JPH10333489A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device where overshooting and temperature ripple are definitely suppressed. SOLUTION: A heat generating metal body is laminated on an endless belt- like fixing heating film 1 brought into press-contact with a pressure roller (not shown), and a field coil 3 is disposed inside the fixing heating film 1 so as to be opposed to the fixing heating film 1. The field coil 3 is supplied with a current from a line input by rectifying it by a rectifying bridge 200 and performing high frequency switching by a FET 201, and an eddy current is generated at the heat generating metal body by magnetic induction, so that heating is performed. Then, based on an output from a temperature detecting circuit 107 during paper non-feeding, and also based on a power pattern obtained by taking the heat absorption of paper into consideration by a power pattern selecting circuit 108 during paper feeding, the width of the driving pulse of the FET 201 is modulated by proportional-plus-integral control by a control circuit 109.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for fixing a developer (toner) image formed by an electrophotographic process by magnetic induction heating, and an image forming apparatus provided with the fixing device.

[0002]

2. Description of the Related Art Conventionally, in this type of apparatus, a halogen heater is disposed inside an opposing metal roller, and the metal roller is heated by heat generated by the halogen heater.
It has been a general technique to fix the paper by passing the print paper between the opposed metal rollers.

However, as a fixing method recently proposed,
The heating power is applied by directly coupling the high-frequency magnetic field to the metal film provided outside the coil, and the undeveloped toner is developed between the heated metal film and the pressure roller disposed opposite to the heated metal film. A method has been proposed in which the unfixed toner is melted and fixed by heat heated by induction heating while passing the printed paper. The schematic diagram is shown in FIG.

In FIG. 13, a heating field coil 5 is provided.
(Hereinafter, abbreviated as a coil), and a cylindrical fixing member 10 which is a member to be heated which rotates following the rotation of the pressure roller 9 is arranged as shown in FIG. The generated magnetic flux is efficiently coupled to the metal film of the fixing film 10, thereby generating an eddy current on the surface of the metal film and efficiently generating heat due to resistance loss due to the eddy current. still,
A ferrite core 13 is provided inside the coil 5 so that magnetic flux can be efficiently coupled to and penetrate the metal film.

Since heating power is applied to the fixing film 10 itself by using such a heating method, heat energy can be efficiently transmitted to the target printing paper surface, and unnecessary portions are not heated without being heated. ,Also,
Since the heat transfer path has a simple configuration and the thermal time constant can be reduced, there is an advantage that a high-speed response (heating) can be realized.

[0006]

However, as described above, even if a high-speed response heating model can be realized, a thermistor temperature sensor 11 (hereinafter, abbreviated as a thermistor) that actually uses a temperature in the past is used. Even if temperature control is performed by performing feedback in accordance with the detected temperature value or the like, a large delay of the sensor is included in the temperature control model due to a delay element of the response speed of the thermistor 11. As a result, the feedback control system oscillates, the system becomes unstable, and the temperature uniformity is impaired.

As described above, the thermistor 11, which actually performs temperature detection, has a response speed of about 2 to 3 seconds when it is normally used in this type of apparatus. Therefore, even if the temperature is detected and controlled by the thermistor 11, as shown in FIG. 13 (b), the advantage of the high-speed response of the target heating device conversely causes the temperature overshoot or the temperature ripple. Will occur. Therefore, it is conceivable as a general method to incorporate the PID technology into the control feedback to stabilize the control. However, even when the feedback is performed by the ideal PID method, the result is a few times due to the detection time constant. There was a technical problem that only a response in seconds could be obtained.

Naturally, as a solution, a thinner thermistor chip or a non-contact infrared temperature sensor can be considered in order to enable a high-speed response. However, all of them are not practical in terms of technical difficulty and cost increase. Absent. Therefore, the advantage of high-speed heating, which is the advantage of magnetic induction heating, could not be fully utilized.

As described above, it is difficult to realize a stable temperature control by suppressing a disturbance with a required high-speed response even if the feedback is directly performed by a conventional detection circuit.

That is, to summarize the above, when a fixing system using induction heating is introduced into the heating section, it is necessary to control the temperature thereof as well known to show a high-speed detection response. However, in temperature feedback by a thermistor temperature sensor or the like, which is a normal temperature sensor, the temperature disturbance cycle in the paper passing state is fast, and the level of the disturbance is large. However, the loop control speed of the feedback circuit is delayed, and it is difficult to provide a sufficiently stable temperature (power) to the print paper.

Therefore, the present invention is capable of forming a good color image by suppressing overshoot and temperature ripple, remarkably improving the life of the fixing device, further increasing the speed, and reducing the cost of the fixing device. And an image forming apparatus.

[0012]

According to a first aspect of the present invention, an object is to provide a film member rotatably disposed around a support, and a film member rotatable while being pressed against the film member. , A field coil disposed inside the film member, a heat-generating metal body disposed to face the field coil, and a high-frequency current applied to the field coil. And a temperature detecting means disposed around the pressure contact portion, and the recording material is heated by an eddy current generated in the heat-generating metal body, and is conveyed by the film member and the pressing member. In the fixing device for fixing an unfixed toner image, the heat-generating metal body is thinned and integrally formed with the film member, and the power supplied to the field coil is a high-frequency current supplied to the field coil. By means of supply, When the material is not nipped and conveyed, based on the value detected by the temperature detecting means for detecting the temperature of the film member, and when the material is nipped and conveyed, based on a power pattern preset in consideration of the amount of heat taken by the recording material, Achieved by controlling stepwise.

Further, according to the second invention of the present application,
In the first aspect, the means for supplying a high-frequency current to the field coil includes a switching means and a drive pulse generation means for the switching means, and a pulse width output from the drive pulse generation means. This is achieved by performing modulation by proportional-integral control based on a value or power pattern detected by the temperature detecting means.

Further, according to a third aspect of the present invention, the above object is achieved in the first or second aspect, wherein the electric power pattern comprises an average value of the detected temperature immediately before the nipping and transporting, and This is achieved by being determined based on the size of the recording material.

According to a fourth aspect of the present invention,
According to the first or second invention, the object is provided with means for measuring the electric power supplied to the field coil, and the electric power pattern is composed of an average value of the measured electric power immediately before the nipping and transporting, and the recording to be nipped. This is achieved by being determined based on the size of the material.

Further, according to the fifth aspect of the present invention, the object is to develop an electrostatic latent image formed on an image carrier based on image information into a toner image, and to form a toner image on a recording material. An image forming apparatus comprising: an image forming unit to be transferred; a fixing device that fixes an unfixed toner image on the recording material; and a unit that supplies a high-frequency current to the fixing device. A film member rotatably disposed around the body, a pressing member rotatably disposed while being pressed against the film member, and a means for supplying the high-frequency current disposed inside the film member A field coil connected to
An image forming apparatus comprising: a heat-generating metal body disposed to face the field coil; and a temperature detecting means disposed around the press-contact portion, wherein heating is performed by eddy current generated in the heat-generating metal body. In the fixing device, the heat generating metal body of the fixing device is thinned and integrally formed with the film member, and the power supplied to the field coil is controlled by the high frequency current supplying means. At the time of non-conveyance, it is steplessly variable based on the value detected by the temperature detecting means for detecting the temperature of the film member, and at the time of nip conveyance, based on a power pattern preset in consideration of the amount of heat taken by the recording material. It is achieved by being controlled to.

That is, according to the first aspect of the present invention, when a high-frequency current is supplied to the field coil, a high-frequency magnetic field is generated in the field coil and magnetically coupled to the heat-generating metal body of the film member. The heating metal body is heated by the eddy current loss caused by magnetism, and the unfixed toner image on the recording material is directly heated. When the recording material is not nipped and conveyed, the power supplied to the field coil is steplessly controlled based on temperature information from the temperature detecting means. In addition, power control with good follow-up to temperature changes is performed. For example, even when the temperature is rapidly increased after the power is turned on and reaches a predetermined target temperature and the target temperature is maintained, overshoot does not occur. Further, when the recording material enters the pressure contact portion between the film member and the pressing member, the heat of the heat-generating metal body is taken away by the recording material, causing a sharp temperature change, which is accompanied by a delay in the response of the temperature detecting means. And the stability of the temperature at the time of nipping and conveying may be impaired, but the electric power supplied to the field coil at the time of nipping and conveying has a power pattern set in advance in consideration of the amount of heat taken by the recording material. Since the temperature is controlled steplessly on the basis of the above, a steep temperature change is not generated as described above, and the temperature stability is maintained.

Further, according to the second invention of the present application,
The means for supplying a high-frequency current to the field coil includes a switching means and a drive pulse generating means for the switching means. The pulse width output from the drive pulse generating means is a value or power pattern detected by the temperature detecting means. Is modulated by proportional-integral control based on
The power supplied to the field coil is controlled in a steplessly variable manner to suppress the occurrence of overshoot and temperature ripple.

Further, according to the third aspect of the present invention, since the power pattern is determined based on the average value of the detected temperatures immediately before the nipping and conveying, the most stable temperature at which the recording material does not absorb heat is performed. Based on the temperature under load conditions,
Stable power control is performed without being affected by the detection delay of the temperature detecting means. In addition, since the size of the recording material to be sandwiched is also taken into consideration, appropriate power control according to the size of the recording material is performed.

According to the fourth aspect of the present invention,
A means for measuring the electric power supplied to the field coil, and since the electric power pattern is determined based on the average value of the electric power measured immediately before the nipping conveyance, the most stable electric power load condition in which the recording material does not absorb heat. Based on the temperature below, stable power control is performed without being affected by the detection delay of the temperature detecting means. In addition, since the size of the recording material to be sandwiched is also taken into consideration, appropriate power control according to the size of the recording material is performed.

Further, according to the fifth aspect of the present invention, when a high-frequency current is applied to the field coil of the fixing device,
A high-frequency magnetic field is generated in the field coil, magnetically coupled to the heat-generating metal body of the film member, and heated by the eddy current loss caused by the magnetism, thereby directly heating the unfixed toner image on the recording material. Let me know. When the recording material is not nipped and conveyed, the power supplied to the field coil is determined by proportional integral control based on temperature information from the temperature detecting means. Linearly stepless variable power control is performed. For example, even when the temperature is rapidly increased after the power is turned on and reaches a predetermined target temperature and the target temperature is maintained, no overshoot occurs. Further, when the recording material enters the pressure contact portion between the film member and the pressing member, the heat of the heat-generating metal body is taken away by the recording material, causing a sharp temperature change, which is accompanied by a delay in the response of the temperature detecting means. And the stability of the temperature at the time of nipping and conveying may be impaired, but the electric power supplied to the field coil at the time of nipping and conveying has a power pattern set in advance in consideration of the amount of heat taken by the recording material. Since it is determined by the proportional integral control based on the above, the temperature stability is maintained without generating a sharp temperature change as described above.

[0022]

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

(First Embodiment) First, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus having a fixing device, FIG. 2 is a diagram showing a fixing device using a film heating method, and FIG.
FIG. 4 is a diagram showing a temperature change immediately after start-up by the control of the present embodiment. FIG. 4 is an overall model in which a high-frequency converter of an induction heating coil of the present invention is connected and temperature detection and temperature control are performed by magnetic induction. FIG. 6 shows an example of a control method including a control circuit, FIG. 6 shows a waveform of a current supplied to a field coil, FIG. 7 shows a temperature change by control using a power pattern, and FIG. FIG. 7 is a diagram illustrating a waveform of a current supplied to a field coil when a trouble such as an excessive voltage is input as an input voltage.

In FIG. 1, reference numeral 71 denotes a photosensitive drum as an image carrier for forming an image of electrophotography, which is disposed rotatably in the direction of the arrow. When the photosensitive drum 71 is charged by the charger 72 and the laser beam L is irradiated by the laser beam scanner 73 in accordance with the image information, an electrostatic latent image is formed on the photosensitive drum 71, and the static latent image is formed. The electrostatic latent image is developed as a toner image by the toner carried on the developing roller 74a of the developing device 74.

On the other hand, the printing paper 12 as a recording material accommodated in the cassette 75 is fed one by one by a feeding roller 76, and is sent to the photosensitive drum 71 side by a feeding roller 78 via a feeding unit 77. Conveyed. Then, when the print paper 12 is guided by the guide 79 to the pressure contact portion 82 between the photosensitive drum 71 and the transfer roller 80, the toner image is transferred onto the print paper 12 by the transfer roller 80 to which a high voltage is applied from the power supply 81. Is transferred to the fixing device 85 via the transfer section 84.

The fixing device 85 includes a fixing heating film (hereinafter, referred to as a fixing film) 1 as a film member and a fixing pressure roller (hereinafter, referred to as a pressure roller) as a pressing member.
The fixing film 1 and the pressure roller 2 start rotating when the printing paper 12 conveyed from the image forming unit passes through the pre-fixing sensor 16. A heating means described later is raised to a predetermined temperature.

When the printing paper 12 to which the unfixed toner image has been transferred is sandwiched between the nips, heat is transmitted to the toner image and the printing paper 12, and the printing is performed by applying pressure at the nip. The toner on the paper 12 is melted, soaked into the fibers of the print paper 12 and fixed.

Further, the printing paper 1 on which the fixing is completed
When the printing paper 2 passes through the paper discharge sensor 17, the rotation of the fixing film 1 and the pressure roller 2 is stopped, and the print paper 12 is discharged onto the discharge tray 86, thereby completing the image formation. At the time of transfer, the toner remaining on the photosensitive drum 71 without being transferred onto the print paper 12 is cleaned by the cleaning unit 83 to prepare for the next image formation.

Next, a fixing device in the image forming apparatus will be described in detail with reference to FIG. As shown in FIG. 2, the fixing device of the present embodiment includes, as heating means, a field coil 3 disposed inside the fixing film 1, and a heat-generating metal body 4 opposed to the field coil 3. The field coil 3 is connected to a high-frequency converter 30 that supplies high-frequency current to the field coil 3.

The high-frequency converter 30 will be described in detail later. When a high-frequency current generated from the high-frequency converter 30 is supplied to the field coil 3 arranged inside the fixing film 1 as shown in FIG. Coil 3
Applies a high-frequency magnetic field to the inner surface of the heat-generating metal body 4 by the high-frequency current, thereby generating an eddy current in the heat-generating metal body 4.
The heat generating metal body 4 generates heat due to eddy current loss.

Therefore, in the present embodiment, a metal foil, for example, a magnetic metal such as nickel is laminated on the surface of the fixing film 1 as the heat-generating metal body 4 so that the surface of the fixing film 1 directly in contact with the toner image is heated. It is composed.

In the case of such a configuration, the magnetic flux flows through a single loop which starts from the center of the coil which gives the magnetomotive force and returns to the center of the coil through the route of the minimum magnetic resistance, that is, the space. A system is formed that follows a path that minimizes (μ0) and the nonmagnetic metal portion. Therefore, the field coil 3
Is provided with a member having high magnetic permeability so that a magnetic flux is efficiently coupled to and penetrates the heat generating metal body 4 to form a magnetic path.

Then, a temperature detecting thermistor (not shown) as a temperature detecting means is attached to a portion close to the nip formed by the fixing film 1 for directly heating and the pressing roller 2 as described above. Based on temperature information from the temperature detection thermistor, a conventionally known proportional-integral control (hereinafter referred to as PI
By performing feedback control using (control), a temperature control with excellent follow-up to temperature changes can be performed in an extremely simple thermal model at the level of primary transfer, so that temperature ripple can be reduced. .

Therefore, as shown in FIG. 3, overshoot at the time of turning on the power supply can be eliminated, and the temperature in the standby state can be maintained exactly at the target temperature.

However, no matter how fast a control circuit and a heating circuit can be constructed, the response speed of a temperature detecting thermistor generally used in this type of device usually has a time constant of 3.5 seconds. Since there is a response delay in the feedback temperature information, only a result depending on the speed of the temperature detection thermistor can be obtained.

The deviation from the target temperature caused by the response delay is not so large because no sharp temperature change occurs during standby or between sheets, and does not affect fixability. It doesn't matter much. However, in the early stage of paper passing, when the paper enters the nip between the fixing film 1 and the pressure roller 2,
Because a large amount of heat is deprived of the paper and a steep temperature change occurs, the deviation from the target temperature caused by the response delay is large, and the fixing at the leading end of the paper may be insufficient. .

Also, during the paper passing, even if the PI control is performed based on the information of the temperature detection thermistor, the amount of heat taken away by the paper is smaller than that during the standby or the paper interval.
Since the amplitude of the temperature subjected to the disturbance and the frequency component of the temperature are increased, the temperature may drop or the temperature may become uneven at the rear end of the paper.

Further, immediately after the sheet is discharged, the amount of heat taken by the sheet disappears, so that a steep temperature change occurs, and due to the above-mentioned response delay, an overshoot as shown in FIG. 16 may occur. Was.

Therefore, in the present invention, the PI control based on the power pattern uniquely determined in consideration of the amount of heat taken by the paper is performed instead of performing the PI control based on the information of the temperature detection thermistor during the paper passing. By doing so, the power is forcibly supplied during the paper passing period, so that the temperature drop and the temperature unevenness at the trailing end of the paper are eliminated.

According to the literature and the like, the power to be supplied to the paper is a power of 3.6 [W / cm 2].
If the throughput is treated as a constant, it is a linear function with respect to time.

If the paper size is A4 width (21 [cm])
If the throughput is S [cm / sec] and the elapsed time from the entry of the paper is t [sec],

[0042]

## EQU1 ## P (t) = 3.6 [W / square cm] × 21 [c]
m] × S [cm / sec] × t [sec] = 75.6 × S × t
[W]

Is as follows. Therefore, for A4 size paper, by supplying power of 75.6 × S [W] every t seconds, it becomes possible to achieve a stable temperature from the leading edge of the paper to the trailing edge of the paper.

The power pattern for supplying power represented by the above temporary function by PI control is as follows:
It becomes a curve that substantially achieves a linear function, and by preparing a plurality of power patterns according to the paper size, it is possible to eliminate the temperature drop and the temperature unevenness during the paper passing period for all the papers.

More specifically, it is necessary to control the power loss that is constantly emitted from the fixing device by the power that is constantly added to the above item. Therefore, the loss power constantly released by the fixing device itself is
The power pattern may be calculated based on the temperature value detected during the sheet interval or the standby state under a stable load condition, and the calculated power loss may be added. In calculating the power loss, an average temperature between the sheets and during standby is calculated based on the information from the temperature detection thermistor in consideration of the response delay described above, and the power loss is calculated based on the average temperature. Just do it.

FIG. 4 is a block diagram of a high-frequency converter 30 for realizing the above-described power control of the present invention. In FIG. 4, the commercial AC input from the line is
The power is rectified by the dual-wave rectifier 200, and high-frequency switching is performed by a power FET 201 serving as switching means connected to one end of the field coil 3, and supplied to the field coil 3 as a high-frequency current. As a result, a high-frequency eddy current is generated in the fixing film 1 provided with the heat-generating metal body 4, and an induction heating phenomenon occurs. Then, the temperature due to the heating is set to a temperature detecting thermistor 10 serving as temperature detecting means attached to a portion close to a nip formed by the fixing film 1 and the pressure roller 2.
6 and the detection information of the temperature detection thermistor 106 is sent to the temperature detection circuit 107. Temperature detection circuit 10
7 converts the detection information into a voltage by a well-known resistance ladder, amplifies it to a necessary level by an operational amplifier, and outputs the voltage to the power pattern selection circuit 108 as a voltage value.

The power pattern selection circuit 108 determines whether or not the paper is being fed by the pre-fixing sensor 16 and the paper discharge sensor 17. Compares and amplifies a target temperature (reference voltage) stored in a sheet interval or a standby state and an output from the temperature detection circuit 107, and outputs a voltage value to the control circuit 109 as a drive pulse generation unit. .

On the other hand, if it is determined that paper is being passed,
In order to select a voltage value output from the temperature detection circuit 107 and a power pattern according to the paper size, the voltage value is divided into blocks, and a heating power pattern corresponding to each block is selected from a plurality of pieces of memory information. Set. Then, the set memory pattern is sequentially output from the memory to the control circuit 109 as a voltage value in a time-series manner at a clock rate at which the set memory pattern is sequentially read together with the sequence time.

The value output to the control circuit 109 as described above is a target value of the pulse width modulation at that moment. The control circuit 109 controls the triangular wave of the modulation circuit to control the pulse width in accordance with the target value. Change the slice level.

By controlling in this way, a stable target can be obtained with a short rise after power-on, without overshoot, and with very little temperature ripple between sheets and during standby. The temperature is maintained, and even during the paper passing, the stable target temperature without the temperature drop and the temperature unevenness is maintained, and the overshoot immediately after the paper discharge can be eliminated.

A specific example of the high-frequency converter 30 as described above will be described with reference to FIG. In FIG. 5, a commercial alternating current input from a line is rectified by a rectifier bridge 200 as a double-wave rectifier, is subjected to high-frequency switching by a power FET 201 connected to one end of the field coil 3, and is supplied to the field coil 3 as a high-frequency current. You. As a result, a high-frequency eddy current is generated in the fixing film 1 having the heat-generating metal body, and an induction heating phenomenon occurs. The fixing film 1
Since the heat generating metal body has magnetic coupling as described above, it is shown in the same equivalent circuit as the switching transformer of the power supply as shown in FIG.

Then, the temperature due to the heating is detected by a temperature detecting thermistor 106 attached to a portion near the nip formed by the fixing film 1 and the pressure roller 2, and information detected by the temperature detecting thermistor 106 is temperature The signal is sent to the detection circuit 107. The temperature detection circuit 107 converts the detection information as a voltage by the resistance ladder 212,
The signal is amplified to a required level by the operational amplifier 215 and output to the power pattern selection circuit 108 as a voltage value.

The voltage output to the power pattern selection circuit 108 is converted into a stable sheet passing temperature by changing the value of the electric power in the blocking circuit 216 in accordance with the detection of the sheet interval temperature as shown in FIG. It is possible to obtain

Therefore, when performing power control inside the memory, a high power pattern is selected if the average temperature between sheets is low, and conversely, if the average temperature between sheets is high, a low power is used according to the average temperature value at the time between sheets. A memory bank is provided so that a pattern can be selected. In order to generate a memory bank switching signal of this power pattern, a memory value is input and a block is designated to designate a memory bank (average temperature between sheets). And generating a bank switching processing signal).

In the memory 217, a power pattern is selected and set according to the paper size using the above-described blocked data as a memory bank switching signal, and the power pattern output of the control circuit 109 via the switching circuit 218 according to the clock rate. Output to terminal 42.

However, not only the power pattern from the memory 217 but also the voltage value from the operational amplifier 215 are output to the switching circuit 218.
When the pre-fixing sensor 16 and the paper discharge sensor 17 determine that the paper is not passing, the normal PI control is performed, so that the output from the operational amplifier 215 is directly output without outputting from the memory 217. The signal is output to the feedback terminal 41 of the control circuit 109.

The control circuit 109 is provided with a current mirror circuit composed of an operational amplifier 34 and transistors 20 to 27 and the like. The current flowing through the resistor 37 connected to the terminal 36 is converted into a capacitor by the current mirror circuit. By charging / discharging 33, a triangular waveform is generated.

This triangular wave is output to the comparator 45, which is connected to the power pattern terminal 4
The error amplifier 44 to which the voltage pattern or the reference voltage 46 is applied by the comparator 45 receives the reference voltage (temperature) from the input of the temperature detection signal sent from the switching circuit. The difference voltage compared with the target value is output as a proportional integration signal. The threshold of a triangular wave is changed by the output to perform the pulse width modulation of the ON width of the gate signal of the power switching semiconductor 201.

That is, when the output of the power pattern is selected by the switching circuit 218, the power pattern is output to the comparator 45 via the power pattern terminal 42, and as described above, the power loss and the paper are taken away. In order to supply electric power to the field coil 3 in consideration of the amount of heat, the power F
Pulse output to the ET 201 is performed.

On the other hand, when the output of the operational amplifier 44 is selected by the switching circuit 218,
Is output to the comparator 45 by the error amplifier 44
The difference voltage obtained by comparing the reference voltage (temperature target value) with respect to the input of the temperature detection signal by the combination of the reference voltage 46 corresponding to the target temperature between the sheets and the standby target temperature and the operational amplifier 44 as a proportional integration signal. A resistor 47 and a capacitor 48, which are externally attached and output, perform phase correction in feedback control.

The proportional integral voltage generated by the operational amplifier 44 is configured to control the ON width of the signal by the triangular wave threshold slice of the comparator 45. Therefore, the electric power corresponding to the temperature detected by the temperature detecting thermistor 106 is applied to the field. A pulse is output to the power FET 201 to supply the power to the coil 3.

Then, as described above, the control circuit 109
The pulse output from drives the gate of the power FET 201 which is switching-driving the field coil 3, and stores electric power as magnetism in the excitation inductance of the field coil 3, and outputs the electric power to the heating metal body corresponding to the load. Magnetic coupling causes eddy currents due to magnetism to flow, generating Joule heat due to the resistance loss of the metal and heating it.
The amount of heating can be controlled by performing the pulse modulation as described above.

Further, in the present embodiment, in order to improve the power factor of the input current waveform of the power supply, control is performed to supply a sine wave current to the field coil 3 as much as possible. That is, FIG.
As shown in FIG. 6, control is performed to modulate the switching cycle in accordance with the voltage value of the input voltage waveform (commercial AC voltage), and the switching waveform (flyback in FIG. The cycle of the switching waveform (flyback waveform 2 in FIG. 6) at a higher voltage in the rectification ripple is shorter than the cycle of waveform 1).

In order to realize such control, in the present embodiment, as shown in FIG.
6 and a resistor 223, the voltage is monitored by an operational amplifier 53, and the transistor 54 controls the capacitor 33, which determines the oscillation frequency, and the resistor 37, which determines the discharge current, according to the voltage. have.

Here, the power pattern in the present embodiment will be described with reference to FIG. FIG. 7 shows the relationship between the power control state between the sheets and at the time of sheet passing and the temperature of the nip portion. In the area of control 1, the temperature power supply was sequentially supplied from zero at a constant rising rate. As a result, the heat is rapidly taken away by the edge of the paper at the initial stage of paper passing, so that the temperature is lowered in the area at the initial stage of paper passing. If such a phenomenon occurs, the fixing at the leading edge of the paper becomes insufficient, and the print quality is reduced (non-uniform gloss).

Therefore, in the present invention, a control method as shown in the area of control 2 is employed. This is a method in which the temperature is measured immediately before the leading edge of the sheet and is controlled by a pattern in which the slope of the heating power pattern is uniformly added. The temperature drop occurring at the leading edge of the sheet can be reduced by momentary pulse power supply.

In order to obtain an ideal control result,
As shown in the area of the control 3, the power is supplied at the same curve as the power taken at the leading edge of the sheet, and the PI control is performed immediately on the overshoot of the temperature at the trailing edge from the trailing edge of the sheet. Immediately, the supply power is rapidly reduced by the power pattern for the time corresponding to the overshoot, and P
A method that does not vibrate in the I control region is also conceivable.
Control 3 shows the case where a power pattern similar to the temperature drop curve is supplied as a pattern that cancels out from the temperature reduction characteristics generated in the system in order to eliminate the temperature drop.

As described above, according to the present invention, since the driving waveform of the field coil is modulated to control the temperature of the fixing section, linear temperature control can be achieved from the target temperature range. It is done.

As described in the conventional example, the ordinary fixing device is
A configuration is adopted in which the high-power halogen heater is guided to a specified temperature by performing ON / OFF control (control in units of 1/2 cycle of commercial AC) depending on whether or not a target temperature has exceeded a specified temperature. Therefore, even if the temperature rise rate and overshoot are 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.

However, according to the linear temperature control by controlling the waveform of the switching state at a high-frequency level as in the present invention, excellent followability to a temperature change can be achieved, and the temperature ripple can be eliminated.

Next, a safety circuit according to the present embodiment will be described. As described above, the direct heating method using the induction heating method, and when the directly heated heat-generating metal body is particularly a film-shaped metal, due to its low specific heat, rapid heating in an extremely short time Indicates an increase in temperature. Therefore,
A safety circuit for preventing overheating is indispensable together with the performance requirements of the temperature detection system that follows this rapid temperature rise. In other words, what kind of situation the equipment has, for example, when an improper excessive voltage is input to the input voltage, and furthermore, the excitation coil of the fixing section is mechanically damaged (cracks, cracks, foreign substances mixed into the magnetic path, etc.) Even if there is a problem from the standpoint of use, safety (especially fire safety) is an absolutely essential condition for equipment without exceeding a certain temperature.

Therefore, in the circuit of FIG.
A current mirror that detects a drain voltage of the ET 201, that is, one end of the field coil 3, detects a zero cross of a flyback voltage waveform by a zero cross detection circuit 219, and uses the detected timing as a synchronization signal to be a start signal of a pulse width modulation circuit. The charge and discharge of the capacitor 33 of the circuit is controlled, and the circuit is switched in synchronization with the flyback waveform.

Further, for example, when an improper excessive voltage is input to the input voltage, or when the field coil of the fixing unit is mechanically damaged (cracks, cracks, foreign matter is mixed in a magnetic path, etc.), the position to be used is changed. If there is a trouble in the above, it is necessary to stop the converter immediately, send the information to the sequence controller, stop the control circuit beforehand, and ensure safety.

FIG. 8 shows waveforms when such a trouble occurs. The ON time width is a width determined by the temperature detection voltage or the like, and the OFF width, that is, the flyback waveform is a well-known ω = 1 / √LC with a period uniquely determined by the inductance of the coil and the resonance capacitor. Therefore, breakage of the magnetic circuit due to any of the above causes,
When inconveniences due to foreign matter mixing or the like occur, the inconvenience can be detected by monitoring the cycle and current waveform because the circuits are synchronized.

In the circuit shown in FIG. 5, the current detection circuit 220 detects an overcurrent by comparing the voltage at the end of the resistor 204 connected to the rectifier bridge 200 with a predetermined reference voltage. Then, the detected value, the temperature information from the operational amplifier 215, the zero-cross from the flyback detection waveform, and the cycle information by the timer or the like are input to the abnormality determination circuit 224, and the abnormality is determined. Examples of the criterion here are: The period is high. 2. The current value is over. 3. The detection value of the temperature detection thermistor 106 exceeds a specified value. Further, as a combination determination, Low temperature rise but high current. Etc. All of the above phenomena indicate abnormalities in the magnetic circuit of the induction heating unit or the temperature detection system,
Immediately, the abnormality determination circuit 224 controls the gate 225 to stop the generation of the triangular wave and stop the converter, and sends the information to the sequence controller to stop the control circuit beforehand.

As described above, in order for the means for supplying high-speed heating such as induction heating to the fixing heating method to function effectively, the temperature detection circuit around it must have a time constant corresponding to the response. Is indispensable, but even in the case where the device has to be configured with a much slower response speed in practice, heating can be effectively and efficiently performed by using the above-described method according to the present invention.

(Second Embodiment) Next, FIGS.
2, a second embodiment of the present invention will be described. In FIG. 9, the circuit configurations of the control circuit 109 and the temperature detection circuit 107 are the same as those described in the first embodiment, and a description thereof will be omitted.

In FIG. 9, reference numeral 250 denotes a processing CPU which performs a print sequence process of, for example, a printer which is a main body device. In the method described in the first embodiment, the power pattern is determined by the power pattern selection circuit with respect to the paper interval and the temperature detected during standby. However, in the present embodiment, the processing CPU 250 sets a constant power interval between papers. Monitor the control state of the electric power controlled to the temperature, and measure the control state, that is, the waveform duty required to keep the fixing device at a constant temperature, and select a power pattern during paper feeding according to the measurement result. It is configured in such a way.

This is because the self-radiation state of the fixing device changes depending on the environment in which the printer is used. This is because the power supplied at that time, that is, the waveform duty can be said to be the minimum required power including the environment.

Therefore, in the present embodiment, the zero crossing of the flyback voltage is detected by the processing CPU 250 shown in FIG. 9 based on the output from the zero crossing detection circuit 219 at the timing immediately before the leading edge of the paper enters the nip portion.
Further, by measuring the waveform duty from the detected timing and monitoring the detection current of the current detection resistor 204, the power required to maintain the temperature of the fixing device between the sheets and at the time of standby is detected and detected. A high-precision temperature control is realized by selecting a power pattern from the obtained power.

Here, since it is desired to measure the input power (preferably the film heating power), it is possible to measure the input voltage and the input current and multiply the two by performing the control with the highest precision. Since it is expensive to transmit the signal to the secondary circuit after insulation processing, the input power can be easily obtained from the switching duty and the input current (realizable with a current transformer: relatively low cost). doing.

The control in this embodiment will be described with reference to the flowchart of FIG. First, it is determined whether or not the paper is passing through based on whether or not the leading edge of the sheet has passed the sensor 16 before fixing (step 400). By detecting the zero-crossing of the flyback voltage waveform based on the output from the output signal 219 and measuring the waveform duty from the detected timing, the power P required to maintain the temperature of the fixing device at the sheet interval and at the standby time is obtained.
i is obtained (step 401). Next, the processing CPU 25
0, the voltage measurement result Pi is used as the initial value of the power pattern, and the power taken by the paper described in the first embodiment is sequentially D / A-converted from the memory according to the clock, and selected as the power pattern value Pm. The power pattern P (t) to be output to the comparator 45 is obtained by adding this Pm and the Pi (step 402). And
This power pattern is output to the terminal 42 of the control circuit 109, and pulse width modulation is performed (step 403).

If it is determined that there is a sheet interval or a standby state (step 400), the terminal 41 of the control circuit 109
Output voltage of the temperature detection circuit 107 and the processing CP
A power FET 201 that performs comparison and amplification of the reference voltage output from U250 to the terminal 40 of the control circuit 109 by the error amplifier 44, performs PI control, and switches the field coil 3 as in the first embodiment. Is controlled to lead to the target temperature (step 404).

Then, while performing the above-described control, the abnormality determination is also performed in this embodiment (step 405). This abnormality determination is performed by the processing CPU 250 by determining whether the temperature of the heating metal body has exceeded the Curie temperature, whether the cycle of the input voltage is a specified value, and whether the input current value is a specified value. Will be First, the Curie temperature is determined as shown in FIG.
The output of the temperature detection circuit 107 is monitored by the processing CPU 250, and the processing CPU 250 compares the output of the temperature detection circuit 107 by A / D conversion with a set value for the Curie temperature. Next, the CPU 25 determines the cycle of the input voltage based on the output of the zero-cross detector 219.
This is performed by comparing the set value with a value obtained by measuring the interval of the zero-cross point by 0. The input current value is determined by monitoring the output of the current detection circuit 220 by the processing CPU 250 and comparing the output value with the set value. It is performed by

These determinations are made by determining the Curie temperature (step 50) as shown in the flowchart of FIG.
0), cycle determination (step 501), and current measurement (step 502). If an abnormality is found in any of the determinations, the processing CPU 250 sends the control circuit 1
The power supply to the field coil 3 is stopped by increasing the voltage of the terminal 42 at step 09 to set the pulse width modulation state to zero, that is, a shutdown state in which the output is turned off (step 503).

With the above operation, the ideal control as shown in FIG. 12 is performed, and the rising can be realized at high speed without any overshoot.

According to the present embodiment, in addition to the effects of the first embodiment, all the information described above can be easily obtained and the arithmetic processing and the like can be performed at low cost by performing control by the processing CPU 250 for controlling the sequence. There is an advantage that it can be configured.

[0088]

As described above, the first embodiment according to the present application is described.
According to the invention, since the heating method is a heating method based on magnetic induction of the heat-generating metal body, it is possible to realize a very monotonous configuration of the heat transfer model from the heat source, and the temperature is detected by the temperature detecting means when the recording material is not nipped and conveyed. Based on the value, the power supplied to the field coil is controlled steplessly variably. In addition, the temperature drop due to the detection delay can be minimized and the overshoot and the temperature ripple can be suppressed.

In addition, even when the recording material is nipped and conveyed, the power supplied to the field coil is controlled steplessly and variably based on a preset power pattern in consideration of the amount of heat taken by the recording material. The temperature at the time of fixing can be appropriately maintained without being affected by the response delay of the temperature detecting means, and a temperature drop and temperature unevenness can be eliminated.

According to the second invention of the present application,
The means for supplying a high-frequency current to the field coil includes a switching means and a drive pulse generating means for the switching means. The pulse width output from the drive pulse generating means is a value or power pattern detected by the temperature detecting means. Is modulated by proportional-integral control based on
The power supplied to the field coil is controlled in a steplessly variable manner, so that temperature ripple and overshoot can be suppressed.

Further, according to the third aspect of the present invention, since the power pattern is determined based on the average value of the detected temperatures immediately before the nipping and conveying, the most stable temperature at which the recording material does not absorb heat is performed. Based on the temperature under load conditions,
Stable power control can be performed without being affected by the detection delay of the temperature detecting means. In addition, since the size of the recording material to be sandwiched is also taken into consideration, it is possible to perform appropriate power control according to the size of the recording material. Further, since the temperature detecting means can sufficiently cope with the speed at which the average temperature can be detected, the range of selection of the temperature detecting means can be expanded.

According to the fourth invention of the present application,
A means for measuring the electric power supplied to the field coil, and since the electric power pattern is determined based on the average value of the electric power measured immediately before the nipping conveyance, the most stable electric power load condition in which the recording material does not absorb heat. Based on the temperature below, stable power control can be performed without being affected by the detection delay of the temperature detecting means. In addition, since the size of the recording material to be sandwiched is also taken into consideration, it is possible to perform appropriate power control according to the size of the recording material.

Further, according to the fifth aspect of the present invention, since the fixing device of the image forming apparatus is a heating method using a magnetic induction of the heat-generating metal body, an extremely monotonous configuration of the heat transfer model from the heat source can be realized. When the recording material is not nipped and conveyed, the power supplied to the field coil is controlled steplessly and variably based on the value detected by the temperature detecting means. Against
Even when a temperature detecting means having a slow rising speed, which is normally present, is used, the temperature drop due to the detection delay can be minimized, the overshoot and the temperature ripple can be suppressed, and a good image can be formed.

Further, even when the recording material is nipped and conveyed, the power supplied to the field coil is controlled steplessly and variably based on a preset power pattern in consideration of the amount of heat deprived of the recording material. The temperature at the time of fixing can be appropriately maintained without being affected by the response delay of the temperature detecting means, and a temperature drop and temperature unevenness can be eliminated. Especially,
In a color image forming apparatus that performs mixed color development of a multi-layer toner, a high-quality image can be output by accurate temperature control.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a schematic configuration of a fixing device according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a state of a temperature change immediately after power-on by the fixing device according to the first embodiment of the present invention.

FIG. 4 is a block diagram for explaining a heating unit and a control device in the fixing device of FIG. 2;

FIG. 5 is an example of a circuit of a control device of a heating unit in the fixing device of FIG. 2;

6 is a diagram showing a waveform of a current supplied to a field coil in the circuit of FIG.

FIG. 7 is a diagram illustrating a power pattern in the circuit of FIG.

8 is a diagram showing a waveform of a current supplied to a field coil when an inappropriate excessive voltage is input as an input voltage in the circuit of FIG. 5;

FIG. 9 is an example of a circuit of a control device for a heating unit of a fixing device according to a second embodiment of the present invention.

FIG. 10 is a flowchart illustrating power control according to a second embodiment of the present invention.

FIG. 11 is a flowchart illustrating an abnormality determination control according to the second embodiment of the present invention.

FIG. 12 is a diagram for describing a power pattern according to the second embodiment of the present invention.

13A and 13B are diagrams illustrating a conventional fixing device, FIG. 13A is a diagram illustrating a configuration of a conventional fixing device, and FIG.
FIG. 5 is a diagram showing a response of a thermistor of the fixing device of FIG.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 fixing film (film member) 2 pressure roller (pressure member) 3 field coil 4 heat-generating metal body 12 printing paper (recording material) 30 high-frequency converter (means for supplying high-frequency current) 71 photoconductor drum (image carrier) 85 fixing device 106 temperature detecting thermistor (temperature detecting means) 109 control circuit (driving pulse generating means of switching means) 201 power FET (switching means) 250 processing CPU (means for measuring power)

Claims (5)

[Claims] 1. A film member rotatably disposed around a support, a pressing member rotatably disposed while being in pressure contact with the film member, and a pressure member disposed inside the film member. A field coil, a heat-generating metal body disposed so as to face the field coil, a unit for supplying a high-frequency current to the field coil, and a temperature detection unit disposed around the pressure contact portion. A fixing device that heats by an eddy current generated in the heat-generating metal body and fixes an unfixed toner image on a recording material nipped and conveyed by the film member and the pressure member. The power to be supplied to the field coil is controlled by means for supplying a high-frequency current to the field coil, and the temperature of the film member is controlled when the recording material is not nipped and conveyed. Temperature detection to detect Based on the value detected by the means,
A fixing device characterized in that it is controlled steplessly based on a preset power pattern in consideration of the amount of heat taken by a recording material during nipping and conveying. 2. A means for supplying a high-frequency current to a field coil includes a switching means and a driving pulse generating means for the switching means, and a pulse width output from the driving pulse generating means is detected by a temperature detecting means. The fixing device according to claim 1, wherein modulation is performed by proportional-integral control based on the set value or the power pattern. 3. The fixing device according to claim 1, wherein the power pattern is determined based on an average value of the detected temperatures immediately before the nipping and conveying, and a size of the nipping recording material. 4. A device for measuring power supplied to a field coil, wherein the power pattern is determined based on an average value of measured power immediately before nipping and transporting and a size of a recording material to be nipped. The fixing device according to claim 1, wherein the fixing device performs the fixing. 5. An image forming section for developing an electrostatic latent image formed on an image carrier based on image information into a toner image and transferring the toner image to a recording material, and an unfixed toner image on the recording material An image forming apparatus comprising: a fixing device for fixing the fixing device; and a unit for supplying a high-frequency current to the fixing device.
A film member rotatably arranged around the support,
A pressure member disposed rotatably while being pressed against the film member; a field coil disposed inside the film member and connected to the means for supplying the high-frequency current; An image forming apparatus comprising: a heat generating metal body arranged to perform heating; and a temperature detecting means arranged around the pressure contact portion, wherein the heating is performed by eddy current generated in the heat generating metal body. The heat-generating metal body is thinned and integrally formed with the film member, and the electric power supplied to the field coil is controlled by the high-frequency current supplying means when the recording material is not nipped and conveyed. Based on the value detected by the temperature detecting means for detecting the temperature of the film member, during the nipping conveyance, the stepless variable control is performed based on a preset power pattern in consideration of the amount of heat taken by the recording material. An image forming apparatus comprising.