Image forming apparatus for forming a more uniform image

• US 6,205,300 B1
• Filed: 08/04/1998
• Issued: 03/20/2001
• Est. Priority Date: 08/04/1997
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Sakai, Chinobu
• Primary Examiner(s): Braun, Fred L
• Application Number:
  US09/128,551
• Time in Patent Office: 959 Days
• Field of Search: 399/66, 399/315, 399/388, 399/398
• US Class Current: 399/66
• CPC Class Codes: G03G 15/165 Arrangements for supporting or transporting the second base in the transfer area, e.g. guides
• CPC Class Codes: G03G 2215/1609 Corotron

Abstract

An image forming apparatus including an image forming unit to form a developer image on an image carrier, a conveying member to convey an image receiving member toward the image carrier, a transfer charger to transfer the developer image formed on the image carrier on the image receiving member by giving a transfer charge to the image receiving member conveyed by the conveying member, a guide member provided between the conveying member and the transfer charger to guide the image receiving member conveyed by the conveying member toward the transfer position and a separation charger arranged at the downstream side of the transfer charger along the transfer direction of the image receiving member to separate the image receiving member with the developer image transferred thereon by the transfer charger. A bias voltage having the same polarity as the transfer charge is applied to the guide member. When the developer image is transferred on the image receiving member by the transfer charger, this bias voltage is controlled so that it is set at a first bias voltage before the image receiving member comes near the separation charger and at a second bias voltage that is larger than the first bias voltage when the image receiving member comes near the separation charger.

Claims

1. An image forming apparatus comprising:

image forming means for forming a developer image on an image carrier;

conveying means for conveying an image receiving member toward the image carrier;

transfer means for supplying a transfer charge to the image receiving member conveyed by the conveying means and transferring the developer image formed on the image carrier to the image receiving member;

a guide member, provided between the conveying means and the transfer means, for guiding the image receiving member conveyed by the conveying means toward the transfer means;

separation means, arranged at the downstream side of the transfer means along the transfer direction of the image receiving member, for supplying a separation charge to the image receiving member to separate the image receiving member having the developer image transferred by the transfer means from the image carrier;

applying means for applying a bias voltage of the same polarity as the transfer charge to the guide member; and

control means for controlling the applying means to apply a first bias voltage to the guide member when a part of the image receiving member receives only the transfer charge from the transfer means and a remaining part of the image receiving member is put on the guide member, and for controlling the applying means to apply a second bias voltage larger than the first bias voltage when a part of the image receiving member receives both of the transfer charge and the separation charge from both of the transfer means and separation means and a remaining part of the image receiving member is put on the guide member.

2. The image forming apparatus according to claim 1, wherein the image forming means includes:

charging means for charging the surface of the image carrier to a specified potential by giving an electric charge thereto;

exposure means for exposing the surface of the image carrier charged by the charging means according to an image signal to form an electrostatic latent image; and

developing means for forming the developer image by supplying a charged developer to the electrostatic latent image formed on the surface of the image carrier.

3. The image forming apparatus according to claim 1, wherein the guide member is made of a conductive member.

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

the image carrier includes a photosensitive drum arranged rotatable centering around a rotary shaft;

the transfer means includes a transfer charger arranged opposing to the surface of the photosensitive drum and having a first charge wire extending nearly in parallel with the rotary shaft of the photosensitive drum to transfer the developer image from the photosensitive drum onto the image receiving member by giving the corona discharge from the first charge wire to the image receiving member;

the separation means includes a separation charger having a second charge wire extending nearly in parallel with the rotary shaft of the photosensitive drum to separate the image receiving member from the drum surface by giving the corona discharge from the second charge wire; and

the control means sets the bias voltage at the first bias voltage until the leading edge of the image receiving member reaches a separation point where the straight line connecting the second charge wire of the separation charger and the rotary shaft crosses the drum surface after the leading edge of the image receiving member in the conveying direction reaches a transfer point where the straight line connecting the first charge wire of the transfer charger and the rotary shaft of the photosensitive drum, and sets the bias voltage at the second bias voltage when the image receiving member is passing the transfer point and its leading edge in the conveying direction reaches the separation point.

5. The image forming apparatus according to claim 1 further comprising:

second conveying means for conveying the image receiving member passed the separation means further to the downstream; and

the applying means also applies the same bias voltage as the bias voltage applied to the guide member to the second conveying means.

6. The image forming apparatus according to claim 5, wherein the second conveying means includes:

an endless conveyor belt; and

a conductive guide member arranged in the inside of the conveyor belt in contact with the conveyor belt and the bias voltage is applied thereto by the applying means.

7. An image forming apparatus comprising:

image forming means for forming a developer image on an image carrier;

conveying means for conveying an image receiving member toward the image carrier;

transfer means for supplying a transfer charge to the image receiving member conveyed by the conveying means and transferring the developer image formed on the image carrier to the image receiving member;

a guide member for guiding the image receiving member conveyed by the conveying means toward the transfer means;

separation means, arranged at the downstream side of the transfer means along the transfer direction of the image receiving member, for separating the image receiving member having the developer image transferred by the transfer means from the image carrier;

applying means for applying a bias voltage of the same polarity as the transfer charge to the guide member; and

control means for controlling the applying means so as to apply the bias voltage to the guide member at the time the image receiving member reaches the separation means when transferring the developer image onto the image receiving member by the transfer means.

8. The image forming apparatus according to claim 7, wherein the image forming means includes:

charging means for charging the surface of the image carrier to a specified potential by giving an electric charge thereto;

exposure means for exposing the surface of the image carrier charged by the charging means according to an image signal to form an electrostatic latent image; and

developing means for forming the developer image by supplying a charged developer to the electrostatic latent image formed on the surface of the image carrier.

9. The image forming apparatus according to claim 7, wherein the guide member is made of a conductive member.

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

the image carrier includes a photosensitive drum arranged rotatable centering around a rotary shaft;

the transfer means includes a transfer charger arranged opposing to the surface of the photosensitive drum and having a first charge wire extending nearly in parallel with the rotary shaft of the photosensitive drum to transfer the developer image from the photosensitive drum onto the image receiving member by giving the corona discharge from the first charge wire to the image receiving member;

the separation means includes a separation charger having a second charge wire extending nearly in parallel with the rotary shaft of the photosensitive drum to separate the image receiving member from the drum surface by giving the corona discharge from the second charge wire; and

the control means controls the applying means to apply the bias voltage to the guide member when a leading edge of the image receiving member reaches a separation point where the straight line connecting the second charge wire of the separation charger and the rotary shaft crosses the drum surface.

11. The image forming apparatus according to claim 7 further comprising:

second conveying means for conveying the image receiving member passed the separation means further to the downstream; and

the applying means also applies the same bias voltage as the bias voltage applied to the guide member to the second conveying means.

12. The image forming apparatus according to claim 11, wherein the second conveying means includes:

an endless conveyor belt; and

a conductive guide member arranged in the inside of the conveyor belt in contact with the conveyor belt and the bias voltage is applied thereto by the applying means.

13. An image forming apparatus comprising:

a photosensitive drum including a drum surface, which is adapted to have a developer image formed thereon;

a conveyor that conveys an image receiving member toward the drum surface;

a transfer charger that supplies a transfer charge to the image receiving member and transfers the developer image to the image receiving member;

a guide member provided between the conveyor and the transfer charger that guides the image receiving member from the conveyor to the transfer charger;

a separation charger downstream from the transfer charger that supplies a separation charge to the image receiving member to separate the image receiving member from the drum surface;

a guide bias voltage source that applies to the guide member a bias voltage having the same polarity as the transfer charger; and

a controller that controls the guide bias voltage source such that the guide bias voltage source applies a first bias voltage to the guide member when a part of the image receiving member receives only the transfer charge and a remaining part of the image receiving member is on the guide member, and such that the guide bias voltage source applies a second bias voltage, which is larger than the first bias voltage, when a part of the imager receiving member receives both the transfer charge and the separation charge and a remaining part of the image receiving member is on the guide member.