Image forming apparatus

Abstract

To provide an image forming apparatus that allows a feedback signal according to applied voltage and an error determination signal for determining an error occurring in a power supply substrate, to be input to the same terminal of a control unit, thereby reducing the number of terminals of the control unit.SOLUTION: A printer 1 comprises: an image forming unit 20; a belt cleaner 16 that recovers a residual toner remaining on a conveying belt 53 to a belt cleaning shaft 16c; a high-voltage power supply substrate 112 that outputs a feedback signal according to the voltage applied to the image forming unit 20 and an error determination signal for determining an error occurring in the belt cleaner 16; and an ASIC 100 to which the feedback signal and error determination signal are input from the high-voltage power supply substrate 112. The feedback signal and the error determination signal are input to a common port AD4 of the ASIC 100.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present application relates to an image forming apparatus that forms an image on a sheet by an electrophotographic method. [Background technology]

[0002] Conventionally, an image forming apparatus that forms an image on a sheet by an electrophotographic method includes a photosensitive drum, a charger that charges the photosensitive drum, a developing roller that supplies toner to the photosensitive drum, a belt that transports the sheet to the photosensitive drum, a transfer unit that transfers the toner image on the photosensitive drum to the sheet, a drum cleaning roller that can collect toner on the photosensitive drum, and a belt cleaner that can collect toner on the belt. Image forming apparatuses that include a voltage application circuit that applies voltage to the charger, the transfer unit, and the belt cleaner are known.

[0003] Patent Document 1 discloses an image forming apparatus equipped with a transfer voltage generating circuit that can perform hardware control to control the output voltage by the circuit itself, without inputting a feedback signal corresponding to the transfer voltage applied to the transfer roller to a control unit such as an ASIC. By not inputting a feedback signal to the control unit, the number of signals input to the control unit can be reduced. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-86733 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the voltage application circuit itself cannot determine and respond to the values ​​of the voltages applied to the charger and transfer unit, or whether any errors have occurred in the belt cleaner, it is necessary to input each signal to the control unit, and it is not possible to reduce the number of signals input to the control unit.

[0006] The present application aims to provide an image forming apparatus in which a feedback signal corresponding to an applied voltage and an error judgment signal for judging an error occurring in a power supply board can be input to the same terminal of a control unit, thereby reducing the number of terminals of the control unit. [Means for solving the problem]

[0007] In order to achieve the above object, the image forming apparatus of the present application comprises an image forming unit having a photosensitive drum, a charger for charging the photosensitive drum, a developing roller for supplying toner to an electrostatic latent image formed on the charged photosensitive drum to form a toner image on the photosensitive drum, an endless belt in contact with the photosensitive drum, and a transfer member arranged opposite the photosensitive drum across the belt, a belt cleaner having a backup roller, a cleaning roller facing the backup roller across the belt, and a recovery member in contact with the cleaning roller and recovering residual toner remaining on the belt into the recovery member, a voltage board for applying voltages to the image forming unit and the belt cleaner, respectively, a power supply board for outputting a feedback signal corresponding to the voltage applied to the image forming unit and an error judgment signal for determining an error that has occurred in the belt cleaner, and a control unit to which the feedback signal and the error judgment signal are input from the power supply board, and the feedback signal and the error judgment signal are input to a common terminal of the control unit.

[0008] Since an error occurring in the belt cleaner is not directly related to image formation of the image forming apparatus, control based on the error judgment signal has a lower priority than control based on the feedback signal. Also, an error occurring in the belt cleaner can be judged even when not forming an image. Therefore, the feedback signal and the belt cleaner error judgment signal can be input to a common terminal of the control unit, and the number of terminals of the control unit can be reduced.

[0009] The power supply board further includes a transfer voltage application circuit which applies a transfer voltage to the transfer member and outputs a transfer feedback signal corresponding to the transfer voltage, a belt cleaning voltage application circuit which applies a belt cleaning voltage to the backup roller, and a belt feedback signal output circuit which outputs an error judgment signal corresponding to the belt cleaning voltage, and the transfer feedback signal and the error judgment signal are input to a common terminal, and the control unit judges that there is an error when the error judgment signal has not been input despite instructing the belt cleaning voltage application circuit to apply the belt cleaning voltage, and judges that there is a normal state when the error judgment signal has been input when instructing the belt cleaning voltage application circuit to apply the belt cleaning voltage.

[0010] This allows the control unit to accurately determine whether an error has occurred or not, even when a transfer feedback signal and an error determination signal, which are different types of signal, are input to a common terminal.

[0011] The power supply board further has a feedback signal common circuit in which the transfer voltage application circuit and the belt feedback signal output circuit are electrically connected to each other and whose output terminal is connected to a common terminal, and the feedback signal common circuit outputs a transfer feedback signal from the output terminal when the belt cleaning voltage application circuit is not applying the belt cleaning voltage, and outputs an error judgment signal from the output terminal without outputting a transfer feedback signal from the output terminal when the belt cleaning voltage application circuit is applying the belt cleaning voltage.

[0012] This enables the feedback signal common circuit to output the transfer feedback signal and the error determination signal from the output terminal without superimposing them.

[0013] The belt cleaning voltage application circuit is characterized by having: a first transformer consisting of a primary winding and a secondary winding, the first transformer having a first auxiliary winding connected to the primary winding; a first reference voltage generation circuit that outputs a first reference voltage corresponding to a first set current value which is a control signal from the control unit; a first voltage generation circuit that generates a first voltage based on the magnitude of a first feedback current flowing through one end of the secondary winding of the first transformer; a first comparison circuit that receives the first reference voltage and the first voltage and outputs a first drive signal corresponding to the difference between the first reference voltage and the first voltage; a first switching element that performs an on / off operation in response to a current flowing through the first auxiliary winding in response to the first drive signal, the first switching element generating a first boosted voltage at the other end of the secondary winding of the first transformer by the on / off operation; and a first rectifying and smoothing circuit that outputs the belt cleaning voltage by rectifying and smoothing the first boosted voltage.

[0014] As a result, the belt cleaning voltage application circuit is configured as a circuit with a hardware control configuration in which no feedback regarding the output is given to the control unit, so that the number of terminals of the control unit can be further reduced.

[0015] The transfer voltage application circuit is characterized by having a second transformer consisting of a primary winding and a secondary winding, the second transformer having a second auxiliary winding connected to its primary winding; a second reference voltage generation circuit that outputs a second reference voltage corresponding to a second set current value which is a control signal from the control unit; a second voltage generation circuit that generates a second voltage based on the magnitude of a second feedback current flowing through one end of the secondary winding of the second transformer; a second comparison circuit to which the second reference voltage and the second voltage are inputted and that outputs a second drive signal corresponding to the difference between the second reference voltage and the second voltage; a second switching element that performs an on / off operation in response to a current flowing through the second auxiliary winding in response to the second drive signal, the second switching element generating a second boosted voltage at the other end of the secondary winding of the second transformer by the on / off operation; and a second rectifying and smoothing circuit that outputs the transfer voltage by rectifying and smoothing the second boosted voltage.

[0016] As a result, the transfer voltage application circuit is configured as a circuit with a hardware control configuration in which no feedback regarding the output is given to the control unit, so that the number of terminals of the control unit can be further reduced.

[0017] The image forming unit further includes a plurality of photosensitive drums, chargers, developing rollers, and transfer members, and includes a plurality of transfer voltage application circuits that apply transfer voltages to the plurality of transfer members, each of the plurality of transfer voltage application circuits including a second transformer, a second reference voltage generation circuit, a second voltage generation circuit, a second comparison circuit, a second switching element, and a second rectifying and smoothing circuit, and a first transfer voltage application circuit, which is one of the plurality of transfer voltage application circuits, further includes a transfer voltage feedback signal output circuit that outputs a first transfer feedback signal corresponding to the first transfer voltage to a common terminal of the control unit.

[0018] As a result, among the multiple transfer voltage application circuits, only the first transfer voltage application circuit has a transfer voltage feedback signal output circuit, making it possible to reduce the number of terminals in the control unit while more stably controlling the output of the first transfer voltage application circuit.

[0019] The power supply board also has a plurality of voltage application circuits that apply voltages to each component of the image forming unit, and the plurality of voltage application circuits each output an application error judgment signal via a common signal line to judge an error that has occurred in the voltage application circuit in response to an on signal from the control unit, and the feedback signal commonization circuit outputs a first transfer feedback signal from an output terminal when the belt cleaning voltage application circuit does not apply the belt cleaning voltage and the control unit does not output an on signal, outputs an error judgment signal from an output terminal when the belt cleaning voltage application circuit applies the belt cleaning voltage and the control unit does not output an on signal, and outputs an application error judgment signal from an output terminal when the belt cleaning voltage application circuit does not apply the belt cleaning voltage and the control unit outputs an on signal.

[0020] This allows a plurality of application error determination signals to be input to one output terminal in addition to the first transfer feedback signal and the error determination signal, thereby making it possible to further reduce the number of terminals of the control unit. [Brief description of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a color laser printer according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing a control configuration of the color laser printer of FIG. [Diagram 3] 3 is a diagram showing an example of a circuit configuration of a transfer voltage application circuit and a belt cleaning voltage application circuit included in FIG. 2. [Figure 4] 3 is a diagram showing an example of a circuit configuration of a feedback signal common circuit included in FIG. 2; [Diagram 5] 10 is a flowchart showing a procedure of a feedback voltage acquisition process of the belt cleaning voltage application circuit. [Figure 6] 10 is a flowchart showing a procedure of a feedback voltage acquisition process of the transfer voltage application circuit. [Figure 7] FIG. 11 is a diagram showing an example of a circuit configuration of a feedback signal common circuit included in a color laser printer according to a second embodiment of the present application. [Figure 8] 8 is a time chart showing how an error determination is performed using the feedback signal common circuit of FIG. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, embodiments of the present application will be described in detail with reference to the drawings.

[0023] (First embodiment) FIG. 1 shows a cross-sectional view of the schematic configuration of a color laser printer (hereinafter, simply referred to as printer) 1 according to a first embodiment of the present application. Printer 1 is a so-called tandem type laser printer that uses four color toners. In the following explanation, as shown in FIG. 1, the explanation will be based on the direction as seen by a user using printer 1. That is, the right side in FIG. 1 will be referred to as the "front", the left side as the "rear", the upper side as the "upper", the lower side as the "lower", the near side as the "left" and the far side as the "right".

[0024] As shown in FIG. 1, the printer 1 includes a main body housing 2, a supply unit 10, and an image forming unit 20. The main body housing 2 is substantially box-shaped. The main body housing 2 houses the supply unit 10, the image forming unit 20, and the like. An output tray 5 is formed on the top surface of the main body housing 2. The printer 1 outputs the sheets S on which images have been formed in a stacked state onto the output tray 5. A front cover 2a is provided on the front surface of the main body housing 2. The front cover 2a is a cover that opens and closes an opening 2b formed on the front surface of the main body housing 2. The front cover 2a can be rotated forward around a rotation shaft 2c provided at the lower end, for example, and can be rotated from a position where the opening 2b shown in FIG. 1 is closed to a position where the opening 2b is opened (opened).

[0025] The supply unit 10 includes a supply tray 11 in which the sheets S are stored, a pickup roller 12, a separation pad 13, a pressure plate 14, and various rollers including a registration roller 15. The sheets S are, for example, standard sheets such as A4 size, but are not limited to paper media such as plain paper or thick paper, and may be other recording media such as OHP film. The supply tray 11 is detachably attached to the lower part of the main body housing 2. The pressure plate 14 is provided in the supply tray 11. A displacement mechanism (not shown) is provided below the pressure plate 14. Prior to image formation, the displacement mechanism displaces the pressure plate 14 to an inclined state so that the front side is higher. As a result, the sheets S stored in the supply tray 11 are brought toward the pickup roller 12 by the pressure plate 14, separated one by one by the pickup roller 12 and the separation pad 13, and the front ends of the sheets S are aligned by the registration roller 15, and then conveyed to the image forming unit 20 by other rollers. The sheet S conveyed out of the supply tray 11 is conveyed along a conveying path R by the image forming unit 20, a discharge roller 65, etc., and is discharged onto a discharge tray 5.

[0026] The image forming unit 20 is provided in the approximate center of the inside of the main body housing 2, and includes the developing cartridges 30Y, 30M, 30C, and 30K, an exposure unit 40, a transfer unit 50, and a fixing unit 60. The developing cartridges 30Y, 30M, 30C, and 30K accommodate yellow, magenta, cyan, and black toners, respectively. The four developing cartridges 30Y to 30K are provided in this order from the front to the rear of the printer 1. The developing cartridges 30Y to 30K can be removed and replaced by opening the front cover 2a and removing them through the opening 2b of the main body housing 2.

[0027] The developing cartridge 30K includes a photosensitive drum 31, a charger 32, a toner cartridge 33K, a drum cleaning roller 38a, and a drum cleaning shaft 38b (see FIG. 2). The other developing cartridges 30C, 30M, and 30Y have different toner colors, but are otherwise similar in configuration to the developing cartridge 30K. For this reason, the following description will mainly focus on the developing cartridge 30K, and descriptions of the other developing cartridges 30C, 30M, and 30Y will be omitted as appropriate.

[0028] The charger 32 is, for example, a scorotron type charger including a charging wire 32a and a grid portion 32b. The charger 32 uniformly charges the surface of the photoconductor drum 31 to a positive charge before forming an electrostatic latent image on the surface of the photoconductor drum 31 in image formation. The device for charging the photoconductor drum 31 is not limited to a scorotron type charger, but may be another device such as a roller-type charging roller. The polarity for charging the photoconductor drum 31 is not limited to a positive charge, but may be a negative charge.

[0029] The toner cartridge 33K includes a toner storage chamber 33a, an agitator 33e, a supply roller 33b, a developing roller 33f, and a layer thickness regulating blade 33d. The toner storage chamber 33a stores black toner. The agitator 33e agitates the toner stored in the toner storage chamber 33a. The supply roller 33b is provided in the toner storage chamber 33a and rotates by a driving force transmitted from a process motor (not shown) provided in the main body housing 2. The supply roller 33b supplies the toner supplied from the toner storage chamber 33a to the developing roller 33f. The photosensitive drum 31 rotates, for example, in a clockwise direction in FIG. 1. The developing roller 33f is provided diagonally behind and below the supply roller 33b and is in contact with the supply roller 33b. The developing roller 33f is also disposed downstream of the charger 32 in the rotation direction of the photosensitive drum 31. The developing roller 33f also rotates by receiving a driving force from the process motor. A positive voltage is applied to the roller shaft of the developing roller 33f. The toner supplied to the developing roller 33f is carried on the developing roller 33f as the developing roller 33f rotates. The layer thickness regulating blade 33d is provided so as to be in pressure contact with the developing roller 33f from above, and regulates the thickness of the toner adhering to the outer peripheral surface of the developing roller 33f to a constant value. The toner cartridges 33C, 33M, and 33Y of the other colors (cyan, magenta, and yellow) shown in FIG. 1 have the same configuration as the toner cartridge 33K.

[0030] As shown in FIG. 2, a roller voltage DCLNA, which is a high voltage, is applied from a DCLNA voltage application circuit 140a to the drum cleaning roller 38a, whereby the drum cleaning roller 38a collects the toner remaining on the photosensitive drum 31.

[0031] The drum cleaning shaft 38b is made of a conductive metal, and a shaft voltage DCLNB higher than the roller voltage DCLNA is applied from the DCLNB voltage application circuit 140b to remove paper dust from the drum cleaning roller 38a. In other words, the drum cleaning shaft 38b removes paper dust generated inside the main body housing 2 by utilizing the shaft voltage DCLNB.

[0032] Normally, toner is positively charged and paper dust is negatively charged, so that the toner and paper dust are individually removed from the photosensitive drum 31 by utilizing the difference in polarity of the charges. During printing, a negative voltage, for example, a roller voltage DCLNA of -400V, is applied to the drum cleaning roller 38a to collect only the toner from the photosensitive drum 31 onto the drum cleaning roller 38a. Then, during the cleaning operation, a positive voltage, for example, a roller voltage DCLNA of 500V, is applied to the drum cleaning roller 38a, and a shaft voltage DCLNB of 700V is applied to the drum cleaning shaft 38b. At this time, the paper dust is collected by the drum cleaning shaft 38b via the drum cleaning roller 38a. The toner is discharged onto the photosensitive drum 31, and then adheres to the surface of the conveyor belt 53 and is collected by the belt cleaner 16.

[0033] The belt cleaner 16 includes a backup roller 16a, a belt cleaning roller 16b, and a belt cleaning shaft 16c. The backup roller 16a faces the belt cleaning roller 16b across the conveyor belt 53, and the belt cleaning roller 16b and the belt cleaning shaft 16c are in contact with each other.

[0034] When a high-voltage (e.g., about 1000 V) belt cleaning voltage BCLN3 is applied to the backup roller 16a by the BCLN (belt cleaning) voltage application circuit 80, a voltage is also applied to the belt cleaning roller 16b and the belt cleaning shaft 16c via the conveying belt 53, and the toner adhering to the surface of the conveying belt 53 is collected via the belt cleaning roller 16b and the belt cleaning shaft 16c.

[0035] Returning to FIG. 1, the exposure unit 40 is provided at the top inside the main body housing 2, and includes a laser light source, a polygon mirror, a lens, a reflecting mirror, etc. (not shown). A laser beam emitted from the laser light source is deflected by a polygon mirror, etc., and is emitted from the exposure unit 40. The exposure unit 40 exposes the surface of the photoconductor drum 31 by emitting a light beam shown by a dashed line in FIG. 1 to the surface of the photoconductor drum 31. As a result, an electrostatic latent image is formed on the surface of the photoconductor drum 31. The toner carried on the development roller 33f moves to the electrostatic latent image on the photoconductor drum 31 due to the potential difference between the development roller 33f and the electrostatic latent image formed on the photoconductor drum 31, and forms a toner image.

[0036] The transfer unit 50 is disposed at a position above the supply unit 10 and below the development cartridge 30C. The transfer unit 50 transports the sheet S supplied by the supply unit 10 toward the discharge tray 5. The transfer unit 50 includes a drive roller 51, a driven roller 52, a conveyor belt 53, and a plurality of (four in this embodiment) transfer rollers 54. The conveyor belt 53 is, for example, an endless belt formed by shaping a belt in a loop, and is stretched between the drive roller 51 located below the rear end side of the development cartridge 30C and the driven roller 52 located below the front end side of the development cartridge 30K.

[0037] Each of the multiple transfer rollers 54 is disposed at a position facing each photosensitive drum 31 in the up-down direction, with a sheet transport surface 53A, which is the outer circumferential surface of the transport belt 53, sandwiched therebetween, and is in contact with the transport belt 53 from the rear side of the sheet transport surface 53A. A negative transfer voltage is applied to each of the multiple transfer rollers 54 in accordance with the transport timing of the sheet S, thereby transferring the toner image carried on the surface of the photosensitive drum 31 to the sheet S transported along the sheet transport surface 53A.

[0038] The fixing unit 60 is provided downstream in the transport direction from the position of the transfer unit 50. The fixing unit 60 includes a heating roller 61 that heats the sheet S, and a pressure roller 62 that sandwiches the sheet S between the heating roller 61. The image forming unit 20 transports the sheet S, on which the toner image has been transferred, to the fixing unit 60. The fixing unit 60 thermally fixes the toner image transferred to the sheet S to the sheet S by transporting the sheet S between the heating roller 61 and the pressure roller 62. The sheet S on which the image has been printed is discharged to the discharge tray 5 by discharge rollers 65.

[0039] Although the fixing unit 60 has a configuration including the heating roller 61 and the pressure roller 62, the present invention is not limited to this. For example, the fixing unit may have a heater, a nip plate that receives radiant heat from the heater, a heating belt that rotates around the nip plate, and a pressure roller.

[0040] The fixing unit may have a substrate on which a heat generating pattern is formed, a belt that rotates around the substrate, and a pressure roller, and the substrate and the belt are in contact with each other. The fixing unit may have a heating roller, a heater, and a pressure belt.

[0041] Next, the control configuration of the printer 1 will be described with reference to Fig. 2. As shown in Fig. 2, the printer 1 further includes an ASIC 100, a ROM 102, a RAM 103, and a non-volatile memory 104.

[0042] The ASIC 100 includes, for example, a CPU (not shown), and performs overall control over each section of the printer 1. The ASIC 100 is electrically connected to a ROM 102, a RAM 103, a non-volatile memory 104, and a high-voltage power supply board 112.

[0043] The ROM 102 stores various control programs and various settings for controlling the printer 1. The programs for the control processes in Fig. 5 and Fig. 6 are included in the various control programs.

[0044] The RAM 103 is used as a working area from which various control programs are read, and as a storage area for temporarily storing image data included in a job. The ASIC 100 (CPU) controls each part of the printer 1 while storing the processing results in the RAM 103 or non-volatile memory 104 in accordance with the control programs read from the ROM 102 and the signals output from the various sensors.

[0045] The high-voltage power supply board 112 is provided with a charging voltage application circuit 120, a developing voltage application circuit 130, a DCLNA voltage application circuit 140a, a DCLNB voltage application circuit 140b, and a transfer voltage application circuit 70 for each of the colors yellow (Y), magenta (M), cyan (C), and black (K). The transfer voltage application circuit 70 has a slightly different circuit configuration for black (K) and the other colors (described later with reference to FIG. 3), but the other circuits 120, 130, 140a, and 140b are the same for each color, so the circuits 120, 130, 140a, 140b, and 70 for yellow (Y), magenta (M), and cyan (C) are not shown as individual blocks but are collectively represented by blocks showing the colors Y, M, and C.

[0046] The charging voltage application circuit 120 generates a charging voltage CHG and a grid voltage GRID in accordance with a PWM signal from a port PWM1 of the ASIC 100, applies the charging voltage CHG to the charging wire 32a of the charger 32, and applies the grid voltage GRID to the grid portion 32b of the charger 32. The charging voltage application circuit 120 also generates a feedback (FB) signal according to the generated voltage and outputs it to a port AD1 of the ASIC 100. The ASIC 100 reads out the AD value of the applied current from the port AD1, and uses it to control the output of the charging voltage application circuit 120.

[0047] The developing voltage application circuit 130 generates a developing voltage DEV according to a PWM signal from a port PWM2 of the ASIC 100, and applies the developing voltage DEV to the developing roller 33f. The developing voltage application circuit 130 also generates an FB signal according to the generated voltage, and outputs it to a port AD2 of the ASIC 100. The ASIC 100 reads out the AD value of the applied voltage of the port AD2, and uses it for output control of the developing voltage application circuit 130.

[0048] The high-voltage power supply board 112 further includes a BCLN (belt cleaning) voltage application circuit 80 (the detailed circuit configuration of which will be described later with reference to FIG. 3), a Zener diode 82 that maintains the applied voltage to the belt cleaning roller 16b at a constant value (e.g., 300 V), an adnexum removal voltage generation circuit 83 consisting of a Zener diode that maintains the applied voltage to the belt cleaning shaft 16c at a constant value (e.g., 100 V), and an FB (feedback) signal common circuit 90 (the detailed circuit configuration of which will be described later with reference to FIG. 4).

[0049] FIG. 3 shows the circuit configurations of the transfer voltage application circuits 70, 70' and the BCLN voltage application circuit 80. As shown in FIG. 3, the transfer voltage application circuit 70 for black (K) is, for example, a self-excited high voltage generation circuit, and is composed of a high voltage maintenance unit 72, a high voltage generation unit 73, and a transfer voltage FB signal generation circuit 75. The high voltage maintenance unit 72 has a reference voltage generation circuit 71, an operational amplifier IC1, and resistors R1 and R2. The high voltage generation unit 73 has a transistor Tr1, a transformer T1, a diode D1, and a capacitor C1. The transfer voltage application circuit 70 generates a transfer voltage TR to be supplied to the transfer roller 54 corresponding to the developing cartridge 30K. The transfer voltage TR is a negative high voltage (for example, 0 to -6500V).

[0050] The reference voltage generating circuit 71 generates a reference voltage Vth in accordance with a PWM signal from the port PWM4 of the ASIC 100, and supplies the reference voltage Vth to the non-inverting input of the operational amplifier IC1. On the other hand, the inverting input of the operational amplifier IC1 receives a voltage Vd=R2×I1 generated across the resistor R2 when a feedback current I1 fed back from one end of the secondary winding of the transformer T1 flows to the ground through resistors R1 and R2.

[0051] Moreover, one end of the primary winding of the transformer T1 is connected to a low-voltage power supply (e.g., 24V), and the other end of the primary winding is connected to the collector of the transistor Tr1. A drive signal Sd1 is supplied to the base of the transistor Tr1, and the drive signal Sd1 controls the base current of the transistor Tr1 to generate a secondary voltage of the transformer T1, that is, a transfer voltage TR. At that time, the operational amplifier IC1 operates to eliminate the difference between the reference voltage Vth and the voltage Vd, and this operation maintains the current I1 flowing through the resistors R1 and R2 at a predetermined value. That is, the transfer current caused by the application of the transfer voltage TR to the transfer roller 54 is maintained at a predetermined value. Here, the predetermined value is a current value used by the ASIC 100 to determine the duty ratio of the PWM signal output from the port PWM4.

[0052] The diode D1 and the capacitor C1 rectify and smooth the secondary voltage of the transformer T1 to generate a transfer voltage TR, which is a DC voltage.

[0053] The other end of the transformer T1 is connected to the collector of the transistor Tr1 as described above, and is also connected to the input side of the transfer voltage FB signal generation circuit 75. The transfer voltage FB signal generation circuit 75 has, for example, a smoothing circuit and a resistor (neither shown), and outputs a signal corresponding to the voltage generated in the primary winding of the transformer T1 as a transfer voltage FB signal to the FB signal common circuit 90. The output of the attachment removal voltage generation circuit 83 is also input to the FB signal common circuit 90.

[0054] In this manner, in this embodiment, the transfer voltage application circuit 70 is subjected to constant current control, but is not limited to this, and the transfer voltage application circuit 70 may be subjected to constant voltage control.

[0055] The transfer voltage application circuits 70' for the colors yellow (Y), magenta (M), and cyan (C) differ from the transfer voltage application circuit 70 for black (K) only in that the transfer voltage FB signal generation circuit 75 is omitted. In other words, the transfer voltage application circuit 70' is a circuit with a hardware control configuration in which no feedback regarding output is given to the ASIC 100. Further explanation of the transfer voltage application circuit 70' will be omitted.

[0056] The BCLN voltage application circuit 80 is configured by partially modifying the circuit configuration of the transfer voltage application circuit 70'. In the BCLN voltage application circuit 80, elements that perform the same functions as those in the transfer voltage application circuit 70' are given the same reference numerals, and the description of those elements is omitted as appropriate. The BCLN voltage application circuit 80 generates a positive high-voltage belt cleaning voltage BCLN3 because the direction of the diode D2 is opposite to that of the transfer voltage application circuit 70'. A power supply voltage of 3.3V is connected to one end of the secondary winding of the transformer T1 via a resistor R6. Therefore, the current I2 flows in the direction of the arrow, so that the voltage Vd = 3.3 - I2 x R6. At that time, the operational amplifier IC6 operates to eliminate the difference between the reference voltage Vth and the voltage Vd, and the current I2 flowing through the resistor R6 is maintained at a predetermined value, that is, the current value used by the ASIC 100 to determine the duty ratio of the PWM signal output from the port PWM6.

[0057] Fig. 4 shows a circuit configuration of the FB signal common circuit 90. As shown in Fig. 4, the FB signal common circuit 90 is composed of a PNP transistor Tr11, an NPN transistor Tr12, resistors R11 to R14, and a capacitor C11.

[0058] The emitter of transistor Tr11 is connected to a power supply voltage of 1.8V and is also connected to the base via resistor R11. The collector of transistor Tr11 is connected to the output terminal OUT. The base of transistor Tr11 is also connected to the collector of transistor Tr12 via resistor R12.

[0059] The emitter of the transistor Tr12 is grounded and is connected to the base via a resistor R13. The base of the transistor Tr12 is connected to the adduct removal voltage generating circuit 83 via a resistor R14 and is grounded via a capacitor C11.

[0060] Furthermore, the transfer voltage FB signal generating circuit 75 is connected to the output terminal OUT, and the output terminal OUT is connected to the port AD 4 of the ASIC 100 .

[0061] As described above, the attachment removal voltage generating circuit 83 outputs the voltage BCLN2 (=100V) when the belt cleaning voltage BCLN3 is applied to the backup roller 16a of the belt cleaner 16, and does not output the voltage BCLN2 when the belt cleaning voltage BCLN3 is not applied to the backup roller 16a. That is, the attachment removal voltage generating circuit 83 outputs either 100V or 0V. When the attachment removal voltage generating circuit 83 outputs 100V, the transistor Tr12 is turned on, so that the transistor Tr11 is also turned on, and the power supply voltage of 1.8V is applied to the output terminal OUT of the FB signal common circuit 90. Therefore, at this time, the power supply voltage of 1.8V is also applied to the port AD4, so that if the AD converter mounted on the ASIC 100 can AD convert voltage values ​​in the range of, for example, 0 to 1.8V with a resolution of 0 to 1023, the ASIC 100 will read out 1023 or a value close to it as the AD value.

[0062] Conversely, when the adnexal removal voltage generating circuit 83 outputs 0V, the transistor Tr12 is turned off, so that the transistor Tr11 is also turned off and the transistor Tr11 is in a high impedance state. Therefore, at this time, 0V is applied to the output terminal OUT of the FB signal common circuit 90, so that 0V is also applied to the port AD4, and the ASIC 100 reads out 0 or a value close to 0 as the AD value. However, at this time, when the transfer voltage FB signal generating circuit 75 is operating and outputting a valid signal, the output voltage of the transfer voltage FB signal generating circuit 75 is applied directly to the output terminal OUT of the FB signal common circuit 90 without being influenced by other circuits, so that the ASIC 100 can detect the value of the transfer voltage FB signal from the transfer voltage FB signal generating circuit 75 by reading out the AD value of the applied voltage at the port AD4.

[0063] As described above, the output of the attachment removal voltage generating circuit 83 varies uniquely depending on whether the belt cleaning voltage BCLN3 is applied to the backup roller 16a of the belt cleaner 16. Therefore, when the attachment removal voltage generating circuit 83 outputs 0V even though the belt cleaning voltage BCLN3 is applied to the backup roller 16a of the belt cleaner 16, that is, when the ASIC 100 reads 0 or a value close to it as the AD value of the voltage applied to the port AD4, the ASIC 100 can determine that an error such as a failure has occurred in the belt cleaner 16. Conversely, when the belt cleaning voltage BCLN3 is applied to the backup roller 16a of the belt cleaner 16, the ASIC 100 can determine that the belt cleaner 16 is normal if the ASIC 100 reads 1023 or a value close to it as the AD value of the voltage applied to the port AD4.

[0064] It is preferable that the time when the output voltage of the attachment removal voltage generating circuit 83, that is, the FB signal of the belt cleaning voltage BCLN3 applied to the belt cleaner 16, is acquired does not overlap with the time when the FB signal of the transfer voltage TR is acquired. However, even if an FB signal exceeding 0V is output from the transfer voltage FB signal generating circuit 75 when the FB signal of the belt cleaning voltage BCLN3 applied to the belt cleaner 16 is acquired, if the attachment removal voltage generating circuit 83 outputs 100V, the power supply voltage of 1.8V will be applied to the output terminal OUT, and if the attachment removal voltage generating circuit 83 outputs 0V, a voltage value lower than the power supply voltage of 1.8V will be applied to the output terminal OUT. Therefore, the ASIC 100 can perform an error determination of the belt cleaner 16.

[0065] The control process executed by the printer 1 configured as above will be described in detail with reference to FIGS.

[0066] 5 shows the procedure of the belt cleaning voltage FB signal acquisition process executed by the ASIC 100 (the CPU of the ASIC 100). This process is started when it is desired to acquire the belt cleaning voltage FB signal. In the following explanation of each process, steps are represented as "S".

[0067] 5, first, the ASIC 100 outputs a signal with a duty ratio of 0 from the port PWM6 of the ASIC 100 (S10). As a result, the BCLN voltage application circuit 80 sets the voltage BCLN3 to 0V and stops generating the application voltage.

[0068] Next, the ASIC 100 outputs a signal with a predetermined duty ratio from the port PWM6 (S12). The signal with a predetermined duty ratio is a signal that indicates the value of a current to be passed through the BCLN voltage application circuit 80, and by passing this current value through the BCLN voltage application circuit 80, the BCLN voltage application circuit 80 can output a voltage value of about 1000V.

[0069] Then, the ASIC 100 waits for a predetermined time (for example, 20 msec) until the applied voltage of the BCLN voltage application circuit 80 becomes stable (S14), and then reads the applied voltage of the port AD4 (S16). At this time, the output voltage of the attachment removal voltage generation circuit 83 is applied to the port AD4, so the ASIC 100 can obtain the AD value of the output voltage of the attachment removal voltage generation circuit 83. When the belt cleaner 16 is operating normally, the attachment removal voltage generation circuit 83 outputs 100V as described above, so that both of the transistors Tr11 and Tr12 of the FB signal common circuit 90 are turned on, and the power supply voltage of 1.8V is applied to the port AD4. In this case, the ASIC 100 reads 1023 or a value close to it as the AD value. On the other hand, when the belt cleaner 16 is not operating normally due to a malfunction or the like, the attachment removal voltage generation circuit 83 outputs 0V as described above, so in this case, the ASIC 100 reads 0 or a value close to it as the AD value. Therefore, the ASIC 100 can use the AD value acquired from the port AD4 to judge an error in the belt cleaner 16.

[0070] Next, the ASIC 100 outputs a signal with a duty ratio of 0 from the port PWM6 (S18) in the same manner as in S10, and then ends the FB signal acquisition process for the belt cleaning voltage. This causes the BCLN voltage application circuit 80 to stop generating the application voltage.

[0071] 6 shows the procedure for acquiring the FB signal of the transfer voltage. This process is started when it is desired to acquire the FB signal of the transfer voltage.

[0072] 6, first, the ASIC 100 outputs a signal with a duty ratio of 0 from the port PWM6 (S20) in the same manner as in S10, which causes the BCLN voltage application circuit 80 to stop generating the application voltage.

[0073] Next, ASIC100 outputs a signal of a specified duty ratio from port PWM4 (S22). The signal of the specified duty ratio is a signal that indicates the value of a current to be passed to the transfer voltage application circuit 70. As described above, the transfer voltage application circuit 70 is capable of outputting a voltage in the range of 0 to -6500V. ASIC100 varies the value of the current to be passed to the transfer voltage application circuit 70 by specifying the duty ratio of the signal to be output from port PWM4 within the range of 0 to 100%, thereby varying the output voltage of the transfer voltage application circuit 70 within the range of 0 to -6500V.

[0074] Then, the ASIC 100 waits for a predetermined time (for example, 20 msec) until the applied voltage of the transfer voltage application circuit 70 becomes stable (S24), and then reads the applied voltage of the port AD4 (S26). At this time, the output voltage of the adnexal removal voltage generation circuit 83 is 0V, both of the transistors Tr11 and Tr12 are turned off and in a high impedance state, and only the output voltage of the transfer voltage FB signal generation circuit 75 is applied to the port AD4, so that the ASIC 100 can obtain the AD value of the output voltage of the transfer voltage FB signal generation circuit 75. Then, the transfer voltage FB signal generation circuit 75 outputs a transfer voltage FB signal having a voltage value according to the output voltage of the transfer voltage application circuit 70 as described above, so that the ASIC 100 obtains any value within the range of 0 to 1023 as the AD value, and can use the obtained AD value of the transfer voltage FB signal for output control of the transfer voltage application circuit 70.

[0075] Next, the ASIC 100 outputs a signal with a duty ratio of 0 from the port PWM4 (S28), and then ends the FB signal acquisition process for the transfer voltage, causing the transfer voltage application circuit 70 to stop generating the application voltage.

[0076] As described above, the printer 1 of the present embodiment includes the photosensitive drum 31, the charger 32 which charges the photosensitive drum 31, the developing roller 33f which supplies toner to an electrostatic latent image formed on the charged photosensitive drum 31 to form a toner image on the photosensitive drum 31, the endless conveyor belt 53 which contacts the photosensitive drum 31, the image forming unit 20 which includes the transfer roller 54 which is disposed at a position facing the photosensitive drum 31 with the conveyor belt 53 interposed therebetween, the backup roller 16a, the belt cleaning roller 16b which faces the backup roller 16a with the conveyor belt 53 interposed therebetween, and the belt cleaning shaft 16c which contacts the belt cleaning roller 16b. 53 to a belt cleaning shaft 16c; a high-voltage power supply board 112 that applies voltages to the image forming unit 20 and the belt cleaner 16, the high-voltage power supply board 112 outputting a feedback signal corresponding to the voltage applied to the image forming unit 20 and an FB signal of a belt cleaning voltage for determining an error that has occurred in the belt cleaner 16; and an ASIC 100 to which the feedback signal and the FB signal of the belt cleaning voltage are input from the high-voltage power supply board 112, and the feedback signal and the FB signal of the belt cleaning voltage are input to a common port AD4 of the ASIC 100.

[0077] Since an error that occurs in the belt cleaner 16 is not directly related to image formation in the printer 1, control based on the error determination signal has a lower priority than control based on the feedback signal. Also, an error that occurs in the belt cleaner 16 can be determined even when an image is not being formed. Therefore, the feedback signal and the error determination signal of the belt cleaner 16 can be input to a common port AD4 of the ASIC 100, and the number of terminals of the ASIC 100 can be reduced.

[0078] The high-voltage power supply board 112 further comprises a transfer voltage application circuit 70 which applies a transfer voltage TR to the transfer roller 54 and outputs a transfer voltage FB signal corresponding to the transfer voltage TR, a BCLN voltage application circuit 80 which applies a belt cleaning voltage BCLN3 to the backup roller 16a, and an adnexal removal voltage generation circuit 83 which outputs a belt cleaning voltage FB signal corresponding to the belt cleaning voltage BCLN3, and the transfer voltage FB signal and the belt cleaning voltage FB signal are input to a common port AD4, and the ASIC 100 judges that there is an error when the belt cleaning voltage FB signal has not been input despite the BCLN voltage application circuit 80 being instructed to apply the belt cleaning voltage BCLN3, and judges that there is a normal state when the belt cleaning voltage FB signal is input when the BCLN voltage application circuit 80 is instructed to apply the belt cleaning voltage BCLN3.

[0079] As a result, even when different types of FB signals, that is, a transfer voltage FB signal and a belt cleaning voltage FB signal, are input to the common port AD4, the ASIC 100 can accurately determine whether an error has occurred or is normal.

[0080] Moreover, the high-voltage power supply board 112 further includes an FB signal common circuit 90 to which the transfer voltage application circuit 70 and the adnexal removal voltage generation circuit 83 are electrically connected, and whose output terminal OUT is connected to a common port AD4, and the FB signal common circuit 90 is characterized in that when the BCLN voltage application circuit 80 is not applying the belt cleaning voltage BCLN3, the FB signal common circuit 90 outputs a transfer voltage FB signal from the output terminal OUT, and when the BCLN voltage application circuit 80 is applying the belt cleaning voltage, the FB signal of the belt cleaning voltage is output from the output terminal OUT without outputting the transfer voltage FB signal from the output terminal OUT.

[0081] This allows the FB signal common circuit 90 to output the transfer voltage FB signal and the belt cleaning voltage FB signal from the output terminal OUT without superimposing them.

[0082] The BCLN voltage application circuit 80 includes a first transformer T1 having a primary winding and a secondary winding, the first transformer T1 having a first auxiliary winding connected to the primary winding, a first reference voltage generation circuit 71 that outputs a first reference voltage Vth according to a first set current value that is a control signal from the ASIC 100, a first voltage generation circuit (power supply voltage 3.3V-R6×I2) that generates a first voltage Vd based on the magnitude of a first feedback current I2 that flows through one end of the secondary winding of the first transformer T1, and a first reference voltage Vth and a first voltage Vd. The first transformer T1 has a first comparison circuit IC6 that outputs a first drive signal Sd1 corresponding to the difference between a reference voltage Vth and a first voltage Vd, a first switching element Tr1 that is turned on and off in response to a current flowing through a first auxiliary winding in response to the first drive signal Sd1, the first switching element Tr1 generating a first boosted voltage at the other end of the secondary winding of the first transformer T1 by the on / off operation of the first switching element Tr1, and a first rectifying and smoothing circuit D2 that outputs a belt cleaning voltage BCLN3 by rectifying and smoothing the first boosted voltage.

[0083] As a result, the BCLN voltage application circuit 80 is configured as a circuit with a hardware control configuration in which no feedback regarding the output is given to the ASIC 100, so that the number of terminals of the ASIC 100 can be further reduced.

[0084] The transfer voltage application circuit 70′ includes a second transformer T1 having a primary winding and a secondary winding, the second transformer T1 having a primary winding to which a second auxiliary winding is connected, a second reference voltage generation circuit 71 that outputs a second reference voltage Vth according to a second set current value that is a control signal from the ASIC 100, second voltage generation circuits R1 and R2 that generate a second voltage Vd based on the magnitude of a second feedback current I1 that flows through one end of the secondary winding of the second transformer T1, and a second reference voltage Vth and a second voltage Vd input to the second reference voltage generation circuit 71. the second comparison circuit IC1 that outputs a second drive signal Sd1 corresponding to the difference between a second reference voltage Vth and the second voltage Vd; a second switching element Tr1 that is turned on and off in response to a current flowing through a second auxiliary winding in response to the second drive signal Sd1, the second switching element Tr1 generating a second boost voltage at the other end of the secondary winding of the second transformer T1 by the on / off operation of the second switching element Tr1; and a second rectifying and smoothing circuit D1 that outputs a transfer voltage TR by rectifying and smoothing the second boost voltage.

[0085] As a result, the transfer voltage application circuit 70' is configured as a circuit with a hardware control configuration in which no feedback regarding the output is given to the ASIC 100, so that the number of terminals of the ASIC 100 can be further reduced.

[0086] The image forming unit 20 further includes a plurality of photosensitive drums 31, chargers 32, developing rollers 33f, and transfer rollers 54, and includes a plurality of transfer voltage application circuits 70, 70' which apply a transfer voltage TR to each of the plurality of transfer rollers 54, and each of the plurality of transfer voltage application circuits 70' includes a second transformer T1, a second reference voltage generation circuit 71, a second voltage generation circuit R1, R2, a second comparison circuit IC1, a second switching element Tr1, and a second rectification smoothing circuit D1, and the first transfer voltage application circuit 70, which is one of the plurality of transfer voltage application circuits 70, 70', further includes a transfer voltage FB signal generation circuit 75 which outputs a first transfer voltage FB signal corresponding to the first transfer voltage TR to a common port AD4 of the ASIC 100.

[0087] As a result, among the multiple transfer voltage application circuits 70, 70', only the first transfer voltage application circuit 70 has a transfer voltage FB signal generation circuit 75, which makes it possible to reduce the number of terminals of the ASIC 100 while more stably controlling the output of the first transfer voltage application circuit 70.

[0088] Second embodiment Next, a second embodiment of the present invention will be described. This embodiment differs from the first embodiment only in a part of the circuit configuration of the FB signal common circuit 90, so the description will focus on the different parts and omit the description of the other parts as appropriate. In addition, the hardware of this embodiment uses the hardware shown in Figures 1 to 3 in the first embodiment, including the reference numerals.

[0089] FIG. 7 shows the circuit configuration of the FB signal common circuit 90′ in this embodiment. In FIG. 7, the same elements as those in FIG. 4 are given the same reference numerals, and the description thereof will be omitted as appropriate. As can be seen by comparing FIG. 7 with FIG. 4, the FB signal common circuit 90′ is configured to be able to connect a plurality of (for example, three) generating circuits A to C in parallel with the adornment removal voltage generating circuit 83. Each of the generating circuits A to C outputs either H or L, similar to the adornment removal voltage generating circuit 83. The outputs of the adornment removal voltage generating circuit 83 and the generating circuits A to C are input to the base of the transistor Tr11 via a common signal line CL. Therefore, by differentiating the timing at which the adornment removal voltage generating circuit 83 and the generating circuits A to C are set to H, the timing at which the transistor Tr11 is turned on can be different, so that the adornment removal voltage generating circuit 83 and the generating circuits A to C can be used to perform error determination.

[0090] 8 shows how the FB signal common circuit 90' is used to perform error determination for the belt cleaner 16 and the generating circuits A to C. At this time, the ASIC 100 executes a process similar to the FB signal acquisition process of the BCLN voltage in FIG. 5, and reads out the AD value of the applied voltage of the port AD4.

[0091] 8, even though the generator circuit A is instructed to output H at time T1, 0 V is applied to the port AD4. Therefore, the ASIC 100 determines that an error has occurred in a device that has not instructed the generator circuit A to output H.

[0092] As described above, the high-voltage power supply board 112 has a plurality of generating circuits A to C that respectively apply voltages to each component of the image forming unit 20, and the plurality of generating circuits A to C each output an application error judgment signal via a common signal line CL for judging an error that has occurred in the generating circuits A to C in response to an ON signal from the ASIC 100, and the FB signal common circuit 90' outputs a first transfer feedback signal from an output terminal OUT when the BCLN voltage application circuit 80 does not apply the belt cleaning voltage BCLN3 and the ASIC 100 does not output an ON signal, outputs an FB signal of the belt cleaning voltage from an output terminal OUT when the BCLN voltage application circuit 80 applies the belt cleaning voltage BCLN3 and the ASIC 100 does not output an ON signal, and outputs an application error judgment signal from an output terminal OUT when the BCLN voltage application circuit 80 does not apply the belt cleaning voltage BCLN3 and the ASIC 100 outputs an ON signal.

[0093] This makes it possible to input multiple application error judgment signals to a single output terminal OUT in addition to the first transfer feedback signal and the FB signal for the belt cleaning voltage, thereby further reducing the number of terminals of ASIC 100.

[0094] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0095] (1) In the above embodiments, a color laser printer has been described as an example of an image forming apparatus, but the image forming apparatus is not limited to this and may be a monochrome laser printer. Also, the image forming apparatus is not limited to a printer and may be a multifunction machine or a copier.

[0096] (2) In the above embodiments, the FB signal common circuits 90, 90' are respectively supplied with a signal whose value changes continuously and a signal whose value changes discretely, but they may also be supplied with signals whose values ​​change discretely. In this case, however, it is necessary to ensure that the timings at which the signal values ​​are acquired do not overlap. [Explanation of symbols]

[0097] 1...color laser printer (image forming apparatus), 16...belt cleaner, 16a...backup roller, 16b...belt cleaning roller, 16c...belt cleaning shaft (recovery member), 20...image forming section, 31...photosensitive drum, 33f...developing roller, 53...conveyor belt, 54...transfer roller (transfer member), 70, 70'...transfer voltage application circuit, 75...transfer voltage FB signal generation circuit (transfer voltage feedback signal output circuit), 80...BCLN voltage application circuit (belt cleaning voltage application circuit), 83...addition removal voltage generation circuit (belt feedback signal output circuit), 90, 90'...FB signal common circuit (feedback signal common circuit), 100...ASIC (control section), 102...ROM, 103...RAM, 104...non-volatile memory, 112...high voltage power supply board, AD4...port (terminal).

Claims

1. an image forming section including a photosensitive drum, a charger for charging the photosensitive drum, a developing roller for supplying toner to an electrostatic latent image formed on the charged photosensitive drum to form a toner image on the photosensitive drum, an endless belt in contact with the photosensitive drum, and a transfer member disposed at a position facing the photosensitive drum with the belt interposed therebetween; a belt cleaner including a backup roller, a cleaning roller facing the backup roller with the belt therebetween, and a recovery member contacting the cleaning roller, and recovering residual toner remaining on the belt into the recovery member; a power supply board which applies voltages to the image forming unit and the belt cleaner, and which outputs a feedback signal corresponding to the voltage applied to the image forming unit and an error determination signal for determining an error occurring in the belt cleaner; a control unit to which the feedback signal and the error determination signal are input from the power supply board, The feedback signal and the error determination signal are input to a common terminal of the control unit.

1. An image forming apparatus comprising:

2. The power supply board includes: a transfer voltage application circuit that applies a transfer voltage to the transfer member and outputs a transfer feedback signal corresponding to the transfer voltage; a belt cleaning voltage application circuit that applies a belt cleaning voltage to the backup roller; a belt feedback signal output circuit that outputs an error determination signal in response to the belt cleaning voltage, the transfer feedback signal and the error determination signal are input to the common terminal; The control unit is determining that an error has occurred when the error determination signal has not been input despite the application of the belt cleaning voltage to the belt cleaning voltage application circuit being instructed; determining that the belt cleaning voltage application circuit is normal if the error determination signal is input when the belt cleaning voltage application circuit is instructed to apply the belt cleaning voltage; 2. The image forming apparatus according to claim 1,

3. The power supply board further comprises: a feedback signal common circuit, the transfer voltage application circuit and the belt feedback signal output circuit being electrically connected to each other and the output terminal of the feedback signal common circuit being connected to the common terminal; The feedback signal common circuit includes: When the belt cleaning voltage application circuit is not applying the belt cleaning voltage, the transfer feedback signal is output from the output terminal; when the belt cleaning voltage application circuit applies the belt cleaning voltage, the error determination signal is output from the output terminal without outputting the transfer feedback signal from the output terminal.

3. The image forming apparatus according to claim 2,

4. The belt cleaning voltage application circuit includes: a first transformer including a primary winding and a secondary winding, the first transformer having a first auxiliary winding connected to the primary winding; a first reference voltage generating circuit that outputs a first reference voltage corresponding to a first set current value that is a control signal from the control unit; a first voltage generating circuit that generates a first voltage based on a magnitude of a first feedback current flowing through one end of a secondary winding of the first transformer; a first comparison circuit that receives the first reference voltage and the first voltage and outputs a first drive signal according to a difference between the first reference voltage and the first voltage; a first switching element that is turned on and off in response to a current flowing through the first auxiliary winding in response to the first drive signal, the first switching element generating a first boost voltage at the other end of the secondary winding of the first transformer by the on and off operation; a first rectifying and smoothing circuit that rectifies and smoothes the first boosted voltage to output the belt cleaning voltage; having 3. The image forming apparatus according to claim 2,

5. The transfer voltage application circuit includes: a second transformer including a primary winding and a secondary winding, the second transformer having a second auxiliary winding connected to the primary winding of the second transformer; a second reference voltage generating circuit that outputs a second reference voltage corresponding to a second set current value that is a control signal from the control unit; a second voltage generating circuit that generates a second voltage based on a magnitude of a second feedback current flowing through one end of a secondary winding of the second transformer; a second comparison circuit that receives the second reference voltage and the second voltage and outputs a second drive signal according to a difference between the second reference voltage and the second voltage; a second switching element that is turned on and off in response to a current flowing through the second auxiliary winding in response to the second drive signal, the second switching element generating a second boost voltage at the other end of the secondary winding of the second transformer by the on and off operation; a second rectifying and smoothing circuit that rectifies and smoothes the second boosted voltage to output the transfer voltage; having 3. The image forming apparatus according to claim 2,

6. the image forming unit includes a plurality of the photosensitive drums, the chargers, the developing rollers, and the transfer members, a plurality of transfer voltage application circuits that apply the transfer voltage to the plurality of transfer members, respectively; each of the plurality of transfer voltage application circuits includes the second transformer, the second reference voltage generation circuit, the second voltage generation circuit, the second comparison circuit, the second switching element, and the second rectification smoothing circuit; a first transfer voltage application circuit which is one of the plurality of transfer voltage application circuits, further includes a transfer voltage feedback signal output circuit which outputs a first transfer feedback signal corresponding to a first transfer voltage applied by the first transfer voltage application circuit to the common terminal of the control unit; 6. The image forming apparatus according to claim 5,

7. The power supply board further comprises: a feedback signal common circuit, the transfer voltage application circuit and the belt feedback signal output circuit being electrically connected to each other and the output terminal of the feedback signal common circuit being connected to the common terminal; The feedback signal common circuit includes: When the belt cleaning voltage application circuit is not applying the belt cleaning voltage, the first transfer feedback signal is output from the output terminal; when the belt cleaning voltage application circuit applies the belt cleaning voltage, the error determination signal is output from the output terminal without outputting the transfer feedback signal from the output terminal.

7. The image forming apparatus according to claim 6,

8. The power supply board includes: a plurality of voltage application circuits that apply voltages to the respective components of the image forming unit, the plurality of voltage application circuits outputting, via a common signal line, an application error determination signal for determining an error that has occurred in the voltage application circuit in response to an ON signal from the control unit; The feedback signal common circuit includes: when the belt cleaning voltage application circuit does not apply the belt cleaning voltage and the control unit does not output the ON signal, the first transfer feedback signal is output from the output terminal; when the belt cleaning voltage application circuit applies the belt cleaning voltage and the control unit does not output the ON signal, outputting the error determination signal from the output terminal; when the belt cleaning voltage application circuit does not apply the belt cleaning voltage and the control unit outputs the ON signal, the application error determination signal is output from the output terminal.

8. The image forming apparatus according to claim 7,

9. The feedback signal common circuit includes: a first transistor of a PNP type having a first emitter connected to a predetermined power supply voltage, a first collector connected to the output terminal, and a first base; a second NPN transistor having a second collector connected to the first base of the first transistor, a second emitter grounded, and a second base to which the error determination signal is input, When the error determination signal is not input, the first transistor is turned off and has a high impedance, and the transfer feedback signal is output from the output terminal. When the error determination signal is input, the first transistor is turned on and outputs the predetermined power supply voltage value from the output terminal.

4. The image forming apparatus according to claim 3.

Images