JP2013251275A - Induction heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating apparatus capable of supplying electric current to each of a plurality of heating means with small loss.SOLUTION: When a positive input power is generated, a pulsating current is smoothed by a smoothing circuit 16A through one diode 42A and an electric current is supplied to an induction coil 3A connected thereto. When a negative input power is generated, a pulsating current is smoothed by a smoothing circuit 16B through the other diode 42B and an electric current is supplied to an induction coil 3B connected thereto. Thus, whether an input power generated from a power source E is positive or negative, a current is supplied to a plurality of induction coils 3A and 3B through a single diode 42A or 42B, respectively, allowing a current to be supplied to each of induction coils 3A and 3B with small loss.

Description

  The present invention relates to an induction heating device applied to a fixing device or the like.

  This type of induction heating apparatus is configured to heat the fixing body by passing an electric current through the heating means as disclosed in, for example, Patent Document 1 so that a temperature change of the fixing body can be obtained. It has become. However, when the temperature of the fixing body changes, there is a concern that the fixing body and the induction heating device are adversely affected.

  In addition, a predetermined part of the fixing body can be heated by moving the fixing body by a driving source. However, if induction heating is performed without moving the fixing body, the fixing body is overheated only locally by the heating means. In this case, there is a concern that the fixing body is adversely affected.

  On the other hand, what heats a fixing body by switching a plurality of heating means is disclosed in, for example, Patent Document 2. In the induction heating apparatus having such a configuration, FIG. 9 shows a waveform diagram of the current IC flowing from the conventional heating means to the switching means. FIG. 9 shows that when the switching means is turned on in a predetermined state. A regenerative current Ir of such switching means is generated.

  Although this regenerative current Ir can be suppressed to some extent, this time, as shown in FIG. 10, a short circuit current Is is generated in the switching means, which becomes a loss of the switching means.

  From the above viewpoint, it is possible to suppress both the regenerative current Ir and the short-circuit current Is by some method, but in that case, a large space is occupied.

  Further, in the induction heating apparatus in which a plurality of heating means are arranged for the fixing body, as shown in FIG. 11, in order to rectify the input, a large number of rectifying means 101A to 101D are provided. A current is supplied to the resonance circuit 108A including the means 106A.

  Conventionally, for example, when an input is generated, current is supplied through a plurality of rectifiers 101A and 101C constituting the rectifier circuit 102 (see current path I in FIG. 11). However, there is a problem that the current passes through the plurality of rectifiers 101A and 101C or the rectifiers 101B and 101D, and the loss increases accordingly.

  On the other hand, this type of induction heating device detects an input to a resonance means including a heating means for performing induction heating, and based on the detection result, the control means changes the frequency of the switching means to control the input. To do. When the frequency of the current to the resonance means becomes equal to or lower than a predetermined frequency, there is a problem that a short-circuit current flows through the switching means. In order to prevent this, it is necessary to detect the current of the resonance means and perform control so that the frequency does not fall below the predetermined frequency, but there is a concern that the circuit configuration becomes complicated.

  As another method, it is conceivable to obtain a frequency in advance from the resonance means and to limit the variable range of the frequency so that the frequency of the switching means does not fall below a predetermined frequency by the control means. However, since the resonance means has variations and the frequency fluctuates, the variable range of the frequency must be designed according to the variations. For this reason, the switching means has to be operated at a frequency.

JP 2006-145887 A JP 2004-214081 A

  In view of the above problems, the present invention is to provide an induction heating apparatus that can supply current to a plurality of heating means with little loss.

  Another object of the present invention is to provide an induction heating apparatus capable of correctly predicting the frequency of the resonance means without using a complicated configuration.

  An induction heating apparatus according to claim 1 of the present invention is an induction heating apparatus that energizes each of a plurality of heating means, and rectifies the input and supplies currents to the first heating means and the second heating means, respectively. 1 rectifying means, second rectifying means, and smoothing means for smoothing the rectified pulsating current.

  An induction heating device according to claim 2 of the present invention includes a resonance unit including a heating unit that performs induction heating, a switching unit that supplies a current to the resonance unit, a detection unit that detects an input to the resonance unit, In the induction heating apparatus comprising a control means for controlling a current flowing through the heating means by changing the frequency of the switching means based on a detection output from the detection means, the control means energizes the heating means. When the switching means is operated at a frequency at which the input becomes a predetermined value or less when performing, the predetermined frequency is set by a detection output from the detection means.

  An induction heating apparatus according to claim 3 of the present invention is configured such that, in the above-described claim 2, when the heating means is energized, the switching means is operated at a frequency equal to or higher than a predetermined frequency of the resonance means. is there.

  According to the first aspect of the present invention, when an input is generated, the pulsating current is smoothed by the smoothing means through the first rectifying means, the current is supplied to the first heating means, and the pulsating current is smoothed through the second rectifying means. Smoothed by the means, and a current is supplied to the second heating means. In this way, the currents of the plurality of heating means are supplied through one rectifying means, and the currents can be supplied to the plurality of heating means with little loss.

  According to the second aspect of the present invention, when the switching means is operated at a frequency at which the input to the resonance means is less than or equal to a predetermined value when the heating means is energized, how much is the actual input? Can be accurately predicted without adopting a complicated configuration. Then, by setting a predetermined frequency for operating the switching means so as not to be lower than the predicted frequency, it is possible to perform control capable of output in a frequency region safe for the switching means.

  According to the invention of claim 3, even when energizing the heating means, the switching means is operated at a frequency equal to or higher than a predetermined frequency considering the variation of the resonance means. Therefore, when energizing the heating means, the switching means Can be operated in a safe frequency range.

It is a block block diagram of the induction heating apparatus in 1st Example of this invention. It is a block block diagram of the induction heating apparatus in 2nd Example of this invention. It is a circuit diagram of the induction heating apparatus in 3rd Example of this invention. The waveform diagrams of the respective parts in the conventional example (before improvement) and the third example (after improvement) are shown. It is a circuit diagram of the induction heating apparatus in 4th Example of this invention. It is a block block diagram of the induction heating apparatus in 5th Example of this invention. FIG. 6 is a characteristic diagram showing the impedance change with respect to the frequency of the resonance circuit. FIG. 5 is a waveform diagram showing a change with time of an inverter current accompanying switching of each switching element. It is a wave form diagram which shows the relationship between the collector-emitter voltage of IGBT which is the conventional switching element, and the electric current which flows into the collector of a switching element from an induction coil. It is another waveform diagram which shows the relationship between the collector-emitter voltage of IGBT which is the conventional switching element, and the electric current which flows into the collector of a switching element from an induction coil. It is a circuit diagram which shows the electrical structure of the conventional induction heating apparatus.

  Hereinafter, preferred embodiments of the induction heating apparatus according to the present invention will be described with reference to the accompanying drawings. In each embodiment, common portions are denoted by common reference numerals, and descriptions of common portions are omitted as much as possible to avoid duplication.

  FIG. 1 shows an electrical configuration of an induction heating device according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an induction heating device having a fixing roller 2 to be heated as a load, which will be described later. Each part of the device 2 operates by receiving AC power from the power source E. Reference numeral 3 denotes an induction coil that electromagnetically heats the fixing roller 2. A series circuit including the induction coil 3 and the oscillation circuit 4 is connected between both ends of the power source E. The fixing roller 2 is provided in the vicinity of the induction coil 3 and is composed of a magnetic member that generates heat upon receiving an alternating magnetic field from the induction coil 3. Further, a switching element (not shown) is provided inside the oscillation circuit 4 and receives a PWM signal which is a control signal from a microcomputer 5 to be described later. And an alternating magnetic field is generated from the induction coil 3 to the fixing roller 2.

  Reference numeral 6 denotes temperature detecting means for detecting the temperature of the fixing roller 2 attached to the copying machine main body (not shown), for example, and converting it into an electrical temperature signal for output. Reference numeral 7 denotes output setting means for setting a heating output from the induction coil 3 to the fixing roller 2 and outputting a setting signal thereof, which is constituted by one or a plurality of switches, for example.

  The microcomputer 5 is provided as a control means for controlling each part of the induction heating device 1. Here, the microcomputer 5 performs PWM control on the oscillation circuit 4 based on the temperature signal from the temperature detection means 6 and the setting signal from the output setting means 7. A (pulse width control) signal is supplied to control the entire operation including the heat generation amount of the induction coil 3.

  Next, the operation of the above configuration will be described. A heating output from the induction coil 3 to the fixing roller 2 is set by the output setting means 7, and a setting signal corresponding to the set heating output is sent from the output setting means 7 to the microcomputer 5. Is output to the oscillation circuit 4, and a high-frequency current is supplied to the induction coil 3. As a result, a magnetic flux is generated between the induction coil 3 and the fixing roller 2, and an eddy current is generated in the fixing roller 2 when the magnetic flux line passes through the fixing roller 2. This eddy current is changed to heat by the electric resistance of the fixing roller 2 and is heated by the heating output set by the fixing roller 2.

  At this time, the temperature detecting means 6 detects the surface temperature of the fixing roller 2 and outputs the temperature signal to the microcomputer 5 as a food back. The microcomputer 5 receives the temperature signal from the temperature detection means 6 and performs abnormal temperature monitoring for calculating the slope of the surface temperature rise of the fixing roller 2. If the temperature rise for a certain time is equal to or higher than a predetermined value, the abnormal temperature It is determined that the current state is present, and transmission of the PWM signal to the oscillation circuit 4 is stopped. As a result, for example, the user mistakenly operates the maximum output button for setting the maximum heating output and the minimum output button for setting the minimum heating output by the output setting means 7, or the maximum output button is unexpectedly pressed due to external noise. Even when the output setting means 7 is operated by mistake, such as when the microcomputer 5 makes an emergency stop of the oscillation circuit 4 when an abnormal temperature state occurs by the temperature signal from the temperature detection means 6. As the fixing roller 2 rapidly rises in temperature, concerns that adversely affect the fixing roller 2 and the induction heating device 1 can be eliminated.

  As described above, in the first embodiment, when the temperature of the fixing roller 2 as a fixing body is suddenly increased, the induction coil is prevented from adversely affecting the fixing roller 2 and the induction heating device 1. 3 is used to calculate the temperature change amount of the fixing roller 2 that is heated by electromagnetic induction, to monitor the abnormal temperature in the fixing roller 2, and to stop the heating to the fixing roller 2 when the temperature is abnormal. A computer 5 is provided in the induction heating apparatus 1.

  In this case, if the fixing roller 2 undergoes a temperature change and the temperature change amount of the fixing roller 2 exceeds a certain value and the temperature change state becomes abnormal, the microcomputer 5 determines that this is an abnormal temperature state. Then, the heating to the fixing roller 2 is urgently stopped. By such temperature control of the microcomputer 5, even when the fixing roller 2 changes in temperature and the temperature rapidly increases, the fixing roller 2 and the induction heating device 1 can be prevented from being adversely affected.

  In the first embodiment, the induction heating device 1 is incorporated in the copying machine including the fixing roller 2 and the output setting means 7. However, the induction heating device 1 uses the fixing roller 2 and the output setting means 7. The unit configuration may be provided, or the induction heating device 1 may be configured to be incorporated in a copying machine. Further, the temperature detection means 6 may be of any form as long as the temperature of the fixing roller 2 can be detected.

  FIG. 2 shows an electrical configuration of the induction heating device 11 in the second embodiment of the present invention. In the figure, the induction heating device 11 here has four diodes 12A to 12D connected in a bridge to full-wave rectify the AC power from the power source E with the fixing roller 2 to be heated as a load. In order to smooth the pulsating current from the rectifier circuit 13, the smoothing circuit 16 composed of the choke coil 14 and the smoothing capacitor 15, and a parallel circuit of the induction coil 3 and the resonant capacitor 17. Switching of the oscillating circuit 4 which is configured to perform switching operation upon receiving a PWM signal from the microcomputer 5 (not shown) and which is smoothed by the smoothing circuit 16 is intermittently applied to the resonant circuit 18. The element 19 and a relay as a switching means for switching power supply from the power source E to the rectifier circuit 13 to enable or disable power supply 0 and configured to include a. The relay 20 includes an open / close switch 21 inserted and connected to a power supply line between the power source E and the rectifier circuit 13 and a coil 22 paired with the open / close switch 21. The open / close switch 21 is turned on or off in response to power interruption.

  Reference numeral 23 denotes a motor as a drive source for moving, that is, rotating the fixing roller 2. The motor 23 is supplied with a driving signal for rotating the fixing roller 2 from a motor control means of a copying machine (not shown) when a high frequency current is supplied to the induction coil 3 and the fixing roller 2 is generating heat. Reference numeral 24 denotes a detecting means for detecting the operating state of the motor 23, that is, whether or not the motor 23 is rotating. This means supplies current to the coil 22 when the motor 23 is rotating. In response to the current supply, the open / close switch 21 of the relay 20 is turned on (closed) so that power can be supplied from the power source E to the induction heating device 11.

  Next, the effect | action is demonstrated about the said structure. When the fixing roller 2 is heated, a PWM signal from the microcomputer 5 is supplied to the switching element 19 and a driving signal for rotating the fixing roller 2 is supplied to the motor 23 from a motor control unit (not shown). As a result, when the motor 23 rotates and the fixing roller 2 associated therewith also rotates, the detecting means 24 supplies current to the coil 22 of the relay 20, the open / close switch 21 is turned on, and the power source E and the rectifier circuit 13 are electrically connected. Connect. Therefore, AC power from the power source E is rectified and smoothed by the rectifier circuit 13 and the smoothing circuit 16, and current from the smoothing circuit 16 is intermittently supplied to the resonance circuit 18 along with the switching operation of the switching element 19. Thus, an alternating magnetic field is generated from the induction coil 3, and the fixing roller 2 is heated by electromagnetic induction.

  On the other hand, when the motor 23 is stopped and the fixing roller 2 is also stopped, the detection means 24 for detecting the rotation of the motor 23 does not supply current to the coil 22 of the relay 20 and the open / close switch 21 is turned off (open). As a result, the power source E and the rectifier circuit 13 are disconnected. Therefore, the supply of AC power from the power source E to the induction heating device 11 is interrupted, and electromagnetic induction heating from the induction coil 3 to the fixing roller 2 becomes impossible. In this way, by monitoring the rotation of the motor 23 and thus the fixing roller 2 so that the fixing roller 2 is not heated when the motor 23 is not operating, the fixing roller 2 is locally heated and the fixing roller 2 is heated. The concern that adversely affects 2 can be cleared.

  As described above, in the second embodiment, the motor 23 as a drive source for moving the fixing roller 2 and the detection means 24 for detecting the operation state of the motor 23 are provided, and when the motor 23 is not operating, The fixing roller 2 is not heated.

  In this case, if the motor 23 is not operating, it is determined that the fixing roller 2 interlocked therewith is also stopped, and the fixing roller 2 is not heated. By monitoring the movement of the fixing roller 2, it is possible to prevent the fixing roller 2 from being locally heated when the fixing roller 2 is not moving, so that the fixing roller 2 is not adversely affected.

  In this example, when the motor 23 is not rotating, the relay 20 is used to cut off the power supply from the power source E. However, for example, the microcomputer 5 receives the detection output of the detection means 24, If the motor 23 is not rotating, the same operation and effect can be obtained even if the PWM signal is not output to the switching element 19.

  FIG. 3 shows an electrical configuration of the induction heating device 21 in the third embodiment of the present invention. In the figure, an induction heating device 21 here includes a rectifier circuit 13 in which four diodes 12A to 12D are bridge-connected in order to full-wave rectify the AC power from the power source E, and the rectifier circuit 13. In order to smooth the pulsating current, a smoothing circuit 16 including a choke coil 14 and a smoothing capacitor 15 is provided in common with the second embodiment. On the other hand, the second embodiment differs from the second embodiment in that the heating circuit 32 as the first heating means and the heating circuit 33 as the second heating means are connected in parallel to the output side of the smoothing circuit 16.

  The first heating circuit 32 is switched by receiving a PWM signal from a resonance circuit 18A constituted by a parallel circuit of an induction coil 3A and a resonance capacitor 17A and a microcomputer (not shown) 5, and the smoothing circuit. And a switching element 19A of the first oscillation circuit 4A that intermittently applies the DC voltage smoothed by 16 to the resonance circuit 18A. Similarly to the first heating circuit 32, the second heating circuit 33 also includes a resonance circuit 18B constituted by a parallel circuit of the induction coil 3B and the resonance capacitor 17B, and a PWM from the microcomputer (not shown) 5. The switching element 19B of the second oscillating circuit 4B is switched by receiving a signal and intermittently applies the DC voltage smoothed by the smoothing circuit 16 to the resonance circuit 18B. That is, in this third embodiment, a plurality of series circuits of the resonance circuit 18 and the oscillation circuit 19 are provided, and the induction coil 3A constituting the first heating circuit 32 is provided at the center of the cylindrical fixing roller 2. The induction coil 3 </ b> B that is disposed to face and constitute the second heating circuit 33 is disposed to face both sides of the cylindrical fixing roller 2. In addition, although it disclosed about the 1st heating circuit 32 and the 3rd heating circuit 33 here, the number of heating circuits beyond that may exist.

  Reference numeral 35 denotes a switch as control signal switching means for switching and supplying the PWM signal from the microcomputer 5 to one of the switching elements 19A and 19B. The switch 35 is given from the microcomputer 5 at an appropriate timing. The operation is performed based on the switching signal. Reference numeral 36 denotes a switch as short-circuit switching means for selectively short-circuiting either the induction coil 3A of the resonance circuit 18A or the induction coil 3B of the resonance circuit 18B. The switch 36 is also operated by a switching signal from the microcomputer 5. Specifically, a switching signal is given to the switch 35 so that a PWM signal is supplied to the switching element 19A, whereby one induction coil 3A is energized and the other induction coil 3B is When not energized, the both ends of the non-energized induction coil 3B are short-circuited by the switch 36 operated by the same switching signal, and conversely switched to the switch 35 so that the PWM signal is supplied to the switching element 19B. A signal is applied, whereby one induction coil 3B is energized and the other induction coil 3A is energized. When not in the across the induction coil 3A which is not the current is short-circuited by the switch 36.

  37A and 37B are diodes connected in reverse parallel between the collectors and emitters of the switching elements 19A and 19B made of IGBT elements. The first oscillation circuit 4A is configured by a parallel circuit of the switching element 19A and the diode 37A. A second oscillation circuit 4B is configured by a parallel circuit of the switching element 19B and the diode 37B. Here again, the fixing roller 2 is rotated by a driving force from a motor 23 (not shown).

  Next, the operation of the above configuration will be described. AC power from the power source 2 is rectified and smoothed by the rectifying circuit 13 and the smoothing circuit 16, and the DC voltage obtained by the smoothing circuit 16 is converted to the first heating circuit 32. Each is applied to the second heating circuit 33. Here, the microcomputer 5 outputs a PWM signal having a pulse conduction width corresponding to the set output power, and supplies a switching signal for repeatedly switching the switch 35 at an appropriate timing to the switch 35. Therefore, the current from the smoothing circuit 16 is intermittently supplied to the resonance circuit 18A while the switch 35 is switched so that the PWM signal is supplied to the switching element 19A constituting the first heating circuit 32. On the other hand, the current from the smoothing circuit 16 is not supplied to the other resonance circuit 18B, an alternating magnetic field is generated from the induction coil 3A, and the center portion of the fixing roller 2 is mainly heated. Further, the current from the smoothing circuit 16 is intermittently supplied to the resonance circuit 18B while the switch 35 is switched so that the PWM signal is supplied to the switching element 19B constituting the second heating circuit 32. On the other hand, the current from the smoothing circuit 16 is not supplied to the other resonance circuit 18A, an alternating magnetic field is generated from the induction coil 3B, and the end of the fixing roller 2 is mainly heated. By repeating such switching operation of the switch 35, the central portion and the end portion of the rotating fixing roller 2 are alternately heated.

  Here, another switch 36 repeats the switching operation in synchronization with the switch 35, and while one induction coil 3A is energized by the PWM signal from the microcomputer 5 to the switching element 19A, the other energization is performed. The non-inductive induction coil 3B is short-circuited by the switch 36, and while the other induction coil 3B is energized by the PWM signal from the microcomputer 5 to the switching element 19B, the other non-energized induction coil 3A is switched to the switch 36. Are short-circuited.

  For example, if the induction coil 3B is energized, the magnetic flux generated by the induction coil 3B passes through the fixing roller 2 that is a magnetic material, so that the induction coil 3A and the fixing roller 2 act as if they are a transformer. Then, an electromotive force is generated in the induction coil 3A that is not energized. At this time, if both ends of the induction coil 3A are short-circuited by the switch 36, a current flows through the induction coil 3A, the magnetic load on the induction coil 3B increases, and the electric vibration amplitude of the induction coil 3B decreases. Become. As a result, no regenerative current is generated as in the prior art. The same effect can be obtained when the non-energized induction coil 3B is short-circuited when the induction coil 3A is in an energized state, and as a result, the loss and noise generated by the switching elements 19A and 19B can be reduced. .

  FIG. 4 shows a comparison of waveforms at various parts in the conventional example (before improvement) and the third embodiment (after improvement). The waveform diagram before the improvement is the same as that of FIG. 9, and the waveform diagram after the improvement is, for example, the collector-emitter voltage VCE of the switching element 19A and the current IC flowing from the induction coil 3A to the collector of the switching element 19A. Shows the relationship. As is apparent from this waveform diagram, it can be seen that the regenerative current Ir is suppressed by the amount of the current I ′.

  As described above, in the third embodiment, in the induction heating device 21 that alternately energizes the induction coils 3A and 3B that are a plurality of heating means, for example, while the induction coil 3A that is one heating means is energized, the other For example, the non-energized induction coil 3B as the heating means is short-circuited by a switch 36, for example.

  In this case, an electromotive force is generated in the other non-energized induction coil 3B due to the magnetic coupling between the one induction coil 3A and the fixing roller 2, and if the other induction coil 3B is short-circuited, When a current flows through the other induction coil 3B, the magnetic load on one induction coil 3A increases, and the regenerative current is suppressed. The same can be said when one induction coil 3B is energized and the other dielectric coil 3A is not energized. Therefore, the regenerative current can be suppressed only by short-circuiting either the non-energized induction coil 3A or the induction coil 3B in a small space, and the loss of the switching elements 19A and 19B and the generation of noise can be reduced.

  FIG. 5 shows the electrical configuration of the induction heating device 41 in the fourth embodiment of the present invention. In the figure, an induction heating device 41 includes a first resonance circuit 18A and a second resonance circuit 18B as described in the third embodiment, and is divided into induction coils 3A and 3B and is a fixing target to be heated. A roller (not shown) is heated. Further, here, in relation to one of the resonance circuits 18A, in order to smooth the rectifying circuit 13A composed of one diode 42A for half-wave rectifying the AC power from the power source E and the pulsating current from the rectifying circuit 13A. And a smoothing circuit 16A comprising a choke coil 14A and a smoothing capacitor 15A. A series circuit of the resonance circuit 18A and the switching element 19A is connected between both ends on the output side of the smoothing circuit 16A, and the other resonance circuit. In relation to 18B, a rectifier circuit 13B comprising one diode 42B for half-wave rectifying AC power from the power source E, and a choke coil 14B and a smoothing capacitor 15B for smoothing the pulsating current from the rectifier circuit 13B. And the smoothing circuit 16B, and between the both ends of the output side of the smoothing circuit 16B, the resonance circuit 18B and the switching element A series circuit of the 19B is connected. Thus, in the fourth embodiment, it is noted that the first induction coil 3A and the second induction coil 3B are each provided with rectifier circuits 13A and 13B for half-wave rectification. Other configurations are common to the third embodiment described above.

  In the present embodiment, during the period in which positive input power is generated from one side of the power supply E (upper side of the power supply E in the figure), the diode 42A constituting the rectifier circuit 13A is conducted while another rectifier circuit 13B is formed. The diode 42B becomes non-conductive, and power is supplied to the smoothing circuit 16A through the single diode 42A (see the current path I in FIG. 5). In addition, when positive input power is generated from the other side of the power source E (the lower side of the power source E in the figure), the diode 42B becomes conductive, while another diode 42A becomes non-conductive, and passes through a single diode 42B. Electric power is supplied to the smoothing circuit 16B. Therefore, each of the induction coils 3A and 3B requires only one diode 42A and 42B through which a current passes, and the loss of one diode can be reduced. The operation of the other resonance circuits 18A and 18B is the same as that of the third embodiment, and the description thereof is omitted here.

  As described above, in the fourth embodiment, in the induction heating device 41, which is a plurality of heating means and energizes the induction coil 3A as the first heating means and the induction coil 3B as the second heating means, respectively. Each of the positive and negative inputs of the input supplied from the power source E, that is, the AC input power, is half-wave rectified, and each of the currents is supplied to the induction coils 3A and 3B. The second diode 42B as the second rectifying means and the smoothing circuits 16A and 16B as the smoothing means for smoothing the rectified pulsating current are provided.

  In this way, when positive input power is generated, the pulsating current is smoothed by the smoothing circuit 16A through one diode 42A, current is supplied to the induction coil 3A connected thereto, and when negative input power is generated, it passes through the other diode 42B. The pulsating current is smoothed by the smoothing circuit 16B, and the current is supplied to the induction coil 3B connected thereto. As described above, even if the input power generated from the power source E is positive or negative, the currents of the plurality of induction coils 3A and 3B are supplied through one diode 42A and 42B, and the loss is small. A current can be supplied to each of the induction coils 3A and 3B.

  FIG. 6 shows the electrical configuration of the induction heating device 51 in the fifth embodiment of the present invention. In the figure, an induction heating device 51 includes a DC rectifier circuit 52 that rectifies and smoothes AC power from a power source E as a main circuit for generating heat from a fixing roller 2 (not shown), and two switching elements 53A each made of an IGBT or the like. , 53B and a resonance circuit 55 comprising a series circuit of the induction coil 3 and the resonance capacitor 17, respectively. Also, diodes 56A and 56B are connected in reverse parallel between the collectors and emitters of the switching elements 53A and 53B. The DC rectifier circuit 52 is constituted by the rectifier circuit 13 and the smoothing circuit 16 shown in the second embodiment, for example. The circuit configuration of the inverter 54 and the resonance circuit 55 is not limited to this.

  Reference numeral 61 denotes input voltage detection means for detecting an input voltage to the resonance circuit 55, and reference numeral 62 denotes input voltage detection means for detecting an input current to the resonance circuit 55. Reference numeral 63 denotes an induction heating control circuit as a control means having a built-in input power detection means 64 and a drive means 65 for the switching elements 53A and 53B, which includes the microcomputer 5 described above. The input power detection means 64 receives each detection output from the input voltage detection means 61 and the input voltage detection means 62 and calculates the input power to the resonance circuit 55. Reference numeral 66 denotes signal input means corresponding to the output setting means 7, which sends a set value of target input power to the induction heating control circuit 63 in order to operate the induction heating control circuit 63 with arbitrary power. To do.

  The driving means 65 supplies a control signal for alternately turning on and off the switching elements 53A and 53B to the respective switching elements 53A and 53B. Here, the input power calculated and detected by the input power detection means 64 is The current supplied to the induction coil 3 is controlled by changing the frequency of the control signal supplied to the switching elements 53A and 53B so as to approach the set value from the signal input means 66.

  FIG. 7 is a characteristic diagram showing a change in impedance with respect to the frequency of the resonance circuit 55. When the frequency of the current supplied to the resonance circuit 55, that is, the switching frequency of the switching elements 53A and 53B coincides with the resonance frequency fo, the impedance of the resonance circuit 55 is minimized, and if the switching frequency is higher than the resonance frequency fo, resonance occurs. While the circuit 55 is inductive, the resonant circuit 55 is capacitive if the switching frequency is lower than the resonant frequency fo.

  FIG. 8 shows changes over time in the current (inverter current Iinv) to the inverter 54 accompanying switching of the switching elements 53A and 53B. As shown in this figure, the switching elements 53A and 53B are alternately turned on and off while having a dead time period in which both of them are turned off by the pulsed control signals supplied from the induction heating control circuit 63. Thus, a sinusoidal inverter current Iinv synchronized with the switching frequency of the switching elements 53A and 53B is supplied from the inverter 54 to the resonance circuit 55.

  Next, the effect | action is demonstrated about the said structure. The AC power from the power source E is rectified and smoothed to DC by the DC rectifying and smoothing circuit 52 and applied to the inverter 54. Here, the induction heating control circuit 63 instructs the target input power (target power) from the signal input means 66 based on the information input from the signal input means 66, and also detects the input voltage detection means 61 and the input current detection. Based on each detection output from the means 62, information on the input voltage and input current is taken in, and the input power detection means 64 incorporated therein integrates these input voltage and input voltage to obtain actual input power. Then, the drive means 65 included in the induction heating control circuit 63 changes the inverter frequency Iinv by changing the switching frequency of the switching elements 53A and 53B so that the input power calculated by the input power detection means 64 becomes the target power. To do.

  Here, as shown in FIG. 7, when the frequency of the inverter current Iinv applied to the resonance circuit 55 becomes equal to or less than the resonance frequency fo, the resonance circuit 55 becomes capacitive, and a short-circuit current flows through the switching elements 53A and 53B. Therefore, the frequency of the inverter current Iinv and thus the switching frequency of the switching elements 53A and 53B needs to be equal to or higher than the resonance frequency fo. In addition, since it is necessary to reduce the inrush current to the inverter 54 and the resonance circuit 55 at the start of heating when the inverter 54 starts to operate, the driving unit 55 is configured to switch the switching elements 53A, 53A, 53B and the inverter 54 is started to operate. At this time, since the impedance of the resonance circuit 55 is high, the input power at the start of heating is low, and the switching frequency of the switching elements 53A and 53B is changed so that the target input power is obtained therefrom. At the start of heating, the switching elements 53A and 53B are operated at a switching frequency at which the input power is 80% or less of the maximum power in the rated state of the induction heating device 51. Thus, the switching elements 53A and 53B can be switched at a sufficiently high frequency with respect to the resonance frequency fo at which the input power to the resonance circuit 55 is maximized.

  By the way, the relationship between the impedance and the frequency of the resonance circuit 55 shown in FIG. 7 varies depending on the circuit elements constituting the resonance circuit 55, specifically, the combination of the induction coil 3 and the resonance capacitor 17. In the range, the resonance frequency fo becomes different for each product while keeping the impedance-frequency relationship shown in FIG. 7 similar by the combination of the reactance of the induction coil 3 and the capacitance of the resonance capacitor 17. Here, the relationship between the heating power for the fixing roller 2 and the switching frequency is substantially equal to the relationship between the impedance of the resonance circuit 55 and the switching frequency.

  That is, the relationship between the heating power and the frequency is a constant relationship depending on the reactance of the induction coil 3 used in each resonance circuit 55 and the capacitance of the resonance capacitor 17. The resonance frequency that becomes the maximum in the combination of the variation range depending on the electrical characteristics of each circuit element is stored in advance, and at the start of heating to start supplying the control signal to the inverter 54, the switching frequency that is higher than the stored resonance frequency that is the maximum By operating the switching elements 53A and 53B and detecting the input power at the frequency by the input power detection means 64, the resonance frequency fo can be predicted for each individual product. The predicted resonance frequency fo is stored in the drive means 65. Thereafter, the drive means 65 sets the lower limit set value of the operating frequency of the inverter 54 so as not to be lower than the predicted resonance frequency fo. The switching elements 53A and 53B are operated at a switching frequency higher than that, and the heating control for the fixing roller 2 is continued. As a result, it is possible to perform control with the maximum power that can be output with respect to the target input power in a frequency region that is safe for the switching elements 53A and 53B.

  As described above, in the fifth embodiment, the resonance circuit 55 as the resonance means including the induction coil 3 as the heating means for performing induction heating, and the switching element 53A as the switching means for intermittently supplying current to the resonance circuit 55 , 53B, the input power detection means 64 as detection means for detecting the input power to the resonance circuit 55, and the switching frequency of the switching elements 53A, 53B based on the detection output from the input power detection means 64. In an induction heating apparatus provided with an induction heating control circuit 63 as a control means for controlling the current flowing through the induction coil 3, the induction heating control circuit 63 is configured so that the input power is preferably in a rated state at the start of heating. The switching elements 53A and 53B are operated at a switching frequency that is equal to or less than a predetermined value of 80% of the maximum power at When the, at slightly lower by the detection output from the input power detecting means 64, but is preferably configured to set the predetermined That minimum switching frequency.

  In this case, since the relationship between the power for heating the induction coil 3 and the switching frequency is constant for each resonance circuit 55, the resonance circuit 55 is supplied to the resonance circuit 55 at the start of energization of the induction coil 3. When the switching elements 53A and 53B are operated at a switching frequency at which the input power of the power supply is less than or equal to a predetermined value, if the actual input power is detected, each individual power can be obtained without adopting a complicated configuration. The resonance frequency fo in the resonance circuit 55 can be correctly predicted. Then, by setting the lowest switching frequency for operating the switching elements 53A and 53B so as not to be lower than the predicted resonance frequency fo, output is performed with respect to the target power in a frequency region safe for the switching elements 53A and 53B. Control can be performed with the maximum possible power.

  In addition, here, the induction heating control circuit 63 is configured to operate the switching elements 53A and 53B at a switching frequency equal to or higher than the maximum resonance frequency in consideration of variation of each element of the resonance circuit 55 at the start of heating. . That is, even when heating is started, the switching elements 53A and 53B are operated at a switching frequency equal to or higher than the maximum resonance frequency in consideration of variations in the resonance circuit 55. Therefore, the switching elements 53A and 53B are operated in a safe frequency region when heating is started. be able to.

  In addition, this invention is not limited to the said Example, It can change in the range which does not deviate from the meaning of this invention. For example, the structure which each combined the characteristic of each Example mentioned above may be sufficient.

3A, 3B induction coil (heating means)
16A, 16B Smoothing circuit (smoothing means)
42A first diode (first rectifying means)
42B Second diode (second rectifier)
53A, 53B Switching element (switching means)
55 Resonant circuit (resonance means)
63 Induction heating control circuit (control means)
64 Input power detection means (detection means)

Claims (3)

In the induction heating device that energizes each of the plurality of heating means,
A first rectifying means and a second rectifying means for rectifying the input and supplying current to the first heating means and the second heating means, respectively;
An induction heating apparatus comprising smoothing means for smoothing the rectified pulsating current. Resonance means including heating means for performing induction heating;
Switching means for supplying a current to the resonance means;
Detection means for detecting an input to the resonance means;
In an induction heating apparatus including a control unit that controls a current that flows through the heating unit by changing a frequency of the switching unit based on a detection output from the detection unit.
The control means sets the slightly lower frequency by a detection output from the detection means when the switching means is operated at a frequency at which the input becomes a predetermined value or less when energizing the heating means. An induction heating device characterized by being.   3. The induction heating apparatus according to claim 2, wherein when the energization is performed to the heating unit, the switching unit is operated at a frequency equal to or higher than a predetermined frequency of the resonance unit.

Images