JP4664753B2 - Cooker - Google Patents

Description

  The present invention relates to a cooking device, and more particularly to a cooking device that can safely and reliably prevent overheating of an object to be heated.

  Most of the heating in the cooking device is performed by electric heating, and various heating methods such as induction heating, heater heating, microwave heating, and infrared lamp heating are employed. In such a heating cooker, a temperature detection circuit using a temperature sensor is provided in order to control the temperature of the object to be heated. In recent years, a microcomputer has been adopted for temperature control in order to improve control accuracy and secure control flexibility, and the output of the temperature detection circuit is periodically A / D converted and taken into the microcomputer. In the microcomputer, the temperature of the object to be heated is calculated from the captured output, and the difference from the target temperature is calculated. Then, a control calculation such as a PI calculation is performed on the difference, and the calculation result is output to the heating unit. A heating part produces | generates the heating energy proportional to the output calculation result, for example, and heats to-be-heated material. By repeating such control calculation, the temperature of the object to be heated is controlled to coincide with the target temperature (see, for example, Patent Document 1).

  However, in such a system in which the output of the temperature detection circuit is A / D converted and the control calculation is performed in the microcomputer, the A / D converter and the microcomputer are caused by the noise of the inverter circuit used in the heating unit, external noise, and the like. May cause malfunction. If a malfunction occurs, the temperature of the object to be heated cannot be accurately recognized, or an erroneous calculation result is output, making temperature control impossible. If such a situation occurs during cooking, not only cooking cannot be performed, but the temperature may rise too much, which may cause danger such as ignition.

In order to avoid such a situation, a dedicated temperature sensor and a temperature detection circuit are separately provided for detecting a temperature abnormality, and an excessive temperature rise is detected by the circuit to stop heating. However, adding one set of the temperature sensor and the temperature detection circuit in this way complicates the circuit and wiring and increases the cost. Further, since the temperature characteristics of the temperature sensor vary, it is necessary to increase the difference between the normal temperature range and the overheat detection temperature to some extent. For this reason, there is a problem that the set temperature for detecting excessive temperature rise for preventing danger must be set higher than the normal temperature range.
Japanese Patent Laid-Open No. 01-105495

  The present invention has been made to solve such problems of the prior art, and the problem is that cooking can safely and reliably stop heating even if a microcomputer used for control computation malfunctions. Is to provide a vessel.

According to a first aspect of the present invention for solving the above-described problem, a temperature detection circuit (22) for generating an output voltage corresponding to a characteristic curve having a fixed relationship with the temperature of an object to be heated, and the temperature detection circuit A comparison circuit (23) for comparing an output voltage with a predetermined threshold voltage; and a microcomputer for outputting a selection signal to the temperature detection circuit, wherein the output voltage of the temperature detection circuit is periodically A / D converted. Then, the temperature of the object to be heated is calculated in light of the characteristic curve corresponding to the selection signal being output, and the control calculation is performed to bring the deviation between the calculated temperature and the target temperature close to zero. Te a microcomputer (25) to the output signal of the operation result, constantly generates heat energy having a certain relationship between the output signal of the microcomputer, the comparison circuit is the temperature detection circuit Heating means configured to stop the generation of the heating energy when it is determined that the output voltage exceeds the threshold voltage, and the microcomputer is configured to detect the temperature detection circuit. When the selection signal of the temperature detection circuit is switched according to the output voltage and the characteristic curve is switched according to the selection signal, and the selection signal is output to the temperature detection circuit by the microcomputer, the temperature detection circuit The characteristic curve is switched to the first characteristic curve to generate an output voltage corresponding to the first characteristic curve, and the microcomputer applies the output voltage of the temperature detection circuit to the switched first characteristic curve. The temperature of the object to be heated is calculated within a first temperature measurement range corresponding to one characteristic curve, and the microcomputer calculates the calculated temperature as the first temperature. When the measurement range is exceeded, by outputting a selection signal to the temperature detection circuit, the temperature detection circuit is switched to a second characteristic curve having higher temperature detection sensitivity than the first characteristic curve. The microcomputer generates an output voltage corresponding to the curve, and the microcomputer outputs the output voltage of the temperature detection circuit within the second temperature measurement range in which the minimum temperature is set to be equal to or higher than the maximum temperature of the first temperature measurement range. The temperature of the object to be heated is calculated by applying to a characteristic curve, and the comparison circuit is configured such that the predetermined threshold voltage to be compared with the output voltage of the temperature detection circuit is determined from the first characteristic curve. The heating means is set to a value higher than the output voltage of the temperature detection circuit for switching to the second characteristic curve, and the heating circuit is configured such that the comparison circuit outputs an output voltage corresponding to the first characteristic curve by the temperature detection circuit. When it is determined that the pressure exceeds the predetermined threshold voltage, the generation of the heating energy is stopped at a first overheat detection temperature higher than the maximum temperature of the first temperature measurement range, and the comparison circuit If the output voltage corresponding to the second characteristic curve by the temperature detection circuit is determined to exceed the predetermined threshold voltage, the first excessive temperature rise is higher than the maximum temperature of the second temperature measurement range. The generation of the heating energy is stopped at a second overheating detection temperature that is higher than the detection temperature .

According to such a configuration, the temperature of the object to be heated is monitored by the comparison circuit configured by hardware, and at the time of detecting the first overheat detection temperature and the second overheat detection temperature , the comparison circuit With this output voltage , the heating operation of the heating means is forcibly terminated. Therefore, even if the microcomputer malfunctions, the first overheat detection temperature and the second overheat detection temperature can be safely and reliably prevented. In addition, since the temperature of the object to be heated is controlled by the output voltage of one temperature detection circuit and the excessive temperature rise is prevented, there is no need to increase the difference between the normal temperature range and the excessive temperature rise detection temperature. A cooker can be realized.

  Further, the invention according to claim 2 is the heating cooker according to claim 1, wherein the temperature detection circuit includes a temperature sensor (Th1) and a first resistor between a reference voltage (Vref) and a ground potential. (R1) is connected in series with the temperature sensor as the reference voltage side, and one or more series circuits of a resistor (R2) and a switching element (TR1) are connected in parallel between both ends of the first resistor. The switching element is configured to control conduction / non-conduction of each switching element by a selection signal output from the microcomputer.

  In such a configuration, only one temperature sensor is used for temperature detection. The output signal of the set of temperature detection circuits using the same is commonly used for both temperature control of the object to be heated and prevention of overheating. Therefore, compared to the conventional method that uses separate temperature sensors for temperature control and overheating prevention, it is not necessary to make a large difference between the normal temperature range and overheating detection temperature, thus realizing a safer cooking device. it can.

  According to a third aspect of the present invention, in the cooking device of the second aspect, a plurality of the temperature sensors are attached, and one of the temperature sensors is selected by a switch (SW1) that is switched by a signal from the microcomputer. Then, it is configured to be connected to the first resistor.

  According to such a structure, the temperature of several places of a to-be-heated material can be taken in into a microcomputer, and arbitrary temperature in it can be used for control.

  According to a fourth aspect of the present invention, in the heating cooker according to the third aspect, the microcomputer switches the switch (SW1) to calculate the temperature of each temperature sensor, and one of the calculated temperatures. The highest temperature is treated as the temperature of the object to be heated.

  According to such a configuration, even when the bottom of a pan or the like to be heated is deformed, a more accurate temperature can be detected, and the temperature at the place where the highest temperature is shown can be controlled to the target temperature. It becomes possible.

The invention according to claim 5 is characterized in that, in the cooking device according to any one of claims 2 to 4, a thermistor is used as the temperature sensor.
Since the thermistor has a large change in resistance with temperature, temperature detection can be performed with high sensitivity.

The invention according to claim 6 is the heating cooker according to any one of claims 1 to 5, wherein the heating means is configured as an induction heating type heating device.
The induction heating type cooking device having such a configuration has the same effects as the effects of the invention described in each claim.

  Hereinafter, an embodiment of a heating cooker according to the present invention will be described in detail with reference to the drawings. This embodiment is an example of a heating cooker that employs induction heating for heating an object to be heated, and FIG. 1 shows a front view of the upper portion of the main body of the heating cooker 1 in cross section.

  This heating cooker 1 is of a type employed in a system kitchen, and is equipped with two induction heating units that operate independently. The outer shell of the cooker main body 1 is composed of a rectangular parallelepiped cabinet 2, and a top plate 3 made of crystallized glass on which an object to be heated such as a cooking container is placed is attached to the upper surface. Two types of spiral heating coils 5, 6 are disposed on the upper surface of the coil bases 10, 11 with the ferrites 7, 8 sandwiched between the top plates 3. Temperature sensors 13 and 14 using a thermistor are attached to the back surface of the top plate 3 which hits the upper center of the heating coils 5 and 6.

  A roaster chamber (not shown) is provided below the left coil base 10, and a door 15 is attached to the front surface thereof. Various control components are disposed below the right coil base 11, and an operation panel 16 is attached to the front surface thereof. The operation panel 16 is provided with an operation switch for setting cooking conditions such as cooking temperature and cooking time, a dial 17 and a display 18 for displaying the cooking state. The heating cooker 1 is attached in such a manner that it is dropped from above into a hole formed in a horizontal top plate of the system kitchen. In this state, the operation panel 16 and the door 15 are slightly exposed forward from the front opening of the system kitchen. . Side decorations 19 are attached to the left and right ends of the front to hide the back gap.

  FIG. 2 shows the configuration of a control circuit corresponding to one set of induction heating units. Hereinafter, temperature control of an object to be heated and countermeasures against malfunction of the control circuit will be described with reference to FIG. The control circuit 21 includes a temperature detection circuit 22, a comparison circuit 23, an A / D converter 24, a microcomputer (hereinafter referred to as a microcomputer) 25, an inverter control unit 26, an inverter circuit 27, a DC power supply circuit 28, and a series resonance circuit 29. It is configured with.

  The temperature detection circuit 22 includes a thermistor Th1 as a temperature sensor, a resistor (first resistor) R1, a resistor R2, and a transistor (switching element) TR1. The thermistor Th1 is for detecting the temperature of the object to be heated, and is attached to the temperature sensor 13 or 14 described above. Since it is difficult to directly detect the temperature of the object to be heated, the temperature of the top plate 3 detected by the temperature sensor 13 or 14 is simulated with the temperature of the object to be heated 30 placed thereon.

  The thermistor Th1 and the resistor R1 are connected in series between the reference voltage Vref and the ground potential GND with the thermistor Th1 on the reference voltage Vref side. The reference voltage Vref is generated in the DC power supply circuit 28. A resistor R2 and a transistor TR1 are connected in series between the junction point N1 of the thermistor Th1 and the resistor R1 and the ground potential GND. The microcomputer 25 controls conduction / non-conduction of the transistor TR1. A bipolar transistor or a MOS transistor is used as the transistor TR1 as a switching element.

  The resistance value of the thermistor Th1 decreases exponentially as the temperature increases. When the transistor TR1 is in a non-conducting state, the relationship between the temperature T of the thermistor Th1 and the voltage Vt at the interconnection point N1 that is the output voltage of the temperature detection circuit 22 is, for example, the curve (1) in FIG. FIG. 3 shows the temperature T of the thermistor Th1 on the horizontal axis and the output voltage Vt of the temperature detection circuit 22 on the vertical axis, and curve (1) shows the characteristic curve of the temperature detection circuit 22 when the transistor TR1 is in a non-conductive state. It represents.

  The output voltage Vt of the temperature detection circuit 22 is converted into a digital value by the A / D converter 24 and read into the microcomputer 25. This reading is performed periodically with a short period. In the microcomputer 25, an approximate expression representing the characteristic curve (1) is stored in advance. The microcomputer 25 calculates the temperature T of the thermistor Th1 by substituting the read output voltage Vt into the approximate expression. Let the calculated temperature be Tf. The microcomputer 25 treats this temperature Tf as the temperature T of the article 30 to be heated.

Although not shown, the microcomputer 25 is also connected to the operation panel 16 and holds the target temperature Ts of the article to be heated 30 input from the operation panel 16. In the microcomputer 25, a deviation ΔT between the target temperature Ts and the detected temperature Tf of the heated object 30 is calculated. Then, a control calculation is performed on the deviation ΔT so that the value approaches zero. For example, the following arithmetic expression for performing PI control (proportional integral control) is used for the control calculation.
Vo = Ai · ∫ΔT · dt + Ap · ΔT (1) where Ai is an integration constant, Ap is a proportionality constant, Vo is a calculation result, and is an output signal of the microcomputer 25.

  The microcomputer 25 outputs the calculation result Vo to the inverter control unit 26 at the next stage. The inverter control unit 26, the inverter circuit 27, the DC power supply circuit 28, and the series resonance circuit 29 correspond to the heating means described in the claims. The inverter control unit 26 is a circuit part that controls the inverter circuit 27 so that heating energy having a certain relationship with the output signal Vo of the microcomputer 25 is output from the inverter circuit 27.

  The inverter circuit 27 is a known inverter circuit in which the switching element is configured as a full bridge or a half bridge. A series resonance circuit 29 of a heating coil L1 and a capacitor C1 is connected to the load of the inverter circuit 27. The inverter circuit 27 is supplied with a DC voltage generated by a DC power supply circuit 28 that uses a commercial power supply 31 as a power supply.

  Several methods are known for controlling the power output from the inverter circuit 27. One is a method of changing the frequency of the high-frequency voltage supplied from the inverter circuit 27 to the series resonance circuit 29 in a state where a constant DC voltage is supplied from the DC power supply circuit 28 to the bridge circuit in the inverter circuit 27. When the series resonance circuit 29 is excited at the resonance frequency, the impedance becomes minimum and the maximum energy is consumed. Most of the energy is consumed for heating the article 30 by induction heating.

  As the frequency of the high-frequency voltage supplied to the series resonance circuit 29 deviates from the resonance frequency, the impedance increases and energy consumption decreases, and the energy supplied to the heated object 30 also decreases. Therefore, the electric power output from the inverter circuit 27 can be controlled by adjusting the switching frequency of the inverter circuit 27, and as a result, the energy given to the object to be heated 30 can be changed.

  Another method is to change the value of the DC voltage supplied from the DC power supply circuit 28 to the bridge circuit of the inverter circuit 27 while keeping the frequency of the high-frequency voltage output from the inverter circuit 27 constant. When the DC voltage applied to the bridge circuit changes, the voltage of the high frequency voltage supplied to the series resonance circuit 29 also changes, and the value of the high frequency current flowing through the series resonance circuit 29 changes. Accordingly, the energy supplied to the object to be heated 30 also changes. In this case, the same result can be obtained by controlling the current or power supplied from the commercial power supply 31 to the DC power supply circuit 28 instead of controlling the output voltage of the DC power supply circuit 28. In these cases, in order to stabilize the control, the output voltage of the DC power supply circuit 28 or the input to the DC power supply circuit 28 so that the value of the current flowing through the series resonance circuit 29 is proportional to the output signal Vo of the microcomputer 25. It is preferred to control the current or input power.

  The inverter control unit 26 controls the inverter circuit 27 and the DC power supply circuit 28 by the method as described above, whereby energy having a certain relationship with the output signal Vo of the microcomputer 25 is output from the inverter circuit 27, and the object to be heated is Control is performed as shown in FIG.

  The microcomputer 25 periodically reads the output voltage Vt of the temperature detection circuit 22 through the A / D converter 24 in a short cycle, and performs the control calculation according to the above equation (1) each time and outputs the result as the output signal Vo. This is given to the inverter control unit 26. The inverter control unit 26 performs control so that energy having a certain relationship with the output signal Vo is output from the inverter circuit 27 and applied to the object to be heated 30. The values of the integral constant Ai and the proportionality constant Ap in the equation (1) are previously determined by experiments and calculations so that the temperature deviation ΔT converges to zero by repeating such control. By repeating such control, the temperature of the object to be heated 30 coincides with the target temperature Ts.

  In the above description, the transistor TR1 in the temperature detection circuit 22 has been turned off. In this case, a characteristic curve of the temperature detection circuit 22 is, for example, a curve (1) in FIG. However, it is difficult to accurately detect a wide range of temperatures with a circuit in which the thermistor Th1 and the resistor R1 are simply connected in series while the transistor TR1 is in a non-conductive state.

  The temperature detection sensitivity of the temperature detection circuit 22 is represented by the tangential gradient of the curve (1). The resistance value of the thermistor Th1 decreases exponentially with increasing temperature. The temperature detection sensitivity is highest when the resistance value of the thermistor Th1 is equal to the resistance value of the resistor R1. When the temperature is exceeded, the gradient of the tangent line becomes smaller and the curve (1) gradually approaches the reference voltage Vref supplied to the temperature detection circuit 22. Accordingly, in a high temperature range, the temperature detection sensitivity is lowered, and accurate temperature detection becomes difficult.

  In order to increase the detection accuracy in a high temperature range, the resistance value of the resistor connected in series to the thermistor Th1 may be reduced according to the resistance value of the thermistor Th1. Therefore, in the cooking device 1 of the present embodiment, the value of the resistance connected as the load of the thermistor Th1 is switched according to the detected temperature range. That is, as shown in FIG. 3, the transistor TR1 is switched between the conductive state and the nonconductive state at the temperature T1.

  According to the output of the microcomputer 25, the transistor TR1 is switched to a non-conductive state at a temperature T1 or lower, and the transistor TR1 is switched to a conductive state in a range exceeding the temperature T1. The resistance R1 value is a value near the intermediate temperature of the measurement range T0 to T1 when the transistor TR1 is turned off, for example, the resistance value of the thermistor Th1 when the temperature is (T1 + T0) / 2.

  On the other hand, when the measurement range when the transistor TR1 is in the conductive state is T1 to T3, the parallel connection resistance value of the resistors R1 and R2 near the intermediate temperature (T3 + T1) / 2 is the resistance of the thermistor Th1 at that temperature. Decide to be equal to the value. The resistance values of the resistors R1 and R2 are determined from the conditions in the two measurement ranges. If the resistance value is determined in this way, temperature detection can be performed with high detection sensitivity in both temperature ranges of the measurement ranges T0 to T1 and T1 to T2.

  A characteristic curve of the temperature detection circuit 22 when the transistor TR1 is in a conductive state is, for example, a curve (2) in FIG. The approximate expression of the curve is also stored in the microcomputer 25 in advance. The microcomputer 25 recognizes the conduction / non-conduction state of the transistor TR1. Therefore, the microcomputer 25 applies the voltage Vt read via the A / D converter 24 to the characteristic curve of (1) or (2) according to the conduction / non-conduction state of the transistor TR1, and the temperature of the object 30 to be heated. Tf is calculated.

  When the temperature Tf calculated when the characteristic curve (1) is measured exceeds T1, the transistor TR1 is switched from non-conductive to conductive when the transistor 25 is turned on / off. When the temperature Tf calculated during the measurement with the curve (2) is equal to or lower than T1, the transistor TR1 is switched from conduction to non-conduction.

  By performing such switching, the temperature Tf of the object to be heated 30 can be detected with high detection sensitivity in a wide temperature range of T0 to T3, and the temperature of the object to be heated 30 is accurately controlled in combination with the temperature control method. can do.

  Next, countermeasures against malfunction of the control circuit 21 shown in FIG. 2 will be described. As described above, the control circuit 21 uses the microcomputer 25 for temperature control and temperature calculation of the object 30 to be heated. Further, the A / D converter 24 is used in order to take the output voltage Vt of the temperature detection circuit 22 into the microcomputer 25 as a digital value. Since the microcomputer 25 and the A / D converter 24 perform digital operations, they are more susceptible to malfunctions due to noise than analog processing circuits.

  In particular, in the cooking device 1 of the present embodiment, noise is easily picked up because the inverter circuit 27 that performs a large current switching operation is provided. If the microcomputer 25 runs away due to noise or external noise generated while cooking oil such as tempura, there is a risk of fire. Therefore, the control circuit 21 checks the value of the output voltage Vt of the temperature detection circuit 22 by hardware, and if the value exceeds a predetermined threshold voltage Vth, the operation of the inverter control unit 26 is immediately stopped. I try to stop heating.

  The comparison circuit 23 is a circuit for this purpose, and is composed of a comparator CP1 and voltage dividing resistors R3 and R4. The voltage dividing resistors R3 and R4 are connected in series between the reference voltage Vref and the ground potential GND to generate a threshold voltage Vth. The output voltage Vt of the temperature detection circuit 22 is input to the non-inverting input terminal of the comparator CP1, and the threshold voltage Vth is input to the inverting input terminal. When the output voltage Vt exceeds the threshold voltage Vth, a high level HALT signal is output from the output of the comparator CP1.

  The high-level HALT signal is input to the inverter control unit 26. When the HALT signal is input, the inverter control unit 26 immediately stops the switching operation of the inverter circuit 27 and stops heating.

  Such a circuit configuration for countermeasure against malfunction has the following advantages. The comparison circuit 23 that monitors the temperature of the article 30 to be heated is configured by hardware, and a heating stop signal is output to the inverter control unit 26 by its output. Therefore, when the temperature of the object to be heated 30 rises regardless of the operation of the microcomputer 25, the heating is forcibly stopped by hardware, so that safety is ensured.

  In the control circuit 21, the same temperature sensor is used for temperature control of the object to be heated 30 and overheating temperature monitoring. When using a separate dedicated temperature sensor for overheating monitoring as in the past, the upper limit of the normal temperature range should be considered in consideration of variations in the characteristics of the temperature sensor and the structural electric heat characteristics of the temperature sensor. It was necessary to make a large difference from the set value of the overheat detection temperature. On the other hand, since this embodiment uses the same temperature sensor, it is not necessary to consider these variations. For this reason, since the difference between the upper limit of the normal temperature range and the set value of the excessive temperature rise detection temperature can be reduced, there is an advantage that the excessive temperature rise can be prevented with high accuracy.

  Further, the excessive temperature rise detection is performed based on the output voltage of the temperature detection circuit 22 in a state where the measurement range is selected by turning on / off the transistor TR. Therefore, when the threshold voltage Vth for detecting the excessive temperature rise is set to a value as shown in FIG. 3, for example, in the measurement range T0 to T1, the measurement is performed at a temperature T2 slightly higher than the temperature T1. In the ranges T1 to T3, the heating is stopped at a temperature T4 slightly higher than the temperature T3. That is, there is an advantage that heating is automatically stopped at the optimum overheat detection temperature corresponding to each measurement range.

  Thus, the heating cooker 1 of this embodiment can detect the temperature T of the article to be heated 30 with high accuracy in a wide temperature range, and can control the temperature with high accuracy. Even if the microcomputer 25 malfunctions, it is possible to reliably stop heating at an excessive temperature rise detection temperature with a small difference from the maximum temperature of each temperature measurement range. .

(Modified embodiment)
The above-described cooking device 1 may be modified as follows.
In the temperature detection circuit 22 of the heating cooker 1 described above, the temperature measurement range is switched to two ranges, but may be switched to more ranges. FIG. 4 shows an example of a temperature detection circuit that can be switched to three ranges. The temperature detection patent of the temperature detection circuit 22a in this case is represented by three characteristic curves as shown in FIG.

  The value of the resistor R1 is set equal to the resistance value of the thermistor Th1 at a temperature near the middle of the measurement ranges T0 to T1. The resistance value of the parallel connection of the resistors R1 and R2 is set equal to the resistance value of the thermistor Th1 at a temperature near the middle of the measurement ranges T1 to T3. The resistance value of the parallel connection of the resistors R1, R2, and R5 is set equal to the resistance value of the thermistor Th1 at a temperature near the middle of the measurement ranges T3 to T5. The values of the resistors R1, R2, and R5 are determined so as to satisfy these three conditions. If the temperature ranges T0 to T5 are divided into a plurality of measurement ranges and detected in this manner, the temperature detection accuracy can be further improved.

  Moreover, in the above-mentioned heating cooker 1, although the temperature sensor was made into one, you may make it attach multiple. This is because the detected temperature differs depending on the mounting position of the temperature sensor. In this case, as shown in FIG. 6, the temperature detection circuit 22 b is configured so that a plurality of thermistors can be switched and selected by the switch SW <b> 1 according to the output of the microcomputer 25. The microcomputer 25 uses, for example, the highest temperature among the temperatures detected by switching the switch SW1 for temperature control. In this way, a more accurate temperature can be detected even when the bottom of a pan or the like that is the object to be heated 30 is deformed.

  Moreover, although the thermistor was used for the temperature sensor in the above-mentioned heating cooker 1, it should just be an element from which resistance value changes with temperature, for example, a varistor, a platinum resistor, the forward resistance of a semiconductor PN junction, a reverse resistance, etc. May be used.

It is a front view which shows the upper part of the heating cooker 1 which concerns on this invention in a cross section. It is a block diagram of the control circuit 21 of an induction heating part. It is an example of the temperature-output voltage characteristic of the temperature detection circuit. It is a block diagram of the temperature detection circuit 22a in the case of switching a temperature measurement range in three steps. It is an example of the temperature-output voltage characteristic in the case of switching a temperature measurement range in three steps. It is a block diagram of the control circuit 21a in the case of providing two temperature sensors.

Explanation of symbols

  In the drawings, 1 is a heating cooker, 22 is a temperature detection circuit, 23 is a comparison circuit, 24 is an A / D converter, 25 is a microcomputer, 26 is an inverter control unit, 27 is an inverter circuit, 28 is a DC power supply circuit, 29 is a series resonance circuit, 30 is an object to be heated, GND is a ground potential, Vref is a reference voltage, R1 is a first resistor, R2 to R5 are resistors, and Th1 is a thermistor.

Claims (6)

A temperature detection circuit (22) for generating an output voltage corresponding to a characteristic curve having a fixed relationship with the temperature of the object to be heated ;
A comparison circuit (23) for comparing the output voltage of the temperature detection circuit with a predetermined threshold voltage ;
A microcomputer for outputting a selection signal to the temperature detection circuit, wherein the output voltage of the temperature detection circuit is periodically A / D converted and taken in, and the taken value corresponds to the selection signal being output. A microcomputer (25) that calculates the temperature of the object to be heated in light of the characteristic curve, performs a control calculation to bring the deviation between the calculated temperature and the target temperature close to zero, and uses the calculation result as an output signal;
Always generates heat energy having a certain relationship between the output signal of the micro computer, the heating energy when the comparison circuit determines that the output voltage of the temperature detection circuit exceeds the threshold voltage and a heating means configured to stop generating,
The microcomputer switches the selection signal of the temperature detection circuit according to the output voltage of the temperature detection circuit to be detected and switches the characteristic curve according to the selection signal.
When a selection signal is output to the temperature detection circuit by the microcomputer, the temperature detection circuit switches the characteristic curve to a first characteristic curve and generates an output voltage corresponding to the first characteristic curve,
The microcomputer applies the output voltage of the temperature detection circuit to the switched first characteristic curve to calculate the temperature of the object to be heated within the first temperature measurement range corresponding to the first characteristic curve,
The microcomputer outputs a selection signal to the temperature detection circuit when the calculated temperature exceeds the first temperature measurement range, so that the temperature detection circuit has a temperature detection sensitivity higher than that of the first characteristic curve. The second temperature measurement range in which the microcomputer is switched to the second characteristic curve with a higher value to generate an output voltage corresponding to the second characteristic curve, and the microcomputer has a minimum temperature set higher than the maximum temperature of the first temperature measurement range And applying the output voltage of the temperature detection circuit to the second characteristic curve to calculate the temperature of the object to be heated.
In the comparison circuit, the predetermined threshold voltage to be compared with the output voltage of the temperature detection circuit is higher than the output voltage of the temperature detection circuit that switches from the first characteristic curve to the second characteristic curve. Set to
The heating means includes
When the comparison circuit determines that the output voltage corresponding to the first characteristic curve by the temperature detection circuit has exceeded the predetermined threshold voltage, a first excess higher than the maximum temperature of the first temperature measurement range. Stop generating the heating energy at the temperature rise detection temperature,
When the comparison circuit determines that the output voltage corresponding to the second characteristic curve by the temperature detection circuit exceeds the predetermined threshold voltage, the first temperature is higher than the maximum temperature of the second temperature measurement range. A cooking device , wherein the generation of the heating energy is stopped at a second overheating detection temperature that is higher than the overheating detection temperature .   2. The cooking device according to claim 1, wherein the temperature detection circuit includes a temperature sensor (Th <b> 1) and a first resistor (R <b> 1) between a reference voltage (Vref) and a ground potential, and the temperature sensor is used as the reference voltage. And one or more series circuits of a resistor (R2) and a switching element (TR1) are connected in parallel between both ends of the first resistor, and each switching element is connected to the microcomputer. A cooking device, wherein conduction / non-conduction is controlled by an output selection signal.   3. The cooking device according to claim 2, wherein a plurality of the temperature sensors are attached, and one of them is selected by a switch (SW1) that is switched by a signal from the microcomputer and connected to the first resistor. The cooking device characterized by comprising in.   4. The cooking device according to claim 3, wherein the microcomputer switches the switch (SW1) to calculate the temperature of each temperature sensor, and treats the highest temperature among the calculated temperatures as the temperature of the object to be heated. A cooking device characterized by that.   The cooking device according to any one of claims 2 to 4, wherein a thermistor is used as the temperature sensor. The cooking device according to any one of claims 1 to 5, wherein the heating means is configured as an induction heating type heating device.

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