IMAGE FORMING APPARATUS

• US 20110311254A1
• Filed: 06/08/2011
• Published: 12/22/2011
• Est. Priority Date: 06/21/2010
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Kitamura, Takuya, Kanazawa, Takayuki, Kawaguchi, Yuji, Kawata, Kentaro
• Granted Patent: US 9,098,005 B2
• Time in Patent Office: Days
• US Class Current: 399/46
• CPC Class Codes: G03G 15/0173 plural rotations of recording member to produce multicoloured copy, e.g. rotating set of developing units G03G15/0163 takes precedence
• CPC Class Codes: G03G 15/065 Arrangements for controlling the potential of the developing electrode

Abstract

An image forming apparatus includes a rotatable image bearing member configured to bear an electrostatic latent image, a plurality of development devices including a developer bearing member configured to bear a developer for developing the electrostatic latent image, a rotatable development device supporting member configured to support the plurality of development devices. In the image forming apparatus, the developer bearing member is configured to execute development while contacting the image bearing member at a development position via the developer, rotating in the same direction as rotating direction of the image bearing member at the development position, and rotating at a speed faster than a surface speed of the image bearing member. In addition, the development device supporting member is configured to rotate in the same direction of a rotating direction of the image bearing member at a position where the development device supporting member and the image bearing member are facing each other, and change a developer bearing member existing at the development position to another developer bearing member by rotating. Furthermore, a relative speed of a surface moving speed of the developer bearing member with respect to a surface moving speed of the image bearing member when the developer bearing member abuts on or separates from the image bearing member due to the rotation of the development device supporting member becomes higher than a relative speed of the surface moving speed of the developer bearing member with respect to the surface moving speed of the surface of the image bearing member when the electrostatic latent image is developed, and a control unit configured to control a first potential difference, which is a potential difference between a potential of a bias applied to the developer bearing member when the developer bearing member abuts on or separates from the image bearing member and a potential of the image bearing member at the development position becomes higher than a second potential difference, which is a potential difference between the potential of the bias applied to the image bearing member and a potential of a non-imaging portion of the image bearing member at the development position.

Claims

1. An image forming apparatus comprising:

a rotatable image bearing member configured to bear an electrostatic latent image;

a plurality of development devices including a developer bearing member configured to bear a developer for developing the electrostatic latent image;

a rotatable development device supporting member configured to support the plurality of development devices,

wherein the developer bearing member is configured to execute development while contacting the image bearing member at a development position via the developer, rotating in the same direction as rotating direction of the image bearing member at the development position, and rotating at a speed faster than a surface speed of the image bearing member,

wherein the development device supporting member is configured to rotate in the same direction of a rotating direction of the image bearing member at a position where the development device supporting member and the image bearing member are facing each other, and change a developer bearing member existing at the development position to another developer bearing member by rotating, and

wherein a relative speed of a surface moving speed of the developer bearing member with respect to a surface moving speed of the image bearing member when the developer bearing member abuts on or separates from the image bearing member due to the rotation of the development device supporting member becomes higher than a relative speed of the surface moving speed of the developer bearing member with respect to the surface moving speed of the surface of the image bearing member when the electrostatic latent image is developed; and

a control unit configured to control a first potential difference, which is a potential difference between a potential of a bias applied to the developer bearing member when the developer bearing member abuts on or separates from the image bearing member and a potential of the image bearing member at the development position becomes higher than a second potential difference, which is a potential difference between the potential of the bias applied to the image bearing member and a potential of a non-imaging portion of the image bearing member at the development position.

2. The image forming apparatus according to claim 1, wherein the control unit is configured to change a bias applied to the developer bearing member to control the first potential difference to be higher than the second potential difference.

3. The image forming apparatus according to claim 1, further comprising a charging unit configured to charge the image bearing member, wherein the control unit is configured to change a bias applied to the charging unit to control the first potential difference to be higher than the second potential difference.

4. The image forming apparatus according to claim 1, wherein the control unit is configured to discontinue applying a development bias when an electric contact provided to the development device configured to apply a bias to the developer bearing member separates from an electric contact provided to an image forming apparatus body.

5. The image forming apparatus according to claim 1, wherein the control unit is configured to switch from the second potential difference to the first potential difference after a region of the image bearing member in which the electrostatic latent image to be developed on a recording sheet has past the development position and before a region of the image bearing member corresponding to a margin of the recording sheet at a trailing edge of the recording sheet passes the development position.

6. The image forming apparatus according to claim 1, wherein the second potential difference is gradually changed according to a variation of the moving speed of the development device supporting member.

7. The image forming apparatus according to claim 1, wherein

the development device supporting member can rotate at a plurality of moving speeds, and

wherein the control unit is configured to execute control for changing the second potential difference according to the moving speed.

8. An image forming apparatus comprising:

a rotatable image bearing member configured to bear an electrostatic latent image;

a plurality of development devices including a developer bearing member configured to bear a developer for developing the electrostatic latent image;

a rotatable development device supporting member configured to support the plurality of development devices,

wherein the developer bearing member is configured to execute development while contacting the image bearing member at a development position via the developer rotating in the same direction as rotating direction of the image bearing member at the development position and rotating at a speed faster than a surface speed of the image bearing member,

wherein the development device supporting member is configured to rotate in the same direction of a rotating direction of the image bearing member at a position where the development device supporting member and the image bearing member are facing each other, and change a developer bearing member existing at the development position to another developer bearing member by rotating,

wherein movement of the development device supporting member when the developer bearing member abuts on or separates from the image bearing member includes a first movement and a second movement, in which a component of a speed in a tangential direction with respect to the image bearing member at the development position is greater than a component of a speed in a tangential direction with respect to the image bearing member at the development position in the first movement, and

wherein either one of a abutment and a separation when the developer bearing member abuts on or separates from the image bearing member is the first movement and the other is the second movement; and

a control unit configured to control a third potential difference and a fourth potential difference to be different from each other, wherein

the third potential difference is a potential difference between a potential of a bias applied to the developer bearing member during the first movement and a potential of the image bearing member at the development position, and

wherein the fourth potential difference is a potential difference between a potential of a bias applied to the developer bearing member during the second movement and a potential of the image bearing member at the development position.

9. The image forming apparatus according to claim 8, wherein a relative speed of a surface moving speed of the developer bearing member with respect to a surface moving speed of the image bearing member becomes higher during the second movement than during the first movement, and

wherein the fourth potential difference is higher than the third potential difference.

10. The image forming apparatus according to claim 8, wherein

the relative speed of the surface moving speed of the developer bearing member with respect to the surface moving speed of the image bearing member becomes lower during the second movement than during the first movement, and

wherein the fourth potential difference becomes lower than the third potential difference.

11. The image forming apparatus according to claim 8, wherein the control unit is configured to change a bias applied to the developer bearing member to control the third potential difference to be different from the fourth potential difference.

12. The image forming apparatus according to claim 8, further comprising a charging unit configured to charge the image bearing member, wherein the control unit is configured to change a bias applied to the charging unit to control the third potential difference to be different from the fourth potential difference.

13. The image forming apparatus according to claim 8, wherein the control unit is configured to discontinue applying a development bias when an electric contact provided to the development device configured to apply a bias to the developer bearing member separates from an electric contact provided to an image forming apparatus body.

14. The image forming apparatus according to claim 8, wherein the control unit is configured to change the second potential difference, the third potential difference, or the fourth potential difference as the second potential difference, which is a potential difference between a potential of a bias applied to the developer bearing member and a potential of a non-imaging portion of the image bearing member at the development position when the electrostatic latent image is developed while a region of the image bearing member corresponding to a margin of a recording sheet at a trailing edge of the recording sheet is moved past the development position.

15. The image forming apparatus according to claim 8, wherein the third potential difference or the fourth potential difference is gradually changed according to a variation of the moving speed of the development device supporting member.

16. The image forming apparatus according to claim 8, wherein

the development device supporting member can rotate at a plurality of moving speeds, and

wherein the control unit is configured to execute control for changing the third potential difference or the fourth potential difference according to the moving speed.