JP2013125066A - Induction heating fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating fixing device that controls a minute current region, and to provide an image forming device.SOLUTION: The induction heating fixing device includes a series resonance circuit, a phase comparison section, a phase control part, a resonance frequency tracking oscillation part, and a PWM signal generation part. The phase comparison section compares a phase of a pulse output from the PWM signal generation part with a phase of a current of the induction coil, outputs a result to the phase control part during phase control, and outputs the result to the resonance frequency tracking oscillation part during PWM control. The phase control part outputs a frequency control signal with a predetermined phase value to the resonance frequency tracking oscillation part on the basis of the output of the phase comparison section and a predetermined coil current phase amount. The resonance frequency tracking oscillation part uses an output of the phase control part to change oscillation frequency so as to cause the resonance frequency to track drive frequency of the series resonance circuit. The PWM signal generation part generates a pulse to drive the series resonance circuit on the basis of the oscillation frequency by the resonance frequency tracking oscillation part. The phase comparison section, the phase control part, the resonance frequency tracking oscillation part, and the PWM signal generation part are digital-controlled.

Description

  The present invention relates to an induction heating fixing device and an image forming apparatus.

  The image forming apparatus includes a fixing device for fixing a toner image transferred onto a sheet as a recording medium to the sheet. The fixing device includes, for example, a fixing roller or a fixing belt (heating roller) that heat-melts toner on the sheet, and a pressure roller that presses the sheet in pressure contact with the fixing roller or the fixing belt.

  In order to heat the fixing roller or the fixing belt, an induction heating type fixing device in which an induction heating coil is arranged inside or outside the fixing roller or the fixing belt is widely used. In the induction heating system, an eddy current is caused to flow inside the fixing roller or the fixing belt by passing the magnetic flux generated by the induction heating coil through the conductor portion of the fixing roller or the fixing belt. The fixing belt is heated.

  As a power control method in the conventional induction heating fixing device, a method of controlling the drive frequency with the LCR resonance circuit configuration and a current amount are controlled by executing PWM control in a state where the resonance circuit is resonating at the resonance frequency f. The method has been carried out. As a conventional method of changing the output power by controlling the driving frequency, there are, for example, Patent Documents 1 and 2.

  On the other hand, FIG. 1 shows a configuration of an inverter power source of an induction heating fixing apparatus 900 of a method of changing a current amount by controlling a current amount by executing PWM control in a state of a conventional resonance frequency f. The output from the AC power source 901 is full-wave rectified by the diode bridge 904 and then passed through the noise filter 905 and supplied to the half-bridge output circuit 906. Reference numeral 902 denotes a fuse, and reference numeral 903 denotes a surge voltage protection varistor.

  The half-bridge output circuit 906 uses an IGBT (Insulated Gate Bipolar Transistor), a FET (Field Effect Transistor), or the like as a switching element.

  In the configuration shown in FIG. 1, the half-bridge output circuit 906 uses IGBTs 907 and 908 as switching elements. The LC series resonance circuit is composed of a low-loss induction heating coil 912 and capacitors 913 and 914, and uses a Litz wire (an electric wire formed by twisting a large number of thin copper wires) constituting the LC series resonance circuit. By applying a high-frequency current to 912, a magnetic field is generated. The magnetic field generated by the low-loss induction heating coil 912 is concentrated on a fixing roller or a fixing belt 910 made of a high magnetic permeability material, and the surface of the heating element is generated by the magnetic field generated by the low-loss induction heating coil 912. An eddy current flows through the fixing roller or the fixing belt 910 and self-heats.

  The output of the current transformer 909 for detecting the current and phase difference of the low-loss induction heating coil 912 connected to the half-bridge output by the IGBTs 907 and 908, and the driving voltage of the half-bridge output by the IGBTs 907 and 908 (one side) Are compared using a phase comparator 928 (for example, using a general-purpose PLL IC (74HC4046, etc.)), and the phase comparison result of the phase comparator 928 is output to an RC sawtooth oscillation type voltage controlled oscillator (VCO) 929. . The oscillation frequency of the VCO 929 is feedback controlled so that the phase difference between the output of the current transformer 909 and the driving voltage of the half bridge output is eliminated.

  The PWM control unit 919 rectifies the PWM On duty value calculated by the PID (Proportional, Integral, Differential) calculation by the PID control unit 917 in the CPU 915 and the output of the current transformer 909 from the information from the heat generating unit temperature detection sensor 911. The signal rectified by the circuit 923 is amplified by the error amplifier 920, the amplified value and the output from the VCO 929 are compared by the comparator 921, and the comparison result is output to the PWM driver 922, so that the PWM driver 922 outputs the PWM signal. Can be output to the light emitting diode and the phototransistors 923 and 924.

JP 2008-51951 A JP 2008-145990 A

  As a power control method in a conventional induction heating fixing device, a method of controlling the drive frequency with a configuration having an LCR resonance circuit has a problem that it becomes uncontrollable when the resonance frequency of the resonance circuit fluctuates. In order to cope with this, as in the invention described in Patent Document 1, it is necessary to obtain a frequency at which the power reaches a peak and control the frequency as a lower limit frequency. In addition, there is a problem that the frequency becomes too high during the low power control and the switching loss of the half-bridge output element is increased, resulting in a reduction in efficiency. As in the invention described in Patent Document 2, large power and medium power It is necessary to switch the power control method between low power and small power. In addition, when the half-bridge element is switched when the drive frequency deviates from the resonance frequency, zero voltage switching is not performed and the element loss increases, which may cause deterioration due to heat generation or thermal destruction.

  On the other hand, in the method of changing the amount of current by controlling the amount of current by executing PWM control in a state where the resonant circuit is resonating at the resonance frequency f, the phase comparator, voltage control oscillator, and PWM in the above-described circuit Since the control unit is configured with an analog circuit, it is necessary to consider variations in component constants and temperature fluctuations, and it is necessary to change all the component constants according to specifications such as setting the resonance frequency tracking range. Also, when there is a frequency range that cannot be used in particular (for example, a specific radio frequency or a resonance frequency of a fixing device mechanism such as a fixing belt), it is difficult to automatically follow the resonance frequency outside the frequency range. It is.

  Furthermore, even if only PWM control is used, control of a minute current region cannot be performed. This is because the switching speed of a switching element such as an IGBT is not fast enough to enable a minute current control by PWM.

  The present invention has been made in view of the above problems, and its object is to perform a minute current region by executing PWM control and phase control by following the resonance frequency without considering variations in component constants and temperature fluctuations. It is an object of the present invention to provide an induction heating fixing device and an image forming apparatus that can be controlled to a minimum.

  According to an embodiment of the present invention, a series resonance circuit having an induction coil and a capacitor, a phase comparison unit, a phase control unit, a resonance frequency tracking oscillation unit, and a PWM (pulse width modulation) signal generation unit are provided. The phase comparison unit compares the phase of the pulse output from the PWM signal generation unit with the phase of the current flowing through the induction coil, and outputs the comparison result to the phase control unit during phase control. , During PWM control, output to the resonance frequency follow-up oscillation unit, the phase control unit outputs a frequency control signal having a predetermined phase value based on the output of the phase comparison unit and a predetermined coil current phase amount The resonance frequency follow-up oscillation unit outputs an output to the resonance frequency follow-up oscillation unit, and the resonance frequency follow-up oscillation unit changes the oscillation frequency so that the drive frequency of the series resonance circuit follows the resonance frequency using the output of the phase control unit. The PWM signal generation unit generates a pulse for driving the series resonance circuit based on the oscillation frequency by the resonance frequency tracking oscillation unit, the phase comparison unit, the phase control unit, the resonance frequency tracking oscillation unit, and the The PWM signal generator is digitally controlled.

  According to an embodiment of the present invention, the phase control unit compares the phase of the pulse output from the PWM signal generation unit with the phase of the current flowing through the induction coil, thereby obtaining a signal corresponding to the phase difference. The counter of the output of the phase comparison unit that outputs the value is compared with a subtractor by the coil current phase amount set value, and based on the result, a frequency control signal is output to the resonance frequency tracking oscillation unit, and the resonance The frequency tracking oscillating unit changes the oscillation frequency by increasing or decreasing the counter based on the signal output from the phase control unit.

  According to an embodiment of the present invention, the phase control is performed in a first region where the current is relatively small, and the PWM control is performed in a second region where the current is relatively large.

  According to an embodiment of the present invention, the image forming apparatus includes an induction heating fixing device.

  As described above, according to the present invention, a new and improved induction heating capable of executing PWM control and phase control by following the resonance frequency without considering variation of component constants and temperature fluctuation. A fixing device and an image forming apparatus can be provided.

It is a figure which shows the structure of the inverter power supply of the conventional induction heating fixing apparatus. It is a figure which shows the structure of the induction heating fixing apparatus concerning one Embodiment of this invention. It is a figure which shows the relationship between the count value of an up / down counter, and an output frequency at the time of specific unusable frequency area | region setting. It is a figure which shows an example of an output characteristic when changing the duty of PWM ON time with a resonant frequency. It is a figure which shows the structural example of the phase comparison part in ASIC. It is a figure which shows the structural example of the resonant frequency tracking oscillation part in ASIC. It is a figure which shows the structural example of the PWM signal generation part in ASIC shown in FIG. It is a figure which shows the operation | movement waveform of a resonance frequency tracking oscillation part. It is a figure which shows the operation | movement waveform of a resonance frequency tracking oscillation part. It is a figure which shows the operation | movement waveform of a resonance frequency tracking oscillation part. It is a figure which shows the detail of the output of a resonant frequency tracking oscillation part and a PWM signal generation part with a timing chart. It is a figure which shows the detail of the output of a resonant frequency tracking oscillation part and a PWM signal generation part with a timing chart. It is a figure which shows the detail of the output of a resonant frequency tracking oscillation part and a PWM signal generation part with a timing chart. It is a figure which shows the structure of an induction heating fixing device. It is a figure which shows operation | movement of an induction heating fixing apparatus. It is a figure which shows the specific structure of a phase control part. FIG. 17 is a diagram illustrating operation waveforms of a drive voltage, a coil current waveform, and a frequency control signal when the coil current phase control amount setting value is changed from 0 through X to Y in the phase control unit of FIG. 16. FIG. 17 is a signal timing diagram in the phase control unit of FIG. 16. FIG. 17 is a signal timing diagram in the phase control unit of FIG. 16.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the present specification and drawings, components having the same or similar functions or configurations are denoted by the same reference numerals. Components with the same last two digits of the reference number correspond to each other.

<One Embodiment of the Present Invention>
First, the configuration of an induction heating fixing device according to an embodiment of the present invention will be described. FIG. 2 is a diagram illustrating a configuration of the induction heating fixing device 100 according to the embodiment of the present invention. Hereinafter, the configuration of the induction heating fixing apparatus 100 according to the embodiment of the present invention will be described with reference to FIG.

  In the induction heating fixing device 100 according to the embodiment of the present invention shown in FIG. 2, in order to heat the fixing roller or the fixing belt, an induction heating coil is arranged inside or outside the fixing roller or the fixing belt. This is a fixing device using the induction heating method.

  As shown in FIG. 2, the induction heating and fixing apparatus 100 according to the embodiment of the present invention includes an AC power supply 101, a fuse 102, a varistor 103, a diode bridge 104, a noise filter 105, and a half bridge output circuit. 106, a CPU 115, a rectifier circuit 120, a limiter circuit 121, and an ASIC (Application Specific Integrated Circuit) 124. The output from the AC power supply 101 is full-wave rectified by the diode bridge 104 and then passed through the noise filter 105 and supplied to the half-bridge output circuit 106.

The induction heating fixing device 100 of FIG. 2 is a method of changing the output power by PWM control in a resonance state that automatically follows the resonance frequency. That is, the amount of current is changed by controlling the amount of current by executing PWM control in a resonance state that automatically follows the resonance frequency f ₀ .

  The half-bridge output circuit 106 includes IBGTs 107 and 108, a current transformer 109, a low-loss induction heating coil 112, and capacitors 113 and 114. An LC resonance circuit is configured by the low-loss induction heating coil 112 and the capacitors 113 and 114.

  The half-bridge output circuit 106 uses an IGBT (Insulated Gate Bipolar Transistor), an FET (Field Effect Transistor), or the like as a switching element.

  In the configuration shown in FIG. 2, IGBTs 107 and 108 are used as switching elements in the half-bridge output circuit 106. The LC series resonance circuit includes a low-loss induction heating coil 112 and capacitors 113 and 114, and uses a Litz wire (an electric wire in which a large number of thin copper wires are twisted) constituting the LC series resonance circuit. By applying a high-frequency current to 112, a magnetic field is generated. The magnetic field generated by the low-loss induction heating coil 112 is concentrated on the fixing roller or fixing belt 110 made of a high magnetic permeability material, and an eddy current flows on the surface of the heating element. Fever.

  The CPU 115 measures the temperature of the fixing roller or fixing belt 110 made of a high magnetic permeability material, and controls the duty of the PWM signal generated by the PWM signal generator 127 described later based on the measured temperature. AD converters (ADC) 116 and 118, a PID control unit 117, and a PWM duty control unit 119 are configured.

  The ASIC 124 generates a PWM signal by following the resonance frequency of the LC resonance circuit composed of the low-loss induction heating coil 112 and the capacitors 113 and 114. The ASIC 124 generates the phase comparison unit 125 and the resonance frequency tracking oscillation. Part 126 and a PWM signal generator 127. In the present embodiment, by configuring the configuration that generates the PWM signal following the resonance frequency of the LC resonance circuit as a digital circuit, it is possible to fit all the configurations including the CPU 115 inside the ASIC (SOC). .

  The phase comparator 125 is one of the two PWM signals generated by the PWM signal generator 127 and the current flowing through the low-loss induction heating coil 112 detected by the current transformer 109 output from the limiter circuit 121. Is detected. That is, the phase comparison unit 125 outputs the current of the low-loss induction heating coil 112 connected to the half bridge output by the IGBTs 107 and 108 and the current transformer 109 for detecting the phase difference, and the half bridge output by the IGBTs 107 and 108. And the phase comparison result is output to the resonance frequency tracking oscillation unit 126.

  The resonance frequency follow-up oscillation unit 126 uses the detection result of the phase difference by the phase comparison unit 125 to perform processing for causing the oscillation frequency of the PWM signal generated by the PWM signal generation unit 127 to follow the resonance frequency of the LC resonance circuit. It is something to execute. Specifically, the resonance frequency tracking oscillating unit 126 changes the oscillation frequency of the PWM signal according to the output of the phase comparison unit 125. For example, the resonance frequency tracking oscillation unit 126 performs drive frequency control so that the phase difference becomes 0 (resonance frequency) by raising and lowering the up / down counter value based on the phase comparison result.

  The PWM signal generation unit 127 generates a PWM signal at an oscillation frequency that changes based on the process of causing the resonance frequency tracking oscillation unit 126 to track the resonance frequency of the LC resonance circuit, and causes the light emitting diode and the phototransistors 128 and 129 to generate the PWM signal. Output. In other words, the PWM signal generation unit 127 calculates the PWM On duty value calculated by the PID (Proportional, Integral, Differential) calculation by the PID control unit 117 in the CPU 115 from the information from the temperature sensor 111 that detects the temperature of the heat generation unit. Can be output to the light emitting diode and the phototransistors 128 and 129.

  The rectifier circuit 120 rectifies the output of the current transformer 109. The rectifier circuit 120 outputs the rectified output of the current transformer 109 to the AD converter 118 of the CPU 115. The limiter circuit 121 outputs the current transformer 109 by limiting the output voltage within a predetermined range. The limiter circuit 121 limits the output voltage of the current transformer 109 within a predetermined range and outputs it to the phase comparison unit 125 of the ASIC 124. The resistor 122 is a resistor for allowing a current to flow from the current transformer 109.

  The induction heating and fixing apparatus 100 according to an embodiment of the present invention shown in FIG. 2 performs full-wave rectification on the output from the AC power supply 101 by the diode bridge 104 and then passes the noise filter 105 to the half-bridge output circuit 106. To supply.

  In the half-bridge output circuit 106, the current that has passed through the noise filter 105 flows to the low-loss induction heating coil 112 via the current transformer 109 by the switching operation in which the IBGTs 107 and 108 are alternately turned on and off. A magnetic field can be generated from the low-loss induction heating coil 112 by flowing a high-frequency current through the low-loss induction heating coil 112. The magnetic field generated by the low-loss induction heating coil 112 is concentrated on the fixing roller or the fixing belt 110 made of a high magnetic permeability material. Due to the magnetic field generated by the low-loss induction heating coil 112, an eddy current flows on the surface of the heating element and self-heats.

  Here, the LC resonance principle used in the induction heating fixing apparatus 100 according to the embodiment of the present invention shown in FIG. 2 will be described. In the LCR series resonance circuit including the LC resistance, the impedance Z of the LCR series resonance circuit is obtained by the following Equation 1.

Here, when the frequency at which X = 0 is expressed by ω ₀ , the series resonance frequency f ₀ is obtained by the following Equation 2.

  Next, when the impedance Z of the LCR series resonance circuit is represented by a complex vector, the impedance Z, the magnitude | Z |, and the phase α are obtained by the following Equation 3.

That is, the magnitude | Z | of the impedance is a minimum value because the inductance and the capacitance cancel each other and only the resistance component R is taken at the resonance frequency f ₀ .

  Then, the current I flowing when the voltage source V is connected to the series resonant circuit, the magnitude | I |, and the phase Φ are obtained by the following Equation 4.

Therefore, as can be seen from Equation 4, when the LCR series resonance circuit is voltage-driven, the current I takes the maximum value at the resonance frequency f ₀ , and the current I and the voltage V have the same phase. The LC resonance principle used in the induction heating fixing apparatus 100 according to the embodiment of the present invention shown in FIG. 2 has been described above.

  FIG. 4 is a diagram illustrating an example of a current output characteristic of the LCR series resonance circuit when the duty of the PWM signal ON time (high time) is changed at the resonance frequency. As described above, the current value (absolute value thereof) changes with the resonance frequency as a boundary, but the current value (absolute value thereof) is also variable by changing the duty of the ON time of the PWM signal. That is, when the ON time of the PWM signal generated by the PWM signal generation unit 127 becomes longer, the time during which the IGBTs 107 and 108 are turned on becomes longer, and the current value of the LCR series resonance circuit also increases.

  The configuration of the induction heating fixing device 100 according to the embodiment of the present invention has been described above with reference to FIG. Next, a detailed configuration example of each unit of the ASIC 124 illustrated in FIG. 2 will be described. First, a configuration example of the phase comparison unit 125 will be described.

  FIG. 5 is a diagram illustrating a configuration example of the phase comparison unit 125 in the ASIC 124 illustrated in FIG. 2. Hereinafter, a configuration example of the phase comparison unit 125 will be described with reference to FIG.

  As shown in FIG. 5, the phase comparison unit 125 includes a delay correction unit 131, JKFFs (flip-flops) 132 and 133, and a NAND gate 134.

  The delay correction unit 131 sets a delay correction value of the coil current phase comparison voltage (Coil_ICV) that originally causes a delay with respect to the drive voltage (Drive_V1) generated by the PWM signal generation unit 127. The delay correction unit 131 receives the drive voltage (Drive_V1), the system clock (System_CL), and the delay clock (Delay_CL), and outputs a clock to the JKFF 132. Further, the coil current phase comparison voltage (Coil_ICV) output from the limiter circuit 121 is supplied to the JKFF 133.

  JKFFs 132 and 133 output a new state to the output terminal Q and its inverted output in synchronism with the clock according to the combination of the states of the input terminals J and K. The JKFF 132 outputs 1 (High) from the Q terminal when the phase of the current flowing through the low-loss induction heating coil 112 is delayed with respect to the drive voltage (Drive_V1) generated by the PWM signal generator 127. As a result, Count_Up becomes High. On the other hand, the JKFF 133 outputs 1 (High) from the Q terminal when the phase of the current flowing through the low-loss induction heating coil 112 is advanced with respect to the drive voltage (Drive_V1) generated by the PWM signal generator 127. As a result, Count_Down becomes High.

  By configuring the phase comparison unit 125 as shown in FIG. 5, when the coil current phase comparison voltage (Coil_ICV) output from the limiter circuit 121 is delayed with respect to the drive voltage (Drive_V1), Count_Up becomes High. Thus, when the coil current advances with respect to the drive voltage (Drive_V1), Count_Down becomes High.

  Next, a configuration example of the resonance frequency tracking oscillation unit 126 will be described. FIG. 6 is a diagram illustrating a configuration example of the resonance frequency tracking oscillation unit 126 in the ASIC 124 illustrated in FIG. Hereinafter, a configuration example of the resonance frequency tracking oscillation unit 126 will be described with reference to FIG.

  As shown in FIG. 6, the resonance frequency follow-up oscillation unit 126 includes an up / down counter 141, a frequency comparison unit 142, a feedback gain correction unit 143, a PWM counter 144, an OSC comparator 145, and a 1-bit counter 146. , NOT gate 147, and AND gate 148.

  The up / down counter 141 receives the output (Count_Up or Count_Down) of the phase comparison unit 125 and other parameters, and counts up while the Count_Up of the outputs of the phase comparison unit 125 is High. Thus, the oscillation frequency is lowered, and while Count_Down is High, the oscillation frequency is set to be counted down to lower the oscillation frequency.

  Other parameters input to the up / down counter 141 correspond to the value of Count_Max to Count_Min (see FIG. 3), which is the range of the value (OSC_OUT [N..1]) output by the frequency comparison unit 142, and Count_Max. F_Min which is a frequency to be operated, f_Max which is a frequency corresponding to Count_Min, and an initial set resonance frequency f_initial.

  Inductive heating and fixing devices do not require as much jitter performance of resonance frequency tracking characteristics as those required for strict performance as in communication devices, and thus follow the resonance frequency of the LCR series resonance circuit. Therefore, the up / down counter 141 having a simple configuration can be used.

  The frequency comparison unit 142 compares the oscillation frequency with a specific unusable frequency region (for example, a specific radio frequency or a resonance frequency in a fixing mechanism such as the fixing roller or the fixing belt 110). As shown in FIG. 6, the frequency comparison unit 142 includes a window comparator 161, a comparison circuit 162, and a latch circuit 163.

  The window comparator 161 compares a specific unusable frequency range (f1_Max to f1_Min, f2_Max to f2_Min,..., Fm_Max to fm_Min) with the output counter value of the up / down counter 141. The window comparator 161 outputs High when the output counter value of the up / down counter 141 corresponds to a specific unusable frequency region.

FIG. 3 is a graph showing the relationship between the count value of the up / down counter 141 and the output frequency when a specific unusable frequency region is set. In the graph shown in FIG. 3, the horizontal axis indicates the frequency, and the vertical axis indicates the output of the up / down counter 141 (FOUT [N... 1]). “F_Initial” corresponds to the initial resonance frequency f ₀ , “Count_Max” corresponds to the lower limit frequency f_Min, and “Count_Min” corresponds to the upper limit frequency f_Max. Thus, the frequency and the count value of the up / down counter 141 are in a proportional relationship.

  When the output value (FOUT [N..1]) of the up / down counter 141 enters the unusable frequency region, the previous frequency value is latched by the latch circuit 163, and the output frequency does not enter the unusable frequency region. Further, the output value (FOUT [N... 1]) of the up / down counter 141 changes. Then, after exiting the unusable frequency region, the output of the latch circuit 163 (OSC_OUT [N..1]) becomes the output frequency at the time of exiting the unusable frequency region.

  The PWM counter 144 outputs a counter value (PWM_OUT [N−1..0]) based on the system clock (System_CL). The OSC comparator 145 compares the output of the frequency comparison unit 142 (OSC_OUT [N..1]) with the output of the PWM counter 144 (PWM_OUT [N-1..0]) and outputs a comparison result (OSC_COMP_OUT). To do. The output of the frequency comparison unit 142 (OSC_OUT [N..1]) is compared with the output of the PWM counter 144 (PWM_OUT [N−1..0]), and when both values match, the OSC comparator 145 determines a predetermined value. During this period, the output is changed from Low to High, and the PWM signal generator 127 is notified that one period of the resonance frequency has been reached.

  Next, a configuration example of the PWM signal generator 127 will be described. FIG. 7 is a diagram illustrating a configuration example of the PWM signal generation unit 127 in the ASIC 124 illustrated in FIG. Hereinafter, a configuration example of the PWM signal generation unit 127 will be described with reference to FIG.

  As shown in FIG. 7, the PWM signal generator 127 includes a multiplier 151, a PWM comparator 152, NOT gates 153 and 154, AND gates 155, 157 and 158, and a DFF 156. .

  The PWM comparator 152 multiplies the information (PWM_Duty) about the duty sent from the PWM duty control unit 119 and the output (OSC_OUT [N... 1]) of the frequency comparison unit 142 by the multiplier 151, and the PWM counter 144 The output (PWM_OUT [N−1..0]) is compared, and the comparison result is output to the NOT gate 154.

  The DFF 156 receives the output (OSC_COMP_OUT) of the OSC comparator 145 and outputs a voltage (Drive_V) that is a basis of the drive voltages Drive_V1 and Drive_V2. The DFF 156 outputs Drive_V to the AND gates 157 and 158. AND gates 157 and 158 output drive voltages Drive_V1 and Drive_V2, respectively, using a signal (PWM_Select) output from 1-bit counter 146.

  That is, the PWM signal generator 127 outputs a voltage (Drive_V) that is a base of the drive voltages Drive_V1 and Drive_V2 that are High only for a predetermined period at a timing when OSC_COMP_OUT becomes High. This predetermined period is instructed by the PWM duty control unit 119, and the information corresponds to PWM_Duty supplied to the PWM comparator 152.

  By configuring the PWM signal generator 127 as shown in FIG. 7, the PWM timing is calculated from the ON duty time calculated by the CPU 115 and the output counter value of the up / down counter 141, and the PWM counter using the reset counter is used. The output value 144 (PWM_OUT [N−1..0]) is compared with the DFF 156, and if they match, the voltage (Drive_V) that is the basis of the drive voltages Drive_V1 and Drive_V2 is set to Low. As a result, drive voltages Drive_V1 and Drive_V2 that are High only during the ON Duty time period are generated, and the light emitting diodes are High only during the High duty period, and the IGBTs 107 and 108 are turned on when the phototransistor is turned on. A current flows through the LC series resonance circuit.

  The configuration examples of the phase comparison unit 125, the resonance frequency tracking oscillation unit 126, and the PWM signal generation unit 127 have been described above. Next, the operation of the resonance frequency tracking oscillation unit 126 will be described. 8 to 10 are diagrams illustrating operation waveforms of the resonance frequency tracking oscillation unit 126. FIG.

  FIG. 8 shows an operation waveform of the resonance frequency follow-up oscillation unit 126 when the drive frequency of the drive voltages (Drive_V1, Drive_V2) and the resonance frequency are operating. FIG. 9 shows an operation waveform of the resonance frequency follow-up oscillation unit 126 when the drive frequency of the drive voltage is higher than the resonance frequency. FIG. 10 shows an operation waveform of the resonance frequency tracking oscillation unit 126 when the resonance frequency of the drive voltage is operating below the drive frequency.

  FIG. 8 shows how the peak value of the current flowing through the coil changes depending on the On Duty of the drive voltages (Drive_V1, Drive_V2). The on duty of the drive voltages (Drive_V 1, Drive_V 2) varies under the control of the PWM duty control unit 119.

  In FIG. 8, since the drive frequency of the drive voltage and the resonance frequency coincide with each other, the output of the phase comparator 125 (Count_Up or Count_Down) is always Low, and therefore the output of the up / down counter 141 ( (UpDown_Count) is not performed.

  9 and 10 detect the phase difference from the operation waveforms of the drive voltage and the coil current, increase / decrease the value of the up / down counter 141, and perform feedback control so that the drive frequency becomes the resonance frequency. The operation is shown.

  First, the operation of the resonance frequency tracking oscillation unit 126 when the drive frequency of the drive voltage is operating above the resonance frequency will be described with reference to FIG. When the drive frequency of the drive voltage is higher than the resonance frequency, the phase of the current flowing through the coil is delayed, and therefore, Count_Up among the outputs of the phase comparison unit 125 becomes High. The period during which Count_Up is High is a period from when the drive voltage (Drive_V1) switches from Low to High until the phase of the coil current becomes zero.

  When Count_Up becomes High among the outputs of the phase comparison unit 125, the up / down counter 141 increases the counter and outputs only during the High period. As a result, the drive frequency of the drive voltage can be made to follow the resonance frequency.

  On the other hand, the operation of the resonance frequency follow-up oscillating unit 126 when the drive frequency of the drive voltage is operating below the resonance frequency will be described with reference to FIG. When the drive frequency of the drive voltage is lower than the resonance frequency, the phase of the current flowing through the coil advances, and therefore, Count_Down among the outputs of the phase comparison unit 125 becomes High. The period in which Count_Down becomes High is a period from when the phase of the coil current becomes 0 to when the drive voltage (Drive_V1) switches from Low to High.

  When Count_Down becomes High among the outputs of the phase comparison unit 125, the up / down counter 141 outputs the output by lowering the counter only during the High period. As a result, the drive frequency of the drive voltages (Drive_V1, Drive_V2) can be made to follow the resonance frequency.

  Next, operations of the resonance frequency tracking oscillation unit 126 and the PWM signal generation unit 127 will be described. FIGS. 11 to 13 are timing charts showing details of outputs of the resonance frequency tracking oscillation unit 126 and the PWM signal generation unit 127.

  FIG. 11 is a timing chart when the induction heating fixing apparatus 100 oscillates at an initial set frequency (= resonance frequency) after the power is turned on. FIG. 12 shows a resonance frequency higher than the initial set frequency. FIG. 13 is a timing chart when the resonance frequency is lower than the initial set frequency.

  First, referring to FIG. 11, the resonance frequency follow-up oscillation unit 126 and the PWM signal generation unit 127 when oscillating at the initial set frequency (= resonance frequency) after the induction heating fixing device 100 is turned on are turned on. Will be described. When the value of the PWM counter 144 (PWM_OUT [N−1..0]) is f_initial, that is, a value corresponding to the initial set frequency, the output of the PWM counter 144 is reset and the output of the OSC comparator 145 (OSC_COMP_OUT) is It changes from Low to High, and the output (Drive_V1) of the DFF 156 switches from Low to High. The drive voltages (Drive_V1 and Drive_V2) are output from the AND gates 157 and 158 in synchronization with the combination of the output of the DFF 156 and the 1-bit counter 146, respectively.

  Next, operations of the resonance frequency follow-up oscillation unit 126 and the PWM signal generation unit 127 when the resonance frequency becomes higher than the initial set frequency will be described with reference to FIG. When the resonance frequency becomes higher than the initial set frequency, Count_Down among the outputs of the phase comparison unit 125 becomes High. This shortens the period in which the output (OSC_COMP_OUT) of the OSC comparator 145 changes from Low to High (Initial → Initial-x → Initial-y → Initial-z), and the output (Driv_V) of the DFF 156 switches from Low to High. The period changes. As a result, control is performed so that the drive frequency of the drive voltage matches the resonance frequency.

  Finally, with reference to FIG. 13, the operation of the resonance frequency follow-up oscillation unit 126 and the PWM signal generation unit 127 when the resonance frequency becomes lower than the initial set frequency will be described. When the resonance frequency becomes lower than the initial set frequency, Count_Up becomes High among the outputs of the phase comparison unit 125. As a result, the cycle in which the output (OSC_COMP_OUT) of the OSC comparator 145 changes from Low to High becomes longer (Initial → Initial + x → Initial + y → Initial + z), and the cycle in which the output (Drive_V) of the DFF 156 switches from Low to High changes. As a result, control is performed so that the drive frequency of the drive voltage matches the resonance frequency.

  As described above, from the detection result of the phase difference between the drive voltage and the coil current, the value of the up / down counter 141 is increased / decreased to control the drive voltage drive frequency to the resonance frequency, and the value of the up / down counter 141 and the temperature The PWM duty control unit 119 calculates a PWM duty value based on the PWM duty correction value obtained by the PID calculation in the PID control unit 117 from the output data value of the sensor 111.

  When the output value of the PWM counter 144 matches the PWM Duty value, the drive voltage is set to Low, and when the output value matches the value of the up / down counter 141, the drive voltage is changed to High to generate the resonance frequency PWM signal (Drive_V). The half-bridge drive signal is output alternately between Drive_V1 and Drive_V2 by putting the output permission signal for each half cycle created by the 1-bit counter 146 and the resonance frequency PWM signal generated by the DFF 156 into the AND gates 157 and 158. Is done.

According to the induction heating fixing device 100, can change the amount of power by controlling the current amount by executing the PWM control with automatic follow-up to the resonant state to the resonant frequency f _0. As a result, the induction heating fixing device 100 has an effect that power efficiency is improved.

<Modification>
FIG. 14 is a diagram illustrating a configuration of the induction heating fixing device 1400. FIG. 15 is a diagram illustrating the operation of the induction heating fixing device 1400.

  The induction heating fixing device 1400 has an ASIC 1424. The ASIC 1424 is different from the ASIC 124 in that it includes a phase comparison unit 1425, a phase control unit 1425P, a resonance frequency tracking oscillation unit 1426, and a PWM signal generation unit 1427. The CPU 1415 includes an ADC 1416, a PID control unit 1417, an ADC 1418, a PWM duty control unit 1419, and a phase control amount setting unit 1419P. The ADC 1416, the PID control unit 1417, the ADC 1418, and the PWM duty control unit 1419 correspond to the ADC 116, the PID control unit 117, the ADC 118, and the PWM duty control unit 119, respectively.

  FIG. 16 is a diagram illustrating a specific configuration of the phase control unit 1425P. When the coil current phase control amount set value Phase_Delay_Value is 0, the same resonance frequency follow-up control as described above with reference to FIG.

The phase comparison unit 1425, the resonance frequency tracking oscillation unit 1426, and the PWM signal generation unit 1427 correspond to the phase comparison unit 125, the resonance frequency tracking oscillation unit 126, and the PWM signal generation unit 127 shown in FIG. The phase comparison unit 1425, the resonance frequency tracking oscillation unit 1426, and the PWM signal generation unit 1427 measure the phase shift time of the drive voltage and the coil current, and perform control to automatically track the resonance frequency where the shift amount is zero. Yes. Specifically resonance frequency f ₀ as shown in FIG. 15 is variable.

  17 shows the drive voltage, coil current waveform, and frequency control signal Count_up, when the coil current phase control amount set value Phase_Delay_Value is changed from 0 through X to Y (where X> Y) by the phase control unit 1425P in FIG. It is a figure which shows the operation | movement waveform of Count_Up2, Count_Down, and Count_Down2.

  When performing the resonance frequency control, the CPU 1415 in FIG. 16 sets the coil current phase control amount set value Phase_Delay_Value to 0. At this time, the Select signal output from Comp1 becomes Low, and Selector 2 and Selector 3 select the A input. As a result, the phase comparison output signals Count_Up and Count_Down are directly input to the resonance frequency tracking oscillation unit 1426 without passing through the phase control unit 1425P. Therefore, resonance frequency control is performed.

  When the coil current phase control amount setting value Phase_Delay_Value is changed from the resonance state 0 to X, the frequency control signal Count_Down2 corresponding to the setting value X is output, the frequency is increased, and the pulse width is reduced as the phase amount setting value X is approached. When the phase amount finally reaches the setting X, the output of the frequency control signal Count_Down2 is stopped.

  Specifically, when performing phase control, the CPU 1415 in FIG. 16 sets the coil current phase control amount setting value Phase_Delay_Value to a value greater than zero. When the coil current phase control amount setting value Phase_Delay_Value is set to a value greater than zero, the output Select signal of Comp1 becomes Hi, and the Selector 2 and the Selector 3 select the B input. As a result, the phase comparison output signals Count_Up and Count_Down are input to the phase control unit 1425P, phase control is performed, and the signals Count_Up2 and Count_Down2 are input to the resonance frequency tracking oscillation unit 1426. Therefore, in this case, phase control is performed.

  When the coil current phase control amount set value Phase_Delay_Value is changed from X to Y (where X> Y), the frequency control signal Count_Up2 proportional to the difference between X and Y is output to increase the frequency and approach the phase amount set value Y. Accordingly, the pulse width is reduced, and when the phase amount finally reaches the setting Y, the output of the frequency control signal Count_Up2 is stopped.

  18 and 19 are timing charts of signals in the phase controller 1425P of FIG. FIG. 18 shows the operation timing when the coil current phase control amount set value Phase_Delay_Value is changed from 0 to X in FIG. FIG. 19 shows the operation timing when the coil current phase control amount set value Phase_Delay_Value in FIG. 17 is changed from X to Y (where X> Y).

<Action and effect>
The induction heating fixing device 100 in FIG. 2 controls the temperature by PWM control. That is, the induction heating fixing device 100 controls the power by calculating the PWM optimum value over the entire current value shown in FIG. In other words, the switching element is switched at the resonance frequency, and its pulse width is changed based on the signal from the temperature sensor.

  On the other hand, the induction heating fixing device 1400 performs PWM control when the current flowing through the coil is large, and performs phase control when the current flowing through the coil is small. Specifically, the ASIC 1424 includes a phase control unit 1425. This phase control unit 1425 realizes phase control of the coil current in the small current region.

  The CPU 1415 having the function of the temperature controller can control the power (that is, temperature) in two modes by calculating the PWM optimum value and the coil current phase optimum value based on the signal from the temperature sensor 111. In the small current region where the current flowing through the coil is small, the phase control unit 1425P performs phase control based on the coil current phase control amount setting value Phase_Delay_Value, thereby controlling the coil current. That is, the magnitude of the current is controlled based on the coil current phase control amount set value Phase_Delay_Value with reference to the followed resonance frequency, and temperature control is thereby performed. As a result, temperature control in the minute power region becomes possible.

  On the other hand, in a large current region where the current flowing through the coil is large, PWM control is performed as in the induction heating fixing device 100 of FIG. With this configuration, as shown in FIG. 15, this modification can control the coil current up to a minute power region, and as a result, finer temperature control can be realized.

  In particular, since the coil current phase delay control circuit is configured by a simple logic circuit (digital circuit), it is possible to digitally perform stable temperature control without being affected by temperature fluctuations and constant fluctuations. Since all the control circuits are composed of digital circuits, they can be easily incorporated into the ASIC, and the cost can be reduced and the size can be reduced.

  In this modification, the phase control is performed only for the minute current control at the time of low power, but the present invention is not limited to this. For example, it is possible to perform power control using phase control also in a large power region and a medium power region.

<Summary>
Induction heating fixing devices according to various embodiments of the present invention can easily make a digital circuit of a resonance frequency tracking oscillation unit and a PWM signal generation unit using an up / down counter and a PWM counter. And the PWM signal generator can be housed inside the ASIC 124.

  Thereby, the induction heating fixing device according to the embodiment of the present invention can reduce the number of hardware parts and improve the cost and assembly as compared with the conventional induction heating fixing device. In addition, the induction heating and fixing apparatus 1400 according to an embodiment of the present invention is configured by a digital circuit, so that it is not necessary to consider variations in component constants and temperature fluctuations. All specifications can be handled without change. This is because when a conventional induction heating fixing device is configured with an analog circuit, it is necessary to consider variations in component constants and temperature fluctuations, and it is necessary to change all component constants according to specifications such as setting the resonance frequency tracking range. It is a big effect compared with what happened.

  Further, since the induction heating fixing device according to an embodiment of the present invention is controlled by a digital circuit, when there is a specific unusable frequency region (a specific radio frequency or a resonance frequency of a fixing device mechanism such as a fixing belt), Control can be easily performed by setting the frequency range.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the specific embodiments described above. A person having ordinary knowledge in the technical field to which the present invention pertains can implement various changes or modifications within the scope of the technical idea described in the claims. Belongs to a range.

  The present invention has been made in view of the above problems, and its object is to perform a minute current region by executing PWM control and phase control by following the resonance frequency without considering variations in component constants and temperature fluctuations. This is useful in that it can provide an induction heating fixing device and an image forming apparatus that can be controlled to a minimum.

1400 Induction Heating Fixing Device 101 AC Power Supply 102 Fuse 103 Varistor 104 Diode Bridge 105 Noise Filter 106 Half Bridge Output Circuit 107, 108 IBGT
109 Current transformer 110 Fixing roller or fixing belt 111 Temperature sensor 112 Low-loss induction heating coil 113, 114 Capacitor 1415 CPU
1416, 1418 AD converter (ADC)
1417 PID Control Unit 1419 PWM Duty Control Unit 1419P Phase Control Amount Setting Unit 120 Rectifier Circuit 121 Limiter Circuit 1424 ASIC
1425 Phase comparison unit 1425P Phase control unit 1426 Resonance frequency tracking oscillation unit 1427 PWM signal generation unit 128, 129 Light emitting diode and phototransistor

Claims (4)

A series resonance circuit having an induction coil and a capacitor, a phase comparison unit, a phase control unit, a resonance frequency tracking oscillation unit, and a PWM (pulse width modulation) signal generation unit;
The phase comparison unit compares the phase of the pulse output from the PWM signal generation unit with the phase of the current flowing through the induction coil, and outputs the comparison result to the phase control unit during phase control,
During PWM control, output to the resonance frequency follow-up oscillation unit,
The phase control unit outputs a frequency control signal having a predetermined phase value to the resonance frequency tracking oscillation unit based on the output of the phase comparison unit and a predetermined coil current phase amount,
The resonance frequency follow-up oscillation unit changes the oscillation frequency so that the drive frequency of the series resonance circuit follows the resonance frequency using the output of the phase control unit,
The PWM signal generation unit generates a pulse for driving the series resonance circuit based on the oscillation frequency by the resonance frequency tracking oscillation unit,
The phase comparison unit, the phase control unit, the resonance frequency follow-up oscillation unit, and the PWM signal generation unit are digitally controlled induction heating fixing devices. The phase control unit compares the phase of the pulse output from the PWM signal generation unit with the phase of the current flowing through the induction coil, thereby outputting the output of the phase comparison unit that outputs a signal corresponding to the phase difference. Count with the counter, compare and calculate the coil current phase amount setting value with the subtractor, and output a frequency control signal to the resonance frequency tracking oscillator based on the result,
The induction heating fixing device according to claim 1, wherein the resonance frequency follow-up oscillation unit changes an oscillation frequency by increasing or decreasing a counter based on a signal output from the phase control unit. The induction heating fixing device according to claim 1, wherein the phase control is performed in a first region where the current is relatively small, and the PWM control is performed in a second region where the current is relatively large.   An image forming apparatus comprising the induction heating fixing device according to claim 1.

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