chip 400. The pads 408-3 and 408-4 are connected to the ground via a ground line. Each circuit in the circuit section 406 and the upper electrode 508 are connected to the ground via the pads 408-3 and 408-4. The clock signal line is connected to the register 1002, the transfer unit 1003, and the latch units 1004-001 to 1004-748 via the pad 408-5. The synchronization signal line and the data signal line are connected to the transfer unit 1003 via the pads 408-6 and 408-7, respectively. The enable signal line and the control signal line are connected to the register 1002 via the pads 408-8 and 408-9, respectively. Control data indicating the magnitude of the drive current to be supplied to each light-emitting element 602 is written to the register 1002, for example.

[0054] Starting from the rising edge of the first synchronization signal SYNC, the transfer unit 1003 receives the input image data DATAn in synchronization with the clock signal CLK. The input image data DATAn includes a series of pixel values indicating whether each of the light-emitting elements 602 emits light. The transfer unit 1003 performs serial-to-parallel conversion on the series of serially received pixel values in units of Y (for example, Y = 4) pixel values. For example, the transfer unit has four cascaded D flip-flops and parallelizes the pixel values DATA-1, DATA-2, DATA-3, and DATA-4 input on four clocks and outputs them to the latch units 1004-001 to 1004-748. The transfer unit 1003 also has four D flip-flops for delaying the first synchronization signal SYNC and outputs the first latch signal LAT1 to the latch unit 1004-001 at a timing delayed by four clocks after the input of the first synchronization signal SYNC.

[0055] The k-th latch unit 1004-k (where k is an integer from 1 to 748) uses a latch circuit to hold four pixel values DATA-1, DATA-2, DATA-3, and DATA-4 that are input from the transfer unit 1003 simultaneously with the input of the k-th latch signal. Except for the last latch unit 1004-748, the k-th latch unit 1004-k delays the k-th latch signal LATk by four clocks and outputs the (k + 1)-th latch signal LAT(k + 1) to the latch unit 1004-(k + 1). The k-th latch unit 1004-k continues to output a drive signal based on the four pixel values held by the latch circuit to the current drive unit 1100 during the signal period of the k-th latch signal. For example, there is a four-clock delay between the timing when the first latch signal is input to the latch unit 1004-1 and the timing when the second latch signal is input to the latch unit 1004-2. Thus, the latch unit 1004-1 outputs a drive signal based on the first, second, third, and fourth pixel values to the current drive unit 1100, while the latch unit 1004-2 outputs a drive signal based on the fifth, sixth, seventh, and eighth pixel values to the current drive unit 1100. Generally, the latch unit 1004-k outputs a drive signal based on the (4k - 3)-th, (4k - 2)-th, (4k - 1)-th, and 4k-th pixel values to the current drive unit 1100. Thus, in Figure 9 the embodiment shown, 748 latch units 1004-001 to 1004-748 transfer 2992 drive signals to the current drive unit 1100 substantially in parallel for controlling the driving of 2992 (= 748 × 4) light-emitting elements 602. Each drive signal is a binary signal indicating one of a high level and a low level.

[0056] The current drive unit 1100 has 2992 light-emitting drive circuits corresponding to the 2992 light-emitting elements 602 in the light-emitting element array 410. Each light-emitting drive circuit causes a drive current having a magnitude indicated by the control data in the register 1002 to flow through the light-emitting layer 506 of the corresponding light-emitting element 602 when the corresponding drive signal is at a high level (which means light emission is turned on). This causes the light-emitting element 602 to emit light with a target light amount. Note that the control data can indicate a separate current value for each light-emitting element 602, a current value for each group of light-emitting elements 602, or a current value common to all light-emitting elements 602.

[0057] Figure 10 An example of a partial configuration of the current drive unit 1100 corresponding to one light-emitting element 602 is shown. Refer to Figure 10, the current driving unit 1100 includes a digital-to-analog converter (DAC) 1101, a first transistor 1102, a second transistor 1103, and a switching circuit 1104. The DAC 1101 performs digital-to-analog conversion on the digital value (current setting value) of the light emission intensity stored in the register 1002, and outputs a corresponding analog signal to the gate of the first transistor 1102. The first transistor 1102 is a current amplifier circuit, and can be, for example, a P-channel MOSFET. The source of the first transistor 1102 is connected to the power supply voltage VCC. The drain of the first transistor 1102 is connected to the source of the second transistor 1103. The first transistor 1102 draws current from the source (the amount of this current depends on the amount of current of the analog signal input to the gate), and outputs the drawn current to the drain. The second transistor 1103 is a switching circuit, and can be, for example, a P-channel MOSFET. During the execution of a normal printing operation, a driving signal (indicating whether light emission is on or off) from the latch unit 1004 is input to the gate of the second transistor 1103 via the switching circuit 1104. The drain of the second transistor 1103 is connected to the lower electrode 504 of the light emitting element 602. When the driving signal input to the gate indicates that light emission is on (for example, high level), the second transistor 1103 outputs the current input to the source to the light emitting element 602 via the drain. Therefore, during the period when the driving signal indicates that light emission is on, a current having an amount corresponding to the parameter value stored in the register 1002 is supplied to the light emitting element 602, so that each light emitting element 602 emits light with the light emission intensity specified by the control data.

[0058] The switching circuit 1104 is a circuit for switching between the normal mode and the test mode. In the normal mode, the switching circuit 1104 applies a driving signal to the gate of the second transistor 1103, while in the test mode, the switching circuit 1104 applies a test mode signal that is always at a high level to the gate of the second transistor 1103. Therefore, in the test mode, the gate of the second transistor 1103 is forcibly held on. The mode of the switching circuit 1104 can be set, for example, by the control data written to the register 1002. The test mode can be used, for example, to check the light emission state of the light emitting elements when manufacturing the device.

[0059] Although Figure 10 only the part corresponding to one light emitting element 602 is shown, the current driving unit 1100 can actually have the same number of similar circuits as the number of light emitting elements 602 (for example, 748×4 = 2992). However, the DAC 1101 can be shared by multiple light emitting elements 602.

[0060] Figure 11 is a signal diagram related to the timing of outputting a driving signal from each latch unit 1004 to the current driving unit 1100.

[0061] Figure 11 The topmost row indicates the second synchronization signal P_SYNC output from the data communication unit 715 to the second CPU 720. The period of the second synchronization signal P_SYNC can be approximated as 105.8 μs, as described above. The second row indicates the first synchronization signal SYNC output from the data communication unit 715 to each light-emitting chip 400. The first synchronization signal SYNC is synchronized with the second synchronization signal P_SYNC. Here, the period of the first synchronization signal SYNC is the same as the period of the second synchronization signal P_SYNC.

[0062] The third row indicates the first latch signal LAT1 input to the first latch unit 1004-001. The period of the first latch signal LAT1 is the same as the period of the first synchronization signal SYNC, but the rising timing of the first latch signal LAT1 is four clocks later than that of the first synchronization signal SYNC. The fourth row indicates the second latch signal LAT2 input to the second latch unit 1004-002. The period of the second latch signal LAT2 is the same as the period of the first synchronization signal SYNC, but the rising timing of the second latch signal LAT2 is four clocks later than that of the first latch signal LAT1. Generally, the rising timing of the k-th latch signal LATk is four clocks later than that of the (k-1)-th latch signal LAT(k-1).

[0063] The transfer unit 1003 of the light-emitting chip 400-1 sequentially receives the image data L1-D1[1] to L1-D1

[2992] during the first row period. Starting from the rising edge of the first latch signal LAT1, the latch unit 1004-001 outputs four drive signals based on the image data L1-D1[1] to L1-D1[4] in parallel to the signal lines PON1-1 to PON1-4. The output of these drive signals is maintained until the next rising edge of the first latch signal LAT1 (i.e., within the time length of one row period). For example, if the image data L1-D1[1] indicates light emission, then the first light-emitting element 602 of the light-emitting chip 400-1 remains in the light-emitting state during the first row period. Moreover, for example, if the image data L1-D1[1] indicates light-off, then the first light-emitting element 602 of the light-emitting chip 400-1 remains in the non-light-emitting state during the first row period. Starting from the rising edge of the second latch signal LAT2, the latch unit 1004-002 outputs four drive signals based on the image data L1-D1[5] to L1-D1[8] in parallel to the signal lines PON2-1 to PON2-4. The output of these drive signals is maintained until the next rising edge of the second latch signal LAT2. The drive signals from the latch units 1004-003 to 1004-748 are output in the same manner.

[0064] Next, the transmission unit 1003 sequentially receives the image data L2-D1[1] to L2-D1

[2992] during the second line period. Starting from the second rise of the first latch signal LAT1, the latch unit 1004-001 outputs four drive signals based on the image data L2-D1[1] to L2-D1[4] to the signal lines PON1-1 to PON1-4 in parallel. The output of these drive signals is maintained until the next rise of the first latch signal LAT1. Starting from the second rise of the second latch signal LAT2, the latch unit 1004-002 outputs four drive signals based on the image data L2-D1[5] to L2-D1[8] to the signal lines PON2-1 to PON2-4 in parallel. The output of these drive signals is maintained until the next rise of the second latch signal LAT2. The drive signals from the latch units 1004-003 to 1004-748 are output in the same manner.

[0065] Therefore, in each line period indicated by the first synchronization signal SYNC, the light-emitting chip 400-n makes the data signal (image data Li-D) input during the line period n ) indicates that the light-emitting element 602 that emits light is maintained in a light-emitting state.

[0066] <3. Variable processing speed>

[0067] <3-1. Related Questions>

[0068] However, when the image forming apparatus uses a variable process speed depending on the print job setting, the configuration of the exposure head 106 described above becomes problematic. For example, there are various types of sheets used for printing, and the basis weight may vary depending on the type of sheet. As an example, the basis weight of plain paper may range from 60 to 105 [g / m 2 ], while the basis weight of thick paper can range from 150 to 300 [g / m 2 ] (However, these basis weight ranges do not limit this embodiment.) The amount of heat required to fuse the toner image to the sheet increases as the basis weight of the sheet increases. This is because basis weight is positively correlated with heat capacity, and the higher the heat capacity, the lower the temperature rise per unit heat received from the fixing roller. Therefore, in order to ensure that the fixing unit 104 has sufficient time to apply heat to the sheet, it is conceivable that the processing speed when printing on sheets with a larger basis weight is slower than when printing on sheets with a smaller basis weight.

[0069] Specifically, in the present embodiment, the main processor 700 serves as a setting unit that sets the rotation speed (i.e., the processing speed) of the photosensitive member 102 according to the sheet type set for the print job. For example, when using plain paper, the main processor 700 sets the rotation speed of the photosensitive member 102 to the first rotation speed P1, and when using thick paper, sets the rotation speed of the photosensitive member 102 to the second rotation speed P2, where P2 is 1 / N of P1 and N is greater than 1. By setting the processing speed slower when using a sheet with a large basis weight in this way, sufficient heat can be applied to the toner image to melt the toner, and the toner can be reliably fixed to the sheet.

[0070] Then, generally speaking, the processing speed is inversely proportional to the line period, such that the slower the processing speed is set, the longer the line period becomes. Additionally, if, like the configuration of the exposure head 106 described above, the light-emitting element 602 is maintained in the light-emitting state within one line period, there is a concern that the long line period will cause overexposure of the photosensitive member.

[0071] Reference will be made to Figure 12 This overexposure will be explained by taking the case where the ratio N of the processing speeds is equal to 2 as an example. Figure 12 is a signal diagram similar to the signal diagram shown in Figure 11 except that Figure 12 the processing speed in Figure 11 is set to 1 / 2 of the processing speed of the example in

[0072] Since the processing speed is set to 1 / 2, Figure 12 the period of the second synchronization signal P_SYNC shown in the top row in

[0073] is approximately 211.6 (= 105.8 × 2) μs. The first synchronization signal SYNC shown in the second row has the same line period as the line period of the second synchronization signal P_SYNC.

[0074] The transfer unit 1003 of the light-emitting chip 400-1 sequentially receives the image data L1-D1[1] to L1-D1

[2992] during the first line period. Starting from the rising edge of the first latch signal LAT1, the latch unit 1004-001 outputs four drive signals based on the image data L1-D1[1] to L1-D1[4] in parallel to the signal lines PON1-1 to PON1-4. The output of these drive signals is maintained until the next rising edge of the first latch signal LAT1. For example, if the image data L1-D1[1] indicates light emission activation, then the first light-emitting element 602 of the light-emitting chip 400-1 remains in the light-emitting state within the first line period spanning approximately 211.6 μs. This also applies to the other light-emitting elements 602 of the light-emitting chip 400-1 and the light-emitting elements 602 of other light-emitting chips 400.

[0075] That is, when the line period indicated by the first synchronization signal SYNC is doubled, the length of time that the light-emitting element 602 corresponding to one pixel value remains in the light-emitting state based on this pixel value is doubled, which means that the exposure amount of the corresponding point on the surface of the photosensitive member 102 is doubled. The increase in the exposure amount of the photosensitive member 102 results in a corresponding increase in the amount of electric charge accumulated in the electrostatic latent image, thereby causing the developed toner image to be too dark. In addition, the excessive increase in the amount of electric charge in the electrostatic latent image may also have an adverse effect of accelerating the deterioration of the photosensitive member 102.

[0076] By causing the light-emitting element 602 to emit light only in a part of the line period extended in response to a change in the processing speed setting, overexposure of the photosensitive member 102 can be prevented. However, this synchronization control complicates the circuits in the light-emitting chip 400, which leads to an increase in the manufacturing and development costs of the image forming apparatus 1 and the exposure head 106.

[0077] <3-2. Prevention of Overexposure>

[0078] In the present embodiment, the second synchronization signal for the drive control of the image forming unit 101 is set to indicate the line period for achieving the desired processing speed. At the same time, in order to prevent the overexposure mentioned above and avoid complicating the circuit configuration, the first synchronization signal for the light emission control of each light-emitting chip is set to indicate a fixed line period regardless of the processing speed. The processing speed can be rewritten as the rotational speed of the photosensitive member. More specifically, the two synchronization signals can indicate the line period as follows:

[0079] - The second synchronization signal P_SYNC

[0080] Indicates the first line period when the photosensitive member 102 rotates at the first rotational speed, and

[0081] Indicates a second line period that is N times the first line period when the photosensitive member 102 rotates at a second rotation speed of 1 / N which is the first rotation speed (N is an integer of 2 or greater).

[0082] - The first synchronization signal SYNC

[0083] Indicates the above-mentioned first line period, regardless of the rotation speed of the photosensitive member 102.

[0084] In addition, when the photosensitive member 102 rotates at the above-mentioned second rotation speed, the data communication unit 715

[0085] - Transmits a line of data signals to the light-emitting chips 400-1 to 400-20 during one line period among the N line periods indicated by the first synchronization signal SYNC, and

[0086] - Transmits non-light-emitting signals for making none of the light-emitting elements 602 emit light to the light-emitting chips 400-1 to 400-20 during the remaining line periods among the N line periods.

[0087] The above configuration makes it possible to avoid complication of the circuit configuration of the light-emitting chips due to variable settings of the processing speed and promotes miniaturization of the device. In addition, overexposure of the photosensitive member is prevented, enabling provision of high-quality printed images and suppressing deterioration of the photosensitive member. An example of the detailed configuration of the data communication unit 715 for implementing such an embodiment will be specifically described in the next section.

[0088] <4. Example Configuration of Data Communication Unit>

[0089] Figure 13 Is a block diagram showing an example of the detailed configuration of the data communication unit 715. Refer to Figure 13 The data communication unit 715 includes a synchronization signal generation unit 731, a control data transmission unit 732, a data buffer 733, a signal selection unit 734, and an image data transmission unit 735.

[0090] <4-1. Details of Each Unit>

[0091] The synchronization signal generation unit 731 generates a clock signal CLK based on the reference clock signal R_CLK input from the clock generation unit 701. The synchronization signal generation unit 731 can variably set the frequency of the clock signal CLK under the control of the first CPU 711. For example, when transmitting control data to the light-emitting chip 400, the frequency of the clock signal CLK can be 3 MHz, and when transmitting image data to the light-emitting chip 400, the frequency of the clock signal CLK can be 30 MHz, as mentioned above. The synchronization signal generation unit 731 outputs the clock signal CLK to the control data transmission unit 732, the image data transmission unit 735, and the printed circuit board 202.

[0092] When the first trigger signal TOP is input from the main processor 700, the synchronization signal generation unit 731 outputs a second trigger signal P_TOP indicating the timing to start transmitting the input image data to the second CPU 720, and starts providing synchronization signals. Specifically, the synchronization signal generation unit 731 generates a second synchronization signal P_SYNC indicating a period corresponding to the rotation speed of the photosensitive member 102, which is set according to the type of sheet used in the printing job. The period indicated by the second synchronization signal P_SYNC is equal to the time length required for the photosensitive member 102 to rotate one pixel. In addition, the synchronization signal generation unit 731 generates a first synchronization signal SYNC that is synchronized with the second synchronization signal P_SYNC but indicates a constant line period independent of the rotation speed of the photosensitive member 102.

[0093] As an example, assume that plain paper is selected in the first printing job. In this case, the rotation speed of the photosensitive member 102 is set to the first rotation speed P1. The line period of the second synchronization signal P_SYNC generated by the synchronization signal generation unit 731 is, for example, equal to 105.8 [μs], and the line period of the first synchronization signal SYNC is also equal to 105.8 [μs]. As another example, assume that thick paper with a basis weight greater than that of plain paper is selected in the second printing job. In this case, the rotation speed of the photosensitive member 102 is set to the second rotation speed P2, which is half of the first rotation speed P1. The line period of the second synchronization signal P_SYNC generated by the synchronization signal generation unit 731 is, for example, equal to 211.6 [μs]. At the same time, the line period of the first synchronization signal SYNC is equal to 105.8 [μs], which is the same as that of the first printing job. When the resolution in the sub-scanning direction is 1200 dpi (approx. 21.16 μm), the first rotation speed P1 can correspond to the circumferential speed of the photosensitive member 102 of 200 [mm / s], and the second rotation speed P2 can correspond to the circumferential speed of the photosensitive member 102 of 100 [mm / s].

[0094] The second synchronization signal P_SYNC is output to the second CPU 720 and is used to control the rotation of the photosensitive member 102 and the conveyance of the sheet using the transfer belt 111. The first synchronization signal SYNC is output to the signal selection unit 734 and the image data transfer unit 735 and is used to control the transfer of data signals to the light-emitting chips 400 line by line.

[0095] When writing control data to the register 1002 of each light-emitting chip 400 of the printed circuit board 202, the control data transfer unit 732 transfers a control signal for writing the control data to the printed circuit board 202 in response to an instruction from the register access unit 714. Here, the instruction from the register access unit 714 is composed of the chip designation signal CHIP_E, the address designation signal ADD, and the control data D CTRL For example, the chip designation signal CHIP_E is a 5-bit signal that designates the light-emitting chip 400 to which data is to be written. The address designation signal ADD is a 4-bit signal that designates the write destination address. The control data D CTRL is 8-bit data to be written to the designated address in the designated light-emitting chip 400. For example, when the chip designation signal CHIP_E indicates "1", the control data transfer unit 732 transfers the designated address and control data to the control signal line for the light-emitting chip 400-1 according to the signal format described Figure 7 The transfer of control data for the light-emitting chips 400-2 to 400-20 is also performed in the same manner.

[0096] The data buffer 733 is a line memory (e.g., SRAM) capable of buffering two lines of the bitmap format image data B generated by the image data generation unit 713. The input and output of the image data via the data buffer 733 will be described in detail below. DATA For each line period indicated by the first synchronization signal SYNC, the signal selection unit 734 selectively outputs a data signal or a non-light-emitting signal based on the image data M input from the data buffer 733 to the image data transfer unit 735. The data signal here includes a series of bits constituting the image data DATA1 to DATA20 described in the reference

[0097] For example, "1" indicates the light emission of the corresponding light-emitting element 602, and "0" indicates the non-light emission of the corresponding light-emitting element 602. At the same time, the non-light-emitting signal is a signal that does not cause the corresponding light-emitting element 602 to emit light and is fixed to "0" regardless of the pixel position. DATA Here, the data signal includes a series of bits constituting the image data DATA1 to DATA20 described in the reference Figure 8 For example, "1" indicates the light emission of the corresponding light-emitting element 602, and "0" indicates the non-light emission of the corresponding light-emitting element 602. At the same time, the non-light-emitting signal is a signal that does not cause the corresponding light-emitting element 602 to emit light and is fixed to "0" regardless of the pixel position.

[0098] The first CPU 711 controls the selection of signal C to be output from the signal selection unit 734 to the image data transmission unit 735 for each line period indicated by the first synchronization signal SYNC according to the rotation speed setting of the photosensitive member 102. DATA For example, when the photosensitive member 102 rotates at the first rotation speed, the signal selection unit 734 selects the data signal based on the input image data from the data buffer 733 in all line periods indicated by the first synchronization signal SYNC. On the other hand, when the photosensitive member 102 rotates at the second rotation speed which is 1 / N of the first rotation speed, the signal selection unit 734 selects the data signal based on the input image data in one line period out of N line periods, and selects the non-light emission signal in the remaining line periods.

[0099] The image data transmission unit 735 transmits the first synchronization signal SYNC to the printed circuit board 202 via the synchronization signal line. In addition, during the line period indicated by the first synchronization signal SYNC, the image data transmission unit 735 transmits the data signal of one line for the light emission control of a plurality of light emitting elements 602 to the light emitting chips 400-1 to 400-20 in parallel via twenty data signal lines. The image data transmission unit 735 may further include a data buffer for serial-to-parallel conversion.

[0100] <4-2. Example of data processing timing>

[0101] (1) In the case of normal processing speed

[0102] Figure 14 is a signal diagram showing an example of the timing of processing image data at the data communication unit 715. Here, the processing speed is set to the normal value, that is, the rotation speed of the photosensitive member 102 is the first rotation speed P1 (for example, printing on plain paper).

[0103] Figure 14 The first trigger signal TOP in the top row in is a pulse signal input from the main processor 700 to the synchronization signal generation unit 731, and indicates the operation start timing of the image production unit 103. The pulse width of the first trigger signal TOP may correspond to one cycle of the clock signal CLK. The fixing unit 104 and the transport unit 105 also start operating according to the operation start timing indicated by the first trigger signal TOP, so that the image formation position in the sub-scanning direction is aligned with an appropriate position on the sheet.

[0104] The second trigger signal P_TOP in the second row is a pulse signal output from the synchronization signal generation unit 731 to the second CPU 720, and indicates the operation start timing of the corresponding part of the image forming unit 101. The pulse width of the second trigger signal P_TOP may correspond to one cycle of the clock signal CLK. The photosensitive member 102 and the transfer belt 111 start operating according to the operation start timing indicated by the second trigger signal P_TOP.

[0105] The functions of the second synchronization signal P_SYNC in the third row and the first synchronization signal SYNC in the fourth row are as described above. Here, these two synchronization signals indicate the same line period (105.8 μs) and are at a high level at the start of the transfer timing for each line of image data. Since the second trigger signal P_TOP, the first synchronization signal SYNC, and the second synchronization signal P_SYNC are synchronized with each other, the image forming position in the main scanning direction can be aligned with an appropriate position on the sheet.

[0106] The fifth row indicates the image data B input from the image data generation unit 713 to the data buffer 733. DATA . The sixth and seventh rows respectively indicate the data stored in the first line area (MEM1) and the second line area (MEM2) of the data buffer 733. In the first line period for each page, the image data L1-D1, …, L1-D 20 for the first line is stored in the first line area of the data buffer 733. In the second line period for each page, the image data L2-D1, …, L2-D 20 for the second line is stored in the second line area of the data buffer 733. In the third line period for each page, the image data L3-D1, …, L3-D 20 for the third line is stored in the first line area of the data buffer 733 (overwriting it). In the fourth line period for each page, the image data L4-D1, …, L4-D 20 for the fourth line is stored in the second line area of the data buffer 733 (overwriting it). Similarly, during the fifth and subsequent line periods, the image data in the odd-numbered lines and the image data in the even-numbered lines are alternately stored in the first and second line areas of the data buffer 733.

[0107] The eighth row indicates the data signal C output from the signal selection unit 734 to the image data transfer unit 735. DATA . In Figure 14In the scenario where the rotation speed of the photosensitive member 102 is the first rotation speed, the signal selection unit 734 selects data signals based on the input image data from the data buffer 733 during all line periods indicated by the first synchronization signal SYNC. Therefore, during the second line period, the signal selection unit 734 outputs a data signal based on the image data L1-D1, ..., L1-D 20 for the first line to the image data transmission unit 735. Next, during the third line period, the signal selection unit 734 outputs a data signal based on the image data L2-D1, ..., L2-D 20 for the second line to the image data transmission unit 735. Next, during the fourth line period, the signal selection unit 734 outputs a data signal based on the image data L3-D1, ..., L3-D 20 for the third line to the image data transmission unit 735. Similarly, during the fifth and subsequent line periods, data signals for the fourth and subsequent lines are sequentially output to the image data transmission unit 735.

[0108] The ninth and tenth lines indicate data signals DATA1 to DATA20 transmitted from the image data transmission unit 735 to the printed circuit board 202. During each line period in the third and subsequent line periods, the image data transmission unit 735 transmits in parallel to the printed circuit board 202 the data signals for the twenty light-emitting chips 400 received and buffered from the signal selection unit 734 during the previous line period. For example, during the third line period, data signals based on the image data L1-D1, ..., L1-D 20 for the first line are transmitted in parallel, and during the fourth line period, data signals based on the image data L2-D1, ..., L2-D 20 for the second line are transmitted in parallel.

[0109] (2) In the case of 1 / N processing speed

[0110] Figure 14 The signal diagram shows the processing timing when the processing speed is set to the normal value, and no non-light-emitting signal appears in this diagram. In contrast, when the processing speed is set to 1 / N of the normal value, non-light-emitting signals are inserted between the normal data signals.

[0111] Figure 15 is a signal diagram showing another example of the timing for processing image data at the data communication unit 715. Here, the processing speed is set to 1 / 2 of the normal value, that is, the rotation speed of the photosensitive member 102 is the second rotation speed P2 (= P1 / 2) (for example, printing on thick paper).

[0112] Figure 15The first trigger signal TOP in the topmost row and the second trigger signal P_TOP in the second row are the same as the trigger signals in the example of Figure 14 the example.

[0113] Since the rotation speed of the photosensitive member 102 here is the second rotation speed P2, the second synchronization signal P_SYNC in the third row indicates a period (211.6 μs) that is twice the period of the example of Figure 14 the example. At the same time, the first synchronization signal SYNC in the fourth row indicates the same period (105.8 μs) as the period in the example of Figure 14 the example, regardless of the rotation speed of the photosensitive member 102. In the following description, the term "line period" refers to the period indicated by the first synchronization signal SYNC.

[0114] As understood from the timing of processing the image data B in the fifth row DATA of the example, the image data from the image data generation unit 713 is stored in the data buffer 733 at a period indicated by the second synchronization signal P_SYNC. That is, in the first line period indicated by the first synchronization signal SYNC, in response to the first rising edge of the second synchronization signal P_SYNC, the image data L1-D1,..., L1-D for the first row 20 is stored in the first row area (MEM1) of the data buffer 733. In the second line period, no new image data is stored in the data buffer 733. In the third line period, in response to the second rising edge of the second synchronization signal P_SYNC, the image data L2-D1,..., L2-D for the second row 20 is stored in the second row area (MEM2) of the data buffer 733. In the fourth line period, no new image data is stored in the data buffer 733.

[0115] Focusing on the eighth row, here, the rotation speed of the photosensitive member 102 is the second rotation speed, and the second rotation speed is 1 / 2 of the first rotation speed. Therefore, the signal selection unit 734 selects the data signal based on the input image data during one of the two line periods and selects the non-light emission signal during the remaining line period. Thus, during the second line period, the signal selection unit 734 will be based on the image data L1-D1,..., L1-D in the first row 20The data signal is output to the image data transmission unit 735. Next, during the third row period, the signal selection unit 734 selects non-light-emitting signals for all the light-emitting elements 602 of all the light-emitting chips 400, and outputs these non-light-emitting signals (a sequence of "0" bits) to the image data transmission unit 735. Similarly, during the fourth and subsequent row periods, the signal selection unit 734 outputs data signals based on the input image data to the image data transmission unit 735 during even-numbered row periods, and outputs non-light-emitting signals during odd-numbered row periods.

[0116] Focusing on the ninth and tenth rows, during the third row period, the image data transmission unit 735 transmits in parallel to the printed circuit board 202 the data signals based on the image data L1-D1,..., L1-D 20 in the first row for twenty light-emitting chips 400. Next, during the fourth row period, the image data transmission unit 735 transmits in parallel to the printed circuit board 202 non-light-emitting signals for twenty light-emitting chips 400. Similarly, during the fifth and subsequent row periods, the signal selection unit 734 transmits data signals based on the input image data to the printed circuit board 202 during odd-numbered row periods, and transmits non-light-emitting signals during even-numbered row periods. Note that the image data transmission unit 735 only repeats the operation of parallelizing the input signals from the signal selection unit 734 and transmitting the resulting signals to the printed circuit board 202 during each row period, without needing to know whether each transmitted signal is a signal based on the input image data or a dummy non-light-emitting signal. Similarly, the light-emitting chips 400-1 to 400-20 on the receiving-side printed circuit board 202 only need to drive the corresponding light-emitting elements 602 according to the corresponding values, without needing to know whether each received signal is based on the input image data or a dummy non-light-emitting signal.

[0117] Figure 16 is a signal diagram related to the timing of outputting drive signals from each latch unit to the current drive unit, corresponding to the example of Figure 15

[0118] Similar to the example of Figure 12 since the processing speed is set to 1 / 2, thus Figure 16 the period of the second synchronization signal P_SYNC shown in the top row in

[0119] ​The period of the first latch signal LAT1 shown in the third line is the same as the period of the first synchronization signal SYNC, but the rising timing of the first latch signal LAT1 is four clocks later than that of the first synchronization signal SYNC. The period of the second latch signal LAT2 shown in the fourth line is the same as the period of the first synchronization signal SYNC, but the rising timing of the second latch signal LAT2 is four clocks later than that of the first latch signal LAT1.

[0120] The transfer unit 1003 of the light-emitting chip 400-1 sequentially receives the image data L1-D1[1] to L1-D1

[2992] during the first line period. Starting from the rising edge of the first latch signal LAT1, the latch unit 1004-001 outputs four driving signals based on the image data L1-D1[1] to L1-D1[4] to the signal lines PON1-1 to PON1-4 in parallel. The output of these driving signals is maintained until the next rising edge of the first latch signal LAT1 (i.e., within the time length of one line period). Starting from the rising edge of the second latch signal LAT2, the latch unit 1004-002 outputs four driving signals based on the image data L1-D1[5] to L1-D1[8] to the signal lines PON2-1 to PON2-4 in parallel. The output of these driving signals is maintained until the next rising edge of the second latch signal LAT2. The driving signals from the latch units 1004-003 to 1004-748 are output in the same manner.

[0121] Next, during the second line period, the transfer unit 1003 sequentially receives 2992 non-light-emitting signals. Starting from the second rising edge of the first latch signal LAT1, the latch unit 1004-001 outputs four driving signals corresponding to the non-light-emitting signals to the signal lines PON1-1 to PON1-4 in parallel. Starting from the second rising edge of the second latch signal LAT2, the latch unit 1004-002 outputs four driving signals corresponding to the non-light-emitting signals to the signal lines PON2-1 to PON2-4 in parallel. The driving signals from the latch units 1004-003 to 1004-748 are output in the same way.

[0122] Next, during the third line period, the transfer unit 1003 sequentially receives the image data L2-D1[1] to L2-D1

[2992] . Starting from the third rising edge of the first latch signal LAT1, the latch unit 1004-001 outputs four drive signals based on the image data L2-D1[1] to L2-D1[4] to the signal lines PON1-1 to PON1-4 in parallel. Starting from the third rising edge of the second latch signal LAT2, the latch unit 1004-002 outputs four drive signals based on the image data L2-D1[5] to L2-D1[8] to the signal lines PON2-1 to PON2-4 in parallel. The drive signals from the latch units 1004-003 to 1004-748 are output in the same manner.

[0123] Therefore, in Figure 16 the example of Figure 12 , each light-emitting chip 400-n maintains the light-emitting element 602 that is instructed to emit light by the input data signal in the light-emitting state in one of the two line periods, and causes the light-emitting element 602 not to emit light in the remaining line period. This avoids the overexposure shown in

[0124] As a result, regardless of the processing speed setting, an image with stable quality can be formed on various types of sheets.

[0125] Figure 17 is a signal diagram showing an example of the timing for processing image data at the data communication unit 715. Here, the processing speed is set to 1 / 3 of the normal value, that is, the rotation speed of the photosensitive member 102 is the third rotation speed P3 (=P1 / 3). When the resolution in the sub-scanning direction is 1200 dpi and the first rotation speed P1 corresponds to the circumferential speed 200 [mm / s] of the photosensitive member 102, the third rotation speed P3 can correspond to the circumferential speed 66.67 [mm / s] of the photosensitive member 102.

[0126] Figure 17 The first trigger signal TOP in the top row and the second trigger signal P_TOP in the second row in Figure 14 are the same as the trigger signals in the example of

[0127] Since the rotation speed of the photosensitive member 102 here is the third rotation speed P3, the second synchronization signal P_SYNC in the third row indicates a period (317.4 μs) that is three times the period in the example of Figure 14 At the same time, the first synchronization signal SYNC in the fourth row indicates the same as Figure 14The periods (105.8 μs) with the same period in the examples are the same, regardless of the rotation speed of the photosensitive member 102. In the following description, the term "line period" refers to the period indicated by the first synchronization signal SYNC.

[0128] Referring to the fifth line, the image data from the image data generation unit 713 is stored in the data buffer 733 at the period indicated by the second synchronization signal P_SYNC. That is, in the first line period indicated by the first synchronization signal SYNC, in response to the first rising edge of the second synchronization signal P_SYNC, the image data L1-D1,..., L1-D for the first line 20 is stored in the first line area (MEM1) of the data buffer 733. In the second and third line periods, no new image data is stored in the data buffer 733. In the fourth line period, in response to the second rising edge of the second synchronization signal P_SYNC, the image data L2-D1,..., L2-D for the second line 20 is stored in the second line area (MEM2) of the data buffer 733. In the fourth and fifth line periods, no new image data is stored in the data buffer 733.

[0129] Focusing on the eighth line, here, the rotation speed of the photosensitive member 102 is the third rotation speed, and the third rotation speed is 1 / 3 of the first rotation speed. Therefore, the signal selection unit 734 selects the data signal based on the input image data in one of the three line periods and selects the non-light-emitting signal in the remaining two line periods. Thus, during the third line period, the signal selection unit 734 outputs the data signal based on the image data L1-D1,..., L1-D in the first line 20 to the image data transmission unit 735. Next, during the fourth line period, the signal selection unit 734 selects non-light-emitting signals for all the light-emitting elements 602 of all the light-emitting chips 400 and outputs these non-light-emitting signals to the image data transmission unit 735. Next, during the fifth line period, the signal selection unit 734 again selects non-light-emitting signals for all the light-emitting elements 602 of all the light-emitting chips 400 and outputs these non-light-emitting signals to the image data transmission unit 735. Similarly, during the sixth and subsequent line periods, the signal selection unit 734 outputs the data signal based on the input image data to the image data transmission unit 735 during one of the three line periods and outputs non-light-emitting signals during the remaining two line periods.

[0130] Focusing on the ninth and tenth lines, during the fourth line period, the image data transmission unit 735 transmits the image data L1-D1,..., L1-D for the first line to the printed circuit board 202 in parallel for twenty light-emitting chips 400 20The data signal. Next, during the fifth line period, the image data transmission unit 735 transmits non-light emission signals for twenty light-emitting chips 400 in parallel to the printed circuit board 202. Next, during the sixth line period, the image data transmission unit 735 transmits non-light emission signals for twenty light-emitting chips 400 in parallel to the printed circuit board 202 again. Although not shown in the figure, during the seventh line period, the image data transmission unit 735 transmits data signals based on the image data L2-D1,..., L2-D for the twenty light-emitting chips 400 in parallel to the printed circuit board 202 20 for the second row. Note that here the image data transmission unit 735 also does not need to know whether each transmitted signal is based on the input image data or a dummy non-light emission signal. Similarly, the light-emitting chips 400-1 to 400-20 only need to drive the corresponding light-emitting elements 602 according to the corresponding values without knowing whether each received signal is based on the input image data or a dummy non-light emission signal.

[0131] Figure 18 is a signal diagram related to the timing of outputting drive signals from each latch unit to the current drive unit, corresponding to the example of Figure 17

[0132] Since the processing speed is set to 1 / 3, therefore Figure 18 the period of the second synchronization signal P_SYNC shown in the top row of

[0133] is approximately 317.4 (= 105.8 × 3) μs. The period of the first synchronization signal SYNC shown in the second row is a constant line period independent of the rotation speed of the photosensitive member 102, that is, 105.8 μs.

[0134] ​The transmission unit 1003 of the light-emitting chip 400-1 sequentially receives the image data L1-D1[1] to L1-D1

[2992] during the first line period. Starting from the rise of the first latch signal LAT1, the latch unit 1004-001 outputs four drive signals based on the image data L1-D1[1] to L1-D1[4] in parallel to the signal lines PON1-1 to PON1-4. Starting from the rise of the second latch signal LAT2, the latch unit 1004-002 outputs four drive signals based on the image data L1-D1[5] to L1-D1[8] in parallel to the signal lines PON2-1 to PON2-4. The drive signals from the latch units 1004-003 to 1004-748 are output in the same manner.

[0135] Next, during the second row period, transfer unit 1003 sequentially receives 2992 non-luminescence signals. Starting from the second rising edge of first latch signal LAT1, latch unit 1004-001 outputs four drive signals corresponding to the non-luminescence signals in parallel to signal lines PON1-1 through PON1-4. Starting from the second rising edge of second latch signal LAT2, latch unit 1004-002 outputs four drive signals corresponding to the non-luminescence signals in parallel to signal lines PON2-1 through PON2-4. Drive signals from latch units 1004-003 through 1004-748 are output in the same manner.

[0136] During the third row period, transfer unit 1003 also sequentially receives 2992 non-luminescence signals. Starting from the third rising edge of first latch signal LAT1, latch unit 1004-001 outputs four drive signals corresponding to the non-luminescence signals in parallel to signal lines PON1-1 through PON1-4. Starting from the third rising edge of second latch signal LAT2, latch unit 1004-002 outputs four drive signals corresponding to the non-luminescence signals in parallel to signal lines PON2-1 through PON2-4. Drive signals from latch units 1004-003 through 1004-748 are output in the same manner.

[0137] During the fourth line period, the transfer unit 1003 sequentially receives image data L2-D1[1] to L2-D1

[2992] . Starting from the fourth rising edge of the first latch signal LAT1, the latch unit 1004-001 outputs four driving signals based on the image data L2-D1[1] to L2-D1[4] to the signal lines PON1-1 to PON1-4 in parallel. Starting from the fourth rising edge of the second latch signal LAT2, the latch unit 1004-002 outputs four driving signals based on the image data L2-D1[5] to L2-D1[8] to the signal lines PON2-1 to PON2-4 in parallel. The driving signals from the latch units 1004-003 to 1004-748 are output in the same manner.

[0138] Therefore, in Figure 18 In the example of , each light-emitting chip 400-n maintains the light-emitting element 602 that emits light as indicated by the input data signal in the light-emitting state in one of the three line periods, and in the remaining line periods, causes none of the light-emitting elements 602 to emit light. This avoids the overexposure mentioned above, and thus a stable-quality image can be formed on various types of sheets without being affected by the processing speed setting.

[0139] With the configuration of the exposure head 106 according to the above-described embodiment, even when the processing speed is variably set, overexposure of the photosensitive member 102 can be avoided without affecting the configuration of the plurality of light-emitting chips 400 of the printed circuit board 202. Therefore, since there is no need to incorporate a complex circuit into the light-emitting chip 400 for driving control of the light-emitting element 602, the manufacturing and development costs of the image forming apparatus 1 and the exposure head 106 can be reduced, and miniaturization of the apparatus can be promoted. In addition, the above-described insertion of the non-light-emitting signal into the signal sequence of the image data is achieved by simple signal selection based on the progress of the line period. Therefore, there is no need to add additional hardware to the image controller 710, which can further reduce costs.

[0140] (3) Other processing speeds

[0141] Depending on the sheet type (or other factors), the rotation speed of the photosensitive member 102 can be set to a value other than 1 / N of the normal value. In the first variation, it is assumed that the photosensitive member 102 rotates at a rotation speed P4, and the rotation speed P4 is M / N of the rotation speed P1. Here, M is an integer satisfying 1 < M < N. In this case, the second synchronization signal P_SYNC indicates a period of N / M that is the line period corresponding to the rotation speed P1. Even when the photosensitive member rotates at the rotation speed P4, the synchronization signal generation unit 731 generates the first synchronization signal SYNC, and the first synchronization signal SYNC indicates the same line period as the line period corresponding to the rotation speed P1. When the photosensitive member 102 rotates at the rotation speed P4, the image data transmission unit 735 repeatedly transmits a data signal of one line to the light-emitting chips 400-1 to 400-20 during M line periods out of the N line periods indicated by the first synchronization signal SYNC. That is, in this case, the data signal in the same line is repeatedly transmitted in M line periods. In addition, the image data transmission unit 735 transmits a non-light-emitting signal for preventing all the light-emitting elements 602 from emitting light to the light-emitting chips 400-1 to 400-20 during the remaining line periods out of the N line periods. By switching between the data signal and the non-light-emitting signal as in the first variation, the exposure amount at each pixel position on each line can be reduced to M / N of the exposure amount when the non-light-emitting signal is not inserted, thereby avoiding overexposure.

[0142] In a second variation, it is assumed that the photosensitive member 102 rotates at a rotational speed P5, and the rotational speed P5 is M / N of the rotational speed P1. Here, M can be any positive number. In the second variation, each light-emitting chip 400 is set to emit light with an amount of light that is M times the normal amount of light. The second synchronization signal P_SYNC indicates a period that is N times the line period corresponding to the rotational speed P1. Even when the photosensitive member rotates at the rotational speed P5, the synchronization signal generation unit 731 generates the first synchronization signal SYNC, and the first synchronization signal SYNC indicates the same line period as the line period corresponding to the rotational speed P1. When the photosensitive member 102 rotates at the rotational speed P5, the image data transmission unit 735 transmits a line of data signals to the light-emitting chips 400-1 to 400-20 during one of the N line periods indicated by the first synchronization signal SYNC. In addition, the image data transmission unit 735 transmits non-light-emitting signals for preventing all the light-emitting elements 602 from emitting light to the light-emitting chips 400-1 to 400-20 during the remaining line periods of the N line periods. Before starting the image forming operation, the control data transmission unit 732 writes control data indicating a current setting value, which is M times the current setting value when the photosensitive member 102 rotates at the rotational speed P1, into the register 1002 of each light-emitting chip 400. Combining signal output control and variable current setting as in the second variation can also reduce the exposure amount at each pixel position in each line to M / N, thereby avoiding overexposure.

[0143] <5. Further variations>

[0144] Although specific numerical values are used for description in this document, these specific numerical values are merely examples, and the present invention is not limited to the specific numerical values used herein. Specifically, the number of light-emitting chips provided on a printed circuit board is not limited to twenty, and can be any number. The size of the light-emitting element array in each light-emitting chip 400 is not limited to 4 rows × 748 columns, and can be any other size. The pitches of the light-emitting elements in the circumferential direction and the axial direction are not limited to approximately 21.16 μm and approximately 5 μm, respectively, and can take any other values. The number of signals grouped by each latch unit 1004 in the circuit portion 406 of each light-emitting chip 400 does not necessarily need to be four, and can alternatively be any other number.

[0145] The configuration of the data communication unit 715 is also not limited to the above example. For example, the conversion of PDL data to binary input image data can be performed at any timing before outputting the signal to the printed circuit board 202. An image data buffer can use a line memory with three or more lines instead of a two-line line memory.

[0146] One or more embodiments of the present invention can also be implemented by a computer that reads and executes computer-executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be more fully referred to as a "non-transitory computer-readable storage medium") to perform the functions of one or more of the above-described embodiments and / or include one or more circuits (e.g., an application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiments, and can be implemented by a method executed by a computer of a system or device, such as reading and executing computer-executable instructions from the storage medium to perform the functions of one or more of the above-described embodiments and / or controlling one or more circuits to perform the functions of one or more of the above-described embodiments. The computer may include one or more processors (e.g., a central processing unit (CPU), a microprocessing unit (MPU)), and may include a network of individual computers or individual processors to read and execute the computer-executable instructions. The computer-executable instructions may be provided to the computer, for example, from a network or a storage medium. The storage medium may include, for example, one or more of a hard disk, a random access memory (RAM), a read only memory (ROM), a storage device of a distributed computing system, an optical disk (such as a compact disk (CD), a digital versatile disk (DVD), or a Blu-ray disk (BD) TM ), a flash device, a memory card, etc.

[0147] Embodiments of the present invention can also be implemented by the following method, that is, by providing software (program) that performs the functions of the above-described embodiments to a system or device through a network or various storage media, and the computer or central processing unit (CPU), microprocessing unit (MPU) of the system or device reads and executes the program.

[0148] Although the present invention has been described with reference to exemplary embodiments, it should be understood that the present invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to cover all such modifications as well as equivalent structures and functions.

Claims

1. An exposure device, comprising: At least one light-emitting chip having a plurality of light-emitting elements arranged in rows parallel to the axial direction of a photosensitive member configured to rotate; A synchronization signal generation unit configured to generate a first synchronization signal synchronized with a second synchronization signal, the second synchronization signal corresponding to the rotation speed of the photosensitive member, the first synchronization signal being used to control the transmission of data signals for each row to the at least one light-emitting chip; And A transmission unit configured to transmit, during a row period indicated by the first synchronization signal, a row of data signals for controlling the light emission of the plurality of light-emitting elements to the at least one light-emitting chip, Wherein the second synchronization signal When the photosensitive member rotates at a first rotation speed, indicates a first row period, and When the photosensitive member rotates at a second rotation speed that is 1 / N of the first rotation speed, indicates a second row period that is N times the first row period, where N is an integer, 1 < N, the synchronization signal generation unit is configured to generate the first synchronization signal indicating the first row period regardless of the rotation speed of the photosensitive member, and When the photosensitive member rotates at the second rotation speed, the transmission unit is configured to: During one row period among the N row periods indicated by the first synchronization signal, transmit a row of data signals to the at least one light-emitting chip; And During the remaining one or more row periods among the N row periods, transmit non-light-emitting signals for not causing the plurality of light-emitting elements to emit light to the at least one light-emitting chip.

2. The exposure device according to claim 1, Among them, Within each row period indicated by the first synchronization signal, the at least one light-emitting chip maintains the light-emitting elements indicated by the data signals input during that row period in a light-emitting state.

3. The exposure device according to claim 1, further comprising: A data generation unit configured to generate image data for controlling the light emission of the plurality of light-emitting elements of the at least one light-emitting chip; A signal selection unit configured to selectively output, for each row period indicated by the first synchronization signal, a data signal or a non-light-emitting signal based on the image data generated by the data generation unit to the transmission unit; And A first control unit configured to control the selection of the signal output from the signal selection unit to the transmission unit for each row period indicated by the first synchronization signal according to the setting of the rotation speed of the photosensitive member.

4. The exposure device according to claim 1, Among them, When the photosensitive member rotates at a third rotation speed that is M / N of the first rotation speed, where M is an integer, 1 < M < N, the transmission unit is configured to: During M row periods among the N row periods indicated by the first synchronization signal, repeatedly transmit a row of data signals to the at least one light-emitting chip; And During the remaining one or more row periods among the N row periods, transmit non-light-emitting signals for not causing the plurality of light-emitting elements to emit light to the at least one light-emitting chip.

5. The exposure device according to claim 1, Among them, When the photosensitive member rotates at a third rotation speed that is M / N of the first rotation speed, the transmission unit is configured to: During one of the N line periods indicated by the first synchronization signal, a data signal for one line is transmitted to the at least one light-emitting chip; and during the remaining one or more of the N line periods, a non-light-emitting signal for preventing the plurality of light-emitting elements from emitting light is transmitted to the at least one light-emitting chip, and when the photosensitive member rotates at a third rotational speed, the plurality of light-emitting elements of the at least one light-emitting chip are set to emit light in an amount that is M times the amount of light emitted when the photosensitive member rotates at a first rotational speed.

6. The exposure apparatus according to claim 1, wherein the plurality of light-emitting elements are organic electroluminescence (EL) elements.

7. An image forming apparatus, comprising: the exposure apparatus according to claim 1; the photosensitive member; a developer configured to develop a latent image formed as a result of the exposure apparatus exposing the photosensitive member and to form a toner image on the surface of the photosensitive member; a fixing unit configured to fix the toner image transferred from the photosensitive member to a sheet onto the sheet; and a setting unit configured to set the rotational speed of the photosensitive member according to the type of the sheet.

8. The image forming apparatus according to claim 7, wherein the setting unit is configured to: when forming an image on a sheet having a first basis weight, set the rotational speed of the photosensitive member to a first rotational speed; and when forming an image on a sheet having a second basis weight greater than the first basis weight, set the rotational speed of the photosensitive member to a second rotational speed.

9. The image forming apparatus according to claim 7, wherein the synchronization signal generation unit is configured to generate a second synchronization signal indicating a line period corresponding to the rotational speed of the photosensitive member set by the setting unit.

10. The image forming apparatus according to claim 9, further comprising: a second control unit configured to synchronously control the rotation of the photosensitive member and the conveyance of the sheet based on the second synchronization signal generated by the synchronization signal generation unit.

Images