JP7757147B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus, for example, an image forming apparatus that uses an electrophotographic method.

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 developing voltage is generated by dividing the charging voltage using a resistor and a switching element. Here, the charging voltage is applied to the charging roller, and the developing voltage is applied to the developing roller. In Patent Document 2, for example, a blade voltage is generated by a transformer, and the developing voltage is generated by dividing the blade voltage using a Zener diode and a resistor. Here, the blade voltage is applied to the developing blade. The developing blade is a blade that comes into sliding contact with the developing roller to evenly distribute the toner on the surface of the developing roller.

Furthermore, when components that contribute to the development process (hereafter referred to as the development system) are separated from the photosensitive drum, if a potential difference continues to exist between the development roller and the development blade for a long period of time while the development roller is stopped from rotating, the following problem occurs. Namely, it is known that the contact area between the development roller surface and the development blade becomes different from the rest, resulting in image defects such as streaks. For this reason, it is possible to consider not supplying voltage to the development system components when they are separated from the photosensitive drum.

JP 2014-238490 A Japanese Patent Application Laid-Open No. 2018-013720

However, a configuration that generates multiple voltages from a single high-voltage circuit through voltage division control presents the following problem. If a voltage is output from a single high-voltage circuit and control is performed so that a voltage connected to a stage lower than that voltage is not output, the load on the transformer that generates the high voltage becomes excessive for normal electrophotographic processing. In other words, the transformer is required to have excessive capacity, which leads to higher transformer costs and an increase in 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.

The present invention was developed in response to these circumstances, and aims to suppress image defects caused by contact points between components involved in the development process using an inexpensive circuit configuration.

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 which it is in contact with the photosensitive member or in a separated state in which it is separated from the photosensitive member, and that in the contact state develops an electrostatic latent image formed on the photosensitive member with toner 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 a third voltage from 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.

This invention makes it possible to suppress image defects caused by contact points between components involved in the development process using an inexpensive circuit configuration.

Schematic cross-sectional view of an image forming apparatus according to first and second embodiments. Circuit diagram of the image forming unit of the first embodiment 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. Flowchart showing voltage control in the first embodiment Circuit diagram of the imaging unit of the second embodiment Flowchart showing voltage control in the second embodiment

The following describes in detail the embodiments of the present invention with reference to the drawings. Hereinafter, the voltage output from a high-voltage circuit that has a transformer and is connected to an AC voltage will be referred to as the "source voltage." Connecting to a lower level than the source voltage is said to be subordinate.

(Configuration of image forming apparatus)
FIG. 1 shows a schematic cross-sectional view of an image forming apparatus 101. The paper feed unit 102 includes 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 includes 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 includes a toner container 136 and a laser scanner 137. 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.

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, connected in series with the positive transfer circuit 141b, apply the 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 device such as a switch, or the negative transfer circuit 141c may be eliminated entirely. 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.

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 paper P transport operation, and the like, in accordance with various programs stored in the ROM 200b and using the RAM 200c as a working area. The control unit 200 also controls the contact and separation operation of the developing roller 133a, which will be described later, and the various circuits that act as the power sources that apply the various voltages, which will be described later. It is also possible to provide a control unit separate from the control unit 200 that controls the image creating unit 103, the fixing unit 105, and the various power sources, and have the control unit 200 control the separately provided control unit.

(Operation of image forming apparatus)
The operation of the image forming unit 103 to form a toner image on the surface of the photosensitive drum 131 will now 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 Example 1 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 agitation.

The toner supply roller 134a supplies toner contained in the toner container 136 to the developing roller 133a. The toner is moved to the surface of the developing roller 133a by the toner supply roller 134a, which is supplied with a negative high voltage from the toner supply R circuit 134b, and adheres to the surface. The developing blade 135a levels 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, it is leveled out by the developing blade 135a, which is supplied with a negative high voltage from the blade circuit 135b. The developing roller 133a, with 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, where an electrostatic latent image is developed. Here, the output voltage of the toner supply R circuit 134b is set to have a larger absolute value than the output voltage of the development circuit 133b, making it easier for negatively charged toner to move to the development roller 133a. Furthermore, the output voltage of the blade circuit 135b is set to have a larger absolute value than the output voltage of the development circuit 133b, making it harder 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 blade circuit 135b are set to -500V.

Next, we will explain the operation of forming an image on paper P. When the image forming apparatus 101 receives a print job, the rollers and laser scanner 137 begin operation. Paper P stored in paper feed tray 121 is fed by paper feed roller 122 and transported along transport path 111, eventually reaching 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, which is supplied with a positive high voltage from transfer positive circuit 141b. At this time, the toner image formed on the surface of photosensitive drum 131 is transferred to paper P. Continuing its transport, paper P then reaches fixing unit 105, where it is pressure-nipped by fixing roller 151 and pressure roller 152, fixing any unfixed toner image on paper P. Paper P is then ejected via ejection rollers 161a and 161b onto ejection tray 162. The process of forming an image on paper P described above will hereinafter be referred to as the image formation process. Furthermore, processes other than the image formation process that are carried out outside of the image formation process will hereinafter be referred to as special processes.

(Developer separation mechanism)
Next, a configuration for separating the developing roller 133a from the photosensitive drum 131 will be described. Because the developing roller 133a rotates while sliding against the photosensitive drum 131, the toner supply roller 134a, and the developing blade 135a, its surface wears and deteriorates with use. Considering the product life of the image forming apparatus 101, the sliding time should be minimized. The image forming apparatus 101 of Example 1 is equipped with a developing separation mechanism (see FIG. 2 ) that is a contact/separation unit that can separate the developing roller 133a from the photosensitive drum 131. The developing roller 133a can be in a contact state with the photosensitive drum 131 or a separated state with the photosensitive drum 131. When in contact, the developing roller 133a develops an electrostatic latent image formed on the photosensitive drum 131 (photoconductor) with toner to form a toner image.

The developer separation mechanism moves the components including the developer roller 133a, toner supply roller 134a, developer blade 135a, and toner container 136, switching the developer 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. That is, the developer blade 135a contacts the developer roller 133a in both the contact state and the separated state, and the toner supply roller 134a also contacts the developer roller 133a in both the contact state and the separated state. Note that in Figure 1, the separated state of the developer roller 133a is shown by the dashed line 133a' as a representative example.

The image forming apparatus 101 has a developer separation mechanism, which is a contact/separation means for switching the developer roller 133a between a contact state and a separated state. In Example 1, 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 Figure 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 the transmitted state), and a state in which drive from the drive motor 256 to the developer separation gear 254 is interrupted (hereinafter referred to as the interrupted state). The control unit 200 controls the drive motor 256 using a drive circuit (not shown), a rotation detection means (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 separates from the photosensitive drum 131, and in the disconnected state, the developing roller 133a contacts 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 Example 1, when the developing roller 133a contacts or separates from the photosensitive drum 131, the toner supply roller 134a, developing blade 135a, and toner container 136 also move in conjunction with the developing roller 133a.

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

(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.

(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) 11. 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 11 and the 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 the two 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.

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 the charging current detection circuit PRI_ISNS, which serves as detection means. The power supply voltage V1 in Example 1 is, for example, 24 V.

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, FET11 turns on, and the drain voltage of FET11 drops to approximately the same potential as ground (hereinafter referred to as GND). This applies a voltage 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, FET11 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 diode D12 and capacitor C12, generating a negative first voltage, the charging voltage Vpri. Capacitor C11, resistor R11, and diode D11 act as a snubber circuit that absorbs surge voltages caused by the leakage inductance of the primary winding T11-1.

The voltage output from the CLK terminal of the control unit 200 is a square wave in which high and low levels alternate. In Example 1, for example, a fixed square wave with a frequency of 50 kHz and a duty cycle of 10% is output. Here, 10% duty refers to the proportion of high-level time within one signal cycle (the sum of high-level time and low-level time), but it can also refer to the proportion of low-level time. Note that 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 Example 1. Furthermore, the frequency and duty of the square wave do not have to be fixed values and may be variable depending on the voltage and load of the controlled object. When FET11 is turned on and off, the flyback voltage generated in the secondary winding T11-2 is rectified and smoothed by diode D12 and capacitor C12, generating the charging voltage Vpri.

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

When the PRI_CONT terminal is in a Hi-Z state, current flows from the power supply voltage V2 via resistors R15 and R16 to charge capacitor C16. On the other hand, when the PRI_CONT terminal is in a low-level state, current discharges capacitor C16 via resistor R16 and flows toward the PRI_CONT terminal. When the PRI_CONT terminal alternates between a Hi-Z state and a low-level state, 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.

Figure 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 (Lo Duty) of the pulse signal output from the PRI_CONT terminal and the vertical axis representing the charging voltage Vpri. Specifically, as shown in Figure 3(a), the greater the low duty of the pulse signal output from the PRI_CONT terminal, the greater the absolute value of the charging voltage Vpri, which is a negative voltage.

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 cycle 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 using power supply voltage V1.

Through the above operations, a stable charging voltage Vpri is generated by the charging circuit 132b and applied to the charging roller 132a. Resistor R132 is provided to limit the output current. Resistor R132 is also provided for the purpose of protecting against external ESD (Electro Static Discharge) when the detachable charging roller 132a is removed from the image forming apparatus 101. Resistor R132 may be added as needed. The value of the charging voltage Vpri in Example 1 is, for example, -1500V.

(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 initiation voltage). Figures 3(e) and 3(f) show the relationship between the charging voltage Vpri and the charging current or the surface potential of the photosensitive drum 131. 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 begins 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 with the charging voltage Vpri as 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 must be accurately detected as the discharge current from the charging roller 132a to the photosensitive drum 131, it must 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.

(developing circuit)
The development circuit 133b generates a development voltage Vdev, which is a negative second voltage, by reducing the charging voltage Vpri through voltage division. In other words, the development circuit 133b is subordinate to the charging circuit 132b. The development 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 development circuit 133b outputs the voltage at the collector terminal of transistor Tr31 as the development 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.

The development circuit 133b also uses feedback control of the development voltage Vdev to maintain a stable, predetermined voltage. The development voltage Vdev is connected to the power supply voltage V2 via resistors R34 and R33. The junction between 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 between 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, contributing to the stability of feedback control. Operational amplifier IC31 operates on power supply voltage V1.

A second pulse signal (hereinafter simply referred to as the 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, 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, current that discharges capacitor C36 flows toward the DEV_CONT terminal through resistor R36. 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.

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

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

Returning to the explanation of Figure 2, the above operation generates a stable development voltage Vdev, which is applied to the development roller 133a. Similar to resistor R132, 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 Example 1 is, for example, -300V.

(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 amount of 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.

In the blade circuit 135b, a transistor Tr51 is 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 short-circuited, and the blade voltage Vbld becomes equal to the development voltage Vdev. Therefore, the blade circuit 135b can be said to be a circuit that selects whether the blade voltage Vbld should have a predetermined potential difference from the development voltage Vdev or be the same potential as the development voltage Vdev. When the transistor Tr51 is turned off, the blade voltage Vbld becomes a value with an absolute value greater than that of the development voltage Vdev (|Vbld| > |Vdev|). Transistor Tr51 functions as a switching device that switches between a first state in which the potential difference between development voltage Vdev and 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. In Example 1, the first potential difference is 0 V (|Vbld| = |Vdev|) and the second potential difference is a Zener voltage, but the first potential difference is not limited to 0 V as long as it is smaller than the second potential difference.

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.

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 terminal and base terminal of transistor Tr51, resistor R51, diode D51, and capacitor C50. It then finally flows into the BLD_SW terminal. When the BLD_SW terminal is in a transitional state switching from low to high, current flowing out of the BLD_SW terminal flows into the power supply voltage V1 via capacitor C50, diode D52, and transistor Tr31. When the pulse signal from the BLD_SW terminal alternates between high and low, an electric charge is charged in capacitor C51, allowing a stable base current to flow from the base terminal of transistor Tr51. When a stable base current flows from the base terminal of transistor Tr51, transistor Tr51 turns on, and both terminals of Zener diode ZD51 are shorted. On the other hand, when the BLD_SW terminal is fixed to a high or low level state, transistor Tr51 turns off, and both terminals of Zener diode ZD51 are not shorted.

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

Figure 3(c) shows the relationship between the low duty cycle of the pulse signal output from the DEV_CONT terminal and the blade voltage Vbld. In Figure 3(c), the horizontal axis represents the low duty cycle (Lo Duty) 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 development voltage Vdev. That is, when a pulse signal that alternates between high and low states is output from the BLD_SW terminal, the blade voltage Vbld is the same as the development voltage Vdev in Figure 3(b). On the other hand, when a pulse signal that alternates between high and low states 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 at either a high or low level, the following occurs: In other words, the absolute value of the blade voltage Vbld is greater than the development voltage Vdev by the Zener voltage ΔVz of the Zener diode ZD51 (|Vbld| = |Vdev| + ΔVz).

Through the above operation, a voltage equal to the development voltage Vdev or a voltage whose absolute value is greater than the development voltage Vdev by the Zener voltage (ΔVz) is applied to the development blade 135a. Resistor R135, like resistors R132 and R133, may be added as needed. In Example 1, the Zener voltage (ΔVz) is, for example, 100 V; in other words, the value of the blade voltage Vbld when there is no short circuit between the two terminals of Zener diode ZD51 is, for example, -400 V (= -300 - 100).

(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, and 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 from the charging voltage Vpri to the power supply voltage V1 via resistor R40 and transistor Tr41, and 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.

The toner supply R circuit 134b also uses feedback control of the toner supply R voltage Vtsr to maintain a stable, predetermined voltage. The toner supply R voltage Vtsr is connected to power supply voltage V2 via resistors R44 and R43. The junction between 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 power supply voltage V2 via resistors R46 and R45, and further to GND via capacitor C46. The junction between 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, contributing to the stability of feedback control. Operational amplifier IC41 operates on power supply voltage V1.

The TSR_CONT terminal outputs a fourth pulse signal (hereinafter simply referred to as the 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, current flows from the power supply voltage V2 via resistors R45 and R46 to charge capacitor C46. On the other hand, when the TSR_CONT terminal is in the low-level state, current flows to the TSR_CONT terminal via resistor R46 to discharge capacitor C46. When the TSR_CONT terminal alternates between the Hi-Z state and the low-level state, the balance between charging and discharging 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 that at the positive input terminal, the output terminal of operational amplifier IC41 becomes high level. Transistor Tr41 is turned off, and the absolute value of the negative toner supply R voltage Vtsr increases. On the other hand, if the voltage at the negative input terminal of operational amplifier IC41 is higher than the voltage at the positive input terminal, the output terminal of operational amplifier IC41 goes low. Transistor Tr41 is turned 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.

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 (Lo 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.

Through the above operation, a stable toner supply R voltage Vtsr is generated and applied to the toner supply roller 134a. Resistor R134, like resistors R132, R133, and R135, may be added as needed. The value of the toner supply R voltage Vtsr in Example 1 is, for example, -400 V.

(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.

However, if a high voltage is applied between the contacting parts when these components 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 toner supply roller 134a are in contact, and the developing roller 133a and developing blade 135a are in contact. Therefore, the potential difference between the contacting parts, i.e., between the developing roller 133a and toner supply roller 134a, and between the developing roller 133a and developing blade 135a, should be small.

The development voltage Vdev and the toner supply R voltage Vtsr are both controlled to the same predetermined voltage, with an absolute value 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 a small value 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 contacted 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 a small value by outputting a pulse signal from the BLD_SW terminal to short-circuit both ends of the Zener diode ZD51.

(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 will be excessive for the electrophotographic process. The control of the first embodiment, which solves these problems, is described below.

In Example 1, 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 using 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 explanation, 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.

When a special process, such as the charging current detection process using the charging current detection circuit PRI_ISNS, is initiated, 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. 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 (PRI_CONT is turned ON).

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 (DEV_CONT is turned ON). In other words, 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 (TSR_CONT is turned ON). In S505, the control unit 200 outputs a pulse signal from the BLD_SW terminal to control the blade voltage Vbld to be the same potential as the development voltage Vdev (BLD_SW is turned ON). Here, the control unit 200 controls the blade voltage Vld so that it has the same potential as the development voltage Vdev, but it may also control the potential difference between the blade voltage Vld and the development 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 (CLK is turned ON). This outputs the charging voltage Vpri, development voltage Vdev, toner supply R voltage Vtsr, and blade voltage Vbld.

At S507, the control unit 200 detects the charging current using the charging current detection circuit PRI_ISNS. At S508, the control unit 200 determines whether detection of the charging current by the charging current detection circuit PRI_ISNS has finished. If the control unit 200 determines at 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. At S509, the control unit 200 stops outputting pulse signals from the CLK terminal (turns CLK OFF). The control unit 200 stops outputting the charging voltage Vpri, development voltage Vdev, toner supply R voltage Vtsr, and blade voltage Vbld. At S510, the control unit 200 stops outputting pulse signals from the PRI_CONT terminal (turns PRI_CONT OFF). In S511, the control unit 200 stops the pulse signal being output 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). In S513, the control unit 200 stops the pulse signal being output from the BLD_SW terminal (turns BLD_SW OFF), and ends processing.

(Voltage settings for image formation process and special process)
Table 1 shows the set values of the output voltages during the image forming 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.

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

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 toner supply R voltage Vtsr are also output at a voltage that matches 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 will actually occur due to circuit constant variations, etc. For this reason, the blade voltage Vbld and development voltage Vdev, and the toner supply R voltage Vtsr and development voltage Vdev are controlled to be as identical as possible within the scope that can solve the problems of this invention, and in that sense, they are output at approximately the same voltage values. In other words, the development voltage Vdev, blade voltage Vbld, and 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, developing blade 135a, and toner supply roller 134a, preventing image defects such as streaks. Furthermore, by making the absolute value of the developing voltage Vdev larger than during the image formation process, the load on the transformer T11 during charging current detection can be reduced compared to during the image formation process.

By performing this type of control, even in an inexpensive configuration in which multiple voltages are generated by a common boost circuit, it is possible to prevent image defects from occurring at the contact points between the developing roller 133a, toner supply roller 134a, and 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.

(Other Modifications)
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 small while outputting the original voltage.
For example, instead of using the charging voltage Vpri generated by the charging circuit 132b, the voltage generated by the negative transfer circuit 141c may be used as the original voltage. 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 fundamental voltage. For example, in the first embodiment, the blade voltage Vbld is controlled by a parallel circuit of a Zener diode ZD51 and a transistor Tr51 connected to the development voltage Vdev. However, a parallel circuit of a Zener diode ZD51 and a 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. Furthermore, the types of voltages to be controlled are not limited to three, but may be two, four, or more. That is, the combination of voltages generated depending on the original voltage and the circuit configuration thereof 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.

As described above, according to Example 1, it is possible to suppress image defects caused by contact points between components involved in the development process using an inexpensive circuit configuration.

Example 2 differs from Example 1 in that the configurations of the blade circuit 135b and the development circuit 133b are similar to the configuration of the toner supply R circuit 134b. In Example 2, only the differences from Example 1 will be described, and descriptions of the same parts as Example 1 will be omitted.

(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 of Fig. 2. Also, the developing separation mechanism is omitted in Fig. 5.

(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.

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

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 connected to GND via capacitor C66. The junction of resistors R65 and R66 is connected to the BLD_CONT terminal of the 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 the stability of feedback control. Operational amplifier IC61 operates on power supply voltage V1.

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, current flows from the power supply voltage V2 via resistors R65 and R66 to charge capacitor C66. On the other hand, when the BLD_CONT terminal is in the low-level state, current discharges capacitor C46 via resistor R66 to the BLD_CONT terminal. 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.

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 the 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 the blade voltage Vbld decreases. This operation controls the blade voltage Vbld to a predetermined voltage.

(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 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 steps as those in the first embodiment ( FIG. 4 ) are assigned the same step numbers, and their descriptions will be omitted. After outputting a control signal from the TSR_CONT terminal in S504 such that the toner supply R voltage Vtsr is −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 is −400 V (turning BLD_CONT ON), and proceeds to the processing of S506. That is, the control unit 200 functions as a switching unit that switches 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.

In Example 2, the control unit 200 can independently select (set) the voltage values of the development voltage Vdev, blade voltage Vbld, and 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 control described above in Example 2 as well, image defects are prevented from occurring at the contact points between the development roller 133a, toner supply roller 134a, and development blade 135a. Furthermore, the charging voltage Vpri can be output with the transformer capacity required during the image formation process, even during special processes.

As described above, according to Example 2, it is possible to suppress image defects caused by contact points between components involved in the development process using an inexpensive circuit configuration.

131 Photosensitive drum 132b Charging circuit 133a Developing roller 133b Developing circuit 135a Developing blade 135b Blade circuit 200 Control unit

Claims (13)

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. 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. 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. 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. 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. 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. The image forming apparatus of claim 6, wherein the control means controls the on state or the off state of the transistor by outputting a signal that controls the third power supply. 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. 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. An image forming apparatus according to claim 9, wherein the fourth voltage is negative, and the absolute value of the fourth voltage increases as the low duty of the fourth pulse signal increases. 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. 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. The image forming apparatus of any one of claims 1 to 12, further comprising a contact/separation unit that switches the developing member between the contact state and the separated state.