JPH09185221A - Electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of each control of an electrifying device performed by switching constant current control and constant voltage control by providing a specified high voltage power source and a controller, and feeding back a current flowing from a charging member to a part other than a member to be electrified to an end on the reference potential side of the high voltage power source. SOLUTION: The controller CNT arithmetically calculates a resistance value R2 to reference potential GND from the charging member through a member to be charged based on voltage V3 generated by an element for detecting a current R3 and voltage 13 obtained by subtracting the voltage V3 from voltage VT generated by elements for detecting voltage R4 and R5. Then, an output voltage adjusting means Q is controlled so that the voltage V3 may agree with a target value when the resistance value R2 is under the set value and the voltage V13 may agree with the target value when the value R2 is equal to or above the set value. The current (current of R1) flowing to the part other than the member to be electrified from the charging means (transfer carrying unit) TTU is fed back to the end on the reference potential side of the high voltage power source HV3. Therefore, the voltage V3 accurately shows a current Iopc flowing between the charging member and the member to be electrified. Since the voltage V13 does not include voltage detection errors caused by the output current Iopc , the output voltage is accurately detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging with a high voltage, and in particular, although not intending to be limited to this, charging a photoreceptor in an electrophotographic image forming apparatus such as a copying machine or a printer. The present invention relates to a charging device.

[0002]

2. Description of the Related Art For example, in this type of image forming apparatus, in order to form an electrostatic latent image on a photoconductor, a charging device for uniformly charging the photoconductor prior to exposure and a developing device formed on the photoconductor. A charging device for transferring an image (toner image) onto a recording paper is provided. The output current values of these charging devices are controlled in order to form the required latent image potential and to realize the required transfer characteristics. For example, in Japanese Patent Application Laid-Open No. 60-257772, the output current value of the charging device is controlled to a target value (constant current control), and when the output current value becomes an abnormal value, the output voltage of the charging device is set to a predetermined value or less. An analog type high-voltage power supply for electrophotography, which is controlled by a constant voltage, is disclosed. Also,
Japanese Unexamined Patent Publication No. 61-236363 discloses a high-voltage power source for a copying machine, which can switch from a constant current output to a constant voltage output.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The high-voltage power supply disclosed in Japanese Patent No. 7772 is a power supply for obtaining a constant current output, and the output voltage detection circuit is a circuit for detecting an overvoltage when a load is abnormal, and cannot obtain a highly accurate constant voltage output. . In the high-voltage power supply disclosed in Japanese Patent Laid-Open No. 61-236363, the voltage detection circuit is provided after the
The error of the voltage detection circuit due to the current detection circuit is eliminated by short-circuiting the current detection circuit with a switch so that a highly accurate constant voltage output can be obtained, but it is necessary to switch the switch and detect the voltage with high accuracy. However, it was not possible to switch from constant current to constant voltage.

A first object of the present invention is to improve the accuracy of constant current control and constant voltage control of a charging device that switches between constant current control and constant voltage control. The second object is to accurately detect the load resistance between the charged member and the member to be charged.

[0005]

[Means for Solving the Problems]

(1) The charging device of the present invention comprises a high voltage generating circuit (Q, TR, D1 to D3, C1, C2) including an output voltage adjusting means (Q), and a high voltage terminal for outputting the high voltage generated by this circuit ( T) and a reference potential terminal (GND), a voltage detection element (R4, R5) that generates a voltage (VT) proportional to the high voltage, a reference potential side end (, FBR, I) of the element.
High-voltage power supply (HV3) including a current detection element (R6) interposed between T) and the reference potential terminal (GND) and generating a voltage (V3) proportional to the current value (Iopc) between the two; reference A charging member (TB) electrically connected to the high-voltage terminal (T) and a member to be charged from which the charging member (OPC) on the conductor connected to the electric potential (GND) contacts or separates A charging means (TTU) including means (TR1, TR2) for returning a current flowing other than (OPC) to the reference potential side end (, FBR, IT) of the high voltage power supply (HV3); and for the current detection The voltage (V3) generated by the element (R6), and the voltage (V13) subtracted from the voltage (VT) generated by the voltage detection elements (R4, R5), corresponding to one of the voltages,
The output voltage adjusting means so that it matches the target value.
A controller (CNT) that controls (Q). In addition, in order to facilitate understanding, symbols of corresponding elements or corresponding items in the embodiments shown in the drawings and described later are added for reference in parentheses.

According to this, the current (current of R1) flowing from the charging means (TTU) other than the charged member (OPC) is supplied to the high voltage power source (HV3).
Since it is fed back to the reference potential side end (, FBR, IT) of, the voltage (V3) generated by the current detection element (R6) is accurately measured by the charging member.
Indicates the current (Iopc) flowing between (TB) / charged member (OPC). Therefore, the constant current control for making the voltage (V3) of the controller (CNT) match the target value becomes accurate. That is, the current (Iopc) flowing through the member to be charged (OPC) is accurately controlled.

Further, the voltage (V3) is converted into a voltage detecting element (R4, R
The voltage (V13) that is subtracted from the voltage (VT) generated by 5) does not include the voltage detection error (V13) due to the output current (Iopc), so the output voltage (V23; V13) is accurately detected, and the control -The constant voltage control that matches the output voltage (V13) of La (CNT) with the target value becomes accurate. That is, the output voltage (V23) of the high voltage power supply (HV3) is accurately controlled. Furthermore, the current (Iopc; V3) between the charging member (TB) / charged member (OPC) and the charging member (TB) applied voltage (V23; V13) can be detected accurately at the same time, so follow them. Charged member (TB) and charged member (O
The resistance value (R2) of the load that is a combination of (PC) can be accurately determined,
The constant current control and the constant voltage control can be switched based on the resistance value (R2), and the selection of the control mode can be accurately matched to the load.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

(2) The controller (CNT) uses the voltage (V3) generated by the current detecting element (R6) and the voltage detecting element (R4, R4).
Based on the voltage (V13) subtracted from the voltage (VT) generated by 5), calculate the resistance value (R2) from the charging member (TB) to the reference potential (GND) via the charged member (OPC). , The voltage generated by the current detecting element (R6) when the resistance value (R2) is less than the set value
(V3) controls the output voltage adjusting means (Q) so that it matches the target value, and when it is above the set value, the subtracted voltage (V13)
The output voltage adjusting means (Q) is controlled so that the output voltage of the output voltage adjusting means matches the target value.

(3) The controller (CNT) has a resistance value (R2)
Is smaller than the set value, and the change in the resistance value (R2) is equal to or larger than the set value, the output voltage adjusting means (Q) is controlled so that the subtracted voltage (V13) matches the target value.

(4) The high-voltage power supply (HV3) is a step-up means (Q, TR, D1 to D3, C) for converting a DC voltage into a high voltage and having a variable output voltage.
1, C2), resistance voltage divider circuit (R4, R5) connected between the high-voltage end () of the boosting means and the reference potential end (), the reference potential end () and the reference potential terminal (GND) of the high-voltage power supply. And a resistor (R6) for current detection connected in series between them; the controller (CNT) is
An operational amplifier (IC) that subtracts the voltage drop (V3) of the current detection resistor (R6) from the divided voltage (VT) of the resistor voltage divider circuit (R4, R5).
2) and a plurality of resistors (R11 ~ R14) includes a differential amplifier circuit, the plurality of resistors (R11 ~ R14) has a resistance value of a value greater than the resistance value of the resistance voltage dividing circuit, Between the non-inverting input () of the operational amplifier (IC2) and the reference potential (R14), and between the non-inverting input () and the voltage divider end of the resistor voltage divider circuit () (R1
3), voltage detection end of inverting input () and current detection resistor (R6)
Between () and (R11), and inverting input () and operational amplifier (IC
It is connected to (R12) between the output () of 2).

(5) The charging means is a metal roller (TR1, TR2) connected to the reference potential side end (, FBR) of the high voltage power supply (HV3),
Transfer belt (TB) wrapped around this, and high voltage terminals
(T) electrically connected to transfer belt (TB) and charged member
The transfer transport unit (TTU) includes a roller electrode (ER) that supplies power to the transfer belt (TB) at a contact portion with (OPC).

(6) The charging means is a high voltage terminal of a high voltage power source.
A corona discharger including a discharge wire electrically connected to (T) and a metal case surrounding the discharge wire and connected to a reference potential side end (, FBR).

(7) The charging means includes a conductive roller electrically connected to a high-voltage terminal (T) of a high-voltage power source, which is in contact with or away from the member to be charged (OPC), and a conductive roller. It is a charging roller including an auxiliary electrode that is in contact with and is connected to a reference potential side end (, FBR).

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0015]

FIG. 1 shows an embodiment of the present invention. This embodiment is a part of an electrophotographic apparatus, and a photosensitive member OPC, which is a member to be charged, is formed on the surface of a conductor drum, and a conductor drum and a metal structure that rotatably supports the conductor drum are used. It is grounded (GND, equipment ground). This ground potential is the reference potential. When the conductor drum is driven to rotate at a constant speed, the photosensitive member OPC moves directly below the corona discharger C having the grid G, and is charged to a uniform potential by the corona discharger C. Image light L is projected on the charging surface, and an electrostatic latent image is formed thereby. This electrostatic latent image is developed by the developing device B and becomes a visible image. The recording paper is fed to the transfer belt TB of the transfer / transport unit TTU in close contact with the belt TB in synchronization with the movement of the visible image. Transfer belt TB
Rotates at the same linear velocity as the moving velocity (peripheral velocity) of the photoconductor OPC. The visible image that has arrived at a position facing the transfer belt TB is transferred onto the recording paper by the transfer electrode ER.

The charger high voltage unit HV1 applies a charging voltage to the corona discharger C, the developing bias voltage high voltage unit HV2 applies a developing bias voltage to the developing device B, and the transfer electrode high voltage unit HV3 transfers the transfer electrode ER. Give voltage. Each of the high-voltage units HV1 to HV3 is a high-piezoelectric circuit including a step-up transformer supplied with DC24V from the DC power supply PSU, a switch element, an output rectifying / smoothing circuit, and an output detecting circuit. La CNT controls. Controller C
PCs, PGs, PBs and PTs of NT are output terminals of pulse signals for driving the respective switch elements, and the duty of the pulse signals causes the high voltage units HV1 to HV1 to
The output voltage of V3 is determined. IC, VC, VB, IT, V
T is an input terminal of detection signals of the voltage and current detection circuits in the high voltage units HV1 to HV3. The detection signal is control
It is converted into digital data by an A / D converter in the LaCNT and read into the controller CNT. Controller C
NT is an A / D converted value (a value represented by digital data: feedback value) which is a target value (corresponding to a constant current control mode) determined in correspondence with the image size and the recording density adjustment value. The target value is the current target value, and the target voltage value in the case of the constant voltage control mode. However, for the high-voltage unit HV2, only the target voltage value of the constant voltage mode) From the output terminals PC, PB and PT to the high voltage units HV1, HV2 and HV3 so as to match the values.
Width of pulse signal given to PWM (duty of PWM pulse)
To determine. That is, the controller CNT is a digital control system and uses high voltage units HV1, HV2 and HV3.
Control the output of This digital control system is
This is described in detail in Japanese Patent No. 10178. Instead of this digital control method, for example, an analog control method using a general-purpose switching control IC may be adopted.

The transfer / transport unit TTU includes a dielectric belt TB stretched between a pair of rollers TR1 and TR2, and a transfer electrode ER which is an auxiliary roller arranged so as to come into contact with the transfer position of the photoconductor OPC. The transfer electrode ER is supplied with a high voltage from the high voltage unit HV3. The electric charge is injected from the transfer electrode ER to the dielectric belt TB and adsorbs the paper. The high voltage applied to the transfer electrode ER is applied to the photoconductor OPC and the stretching roller TR via the dielectric belt TB.
1, flows to TR2. In order to optimally transfer the visible image on the photoconductor OPC to the paper, it is necessary to control so that a predetermined current flows from the transfer electrode ER to the photoconductor OPC. The optimum value of this predetermined current varies depending on the size of the paper, environmental conditions, and the like.
The stretching rollers TR1 and TR2 are the GND of the electrophotographic apparatus.
Is insulated from the transfer electrode ER and fed back to the high voltage unit HV3 separately from the current flowing through the photoconductor OPC from the transfer electrode ER (FB
R). Microscopically, the transfer characteristic of the dielectric belt TB varies slightly or largely depending on the position on the belt as a whole or with time. The transfer characteristic of the dielectric belt TB can be determined from the voltage and current output from the high voltage unit HV3, and according to the result, for example, the resistance value of the dielectric belt TB is higher than a predetermined value or the resistance in a short time. When the value fluctuation is large, stable transfer can be performed by switching the output of the high voltage unit HV3 from constant current control to constant voltage control.

FIG. 2 shows an electric circuit configuration of the high voltage unit HV3. The primary side of the transformer TR is connected to the 24V of the DC power supply PSU and the COM (device ground) via the FET Q. The alternating current generated on the secondary side by repeating the switching (ON / OFF) of the FET Q is converted into high DC voltage by the voltage doubler rectifying circuit which is a combination of the diodes D2 and D3 and the capacitors C1 and C2. This DC high voltage is supplied to the transfer transport unit TTU, which is a load, via the output protection resistor R3. Transfer transport unit TTU
From the transfer electrode ER, which is an auxiliary roller, to the photoconductor OP
The load resistance R2 of the current component flowing in C is the high voltage unit H
From the GND terminal of V3 via the current detection resistor R6 of the high voltage unit HV3, the rectifying / smoothing circuit (D2, D3, C1,
Returned to C2). Transfer electrode ER to dielectric belt T
The load resistance R1 of the current component flowing through the tension rollers TR1 and TR2 via B is rectified and smoothed from the FBR terminal of the high voltage unit HV3 without passing through the current detection resistance R6.
3, C1, C2). Therefore, only the current flowing from the high-voltage unit HV3 to the photoconductor OPC flows to the current detection resistor R6.

Rectifying and smoothing circuit (D2, D3, C1, C2)
A series circuit of a resistor R4 and a resistor R5 is connected between the output terminals of the resistors R4 and R5, and the low voltage divided by the resistors R4 and R5 is applied to the voltage detection signal input terminal VT of the controller CNT.
Join. The resistors R4 and R5 also have a function as dummy resistors of the high voltage unit HV3.

The controller CNT is a high voltage unit HV.
Operational amplifier IC destined for 3 (transfer transport unit TTU)
1, IC2, and N for the microcomputer IC3 and the high voltage unit HV3 which are also common to the other high voltage units.
It includes an OR element IC2. A voltage of ± 12 V is supplied to the operational amplifiers IC1 and IC2.

Since the current detection signal terminal IT to which the current detection resistor R6 is connected has a negative voltage, the operational amplifier I
After reversing the polarity at C1, microcomputer IC3
Is applied to the A / D conversion input terminal AN0. Operational amplifier I
The non-inverting input of C1 is connected to GND, the inverting input is connected to the IT terminal of the high-voltage unit HV3 via the resistor R9, and the inverting input and output of the operational amplifier IC1 are connected to the resistor R10. The resistance values of these resistors R9 and R10 are the same.
Here, the output current value of the high-voltage unit HV3 is Iopc, and the output voltage of the rectifier circuit (D2, D3, C1, C2) is V2.
3. If the voltage of the output terminal of the operational amplifier IC1 is V9, then Iopc = V9 / R6. When the values of the load resistors R2 and V23 change, the output voltage V9 of the operational amplifier IC1 changes as shown in FIG.

If the voltage obtained by dividing the output voltage of the rectifier circuit (D2, D3, C1, C2) (the voltage at the connection point of the resistors R5 and R5 with respect to the equipment ground) is V1,
When the values of the load resistance R2 and V23 change, V1 changes as shown in FIG. That is, the output voltage V23 of the rectifier circuit
It can be seen that the voltage V1 at the connection point also fluctuates when the load resistance R2 changes, that is, when the output current Iopc changes even if the same.

The voltage V1 at the connection point between the resistors R4 and R5 of the high voltage unit HV3 with respect to the equipment ground GND is
It is added to the detection voltage input terminal VT of the controller CNT.
In the controller CNT, the voltage is applied from the terminal VT to the non-inverting input of the operational amplifier IC2 via the resistor R13, and the non-inverting input is simultaneously connected to the GND via the resistor R14. Resistance R5 of high voltage unit HV3
The voltage V3 with respect to the GND at the connection point of R6 and R6 is applied to the inverting input of the operational amplifier IC2 via the terminal IT and the resistor R11, and the inverting input and the output of IC2 are connected by the resistor R12. As a result, the operational amplifier I
At the output end of C2, a voltage V7 is obtained by subtracting the voltage V3 seen from GND from the voltage V1 seen from GND, which is a voltage (potential difference) V13 between: V13 = V1-V3 = V23 × R5 / (R4 + R5) The voltage drop V3 due to the resistor R6 is several V, which can be ignored when viewed from the high voltage output voltage V23 of several KV of the rectifier circuit, so V23 = output voltage.

FIG. 5 shows changes in the output voltage V7 of the operational amplifier IC2 when the load resistances R2 and V23 are changed. As a result, even if the load resistance R2 changes, that is, the output current Iopc changes, the detection voltage V7 of the output voltage V23 of the high voltage unit HV3 does not substantially change.

Output of operational amplifier IC2 (voltage V7)
Is an A / D conversion input AN of the microcomputer IC3
1 is applied. The microcomputer IC3 controls the F of the high-voltage unit HV3 so that the voltage V7 read by A / D conversion matches the target value calculated and held by itself.
The ON width (energization duty) of the pulse signal for driving the ET Q is calculated and output to the output port T0. The high-voltage unit H is connected to the output port P0 of the microcomputer IC3.
An output on / off control signal that determines whether V3 outputs a high voltage output is output. A signal obtained by NANDing the output ports P0 and T0 of the microcomputer IC3 is output from the NAND gate IC4 to the output terminal PT of the controller CNT.
Through the FET Q of the high voltage unit HV3. That is, the signal at the output end PT becomes the gate signal of the FET Q.

The FET Q gate of the high voltage unit HV3
A resistor R7 and a resistor R8 connected to the FET Q are gate resistances of the FET Q, and a diode D1 connected in parallel to the FET Q is for protecting the FET Q.

The values of the A / D conversion inputs (V9, V7) of the microcomputer IC3 accurately indicate the current Iopc flowing through the photoconductor OPC and the voltage V23 applied to the photoconductor OPC. Load resistance R2
Is calculated accurately and the high voltage unit H is
The output target value of V3 can be set. The micro computer IC3 is provided with the image size to be recorded and the density adjustment value (given before the transfer process).
Then, the target current value, target voltage value, load resistance reference value and load resistance change reference value corresponding to them are calculated and set in a register (target value table).
Current Iopc (V9) flowing through PC and applied voltage V23
(V7) is read repeatedly to calculate the value of the load resistance R2,
Compare this value with the load resistance reference value of the target value table,
When it is smaller than the reference value, the "constant current control mode" is set, and when it is larger, the "constant voltage mode" is set, and when it is smaller than the reference value, the rate of change of the load resistance R2 (unit of belt TB). Change amount per movement amount) and calculate this as the target value
If the rate of change is equal to or greater than the reference value, the "constant voltage mode" is set. In addition,
The "constant current mode" is set at the beginning of the transfer period. Then, the output control of the set mode is performed.

That is, when the "constant current mode" is set, the current Iopc (V9) flowing through the photoreceptor OPC is set.
Adjusts the duty of the PWM pulse to be output to the output port PO so that the current value matches the current target value of the target value table. When the "constant voltage mode" is set, the duty of the PWM pulse output to the output port PO is set so that the applied voltage V23 (V7) matches the voltage target value of the target value table. Adjust.

A power supply circuit similar to the above-mentioned high voltage unit HV3 is also included in the high voltage unit HV1 in order to apply a high voltage to the corona discharger C, and the discharge wire of the corona discharger C is the high voltage terminal of the high voltage unit HV1. A metal case electrically connected to (T) and surrounding the discharge wire is connected to the reference potential side end (, FBR). Controller CN
In T, the same input / output circuit elements including IC1, IC2 and IC4 shown in FIG. 2 are included for the corona discharger C and are connected to the microcomputer IC3. The output voltage to the corona discharger C is controller CN
A current (chart) that is read from the terminal VC of T to the controller CNT and is flown to the photoconductor OPC by the corona discharger C.
Current) is read from the terminal IC of the controller CNT into the controller CNT. Micro computer IC
Similarly to the above-described output control for the high voltage unit HV3, the controller 3 also controls the power supply circuit for applying a high voltage to the corona discharger C of the high voltage unit HV1 by the controller C.
A PWM pulse is applied through the output terminal PC of NT to control the applied voltage and the charge current of the corona discharger C.

In the second embodiment in which the transfer transport unit TTU is replaced with a transfer corona discharger, the discharge wire of the transfer corona discharger is connected to the high voltage output terminal (T) of the high voltage unit (HV3) to discharge. Connect the metal case surrounding the wire to the end on the reference potential side of the high voltage unit (HV3) (, FB
R). In this case, the output voltage of the high voltage unit,
Although the current value is different from that of the transfer / transport unit TTU, the functions of the high-voltage unit and the controller CNT are substantially the same as those of the above-described first embodiment, and therefore detailed description thereof will be omitted.

Similarly, in the third embodiment in which the transfer transport unit TTU is replaced by a transfer charging roller, the charging roller is connected to the high voltage output terminal (T) of the high voltage unit (HV3) to charge the charging roller. The auxiliary electrode provided in contact with the battery is connected to the reference potential side end (, FBR) of the high voltage unit (HV3). Also in this third embodiment, the output voltage and current value of the high-voltage unit are different from those of the transfer transport unit TTU, but the functions of the high-voltage unit and the controller CNT are substantially the same as those of the first embodiment described above. , Detailed description is omitted.

In the above, the embodiment of the charging device of the present invention has been mainly described in the transfer mode. However, the charging device for charging the photoreceptor OPC prior to the exposure to form an electrostatic latent image. The above embodiments can be similarly applied to the above.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of an embodiment of the present invention, which is a charging device of an electrophotographic image forming apparatus for charging a photoreceptor OPC prior to exposure in order to form an electrostatic latent image, 1 shows a power supply that applies a developing bias to a developing device that develops an electrostatic latent image, and a transfer conveyance unit that transfers a visible image formed on a photoconductor OPC to a recording sheet.

FIG. 2 is an electric circuit diagram showing a configuration of a high voltage unit HV3 shown in FIG. 1 and a configuration of a part of a controller CNT.

FIG. 3 shows the value of the load resistance R2 and the output voltage V23 of the high voltage unit HV3 shown in FIG. 2, and the operational amplifier IC1.
5 is a graph showing the relationship of the output voltage V9 of FIG.

FIG. 4 shows the value of the load resistance R2 and the output voltage V23 of the high voltage unit HV3 shown in FIG. 2, and the voltage V at the voltage dividing end.
It is a graph which shows the relationship of 1.

5 is an output voltage V of the high voltage unit HV3 shown in FIG.
23 is a graph showing the relationship between the value of 23 and the output voltage V7 of the operational amplifier IC2.

[Explanation of symbols]

OPC: Photoconductor GND: Equipment
S C: Corona discharger G: Grid L: Image light B: Developing device TTU: Transfer transport unit TB: Transfer belt ER: Transfer electrode HV1 to 3: High voltage unit PSU: DC power supply TR: Boosting transformer Q: Switch element D2 , D3, C
1, C2: rectifying / smoothing circuit CNT: controller

Claims (7)

[Claims] 1. A high voltage generating circuit including output voltage adjusting means, a high voltage terminal and a reference potential terminal for outputting the high voltage generated by the circuit, a voltage detecting element for generating a voltage proportional to the high voltage, and a device for detecting the voltage. A high-voltage power supply including a current detection element that is interposed between a reference potential side end and the reference potential terminal and that generates a voltage proportional to the current value between these ends; to a charged member on a conductor connected to the reference potential Charging means including a charging member electrically connected to the high-voltage terminal and facing each other in contact with or away from the high-voltage terminal, and means for returning a current flowing from other than the charged member to the reference potential side end of the high-voltage power source; and , A voltage generated by the current detection element, and a voltage obtained by subtracting the voltage from the voltage generated by the voltage detection element,
A charging device, which corresponds to one of the above, and controls the output voltage adjusting means so that it matches a target value. 2. The controller is configured such that a voltage is generated by the current detecting element and a voltage obtained by subtracting the voltage from a voltage generated by the voltage detecting element from a charging member via a charged member. The resistance value up to the reference potential is calculated, and when the resistance value is less than the set value, the output voltage adjusting means is controlled so that the voltage generated by the current detection element matches the target value, The charging device according to claim 1, wherein the output voltage adjusting unit is controlled so that the subtracted voltage matches a target value. 3. The controller controls the output voltage adjusting means so that the subtracted voltage matches a target value when the resistance value is smaller than a set value and the change in the resistance value is equal to or larger than the set value. The charging device according to claim 2, which is controlled. 4. The high-voltage power supply includes a boosting means for converting a DC voltage into a high voltage, which has a variable output voltage, a resistance voltage dividing circuit connected between a high-voltage end of the boosting means and a reference potential end, and the reference potential end. The current detection resistor connected in series between the reference potential terminals of the high voltage power supply; the controller subtracts the voltage drop of the current detection resistor from the divided voltage of the resistance voltage divider circuit An amplifier and a differential amplifier circuit including a plurality of resistors, wherein the plurality of resistors have a resistance value larger than a resistance value of the resistance voltage dividing circuit, each of which has a non-inverting input of the operational amplifier and a reference. Connected to the potential, between the non-inverting input and the voltage divider end of the resistor divider, between the inverting input and the voltage detector end of the current detecting resistor, and between the inverting input and the output of the operational amplifier. The charging device according to claim 1, claim 2 or claim 3. 5. The charging means is a metal roller connected to the reference potential side end of a high-voltage power supply, a transfer belt wound around the metal roller, and electrically connected to the high-voltage terminal, and is electrically connected to the transfer belt. The charging device according to claim 1, wherein the charging device is a transfer conveyance unit including a roller electrode that supplies power to the transfer belt at a contact portion with a member. 6. A corona discharger including a discharge wire electrically connected to the high-voltage terminal of a high-voltage power supply, and a metal case surrounding the discharge wire and connected to the reference potential side end. The charging device according to claim 1, claim 2 or claim 3. 7. The charging means is in contact with the member to be charged or is opposed to the member to be separated therefrom, and is electrically connected to the conductive roller electrically connected to the high-voltage terminal of the high-voltage power source, and is in contact with the conductive roller.
The charging roller according to claim 1, wherein the charging roller includes an auxiliary electrode connected to the end on the reference potential side.