Charging device

Abstract

A charging device for contact-charging a member to be charged. A charging device for charging a movable member to be charged includes a contacting member adapted to contacting the member to be charged, and means for forming a vibratory electric field between the member to be charged and the contacting member, the vibratory electric field forming means applying between the members a vibratory voltage having a peak-to-peak value not less than twice an absolute value of a charge starting voltage to the member to be charged. The member to be charged can be uniformly charged.

Description

contact memberαis of a laser beam type, but this is not limiting, and the present invention is applicable to an electrophotographic apparatus having a conventional analog type exposure optical system.

As described in foregoing, according to the present invention, a vibratory voltage having a peak-to-peak voltage, which is not less than twice the absolute value of the charge starting voltage to a member to be charged, is applied between the member to be charged and a contacting member contacted thereto. This forms a vibratory electric field therebetween to charge the member to be charged, whereby no spotty charging occurs on the member to be charged, so that it can be uniformly charged to a predetermined always stable potential. According to the charging device of the present invention, a low voltage is usable used for charging a member as compared with the corona discharging device.

While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

Claims

1. A charging device for charging a movable member to be charged, comprising:

a contacting member adapted to contacting contact the member to be charged; and

means for forming a vibratory electric field between the member to be charged and the contacting member, the vibratory electric field forming means applying between the members a vibratory voltage having a peak-to-peak value not less than twice an absolute value of a charge starting voltage to the member to be charged a voltage applying means for applying, between said member to be charged and said contacting member, a vibratory voltage to form a vibratory electric field between said member to be charged and said contacting member, said vibratory voltage having a peak-to-peak voltage which is not less than twice an absolute value of a charge starting voltage of the member to be charged.

2. A charging device according to claim 1, wherein said contacting member has a portion which is increasingly away from continuous with a contact portion of said contacting member, to provide an increasing distance between said contacting member and the member to be charged toward in a downstream direction from a said contact portion therebetween with respect to movement of the member to be charged.

3. A charging device according to claim 2, wherein said contacting member is a rotational member.

4. A charging device according to claim 3, wherein said contacting member is a conductive roller.

5. A charging device according to claim 1 or 2, wherein said vibratory electric field is provided by a vibratory voltage provided by superposing a DC voltage and an AC voltage vibration voltage is an AC voltage biased with a DC voltage.

6. A charging device according to claim 5, wherein said charge starting voltage is a DC voltage when a charging starts with the DC voltage alone is being applied between the contacting member and the member to be charged.

7. A charging device according to claim 1, wherein said member to be charged is a photosensitive member.

8. A charging device according to claim 1, wherein the vibratory voltage has a sine curve wave form.

9. A charging device according to claim 1, wherein said contacting member is coated with a material having a resistivity in the range of 10² to 10¹0 ohm-cm.

10. A charging device according to claim 1, wherein the potential of the member to be charged after being charged by said contacting member is uniform irrespective of its potential before charging.

11. A charging device according to claim 3, wherein said contacting member is a rotational member which rotates to follow the movement of the member to be charged.

12. A charging device according to claim 4, wherein the contacting member comprises a conductive roller having a core member, a layer covering said core member, and a surface layer formed thereon.

13. A charging device according to claim 7, wherein the member to be charged is composed of an organic photoconductive material.

14. A method for electrically charging a member to be charged by a charging member contactable to the member to be charged, comprising the steps of:

disposing the charging member so that a portion of the charging member is separated from the member to be charged by an increasing distance; and

applying between the charging member and the member to be charged a vibratory oscillating voltage having a peak-to-peak voltage which is not less than twice an absolute value of a charge starting voltage of the member to be charged, so that a vibratory electric field is formed between a surface of the member to be charged and the portion of the charging member.

15. A method according to claim 14, wherein the vibratory voltage applied between the charging member and the member to be charged is in the form of a DC-biased AC voltage. 16. A method according to claim 14, wherein the charging member is in the form of a roller. 17. A method according to claim 14, wherein the charging member is in the form

of a pad. 18. A method according to claim 14, wherein said charge starting voltage is a DC voltage at which charging starts when a DC voltage alone is applied between the charging member and the member to be

charged. 19. A method according to claim 14, wherein the potential of the member to be charged after being charged by said charging member is uniform irrespective of its potential before charging. 20. An image forming apparatus, comprising:

an image bearing member;

a charging member, contactable to said image bearing member, for electrically charging said image bearing member; and

voltage applying means for applying, between the charging member and said image bearing member, a vibratory oscillating voltage to form a vibratory electric field between said image bearing member and said charging member, said vibratory oscillating voltage having a peak-to-peak voltage which is not less than twice an absolute value of a charge starting voltage of said image bearing member to be charged. 21. An apparatus according to claim 20, wherein said charge starting voltage is a DC voltage when charging starts with the DC voltage alone being applied between the charging member and the image bearing member.

. An apparatus according to claim 21, wherein the charging member has a portion continuous with a contact portion of the charging member, to provide an increasing distance between the charging member and said image bearing member in a downstream direction from said contact portion with respect to a movement direction of said image bearing member.