JPH012068A - electrophotographic equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electrophotographic apparatus using a photosensitive drum and toner.

BACKGROUND ART An electrophotographic apparatus using a photosensitive drum and toner generally has two power supplies: a high voltage power supply for charging the photosensitive drum and a high voltage power supply for applying a constant bias voltage to a developing device. There is.

An example of a high voltage power supply device used in such a conventional electrophotographic apparatus will be described below with reference to FIGS. 3 and 4.

What is shown in FIG. 3 is a high voltage power supply device for charging the photosensitive drum. Here, El is a DC power supply and supplies current to the control drive unit 1 and the winding Wl of the transformer TI. Further, the transistor Qr is connected in series with the winding Wl, and its base is connected to the control drive device 1. W2
is the secondary winding of the transformer TI, and one end of the secondary winding W2 is connected to a parallel circuit of a capacitor CI and a resistor R+ via a rectifier diode D'I, and is connected to a charger L1 via a resistor R2. There is. The other end of the secondary winding W2 is connected to ground via a parallel circuit of a variable resistor R3 and a capacitor C2. Further, the movable terminal of the variable resistor R3 is connected to one input terminal of a comparator Co, and the other input terminal of the comparator Co is connected to a reference power source.

The output terminal of the comparator Co is connected to the control terminal of the control drive unit l. Sl is a power switch.

What is shown in FIG. 4 is a high voltage power supply for applying a bias voltage to the developing device. Here, E2 is a DC power supply that supplies current to the control drive unit 1 and the winding W1 of the transformer T2. Further, the transistor Q2 is connected in series with the winding W3, and its base is connected to the control drive device 1. W4 is a secondary winding of the transformer TI, and one end of the secondary winding W4 is connected to a capacitor C via a rectifier diode D2.
3, connected to a series circuit of a resistor R4 and a variable resistor R5, and further connected to a developing device L2. The other end of the secondary winding W4 is connected to ground. Also, variable resistance R
The movable terminal 5 is connected to one input terminal of a comparator CO, and the other input terminal of the comparator CO is connected to a reference power supply Vs. The output terminal of the comparator CO is connected to the control terminal of the control driver l. S
2 is a power switch.

The high-voltage power supply device for charging the photosensitive drum and the high-voltage power supply device for biasing the developing unit of a conventional electrophotographic apparatus are configured as described above, and when the power switch Sl is turned on, the control drive unit 1 starts oscillating. Along with this, the transistor Q1 is repeatedly turned on and off. Then, an alternating high voltage is generated in the secondary winding W2, rectified by the diode DIl, smoothed by the capacitor C1, and applied to the charger Lll. Here, when the current flowing through the charger L1 increases, the voltage at the movable terminal of the variable resistor R3 increases, and this voltage becomes higher than the voltage of the reference power supply (when this voltage becomes higher than the voltage of the reference power supply, a voltage appears at the output terminal of the comparator Co, and the control drive unit 1 The waveform of the pulsed voltage controlled and applied to the transistor QI changes, and the voltage generated in the secondary winding W2 becomes low, and the current flowing to the charger Ll becomes small.In other words, this high voltage power supply is a constant current power supply. It is a device.

The high-voltage power supply device for applying a bias voltage to the developing device shown in FIG. , closed-loop control works to keep the output voltage at a constant value. This high voltage power supply is a constant voltage power supply.

When forming an image, first, the power switch Sl is turned on and a voltage is immediately applied to the charging device to bring the surface of the photosensitive drum into a charged state. Next, the photosensitive drum is exposed to light to create a latent image on the surface of the photosensitive drum. After this, turn on the power switch
2 is turned on, toner is deposited on the photosensitive drum while applying a developing bias voltage, and the latent image is visualized. Next, the toner on the photosensitive drum is transferred to copy paper, and the toner on the copy paper is fixed.

Problems to be Solved by the Invention When starting a series of operations described above, if the power switch S2 is not turned on after the power switch S1 is turned on, problems such as deterioration of image quality will occur. This is because if a developing bias is applied prior to charging, development will be performed with no charge on the drum, and the toner will stick to the drum. When such a situation occurs, there is a problem in that toner is significantly consumed. Furthermore, since too much toner adheres to the drum, the remaining toner may not be completely cleaned, and there is a problem in that the entire image becomes dim when a subsequent printing operation is performed.

For this reason, conventional electrophotographic apparatuses require a control device that controls the sequence of turning on the two switches, and if this control device should malfunction, the above-mentioned problems may occur.

The present invention solves the above problems, and provides electrophotography in which the above problems do not occur even if the control device that controls the turn-on sequence of the power source for charging and the power source for applying developing bias fails. What you get is the device.

Means for Solving the Problems In order to achieve the above-mentioned objects, the electrophotographic apparatus of the present invention includes a charging power source that generates an applied voltage for charging the photosensitive drum, and a charging power source that generates an applied voltage that charges the photosensitive drum. A timer is provided for transmitting the output voltage of the charging power source to the means for applying a developing bias to the photosensitive drum after the elapse of the period of time.

Operation With the above configuration, the electrophotographic apparatus of the present invention transmits the output voltage of the charging power supply to the developing bias applying means by the timer, so that even if the timer fails, the developing bias voltage will not change to the charging voltage. It is not applied earlier.

EXAMPLE Hereinafter, an example of the electrophotographic apparatus of the present invention will be described in detail.

FIG. 2 is a side sectional view of the electrophotographic apparatus of the present invention. Charger8. The developing bias charger 9 and the developing device 15 are housed in the main body case 10 facing the drum 7. Reference numeral 11 denotes a paper cassette in which a large number of copy papers are stored.

12.13 is the paper transport roller that transports the copy paper to the main case 10.
It acts to send internally. Reference numeral 14 denotes a heat fixing device, in which heating means is provided on one of a pair of rollers facing each other. A high voltage generation circuit is provided for applying a high voltage to the charger 8 and the developing bias charger 9.

FIG. 1 is a circuit diagram showing a high voltage generating circuit portion of the circuit of the electrophotographic apparatus of the present invention. Here, E3 is a DC power supply, which supplies current to the control drive unit 1 and the winding W1 of the transformer TI. A beam/ray 3 is connected between the DC power source E3 and the winding Wl of the transformer TI. Further, the transistor QI is connected in series with the winding W+, and its base is connected to the control drive device 1. W2 is transformer TI
The secondary winding W2 is the secondary winding of the diode D3. D
4 and a capacitor ('s, CB) are connected to a voltage doubler rectifier circuit. 8 is a charger which is connected to the above voltage doubler rectifier circuit via a resistor R6. R7 is a variable resistor. The movable contact of the variable resistor R7 is connected in parallel with the capacitor C7, and between the voltage doubler rectifier circuit and the ground.The movable contact of the variable resistor R7 is connected to one input terminal of the comparator Co; A reference power supply Vs is connected to the input terminal of the comparator Co.Furthermore, the output terminal of the comparator Co is connected to the control terminal of the control drive unit 1.R8 is a resistor connected between the constant voltage circuit 4 and the resistor R6. A relay 5 is operated by an output signal from an operation sequence control circuit 6 and is connected between the constant voltage circuit 4 and the developing bias charger 9.

Here, the configuration of the operation sequence control circuit 6 will be explained. t −G 4 are the gates, respectively, and TI
, T2 are delay circuits. Gates G1 and 64 have negative logic inputs, and gates G2 and 63 have positive logic inputs. For each gate, l-G4 is a switch S.
3 to the DC power supply E4. Further, the delay time of the delay circuit T1 is shorter than the delay time of the delay circuit T2.

The output signal of the gate G2 is input to the delay circuit TI, and the output signal of the delay circuit T1 is input to the control terminal of the relay 3 together with the output signal of the gate Gl. Furthermore, the output signal of the gate G4 is input to the delay circuit T2, and the output signal of the delay circuit T2 is input to the control terminal of the relay 4 together with the output signal of the gate G3.

The electrophotographic apparatus of the present invention is constructed as described above, and its operation will be explained next.

First, the drum 7 rotates while a high voltage is applied to the charger 8. Then, the surface of the drum 7 becomes charged. Here, image information of the document is projected onto the drum 7 while the document placed on the top surface of the electrophotographic apparatus moves relative to the drum 7. As a result, a latent image of image information of the document is formed on the drum 7. Toner is adhered by the developing device 15 onto the drum 7 on which the latent image is formed, and the latent image becomes a developed image. Next, the copy paper in the paper cassette is sent toward the drum 7 by the feed roller 12, and the toner on the drum 7 is assisted by the voltage of the developing bias charger 9 and transferred onto the copy paper. Thereafter, the toner on the copy paper is fixed on the copy paper by the thermal fixing device 14, and the fixed copy paper is discharged to the outside of the main body case 10 by the discharge roller 13.

Here, the operation of the high voltage generation circuit will be explained. First, when the switch S3 is turned on, the voltage of the DC power supply E4 applied to the gate circuits 61 to G4 becomes zero. Then, gate circuit Gl is opened and gate circuit G2 is closed. Therefore, the output of gate circuit G1 is applied to relay 3. Similarly, gate circuit G3 is closed and gate circuit G4 is closed.
will be opened.

Therefore, the output of gate circuit G4 is applied to delay circuit T2. Therefore, when the switch S3 is turned on, the relay 3 is turned on immediately and the relay 5 is turned on after the time set in the delay circuit T2. Next, when the switch S3 is turned off, the voltage applied to the gate circuit GI-04 rises from zero to near the output voltage of the DC power source E4. Then, gate circuit Gl is closed and gate circuit G2 is opened. Then, the output signal is output with a delay of the time set in the delay circuit T1. On the other hand, gate circuit G3 is opened and gate circuit G4
is closed. Therefore, when the switch S3 is turned off, the relay 3 is turned off with a delay of the time set in the delay circuit T1, and the relay 5 is turned off immediately. In other words, switch S3
When turned on after being turned off, a high voltage is applied to the charger 8, and after a certain period of time has elapsed, a high voltage is applied to the developing bias charger 9.

Suppose here that the operation sequence control circuit 6 fails and the relay 5 is turned on immediately after the switch S3 is turned off. Even in this state, unless the relay 3 is turned on and a high voltage is not applied to the charger 8, a high voltage will not be applied to the developing bias charger 9.

Effects of the Invention The electrophotographic apparatus of the present invention includes a charging power source that generates an applied voltage for charging a photosensitive drum, and a charging power source that applies the charging voltage to the photosensitive drum and then changes the output voltage of the charging power source to the photosensitive drum after a specific period of time has elapsed. Since it is equipped with a timer that transmits the developing bias to the drum to the application means, even if a failure occurs, the developing bias voltage will be applied to the photosensitive drum before the charging voltage is applied to the photosensitive drum. There isn't. Therefore, there is an inconvenience that occurs because the developing bias voltage is applied to the photosensitive drum before the charging voltage is applied to the photosensitive drum. In other words, since the development is performed with no charge on the drum, toner is not deposited on the drum. The remaining toner may stick to the drum, resulting in significant toner consumption, or because too much toner adheres to the drum, the remaining toner cannot be completely cleaned, resulting in the inconvenience that the entire image becomes dim during subsequent printing operations. There's nothing to do.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a high voltage generating section in an embodiment of an electrophotographic apparatus of the present invention, FIG. 2 is a sectional view of the same side, and FIGS. 3 and 4 are a high voltage generating section of a conventional electrophotographic apparatus. FIG. 1... Control drive unit 3... Relay 4... Constant voltage circuit 5... Relay 6... Operation sequence control circuit 7... Drum 8.
...Charger 9...Charger for developing bias 10...
・Main body case 11...Paper cassette 12
...Feed roller 13...Discharge roller 1
4... Heat fixing device G l-G 4... Gate
TI, T2... Name of delay circuit agent Patent attorney Toshio Nakao and 1 other person Figure 2 Kuumata H-@Beast, Sword Bit

Claims (1)

[Claims] A charging power source that generates a charging voltage for charging the photosensitive drum, and a developing bias applied to the photosensitive drum using the output voltage of the charging power source after a certain period of time after applying the charging voltage to the photosensitive drum. An electrophotographic device characterized by being provided with a timer for transmitting information to a means.