JP3014072B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method for developing an electrostatic latent image formed on a photosensitive drum with a charged toner.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a laser printer, usually, the surface of a photosensitive drum is charged to, for example, -610 V by a charging charger, and then the photosensitive drum is exposed to image information. An electrostatic latent image having a potential of about 0 V is formed, and the electrostatic latent image is developed with a negatively charged toner. For the development of the electrostatic latent image on the photoconductor drum, for example, a magnet roller that transports negatively charged toner together with the carrier is used. By applying a bias voltage, the negatively charged toner on the surface of the magnet roller adheres to the electrostatic latent image on the surface of the photosensitive drum by an electric field between the magnet roller and the electrostatic latent image of about 0 V on the photosensitive drum. Thus, the electrostatic latent image is developed with toner. The toner image on the photosensitive drum is transferred and fixed on the recording paper.

[0003]

In such an image forming method, the photoreceptor drum and the magnet roller become 0 V before and after the start of the image forming process because no bias voltage is applied. In this state, the surface of the photosensitive drum is charged to -610V. However, when the photosensitive drum is rapidly charged from 0 V to -610 V, the toner and the carrier on the magnet roller at the potential of 0 V are removed before the image information is exposed due to the time delay during charging. May adhere to the surface. For this purpose, the surface of the photosensitive drum is once charged to −330 V having the same potential as the bias voltage applied to the magnet roller, and after applying a bias voltage of −330 V to the magnet roller, the surface of the photosensitive drum is reduced to −610 V. It is designed to be charged. By doing so, there is no possibility that the negatively charged toner conveyed on the surface of the magnet roller adheres to the surface of the photosensitive drum due to a time delay when the surface of the photosensitive drum is charged.

However, at the start and end of the image forming process, the surface of the photosensitive drum and the magnet roller are at the same potential of 0 V because no bias voltage is applied. Therefore, when the image forming process is started and when the image forming process is completed, the negatively charged toner conveyed on the surface of the magnet roller moves to the surface of the photosensitive drum, and May adhere to the surface. The toner adhering to the photoconductor drum is not directly related to the image formed in the image forming process, and thus is removed by the cleaning device. Accordingly, at the start and end of the image forming process, there is a problem that the toner is wasted and the toner consumption increases.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide an image forming apparatus capable of preventing wasteful toner from adhering to the outside of an image forming area of a photosensitive drum and reducing toner consumption. It is to provide a method.

[0006]

According to the image forming method of the present invention, an electrostatic latent image is formed by irradiating light to a photosensitive drum charged to a predetermined polarity, and the photosensitive drum is conveyed by rotation of a magnet roller. An image forming method for developing the electrostatic latent image with a toner charged to a polarity by a potential difference between a magnet roller and a photosensitive drum, wherein the toner is applied to the magnet roller at the start and end of an image forming process. Then, a first potential having a polarity opposite to the charging characteristic of the toner is applied to both the photosensitive drum and the magnet roller . applying a second potential, then as the photosensitive drum becomes a predetermined potential, the procedure of applying a third potential of the charging characteristics of the same polarity as the toner to the photosensitive drum
The second potential is lower than the first potential, and
The potential of No. 3 is set lower than the second potential, thereby achieving the above object.

[0007]

According to the image forming method of the present invention, at the start and end of the image forming process, a first potential having a polarity opposite to the charging polarity of the toner is applied to the magnet roller.
A second electric potential having the same polarity as that of the toner and having the same polarity as that of the toner and applied to the magnet roller during development is applied to both the photoconductor drum and the magnet roller. A step of applying a third potential having the same polarity as the charging characteristic of the toner to the drum ;
The potential is lower than the first potential and the third potential is lower than the second potential.
It is set lower than the order. As described above, the voltage applied to the photosensitive drum and the magnet roller is changed to the first potential and the first potential.
Second potential by a third potential stepwise obtain each time a staggered given <br/>, as both a potential difference is not increased, the charged toner conveyed on the magnet roller is photosensitive the magnet roller Adhesion to the body drum is prevented.

[0008]

Embodiments of the present invention will be described below. FIG. 1 shows a main part of a printer used for carrying out the image forming method of the present invention. This printer has a photosensitive drum 10 rotated in the direction of arrow A in the center of the machine. The photoconductor drum 10 is charged to, for example, −660 V by a charging charger 13, and image information is exposed by an optical system 11 on the surface of the photoconductor drum 10 charged by the charging charger 13. And the photosensitive drum 10
The potential of the exposed portion on the surface becomes almost 0 V, whereby an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 10. The electrostatic latent image formed on the photoreceptor drum 10 is developed by a charged toner carried by a magnetic brush on a magnet roller 14 disposed in a developing device. Recording paper is conveyed to the photoconductor drum 10 by a pair of paper feed rollers 21 and 21, and the toner image on the photoconductor drum 10 is transferred onto the recording paper 20 by the transfer charger 15. Transcribed. The recording paper to which the toner image has been transferred is conveyed to a fixing unit having a heating roller 22 and a pressure roller 23, and passes between the rollers 22 and 23, whereby the toner image on the recording paper is fixed. The surface of the photosensitive drum 10 to which the toner image has been transferred is cleaned by the cleaning device 16.

[0009] Magnet roller 14 disposed in the developing device
, A high voltage generated by the control circuit 40 operated by the power supply 30 is applied as a bias voltage. The magnet roller 14 conveys the toner charged to the negative polarity to the photosensitive drum 10 by a magnetic brush formed around the magnet roller 14 by its rotation. The charged toner carried by the magnetic brush is transferred to the magnet roller 14 and the photosensitive drum.
The photosensitive drum 10 is transferred onto the photosensitive drum 10 by a potential difference between the photosensitive drum 10 and the photosensitive drum 10.

FIG. 2 shows a control circuit 40 for controlling the bias voltage applied to the magnet roller 14. The control circuit 40 includes:
It has a positive bias terminal and a negative bias terminal. The positive bias terminal is connected to one input terminal of the exclusive OR circuit 51 and is connected to one of the AND circuits 52 in the pair of AND circuits 52 and 53. Connected to one input terminal. The negative bias terminal is connected to the other input terminal of the exclusive OR circuit 51 and to one input terminal of the other AND circuit 53. Each AND circuit 52 and
An exclusive OR circuit 51 is connected to the other input terminal of each
Are connected respectively. Also, exclusive O
The output of the R circuit 51 is also input to the high voltage generation circuit 41. The output of each of the AND circuits 52 and 53 is a transistor T
R1 and TR2.

When either the positive bias terminal or the negative bias terminal goes to a high level, the output of the exclusive OR circuit 51 goes to a high level, and a high-level bias-on signal indicating that a bias voltage should be applied is high. Generator 41
Is output to At the same time, when the positive bias terminal is at a high level, the output of one AND circuit 52 is at a high level, and the transistor TR1 is turned on.
When the negative bias terminal goes high, the other A
When the output of the ND circuit 53 goes high, the transistor T
R2 is turned on.

One transistor TR1 is provided between the diode 55 of the photocoupler PC1 and the ground, and the diode 55 of the photocoupler PC1 is connected to a resistor R7.
Is connected to a power supply 54 of 5V. When the transistor TR1 turns on, the diode of the photocoupler PC1
55 is energized to turn on a transistor 56 described later. Similarly, the other transistor TR2 is provided between the diode 57 of the photocoupler PC2 and the ground, and the diode 57 of the photocoupler PC2 is connected to the resistor R8.
Is connected to a power supply 54 of 5V. Then, when the transistor TR2 is turned on, the diode 57 of the photocoupler PC2 is energized, and a transistor 58 described later is turned on.

The high voltage generator 41 is connected to the 24 V power supply 30 and is operated by a high level bias-on signal. The output terminal of the high voltage generation circuit 41 is connected to the primary side of the high voltage transformer 42. A positive bias voltage and a negative bias voltage are taken out from a secondary coil of the high voltage transformer. A capacitor C1 and a resistor R1 are connected in parallel between the positive terminal of the secondary coil and the ground.
A diode D1 is provided between the resistor R1.
Furthermore, between the positive terminal of the secondary coil and the ground,
The resistor R2 and the transistor 56 of the photocoupler PC1
And a series circuit of a resistor R3. And
A 70 V potential at the connection point between the transistor 56 of the photocoupler PC1 and the resistor R3 is applied to the magnet roller 14 as a bias voltage.

A capacitor C2 is provided between the negative terminal of the secondary coil and the ground, and a resistor R6 and the photocoupler PC are connected in parallel with the capacitor C2.
A series circuit of two transistors 58 and a resistor R5 is provided. A diode D2 is provided between the series circuit and the capacitor C2. Further, a resistor R4 is provided between the negative terminal of the secondary coil and the ground. Then, the transistor 58 of the photocoupler PC2
, And a potential of −330 V at a connection point with the resistor R5 is applied to the magnet roller 14 as a bias voltage.

An output detection coil is provided on the primary side of the high-voltage transformer 42, and the output detection circuit 43
Are connected, and based on the output of the output detection circuit 43, it is detected that a predetermined bias voltage is applied to the magnet roller 14.

The operation of the printer having such a configuration will be described with reference to a time chart shown in FIG. When the power is turned on, the standby lamp is turned on and the discharge toner display can be turned on. At the same time, the heater in the heating roller 22 of the fixing unit is operated intermittently, and the temperature of the surface of the heating roller 22 increases accordingly. When the temperature of the surface of the heating roller 22 reaches a predetermined temperature T1, the main motor is driven to start the image forming process.

Simultaneously with the start of the image forming process, the positive bias terminal of the bias voltage control circuit 40 for the magnet roller 14 becomes high level. As shown in FIG. 4, a bias voltage of +70 V is applied to the magnet roller 14 for a predetermined time. Applied over t1. At this time, the photosensitive drum 1
Since the surface potential D of 0 is not charged by the charging charger 13, it is 0V at the start T1 of the image forming process. Therefore, the negatively charged toner conveyed on the surface of the magnet roller 14 is not likely to be transferred to the surface of the photosensitive drum 10.

Then, the starting point T1 of the image forming process
Then, as shown in FIG. 3, when a predetermined time t2 elapses before the time until the positive bias terminal changes from the high level to the low level elapses, the charging charger 13 is driven,
The surface of the photosensitive drum 10 is charged. As a result, the potential on the surface of the photosensitive drum 10 is set to a potential of -330 V at the time point T2 when the positive bias terminal goes low.

At a time T3 after a lapse of a predetermined time t3 after the positive bias terminal of the bias voltage control circuit 40 goes low, the negative bias terminal of the bias voltage control circuit 40 goes high, and the magnet roller 14 A bias voltage of -330 V is applied for a predetermined time t4.

At this time, a voltage of -330 V is applied to the magnet roller 14.
While the bias voltage of
The surface is set to a potential of -610 V at a predetermined time T4 by charging by the charging charger 13.

As described above, the surface potential of the photosensitive drum 10 is once set to −330 V which is equal to the bias potential of the magnet roller 14,
After the bias voltage of V is applied, the potential is set to -610V. When the potential of the surface of the photosensitive drum 10 is rapidly changed from 0 V to -610 V,
There is a risk that the negatively charged toner may move from the magnet roller 14 to the photosensitive drum 10 due to a time delay until the potential of the magnetic roller 14 reaches -610 V and a time delay until the potential of the magnet roller 14 reaches -330 V. However, after setting the potential of the surface of the photosensitive drum 10 to a potential of -330 V which is equal to the surface potential of the magnet roller 14,
By setting the potential to 10 V, there is no possibility that the negatively charged toner adheres to the photosensitive drum 10.

Further, while the negative bias voltage is applied to the magnet roller 14, the recording paper is conveyed to the photosensitive drum 10 by driving the paper feed roller 21, and the recording paper is further exposed to light. While being conveyed to the body drum 10, image information is exposed on the surface of the photosensitive drum 10 by the optical system 11.

When image information is exposed on the surface of the photosensitive drum 10, the potential of the exposed portion on the surface of the photosensitive drum 10 becomes -610 V
To about 0V, and about 33V between it and the magnet roller 14.
Due to the 0 V potential difference, the magnet roller 1
4 The toner on the surface adheres to the photosensitive drum surface. In an area where light is not irradiated on the surface of the photosensitive drum 10,
Since the potential of -610 V is maintained, the negatively charged toner conveyed by the magnet roller 14 does not adhere to that area. In this way, when the electrostatic latent image formed on the surface of the photoconductor drum 10 is developed with toner, in synchronization with the recording paper conveyed to the photoconductor drum 10 by the paper feed roller 21,
The transfer charger 15 is turned on, and the toner image on the surface of the photosensitive drum 10 is transferred onto the recording paper. And the photosensitive drum
When the exposure of the document image on the surface of the photoconductor drum 10 is completed, at time T5, the charging of the surface of the photoconductor drum 10 by the charging charger 13 is stopped, and the potential of the surface of the photoconductor drum 10 becomes −
After being changed from 610V to -330V, at time T7, 0V
It is said.

At time T6 after the surface of the photosensitive drum 10 is set to -330 V, the application of the bias voltage of -330 V is stopped by turning the negative bias terminal to low level. The potential on the surface of the roller 14 is set to 0V. Then, at time T7 when the surface of the photosensitive drum 10 reaches the potential of 0 V, the negative bias terminal in the bias voltage control circuit 40 of the magnet roller 14 is set to the high level for a predetermined time t5, and the bias voltage of +70 V is applied to the magnet roller 14. Is applied. As a result, there is no possibility that the negatively charged toner on the magnet roller 14 is transferred to the surface of the photosensitive drum 10 having the surface potential of 0V.

When a bias voltage of +70 V is applied to the magnet roller 14 for a predetermined time t5, the image forming process ends, and the driving of the main motor is stopped.

In the image forming method of the present invention, the number of sheets that can be single-printed on dedicated recording paper was determined by experiment, with a printing ratio of 4.8%, a black-and-white ratio of 8%, and a toner consumption of 7.9 mg / sheet. , About 47,000 sheets. In the conventional image forming method, only about 26,000 sheets could be printed under the same conditions. From this experimental result, the amount of extra toner consumed at the start and end of the image forming process is
Conventionally, it is 9.6 mg / process, but in the present invention, it is reduced to 1.83 mg / process.

[0027]

According to the image forming method of the present invention, at the start and end of the image forming process , the first potential having the opposite polarity to the charged toner conveyed on the magnet roller is applied to the magnet roller. Then, a second potential having the same polarity as that of the toner and having the same polarity as that of the toner and applied to the magnet roller during development is applied to both the photosensitive drum and the magnet roller. So that the photosensitive drum has a third polarity having the same polarity as the charging characteristic of the toner .
Has the steps of applying a potential, the second potential is the first potential
Lower and the third potential is set lower than the second potential.
Because it is, the voltage applied to the photosensitive drum and the magnet roller, the first potential, the second potential, by providing shifting each time the third potential and the step <br/> Kaiteki, both Can be prevented from increasing . That
As a result, at the start and end of the image forming process, it is possible to prevent toner unnecessary for image formation from being transferred from the magnet roller to the photosensitive drum, and it is possible to greatly reduce the amount of toner consumption.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of a printer used for performing an image forming method of the present invention.

FIG. 2 is a circuit diagram of a bias voltage control circuit applied to a magnet roller used in the printer.

FIG. 3 is a time chart illustrating an image forming process of the printer.

FIG. 4 is a graph showing potentials of a photosensitive drum and a magnet roller in an image forming process of the printer.

[Description of Signs] 10 Photoconductor drum 13 Charger 14 Magnet roller 30 Power supply 40 Control circuit

Claims (1)

(57) [Claims] An electrostatic latent image is formed by irradiating a photosensitive drum charged to a predetermined polarity with light to form an electrostatic latent image. An image forming method for developing the electrostatic latent image based on a potential difference from a body drum, wherein a first polarity having a polarity opposite to a charging characteristic of the toner is applied to the magnet roller at the start and end of the image forming process .
The potential applied, then, to both the photosensitive drum and the magnet roller, the charging characteristics of the same polarity as the toner, and the second potential applied to the magnet roller is applied at the time of development, then the Applying a third potential having the same polarity as the charging characteristic of the toner to the photosensitive drum so that the photosensitive drum has a predetermined potential; and Lower than the first potential and the third potential
An image forming method in which the potential is set lower than the second potential .