JP3376785B2 - Induction heating fixing device - Google Patents

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 particularly to a fixing device that fixes toner images on a recording medium by using induction heating. .

[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. This fixing device has, for example, a fixing roller that heat-melts the toner on the sheet, and a pressure roller that presses the fixing roller to sandwich the sheet. The fixing roller is formed in a cylindrical shape, and a heating element is held by a holding means on the central axis of the fixing roller. The heating element is composed of, for example, a halogen lamp or the like, and generates heat when a predetermined voltage is applied. Since this heating element is located on the central axis of the fixing roller, the heat generated from the heating element is radiated uniformly to the inner wall of the fixing roller, and the temperature distribution of the outer wall of the fixing roller becomes uniform in the circumferential direction. The outer wall of the fixing roller is heated until its temperature reaches a temperature suitable for fixing (for example, 150 to 200 ° C.).
In this state, the fixing roller and the pressure roller rotate in opposite directions while slidingly contacting each other, and sandwich the sheet to which the toner is attached. At the sliding contact portion (hereinafter referred to as a nip portion) between the fixing roller and the pressure roller, the toner on the sheet is melted by the heat of the fixing roller and is fixed on the sheet by the pressure applied from both rollers. After the toner is fixed, the sheet is conveyed by the discharge rollers and discharged onto the discharge tray as the fixing roller and the pressure roller rotate.

In the above fixing device provided with a heating element composed of a halogen lamp or the like, after the power is turned on,
It takes a long time for the temperature of the fixing roller to reach a predetermined temperature suitable for fixing, and during that time, the user cannot use the copying machine or the like and is forced to wait.

Therefore, in order to enhance the value of a product such as a copying machine, the operability of the user is improved (quick print).
It is becoming more and more important and important to achieve this.

Therefore, for the quick print, an induction heating type fixing device has been proposed (Japanese Patent Laid-Open No. 59-59).
No. 33788). In this induction heating fixing device, a spirally wound coil is concentrically arranged inside a fixing roller made of a metal conductor, and a high-frequency current is caused to flow through the coil close to the inner surface of the fixing roller. An induced eddy current is generated in the fixing roller by the high frequency magnetic field, and Joule heat is generated in the fixing roller itself by the inherent resistance of the fixing roller itself.

This induction heating method has the following advantages over other heating methods. First of all, the temperature rises faster than indirect heating such as near infrared heating of halogen lamps,
Little heat and heat transfer to parts other than the fixing roller. Further, there is no loss corresponding to the light leakage of the halogen lamp. Second,
Compared to surface heating, which has a solid resistance heating element on the surface of the fixing roller, the heat generation efficiency is better due to the skin effect peculiar to electromagnetic induction, and the reliability of the fixing device is also high for a long time because there is no sliding contact.

In recent years, development of low fixing temperature toner has progressed, and due to the spread and cost reduction of inverter circuit switching elements in high frequency power supplies for home appliances, it has become possible to realize an induction heating fixing device having the above characteristics. is there.

[0008]

The induction heating fixing device having such advantages has a problem, and one of the problems is that an object to be heated has an abnormally high temperature because of the advantage that the temperature rising rate is high. There is a difficulty in safety measures in case of (overheating).

As a safety measure against this abnormally high temperature, in the case of a conventional fixing device using a halogen lamp, a thermostat, a temperature fuse, or the like is brought into contact with the fixing roller or is arranged in the vicinity thereof so that the fixing roller is kept at a constant temperature. When it reaches, the current path to the halogen lamp is cut off to prevent overheating of the fixing roller.

However, there is a certain time lag in the operation of thermostats and thermal fuses. In the case of a halogen lamp having a slow temperature rising rate, overheating of the fixing roller can be sufficiently prevented, but in the case of induction heating, the temperature rising rate is high, so that a sufficient effect cannot be obtained. FIG. 11 shows an example thereof. Even in the case of a thermostat in which a bimetal is directly contacted with the fixing roller, the fixing roller has an abnormally high temperature T0, and it takes about 50 to 60 seconds (t0 to t) before the temperature T0 is detected.
The time of 1) is required, and in the case of the thermal fuse, it is not possible to directly contact the fixing roller, so that it takes about 100 seconds longer (t0 to t2). Meanwhile, the temperature of the fixing roller rises from the abnormal temperature T0 to temperatures T1 and T2.

Therefore, in the case of induction heating, it is necessary to use a high-temperature heat-resistant member that can withstand the temperatures (T1, T2) rising during such a delay in heat transfer, and a bimetal having a fast response speed. It is also necessary to use, and there is a problem that the cost of the product is increased.

SUMMARY OF THE INVENTION An object of the present invention is to provide an induction heating fixing device which takes measures against abnormal high temperature and has a fast response speed, which replaces the thermostat and the thermal fuse.

[0013]

[0014]

[0015]

A solution for the present invention of claim 1, wherein in order to achieve the above object, a fixing device for fixing a toner image formed on the recording medium to the recording medium, a conductive member A heated body formed by the above, a coil disposed in the vicinity of the heated body to generate an induced current in the heated body to generate heat, and a heating output of the heated body is arbitrarily controlled. a heating output controller for outputting the control voltage for the high-frequency power supply circuit for supplying an alternating current to the coil according to the control voltage from the heating output control means, and a coil voltage detecting means for detecting a voltage of said coil The operation of the high frequency power supply circuit when the maximum value of the coil voltage detected by the coil voltage detection means is equal to or lower than a voltage value determined in proportion to the control voltage output by the heating output control means. High frequency to stop A source circuit stop means, an induction heat fixing apparatus characterized by having a.

The present invention according to claim 2 is the same as the above claim.
In the present invention described in 1 , the high frequency power supply circuit has a switch for supplying an alternating current to the coil, and timing determining means for determining the on / off timing of the switch, and the timing determining means is a timer circuit. more becomes, on of the switch to measure a period of time depending on the control voltage from the timer circuit the heating output control means, you and determining a timing of off.

According to a third aspect of the present invention, in the first aspect of the present invention, the high-frequency power supply circuit determines a switch for supplying an alternating current to the coil, and the on / off timing of the switch. Timing determining means, the timing determining means has a coil current detecting means for detecting a coil current of the coil, the coil current detected by the coil current detecting means is converted into a voltage value,
Compared to the control voltage from the heating output control means, on the switches to make and determining a timing of off.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention configured as described above will be described with reference to the accompanying drawings.

< Premise Form > FIG. 1 is a premise for explaining an embodiment of the present invention.
Is a block diagram of a control system of the induction heat fixing apparatus that. In this induction heating fixing device, an induction heating coil 9 for generating an induction current in the object to be heated 30 is arranged in the vicinity of the object to be heated 30 such as a metal fixing roller or a metal plate. The induction heating coil 9 has a commercial power source (AC100
The alternating current (V) 45 is rectified into a direct current (DC) by the rectifier circuit 48, converted into a high frequency by the inverter circuit 60 which is a high frequency power supply circuit, and applied.

The high frequency current (alternating current) to the induction heating coil 9 is applied to the induction heating coil 9 and the resonance capacitor 49 which constitute the LC resonance circuit after AC 100 V is rectified to DC by the rectification circuit 48, and Rectifier circuit 48
And the LC resonance circuit are connected in series, and are supplied by switching the switch 44 composed of, for example, a transistor, an FET, or an IGBT by the drive circuit 53. The on timing of the switch 44 is determined by the voltage detection circuit 54, and the off timing of the switch 44 is determined by the timer circuit 51.

The ON timing of the switch 44 is driven by the voltage detection circuit 54 detecting that the voltage generated by the resonance of the induction heating coil 9 and the resonance capacitor 49 has reached a certain voltage value or less, here 0V. A signal is output to the circuit 53, and the drive circuit 53 outputs the signal to the switch 44.
Turn on. On the other hand, as for the off timing of the switch 44, the timer circuit 51 outputs a signal for a predetermined time to the drive circuit 53 as described later, and the drive circuit 5 is driven by the signal.
3 turns off switch 44. Therefore, the voltage detection circuit 54, the timer circuit 51, and the drive circuit 53 function as timing determination means.

The timer circuit 51 has a simple circuit configuration consisting of a resistor and a capacitor, and the drive circuit 53 is turned off after a certain time determined by the CR charge / discharge characteristic by an ON signal of a constant voltage from the control circuit 50 described later. Outputting a signal.

By such a switching operation, a high frequency is applied to the induction heating coil 9, and an induction current is generated in the object to be heated 30 to generate heat.

The control circuit 50 is a heating output control means, and the temperature of the heated body 30 becomes the temperature required for fixing from the temperature detected by the thermistor 6 which is in contact with or in the immediate vicinity of the heated body 30. As described above, a constant voltage on / off signal is output to the timer circuit 51.

In this control system, a maximum coil voltage detection circuit 55 for detecting the maximum value of the coil voltage is provided in order to prevent overheating of the object 30 to be heated. The maximum coil voltage detection circuit 55 outputs an ON (Hi level) signal to the drive circuit 53 when the maximum value of the detected coil voltage is equal to or higher than a predetermined reference voltage value,
When the maximum value of the coil voltage becomes equal to or lower than a predetermined reference voltage value, the signal is turned off (Lo level), and the drive circuit 53 is controlled to turn off the switch 44. As a result, when the signal from the maximum coil voltage detection circuit 55 to the drive circuit 53 is turned off, the operation of the inverter circuit 60 is completely stopped, the supply of the high frequency current to the induction heating coil 9 is cut off, and the heated object is Overheating of 30 is prevented. Therefore, the maximum coil voltage detection circuit 55 functions as a coil voltage detection means, and the drive circuit 53 functions as a high frequency power supply circuit stop means here.

Here, the operation for preventing overheating of the object to be heated will be described.

The object to be heated formed by the metal member has a characteristic that the metal resistance increases due to the temperature increase due to induction heating. The rate of change in resistance due to this temperature rise is expressed by the following equation (1). Resistance change rate TCR = (ΔR / R0) × (1 / ΔT) (1) (where ΔR is the change in resistance, R0 is the resistance value at the reference temperature (for example, room temperature), and ΔT is the change in temperature. Minutes).

The heating output W of the object to be heated is expressed by the following equation (2). W = V ² / RT = V ² / (R 0 + ΔR) = (V ² / R 0) × (1 / (1 + TCR × ΔT) (2) (where V is the induced voltage of the heated object, RT Is the resistance of the heated object at the current temperature).

The heating output W of the object to be heated is proportional to the electric power stored in the coil, and the electric power stored in the coil is maintained only during the time when the resonance capacitor forming the resonance circuit together with the coil is turned on. It has the same value as the stored electric power and is expressed as in (3) below. 1 / 2CVL ² = 1 / 2LI ² ∝W (3) (where C is the capacitance of the resonance capacitor, VL is the coil voltage, L is the coil inductance, and I is the coil current).

By substituting the equation (2) for W, the equation (3) is transformed into the following equation (4). VL ∝1 / √ (1 + TCR × ΔT) (4) From this equation (4), it is understood that the coil voltage is inversely proportional to the temperature of the heated object. That is, as shown in FIG. 2, when the temperature of the object to be heated increases, the coil voltage decreases.

Therefore, by detecting the coil voltage that decreases as the temperature of the object to be heated rises and cutting off the supply of electric power when it becomes a certain value VD0 or less, the temperature T0 of the object to be heated or more at that time is exceeded. Further, it is possible to prevent the heated body from being heated and heated. That is, in the present premise , the maximum coil voltage detection circuit 55 detects this coil voltage VL, and if the detected voltage is VD0 or higher, an ON signal is output to the drive circuit 53, and the detected voltage becomes VD0 or lower. By turning off the ON signal when the temperature rises, it is taken as a measure to prevent overheating when the heated object becomes abnormally hot. However, the detected coil voltage VL is the maximum voltage value of the high frequency applied by the inverter circuit.

This operation will be described with reference to the time chart shown in FIG. 3. When the temperature of the heated body 30 exceeds the abnormal temperature T0 for some reason, the temperature of the heated body 30 decreases with an increase in temperature. The maximum value of the applied coil voltage becomes lower than the reference voltage Vref. This allows Hi until then
The signal from the maximum coil voltage detection circuit 55 which has been at the level becomes Lo level, the output from the drive circuit 53 is stopped, and the switch 44 is turned off. As a result, all the operations of the inverter circuit 60 are stopped and the high frequency current is not supplied to the induction heating coil 9, so that the heated body 30 does not generate more heat.

[0033] FIG. 4 <Embodiment 1> is a block diagram of a control system of the induction heat fixing apparatus of the implementation of embodiments according to the present invention. This control system is
In the premise , the control circuit 50 to the timer circuit 5
While the output signal to 1 is only the output of a constant voltage, the heating output can be arbitrarily controlled by changing the voltage output from the control circuit 50a in an analog manner.

That is, by changing the voltage applied to the timer circuit 51 consisting of a resistor and a capacitor, the amount of charge stored in the capacitor changes, and the time of the timer circuit determined by the CR charge / discharge characteristics changes.
As a result, the off-timing time of the switch 44 changes, so the amount of electric power stored in the induction heating coil 9 changes and the heating output changes. Therefore, when the voltage of the control signal is increased, the off-timing time output from the timer circuit 51 is extended, the amount of electric power stored in the induction heating coil 9 is increased, and the heating output is increased. On the other hand, if the voltage of the control signal is lowered, the off-timing time is shortened and the heating output is lowered.

With the control of this heating output, the maximum value of the coil voltage naturally changes. Therefore, in this control system, with respect to the voltage value detected by the maximum coil current detection circuit 55, a reference voltage for preventing overheating of the heated object 30 is set in proportion to the voltage value of the control signal. I decided to do it.

That is, when the voltage of the control signal is low, the maximum value of the coil voltage corresponding to the abnormal temperature that causes overheating also becomes low, so the reference voltage is set low, and conversely, when the control voltage is high. , The reference voltage is set high.

The maximum coil voltage detection circuit 55 compares the reference voltage set in this way with the maximum value of the detected coil voltage, and when the maximum value of the coil voltage becomes lower than the reference voltage, the drive circuit The signal output to 53 is set to Lo level, and the operation of the inverter circuit 60 is stopped. As a result, overheating of the object to be heated 30 is prevented in the same manner as the above-described premise . Therefore, the maximum coil voltage detection circuit 55 functions as a coil voltage detection means, and the drive circuit 53 functions as a high frequency power supply circuit stopping means.

The other configurations and operations are the same as those of the above-described premise, and the description thereof will be omitted.

< Second Embodiment> FIG. 5 is a block diagram of a control system of an induction heating fixing device according to another embodiment of the present invention.

In this induction heating fixing device, an induction heating coil 9 for generating an induction current in the object to be heated 30 is arranged in the vicinity of the object to be heated 30 such as a metal fixing roller or a metal plate. The alternating current of the commercial power supply (AC 100 V) 45 is rectified into DC by the rectifier circuit 48, converted into high frequency by the inverter circuit 60, and applied to the induction heating coil 9.

The high frequency current (alternating current) to the induction heating coil 9 is applied to the induction heating coil 9 and the resonance capacitor 49 which compose the LC resonance circuit after AC100V is rectified to DC by the rectification circuit 48, and Rectifier circuit 48
And the LC resonance circuit are connected in series, and are supplied by switching the switch 44 composed of, for example, a transistor, an FET, or an IGBT by the drive circuit 53. The ON timing of the switch 44 is determined by the voltage detection circuit 54, and the OFF timing of the switch 44 is determined by the current detection circuit 52. Therefore, the voltage detection circuit 54, the current detection circuit 52, and the drive circuit 53.
Will function as timing determination means.

The off timing of the switch 44 is detected by detecting the voltage generated by the current detection resistor included in the current detection circuit 51 when the switch 44 is turned on and a current flows through the induction heating coil 9. When the generated voltage exceeds the voltage value of the control signal from the control circuit 50b, which will be described later, a signal is output to the drive circuit 53 to turn off the switch 44, and the drive circuit 53 turns off the switch 44 by the signal. Controlled. On the other hand, at the on-timing, when the voltage detection circuit 54 detects that the coil voltage of the induction heating coil 9 has dropped to around 0V,
It is controlled by sending a signal to the drive circuit 53 so as to turn on the switch 44.

As a result, a high-frequency current (alternating current) is applied to the induction heating coil 9, and the object to be heated 30 is induction-heated to generate heat.

Like the first embodiment, the control circuit 50b is configured to change the voltage output from the control circuit 50b in an analog manner so that the heating output can be arbitrarily controlled. The signal output from the control circuit 50b is supplied to the current detection circuit 52 and becomes a voltage for determining the off timing. Therefore, if the voltage of the control signal is increased, the off-timing time output by the current detection circuit 52 is increased, the amount of electric power stored in the induction heating coil 9 is increased, and the heating output is increased. on the other hand,
On the contrary, if the voltage of the control signal is lowered, the off-timing time is shortened and the heating output is lowered.

Further, with respect to the voltage value detected by the maximum coil current detection circuit 55, the reference voltage for preventing overheating of the object to be heated 30 is set so as to be proportional to the voltage value of the control signal. . That is, when the voltage of the control signal is low, the maximum value of the coil voltage corresponding to the abnormal temperature that causes overheating also becomes low, so the reference voltage is set low,
On the contrary, when the control voltage is high, the reference voltage is set high. The maximum coil voltage detection circuit 55 compares the reference voltage set in this way with the maximum value of the detected coil voltage, and when the maximum value of the coil voltage becomes lower than the reference voltage, outputs it to the drive circuit 53. The signal is turned to Lo level, and the operation of the inverter circuit 60 is stopped. As a result, overheating of the object to be heated 30 is prevented as in the first embodiment. Therefore, the maximum coil voltage detection circuit 55
Is a coil voltage detecting means, and the drive circuit 53 functions as a high frequency power supply stopping means.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an induction heating fixing device to which the present invention is applied will be described below with reference to the drawings. It should be noted that members having the same function are denoted by the same reference numerals as those in the above-described drawings, and description thereof will be omitted.

Embodiment 1 FIG. 6 is a schematic sectional view of an induction heating fixing device to which the present invention is applied. As shown in FIG. 6, an induction heating fixing device incorporated in a printer or the like includes a fixing roller 1 rotatably driven in the direction of arrow a and a rotation of the fixing roller 1 provided in pressure contact with the fixing roller 1. And a pressure roller 2 that is driven to rotate. The fixing roller 1 is a cylindrical hollow pipe made of a conductive material, and is made of a conductive material such as a carbon steel pipe, a stainless alloy pipe, or a nickel alloy pipe.
The outer peripheral surface is coated with a fluororesin, and a heat-resistant release layer is formed on the surface. Further, the fixing roller 1 is
More preferably, it is formed from a conductive magnetic member. On the other hand, in the pressure roller 2, a silicon rubber layer 5 which is a surface releasable heat resistant rubber layer is formed around the shaft core 4.

Inside the fixing roller 1, the fixing roller 1
A plurality of coil assemblies 3 for generating an induced current to heat the fixing roller 1 are arranged in the coil assembly 3 such that the fixing roller 1 is rotatable between each coil assembly 3. It is housed in a holder 11 which is fixed with a slight gap therebetween.

Further, as shown in FIG. 7, the coil assembly 3 has a square-shaped through hole, and the bobbin 8 is provided so as to surround the core 10 by inserting the core 10 into the through hole.
A coil 3 is formed by winding a copper wire around the bobbin 8. The coil 3 has a fusion layer and an insulating layer on the surface and has a diameter of 0.
It is wound around the bobbin 8 in the direction along the rotation axis of the fixing roller 1 using a single or litz copper wire of 8 mm.

The core 10 is made of, for example, a ferrite core or a laminated core, and the bobbin 8 is made of, for example, ceramic or heat-resistant insulating engineering plastic, and plays a role of pressing the coil 3 and adjusting its shape.

As shown in FIG. 8, the holder 11 for accommodating the coil assembly 3 has a shape having a plurality of holes penetrating vertically and horizontally around the circumference of a cylinder, and both ends of which are fixed to the apparatus body. Is provided with a protrusion 1a. The holder 11 is made of a heat-resistant insulating material such as PP.
It is made of S (polyphenylene sulfide) or liquid crystal polymer. In the coil assembly 3, for example, the bobbin 8 is inserted into the left and right holes provided in the holder 11, and then the core 10 is inserted into the upper and lower holes, so that the holder 1
Incorporated into 1. The plurality of coils 9 are electrically connected in series in the holder 11, and lead wires 12 for flowing a high frequency current to the coils 9 are provided at both ends of the holder 11.
Has been pulled out.

The fixing roller 1 has sliding bearings formed on both ends thereof and is rotatably attached to the fixing unit frame. 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, a thermistor 6 for detecting the temperature of the fixing roller is provided above the fixing roller 1.

As the control system for supplying a high frequency current to the coil 9 of this fixing device, the control system already described with reference to FIG . 4 or FIG. 5 is used, and the control circuit 50 causes the outer peripheral surface of the upper portion of the fixing roller 1 to operate. The required amount of heat generation (heating output) is determined according to the temperature detected by the thermistor 6 disposed at, and a control signal is output, and a high frequency current flowing through the coil 9 is applied. At this time, if the temperature of the fixing roller 1 becomes abnormally high, the maximum coil voltage detection circuit 55
The output signal from becomes the Lo level, and the inverter circuit 60 is immediately stopped, so that the overheating of the fixing roller 1 is prevented.

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. The sheet 14 is conveyed through the nip portion while the heat of the fixing roller 1 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 portion is naturally separated from the fixing roller 1 or, as shown in FIG. 6, is fixed by a separation claw 7 or a separation guide that is provided so that the leading end of the sheet 14 slides on the surface of the fixing roller 1. It is forcibly separated from the roller 1 and conveyed rightward in FIG. The sheet 14 is conveyed by a paper discharge roller (not shown) and discharged onto the paper discharge tray.

Embodiment 2 Next, an embodiment of another induction heating fixing device to which the present invention is applied will be described. FIG. 9 is a schematic sectional view of the induction heating fixing device of the second embodiment. In the second embodiment, an upper pre-fixing guide 37 as a guide member formed of a conductor is provided as a heat generating member, and a coil assembly for generating an induced eddy current in the upper pre-fixing guide 37. 15a,
Roller pairs 35 and 36 for nipping and conveying the sheet 14
And have. As shown in FIG. 10, the coil assembly 15a includes a core 2a held by the bobbin 1a and a coil 3a, and is attached to a position facing the sheet 14 via an upper pre-fixing guide 37. The roller pairs 35 and 36 are provided immediately downstream of the upper pre-fixing guide 37. Here, the surface of each roller of the roller pair 35 and 36 is coated with a member having releasability to toner, such as fluororesin or silicone rubber.

In the second embodiment, an induction current is generated in the upper pre-fixing guide 37 by the high frequency current flowing through the coil 3a, and the upper pre-fixing guide 37 generates heat. The sheet 14 onto which the toner image has been transferred is fed from the left side of FIG. 6, and is heated in a non-contact manner by the upper pre-fixing guide 37 which has generated heat. At this portion, the toner is softened to some extent, and the toner and the sheet 1
A certain amount of heat is stored in 4. Then sheet 1
4 is fed into the nip formed by roller pairs 35 and 36. Then, due to the pressure in the nip portion and the heat accumulated in the toner and the sheet 14, the toner is removed from the sheet 1.
It is fixed at 4.

In the second embodiment, the high-frequency current flowing through the coil 3a is supplied by the control system already described with reference to FIG . 4 or FIG. When the front guide 37 reaches an abnormally high temperature, the inverter circuit 60 is immediately stopped to prevent overheating.

[0058]

According to the present invention as described above, according to the present invention, the
Induction processing that can arbitrarily control the heating output of the heating element
In the thermal fixing device, changes at the same time as the temperature of the heated object
The change in coil voltage
Value to detect abnormally high temperature of the heated object, and
Stop the high frequency power supply circuit that supplies alternating current
Since it was decided to use heat transfer compared to conventional safety devices.
Measures against abnormally high temperature in induction heating fixing device
As a safety mechanism for heat transfer and delay due to heat transfer
It is possible to use materials with lower heat resistance than
It is possible to reduce the equipment cost.

[0059]

[0060]

[0061]

[Brief description of drawings]

FIG. 1 is a block diagram for explaining a premise form of an induction heating fixing device of the present invention.

FIG. 2 is a diagram showing a relationship between a temperature of a heated object and a coil voltage.

FIG. 3 is a time chart for explaining the operation in the above-described premise .

Is a block diagram for explaining the implementation of the form of the induction heat fixing apparatus of the present invention; FIG.

FIG. 5 is a block diagram for explaining another embodiment of the induction heating fixing device of the present invention.

FIG. 6 is a sectional view showing an embodiment of an induction heating fixing device to which the present invention is applied.

7 is a perspective view for explaining the coil assembly shown in FIG.

FIG. 8 is a perspective view showing the holder shown in FIG.

FIG. 9 is a sectional view showing another embodiment of the induction heating fixing device to which the present invention is applied.

10 is a perspective view illustrating the coil assembly shown in FIG. 9. FIG.

FIG. 11 is a diagram showing response characteristics of a thermostat bimetal and a thermal fuse with respect to a temperature rise of an object to be heated.

[Explanation of symbols]

1 ... Fixing roller, 2 ... Pressure roller, 3, 15a ... Coil assembly, 9, 3a ... Induction heating coil, 10, 2a ...
Core, 30 ... Object to be heated, 37 ... Pre-fixing guide, 44 ...
Switches, 50, 50a, 50b ... Control circuit, 51 ... Timer circuit.

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 13/20 G03G 15/20 H05B 6/00-6/44

Claims (3)

(57) [Claims] 1. A toner image formed on a recording medium
A fixing device for fixing to a recording medium, A heated object made of a conductive material and close to the heated object
Are placed in the heating element and generate an induced current in the heated object to generate heat.
A coil for A control voltage for arbitrarily controlling the heating output of the object to be heated.
Heating output control means for outputting pressure, The coil according to the control voltage from the heating output control means
A high-frequency power supply circuit that supplies alternating current to Coil voltage detecting means for detecting the voltage of the coil, Maximum value of coil voltage detected by the coil voltage detection means
Is compared with the control voltage output by the heating output control means.
For example, when the voltage becomes lower than the value determined,
High frequency power supply circuit stopping means for stopping the operation of the wave power supply circuit
And an induction heating fixing device. 2. The high frequency power supply circuit has a switch for supplying an alternating current to the coil, and a timing determination means for determining the on / off timing of the switch,
Claim 1, wherein the timing decision unit is made of a timer circuit, on the switch by measuring the time in response to the control voltage from the timer circuit the heating output control means, and determines the timing of the off The induction heating fixing device described. 3. The high-frequency power supply circuit has a switch for supplying an alternating current to the coil, and timing determination means for determining the on / off timing of the switch,
The timing determination means has a coil current detection means for detecting a coil current of the coil, converts the coil current detected by the coil current detection means into a voltage value, and outputs the control voltage from the heating output control means. in comparison, on of the switch, the induction heat fixing apparatus according to claim 1, wherein the determining the timing off.