JP2000066543A - Induction heating fixing device - Google Patents

Abstract

(57) [Problem] To provide an induction heating type fixing device capable of eliminating temperature unevenness in the axial direction of the surface of a fixing roller accompanying a fixing operation. In an induction heating fixing device in which an induction heating coil composed of a conducting wire wound around a winding frame is disposed in a heating roller, the heating roller has an end in accordance with the temperature of the end in the axial direction. The magnetic flux passing through the section is variable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used for an image forming apparatus such as a printer, a facsimile, and a copying machine, and more particularly to a fixing device for fixing a toner image to a recording medium such as a cut sheet by an induction heating method. is there.

[0002]

2. Description of the Related Art An image forming apparatus is provided with a fixing device for fixing a toner image transferred onto a sheet as a recording medium to the sheet. The fixing device includes, for example, a fixing roller (heating roller) that thermally fuses the toner on the sheet and a pressure roller that presses the sheet by pressing the fixing roller. In addition, an induction heating system in which an induction heating coil is disposed inside the roller in place of the halogen lamp built-in type having poor heat efficiency is becoming popular due to recent demand for energy saving. In this method, an eddy current flows inside the fixing roller by passing a magnetic flux generated by an induction heating coil through a conductor portion of the fixing roller, and the fixing roller is heated by Joule heat due to the eddy current.

[0003]

The induction heating method is as follows.
Since the fixing roller itself generates heat, the temperature of the fixing roller rises faster and energy saving is achieved as compared with a conventional radiation method such as a halogen lamp.

However, even in such an induction heating method, when a recording medium having a width shorter than the axial length (width direction) of the fixing roller is conveyed, only the central portion of the fixing roller heats the recording medium. When this was repeated, the temperature at both ends became relatively high. If there is uneven temperature in the axial direction on the surface of the fixing roller,
There is a problem that poor fixing and generation of wrinkles on the sheet occur.

A proposal for making the temperature distribution in the axial direction of the fixing roller uniform in the induction heating type fixing device is disclosed in, for example, Japanese Patent Application Laid-Open No. 10-31379. However, in this proposed technique, when viewed locally in the core around which the induction heating coil is wound, the magnetic flux distribution becomes convex toward the both ends with the central part of the fixing roller being convex, and the heat generation amount at the end of the fixing roller is central. The temperature distribution for solving the problem in the static state, that is, both of the lowering than the central part and the amount of heat dissipation at the end of the fixing roller is larger than that of the central part. As described above, it does not solve the temperature unevenness due to the continuous fixing operation.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an induction heating type fixing device capable of eliminating temperature unevenness in the axial direction of the surface of a fixing roller due to a fixing operation.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided an induction heating fixing apparatus comprising a heating roller and an induction heating coil comprising a conductor wound around a winding frame. The problem is solved by configuring the magnetic flux passing through the end portion to be variable depending on the temperature of the end portion in the direction.

A magnetic body movable in the axial direction is disposed near the end of the winding frame, and a temperature sensor is disposed in each of a central area and an end area of the heating roller. It is preferable that the magnetic body be controlled so as to move from the outside of the reel to the inside of the reel when it is detected that the temperature of the region is higher. Further, the induction heating coil has a first conductor wound around a center region of the winding frame and a second conductor wound around an end region, and the second conductor is connected to the first conductor via a current limiting element. Even if it is configured to be connected to an induction heating power supply in parallel with the heating roller and to control the current flowing through each lead wire in accordance with the temperature difference detected by the temperature sensors arranged in the central area and the end area of the heating roller, respectively. It is.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on an example shown in the drawings. FIG. 1 is an end view showing a schematic configuration of an induction heating type fixing device (hereinafter, simply referred to as a fixing device) to which the present invention is applied, and FIG. 2 is a diagram showing a configuration of a heating roller portion of the fixing device. is there. In the present embodiment, a so-called “center-based transport method” is adopted in which the transfer paper as a recording medium is transported such that the center of the transfer paper coincides with the center of the heating roller.

This fixing device includes a heating roller 4 rotatably driven in a clockwise direction as viewed in FIG. 1, a pressing roller 5 pressed against the heating roller 4 and driven to rotate with the rotation of the heating roller. have. The induction heating coil 2 is arranged inside the heating roller 4, and the coil is fixed to the device independently of the heating roller 4.

The transfer paper P enters the nip formed by the heating roller 4 and the pressure roller 5 from the right side in FIG. 1 and passes between the nips. The toner T is fixed, and is carried out to a discharge unit (not shown).

As shown in FIG. 2, journals 4a for supporting the heating roller 4 are fitted to both ends of the heating roller 4, and are rotatable to the apparatus main body via bearings 4b next to the outside thereof. , The heating roller is fixed. A gear 4 for rotational drive is provided at one end of the journal 4a.
c is provided. The induction heating coil 2 arranged inside the cylindrical heating roller 4 is a cylindrical bobbin (winding frame).
A coil wire 3a is wound around the outer periphery of 2a.
The magnetic bodies 6a and 6b for changing the magnetic flux passing through the end of the heating roller are arranged at the end of the bobbin 2a in a state where the magnetic bodies 6a and 6b can move in the axial direction of the heating roller. It is located outside the part. Temperature sensors 7a and 7b are provided at two locations, a central portion and an end portion of the heating roller 4.
Are arranged to contact the roller surface. These temperature sensors 7a and 7b are connected to a control unit (not shown).

When the fixing device is activated with the above-described configuration and a current flows through the coil wire 3a, a magnetic flux is generated and passes through the heating roller 4. As a result, an eddy current flows inside the heating roller, and the heating roller 4 generates heat by Joule heat. The current to the coil wire is controlled so that the temperature detected by the temperature sensor 7a at the center becomes a predetermined value. When the temperature of the heating roller 4 reaches the target value, the machine equipped with the fixing device is started to fix the transfer paper. At this time, if the transfer paper of a small size having a short paper width is continuously fixed and conveyed, heat at the center of the heating roller 4 is taken by the transfer paper, so that more current flows through the coil wire 3a to compensate for this. Will be controlled as follows. As a result, the temperature of the roller end, which emits less heat, rises. When the temperature detected by the temperature sensor 7b at the end becomes higher than a predetermined value, the magnetic bodies 6a and 6b
(Only 6b is shown for convenience)
Move toward the center of the coil wire 3a. Due to this movement, the magnetic flux on the outside of the induction heating coil decreases, and more magnetic flux passes through the inner magnetic bodies 6a and 6b, so that the heat generation at the end of the heating roller 4 decreases.

Therefore, the magnetic bodies 6a and 6b are moved in accordance with the temperature of the end of the heating roller 4 to make the magnetic flux passing through the end of the heating roller variable, thereby suppressing the temperature unevenness between the end and the center. be able to. Further, by moving the magnetic bodies 6a and 6b according to the temperature difference between the end and the center of the heating roller 4, the temperature difference can be further reduced.

FIG. 3 is a diagram showing a configuration of a heating roller portion of a fixing device according to another configuration. Since the supporting and driving mechanism of the heating roller 4 is the same as that of FIG. 2, the description is omitted by attaching the same reference numerals. The induction heating coil 2 disposed inside the heating roller 4 is configured by winding a first coil wire 3a 'and a second coil wire 3b' around the outer periphery of a cylindrical bobbin 2a. The first coil wire 3a 'and the second coil wire 3b' are connected at one end, and are connected to the driving element Q of the induction heating power supply 8. The other end of the first coil wire 3a 'wound around the center area of the bobbin 2a is connected to a coil L and a capacitor C.
And directly connected to the filter circuit consisting of On the other hand, the other end of the second coil wire 3b 'wound around the bobbin end is connected to the filter circuit via current limiting elements R1 and R2. Relays RA1 and RA2 are connected in parallel to current limiting elements R1 and R2, respectively.
Relays usually have their contacts closed. The temperature sensors 7a and 7b are arranged so as to be in contact with the roller surface at two positions, that is, the center and the end of the heating roller 4, and are connected to a control unit (not shown) as in the example of FIG. .

When the fixing device is started up with the above-described configuration and a current flows through the coil wires 3a 'and 3b', a magnetic flux is generated and passes through the heating roller 4. As a result, an eddy current flows inside the roller, and the roller generates heat by Joule heat. The control unit INV of the induction heating power supply 8 controls the coil wire 3 so that the temperature detected by the temperature sensor 7a at the center becomes a predetermined value.
The drive currents of a 'and 3b' are controlled. When the temperature of the heating roller 4 reaches the target value, the machine equipped with the fixing device is started to fix the transfer paper. If the transfer paper of a small size having a short paper width is continuously fixed and conveyed, and the heat at the center of the roller is taken away by the transfer paper, the control unit INV supplies more coil wires 3a 'and 3b' to compensate for this. Control is performed so that current flows. As a result, the temperature of the roller end, which emits less heat, rises. When the difference between the temperature detected by the temperature sensor 7b at the end and the temperature detected by the temperature sensor 7a at the center becomes higher than a predetermined value, the contacts of the relays RA1 and RA2 are opened, and the second coil wire 3b 'at the end is opened. Drive current.
Thereby, the magnetic flux at the end of the heating roller 4 can be reduced according to the temperature difference between the end and the center of the heating roller 4, and the temperature unevenness can be reduced.

[0017]

According to the present invention, in an induction heating fixing device in which an induction heating coil composed of a conductive wire wound around a winding frame is disposed in a heating roller, the temperature of the heating roller depends on the temperature at the axial end. Since the magnetic flux passing through the end portion is variable, the temperature unevenness of the heating roller can be reduced according to the temperature of the end portion of the heating roller.

In particular, a magnetic body movable in the axial direction is disposed near the end of the winding frame, and a temperature sensor is disposed at each of a central area and an end area of the heating roller. By controlling the magnetic material to move from the outside of the reel to the inside of the reel when it is detected that the end region is higher in temperature, it is possible to further reduce the temperature unevenness in the end and central regions. Can be. Further, the induction heating coil has a first conductor wound around a center region of the winding frame and a second conductor wound around an end region, and the second conductor is connected to the first conductor via a current limiting element.
Connected to the induction heating power supply in parallel with the conductor, by controlling the current flowing through each conductor according to the temperature difference detected by the temperature sensors arranged in the central area and the end area of the heating roller, the roller end Magnetic flux can be reduced to reduce temperature unevenness.

[Brief description of the drawings]

FIG. 1 is a layout diagram showing a basic configuration of a fixing device according to the present invention.

FIG. 2 is a schematic sectional view of a heating roller portion showing a first configuration example.

FIG. 3 is a schematic sectional view of a heating roller portion showing a second configuration example.

[Explanation of symbols]

 2 Induction heating coil 2a Bobbin 3a Coil wire 4 Heating roller 6a, 6b Magnetic body 7a, 7b Temperature sensor

Claims (3)

[Claims] In an induction heating fixing device in which an induction heating coil formed of a conductive wire wound around a winding frame is disposed in a heating roller, the induction heating coil passes through the end of the heating roller in accordance with the temperature of the end in the axial direction. A fixing device configured to change a magnetic flux generated by the fixing device. 2. A magnetic body movable in the axial direction is disposed near the end of the winding frame, and a temperature sensor is disposed in each of a central area and an end area of the heating roller. 2. The fixing device according to claim 1, wherein, when it is detected that the temperature of the end portion is higher, the magnetic material is controlled to move from outside the reel to the inside of the reel. 3. The induction heating coil has a first conductor wound around a center region of the winding frame and a second conductor wound around an end region, and the second conductor is connected via a current limiting element. Connected to an induction heating power source in parallel with the first conductive wire, and controls a current flowing through each conductive wire according to a temperature difference detected by a temperature sensor disposed at each of a central area and an end area of the heating roller. The fixing device according to claim 1.