JPH04204568A - Bias applying method for developing machine - Google Patents

Abstract

PURPOSE:To reduce a developer quantity adhering to a developing roll by making biases of developing rolls and a cleaning roll reversed polarity at the time of a developing action, and homopolarity at other than the time. CONSTITUTION:With a controller 22, a bias to a cleaning roll 4 is made homopolar with biases of first and second developing rolls 2 and 3 during from after main motor ON to before starting a developing action and from after finishing the developing action to main motor OFF, and is made reversed-polar with biases of the developing rolls 2 and 3 during starting and finishing the developing action. Consequently a potential difference between the developing rolls 2 and 3 and the cleaning roll 4 becomes small at other than the time of the developing action. This causes the reduction of a developer quantity adhering to the developing rolls, and the slight variation of a toner carrying quantity of them, enabling a visible image having desired concentration to be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a developing machine that develops an electrostatic latent image formed on an image carrier into a visible image in an image forming apparatus such as an electrophotographic copying machine or a printer. The present invention relates to a method of applying a bias to a developing roll and a cleaning roll.

[Conventional technology]

The image forming device includes a primary charger, a
An image forming device such as an image exposure section, a developing device, a transfer charger, a cleaner, etc. is installed, and after the surface of the image carrier is uniformly charged with a blower, an electrostatic latent image is formed by image exposure. Then, the electrostatic latent image is developed into a visible image using a developing machine, the visible image is transferred onto paper using a transfer charger, and the paper is sent to a fixing unit where it is fixed. A device in which residual toner is cleaned with a cleaner is known.

Various types of developing machines are known for use in such image forming apparatuses.

For example, as shown in FIG. 4, first and second developing rolls 2 and 3 and a cleaning roll 4 called a kitchen roll are provided inside the housing 1, and a two-component developing system consisting of toner and carrier is installed inside the housing 1. The first and second developing rolls 2.3 and the cleaning roll 4 are biased with different polarities, for example, the first and second developing rolls 2.3 and 2.3.
Applying 300 V and +550 V to the cleaning roll 4, the developer is applied to the surfaces of the first and second developing rolls 2°3, and the toner of the developer is applied to the electrostatic latent image on the image carrier 5, thereby forming an image. 2. Description of the Related Art A developing machine is known in which carrier attached to a support 5 is removed by a cleaning roll 5.

That is, as shown in FIG. 5, the toner 6 is charged (+) and the carrier 7 is charged (-), and the electrostatic latent image 8 on the image carrier 5 is charged.
is (-), so the toner 6 adheres to the electrostatic latent image 8, but the carrier 7 also slightly adheres to the image carrier 5, so the cleaning roll 4 to which a (+) bias is applied The carrier 7 on the image carrier 5 is removed.

[Problem to be solved by the invention]

However, as shown in FIG. 6, the bias to the first and second developing rolls 2, 3 and cleaning roll 4 described above is applied continuously from when the main motor is turned on to when the main motor is turned off, that is, during the image forming operation. Therefore, a large potential difference continuously occurs between the developing roll and the cleaning roll 4 during the image forming operation, and the developer adhering to the cleaning roll 4 adheres to the developing roll, reducing the amount of toner conveyed by the developing roll. As the density varies, the developing efficiency may vary and a visible image with the desired density may not be obtained.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for applying a bias to a developing machine that can solve the above-mentioned problems.

[Means and effects for solving the problem] During development, the bias of the developing roll and the bias of the cleaning roll are set to opposite polarities, and the polarities are the same at other times, and the time during which the potential difference between the developing roll and the cleaning roll is large is shortened. This is designed to reduce the amount of developer that adheres to the roll.

〔Example〕

As shown in FIG. 3, a charger 11 is placed around the photoreceptor 10,
Image exposure section 12, developing device 13, transfer device 14, peeling claw 15,
A cleaner 16 and the like are sequentially disposed, and the surface of the photoconductor 10 uniformly exposed by the charger 11 is irradiated with an original image from the image exposure section 12 to form an electrostatic latent image. 13, the visible image is developed into a visible image, and the visible image is transferred to the paper supply unit in the transfer device 14]
7, the paper 18 is peeled off from the photoreceptor 1o by the peeling claw 15, and sent to the fixing device 19 where it is fixed.
Cleaned at 6.

As mentioned above, the developing device 13 has a first one in the housing 1.
・A second developing roll 2.3 and a cleaning roll 4 are provided, and as shown in FIG. The voltage is applied as a bias voltage through a section 21, and the switching section 21 is operated by a controller 22 to control the polarity and magnitude of the voltage applied to the cleaning roll 4.

The controller 22 controls the operation of each image forming device described above based on a predetermined sequence, and controls the main motor after turning on the main motor until before the start of the developing operation, and after the end of the developing operation turning off the main motor (until the developing machine stops driving). ), the bias to the cleaning roll 4 is set to the same polarity as the bias of the first and second developing rolls 2.3, and the bias to the cleaning roll 4 is set to the same polarity as the bias of the first and second developing rolls 2.3. Apply bias to the first and second developing rolls 2 and 3.
The polarity is opposite to that of the bias.

For example, as shown in FIG. 2, the bias of the cleaning roll 4 is set to (+) 550 V during the developing operation, and the bias of the first and second developing rolls 2.3 is set to (+) at other times.
-) Must be 300V or more.

〔Effect of the invention〕

A developing roll and a cleaning roll 4 are placed outside the start of the developing operation.
As the potential difference between the cleaning roll 4 and the developing roll becomes smaller, the carrier that has adhered to the cleaning roll 4 is less likely to adhere to the developing roll, the amount of developer that adheres to the developing roll is reduced, and the amount of toner conveyed by the developing roll does not fluctuate much. A visible image of the desired density is obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a bias application circuit, FIG. 2 is a chart showing applied bias potentials, and FIG. 3 is a chart showing bias potentials applied to an image. ko is a housing, 2 and 3 are first and second developing rolls, and 4 is a cleaning roll. Applicant Fuji Xerox Co., Ltd.

Claims (1)

[Scope of Claims] In a developing machine that develops an electrostatic image on an image carrier into a visible image by providing a developing roll and a cleaning roll 4 in a housing 1, the developing roll and the cleaning roll 4 have opposite polarities during a developing operation. A developing machine bias application method in which a bias of the same polarity is applied at other times, and a bias of the same polarity is applied at other times.