Fixing device and image forming apparatus

Abstract

A Fixing device has a heat roller, a magnetic flux generating element, and a magnetic flux block section. The magnetic flux block section for blocking magnetic flux flowing from a magnetic flux generating element to a heat roller is moved to a position at which the magnetic flux does not cause the heat roller to generate heat when rotation of the heat roller stops. The magnetic flux block section is moved to a position at which the heat roller generates heat when the heat roller rotates. Therefore, when rotation of the heat roller stops, even if electric current is applied to the magnetic flux generating element to generate magnetic flux from the magnetic flux generating element, heat generation by the magnetic flux generating element is prevented, so that smoking and firing of the heating element is suppressed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 shows a cross sectional view of a fixing device in a first embodiment of the present invention;

FIG. 2 is a side view of the fixing device as viewed from an axial end side of a heat roller;

FIG. 3 is a partially cut perspective view of a damper;

FIG. 4A is an operation explanation view of a magnetic flux block section to show a position thereof in the case where the rotation speed of the heat roller is low;

FIG. 4B is an operation explanation view of the magnetic flux block section to show a position thereof in the case where the rotation speed of the heat roller is high;

FIG. 5 is a simplified structure view of a fixing device in a second embodiment of the present invention;

FIG. 6 is a simplified structure view of a fixing device in a third embodiment of the present invention; and

FIG. 7 is a simplified structure view of an image forming apparatus according to the present invention.

Claims

1. A fixing device, comprising: a magnetic flux generating element for generating magnetic flux;a rotatable heating element for generating heat by magnetic flux from the magnetic flux generating element;a magnetic flux block section placed movably into between the magnetic flux generating element and the heating element, and blocking at least part of the magnetic flux flowing from the magnetic flux generating element to the heating element when being positioned between the magnetic flux generating element and the heating element;a movement control section for moving the magnetic flux block section to a position at which the magnetic flux from the magnetic flux generating element causes the heating element to generate no heat when rotation of the heating element stops, whereas moving the magnetic flux block section to a position at which the magnetic flux from the magnetic flux generating element causes the heating element to generate heat when the heating element rotates.

2. The fixing device according to claim 1, wherein the movement control section moves the magnetic flux block section in such a way that an amount of blocked magnetic flux flowing from the magnetic flux generating element to the heating element decreases as a rotation speed of the heating element increases.

3. The fixing device according to claim 1, wherein the movement control section moves the magnetic flux block section in conjunction with rotation of the heating element.

4. The fixing device according to claim 1, wherein when rotation of the heating element stops, the movement control section moves the magnetic flux block section to a position at which the magnetic flux flowing from the magnetic flux generating element to the heating element is completely blocked.

5. The fixing device according to claim 1, further comprising another rotor which rotates following after rotation of the heating element, whereinthe movement control section moves the magnetic flux block section in conjunction with rotation of the rotor.

6. The fixing device according to claim 1, wherein the magnetic flux generating element has a coil, anda coil control section is provided for turning off application of electric current to the coil when rotation of the heating element stops.

7. The fixing device according to claim 1, wherein the magnetic flux generating element has a coil,the coil is connected to a converter, anda converter control section is provided for turning off application of electric current to the converter when rotation of the heating element stops.

8. An image forming apparatus comprising the fixing device according to claim 1.