JPH09197851A - Fixing device with induction heating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To immediately and accurately detect a change in temperature and to accurately control the temp. of a heat generating member, without predicting the temp. by detecting it with the self-heat-generation of a temperature sensing member generating heat with induction by a coil assembly. SOLUTION: The coil assembly 3 for causing an induced current to flow in a fixing roller 1 is disposed in the direction of a rotary shaft, inside the fixing roller 1. Further, a thermostat 16 for controlling the temp. of the roller 1 is disposed at a distance nearly equal to the distance between the roller 1 and the coil assembly 3. The thermostat 16 is provided with a bimetal member deformed by the change in the temp. and generates the heat with the induction in the same way as the generation of the heat of the roller 1, so that the temp. of the thermostat 16 rises at the same speed as the roller 1. Since at the temp. of executing a fixing operation, a high frequency current flows in the coil 9 of the coil assembly 3 by an inverter circuit, the roller 1 and the bimetal member of the thermostat 16 generate the heat, to adjust the temp., so that the temp. of the roller 1 is about 180-200 deg.C.

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 in electrophotographic copying machines, printers, facsimiles and the like, and more specifically, induction heating fixing for fixing a toner image to a recording medium by using induction heating. Regarding the device.

[0002]

2. Description of the Related Art An electrophotographic copying machine or the like is provided with a fixing device for fixing a toner image transferred onto a sheet such as recording paper or a transfer material as a recording medium onto the sheet. In such a fixing device, the toner image on the recording paper that is nipped and conveyed between the fixing roller heated to a predetermined temperature set in advance and the pressure roller that is pressed against the fixing roller is attached to the fixing roller. By applying heat, the toner is melted and fixed to the recording paper. At that time, if the temperature of the fixing roller is too high, the toner will be melted too much and a high temperature offset will occur on the fixing roller, which will disturb the image on the recording paper. Conversely, if the temperature of the fixing roller is too low, the toner will be insufficient. Heat is not transmitted and low-temperature offset occurs, which may disturb the image.

Therefore, a temperature detecting element for detecting the temperature of the fixing roller is usually provided near the fixing roller, and the temperature of the fixing roller is controlled by the temperature detected by the temperature detecting element. The simplest type of temperature control for such a fixing roller is to use a thermostat in which a temperature detecting element and a switch for controlling energization of a heat source are integrated, and the temperature of the fixing roller can be detected. For example, a control circuit is provided for predicting the temperature reached by the fixing roller by calculating the rate of increase or the rate of decrease, and for controlling the temperature to be the optimum temperature of the fixing roller. In the case of providing a control circuit, it is usual to use a thermistor using a semiconductor or a thermocouple using thermoelectromotive force between different metals as the temperature detecting element.

[0004]

All of such temperature detecting elements detect heat which is directly contacted with or indirectly transmitted to the fixing roller, so that the responsiveness thereof tends to be slow, and in recent years, quick response has occurred. In the fixing device using induction heating, which is attracting attention from the start and the demand for energy saving,
There is a problem that the temperature of the fixing roller rises quickly and the temperature detecting element for detecting heat transmitted directly or indirectly cannot accurately detect the temperature. In addition, even in the method of predicting the temperature reached by the fixing roller, in the case of the induction heating fixing device in which the temperature rises rapidly, if a circuit that predicts the reached temperature faster than the temperature rise is manufactured, the circuit configuration becomes complicated and the cost increases. There was a problem that became.

Therefore, an object of the present invention is to provide an induction heating fixing device capable of accurately detecting temperature without performing predictive control.

[0006]

To achieve the above object, the present invention according to claim 1 is a fixing device for fixing a toner image formed on a recording medium to the recording medium, wherein magnetic flux is generated by energization. Magnetic flux generating means for generating, a heat generating member for inductively generating heat by the magnetic flux generated by the magnetic flux generating means, and at least one temperature detecting means constituted by a temperature sensitive member for inductively generating heat by the magnetic flux generated by the magnetic flux generating means. And an induction heating fixing device.

According to a second aspect of the present invention, in the induction heating fixing device according to the first aspect, the temperature raising rate of the temperature sensitive member is substantially equal to the temperature raising rate of the heat generating member. .

According to a third aspect of the present invention, in the induction heating fixing device according to the first or second aspect, the relative magnetic permeability of the temperature sensitive member is substantially equal to the relative magnetic permeability of the heat generating member. Is characterized by.

According to a fourth aspect of the present invention, in the induction heating fixing device according to any one of the first to third aspects, the distance between the temperature sensitive member and the magnetic flux generating means is the heat generating member. And the magnetic flux generating means are substantially equal to each other.

[0010]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings. 1 is a schematic side view showing the configuration of an induction heating fixing device to which the present invention is applied, and FIG. 2 is a sectional view of a fixing roller portion (however, the bobbin 8 and the holder 11 are omitted in FIG. 2).

As shown in FIG. 1, this induction heating fixing device is provided with a fixing roller 1 rotatably driven in the direction of an arrow a and a fixing roller 1 provided in pressure contact with the fixing roller 1 as the fixing roller 1 rotates. And a pressure roller 2 that is driven to rotate. The fixing roller 1 is a cylindrical hollow pipe made of a conductor, and a coil assembly 3 for generating an induced current in the fixing roller 1 is provided inside the fixing roller 1 along the rotation axis direction (cylindrical axis direction). Has been done. Further, a thermostat 16 for controlling the temperature of the fixing roller 1, which is arranged at a distance substantially equal to the distance between the fixing roller 1 and the coil assembly 3, is provided.

The coil assembly 3 is provided with a core 10 and a bobbin 8 surrounding the core 10.
A copper wire is wound around the bobbin 8 to form a coil 9, which is housed in a cylindrical holder 11.

The core 10 is made of, for example, a ferrite core or a laminated core, and one end of the core 10 is formed in a substantially C shape as shown in FIG. 3, and is formed by the core 10 and the fixing roller. A magnetic path substantially similar to the path is formed at the position where the thermostat 16 is arranged. As a result, the thermostat 1 will be described later.
The bimetal member provided inside 6 is the fixing roller 1.
Induction heat is generated in the same manner as above, and the temperature of the fixing roller 1 is controlled.

The bobbin 8 is formed of ceramic or heat resistant insulating engineering plastic, and plays a role of pressing at least the lowermost layer portion of the coil to adjust its shape.

The coil 9 is a 0.8 mm diameter single or litz copper wire having a fusion layer and an insulating layer on its surface, and is wound around the bobbin 8 in the direction along the rotation axis of the fixing roller 1. Has been done.

The holder 11 is made of a heat-resistant insulating material such as PPS (polyphenylene sulfide) or liquid crystal polymer so that the side surface of the coil 9 and the inner surface of the fixing roller 1 do not come into direct contact with each other. The current is prevented from flowing to the fixing roller 1 when the coating of the coil 9 is damaged.

The fixing roller 1 is formed of a conductive member such as a carbon steel tube, a stainless alloy tube, an aluminum tube, or a nickel tube. The outer peripheral surface of the fixing roller 1 is coated with fluororesin, and a heat-resistant release layer is formed on the surface. ing. The fixing roller 1 is more preferably formed of a conductive magnetic member.

In the pressure roller 2, a silicon rubber layer 19 which is a surface-releasing heat resistant rubber layer is formed around a shaft core 18.

As shown in FIG. 4, the thermostat 16 has a bimetal member 30 which is deformed by a change in temperature. The deformation of the bimetal member 30 is transmitted by a pin 21 and a contact 23 supported by a spring member 22 is formed. It is operated, and switching is performed with the fixed contact 24.

As shown in FIG. 5, the bimetal member 30 is made of two kinds of metals having different coefficients of thermal expansion, one of which has a large coefficient of thermal expansion 31, and the other of which has a small coefficient of thermal expansion. The member 32. Then, one of the two types of metal is formed of a metal having the same relative magnetic permeability as the fixing roller. Specifically, it is preferably formed of the same material (metal) as the fixing roller 1.

For example, when the fixing roller 1 is made of nickel (Ni), the coefficient of thermal expansion of nickel is 13.
Since it is 3 × 10 ⁻⁶ / K, it is preferable that nickel is used as the member 32 having a small coefficient of thermal expansion of the bimetal member 30 and aluminum (Al) is used as a member having a large coefficient of thermal expansion to form the bimetal member 30. Further, the fixing roller 1
When is made of SUS430 (stainless alloy), the coefficient of thermal expansion of SUS430 is 10.4 × 10 ⁻⁶ / K.
Therefore, SUS630 may be used as the member 32 having a small coefficient of thermal expansion of the bimetal member 30, and SUS304 may be used as a member having a large coefficient of thermal expansion to form the bimetal member 30.

Table 1 shows an example of the metal forming the fixing roller 1 and the bimetal member 30. Generally, the metal to be induction-heated preferably has a high relative magnetic permeability, but a metal having a low relative magnetic permeability can be used depending on the shape and thickness of the fixing roller and the core shape. As did
It is preferable that the same metal as the fixing roller is used as one of the metals of the bimetal, and the other metal is combined with a metal having a different thermal expansion coefficient to form the bimetal member. As long as the object of the present invention can be achieved, this Table 1
Other metals than those listed in (1) can be used, and the present invention is not limited to these metals.

[0023]

[Table 1]

The thickness and shape of the bimetal member 30 are preferably formed so that a temperature rising rate substantially equal to the temperature rising rate of the fixing roller can be obtained as described later.
Further, if the temperature rising rate can be the same, it is not always necessary to use a metal material having the same relative magnetic permeability. In such a case, the core shape and the distance between the coil and the thermostat are appropriately changed to raise the temperature. The speeds should be approximately equal.

Thermostat 16 formed in this way
Then, as shown in FIG. 6, the internal bimetal member 30 induces heat in the same manner as the heat generated by the fixing roller 1, and exhibits a temperature rise at substantially the same rate of temperature rise as the fixing roller 1.
As a result, the bimetal member 30 is deformed by the temperature change of one metal of the bimetal member 30 and the contacts 23 and 2
4 will be turned on or off. Therefore, like the general thermostat, the pin 21 of the thermostat 16 is
The contact points 23 and 2 when the required temperature is reached.
The temperature of the fixing roller 1 can be controlled by adjusting so that the fixing roller 4 is cut. In the case shown in FIG. 6, nickel having a thickness of 30 μm is used as the fixing roller,
The bimetal member 30 uses one metal of 30 μm thick nickel and the other metal of 30 μm thick Cu—Al alloy (aluminum bronze). For comparison, FIG. 6 also shows the result of indirectly measuring the temperature of the fixing roller 1 with a thermocouple. As can be seen from this figure, the temperature measurement with the thermocouple shows that the temperature of the fixing roller 1 rises. You can see that it does not match.

The relationship between the temperature rising rate of the fixing roller 1 and the temperature rising rate of the bimetal member 30 is such that in the case of induction heating, the fixing roller 1 has a predetermined temperature (180 to 200) necessary for melting the toner. It takes about 4 seconds to reach the same temperature (180 to 200 ° C.) in about 4 seconds, but the image is disturbed when the toner is melted and fixed. Since there is a range in the temperature range in which the temperature does not occur, the temperature rising rate of the bimetal member 30 is
There may be a slight difference from the temperature rising rate of the fixing roller. For example, if the difference is about ± 6%, more preferably ± 3%, the temperature of the fixing roller 1 can be sufficiently controlled. Further, the temperature reached by the bimetal member 30 itself does not necessarily have to match the temperature reached by the fixing roller 1, and the temperature of the fixing roller 1 can be controlled if the temperature rising rate (temperature rising rate) is the same. .

The fixing roller 1 has sliding bearing portions (not shown) formed at both ends thereof and is rotatably attached to the fixing unit frame. Further, the fixing roller 1
Has a drive gear (not shown) fixed to one end thereof, and is rotationally driven by a drive source (not shown) such as a motor connected to the drive gear. Further, the holder 11 is housed inside the fixing roller 1 with a minimum gap of a predetermined dimension maintained between the holder 11 and the inner peripheral surface of the fixing roller 1, and is fixed to the fixing unit frame so as not to rotate. The sliding bearing and the separating claw 15 are formed of heat resistant sliding engineering plastic or the like.

The induction heating fixing device configured as described above operates as follows. First, the sheet 14 on which the unfixed toner image is transferred is conveyed from the left side in FIG.
It is fed toward the nip portion between the fixing roller 1 and the pressure roller 2. At the same time, a high-frequency current of, for example, about 10 kHz to 100 kHz is applied to the coil 9 by an inverter circuit (not shown), the fixing roller 1 and the bimetal member 30 of the thermostat 16 generate heat, and the temperature of the fixing roller 1 is 180 to 200 ° C. The temperature is controlled to a certain degree. The sheet 14 is conveyed through the nip portion while the heat of the fixing roller 1 generated by induction heat generation and the pressure acting from both rollers 1 and 2 are applied. As a result, the unfixed toner is fixed, and a fixed toner image is formed on the sheet 14. The sheet 14 that has passed through the nip is the fixing roller 1
1, or as shown in FIG. 1, the tip is forcibly separated from the fixing roller 1 by a separation claw 15 or a separation guide provided so that the front end of the fixing roller 1 is in sliding contact with the surface of the fixing roller 1. Transported to the right. The sheet 14 is conveyed by a paper discharge roller (not shown) and discharged onto the paper discharge tray.

Although the embodiment described above uses the fixing roller as the heat-generating member, the present invention is not limited to this. For example, a flexible metal thin film is used as the heat-generating member, and other than the fixing roller. It can be suitably applied to a heat-generating member that heats by induction heating.

[0030]

The present invention described above has the following effects according to the claims. According to the induction heating fixing device of the first aspect of the present invention, the temperature detecting means for detecting the temperature of the heat generating member that generates heat by induction heating has the same feeling as the heat generating member that induction heat is generated by the magnetic flux generating means. Since the temperature detecting means detects the temperature due to the self-heating of the temperature-sensitive member, it is possible to immediately and accurately detect a temperature change substantially similar to the temperature change of the heat-generating member. It becomes possible to perform temperature control accurately. Further, it is possible to easily manufacture without requiring a circuit configuration for predicting temperature.

According to the induction heating fixing device of the second aspect of the present invention, the temperature rise of the temperature-sensitive member and the temperature rise of the heat-generating member are made equal to each other, so that the temperature detecting means substantially changes the temperature of the heat-generating member. The temperature change can be detected immediately and accurately, and the temperature of the heat generating member can be accurately controlled.

According to the induction heating fixing device of the present invention as defined in claim 3, the magnetic permeability of the temperature-sensitive member and the magnetic permeability of the heat-generating member are made equal to each other, so that the amount of heat generated by induction heat generation by the magnetic flux generating means is temperature-sensitive. Since the member and the heat generating member are substantially equal to each other, the temperature detecting means can immediately and accurately detect a temperature change substantially the same as the temperature change of the heat generating member, and the temperature of the heat generating member can be accurately controlled. .

According to the induction heating fixing device of the present invention, the distance between the temperature sensitive member and the magnetic flux generating means and the distance between the heat generating member and the magnetic flux generating means are equalized. The amount of heat generated by induction heat generation is substantially equal between the temperature-sensitive member and the heat-generating member, and the temperature detection means can immediately and accurately detect a temperature change substantially similar to the temperature change of the heat-generating member. It can be done accurately.

[Brief description of drawings]

FIG. 1 is a schematic side view showing an induction heating fixing device to which the present invention is applied.

FIG. 2 is a sectional view of the fixing roller shown in FIG.

3 is a perspective view of the core shown in FIG. 1. FIG.

4 is a cross-sectional view of the thermostat shown in FIG.

5 is a cross-sectional view of the bimetal member shown in FIG.

FIG. 6 is a diagram showing temperature rise characteristics of a fixing roller and a thermostat of the induction heating fixing device and a thermocouple for comparison.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fixing roller 2 ... Pressure roller 3 ... Coil assembly 9 ... Coil 10 ... Core 16 ... Thermostat, 30 ... Bimetal member.

Claims (4)

[Claims] 1. A fixing device for fixing a toner image formed on a recording medium to the recording medium, wherein magnetic flux generating means for generating magnetic flux by energization and induction heat generation by the magnetic flux generated by the magnetic flux generating means. An induction heating fixing device comprising: a heat generating member; and at least one temperature detecting unit constituted by a temperature sensitive member that induces heat by the magnetic flux generated by the magnetic flux generating unit. 2. The induction heating fixing device according to claim 1, wherein the temperature raising rate of the temperature sensitive member is substantially equal to the temperature raising rate of the heat generating member. 3. The induction heating fixing device according to claim 1, wherein a relative magnetic permeability of the temperature sensitive member is substantially equal to a relative magnetic permeability of the heat generating member. 4. The distance between the temperature sensitive member and the magnetic flux generating means is substantially equal to the distance between the heat generating member and the magnetic flux generating means. Induction heating fixing device.