JP2023074341A - Image forming apparatus - Google Patents

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

The present invention relates to an image forming apparatus, and for example, to an image forming apparatus using an electrophotographic method.

Conventionally, a configuration has been proposed in which a plurality of voltages are generated from one high-voltage circuit to achieve cost reduction. For example, in Patent Document 1, a developing voltage is generated by generating a charging voltage with a transformer and dividing the charging voltage with 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. Further, for example, in Patent Document 2, a developing voltage is generated by generating a blade voltage with a transformer and dividing the blade voltage with a Zener diode and a resistor. Here, the blade voltage is applied to the developer blade. Incidentally, the developing blade is a blade for uniformizing the toner on the surface of the developing roller by sliding in contact with the developing roller.

Further, when the components that contribute to the development process (hereinafter referred to as "development system") are separated from the photoreceptor, the rotation of the development roller is stopped, and there is a long period of time between the development roller and the development blade. If the potential difference continues to occur, the following problems arise. That is, it is known that the contact portion of the developing roller surface with the developing blade is in a different state from the others, resulting in image defects such as streaks. Therefore, it is conceivable not to supply a voltage to the components of the development system when the components of the development system are separated from the photoreceptor.

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

However, the configuration in which a plurality of voltages are generated by voltage division control from one high voltage circuit has the following problems. When a voltage is output from one high voltage circuit and controlled so that a voltage connected to a stage lower than that voltage is not output, the load applied to the transformer that generates the high voltage is reduced for normal electrophotographic process execution. excessive. That is, the ability required for the transformer becomes excessive, leading to an increase in the cost and size of the transformer. For this reason, it is desired to suppress image defects caused by contact portions between members involved in development processing with an inexpensive circuit configuration.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to suppress image defects caused by contact between members involved in development processing with an inexpensive circuit configuration.

In order to solve the above problems, the present invention has the following configurations.
(1) The photoreceptor can be in a contact state in which the photoreceptor is in contact with the photoreceptor or in a separated state in which the photoreceptor is separated from the photoreceptor. a developing member that develops an image 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; and a transformer, and generates a first voltage. a first power source, a second power source that generates a second voltage to be applied to the developing member from the first voltage, a third voltage that is generated from the second voltage generated by the second power source, and a third voltage that is generated from the second voltage. A third power source that applies a voltage to the first contact member, 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. and control means for controlling so that the first potential difference is formed in the separated state, and controlling so that the second potential difference is formed in the contact state; An image forming apparatus, wherein control is performed such that the absolute value of the second voltage in the separated state is larger than the absolute value of the second voltage in the contact state.

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.

Schematic cross-sectional configuration diagrams of image forming apparatuses of Examples 1 and 2 Circuit diagram of image forming unit of embodiment 1 FIG. 3 shows the relationship between the set value (pulse signal) of each circuit and the output voltage, and the relationship between the potential of the surface of the photosensitive drum or the charging current and the charging voltage. 4 is a flow chart showing voltage control in the first embodiment; Circuit diagram of the image forming unit of the second embodiment Flowchart showing voltage control in embodiment 2

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. Hereinafter, the voltage output from one high-voltage circuit that has a transformer and is connected to an AC voltage is referred to as the original voltage. Being connected to a lower stage than the original voltage is said to be subordinate.

(Configuration of image forming apparatus)
FIG. 1 shows a schematic cross-sectional view of the image forming apparatus 101. As shown in FIG. The paper feed unit 102 has a paper feed tray 121 and a paper feed roller 122 , and paper P to be printed is stored in the paper feed tray 121 . The image forming unit 103 includes a photosensitive drum 131 that is a photosensitive member, a charging roller 132a that is a charging member, a developing roller 133a that is a developing member, a toner supply roller 134a that is a second contact member (supply roller), and a first contact member. It has a developing blade 135a as a 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 the first power supply, applies the generated high voltage to the charging roller 132a. The developing circuit 133b, which is the second power source, applies the generated high voltage to the developing roller 133a. The toner supply R circuit 134b, which is the fourth power supply, applies the generated high voltage to the toner supply roller 134a. The blade circuit 135b, which is the third power supply, 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 as 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. Here, the transfer negative circuit 141c may be connected in parallel with the transfer positive circuit 141b, and the connection to the transfer roller 141a may be switched by switching means such as a switch, or the transfer negative circuit 141c itself may be eliminated. Also, the transfer roller 141 a is in contact with the photosensitive drum 131 . The fixing section 105 has a fixing roller 151 and a pressure roller 152 . Also, the discharge unit 106 includes discharge rollers 161 a and 161 b and a discharge tray 162 .

A control unit 200, which is control means, has a CPU 200a, a ROM 200b, and a RAM 200c. The CPU 200a controls the image forming operation by the image forming unit 103, the fixing operation by the fixing unit 105, the conveying operation of the paper P, etc. according to various programs stored in the ROM 200b and using the RAM 200c as a work area. The control unit 200 also controls the contact operation or separation operation of the developing roller 133a, which will be described later, and each circuit, which is each power source for applying each voltage, which will be described later. Note that a control unit for controlling the image forming unit 103, the fixing unit 105, and each power supply may be provided separately from the control unit 200, and the control unit 200 may control the separately provided control unit.

(Operation of image forming apparatus)
An operation of forming a toner image on the surface of the photosensitive drum 131 by the image forming unit 103 will be described. The charging roller 132 a to which a negative high voltage is applied from the charging circuit 132 b 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 slight gap (GAP), and the charging roller 132a charges the surface of the photosensitive drum 131 by utilizing the discharge in the gap. The laser scanner 137 irradiates the photosensitive drum 131 with laser light according to image data to form a latent image on the surface of the photosensitive drum 131 . The toner accommodated (stored) in the toner container 136 is, for example, negatively charged by agitation.

The toner supply roller 134a supplies the toner contained in the toner container 136 to the development roller 133a. The toner is moved to the surface of the developing roller 133a by the toner supply roller 134a to which a high negative voltage is applied from the toner supply R circuit 134b, and adheres to the surface. The development blade 135a smoothes the toner supplied to the development roller 133a by the toner supply roller 134a. Since the height of the toner adhering to the surface of the developing roller 133a is uneven depending on the location, the toner is evenly leveled by the developing blade 135a to which a negative high voltage is applied by the blade circuit 135b. The developing roller 133a, which has toner attached to its surface, uses a 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, by setting the output voltage of the toner supply R circuit 134b to be larger in absolute value than the output voltage of the developing circuit 133b, the negatively charged toner can be easily moved to the developing roller 133a. Further, by setting the output voltage of the blade circuit 135b to be larger in absolute value than the output voltage of the developing circuit 133b, it is made difficult for the negatively charged toner to adhere to the developing blade 135a. For example, the output voltage of the developing circuit 133b is set to -300V, and the output voltage of the toner supply R circuit 134b and the blade circuit 135b is set to -500V.

Next, the operation of forming an image on paper P will be described. When the image forming apparatus 101 receives a print job, each roller and the laser scanner 137 start operating. The paper P stored in the paper feed tray 121 is fed by the paper feed roller 122, transported along the transport path 111, and eventually reaches a position where the photosensitive drum 131 and the transfer roller 141a face each other. The paper P is nipped (hereinafter referred to as nip) between the photosensitive drum 131 and the transfer roller 141a to which a positive high voltage is applied from the positive transfer circuit 141b. is transferred to the paper P. The sheet P that continues to be conveyed next reaches the fixing section 105 and is pressure-nipped between the fixing roller 151 and the pressure roller 152, and the unfixed toner image on the sheet P is fixed. After that, the paper P is discharged to the discharge tray 162 via the discharge rollers 161a and 161b. The process of forming an image on the paper P as described above is hereinafter also referred to as an image forming process. A process other than the image forming process, which is performed while avoiding the image forming process, is hereinafter referred to as a special process.

(Development separation mechanism)
Next, a configuration for separating the developing roller 133a from the photosensitive drum 131 will be described. Since the developing roller 133a rotates while sliding against the photosensitive drum 131, the toner supply roller 134a, and the developing blade 135a, the surface of the developing roller 133a wears and deteriorates as the use progresses. Considering the product life of the image forming apparatus 101, the sliding time should be minimized. The image forming apparatus 101 of the first embodiment includes a developing separation mechanism (see FIG. 2) which is a contact separating means capable of separating the developing roller 133 a 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 forms static electricity on the photosensitive drum 131 (on the photoreceptor). The electrostatic latent image is developed with toner to form a toner image.

The developing separation mechanism moves a portion including the developing roller 133a, the toner supply roller 134a, the developing blade 135a, and the toner container 136, so that the developing roller 133a is separated from the photosensitive drum 131, and is in contact with the photosensitive drum 131. and switch to That is, the developing blade 135a contacts the developing roller 133a in a contact state and a separated state, and the toner supply roller 134a also contacts the developing roller 133a in a contact state and a separated state. In FIG. 1, the broken line 133a' representatively indicates the state in which the developing roller 133a is separated.

The image forming apparatus 101 has a developing/separating mechanism which is a contact/separating means for switching the developing roller 133a between the contact state and the separated state. In Embodiment 1, the contact/separation mechanism includes a clutch drive circuit 250, a development separation clutch 252, a development separation gear 254, and a drive motor 256 (see FIG. 2). The control unit 200 controls the contact/separation mechanism. The developing separation clutch 252 is driven through the clutch drive circuit 250 . The development separating clutch 252 has a state in which drive is transmitted from the drive motor 256 to the development separation gear 254 (hereinafter referred to as a transmission state) and a state in which the drive from the drive motor 256 to the development separation gear 254 is interrupted (hereinafter referred to as a disconnection state). state) can be switched. The control unit 200 controls the drive motor 256 by means of a drive circuit (not shown), rotation detection means (not shown) such as an encoder, and the like. The control section 200 controls the developing separation clutch 252 via the clutch drive circuit 250 . The developing roller 133a is separated from the photosensitive drum 131 in the transmitting state, and the developing roller 133a contacts the photosensitive drum 131 in the blocking state. The controller 200 can switch the developing roller 133a between the contact state and the separation state at a predetermined timing. An electromagnetic clutch can be used as the developing separation clutch 252 . Alternatively, a toothless gear and a solenoid may be used as the developing separation clutch 252 to switch between the transmission state (abutment state) and the cut-off state. As described above, in the first embodiment, when the developing roller 133a comes into contact with the photosensitive drum 131 or separates 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. Moving.

The development separating mechanism also has a function of removing (releasing) the rotation driving gear (not shown) of the developing roller 133a during separation, and the development roller 133a and the toner supply roller 134a stop rotating in the separated state. The image forming apparatus 101 controls the developing separation mechanism to the separated state when the image forming operation is not performed (hereinafter referred to as "non-image forming time"). This eliminates sliding between the developing roller 133a, the photosensitive drum 131, the toner supply roller 134a, and the developing blade 135a, thereby improving durability.

(Configuration and operation of high voltage generation circuit)
The configuration and operation of the charging circuit 132b, developing circuit 133b, toner supply R circuit 134b, and 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 the power supply voltage V1, and the other terminal is connected to a field effect transistor (hereinafter referred to as a field effect transistor). FET) 11 is connected. The black circles of the primary winding T11-1 and secondary winding T11-2 indicate the winding start (in other words, polarity) of the coil. A resistor R 12 is connected between the gate terminal of FET 11 and the source terminal, and a resistor R 17 is connected between the CLK terminal of the control unit 200 . A parallel circuit in which a capacitor C11 and a resistor R11 are connected in parallel, a diode D11 and a are connected in series. The diode D11 has a cathode terminal connected to the 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.

On the other hand, a diode D12 and a capacitor C12 are connected between both terminals of the secondary winding T11-2. The diode D12 has a cathode terminal connected to one terminal of the secondary winding T11-2 of the transformer T11, and an anode terminal 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 is a detection means. Note that the power supply voltage V1 in the first embodiment is, for example, 24V.

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 is turned on, and the drain voltage of the FET 11 drops to approximately the same potential as the ground (hereinafter referred to as GND). As a result, a voltage is applied across the primary winding T11-1 of the transformer T11, and an exciting current flows. In this state, when the voltage output from the CLK terminal changes to a low level state, the FET11 is turned off and a flyback voltage is generated across the primary winding T11-1. Along with this, a flyback voltage corresponding to the turns ratio between the primary winding T11-1 and the secondary winding T11-2 is also generated in the secondary winding T11-2. The generated flyback voltage is rectified and smoothed by the diode D12 and the capacitor C12 to generate the charging voltage Vpri, which is the negative first voltage. Note that the capacitor C11, the resistor R11, and the diode D11 serve as a snubber circuit that absorbs a surge voltage due to the leakage inductance of the primary winding T11-1.

The voltage output from the CLK terminal of the control unit 200 is a rectangular wave in which a high level state and a low level state alternately occur. In Example 1, for example, a fixed square wave having a frequency of 50 kHz and a duty of 10% is output. Here, the duty of 10% is the ratio of the high level time in one period of the signal (the sum of the high level time and the low level time), but it may be the ratio of the low level time. . Note that the frequency and duty of the rectangular wave should be designed to optimum values for each circuit, and are not limited to the values in the first embodiment. Furthermore, the frequency and duty of the rectangular wave may not be fixed values, and may be variable depending on the voltage and load of the controlled object. By turning on/off the FET11, the flyback voltage generated in the secondary winding T11-2 is rectified and smoothed by the diode D12 and the capacitor C12 to generate the charging voltage Vpri.

The charging circuit 132b feedback-controls the charging voltage Vpri in order to control the charging voltage Vpri to a stable and predetermined voltage. The charging voltage Vpri is connected to the power supply voltage V2 through resistors R14 and R13. A connection point between the resistor R14 and the resistor R13 is connected to the positive input terminal (non-inverting input terminal, + terminal) of the comparator IC11. The negative input terminal (inverting input terminal, - terminal) of the comparator IC11 is connected to the power supply voltage V2 via the resistors R16 and R15, and further connected to GND via the capacitor C16. A connection point between the resistor R15 and the resistor R16 is connected to a PRI_CONT terminal of the control section 200 . Also, the output terminal of the comparator IC11 is connected to the gate terminal of the FET11. The PRI_CONT terminal outputs 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.

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

FIG. 3(a) is a graph showing the relationship between the pulse signal output from the PRI_CONT terminal and the charging voltage Vpri. The charging voltage Vpri is shown on the axis. Specifically, as shown in FIG. 3A, as the low duty of the pulse signal output from the PRI_CONT terminal increases, the absolute value of the charging voltage Vpri, which is a negative voltage, increases.

Returning to the description of FIG. When the voltage at the negative input terminal of comparator IC11 is lower than the voltage 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 the control unit 200 is directly input to the gate terminal of the FET 11 to drive the FET 11 on and off. On the other hand, when the voltage of the negative input terminal of the comparator IC11 is higher than the voltage of the positive input terminal, the output terminal of the comparator IC11 becomes low level. At this time, the current output from the CLK terminal is pulled by the output terminal of the comparator IC11, and the gate voltage of the FET11 is forcibly set to low level. As a result, the FET 11 cannot be turned on at the timing when it should be turned on, which promotes 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. Since the power supply voltage V2 affects the voltages of the positive and negative input terminals of the comparator IC11, it should be noted that a power supply with relatively high voltage accuracy should be used for the power supply voltage V2. The comparator IC11 operates with the power supply voltage V1.

Through the above operation, the charging circuit 132b generates a stable charging voltage Vpri and applies it to the charging roller 132a. A resistor R132 is provided to limit the output current. Furthermore, the resistor R132 is also provided for the purpose of protecting the charging roller 132a detachable from the image forming apparatus 101 from external ESD (Electro Static Discharge) when the image forming apparatus 101 is detached. Resistor R132 may be inserted as required. Also, the value of the charging voltage Vpri in Example 1 is -1500V, for example.

(Charging current detection)
The charging current detection circuit PRI_ISNS is a circuit for detecting the current supplied to the charging roller 132a (hereinafter referred to as charging current). As a method of accurately detecting the potential of the surface of the photosensitive drum 131, a method of detecting a voltage at which discharge from the charging roller 132a to the photosensitive drum 131 is started (hereinafter referred to as discharge start voltage) is known. 3E and 3F show the relationship between the charging voltage Vpri and the charging current or the surface potential of the photosensitive drum 131. FIG. In FIG. 3(e), the horizontal axis indicates the charging voltage (negative), and the vertical axis indicates the charging current. In FIG. 3F , the horizontal axis indicates the charging voltage (negative), and the vertical axis indicates the surface potential of the photosensitive drum 131 . 3E and 3F, the transition of the charging current and the surface potential of the photosensitive drum 131 when the absolute value of the charging voltage Vpri is gradually increased from 0V will be described. The charging voltage Vpri starts to rise from 0 V, and the state (0 A) in which the charging current does not flow continues for a while. When the charging voltage Vpri reaches the discharge start voltage, discharging from the charging roller 132a to the photosensitive drum 131 is started, and charging current begins to flow (FIG. 3(e)). The surface potential of the photosensitive drum 131 is 0 V at this time, and thereafter increases while maintaining the same potential difference as the discharge start voltage (that is, the lines in the graph are kept parallel) with the charging voltage Vpri. Go (Fig. 3(f)). Therefore, by detecting the discharge start voltage, it is possible to accurately detect the surface potential of the photosensitive drum 131 based on the charging voltage Vpri and the discharge start voltage. However, since it is necessary to correctly detect the discharge current from the charging roller 132a to the photosensitive drum 131, it is necessary to detect the charging current while the developing roller 133a is separated from the photosensitive drum 131. FIG. That is, when the charging current detection circuit PRI_ISNS detects the current flowing through the charging roller 132a, the control unit 200 controls the developing roller separation mechanism so that the developing roller 133a is in the separated state. In the first embodiment, during non-image formation, the charging current detection is performed while the developing separation mechanism is controlled to be in the separated state. That is, the detection of charging current can be said to be an example of a special process.

(development circuit)
The development circuit 133b is a circuit that reduces the charging voltage Vpri by dividing the voltage to generate a development voltage Vdev that is a negative second voltage. That is, it can be said that the developing circuit 133b is subordinate to the charging circuit 132b. The developing circuit 133b is connected from the charging voltage Vpri to the power supply voltage V1 via the resistor R50, Zener diode ZD51, and transistor Tr31. The development circuit 133b outputs the voltage of the collector terminal of the transistor Tr31 as the development voltage Vdev. A resistor R39 is connected between the base terminal of the transistor Tr31 and the emitter terminal, and a resistor R38 is connected to the output terminal of the operational amplifier IC31.

The developing circuit 133b also feedback-controls the developing voltage Vdev in order to control the developing voltage Vdev to a stable and predetermined voltage. The development voltage Vdev is connected to the power supply voltage V2 via resistors R34 and R33. A connection point between the resistor R34 and the resistor R33 is connected to the positive input terminal of the operational amplifier IC31. The negative input terminal of the operational amplifier IC31 is connected to the power supply voltage V2 via the resistors R36 and R35, and further connected to GND via the capacitor C36. A connection point between the resistor R35 and the resistor R36 is connected to the DEV_CONT terminal of the control section 200 . A resistor R37 and a capacitor C37 are connected in series between the negative input terminal and the output terminal of the operational amplifier IC31. A resistor R37 and a capacitor C37 are provided for phase compensation of the operational amplifier IC31 and contribute to stabilization of feedback control. The operational amplifier IC31 operates with the power supply voltage V1.

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

When the voltage of the negative input terminal of the operational amplifier IC31 is lower than that of the positive input terminal, the output terminal of the operational amplifier IC31 becomes high level. As a result, the transistor Tr31 is turned off and the absolute value of the developing voltage Vdev increases. On the other hand, when the voltage of the negative input terminal of the operational amplifier IC31 is higher than the voltage of the positive input terminal, the output terminal of the operational amplifier IC31 becomes low level. As a result, the transistor Tr31 is turned on and the absolute value of the development voltage Vdev is lowered. This operation enables the development voltage Vdev to be controlled to a predetermined voltage. The control unit 200 controls the developing circuit 133b, which is the second power supply, by outputting the 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.

FIG. 3(b) is a graph showing the relationship between the pulse signal output from the DEV_CONT terminal and the developing voltage Vdev, where the horizontal axis represents the low duty of the pulse signal output from the DEV_CONT terminal, and the vertical axis represents the Lo Duty. The axis indicates the development voltage Vdev. As shown in FIG. 3B, 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.

Returning to the description of FIG. Through the above operation, a stable development voltage Vdev is generated and applied to the development roller 133a. Similar to the resistor R132, the resistor R133 may be inserted if necessary for the purpose of limiting the output current and protecting the developing roller 133a from the image forming apparatus 101 from external ESD. good. Also, the value of the developing 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 through a Zener diode ZD51. The Zener diode ZD51 has an anode terminal connected to the charging voltage Vpri via a resistor R50, and an anode terminal side to the blade voltage Vbld. That is, the blade voltage Vbld has a larger absolute value than the development voltage Vdev by the Zener voltage of the Zener diode ZD51. The Zener diode ZD51 has a cathode terminal connected to the development voltage Vdev output from the development circuit 133b and an anode terminal connected to the blade voltage Vbld output from the blade circuit 135b.

Blade circuit 135b has transistor Tr51 connected in parallel with Zener diode ZD51. Specifically, the Zener diode ZD51 has an anode terminal connected to the collector terminal of the transistor Tr51 and a cathode terminal connected to the emitter terminal of the transistor Tr51. When the transistor Tr51 is turned on, the two 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 has a predetermined potential difference with respect to the development voltage Vdev or has the same potential. When the transistor Tr51 is turned off, the blade voltage Vbld has a larger absolute value than the development voltage Vdev (|Vbld|>|Vdev|). The transistor Tr51 functions as switching means for switching between a first state in which the potential difference between the development voltage Vdev and the blade voltage Vbld is the first potential difference and a second state in which the potential difference is the second potential difference larger than the first potential difference. . In Example 1, the first potential difference is 0 V (|Vbld|=|Vdev|) and the second potential difference is the 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 through resistors R51 and R52. A capacitor C51 is connected in parallel with the resistor R52. A connection point between the resistors R51 and R52 is connected to the anode terminal of the diode D51, and the cathode terminal of the diode D51 is connected to the anode terminal of the diode D52. The diode D52 has a cathode terminal connected to the emitter terminal of the transistor Tr51. The diode D51 has a cathode terminal connected to the BLD_SW terminal of the control unit 200 via the capacitor C50. The diode D52 has an anode terminal connected to the BLD_SW terminal of the control unit 200 via the capacitor C50.

A pulse signal that alternately repeats a high level state and a low level state is output from the BLD_SW terminal. When the BLD_SW terminal is in a transient state in which the BLD_SW terminal switches from a high level state to a low level state, current flows from the power supply voltage V1 through the transistor Tr31, the emitter terminal and base terminal of the transistor Tr51, the resistor R51, the diode D51, and the capacitor C50 in that order. Finally, it flows into the BLD_SW terminal. In the transient state where the BLD_SW terminal switches from the low level state to the high level state, the current flowing out from the BLD_SW terminal flows to the power supply voltage V1 via the capacitor C50, the diode D52, and the transistor Tr31. When the pulse signal from the BLD_SW terminal repeats a high level state and a low level state, the capacitor C51 is charged and a base current stably flows out from the base terminal of the transistor Tr51. When the base current from the base terminal of the transistor Tr51 flows stably, the transistor Tr51 is turned on and the two terminals of the Zener diode ZD51 are short-circuited. On the other hand, when the BLD_SW terminal is fixed to the high level state or the low level state, the transistor Tr51 is turned off and the two terminals of the Zener diode ZD51 are not short-circuited.

The first state described above is a state in which the transistor Tr51 is turned on to short-circuit the anode terminal and the cathode terminal of the Zener diode ZD51. The second state described above is a state in which the transistor Tr51 is turned off so that the anode terminal and the cathode terminal of the Zener diode ZD51 are not short-circuited. The control unit 200 controls the transistor Tr51 so as to be in the first state in the separated state, and controls the transistor Tr51 so as to be in the second state in the contact state. The control unit 200 outputs a signal for controlling the blade circuit 135b from the BLD_SW terminal, thereby controlling the ON state or OFF state of the transistor Tr51.

FIG. 3(c) shows the relationship between the low duty of the pulse signal output from the DEV_CONT terminal and the blade voltage Vbld. In FIG. 3(c), the horizontal axis indicates the low duty (Lo Duty) of the pulse signal output from the DEV_CONT terminal, and the vertical axis indicates the blade voltage Vbld. When a pulse signal is output from the BLD_SW terminal (in the figure, the graph when BLD_SW is ON), the blade voltage Vbld is the same voltage as the development voltage Vdev. That is, when a pulse signal that repeats a high level state and a low level state is output from the BLD_SW terminal, the blade voltage Vbld becomes the same voltage as the development voltage Vdev in FIG. 3(b). On the other hand, when the pulse signal that repeats the high level state and the low level state is not output from the BLD_SW terminal (graph at BLD_SW OFF in the figure), in other words, the signal is fixed at the high level state or the low level state. When it goes like this: That is, the absolute value of the blade voltage Vbld is larger than the development voltage Vdev by the Zener voltage ΔVz of the Zener diode ZD51 (|Vbld|=|Vdev|+ΔVz).

As a result of the above operation, a voltage equal to the development voltage Vdev or a voltage having a larger absolute value than the development voltage Vdev by the Zener voltage (ΔVz) is applied to the development blade 135a. It should be noted that the resistor R135 may be inserted as required, like the resistors R132 and R133. Further, 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). .

(Toner supply R circuit)
The toner supply R circuit 134b is a circuit that generates the toner supply R voltage Vtsr, which is the negative fourth voltage, by reducing the charging voltage Vpri by partial pressure, and has substantially the same configuration as the development circuit 133b. The difference is that there is no Zener diode in the voltage dividing 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 the resistor R40 and the transistor Tr41, and the voltage of the collector terminal of the transistor Tr41 becomes the toner supply R voltage Vtsr. A resistor R49 is connected between the base terminal of the transistor Tr41 and the emitter terminal, and a resistor R48 is connected to the output terminal of the operational amplifier IC41.

The toner supply R voltage Vtsr is also feedback-controlled in the toner supply R circuit 134b in order to control the toner supply R voltage Vtsr to a stable and predetermined voltage. The toner supply R voltage Vtsr is connected to the power supply voltage V2 via resistors R44 and R43. A connection point between the resistor R44 and the resistor R43 is connected to the positive input terminal of the operational amplifier IC41. The negative input terminal of the operational amplifier IC41 is connected to the power supply voltage V2 via the resistors R46 and R45, and further connected to GND via the capacitor C46. A connection point between the resistor R45 and the resistor R46 is connected to the TSR_CONT terminal of the control section 200 . A resistor R47 and a capacitor C47 are connected in series between the negative input terminal and the output terminal of the operational amplifier IC41. A resistor R47 and a capacitor C47 are provided for phase compensation of the operational amplifier IC41 and contribute to stabilization of feedback control. The operational amplifier IC41 operates with the power supply voltage V1.

The TSR_CONT terminal outputs a fourth pulse signal (hereinafter simply referred to as a pulse signal) that alternately repeats the Hi-Z state and the low level state. When the TSR_CONT terminal is in the Hi-Z state, a current flows from the power supply voltage V2 through the resistors R45 and R46 to charge the capacitor C46. On the other hand, when the TSR_CONT terminal is in the low level state, the current discharging the capacitor C46 flows through the resistor R46 toward the TSR_CONT terminal. When the TSR_CONT terminal repeats the Hi-Z state and the low level state, the charge/discharge balance of the capacitor C46 stabilizes at a predetermined voltage. Therefore, the voltage of the negative input terminal of the operational amplifier IC41 is determined according to the duty of the pulse signal output from the TSR_CONT terminal. When the voltage of the negative input terminal of the operational amplifier IC41 is lower than that of the positive input terminal, the output terminal of the operational amplifier IC41 becomes high level. The 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 of the negative input terminal of the operational amplifier IC41 is higher than the voltage of the positive input terminal, the output terminal of the operational amplifier IC41 becomes low level. The transistor Tr41 is turned on, and the absolute value of the toner supply R voltage Vtsr is lowered. 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.

FIG. 3D is a graph showing the relationship between the pulse signal output from the TSR_CONT terminal and the toner supply R voltage Vtsr. In FIG. 3D, the horizontal axis indicates the low duty (Lo Duty) of the pulse signal output from the TSR_CONT terminal, and the vertical axis indicates the toner supply R voltage Vtsr. As shown in FIG. 3D, 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. It should be noted that the resistor R134 may be inserted if necessary, like the resistors R132, R133, and R135. Further, the value of the toner supply R voltage Vtsr in Example 1 is -400V, for example.

(Control during development separation)
As described above, the image forming apparatus 101 according to the first embodiment detects the charging current while the developing separation mechanism is controlled to be in 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 from each other. Therefore, during detection of the charging current, the developing voltage Vdev, the blade voltage Vbld, and the toner supply R voltage Vtsr can be functionally any values.

However, if a high voltage is applied between the contacting parts while these members are not rotating, the contacting part will be in a different state from the others, causing image defects such as streaks. Even when the developing 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, that is, 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.

The development voltage Vdev and the toner supply R voltage Vtsr are both controlled to the same predetermined voltage with a larger absolute value than the voltage during the image forming process. As a result, the potential difference between the developing roller 133a and the toner supply roller 134a can be controlled to be small while suppressing the load applied to the transformer. That is, the control unit 200 outputs the 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 the fourth pulse signal in which the potential difference is larger than the third potential difference in the contact state. A fourth pulse signal is output to produce a potential difference. As a result, the potential difference between the developing roller 133a and the toner supply roller 134a is also controlled to change between the image forming process and the special process. On the other hand, the blade voltage Vbld can control the potential difference between the developing roller 133a and the developing blade 135a to be small by outputting a pulse signal from the BLD_SW terminal and short-circuiting both ends of the Zener diode ZD51.

(Control of Example 1)
The power supply of Example 1 is configured to generate a primary voltage from one transformer and generate a plurality of different voltages through voltage division control. Here, the original voltage is the charging voltage Vpri generated by the charging circuit 132b. In such a configuration, when control is performed to turn off the unused voltage in order to reduce the potential difference between the developing components while the developing components are stopped, the specifications required for the transformer T11 are as follows. The specifications are higher than those required for the electrophotographic process. It should be noted that the development components are stopped during the special process. If a transformer meeting the required specifications is used with the developing components stopped, the transformer specifications become excessive for the electrophotographic process. Hereinafter, the control of the first embodiment for solving such problems will be described.

In the first embodiment, the control of 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 FIG. explain. 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 are expressed as between the developing roller 133a and the toner supply roller 134a and the developing blade 135a. In the following description, the above-described charging current detection (hereinafter referred to as a charging current detection process) will be described as an example of the special process.

When the special process, for example, the charging current detection processing by the charging current detection circuit PRI_ISNS, is started, the control unit 200 executes the processing from step (hereinafter referred to as S) 501 and subsequent steps. In S501, the control unit 200 controls the developing separation mechanism so that the photosensitive drum 131 and the developing member 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, eg, -1500 V (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, eg, -400 V (DEV_CONT is turned ON). That is, the controller 200 controls the absolute value of the developing voltage Vdev (for example, |-400|V) during the charging current detection process to be higher than the absolute value (for example, |-300|V) of the developing voltage Vdev during the image forming process. Control to grow. 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, eg, -400 V (TSR_CONT is turned ON). In S505, the control unit 200 outputs a pulse signal from the BLD_SW terminal, and controls the blade voltage Vbld to have the same potential as the development voltage Vdev (BLD_SW is turned on). Here, the control unit 200 controls the blade voltage Vld to have the same potential as the development voltage Vdev, but the potential difference between the blade voltage Vld and the development voltage Vdev is smaller than the potential difference during the image forming process. can be controlled as follows. In S506, the control unit 200 outputs a pulse signal from the CLK terminal (CLK is turned ON). As a result, the charging voltage Vpri, the developing voltage Vdev, the toner supply R voltage Vtsr, and the blade voltage Vbld are output.

In S507, the control unit 200 detects the charging current by the charging current detection circuit PRI_ISNS. In S508, the control unit 200 determines whether the detection of the charging current by the charging current detection circuit PRI_ISNS has ended. If the control unit 200 determines in S508 that the detection of the charging current has not ended, the process returns to S508, and if it determines that the detection has ended, the process proceeds to S509. In S509, the control unit 200 stops outputting the pulse signal from the CLK terminal (CLK is turned OFF). The controller 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 the pulse signal output from the PRI_CONT terminal (PRI_CONT is turned OFF). In S511, the control unit 200 stops the pulse signal output from the DEV_CONT terminal (DEV_CONT is turned OFF). In S512, the control unit 200 stops the pulse signal output from the TSR_CONT terminal (TSR_CONT is turned OFF). In S513, the control unit 200 stops the pulse signal output from the BLD_SW terminal (BLD_SW is turned OFF), and ends the process.

(Set values for each voltage during image forming process and special process)
Table 1 is a table showing set values of each output voltage during the image forming process and during the special process (during the charging current detection process) in Example 1. Table 1 lists the values in the detection of charging current as a special process as described above.

表１は、１列目に各プロセス（画像形成プロセス、帯電電流検知プロセス）、２列目に帯電電圧Ｖｐｒｉ、３列目に現像電圧Ｖｄｅｖ、４列目にブレード電圧Ｖｂｌｄ、５列目にトナー供給Ｒ電圧Ｖｔｓｒをそれぞれ示している。

Table 1 shows each process (image forming process, charging current detection process) in the 1st column, charging voltage Vpri in the 2nd column, development voltage Vdev in the 3rd column, blade voltage Vbld in the 4th column, and toner in the 5th column. The supply R voltage Vtsr is shown respectively.

The set value of the developing voltage Vdev at the time of detecting the charging current is set to a voltage having a larger absolute value than the set value at the time of the image forming process, for example, -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 matching the development voltage Vdev, eg, -400 V (Vbld=Vdev, Vtsr=Vdev). However, when −400 V is output as the set value during the charging current detection process, an output error actually occurs due to variations in circuit constants and the like. Therefore, 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 the same voltage as much as possible within the scope of solving the problems of the present invention. Output with the same voltage value. That is, the development voltage Vdev, the blade voltage Vbld, and the toner supply R voltage Vtsr at the time of detecting the charging current are output with the same or substantially the same value. As a result, the potential difference between the developing roller 133a, the developing blade 135a, and the toner supply roller 134a is small, and image defects such as streaks can be suppressed. Further, by making the absolute value of the developing voltage Vdev larger than during the image forming process, the load applied to the transformer T11 during the detection of the charging current can be made smaller than during the image forming process.

By performing such control, even in an inexpensive configuration in which a plurality of voltages are generated by a common booster circuit, it is possible to suppress the occurrence of image defects at the contact portion between the developing roller 133a, the toner supply roller 134a, and the developing blade 135a. . Furthermore, the transformer capability required during the image forming process can output the charging voltage Vpri even during the special process.

(Other modifications)
Although the above-described embodiment shows a circuit that generates each voltage from the charging voltage Vpri, the configuration of the present invention is not limited to this. For example, it may be configured to generate a plurality of voltages from the same power supply, and control may be performed to reduce the potential difference between the plurality of subordinate voltages 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 transfer negative circuit 141c corresponds to the first power supply, and the transfer negative voltage corresponds to the first voltage.
Also, the circuit configuration for generating the development voltage Vdev, the blade voltage Vbld, and the toner supply R voltage Vtsr may be a circuit generated depending on the original voltage. For example, in Example 1, 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 Zener diode ZD51 and transistor Tr51 may be connected to toner supply R voltage Vtsr instead of 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. . The second contact member corresponds to the developing blade 135a, and the first contact member corresponds to the toner supply roller 134a. Also, the types of voltages to be controlled are not limited to three types, and may be two types or four types or more. That is, the combination of voltages generated depending on the original voltage and the circuit configuration thereof are not limited to the above-described embodiment.
Furthermore, the control section 200 may control the ON state or 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 the first embodiment, it is possible to suppress image defects caused by contact portions between members involved in development processing with an inexpensive circuit configuration.

The second embodiment differs from the first embodiment in that the configuration of the blade circuit 135b and the development circuit 133b is the same as the configuration of the toner supply R circuit 134b. In the second embodiment, only the parts different from the first embodiment will be explained, and the explanation of the same parts as the first embodiment will be omitted.

(Configuration and operation of high voltage generation circuit)
FIG. 5 is a circuit diagram of the imaging unit 103 of the second embodiment. The configurations of the blade circuit 135b and the development circuit 133b are different from those in FIG. In addition, the developing separation mechanism is omitted in FIG.

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

Also, the blade circuit 135b is connected from the charging voltage Vpri to the power supply voltage V1 via the resistor R60 and the transistor Tr61. In the blade circuit 135b, the voltage of the collector terminal of the transistor Tr61 becomes the blade voltage Vbld. A resistor R69 is connected between the base terminal and the emitter terminal of the transistor Tr61. One end of the 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.

Blade voltage Vbld is connected to supply voltage V2 through resistors R64 and R63. A connection point between the resistor R64 and the resistor R63 is connected to the positive input terminal of the operational amplifier IC61. The negative input terminal of the operational amplifier IC61 is connected to the power supply voltage V2 via the resistors R66 and R65, and further connected to GND via the capacitor C66. A connection point between the resistors R65 and R66 is connected to the BLD_CONT terminal of the control unit 200 . A resistor R67 and a capacitor C67 are connected in series between the negative input terminal and the output terminal of the operational amplifier IC61. A resistor R67 and a capacitor C67 are provided for phase compensation of the operational amplifier IC61 and contribute to stabilization of feedback control. The operational amplifier IC61 operates with the power supply voltage V1.

The BLD_CONT terminal outputs a third pulse signal (hereinafter simply referred to as a pulse signal) that alternately repeats the Hi-Z state and the low level state. When the BLD_CONT terminal is in the Hi-Z state, a current for charging the capacitor C66 flows from the power supply voltage V2 through the resistors R65 and R66. On the other hand, when the BLD_CONT terminal is in the low level state, the current discharging the capacitor C46 flows through the resistor R66 toward the BLD_CONT terminal. When the BLD_CONT terminal repeats the Hi-Z state and the low level state, the charge/discharge balance of the capacitor C66 stabilizes at a predetermined voltage. Therefore, the voltage of the negative input terminal of the operational amplifier IC61 is determined according to the duty of the pulse signal output from the BLD_CONT terminal. That is, the greater the low duty of the pulse signal output from the BLD_CONT terminal, the greater the absolute value of the negative blade voltage Vbld.

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

(Control of Example 2)
In the second embodiment, control by the image forming apparatus 101 to reduce the potential difference between the developing roller 133a, the developing blade 135a, and the toner supply roller 134a will be described with reference to FIG. In FIG. 6, the above-described charging current detection will be described as an example of the special process. It should be noted that the same step numbers are assigned to the same processes as those of the first embodiment (FIG. 4), and descriptions thereof are omitted. After outputting a control signal from the TSR_CONT terminal in S504 so that the toner supply R voltage Vtsr becomes −400 V, in S805, the control unit 200 performs the following control. That is, the control unit 200 outputs a control signal from the BLD_CONT terminal so that the toner supply R voltage Vtsr becomes −400 V (BLD_CONT is turned ON), and the process proceeds to S506. That is, the control unit 200 switches between a first state in which the potential difference between the development voltage Vdev and the blade voltage Vbld is the first potential difference and a second state in which the potential difference is the second potential difference larger than the first potential difference. function as 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 (BLD_CONT is turned OFF) in S812, and ends the process.

In the second embodiment, the controller 200 can independently select (set) the voltage values of the development voltage Vdev, the blade voltage Vbld, and the toner supply R voltage Vtsr. That is, since the number of options for each voltage value that can be set increases, more complicated voltage control becomes possible. Also in the second embodiment, by performing the above-described control, image defects do not occur at the contact portion between the developing roller 133a, the toner supply roller 134a, and the developing blade 135a. With the transformer capability required during the image forming process, it is possible to output the charging voltage Vpri even during the special process.

As described above, according to the second embodiment, it is possible to suppress image defects caused by contact portions between members involved in development processing with 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;
The electrostatic latent image formed on the photoreceptor can be in a contact state in which the photoreceptor is in contact with the photoreceptor or in a separated state in which the photoreceptor is separated from the photoreceptor. an image-forming development member;
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;
When 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, the first potential difference is formed in the separated state. a control means for controlling so that the second potential difference is formed in the contact state;
with
The image forming apparatus, wherein the control means performs control such that the absolute value of the second voltage in the separated state is larger than the absolute value of the second voltage in the contact state. A charging member that charges the photoreceptor,
2. The image forming apparatus according to claim 1, wherein the first power supply applies the first voltage to the charging member. a charging member that charges the photoreceptor;
a transfer member that transfers the toner image formed on the photoreceptor;
with
2. The image forming apparatus according to claim 1, wherein said first power supply applies said first voltage to said 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 supply is
a Zener diode having a cathode terminal connected to the second voltage output by the second power supply and an anode terminal connected to the third voltage output by the third power supply;
a transistor having an emitter terminal connected to the cathode terminal of the Zener diode and having a collector terminal connected to the anode terminal of the Zener diode;
has
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 so that the anode terminal and the cathode terminal of the Zener diode are not short-circuited. 7. The image forming apparatus according to claim 6, wherein the control means controls the ON state or the OFF state of the transistor by outputting a signal for controlling 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 contacting the developing member in the contact state and the separated state;
a fourth power supply that generates a fourth voltage and applies the fourth voltage to the second contact member;
with
The control means is
controlling the fourth power supply by outputting a fourth pulse signal;
In the separated state, the fourth pulse signal is output so that the potential difference between the second voltage and the fourth voltage becomes a third potential difference, and in the contact state, the fourth potential difference is larger than the third potential difference. 9. The image forming apparatus according to claim 7, wherein the fourth pulse signal is output as a potential difference. 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. a toner container containing 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;
with
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 11. The image forming apparatus according to claim 9, wherein: a detecting means for detecting a current flowing through the charging member;
12. The image according to any one of claims 2 to 11, wherein the control means performs control so as to achieve the separated state when the current flowing through the charging member is detected by the detection means. forming device. 13. The image forming apparatus according to claim 1, further comprising contact/separation means for switching the developing member between the contact state and the separated state.

Images