Abstract:
A heating apparatus includes a coil for generating a magnetic field; a heating element for generating heat by eddy currents generated by the magnetic field; an electroconductive member for generating an electromotive force by a current flowing through the coil; and an electric circuit for generating a voltage by electrical collection from the electroconductive member.

Description:
The present invention relates to a DC voltage generating device using an induction heating type type. 
   An image forming apparatus of an electrophotographic type includes heating means (roller, endless belt member or the like) and pressing means (roller, endless belt member or the like) which are rotated while being in press-contact with each other to form a nip through which a transfer material electrostatically carrying toner which is made of resin material, magnetic particle, coloring material and so on. While it is passed through the press-contact portion (nip), the toner is fused and fixed. 
   The fixing device may be of a halogen heater type, wherein the heat is produced. In this type, a halogen heater is provided in a fixing roller to radiate heat to the inner surface of the fixing roller such that outer surface of the fixing roller is maintained at a predetermined temperature. However, with this method, the space existing between the halogen heater and the fixing roller has to be heated the heat loss is relatively large. In addition, since the fixing roller is indirectly heated by the halogen heater, the start-up time is relatively long. 
   As a measure to solve such problems, an induction heating type fixing device attracts attention. 
   In this type, a high frequency current is applied to an excitation coil to generate a high frequency magnetic field which acts on the inner surface layer of the heat roller, thus generating eddy currents in the electroconductive layer of the fixing roller. The eddy current generates joule heat, so that self-heat-generation occurs in the heat roller per se. 
   With this heating method, the inner surface layer of the heat roller itself is a heat generating element (direct heating), and therefore, the heat generating efficiency is high, and the heat roller can be quickly heated up to the required fixing temperature. This accomplishes quick start-up. In addition, the electric power using efficiency is high, and therefore, the electric energy consumption can be significantly reduced. 
   Here, the inner surface of the fixing roller opposed to the excitation coil is a metal layer (electroconductive layer). with such a structure, an electromotive force is generated in the metal layer by the AC current flowing through the halogen heater or excitation coil, as is known. The electromotive force is influenced by impedance Z—1/(2πfC). Where f is a frequency of the AC current flowing through the halogen heater and the excitation coil, C is an electric capacity between the metal layer and the halogen heater or the excitation coil. Normally, the frequency of the halogen heater is equivalent to the frequency of the commercial power source having a frequency of 50 Hz or 60 Hz. On the other hand, the frequency of the AC current flowing through the excitation coil is high enough to generates the sufficient joule heat in the electroconductive layer, for example, 20 KHz-1 MHz. Although the electromotive force is small in the fixing type using the halogen heater, a larger electromotive force is generated in the metal layer in the induction heating type than in the halogen heater type because the frequency is high, and therefore, the impedance is small. It is preferable to utilize the electromotive force. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is a principal object of the present invention to utilize an electromotive force generated in an electroconductive member by flow of a current in a coil in an induction heating type. It is another object of the present invention to accomplish saving of electric power consumption. 
   According to an aspect of the present invention, there is provided a heating apparatus includes a coil for generating a magnetic field; a heating element for generating heat by eddy currents generated by the magnetic field; an electroconductive member for generating an electromotive force by a current flowing through the coil; and an electric circuit for generating a voltage by electrical collection from the electroconductive member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of an image forming apparatus. 
       FIG. 2  is a sectional view of an induction heating type fixing device. 
       FIG. 3  is a schematic block diagram of a circuit according to a first embodiment of the present invention. 
       FIG. 4  illustrates a structure of a fixing device using a rectifying bias voltage circuit according to a first embodiment of the present invention. 
       FIG. 5  illustrates a detail of the inside of a heat roller according to the first embodiment. 
       FIG. 6  illustrates a heating apparatus according to a second embodiment of the present invention wherein mounting operation is easy. 
       FIG. 7  is a schematic block diagram of a circuit according to a third embodiment of the present invention. 
       FIG. 8  illustrates a structure of a fixing device using a rectifying bias voltage circuit according to a third embodiment of the present invention. 
       FIG. 9  illustrates a detail of the inside of a heat roller according to the third embodiment. 
       FIG. 10  is a diagram of a circuit according to a fourth embodiment of the present invention using wiring effective to a bias voltage which is efficient. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , the description will be made as to a series of process operations for an image formation. 
     FIG. 1  substantially shows a structure a 4 drum laser beam printer (printer) including a plurality of light scanning means, as an example of an image forming apparatus according to an embodiment of the present invention. As shown in  FIG. 1 , the printer of this embodiment comprises four image forming stations (image forming means) each including an electrophotographic photosensitive member as a latent image bearing member (photosensitive drum), and a charging device, developing device, cleaning device and the like around the electrophotographic photosensitive member. Images formed on the photosensitive drums formed in the respective image forming stations are transferred onto a recording material such as paper carried on feeding means passing by the latent image bearing member photosensitive drum. 
   The image forming stations Pa, Pb, Pc, Pd functions to form images of magenta, cyan, yellow and black colors respectively and have the photosensitive drums  1   a ,  1   b ,  1   c ,  1   d , and the photosensitive drums are rotatable in the direction indicated by an arrow. As regards the photosensitive drums  1   a ,  1   b ,  1   c ,  1   d , there are provided chargers  5   a ,  5   b ,  5   c ,  5   d  for electrically charging the surfaces of the photosensitive drums, respectively; developing devices  2   a ,  2   b ,  2   c ,  2   d  for developing image information to which the photosensitive drums  1   a ,  1   b ,  1   c ,  1   d  are exposed after being charged by the chargers  5   a ,  5   b ,  5   c ,  5   d , respectively; and cleaners  4   a ,  4   b ,  4   c ,  4   d  for removing the residual toner from the photosensitive drum after the images are transferred, respectively. They are disposed in the order named around each of the photosensitive drum  1   a ,  1   b ,  1   c ,  1   d  in the rotational direction. Below the photosensitive drum, there is provided a transfer portion  3  for transferring the toner images from the photosensitive drums onto the recording material. The transfer portion  3  includes a transfer belt  31  (recording material feeding means) which is common to the image forming stations, and chargers  3   a ,  3   b ,  3   c ,  3   d  for transfer charging operations, respectively. 
   In such a printer, the paper P is supplied from the sheet feeding cassette  61  (recording material supplying means), as shown in  FIG. 1 , is passed through the respective image forming stations on the transfer belt  31 , and received the color toner images from the respective photosensitive drum. By the transfer step, unfixed toner images are formed on the recording material. The recording material P carrying the unfixed toner images is separated from the transfer belt  31  and is transported by a conveyer belt  62  (recording material guiding means) to the fixing device  5 . 
   The description will be made as to the structures of the fixing device  7 . 
     FIG. 2  is a sectional view of a fixing device according to an embodiment of the present invention. 
   The fixing roller  71  (rotatable member or fixing rotatable member) comprises a core metal cylinder of steel having an outer diameter of 32 mm and a thickness of 0.7 mm, and a parting layer of PTFE or PFA having a thickness of 10-50 μm which improves the surface parting property. As a material of the fixing roller, the use may be made with a magnetic material (magnetic metal) such as magnetic stainless steel that has a relatively high magnetic permeability and a proper resistivity. A non-magnetic material is usable if it is electroconductive (metal)and if it is thin enough. The pressing roller  72  (pressing member) has a core metal made of steel having an outer diameter of 20 mm, an elastic layer of silicone rubber having a thickness of 5 mm on the outer periphery of the core metal, and a parting layer of PTFE or PFA which improves the surface parting property having a thickness of 10-50 μm into an outer diameter of 30 mm, similarly to the fixing roller  71 . The fixing roller  71  and the pressing roller  72  are rotatably supported, and the fixing roller  71  is driven to rotate by a motor (driving means). The pressing roller  72  is press-contacted to the surface of the fixing roller  71 , and is driven by frictional force at the press-contact portion (nip). The pressing roller  72  is pressed by a mechanism by a spring in an axial direction of the fixing roller  71 . The temperature sensor  73  (temperature sensor) is disposed so as to be contacted to the surface of the fixing roller  71 , and compares the output of the temperature sensor  73  with the target temperature of the fixing roller  71  in the temperature detecting portion. In accordance with the result of comparison, the fixing roller  71  to the induction coil  78   a  (coil) is increased or decreased by an induction heating control circuit (electric power supply control means or IH control circuit), thus effecting an automatic control to provide a predetermined constant temperature at the surface of the fixing roller  71 . Detailed description will be made as to the induction heating coil unit  78  (coil unit). The induction coil  78   a  is supplied with a high frequency electric power of 100-2000 kW, and therefore, it is made of Litz comprising several fine wires. The litz wire is wound and is integrally molded with a resin material (non-magnetic member). The resin material may be PPS, PBT, PET, LCP (liquid crystal polymer) or the like resin material which is non-magnetic. Designated by  76   a ,  76   b  and  76   c  are magnetic cores which comprise high magnetic permeability and low loss material such as ferrite. When an alloy such as permalloy is used, a laminated structure may be used since otherwise the eddy current loss in the core is large when the frequency is high. The core is used to raise the efficiency of the magnetic circuit and to provide a magnetic blocking effect. The coil unit  78  is mounted to a stay  75  and is fixed relative to the fixing device. The description will be made as to an electric circuit of an induction heating type and a rectifying circuit therefor in this embodiment of the present invention.  FIG. 3  is a block diagram of an induction heating type fixing device according to the present invention. Designated by TRI is a MOS-FET which is a TRI; C 2  is a resonance capacitor for making a resonance waveform from the high frequency AC applied to the dielectric heating coil  78   a  which is a load; D 5  is a flywheel diode for regenerating the electric power accumulated in the dielectric heating coil  78   a . The thermister  73  (temperature sensor) is contacted to the fixing roller  71  in the structure shown in  FIG. 4 , and the output therefrom is inputted to the temperature detection/comparison circuit IC 2 . The circuit IC 2  compares the input signal for the temperature control and the output from the circuit IC 2 , and the difference therebetween is fed, as a control signal, to the pulse modulation (PFM) oscillation circuit having the circuit IC 1 . The circuit IC 1  generates PFM pulses in accordance with the control signal value and supplies the output to a gate of the MOS-FET to switch TRI. 
   Designated by D 1 -D 4  are diodes for input electric energy rectification for rectifying AC, and it supplies rectified pulsating flow to the electric power control circuit portion. A noise filter NF 1  and the capacitor C 1  constitutes a noise filter and are set to provide such a constant as to give a sufficient attenuation amount is assured with respect to the switching frequency of TR 1  and as to pass without attenuation with respect to the voltage source frequency. A collector member  103  is electrically contacted to the fixing roller  71  to keep electric connection, and an electrode thereof is connected with a capacitor C 10  and a resistor R 10 . 
   The capacitor C 10  is connected with diodes D 10 , D 11  and a capacitor C 12 , and the diodes D 10  and D 11  are connected to the opposite ends of the capacitor C 11  to constitute a so-called doubling rectification circuit. 
   The description will be made as to the operation. 
   Referring to  FIG. 5 , when an AC input voltage is applied to the input terminal, the voltage is rectified by the rectifying element comprising the diodes D 1 -D 4  into pulsating flow, and the voltage thereof is applied across the opposite ends of the capacitor C 1  through the noise filter NF 1 . The end-to-end voltage of the capacitor C 1  has a waveform of rectified AC input voltage. 
   When the temperature control input signal Vc is inputted to the temperature detection/comparison circuit IC 2 , the temperature detection/comparison circuit IC 2  compares the output of the temperature detecting element, namely, the thermister  73  with the target temperature of the input signal Vc. The output indicative of the result of comparison is fed to the PFM oscillation circuit IC 1  as a control signal. The comparison circuit IC 1  produces a PFM signal having a pulse corresponding to the control signal value, and the output thereof is applied across the gate sources of TR 1 , which in turn switches in accordance with the output pulse of the circuit IC 1  to flow the drain current ID, thus supplying the electric power to the induction coil  78   a.    
   Since the induction coil  78   a  accumulates the current provided by actuation of TR 1 , it generates a counterelectromotive voltage upon deactuation of TR 1 , by which the cumulative current in the coil is charged into the resonance capacitor C 2 . 
   The cumulative current thus supplied raises the resonance capacitor voltage. The current flowing out of the coil  78   a  attenuates in inverse-proportional with rise of the voltage across the resonance capacitor C 2  down to zero coil current, and then after the zero point, the charge accumulated in the resonance capacitor C 2  produces a current flowing into the induction coil  78   a.    
   Thereafter, the charge accumulated in the resonance capacitor C 2  returns to the induction coil  78   a , and simultaneously therewith, the voltage of the induction coil  78   a  lowers such that drain voltage of the TR 1  becomes lower than the source voltage, by which the flywheel diode D 5  is actuated to produce a forward current. Upon actuation of TR 1 , the current flows through the induction coil  78   a , thus repeating accumulation of the current in the induction coil  78   a . This produces eddy current in the fixing roller  71  which is a load electrically connected with and opposed to the induction coil  78   a . Thus, the fixing roller  71  made of the electroconductive material generates joule heat which is roller resistance value of itself multiplied by induced current squared. 
   The current flowing through the switching element TR 1  and induction coil  78   a  is smoothed by the capacitor C 1  charging and discharge the high frequency component. Therefore, the high frequency current does not flow through the input noise filter NF 1 , and only the AC-rectified input current waveform flows. 
   The current flowing through the rectifying diodes D 1 -D 4  has a current waveform provided by filtering the current waveform flowing through the TR 1  and the induction heating coil  78   a  with the noise filter constituted by the capacitor C 1  and the noise filter NF 1 , so that AC input current waveform before the rectification approximates the AC input voltage waveform, and therefore, the higher harmonics wave component in the input current can be significantly reduced. This significantly improves a power factor of the input current into the temperature control circuit in the fixing heating circuit. The noise filter NF 1  and the capacitor C 1  used in the circuit may be any if it provides a filtering effect with respect to the high oscillation frequency provided by IC 1 . Since the capacity of the capacitor C 1  and the inductance value of the noise filter NF 1  can be made small, the size and weight can be reduced. 
   The inputting of the temperature control signal into the dielectric heating voltage source produces a high frequency AC voltage having a frequency of approx. 20 KHz-1 MHz at the output terminal of the induction heating voltage source. The output of the temperature sensor comprising a thermister  73  for measuring a surface temperature of the fixing roller  71  is inputted into the temperature detection/comparison circuit IC 2  at proper timing, and is compared with the target temperature, and then difference therebetween is fed back to the circuit IC 1 . The circuit IC 2  functions to generate a feedback signal to maintain a constant surface temperature of the fixing roller using a control system such as a proportional control in which the applied high frequency electric power is decreased when the thermister detected temperature approaches to the set target temperature or a so-called PID. 
   The circuit IC 1  receives the signal indicative of the difference from the target temperature detected by the circuit IC 2 , and in accordance with the difference, the on-time of the gate of TR 1  is determined to adjust the supplied electric power to the TR 1 , so as to control the electric power supplied to the fixing roller  71 . In this manner, the heating value of the roller is controlled, ant the fixing temperature for toner fixing is stabilized. To effect such an effect, a resonance voltage of approx. 100-600V is applied across the induction coil  78   a  disposed inside the fixing roller shown in FIG.  3 . 
   As shown in  FIG. 5 , electric force lines are generated in the fixing roller  71  which is made of the electroconductive material, by the induction coil  78   a , so that induced voltage of high frequency corresponding to the oscillation frequency of the induction heating voltage source is generated, that is, the electromotive force is generated, for the fixing roller  71 . The induced high frequency voltage is collected from the electroconductive layer of the fixing roller  71  by a collector member  103 , and is fed to a bias circuit  104 . Thus, when the high frequency current is applied from the dielectric heating voltage source to the induction coil  78   a , a potential difference E(L)=ωLi is generated between the opposite ends of the induction heating coil  78   a , where L=induction coil inductance, i=applied voltage. 
   The potential difference forms the lines of electric force  107  in the Figure from the surface of the heating coil to the core metal. As a result, the core metal potential generates a potential proportional to the voltage applied to the induction heating coil. 
   By the bias circuit  104 , the high frequency AC voltage injected from the capacitor C 10  is rectified by the D 10 , and the capacitor C 10  is charged to the peak value of the AC voltage waveform. The charge accumulated in the capacitor C 10  charges capacitor C 11  by conduction of D 12  in the next cycle, so that capacitor C 11  generates a DC voltage corresponding to the cycle of the AC voltage inputted to the capacitor C 10 . 
   The capacitor C 10 , the diodes D 10  to D 12  and the capacitor C 11  constitutes a so-called doubling rectification circuit of one stage. In this example, there is provided a four fold structure, so that 4times voltage rectifying circuit is provided. When, for example, the potential induced in the fixing roller  71  from the induction heating coil  78   a  has a peak-to-peak voltage of 150 Vp-p, a DC potential of −150V is generated by the capacitor C 11 , and a DC potential of −600V is generated at a connection point between the D 17  and a capacitor C 17  at the fourth stage. 
   The DC potential is supplied to a collector member  103  through a limiting resistance R 10 , by which a DC potential of −600V relative to the ground level can be supplied to the fixing roller  71 . The limiting resistor R 10  preferably has a resistance value of not less than 1 MΩ.  FIG. 4  is a block diagram wherein the above-described system is incorporated in a fixing device. As shown in the Figure, according to this embodiment of the present invention, the bias circuit can be constituted as a circuit block on a printed board or ceramic substrate, and therefore, only two wiring lines are required, wherein one is a wiring line to the collector member and the other is to ground the bias circuit  104 , and the circuit structure per se is simple. For this reason, the system can be directly mounted on the outer casing portion of the fixing device, thus accomplishing the roller bias voltage supply with a very simple structure. 
   In this embodiment, the bias circuit supplies the electric power to the fixing roller  71  for the following reasons. The toner image formed through the image forming process is electrically charged. In order to avoid that toner is deposited onto the fixing roller  71  while passing through the nip (toner offset), the core metal of the fixing roller  71  is supplied with a voltage having the same polarity as the charged potential of the toner. Conventionally, it is necessary to provide an additional bias voltage source for producing the voltage applied to the core metal, so that relatively large space is required, with the result of bulkiness of the image forming apparatus and lager consumption of the electric power. In this embodiment, the fixing roller  71  for fixing the toner which is charged to the negative polarity is supplied with the approx. −600V generated by the bias circuit. The parting layer which is a surface layer of the fixing roller  71  is give a proper degree of electroconductivity to accomplish effective function of the bias potential applied to the core metal  109  for the surface of the fixing roller. In order to raise the parting property of the fixing roller relative to the sheet of paper, the use can be made with an electroconductive Teflon coating (registered Trademark) or tube in place of the parting layer. In this embodiment, the voltage is −600V, but this value is not limiting. As described in the foregoing, in the induction heating type heating apparatus, the electromotive force generated in the electroconductive member by the flow of the current through the coil is utilized to apply a voltage to a part requiring a voltage supply. By doing so, the voltage source can be eliminated so that space and power consumption can be saved. 
   Second Embodiment 
     FIG. 6  shown an apparatus according to another embodiment of the present invention. Collector member  103  is provided on a bias circuit board  104 , and a grounding electrode  111  is provided on the bias circuit board  104 . The grounding electrode on the bias circuit board  104  is contacted and electrically grounded to the fixing device casing  102  by a screw  112  for fixed the bias circuit board  104  with the screw bore for fixing to the fixing device casing  102 . On the bias circuit substrate, there is provided a sliding electrode, too, which is in sliding contact with the fixing roller  71 , and the sliding electrode  103  is so arranged that when the bias circuit  104  is mounted by the screw  112 , the sliding electrode  103  is contacted to the fixing roller  71 . Therefore, by mounting the bias circuit  104  on the fixing device casing  102  by a mounting screw or the like, the grounding and the contact of the electric energy supply member  103  to the fixing roller is accomplished such that necessity for the roller bias wiring can be eliminated. Thus, the fixing bias can be supplied to the fixing roller  71  with a very simple structure. 
   Third Embodiment 
   A further embodiment will be described. In the further embodiment, the same reference numerals as with the foregoing embodiment are assigned to the elements having the corresponding functions, and the detailed descriptions for such elements are omitted for simplicity.  FIG. 7  is a block diagram of a fixing device actuating circuit of an induction heating type according to a third embodiment of the present invention. 
   To the fixing roller  71 , an electric energy supply member  103  is electrically contacted to keep the electroconductive state, and the electrode is connected with a bias circuit output terminal  104 . In this embodiment, there is provided a collecting electrode  105  of an electroconductive metal such as a steel or the like. The collecting electrode  105  disposed in the fixing roller  71  is connected to the diodes D 10 , D 11  and to the capacitor C 12 . The diodes D 10  and D 11  are connected to the opposite ends of the capacitor C 11  to constitute a so-called doubling rectification circuit. By flowing the current through the induction coil  78   a , the heat is generated in the fixing roller  71 , similarly to the foregoing embodiment. Here, a resonance voltage of approx. 100-600V is applied across the induction coil  78   a  disposed in the heat generation roller as shown in  FIG. 9  to effect a heating operation. 
   The collecting electrode  105  is made of an electroconductive material which is electrically isolated from the induction coil  78   a . Lines of electric force are produced for the collecting electrode as shown in FIG.  9 . Therefore, an induced voltage is generated for the collecting electrode  105  by a high frequency electromotive force having an oscillation frequency from the induction heating voltage source. The induced high frequency voltage is supplied to the bias circuit  104  to rectify it. In the bias circuit  104 , the high frequency AC voltage injected from the collecting electrode  105  is rectified by the diode D 11 , so that capacitor C 11  is charged to a peak value of the AC voltage waveform. The charge accumulated in the capacitor C 11  electrically charges the capacitor C 12  by electric conduction of the diodes D 12  in the next cycle, and a DC voltage corresponding to the peak value of the AC voltage supplied to the capacitor C 11  is generated in the capacitor C 12 . The capacitor C 11 , diode D 10  to diode D 12  and capacitor C 11  and so on constitute a so-called doubling rectification circuit of one stage. In this example, there is provided a four fold structure, so that 4times voltage rectifying circuit is provided. 
   When, for example, the potential induced in the collector  105  from the induction coil  78   a  has a peak-to-peak voltage of 150 Vp-p, a DC potential of −150V is generated by the capacitor C 11 , and a DC potential of −600V is generated at a connection point between the diode D 17  and capacitor C 17  at the fourth stage. The DC potential is supplied to a collector member  103 , by which a DC potential of −600V relative to the ground level can be supplied to the surface of the fixing roller  71 .  FIG. 8  is a block diagram in which the system of the present invention is incorporated in the fixing device. As shown in the Figure, according to this embodiment of the present invention, the bias circuit can be constituted as a circuit block on a printed board or ceramic substrate, and therefore, only the supply wiring line from the collector member  105 , a grounding wiring line for grounding the bias circuit  104  and an electric energy supply member  103  for supplying a bias potential to the heat roller  100  are required, and the circuit structure per se is simple. For this reason, the system can be directly mounted on the outer casing portion of the fixing device, thus accomplishing the roller bias voltage supply with a very simple structure. The collecting electrode  105  comprises a ferrite core  76 , behind which there is provided an electroconductive material (generally a metal member), and it mechanically supports the induction heating coil  78   a . Thus, when the high frequency current is applied from the dielectric heating actuating voltage source to the induction coil  78   a , a potential difference E(L)=ωLi is generated between the opposite ends of the induction heating coil  78   a , where L=induction coil inductance, i=applied voltage. 
   This potential produces lines of electric force  107  for the ferrite core  76  and the collecting electrode  105  at the back side of the induction coil. Since the ferrite core  76  is electroconductive, the line of electric force induces in the ferrite core  76  a potential which is collected through the inside of the ferrite core  76  by the collecting electrode  105 . The potential of the collecting electrode  105  is proportional to the applied induction coil voltage. By introducing the voltage to the rectifying circuit, a DC voltage is generated. In this embodiment, the fixing roller  71  is supplied with a voltage having the same polarity as the polarity of the toner to prevent toner offset. The surface layer of the fixing roller  71  has a parting layer  71   a  which has a proper degree of electroconductivity to effectively apply the bias potential applied to the core metal to the surface of the fixing roller. In addition, in order to raise the parting property of the fixing roller relative to the sheet of paper, the use can be made with an electroconductive Teflon coating (registered Trademark) or tube in place of the parting layer  71   a . By introducing the high frequency potential change to the rectifying circuit  104 , the fixing bias potential effective to reduce the fixing offset can be efficiently generated. According to this embodiment, the amount of electric power collected by the collecting electrode  105  is that generated by the collecting electrode per se plus that of the electromotive force generated in the ferrite core  76 , and therefore, the electric power generated in the rectifying bias voltage circuit is larger than the power in the foregoing embodiments. Therefore, a high voltage can be generated without use of an external voltage source and without enlarging the rectifying bias voltage circuit. 
   Fourth Embodiment 
     FIG. 10  illustrates a further embodiment, by which a bias voltage is further efficiently generated. In this embodiment, as shown in  FIG. 9 , in the function of the lines of electric force on the collecting electrode  105 , the lines of electric force generated from the winding end portion of the induction coil  78   a , functions on the collecting electrode  105  more efficiently than the lines  107  of electric force generated from the winding start portion of the induction coil  78   a  (lower side in FIG.  9 ); a drain side of a main switch element TR 1  of the high frequency power applying device where a highest level of voltage is generated is connected to the end side of the induction heating coil  78   a ; and then, the high frequency potential change can efficiently act on the collecting electrode  105 , so that generated voltage by the collecting electrode  105  is higher. By doing so, the number of stages of the doubling rectifications can be reduced. In this embodiment, the voltage is applied to the fixing roller, but it may be supplied to the other portion requiring the voltage application, for example, to a discharging brush for electrically discharging the recording material, or the like. As described in the foregoing, in the induction heating type heating apparatus, the electromotive force generated in the electroconductive member by the flow of the current through the coil is utilized to apply a voltage to a part requiring a voltage supply. By doing so, the voltage source can be eliminated so that space and power consumption can be saved. 
   While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.