JP6108193B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a technique for controlling a transfer current flowing in a transfer body of an image forming apparatus.

  Patent Document 1 below discloses a technique for generating a reverse transfer voltage from a charging voltage using a constant voltage circuit using a varistor. In this circuit, the transfer current flows to the ground through the transfer roller, the forward transfer bias application circuit, and the varistor.

JP 2006-030554 A

  In order to maintain the image quality, it is preferable to control the transfer current to the target level by monitoring the transfer current and performing feedback control. However, in the circuit of Patent Document 1, the forward transfer bias application circuit is connected to the ground via a non-linear varistor, and a non-linear element is included in the feedback system that controls the transfer current to the target value. Therefore, there is a concern that the transfer current cannot be controlled with high accuracy even if the transfer current is detected and feedback is applied.

  The present invention has been completed based on the above circumstances, and an object thereof is to control a transfer current with high accuracy.

  An image forming apparatus disclosed in this specification includes a photoconductor, a charger for charging the photoconductor, a developer for supplying a developer to the photoconductor, and a developer image carried on the photoconductor. A transfer body that is transferred to a recording medium; a charging transformer that is switched by a switching element; a charging voltage application circuit that applies a charging voltage to the charger; and a transfer transformer that is switched by the switching element A transfer voltage applying circuit for applying a transfer voltage having a polarity opposite to the charging voltage to the transfer body, a first resistor connected in series between the output line of the charging voltage applying circuit and the ground, and a second resistor, A resistor voltage dividing circuit that divides the charging voltage by a resistance ratio, a connection for connecting a connection point between the first resistor and the second resistor, and a low voltage side of the secondary winding of the transfer transformer. In, a charging voltage detection unit that detects the charging voltage, a current detection unit that detects a current value flowing through the second resistance of the resistance voltage dividing circuit, and a control device, and the control device includes the charging device. Processing for calculating a transfer current flowing in the transfer body based on a detection value of the voltage detection unit, a detection value of the current detection unit, a resistance value of the first resistor, and a resistance value of the second resistor; The process of controlling the transfer voltage applying circuit is performed so that the transferred current becomes a target value.

  In this configuration, the reverse transfer voltage is generated from the charging voltage using a resistance voltage dividing circuit. Since the resistor is a linear element, it is easier to control the current than a non-linear element such as a varistor. Therefore, the transfer current can be controlled with high accuracy.

In the image forming apparatus, the following is preferable.
The control device determines abnormal discharge when the detection value of the charging voltage detection unit is equal to or higher than an upper limit value. In this configuration, abnormal discharge is determined using the detection value of the charging voltage detection circuit provided for detecting the transfer current. Therefore, the circuit configuration is simpler than that in the case of having a dedicated circuit for detecting abnormal discharge.

A third step-down resistor connected to a connection point between the first resistor and the second resistor, the output voltage of the charging voltage application circuit being stepped down by the first resistor and the third resistor, and the development A developing voltage application circuit for applying a developing voltage to the container, and a developing voltage detector for detecting the developing voltage, and the control device includes a detection value of the charging voltage detector, a detection value of the current detector, and The transfer current flowing through the transfer body is calculated based on the detection value of the developing voltage detection unit, the resistance value of the first resistor, the resistance value of the second resistor, and the resistance value of the third resistor. . In this configuration, the development voltage is generated from the output of the charging voltage application circuit. Therefore, the circuit configuration can be simplified as compared with the case where the development voltage is generated by a dedicated circuit.

The control device controls the development voltage application circuit to an output state when returning the developer attached to the transfer body to the photoconductor after completion of the printing process. In the state where the development voltage application circuit stops outputting, the development voltage becomes zero volts, so that the reverse transfer voltage is hardly increased. In this configuration, when the developer attached to the transfer member is returned to the photosensitive member, the development voltage application circuit is controlled to the output state, so that the reverse transfer voltage can be set to the target level. Therefore, there is little risk of causing a developer recovery failure.

  An image forming apparatus disclosed in this specification includes a photoconductor, a charger for charging the photoconductor, a developer for supplying a developer to the photoconductor, and a developer image carried on the photoconductor. A transfer body that is transferred to a recording medium; a charging transformer that is switched by a switching element; a charging voltage application circuit that applies a charging voltage to the charger; and a transfer transformer that is switched by the switching element A transfer voltage applying circuit for applying a transfer voltage having a polarity opposite to the charging voltage to the transfer body, and a first resistor, a current detecting resistor, and a second resistor connected in series between the output line of the charging voltage applying circuit and the ground. A voltage dividing circuit that divides the charging voltage according to a resistance ratio, a connection point between the current detection resistor and the second resistor, and a low voltage of the secondary winding of the transfer transformer A voltage detection unit that detects a voltage at a connection point between the first resistor and the current detection resistor, and a current detection unit that detects a current value flowing through the second resistor of the resistance voltage dividing circuit. And a control device, the control device, the detection value of the voltage detection unit, the detection value of the current detection unit, the resistance value of the first resistor, the resistance value of the current detection resistor, Based on the resistance value of the second resistor, a process of calculating a transfer current flowing through the transfer body and a process of controlling the transfer voltage application circuit so that the calculated transfer current becomes a target value.

  In this configuration, the reverse transfer voltage is generated from the charging voltage using a resistance voltage dividing circuit. Since the resistor is a linear element, it is easier to control the current than a non-linear element such as a varistor. Therefore, the transfer current can be controlled with high accuracy.

In the image forming apparatus, the following is preferable.
The control device includes a detection value of the voltage detection unit, a detection value of the current detection unit, a resistance value of the first resistor, a resistance value of the second resistor, and a resistance value of the voltage detection unit. The charging voltage is calculated based on the resistance value of the current detection resistor, and when the calculated charging voltage is equal to or higher than the upper limit value, it is determined that abnormal discharge has occurred. In this configuration, the circuit configuration is simple compared to a case where a circuit for detecting abnormal discharge is dedicated.

  The image forming apparatus disclosed in this specification can control the transfer current with high accuracy.

1 is a cross-sectional side view of the center of a printer according to a first embodiment. Diagram showing the structure of the charger Block diagram showing the electrical configuration of the printer High-voltage power supply circuit diagram Circuit diagram of high-voltage power supply device in Embodiment 2 Diagram showing high-pressure sequence Circuit diagram of high-voltage power supply device in Embodiment 3

<Embodiment 1>
A first embodiment of the present invention will be described with reference to FIGS.
(1-1) Configuration of Printer FIG. 1 is a side sectional view of an essential part of a laser printer 1 (an example of an image forming apparatus). The laser printer 1 (hereinafter referred to as “printer”) includes a main body frame 2, a paper feeding unit 4, an image forming unit 5, a fixing unit 18, and the like.

  The paper feed unit 4 includes a paper feed tray 6 on which printing paper 3 (an example of a recording medium) is stacked, a pressing plate 7, and a paper feed roller 8. The pressing plate 7 is rotatable around its rear end, and the printing paper 3 on the pressing plate 7 is pressed toward the paper feed roller 8. As the paper feed roller 8 rotates, the printing paper 3 is sent out one by one to the transport path.

  The fed printing paper 3 is sent to the transfer position X after being registered by the registration roller 12. The transfer position X is a position where the toner image on the photosensitive drum (an example of the “photosensitive member” of the present invention) 27 is transferred to the printing paper 3, and the photosensitive drum 27 and the transfer roller (the “transfer member” of the present invention). An example) It is a contact position with 30.

  The image forming unit 5 forms a toner image on the printing paper 3 and includes a scanner unit 16, a process cartridge 17, a transfer roller 30, and the like. The scanner unit 16 includes a laser light emitting unit (not shown), a polygon mirror 19 and the like. Laser light emitted from the laser light emitting unit (a chain line in the drawing) is irradiated onto the surface of the photosensitive drum 27 while being deflected by the polygon mirror 19.

  The process cartridge 17 includes a photosensitive drum 27, a developing roller (an example of the “developer” of the present invention) 31, and a scorotron charger 29. The photosensitive drum 27 has a positively chargeable photosensitive layer formed on, for example, an aluminum base, and the aluminum base is grounded.

  The developing roller 31 is disposed opposite to the supply roller 33 at the lower part of the toner case. The developing roller 31 functions to supply toner onto the photosensitive drum 27 as a uniform thin layer. A developing voltage is applied to the roller shaft of the developing roller 31, and the toner supplied to the photosensitive drum 27 is positively charged by the developing voltage.

  The charger 29 is a scorotron charger, and includes a shield case 29A, wires 29B, and a metal grid electrode 29C as shown in FIG. The shield case 29 </ b> A has a rectangular tube shape that is long in the direction of the rotation axis of the photosensitive drum 27. In the shield case 29A, the surface facing the photosensitive drum 27 is opened as a discharge port.

  The wire 29B is made of, for example, a tungsten wire. The wire 29B is stretched in the direction of the rotation axis (left and right direction in FIG. 2) in the shield case 29A, and a high voltage (charging voltage V1) of 5 kV to 8 kV is applied by a high voltage power supply device 100 described later. The wire 29B causes a corona discharge in the shield case 29A when a high voltage is applied. Then, ions generated by corona discharge flow from the discharge port to the photosensitive drum 27 as a discharge current, so that the surface of the photosensitive drum 27 is uniformly charged to positive polarity (800 V as an example).

  A plate-shaped grid electrode 29C having slits and through holes is attached to the discharge port of the shield case 29A. By controlling the voltage applied to the grid electrode 29C, the surface voltage of the photosensitive drum 27 can be controlled. The surface of the photosensitive drum 27 is uniformly charged to a positive polarity by the charger 29 and then exposed to the laser light emitted from the scanner unit 16 to form an electrostatic latent image. Next, the toner carried on the surface of the developing roller 31 is supplied to the electrostatic latent image formed on the photosensitive drum 27 and developed.

  The transfer roller 30 is formed by coating a metal roller shaft with a roller made of a conductive rubber material, and is disposed opposite to the photosensitive drum 27 below the photosensitive drum 27.

  A negative transfer voltage is applied to the roller shaft of the transfer roller 30 via a high-voltage power supply device 100 described later during printing (transfer). By applying the transfer voltage, the toner on the surface of the photosensitive drum 27 is electrically drawn to the transfer roller 30 side. Therefore, when the printing paper 3 passes through the transfer position X, the toner image (developer image) carried on the surface of the photosensitive drum 27 can be transferred to the paper surface.

  Further, a reverse transfer voltage having a polarity opposite to the forward transfer voltage can be applied to the transfer roller 30 via the high-voltage power supply device 100. The reason for applying the reverse transfer voltage is to electrically discharge the residual toner attached to the transfer roller 30 onto the photosensitive drum 27, for example, after a printing operation or when a paper jam occurs. The residual toner returned to the photosensitive drum 27 side is collected by the cleaning roller 35 or the developing roller 31.

  The fixing unit 18 includes a heating roller 41, a pressing roller 42, and the like. The fixing unit 18 heat-fixes the toner image on the printing paper 3 while the printing paper 3 passes between the heating roller 41 and the pressing roller 42. The printing paper 3 on which the toner is thermally fixed is discharged onto a paper discharge tray 46 via a paper discharge path 44.

(1-2) Printer Electrical Configuration FIG. 3 is a block diagram showing the electrical configuration of the printer 1.
The printer 1 includes a main control unit 50, a ROM 51, a RAM 52, a paper feeding unit 4, an image forming unit 5, a fixing unit 18, a display unit 54, an operation unit 55, a communication unit 56 that communicates data with an information terminal device, A high-voltage power supply device 100 is provided. The high-voltage power supply device 100 is a device that generates a high voltage such as a charging voltage applied to the wire 29B of the charger 29, a transfer voltage applied to the transfer roller 30, and a reverse transfer voltage.

  The main control unit 50 controls each unit of the printer 1 by executing various programs stored in the ROM 51. The ROM 51 stores various programs executed by the main control unit 50, tables that the main control unit 50 refers to in various processes, and the like. The RAM 52 is used as a main storage device for the main control unit 50 to execute various processes.

  The display unit 54 includes various lamps and a liquid crystal panel. The operation unit 55 includes an input panel and the user can operate the operation unit 55 while referring to the display unit 54 to instruct printing.

(1-3) Configuration of High Voltage Power Supply Device 100 As shown in FIG. 4, the high voltage power supply device 100 includes a PWM signal smoothing circuit 210, a charging voltage application circuit 200, a charging voltage detection circuit (the “charging voltage detection unit of the present invention”). ”240, a PWM signal smoothing circuit 310, a transfer voltage applying circuit 300, a resistance voltage dividing circuit 400, and a control device 110.

  The PWM signal smoothing circuit 210 is an integrating circuit composed of a resistor and a capacitor. The PWM signal smoothing circuit 210 smoothes the PWM signal S1 output from the PWM port P1 of the control device 110, and is provided in the charging voltage applying circuit 200. Output to the base of.

  The charging voltage application circuit 200 functions to generate a charging voltage V1 of about 6 kV to 8 kV from an input voltage of DC 24 V and apply it to the wire 29B of the charger 29. In the present embodiment, a self-excited flyback converter (RCC) is used for the charging voltage application circuit 200, and the charging voltage application circuit 200 is the primary of the charging transformer 201, the smoothing circuit 203, and the charging transformer 201. A transistor (an example of the “switching element” of the present invention) Tr1 provided on the side and a feedback coil 205 are provided.

  The transistor TR1 switches the charging transformer 201, and has an emitter connected to the ground and a collector connected to the primary winding of the charging transformer 201. A PWM signal smoothing circuit 210 is connected to the base via a feedback coil 205. The smoothing circuit 203 is provided on the secondary side of the charging transformer 201 and includes a diode and a capacitor.

  The wire 29B of the charger 29 is connected to the output line L1 of the charging voltage application circuit 200, and the output voltage V1 of the charging voltage application circuit 200 is applied to the wire 29B of the charger 29. .

  The charging voltage detection circuit 240 detects the output voltage V1 of the charging voltage application circuit 200, and includes an auxiliary winding 241 provided on the primary side of the charging transformer 201, and an integration circuit 243 including a resistor and a capacitor. Has been. The charging voltage detection circuit 240 is connected to the A / D port A1 of the control device 110, and is configured such that data of the output voltage V1 of the charging voltage application circuit 200 is taken into the control device 110. The A / D port means an input port having an A / D conversion function.

  The PWM signal smoothing circuit 310 is an integrating circuit composed of a resistor and a capacitor. The PWM signal smoothing circuit 310 smoothes the PWM signal S2 output from the PWM port P2 of the control device 110, and the transistor Tr2 provided in the transfer voltage applying circuit 300. Output to the base. The PWM port means an output port having a PWM signal output function.

  The transfer voltage application circuit 300 functions to generate a negative transfer voltage from the DC 24 V input voltage and apply it to the roller shaft of the transfer roller 30. In this embodiment, a self-excited flyback converter (RCC) is used for the transfer voltage application circuit 300, and the transfer voltage application circuit 300 is a primary of the transfer transformer 301, the smoothing circuit 303, and the transfer transformer 301. A transistor (an example of the “switching element” of the present invention) Tr2 provided on the side and a feedback coil 305 are provided.

  The transistor Tr2 switches the transfer transformer 301. The emitter is connected to the ground, and the collector is connected to the primary winding of the transfer transformer 301. A PWM signal smoothing circuit 310 is connected to the base via a feedback coil 305. The smoothing circuit 303 is provided on the secondary side of the transfer transformer 301 and includes a diode and a capacitor. The direction of the diode of the smoothing circuit 303 is opposite to that of the diode of the smoothing circuit 203, and a transfer voltage having a polarity opposite to the charging voltage is generated.

  A roller shaft of the transfer roller 30 is connected to the output line L2 of the transfer voltage application circuit 300, and a transfer voltage V2 of about −2 kV is applied to the roller shaft of the transfer roller 30 through the transfer voltage application circuit 300. It becomes the composition which is done. More specifically, on the low voltage side (reference voltage side) of the transfer transformer 301 of the transfer voltage application circuit 300, about 1. 5 kV (an example) is added. When the transfer voltage application circuit 300 is operated, a voltage Vs of about −3.5 kV is generated across the capacitor C provided on the secondary side of the transfer transformer 301. Therefore, a voltage of about −2 kV obtained by subtracting +1.5 kV generated by the voltage dividing resistor circuit 400 from the −3.5 kV voltage Vs generated by the transfer voltage applying circuit 300 is applied to the roller shaft of the transfer roller 30 through the output line L2. It is to be applied.

  The resistance voltage dividing circuit 400 includes a first resistor 410 and a second resistor 420. As shown in FIG. 4, the first resistor 410 and the second resistor 420 are connected in series between the output line L1 of the charging voltage application circuit 200 and the ground. The connection point A between the first resistor 410 and the second resistor 420 is connected to the low voltage side (reference voltage side) of the secondary winding of the transfer transformer 301 via the connection line L. As a result, a voltage obtained by dividing the output voltage V1 of the charging voltage application circuit 200 by the resistance ratio of the two resistors 410 and 420 to the low voltage side (reference voltage side) of the transfer transformer 301 (for example, 1.5 kV). ) Is added. Therefore, when the output of the transfer voltage application circuit 300 is stopped, a reverse transfer voltage having a positive polarity with respect to the roller shaft of the transfer roller 30, that is, a voltage obtained by dividing the output voltage V1 by a resistance ratio (1.5 kV as an example). Join.

  In addition, a current detection resistor (an example of the “current detection unit” of the present invention) 430 is provided between the second resistor 420 and the ground. A connection point between the current detection resistor 430 and the second resistor 420 is connected to an A / D port A2 provided in the control device 110 via a signal line, and is proportional to the magnitude of the current Ib flowing through the second resistor 420. The voltage Vb is input to the A / D port A2. Therefore, by reading the input voltage level of the A / D port A2, the control device 110 can detect the current Ib flowing through the second resistor 420 of the resistance voltage dividing circuit 400.

  The control device 110 has a function of applying the charging voltage V1 to the charger 29 via the charging voltage application circuit 200 and a function of controlling the transfer current It flowing to the roller shaft of the transfer roller 30 via the transfer voltage application circuit 300. It has two PWM ports P1 and P2 and two A / D ports A1 and A2. The control device 110 can be configured with a built-in CPU or an application specific integrated circuit (ASIC). The control device 110 incorporates a nonvolatile storage unit (not shown), and stores data for controlling the transfer current It described below and data for controlling the charging voltage V1 therein. Yes.

(1-4) Transfer Current Control During the printing operation, the control device 110 calculates the current value of the transfer current It based on the data (a) to (e) so that the calculated current value becomes the target value. In addition, the transfer current It is feedback controlled via the transfer voltage application circuit 300.

(A) Charging voltage V1 (detected value of charging voltage detection circuit 240)
(B) Input voltage Vb to A / D port A2 (detected value of current detection resistor 430)
(C) Resistance value R1 of the first resistor 410
(D) Resistance value R2 of the second resistor 420
(E) Resistance value R7 of the current detection resistor 430

Hereinafter, a method for calculating the transfer current It will be described.
The voltage Va at the connection point A between the resistors 410 and 420 and the current Ia flowing through the first resistor 410 satisfy the equations (1) and (2).

Va = (R2 + R7) × Ib (1)
Ia = (V1-Va) / R1 (2)

Since the transfer current It satisfies the expression (3), the current value of the transfer current It can be obtained from the expression (4).
It = Ib−Ia (3)
It = (R1 + R2 + R7) × Ib / R1-V1 / R1 (4)

When Ib is replaced with Vb / R7, equation (4) becomes equation (5).
It = Vb × (R1 + R2 + R7) / (R1 × R7) −V1 / R1 (5)

  The control device 110 calculates the transfer current Ib based on the above equation (5) during the printing operation. When the calculated value of the transfer current It is smaller than the target value, control is performed to increase the output voltage V2 of the transfer voltage application circuit 300 (increase the voltage difference with respect to the circuit reference voltage of zero volts). On the other hand, when the calculated value of the transfer current It is larger than the target value, control is performed to lower the output voltage V2 of the transfer voltage application circuit 300 (to reduce the voltage difference with respect to zero volts, which is the reference voltage of the circuit). Thereby, the current value of the transfer current It can be controlled to the target value.

  In this configuration, a reverse transfer voltage is generated from the charging voltage V <b> 1 using the resistance voltage dividing circuit 400. Therefore, it is possible to configure a loop for feedback control of the transfer current It using only linear elements. Therefore, the transfer current It can be controlled with high accuracy. Thereby, the following merits are obtained. The flow of current from the photosensitive drum 27 to the printing paper 3 varies depending on conditions such as temperature and humidity, paper material, and paper size. In this embodiment, since the transfer current It can be controlled with high accuracy, an optimum target value is set according to conditions such as temperature and humidity, paper material, paper size, etc. Transfer current It can flow. Therefore, it is possible to obtain a good image quality.

  In the first embodiment, the current Ib is detected by the current detection resistor 430. It is also possible to detect the current Ib using a Hall element or the like. In this case, the transfer current It can be calculated by the following equation (6), and the data (e) is not necessary for calculating the transfer current It.

  It = (R1 + R2) × Ib / R1-V1 / R1 (6)

(1-5) Detection of Abnormal Discharge Further, the control device 110 compares the charging voltage V1 detected by the charging voltage detection circuit 240 with the upper limit value (8 kV as an example) after the application of the charging voltage V1 is started. If the charging voltage V1 is equal to or higher than the upper limit value, it is determined that the discharge is abnormal.

  When determining that the discharge is abnormal, the control device 110 stops the output of the charging voltage application circuit 200 and performs a process of displaying an error message on the display unit 54 via the main control unit 50. By doing so, it is possible to stop abnormal discharge of the charger 29 at an early stage. In this configuration, abnormal discharge is determined using the detection value of the charging voltage detection circuit 240 provided for detecting the transfer current. Therefore, the circuit configuration is simpler than that in the case of having a dedicated circuit for detecting abnormal discharge. Note that, according to the above equation (4) or (5), “the control device 100 can detect the detection value V1 of the charging voltage detector 240 and the detection value Ib (Vb) of the current detector 430. The transfer current It is calculated based on the resistance value R1 of the first resistor 410 and the resistance value R2 of the second resistor 420 ".

<Embodiment 2>
Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, a development voltage application circuit 450 is added to the high-voltage power supply device 100 of the first embodiment.

  The development voltage application circuit 450 includes a third resistor 460 and a transistor Tr3. One end of the third resistor 460 is connected to a connection point A between the first resistor 410 and the second resistor 420. The other end of the third resistor 460 is connected to the collector of the transistor Tr3.

  The transistor Tr3 is an NPN transistor, and has a collector connected to the other end of the third resistor 460 and an emitter connected to the ground. The base of the transistor Tr3 is connected to the PWM port P3 of the control device 110 via the PWM signal smoothing circuit 510.

  The PWM signal smoothing circuit 510 is an integrating circuit including a capacitor C and a resistor R, and has a configuration in which the PWM signal S3 output from the PWM port P3 of the control device 110 is smoothed and applied to the base of the transistor Tr3.

  An output line L3 is drawn from a connection point d between the third resistor 460 and the transistor Tr3, and a roller shaft of the developing roller 31 is connected to the output line L3. Therefore, the level of the developing voltage Vd applied to the roller shaft of the developing roller 31 can be adjusted by controlling the collector current of the transistor Tr3 by the PWM signal S3 output from the PWM port P3. The developing voltage Vd is a voltage obtained by subtracting the voltage drop due to the resistors 410 and 460 from the output voltage V1 of the charging voltage application circuit 200.

  Further, development voltage detection resistors 470 and 480 for detecting the development voltage Vd are provided between the output line L3 of the development voltage application circuit 450 and the ground. The development voltage detection resistors 470 and 480 are connected in series between the output line L3 and the ground, and the voltage at the intermediate connection point between the resistors 470 and 480 is input to the A / D port A3 of the control device 110. It has become. Thereby, the developing voltage Vd can be detected from the input value of the A / D port A3. The control device 110 adjusts the output of the development voltage application circuit 450 based on the PWM signal S3 based on the input value of the A / D port A3, and performs feedback control so that the development voltage Vd becomes a target value. The developing voltage resistors 470 and 480 correspond to the developing voltage detector of the present invention.

  Further, the control device 110 calculates the current value of the transfer current It based on the data (a) to (e) during the printing operation, and the transfer voltage application circuit 300 so that the calculated current value becomes the target value. , The transfer current It is feedback-controlled.

(A) Charging voltage V1 (detected value of charging voltage detection circuit 240)
(B) Input voltage Vb to A / D port A2 (detected value of current detection resistor 430)
(C) Resistance value R1 of the first resistor 410
(D) Resistance value R2 of the second resistor 420
(E) Resistance value R7 of the current detection resistor 430
(F) Resistance value R3 of the third resistor 460
(G) Input voltage Vd of A / D port A3 (detection value of developing voltage resistors 470 and 480)

Hereinafter, a method for calculating the transfer current It will be described.
The voltage Va at the connection point A between the resistors 410 and 420 and the current Ic flowing through the first resistor 410 satisfy the equations (1) and (7).

Va = (R2 + R7) × Ib (1)
Ic = (V1-Va) / R1 (7)

The branch currents Ic1 and Ic2 of the current Ic satisfy the expressions (8) and (9).
Ic = Ic1 + Ic2 (8)
Ic2 = (Va−Vd) / R3 (9)

Since the transfer current It satisfies Expression (10), the current value of the transfer current It can be obtained from Expression (11).
It = Ib-Ic1 (10)
It = Ib * Rc / (R1 * R3) -V1 / R1-Vd / R3 (11)
Note that “Rc” = “R1 × R3 + R1 × R2 + R1 × R7 + R3 × R2 + R3 × R7”.

Then, when Ib is replaced with Vb / R7, equation (11) becomes equation (12).
It = Vb * Rc / (R1 * R3 * R7) -V1 / R1-Vd / R3 (12)

  The controller 110 calculates the transfer current Ib based on the above equation (12) during the printing operation. When the calculated value of the transfer current It is smaller than the target value, control is performed to increase the output voltage V2 of the transfer voltage application circuit 300 (increase the voltage difference with respect to the circuit reference voltage of zero volts). On the other hand, when the calculated value of the transfer current It is larger than the target value, control is performed to lower the output voltage V2 of the transfer voltage application circuit 300 (to reduce the voltage difference with respect to zero volts, which is the reference voltage of the circuit). Thereby, the current value of the transfer current It can be controlled to the target value.

  In this configuration, a reverse transfer voltage is generated from the charging voltage V <b> 1 using the resistance voltage dividing circuit 400. Therefore, it is possible to configure a loop for feedback control of the transfer current It using only linear elements. Therefore, similarly to the first embodiment, the transfer current It can be controlled with high accuracy.

  In the second embodiment, the current Ib is detected using the current detection resistor 430. However, it is also possible to detect the current Ib using a Hall element or the like. In this case, the data (e) is not necessary for calculating the transfer current It.

  In the case of this configuration, the development voltage application circuit 450 is connected in parallel to the second resistor 420 of the resistance voltage dividing circuit 400 that generates the reverse transfer voltage. Therefore, when the output of the developing voltage application circuit 450 is stopped and the developing voltage Vd is set to zero volts with the end of the printing operation, that is, when the collector-emitter of the transistor Tr3 is brought into a conductive state of substantially zero voltage, the first resistance Since the voltage at the connection point A between 410 and the second resistor 420 is lowered, the reverse transfer voltage is hardly increased.

  In this case, the electric field from the transfer roller 30 side to the photosensitive drum 27 side becomes weak, and there is a possibility that a toner collection failure on the transfer roller 30 may occur.

  In the second embodiment, as shown in FIG. 6, when the toner adhering to the transfer roller 30 is returned to the photosensitive drum 27 after the printing operation (period F in FIG. 6), the developing voltage application circuit 450 is set to the output state. The developing voltage Vd is controlled to 300 to 400V. That is, the base current of the transistor Tr3 is controlled by the PWM signal S3 so that the collector voltage of the transistor Tr3 is 300 to 400V.

  For this reason, it is possible to suppress the voltage drop of the reverse transfer voltage, and an electric field of a certain level sufficient to attract toner is generated from the transfer roller 30 side to the photosensitive drum 27 side. Therefore, the toner adhering to the transfer roller 30 can be reliably returned to the photosensitive drum 27 side. According to the above expression (11) or (12), “the control device 110 can detect the detection value V1 of the charging voltage detection unit 240 and the detection value Ib (Vb) of the current detection unit 430. , Based on the detection value Vd of the developing voltage detectors 470 and 480, the resistance value R1 of the first resistor 410, the resistance value R2 of the second resistor 420, and the resistance value R3 of the third resistor 460, “Calculating the transfer current It” is embodied.

<Embodiment 3>
Next, Embodiment 3 of the present invention will be described with reference to FIG. The high-voltage power supply device 100 according to the third embodiment is obtained by adding the current detection resistor 510 and the voltage detection resistors 550 and 560 to the high-voltage power supply device 100 according to the first embodiment and omitting the charging voltage detection circuit 240. The current detection resistor 510 is provided between the first resistor 410 and the second resistor 420 as shown in FIG. That is, in the third embodiment, the resistor voltage dividing circuit 400 that divides the charging voltage V1 includes the current detection resistor 510 in addition to the first resistor 410 and the second resistor 420. The connection point A between the current detection resistor 510 and the second resistor 420 is connected to the low voltage side (reference voltage side) of the secondary winding of the transfer transformer 301 via the connection line L.

  The voltage detection resistors 550 and 560 are connected in series between the connection point E between the resistors 410 and 510 and the ground. The voltage at the connection point j between the two voltage detection resistors 550 and 560 is input to the input port A4 of the control device 110. Therefore, the voltage Ve at the connection point E can be detected from the input voltage V4 of the input port A4 and the resistance values R5 and R6 of both resistors 550 and 560. The voltage detection resistors 550 and 560 are examples of the voltage detection unit of the present invention.

  Then, during the printing operation, the control device 110 calculates the current value of the transfer current It based on the data (b) to (e), and the transfer voltage application circuit 300 so that the calculated current value becomes the target value. The transfer current It is feedback controlled via

(B) Input voltage Vb to A / D port A2 (detected value of current detection resistor 430)
(D) Resistance value R2 of the second resistor 420
(E) Resistance value R7 of the current detection resistor 430
(H) Resistance value R4 of the current detection resistor 510
(I) Input voltage V4 to A / D port A4 (detected values of voltage detection resistors 550 and 560)

Hereinafter, a method for calculating the transfer current It will be described.
The voltage Va at the connection point A between the second resistor 420 and the current detection resistor 510 satisfies the equation (1), and the current Ie flowing through the current detection resistor 510 satisfies the equation (13).

Va = (R2 + R7) × Ib (1)
Ie = (Ve−Va) / R4 (13)

Since the transfer current It satisfies the equation (14), the current value of the transfer current It can be obtained from the equation (15).
It = Ib−Ie (14)
It = Ib × (R2 + R4 + R7) / R4-Ve / R4 (15)

When Ib is replaced with Vb / R7 and Ve is replaced with (R5 + R6) / R6 × V4, equation (15) becomes equation (16).
It = Vb × (R2 + R4 + R7) / (R4 × R7) −V4 × (R5 + R6) / (R4 × R6) (16)

  The controller 110 calculates the transfer current Ib based on the above equation (16) during the printing operation. When the calculated value of the transfer current It is smaller than the target value, control is performed to increase the output voltage V2 of the transfer voltage application circuit 300. On the other hand, when the calculated value of the transfer current It is larger than the target value, control is performed to lower the output voltage V2 of the transfer voltage application circuit 300. Thereby, the current value of the transfer current It can be controlled to the target value.

  In this configuration, a reverse transfer voltage is generated from the charging voltage V <b> 1 using the resistance voltage dividing circuit 400. Therefore, it is possible to configure a loop for feedback control of the transfer current with only linear elements. Therefore, the transfer current It can be controlled with high accuracy.

  In the third embodiment, the current Ib is detected using the current detection resistor 430. However, it is also possible to detect the current Ib using a Hall element or the like. In this case, the data (e) is not necessary for calculating the transfer current It.

Further, the control device 110 calculates the charging voltage V1 from the following formulas (14) to (18).
V1 = (R1 + R5 + R6) × If + R1 × Ie (14)
If = V4 / R6 (15)
Ie = (Ve−Va) / R4 (16)
Va = (R2 + R7) × Vb / R7 (17)
V1 = V4 × (D1 + D2) −Vb × D3 (18)

  Note that D1 = (R1 + R4) × (R5 + R6) / (R4 × R6), and D2 = R1 / R6. And D3 = R1 (R2 + R7) / (R7 × R4).

  And the control apparatus 110 judges that it is abnormal discharge, when the calculated charging voltage V1 becomes more than an upper limit (for example, 8 kV). When determining that the discharge is abnormal, the control device 110 stops the output of the charging voltage application circuit 200 and performs a process of displaying an error message on the display unit 54. By doing so, it is possible to stop abnormal discharge of the charger 29 at an early stage. Note that, according to the above expression (15) or (16), “the control device 110 detects the detection value Ve (V4) of the voltage detection units 550 and 560 and the detection value Ib of the current detection unit 430”. The transfer current It is calculated based on (Vb), the resistance value R4 of the current detection resistor 510, and the resistance value R2 of the second resistor 420 ". Further, according to the above equation (18), “the control device 110 can detect the detection value V4 of the voltage detection units 550 and 560, the detection value Vb of the current detection unit 430, and the resistance of the first resistor 410”. The charging voltage is calculated based on the value R1, the resistance value R2 of the second resistor 420, the resistance values R5 and R6 of the voltage detection units 550 and 560, and the resistance value R4 of the current detection resistor 510. It is embodied.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  (1) In the first to third embodiments, a self-excited flyback converter is used as an example of the charging voltage application circuit 200 and the transfer voltage application circuit 300, but another excitation type may be used.

DESCRIPTION OF SYMBOLS 1 ... Printer 27 ... Photosensitive drum (an example of the "photosensitive body" of this invention)
29 ... Charger 30 ... Transfer roller (an example of the "transfer body" of the present invention)
31... Developing roller (an example of the “developer” of the present invention)
DESCRIPTION OF SYMBOLS 100 ... High voltage power supply device 110 ... Control apparatus 200 ... Charging voltage application circuit 201 ... Charging transformer 240 ... Charging voltage detection circuit (an example of "charging voltage detection part" of this invention)
DESCRIPTION OF SYMBOLS 300 ... Transfer voltage application circuit 301 ... Transfer transformer 400 ... Resistance voltage dividing circuit 410 ... First resistance 420 ... Second resistance 430 ... Current detection resistance (an example of the "current detection section" of the present invention)
460: Third resistor 450: Development voltage application circuit 470, 480: Development voltage detection resistor (an example of the “development voltage detection unit” of the present invention)
510: Current detection resistor Tr1: Transistor (an example of the “switching element” of the present invention)
Tr2 ... transistor (an example of the “switching element” of the present invention)

Claims (2)

A photoreceptor,
A charger for charging the photoreceptor;
A developer for supplying a developer to the photoreceptor;
A transfer body for transferring the developer image carried on the photoreceptor to a recording medium;
A charging voltage application circuit that has a charging transformer switched by a switching element and applies a charging voltage to the charger;
A transfer voltage application circuit having a transfer transformer switched by a switching element, and applying a transfer voltage having a polarity opposite to the charging voltage to the transfer body;
A first resistor and a second resistor connected in series; the first resistor is connected to an output line of the charging voltage application circuit; and the second resistor is connected between the first resistor and the ground. A resistive voltage divider circuit;
A connection line connecting a connection point between the first resistor and the second resistor, and a low voltage side of a secondary winding of the transfer transformer;
A charging voltage detector for detecting the charging voltage;
A current detector for detecting a current value flowing through the second resistor of the resistor voltage dividing circuit;
And a third step-down resistor connected to a connection point between the first resistor and the second resistor, and the output voltage of the charging voltage applying circuit is stepped down by the first resistor and the third resistor. A development voltage application circuit for applying a development voltage to
A developing voltage detector for detecting the developing voltage;
A control device,
The controller is
In the printing operation, the detection value of the charging voltage detecting unit, and the detection value of the current detector, and the detected value of the developing voltage detecting unit, and the resistance value of the first resistor, the resistance value of the second resistor Calculating a transfer current flowing through the transfer body based on the resistance value of the third resistor, and controlling the transfer voltage application circuit so that the calculated transfer current becomes a target value ;
After the printing operation is completed, when the developer attached to the transfer body is returned to the photoreceptor, the transfer voltage application circuit is controlled to output a reverse transfer voltage having the same polarity as the charging voltage, and the development voltage A process for controlling the application circuit to output a developing voltage having the same polarity as the charging voltage;
An image forming apparatus for performing. The controller is
The image forming apparatus according to claim 1, wherein the transfer voltage application circuit is stopped and a reverse transfer voltage having the same polarity as the charging voltage is applied to the transfer body.

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