JPH04309972A - Contact electrostatic charging device - Google Patents

Abstract

PURPOSE:To average electrostatic charging states at the respective points of a photosensitive body and to prevent the irregularity of electrostatic charging from occurring by oscillating voltage impressed on the photosensitive body by a wavy surface formed on the surface of an abutting member. CONSTITUTION:The projecting parts 32a-32f of the wavy surface 24 formed on the surface of an electrostatic charging roller 2 are elastically deformed by abutting on the surface of the photosensitive drum 1, and distances between the surface of the drum 1 and the recessed parts 31a-31e are changed to be long or short. Since there is a relative speed difference between the surface of the drum 1 and the surface of the electrostatic charging roller 2, the optional point on the surface of the drum 1 is opposed to the plural recessed parts and the impressed voltage is oscillated while it abuts on the surface of the roller 2.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a charging device that applies a voltage to the surface of a photoreceptor in an apparatus such as a printer to which electrophotography is applied, and in particular, it relates to a charging device that applies a voltage to the surface of a photoreceptor. The present invention relates to a contact charging device that applies .

0002

2. Description of the Related Art Corona discharge from a wire electrode is generally used to charge a photoreceptor in electrophotography. However, in this corona discharge, a high voltage must be applied to the wire electrode in order to give a predetermined surface potential to the surface of the photoreceptor, which increases the cost due to the increase in the size of the power supply device, and also reduces the image quality due to the generation of ozone. There are problems such as deterioration and adverse effects on the human body. Therefore, a method has been developed in which a conductive member is brought into direct contact with the surface of the photoreceptor and a relatively low DC voltage is applied to the conductive member, thereby directly injecting charges into the surface of the photoreceptor to obtain a predetermined surface potential. Proposed.

When using a contact charging device in which such a conductive member is brought into direct contact with the surface of a photoreceptor, a uniform charging state cannot be obtained on the surface of the photoreceptor, and uneven charging may occur. For this reason, for example, JP-A-63-14
In the contact charging method disclosed in Japanese Patent Publication No. 9668 and Japanese Patent Application Laid-Open No. 63-149669, a pulsating current voltage is applied to the photoreceptor along with a DC voltage to a conductive member in contact with the surface of the photoreceptor. The voltage value is oscillated and averaged to prevent uneven charging on the surface of the photoreceptor.

0004

[Problems to be Solved by the Invention] However, in the above contact charging method, since a pulsating current voltage is superimposed on a DC voltage and applied to a conductive member, an AC superimposed power supply is required in addition to a DC power supply. There was a problem that the device became larger and the cost increased.

An object of the present invention is to bring a contact member having a wavy surface into contact with the surface of a photoreceptor by applying a relative velocity difference, and to apply a DC voltage to this contact member to superimpose a pulsating voltage. It is an object of the present invention to provide a contact charging device that can uniformize the charging state of the photoreceptor surface by oscillating the voltage value applied to the photoreceptor surface without causing any problems.

[0006]

[Means for Solving the Problems] A contact charging device of the present invention is a contact charging device that applies a DC voltage to the photoreceptor from a contact member that contacts the surface of the photoreceptor, in which the surface of the contact member is connected to the surface of the photoreceptor. The contact member is made of a conductive elastic body having a continuous wavy surface in a direction perpendicular to the axial direction of the photoreceptor, and the surface of the contact member is made to have a relative velocity difference with respect to the surface of the photoreceptor. It is characterized by:

[0007]

In the present invention, charges are injected onto the surface of the photoreceptor from a contact member made of a conductive elastic body having a continuous wavy surface in a direction perpendicular to the axial direction of the photoreceptor.

[0008] The unevenness constituting the wavy surface on the surface of the abutment member is elastically deformed by contact with the photoreceptor surface, and the distance of the separated portion formed between the recess of the abutment member and the photoreceptor surface changes. do. Since the surface of the contact member contacts the surface of the photoreceptor with a constant curvature, the above-mentioned separation distance becomes non-uniform in the contact range (so-called nip width) between the contact member and the photoreceptor.

Since this distance affects the value of the charge injected onto the surface of the photoreceptor, the charge injected becomes non-uniform within the contact range, and the charged state on the surface of the photoreceptor becomes non-uniform. At this time, the surface of the contact member is given a relative speed difference with respect to the surface of the photoreceptor, and the distance between the recess of the contact member and the recess at any point on the surface of the photoreceptor is determined by the surface of the contact member. During the contact, the voltage value applied from the contact member changes from a relatively large state through a relatively short state to a relatively large state again, and the voltage value applied from the contact member oscillates. Therefore, while an arbitrary point on the surface of the photoreceptor moves through the range of contact with the contact member, the distance from the recess is averaged, and the charging state at an arbitrary point on the surface of the photoreceptor is also averaged. Charges on the entire surface of the photoreceptor are made uniform.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the structure of a contact charging device according to an embodiment of the present invention. The photosensitive drum 1 is rotatably supported by a rotating shaft 4 inside the electrophotographic apparatus, and is rotated in the direction of the arrow at a circumferential speed of Vd by a drive device (not shown). A charging roller 2, which is a contact member of the present invention, is in contact with the circumferential surface of the photoreceptor drum 1. The charging roller 2 is rotatably supported by a rotating shaft 5 in the electrophotographic apparatus, and is rotated in the direction of the arrow at a circumferential speed of Vr by a drive device (not shown). The photosensitive drum 1 is grounded at a rotating shaft 4, and a DC voltage is applied to the rotating shaft 5 of the charging roller 2 from a power source 3. This charging roller 2 is in contact with the circumferential surface of the photosensitive drum 1 within a length L range.

FIG. 2 is a diagram showing the structure of the charging roller. The charging roller 2 has a metal core 23 whose circumferential surface is covered with a conductive elastic rubber layer consisting of two layers, a low resistance layer 22 and a high resistance layer 21 . As a material for this conductive elastic rubber layer, carbon-dispersed silicone rubber or urethane rubber can be used. A wavy surface 24 is formed on the surface of the resistance layer 21 and continues in a direction perpendicular to the rotation axis. This wavy surface 24 has a pitch p of about 100 μm and a depth D
is preferably 2×p or less and 50 μm or more. This value takes into account paper powder and dust adhering to the surface of the photoreceptor, the particle size of the developer, and the moldability of the uneven surface.

Specific examples of the circumferential speed Vr of the charging roller 2 and the circumferential speed Vr of the photosensitive drum 1 include, for example, Vd=25 mm/s, d=200 μm, p=500 μm.
Assuming that m, l = 2 mm and Vr = -10 mm/s, five to six convex portions come into contact with the surface of the photoreceptor drum 1 in the contact range between the charging roller 2 and the photoreceptor drum 1. Also, Vd=50mm/s, d=0.5mm, p=0.5m
Approximately eight convex portions may be brought into contact with the surface of the photoreceptor drum 1 in the contact range at m, l = 2 mm and Vr = 50 mm/s.

FIG. 3 is a diagram showing a state in which the photosensitive drum and the charging roller are in contact with each other. A wavy surface 24 formed on the circumferential surface of the charging roller 2 comes into contact with the surface of the photosensitive drum 1 . In this case, since the resistance layer 21 on which the wavy surface 24 is formed is made of an elastic material, the convex portions 32a to 32f located in the contact range of the photoreceptor drum 1 and the charging roller 2 are located at the radius of the charging roller 2. elastically deforms in the direction. Since both the photosensitive drum 1 and the charging roller 2 have a cylindrical shape, they abut with a certain curvature. Therefore, the amount of deformation of the convex portions 32c and 32d located at the center of the contact range is the same as that of the convex portions 32a, 32b, 32e, and 32f located on the outside.
As a result, the distances between the recesses 31a to 31e and the surface of the photoreceptor drum 1 are different from each other.

This distance is from the charging roller 2 to the photoreceptor 1.
This has a great influence on the charging state when charging the surface of the photosensitive drum 1.
The charged potentials of the portions 31e facing each other become non-uniform. Here, a difference is given to the respective circumferential speeds of the photoreceptor drum 1 and the charging roller 2, and in particular, in the above two specific examples, the moving direction is reversed in the contact range, and the surface of the photoreceptor drum 1 is The surface of the charging roller 2 and the surface of the charging roller 2 are configured to slide against each other. As a result, an arbitrary point on the surface of the photoreceptor drum 1 faces the plurality of recesses 31a to 31e, and the applied voltage value oscillates, so that the charging state of an arbitrary portion on the photoreceptor surface is averaged. be converted into By averaging the charging state, the charging potential on the surface of the photoreceptor drum 1 can be made uniform.

Note that as shown in FIG. 4, the photosensitive drum 1
The pad 41 that comes into contact with the
A member fixed by the fixing member 43 via the fixing member 43 can also be used as the abutting member.

In this case, since the abutting member is stationary with respect to the photosensitive drum 1, a relative speed difference can be provided between the abutting surfaces of the two.

[0017]

According to the present invention, by oscillating the voltage applied to any point on the photoreceptor surface, the charging state at each point on the photoreceptor surface is averaged, and a uniform charging state is achieved over the entire surface of the photoreceptor. This has the advantage of preventing uneven charging.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of a contact charging device that is an embodiment of the present invention.

FIG. 2 is a diagram showing a charging roller that is a contact member constituting the contact charging device.

FIG. 3 is a diagram showing a state of contact between a photosensitive drum and a charging roller in the contact charging device.

FIG. 4 is a schematic diagram showing the configuration of a contact charging device according to another embodiment of the present invention.

[Explanation of symbols]

1-Photoreceptor drum 2-Charging roller (contact member) 3-DC power supply 24 - Wavy surface

Claims (1)

[Claims] 1. A contact charging device that applies a DC voltage to the photoreceptor from a contact member that contacts the surface of the photoreceptor, in which the surface of the contact member is brought into contact with the surface of the photoreceptor at a constant curvature, and the axis of the photoreceptor is 1. A contact charging device comprising an electrically conductive elastic body having a continuous wavy surface in a direction perpendicular to the direction of the contact charging device, and characterized in that the surface of the contact member is given a relative velocity difference with respect to the surface of a photoreceptor.