IMAGE FORMING APPARATUS

• US 20140064761A1
• Filed: 08/27/2013
• Published: 03/06/2014
• Est. Priority Date: 08/31/2012
• Status: Active Grant

• Current Assignee: KYOCERA Document Solutions, Inc. (Kyocera Corporation)
• Original Assignee: KYOCERA Document Solutions, Inc. (Kyocera Corporation)
• Inventors: Hayashi, Eriko
• Granted Patent: US 9,042,795 B2
• Time in Patent Office: Days
• US Class Current: 399/66
• CPC Class Codes: G03G 15/163 using the force produced by an electrostatic transfer field formed between the second base and the electrographic recording member, e.g. transfer through an air gap
• CPC Class Codes: G03G 15/1675 with means for controlling the bias applied in the transfer nip
• CPC Class Codes: G03G 15/6535 using electrostatic means, e.g. a separating corona
• CPC Class Codes: G03G 15/657 Feeding path after the transfer point and up to the fixing point, e.g. guides and feeding means for handling copy material carrying an unfused toner image

Abstract

A transfer bias voltage supplier supplies, to a transfer member, a transfer bias voltage of a polarity opposite to the polarity of toner. The absolute value of transfer bias voltage to be supplied to the transfer member when a leading/trailing end of the sheet is passed through the nip portion is set smaller than when a toner image transfer region of the sheet is passed through the nip portion. A separation bias voltage supplier supplies, to a discharging electrode member, a separation bias voltage of a polarity opposite to the polarity of transfer bias voltage. The absolute value of separation bias voltage to be supplied to the discharging electrode member when the leading/trailing end of the sheet is passed through a discharging gap is set smaller than when the transfer region is passed through the discharging gap.

Claims

1. An image forming apparatus, comprising:

an image carrier;

a charging portion which charges the image carrier;

an exposing portion which forms an electrostatic latent image on the image carrier charged by the charging portion;

a developing portion which supplies toner to the electrostatic latent image for forming a toner image on the image carrier;

a transfer member which forms a nip portion by cooperation with the image carrier, the nip portion being configured to nip a sheet on which the toner image is to be transferred;

a discharging electrode member disposed to face the image carrier on a downstream side of the nip portion in a conveying direction of the sheet;

a sheet conveying unit which conveys the sheet in such a manner that the sheet is passed through the nip portion and through a discharging gap, the discharging gap being formed by the discharging electrode member and the image carrier;

a transfer bias voltage supplier which supplies, to the transfer member, a transfer bias voltage of a polarity opposite to a polarity of the toner for use in forming the toner image for transferring the toner image carried on the image carrier onto the sheet in the nip portion; and

a separation bias voltage supplier which supplies, to the discharging electrode member, a separation bias voltage of a polarity opposite to the polarity of the transfer bias voltage for separating the sheet carrying the transferred toner image thereon from the image carrier, wherein

the transfer bias voltage supplier is so configured that an absolute value of the transfer bias voltage to be supplied to the transfer member when at least one of a leading end and a trailing end of the sheet is passed through the nip portion is set smaller than an absolute value of the transfer bias voltage to be supplied to the transfer member when a transfer region of the toner image on the sheet is passed through the nip portion, and

the separation bias voltage supplier is so configured that an absolute value of the separation bias voltage to be supplied to the discharging electrode member when the at least one of the leading end and the trailing end of the sheet is passed through the discharging gap is set smaller than an absolute value of the separation bias voltage to be supplied to the discharging electrode member when the transfer region is passed through the discharging gap, the at least one of the leading end and the trailing end of the sheet being such that the absolute value of the transfer bias voltage to be supplied thereto is set smaller when the at least one of the leading end and the trailing end is passed through the nip portion.

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

a photosensitive layer of the image carrier is constituted of a single-layer organic photosensitive member, the organic photosensitive member being configured such that an electric charge generation layer and an electric charge carrier layer are not separated from each other.

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

the charging portion includes a charging roller configured to be contacted with the image carrier for charging the image carrier with use of the charging roller.

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

the transfer bias voltage supplier is configured to supply, to the transfer member, the transfer bias voltage in such a manner that the relationship:

A<

B<

C is satisfied, and

the separation bias voltage supplier is configured to supply, to the discharging electrode member, the separation bias voltage in such a manner that the relationship;

D<

E<

F is satisfied, where

A;

an absolute value of a first transfer bias voltage, the first transfer bias voltage being the transfer bias voltage to be applied when the leading end of the sheet is passed through the nip portion and when the trailing end of the sheet is passed through the nip portion;

B;

an absolute value of a second transfer bias voltage, the second transfer bias voltage being the transfer bias voltage to be applied before the sheet is passed through the nip portion and after the sheet is passed through the nip portion;

C;

an absolute value of a third transfer bias voltage, the third transfer bias voltage being the transfer bias voltage to be applied when the transfer region of the sheet is passed through the nip portion;

D;

an absolute value of a first separation bias voltage, the first separation bias voltage being the separation bias voltage to be applied when the leading end of the sheet is passed through the discharging gap and when the trailing end of the sheet is passed through the discharging gap;

E;

an absolute value of a second separation bias voltage, the second separation bias voltage being the separation bias voltage to be applied before the sheet is passed through the discharging gap and after the sheet is passed through the discharging gap; and

F;

an absolute value of a third separation bias voltage, the third separation bias voltage being the separation bias voltage to be applied when the transfer region of the sheet is passed through the discharging gap.

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

a period of time when the separation bias voltage supplier supplies the first separation bias voltage to the discharging electrode member is substantially equal to a period of time when the transfer bias voltage supplier supplies the first transfer bias voltage to the transfer member,

a period of time when the separation bias voltage supplier supplies the second separation bias voltage to the discharging electrode member is substantially equal to a period of time when the transfer bias voltage supplier supplies the second transfer bias voltage to the transfer member, and

a period of time when the separation bias voltage supplier supplies the third separation bias voltage to the discharging electrode member is substantially equal to a period of time when the transfer bias voltage supplier supplies the third transfer bias voltage to the transfer member.

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

a timing of starting supply of the first separation bias voltage to the discharging electrode member by the separation bias voltage supplier is later than a timing of starting supply of the first transfer bias voltage to the transfer member by the transfer bias voltage supplier,

a timing of starting supply of the second separation bias voltage to the discharging electrode member by the separation bias voltage supplier is later than a timing of starting supply of the second transfer bias voltage to the transfer member by the transfer bias voltage supplier, and

a timing of starting supply of the third separation bias voltage to the discharging electrode member by the separation bias voltage supplier is later than a timing of starting supply of the third transfer bias voltage to the transfer member by the transfer bias voltage supplier.

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

a value of the first transfer bias voltage, a value of the second transfer bias voltage, and a value of the third transfer bias voltage to be supplied to the transfer member by the transfer bias voltage supplier are respectively set to constant values, and

a value of the first separation bias voltage, a value of the second separation bias voltage, and a value of the third separation bias voltage to be supplied to the discharging electrode member by the separation bias voltage supplier are respectively set to constant values.

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

the sheet conveying unit includes a sheet conveying path along which the sheet is conveyed for feeding the sheet to the nip portion and to the discharging gap with use of the conveying path.

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

the sheet conveying unit includes a sheet conveyor belt on which the sheet is placed for feeding the sheet to the nip portion and to the discharging gap by driving the sheet conveyor belt.