Image forming apparatus

Abstract

To provide an image forming apparatus that can accurately control output of a high-voltage power supply circuit.SOLUTION: A control unit acquires, from a theoretical value of first voltage and a theoretical value of second voltage, a theoretical AD value that is a theoretical value of feedback voltage after AD conversion. The control unit acquires, during non-execution of feedback control, a correction value being the difference between the theoretical AD value and a first AD value being a value after the feedback voltage is subjected to AD conversion (S2). When executing the feedback control, the control unit executes the feedback control by using the correction value.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] Conventionally, in an image forming apparatus such as a laser color printer, a high voltage generated by a high voltage circuit is applied to a charger, a transfer roller, a cleaning roller, and the like. When controlling the output voltage of this high voltage circuit, the control unit transmits a control signal to the high voltage circuit and receives a feedback signal from the high voltage circuit to control the output voltage.

[0003] For example, in the image forming apparatus of Patent Document 1, the control unit applies a belt cleaning voltage from a belt cleaning voltage generation circuit to a belt cleaning roller and receives a current detection signal by a current detection circuit. Then, the control unit transmits a PWM signal to the belt cleaning voltage generation circuit based on the AD-converted current detection value, thereby controlling the belt cleaning voltage generation circuit so that the belt cleaning voltage becomes constant.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, with the progress of miniaturization of semiconductor circuits, the allowable range of the input voltage of the AD conversion circuit that can be mounted on the semiconductor circuit has been narrowing. Therefore, by setting the voltage value output to the feedback voltage output circuit and the reference voltage value serving as the reference for AD conversion to different values, it may be possible to reduce the input voltage value of the AD conversion circuit.

[0006] In this case, since the voltage output to the high-voltage power supply circuit is different from the reference voltage value for AD conversion, a tolerance occurs for each voltage, resulting in a problem that an error occurs in the AD value obtained by AD-converting the feedback voltage by the image forming apparatus.

[0007] The present invention has been made to solve the above-described problems, and an object thereof is to provide an image forming apparatus capable of controlling the output of a high-voltage power supply circuit with high precision.

Means for Solving the Problems

[0008] In order to solve the above problems, an image forming apparatus according to Embodiment 1 of the present invention includes an image forming unit that forms an image on a sheet, a high-voltage power supply circuit that outputs an output voltage corresponding to an input control signal to the image forming unit, a first voltage output circuit that outputs a first voltage to the high-voltage power supply circuit, a second voltage output circuit that outputs a second voltage different from the first voltage, a feedback voltage output circuit that inputs the first voltage and outputs a feedback voltage that is a voltage obtained by adding or subtracting a voltage corresponding to the output voltage to a divided voltage obtained by dividing the first voltage, an AD conversion circuit that AD-converts the feedback voltage input from the feedback voltage output circuit with reference to the second voltage, and a control unit that executes feedback control so that the output voltage becomes a target voltage by outputting the control signal to the high-voltage power supply circuit.

[0009] Then, the control unit acquires a theoretical AD value, which is a theoretical value after AD conversion of the feedback voltage by the AD conversion circuit, from the theoretical value of the first voltage and the theoretical value of the second voltage, and acquires a correction value, which is a difference between a first AD value, which is a value after the feedback voltage is AD-converted by the AD conversion circuit when the feedback control is not executed, and the theoretical AD value, and executes the feedback control using the correction value.

[0010] According to the image forming apparatus having the above-described configuration, the control unit performs feedback control of the output voltage of the high-voltage power supply circuit using a correction value that is the difference between a first AD value, which is a value after AD-converting the feedback voltage, and a theoretical AD value. Thereby, even when the first voltage output by the first voltage output circuit and the second voltage output by the second voltage output circuit are different, the output of the high-voltage power supply circuit can be controlled with high precision.

[0011] Further, in the image forming apparatus according to Embodiment 2 of the present invention, in the feedback voltage output circuit, the maximum value of the feedback voltage is a divided voltage obtained by dividing the first voltage, and the feedback voltage is a voltage obtained by subtracting a voltage corresponding to the output voltage from the divided voltage.

[0012] According to the image forming apparatus having the above-described configuration, without matching the first voltage output by the first voltage output circuit and the second voltage that is a reference of the AD conversion circuit, by correcting the AD value obtained by AD-converting the feedback voltage, the accuracy of the feedback control by the control unit can be improved. Thereby, while coping with the miniaturization of the semiconductor circuit equipped with the AD conversion circuit, the output voltage of the high-voltage power supply circuit can be controlled with high precision.

[0013] Further, in the image forming apparatus according to Embodiment 3 of the present invention, during the execution of the feedback control, the control unit corrects a second AD value, which is a value obtained by AD-converting the feedback voltage by the AD conversion circuit, with the correction value, and performs feedback control for outputting the control signal based on the corrected second AD value.

[0014] According to the image forming apparatus having the above-described configuration, the control unit can control the output of the high-voltage power supply circuit with high precision by correcting a second AD value, which is a value obtained by AD-converting the feedback voltage by the AD conversion circuit, with the correction value.

[0015] In addition, the image forming apparatus according to Embodiment 4 of the present invention further includes a low-voltage power supply that outputs a low voltage, and an on-off circuit that switches between a state of outputting the low voltage from the low-voltage power supply to the high-voltage power supply circuit and a state of not outputting the low voltage. The high-voltage power supply circuit outputs the output voltage by boosting the low voltage output from the low-voltage power supply. When the on-off circuit is in a state of not outputting the low voltage from the low-voltage power supply to the high-voltage power supply circuit, the control unit acquires the correction value.

[0016] According to the image forming apparatus having the above-described configuration, the control unit can acquire the correction value when feedback control is not executed by setting the on-off circuit to a state where the low voltage is not output from the low-voltage power supply to the high-voltage power supply circuit.

[0017] The image forming apparatus according to Embodiment 5 of the present invention further includes a photosensitive drum, an endless belt disposed opposite to the photosensitive drum, and a belt cleaning roller capable of holding deposits adhering to the surface of the endless belt. The high-voltage power supply circuit outputs a belt cleaning voltage as the output voltage to the belt cleaning roller, and the feedback voltage output circuit outputs the feedback voltage, which is a value obtained by subtracting a value corresponding to the belt cleaning voltage from the divided voltage.

[0018] According to the image forming apparatus having the above-described configuration, the control unit can perform feedback control so that the belt cleaning roller voltage becomes the target voltage, and the belt cleaning roller can satisfactorily collect deposits adhering to the surface of the endless belt.

[0019] In the image forming apparatus according to Embodiment 6 of the present invention, the control unit acquires the correction value during the warm-up operation by the image forming unit.

[0020] According to the image forming apparatus having the above-described configuration, since the control unit acquires the correction value during the warm-up operation by the image forming unit, the output of the high-voltage power supply circuit can be controlled with high accuracy when forming an image on a sheet.

Advantages of the Invention

[0021] According to one aspect of the present invention, the output of the high-voltage power supply circuit can be controlled with high precision.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0023] 〔Embodiment 1〕 Hereinafter, the image forming apparatus 1 in Embodiment 1 of the present invention will be described with reference to FIGS. 1 to 6.

[0024] FIG. 1 is a schematic diagram showing an example of the internal configuration of an image forming apparatus 1 according to Embodiment 1. As shown in FIG. 1, the image forming apparatus 1 is, for example, a color LED printer, and includes a paper feed tray 21, a discharge tray 22, and an image forming unit 3 inside a housing 10. In the following description, as indicated by the arrows in FIG. 1, the vertical direction, the front-rear direction, and the left-right direction of the image forming apparatus 1 are defined.

[0025] The paper feed tray 21 is provided at the bottom of the housing 10 and houses a plurality of sheets P. The sheet P is, for example, plain paper. A paper feed roller 23 is provided on the paper feed tray 21. The paper feed roller 23 picks up the sheet P in the paper feed tray 21 and conveys it to the registration roller 24 side. The registration roller 24 corrects skew of the sheet P and then conveys the sheet P onto the belt unit 31 of the image forming unit 3.

[0026] The image forming unit 3 includes a belt unit 31, an exposure unit 32, a monochrome cartridge 33K, color cartridges 33Y, 33M, 33C, four transfer rollers 36Y, M, C, K, a belt cleaning device 37, and a fixing unit 5.

[0027] The image forming unit 3 forms toner images of four colors (black, yellow, magenta, cyan) on the sheet P. The sheet P on which an image is formed by the image forming unit 3 is discharged to the discharge tray 22 by a discharge roller 25. Hereinafter, when distinguishing each component by color, a symbol meaning each color, that is, K (black), Y (yellow), M (magenta), C (cyan) is attached to the end of the reference numeral of the component.

[0028] The belt unit 31 includes a pair of front and rear support rollers 31a and an endless belt 31b disposed opposite to each photosensitive drum 35K, 35Y, 35M, 35C. The belt unit 31 is configured such that the rear support roller 31a is rotationally driven by a motor (not shown), and the endless belt 31b circulates. Thereby, the sheet P is conveyed rearward along the upper surface of the endless belt 31b.

[0029] The exposure unit 32 consists of, for example, LED units corresponding to four colors. The exposure unit 32 exposes the surfaces of the photosensitive drums 35K, 35Y, 35M, and 35C by emitting light from respective light-emitting units (not shown). Each light-emitting unit is controlled for light emission by the CPU 111 based on the image data to be formed.

[0030] The monochrome cartridge 33K has a photosensitive drum 35K, a charger 38, a cleaning roller 39, and a developing cartridge 41K. The charger 38 charges the surface of the photosensitive drum 35K. The developing cartridge 41K is a container for containing black toner and is provided with a supply roller 42K and a developing roller 43K.

[0031] Note that although not shown, the monochrome cartridge 33K is provided with a CHG terminal for receiving a charging voltage, a GRID terminal for receiving a grid voltage, a DEV terminal for receiving a developing bias, a DCLNA terminal for receiving a cleaning roller voltage DCLNA, a DCLNB terminal for receiving a cleaning shaft voltage, and the like.

[0032] Each color cartridge 33Y, 33M, 33C has, similar to the monochrome cartridge 33K, a photosensitive drum 35Y, 35M, 35C, a charger 38, a cleaning roller 39, and developing cartridges 41Y, 41M, 41C, respectively. Each developing cartridge 41Y, 41M, 41C is a container for containing toner of each color and is provided with a supply roller 42Y, 42M, 42C and a developing roller 43Y, 43M, 43C, respectively.

[0033] Note that each color cartridge 33Y, 33M, 33C is provided with a CHG terminal, a GRID terminal, a DEV terminal, and a DCLNA terminal, although not shown, similar to the monochrome cartridge 33K.

[0034] The cleaning roller 39 recovers the toner remaining on the surfaces of the photosensitive drums 35K, 35Y, 35M, and 35C when a cleaning roller voltage, which is a high voltage, is applied. Note that a cleaning shaft (not shown) is disposed at a position facing the cleaning roller 39 corresponding to the monochrome cartridge 33K. The cleaning shaft removes paper dust on the surface of the cleaning roller 39 when a voltage higher than the belt cleaning voltage BCLN is applied.

[0035] The belt cleaning device 37 includes a belt cleaning roller 37a and a belt cleaning shaft 37b. The belt cleaning device 37 recovers deposits such as toner adhering to the surface of the endless belt 31b by the belt cleaning roller 37a and the belt cleaning shaft 37b when a belt cleaning roller voltage BCLN is applied to the belt cleaning roller 37a.

[0036] The belt cleaning device 37 has a BCLN terminal for receiving the belt cleaning roller voltage BCLN.

[0037] The four transfer rollers 36Y, 36M, 36C, and 36K are respectively provided at positions facing the respective photosensitive drums 35Y, 35M, 35C, and 35K inside the endless belt 31b.

[0038] The belt unit 31 has TRCC1 terminals, TRCC2 terminals, RCC3 terminals, and TRCC4 terminals for receiving the transfer voltages TRCC1, TRCC2, TRCC3, and TRCC4 applied to the respective transfer rollers 36Y, 36M, 36C, and 36K. The belt unit 31 is mounted on a belt unit mounting portion (not shown).

[0039] The fixing unit 5 includes a heating roller 51 having a heat source and a pressure roller 52 that presses the sheet P toward the heating roller 51. The fixing unit 5 thermally fixes the toner image transferred onto the sheet P to the sheet P. Then, the sheet P thermally fixed by the fixing unit 5 is conveyed upward and discharged onto a discharge tray 22 provided on the upper surface of the housing 10.

[0040] [Circuit Configuration of Image Forming Apparatus] FIG. 2 is a schematic circuit diagram of the image forming apparatus 1 according to Embodiment 1. As shown in FIG. 2, the image forming apparatus 1 includes a main board 100, a belt cleaning voltage generation circuit 80 which is an example of a high-voltage power supply circuit, transfer voltage generation circuits 70K, 70Y, 70M, 70C, and a low-voltage power supply 180. Note that the image forming apparatus 1 can receive a start command for image forming processing via a communication I / F (communication interface) not shown.

[0041] The belt cleaning voltage generation circuit 80 outputs a belt cleaning voltage BCLN which is an output voltage by boosting the low voltage output from the low-voltage power supply 180 by a transformer T2. The belt cleaning voltage generation circuit 80 applies an output voltage corresponding to a control signal input to the belt cleaning voltage generation circuit 80 to the belt cleaning roller 37a of the image forming unit 3.

[0042] The belt cleaning voltage generation circuit 80 is, for example, a self-excited high-voltage generation circuit and includes a transistor Tr2, a transformer T2, a diode D2, a capacitor C2, and a feedback voltage output circuit 81. Note that the high-voltage power supply circuit is not limited to the belt cleaning voltage generation circuit 80 and may be the transfer voltage generation circuits 70K, 70Y, 70M, 70C, or may be the belt cleaning voltage generation circuit 80 and the transfer voltage generation circuits 70K, 70Y, 70M, 70C.

[0043] Note that in FIG. 2, since the configurations of the transfer voltage generation circuits 70Y, 70M, and 70C of the respective transfer rollers 36Y, 36M, and 36C corresponding to the respective color cartridges 33Y, 33M, and 33C are the same as those of the transfer voltage generation circuit 70K of the transfer roller 36K corresponding to the monochrome cartridge 33K, the details of the internal configuration and its description are omitted.

[0044] The main board 100 is provided with an ASIC (Application Specific Integrated Circuit) 110, a ROM (Read Only Memory) 120, a RAM (Random Access Memory) 130, an EEPROM (registered trademark) 140, a second voltage output circuit 150, a first voltage output circuit 160, an on-off circuit 170, and the like.

[0045] The ASIC 110 incorporates a CPU (Central Processing Unit) 111 which is an example of a control unit, and an AD conversion circuit 112. The CPU 111 performs overall control over each part of the image forming apparatus 1. The ASIC 110 is connected to the ROM (Read Only Memory) 120, the RAM (Random Access Memory) 130, and the EEPROM 140 by internal buses respectively.

[0046] The ROM 120 stores various control programs and various settings for controlling the image forming apparatus 1. The RAM 130 is used as a work area from which various control programs are read, and a storage area for temporarily storing image data.

[0047] The EEPROM 140 stores in advance various data (see FIG. 5) and the like used when executing feedback control processing.

[0048] The first voltage output circuit 160 outputs a first voltage V1 to the feedback voltage output circuit 81. The value of the first voltage V1 is set to, for example, +3.3 [V]. The second voltage output circuit 150 outputs a second voltage V2, which is a reference voltage for AD conversion, to the AD conversion circuit 112. The value of the second voltage V2 is set to a value different from the value of the first voltage V1, and is set to, for example, +1.8 [V].

[0049] The first voltage output circuit 160 is provided on the main board 100, but the first voltage output circuit 160 may be separately provided on a sub-board.

[0050] The feedback voltage output circuit 81 outputs a feedback voltage Vf to the AD conversion circuit 112. The first voltage V1 is input to the feedback voltage output circuit 81. The feedback voltage Vf is a voltage obtained by subtracting a voltage corresponding to the belt cleaning voltage BCLN from a divided voltage obtained by dividing the first voltage V1. The divided voltage is set to, for example, +1.76 [V]. The maximum value of the feedback voltage Vf is the divided voltage obtained by dividing the first voltage V1.

[0051] The on-off circuit 170 is for switching between a state of outputting a low voltage from the low-voltage power supply 180 to the transformer T2 of the belt cleaning voltage generation circuit 80 and a state of not outputting a low voltage. The on-off circuit 170 is connected to the CPU 111 via a signal line (not shown), and based on a control signal from the CPU 111, switches between an on state of outputting a low voltage to the belt cleaning voltage generation circuit 80 and an off state of not outputting a low voltage. The low voltage is set to, for example, +24 [V]. Note that the CPU 111, for example, turns off the on-off circuit 170 when the front cover (not shown) is open, and turns on the on-off circuit 170 when the front cover is closed.

[0052] The belt cleaning voltage generation circuit 80 applies a belt cleaning voltage BCLN to the belt cleaning roller 37a. The transformer T2 boosts the input low voltage. Diode D2 and capacitor C2 rectify and smooth the secondary-side voltage of transformer T2 to generate the belt cleaning voltage BCLN. The belt cleaning voltage BCLN is a high voltage with a positive polarity. CPU111 outputs a control signal to the belt cleaning voltage generation circuit 80 to perform feedback control so that the belt cleaning voltage BCLN becomes the target voltage.

[0053] Specifically, when CPU111 outputs a PWM (Pulse Width Modulation) signal from the PWM5 port, a drive signal Sd2 corresponding to the PWM signal is generated by a drive circuit (not shown), and the drive signal Sd2 is supplied to the base of transistor Tr2 to drive the primary side of transformer T2. Then, by controlling the base current of transistor Tr2 with the drive signal Sd2, the secondary-side voltage of transformer T2, that is, the belt cleaning voltage BCLN, is output.

[0054] At this time, CPU111 controls the belt cleaning voltage generation circuit 80 so that the belt cleaning voltage BCLN becomes constant by controlling the pulse width of the PWM signal based on the feedback voltage signal Svd from the feedback voltage output circuit 81.

[0055] The feedback voltage output circuit 81 has resistors R3 and R4. One end of resistor R3 is connected to the +3.3V voltage terminal and one end of the secondary winding of transformer T2, and the other end is connected to the AD conversion circuit 112 of CPU111 and one end of the voltage-dividing resistor R4. The other end of resistor R4 is connected to ground. The feedback voltage signal Svd is a signal for detecting the feedback voltage Vf and is input to the AD conversion circuit 112.

[0056] Based on the feedback voltage signal Svd received from the feedback voltage output circuit 81, CPU111 outputs a PWM signal to the belt cleaning voltage generation circuit 80 so that the target voltage is applied to the belt cleaning roller 37a, as will be described later.

[0057] The transfer voltage generation circuit 70K is, for example, a self-excited high-voltage generation circuit, and includes a reference voltage generation circuit 71, an operational amplifier IC1, a transistor Tr1, a transformer T1, a diode D1, a capacitor C1, and voltage-dividing resistors R1 and R2.

[0058] The transfer voltage generation circuit 70K generates a transfer voltage TRCC1 to be supplied to a transfer roller 36K corresponding to the monochrome cartridge 33K. The transfer voltage TRCC1 is a high voltage of negative polarity. The reference voltage generation circuit 71 generates a reference voltage according to the PWM signal from the PWM1 port of the CPU111 and supplies the reference voltage to the non-inverting input of the operational amplifier IC1.

[0059] A divided voltage Vd by the voltage-dividing resistors R1 and R2 is input to the inverting input of the operational amplifier IC1. The operational amplifier IC1 generates a drive signal Sd1 for driving the primary side of the transformer T1 based on the reference voltage and the divided voltage. One end of the voltage-dividing resistor R1 is connected to one end of the secondary winding of the transformer T1, and the other end is connected to the inverting input of the operational amplifier IC1. One end of the voltage-dividing resistor R2 is connected to the inverting input of the operational amplifier IC1, and the other end is connected to the ground.

[0060] The drive signal Sd1 is supplied to the base of the transistor Tr1, and by controlling the base current of the transistor Tr1 by the drive signal Sd1, the secondary side voltage of the transformer T1, that is, the transfer voltage TRCC1 is generated. The operational amplifier IC1 operates to eliminate the difference between the reference voltage and the divided voltage, thereby maintaining the current I1 flowing through the voltage-dividing resistors R1 and R2 at a predetermined value. The diode D1 and the capacitor C1 rectify and smooth the secondary side voltage of the transformer T1 to generate the transfer voltage TRCC1 of a DC voltage.

[0061] [Printing Process by the CPU of the Image Forming Apparatus] FIG. 3 is a flowchart showing an example of the flow of printing processing by the CPU 111 of the image forming apparatus 1 according to Embodiment 1. In the flowchart shown in FIG. 3, when a power supply (not shown) is turned on, first, the CPU 111 starts a warm-up operation (S1). Specifically, in S1, as a warm-up operation, the CPU 111 executes an operation of raising the temperature of the heating roller 51 of the fixing unit 5 to a predetermined temperature, for example.

[0062] After S1, the CPU 111 acquires a correction value ΔVd (S2). Here, the correction value ΔVd is the difference between a first AD value Vd1, which is a value obtained by AD-converting a feedback voltage Vf by the AD conversion circuit 112 when feedback control is not executed, and a theoretical AD value Vth.

[0063] After S2, the CPU 111 determines whether or not the above-described warm-up operation has ended (S3). If the warm-up operation has not ended (S3: NO), the CPU 111 repeats S3, and if the warm-up operation has ended (S3: YES), the CPU 111 proceeds to S4.

[0064] In S4, the CPU 111 determines whether or not there is a start command for image forming processing. If there is a start command for image forming processing (S4: YES), the CPU 111 executes feedback control processing (S5).

[0065] After S5, the CPU 111 executes image forming processing (S6). Specifically, the CPU 111 rotates the photosensitive drums 35K, 35Y, 35M, and 35C by driving a motor (not shown), and uniformly charges the surfaces of the photosensitive drums 35K, 35Y, 35M, and 35C with the charger 38. Then, the CPU 111 forms an electrostatic latent image corresponding to the image to be formed on the sheet P on the surfaces of the photosensitive drums 35K, 35Y, 35M, and 35C by driving the exposure unit 32.

[0066] Subsequently, the CPU 111 rotates each developing roller 43K, 43Y, 43M, 43C to supply toner corresponding to each color to the electrostatic latent image formed on the surface of each photosensitive drum 35K, 35Y, 35M, 35C, and forms a toner image on the surface of each photosensitive drum 35K, 35Y, 35M, 35C.

[0067] Then, the CPU 111 conveys the sheet P by the endless belt 31b, and sequentially transfers the toner images formed on the surfaces of the photosensitive drums 35K, 35Y, 35M, 35C to the sheet P by the transfer rollers 36K, 36Y, 36M, 36C. The toner image transferred to the sheet P is thermally fixed by the fixing unit 5.

[0068] After S6, the CPU 111 determines whether the image formation process has ended (S7). If the image formation process has not ended (S7: NO), the CPU 111 repeats S7. If the image formation process has ended (S7: YES), the CPU 111 returns to S4.

[0069] In S4, if the start command for the image formation process has not been received (S4: NO), the CPU 111 ends the printing process shown in FIG. 3.

[0070] <Correction value acquisition process> Next, the correction value acquisition process S2 in FIG. 3 will be described with reference to FIGS. 4 and 5. FIG. 4 is a flowchart showing an example of the flow of the correction value acquisition process S2 by the CPU 111 of the image forming apparatus 1 in the first embodiment. FIG. 5 is a table showing the relationship between the set current, the target feedback voltage, and the target AD value when the feedback control is executed by the CPU 111 of the image forming apparatus 1 in the first embodiment. The set current is the current flowing through the feedback voltage output circuit 81, and the target feedback voltage is set according to the magnitude of the set current.

[0071] In the flowchart shown in FIG. 4, the CPU 111 determines whether or not feedback control is not being executed (S21). In Embodiment 1, when feedback control is not being executed, it means that no PWM signal is output from the PWM5 port of the CPU 111.

[0072] If the CPU 111 is not in the non-execution state of feedback control (S21: NO), it repeatedly executes S21. If it is in the non-execution state of feedback control (S21: YES), it acquires the first AD value Vd1 (S22).

[0073] Specifically, the CPU 111 outputs +3.3 [V] as the first voltage V1 from the first voltage output circuit 160 to the feedback voltage output circuit 81. Then, the CPU 111 acquires the first AD value Vd1 by AD-converting the feedback voltage Vf from the belt cleaning voltage generation circuit 80 by the AD conversion circuit 112.

[0074] Subsequently, the CPU 111 calculates a correction value ΔVd (S23). Specifically, in S23, the CPU 111 calculates the correction value ΔVd by subtracting the theoretical AD value Vth from the first AD value Vd1 acquired in S22.

[0075] Here, the theoretical AD value Vth is the theoretical value after AD conversion of the feedback voltage Vf by the AD conversion circuit 112 from the theoretical value of the first voltage V1 and the theoretical value of the second voltage V2, and is preset according to the design specifications of the image forming apparatus 1. In this case, the theoretical AD value Vth corresponds to the target AD value when the set current is 0 [μA] in the table of FIG. 5 and is 978 [dec].

[0076] The CPU 111 acquires the theoretical AD value Vth stored in advance in the EEPROM 140, and calculates the correction value ΔVd by obtaining the absolute value obtained by subtracting the theoretical AD value Vth from the first AD value Vd1. For example, if the first AD value Vd1 acquired in S22 is 970 [dec], the correction value ΔVd is 8 [dec], which is the absolute value obtained by subtracting 978 [dec] from 970 [dec].

[0077] Next, the CPU 111 stores the correction value ΔVd calculated in S23 in the EEPROM 140 (S24). After S24, the CPU 111 determines whether the correction value acquisition process S2 has ended (S25). If the correction value acquisition process S2 has not ended (S25: NO), the process returns to S21. On the other hand, when the correction value acquisition process S2 has ended (S25: YES), the CPU 111 ends the correction value acquisition process S2 shown in FIG. 4.

[0078] <Feedback control process> Next, the feedback control process S5 in FIG. 3 will be described with reference to FIG. 6. FIG. 6 is a flowchart showing an example of the flow of the feedback control process S5 by the CPU 111 of the image forming apparatus 1 in the first embodiment.

[0079] In the flowchart shown in FIG. 6, first, the CPU 111 turns on the on-off circuit 170 and outputs +24 [V] as a low voltage to the transformer T2 of the belt cleaning voltage generation circuit 80. Then, while referring to the table in FIG. 5, the CPU 111 outputs a PWM signal from the main board 100 to the belt cleaning voltage generation circuit 80 so as to approach the target AD value (S51).

[0080] Subsequently, the CPU 111 receives the feedback voltage Vf from the belt cleaning voltage generation circuit 80 and acquires the second AD value Vd2 (S52). The second AD value Vd2 is a value after the feedback voltage Vf is AD-converted by the AD conversion circuit 112. Note that in S52, the CPU 111 may use the average value of each second AD value obtained by receiving the feedback voltage signal Svd a plurality of times, for example, 10 times, as the second AD value Vd.

[0081] After S52, the CPU 111 calculates a second AD value Vd2A corrected by a correction value ΔVd (S53). Specifically, the CPU 111 calculates the corrected second AD value Vd2A by subtracting the correction value ΔVd obtained in S2 from the second AD value Vd2 obtained in S52. For example, when the second AD value Vd2 obtained in S52 is 900 [dec], the corrected second AD value Vd2A is 892 [dec] obtained by subtracting 8 [dec] from 900 [dec].

[0082] Next, the CPU 111 determines whether the corrected second AD value Vd2A is within an allowable range (S54). Here, the "allowable range" is set, for example, within a range of ±10 [%] of the theoretical AD value Vth.

[0083] If the corrected second AD value Vd2A is not within the allowable range (S54: NO), the CPU 111 changes the PWM signal so that the belt cleaning voltage BCLN becomes the target FB voltage (see FIG. 5) (S55).

[0084] On the other hand, if the corrected second AD value Vd2A is within the allowable range (S54: YES), or after S55, the CPU 111 determines whether the output of the belt cleaning voltage BCLN has ended (S56).

[0085] If the output of the belt cleaning voltage BCLN has not ended (S56: NO), the CPU 111 returns to S52. On the other hand, if the output of the belt cleaning voltage BCLN has ended (S56: YES), the CPU 111 ends the feedback control process S5 shown in FIG. 6.

[0086] In the image forming apparatus 1 of Embodiment 1 described above, the CPU 111 obtains a correction value ΔVd, which is the difference between a first AD value Vd1, which is the value after AD-converting the feedback voltage Vf, and a theoretical AD value Vth (S2), and executes feedback control processing (S5) for the output voltage of the belt cleaning voltage generation circuit 80, which is a high-voltage power supply circuit, that is, the belt cleaning voltage BCLN. Then, during the execution of the feedback control, the CPU 111 corrects a second AD value Vd2, which is the value after AD-converting the feedback voltage Vf by the AD conversion circuit 112, with the correction value Δd, and executes feedback control for outputting a control signal based on the corrected second AD value Vd2A.

[0087] According to the image forming apparatus 1 having the above configuration, even when the first voltage V1 output by the first voltage output circuit 160 and the second voltage V2 output by the second voltage output circuit 150 are different, the output of the belt cleaning voltage generation circuit 80 can be controlled with high precision. As a result, the value of the belt cleaning roller voltage BCLN can be made to be the target voltage, and the toner adhering to the surface of the endless belt 31b can be satisfactorily recovered by the belt cleaning roller 37a and the belt cleaning shaft 37b.

[0088] Further, since the feedback voltage Vf is a voltage obtained by subtracting a voltage corresponding to the output voltage from the divided voltage obtained by dividing the first voltage V1, the feedback control process S5 by the CPU 111 can be executed without matching the first voltage V1 output by the first voltage output circuit 160 and the second voltage V2 that is the reference of the AD conversion circuit 112. As a result, while corresponding to the miniaturization of the ASIC 110 equipped with the AD conversion circuit 112, the belt cleaning voltage BCLN of the belt cleaning voltage generation circuit 80 can be controlled with high precision.

[0089] [Embodiment 2] Next, the image forming apparatus 1 according to Embodiment 2 of the present invention will be described with reference to FIG. 7. FIG. 7 is a flowchart showing an example of the flow of correction value acquisition processing S2A by the image forming apparatus 1 according to Embodiment 2. For the sake of convenience of explanation, members having the same functions as those described in the above Embodiment 1 are denoted by the same reference numerals, and the description thereof will not be repeated.

[0090] <Correction value acquisition processing> In the image forming apparatus 1 of Embodiment 2, the flow of the correction value acquisition processing S2 in FIG. 3 is different from that in Embodiment 1. In the correction value acquisition processing S2A of Embodiment 2, when the on-off circuit 170 outputs no low voltage from the low-voltage power supply 180 to the belt cleaning voltage generation circuit 80 which is a high-voltage power supply circuit, the correction value ΔVd is acquired.

[0091] In the flowchart shown in FIG. 7, the CPU 111 determines whether the on-off circuit 170 is in the off state (S31). When the on-off circuit 170 is in the off state (S31: YES), the CPU 111 acquires the first AD value Vd1 (S32). The first AD value Vd1 is the value obtained by AD-converting the feedback voltage Vf by the AD conversion circuit 112 when the feedback control is not executed, in this case, when the on-off circuit 170 is in the off state.

[0092] When the on-off circuit 170 is in the on state (S31: NO), or after S32, the CPU 111 calculates the correction value ΔVd (S33). Specifically, in S33, the CPU 111 calculates the correction value ΔVd by subtracting the theoretical AD value from the first AD value Vd1.

[0093] After S33, the CPU 111 stores the correction value ΔVd calculated in S33 in the EEPROM 140 (S34). Then, the CPU 111 determines whether the correction value acquisition processing S2A has ended (S35). When the correction value acquisition processing S2A has not ended (S35: NO), the process returns to S31. On the other hand, when the CPU 111 determines that the correction value acquisition processing S2A has ended (S35: YES), the flow shown in FIG. 6 ends.

[0094] Even with the image forming apparatus 1 of Embodiment 2 described above, the same effects as those of the image forming apparatus 1 of Embodiment 1 can be obtained. That is, when the CPU 111 is in a state where the on-off circuit 170 does not output a low voltage from the low-voltage power supply 180 to the belt cleaning voltage generation circuit 80, the correction value acquisition process S2A is performed to acquire the correction value ΔVd, and the acquired correction value ΔVd is used to execute feedback control, thereby enabling highly accurate control of the output voltage of the belt cleaning voltage generation circuit 80.

[0095] 〔Other Embodiments〕 Although the image forming apparatus 1 in the above-described Embodiments 1 and 2 is assumed to be a color LED printer, the present invention is not limited thereto, and other devices having a printing function, such as a color laser printer, a multifunction machine, and a FAX apparatus, can also be applied. Further, although the sheet P is assumed to be plain paper, the present invention is not limited thereto, and other papers such as thick paper or thin paper may also be used.

[0096] In the image forming apparatus 1 in the above-described Embodiments 1 and 2, the CPU 111 is assumed to acquire the correction value ΔVd during the warming-up operation by the image forming unit 3, but the present invention is not limited thereto. For example, the CPU 111 may perform the correction value acquisition processes S2 and S2A after receiving a start command for the image forming process (S4: YES) and before starting the image forming process S6.

[0097] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Explanation of Reference Numerals

[0098] 1 Image forming apparatus 3 Image forming unit 5 Fixing unit 31b Endless belt 33K Monochrome cartridge 33Y, 33Y, 33M, 33C Color cartridges 35K, 35Y, 35M, 35C photosensitive drums 37a belt cleaning roller 38 charger 80 belt cleaning voltage generation circuit 81 feedback voltage output circuit 100 main board 111 CPU 112 AD conversion circuit 115 EEPROM 150 second voltage output circuit 160 first voltage output circuit 180 low voltage power supply P sheet V1 first voltage V2 second voltage Vf feedback voltage Vd1 first AD value Vd2 second AD value ΔVd correction value

Claims

1. An image forming unit that forms an image on a sheet; A high-voltage power supply circuit that outputs an output voltage corresponding to an input control signal to the image forming unit; A first voltage output circuit that outputs a first voltage to the high-voltage power supply circuit; A second voltage output circuit that outputs a second voltage different from the first voltage; A feedback voltage output circuit that receives the first voltage, and outputs a feedback voltage which is a voltage obtained by adding or subtracting a voltage corresponding to the output voltage to a divided voltage obtained by dividing the first voltage; An AD conversion circuit that AD-converts the feedback voltage input from the feedback voltage output circuit with reference to the second voltage; A control unit that performs feedback control so that the output voltage becomes a target voltage by outputting the control signal to the high-voltage power supply circuit; Comprising: The control unit: Obtains a theoretical AD value, which is a theoretically obtained value after AD conversion of the feedback voltage by the AD conversion circuit, from the theoretical value of the first voltage and the theoretical value of the second voltage; Obtains a correction value, which is a difference between a first AD value, which is a value obtained by AD-converting the feedback voltage by the AD conversion circuit when the feedback control is not executed, and the theoretical AD value; An image forming apparatus, characterized in that the feedback control is executed using the correction value.

2. In the feedback voltage output circuit: The maximum value of the feedback voltage is the divided voltage obtained by dividing the first voltage; The image forming apparatus according to claim 1, wherein the feedback voltage is a voltage obtained by subtracting a voltage corresponding to the output voltage from the divided voltage.

3. The control unit: When the feedback control is executed, corrects a second AD value, which is a value obtained by AD-converting the feedback voltage by the AD conversion circuit, by the correction value, and executes feedback control for outputting the control signal based on the corrected second AD value. The image forming apparatus according to claim 1 or 2.

4. A low-voltage power supply that outputs a low voltage; An on-off circuit that switches between a state of outputting the low voltage from the low-voltage power supply to the high-voltage power supply circuit and a state of not outputting the low voltage; Further comprising: The high-voltage power supply circuit outputs the output voltage by boosting the low voltage output from the low-voltage power supply; The control unit: The image forming apparatus according to any one of claims 1 to 3, characterized in that the correction value is obtained when the on-off circuit is in a state where the low voltage is not output from the low-voltage power supply to the high-voltage power supply circuit.

5. A photosensitive drum, An endless belt disposed opposite to the photosensitive drum, A belt cleaning roller capable of holding deposits adhering to the surface of the endless belt, further comprising: The high-voltage power supply circuit outputs a belt cleaning voltage as the output voltage to the belt cleaning roller, The image forming apparatus according to claim 4, characterized in that the feedback voltage output circuit outputs the feedback voltage, which is a value obtained by subtracting a value corresponding to the belt cleaning voltage from the divided voltage.

6. The control unit, The image forming apparatus according to any one of claims 1 to 5, characterized in that the correction value is obtained during a warm-up operation by the image forming unit.

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