JP5307340B2 - Electromagnetic induction heating fixing device and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve controllability, that will not apply excessive load on the switching element of a high-frequency power source and to save energy, by avoiding deterioration in heating efficiency in an electromagnetic induction heating fixing unit using magnetic shunt alloy in a body to be heated. <P>SOLUTION: An IH control part 50 for controlling the switching element 44 so that power supplied to an excitation coil 32 has power-varying control carried out adjusting supplied power according to detected temperature of a thermistor 49, in order to maintain a heat roller 21 at a fixing temperature after termination of warming up, when power required for maintaining the fixing temperature reaches a minimum power value; a fixed power intermittent control is carried out intermittently carrying out power supply in which casted power is fixed according to the detected temperature of the thermistor; a minimum power value which is to become a reference, when power varying control is switched to fixed power intermittent control is determined, based on the input voltage and the detected temperature of the thermistor. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electromagnetic induction heating and fixing apparatus that heats a heated object such as a heating roller by electromagnetic induction and an image forming apparatus including the same, and more particularly, to an electromagnetic induction heating and fixing apparatus that uses a magnetic shunt alloy for the heated object, and The present invention relates to an image forming apparatus including the same.

  In an image forming apparatus (such as a printer, a facsimile machine, a copying machine, and a multi-function machine) that forms an image on recording paper by an electrophotographic process, unfixed toner transferred from the photosensitive member onto the recording paper is recorded by heat and pressure. There is provided a fixing device for fixing the toner. In this fixing device, an electromagnetic induction heating method in which a heated object such as a heating roller is heated by Joule heat due to electromagnetic induction has an advantage of excellent heating efficiency and thermal responsiveness. It has become like this.

In such an electromagnetic induction heating type fixing device, a magnetic shunt alloy having a temperature-dependent magnetic transformation characteristic in which the relative permeability rapidly decreases when the Curie temperature is reached is used as a heating roller. A technique for performing self-temperature control using the above is known (see Patent Document 1). According to this, by using a magnetic shunt alloy having a Curie temperature higher than the fixing temperature and in the vicinity thereof for the heating roller, an abnormal temperature rise in which the temperature of the heating roller greatly exceeds the fixing temperature can be easily and reliably performed. Can be prevented.
JP 2004-325678 A

  However, in the fixing device, when the temperature of the heating roller reaches a predetermined fixing temperature due to warm-up, temperature control is performed to keep the heating roller constant at the fixing temperature so that stable fixing processing is performed. In the induction heating type fixing device, the inverter is controlled to increase or decrease the input power to adjust the heating amount. At this time, in order to maintain the fixing temperature according to the decrease in the amount of heat radiation accompanying the surrounding temperature increase. Since the necessary amount of heating is reduced, it is necessary to gradually reduce the input power.

  In this case, in the high frequency power supply, when the input power is reduced, the drive frequency of the high frequency power supply increases. When the input power is large and the drive frequency is low, as shown in FIG. The collector current Ic rises ideally at the zero cross point where the inter-voltage Vce becomes zero, and the resonance circuit of the high frequency power supply can be driven normally. However, when the input power is small and the drive frequency is high, the resonance capacitor A phenomenon of shifting to the next operation occurs before the discharge is completed, and as shown in FIG. 7B, the voltage Vce instantaneously drops to 0 at the timing of zero crossing, and an abnormal current is generated in the switching element. .

  The abnormal current in the switching element generates heat in the switching element, so that the heat generation efficiency is reduced due to the energy loss, and a large load is applied to the switching element, and in the worst case, the switching element is destroyed. Therefore, it is desirable to avoid it. Therefore, in order not to give an excessive load to the switching element, a minimum power value is set in advance as a lower limit value of power that can be input, and the input power is below the minimum power value during temperature control after warm-up. By controlling so as not to occur, destruction of the switching element can be prevented.

  When the heating roller is not a magnetic shunt alloy, the minimum power value increases as the input voltage increases as shown in FIG. 8A, but normally, in the temperature range used for fixing, Since there is no significant difference with respect to the temperature change of the heating roller, the minimum power value may be set uniformly according to the input voltage.

  On the other hand, when a magnetic shunt alloy having a Curie temperature higher than the fixing temperature and set in the vicinity thereof is used for the heating roller as described above, as shown in FIG. As the value rises, the minimum power value increases. This is because, as the temperature of the heating roller approaches the Curie temperature of the magnetic shunt metal constituting the heating roller, the zero crossing in the voltage resonance with the high frequency power source becomes difficult, and the minimum power value according to the input voltage. Is uniformly set, the minimum power value becomes a large value as compared with the case where the heating roller is not a magnetic shunt alloy, thereby reducing the control range of the power, resulting in a problem that the controllability is deteriorated.

  The present invention has been devised to solve such problems of the prior art, and its main purpose is to provide controllability in an electromagnetic induction heating and fixing apparatus using a magnetic shunt alloy as a heated object. An electromagnetic induction heating and fixing device configured to improve the energy efficiency of the switching element of the high-frequency power source without causing an excessive load and to avoid a decrease in heating efficiency and an image including the same It is to provide a forming apparatus.

The present invention provides a heated body made of a magnetic shunt alloy having a Curie temperature higher than the fixing temperature, an excitation coil for generating heat by electromagnetic induction, and detecting the temperature of the heated body. Temperature detecting means, a switching element provided on a power supply path to the excitation coil, and a switching element control means for controlling the switching element to adjust the power supplied to the excitation coil. The switching element control means performs power variable control for adjusting the supply power according to the detected temperature of the temperature detecting means so as to maintain the heated body at the fixing temperature after the warm-up is completed, and the power required for maintaining the fixing temperature. line but reaches the minimum power value, the power fixed intermittent control for intermittently based a fixed power supply input power to the detected temperature of said temperature detecting means An electromagnetic induction heating fixing device, having said minimum power value information minimum power value is set higher as the detected temperature increases of the temperature detecting means, said switching element control means, from the power variable control It said minimum power value used as a reference when switching to the power fixed intermittent control, a configuration which is adapted to determine from said minimum power value information in accordance with the detected temperature before Symbol temperature detecting means.

  According to the present invention, the control range of the input power can be widened, so that the controllability can be improved, and it is possible to surely avoid applying an excessive load to the switching element of the high-frequency power source, and switching. It is possible to save energy by avoiding that power is wasted due to heat generated by the element and heating efficiency is lowered.

A first invention made to solve the above-described problems is a heated body made of a magnetic shunt alloy having a Curie temperature higher than the fixing temperature and a Curie temperature in the vicinity thereof, and excitation that causes the heated body to generate heat by electromagnetic induction. A coil, temperature detecting means for detecting the temperature of the object to be heated, a switching element provided on a power supply path to the exciting coil, and controlling the switching element to adjust power supplied to the exciting coil Switching element control means for controlling the power supply to adjust the supply power according to the detected temperature of the temperature detecting means so as to maintain the heated body at the fixing temperature after the warm-up is completed. When the power required for maintaining the fixing temperature reaches the minimum power value, the power supply with the fixed input power is adjusted according to the detected temperature of the temperature detecting means. Cormorant line intermittently power fixed intermittent control performed Te an electromagnetic induction heating fixing device, has a minimum power value information said minimum power value is set higher as the detected temperature increases of the temperature detecting means, so that the switching element control means, determines the minimum power value as a reference when switching from the power variable control to the power fixed intermittent control, from the minimum power value information in accordance with the detected temperature before Symbol temperature detecting means The configuration is as follows.

  According to this, since the actual temperature of the object to be heated is low and there is a sufficient margin up to the Curie temperature, the minimum power value is set to a low value when voltage resonance is easily performed appropriately. Therefore, the control range of input power can be widened, and controllability can be improved. On the other hand, since the actual temperature of the object to be heated is high and close to the Curie temperature, it is difficult to properly perform voltage resonance, so the minimum power value is set to a high value. It is possible to surely avoid applying an excessive load to the switching element, and it is possible to save energy by avoiding power consumption being wasted due to heat generated by the switching element and reducing the heating efficiency. .

A second invention has been made in order to solve the above problems, the minimum power value information, the minimum power value for each detected temperature region divided into a plurality are configured as a constituent Ru Empire.

  According to this, the minimum power value information indicating the correlation between the input voltage and the detected temperature of the temperature detecting means and the minimum power value can be a simple table, reducing the amount of data, and obtaining by a calculation formula. Complex calculation processing is not required.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a copying machine to which the present invention is applied. The copying machine (image forming apparatus) includes an original reading unit 1 that reads an image of an original, an image forming unit 2 that forms an image of the original read here on a recording paper (image forming medium) with toner, A fixing unit (electromagnetic induction heating fixing device) 3 for fixing a toner image formed on the recording paper. The recording paper is supplied from the paper supply unit 4 to the image forming unit 2, and the fixing unit 3 performs fixing processing. The finished recording paper is discharged to the paper discharge unit 5.

  In the image forming unit 2, the photosensitive drum 12 uniformly charged by the charging roller 11 is irradiated with laser light from the laser scanning unit 13 to form an electrostatic latent image on the image forming surface of the photosensitive drum 12. After that, the toner in the developing unit 14 is supplied to the photosensitive drum 12 through the developing roller 15 to develop the electrostatic latent image on the image forming surface, and the toner image formed thereby is transferred. The image is transferred onto the recording paper by the roller 16.

  FIG. 2 is a cross-sectional view showing a main part of the fixing unit 3 shown in FIG. The fixing unit 3 includes a heating roller (heated body) 21 that heat-melts the toner image on the recording paper (image forming medium) S, and a pressure roller that is urged by a spring (not shown) so as to be in pressure contact with the heating roller 21. The recording paper S is fed into the nip portion between the heating roller 21 and the pressure roller 22, and the toner on the recording paper S is fixed to the recording paper S by the action of heat and pressure.

  The heating roller 21 has a hollow cylindrical roller body 24 made of a magnetic shunt alloy such as an iron-nickel alloy, and an electromagnetic induction heating unit 25 is accommodated in the roller body 24. The electromagnetic induction heating unit. 25 is driven by a high frequency power source 26, and the roller body 23 generates heat by a high frequency magnetic field generated by the exciting coil 32. A release layer (not shown) made of a fluorine resin or the like is formed on the surface of the roller body 24.

  The Curie temperature of the magnetic shunt alloy constituting the heating roller 21 is set higher than and near the fixing temperature, and when the temperature of the heating roller 21 exceeds the fixing temperature and approaches the Curie temperature, the relative magnetic permeability is set. And the heat generation of the heating roller 21 is suppressed, and an abnormal temperature rise that is significantly higher than the fixing temperature can be prevented.

  A nonmagnetic metal layer 27 for improving the heat generation efficiency is formed on the inner peripheral surface of the roller body 24 via an electrically insulating layer 28. The roller body 24 and the roller body 24 are not coated with a high frequency magnetic field generated by the excitation coil 32. The magnetic metal layer 27 generates heat. The nonmagnetic metal layer 27 has a mode in which a part in the circumferential direction is removed for the purpose of normally driving the resonance circuit of the high frequency power supply while suppressing an increase in the resistance load of the exciting coil 32 due to the influence of the nonmagnetic metal layer. A notch 29 is formed.

  The pressure roller 22 has a metal core 30 made of an aluminum alloy material and an elastic layer 31 made of a sponge material such as foamed silicone rubber formed around the metal core 30.

  FIG. 3 is a cross-sectional view of the heating roller 21 shown in FIG. 2 in the axial direction. The electromagnetic induction heating unit 25 housed in the heating roller 21 includes a plurality of exciting coils 32 provided in series in the axial direction, and a magnetic core 33 provided individually in the plurality of exciting coils 32. In order to hold the exciting coil 32 and the magnetic core 33, the core 34 is made of a nonmagnetic material such as aluminum extending in the axial direction.

  The exciting coil 32 is formed coaxially with the heating roller 21 by a conducting wire (Litz wire) 36 wound around the center line of the heating roller 21. Each of the exciting coils 32 is provided with two magnetic cores 33 at the same axial position and at symmetrical positions with the center line of the heating roller 21 as the center. An exciting coil 32 is formed by winding a conducting wire 36 around the wire. In addition, the magnetic core 33 and the magnetic cores 33 adjacent to each other in the axial direction are shifted from each other by 90 degrees in the circumferential direction with respect to the center line of the heating roller 21.

  The magnetic core 33 is made of a ferromagnetic material such as ferrite, protrudes from the base 33 a extending inside the exciting coil 32 to the outside of the exciting coil 32, and the tip is the inner peripheral surface of the heating roller 21. Is provided with a pair of projecting portions 33b. The magnetic flux generated by the exciting coil 32 is guided by the magnetic core 33 and proceeds in a substantially radial direction from the front end surface of the protruding portion 33 b and enters in a direction substantially orthogonal to the inner peripheral surface of the roller body 24.

  FIG. 4 is a block diagram showing a schematic configuration of the high-frequency power source 26 shown in FIG. The high-frequency power source 26 controls the power supply to the exciting coil 32, the rectifying circuit 42 that rectifies the alternating current from the AC power source 41, the resonance capacitor 43 that is connected in parallel to the exciting coil 32 and constitutes the LC resonance circuit. A switching element 44 such as an insulated gate bipolar transistor (IGBT), a diode 45 connected in parallel to the switching element 44, a drive circuit 46 for driving the switching element 44, and a circuit block including the exciting coil 32 are input. A current detector 47 for detecting a current value, a voltage detector 48 for detecting a voltage value input to a circuit block including the exciting coil 32, a thermistor (temperature detector) 49 for detecting the temperature of the heating roller 21, Excitation based on current, voltage, and temperature detected by current detector 47, voltage detector 48, and thermistor 49 IH control unit for controlling power supply to yl 32 and a (switching element control unit) 50.

  The IH control unit 50 includes an A / D conversion unit 52 that performs A / D conversion on the output signals of the current detection unit 47, the voltage detection unit 48, and the thermistor 49, and the current, voltage, And a CPU 53 for controlling the switching operation of the switching element 44 via the drive circuit 46 based on each value of the temperature, a ROM 54 for storing a processing program executed by the CPU 53, and a work area for the calculation of the CPU 53. And a RAM 55.

  Further, here, in order to perform power fixed intermittent control that intermittently supplies power with fixed input power, a drive signal (ON signal) output from the drive circuit 46 in response to a power control signal from the IH control unit 50. Is provided with an intermittent control switching element 56 that prevents or allows input of power to the power adjustment switching element 44, and a drive circuit 46 that drives the switching element 56. Thus, the switching operation of the switching element 56 is controlled via the drive circuit 46.

  The switching element 56 for intermittent control is provided so as to short-circuit the emitter and the gate of the switching element 44 for power adjustment in the on state, and a drive circuit according to an on / off control signal input from the IH control unit 50 When the switching element 56 is turned on by the drive signal (ON signal) output from the drive circuit 57, the drive signal output from the drive circuit 46 is prevented from being input to the switching element 44 for power adjustment. Regardless of whether the drive signal from 46 is on or off, the switching element 44 remains off and no power is supplied to the exciting coil 32.

  On the other hand, when the switching element 56 for intermittent control is turned off by the drive signal (off signal) output from the drive circuit 57, the drive signal output from the drive circuit 46 is input to the switching element 44 for power adjustment. In response to the drive signal from the drive circuit 46, the switching element 44 for power adjustment is turned on / off, and the required power is supplied to the exciting coil 32.

  FIG. 5 shows a change state of the temperature of the heating roller 21 shown in FIG. 4 and the power supplied from the high frequency power supply 26 to the exciting coil 32. Here, when the power is turned on, the maximum power (for example, 1300 W) is turned on to warm up the heating roller 21 rapidly, and the reference temperature is set lower than the fixing temperature (for example, 200 ° C.). When it reaches, temperature control for maintaining the heating roller 21 at the fixing temperature is started.

  In this temperature control, first, variable power control is performed to adjust the supplied power in accordance with the detected temperature of the thermistor 49, and the electric power necessary to maintain the fixing temperature in accordance with a decrease in the amount of heat radiation accompanying an increase in ambient temperature. When becomes smaller than the minimum power value, fixed power intermittent control is performed in which power supply with fixed input power is intermittently performed according to the detected temperature of the thermistor 49.

  In the variable power control, the amount of power supplied to the exciting coil 32 is adjusted based on the temperature detected by the thermistor 49 so that the temperature of the heating roller 21 is kept constant at the fixing temperature. By changing the on-duty of the power control signal (the ratio of the time during which the switching element 44 is turned on), the power necessary to keep the temperature of the heating roller 21 constant at the fixing temperature is supplied to the exciting coil 32. Is done.

  In the power fixed intermittent control, the power supply fixed to the minimum power value is intermittently performed according to the detected temperature of the thermistor 49. At this time, the power control signal by the on-duty corresponding to the minimum power value is used for power adjustment. Of the switching element 56 for intermittent control that blocks / allows input of the driving signal (ON signal) output from the driving circuit 46 to the switching element 44, while being output to the driving circuit 46 that drives the switching element 44. By changing the ON / OFF time, electric power necessary for maintaining the temperature of the heating roller 21 at the fixing temperature constant is supplied to the exciting coil 32.

  The minimum power value serving as a reference when switching from variable power control to fixed power intermittent control is a lower limit value of power that can be input to protect the switching element 44 of the high-frequency power supply 26, and the input voltage and the detected temperature of the thermistor 49. It is determined based on. In obtaining this minimum power value, a calculation formula or table is created as minimum power value information indicating the correlation between temperature and minimum power value for each input voltage based on experiments in advance, and the minimum power value information is controlled by IH control. The CPU 53 executes processing for obtaining the minimum power value by referring to the minimum power value information and stored in the ROM 54 of the unit 50.

  In the experiment for creating the minimum power value information, as shown in FIG. 7B, the magnitude of the abnormal current generated in the switching element 44 is measured while changing the power value for each temperature. Comparing the abnormal current value with a predetermined threshold value indicating an allowable limit that does not result in an excessive load that destroys the switching element 44, the minimum power value that satisfies the condition that the abnormal current value falls below the threshold value is obtained. As shown in FIG. 8, data indicating the correlation between the fixing temperature and the minimum power value is acquired as the minimum power value.

  In this way, by switching from the variable power control to the fixed power intermittent control based on the minimum power value determined based on the input voltage and the detected temperature of the thermistor 49, the temperature of the heating roller 21 is low, and the Curie temperature is sufficient. Because there is a sufficient margin, when the voltage resonance at the high frequency power supply 26 is in a state where it is easily performed, the minimum power value is set to a low value. It can be expanded and controllability can be improved.

  On the other hand, since the temperature of the heating roller 21 is high and close to the Curie temperature, the minimum power value is set to a high value when voltage resonance at the high frequency power supply 26 is difficult to be performed properly. In addition, it is possible to reliably avoid applying an excessive load to the switching element 44 of the high-frequency power supply 26. Also, it is possible to avoid that power is wasted due to heat generated in the switching element 44 and heating efficiency is reduced. Energy saving can be achieved.

  FIG. 6 is a graph for explaining a procedure for obtaining the minimum power value shown in FIG. 5 from the input voltage and the detected temperature of the thermistor 49. In the example shown in FIG. 6A, the minimum power value is indicated by a curve that continuously changes in the temperature fluctuation range (here, 150 ° C. to 210 ° C.) of the heating roller 21 predicted at the time of variable power control. In this case, as shown in FIG. 8, a calculation formula indicating the correlation between the detected temperature and the minimum power value is set for each input voltage based on the minimum power value for each temperature obtained by experiment. The minimum power value is obtained from the input voltage and the detected temperature of the thermistor 49 according to this calculation formula.

  In the example shown in FIG. 6B, the minimum power value is indicated by a straight line that changes stepwise in the temperature fluctuation range (150 ° C. to 210 ° C. in this case) of the heating roller 21 predicted during the variable power control. The minimum power value is set for each of a plurality of temperature regions (here, 10 ° C. unit). In this case, as shown in FIG. 8, based on the minimum power value for each temperature obtained by experiment, A table indicating the correlation between the temperature region and the minimum power value is set for each input voltage, and the minimum power value is obtained from the input voltage and the detected temperature of the thermistor 49 according to this table. In particular, here, the minimum power value for each temperature region is set to the highest value that is on the safe side within the temperature region.

  In the above example, the configuration in which the pressure roller is brought into pressure contact with the heating roller in which the induction heating unit is accommodated and the recording paper is passed through the nip formed between the two is described. In order to improve the characteristics, a configuration using a heating belt having a smaller heat capacity than that of the roller can be similarly applied. In this case, an endless belt-shaped heating belt is wound around the heating roller and the fixing roller in which the induction heating unit is accommodated, and a pressure roller disposed opposite to the fixing roller and a portion where the heating belt is wound around the fixing roller. By passing the recording paper between them, the toner on the recording paper is fixed to the recording paper by the action of heat and pressure.

  The electromagnetic induction heating fixing device and the image forming apparatus including the same improve the controllability, do not apply an excessive load to the switching element of the high frequency power supply, and avoid a decrease in heating efficiency. An electromagnetic induction heating and fixing device having an effect of energy saving and using a magnetic shunt alloy for a heated object such as a heating roller, and an image forming apparatus including the same, such as a printer, a facsimile machine, a copying machine, and a composite It is useful as a machine.

Schematic sectional view showing a schematic configuration of a copying machine to which the present invention is applied Sectional drawing which shows the principal part of the fixing | fixed part shown in FIG. A sectional view in the axial direction of the heating roller shown in FIG. The block diagram which shows schematic structure of the high frequency power supply shown in FIG. The figure which shows the change condition of the electric power supplied to the exciting coil from the temperature of a heating roller shown in FIG. 4, and a high frequency power supply The figure explaining the point which calculates | requires the minimum electric power value shown in FIG. 5 from input voltage and the detection temperature of a thermistor. The figure which shows the change condition of the voltage and electric current of a switching element (IGBT) Diagram showing correlation between fixing temperature and minimum power value

Explanation of symbols

3 Fixing part (electromagnetic induction heating fixing device)
21 Heating roller (object to be heated)
24 Roller body 25 Electromagnetic induction heating unit 26 High frequency power supply 32 Excitation coil 44 Switching element 46 Drive circuit 47 Current detection part 48 Voltage detection part 49 Thermistor 50 IH control part (switching element control means)
56 switching element 57 drive circuit

Claims (3)

A heated body made of a magnetic shunt alloy having a Curie temperature higher than the fixing temperature and a Curie temperature in the vicinity thereof, an exciting coil that heats the heated body by electromagnetic induction, and a temperature detection means for detecting the temperature of the heated body And a switching element provided on a power supply path to the excitation coil, and a switching element control means for controlling the switching element to adjust the power supplied to the excitation coil,
The switching element control means performs variable power control for adjusting the supply power according to the temperature detected by the temperature detecting means so as to maintain the heated body at the fixing temperature after the warm-up is completed, and is required for maintaining the fixing temperature. When the power reaches a minimum power value, a row cormorants electromagnetic induction heating fixing device power fixed intermittent control for intermittently based a fixed power supply input power to the detected temperature of said temperature detecting means,
The minimum power value information is set such that the minimum power value is set higher as the detection temperature of the temperature detection means becomes higher,
So that the switching element control means, determines the minimum power value as a reference when switching from the power variable control to the power fixed intermittent control, from the minimum power value information in accordance with the detected temperature before Symbol temperature detecting means An electromagnetic induction heating fixing device characterized by that. It said minimum power value information electromagnetic induction heating fixing device according to claim 1 minimum power value for each detected temperature area divided into a plurality, characterized in Tei Rukoto is set.   An image forming apparatus comprising the electromagnetic induction heating and fixing device according to claim 1.

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