JPH0497167A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent sticking of excess toner to a photosensitive drum and to prolong service life of a cleaner by providing a developing bias delay shutting circuit which retains impressing of developing bias voltage for a fixed period of time when an unexpected failure occurs in a driving system of a photosensitive drum and a means to brake rotation of the photosensitive drum. CONSTITUTION:The developing bias voltage VDE is prevented from becoming 0V after the failure occurrence, a constant voltage is retained for a fixed period of time, and the stopping distance of the photosensitive drum 1 is kept constant. In this case, variation of backside potential VDE of a developing sleeve is delayed and retained for a fixed period of time by the developing bias delay shutting circuit 33. And on the other hand, a processor 31 and a motor driver IC41 to make the stopping distance of the photosensitive drum constant are provided. Thus, when unexpected failure such as a sudden stop of a motor 42 driving the photosensitive body 1 during printing occurs or when accidents such as electrical power source being suddenly cut off occur, carrier 12 or excess toner 11 are prevented from sticking to the photosensitive drum 1, and the service life of the cleaner is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrophotographic apparatus that employs a two-component developing system that uses a two-component developing device of toner and carrier.

(Prior Art) Conventionally, in an electrophotographic apparatus using a two-component development method, a developing device applies toner to an electrostatic latent image on a photoreceptor drum that is uniformly charged by a charger and then exposed to light. It is designed to be developed using a carrier.

FIG. 4 shows a schematic diagram of a conventional electrophotographic apparatus.

In the figure, a photosensitive drum 1 with a photosensitive layer formed on its outer peripheral surface
is rotationally driven in the direction of arrow 2 by a motor (not shown). Around the photosensitive drum 1, a charging device 3, an exposure section 4, a developing device 5, and a transfer device 6 are arranged in order along the rotation direction 2.
is placed.

The charger 3 uniformly charges the outer peripheral surface of the photosensitive drum 1, and the exposure section 4 forms an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum. A developing device 5 develops the electrostatic latent image with toner to form a toner image, and a transfer device 6 transfers the upper toner image onto a printing paper 8 that is conveyed in the direction of an arrow 7. Thereafter, the printing paper 8 is discharged through a fixing device (not shown) or the like.

Here, there is a developing device 5 using a so-called two-component developer. As shown in the figure, the developing device 5 has a structure in which a non-magnetic metal developing sleeve 9 to which a constant developing bias voltage is applied rotates outside a magnet roll 10. In the case of this developing device 5, magnetic particles, that is, carriers 12, having toner 11 electrostatically adhered to their outer surfaces are used.

The carrier 12 is attracted like a brush to the outer peripheral surface of the developing sleeve 9 along the lines of magnetic force, and comes into contact with the photosensitive drum 1 during development. Also, the toner 11 is applied to the photosensitive drum 1.
The carrier 12 is electrostatically attracted to the outer circumferential surface of the carrier 12 , but the carrier 12 is attracted by the magnet roll 10 and returns to the inside of the developing device 5 .

By the way, in the electrophotographic apparatus having the above configuration, since the charged area of the photosensitive drum 1 that does not require development faces the developing device 5, the toner 11 and carrier 12 are transferred to the photosensitive drum when the power is turned on or off. 1 may be electrostatically attracted.

Therefore, in order to prevent this, the charging voltage supplied to the charger 3 and the developing bias voltage supplied to the developing sleeve 9 in the developing device 5 are controlled on and off in a fixed sequence.

However, if a sudden failure occurs, such as the motor driving the photosensitive drum suddenly stopping, or if an accident occurs, such as a sudden power cut, the above sequence cannot be taken, and the developing bias voltage and photosensitive drum The potential difference between the charged voltages of the drum 1 increases, and the carrier 12 is attracted to the photosensitive drum 1. Therefore, a development bias delay circuit is provided in the development bias control section that controls the development bias voltage, and the time until the application of the development bias voltage stops when the above-mentioned failure occurs is delayed by a certain period of time ( (See Japanese Patent Application Laid-Open No. 1-282573).

FIG. 5 is a diagram showing changes in potential difference in a developing unit of a conventional electrophotographic apparatus.

During normal operation, the band IT pressure V of the photosensitive drum 1 is -600V as shown in (a), and the developing bias voltage V of the developing sleeve 9 is -600V. is -450v as shown in (b)
The toner 11 is attracted to the photosensitive drum 1 from the developing device 5 by the potential difference VDI VS -150v.

Here, if some kind of failure occurs at time Tx, the developing bias delay circuit will reduce the developing bias voltage ■. , is maintained at about -450V for a certain period of time, and the carrier 12 is prevented from adhering to the photosensitive drum 1.

(Problem to be Solved by the Invention) However, in the above-mentioned conventional electrophotographic apparatus, since the continuous circuit for holding the developing bias voltage VDI for a certain period of time is composed of a resistor and a capacitor, the holding time varies. is thick (carrier 12 and excess toner 11 adhere to the photosensitive drum l).

The photosensitive drum 1 continues to rotate due to inertia even after the drive of the motor is cut off. If the device is used for a long period of time, the rotational load will decrease due to wear of the rotating parts, and the distance that the photosensitive drum 1 will rotate after the cutoff will become longer. During this time, the charging voltage of the photosensitive drum 1 becomes Ov, but since the developing bias voltage VOW is maintained, excess toner 11 adheres to the photosensitive drum 1. As a result, toner consumption is high and the life of the cleaner is shortened.The present invention solves the above-mentioned problems of conventional electrophotographic devices, and the motor that drives the photosensitive drum suddenly stops during printing. An electronic system that prevents carrier and excess toner from adhering to the photosensitive drum and shortening the lifespan of the cleaner in the event of a sudden failure such as a sudden failure, or an accident such as a sudden power cut. The purpose is to provide photographic equipment.

(Means for Solving the Problems) For this purpose, the present invention provides a developing bias voltage that applies a developing bias voltage to a developing sleeve of a developing device in an electrophotographic apparatus that employs a two-component developing method using a carrier to which toner is attached. An i source is provided.

A developing bias delay circuit is provided that maintains the application of the developing bias voltage for a certain period of time when a sudden failure occurs in the photosensitive drum drive system, such as when the motor driving the photosensitive drum suddenly stops.

(Function) According to the present invention, in an electrophotographic apparatus that employs a two-component developing method using a carrier to which toner is attached as described above, a developing bias power supply section that applies a developing bias voltage to a developing device and a photosensitive drum are provided. When a sudden failure occurs in the drive system, the development bias delay circuit maintains the application of the development bias voltage for a certain period of time, so the potential difference between the development sleeve surface potential and the photosensitive drum surface potential increases rapidly. There's nothing left to do.

Furthermore, when a sudden failure occurs in the drive system of the photosensitive drum, there is a means for applying a brake to the rotation of the photosensitive drum, so that the rotation area due to the inertia of the photosensitive drum, drive motor, etc. I can do it.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of an electrophotographic apparatus showing an embodiment of the present invention.

In the figure, 1 is a photosensitive drum, 3 is a charger, 4 is an exposure section, 5 is a developer, 20 is a development bias power supply section, 30 is a control section, 36 is an ACLO-detection circuit, 37 is a cover open detection circuit, 40 is a motor control section, and 42 is a DC motor.

The photosensitive drum 1 is rotated in the direction of the arrow 2 by a DC motor 42 .

The charger 3 uniformly charges the outer peripheral surface of the photosensitive drum 1, and the exposure section 4 forms an electrostatic latent image corresponding to an image to be printed on the charged outer peripheral surface of the photosensitive drum.

A developing sleeve 9 is provided inside the developing device 5, and a magnet roll 10 is provided within the developing sleeve 9. A carrier 1 with toner 11 attached to the outer periphery of the developing sleeve 9
2 is adsorbed. The carrier 12 is attracted like a brush to the outer peripheral surface of the developing sleeve 9 along the lines of magnetic force, and comes into contact with the photosensitive drum 1 during development. Further, the toner 11 is electrostatically attracted to the outer circumferential surface of the charged photosensitive drum 1, while the carrier 12 is attracted by the magnet roll 10 and returned into the developing device 5.

Further, the developing bias 111a section 20 includes a DC voltage element 2.
A bias tiff 21 that generates 4V, an inverter 22 that converts the generated DC voltage into an AC voltage, a high voltage transformer 23 that steps up the AC voltage, and a rectifier circuit 24 that rectifies the stepped up voltage to obtain a high DC voltage. It is provided.

The control unit 30 includes a processor 31, a driver 32
, development bias delay circuit 33, processor power supply 34,
Reset signal generation circuit 35.2 is composed of two NAND gates 38 and two AND gates 39. The professional sensor 31 is provided to control the operation of the entire electrophotographic apparatus, but only its developing bias voltage control circuit portion and DC motor control circuit portion are shown here.

The processor 31 is supplied with a voltage of +5V for driving from a processor power supply 34. Further, the reset signal generation circuit 35 sends a certain reset signal to the processor 3 when turning on/off the main power of the electrophotographic apparatus.
output towards. The driver 32 also connects the output of the processor 31 to the inverter 22 of the developing bias power supply unit 20.
Output to.

On the other hand, the developing bias delay circuit 33 has a diode D.
, a capacitor C1, a resistor R, and a switching transistor TR.

The diode D has an anode connected to the output side of the reset signal generation circuit 33, and a cathode connected to the resistor R and one end of the capacitor C. The other end of the capacitor C is grounded, and the other end of the resistor R is connected to the base of the switching transistor TR. The collector of the switching transistor TR is connected to the output side of the driver 32, and the emitter is grounded.

Further, the output of the ACLO-detection circuit 36 and the output of the cover oven detection circuit 37 are both grounded to the input of the 28AND gate 38.

The motor-on signal output from the professional sensor 31 includes the motor driver rc41 of the motor control unit 40.
m2 NAND gate 39 is connected to the input of m2 NAND gate 39 along with the output of 2 NAND gate 38 via inverter 39a, and the output of m2 NAND gate 39 is connected to the input of processor 31.

Further, the ACLO-detection circuit 36 detects the AC input voltage when turning on and off the main power supply of the electrophotographic apparatus, and outputs a high-level signal when the voltage exceeds a certain level.

Further, the cover oven detection circuit 37 outputs a low level signal when the cover of the electrophotographic apparatus is opened.

Next, the motor control section 40 controls the motor driver I.
It is composed of C41 and its peripheral circuits, and generates a drive signal for the DC motor 42 in response to a rotation direction signal j and a motor-on signal k from the processor 31.

The DC motor 42 is for driving the photosensitive drum 1, and rotates in the direction of arrow 43 when the current output from the motor driver IC 41 flows in the i1 direction, and in the direction of arrow 44 when it flows in the 12 direction.

Here, for example, when the processor 31 supplies the low-level control at pressure d to the inverter 22 via the driver 32, the inverter 22 receives the bias power supply 21 and operates the high-voltage transformer 23, and supplies the rectifier circuit 24 with an AC high voltage. supply. The rectifier circuit 24 rectifies this into a DC voltage, and applies a predetermined developing bias voltage to the developing sleeve 9. When the high-level control voltage d is input to the inverter 22, the supply of the developing bias voltage VOS is stopped.

The developing bias voltage (1) was set to 450V as described above. On the other hand, charger 3 is supplied with 1,600 volts from another power source.
A charging voltage of v is applied.

When the processor 31 supplies the high-level rotation direction signal j and the low-level motor on signal k to the motor control unit 40, the motor driver IC 41 supplies the motor power $1 i z to the DC motor 42, and the arrow Torque is generated in the 44 direction and the rotational speed rapidly decreases.

FIG. 2 is a diagram showing changes in potential difference in the developing unit of the electrophotographic apparatus of the present invention.

In a conventional electrophotographic apparatus, when some kind of failure occurs at times T and I, the charging voltage ■s of the photosensitive drum 1 becomes Ov.
Since the developing bias voltage V is maintained even when the voltage V is reached, the difference between the surface potential of the photosensitive drum and the surface potential V may become 450 V as shown by the solid line in the figure.

In contrast, the electrophotographic apparatus of the present invention prevents the developing bias voltage VDI from becoming OV as shown by the solid line after the failure occurs, and maintains it at about -450V for a certain period of time as shown by the broken line.
In addition, the stopping distance of the photosensitive drum 1 is made constant. In this case, the development bias delay cut-off circuit 1s33 delays and holds the change in the surface potential V□ of the development sleeve for a certain period of time. On the other hand, a processor 31 and a motor driver IC 41 are provided to make the stopping distance of the photosensitive drum constant.

Next, the operation of the electrophotographic apparatus of the present invention will be explained in detail.

FIG. 3 is an operation time chart of the electrophotographic apparatus of the present invention.

First, it is assumed that the voltage a of the processor 34 changes as shown in the figure. That is, the processor power supply 34 is
When it is turned on at time T0, it rises at a constant slope and +
Stable at 5v. However, if some kind of failure occurs at time T, the voltage starts to drop at time T11, and
1t becomes almost Ov. After that, the cause of the failure is eliminated and the power is turned on again at time T14, and the power is turned on again at time T +
The voltage returns to a constant voltage again as shown by s''-T+m.

When the voltage a of the processor voltage i[34 changes as described above, the electrophotographic apparatus operates as follows.

That is, when ts is input at time 'A''ro as shown by a, the reset signal generation circuit 35 outputs a reset signal S from time T to T, and inputs it to the processor 31.

The output C+J+k of the processor 31 is at half level while the reset signal is at high level according to its program, but after the reset signal falls at time T, it is kept at a predetermined high level.

On the other hand, the reset signal is the developing bias delay circuit 33.
It is also input to T, and it starts up at time T.

When the switch control voltage e on the cathode side of the diode D rises at time T1, the switch control voltage e decreases at a constant time constant from the rise time T. The time constant is determined by the values of the capacitor C and the resistor R of the developing bias delay circuit 33.

As a result, the switching transistor TR is in an on state from time T1 to time T4, and the control voltage d output from the driver 32 is maintained at a low level during the on state.

Then, at time T4, the switching transistor T
When R is turned off, the driver output d becomes high level due to the processor output C, which is input to the inverter 22.

On the other hand, the inverter 22 starts operating at the same time as the power is turned on, and a predetermined developing bias voltage (2) is applied. However, when the output d of the driver 32 becomes high level, the output is stopped. Therefore, when the bias power supply 21 is turned on at time T,! As shown by, application of the developing bias voltage {circle around (2)} is started, and when the driver output d rises at time T4, the application is stopped.

In addition, the cover open signal g and the 2 NAND gate output rise at a constant slope and stabilize at +5V like the processor power supply 34, but the ACLO- signal r output from the ACLO- detection circuit 36 rises at time T2. and 2 NAND gate output falls.

Thereafter, when the processor 31 lowers the motor-on signal k at time T while keeping the rotation direction signal j at high level, D
C motor 42 rotates in the direction of arrow 43.

Then, when the charger 3 starts charging the photosensitive drum l after the rotation becomes stable, the processor output C falls to a low level at time T when the belt @ area reaches the developer 5, and at the same time The driver output d falls to a low level and is input to the inverter 22, and the developing bias voltage l is applied again. At this time, the charging voltage V of the charging area on the photosensitive drum facing the developing device 5 is also maintained at a constant voltage as shown by m.

Here, when some kind of failure occurs at time T and the main power supply is cut off, first the ACLOW signal signal is output at time T.
, and this causes the 2 NAN[l gate output signal to rise. Furthermore, at this time, since the motor-on signal is at a low level, the 2 AND gate output signal rises. As a result, the processor 31 sets the motor-on signal k to a high level and the rotation direction signal j to a low level at time T.

Furthermore, when the motor-on signal k is set to low level again at time T, the motor driver IC 41 causes the motor current to flow in the direction of the arrow 12 to the DC motor 42 .

As a result, the DC motor 42 is prevented from rotating in the direction of the arrow 43 and starts to stop rapidly.

Next, when the power is cut off and the reset signal rises between time TIO and T, the output signals c, j, and k of the pro-sensor 31 rise. On the other hand, the switch control voltage e in the developing bias delay circuit 33 also rises at the same time. As a result, the switching transistor TR is turned on, and the driver output d becomes low level. Thereafter, even if the switch control voltage e decreases, the processor output C also decreases during that time, so the battriver output d is held at a low level as shown by the solid line.

As a result, the developing bias power supply section 20 remains in a state where the developing bias voltage VDI is applied as shown in 2.

On the other hand, if there is no DC motor/brake circuit and development bias delay circuit 33, from time T8 to T1°, as shown by the broken line, the rotation direction signal j is at a high level and the motor on signal is at a low level, and at time T1°. The driver output d is at a high level from T11 to T11.

By the way, when the normal power supply is cut off, the time T, due to the action of a capacitor inserted in the power supply circuit. ,
T11. The electric voltage gradually decreases as time passes like TIx. On the other hand, even if the power is cut off, the DC motor 42 changes time from T1° to T,..., T, due to its inertia.
It tries to rotate until it passes □ and reaches Ti1. However, since the DC motor 42 is stopped by the DC motor brake circuit, it can be stopped just before time T1□.

That is, since the extra rotation range of the DC motor 42 is eliminated due to inertia, the developing bias voltage VDI (1 in FIG. 3) and the band ti! A large potential difference does not occur between the voltages Vs (m in FIG. 3) as shown by the broken line.

Note that after time T, the output signals c, j, and k of the processor 31 gradually decrease because the power supply voltage decreases, and the switch control voltage e also gradually decreases due to discharge, and the developing bias voltage ■ and the band 1111 pressure Vs .

Also returns to Ov. Thereafter, when the power is turned on again at time T14, the reset signal S is output again from time T15 to TI7, and the above-described operation is performed, and the developing bias voltage l is applied from time T to Tlff. Ru.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

For example, in the above embodiment, the photosensitive drum 1 is charged to a negative potential to perform development, but it may be charged to a positive potential.

Further, when the ACLOW signal f and the cover open signal g are output, the motor driver rc41 controls the DC motor 42 by the corresponding output signals j and k of the processor 31.
Although the brake is applied to the photosensitive drum 1, any signal that triggers when the photosensitive drum 1 cannot be stopped in the normal sequence can be used, and circuits with various configurations can be adopted as necessary. .

Further, although the brake is applied by applying a reverse current to the DC motor 42, other methods such as a brake band or an electromagnetic brake may be used.

(Effects of the Invention) As described in detail above, according to the present invention, in an electrophotographic apparatus that employs a two-component development method using a carrier to which toner is attached, a developing bias voltage is applied to a developing device. When a sudden failure occurs in the power supply section and the drive system of the photosensitive drum, a sudden failure occurs in the development bias delay circuit that maintains the application of the development bias voltage for a certain period of time and the drive system of the photosensitive drum. Since it has a means to brake the rotation of the photosensitive drum when the photosensitive drum is rotated, it prevents excess toner from adhering to the photosensitive drum due to the inertia of the photosensitive drum, drive motor, etc., and also extends the life of the cleaner. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an electrophotographic apparatus showing an embodiment of the present invention;
FIG. 2 is a diagram showing potential difference changes in the developing device of the electrophotographic apparatus of the present invention, FIG. 3 is an operation time chart of the electrophotographic apparatus of the present invention, and FIG. 4 is a schematic diagram of a conventional electrophotographic apparatus.
FIG. 5 is a diagram showing changes in potential difference in a developing unit of a conventional electrophotographic apparatus. 20... Development bias power supply section, 33... Development bias delay circuit, 35... Reset signal generation circuit, 36.
...ACLOW circuit, 37...Cover open detection circuit, 40...Motor control section, 41...Motor driver IC. Patent applicant Oki Data Systems Co., Ltd. (1 other person) Agent Patent attorney M. Kawai (1 other person) J.
＠'壬ツ [j1 5 [9 magashishi (ware,) 2 fixed,. 15
2nd figure capture fever (Child photo section hawk figure 4th figure 0 σ and autopsy; 1.: O. 114 Length L” Sniffen I7, Shi?] Figure 5 Procedural Amendment (Method) Display of the Case 1990 Patent Application No. 209329 Name of the Invention Electrophotographic Device Person Who Amends the Case Related address name

Claims (1)

[Claims] In an electrophotographic apparatus that employs a two-component development method using a carrier to which toner is attached, there is provided: (a) a development bias power supply unit that applies a development bias voltage to a developing device; (b) a photosensitive drum; (c) a developing bias delay circuit that maintains the application of the developing bias voltage for a certain period of time when a sudden failure occurs in the drive system of the photosensitive drum; An electrophotographic apparatus comprising means for applying a brake to the rotation of the drum.