JPH07168403A - Image forming device - Google Patents

Abstract

PURPOSE:To shorten a rise time in the case of switching a transfer current without causing cost inclease of a power source and making the power source larger even when contact electrostatic charging is used for transfer process in an image forming device such as an electrophotographic color copying machine or printer. CONSTITUTION:The output sides of positive and negative high voltage power sources E1 and E2 being output variable DC-DC converter are connected in series, and power is supplied to the load L of a transfer brush from one end of the power source. In such a case, output voltage and output current(load current) from the power sources E1 and E2 are detected and compared with a reference value from a microcomputer 21 by error amplifiers 13 and 14. Then, output from the amplifiers 13 and 14 is selected by analog switches Q1 and Q2. The output voltage and output current in specified timing are detected and stored in a memory in the microcomputer 21, then the stored value is switched to a reference value. By setting the intermediate value of the output level of the selected amplifier 13 or 14 as a threshold, the power sources E1 and E2 are selectively actuated to switch constant-voltage control and constant- current control of both polarities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine and a printer, and more particularly to an image forming apparatus equipped with a high-voltage power supply device suitable for developing, charging, transferring and discharging electricity. is there.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus such as a color copying machine or a color printer, a process of transferring a toner image (powder image) on a photosensitive drum which has been developed onto a transfer paper is usually a corona process. Charging is used, and the corona wire is approximately 6-9 KV, 0.1-1 mA.
Power is supplied by the constant current source.

Further, as the output voltage generating means of both positive and negative polarities, positive and negative power supplies are connected in series, and the polarity side having a small output range is fixed output and the opposite polarity side is variable,
The one that covers the required positive and negative output range is generally used.

[0004]

By the way, in recent years, the transfer process has been reviewed to improve the color image quality, and the corona charging is switched to the contact charging. In order to attract the toner on the photosensitive drum to the transfer paper, a transfer brush is brought into contact with the back side of the transfer paper via a Mylar film, and a high voltage of the opposite polarity to the toner is applied to the transfer brush. is there.

At that time, in the contact charging, the applied voltage is increased stepwise every time the number of times of transfer is increased in order to transfer the toners of four colors of yellow, magenta, cyan and black onto the same transfer paper. Therefore, 1 for the fourth color
The voltage exceeds 0 KV, which causes adverse effects such as leakage. So, to prevent this,
The applied voltage has both positive and negative polarities so that the maximum absolute value of the applied voltage is halved.

That is, a negative high voltage is applied before the transfer of the first color, and a positive high voltage of the same level as the negative high voltage at the approximate start is applied to the fourth color. There is.

However, in particular, the conventional positive / negative bipolar voltage generating means has a problem that the output range of the power source on the variable output side is significantly widened, resulting in an increase in cost, an increase in size, and a decrease in reliability.

Further, since it is the transfer current that essentially contributes to the transfer process, it is desirable to stabilize the transfer current by performing constant current control. Due to the floating capacitance between the transfer paper and the photosensitive drum, there is a problem that the rise time is significantly increased.

That is, from the transfer brush 7 shown in FIG.
An equivalent circuit of the system in which the photosensitive drum 1 is viewed through the transfer drum 2 and the transfer paper P is represented by a CR parallel circuit shown in FIG.
In FIG. 3, C is a transfer brush 7, a transfer drum 2, a transfer paper P,
The stray capacitance between the photosensitive drums 1, R is a spatial impedance corresponding to a minute corona current Ir flowing from the transfer brush 7 to the photosensitive drum 1. E is a high voltage power supply.

Here, of course, it is the corona current Ir that essentially contributes to the transfer, but since it is impossible to separate C and R, the current is detected as the corona current Ir and the stray capacitance. It becomes the sum of the charging / discharging current Ic (= dVc / dt) of C. Generally, the set transfer current, that is, the corona current Ir is several tens of microamperes or less. Therefore, if the changing speed of the output voltage of the high voltage power supply is increased at the time of current switching, the charging / discharging current Ic becomes the target value of the constant current or more. Therefore, there is a problem that the rise time and fall time of the high-voltage power supply are limited by the charge / discharge time of the stray capacitance C. For this reason, the corona current Ir reaches the target value significantly late, and as a result, the image forming time has to be lengthened to compensate for this.

The present invention has been made by paying attention to the above problems, and the rise time at the time of switching the transfer current is shortened and the image formation time is shortened without increasing the cost, increasing the size and decreasing the reliability. An object is to obtain an electrophotographic image forming apparatus that does not become long.

[0012]

The image forming apparatus of the present invention is configured as follows. (1) Positive and negative high-voltage power supplies whose outputs are connected in series and each output is variable, and an output of the high-voltage power supply. Each error amplifier that compares the detected value of the voltage and the output current with each reference value, a switch that selects the output of these error amplifiers, and the output voltage or output current of the high-voltage power supply at a predetermined timing is stored, and the storage A control means for setting the reference value based on a value, and a bipolar constant voltage control and a constant current for selectively operating the positive and negative high voltage power supplies with the intermediate value of the output level of the error amplifier as a threshold value. Equipped with a switchable high-voltage power supply device that can be controlled.

(2) In the above apparatus (1), when a high voltage power supply supplies electric power to a contact type transfer brush or transfer roller to attract toner from the photoconductor to the transfer paper or transfer drum or transfer belt. Constant current control is performed at a predetermined target value, the output voltage during this constant current control is stored, and the next time the target value for constant current control is switched, the output voltage stored at that initial value is used for constant voltage control. The voltage is controlled.

(3) In the apparatus of (1) above, the output of the high-voltage power supply is used for transfer and suction of transfer paper,
Constant current control at the time of transfer and adsorption is performed based on a different reference value for each color, and when the reference value is switched, constant voltage control based on the reference value is performed at the initial timing of the switching.

(4) In the device of (2), the limiter operation is performed with the target value of the constant current control switched immediately after the constant voltage control operation as the current limiter value.

(5) In the apparatus of (3) above, the reference value for constant voltage control is the output voltage of each high voltage power source when an image is formed in the constant current mode for each color.

(6) In the device of (3), when the output voltage exceeds the first level during constant current control, the second level, which is lower than the first level by a predetermined voltage for a predetermined timing, is set as a target value. As a result, constant voltage control is performed.

(7) In the apparatus of (3), the constant voltage control is performed at a predetermined timing when the transfer of each color is completed, and then the constant current control is performed.

(8) In the device of (3) or (5), the limiter operation is performed with the target value of the constant current control switched immediately after the constant voltage control operation as the current limiter value.

(9) In the above apparatus (7), the target value for constant voltage control is the output voltage of the high voltage power source during constant current control at the corresponding sequence timing in advance.

(10) Positive and negative high-voltage power supplies whose output sides are connected in series, a voltage detection circuit for dividing an output voltage supplied from one end of the high-voltage power supply to the load to a predetermined ratio, and an output of the voltage detection circuit and a predetermined voltage. Error amplifier for comparing the reference voltage of the above, a current detection circuit inserted between the other end of the high-voltage power supply and the ground, and a second error amplifier for comparing the output of the current detection circuit with a predetermined reference voltage. And the first and second
An electronic switch for selecting the output of the error amplifier of FIG. 2 by a control signal, and an inverting amplifier and a non-inverting amplifier for amplifying the difference voltage between the output of the error amplifier selected by the electronic switch and the intermediate value of the output level of the error amplifier. , A drive circuit that controls the output of the positive and negative high-voltage power supplies according to the outputs of the inverting amplifier and the non-inverting amplifier, and the positive and negative high-voltage power supplies by comparing the output of the selected error amplifier and the intermediate value. A comparator that selectively operates, an A-D converter that converts the analog output signal of the voltage detection circuit into a digital signal, and an output signal of the A-D converter,
A microcomputer that generates a reference signal for the first and second error amplifiers at a predetermined sequence timing, and a digital reference signal that is converted into an analog signal and given to the first and second error amplifiers as the reference voltage D A switching type high-voltage power supply device having a bipolar constant voltage control and a constant current control having an -A converter was provided.

[0022]

In the image forming apparatus of the present invention, both positive and negative high-voltage power supplies connected in series on the output side have variable outputs, and power is supplied from the high-voltage power supply to a load such as a transfer brush or a suction brush. Then, the output voltage and the output current (load current) of the high-voltage power supply are detected, and the positive and negative high-voltage power supplies are selectively operated according to the detected output.

Further, the transfer voltage and the attraction voltage for each color are detected and the values are stored in the memory. Then, at the time of actual image formation, constant voltage control is performed at the start of the image formation and at the initial timing of color switching with reference to the stored output voltage value.

[0024]

【Example】

[Embodiment 1] FIG. 1 is a circuit diagram showing the construction of the first embodiment of the present invention, showing the construction of a high-voltage power supply unit provided in an electrophotographic image forming apparatus.

In FIG. 1, T1 and T2 are positive and negative high-voltage power supplies (DC-) whose outputs are connected in series and whose outputs are variable.
DC converter) E1, E2 high voltage transformer, 11, 1
Reference numeral 2 is a drive circuit for driving the primary side thereof, 13 to 16 are error amplifiers, and 17 and 18 are power amplifiers.

The outputs of the secondary side high voltage windings S1 and S2 of the high voltage transformers T1 and T2 are the high voltage rectifying diode D, respectively.
1, D2 is rectified, but the rectified output side of the diode D2 is the side opposite to the high voltage diode connection side (one end side connected to the load L) of the high voltage winding of the transformer T1 via the high voltage terminals P2 and P3. It is connected to the. In addition, high voltage transformer T
The load current (output current) is detected by the resistor R3 that is inserted between the high voltage winding S2 of the second high voltage winding S2 and the side opposite to the high voltage diode connection side (the other end side), and that is inserted between the grounds. The value of the resistor R3 is selected to be sufficiently small. The output voltage is a predetermined ratio (here, equal) of the rectified outputs of the output detection windings L1 and L2 of the high-voltage transformers T1 and T2 by the coupling resistors R9 and R10 forming the voltage detection circuit.
Is detected by being divided by the A / D converter 19
After conversion, it is input to the microcomputer 21,
It is stored in the internal memory.

The values of the bleeder resistances R1 and R2 connected in parallel to the high-voltage rectification output side of the high-voltage power supplies E1 and E2 are selected to be at least ⅓ or less of the load resistance RL.

The error amplifier 13 detects the load current input from the non-inverting input side and the reference voltage, which is input from the inverting input side, of the microcomputer 21 and converted into analog by the DA converter 20. To compare.
Further, the error amplifier 14 outputs the detection output of the output voltage input from the inverting input side and the control output of the microcomputer 21 input from the non-inverting input side to the DA converter 2
0 is compared with the reference voltage analog-converted.

The error amplifiers 13 to 16 are driven by positive and negative power supplies + Vcc and -Vee. This + Vcc, -V
Since ee has the same potential difference as + 15V and -15V, respectively, the intermediate value of the output level of the error amplifier becomes the ground potential.

The error amplifiers 15 and 16 are an inverting amplifier and a non-inverting amplifier, and the outputs of the error amplifiers 13 and 14 selected by the analog switches (electronic switches) Q1 and Q2 are centered on the ground potential, respectively. Inverted and non-inverted amplification is performed at a predetermined ratio, and each output is a diode D
It is input to the power amplifiers 17 and 18 via 3, D4.

The drive circuits 11 and 12 on the primary side of each of the high-voltage transformers T1 and T2 are composed of an oscillating circuit, a switching circuit, and the like. It plays the role of adding to F2.

When the outputs of the error amplifiers 13 and 14 selected by the analog switches Q1 and Q2 are positive, the output of the error amplifier 16 becomes positive, the power amplifier 17 operates, and a positive high voltage is applied to the terminal P1. Occur. At this time, the error amplifier 1
The output of 5 becomes negative, the diode D4 is cut off, the output of the power amplifier 16 becomes zero, no voltage is generated in the secondary winding S2 of the high voltage transformer T2, and the high voltage diode D2
Shut off.

Further, the positive high voltage generated between the terminals P1 and P2 is applied to the load L and the bleeder resistance R2, but as described above, the resistance R2 is selected to be sufficiently smaller than the load resistance RL, so that it is large. The part will be fed to the load L.

When the outputs of the error amplifiers 13 and 14 selected by the analog switches Q1 and Q2 are negative, the high-voltage transformer T1 is cut off and the high-voltage transformer T2 is turned on, contrary to the case of positive output.
Is activated, and a negative high voltage is supplied to the load L.

For the error amplifier 13, an FET input type with a very small input leakage current is selected in order to improve the accuracy of constant current control.

In addition, in FIG. 1, D5 and D6 are rectifying diodes, Q3 is an inverter (inverter), Q41 is a buffer, Q42 and Q43 are inverters, and Q51 and Q52.
Is an AND gate, Q53 is an OR gate, and Q54 is an inverter.

From the high-voltage power supply device configured as described above, electric power is supplied as a load L to, for example, a contact type transfer brush or a suction brush. FIG. 2 shows a schematic configuration around the photosensitive drum and the transfer drum. FIG. 3 is a diagram showing an equivalent circuit of the load L.

In FIG. 2, the toner image (powder image) formed on the photosensitive drum 1 through the image exposure by the primary charging device 3, the laser beam 5 and the developing process by the developing device 4 is
The image is transferred onto the transfer paper P adsorbed on the transfer drum 2. The transfer drum 2 is formed by winding a thin Mylar film around a cylindrical frame, and an image forming portion that contacts the photosensitive drum 1 is composed of a single film.

The suction brush 6 plays a role of adsorbing the transfer paper P, which has passed through the transfer guide, to the transfer drum 2 with an electrostatic force, and the transfer brush 7 transfers the toner on the photosensitive drum 1 to the transfer paper by an electrostatic force. It plays the role of transferring onto P. The inner and outer post-transfer chargers 8 and 9 are used to reduce the absolute value of the voltage applied to the transfer brush 7, which will be described later, and the separation charger 10 performs AC + DC corona charging to transfer the transfer paper. It serves to completely eliminate the electrostatic attraction force between P and the transfer drum 2.

FIG. 4 shows the operation sequence timing of the charger and the charging brush around the transfer drum 2. The transfer drum 2 has such a circumferential length that one A3 sheet can be vertically stuck as the transfer sheet P, and FIG. 4 shows a case where one A4 sheet is copied.

When the transfer paper P is sent from the paper carrying system,
The high-voltage power supply device causes +15 μA to flow to the suction brush 6 in the constant current control mode to attract the transfer paper P to the transfer drum 2. Further, a negative high voltage is applied to the inner post transfer charger 8 to charge the inside of the transfer drum 2 to −6 KV. At the same time, a positive high voltage is applied to the outer post transfer charger 9,
The peeling of the transfer paper 9 is prevented.

When the transfer paper P is attracted to the transfer drum 2 and the inside of the transfer drum 2 is further charged to −6 KV, +10 μA is caused to flow to the transfer brush 7 in the constant current control mode, and the transfer paper is transferred from the photosensitive drum 1. The toner image is transferred to P. It goes without saying that this transfer process is repeated for every four colors of magenta (M), cyan (C), yellow (Y), and black (Bk). Further, as shown in (f) of FIG. 4, the power supply voltage of the transfer brush 7 at this time remains at about −6 KV between the sheets, but the previous charge is retained at the transfer timing to the transfer sheet P. Therefore, it increases in about 2 KV steps for each color. (In (f), the third and subsequent colors are omitted).

When the transfer of the fourth color is completed, a high voltage of AC + DC is applied to the separation charger 10 (not shown) to charge the transfer paper P and the transfer drum 2 by corona charging, and the transfer paper P is discharged. Is separated from the transfer drum 2.

As is clear from the above description, the power supply for supplying power to the transfer brush 7 and the suction brush 6 must be a constant-current power supply with both positive and negative polarities. More specifically, it is necessary to supply a constant current to the load L while coping with a voltage source that is equivalently included in the load L and that changes over a wide range of −6 KV to +6 KV.

FIG. 4A shows the load current of the suction brush 6 (control value: +15 μA), (B) the load current of the inner post transfer charger 8 (control value: −200 μA), and (C) the outer post. Load current of transfer charger 9 (control value: + 200μ
A) and (d) are load currents of the transfer brush 7 (control value: +1)
0 μA), (e) is the output voltage of the suction brush 6 (-6 KV
~ + 6KV), (f) is the output voltage of the transfer brush 7 (-6
KV to 0V) are shown.

5 and 6 are timing charts showing the operation of this embodiment, FIG. 5 shows the transfer timing in the adjustment mode, and FIG. 6 shows the transfer timing during actual image formation.

5A to 5D show transfer timings of magenta (M), cyan (C), yellow (Y), and black (Bk) in constant current control,
(I) shows the sampling timing of the transfer output voltage. 6A to 6D are transfer timings of magenta, cyan, yellow, and black under constant current control, and (H) to (H) are start-up of magenta, cyan, yellow, and black under constant voltage control. The timing is shown.

FIG. 7 is a flow chart showing the operation of this embodiment. First, the adjustment mode is selected when the product is shipped from the factory, or when maintenance or inspection is performed in the market. When this adjustment mode is entered (step 101), as shown in FIG. 5, constant current control is performed in the order of magenta, cyan, yellow, and black (steps 102 to 105). The target value (reference value) of the constant current at this time is (a), (b),
It is +10 μA in the image section shown in (C) and (D), and 0 μA in the other non-image sections. The figure also shows a case of A4 size paper.

Then, the transfer voltages Vtm, Vtc, Vty, and Vtbk of magenta, cyan, yellow, and black are detected and measured at the timing when the constant current control is sufficiently stabilized, and are digitally converted by the AD converter 19.
It is stored in the memory in the microcomputer 21.

Next, in the image forming mode (step 1
06), as shown in FIG. 6, constant voltage control is performed prior to the constant current control, and the load capacities (floating capacities between the transfer brush and the ground and the transfer roller) are stored as the target values Vtm, Vtc, and Vty. , Vtbk is charged rapidly. After the constant voltage control, the constant current control is immediately switched to (steps 107 to 114).

The high-voltage power supply device for supplying electric power to the suction brush 6 and the transfer brush 7 is a positive / negative high-voltage power supply E1 and E2 whose output sides are connected in series as shown in FIG.
Output is variable, and high voltage power supplies E1 and E2
Since the positive and negative high voltage power supplies E1 and E2 selectively operate according to the detected output voltage and output current (load current) of
The rise time at the time of switching the transfer current is shortened without increasing the cost, increasing the size, and decreasing the reliability, and therefore the image forming time is not extended.

[Second Embodiment] FIGS. 8 and 9 are timing charts showing the operation of the second embodiment of the present invention. FIG. 8 shows the transfer timing in the adjustment mode, and FIG. 9 shows the actual transfer timing. Shows.

8A to 8D are magenta (M), cyan (C), and yellow (Y) in the constant current control.
And black (Bk) transfer timing, and (ri) the transfer output voltage sampling timing. Figure 9
(A) to (c) are magenta start-up, transfer and fall timings (d) to (f) are cyan start-up, transfer, and fall timings, and (to) to (re) are yellow. Start-up, transfer and fall timing, (nu) ~ (wo)
Indicates the timing of black start-up, transfer, and fall, respectively.

FIG. 10 is a flow chart showing the operation of the second embodiment. In the present embodiment, the non-image section, that is, the space between sheets is quickly converged to 0 μA, and after the transfer is completed, a constant voltage is applied to the transfer brush 7 to rapidly charge the load capacity. Is.

First, the adjustment mode is selected when the product is shipped from the factory, or when maintenance or inspection is performed in the market. When the adjustment mode is entered (step 201), constant current control is performed in the order of magenta, cyan, yellow, and black as shown in FIG. 8 (steps 202 to 209). The target value of the constant current at this time is (a), (b), (c) of FIG.
It is +10 μA in the image section shown in (d) and 0 μA in the other non-image sections. The figure shows a case of A4 size paper.

At the timing when the constant current control is sufficiently stabilized, the transfer voltages Vtm, Vtc, Vty, Vtbk for magenta, cyan, yellow, and black, as well as the inter-sheet voltages Vtm, Vtc, Vty, Vtbk are transferred.
Is detected and measured, digitally converted by the AD converter 19, and stored in the memory in the microcomputer 21.

Next, in the image forming mode (step 2
10), as shown in FIG. 9, prior to the transfer timing,
Constant voltage control is performed, and the load capacity (floating capacity between the transfer brush and the ground and the transfer roller) is rapidly charged until the stored target values Vtm, Vtc, Vty, and Vtbk are reached. Then, immediately after the constant voltage control, the target value 1
Switching to constant current control of 0 μA (steps 211 to 211)
226).

After the transfer is completed, constant voltage control is performed with Vtm, Vtc, Vty, and Vtbk as target values at predetermined timings, and then the constant current control is switched to the target value of 0 μA (step 227). When these operations are completed, the high voltage power supply is shut off (step 22).
8).

[Third Embodiment] FIG. 11 is a flow chart showing the operation of the third embodiment of the present invention. This embodiment is an example in which an output overvoltage limiter is provided, and during constant current control, an excessive voltage is applied to the load L due to fluctuations in the load impedance, causing spark leakage and pinholes in the transfer drum 2. It is intended to prevent an accident that causes an image defect and deterioration of the transfer drum 2 and the photosensitive drum 1.

The flowchart of FIG. 11 shows a limiter processing routine time-divisionally managed by an internal timer of the microcomputer 21, and when the control flag becomes 1 at the allocation timing of this limiter processing (step 301), The output Vout of the A / D converter 19 is read (step 302), and Vlimit (-6.
5 kv) (step 303).

The output voltage Vout is Vlimit.
When (-6.5 KV) is exceeded, Vlimi is forced.
300V lower than t (-6.5KV) (-6.2K
The constant voltage control mode in which V) is the target value is switched to (step 304). When the internal counter of the microcomputer 21 keeps this state for a predetermined timing To (steps 305 and 306), it returns to the normal control routine.

Here, the above timing To is sufficiently small so as not to affect the normal control sequence, and when the limiter operation is completed and the normal control routine is returned to, the limiter level is immediately exceeded. You must choose a value that does not.

Each embodiment of the present invention has been described above. Here, in the circuit of FIG. 1, the error amplifier 14 compares the output of the voltage detection circuit (resistors R9 and R10) with a predetermined reference voltage. The error amplifier serves as a second error amplifier that compares the output of the current detection circuit (R3) with a predetermined reference voltage. And analog switch Q
The difference voltage between the output of the error amplifiers 13 and 14 selected by 1 and Q2 and the intermediate value of the output levels of the error amplifiers 13 and 14 is inverted and amplified by the error amplifiers 15 and 16 which are non-inverting amplifiers, and the amplification thereof is performed. Drive circuits 11 and 12 according to the output
Thus, the outputs of the high voltage power supplies E1 and E2 are controlled.

At this time, the selected error amplifier 13,
A comparator for comparing the output of 14 and the above-mentioned intermediate value is provided, and the output of this comparator supplies positive and negative high-voltage power supplies E,
E2 may be selectively operated to perform bipolar constant voltage control and constant current control.

[0065]

As described above, according to the present invention, it is possible to prevent the rise time at the time of switching the transfer current from being shortened and the image formation time to be prolonged without increasing the cost, increasing the size and reducing the reliability. be able to. That is, the following effects are obtained.

(1) When a high voltage charging load with a small current as a target value is subjected to constant current control, the charging current discharge time significantly increases the charging current rise time and fall time. To reduce the image formation speed,
It can be completely overcome without increasing the overshoot when switching the current.

(2) The deterioration of the transfer drum, the photosensitive drum, etc. is completely achieved because the limiter that can limit the overvoltage at the time of load abnormality with high accuracy and quickly can be realized easily, that is, without adding any hardware circuit. Therefore, the deterioration of the image can be suppressed to a minimum.

(3) Compared to the bipolar high-voltage generation system in which the conventional fixed output DC-DC converter and variable output DC-DC converter are connected in series, both positive and negative DC-DC are generated.
Since the converter is variable, the dynamic range of each DC-DC converter can be reduced.

(4) A constant current can be automatically and stably supplied to any variation in the resistance component and the voltage source component included on the load side.

(5) Since the positive and negative DC-DC converters are switched using the intermediate value of the output of the error amplifier as the threshold value, the operation of the positive and negative DC-DC converters is smoothly switched, and the output is abnormal. Does not occur.

(6) The output of the error amplifier is amplified centering on the intermediate level of the output and added to the DC-DC converter, whereby the positive / negative DC-DC described in the above item (3).
The converter switching operation can be made smoother.

(7) The output of the error amplifier is compared with the intermediate level of the output by the comparator, and DC-DC on the non-selected side
By stopping the comparator, (3),
The switching operation of the positive / negative DC-DC comparator described in (4) can be further smoothed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a configuration diagram around a photosensitive drum and a transfer drum of an image forming apparatus.

FIG. 3 is an equivalent circuit diagram of the load shown in FIG.

FIG. 4 is a waveform diagram showing an operation sequence of a charger and a charging brush around the transfer drum shown in FIG.

FIG. 5 is a timing chart showing transfer timing in the adjustment mode of the first embodiment.

FIG. 6 is a timing chart showing the actual transfer timing of the first embodiment.

FIG. 7 is a flowchart showing the operation of the first embodiment.

FIG. 8 is a timing chart showing transfer timing in the adjustment mode of the second embodiment.

FIG. 9 is a timing chart showing the actual transfer timing of the second embodiment.

FIG. 10 is a flowchart showing the operation of the second embodiment.

FIG. 11 is a flowchart showing the operation of the third embodiment.

[Explanation of symbols]

 1 Photosensitive Drum 2 Transfer Drum 3 Primary Charger 4 Developing Device 6 Adsorption Brush 7 Transfer Brush 8 Post Transfer Charger 9 Post Transfer Charger 10 Separation Charger 11 Primary Drive Circuit 12 Primary Drive Circuit 13 Error Amplifier 14 Error amplifier 15 Error amplifier (inverting amplifier) 16 Error amplifier (non-inverting amplifier) 19 A-D converter 20 D-A converter 21 Microcomputer (control means) E1 High-voltage power supply E2 High-voltage power supply L load Q1 Analog switch (electronic switch) Q2 Analog switch (electronic switch) P Transfer paper

Claims (10)

[Claims] 1. An output variable positive and negative high voltage power source connected in series, respective error amplifiers for comparing detected values of output voltage and output current of the high voltage power source with respective reference values, and these error amplifiers. A switch for selecting the output of the high-voltage power supply, and a control means for storing the output voltage or output current of the high-voltage power supply at a predetermined timing and setting the reference value based on the stored value. An electrophotographic image forming apparatus comprising a switching type high-voltage power supply device capable of performing bipolar constant voltage control and constant current control for selectively operating the positive and negative high voltage power supplies with an intermediate value as a threshold value. apparatus. 2. A constant-current control is performed with a predetermined target value when electric power is supplied from a high-voltage power supply device to a contact-type transfer brush or transfer roller and toner is adsorbed from a photoconductor onto a transfer paper, a transfer drum, or a transfer belt. The output voltage at the time of this constant current control is stored, and when the target value of the constant current control is switched next, the constant voltage control by the stored output voltage is performed at the initial timing of the switching. The image forming apparatus according to claim 1. 3. The output of the high-voltage power supply device is used for transfer and adsorption of transfer paper, and constant current control at the time of transfer and adsorption is performed based on a different reference value for each color, and the reference value is switched when switching. The image forming apparatus according to claim 1, wherein the constant voltage control is performed based on the reference value at an initial timing of. 4. The image forming apparatus according to claim 2, wherein during the constant voltage control operation, a limiter operation is performed with a target value of constant current control that is switched immediately after as a current limiter value. 5. The image forming apparatus according to claim 3, wherein the reference value of the constant voltage control is an output voltage of each high voltage power source when an image is formed in a constant current mode for each color. 6. When the output voltage exceeds the first level during constant current control, constant voltage control is performed with a second level that is lower than the first level by a predetermined voltage for a predetermined timing as a target value. The image forming apparatus according to claim 3. 7. A predetermined timing at the end of transfer of each color,
4. The image forming apparatus according to claim 3, wherein the constant current control is performed after the constant voltage control is performed at each predetermined target value. 8. The image forming apparatus according to claim 3, wherein a limiter operation is performed with a target value of constant current control switched immediately after the constant voltage control operation as a current limiter value. 9. The image forming apparatus according to claim 7, wherein the target value of the constant voltage control is the output voltage of the high voltage power source during the constant current control at the corresponding sequence timing in advance. 10. A positive / negative high-voltage power supply whose output side is connected in series, a voltage detection circuit for dividing an output voltage supplied from one end of this high-voltage power supply to a load to a predetermined ratio, and an output of this voltage detection circuit and a predetermined voltage. A first error amplifier for comparing a reference voltage, a current detection circuit inserted between the other end of the high voltage power supply and the ground, and a second error amplifier for comparing an output of the current detection circuit with a predetermined reference voltage. , An electronic switch for selecting the outputs of the first and second error amplifiers by a control signal, and amplifying a difference voltage between the output of the error amplifier selected by the electronic switch and the intermediate value of the output level of the error amplifier. An inverting amplifier and a non-inverting amplifier, a drive circuit for controlling the outputs of the positive and negative high-voltage power supplies according to the outputs of the inverting amplifier and the non-inverting amplifier, and a comparison between the output of the selected error amplifier and the intermediate value. In comparison, a comparator that selectively operates the positive and negative high-voltage power supplies, an A-D converter that converts an analog output signal of the voltage detection circuit into a digital signal, and an output signal of the A-D converter are stored and stored in a predetermined manner. And a microcomputer that generates a reference signal for the first and second error amplifiers at the sequence timing of D, and a digital reference signal that is converted into an analog signal and given to the first and second error amplifiers as the reference voltage.
An electrophotographic image forming apparatus comprising a switching type high-voltage power supply device capable of performing bipolar constant voltage control and constant current control having an A converter.