JPH07181821A - Fixing device - Google Patents

Abstract

PURPOSE:To make it possible to quickly heat a fixing device quickly heat and to improve the efficiency without generation of heat in a field coil by applying a high frequency current to the field coil in the pressurizing means of the lower part and a high-frequency magnetic field to the magnetic metal surface of the upper part so as to generate the heat. CONSTITUTION:When a high frequency current from a high frequency converter 30 is supplied to a coil 22-2 wound on the core 22-1 of a field coil plate included in a pressure roller 21, a high frequency magnetic flux returning to the core 22-1 via a magnetic metal 24 from the core 22-1 is formed, and eddy current is generated in the magnetic metal 24 and its nip surface is heated because of Joule heat by the resistance of metal. Since the core 22-1 and the magnetic metal 24 face each other in parallel with the nip surface 28 and with a gap length sufficiently shorter than a magnetic flux path length, the magnetic metal 24 can be efficiently heated. Since the field coil 22-2 is provided in the lower part of the magnetic metal 24 as a heating element, the coil 22-2 is never heated and the efficiency is enhanced.

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 devices, electrostatic recording devices and the like.

[0002]

2. Description of the Related Art In electrophotographic printers, a heating method, particularly a heat roller fixing method, is widely used for fixing an unfixed image. In this system, basically, a heating roller and a lower pressure roller that is in pressure contact with the heating roller are integrally configured (both of them are referred to as a fixing roller), and a recording material supporting an unfixed image is passed between them. It is to fix.

FIG. 8 shows a block diagram of such a fixing device. In the apparatus shown in the figure, the recording material 51 supporting the unfixed powder toner image conveyed in the direction of the arrow is conveyed by the conveying belt 52. On the other hand, the motor 55 connected to the upper heating roller 53 and the lower pressure roller 54 drives both rollers to rotate, so that the recording material 51 conveyed to the nip portion of both rollers is heated and pressurized at the nip portion. It is fixed.

Reference numeral 56 is a halogen heater which generates heat when supplied with electric power, and is provided with a switching control element so that the resistance value of a thermistor 58, which is a temperature detecting element provided in contact with the surface of the heating roller, is constant with respect to a reference value. AC
Energization is controlled.

Reference numeral 59 is a cored bar, which is provided to maintain the rigidity of the entire roller against the pressure applied between the upper and lower rollers and to average the temperature distribution. 61 is heat resistant rubber,
It is attached to the outside of the core to improve the fixing property.

[0006]

However, in this type of apparatus, in order to prevent the so-called offset phenomenon in which the toner is transferred to the heating roller, it is necessary to maintain the heating roller at an optimum temperature, and the heat capacity of the heating element is reduced. There is a problem in that the larger the heat capacity, the longer the time for raising the temperature to a predetermined temperature and the longer the standby time. Further, in the above-mentioned conventional example, since the temperature detecting element was brought into contact with the rotating roller, the temperature detecting element floated, the fixing roller was scratched, resulting in deterioration of image quality, and toner adhered to the scratch. There was a risk of ignition because accurate temperature detection was hindered.

The present invention solves the above problems, remarkably improves the life of the fixing device, increases the speed, and enhances the safety.

[0008]

According to the present invention, a high frequency current is applied to a field coil and a high frequency magnetic field is applied to a metal surface facing the field coil to generate Joule heat due to an eddy current. By fixing the fixing device to heat it, it becomes possible to perform rapid heating.

Further, by installing the field coil in the lower portion, it is possible to improve the efficiency without generating heat in the field coil.

Further, by forming the temperature detecting element on the magnetic metal plate facing the field coil, it is possible to prevent the temperature detecting element from floating and to provide a highly reliable fixing device without damaging the fixing roller. Is possible.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram showing the structure of the fixing device of the present invention, but the drive section is omitted because it is the same as the conventional example.

In the figure, 21 is a pressure roller made of a non-metallic material, 22 is a field coil plate contained in the pressure roller 1, 23 is a heat-resistant film made of polyester or the like, and 24 is a high magnetic permeability and appropriate. Magnetic metal with a high specific resistance,
Reference numeral 25 is a support member that supports the magnetic metal 24 with heat insulation and also supports the film guide 26. 23 to 26 integrally perform the same function as that of the conventional fixing roller, and the unfixed toner on the recording material 27 is softened and melted and fixed by the pressure roller.

FIG. 2 is an enlarged view of the vicinity of the nip portion shown in FIG. The field coil plate 22 is an E type and is a pressure roller 21.
The surface facing the inner surface of the has a surface parallel to the nip image 28,
It is composed of a core 22-1 made of a magnetic material having high magnetic permeability and low loss, and a coil 22-2 wound around the central core of the core 22. Further, the magnetic metal 24 has a surface opposed to the pressure roller parallel to the nip surface, is mounted in close proximity to the core 22-1, and a thermistor 29 is mounted on the opposite surface. Reference numeral 30 is a high frequency converter for supplying high frequency power to the heating body.

Incidentally, this figure is a sectional view, and the core 22-
1. The magnetic metal 24 has a length in the direction perpendicular to the paper surface.

In the above structure, when a high frequency current is supplied to the coil 22-2 from the high frequency converter 30, a high frequency magnetic flux returning from the core through the magnetic metal to the core is formed, and an eddy current is generated in the magnetic metal 24. , The nip surface of the magnetic metal 24 is heated by Joule heat due to the resistance of the metal. In this configuration, the core 22-1 and the magnetic metal 24 are opposed to each other with the gap length parallel to the nip surface 28 and sufficiently shorter than the magnetic path length, so that the magnetic metal can be efficiently heated. .

Next, regarding the fixing device of the present invention, a temperature control method using a high frequency converter will be described.

FIG. 3 is a block diagram of the temperature control circuit, FIG. 4 is an operation diagram of the PWM generation circuit, and FIG. 5 is an operation of the high frequency converter section.

In FIG. 3, the AC power source is rectified by the rectifier circuit 2, and a full-wave rectified waveform as shown in FIG. The fixing device shown in FIG. 2 is represented by an equivalent circuit as shown by the inherent capacitance 6 and inductance 7. The PWM generator circuit, as shown in FIG.
A pulse wave is generated by internally generating a triangular wave, inputting a DC voltage from an adder 11 to be described later, and slicing the triangular wave with the DC voltage. That is, when the DC voltage from the adder 11 is low, the pulse width is long as shown in the figure, and when it is high, the pulse width is short as shown in (c).

The high frequency converter 5 includes a PWM generation circuit 4
The fixing device 3 is driven by the pulse width modulation wave supplied from the above and the full-wave rectified waveform described above.

In FIG. 5, (b), (c) and (d) show output waveforms of the high frequency converter 5 in which the minute region 41 of (a) is enlarged. In the same figure (b), when the input pulse falls, the output 5-1 of the high-frequency converter has a damping vibration having a resonance frequency determined by the inherent capacitance 6 and inductance 7 of the fixing device with respect to the rectified voltage value 42 at that time. The waves are superposed and fall to 0V when the pulse rises. In (b), as an example, the repetition frequency and the resonance frequency are selected so that 1 cycle is obtained when the negative pulse width is maximum.

FIGS. 3C and 3D show the case where the negative pulse width is the center value and the minimum value, respectively. (C) is a 3/4 cycle, (D) is a half cycle.

As described above, the temperature rising speed of the fixing device can be controlled by changing the electric power supplied to the fixing device 3.

Next, details of the actual power control will be described.

The voltage / current converter 8 converts the current flowing through the fixing device 3 via the high frequency converter 5 into a voltage. The multiplier 9 calculates the multiplication result of the voltage applied to the fixing device 3 and the current converted into the voltage, that is, the power supplied to the fixing device, and supplies it to the subsequent differential amplifier 10. Differential amplifier 10
Is applied to one input of the adder 11, and the output of the constant temperature control circuit 12 is applied to the other input of the adder 11. The output of the adder 11 is the PWM generation circuit 4 as described above.
And becomes a DC voltage input to form a feedback loop.

The constant temperature control circuit 12 receives a voltage ref1 corresponding to the target temperature and a voltage Vt from the thermistor corresponding to the current temperature as inputs, and maintains the constant temperature, as in the temperature control of the conventional example. , It does not work when the temperature is raised.

If a fixed voltage Vref2 (corresponding to the target power) is set at the other input of the differential amplifier 10, the output of the multiplier 9, that is, the fixing device 3 is assumed.
When the power supplied to F is smaller than the target power, the difference amplifier 1
The output of 0 increases, and the output pulse width of the PWM generation circuit becomes smaller (the negative pulse width becomes larger) as shown in FIG. As a result, the electric power supplied to the fixing device 3 increases as shown in FIG. Conversely, the output of the multiplier 9, that is, the fixing device 3
If the power supplied to the differential amplifier is greater than the target power, the differential amplifier 1
The output of 0 decreases and the output pulse width of the PWM generating circuit increases (the negative pulse width decreases) as shown in FIG. As a result, the electric power supplied to the fixing device 3 is reduced as shown in FIG. That is, the fixing device 3 is started up with the target power set by Vref2, in other words, Vref.
The value of 2 can control the rising speed.

Actually, the control of the intermediate process between the above-mentioned start-up process and the above-mentioned constant temperature control is performed as follows.

The voltage Vref1 corresponding to the target temperature and the voltage Vt from the thermistor corresponding to the current temperature are supplied to the proportional operating element l3 composed of a differential amplifier and a coefficient device, and the output of the proportional operating element l3 consists of an integrator. Integral action element 1
It is input to the above-mentioned difference amplifier 10 via 4. That is,
Vref2 is made variable and a well-known PI (proportional / integral) operation is performed. By doing so, a large amount of electric power is supplied to the fixing device 3 at the initial stage of rising, the fixing device 3 starts up at a high speed, becomes gradually closer to the target value, and when the target value is reached, control is entrusted to the constant temperature control system.

The priority of the rising control system and the constant temperature control system can be realized by using a direction control element such as a diode in the adder 11.

As described above, temperature control without ripples can be performed as shown in FIG. Further, by manipulating the coefficient of the proportional action element 13, it is possible to control the rising speed.

In the fixing device having the above structure,
The magnetic metal has a small heat capacity and can instantly reach the fixing temperature even when energized only when necessary. The toner image made of the heat-melted toner on the recording material 27 is first transferred to the heat resistant sheet 2.
It is heated by the magnetic metal 24 through 3, and at least its surface layer portion is completely softened and melted. Then, before the toner image is separated from the magnetic metal 24 and reaches a separation roller (not shown), the toner image naturally radiates heat to cool and solidify, and the heat-resistant sheet 23 separates from the recording material 27.

Further, since the field coil is provided below the magnetic metal as the heating element, it is not heated and the efficiency is high. Further, since the temperature detecting element is formed on the magnetic metal, highly reliable temperature detection / control can be performed without contacting the sliding surface.

<Other Embodiments> FIG. 7 is a block diagram of the fixing device in the second embodiment of the present invention. The difference from FIG. 1 is that there is no magnetic metal 24, and instead, a heat resistant film 33 such as polyimide is deposited with magnetic metal. In this embodiment, since the nip surface of the heat-resistant film 33 on which the magnetic metal is vapor-deposited is directly heated, it is possible to further improve the efficiency. Other advantages are the same as those of the first embodiment.

In the above embodiment, the heating means having the magnetic metal and the heat-resistant film has been described as an example, but a heating roller may be used.

[0036]

As described above, according to the present invention, a high frequency current is applied to a field coil and a high frequency magnetic field is applied to a metal surface facing the field coil to generate Joule heat due to an eddy current. By fixing the fixing device to heat it, it becomes possible to perform rapid heating.

Further, by installing the field coil on the lower surface, it is possible to improve the efficiency without generating heat in the field coil.

Further, by forming the temperature detecting element in the metal plate facing the field coil, the temperature detecting element can be prevented from floating, and a highly reliable fixing device can be provided without damaging the fixing roller. It will be possible.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a fixing device according to a first embodiment of the present invention.

FIG. 2 is a detailed view of the fixing device according to the first embodiment of the present invention.

FIG. 3 is a block diagram of temperature control according to an embodiment of the present invention.

FIG. 4 is an operation diagram of the apparatus according to the embodiment of the present invention.

FIG. 5 is an operation diagram of the apparatus according to the embodiment of the present invention.

FIG. 6 is a temperature characteristic diagram of the device according to the first embodiment of the present invention.

FIG. 7 is a configuration diagram of a fixing device according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram of an example of a conventional fixing device.

[Explanation of symbols]

21 ... Pressure roller 22 ... Field coil plate 22-1 ... Core 22-2 ... Coil 23 ... Heat-resistant film 24 ... Magnetic metal 25 ... Support 26 ... Guide 27 ... Recording material 28 ... Nip surface 29 ... Temperature detector 30 … High frequency converter

Claims (4)

[Claims] 1. A fixing device comprising a heating means and a pressing means for fixing a recording material between the heating means and the pressing means, wherein a high frequency current is applied to a field coil provided in the pressing means installed at a lower portion. A fixing device, which generates heat by applying a high-frequency magnetic field to a magnetic metal surface provided on an upper portion of the magnetic coil so as to face the field coil. 2. The fixing device according to claim 1, wherein the temperature detecting element is formed on the magnetic metal. 3. A heat-resistant film and an interface, one surface of which is in contact with a magnetic metal, the other surface of which is in contact with a recording material supporting a toner image, and which moves along a guide attached to a heat-resistant support material for fixing the magnetic metal. 2. The fixing device according to claim 1, further comprising a pressurizing unit including a magnetic coil. 4. One surface contacts a heat-resistant support material having a guide attached, and the other surface contacts a recording material supporting a toner image,
2. The fixing device according to claim 1, further comprising a heat-resistant film having a magnetic metal vapor-deposited thereon, which moves along the guide, and a pressing means including a field coil.