# US 7,613,406 B2 · Image forming apparatus that detects a presence of a conductive foreign object on a recording material

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- Number: US 7,613,406 B2
- Document ID: US7613406B2
- Status: Granted
- Kind: B2
- Application number: 11/406,251
- Filed: 2006-04-19
- Published: 2006-11-02
- Granted: 2009-11-03
- Earliest claimed: 2005-04-28
- Assignees: Canon Kabushiki Kaisha
- Inventors: Masami Takeda
- Web page: https://patentgrep.com/patent/US7613406B2

## CPC

- G03G 15/65: {Apparatus which relate to the handling of copy material (handling sheets or webs in general B65H; for photographic purposes in general G03B)}
- G03G 15/55: {Self-diagnostics; Malfunction or lifetime display}
- G03G 2215/00632: Electric detector, e.g. of voltage or current
- G03G: ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY

## Abstract

The image forming apparatus includes a conductive member provided in a conveying path of a recording material, a voltage applying device for applying a voltage to the conductive member, a current detecting device for detecting a current flowing in the conductive member when the recording material passes through the conductive member to which a voltage is applied by the voltage applying device, and a judgment device for judging, based on an output from the current detecting device, whether a conductive foreign object is present on the recording material. Thus there is provided an image forming apparatus capable of detecting a foreign object attached to a recording material by a simple method.

## Claims

### Claim 1

An image forming apparatus comprising:
an image bearing member on which a toner image is formed;
a transfer member that forms a transfer nip portion with said image bearing member, wherein said transfer member transfers the toner image formed on said image bearing member onto a recording material by applying a voltage into said transfer member;
a fixing device that fixes the toner image transferred onto the recording material, on the recording material, said fixing device having a heater, a film and a roller that forms a fixing nip portion with the heater through the film, wherein the film contacts a recording material at the fixing nip portion;
a current detecting device that detects a current flowing in said transfer member, when the recording material passes through the transfer nip portion;
a judgment device for judging, based on an output from said current detecting device, whether or not a conductive foreign object is present on the recording material;
a leading edge detecting device that is provided at an upstream side of said transfer member with regard to a conveyance direction of the recording material and detects a leading edge of a recording material; and
a controller that controls said image forming apparatus,
wherein when t1 denotes a timing to detect the leading edge of a recording material by said leading edge detecting device, t2 denotes a timing to detect a conductive foreign object by said current detecting device and T denotes a time in which a recording material passes through the nip portion between the leading edge detecting device and said fixing nip portion, if (t2−t1) is less than T, said controller stops conveying a recording material before the leading edge of the recording material comes into said fixing nip portion, and if (t2−t1) is equal to or more than T, said controller stops conveying a recording material and notifies a user that the recording material is to be removed in an upstream direction of said fixing device with regard to the conveyance direction of the recording material.

### Claim 2 (depends on 1)

An image forming apparatus according to claim 1,
wherein said transfer member has a volume resistivity of 1×106 to 1×1010 Ω·cm.

### Claim 3 (depends on 1)

An image forming apparatus according to claim 1, wherein said fixing device includes a pressure device to obtain a pressure for pinching the recording material and a pressure release device to release the pressure applied by said pressure device, wherein when said judgment device judges a presence of a conductive foreign object on the recording material, in a case where (t2−t1) is equal to or more than T, the pressure release device releases the pressure.