JP2951993B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an image forming apparatus using an electrophotographic process, and more particularly to an image forming apparatus using a transfer roller in an electrophotographic process. Things.

[Prior Art] Conventionally, control of a high-voltage power supply using a contact transfer method has been described in Section 10.
It is performed with the basic configuration as shown in the figure.

In the electrophotographic process of the present embodiment, a positive high voltage is applied to a transfer roller 2 serving as a transfer means adjacent to a drum-shaped photosensitive member 1 to transfer a toner image on the photosensitive drum 1 onto a transfer material 3. . Here, the toner image is transferred to a primary charger, a developing device 5
And a known electrophotographic process comprising high-voltage power supplies 7, 6 and exposure means such as a laser for forming an electrostatic latent image. The developing high-voltage power supply 6 and the primary charging high-voltage power supply 7 are turned on by control signals CONT3 and CONT4 from the high-voltage control unit 8.
N / OFF control is performed.

The high voltage applied to the transfer roller 2 is output from the inverter transformer 9 shown in FIG. The inverter transformer 9 is driven via a transistor 10 by a pulse signal OSC from the high voltage control unit 8. The pulse signal is rectified on the secondary side of the inverter transformer 9 and (the diode 1
1, capacitor 12) Applied to the transfer roller 2. Here, the DC level of the transfer high voltage output is proportional to the emitter potential of the transistor 13. ON / OFF control is performed via the transistor 14 by a control signal CONT2 from the high voltage control unit 8.

FIG. 11 shows a sequence of the high-pressure control. When the system enters the printing operation and drives the photosensitive drum, the control signals CONT4,
Primary voltage, development and transfer are output at high voltage by CONT3 and CONT2.

At the time of the pre-rotation and the paper interval, the analog switches 16a and 16c are turned ON and the analog switches 16b are turned OFF and the constant current operation is started with the CONT1 at the "H" level. At this time, the output of the operational amplifier 15 is input to the operational amplifier 17 through the analog switch 16a. Therefore, the emitter potential of the output transistor 13 of the operational amplifier 15 is determined.
The output of the inverter transformer 9 is the transistor 13
, The output of the operational amplifier 15 determines the transfer output value. Further, the output of the operational amplifier 15 is charged into the low-leakage capacitor 18 through the analog switch 16c, so that the output voltage during the constant current operation is equivalently stored. The current value It during the constant current operation is determined by the divided voltage value of Vcc by the resistors 19 and 20, and the resistance value of the resistor 21. That is, in this example, It = Vcc * R19 / (R19 + R20) / R21.

At the time of printing, CONT1 is at the "L" level, the analog switches 16a and 16c are turned off, 16b is turned on, and the constant voltage operation is started.
In the constant voltage operation, the potential charged in the low leakage capacitor 18 is applied to the transistor 13 through the analog switch 16b.
The transfer output voltage is determined by the potential charged in the low-leakage capacitor 18 during the constant current operation.

The transfer output voltage is as shown in FIG. During a constant current operation, the voltage fluctuates due to load fluctuation (resistance unevenness in the circumferential direction of the transfer roller). The output of the operational amplifier 15 is charged into the low-leakage capacitor 18 by averaging it with the time constant of the resistor 36 and the capacitor 18.

[Problems to be Solved by the Invention] However, in the above-described conventional example, the following problems have been caused because the hardware using a capacitor is used as a means for storing the output voltage during the constant current operation.

1) The circuit configuration is complicated.

2) The capacitor voltage fluctuates due to the leak current, and the output voltage changes during the constant voltage operation.

3) The constant current operation must be repeated for each print for item 2), which complicates the sequence.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to simplify a circuit configuration and a sequence and obtain a stable transfer high-voltage output in an image forming apparatus using a contact transfer system.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a transfer unit including a transfer roller for transferring a developer on a photoreceptor to a transfer material, and supplying a high pressure to the transfer unit. A power supply, a current detecting means for detecting a current value flowing to the transfer means when a high voltage is supplied to the transfer means, and a control for controlling a current detected by the current detecting means to a predetermined value during an image forming preparation operation. Control means for supplying a value to the power supply, calculating an average of the control values for a predetermined period, and supplying the average value of the obtained control values to the power supply during image formation after the preparation operation. .

Embodiment 1 Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive drum which is a photosensitive member in an electrophotographic process, 2 denotes a transfer roller which is a transfer means in a contact transfer system, 3 denotes paper as a transfer material, 4 denotes a primary charger, 5 Is a developing unit, 6 is a developing high voltage power supply, 7 is a primary charging high voltage power supply, 8
Denotes a high-voltage power supply control unit. Circuits indicated by 9 and thereafter are transfer high-voltage power supplies.

In the present embodiment, a positive high voltage is applied to a transfer roller 2 serving as a transfer means adjacent to a drum-shaped photosensitive member 1 to transfer a toner image on the photosensitive drum 1 onto a transfer material 3. Here, the toner image is formed by a well-known electrophotographic process including a primary charger 4, a developing unit 5, respective high-voltage power supplies 7, 6 and an exposure unit for forming an electrostatic latent image. The developing high voltage power supply 6 and the primary charging high voltage power supply 7 are ON / OFF controlled by control signals CONT3 and CONT4 from the high voltage control unit 8.

The high voltage applied to the transfer roller 2 is output from the inverter transformer 9 shown in FIG. The inverter transformer 9 is driven via a transistor 10 by a pulse signal OSC from the high voltage control unit 8. The pulse signal is rectified on the secondary side of the inverter transformer 9 and (the diode 1
1, capacitor 12) Applied to the transfer roller 2.

Here, the DC level of the transfer high voltage output is
Is proportional to the emitter potential. Further, the output HVTIN1 (DC level signal) from the high voltage control unit 8 is amplified by the operational amplifier 100 and input to the base of the transistor 13. Therefore, the transfer output voltage increases as HVTIN1 increases. The output current at this time can be detected by observing the voltage drop of the resistor 102 by the operational amplifier 101. The high-voltage control unit 8 can calculate the output current It from the output (HVTOUT1) of the operational amplifier 101 as It = (5-HVTOUT1) / R102.

In the high-voltage controller 8, HVTIN1 is D / A output, and HVTOUT1 is
A / D input.

FIGS. 2 and 3 show the high-voltage control sequence and the pre-rotation in the high-voltage control unit 8 in this embodiment (at the time of constant current operation).
The flowchart of FIG.

When the system enters the printing operation and drives the photosensitive drum (S0), the primary charging high voltage power supply 7,
The high voltage is output from the developing high voltage power supply 6 (S1). Set the initial value (S3) and start the timer.

HVTIN1 is incremented by one bit (S5), and it is determined whether HVTOUT1 has reached the target current value K (S4). HVTOUT1 is K
If so, it is determined that the current value has not reached the target value, and the operation of increasing HVTIN1 by 1 bit is repeated. If HVTOUT1 is K or less, it is determined that the target current value has been reached and HV
TIN1 is summed (S6), HVTIN1 is reduced by 1 bit (S6
7), repeat the judgment.

These constant current operations are performed until the timer reaches t1, that is, for one rotation of the transfer roller (S8). Then, the average output voltage during the constant current operation is obtained from the result of this operation (S9).

Thereafter, the constant current operation is continued until the printing operation is started (S10 to S13), and the printing operation is started and the constant voltage operation based on the voltage obtained in S9 is started. That is, HVTIN1 is fixed to the obtained value CV (S14).

During continuous printing, HVTIN1 is set to “0” between sheets, and the constant voltage value obtained earlier is output at the timing of printing (HV
TIN1 = CV).

After printing is completed, CONT3, CONT4, and HVTIN1 are turned off, and after the post-rotation processing, the drive of the photosensitive drum 1 is stopped.

Embodiment 2 FIG. 4 shows a second embodiment of the present invention. In the figure, portions corresponding to the first embodiment are denoted by the same reference numerals. FIGS. 5 and 6 show a high-voltage control sequence and a flowchart of the high-pressure control unit 8 during pre-rotation (at the time of constant current operation) in this embodiment. Here, the description of the operation corresponding to the first embodiment will be omitted.

In the high-voltage control unit 8, HVTIN2 is a PWM output, and HVTOUT1 is a
A / D input.

The DC level of the transfer high voltage output is proportional to the emitter potential of the transistor 13. Also, the output HV from the high-voltage controller 8
TIN2 (PWM signal) is converted into a DC level signal by a low-pass filter (LPF) composed of a resistor and capacitors 103 to 106, amplified by the operational amplifier 100, and input to the base of the transistor 13. Therefore, the transfer output voltage increases with an increase in HVTIN2. The output current at this time is
It can be detected by observing the voltage drop of the resistor 102 by the operational amplifier 101. The high-voltage controller 8 outputs the output of the operational amplifier 101 (H
VTOUT1), the output current It can be calculated as It = (5-HVTOUT1) / R102.

 The constant current control is performed as follows.

The duty ratio of HVTIN2 (PWM signal) is increased by one resolution (S5-2), and it is determined whether HVTOUT1 has reached the target current value K (S4). If HVTOUT1 is equal to or larger than K, it is determined that the target current value has not been reached, and the operation of increasing HVTIN2 by one resolution is repeated. If HVTOUT1 is equal to or smaller than K, it is determined that the target current value has been reached, the duty ratio of HVTIN2 is summed (S6-2), the duty ratio of HVTIN2 is reduced by one resolution (S7), and the determination is repeated.

These constant current operations are performed until the timer reaches t1, that is, for one rotation of the transfer roller (S8). From the result of this operation, the average output voltage during the constant current operation is obtained as the duty ratio of the PWM control (S9). Thereafter, the constant current operation is continued until the printing operation is started (S10 to S13), and at the same time the printing operation is started, the constant voltage operation based on the duty ratio obtained in S9 is started (HVTIN2 is fixed at the obtained value CV) S14.

In this embodiment, the LPF is a secondary LPF based on CRs (103 to 106). However, the LPF may have any configuration as long as the cutoff frequency is sufficiently lower than the PWM repetition frequency.

Third Embodiment FIG. 7 shows a third embodiment of the present invention. In the figure, portions corresponding to the first embodiment are denoted by the same reference numerals. FIGS. 8 and 9 show a high-voltage control sequence and a flowchart of the high-voltage control unit 8 during pre-rotation (at the time of constant current operation) in this embodiment. Here, the description of the operation corresponding to the first embodiment will be omitted.

In the high voltage controller 8, HVTIN1 is a D / A output, and HVTOUT2 is an input of an "H" or "L" level signal.

In this embodiment, the current value during the constant current operation is
Determined by the 5V divided voltage value divided by The comparator 107 compares the voltage value with the output current It and the voltage drop from 5 V due to the resistor 102 to output HVTOUT2. Therefore, the output current It is controlled such that It = 5 * R108 / (R108 + R109) / R102.

 The constant current control is performed as follows.

HVTIN1 is incremented by one bit (S5), and when the current value reaches the target current value, HVTOUT2 changes from "L" to "H" level.

If HVTOUT2 is at "L" level, it is determined that the target current value has not been reached (S4-3), and the operation of increasing HVTIN1 by 1 bit is repeated. If HVTOUT2 is “H” level,
It is determined that the target current value has been reached (S4-3), and HVTIN1
(S6), reduce HVTIN1 by 1 bit (S7),
Repeat the decision.

In this embodiment, it is also possible to adopt a configuration using PWM control as in the second embodiment.

[Effects of the Invention] As described above, according to the present invention, during the preparatory operation for image formation, a control value such that the current flowing through the transfer unit becomes a predetermined value is supplied to the power source, and the control value for one rotation of the transfer roller is supplied. By obtaining the average of the above-mentioned control values during the image formation and supplying the average of the obtained control values to the above-mentioned power source at the time of image formation after the above-mentioned preparation operation, 1) stable constant voltage operation of the transfer means can be performed.

2) The circuit configuration is simplified.

3) The transfer sequence is simplified.

4) The degree of freedom of transfer control is large.

And so on.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of the first embodiment, FIG. 2 is a timing chart showing a sequence of the first embodiment, and FIG. 3 is a diagram showing a constant current operation (pre-rotation) of the first embodiment. Flowchart, FIG. 4 is a diagram showing a configuration of the second embodiment, FIG. 5 is a timing chart showing a sequence of the second embodiment, and FIG. 6 is a constant current operation (pre-rotation) of the second embodiment. FIG. 7 is a diagram showing a configuration of the third embodiment, FIG. 8 is a timing chart showing a sequence of the third embodiment, and FIG. 9 is a constant current operation of the third embodiment (before). 10 is a diagram showing a configuration of a conventional example, and FIG. 11 is a timing chart showing a sequence of the conventional example. 1 is a photosensitive drum, 2 is a transfer roller, 3 is paper, 4 is a primary charger, 5 is a developing unit, 6 is a developing high-voltage power supply, 7 is a primary charging high-voltage power supply, 8 is a high-voltage power supply control unit, and 9 is an inverter. The circuits shown after the transformer 9 are transfer high-voltage power supplies. CONT3 is an ON / OFF control signal for developing high voltage, CONT4 is an ON / OFF control signal for primary charging high voltage, OSC is a pulse signal for driving the inverter transformer 9, HVTIN is an input from the voltage control unit 8, H
VTOUT is an output from the voltage control unit 8.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinpei Matsuo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yoji Serizawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside (72) Inventor Masaji Uchiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Kazuro Yamada 3-30-2, Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-63-183474 (JP, A) JP-A-2-212872 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 15/16 G03G 15 / 02

Claims (2)

(57) [Claims] A transfer means for transferring a developer on a photosensitive member to a transfer material, the transfer means including a transfer roller; a power supply for supplying a high voltage to the transfer means; and a power supply for supplying a high pressure to the transfer means. Current detection means for detecting a value of a flowing current; and during a preparation operation for image formation, a control value such that a current detected by the current detection means becomes a predetermined value. Control means for obtaining an average and supplying the average value of the obtained control values to the power supply at the time of image formation after the preparatory operation. 2. An image forming apparatus according to claim 1, wherein the control value supplied to said power supply by said control means is a DC signal or a PWM signal.