Image forming device

Abstract

To prevent, with an inexpensive circuit configuration, an image defect caused by a contact part between members related to developing processing.SOLUTION: An image forming apparatus comprises: a photoconductor drum 131; a developing roller 133a; a developing blade 135a; an electrifying circuit 132b that generates an electrifying voltage Vpri; a developing circuit 133b that generates a developing voltage Vdev; a blade circuit 135b that applies the blade voltage Vbld to the developing blade 135a; and a control unit 200 that, when a potential difference between the developing voltage Vdev and the blade voltage Vbld is defined as a first potential difference and a potential difference larger than the first potential difference as a second potential difference, controls such that the first potential difference is formed in a separation state and the second potential difference is formed in a contact state. The control unit 200 performs control to increase an absolute value of the developing voltage Vdev in the contact state compared with the absolute value of the developing voltage Vdev in the separation state.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, for example, an image forming apparatus that uses an electrophotographic method. [Background technology]

[0002] Conventionally, configurations have been proposed that generate multiple voltages from a single high-voltage circuit, thereby reducing costs. For example, in Patent Document 1, a charging voltage is generated by a transformer, and the charging voltage is divided by a resistor and a switching element to generate a developing voltage. Here, the charging voltage is applied to a charging roller, and the developing voltage is applied to a developing roller. Also, in Patent Document 2, for example, a blade voltage is generated by a transformer, and the blade voltage is divided by a Zener diode and a resistor to generate a developing voltage. Here, the blade voltage is applied to a developing blade. The developing blade is a blade that comes into sliding contact with the developing roller to uniformly distribute the toner on the surface of the developing roller.

[0003] Furthermore, if a potential difference continues to occur between the developing roller and the developing blade for a long period of time while the developing roller is stopped from rotating when the components that contribute to the development process (hereinafter referred to as the "development system") are separated from the photosensitive member, the following problem occurs: That is, it is known that the contact area between the developing roller surface and the developing blade becomes different from the rest, resulting in image defects such as streaks. For this reason, it is conceivable to stop supplying voltage to the components of the development system when they are separated from the photosensitive member. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-238490 [Patent Document 2] Japanese Patent Application Publication No. 2018-013720 Summary of the Invention [Problem to be solved by the invention]

[0005] However, generating multiple voltages from a single high-voltage circuit through voltage division control poses the following problem. If one high-voltage circuit outputs a voltage and controls the voltages connected to lower stages to not output that voltage, the load on the transformer that generates the high voltage becomes excessive for normal electrophotographic processes. This means that the transformer is required to have excessive capacity, which leads to higher transformer costs and larger size. For this reason, there is a need for an inexpensive circuit configuration that can suppress image defects caused by contact points between components involved in the development process.

[0006] The present invention has been made under these circumstances, and has as its object to suppress image defects caused by contact portions between members involved in development processing using an inexpensive circuit configuration. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention has the following configuration. (1) A developing device including: a photosensitive member; a developing member that can be in a contact state in contact with the photosensitive member or in a separated state from the photosensitive member, and that develops an electrostatic latent image formed on the photosensitive member with toner in the contact state to form a toner image; a first contact member that is in contact with the developing member in the contact state and the separated state; a first power source having a transformer and that generates a first voltage; a second power source that generates a second voltage from the first voltage to be applied to the developing member; and a third voltage that is generated from the second voltage generated by the second power source and that generates the third voltage. an image forming apparatus comprising: a third power source that applies a voltage to the first contact member; and a control means that, when a potential difference between the second voltage and the third voltage is defined as a first potential difference and a potential difference greater than the first potential difference is defined as a second potential difference, controls so that the first potential difference is formed in the separated state and so that the second potential difference is formed in the contact state, wherein the control means controls so that the absolute value of the second voltage in the separated state is greater than the absolute value of the second voltage in the contact state. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress image defects caused by contact portions between members involved in development processing with an inexpensive circuit configuration. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic cross-sectional view of the image forming apparatus according to the first and second embodiments. [Figure 2] Circuit diagram of the imaging unit of the first embodiment [Figure 3] FIG. 1 is a diagram showing the relationship between the set value (pulse signal) of each circuit and the output voltage in the first embodiment; and FIG. 2 is a diagram showing the relationship between the potential of the photosensitive drum surface or the charging current and the charging voltage. [Figure 4] Flowchart showing voltage control in the first embodiment [Figure 5] Circuit diagram of the imaging unit of the second embodiment [Figure 6] Flowchart showing voltage control in the second embodiment DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, the voltage output from one high-voltage circuit having a transformer and connected to an AC voltage will be referred to as the "main voltage." Connecting to a lower level than the main voltage is said to be subordinate. [Example]

[0011] (Configuration of image forming device) FIG. 1 shows a schematic cross-sectional view of an image forming apparatus 101. The paper feed unit 102 has a paper feed tray 121 and a paper feed roller 122. The paper feed tray 121 stores paper P to be printed. The image forming unit 103 has a photosensitive drum 131, a charging roller 132a, a developing roller 133a, a toner supply roller 134a, a second contact member (supply roller), and a developing blade 135a, a first contact member (blade). The image forming unit 103 also has a toner container 136, a laser scanner 137, and the like. The charging circuit 132b, which is a first power source, applies a generated high voltage to the charging roller 132a. The developing circuit 133b, which is a second power source, applies a generated high voltage to the developing roller 133a. The toner supply R circuit 134b, which is a fourth power source, applies a generated high voltage to the toner supply roller 134a. The blade circuit 135b, which is a third power source, applies the generated high voltage to the developing blade 135a. The developing roller 133a, the toner supply roller 134a, and the developing blade 135a are also referred to as developing components.

[0012] The transfer unit 104 has a transfer roller 141a, which is a transfer member. A positive transfer circuit 141b and a negative transfer circuit 141c, which is connected in series with the positive transfer circuit 141b, apply a generated high voltage to the transfer roller 141a. The negative transfer circuit 141c may be connected in parallel with the positive transfer circuit 141b, and its connection to the transfer roller 141a may be switched by a switching means such as a switch, or the negative transfer circuit 141c itself may be eliminated. The transfer roller 141a is in opposing contact with the photosensitive drum 131. The fixing unit 105 has a fixing roller 151 and a pressure roller 152. The discharge unit 106 includes discharge rollers 161a and 161b and a discharge tray 162.

[0013] The control unit 200, which serves as a control means, has a CPU 200a, a ROM 200b, and a RAM 200c. The CPU 200a controls the image forming operation by the image creating unit 103, the fixing operation by the fixing unit 105, the conveyance operation of the paper P, and the like, in accordance with various programs stored in the ROM 200b and using the RAM 200c as a work area. The control unit 200 also controls the contact and separation operation of the developing roller 133a, which will be described later, and each circuit, which is a power source that applies each voltage, which will be described later. Note that a control unit that controls the image creating unit 103, the fixing unit 105, and each power source may be provided separately from the control unit 200, and the control unit 200 may control the separately provided control unit.

[0014] (Operation of image forming device) The operation of the image forming unit 103 to form a toner image on the surface of the photosensitive drum 131 will be described. The charging roller 132a, to which a negative high voltage is applied from the charging circuit 132b, charges the surface of the photosensitive drum 131. The charging process in the first embodiment employs, for example, a roller charging method. The charging roller 132a and the photosensitive drum 131 face each other with a small gap (GAP), and the charging roller 132a charges the surface of the photosensitive drum 131 by utilizing discharge in the gap. The laser scanner 137 irradiates the photosensitive drum 131 with laser light in accordance with image data, forming a latent image on the surface of the photosensitive drum 131. The toner contained (stored) in the toner container 136 is charged, for example, negatively by stirring.

[0015] The toner supply roller 134a supplies toner stored in a toner container 136 to the developing roller 133a. The toner supply roller 134a, to which a negative high voltage is applied from the toner supply R circuit 134b, moves the toner to the surface of the developing roller 133a and adheres to the surface. The developing blade 135a evens out the toner supplied to the developing roller 133a by the toner supply roller 134a. Because the toner adhering to the surface of the developing roller 133a varies in height depending on the location, the developing blade 135a, to which a negative high voltage is applied from the blade circuit 135b, evens out the toner. The developing roller 133a, with the toner adhering to its surface, uses the negative high voltage applied from the developing circuit 133b to move the toner to the surface of the photosensitive drum 131, thereby developing an electrostatic latent image. Here, the absolute value of the output voltage of the toner supply R circuit 134b is set to be greater than the output voltage of the developing circuit 133b, making it easier for the negatively charged toner to move to the developing roller 133a. Furthermore, the output voltage of the blade circuit 135b is set to be greater in absolute value than the output voltage of the development circuit 133b, thereby making it difficult for negatively charged toner to adhere to the development blade 135a. For example, the output voltage of the development circuit 133b is set to -300V, and the output voltages of the toner supply R circuit 134b and the blade circuit 135b are set to -500V.

[0016] Next, the operation of forming an image on paper P will be described. When image forming apparatus 101 receives a print job, each roller and laser scanner 137 start operating. Paper P stored in paper feed tray 121 is fed by paper feed roller 122, transported along transport path 111, and eventually reaches a position where photosensitive drum 131 and transfer roller 141a face each other. Paper P is nipped (hereinafter referred to as nip) between photosensitive drum 131 and transfer roller 141a to which a positive high voltage is applied from positive transfer circuit 141b, and at this time, the toner image formed on the surface of photosensitive drum 131 is transferred to paper P. Continuing transport, paper P then reaches fixing unit 105, where it is pressure-nipped by fixing roller 151 and pressure roller 152, and the unfixed toner image on paper P is fixed. Paper P is then discharged via discharge rollers 161a and 161b to discharge tray 162. The process of forming an image on paper P described above will be referred to as the image forming process hereinafter. In addition, a process other than the image forming process that is performed outside the image forming process will be referred to as a special process hereinafter.

[0017] (Developer separation mechanism) Next, a configuration for separating the developing roller 133a from the photosensitive drum 131 will be described. The developing roller 133a rotates while sliding against the photosensitive drum 131, the toner supply roller 134a, and the developing blade 135a, and therefore its surface wears and deteriorates with use. Considering the product life of the image forming apparatus 101, the sliding time should be kept to a necessary minimum. The image forming apparatus 101 of the first embodiment is equipped with a developing separation mechanism (see FIG. 2) that is a contact / separation means that can separate the developing roller 133a from the photosensitive drum 131. The developing roller 133a can be in a contact state in which it is in contact with the photosensitive drum 131 or in a separated state in which it is separated from the photosensitive drum 131. In the contact state, the developing roller 133a develops an electrostatic latent image formed on the photosensitive drum 131 (on the photosensitive member) with toner to form a toner image.

[0018] The developer separation mechanism switches the developing roller 133a between a separated state in which it is separated from the photosensitive drum 131 and a contact state in which it is in contact with the photosensitive drum 131 by moving a portion including the developing roller 133a, the toner supply roller 134a, the developing blade 135a, and the toner container 136. That is, the developing blade 135a is in contact with the developing roller 133a in both the contact state and the separated state, and the toner supply roller 134a is also in contact with the developing roller 133a in both the contact state and the separated state. In FIG. 1, the separated state of the developing roller 133a is shown by a dashed line 133a' as a representative example.

[0019] The image forming apparatus 101 has a developer separation mechanism, which is a contact / separation unit that switches the developing roller 133a between a contact state and a separated state. In the first embodiment, the contact / separation mechanism includes a clutch drive circuit 250, a developer separation clutch 252, a developer separation gear 254, and a drive motor 256 (see FIG. 2). The control unit 200 controls the contact / separation mechanism. The developer separation clutch 252 is driven via the clutch drive circuit 250. The developer separation clutch 252 can switch between a state in which drive is transmitted from the drive motor 256 to the developer separation gear 254 (hereinafter referred to as a transmission state) and a state in which drive from the drive motor 256 to the developer separation gear 254 is interrupted (hereinafter referred to as a disconnection state). The control unit 200 controls the drive motor 256 using a drive circuit (not shown), a rotation detection unit (not shown) such as an encoder, and the like. The control unit 200 controls the developer separation clutch 252 via the clutch drive circuit 250. In the transmitted state, the developing roller 133a is separated from the photosensitive drum 131, and in the disconnected state, the developing roller 133a is brought into contact with the photosensitive drum 131. The control unit 200 can switch the developing roller 133a between the contact state and the separated state at a predetermined timing. An electromagnetic clutch can be used as the developing separation clutch 252. Alternatively, a partially toothed gear and a solenoid can be used as the developing separation clutch 252 to switch between the transmitted state (contact state) and the disconnected state. As described above, in the first embodiment, when the developing roller 133a is brought into contact with or separated from the photosensitive drum 131, the toner supply roller 134a, the developing blade 135a, and the toner container 136 also move in conjunction with the developing roller 133a.

[0020] The developer separation mechanism also has the function of disengaging (releasing) the rotation drive gear (not shown) of the developing roller 133a during separation, and the developing roller 133a and toner supply roller 134a stop rotating in the separated state. The image forming apparatus 101 controls the developer separation mechanism to the separated state when no image formation operation is being performed (hereinafter referred to as non-image formation time). This eliminates sliding between the developing roller 133a and the photosensitive drum 131, the toner supply roller 134a, and the developing blade 135a, thereby improving durability.

[0021] (Configuration and operation of high voltage generation circuit) The configurations and operations of the charging circuit 132b, the developing circuit 133b, the toner supply R circuit 134b, and the blade circuit 135b in the image forming unit 103 will be described with reference to FIG.

[0022] (Charging circuit) The transformer T11 has a primary winding T11-1 and a secondary winding T11-2. One terminal of the primary winding T11-1 is connected to a power supply voltage V1, and the other terminal is connected to a field effect transistor (hereinafter referred to as FET) T11. The black circles on the primary winding T11-1 and secondary winding T11-2 indicate the start of the coil winding (in other words, the polarity). A resistor R12 is connected between the gate terminal of the FET T11 and its source terminal, and a resistor R17 is connected between the gate terminal and the CLK terminal of the control unit 200. Between one terminal and the other terminal of the primary winding T11-1 (hereinafter referred to as between both terminals), a parallel circuit in which a capacitor C11 and a resistor R11 are connected in parallel, and a diode D11 are connected in series. The diode D11 has a cathode terminal connected to a parallel circuit of the capacitor C11 and the resistor R11, and an anode terminal connected to the other terminal of the primary winding T11-1 and the drain terminal of the FET11.

[0023] Meanwhile, a diode D12 and a capacitor C12 are connected between both terminals of the secondary winding T11-2. The cathode terminal of the diode D12 is connected to one terminal of the secondary winding T11-2 of the transformer T11, and the anode terminal is connected to one terminal of the capacitor C12. The other terminal of the capacitor C12 is connected to a charging current detection circuit PRI_ISNS, which serves as detection means. The power supply voltage V1 in the first embodiment is, for example, 24 V.

[0024] The control unit 200 outputs a high-level or low-level signal from the CLK terminal. When a high-level signal is output from the CLK terminal, the FET 11 turns on, and the drain voltage of the FET 11 drops to approximately the same potential as ground (hereinafter referred to as GND). As a result, a voltage is applied across the primary winding T11-1 of the transformer T11, causing an excitation current to flow. In this state, when the voltage output from the CLK terminal changes to a low-level state, the FET 11 turns off, and a flyback voltage is generated across the primary winding T11-1. At the same time, a flyback voltage is generated in the secondary winding T11-2 according to the turns ratio between the primary winding T11-1 and the secondary winding T11-2. The generated flyback voltage is rectified and smoothed by the diode D12 and the capacitor C12, generating a charging voltage Vpri, which is a negative first voltage. The capacitor C11, resistor R11, and diode D11 function as a snubber circuit that absorbs surge voltages due to the leakage inductance of the primary winding T11-1.

[0025] The voltage output from the CLK terminal of the control unit 200 is a square wave in which high-level and low-level states alternate. In the first embodiment, a fixed square wave with a frequency of 50 kHz and a duty of 10% is output. Here, the 10% duty refers to the proportion of high-level time in one signal period (the sum of high-level time and low-level time), but it may also refer to the proportion of low-level time. The frequency and duty of the square wave should be designed to optimal values ​​for each circuit and are not limited to the values ​​in the first embodiment. Furthermore, the frequency and duty of the square wave do not need to be fixed values ​​and may be variable depending on the voltage and load of the controlled object. When the FET 11 is turned on and off, the flyback voltage generated in the secondary winding T11-2 is rectified and smoothed by the diode D12 and capacitor C12, generating the charging voltage Vpri.

[0026] The charging circuit 132b performs feedback control of the charging voltage Vpri to stabilize and maintain the charging voltage Vpri at a predetermined voltage. The charging voltage Vpri is connected to a power supply voltage V2 via resistors R14 and R13. The connection point between the resistors R14 and R13 is connected to the positive input terminal (non-inverting input terminal, + terminal) of a comparator IC11. The negative input terminal (inverting input terminal, - terminal) of the comparator IC11 is connected to the power supply voltage V2 via resistors R16 and R15, and further to GND via a capacitor C16. The connection point between the resistors R15 and R16 is connected to the PRI_CONT terminal of the control unit 200. The output terminal of the comparator IC11 is connected to the gate terminal of the FET11. A first pulse signal (hereinafter simply referred to as a pulse signal) that alternately repeats a high-impedance (hereinafter referred to as Hi-Z) state and a low-level state is output from the PRI_CONT terminal.

[0027] When the PRI_CONT terminal is in the Hi-Z state, a current flows from the power supply voltage V2 through resistors R15 and R16 to charge capacitor C16. On the other hand, when the PRI_CONT terminal is in the low-level state, a current flows to the PRI_CONT terminal through resistor R16 to discharge capacitor C16. When the PRI_CONT terminal alternates between the Hi-Z and low-level states, the balance between charging and discharging capacitor C16 stabilizes at a predetermined voltage. Therefore, the voltage at the negative input terminal of comparator IC11 is determined according to the duty cycle of the pulse signal output from the PRI_CONT terminal.

[0028] 3(a) is a graph showing the relationship between the pulse signal output from the PRI_CONT terminal and the charging voltage Vpri, with the horizontal axis representing the low duty of the pulse signal output from the PRI_CONT terminal and the vertical axis representing the charging voltage Vpri. Specifically, as shown in FIG. 3(a), the larger the low duty of the pulse signal output from the PRI_CONT terminal, the larger the absolute value of the charging voltage Vpri, which is a negative voltage.

[0029] Returning to the explanation of Figure 2, when the voltage at the negative input terminal of comparator IC11 is lower than that at the positive input terminal, the output terminal of comparator IC11 becomes Hi-Z. At this time, the signal output from the CLK terminal of control unit 200 is input directly to the gate terminal of FET11, driving FET11 on and off. On the other hand, when the voltage at the negative input terminal of comparator IC11 is higher than that at the positive input terminal, the output terminal of comparator IC11 becomes low. At this time, the current output from the CLK terminal is drawn by the output terminal of comparator IC11, forcing the gate voltage of FET11 to become low. This prevents FET11 from turning on at the correct timing, thereby accelerating a decrease in the absolute value of the charging voltage Vpri. This operation makes it possible to control the charging voltage Vpri to a predetermined voltage. The control unit 200 performs feedback control of the charging voltage Vpri by controlling the low duty of the signal output from the PRI_CONT terminal. Here, the power supply voltage V2 in Example 1 is 5V. Because power supply voltage V2 affects the voltages at the positive and negative input terminals of comparator IC11, it is important to note that a power supply with relatively high voltage accuracy should be used for power supply voltage V2. Comparator IC11 operates on power supply voltage V1.

[0030] Through the above operation, a stable charging voltage Vpri is generated by the charging circuit 132b and applied to the charging roller 132a. The resistor R132 is provided to limit the output current. The resistor R132 is also provided for the purpose of protecting the charging roller 132a, which is detachable from the image forming apparatus 101, from external ESD (Electro Static Discharge) when the charging roller 132a is removed from the image forming apparatus 101. The resistor R132 may be added as needed. The value of the charging voltage Vpri in the first embodiment is, for example, −1500 V.

[0031] (Charging current detection) The charging current detection circuit PRI_ISNS detects the current supplied to the charging roller 132a (hereinafter referred to as the charging current). One known method for accurately detecting the surface potential of the photosensitive drum 131 is to detect the voltage at which discharge from the charging roller 132a to the photosensitive drum 131 begins (hereinafter referred to as the discharge start voltage). The relationship between the charging voltage Vpri and the charging current or the surface potential of the photosensitive drum 131 is shown in Figures 3(e) and 3(f). In Figure 3(e), the horizontal axis represents the negative charging voltage, and the vertical axis represents the charging current. In Figure 3(f), the horizontal axis represents the negative charging voltage, and the vertical axis represents the surface potential of the photosensitive drum 131. Using Figures 3(e) and 3(f), we will explain the transition of the charging current and the surface potential of the photosensitive drum 131 as the absolute value of the charging voltage Vpri is gradually increased from 0 V. The charging voltage Vpri begins to increase from 0 V, and a state in which no charging current flows (0 A) continues for a while. When the charging voltage Vpri reaches the discharge start voltage, discharge from the charging roller 132a to the photosensitive drum 131 begins, and a charging current starts to flow (FIG. 3(e)). The surface potential of the photosensitive drum 131 is 0 V at this point and then rises while maintaining the same potential difference as the charging voltage Vpri and the discharge start voltage (i.e., the lines on the graph remain parallel) (FIG. 3(f)). Therefore, by detecting the discharge start voltage, the surface potential of the photosensitive drum 131 can be accurately detected based on the charging voltage Vpri and the discharge start voltage. However, since the charging current needs to be accurately detected as the discharge current from the charging roller 132a to the photosensitive drum 131, it needs to be detected while the developing roller 133a is separated from the photosensitive drum 131. That is, when the control unit 200 detects the current flowing through the charging roller 132a using the charging current detection circuit PRI_ISNS, it controls the developing separation mechanism so that the developing roller 133a is in the separated state. In the first embodiment, the charging current is detected while the developer separation mechanism is controlled to the separation state during non-image formation. That is, the detection of the charging current can be said to be an example of a special process.

[0032] (developing circuit) The developing circuit 133b generates a developing voltage Vdev, a second negative voltage, by reducing the charging voltage Vpri through voltage division. In other words, the developing circuit 133b is subordinate to the charging circuit 132b. The developing circuit 133b is connected to the power supply voltage V1 from the charging voltage Vpri via resistor R50, Zener diode ZD51, and transistor Tr31. The developing circuit 133b outputs the voltage at the collector terminal of transistor Tr31 as the developing voltage Vdev. A resistor R39 is connected between the base terminal of transistor Tr31 and the emitter terminal, and a resistor R38 is connected to the output terminal of operational amplifier IC31.

[0033] The development circuit 133b also performs feedback control of the development voltage Vdev to maintain a stable and predetermined voltage. The development voltage Vdev is connected to the power supply voltage V2 via resistors R34 and R33. The junction of resistors R34 and R33 is connected to the positive input terminal of operational amplifier IC31. The negative input terminal of operational amplifier IC31 is connected to the power supply voltage V2 via resistors R36 and R35, and further to GND via capacitor C36. The junction of resistors R35 and R36 is connected to the DEV_CONT terminal of the control unit 200. Resistor R37 and capacitor C37 are connected in series between the negative input terminal and output terminal of operational amplifier IC31. Resistor R37 and capacitor C37 are provided for phase compensation of operational amplifier IC31 and contribute to stabilizing feedback control. The operational amplifier IC31 operates on the power supply voltage V1.

[0034] A second pulse signal (hereinafter simply referred to as a pulse signal) that alternates between a Hi-Z state and a low-level state is output from the DEV_CONT terminal of the control unit 200. When the pulse signal from the DEV_CONT terminal is in the Hi-Z state, a current flows from the power supply voltage V2 through resistors R35 and R36 to charge capacitor C36. On the other hand, when the pulse signal from the DEV_CONT terminal is in the low-level state, a current flows toward the DEV_CONT terminal through resistor R36 to discharge capacitor C36. When the DEV_CONT terminal alternates between the Hi-Z state and the low-level state, the balance between charging and discharging capacitor C36 stabilizes at a predetermined voltage. Therefore, the voltage at the negative input terminal of operational amplifier IC31 is determined according to the duty cycle of the pulse signal output from the DEV_CONT terminal.

[0035] When the voltage at the negative input terminal of the operational amplifier IC31 is lower than that at the positive input terminal, the output terminal of the operational amplifier IC31 goes high. This turns off the transistor Tr31, and the absolute value of the developing voltage Vdev increases. On the other hand, when the voltage at the negative input terminal of the operational amplifier IC31 is higher than that at the positive input terminal, the output terminal of the operational amplifier IC31 goes low. This turns on the transistor Tr31, and the absolute value of the developing voltage Vdev decreases. This operation makes it possible to control the developing voltage Vdev to a predetermined voltage. The control unit 200 controls the developing circuit 133b, which is the second power supply, by outputting a second pulse signal. The control unit 200 performs feedback control of the developing voltage Vdev by controlling the low duty of the pulse signal output from the DEV_CONT terminal.

[0036] 3(b) is a graph showing the relationship between the pulse signal output from the DEV_CONT terminal and the developing voltage Vdev, with the horizontal axis representing the low duty of the pulse signal output from the DEV_CONT terminal and the vertical axis representing the developing voltage Vdev. As shown in FIG. 3(b), the greater the low duty of the pulse signal output from the DEV_CONT terminal, the greater the absolute value of the developing voltage Vdev.

[0037] Returning to the explanation of Figure 2, the above operation generates a stable development voltage Vdev and applies it to the development roller 133a. Similar to the resistor R132, the resistor R133 may be inserted as needed to limit the output current and to provide ESD protection from the outside when the development roller 133a is removed from the image forming apparatus 101. The value of the development voltage Vdev in the first embodiment is, for example, -300V.

[0038] (Blade Circuit) The blade circuit 135b is a circuit that generates a blade voltage Vbld, which is a third voltage having a predetermined potential difference with respect to the development voltage Vdev. The blade voltage Vbld is connected to the development voltage Vdev via a Zener diode ZD51. The anode terminal of the Zener diode ZD51 is connected to the charging voltage Vpri via a resistor R50, and the anode terminal side is the blade voltage Vbld. In other words, the absolute value of the blade voltage Vbld is greater than the development voltage Vdev by the Zener voltage of the Zener diode ZD51. The cathode terminal of the Zener diode ZD51 is connected to the development voltage Vdev output by the development circuit 133b, and the anode terminal is connected to the blade voltage Vbld output by the blade circuit 135b.

[0039] The blade circuit 135b has a transistor Tr51 connected in parallel with a Zener diode ZD51. Specifically, the anode terminal of the Zener diode ZD51 is connected to the collector terminal of the transistor Tr51, and the cathode terminal is connected to the emitter terminal of the transistor Tr51. When the transistor Tr51 is turned on, both terminals of the Zener diode ZD51 are shorted, and the blade voltage Vbld becomes equal to the developing voltage Vdev. Therefore, the blade circuit 135b can be considered a circuit that selects whether the blade voltage Vbld has a predetermined potential difference with respect to the developing voltage Vdev or is the same potential as the developing voltage Vdev. When the transistor Tr51 is turned off, the blade voltage Vbld has an absolute value greater than that of the developing voltage Vdev (|Vbld|>|Vdev|). The transistor Tr51 functions as a switching means that switches between a first state in which the potential difference between the developing voltage Vdev and the blade voltage Vbld is a first potential difference and a second state in which the potential difference is a second potential difference greater than the first potential difference. In the first embodiment, the first potential difference is 0V (|Vbld|=|Vdev|) and the second potential difference is a Zener voltage, but the first potential difference is not limited to 0V as long as it is smaller than the second potential difference.

[0040] The base terminal of transistor Tr51 is connected to the emitter terminal via resistors R51 and R52. A capacitor C51 is connected in parallel to resistor R52. The junction of resistors R51 and R52 is connected to the anode terminal of diode D51, and the cathode terminal of diode D51 is connected to the anode terminal of diode D52. The cathode terminal of diode D52 is connected to the emitter terminal of transistor Tr51. The cathode terminal of diode D51 is connected to the BLD_SW terminal of the control unit 200 via capacitor C50. The anode terminal of diode D52 is connected to the BLD_SW terminal of the control unit 200 via capacitor C50.

[0041] The BLD_SW terminal outputs a pulse signal that alternates between high and low states. When the BLD_SW terminal is in a transitional state, switching from high to low, current flows from the power supply voltage V1 through transistor Tr31, the emitter and base terminals of transistor Tr51, resistor R51, diode D51, and capacitor C50. The current then flows into the BLD_SW terminal. When the BLD_SW terminal is in a transitional state, switching from low to high, current flows from the BLD_SW terminal to the power supply voltage V1 through capacitor C50, diode D52, and transistor Tr31. When the pulse signal from the BLD_SW terminal alternates between high and low, capacitor C51 is charged, allowing a stable base current to flow from the base terminal of transistor Tr51. When the stable base current flows from the base terminal of transistor Tr51, transistor Tr51 turns on, shorting the two terminals of Zener diode ZD51. On the other hand, when the BLD_SW terminal is fixed to a high level state or a low level state, the transistor Tr51 is turned off, and the two terminals of the Zener diode ZD51 are not short-circuited.

[0042] The first state described above is a state in which the transistor Tr51 is turned on, shorting the anode terminal and cathode terminal of the Zener diode ZD51. The second state described above is a state in which the transistor Tr51 is turned off, not shorting the anode terminal and cathode terminal of the Zener diode ZD51. The control unit 200 controls the transistor Tr51 to be in the first state in the separated state and to be in the second state in the abutted state. The control unit 200 controls the on / off state of the transistor Tr51 by outputting a signal that controls the blade circuit 135b from the BLD_SW terminal.

[0043] The relationship between the low duty cycle of the pulse signal output from the DEV_CONT terminal and the blade voltage Vbld is shown in Figure 3(c). In Figure 3(c), the horizontal axis represents the low duty cycle of the pulse signal output from the DEV_CONT terminal, and the vertical axis represents the blade voltage Vbld. When a pulse signal is output from the BLD_SW terminal (the graph in the figure shows when BLD_SW is ON), the blade voltage Vbld is the same as the developing voltage Vdev. In other words, when a pulse signal that alternates between high and low levels is output from the BLD_SW terminal, the blade voltage Vbld is the same as the developing voltage Vdev in Figure 3(b). On the other hand, when a pulse signal that alternates between high and low levels is not output from the BLD_SW terminal (the graph in the figure shows when BLD_SW is OFF), in other words, when the signal is fixed to a high or low level, the following occurs. That is, the absolute value of the blade voltage Vbld is greater than the developing voltage Vdev by the Zener voltage ΔVz of the Zener diode ZD51 (|Vbld|=|Vdev|+ΔVz).

[0044] By the above operation, a voltage equal to the developing voltage Vdev or a voltage whose absolute value is greater than the developing voltage Vdev by the Zener voltage (ΔVz) is applied to the developing blade 135a. Note that, like resistors R132 and R133, resistor R135 may be inserted as needed. In addition, the Zener voltage (ΔVz) in Example 1 is, for example, 100 V; that is, the value of the blade voltage Vbld when both terminals of the Zener diode ZD51 are not short-circuited is, for example, −400 V (= −300 − 100).

[0045] (Toner supply R circuit) The toner supply R circuit 134b generates a negative fourth voltage, the toner supply R voltage Vtsr, by reducing the charging voltage Vpri through voltage division. It has a configuration similar to that of the developing circuit 133b. The only difference is that there is no Zener diode in the voltage division line with the charging voltage Vpri. The toner supply R circuit 134b is connected to the power supply voltage V1 via resistor R40 and transistor Tr41 from the charging voltage Vpri. The voltage at the collector terminal of transistor Tr41 becomes the toner supply R voltage Vtsr. A resistor R49 is connected between the base terminal of transistor Tr41 and the emitter terminal, and a resistor R48 is connected to the output terminal of operational amplifier IC41.

[0046] The toner supply R circuit 134b also performs feedback control of the toner supply R voltage Vtsr to maintain a stable, predetermined voltage. The toner supply R voltage Vtsr is connected to the power supply voltage V2 via resistors R44 and R43. The junction of resistors R44 and R43 is connected to the positive input terminal of operational amplifier IC41. The negative input terminal of operational amplifier IC41 is connected to the power supply voltage V2 via resistors R46 and R45, and further to GND via capacitor C46. The junction of resistors R45 and R46 is connected to the TSR_CONT terminal of the control unit 200. Resistor R47 and capacitor C47 are connected in series between the negative input terminal and output terminal of operational amplifier IC41. Resistor R47 and capacitor C47 are provided for phase compensation of operational amplifier IC41 and contribute to stabilizing feedback control. Operational amplifier IC41 operates on power supply voltage V1.

[0047] The TSR_CONT terminal outputs a fourth pulse signal (hereinafter simply referred to as a pulse signal) that alternates between a Hi-Z state and a low-level state. When the TSR_CONT terminal is in the Hi-Z state, a current flows from the power supply voltage V2 through resistors R45 and R46 to charge capacitor C46. On the other hand, when the TSR_CONT terminal is in the low-level state, a current flows through resistor R46 to discharge capacitor C46 toward the TSR_CONT terminal. When the TSR_CONT terminal alternates between the Hi-Z state and the low-level state, the charge / discharge balance of capacitor C46 stabilizes at a predetermined voltage. Therefore, the voltage at the negative input terminal of operational amplifier IC41 is determined according to the duty cycle of the pulse signal output from the TSR_CONT terminal. When the voltage at the negative input terminal of operational amplifier IC41 is lower than the voltage at the positive input terminal, the output terminal of operational amplifier IC41 goes high. Transistor Tr41 is turned off, and the absolute value of the negative toner supply R voltage Vtsr increases. On the other hand, when the voltage at the negative input terminal of operational amplifier IC41 is greater than the voltage at the positive input terminal, the output terminal of operational amplifier IC41 goes low. Transistor Tr41 turns on, and the absolute value of the toner supply R voltage Vtsr decreases. This operation makes it possible to control the toner supply R voltage Vtsr to a predetermined voltage. The control unit 200 performs feedback control of the toner supply R voltage Vtsr by controlling the low duty of the pulse signal output from the TSR_CONT terminal.

[0048] Figure 3(d) is a graph showing the relationship between the pulse signal output from the TSR_CONT terminal and the toner supply R voltage Vtsr. In Figure 3(d), the horizontal axis represents the low duty of the pulse signal output from the TSR_CONT terminal, and the vertical axis represents the toner supply R voltage Vtsr. As shown in Figure 3(d), the greater the low duty of the pulse signal output from the TSR_CONT terminal, the greater the absolute value of the toner supply R voltage Vtsr.

[0049] Through the above operation, a stable toner supply R voltage Vtsr is generated and applied to the toner supply roller 134a. Note that resistor R134 may be inserted as needed, similar to resistors R132, R133, and R135. The value of the toner supply R voltage Vtsr in the first embodiment is, for example, −400 V.

[0050] (Control during development separation) As described above, the image forming apparatus 101 of the first embodiment detects the charging current while the developer separation mechanism is controlled to the separated state. Specifically, the charging current is detected while the developing roller 133a, the developing blade 135a, and the toner supply roller 134a are separated. Therefore, during the detection of the charging current, the developing voltage Vdev, the blade voltage Vbld, and the toner supply R voltage Vtsr can functionally take any values.

[0051] However, if a high voltage is applied between the contacting parts when these members have stopped rotating, the contact points will be in a different state from the others, which can cause image defects such as streaks. Even when the developer separation mechanism is in the separated state, the developing roller 133a and the toner supply roller 134a are in contact, and the developing roller 133a and the developing blade 135a are in contact. Therefore, the potential difference between the contacting parts, i.e., between the developing roller 133a and the toner supply roller 134a, and between the developing roller 133a and the developing blade 135a, should be small.

[0052] The development voltage Vdev and the toner supply R voltage Vtsr are both controlled to the same predetermined voltage, the absolute value of which is greater than the voltage during the image formation process. This allows the potential difference between the development roller 133a and the toner supply roller 134a to be controlled to be small while minimizing the load on the transformer. That is, the control unit 200 outputs a fourth pulse signal such that the potential difference between the second voltage and the fourth voltage becomes the third potential difference in the separated state, and outputs a fourth pulse signal such that the potential difference becomes the fourth potential difference, which is greater than the third potential difference, in the contact state. This controls the potential difference between the development roller 133a and the toner supply roller 134a to be different between the image formation process and the special process. Meanwhile, the blade voltage Vbld can be controlled to be small by outputting a pulse signal from the BLD_SW terminal to short-circuit both ends of the Zener diode ZD51.

[0053] (Control of Example 1) The power supply of the first embodiment is configured to generate a base voltage from a single transformer and generate multiple different voltages through voltage division control. Here, the base voltage is the charging voltage Vpri generated by the charging circuit 132b. In this configuration, when control is performed to turn off unused voltages to reduce the potential difference between the developing components while the developing components are stopped, the specifications required for the transformer T11 are higher than the specifications required for the electrophotographic process. Note that the developing components are stopped during a special process. If a transformer tailored to the specifications required when the developing components are stopped is used, the transformer specifications would be excessive for the electrophotographic process. The control of the first embodiment, which solves these problems, is described below.

[0054] In the first embodiment, the control by the image forming apparatus 101 to reduce the potential difference between the developing roller 133a and the toner supply roller 134a and the potential difference between the developing roller 133a and the developing blade 135a will be described with reference to Figure 4. Hereinafter, the space between the developing roller 133a and the toner supply roller 134a and the space between the developing roller 133a and the developing blade 135a will be referred to as the space between the developing roller 133a and the toner supply roller 134a and the space between the developing roller 133a and the developing blade 135a. In the following description, the detection of the charging current described above (hereinafter referred to as the charging current detection process) will be used as an example of a special process.

[0055] When a special process, for example, the process of detecting the charging current by the charging current detection circuit PRI_ISNS, is started, the control unit 200 executes the processes from step (hereinafter referred to as S) 501 onwards. In S501, the control unit 200 controls the development separation mechanism so that the photosensitive drum 131 and the development components are separated from each other. In S502, the control unit 200 outputs a control signal from the PRI_CONT terminal so that the charging voltage Vpri becomes a predetermined voltage, for example, -1500V (turning PRI_CONT ON).

[0056] In S503, the control unit 200 outputs a control signal from the DEV_CONT terminal so that the development voltage Vdev becomes a predetermined voltage, for example, -400V (turning DEV_CONT ON). That is, the control unit 200 controls the absolute value of the development voltage Vdev during the charging current detection process (for example, |-400|V) to be greater than the absolute value of the development voltage Vdev during the image formation process (for example, |-300|V). In S504, the control unit 200 outputs a control signal from the TSR_CONT terminal so that the toner supply R voltage Vtsr becomes a predetermined voltage, for example, -400V (turning TSR_CONT ON). In S505, the control unit 200 outputs a pulse signal from the BLD_SW terminal and controls the blade voltage Vbld to be the same potential as the development voltage Vdev (turning BLD_SW ON). Here, the control unit 200 controls the blade voltage Vld so that it has the same potential as the developing voltage Vdev, but it may also control the potential difference between the blade voltage Vld and the developing voltage Vdev so that it is smaller than the potential difference during the image formation process. In S506, the control unit 200 outputs a pulse signal from the CLK terminal (turns CLK ON). This outputs the charging voltage Vpri, the developing voltage Vdev, the toner supply R voltage Vtsr, and the blade voltage Vbld.

[0057] In S507, the control unit 200 detects the charging current using the charging current detection circuit PRI_ISNS. In S508, the control unit 200 determines whether or not detection of the charging current using the charging current detection circuit PRI_ISNS has finished. If the control unit 200 determines in S508 that detection of the charging current has not finished, it returns to S508; if it determines that detection has finished, it proceeds to S509. In S509, the control unit 200 stops outputting the pulse signal from the CLK terminal (turns CLK OFF). The control unit 200 stops outputting the charging voltage Vpri, the developing voltage Vdev, the toner supply R voltage Vtsr, and the blade voltage Vbld. In S510, the control unit 200 stops outputting the pulse signal from the PRI_CONT terminal (turns PRI_CONT OFF). In S511, the control unit 200 stops outputting the pulse signal from the DEV_CONT terminal (turns DEV_CONT OFF). In S512, the control unit 200 stops the pulse signal being output from the TSR_CONT terminal (turns TSR_CONT OFF), and in S513, the control unit 200 stops the pulse signal being output from the BLD_SW terminal (turns BLD_SW OFF), and ends the process.

[0058] (Voltage settings for image formation process and special process) Table 1 shows the set values ​​of each output voltage during the image formation process and the special process (charging current detection process) in Example 1. In Table 1, the values ​​in the detection of the charging current are listed as the special process, as described above.

[0059] [Table 1] Table 1 shows each process (image formation process, charging current detection process) in the first column, the charging voltage Vpri in the second column, the developing voltage Vdev in the third column, the blade voltage Vbld in the fourth column, and the toner supply R voltage Vtsr in the fifth column.

[0060] The set value of the development voltage Vdev during charging current detection is set to a voltage with a larger absolute value than the set value during the image formation process, such as -400V (|-400|>|-300|). During the charging current detection process, the blade voltage Vbld and the toner supply R voltage Vtsr are also output at voltages that match the development voltage Vdev, such as -400V (Vbld = Vdev, Vtsr = Vdev). However, when -400V is output as the set value during the charging current detection process, output errors actually occur due to variations in circuit constants, etc. For this reason, the blade voltage Vbld and the development voltage Vdev, and the toner supply R voltage Vtsr and the development voltage Vdev are controlled to be as identical as possible within the scope that can solve the problems of the present invention, and in that sense, are output at approximately the same voltage values. In other words, the development voltage Vdev, the blade voltage Vbld, and the toner supply R voltage Vtsr during charging current detection are output at the same or approximately the same values. This reduces the potential difference between the developing roller 133a, the developing blade 135a, and the toner supply roller 134a, making it possible to suppress image defects such as streaks. Also, by making the absolute value of the developing voltage Vdev larger than that during the image formation process, the load on the transformer T11 during charging current detection can be made smaller than that during the image formation process.

[0061] By performing such control, even in an inexpensive configuration in which multiple voltages are generated by a common boost circuit, it is possible to suppress the occurrence of image defects at the contact points between the developing roller 133a, the toner supply roller 134a, and the developing blade 135a. Furthermore, with the transformer capacity required during the image formation process, it is possible to output the charging voltage Vpri even during special processes.

[0062] (Other variations) In the above-described embodiment, a circuit for generating each voltage from the charging voltage Vpri is shown, but the configuration of the present invention is not limited to this. For example, it is sufficient if the configuration generates multiple voltages from the same power supply and controls the potential difference between multiple dependent voltages to be reduced while outputting the original voltage. For example, instead of using the charging voltage Vpri generated by the charging circuit 132b as the original voltage, the voltage generated by the negative transfer circuit 141c may be used. In this case, the negative transfer circuit 141c corresponds to the first power supply, and the negative transfer voltage corresponds to the first voltage. Furthermore, the circuit configurations for generating the development voltage Vdev, blade voltage Vbld, and toner supply R voltage Vtsr may be any circuits that generate the voltages dependent on a source voltage. For example, in the first embodiment, the blade voltage Vbld is controlled by a parallel circuit of Zener diode ZD51 and transistor Tr51 connected to the development voltage Vdev. However, a parallel circuit of Zener diode ZD51 and transistor Tr51 may be connected to the toner supply R voltage Vtsr instead of the development voltage Vdev. In this case, the toner supply R circuit 134b corresponds to the third power supply, the toner supply R voltage Vtsr corresponds to the third voltage, the blade circuit 135b corresponds to the fourth power supply, and the blade voltage Vbld corresponds to the fourth voltage. Furthermore, the second contact member corresponds to the development blade 135a, and the first contact member corresponds to the toner supply roller 134a. The number of controlled voltages is not limited to three, and may be two, four, or more. In other words, the combinations of voltages generated dependent on the source voltage and their circuit configurations are not limited to those in the above-described embodiment. Furthermore, the control unit 200 may control the on / off state of the transistor Tr51 by switching the frequency of the second pulse signal output to the second power supply.

[0063] As described above, according to the first embodiment, it is possible to suppress image defects caused by contact portions between members involved in the development process with an inexpensive circuit configuration. [Example]

[0064] The second embodiment differs from the first embodiment in that the configurations of the blade circuit 135b and the developing circuit 133b are the same as the configuration of the toner supply R circuit 134b. In the second embodiment, only the differences from the first embodiment will be described, and the description of the same parts as the first embodiment will be omitted.

[0065] (Configuration and operation of high voltage generation circuit) Fig. 5 is a circuit diagram of the image forming unit 103 of the second embodiment. The configurations of the blade circuit 135b and the developing circuit 133b are different from those in Fig. 2. Also, the developing separation mechanism is omitted in Fig. 5.

[0066] (development circuit, blade circuit) The developing circuit 133b is connected from the charging voltage Vpri to the power supply voltage V1 via a resistor R30 and a transistor Tr31. In the developing circuit 133b, the voltage at the collector terminal of the transistor Tr31 becomes the developing voltage Vdev.

[0067] The blade circuit 135b is connected to the power supply voltage V1 via a resistor R60 and a transistor Tr61 from the charging voltage Vpri. In the blade circuit 135b, the voltage at the collector terminal of the transistor Tr61 becomes the blade voltage Vbld. A resistor R69 is connected between the base and emitter terminals of the transistor Tr61. One end of a resistor R68 is connected to the base terminal of the transistor Tr61, and the other end of the resistor R68 is connected to the output terminal of the operational amplifier IC61.

[0068] The blade voltage Vbld is connected to the power supply voltage V2 via resistors R64 and R63. The junction of resistors R64 and R63 is connected to the positive input terminal of operational amplifier IC61. The negative input terminal of operational amplifier IC61 is connected to the power supply voltage V2 via resistors R66 and R65, and further to GND via capacitor C66. The junction of resistors R65 and R66 is connected to the BLD_CONT terminal of control unit 200. Resistor R67 and capacitor C67 are connected in series between the negative input terminal and output terminal of operational amplifier IC61. Resistor R67 and capacitor C67 are provided for phase compensation of operational amplifier IC61 and contribute to stabilizing feedback control. Operational amplifier IC61 operates on power supply voltage V1.

[0069] The BLD_CONT terminal outputs a third pulse signal (hereinafter simply referred to as the pulse signal) that alternates between a Hi-Z state and a low-level state. When the BLD_CONT terminal is in the Hi-Z state, a current flows from the power supply voltage V2 through resistors R65 and R66 to charge capacitor C66. On the other hand, when the BLD_CONT terminal is in the low-level state, a current flows to the BLD_CONT terminal through resistor R66 to discharge capacitor C66. When the BLD_CONT terminal alternates between the Hi-Z state and the low-level state, the balance between charging and discharging capacitor C66 stabilizes at a predetermined voltage. Therefore, the voltage at the negative input terminal of operational amplifier IC61 is determined according to the duty cycle of the pulse signal output from the BLD_CONT terminal. In other words, the greater the low duty cycle of the pulse signal output from the BLD_CONT terminal, the greater the absolute value of the blade voltage Vbld, which is a negative voltage.

[0070] When the voltage at the negative input terminal of operational amplifier IC61 is lower than that at the positive input terminal, the output terminal of operational amplifier IC61 goes high. At this time, transistor Tr61 is turned off, and the absolute value of blade voltage Vbld increases. On the other hand, when the voltage at the negative input terminal of operational amplifier IC61 is higher than that at the positive input terminal, the output terminal of operational amplifier IC61 goes low. At this time, transistor Tr61 is turned on, and the absolute value of blade voltage Vbld decreases. This operation controls the blade voltage Vbld to a predetermined voltage.

[0071] (Control of Example 2) In the second embodiment, the control of the image forming apparatus 101 to reduce the potential difference between the developing roller 133a and the developing blade 135a and between the developing roller 133a and the toner supply roller 134a will be described with reference to FIG. 6. In FIG. 6, the above-mentioned charging current detection will be described as an example of a special process. Note that the same step numbers are used for the same processes as those in the first embodiment (FIG. 4), and descriptions thereof will be omitted. After outputting a control signal from the TSR_CONT terminal in S504 such that the toner supply R voltage Vtsr becomes −400 V, the control unit 200 performs the following control in S805. That is, the control unit 200 outputs a control signal from the BLD_CONT terminal such that the toner supply R voltage Vtsr becomes −400 V (turning BLD_CONT ON), and proceeds to the processing of S506. That is, the control unit 200 functions as a switching means for switching between a first state in which the potential difference between the development voltage Vdev and the blade voltage Vbld is a first potential difference, and a second state in which the potential difference is a second potential difference that is larger than the first potential difference. After stopping the pulse signal output from the TSR_CONT terminal in S512, the control unit 200 stops the pulse signal output from the BLD_CONT terminal in S812 (turns BLD_CONT OFF), and ends the process.

[0072] In the second embodiment, the control unit 200 can independently select (set) the voltage values ​​of the development voltage Vdev, the blade voltage Vbld, and the toner supply R voltage Vtsr. In other words, the number of options for each voltage value that can be set increases, enabling more complex voltage control. By performing the above-described control in the second embodiment as well, image defects are prevented from occurring at the contact points between the development roller 133a, the toner supply roller 134a, and the development blade 135a. Furthermore, the charging voltage Vpri can be output even during special processes with the transformer capacity required during the image formation process.

[0073] As described above, according to the second embodiment, it is possible to suppress image defects caused by contact portions between members involved in the development process with an inexpensive circuit configuration. [Explanation of symbols]

[0074] 131 Photosensitive drum 132b Charging circuit 133a Developing roller 133b Development circuit 135a Developing Blade 135b Blade Circuit 200 control section

Claims

1. A photoreceptor; a developing member that can be in a contact state in which it is in contact with the photosensitive member or in a spaced state in which it is spaced from the photosensitive member, and that develops an electrostatic latent image formed on the photosensitive member with toner in the contact state to form a toner image; a first contact member that contacts the developing member in the contact state and the separated state; a first power supply having a transformer and generating a first voltage; a second power supply that generates a second voltage to be applied to the developing member from the first voltage; a third power source that generates a third voltage from the second voltage generated by the second power source and applies the third voltage to the first contact member; a control means for controlling the first potential difference to be formed in the separated state and the second potential difference to be formed in the contact state, where the potential difference between the second voltage and the third voltage is defined as a first potential difference and the potential difference greater than the first potential difference is defined as a second potential difference; Equipped with The image forming apparatus according to claim 1, wherein the control means controls the second voltage so that the absolute value of the second voltage in the separated state is greater than the absolute value of the second voltage in the contact state.

2. a charging member for charging the photoreceptor; 2. The image forming apparatus according to claim 1, wherein the first power source applies the first voltage to the charging member.

3. a charging member for charging the photoreceptor; a transfer member that transfers the toner image formed on the photosensitive member; Equipped with 2. The image forming apparatus according to claim 1, wherein the first power source applies the first voltage to the transfer member.

4. the control means controls the first power supply by outputting a first pulse signal; 4. The image forming apparatus according to claim 2, wherein the first voltage has a negative polarity, and the absolute value of the first voltage increases as the low duty of the first pulse signal increases.

5. the control means controls the second power supply by outputting a second pulse signal; 5. The image forming apparatus according to claim 4, wherein the second voltage has a negative polarity, and the absolute value of the second voltage increases as the low duty of the second pulse signal increases.

6. The third power source is a Zener diode having a cathode terminal connected to the second voltage output from the second power supply and an anode terminal connected to the third voltage output from the third power supply; a transistor having an emitter terminal connected to the cathode terminal of the Zener diode and a collector terminal connected to the anode terminal of the Zener diode; and In the separated state, the transistor is turned on to short-circuit the anode terminal and the cathode terminal of the Zener diode, 6. The image forming apparatus according to claim 5, wherein in the contact state, the transistor is turned off to prevent a short circuit between the anode terminal and the cathode terminal of the Zener diode.

7. 7. The image forming apparatus according to claim 6, wherein the control unit controls the on state or the off state of the transistor by outputting a signal that controls the third power supply.

8. the control means controls the third power supply by outputting a third pulse signal; 6. The image forming apparatus according to claim 5, wherein the third voltage has a negative polarity, and the absolute value of the third voltage increases as the low duty of the third pulse signal increases.

9. a second contact member that contacts the developing member in the contact state and the separated state; a fourth power source that generates a fourth voltage and applies the fourth voltage to the second contact member; Equipped with The control means outputting a fourth pulse signal to control the fourth power supply; 9. The image forming apparatus according to claim 7, wherein the fourth pulse signal is output so that the potential difference between the second voltage and the fourth voltage becomes a third potential difference in the separated state, and the fourth pulse signal is output so that the potential difference becomes a fourth potential difference greater than the third potential difference in the contact state.

10. 10. The image forming apparatus according to claim 9, wherein the fourth voltage has a negative polarity, and the absolute value of the fourth voltage increases as the low duty of the fourth pulse signal increases.

11. a toner container for storing toner; a supply roller that supplies the toner contained in the toner container to the developing member; a blade for leveling the toner supplied to the developing member by the supply roller; Equipped with 11. The image forming apparatus according to claim 9, wherein the first contact member is the blade and the second contact member is the supply roller, or the first contact member is the supply roller and the second contact member is the blade.

12. a detection means for detecting a current flowing through the charging member; 12. The image forming apparatus according to claim 2, wherein the control unit controls the charging member to be in the separated state when the detection unit detects the current flowing through the charging member.

13. 13. The image forming apparatus according to claim 1, further comprising a contact / separation unit that switches the developing member between the contact state and the separated state.

Images