# US 9,436,140 B2 · Fixing device controlling frequency of AC current caused to flow through helical coil causing electroconductive layer of rotatable member to generate heat through electromagnetic induction

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- Number: US 9,436,140 B2
- Document ID: US9436140B2
- Status: Granted
- Kind: B2
- Application number: 14/837,555
- Filed: 2015-08-27
- Published: 2016-03-03
- Granted: 2016-09-06
- Earliest claimed: 2014-08-28
- Assignees: Canon Kabushiki Kaisha
- Applicants: Canon Kabushiki Kaisha
- Inventors: Hideaki Yonekubo; Hisashi Nakahara
- Web page: https://patentgrep.com/patent/US9436140B2

## CPC

- G03G 15/2039: {with means for controlling the fixing temperature}
- G03G 15/205: {specially for the mode of operation, e.g. standby, warming-up, error (G03G15/2046 takes precedence)}
- G03G 15/2053: {Structural details of heat elements, e.g. structure of roller or belt, eddy current, induction heating}
- G03G: ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY

## Abstract

A fixing device includes: a rotatable member; a helical coil; a magnetic core; and a controller for controlling the frequency of an AC current caused to flow through the coil. The AC current is caused to flow through the coil to cause an electroconductive layer of the rotatable member to generate heat through electromagnetic induction heating, thereby heating and fixing the toner image on the recording material by heat of the rotatable member. The controller controls the frequency in a period so that when the frequency is f and a resistance of the electroconductive layer with respect to a circumferential direction is R, f/R is substantially constant.

## Claims

### Claim 1

A fixing device for fixing a toner image on a recording material, comprising:
a rotatable member including an electroconductive layer;
a helical coil provided at a hollow portion of said rotatable member, a helical axis of said helical coil extending along a generatrix direction of said rotatable member;
a magnetic core provided inside a helically shaped portion formed by said helical coil; and
a controller configured to control a frequency of an AC current caused to flow through said helical coil,
wherein the AC current is caused to flow through said helical coil to cause the electroconductive layer to generate heat through electromagnetic induction heating to thereby heat and fix the toner image on the recording material by heat of said rotatable member, and
wherein said controller controls the frequency in a predetermined period so that, when the frequency is denoted by f and a resistance of the electroconductive layer with respect to a circumferential direction is denoted by R, f/R is substantially constant.

### Claim 2 (depends on 1)

The fixing device according to claim 1, wherein the predetermined period is a period in which the warm up of the fixing device is executed.

### Claim 3 (depends on 1)

The fixing device according to claim 1, wherein the period is a period in which a fixing process is executed.

### Claim 4 (depends on 1)

The fixing device according to claim 1, further comprising a temperature detecting member configured to detect the surface temperature of said rotatable member,
wherein when the detection temperature of said temperature detecting member and the frequency when a warm up of the fixing device is started are denoted by T0 and f0, respectively, the detection temperature of said temperature detecting member and the frequency during a period in which the warm up of the fixing device is executed are denoted by T1 and f1, respectively, and a temperature coefficient of resistance of the electroconductive layer is TCR, the fixing device satisfies: f1=f0(1+TCR×(T1−T0)).

### Claim 5 (depends on 1)

The fixing device according to claim 1, wherein the frequency is controlled in a range of 20.05 kHz<f<100 kHz.

### Claim 6 (depends on 1)

The fixing device according to claim 1, wherein said rotatable member is a film.

### Claim 7 (depends on 6)

The fixing device according to claim 6, further comprising, a nip forming member contacting an inner surface of said film, and
a pressing member configured to form a nip in cooperation with said nip forming member, said film being interposed between said pressing member and said nip forming member.

### Claim 8 (depends on 1)

The fixing device according to claim 1, wherein the fixing device is constituted so that 70% or more of magnetic flux coming out of one end of said magnetic core passes through an outside of the electroconductive layer and enters the other end of said magnetic core.

### Claim 9 (depends on 1)

The fixing device according to claim 1, wherein the electroconductive layer generates heat by a induced current flowing in the electroconductive layer in a circumferential direction of said rotatable member, the induced current being induced by the AC current.

### Claim 10

A fixing device for fixing a toner image on a recording material, comprising:
a rotatable member including an electroconductive layer;
a helical coil provided at a hollow portion of said rotatable member, a helical axis of said helical coil extending along a generatrix direction of said rotatable member;
a magnetic core provided inside a helically shaped portion formed by said helical coil; and
a controller configured to control a frequency of an AC current caused to flow through said helical coil,
wherein the AC current is caused to flow through said helical coil to cause the electroconductive layer to generate heat through electromagnetic induction heating to thereby to heat and fix the toner image on the recording material by heat of said rotatable member, and
wherein said controller controls the frequency in a period in which a warm up of the fixing device is executed so that when the frequency is denoted by f and a resistance of the electroconductive layer with respect to a circumferential direction is denoted by R, f/R starting from a value larger than an predetermined value converges to the predetermined value.

### Claim 11 (depends on 10)

The fixing device according to claim 10, further comprising a temperature detecting member configured to detect a surface temperature of said rotatable member,
wherein when a detection temperature of said temperature detecting member and the frequency when a warm up of the fixing device is started are denoted by T0 and f0, respectively, the detection temperature of said temperature detecting member and the frequency during a period in which the warm up of the fixing device is executed are denoted by T1 and f1, respectively, and a temperature coefficient of resistance of the electroconductive layer is TCR, the fixing device satisfies: f1=f0(1+TCR×(Ti−T0)).

### Claim 12 (depends on 10)

The fixing device according to claim 10, wherein the frequency is controlled in a range of 20.05 kHz<f<100 kHz.

### Claim 13 (depends on 10)

The fixing device according to claim 10, wherein said rotatable member is a film.

### Claim 14 (depends on 13)

The fixing device according to claim 13, further comprising,
a nip forming member contacting an inner surface of said film, and
a pressing member configured to form a nip in cooperation with said nip forming member, said film being interposed between said pressing member and said nip forming member.

### Claim 15 (depends on 10)

The fixing device according to claim 10, wherein the fixing device is constituted so that 70% or more of magnetic flux coming out of one end of said magnetic core passes through an outside of the electroconductive layer and enters the other end of said magnetic core.

### Claim 16 (depends on 10)

The fixing device according to claim 10, wherein the electroconductive layer generates heat by a induced current flowing in the electroconductive layer in a circumferential direction of said rotatable member, the induced current being induced by the AC current.