Image forming apparatus having rotatable charging brush with varying charging voltage

• US 5,845,172 A
• Filed: 11/12/1996
• Issued: 12/01/1998
• Est. Priority Date: 11/09/1994
• Status: Expired due to Term

• Current Assignee: Minolta Co., Ltd. (Konica Minolta Inc.)
• Original Assignee: Minolta Co., Ltd. (Konica Minolta Inc.)
• Inventors: Saito, Hitoshi, Yamamoto, Masashi, Shimazoe, Makoto
• Primary Examiner(s): Grimley, Arthur T.
• Assistant Examiner(s): GRAINGER, QUANA MASHELL
• Application Number:
  US08/748,005
• Time in Patent Office: 749 Days
• Field of Search: 399/98-100, 399/168, 399/169, 399/50, 361/225
• US Class Current: 399/50
• CPC Class Codes: G03G 15/0216 by bringing a charging member into contact with the member to be charged, e.g. roller, brush chargers
• CPC Class Codes: G03G 21/0064 using the developing unit, e.g. cleanerless or multi-cycle apparatus
• CPC Class Codes: G03G 2221/0005 Cleaning of residual toner

Abstract

In order to achieve such effects that memories such as image memory due to untransferred residual toner can be sufficiently prevented, and good images can be obtained by suppressing base fogging and reduction of entire image density for a long term, an oscillating voltage composed of a DC ingredient and an oscillating ingredient is applied to a charging device for charging a photosensitive member, while the charging device is in a position facing an image forming region of the photosensitive member. While the charging device is in a position facing an image non-forming region of the photosensitive member, only a DC voltage is applied to the charging device for at least a predetermined time.

Claims

1. An image forming apparatus which does not use a dedicated cleaning device, said apparatus comprising:

a photosensitive member having a surface;

a rotatable charging brush which is in contact with said surface of said photosensitive member, said rotatable charging brush charging the surface of said photosensitive member to form an electrophotographic latent image by image exposure;

a power source for applying electric power to said rotatable charging brush;

a developing device for developing said latent image by developer charred to a normal polarity and for collecting residual developer remaining on said surface of said photosensitive member after a thus developed image is transferred to a transfer member; and

control means for controlling said power source to apply an oscillating voltage composed of a direct current component and an alternating current component to said rotatable charging brush while said rotatable charging brush contacts a part of said surface of said photosensitive member on which an image is to be formed so as to charge said surface uniformly and to disturb the residual developer residing on said surface of said photosensitive member into an unpatterned form, and to apply only a direct current component to said rotatable charging brush for at least a predetermined time while said rotatable charging brush contacts a part of said surface of said photosensitive member in which no image is to be formed so as to charge any uncharged or oppositely charged residual developer to the normal polarity.

2. The image forming apparatus as claimed in claim 1, wherein said developing device develops the latent image with a mono-component developer.

3. The image forming apparatus as claimed in claim 1, wherein said control means switches the voltage of the direct current component applied by said power source from a first level to a second level, at which a gap of potential with respect to a ground voltage is smaller than that of the first level, to release developer adhering to said rotatable charging brush onto said surface of said photosensitive member, and thereafter switches said voltage of the direct current component from said second level to said first level.

4. The image forming apparatus as claimed in claim 3, wherein said second level is a ground voltage.

5. The image forming apparatus as claimed in claim 1, wherein said control means applies the oscillating voltage by periodically switching the direct current component applied by said power source.

11. The image forming apparatus as claimed in claim 1, wherein said control means provides for applying a first amount of the direct current component when applying the oscillating voltage and provides for applying a second amount of the direct current component when applying only a direct current component.

6. An image forming apparatus which does not use a dedicated cleaning device, said apparatus comprising:

a photosensitive member having a surface;

a rotatable charging brush which is in contact with the surface of said photosensitive member, said rotatable charging brush charging the surface of said photosensitive member;

an exposure device for exposing an image and forming an electrophotographic latent image on the surface of said photosensitive member charged by said rotatable charging brush;

a DC power source for applying an amount of direct current electric power to said rotatable charging brush;

an AC power source for applying an amount of alternating current electric power to said rotatable charging brush;

a developing device for developing the latent image by developer charged to a normal polarity and for collecting residual developer remaining on said surface of said photosensitive member after the developed image is transferred to a transfer member; and

control means for operating both said DC power source and said AC power source while said rotatable charging brush contacts a portion of said surface of said photosensitive member in which the latent image is to be formed by said exposure device so as to charge said surface uniformly and to disturb the residual developer residing on said surface of said photosensitive member into an unpatterned form, and for operating only said DC power source for at least a predetermined time while said rotatable charging brush contacts a remaining portion of said surface of said photosensitive member so as to charge any uncharged or counter charged residual developer to the normal polarity.

7. The image forming apparatus as claimed in claim 6, wherein said developing device develops the latent image with a mono-component developer.

8. The image forming apparatus as claimed in claim 6, wherein said control means switches the voltage to be applied during a period for operating only the DC power source from a first level to a second level in which a gap of potential with respect to a ground voltage is smaller than that of the first level to release developer adhering to said rotatable charging brush onto said photosensitive member, and thereafter switches the applied voltage from said second level to said first level and rotates said photosensitive member more than one rotation.

9. The image forming apparatus as claimed in claim 8, wherein said second voltage is a ground voltage.

10. The image forming apparatus as claimed in claim 6, wherein said control means provides for a first amount of the direct current electric power to be applied by the power source to the rotatable charging brush when applying an amount of alternating current electric power to the rotatable charging brush, and provides for a second amount of the direct current electric power to be applied by the power source to the rotatable charging brush when applying only a direct current electric power to the rotatable charging brush.

12. An image forming apparatus comprising:

an image receiving surface on which an image is formed;

a rotatable charging brush which is in contact with said image receiving surface, said rotatable charging brush being rotatably mounted for charging said image receiving surface;

an image forming means for forming a toner image on said image receiving surface previously charged by said rotatable charging brush by using toner particles charged to a normal polarity;

an electrical power source; and

a controller which controls said electrical power source to apply an oscillating voltage, composed of a direct current component and an alternating current component, to said rotatable charging brush while said rotatable charging brush is in contact with a portion of said image receiving surface on which an image is to be formed by said image forming means so as to charge said surface uniformly and to disturb a residual toner image residing on said surface into an unpatterned form, and to apply a voltage having only a direct current component for at least a predetermined time while said rotatable charging brush is in contact with a portion of said image receiving surface on which no image is to be formed so as to charge any uncharged or counter charged residual toner particles to the normal polarity.

13. An image forming apparatus in accordance with claim 12, said image forming means comprising:

an exposure device for exposing said image receiving surface to form an electrical latent image on said image receiving surface; and

a developing device, which accommodates toner particles, for forming a toner image on said image receiving surface in accordance with the latent image.

14. An image forming apparatus in accordance with claim 13, wherein said developing device collects residual toner particles from said image receiving surface.

15. An image forming apparatus in accordance with claim 12, wherein said image receiving surface is a photosensitive surface.

16. An image forming apparatus in accordance with claim 15, further comprising an exposure device having a light source.