Optical print head and image forming apparatus including the same

Abstract

To solve the problem with a control section of an image forming apparatus in prior art, that one light-emitting chip among a plurality of light-emitting chips is specified and transmission of control data to the specified light-emitting chip is repeated, when transmitting control data to each light-emitting chip, and in such a constitution, there is risk of increasing the time required for transmitting control data to all light-emitting chips mounted on a substrate.SOLUTION: A plurality of light-emitting chips respectively is connected to a controller IC by the different one among a plurality of signal wires, and control data is transmitted to each of the light-emitting chips connected by the different one among the plurality of signal wires.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms an image using an exposure unit having a plurality of light emitting units.

Background Art

[0002] In an electrophotographic image forming apparatus, an electrostatic latent image is formed on a photoreceptor by exposing the photoreceptor that is rotationally driven, and an image is formed by developing the electrostatic latent image with toner. Note that the direction parallel to the rotation axis of the photoreceptor is referred to as the main scanning direction. Patent Document 1 discloses an image forming apparatus that uses an exposure unit in which a plurality of light emitting units are arranged in a plurality in the main scanning direction. In Patent Document 1, a plurality of light emitting chips in which an electrode, an organic EL (Electro-Luminescence) film, and a circuit unit for causing the organic EL film to emit light are formed on a silicon wafer are mounted on a substrate. Control data regarding, for example, the magnitude of a voltage to be applied to the electrode (current to be supplied to the organic EL film) is transmitted from the control unit of the image forming apparatus to the circuit unit of each light emitting chip. The control data is stored in a register provided in the circuit unit. The circuit unit applies a voltage to the electrode based on the image data transmitted from the control unit of the image forming apparatus and the control data regarding the magnitude of the voltage stored in the register. As a result, the organic EL film emits light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, in order to transmit control data from the control unit of the image forming apparatus to each light emitting chip, the control unit of the image forming apparatus and each light emitting chip are connected in a bus shape by signal lines.

[0005] Therefore, when the control unit of the image forming apparatus transmits control data to each light emitting chip, it repeatedly specifies one of the plurality of light emitting chips and transmits the control data to the specified light emitting chip. In such a configuration, there is a risk that the time required to transmit control data to all the light emitting chips mounted on the substrate will increase.

[0006] In view of the above problems, an object of the present invention is to shorten the transmission time of control data to a plurality of light emitting chips.

Means for Solving the Problems

[0007] The image forming apparatus according to the present invention includes: a rotating photoreceptor; a silicon substrate, a plurality of light emitting portions provided on the silicon substrate that emit light for exposing the photoreceptor, a circuit portion provided on the silicon substrate that turns on and off the plurality of light emitting portions based on image data for controlling the turning on and off of the plurality of light emitting portions, and a storage portion provided on the silicon substrate that stores control data indicating the target light amount of the plurality of light emitting portions, and a plurality of light emitting chips arranged along the rotation axis direction of the photoreceptor; a controller that outputs the control data; and is characterized in that each of the plurality of light emitting chips is connected to the controller via a different one of a plurality of signal lines; the control data transmitted via a different one of the plurality of signal lines is stored in the storage portion; The controller reads out the control data from each of the memory units provided in the plurality of light-emitting chips via a different one of the plurality of signal lines, and based on that the read control data matches the control data transmitted from the controller to each of the plurality of light-emitting chips via a different one of the plurality of signal lines, transmits the image data to each of the light-emitting chips via a different one of the plurality of signal lines.

Effects of the Invention

[0008] According to the present invention, it is possible to shorten the transmission time of control data to a plurality of light emitting chips.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Preferred embodiments for carrying out the present invention will be described below with reference to the accompanying drawings. However, the components described in this description are merely examples, and the present invention is not limited to the embodiments described in this description.

[0011] [Embodiment 1] FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. A reading unit 100 optically reads a document placed on a document table and generates image data representing the reading result. An image forming unit 103 forms an image on a sheet based on, for example, the image data generated by the reading unit 100 or the image data received from an external device via a network.

[0012] The image forming unit 103 includes image forming units 101a, 101b, 101c, and 101d. The image forming units 101a, 101b, 101c, and 101d form toner images of black, yellow, magenta, and cyan, respectively. The configurations of the image forming units 101a, 101b, 101c, and 101d are the same, and hereinafter, they will also be collectively referred to as the image forming unit 101.

[0013] During image formation, the photoreceptor 102 of the image forming unit 101 is rotationally driven in the clockwise direction in the figure.

[0014] The charger 107 charges the photoreceptor 102. The exposure head 106, which is an exposure device, exposes the photoreceptor 102 according to image data to form an electrostatic latent image on the photoreceptor 102. The developing unit 108 develops the electrostatic latent image on the photoreceptor 102 with toner. The toner image on the photoreceptor 102 is transferred to a sheet being conveyed on the transfer belt 111. Note that by overlapping the toner images on each photoreceptor 102 and transferring them to the sheet, colors different from black, yellow, magenta, and cyan can be reproduced.

[0015] The conveyance unit 105 controls the feeding and conveyance of the sheet. Specifically, the conveyance unit 105 feeds the sheet from a designated unit among the internal storage units 109a and 109b, the external storage unit 109c, and the manual unit 109d to the conveyance path of the image forming apparatus.

[0016] The fed sheet is conveyed to the registration roller 110. The registration roller 110 conveys the sheet onto the transfer belt 111 at a predetermined timing so that the toner image on each photoreceptor 102 is transferred to the sheet. As described above, while being conveyed 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 fixing of the toner image, the sheet is discharged outside the image forming apparatus by the discharge roller 112.

[0017] FIG. 2(A) and FIG. 2(B) show the photoreceptor 102 and the exposure head 106. The exposure head 106 includes a light emitting point group 201, a printed circuit board 202 on which the light emitting point group 201 is mounted, a rod lens array 203, and a housing 204 that holds the rod lens array 203 and the printed circuit board 202. The rod lens array 203 condenses the light emitted from the light emitting point group 201 onto the photoreceptor 102 to form an imaging spot of a predetermined size on the photoreceptor 102.

[0018] Figs. 3(A) and 3(B) show the printed circuit board 202. Note that Fig. 3(A) shows the surface on which the connector 305 is mounted, and Fig. 3(B) shows the surface on which the light-emitting point group 201 is mounted (the surface opposite to the surface on which the connector 305 is mounted). In the present embodiment, the light-emitting point group 201 includes 20 light-emitting chips 400-1 to 400-20. The light-emitting chips 400-1 to 400-20 are arranged in a staggered pattern in two rows along the main scanning direction. In the following description, the light-emitting chips 400-1 to 400-20 are also collectively referred to as the light-emitting chip 400. The light-emitting chip 400 has a plurality of light-emitting points (light-emitting elements). Each light-emitting chip 400 on the printed circuit board 202 is connected to an image controller 700 (Fig. 7), which is a control unit, via the connector 305.

[0019] Fig. 4 is an explanatory diagram of the arrangement of the light-emitting chip 400 and the light-emitting points 602 provided on the light-emitting chip 400. One light-emitting chip 400 has a plurality of sets of 748 light-emitting points 602 arranged along the main scanning direction. Note that the plurality of sets are arranged along the sub-scanning direction orthogonal to the main scanning direction. In this way, the calling chip 400 is arranged two-dimensionally along both the main scanning direction and the sub-scanning direction. In the following description, as an example, the number of sets is set to 4. That is, in the following exemplary embodiment, the light-emitting chip 400 has four sets of 748 light-emitting points 602 arranged along the main scanning direction, that is, a total of 2992 light-emitting points 602. The pitch between adjacent light-emitting points 602 in the main scanning direction corresponds to approximately 21.16 μm for a resolution of 1200 dpi. Therefore, the length of one set of 748 light-emitting points 602 in the main scanning direction is approximately 15.8 mm. Also, the pitch (length P in Fig. 4) between adjacent light-emitting points 602 in the sub-scanning direction also corresponds to approximately 21.16 μm for a resolution of 1200 dpi. Furthermore, the pitch (length L in Fig. 4) between the light-emitting points 602 of two adjacent light-emitting chips 400 in the main scanning direction also corresponds to approximately 21.16 μm for a resolution of 1200 dpi.

[0020] FIG. 5 is a plan view of the light-emitting chip 400. A plurality of light-emitting points 602 of the light-emitting chip 400 are formed, for example, on a light-emitting substrate 402 which is a silicon substrate. Further, a circuit portion 406 for controlling the plurality of light-emitting points 602 is provided on the light-emitting substrate 402. Signal lines for communicating with the image controller 700, power lines for connecting to a power supply, and ground lines for connecting to a ground are connected to the pads 408-1 to 408-10. The signal lines, power lines, and ground lines are, for example, wires made of gold.

[0021] FIG. 6 shows a part of the cross section taken along the line A-A in FIG. 5. A plurality of lower electrodes 504 are formed on the light-emitting substrate 402. A gap of length d is provided between two adjacent lower electrodes 504. A light-emitting layer 506 is provided on the lower electrode 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 predetermined voltage is applied between the lower electrode 504 and the upper electrode 508, a current flows from the lower electrode 504 to the upper electrode 508, and the light-emitting layer 506 emits light. Therefore, the region of the light-emitting layer 506 corresponding to the region of one lower electrode 504 corresponds to one light-emitting point 602. That is, in the present embodiment, the light-emitting substrate 402 includes a plurality of light-emitting points. Note that the light-emitting point may be called a light-emitting portion.

[0022] For the light-emitting layer 506, for example, an organic EL film can be used. Also, an inorganic EL film can be used for the light-emitting layer 506. The upper electrode 508 is composed of a transparent electrode such as indium tin oxide (ITO) so as to transmit the light-emitting wavelength of the light-emitting layer 506.

[0023] Note that in the present embodiment, the entire upper electrode 508 transmits the light-emitting wavelength of the light-emitting layer 506, but it is not necessary for the entire upper electrode 508 to transmit the light-emitting wavelength. Specifically, it is sufficient that the region from which the light from each light-emitting point 602 is emitted transmits the light-emitting wavelength.

[0024] Note that in this embodiment, the light-emitting layer 506 is common to all the lower electrodes 504 provided on the light-emitting chip 400, but this is not the limit. For example, a configuration may be adopted in which a first plurality of lower electrodes 504 among the plurality of lower electrodes 504 provided on the light-emitting chip 400 are covered by a first light-emitting layer 506, and a second plurality of lower electrodes 504 among the plurality of lower electrodes 504 provided on the light-emitting chip 400 are covered by a second light-emitting layer 506. Even in such a configuration, the region of the light-emitting layer 506 corresponding to the region of one lower electrode 504 corresponds to one light-emitting point 602. Further, the light-emitting layer 506 may be individually provided for each of the plurality of lower electrodes 504 provided on the light-emitting chip 400. Even in such a configuration, the region of the light-emitting layer 506 corresponding to the region of one lower electrode 504 corresponds to one light-emitting point 602.

[0025] FIG. 7 shows the control configuration of the light-emitting chip 400. The data switching unit 705 and each light-emitting chip 400 are connected by a plurality of signal lines (wires). Specifically, the data switching unit 705 and the light-emitting chip 400-n (n is an integer from 1 to 20) are connected by a signal line DATAn, a signal line WRITEn, and a signal line READn. The signal line DATAn is used for the data switching unit 705 to transmit image data to the light-emitting chip 400-n. The signal line WRITEn is used for the data switching unit 705 to write control data to the register of the light-emitting chip 400-n or to notify the light-emitting chip 400-n of the reading of the control data. The signal line READn is used for the data switching unit 705 to read the control data stored in the register of the light-emitting chip 400-n.

[0026] Further, the data switching unit 705 and all the light-emitting chips 400 are connected by one signal line CLK, one signal line SYNC, and one signal line EN. The signal line CLK is used to transmit a clock signal for data transmission and reception on the signal lines DATAn, signal line WRITEn, and signal line READn. The data switching unit 705 outputs a clock signal generated based on the reference clock signal from the clock generation unit 702 to the signal line CLK. The signals transmitted to the signal line SYNC and the signal line EN will be described later.

[0027] The CPU 701 controls the entire image forming apparatus. The image data generation unit 703 performs various image processes such as halftone processing on the image data received from the reading unit 100 or an external device, and generates image data for controlling the on / off of the light emission of the light-emitting points 602 of each light-emitting chip 400. The image data generation unit 703 transmits the generated image data to the data switching unit 705. When writing control data to the registers in each light-emitting chip 400, the register access unit 704 receives the control data from the CPU 701 and transmits it to the data switching unit 705. Also, the register access unit 704 outputs the control data read from the registers in each light-emitting chip 400 to the CPU 701.

[0028] FIG. 8 shows the signals of each signal line when transmitting image data to each light-emitting chip 400. A periodic line synchronization signal indicating the exposure timing of each line in the photoreceptor 102 is output to the signal line SYNC. When the peripheral speed of the photoreceptor 102 is 200 mm / s and the resolution in the sub-scanning direction is 1200 dpi (about 21.16 μm), the line synchronization signal is output with a period of about 105.8 μs. The data switching unit 705 transmits the image data to the signal lines DATA1 to DATA20 in synchronization with the rising edge of the line synchronization signal. In the present embodiment, since each light-emitting chip 400 has 2992 light-emitting points 602, it is necessary to transmit image data indicating the light emission / non-light emission of each of the 2992 light-emitting points 602 to each light-emitting chip 400 within a period of about 105.8 μs. In order to transmit the image data for a total of 2992 light-emitting points 602 within a period of about 105.8 μs, in this example, as shown in FIG. 8, when transmitting the image data, the data switching unit 705 sets the frequency of the clock signal transmitted to the signal line CLK to 30 MHz.

[0029] FIG. 9 shows the signals of each signal line when writing control data to the register of the light-emitting chip 400. An enable signal indicating that it is at a high level and in communication during communication is output to the signal line EN. The data switching unit 705 transmits a start bit to the signal line WRITEn in synchronization with the rising edge of the enable signal. Subsequently, the data switching unit 705 transmits a write identification bit indicating a write operation, and then transmits the address (4 bits in this example) of the register to which the control data is to be written and the control data (8 bits in this example). The start bit, write identification bit, and address are command data for instructing an operation on the register. Since the data amount of the control data is smaller than the data amount of the image data, the frequency of the clock signal output to the signal line CLK can be set lower than when transmitting the image data. In this example, the frequency of the clock signal during the read / write of the control data is set to 3 MHz.

[0030] FIG. 10 shows the signals of each signal line when reading the control data stored in the register of the light-emitting chip 400. An enable signal that becomes high level during communication to indicate that communication is in progress is output to the signal line EN. The data switching unit 705 transmits a start bit to the signal line WRITEn in synchronization with the rising edge of the enable signal. Subsequently, the data switching unit 705 transmits a read identification bit indicating a read operation following the identification bit, and then transmits the address of the register from which the control data is to be read.

[0031] The start bit, read identification bit, and address are command data for instructing operations on the register. The light-emitting chip 400-n reads the control data stored at the address specified by the command from the register in response to the command data and outputs it to the signal line READn.

[0032] FIG. 11 is a functional block diagram of one light-emitting chip 400-n. As also shown in FIG. 5, the light-emitting chip 400 has ten pads 408-1 to 408-10. The pad 408-1 and the pad 408-2 are connected to the power supply voltage VCC by a power supply line. Electric power by this power supply voltage VCC is supplied to each circuit of the circuit unit 406 of the light-emitting chip 400. The pad 408-3 and the pad 408-4 are connected to the ground by a ground line.

[0033] Each circuit of the circuit section 406 and the upper electrode 508 are connected to the ground via the pads 408-3 and 408-4. The signal lines CLK, SYNC, and DATAn are connected to the image data holding section 1103 via the pads 408-5 to 408-7. Note that the image data holding section 1103 and the pads 408-5 to 408-7 are connected by signal lines corresponding to the signal lines CLK, SYNC, and DATAn, respectively. The signal lines EN, WRITEn, and READn are connected to the register 1102 via the pads 408-8 to 408-10. The register 1102 and the pads 408-8 to 408-10 are connected by signal lines corresponding to the signal lines EN, WRITEn, and READn, respectively. Note that the clock signal from the signal line CLK is also input to the register 1102. As described above, control data indicating control information is stored in the register 1102. Details of the control information will be described later.

[0034] When the image data holding section 1103 receives the image data corresponding to each light emitting point 602, it generates a drive signal for controlling the light emission of each light emitting point 602 based on the image data corresponding to each light emitting point 602 and outputs it to the current drive section 1104.

[0035] FIG. 12 is a diagram showing the configuration of the drive section 1104. The drive section 1104 is connected to each light emitting point on a one-to-one basis. In the present embodiment, for simplicity of explanation, one light emitting point will be described, but the same drive sections exist in the number of the light emitting points 602. That is, in the present embodiment, there are 748 × 4 columns = 2992 drive circuits for one light emitting element array chip.

[0036] The drive section 1104 is composed of a reference power supply 1200, a switch 1204, a DAC 1201, a control MOSFET 1202 for control, and a MOSFET 1203 for switching. The drive section 1104 corresponds to the drive section.

[0037] The reference power supply 1200 outputs a reference voltage and a reference current used by the drive unit 1104 from the voltage VCC supplied from the power supply. That is, the reference power supply 1200 corresponds to a voltage source. The DAC 1201 receives the control data stored in the register unit 1102 as a digital value, and generates and outputs a voltage (= analog value) corresponding to the digital value based on the reference voltage by dividing the reference voltage. That is, the control data corresponds to a digital signal.

[0038] The switch 1204 is configured to switch ON / OFF according to an instruction from the register unit 1102. When it is ON, the reference voltage output from the reference power supply 1200 is supplied to the DAC 1201. When it is OFF, the electrical connection between the reference power supply 1200 and the DAC 1201 is broken, and the reference current and the reference voltage are not supplied to the DAC 1201. That is, the state where the switch 1024 is ON corresponds to the first state, and the state where the switch 1024 is OFF corresponds to the second state. By switching the ON and OFF of the switch 1204, the connection state between the reference power supply 1200 and the switch 1204 can be switched. When the switch 1204 is OFF, no power is consumed by the DAC 1201, so the power consumption of the light-emitting chip 400 is suppressed, and the heat generation of the light-emitting chip 400 is reduced. Note that the reference power supply 1200, the DAC 1201, and the switch 1204 may each be a single common circuit for a plurality of light-emitting points.

[0039] The control MOSFET 1202 of the present embodiment is a Pch MOSFET, the source terminal is connected to the power supply voltage VCC, and the gate terminal is connected to the output of the DAC 1201. The larger the current flowing from the DAC 1201 to the gate, the larger the current flowing from the source to the drain.

[0040] In this embodiment, the switching MOSFET 1203 is also a Pch MOSFET. The source terminal is connected to the drain terminal of the control MOSFET 1202, and the drive signal output from the image data holding unit 1103 is input to the gate terminal. The drive signal is a binary signal that can be either Hi level or Low level. When the Hi level is input, the switching MOSFET 1203 turns ON, and a current controlled by the control MOSFET 1202 flows from the source to the drain. The drain terminal is connected to the light emitting layer 506 via the lower electrode 504, and when current flows, the light emitting point emits light. The light emission intensity of the light emitting point 602 changes according to the current flowing through the light emitting layer 506, and the value of the current is controlled by the analog voltage output by the DAC 1501. That is, the light emission intensity of each light emitting point 602 is controlled by the control data stored in the register 1102. Note that the control data may individually indicate digital values set for each DAC 1201 corresponding to each light emitting point 602, or may indicate one digital value set for a group of a plurality of light emitting points 602.

[0041] FIG. 13 is an example of the circuit diagram of the DAC 1201. The DAC 1201 includes a plurality of resistors 1205, voltage dividing switches 1206 having the same number as the resistors 1205, and a decoder 1207. The reference current generated by the reference power supply 1200 flows to the ground via a plurality of resistors 1205 connected in series. A voltage dividing switch 1206 is connected to each resistor 1205.

[0042] The decoder 1207 turns on an arbitrary voltage-dividing switch 1206 according to the set value received from the register unit 1102. As a result, the reference voltage is divided by the number of resistors 1205 corresponding to the position of the turned-on voltage-dividing switch 1206, and the divided voltage (analog value) is output from the DAC 1201. That is, the DAC 1201 corresponds to a D / A converter. When the reference voltage is supplied to the DAC 1201 regardless of whether the light-emitting point 602 emits light or not, Joule heat is generated from each resistor 1205 due to the voltage being supplied to each resistor 1205. In the present embodiment, since the reference voltage is not supplied to the DAC 1201 when the switch 1204 is turned off, generation of Joule heat from the resistor 1205 is suppressed. That is, generation of heat from the DAC 1201 is suppressed. Note that the DAC 1201 shown in FIG. 13 is an example of the D / A converter in the present embodiment. The D / A converter may be of a type that divides the reference voltage using switching elements without using resistors. That is, the D / A converter may be of another type that receives a digital signal and outputs an analog signal.

[0043] FIG. 14 is a timing chart of each signal in the image controller unit 700 when a print request is received from the user. In FIG. 14, for simplicity, the timing chart of each signal in the case where a single-color image is formed is shown.

[0044] When the device controller unit 708 receives a printing request from the user, it checks whether the scanner unit 100, the image forming unit 103, and the fixing unit 104 satisfy predetermined conditions for printing. The predetermined conditions include, for example, whether the temperature of the fixing unit 104 satisfies a predetermined temperature at which fixing is possible. When the device controller unit 708 confirms that the scanner unit 100, the image forming unit 103, and the fixing unit 104 satisfy the predetermined conditions for printing, it sends an itop signal to the image controller unit 700. The itop signal is a signal transmitted from the device controller unit 708 to the image controller unit 700 based on the instruction of the user who instructs the start of the image forming job for the image forming apparatus. That is, the device controller unit 708 corresponds to the transmission unit.

[0045] The image controller unit 700 that has received the itop signal from the device controller unit 708 transmits image data corresponding to each light emitting chip (400-1 to 400-20) after a predetermined time has elapsed. Each light emitting chip (400-1 to 400-20) has its lighting controlled based on the received image data, and a latent image is formed on the surface of the photosensitive drum by the light emitted from the light emitting chip 400. That is, the image controller unit 700 starts transmitting the image data to the light emitting chip 400 based on the timing when the itop signal is received. That is, the itop signal corresponds to the reference signal. Also, the image data corresponds to the image signal.

[0046] When executing an image forming job to continuously form images on a plurality of recording media, after forming a latent image corresponding to one page of image data on the surface of the photosensitive drum, the next itop signal is transmitted after a predetermined time. When the rotation speed of the photosensitive drum is constant, based on the elapse of a first time, which is a predetermined time after the image controller unit 700 receives the itop signal, the image controller unit 700 determines that the formation of the latent image corresponding to one page of image data has ended. That is, the timing when the first time has elapsed after the image controller unit 700 receives the itop signal corresponds to the first timing. The first time is defined, for example, by the image controller unit 700 emitting a predetermined number of CLK signals to the light emitting chip 400.

[0047] At the first timing, which is the timing when the formation of one page of the image is completed, the image controller unit 700 transmits register data for turning off the switch 1024 to the register unit 1102 in the light emitting chip 400. That is, the image controller unit 700 corresponds to the control unit. The switch 1024 turned off by the image controller unit 700 remains in the off state until it is turned on by the image controller unit 700. Through the above-described processing, the image controller unit 700 determines the end of the formation of one page of the image, and can cut off the voltage supplied to the DAC 1201 during a period when the light emission of the light emitting unit is unnecessary.

[0048] Note that the image controller unit 700 transmits one page of image data to the image data holding unit 1103 for each line in the sub-scanning direction. In one page, the image controller unit 700 may determine the end of the formation of the latent image corresponding to one page when the image data of the final line in the sub-scanning direction is transmitted to the image data holding unit 1103. That is, in one page, the timing when the transmission of the image data of the final line in the sub-scanning direction to the image data holding unit 1103 is completed may be set as the first timing.

[0049] In addition, in the image forming apparatus according to the present embodiment, a registration sensor 114 is installed immediately before a registration roller 110 on the conveyance path of the recording medium in the conveyance direction of the recording medium. It may be determined that the image formation for one page has been completed based on the elapse of a third time, which is a predetermined time, after the registration sensor 114 detects the leading edge of the recording medium. That is, the registration sensor 114 corresponds to the detection means, and the timing when the third time has elapsed after the registration sensor 114 detects the leading edge of the recording medium corresponds to the third timing. The third time is a time such that an image is formed on the recording medium by a latent image formed on the photosensitive drum when the third time has elapsed after the registration sensor 114 detects the leading edge of the recording medium. The third time is defined, for example, by the image controller unit 700 emitting a predetermined number of CLK signals to the light emitting chip 400.

[0050] The image controller unit 700 determines that the image formation for one page of the image data for the next page has started based on the elapse of a second time, which is a predetermined time, after receiving the itop signal. That is, the timing when the second time has elapsed after the image controller unit 700 receives the itop signal corresponds to the second timing. The second time is longer than the first time, and the second time is defined, for example, by the image controller unit 700 emitting a predetermined number of CLK signals to the light emitting chip 400.

[0051] At the second timing, which is the timing when the image controller unit 700 starts the image formation for the next page, the image controller unit 700 transmits register data for turning on the switch 1024 to the register unit 1102 in the light emitting chip 400. The switch 1024 turned on by the image controller unit 700 remains in the on state until it is turned off by the image controller unit 700. By the above-described processing, the image controller unit 700 determines the start of the image formation for the next page and can supply current to the DAC 1201 during the period when the light emitting unit needs to emit light.

[0052] Note that the image controller unit 700 transmits the image data for one page to the image data holding unit 1103 line by line in the sub-scanning direction. In the next page, the image controller unit 700 may determine the start of forming a latent image of the next page when the image data of the first line in the sub-scanning direction is transmitted to the image data holding unit 1103. That is, in the next page, the timing when the transmission of the image data of the first line in the sub-scanning direction to the image data holding unit 1103 is started may be set as the second timing.

[0053] Also, it may be determined that the image formation for one page has ended based on the elapse of a fourth time, which is a predetermined time after the registration sensor 114 detects the leading edge of the recording medium. That is, the timing when the fourth time has elapsed after the registration sensor 114 detects the leading edge of the recording medium corresponds to the fourth timing. The fourth time is defined, for example, by the image controller unit 700 emitting a predetermined number of CLK signals to the light emitting chip 400.

[0054] By the image controller unit 700 performing the above processing, the supply of the reference voltage to the DAC 1201 is cut off during the period when the light emitting chip 400 does not emit light, and the generation of Joule heat in the resistor 1205 is suppressed, so that the heat generation from the DAC 1201 can be suppressed.

[0055] Note that in this embodiment, the timing for transmitting the register data for turning off the switch 1024 to the register unit 1102 in the light emitting chip 400 is set as the first timing, but it is not limited to this and other timings may be used. The timing for turning off the switch 1024 may be any timing as long as it is, for example, within the period between the first timing and the second timing.

[0056] In addition, in this embodiment, the timing for transmitting register data for turning on the switch 1024 to the register unit 1102 in the light-emitting chip 400 is set as the second timing, but it is not limited to this, and other timings may be used. The timing for turning on the switch 1024 may be any timing as long as it is within the period between the timing when the switch 1024 is turned off and the second timing.

[0057] That is, during the period between the first period and the second period, the period when the switch 1024 is in the OFF state corresponds to the first period. Also, the start point of the first period may be the timing when the third time has elapsed since the resist sensor 114 detected the leading edge of the recording medium. Further, the end point of the first period may be the timing when the fourth time has elapsed since the resist sensor 114 detected the leading edge of the recording medium.

[0058] FIG. 15 is a timing chart of each signal when forming an image in four colors of yellow (Y), magenta (M), cyan (C), and black (K). When forming an image in color, the image forming units 103 of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in the direction in which the recording medium is conveyed. After a predetermined time has elapsed since the formation of the yellow toner image was started, the magenta, cyan, and black toner images are sequentially formed by the four image forming units. T1, T2, and T3 in FIG. 15 correspond to the predetermined times for magenta, cyan, and black, respectively. By forming a toner image after T1, T2, and T3 have elapsed from yellow, a color image without color misregistration can be formed on the recording medium. Even when forming a color image, heat generation from the drive unit can be suppressed by performing the same processing as in FIG. 15 for each color after T1, T2, and T3 have elapsed since the yellow image formation was performed.

[0059] FIG. 16 is a flowchart of the control by the image controller unit 700 for the register 1002 included in the light-emitting chip 400 when a print request is received from the user.

[0060] When there is a printing request from the user, in S1301, the image controller unit 700 writes register data including the setting value of the DAC1201 to the register unit 1002 in the light-emitting chip 400.

[0061] In S1302, after the image controller unit 700 receives the itop signal, when it has sent the CLK signal to the light-emitting chip 400 a predetermined number of times, it determines that this is the printing start timing and proceeds with the process to S1303.

[0062] In S1303, the image controller unit 700 makes a setting to turn on the switch 1204 for the register unit 1002 in the light-emitting chip 400 before starting printing.

[0063] In S1304, the image controller unit 700 transmits image data based on the image file instructed by the user to the 20 light-emitting chips 400. The image data continues to be transmitted until printing of one page is completed.

[0064] In S1305, when the image controller unit 700 determines that printing of one page is completed when it has sent the CLK signal for a predetermined period after receiving the itop signal, it proceeds with the process to S1306.

[0065] In S1306, the image controller unit 700 makes a setting to turn off the switch 1204 for the register unit 1002 in the light-emitting chip 400.

[0066] In S1307, when the registration sensor 114 installed immediately before the registration roller 110 detects the leading edge of the recording medium, it transmits the detection of the leading edge of the recording medium to the image controller unit 700. The image controller unit 700 determines that there is a next page when the leading edge of the recording medium is detected. If it is determined that there is a next page, the process returns to S1302, and the image controller unit 700 executes S1302 to S1307.

[0067] If a resist sensor 114 (not shown) installed immediately before the registration roller 110 at S1307 fails to detect the leading and trailing edges of the recording medium even after a predetermined time has elapsed, it transmits to the image controller unit 700 the fact that it has not detected the leading and trailing edges of the recording medium. The image controller unit 700 determines that there is no next page when the leading and trailing edges of the recording medium have not been detected within a predetermined time, and ends the printing operation.

[0068] In this embodiment, in a configuration where the light emitting part and the drive circuit are formed on the same chip, at timings when printing is not performed, such as between pages, the supply of current to the DAC 1201 included in the drive circuit of the light emitting chip 400 is cut off, and the generation of heat of the DAC 1201 included in the drive circuit of the exposure head can be suppressed. That is, the generation of heat from the D / A converter that converts the digital signal into a voltage can be suppressed.

[0069] FIG. 17 is a flowchart of processing related to writing and reading of control data executed by the image controller 700 when a print request is received from the user. At S10, the image controller 700 writes control data in parallel to the register 1102 of each light emitting chip 400 using the signal lines WRITE1 to WRITE20. The control data includes data for controlling the emission intensity of each light emitting point 602. At S11, the image controller 700 checks whether the control data has been correctly written to the register 1102. Specifically, at S11, the image controller 700 reads out in parallel the control data stored in the register 1102 of each light emitting chip 400 using the signal lines WRITE1 to WRITE20 and the signal lines READ1 to READ20. If the control data written at S10 does not match the control data read from the register 1102 at S11, the image controller 700 repeats the process from S10 (S12). Note that it is also possible to set an upper limit on the number of repetitions of S10 and S11, and when the number of repetitions reaches the upper limit, abort the process of FIG. 17 and notify the user of an error.

[0070] When the control data written in S10 matches the control data read from register 1102 in S11, when the timing to start image formation arrives, the image controller 700 proceeds to S13. In S13, the image controller 700 transmits the image data to each light-emitting chip 400 in parallel using signal lines WRITE1 to WRITE20. In S14, the image controller 700 determines whether image formation has been completed. If image formation has not been completed, the process is repeated from S13. On the other hand, if image formation has been completed, the image controller 700 ends the process of FIG. 17.

[0071] Also, the image forming apparatus performs gradation correction control. For example, the image forming apparatus forms a test pattern for gradation correction control on a sheet. FIG. 8 shows an example of the test pattern used in the description of the present embodiment. As shown in FIG. 18, the test pattern includes five test images PT1 to PT5 with different densities. In the sheet conveyance direction, an interval (pattern interval) is provided between each test image. The user operates the image forming apparatus to cause the reading unit 100 to read the sheet on which the test pattern is formed. Thereby, the image forming apparatus detects the density of each of the test images PT1 to PT5 included in the test pattern, and corrects the image formation conditions regarding density so that the density of each of the test images PT1 to PT5 approaches the target density. Specifically, for example, the control data is rewritten by the image controller 700 so that the density of each of the test images PT1 to PT5 approaches the target density.

[0072] FIG. 19 is a flowchart of the processing executed by the image controller 700 when forming a test pattern. In S20, the image controller 700 initializes the index q of the test image to 1. In S21, the image controller 700 uses signal lines WRITE1 to WRITE20 to write the control data for forming the test image PTq into the register 1102 of each light-emitting chip 400 in parallel. The control data includes data for controlling the light-emitting intensity of each light-emitting point 602. The data for controlling the light-emitting intensity of each light-emitting point 602 may be referred to as data regarding the magnitude of the voltage to be applied to the electrode or data regarding the magnitude of the current to be supplied to the organic EL film. In S22, the image controller 700 inspects whether the control data is correctly written into the register 1102. Specifically, in S22, the image controller 700 uses signal lines WRITE1 to WRITE20 and signal lines READ1 to READ20 to read out the control data stored in the register 1102 of each light-emitting chip 400 in parallel. If the control data written in S21 does not match the control data read from the register 1102 in S22, the image controller 700 repeats the processing from S21 (S23). Note that it is also possible to set an upper limit on the number of repetitions of S21 and S22, and when the number of repetitions reaches the upper limit, the processing of FIG. 19 is aborted and an error is notified to the user.

[0073] When the control data written in S21 matches the control data read from register 1102 in S22, when the timing for starting image formation arrives, the image controller 700 proceeds to S24. In S24, the image controller 700 transmits test pattern image data in parallel to signal lines DATA1 to DATA20 and starts exposing the photoreceptor 102. In S25, the image controller 700 determines whether the formation of the test image PTq is completed. If not completed, the process is repeated from S24. On the other hand, when the formation of the test image PTq is completed, the image controller 700 determines in S26 whether q = 5. If q is not equal to 5, since the formation of all the test images PT1 to PT5 of the test pattern is not completed, the image controller 700 increments q by 1 in S27 and repeats the process from S21. On the other hand, when q = 5, the image controller 700 ends the process of FIG. 19.

[0074] In this embodiment, the emission intensity of the light emitting point 602 is made different according to the density of the test images PT1 to PT5 to be formed by the control data set in the register 1102 in S21. Therefore, the image data of the test pattern transmitted in S24 can be the same regardless of the test images PT1 to PT5 to be formed.

[0075] As described above, the image controller 700 and each of the plurality of light-emitting chips 400 are individually connected via dedicated signal lines WRITEn and READn so that the image controller 700 can access the registers 1102 of each of the plurality of light-emitting chips 400 in parallel. With this configuration, compared to accessing each light-emitting chip 400 sequentially via one signal line WRITE and one signal line READ, the transmission time of control data to each light-emitting chip 400 can be shortened. Also, by rewriting the control data of the register 1102, the exposure intensity can be changed in a short time. Therefore, when forming a plurality of test images with different densities, the interval between the test images in the sheet conveyance direction can be reduced. Accordingly, the number of test images that can be formed on the sheet can be increased, and the number of sheets (or pages) of the sheet required to form the test pattern can be reduced.

[0076] In this embodiment, the image controller 700 and each of the plurality of light-emitting chips 400 are individually connected via dedicated signal lines WRITEn and READn, but the connection method is not limited. For example, there may be a plurality of groups of light-emitting chips included in the plurality of light-emitting chips 400, and these plurality of groups of light-emitting chips and the image controller may be connected via dedicated signal lines WRITEn and READn, respectively. At this time, the number of groups of light-emitting chips is not limited to two, and may be three or more. Further, the number of light-emitting chips 400 included in the group of light-emitting chips may vary depending on the group of light-emitting chips, and may include the case where the number of light-emitting chips included in the group of light-emitting chips is one. By sharing the dedicated signal lines WRITEn and READn within the group of light-emitting chips, the number of signal lines can be reduced compared to the case where the image controller 700 and each of the plurality of light-emitting chips 400 are individually connected via dedicated signal lines WRITEn and READn, and the manufacturing cost of the exposure head 106 can be reduced.

[0077] [Embodiment 2] Next, the differences between the first embodiment and the second embodiment will be mainly described. FIG. 20 shows the control configuration of the light-emitting chip 400 according to this embodiment. In the first embodiment, signal lines READ1 to READ20 were provided in a one-to-one correspondence with each of the light-emitting chips 400-1 to 400-20. In this embodiment, a common signal line READ is used for all the light-emitting chips 400-1 to 400-20. More specifically, one (common) signal line READ is connected to the data switching unit 705 of the image controller 700. In the printed circuit board 202, a total of 20 signal lines (hereinafter, the in-board signal line READ) from each of the light-emitting chips 400-1 to 400-20 are connected to this one signal line READ. Note that one signal line READ is pulled up to a predetermined first potential via a pull-up resistor 1506 in the printed circuit board 202.

[0078] FIG. 21 shows a timing chart when control data is read from the registers 1102 of the light-emitting chips 400-1 to 400-20 respectively. The image controller 700 transmits command data to the signal line WRITE1 in synchronization with the rising edge of the enable signal from the signal line EN in order to read the control data from the register 1102 of the light-emitting chip 400-1. When transmitting the start bit (high level) of the command data to the signal line WRITE1, the signal lines WRITE2 to 20 are fixed at the low level. That is, the start bit is transmitted only to the signal line WRITE1 and not to the signal lines WRITE2 to 20. In response to the command data from the image controller 700, the register 1102 of the light-emitting chip 400-1 reads the control data stored at the address specified by the command data and outputs it to the signal line READ. Subsequently, the image controller 700 transmits command data to the signal line WRITE2 in synchronization with the rising edge of the enable signal from the signal line EN in order to read the control data from the register 1102 of the light-emitting chip 400-2. In response to the command data from the image controller 700, the register 1102 of the light-emitting chip 400-2 reads the control data stored at the address specified by the command data and outputs it to the signal line READ. The image controller 700 repeats the same process for the light-emitting chips 400-3 to 400-20 in order. Note that the transmission of image data and the writing of control data are the same as in the first embodiment.

[0079] FIG. 22 is a functional block diagram of the light-emitting chip 400-n according to the present embodiment. Compared with the light-emitting chip 400-n of the first embodiment, the light-emitting chip 400-n of the present embodiment has an FET 1701. Also, the pad 408-10 is connected to the in-substrate signal line READ described above and is also connected to the drain terminal of the FET 1701. Further, the source terminal of the FET 1701 is connected to a second potential smaller than the first potential to which the pull-up resistor 1506 is connected, in this example, to ground. And the gate terminal of the FET 1701 is connected to the terminal of the register 1102 that transmits control data. The FET 1701 constitutes a switching unit that can be switched between an on state and an off state based on the level of the signal from the register 1102. In the on state, the in-substrate signal line READ is connected to the second potential, and in the off state, the connection of the in-substrate signal line READ to the second potential is disconnected, and the in-substrate signal line READ becomes a high-impedance state. The register 1102 turns off the FET 1701 while not transmitting control data to the image controller 700. In this way, by the FET 1701 and the pull-up resistor 1506, the in-substrate signal line READ is configured as an open-drain output. On the other hand, while the register 1102 is transmitting control data to the image controller 700, it turns the FET 1701 on or off according to the data value. In the on state, a low-level signal based on the second potential is output to the signal line READ. On the other hand, in the off state, a high-level signal based on the first potential is output to the signal line READ by the pull-up resistor 1506 of the printed circuit board 202.

[0080] In this way, by configuring the in-substrate signal line READ as an open-drain output, while reading control data from the register 1102 of a certain light-emitting chip 400, the pads 408-10 of other light-emitting chips 400 are in a high-impedance state. Therefore, the potential of the in-substrate signal line READ from other light-emitting chips 400 does not affect the signal line READ, and one signal line READ can be shared.

[0081] In this embodiment, the processing when a print request is received from the user is the same as that in the first embodiment shown in FIG. 17. However, the reading of the control data in S11 cannot be performed in parallel for the light-emitting chips 400-1 to 400-20, and must be performed sequentially. The same applies to the processing in FIG. 19 for forming the test pattern.

[0082] As described above, in this embodiment, compared with the first embodiment, it takes time to read the control data from the light-emitting chip 400. However, the transmission time of the control data to each light-emitting chip 400 can be shortened. Also, in this embodiment, compared with the first embodiment, the number of signal lines READ can be reduced, and the cost can be suppressed.

[0083] [Embodiment 3] Subsequently, the differences between the third embodiment and the first and second embodiments will be mainly described. In the first and second embodiments, the image controller 700 transmitted the image data to the light-emitting chip 400-n via the signal line DATAn and the control data via the signal line WRITEn. Also, when transmitting the image data to the light-emitting chip 400-n, the image controller 700 transmitted the line synchronization signal via the signal line SYNC, and when accessing the register 1102 of the light-emitting chip 400-n, the image controller 700 transmitted the enable signal via the signal line EN. In this embodiment, the image controller 700 transmits the image data and the control data to the light-emitting chip 400-n via the signal line DATAn, and transmits the line synchronization signal and the enable signal via the signal line SYNC. That is, in this embodiment, the signal lines WRITEn and EN are not used. Therefore, in the first and second embodiments, as shown in FIG. 5, a total of 10 pads, pads 408-1 to 408-10, were provided on the light-emitting chip 400. However, in this embodiment, only 8 pads, pads 408-1 to 408-8, are provided on the light-emitting chip 400.

[0084] Figs. 23 to 25 show the signals of each signal line when the data switching unit 705 outputs various types of data to each light-emitting chip 400. In Figs. 23 to 25, it is assumed that the bit value is "1" when the signal level is Hi (high), and the bit value is "0" when the signal level is Lo (low).

[0085] Fig. 23 shows the case where the data type is "image". When the data type is "image", a line synchronization signal indicating the exposure timing of one line in the photoreceptor 102 is output to the signal line SYNC. In this example, the peripheral speed of the photoreceptor 102 is 200 mm / s, and the resolution in the sub-scanning direction is 1200 dpi (about 21.16 μm). Therefore, the line synchronization signal is output every about 105.8 μs, which is the period during which the surface of the photoreceptor 102 moves by about 21.16 μm. The data switching unit 705 transmits an identification bit of value "11" indicating that the data type is "image" to the signal line DATAn in synchronization with the rising edge of the line synchronization signal, and then transmits the image data. In the present embodiment, since each light-emitting chip 400 has 2992 light-emitting points 602, it is necessary to transmit image data indicating the light emission / non-light emission of each of the 2992 light-emitting points 602 within a period of about 105.8 μs. In order to transmit the image data for a total of 2992 light-emitting points 602 within a period of about 105.8 μs, in this example, as shown in Fig. 23, when transmitting the image data, the data switching unit 705 sets the frequency of the clock signal transmitted to the signal line CLK to 30 MHz.

[0086] Figures 24(A) and 24(B) show the case where the data type is "control". Note that Figure 24(A) shows the case of writing control data to the register of the light-emitting chip 400, and Figure 24(B) shows the case of reading the control data stored in the register of the light-emitting chip 400. When the data type is "control", an enable signal indicating that it is at a high level and in communication is output to the signal line SYNC during communication. The data switching unit 705 transmits an identification bit with a value of "10" indicating that the data type is "control" to the signal line DATAn in synchronization with the rising edge of the enable signal. When writing control data, the data switching unit 705 transmits a write identification bit indicating a write operation following the identification bit, and then transmits the address (4 bits in this example) of the register to which the control data is to be written and the control data (8 bits in this example). Note that the transmission order of the address and the control data may be reversed. When reading control data, the data switching unit 705 transmits a read identification bit indicating a read operation following the identification bit, and then transmits the address of the register from which the control data is to be read. In this case, the light-emitting chip 400-n reads the control data stored at the specified address from the register and outputs it to the signal line READn. Since the data amount of the control data is less than that of the image data, the frequency of the clock signal output to the signal line CLK can be made lower than when transmitting the image data. As an example, the frequency of the clock signal during reading and writing of the control data can be set to 3 MHz. However, the configuration may be such that the frequency of the clock signal during reading and writing of the control data is the same as when transmitting the image data.

[0087] Figure 25 shows the case where the data type is "invalid". When the data type is "invalid", a trigger signal indicating the transmission of identification bits is output to the signal line SYNC. The data switching unit 705 transmits identification bits with a value of "0x" indicating that the data type is "invalid" to the signal line DATAn in synchronization with the rising edge of the trigger signal. When transmitting the data type "invalid", the data switching unit 705 can make the frequency of the clock signal output to the signal line CLK the same as that during the transmission of image data. Alternatively, when transmitting the data type "invalid", the data switching unit 705 can make the frequency of the clock signal output to the signal line CLK the same as that during the access to the register. Further, when transmitting the data type "invalid", the data switching unit 705 can make the frequency of the clock signal output to the signal line CLK the same as the frequency before transmitting the data type "invalid". Further, when transmitting the data type "invalid", the data switching unit 705 can make the frequency of the clock signal output to the signal line CLK a predetermined value different from that during the transmission of image data and during the access to the register.

[0088] Figure 26 is a functional block diagram of the light-emitting chip 400-n according to the present embodiment. In the present embodiment, an interface circuit 1101 is provided in the circuit unit 406, and the interface circuit 1101 is connected to the signal lines CLK, SYNC, DATAn, and READn via the pads 408-5 to 408-8.

[0089] The interface circuit 1101 manages its state based on the identification bits received on the signal line DATAn in synchronization with the rising edge of the signal received on the signal line SYNC. Figure 27 is a state transition diagram of the interface circuit 1101. The initial state when power is supplied by the power supply voltage VCC is the invalid state. In the invalid state, when receiving an identification bit indicating the type "invalid", the interface circuit 1101 remains in the invalid state. Note that in the invalid state, the interface circuit 1101 only receives the identification bits and does not perform data transmission to other circuits or the like.

[0090] When the interface circuit 1101 receives an identification bit indicating the type "image" in the invalid state, it transitions to the image reception state. In this case, the interface circuit 1101 transmits the image data received on the signal line DATAn following the identification bit to the image data holding unit 1103. At this time, the interface circuit 1101 also transmits the clock signal received on the signal line CLK and the line synchronization signal received on the signal line SYNC to the image data holding unit 1103. When the interface circuit 1101 receives an identification bit indicating the type "image" in the image reception state, its state does not transition, and the interface circuit 1101 transmits the image data received on the signal line DATAn following the identification bit to the image data holding unit 1103. On the other hand, when the interface circuit 1101 receives an identification bit indicating the type "invalid" in the image reception state, it transitions to the invalid state.

[0091] When the interface circuit 1101 receives an identification bit indicating the type "control" in the invalid state, it transitions to the control state. In this case, the interface circuit 1101 writes control data to the register 1102 and reads the control data stored in the register 1102 based on the data received on the signal line DATAn following the identification bit. At this time, the interface circuit 1101 also transmits the clock signal received on the signal line CLK and the enable signal received on the signal line SYNC to the register 1102. When the interface circuit 1101 receives an identification bit indicating the type "control" in the control state, its state does not transition, and it writes and reads control data to / from the register 1102 based on the data received on the signal line DATAn following the identification bit. On the other hand, when the interface circuit 1101 receives an identification bit indicating the type "invalid" in the control state, it transitions to the invalid state.

[0092] On the one hand, when the interface circuit 1101 receives an identification bit indicating the type "control" in the image reception state, it remains in the image reception state and does not transition to other states. In this case, for the data received on the signal line DATAn until the next identification bit is received, the interface circuit 1101 determines that it is neither image data nor control data, discards the data, and does not perform output to other circuits. Similarly, in the control state, when the interface circuit 1101 receives an identification bit indicating the type "image", it remains in the control state and does not transition to other states. In this case, for the data received on the signal line DATAn until the next identification bit is received, the interface circuit 1101 determines that it is neither image data nor control data, discards the data, and does not perform output to other circuits.

[0093] In this way, in the present embodiment, direct transition from the image reception state to the control state and direct transition from the control state to the image reception state are prohibited. This is to prevent the interface circuit 1101 from malfunctioning due to errors in the identification bits received by the interface circuit 1101 caused by external noise, static electricity, etc. That is, in the present embodiment, the transition between the "image reception state" and the "control state" is made through the "invalid state", and the data type "invalid" is provided to transition the interface circuit 1101 to the "invalid state".

[0094] When the image data holding unit 1103 receives image data for one line based on the line synchronization signal, it generates a drive signal for controlling the emission of each light emitting point 602 based on this image data and outputs it to the current drive unit 1104.

[0095] As described above, also in this embodiment, control data is transmitted in parallel to each of the light-emitting chips 400-1 to 400-20 through dedicated signal lines DATA1 to DATA20. Therefore, the transmission time of the control data to each light-emitting chip 400 can be shortened. Further, in this embodiment, since the signal lines DATA1 to DATA20 are shared for the transmission of image data and control data, the number of signal lines can be reduced as compared with the first embodiment, and thus the cost can be suppressed.

[0096] Note that, in order to notify the light-emitting chip 400 whether the data transmitted to the shared signal line, that is, the signal line DATA, is control data or image data, identification information indicating the data type is transmitted through the signal line DATA prior to the data transmission. As a result, the interface circuit 1101 can determine whether the data transmitted from the image controller 700 is control data or image data. That is, while reducing the number of signal lines connecting the image controller 700 and the printed circuit board 202, it is possible to control the lighting and extinguishing of each light-emitting point 602 and adjust the amount of current (voltage to be applied to the electrode) supplied to each light-emitting point 602. That is, it is possible to control the light emission of each light-emitting point 602 while suppressing an increase in the cost of the image forming apparatus.

[0097] Also, in this embodiment, when the image controller 700 switches between the data types "control" and "image", first, the data type "invalid" is transmitted and then the switch is made to another data type. With this configuration, it is possible to reduce the malfunction of the image forming apparatus due to misdetection of the data type caused by disturbances such as noise and static electricity.

[0098] In the above embodiment, the "image reception state" and the "control state" in the interface circuit 1101 are transitioned through the "invalid state". Therefore, the data switching unit 705 transmits an identification bit indicating the type "invalid" after transmitting the image data or after the access to the register 1102 is completed. However, a configuration that enables direct transition between the "image reception state" and the "control state" without providing the "invalid state" may be adopted. In this case, the data switching unit 705 only needs to transmit an identification bit indicating the type "image" before transmitting the image data and transmit an identification bit indicating the type "control" before accessing the register 1102. Even in such a configuration, the number of signal lines for connecting the image controller 700 and the printed circuit board 202 can be reduced.

[0099] In FIG. 26, dedicated signal lines READ1 to READ20 are provided for each of the light-emitting chips 400-1 to 400-20 as in the first embodiment. However, similar to the second embodiment, a configuration in which one common signal line READ is provided for each light-emitting chip 400 can also be adopted.

[0100] In the above embodiment, specific numerical values are used for the purpose of explanation. However, these specific numerical values are merely examples, and the present invention is not limited to the specific numerical values used in the embodiment. Specifically, the number of light-emitting chips 400 provided on one printed circuit board 202 is not limited to 20, and can be any number of one or more. Also, the number of light-emitting points 602 included in each light-emitting chip 400 is not limited to 2992, and other numbers may be used. Further, in the present embodiment, one light-emitting chip 400 has four sets of 748 light-emitting points arranged along the main scanning direction, but the number of sets can be any number of one or more. Also, the light-emitting points 602 are arranged at a pitch of approximately 21.16 μm corresponding to a resolution of 1200 dpi in the main scanning direction, but the arrangement interval of the light-emitting points 602 may also be other values.

[0101] In the above-described embodiment, the image forming apparatus transfers the toner images formed on each photoreceptor 102 to the sheet conveyed by the transfer belt 111. However, the image forming apparatus may transfer the toner images of each photoreceptor 102 to the sheet via an intermediate transfer member. Further, the image forming apparatus may be a color image forming apparatus that forms an image using a plurality of colors of toner, or a monochrome image forming apparatus that forms an image using one color of toner.

[0102] [Embodiment 4] Subsequently, the fourth embodiment will be described focusing on the differences from the first to third embodiments. When performing gradation correction control, the image forming apparatuses in the first to third embodiments form a test pattern for gradation correction control on the sheet. Then, the sheet on which the test pattern is formed is read by the reading unit 100. The image forming apparatus detects the density of each of the test images PT1 to PT5 included in the test pattern, and corrects the image forming conditions regarding density so that the density of each of the test images PT1 to PT5 approaches the target density. Specifically, for example, the control data was rewritten by the image controller 700 so that the density of each of the test images PT1 to PT5 approaches the target density.

[0103] FIG. 28 is a diagram for explaining the image forming apparatus 120 in the present embodiment. Note that the image forming apparatus 120 of the present embodiment may be applied to each of the first to third embodiments.

[0104] The image forming units 20a, 20b, 20c, and 20d form toner images of yellow "Y", magenta "M", cyan "C", and black "K", respectively. In the following, the same reference numerals are assigned to a plurality of identical or similar components. When distinguishing a plurality of components, an alphabet is added to the end of the reference numeral. When common matters are described for a plurality of components, the alphabet at the end of the reference numeral is omitted. Note that the exposure head 23 in the following description has the same configuration as the exposure head 106 described in each of the first to third embodiments.

[0105] The photoreceptor 21 is an image carrier that bears an electrostatic latent image and a toner image. The charger 22 charges the surface of the photoreceptor 21. The exposure head 23 exposes the photoreceptor 21 to form an electrostatic latent image. The developing device 24 develops the electrostatic latent image using toner to form a toner image. The primary transfer roller 25 transfers the toner image from the photoreceptor 21 to the intermediate transfer belt 27. The intermediate transfer belt 27 conveys the toner image to the secondary transfer device 28.

[0106] The feeding device 1 feeds the sheet P held in the sheet storage to the conveyance path. The conveyance device 2 conveys the sheet P to the registration device 3. The registration device 3 corrects the skew of the sheet P and conveys the sheet P to the secondary transfer device 28.

[0107] The secondary transfer device 28 transfers the toner image from the intermediate transfer belt 27 to the sheet P. The fixing device 29 applies heat and pressure to the sheet P to fix the toner image on the sheet P. The discharge conveyance device 4 conveys and discharges the sheet P with the toner image fixed thereon to the outside of the image forming apparatus 120.

[0108] In this embodiment, a current based on the value of control data set based on a test pattern is supplied to each light emitting unit, and as a result, the photoreceptor 21 is exposed. During an image forming job in which the image forming apparatus 120 forms images on a plurality of sheets, when the number of sheets on which images are formed reaches a predetermined number, a plurality of patch images for gradation correction control are formed on the intermediate transfer belt 27. Note that the density of each of the plurality of patch images corresponds to the density of each of the test images PT1 to PT5 in the first embodiment, for example.

[0109] The image controller 700 causes a sensor 30 provided adjacent to the intermediate transfer belt 27 to read a patch image formed on the intermediate transfer belt 27, and detects the density of each patch image. The image controller 700 rewrites control data, for example, so that the density of each patch image approaches the target density. Note that the target density corresponds to the target density when control data is set based on a test pattern (FIG. 18). Any of the configurations of the first to third embodiments is applied to the writing of the control data.

[0110] Note that when the number of sheets on which an image is formed reaches a predetermined number, the image forming apparatus 120 may temporarily stop the conveyance of the sheets (image forming job) and form a plurality of patch images having densities corresponding to each of the test images PT1 to PT5 on the intermediate transfer belt 27. The image controller 700 may cause the sensor 30 to read the plurality of patch images and rewrite the control data based on the reading result. The image forming apparatus 120 may resume the image forming job when the rewriting of the control data is completed.

[0111] Also, during an image formation job, the image forming apparatus 120 may form an electrostatic latent image corresponding to a patch image having a density corresponding to the test image PT1 on the photoreceptor 21 (i.e., form the patch image on the intermediate transfer belt 27) during the period from when the electrostatic latent image of the first page is formed on the photoreceptor 21 until the electrostatic latent image of the second page, which is the next page after the first page, is formed on the photoreceptor 21. Thereafter, the image forming apparatus 120 may form an electrostatic latent image corresponding to a patch image having a density corresponding to the test image PT2 on the photoreceptor 21 (i.e., form the patch image on the intermediate transfer belt 27) during the period from when the electrostatic latent image of the second page is formed on the photoreceptor 21 until the electrostatic latent image of the third page, which is the next page after the second page, is formed on the photoreceptor 21. In this way, the image forming apparatus 120 may form an electrostatic latent image corresponding to a patch image on the photoreceptor 21 (i.e., form the patch image on the intermediate transfer belt 27) during the period from when the electrostatic latent image for one page is formed on the photoreceptor 21 until the latent image of the next page after that one page is formed on the photoreceptor 21. The image controller 700 may cause the sensor 30 to read the patch image each time the patch image is formed, and when the reading results from the test images PT1 to PT5 are obtained, the image controller 700 may rewrite the control data based on the reading results.

[0112] As described above, the image controller 700 and each of the plurality of light-emitting chips 400 are individually connected via dedicated signal lines WRITEn and READn so that the image controller 700 can access the registers 1102 of each of the plurality of light-emitting chips 400 in parallel. With this configuration, compared to accessing each light-emitting chip 400 in order via one signal line WRITE and one signal line READ, the transmission time of control data to each light-emitting chip 400 can be shortened. Such a configuration is particularly effective when it is necessary to form an electrostatic latent image corresponding to a patch image on the photoreceptor 21 (i.e., form the patch image on the intermediate transfer belt 27) in a relatively short period, such as from when an electrostatic latent image for one page is formed on the photoreceptor 21 until an electrostatic latent image for the next page of that one page is formed on the photoreceptor 21. Note that the gradation correction control described in this embodiment detects the densities of a plurality of patch images on the intermediate transfer belt 27 instead of detecting the densities of the plurality of test images PT1 to PT5 of the sheet P described in the first embodiment. Therefore, the plurality of patch images in this embodiment can be regarded as the plurality of test images in the first embodiment.

[0113] [Embodiment 5] Subsequently, the differences between the fifth embodiment and the first to fourth embodiments will be mainly described. In this embodiment, as shown in FIG. 29, a temperature sensor 31 for detecting the temperature on the surface of the printed circuit board 202 where the light-emitting point group 201 of the printed circuit board 202 is mounted (the temperature of the light-emitting chip 400, the temperature of the light-emitting point or the light-emitting portion 602) is provided. Note that the temperature sensor 31 may be provided on the surface of the printed circuit board 202 opposite to the surface where the light-emitting point group 201 is mounted (FIG. 3(A)).

[0114] FIG. 30 is a diagram showing the relationship between the temperature of the light-emitting portion and the amount of light when a predetermined current is supplied to the light-emitting portion. Note that the relationship shown in FIG. 30 is an example, and the relationship between temperature and light amount is not necessarily linearly represented.

[0115] As shown in FIG. 29, the amount of light emitted from the light-emitting unit supplied with a predetermined current increases as the temperature increases. In the present embodiment, the relationship between the temperature and the amount of light for each chip shown in FIG. 30 is stored, for example, in a memory provided in the image controller 700. Based on the detection result of the temperature sensor 31 and the relationship between the temperature and the amount of light stored in the memory, the image controller 700 rewrites the control data stored in the register 1102 so that, for example, the current supplied to the light-emitting unit decreases when the temperature rises.

[0116] The rewriting of the control data is performed, for example, in an image forming job in which images are formed on a plurality of sheets, during the period from when an image for one page is formed on the intermediate transfer belt 27 until an image for the next page of the one page is formed on the intermediate transfer belt 27.

[0117] As described above, the image controller 700 and each of the plurality of light-emitting chips 400 are individually connected via dedicated signal lines WRITEn and signal lines READn so that the image controller 700 can access the registers 1102 of each of the plurality of light-emitting chips 400 in parallel. With this configuration, the transmission time of the control data to each light-emitting chip 400 can be shortened as compared with accessing each light-emitting chip 400 in order via one signal line WRITE and one signal line READ. Such a configuration is particularly effective when it is necessary to rewrite the control data during the period from when an electrostatic latent image for one page is formed on the photoreceptor 21 until an electrostatic latent image for the next page of the one page is formed on the photoreceptor 21.

[0118] In each of the above embodiments, specific numerical values were used for the purpose of explanation. However, these specific numerical values are merely illustrative, and the present invention is not limited to the specific numerical values used in the embodiments. Specifically, the number of light-emitting chips 400 provided on one printed circuit board 202 is not limited to 20, and can be any number of one or more. Also, the number of light-emitting points 602 included in each light-emitting chip 400 is not limited to 2992, and other numbers may be used. Further, in the present embodiment, one light-emitting chip 400 had four sets of 748 light-emitting points arranged along the main scanning direction, but the number of sets can be any number of one or more. Also, although the light-emitting points 602 were arranged at a pitch of approximately 21.16 μm corresponding to a resolution of 1200 dpi in the main scanning direction, the arrangement interval of the light-emitting points 602 may be other values.

[0119] Also, in each of the above embodiments, the image forming apparatus transferred the toner image formed on each photoreceptor 102 to the sheet conveyed by the transfer belt 111. However, the image forming apparatus may transfer the toner image of each photoreceptor 102 to the sheet via an intermediate transfer member. Also, the image forming apparatus may be a color image forming apparatus that forms an image using a plurality of colors of toner, or a monochrome image forming apparatus that forms an image using one color of toner.

Explanation of Reference Numerals

[0120] 101 Image forming unit 102 Photoreceptor 400 Light-emitting chip 602 Light-emitting point 700 Image controller unit 705 Data switching unit 1102 Register unit 1104 Driving unit 1200 Reference power supply 1201 DAC 1204 Switch 1205 Resistor 1206 Voltage dividing switch

Claims

1. A rotating photoreceptor, a silicon substrate, a plurality of light-emitting portions provided on the silicon substrate and emitting light for exposing the photoreceptor, a circuit portion provided on the silicon substrate and performing lighting and extinguishing of the plurality of light-emitting portions based on image data for controlling lighting and extinguishing of the plurality of light-emitting portions, and a storage portion provided on the silicon substrate and storing control data indicating a target light amount of the plurality of light-emitting portions, and a plurality of light-emitting chips arranged along the rotation axis direction of the photoreceptor, a controller that outputs the control data, comprising: each of the plurality of light-emitting chips is connected to the controller via a different one of a plurality of signal lines, the control data transmitted via a different one of the plurality of signal lines is stored in the storage portion, the controller reads out the control data from each of the storage portions provided in the plurality of light-emitting chips via a different one of the plurality of signal lines, and based on the fact that the read control data and the control data transmitted from the controller to each of the plurality of light-emitting chips via a different one of the plurality of signal lines match, transmits the image data to each of the light-emitting chips via a different one of the plurality of signal lines, An image forming apparatus characterized by the above.

2. Each of the plurality of light-emitting chips includes a D / A converter that converts the control data into an analog signal, the plurality of light-emitting portions emit light with a light amount based on the analog signal, The image forming apparatus according to claim 1, characterized by the above.

3. The image forming apparatus includes a first substrate provided with the plurality of light-emitting chips, a second substrate provided with the controller, comprising: the plurality of signal lines connect the first substrate and the second substrate, The image forming apparatus according to claim 1, characterized by the above.

4. the plurality of signal lines are a plurality of first signal lines, each of the plurality of light-emitting chips is connected to the controller via a different one of a plurality of second signal lines, The controller reads out the control data from each of the storage units provided in the plurality of light-emitting chips via a different one of the plurality of second signal lines, and based on the fact that the read control data matches the control data transmitted from the controller to each of the plurality of light-emitting chips via a different one of the plurality of first signal lines, transmits the image data to each of the light-emitting chips via a different one of the plurality of second signal lines. The image forming apparatus according to claim 1, characterized in that.

5. Each of the plurality of light-emitting chips exposes a latent image indicating a plurality of test images with different densities on the surface of the photoreceptor. The controller transmits the control data corresponding to the plurality of test images to each of the storage units of the plurality of light-emitting chips via the plurality of signal lines. The image forming apparatus according to claim 1, characterized in that.

6. The image forming apparatus includes detection means for detecting the temperature of the light-emitting unit. When the detection means detects an increase in the temperature of the light-emitting unit, the controller outputs the control data indicating a current value for reducing the light amount of the light-emitting unit, and when the detection means detects a decrease in the temperature of the light-emitting unit, the controller outputs the control data indicating a current value for increasing the light amount of the light-emitting unit. The image forming apparatus according to claim 1, characterized in that.

7. A rotating photoreceptor. A silicon substrate, a plurality of light-emitting units provided on the silicon substrate that emit light for exposing the photoreceptor, a circuit unit provided on the silicon substrate that controls the lighting and extinguishing of the plurality of light-emitting units based on image data, and a storage unit provided on the silicon substrate that stores control data indicating the target light amount of the plurality of light-emitting units, and a plurality of light-emitting chips arranged along the rotation axis direction of the photoreceptor. A controller that outputs the control data. Comprising. Each of the plurality of light-emitting chips is connected to the controller via a different one of the plurality of signal lines. The control data transmitted via a different one of the plurality of signal lines is stored in the storage unit. The storage unit is a first storage unit. Each of the plurality of light-emitting chips has a second storage unit for storing the image data, and a receiving unit for receiving the control data and the image data transmitted from the controller. The controller transmits the control data to each of the first storage units included in the plurality of light-emitting chips via the plurality of signal lines, and transmits the image data to each of the second storage units included in the plurality of light-emitting chips via the plurality of signal lines. The receiving unit transmits the received control data to the first storage unit, transmits the received image data to the second storage unit, transitions to a first state in which the control data is stored in the first storage unit when receiving first identification information, and transitions to a second state in which the image data is stored in the second storage unit when receiving second identification information. An image forming apparatus characterized by the above.

8. When the receiving unit receives third identification information, it transitions to a third state. When the receiving unit is in the third state, the control data is not stored in the first storage unit, and the image data is not stored in the second storage unit. The image forming apparatus according to claim 7, characterized by this.

9. The image forming apparatus according to claim 1, characterized in that the light-emitting unit is an organic EL.

10. The image forming apparatus according to claim 7, characterized in that the light-emitting unit is an organic EL.

Images