JP2018037219A - Electromagnetic induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic induction heating device capable of performing a heating operation at a timing of zero-crossing by a program without additional cost.SOLUTION: An electromagnetic induction heating device of the present invention includes: a trigger detection circuit 31 measuring a generation timing of self oscillation of an inverter 11; and a control circuit 15 which receives a measurement result from the trigger detection circuit 31 to generate a second timer 51B by zero-crossing timing generation means 51, the second timer starting at each zero-crossing of AC from an AC power supply 1, and which controls the on-off operation of a switching element 9 by inverter oscillation control means 52, in synchronous with the start of the second timer 51B.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electromagnetic induction heating device that heats a load with an alternating magnetic field generated from a heating means.

  As a prior art, for example, Patent Document 1 discloses an electromagnetic induction heating device shown in FIG. In the figure, 1 is an AC power supply such as a commercial power supply for supplying AC power to an electromagnetic induction heating device, and 2 is a rectifying and smoothing circuit comprising a diode bridge 3, a choke coil 4 and a smoothing capacitor 5. Since the alternating current supplied from the alternating current power supply 1 is rectified and smoothed by the rectifying and smoothing circuit 2, the rectifying and smoothing circuit 2 connected to the alternating current power supply 1 can be regarded as a direct current power source that converts alternating current into direct current.

  Reference numeral 7 denotes a heating coil for electromagnetic induction heating of a heat roller (not shown) of a fixing device as a load to be heated by an alternating magnetic field. A resonance capacitor 8 is connected in parallel to the heating coil 7, and an LC resonance circuit is formed by the heating means 7 and the resonance capacitor 8. Reference numeral 9 denotes a switching element made of an IGBT having a built-in flywheel diode. The resonance capacitor 8 and the switching element 9 constitute an inverter 11 connected to the rectifying and smoothing circuit 2.

  Reference numeral 15 denotes a control circuit composed of a microcomputer that sends a pulse drive signal to the switching element 9 to turn on / off the switching element 9 in order to generate an alternating magnetic field in the heating coil 7 serving as a heating means. The control circuit 15 controls the on / off operation of the switching element 9 by applying a pulse drive signal having a predetermined period and width for turning on the switching element 9 in accordance with a control sequence stored in advance or an external input signal. is there. Along with the on / off operation of the switching element 9, the DC voltage rectified and smoothed by the rectifying and smoothing circuit 2 is intermittently applied to the heating coil 7, and an alternating magnetic field is generated from the heating coil 7 by the high-frequency current flowing through the heating coil 7. Is generated, and the heating operation to the heated load is performed.

  Reference numeral 21 denotes a zero cross detection means for detecting a zero cross where the value of the AC voltage supplied from the AC power supply 1 becomes zero. The zero-cross detection means 21 is connected to the AC power source 1 via a resistor 22 for voltage drop, and a diode bridge 23 that full-wave rectifies the AC voltage of the AC power source 1, and a voltage that is full-wave rectified by the diode bridge 23. Is constituted by a photocoupler 24 that electrically insulates the timing at which zero becomes zero, that is, the timing of zero crossing, and transmits it to the control circuit 15.

  Reference numeral 25 denotes a power detection circuit for detecting the power consumption of the heating coil 7, which detects the input voltage and the input current to the rectifying and smoothing circuit 2, and detects the power consumption from the value obtained by multiplying them. It is configured.

  And the control circuit 15 here contains the heating coil 7 by receiving the zero cross detection signal from the zero cross detection means 21, and starting the output of the pulse drive signal to the switching element 9 according to the timing of zero cross. Start oscillation of the resonant circuit. That is, when the output of the pulse drive signal to the switching element 9 is started, the direct current from the rectifying and smoothing circuit 2 is intermittently applied to the heating coil 7 at the same timing as the pulse drive signal.

  Further, the control circuit 15 controls the energization rate of the heating coil 7 every half cycle of the AC voltage from the AC power supply 1 so that the power consumption detected by the power detection circuit 25 becomes a set value. That is, the power supplied to the heating coil 7 is adjusted by the control circuit 15 every half cycle of the AC voltage in synchronization with the zero cross. Specifically, the power supplied to the heating coil 7 is synchronized with the energization rate, which is the ratio of the energization time during which the pulse drive signal is repeatedly supplied to the switching element 9, that is, when the switching element 9 is turned on / off. Thus, the energization rate of the heating coil 7 to which the high-frequency current is supplied to the heating coil 7 is adjusted by controlling every half cycle of the AC voltage.

  Here, the energization rate of the heating coil 7 refers to the ratio of the time during which high-frequency current is supplied to the heating coil 7 for one half cycle of the AC voltage. For example, since the half cycle is 10 milliseconds when the frequency of the AC voltage is 50 Hz, when the energization rate is 50%, the time for supplying the high-frequency current to the heating coil 7 is 5 for each half cycle of the AC voltage. Milliseconds. Therefore, when the pulse drive signal is repeatedly sent over the entire range of the half cycle of the AC voltage, that is, when the power supplied to the heating coil 7 is 600 W when the power supply rate of the heating coil 7 is 100%, At 50%, the pulse drive signal is repeatedly sent from the zero cross for 5 milliseconds every half cycle, and the power supplied to the heating coil 7 is 300 W.

  The conventional electromagnetic induction heating device uses a single-ended resonance type high frequency inverter 11 having a simple circuit configuration and a small number of components in order to supply a high frequency current to the heating coil 7. The single-ended resonance type high frequency inverter 11 uses a single switching element 9 and is frequently used because of its low cost.

JP 2009-295392 A

  In the above-described electromagnetic induction heating device, when the output of the pulse drive signal to the switching element 9 is started at a timing when the peak value of the AC voltage from the AC power supply 1 is high, it is stored in the smoothing capacitor 5 before the operation of the switching element 9. The electric charge and the electric power from the rectifying / smoothing circuit 2 are simultaneously applied, and a large current load is applied to the switching element 9, which shortens the product life. Therefore, by using a zero cross detection means 21 as shown in FIG. 7, when the peak value of the AC voltage is near zero, the output of the pulse drive signal to the switching element 9 is started to heat the load to be heated. Although the operation was performed, the introduction of the zero-crossing detection circuit 21 caused a problem of extra cost.

  Further, as described in Patent Document 1, the single-ended inverter 11 is difficult to control in a region where the power consumption of the heating coil 7 is small, and when trying to expand the lower limit of the power consumption setting range, the switching element 9 had a limit because an excessive current flowed. Therefore, when a conventional electromagnetic induction heating apparatus including a single-ended inverter 11 is used as a heat source for fixing toner in a copying machine, for example, it is difficult to control power consumption in a region where power consumption is small. This is inconvenient because unevenness occurs in the toner-fixed image. On the other hand, the half-bridge type inverter is capable of stable control even with a small amount of power consumption, but has a drawback in that the cost is increased due to the use of a plurality of switching elements.

  Therefore, in Patent Document 1, as a solution, the idea of controlling the energization rate of the heating coil 7 every half cycle starting from the zero cross was proposed, but the energization of the heating coil 7 was stopped within the remaining time of the half cycle. When performing soft stop, there was a problem that inrush current was large and abnormal noise was generated.

  In view of the above problems, it is a first object of the present invention to provide an electromagnetic induction heating apparatus that can perform a heating operation at a zero-cross timing by a program without incurring additional costs.

  In addition, the second object of the present invention is to use a single-ended inverter to stably control the power consumption of the heating coil even in a region where the power consumption is small, so that electromagnetic induction does not generate abnormal noise. It is to provide a heating device.

  The electromagnetic induction heating device of the present invention includes a power source that converts alternating current into direct current, an inverter that includes switching means, and a heating means that is connected to the inverter. In an electromagnetic induction heating device that applies a direct current from the heating means intermittently to heat the load by electromagnetic induction heating, a measuring means that measures the occurrence timing of self-excited oscillation of the inverter, and a measurement result from the measuring means And a control unit that generates a timer that starts every zero crossing of the alternating current and controls the on / off operation of the switching unit in synchronization with the start of the timer.

  According to the first aspect of the present invention, the timing at which the self-excited oscillation of the inverter occurs in the vicinity of the AC zero cross is taken into the control means from the measurement result of the measuring means, and the timer that starts every AC zero cross is generated by the control means. As a result, the on / off operation of the switching means and the heating operation of the load in synchronism with the timing of the zero cross can be performed by a program without using the zero cross detection circuit and without additional cost.

  According to the second aspect of the present invention, the basic unit is a very short cycle of a half cycle of alternating current, and it is determined whether or not the switching means is turned on / off over the whole period every half cycle. In order to control the energization rate of the means, it is possible to make it equivalent to continuous energization with low power like a half-bridge type inverter. In addition, the power supplied to the heating coil can be stably controlled.

  According to the invention of claim 3, since the oscillation of the inverter starts at the timing of alternating zero crossing, there is no physical or electrical shock at the start of the on / off operation of the switching means. Further, not only the start of the on / off operation of the switching means but also the end of the on / off operation can be synchronized with the alternating zero cross, and an electromagnetic induction heating device that does not generate abnormal noise can be provided.

  According to the invention of claim 4, since the energization rate control of the heating means is performed so that the power consumption of the heating means becomes a predetermined value, the power consumption is maintained at a predetermined value even in a region where the power consumption is small. Is possible.

It is a circuit diagram of the electromagnetic induction heating device in the first embodiment of the present invention. It is a flowchart which shows the operation | movement procedure of a zero cross timing production | generation means same as the above. It is a waveform diagram of each part immediately after the operation start of the electromagnetic induction heating device. FIG. 3 is a waveform diagram of each part in which the vicinity of the zero cross of the power supply voltage is enlarged in FIG. It is a waveform diagram of each part after detecting the zero cross of the power supply voltage. It is a circuit diagram of the electromagnetic induction heating apparatus in 2nd embodiment of this invention. It is a circuit diagram of the conventional electromagnetic induction heating apparatus.

  Hereinafter, preferred embodiments of the electromagnetic induction heating device of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same part as the structure shown in FIG. 7 as a prior art example, and description of a common part is abbreviate | omitted as much as possible.

  1 to 5 show an electromagnetic induction heating device for a copying machine incorporated in a fixing device according to a first embodiment of the present invention. In FIG. 1 showing a circuit configuration, an inverter 11 constituting the electromagnetic induction heating device of this embodiment is of a single end type, and is supplied from an AC power source 1 and an AC power source 1 that supply power to the electromagnetic induction heating device. A rectifying / smoothing circuit 2 as a power source for rectifying and smoothing an AC voltage by a diode bridge 3 serving as a rectifying circuit, a choke coil 4 serving as a smoothing circuit, and a smoothing capacitor, and heating as a heating means for inductively heating a heated load Coil 7, resonance capacitor 8 constituting a resonance circuit together with heating coil 7, single switching element 9 constituting switching means, control circuit 15 for controlling on / off operation of switching element 9, and power consumption of heating coil 7 The power detection circuit 25 for detecting the same is the same as the conventional example. The control circuit 15 may be composed of an ASIC incorporating a predetermined control sequence in addition to the microcomputer shown in the conventional example.

  In the present embodiment, a trigger detection circuit 31 that outputs a trigger signal in synchronization with the oscillation timing of the inverter 11 is provided instead of the zero cross detection means 21 shown in the conventional example. The trigger detection circuit 31 outputs a trigger signal synchronized with the high-frequency current to the control circuit 15 when a high-frequency current flows through the heating coil 7, and the AC voltage from the AC power source 1 is heated near the zero cross. When the current of No. 7 becomes near zero and the inverter 11 is in a self-excited oscillation state, the trigger signal is temporarily not output.

  In addition to the power detection circuit 25 and the trigger detection circuit 31, the control circuit 15 includes a drive circuit 33, an EEPROM (Electrically Erasable Programmable Read-Only Memory) 34 as a nonvolatile memory, various safety circuits 35, and an interface circuit 36. Are connected to each other. In FIG. 1, reference numeral 41 denotes a power plug of an electromagnetic induction heating device that can be attached to and detached from an outlet (not shown) of the AC power supply 1, 42 denotes a protection circuit connected to the input side of the diode bridge 3, and 43 denotes rectification of the diode bridge 3. This is a power supply circuit that generates a DC operating voltage of, for example, 20 V or 5 V from the output and supplies it to each part of the electromagnetic induction heating device. The protection circuit 42 includes a fuse 44 for overcurrent protection, a varistor 45 for overvoltage protection, and a capacitor 46 connected in parallel to the varistor 45.

  The drive circuit 33 receives a pulse control signal of, for example, 20 to 40 kHz from the control circuit 15 and generates and outputs a pulse drive signal that allows the switching element 9 to be turned on / off to the control terminal (gate) of the switching element 9. Therefore, the pulse control signal and the pulse drive signal here can be regarded as substantially the same signal.

  The EEPROM 34 as a storage means records and holds various set values, a program for causing the control circuit 15 to function as a zero cross timing generation means 51 and an inverter oscillation control means 52 described later, and the like. Various storage means other than the EEPROM 34 may be used instead.

  The various safety circuits 35 send a forcible stop signal to the control circuit 15 to forcibly stop the supply of the pulse drive signal to the switching element 9 when, for example, the heat roller of the fixing device is heated to an unintended temperature or higher. It has a function to send out. In addition, the various safety circuits 35 may have a function of increasing the safety of the electromagnetic induction heating device.

  The interface circuit 36 exchanges various signals with a fixing device (not shown). Here, the output signal OUTPUT from the control circuit 15 is fixed while being electrically insulated by the first photocoupler 37A. While being sent to the apparatus, the input signal INPUT from the fixing device is taken into the control circuit 15 in a state where it is electrically insulated by another second photocoupler 37B. The input signal INPUT here includes a power setting signal for setting the power consumption of the heating coil 7 and the like.

  The control circuit 15 mainly includes a zero-cross timing generation unit 51 and an inverter oscillation control unit 52 that function by executing a program read from the EEPROM 34. The zero cross timing generation means 51 takes in the generation timing of the self-excited oscillation of the inverter 11 detected by the trigger detection circuit 31 as a measurement result from the trigger detection circuit 31 each time, and from there every zero cross of the AC voltage of the AC power source 1 from there. The timer to be started at the time is generated inside the control circuit 15. Here, every time the two self-excited oscillations of the inverter 11 occur, that is, the period (time) until the next self-excited oscillation occurs. When the average value of a plurality of cycles of self-oscillation measured by the first timer 51A is set as a cycle near the zero cross of the AC voltage, for each set cycle And a second timer 51B to be started.

  The inverter oscillation control means 52 sends an appropriate pulse drive signal to the gate of the switching element 9 so that the switching element 9 is turned on / off in synchronization with the start of the second timer 51B. It is. In particular, the inverter oscillation control means 52 of the present embodiment has a half of the AC voltage from the AC power supply 1 so that the power consumption detected by the power detection circuit 25 becomes a set value corresponding to the power setting signal from the fixing device. By determining whether or not the switching element 9 is to be turned on / off over the entire period for each cycle, the power supply rate of the heating coil 7 is controlled. Therefore, the energization rate of the heating coil 7 here is a ratio of time for supplying the high-frequency current to the heating coil 7 with respect to a plurality of half cycles of the AC voltage, and the heating coil 7 has the half cycle as a basic unit. The energization rate is variably adjusted.

  When the inverter oscillation control means 52 determines that the switching element 9 is to be turned on / off, the inverter timer control unit 52 outputs the pulse drive signal to the switching element 9 at the timing of the zero crossing of the AC voltage when the second timer 51B starts. The pulse drive signal is repeatedly output to the switching element 9 over the entire period of the half cycle of the AC voltage until it is determined that the switching element 9 is not turned on / off, and the switching element 9 is turned on / off. If it is determined not to be operated, the output of the pulse drive signal to the switching element 9 is stopped at the timing when the second timer 51 is restarted.

  Next, the operation of the above configuration will be described with reference to the flowchart of FIG. 2 and the waveform diagrams of FIGS. 3 and 4 are both immediately after the start of the electromagnetic induction heating device, from the upper stage, the AC voltage waveform from the AC power source 1, the full-wave rectification waveform from the diode bridge 3, the current waveform of the heating coil 7, both ends of the switching element 9. The time change of the voltage waveform and the output signal waveform from the trigger detection circuit 31 is shown. FIG. 5 shows the time variation of the AC voltage waveform from the AC power supply 1 (“power supply voltage” in the figure) and the gate voltage waveform of the switching element 9 (“IGBT gate voltage” in the figure). As an example, the frequency of the AC voltage shown in each figure is 50 Hz, that is, the half cycle of the AC voltage is 10 milliseconds.

  When a sine wave AC voltage from the AC power source 1 is input to the rectifying / smoothing circuit 2 as a power source, the rectifying / smoothing circuit 2 rectifies and smoothes the AC voltage and converts it into a DC voltage to the inverter 11 and outputs it. The power supply circuit 43 supplies a DC operating voltage for each part of the electromagnetic induction heating device.

  Here, when an electromagnetic induction heating device start signal is sent to the control circuit 15 through the interface circuit 36 as an input signal from the fixing device, the zero-cross timing generating means 51 of the control circuit 15 is activated, and the zero-cross of the AC voltage is detected. An initial operation for setting the cycle in the second timer 51B starts. In response to this, when a pulse drive signal is given from the drive circuit 33 to the gate of the switching element 9 by the pulse control signal from the control circuit 15, the switching element 9 is repeatedly turned on and off, and the heating coil 7 and the resonant capacitor A DC voltage is intermittently applied to the parallel circuit consisting of 8, the inverter 11 oscillates, and a high-frequency current whose peak value changes in a sine wave shape as shown in FIGS. 3 and 4 flows through the heating coil 7. Thereby, an alternating magnetic field is generated from the heating coil 7, an eddy current is generated in the heat roller of the fixing device as a load, and the heat roller is electromagnetically heated.

  In the oscillating inverter 11, the current flowing through the heating coil 7 is interrupted by the switching element 9, so that a current corresponding to the AC voltage flows through the heating coil 7 when the switching element 9 is turned on. Further, when the inverter 11 is oscillating, a resonance voltage corresponding to the current of the heating coil 7 is generated between both ends of the switching element 9 when the switching element 9 is turned off. At this time, the trigger detection circuit 31 sends a pulse waveform for taking the oscillation timing of the inverter 11 from the voltage generated between both ends of the switching element 9 to the control circuit 15 as a trigger signal.

  In this way, when the trigger signal is output from the trigger detection circuit 31 to the control circuit 15 in synchronization with the oscillation of the inverter 11 accompanying the on / off operation of the switching element 9, the control circuit 15 takes the timing with this trigger signal. Then, a pulse control signal having a predetermined width and frequency is sent to the drive circuit 33 as an oscillation signal. That is, the control circuit 15 controls the electromagnetic induction heating using the trigger signal from the trigger detection circuit 31 when heating the heat roller.

  On the other hand, in the vicinity of the zero cross of the AC voltage from the AC power supply 1, the current flowing through the heating coil 7 decreases, and the trigger detection circuit 31 cannot output a trigger signal. For this reason, while the trigger signal is not detected for a certain period, the inverter 11 oscillates even when there is no trigger signal. The trigger detection circuit 31 of this embodiment also has a function as a measurement unit that detects and measures the occurrence of self-excited oscillation of the inverter 11.

  FIG. 2 is a flowchart showing the operation procedure of the zero cross timing generation means 51. In the figure, when the inverter 11 is oscillated with the zero cross timing generation means 51 activated, and the trigger signal from the trigger detection circuit 31 is temporarily not output, the zero cross timing generation means 51 determines the timing at step S1. Determines whether or not 12 ms or more, which is the first time, has elapsed since the previous self-excited oscillation occurrence timing. Here, when self-excited oscillation occurs for the first time after starting the zero-cross timing generation means 51, the timing at which the trigger signal is not output from the trigger detection circuit 31 and the generation timing of the previous self-excited oscillation are the first time. Since the time has passed, it is determined that the first self-excited oscillation has occurred, and the process proceeds to steps S2 to S5. In other cases, the process proceeds to steps S11 to S21.

  In step S2, the zero cross timing generation means 51 resets a self-excitation interval counter that measures the interval of self-excited oscillation of the inverter 11, stops the first timer 51A in the next step S3, and then sets the first timer 51A. It starts and starts from the state where the count of the first timer 51A is reset. Then, the zero cross timing generation unit 51 resets another cycle count in step S4, resets the cycle acquired in step S5, and then waits for no trigger signal to be output from the zero cross detection unit 31. As described above, in the present embodiment, after the zero cross timing generation unit 51 is activated, the trigger detection circuit 31 detects that the self-excited oscillation of the inverter 11 is first generated. One timer 51A is activated and starts counting.

  Thereafter, when the trigger signal is no longer output from the zero-cross detection means 31 at an interval of less than 12 ms from the occurrence of the previous self-excited oscillation, the zero-cross timing generation means 51 determines that the timing is the occurrence of the previous self-excited oscillation in step S11. It is determined whether or not the second time of 7 ms or more has elapsed from the timing.

  If 7 ms or more has elapsed, the zero cross timing generation means 51 determines that the self-excited oscillation of the inverter 11 has occurred again, proceeds to step S12, resets the self-excitation interval counter, and performs the next step S13. Then, the first timer 51A is stopped. In the subsequent step S14, the value counted by the first timer 51A so far, that is, the period from the previous self-excited oscillation generation timing to the current self-excited oscillation generation timing is acquired. Further, in step S15, the count of the first timer 51A is started from the reset state, and in the next step S16, the number of period counts is increased by 1, and then the number of period counts is set to a preset number (= n) It is determined in step S17 whether or not it is equal to or greater than n. Note that both the period acquired in step S14 and the value of the cycle count incremented in step S16 are stored in the EEPROM 34.

  On the other hand, if 7 ms or more has not elapsed in step S11, the zero cross timing generation means 51 determines that it is a factor other than the self-excited oscillation of the inverter 11, and performs the following steps without performing steps S12 to S21. It waits until the trigger signal is no longer output from the zero cross detection means 31.

  In step S17, if the number of period counts is less than n, it waits for the trigger signal not to be output from the zero cross detection means 31 next. Thereafter, when the trigger signal is not output again from the zero cross detection means 31 at an interval of 7 ms to less than 12 ms since the previous occurrence of the self-excited oscillation, the zero-cross timing generation means 51 determines that this is due to the self-excited oscillation of the inverter 11. Judgment is performed, and each procedure of step S12 to step S17 is repeated. In step S17, when the number of cycle counts reaches n or more, the process proceeds to step S18, and the average value of the cycles obtained so far is calculated as a cycle near the zero cross of the AC voltage, and in step S19. The value is set in the counter of the second timer 51B. Thereafter, the zero cross timing generation means 51 stops the second timer 51B in step S20, starts the second timer 51B in the next step S21, and starts the second timer 51B, so that each zero cross of the AC voltage is started. The second timer 51B to be restarted is completed.

  Thus, every time the self-excited oscillation of the inverter 11 occurs, the zero cross timing generation unit 51 of the present embodiment acquires the value counted so far by the first timer 51A and restarts the first timer 51A. By repeating the operation a plurality of times, the average of the values obtained from the first timer 51A each time is set in the second timer 51B as a cycle near the zero cross of the AC voltage. Then, by starting the second timer 51B, the second timer 51B that restarts every zero cross of the AC voltage can be generated by a program that does not require additional cost without providing the conventional zero cross detection means 21. .

  In the above-described series of procedures, the first time is longer than the second time, and the value may be set as appropriate in consideration of the frequency of the AC voltage, the duration of self-excited oscillation of the inverter 11, and the like. Further, even when the frequency of the AC voltage fluctuates in the middle, the zero-cross timing generation means 51 is started at every predetermined time during the oscillation of the inverter 11 so that the second timer 51B can be started correctly every zero-cross of the AC voltage. The series of procedures described above may be performed each time.

  Next, the operation of the inverter oscillation control means 52 using the second timer 51B will be described with reference to FIG.

  When the second timer 51B that is started for each zero cross of the AC voltage is generated by the zero cross timing generation means 51, the inverter oscillation control means 52 uses the power setting signal from the fixing device as the power consumption detected by the power detection circuit 25. In order to control the gate output of the switching element 9 in accordance with the energization rate of the heating coil 7 every half cycle of the AC voltage from the AC power supply 1 so as to become a set value corresponding to It is determined whether or not the switching element 9 is turned on / off over a period of time. Here, if it is determined that the switching element 9 is to be turned on / off, the output of the pulse drive signal to the switching element 9 is started at the timing when the second timer 51B is activated, thereby including the heating coil 7. Start oscillation of the resonant circuit. That is, when the output of the pulse drive signal to the switching element 9 is started, the direct current converted from the alternating current by the rectifying and smoothing circuit 2 is applied to the heating coil 5 at the same timing as the pulse.

  As shown in FIG. 5, the on / off operation start timing t1 of the switching element 9 is the zero cross of the AC voltage that minimizes the short-circuit energy when the switching element 9 is turned on. The noise at the time can be reduced and the switching loss can be reduced. That is, when the output of the pulse drive signal is started at a timing other than the zero-cross timing, the charge stored in the smoothing capacitor 5 and the power from the AC power supply 1 are simultaneously applied to the switching element 9 before the operation of the switching element 9. Since a large current flows, noise (noise) and switching loss are large, and there is a possibility that the switching element 9 may be damaged, but this is not the case when the output of the pulse drive signal is started at the zero cross timing.

  At the start of output of the pulse drive signal to the switching element 9, the width of the pulse drive signal is set to about 2.5 microseconds, which is narrower than normal, and then gradually widened to about 5 microseconds at normal time. In combination, the noise at the start timing of the on / off operation of the switching element 9 can be further effectively reduced, and the switching loss can be reduced.

  In the present embodiment, the energization period A of the heating coil 7 for turning on / off the switching element 9 and the non-energization period B of the heating coil 7 for not turning on / off the switching element 9 are both half cycles of the AC voltage. Continue for the entire period of. For this reason, not only the on / off operation start timing t1 of the switching element 9 but also the on / off operation end timing t2 of the switching element 9 is synchronized with the zero cross of the AC voltage, and abnormal noise when the energization of the heating coil 7 is stopped. Can also be prevented.

  The power supplied to the heating coil 7 is determined by the control circuit 15 whether or not the switching element 9 is turned on / off over the entire period of the half cycle every half cycle of the AC voltage in synchronization with the zero cross. It is adjusted by doing. Accordingly, the energization rate of the heating coil 7 here is a ratio of the energization period A of the heating coil 7 to a plurality of half periods in the AC voltage, that is, a plurality of zero cross periods S.

  For example, when the frequency of the AC voltage is 50 Hz, the zero-cross period which is a half period is 10 milliseconds, and when the pulse drive signal is repeatedly sent over the entire range of a plurality (three in this example) of zero-cross periods S, That is, when the energization rate of the heating coil 7 is 100% and the power supplied to the heating coil 7 is 600 W, the inverter oscillation control means 52 includes the energization period of the heating coil 7 over the entire range of two zero cross cycles. Assuming that A is set and the non-energization period B of the heating coil 7 is set over the entire range of one zero cross cycle, the energization rate of the heating coil 7 is 100 × 2/3% and is supplied to the heating coil 7. The power is controlled to 400W on average.

  As described above, in the present embodiment, by determining whether or not the switching element 9 is turned on / off over the entire period for every half cycle of the AC voltage from the AC power supply 1, Since the current supply rate is controlled to adjust the power supplied to the heating coil 7, it is not necessary to reduce the width of the pulse drive signal for turning on the switching element 9 when the power supplied to the heating coil 5 is reduced. Accordingly, the next pulse drive signal can be reliably supplied at the timing when the voltage between the emitter and collector, which is the voltage across the switching element 9, becomes zero, and the switching element 9 is excessively large between the emitter and collector. Current is prevented from flowing.

  Further, in a very short cycle of every half cycle of the AC voltage, it is determined whether or not the switching element 9 is turned on / off every half cycle for controlling the energization rate of the heating coil 7. Therefore, when the energization rate is reduced, it is equivalent to the case where continuous energization is performed with low power like a half-bridge inverter. Therefore, the power supplied to the heating coil 7 can be stably controlled even in the region where the power consumption is small, even though the single-ended resonance type high frequency inverter 11 is used.

  In the present embodiment, the power supplied to the heating coil 7 is set according to the target power setting signal by feedback control by the inverter oscillation control means 52 based on the power detected by the power detection circuit 25. Kept at the value. The supply power here is controlled by adjusting the energization rate of the pulse drive signal applied to the switching element 9 as described above.

  At the end of the energization period A, the pulse drive signal applied to the switching element 9 is not stopped suddenly, but is terminated by gradually reducing the width of the pulse drive signal by the control circuit 15. This further prevents noise at the end.

  As described above, the electromagnetic induction heating device according to the present embodiment includes the AC power source 1 serving as a power source that converts AC voltage into DC voltage, the inverter 11 including the switching element 9 serving as switching means, and the resonance capacitor of the inverter 11. 8 and a heating coil 7 as a heating means constituting the resonance circuit. The switching coil 9 is turned on / off to convert the direct current from the AC power source 1 into the heating coil 7. For example, a heat roller of a fixing device, which is a load, is electromagnetically heated, and here, in particular, a trigger detection circuit 31 as a measuring means for measuring the occurrence timing of self-excited oscillation of the inverter 11. In response to the measurement result from the trigger detection circuit 31, the timer that starts every zero crossing of the AC voltage from the AC power supply 1 is A control circuit 15 as a control means for generating the second timer 51B by the cross timing generation means 51 and controlling the on / off operation of the switching element 9 by the inverter oscillation control means 52 in synchronization with the activation of the second timer 51B. And.

  In this case, the timing at which the self-excited oscillation of the inverter 11 occurs in the vicinity of the zero cross of the AC voltage from the AC power supply 1 is taken into the control circuit 15 from the measurement result of the trigger detection circuit 31 and is activated every zero cross of the AC voltage. By generating the 2-timer 51B by the control circuit 15, the on / off operation of the switching element 9 and the heating operation of the heat roller as a load can be performed in synchronization with the zero cross timing without using the conventional zero cross detection circuit 21. , It can be done programmatically without additional costs.

  Further, the inverter 11 of the present embodiment is a single-ended inverter 11 including a single switching element 7, and the control circuit 15 covers the entire period every half cycle of the AC voltage from the AC power supply 1. Thus, by determining whether or not the switching element 9 is to be turned on / off, the power supply rate of the heating coil 7 is controlled.

  In this case, the basic unit is a very short cycle of a half cycle of the AC voltage, and it is determined whether or not the switching element 9 is turned on / off for every half cycle. Since the rate control is performed, it is possible to make the paddle equivalent to continuous energization with a small amount of power like a half-bridge type inverter. The power supplied to the heating coil 7 can be stably controlled.

  In addition, the control circuit 15 of the present embodiment is configured to start the on / off operation of the switching element 9 and thus the energization of the heating coil 7 at the timing of the zero crossing of the AC voltage.

  In this case, since the oscillation of the inverter 11 starts at the timing of the zero crossing of the AC voltage, there is no physical or electrical shock (noise generation, element breakage) at the start of the on / off operation of the switching element 9. Further, not only the start of the on / off operation of the switching element 9 but also the end of the on / off operation can be synchronized with the zero cross of the AC voltage, and an electromagnetic induction heating device in which no abnormal noise is generated can be provided.

  The electromagnetic induction heating device of this embodiment further includes a power detection circuit 25 as power detection means for detecting the power consumption of the heating coil 7, and the control circuit 15 sets the power consumption detected by the power detection circuit 25. By determining whether or not the switching element 9 is to be turned on / off over the entire period for every half cycle of the AC voltage from the AC power supply 1 so as to obtain the value obtained, It is set as the structure which performs control.

  In this case, since the energization rate control of the heating coil 7 is performed so that the power consumption of the heating coil 7 becomes a predetermined value, the power consumption of the heating coil 7 is set to a predetermined value even in a region where the power consumption of the heating coil 7 is small. Can be maintained.

  FIG. 6 shows an electromagnetic induction heating device for a copying machine according to the second embodiment of the present invention. In this figure, in the present embodiment, the power detection circuit 25 described above is composed of an input current detection circuit 25A provided on the input side of the rectification smoothing circuit 2 and an input voltage detection circuit 25B provided on the output side of the rectification smoothing circuit 2. It is composed. The input current detection circuit 25A detects an input current from the AC power supply 11 and sends the current detection signal to the control circuit 15. The input voltage detection circuit 25B detects the input voltage from the AC power supply 11. Then, the voltage detection signal is sent to the control circuit 15.

  As in the first embodiment, the control circuit 15 takes in the current detection signal from the input current detection circuit 25A and the voltage detection signal from the input voltage detection circuit 25B, and multiplies these values to input power. Based on this input power, the inverter 11 is feedback controlled so that the power supplied to the heating coil 7 is maintained at a target set value. In particular, in the present embodiment, when the power supplied to the heating coil 7 is low and the power is low, the higher the input voltage from the AC power supply 1 is, the larger the short-circuit current at the time of switching of the switching element 9 is, and noise is generated. It becomes a factor. Therefore, in order to reduce the influence of such noise generation from the switching element 9, the control circuit 15 sets the lower limit value of the supply power that can be output by the heating coil 7 according to the voltage detection signal from the input voltage detection circuit 25B by software. The configuration is variable.

  Specifically, the inverter oscillation control means 52 of the control circuit 15 is configured so that the lower limit value of the power supplied to the heating coil 7 increases as the value of the input voltage detected by the input voltage detection circuit 25B increases. Conversely, as the value of the input voltage detected by the input voltage detection circuit 25B decreases, the lower limit value of the power supplied to the heating coil 7 is varied. As a result, even if the input voltage from the AC power supply 2 increases, the power supplied to the heating coil 7 is regulated so that noise due to the short-circuit current of the switching element 9 does not occur, and the short-circuit current of the switching element 9 Can reduce noise.

  Further, the input current detection circuit 25A and the input voltage detection circuit 25B here are also used for abnormality detection for stopping the operation of the inverter 11 by the control circuit 15 when an abnormal input current or input voltage is generated. . At that time, the control circuit 15 detects and takes in the current detection signal from the input current detection circuit 25A and the voltage detection signal from the input voltage detection circuit 25B in a short time of the order of 1 μs, and inputs the input current and the input in real time. It has a configuration for monitoring the voltage status. Thereby, the accuracy of the input voltage can be improved for the control circuit 15 to feedback control the inverter 11. Further, it is possible to quickly catch the occurrence of an abnormality and immediately stop the operation of the inverter 11, and to reduce the cost by deleting the surge detection circuit and the instantaneous power failure detection circuit for detecting the abnormality. it can.

  Further, the voltage detection signal from the input voltage detection circuit 25B is monitored by the control circuit 15 in the order of 1 μs, and the switching element 9 is turned on at the timing when the input voltage becomes zero cross based on the monitoring result. -It is preferable that the off operation is started. In other words, by finely monitoring the AC input voltage from the AC power supply 2, it is possible to accurately start the on / off operation of the switching element 9 at the zero-cross timing, and to ensure noise and switching loss from the switching element 9. Can be reduced.

  Although not shown in FIG. 6, other configurations can be made common to the first embodiment, and the function and effect of the configuration are as described in the first embodiment. In addition, the monitoring result from the input voltage detection circuit 25B is added to the measurement result from the trigger detection circuit 31, and the switching element 9 is turned on / off, that is, the heating coil 7 is energized at the zero-cross timing of the AC voltage. It is good also as composition to do.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, anything described as “circuit” in each of the above embodiments can be replaced with “means”. Moreover, you may use switching means other than IGBT which can supply a high frequency current to the heating coil 7. FIG.

1 AC power supply
7 Heating coil (heating means)
9 Switching elements (switching means)
11 Inverter 15 Control circuit (control means)
25 Power detection circuit (power detection means)
31 Trigger detection circuit (measurement means)

Claims (4)

A power source for converting alternating current into direct current, an inverter provided with switching means, and a heating means connected to the inverter,
In the electromagnetic induction heating apparatus that applies a direct current from the power source to the heating means intermittently by the on / off operation of the switching means, and electromagnetically heats the load,
Measuring means for measuring the occurrence timing of self-excited oscillation of the inverter;
Receiving a measurement result from the measurement means, generating a timer that starts every zero cross of the alternating current, and controlling means for controlling the on / off operation of the switching means in synchronization with the start of the timer, An electromagnetic induction heating device. The inverter is a single-ended inverter equipped with a single switching means,
The control means is configured to control the energization rate of the heating means by determining whether or not the switching means is turned on / off over the entire period every half cycle of the alternating current. The electromagnetic induction heating device according to claim 1.   3. The electromagnetic induction heating apparatus according to claim 2, wherein the control unit is configured to start energization of the heating unit at the timing of the alternating zero crossing. Comprising power detection means for detecting power consumption of the heating means,
The control means determines whether or not to turn the switching means on and off over the entire period every half cycle of the alternating current so that the power consumption detected by the power detection means becomes a set value. The electromagnetic induction heating apparatus according to claim 2 or 3, wherein a power supply rate control of the heating means is performed by making a determination.

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