JPH08220912A - Fixing device by electromagnetic induction heating - Google Patents

Abstract

PURPOSE: To solve such problems that it is difficult to control the temperature of the roller surface constant and also the heat efficiency is low because of not only heating a recording paper but also heating the whole roller, as for a system for heating the heating roller by a halogen heater arranged inside the heating roller. CONSTITUTION: As for a thermal fixing device for a printer using an electrophotographic copying process, and for fixing a toner image transferred to a print paper on the recording paper, the device is provided with an energizing coil 9, a roller 1 constituted of magnetic material, or metal and arranged so as to magnetically couple to the generated magnetic field of the energizing coil, a high frequency converter 12 for supplying a high frequency power to the energizing coil, and the device is also provided with a means 10 for always concentrating a magnetic flux on a part near the recording paper P irrespective of the rotation of the roller, and only the roller part required for fixing is heated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device for a developer (toner) image formed in an electrophotographic process, and more particularly to a heat fixing device using electromagnetic induction heating as a heating means.

[0002]

2. Description of the Related Art Conventionally, fixing of a printer apparatus using an electrophotographic process is performed by passing a recording material supporting an unfixed image between the heating roller and a pressure roller in pressure contact with the fixing roller. It is something to do. In this configuration, the electric power supplied to the halogen heater, which is usually a heat source, causes the heater to generate heat and emit light, and the heat heats the roller generally made of aluminum metal by radiation and convection.

This aluminum metal roller serves to conduct the received heat to the entire roller without any temperature difference. The roller having a uniform temperature distribution in this way heats and melts the unfixed toner on the recording paper through the heat-resistant rubber coated on the upper layer, so that the unfixed toner is impregnated into the recording paper medium and fixed.

Usually, a halogen heater which is a heat source is a glass-sealed slender rod-shaped halogen heater which is passed through a hollow portion in the center of the roller. The halogen heater is usually connected to an AC power source (line input power source) through a switching control element. Current is applied to heat the roller. Therefore, the fixing roller temperature control detects the roller temperature by a temperature detecting element arranged in the vicinity of the roller, generally a thermistor thermosensitive element, and a switching element provided between the AC power source and the halogen heater, for example, a triac. Therefore, on / off control is performed,
It is controlled so that the target constant temperature can be obtained.

FIG. 15 shows an image heating and fixing device for carrying out heating and fixing. In the apparatus shown in FIG. 15, the recording material P supporting the unfixed powder toner image, which is conveyed in the arrow direction, is
It is conveyed by the conveyor belt 71 and passes through the sensor 72.
As a result, the motor 75 connected to the heating roller 73 and the pressure roller 74 starts driving, and the heating roller 7
3 and the pressure roller 74 start rotating. Then, the recording material P is conveyed to the nip portion between the heating roller 73 and the pressure roller 74, is heated and pressurized in the nip portion, is discharged, and passes through the sensor 76. Then sensor 7
The signal 6 changes from on to off, and the driving of the motor 75 is stopped.

The heating at the nip portion is performed by the heating roller 7
Electric power is supplied to the halogen heater 77 included in No. 3 to generate heat. The energization of the halogen heater 77 is controlled so that the resistance value of the thermistor 78, which is a temperature detecting element provided in contact with the surface of the pressure roller, is constant with respect to the reference value. As a result, the heating roller 73 is configured to maintain the temperature required for fixing and perform good fixing.

Further, if the temperature of the heating roller 73 is always maintained at a temperature required for fixing, power consumption increases and abnormal heating of the roller may occur. The temperature at the time of stop is controlled to be lower than that at the time of rotation.

[0008]

In the conventional fixing system,
Since the heating roller is heated by the halogen heater placed inside it, there are heat transfer processes such as radiation, convection, and conduction before the heat of the halogen heater is transferred to the heating roller, and the responsiveness during temperature control is extremely high. Bad for Further, the heater control method uses an on / off control method by a switching control element provided between the AC power source and the heater, such as a triac, but with such a configuration, temperature control is very difficult and complicated. It becomes something.

Details of the conventional heater control will be described below.

First, when the power is turned on, since the temperature of the fixing roller is lower than the target temperature, the control circuit turns on the switching element to supply the maximum power. The temperature control feedback turns on when the detected value is smaller than the target temperature.Therefore, even if the temperature rises and reaches the vicinity of the target temperature, the control circuit turns on the switch. Since the power is still being held, the maximum power continues to be supplied, which is the same as when starting up.Even if the switch is turned off when the temperature reaches the target temperature, the target temperature is far exceeded because of the power supplied up to that point. , Overshoot.

Such overshoot is about 5% of the target temperature when the above simple control means is used.
It is known that the degree will occur. The above is the control point in the conventional fixing method.

In the conventional fixing method, as described above, the halogen heater arranged inside the roller and on the central axis heats the entire circumferential surface from the inside of the roller. In this case, much heat escapes from the roller surface in addition to heating the paper, and the thermal efficiency at the time of fixing is lowered.

[0013]

In order to solve the above-mentioned problems, the fixing device by electromagnetic induction heating of the present invention comprises:
In a thermal fixing device for fixing a toner image transferred on a print paper to a recording paper of a printer device using an electrophotographic process, it is arranged so as to be magnetically coupled to an exciting coil and a magnetic field generated by the exciting coil. Roller having a magnetic material or metal and a high-frequency converter for supplying high-frequency power to the exciting coil, and means for always concentrating the magnetic flux near the recording paper regardless of the rotation of the roller. Is characterized by. In general, the fixing roller heater has a magnetic metal or a roller made of metal, a magnetic field generating coil, and a high-frequency switching means.

A high frequency switching current is passed through the magnetic field generating coil to magnetically couple the generated high frequency magnetic field to the metal inside the fixing roller, and the magnetic metal is heated by the eddy current loss caused by the magnetism and transferred to the fixing roller.

Therefore, the temperature control is to control the amount of magnetic flux, and the ripple of the control temperature is minimized by making the power control linearly and continuously variable.

Further, in the magnetic path consisting of the core, which is the heating element, and the coil, the open portion of the magnetic circuit is directed to the portion of the heating roller near the recording paper so that the magnetic flux is concentrated to optimize the heat generating portion. Limit to position only.

[0017]

【Example】

(Embodiment 1) FIG. 1 is a schematic cross-sectional view of an induction heating fixing device and its vicinity which best show the features of the present invention. In FIG. 1, 1 is a fixing heating roller, 2 is a fixing pressure roller, P is a recording paper in the conveying process after the unfixed toner is transferred, and 4 is a conveying for conveying the recording paper to a fixing device. The rollers 5 are photosensitive drums for forming an electrophotographic image, and 6 is a transfer electrode for transferring the toner image formed on the photosensitive drums to a recording paper. Reference numeral 7 denotes a rotary bearing that is integrated with the heating roller and rotates together with the heating roller, and is rotatably coupled to the fixed central shaft 8. Reference numeral 9 is an exciting coil winding, and 10 is a core.

The winding of the exciting coil is, as shown in FIG.
This is a structure in which a conductive wire is wound around the middle leg of the elongated core 10 having an E-shaped cross section. Reference numeral 11 denotes a joint that connects the core and the coil (which will be referred to as a heating body) with the central shaft 8. Further, FIG. 2 is a diagram showing only the heating roller portion, and the reference numerals of the respective portions in FIG. 2 are the same as those in FIG. In FIG. 2, reference numeral 12 is a high frequency converter for supplying high frequency power to the heating element.

In FIG. 1, the basic operation part of the electrophotographic apparatus is omitted because it is well known.

An image formed by toner in a series of electrophotographic processes is attracted and transferred to the transfer paper P by the high voltage transfer electrode 6. This transfer paper or recording paper is conveyed to a fixing unit by a conveying roller at a constant electrophotographic process speed, and is guided by a nip portion composed of a heating roller 1 of the fixing roller and a pressure roller 2 to generate heat. The toner on the transfer paper is melted by the pressure, soaks into the fibers of the paper, and is fixed.

As described above, the material of the heating roller has a relatively high magnetic permeability μ such as a magnetic material (magnetic metal),
A material having an appropriate resistivity ρ is used. For example, magnetic stainless steel. Further, even non-magnetic materials, conductive materials such as metals can be used by making the material into a thin film or by increasing the frequency of the converter.

Details of the high frequency converter portion for supplying the high frequency electric power to the field coil will be described later. A temperature detecting element for heat detection, for example, a thermistor is used.

In the device configuration as described above, the high frequency converter 12 will be described later in detail when the device is in operation.
When a high-frequency current is supplied from the field coil 9, the field coil 9 generates a high-frequency magnetic field. Since this coil is used at high frequencies, a litz wire was used as the thin wire, and a heat resistant one was used for the coating in order to transfer heat to the winding. Further, the core 10 is a magnetic material core having high magnetic permeability and low loss, and is made of ferrite or permalloy having high magnetic permeability and low loss. In the case of an alloy such as Permalloy, the eddy current loss in the core increases at high frequencies, so a laminated structure may be used. The core increases the efficiency of the magnetic circuit,
It is used for magnetic shielding. The magnetic circuit portion of the coil and the core may be air-core if there is a means capable of providing a sufficient magnetic shield. The high frequency magnetic field generated as described above is applied to the heating roller 1.

The heating roller may be processed on the roller itself or coated with rubber or the like in order to make the μ of the portion in contact with the paper (this is the friction coefficient μ) appropriate.

When the magnetic field is applied to the heating roller,
In the metal (or magnetic material) of the heating roller, an eddy current is generated by the magnetic field and the resistance of the metal causes loss (Joule loss).
And become feverish. Since it is a high frequency magnetic field, the roller is heated from the surface close to the field coil. This heat causes the toner attached to the recording material to be thermally fixed.

FIG. 4 shows how the high frequency converter supplies the switching power. In FIG. 4, the commercial alternating current supplied from the line is rectified by the double-wave rectifier and supplied to one end of the field coil. The supplied electric power is high-frequency switched by a switching element (FET). This switching timing is synchronized when the voltage or current between the source and drain of the FET becomes 0 in order to avoid switching loss, improve efficiency, and eliminate switching noise. This is a method called a resonance type switching operation in a DC-DC converter. Also, the fixing roller is
It can be shown by the same equivalent circuit as the switching transformer in the switching power supply. This will be described in detail later with reference to FIG.

In FIG. 4, reference numeral 206 denotes a control IC, which represents a part of the circuit configuration for explaining the operation. The heating body metal 1 is excited and heated by the heating exciting coils 100 to 103, and the heated heating body metal is excited. The generated temperature of is converted into a voltage by a thermistor. Therefore, the above detection voltage is applied to the terminal 3
1 (FIG. 5) is entered as the temperature.

Reference numerals 31 to 56 in FIG. 5 are descriptions of the control IC in FIG. That is, the temperature detecting means 204
The temperature information (voltage value) is compared with the reference voltage 31, and the ON time (ON duty) of the switch element is changed to adjust the temperature.

The basic cycle is the charging time (determined by the transistors 40, 41 and 43 and the resistors 50 and 51) to the capacitor 35 and the discharging time (from the transistors 42 and 44 and the resistors 52 and 55). Will be determined). Immediately after the power is turned on (at the time of startup), a so-called soft start function is provided to gradually increase the on-time from 0.

When the detected voltage is input to the terminal 31 as described above, the detected voltage is compared and amplified with the target temperature 218 and the converter 32 performs pulse width modulation according to the voltage input. This pulse width modulation is applied to the heating field coils 100 to 103.
Is driving the gate of the FET 201 which is switching-driven, and the supply power (switching waveform) thereof is varied.

FIG. 6 shows characteristic waveforms of each part. In the figure, 250 indicates an AC line voltage. This is a commercial AC waveform, which is 280 V _PP and a frequency of 50 to 60 Hz. In the figure, reference numeral 251 is a voltage waveform when the AC line voltage is rectified and switched. Since the switching frequency of the converter device is higher than the AC line voltage, such a waveform is obtained.

252 and 253 in the figure are obtained by expanding the switching waveform in the time axis direction and extracting only one switching period. As can be seen by comparing these two waveforms, the on-time is adjusted by the line voltage to prevent temporal heating unevenness, suppress temperature ripples, and realize uniform heating.

By heating with such an apparatus, as shown in FIG.
It is possible to realize heating without temperature ripple and overshoot with respect to the target value as shown in.

With the above-described structure, the control is performed by the drive waveform (high frequency) modulation of the field coil, so that the linear temperature control is achieved in the target temperature range.

The reason why the linear control is regarded as an important function is that a normal fixing device uses a high-power halogen heater with respect to a target value temperature as described in the conventional example.
By performing ON / OFF control (control in 1/2 cycle units of commercial AC) depending on whether or not the specified temperature is exceeded,
It was configured to lead to the specified temperature. Even if the rate of temperature rise or overshoot is managed and the switching state is changed in a complicated manner, it is impossible to eliminate the temperature ripple determined by the transfer element due to the heat capacity of the heating element. Therefore, the temperature control by the waveform control of the switching state at the high frequency level works effectively as a solution to the above problem.

When the rectified wave ripple voltage applied to one end of the coil is subjected to switching control by the high frequency switching element, electric power is stored as magnetic in the exciting inductance of the field winding and the heating metal corresponding to the load is also stored. Magnetically coupled, an electric current flows by magnetism, and Joule heat is generated and heated due to resistance loss of the metal.

As described above, in the above-mentioned structure, since the heating element is the metal drum itself, the heat transfer model from the heat source has a very monotonous structure, and besides the temperature control can be performed easily, the magnetic metal can be easily controlled. Since the distance where the magnetic flux intersects is short and local heating is possible, it saves power compared to heating the entire roller, and because the magnetic path is short, there is little magnetic leakage and efficiency is high. Since the environmental impact is small and the magnetic unevenness is small, the temperature unevenness is also small and it is possible to reduce the unevenness of the fixed image.

(Embodiment 2) FIG. 8 shows the vicinity of a fixing portion of an electromagnetic induction heating fixing device according to a second embodiment of the present invention. In FIG. 8, 1 is a fixing heating roller, 2 is a fixing pressure roller, 3 is a recording paper immediately before entering the fixing process,
Reference numeral 4 is an exciting coil, 5 is a core, and 6 is a high frequency converter for supplying high frequency power to the exciting coil. The same materials as those described in the first embodiment of the present invention are used for the material of each part. In this embodiment, the fixing device using the same principle as that of the above embodiment is realized by placing the heating body outside the roller.

FIG. 8 shows a coil, which is a heating element, and a magnetic circuit portion of the core, which are arranged on the opposite side of the roller with the recording paper sandwiched therebetween. The recording paper is fed at the electrophotographic process speed in the direction of the arrow in the figure. Although not shown in the figure, the recording paper may not be passed between the heating element (core and coil) facing the roller. (It passes only between the fixing heating roller and the fixing pressure roller.) By thus constructing the core and coil on the outside of the roller, the core and coil supporting parts can be simplified, and heat conduction to the magnetic circuit can be further achieved. It has realized to suppress the heat dissipation and to enhance the heat dissipation effect.

(Embodiment) FIG. 9 shows a heating body (core and coil) of an electromagnetic induction heating fixing device according to a third embodiment of the present invention.
It shows the structure of. In FIG. 9, 1 is a coil and 2 is a core. As shown in FIG. 9, the coil is divided in the major axis direction and wound to obtain a heating width corresponding to the size of the paper such as wide paper. In the structure of FIG. 9, a magnetic field in the direction of the arrow is generated when a direct current is applied, and the magnetic field generated by the coil is in the same direction, so that torque is generated, which causes vibration and the like. The structure for preventing this is shown in FIG. In the structure shown in FIG. 10, the magnetic fields generated by the coils adjacent to each other have different directions, and therefore the torques cancel each other out.

(Embodiment 4) FIGS. 11 and 12 show a structure around a heat fixing roller of an electromagnetic induction heat fixing apparatus according to a fourth embodiment of the present invention. In FIG. 11, 1 is a fixing heating roller, 2 is an exciting coil, and 3A is a low-loss core, which is used to concentrate magnetic flux. This uses a laminated structure of ferrite or permalloy which is the same low loss material as the core described in the first embodiment. Four
Is a lossy core that becomes a heating element. In the case of this structure, the fixing heating roller 1 does not have to be made of metal, and may have a small thickness. The heating element may be arranged outside the roller. Although not shown in the figure, the roller is composed of a thick plate of a high magnetic permeability material (such as a magnetic metal) having the same high magnetic loss as in Example 1 above, and this is shown in FIG.
Alternatively, the heating elements 4 of 12 and 12 may be used instead. Reference numeral 5 is a high frequency converter for supplying high frequency power to the exciting coil.

This structure has a simple structure and is low in cost. Further, the magnetic circuit can be designed with a high degree of freedom, magnetic leakage can be reduced, and heating can be performed uniformly. (Embodiment 5) FIG. 13 shows a structure around a heat fixing roller of an electromagnetic induction heat fixing apparatus according to a fifth embodiment of the present invention. In the figure, 1 is a fixing heating roller and 2 is a fixing heating roller.
Is an exciting coil, and 3B is a bobbin for fixing the exciting coil. Reference numeral 4 is a high frequency converter for supplying a high frequency power to the exciting coil. In FIG. 13, the fixing heating roller 1 has a high magnetic permeability and a large volume resistivity. With this structure, there are many magnetic leaks,
In addition to providing a shield, the diameter of the roller is made smaller and the thickness of the roller is made larger in order to shorten the magnetic path, thus preventing a decrease in efficiency. The direction of the magnetic field in this structure is as shown in the figure. This makes it possible to uniformly heat the entire roller.

(Sixth Embodiment) FIG. 14 shows a structure around a heat fixing roller of an electromagnetic induction heat fixing apparatus according to a sixth embodiment of the present invention. In the figure, 1 is a fixing heating roller, 2 is an exciting coil, and 3C is a core. As shown in the first embodiment, this core is formed in a drum shape with a laminated structure of ferrite and permalloy having a small loss. Further, the roller portion, which is a heating element, is made of the same material as the roller shown in Example 1, which has high magnetic permeability and high magnetic loss. In this configuration, the magnetic field is generated in the direction of the arrow in the figure. With this configuration, the entire roller can be heated uniformly, and the magnetic leakage can be made very small.

[0044]

As described above, according to the present invention, the heating element is the drum itself, and the magnetic flux is concentrated on the portion of the heating roller near the recording paper, whereby the efficiency at the time of heat fixing is improved. I realized that I got a good result. In addition, the structure that eliminates the magnetic flux unevenness achieves uniform heating without temperature unevenness.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a heating roller portion of the first embodiment of the fixing device according to the present invention.

FIG. 3 is a diagram showing a core portion of a first embodiment of a fixing device according to the present invention.

FIG. 4 is a diagram showing a heating circuit of the first embodiment of the fixing device according to the present invention.

FIG. 5 is a control I of the first embodiment of the fixing device according to the present invention.
Diagram showing details of C

FIG. 6 is a diagram showing voltage waveforms of the first embodiment of the fixing device according to the present invention.

FIG. 7 is a diagram showing a temperature control state of the first embodiment of the fixing device according to the present invention.

FIG. 8 is a diagram showing a second embodiment of the present invention.

FIG. 9 is a diagram showing a third embodiment of the present invention.

FIG. 10 is a diagram showing a modification of the third embodiment of the present invention.

FIG. 11 is a diagram showing a fourth embodiment of the present invention.

FIG. 12 is a diagram showing a modification of the fourth embodiment of the present invention.

FIG. 13 is a diagram showing a fifth embodiment of the present invention.

FIG. 14 is a diagram showing a sixth embodiment of the present invention.

FIG. 15 is a diagram showing an example of a conventional heat fixing device.

[Explanation of symbols]

1 ... Heating roller 2 ... Pressure roller 3, 10 ... Core 8 ... Shaft 9 ... Coil 12 ... High frequency converter 15 ... Photosensitive drum

Claims (5)

[Claims] 1. A thermal fixing device for fixing a toner image transferred on a print paper to a recording paper of a printer device using an electrophotographic process, wherein an exciting coil and a magnetic field generated by the exciting coil are magnetically It has a roller made of magnetic material or metal arranged so as to couple with it, and a high-frequency converter that supplies high-frequency power to the above-mentioned exciting coil, and regardless of the rotation of the roller, the magnetic flux is always concentrated near the recording paper. A fixing device by means of electromagnetic induction heating, characterized in that it has means for making it possible. 2. As a means for concentrating the magnetic flux, a magnetic path cross-sectional area provided so as to intensively induce the magnetic flux in the heating metal is more preferable than a magnetic path cross-sectional area contained in the coil of the exciting coil. 2. The structure according to claim 1, wherein the structure is large.
A fixing device by the electromagnetic induction heating described. 3. A thermal fixing device for fixing a toner image transferred on a print paper to a recording paper of a printer device using an electrophotographic process, wherein an exciting coil and a magnetic field generated by the exciting coil are magnetically applied. An electromagnetic wave characterized by having a roller made of a magnetic material or a metal arranged so as to couple with each other, and a high frequency converter for supplying high frequency power to the exciting coil, and forming a magnetic path in the circumferential direction of the roller. Fixing device by induction heating. 4. An exciting coil and a magnetic field generated by the exciting coil in a thermal fixing device for fixing a toner image transferred on a print paper to a recording paper in a printer using an electrophotographic process. Electromagnetic induction heating characterized by having a roller made of a magnetic material or a metal arranged as described above, and a high-frequency converter for supplying high-frequency power to the exciting coil, and the magnetic field intersects the roller in a vertical direction. Fixing device by. 5. An exciting coil and a magnetic field generated by the exciting coil in a thermal fixing device for fixing a toner image transferred on a print paper to a recording paper in a printer using an electrophotographic process. Fixing by electromagnetic induction heating, characterized in that it has a roller made of magnetic material or metal arranged so that a magnetic field is in the axial direction of the roller, and a high-frequency converter that supplies high-frequency power to the exciting coil. apparatus.