The present invention relates to an induction heating cooker which performs induction-heating of a cooking container, and more particularly, to an induction heating cooker which controls heating based on temperature of the cooking container detected by an infrared ray sensor.
An amount of infrared energy outputted from an infrared ray sensor changes due to temperature of a infrared ray sensor. Hence, to suppress change of an output of the infrared ray sensor caused by a rise in the temperature of the infrared ray sensor, a conventional induction heating device (for example, fixing device) is provided with cooling means for cooling the infrared ray sensor by supplying air to a temperature detecting module (including infrared ray sensor) (see, for example, Patent Document 1).
However, a conventional configuration requires the cooling means and therefore has the following various problems. For example, when a cooling fan is used as the cooling means, a device would become larger and an operating sound of the cooling fan would give discomfort to a user. Further, when a configuration using a Peltier element as the cooling means to make a temperature of an infrared ray sensor constant is employed, there is a problem that cost of a device is high. In contrast, when the cooling means is not used, the amount of infrared energy outputted by the infrared ray sensor changes according to the temperature of the infrared ray sensor, and therefore it is not possible to accurately detect the temperature of a measurement object (specifically, a cooking container).
The present invention is made to solve the above conventional problems, and an object of the present invention is to provide an induction heating cooker which can accurately detect a temperature of a measurement object (specifically, the cooking container) without the cooling means.
An induction heating cooker according to the present invention includes a top plate on which a cooking container is placed, a temperature measuring device which includes an infrared ray sensor operable to detect infrared rays radiated from the cooking container and a temperature converting unit operable to calculate a temperature of the cooking container from an output of the infrared ray sensor, and which is operable to detect the infrared rays radiated from the cooking container through the top plate to measure the temperature of the cooking container, a heating coil operable to generate an induction magnetic field for heating the cooking container by receiving a supply of a high frequency current, and a heating control unit operable to control power for heating the cooking container by controlling the high frequency current of the heating coil based on the temperature measured by the temperature measuring device, wherein the temperature measuring device further includes a temperature detecting unit operable to measure a temperature of the infrared ray sensor, and calculates the temperature of the cooking container from an output of the infrared ray sensor based on the temperature of the infrared ray sensor measured by the temperature detecting unit. Accordingly, it is possible to accurately detect the temperature of the measurement object (specifically, the cooking container) without using the cooling means.
The temperature measuring device may further include a voltage converting unit operable to convert the output of the infrared ray sensor into a voltage based on a first predetermined amplification factor, an amplifying unit operable to amplify an output of the voltage converting unit based on a second predetermined amplification factor to output to the temperature converting unit, and an amplification factor setting unit operable to change the first predetermined amplification factor and/or the second predetermined amplification factor according to the temperature of the infrared ray sensor measured by the temperature detecting unit. Accordingly, it is possible to prevent the temperature of the infrared ray sensor from rising and a measurable temperature range of a high temperature region from becoming narrow.
The temperature measuring device may further include a voltage converting unit operable to convert the output of the infrared ray sensor into a voltage, and add the converted output of the infrared ray sensor on a reference voltage to output, an amplifying unit operable to amplify an output of the voltage converting unit to output to the temperature converting unit, and a reference voltage changing unit operable to change a value of the reference voltage according to the temperature of the infrared ray sensor measured by the temperature detecting unit. Accordingly, it is possible to prevent the temperature of the infrared ray sensor from rising and a measurable temperature range of a low temperature region from becoming narrow.
The temperature measuring device may further include a voltage converting unit operable to convert the output of the infrared ray sensor into a voltage based on a first predetermined amplification factor, and add the converted output of the infrared ray sensor on a reference voltage to output, an amplifying unit operable to amplify an output of the voltage converting unit based on a second predetermined amplification factor to output to the temperature converting unit, an amplification factor changing unit operable to change the first predetermined amplification factor and/or the second predetermined amplification factor according to the temperature of the infrared ray sensor measured by the temperature detecting unit, and a reference voltage changing unit operable to change a value of the reference voltage according to the temperature of the infrared ray sensor measured by the temperature detecting unit.
The temperature measuring device may change the reference voltage preferentially over a change of an amplification factor.
The temperature measuring device may simultaneously change the first predetermined amplification factor of the voltage converting unit and/or the second predetermined amplification factor of the amplifying unit when the reference voltage is switched.
The temperature measuring device may change the reference voltage when an output voltage of the amplifying unit becomes lower than the reference voltage.
The temperature measuring device may change the reference voltage when the temperature measured by the temperature detecting unit reaches a predetermined temperature or more.
The temperature measuring device may set the first predetermined amplification factor of the voltage converting unit greater than the second predetermined amplification factor of the amplifying unit. Accordingly, it is possible to prevent deterioration of an S/N ratio.
The infrared ray sensor may be a quantum-type infrared ray sensor. According to the present invention, even very small infrared energy can be detected.
In the present invention, by correcting an output value of the infrared ray sensor according to the temperature of the infrared ray sensor and calculating the temperature of a cooking container from the corrected output of the infrared ray sensor, the temperature of the measurement object (specifically, the cooking container) can be accurately detected without using the cooling means. For example, by changing the amplification factor of at least one of the voltage converting unit operable to convert the output of the infrared ray sensor into the voltage and the amplifying unit operable to amplify the output of the voltage converting unit, according to the temperature of the infrared ray sensor, it is possible to prevent the measurable temperature range of the high temperature region from becoming narrow. Further, for example, by changing the value of the reference voltage on which the output voltage of the infrared ray sensor is added in the voltage converting unit according to the temperature of the infrared ray sensor, it is possible to prevent the measurable temperature range of the low temperature region from becoming narrow. Consequently, according to the present invention, the temperature of a cooking container in a wide range can be measured without cooling the infrared ray sensor.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In an induction heating cooker according to Embodiment 1 of the present invention, by changing an amplification factor for amplifying an output of an infrared ray sensor based on a temperature of the infrared ray sensor, a measurable temperature range of the high temperature region can be prevented from becoming narrow, and the temperature of a cooking container can be accurately detected.
The induction heating cooker according to the present embodiment further includes a temperature measuring device 2 which detects infrared rays radiated from the cooking container 13 through the top plate 1, and measures the temperature of the cooking container 13, and a heating control unit 4 which controls power for heating the cooking container 13 by controlling a high frequency current to be supplied to the heating coil 3 based on the temperature measured by the temperature measuring device 2. The temperature measuring device 2 is provided in a position opposed to the cooking container 13, and receives the infrared rays radiated from the cooking container 13. The heating control unit 4 includes an inverter circuit 6 which supplies the high frequency current to the heating coil 3.
The temperature measuring device 2, the heating coil 3 and the heating control unit 4 are accommodated in an outer case 5. The top plate 1 is provided in the upper part of the outer case 5, and forms a part of an outer.
The induction heating cooker according to the present embodiment further includes an operating unit 14 which receives an input of a control command to start or stop heating of the heating cooker 13 from a user. In addition to making a determination of heating output, the operating unit 14 is operated in receiving an input of a control command to select a timer function or functions such as automatic cooking setting.
The temperature measuring device 2 and the operating unit 14 are electrically connected to the heating control unit 4. The inverter circuit 6 of the heating control unit 4 controls power for heating the cooking container 13 by controlling the high frequency current to be supplied to the heating coil 3, based on the temperature measured by the temperature measuring device 2 and the control command inputted through the operating unit 14.
The infrared ray sensor 7 receives light of an infrared region radiated from the cooking container 13. The output of the infrared ray sensor 7 changes according to the amount of received light. The output of the infrared ray sensor 7 is converted into an electric signal to obtain necessary information. Generally, an infrared ray sensor is roughly classified into a thermal-type infrared ray sensor and a quantum-type infrared ray sensor. In the present embodiment, the quantum-type infrared ray sensor (specifically, a photodiode) is used as the infrared ray sensor 7. The quantum-type infrared ray sensor 7 converts light energy into electric energy and detects the same by utilizing an electric phenomenon caused by light. In the case of a photodiode, a photovoltaic effect is utilized, that is, an effect that a current proportional to the amount of light flows when light is received is utilized.
The temperature detecting unit 8 measures the temperature of the infrared ray sensor 7. The temperature detecting unit 8 is, for example, a thermistor which detects temperature by thermal conduction. The output of the infrared ray sensor 7 changes according to the temperature of the infrared ray sensor 7 (see
The voltage converting unit 9 converts the output of the infrared ray sensor 7 into a voltage. In the present embodiment, a photodiode which outputs a current is used as the infrared ray sensor 7, and therefore a current-voltage converting circuit is used as the voltage converting unit 9 (which will be described below with reference to
The amplifying unit 10 amplifies the output voltage of the voltage converting unit 9. When the infrared ray sensor 7 is a photodiode, although it depends on the temperature of the cooking container 13 or the chip size of the photodiode, output valve of a current Is outputted from the infrared ray sensor 7 is typically equal to or less than the order of μA. Only several mV is obtained by converting the current Is into a voltage by the voltage converting unit 9, where the voltage is weak against noise, and even if the current Is is further A/D converted by a microcomputer or the like, resolution is low and its usability is low. Hence, the amplifying unit 10 amplifies the voltage outputted from the voltage converting unit 9 to a required and sufficient voltage value.
The temperature converting unit 11 receives an input of the voltage amplified by the amplifying unit 10, and converts the inputted voltage value into the temperature of the cooking container 13. For example, a microcomputer or DSP can be used for the temperature converting unit 11.
The amplification factor determined as a resistance value Rf of the feedback resistance 92 of the voltage converting unit 9 and the amplification factor of the amplifying unit 10 can be set as necessary. In the present embodiment, the amplification factor of the voltage converting unit 9 is set larger than the amplification factor of the amplifying unit 10. When the infrared ray sensor 7 is a photodiode, the current outputted from the infrared ray sensor 7 is equal to or less than the order of μA, and this small current is amplified to several volt which a microcomputer or the like can handle. The current of the photodiode is very small, and therefore, when the amplification factor of the voltage converting unit 9 is small, there is a risk that the output of the voltage converting unit 9 includes noise when the output is inputted to the amplifying unit 10. Consequently, by increasing the amplification factor of the voltage converting unit 9 more than the amplification factor of the amplifying unit 10, it is possible to prevent deterioration of the S/R ratio.
When the temperature of the cooking container 13 becomes high and the temperature of the photodiode becomes high, the output current Is becomes large and therefore a measurable temperature range becomes narrow. This reason will be described with reference to
As illustrated by the broken line of
Hence, in the present embodiment, the amplification factor setting unit 15 illustrated in
The operation of the induction heating cooker according to the present embodiment will be described with reference to
When the user presses the switch of the operating unit 14 for inputting a control command to start heating, the control command to start heating is inputted from the operating unit 14 to the heating control unit 4. The heating control unit 4 operates the inverter circuit 6 and supplies the high frequency current to the heating coil 3. Accordingly, the high frequency magnetic field is generated from the heating coil 3, and heating of the cooking container 13 starts (S501). At this time, heating starts with heating power set in advance. When the control command to change the heating power is inputted through the operating unit 14, the heating control unit 4 controls the inverter circuit 6 and heats the cooking container 13 based on the changed heating power. More specifically, the heating control unit 4 detects the current inputted to the inverter circuit 6, compares the heating power set by the user and the current inputted to the inverter circuit 6, and changes the operating state of the inverter circuit 6 based on the comparison result. The heating control unit 4 controls the inverter circuit 6 to provide heating power set by the user, by repeating this operation, and maintains the set heating power.
In the temperature measuring device 2, the temperature detecting unit 8 detects the temperature of the infrared ray sensor 7 (S502). The amplification factor setting unit 15 determines whether or not the detected temperature of the infrared ray sensor 7 is equal to or greater than a predetermined temperature (for example, 250° C.) (S503). If the temperature of the infrared ray sensor 7 is equal to or greater than the predetermined temperature (Yes in S503), the amplification factor setting unit 15 decreases the amplification factor of the amplifying unit 10 (S504). If the temperature of the infrared ray sensor 7 is less than a predetermined temperature (No in S503), the amplification factor setting unit 15 increases the amplification factor of the amplifying unit 10 (S505). More specifically, in the present embodiment, the amplification factor is decreased less than the initial value in step S504, and the amplification factor of the amplifying unit 10 is returned to the initial value in step S505.
The temperature measuring device 2 calculates the temperature of the cooking container 13 (S506). More specifically, the voltage converting unit 9 converts the output of the infrared ray sensor 7 into a voltage, the amplifying unit 10 amplifies the output value of the voltage converting unit 9 based on the amplification factor set in step S504 or S505, and the temperature converting unit 11 converts the amplified voltage value into the temperature of the cooking container 13. The temperature measuring device 2 transmits the converted temperature to the heating control unit 4.
The heating control unit 4 determines whether or not the temperature of the cooking container 13 received from the temperature measuring device 2 is equal to or more than a predetermined set value (for example, 300° C.) (S507). If the temperature of the cooking container 13 is equal to or more than the predetermined set value (Yes in S507), The heating control unit 4 determines that the cooking container 13 is abnormally heated, and the heating control unit 4 temporarily stops the inverter circuit 6 and temporarily stops heating (S508). For example, the heating control unit 4 stops the heating until the temperature of the cooking container 13 becomes less than the predetermined set value. If the temperature of the cooking container 13 is not equal to or more than the predetermined set value (No in S507), the heating control unit 4 determines that the cooking container 13 is heated normally, and the heating control unit 4 continues the heating.
The heating control unit 4 determines whether or not the control command to finish the heating is inputted through the operating unit 14 (S509). If the control command to finish the heating is inputted (Yes in S509), the heating control unit 4 stops the operation of the inverter circuit 6 and finishes the heating. If the control command to finish the heating is not inputted (No in S509), the process returns to step S501 and continues the heating with the set heating power.
The induction heating cooker according to the present embodiment decreases the amplification factor of the amplifying unit 10 if the temperature of the infrared ray sensor 7 is higher than a predetermined temperature. Consequently, even when the temperature of the infrared ray sensor 7 is high, the output voltage Va of the amplifying unit 10 is unlikely to be saturated, so that it is possible to prevent the measurable temperature range of the high temperature region of the cooking container 13 from becoming narrow. Accordingly, it is possible to measure the temperature of the cooking container 13 in a wide range without cooling the infrared ray sensor 7. Consequently, it is possible to accurately detect the temperature of the cooking container 13.
Although the amplification factor of the amplifying unit 10 is changed based on the temperature of the infrared ray sensor 7 in the present embodiment, the amplification factor of the voltage converting unit 9 may be changed. Further, both of the amplification factors of the amplifying unit 10 and the voltage converting unit 9 may be changed.
Further, although a quantum-type infrared ray sensor is used as the infrared ray sensor 7 in the present embodiment, a thermal-type infrared ray sensor may be used. The thermal-type infrared ray sensor detects change in electric property of an element generated by rise of temperature of the element of the sensor heated by the thermal effect of infrared rays. For example, when a thermopile is used as the thermal-type infrared ray sensor, the thermopile generates an output (signal) according to infrared energy. The temperature detecting unit 8 can measure the temperature of the cooking container 13 based on the signal outputted from the thermopile and the temperature of the thermopile. Since the quantum-type infrared ray sensor receives a greater degree of influence of characteristic change caused by the temperature of the infrared ray sensor 7 than the thermal-type infrared ray sensor, the quantum type infrared ray sensor provides a greater effect of controlling the amplification factor in the present embodiment.
Although a case that the inverter circuit 6 is controlled based on the set heating power is described as an example of the induction heating cooker in the above embodiment, setting of the amplification factor of the present embodiment can be applied to other heating control. For example, the present embodiment is also applicable to cooking of fried food which is one of automatic cooking functions. In the case of fried food cooking, when the user presses a fried food automatic cooking start-switch of the operating unit 14, and then sets the set temperature to, for example, 180° C. by a temperature adjustment switch of the operating unit 14, the heating control unit 4 controls the inverter circuit 6 based on the temperature of the temperature measuring device 2 such that the temperature of oil in the cooking container 13 reaches 180° C. of the set temperature. When ingredients are put into the cooking container 13 and the oil temperature goes below 180° C., the heating control unit 4 changes the operating state of the inverter circuit 6 and performs control such that the oil temperature becomes 180° C. In such an induction heating cooker, heat generated in the heating coil 3 and heat of the cooking container 13 are transmitted to the top plate 1, and the temperature of the temperature measuring device 2 rises due to, for example, radiation from the top plate 1. When the cooling means is provided to the induction heating cooker as in the conventional technique to prevent the rise in the temperature, there are problems in that a device becomes larger or the operating sound of the cooling fan gives discomfort to the user. However, according to the present embodiment, the amplification factor of the voltage converting unit 9 and/or the amplification factor(s) of the amplifying unit 10 are changed based on the temperature of the infrared ray sensor 7, so that even if the temperature of the infrared ray sensor 7 rises, it is possible to prevent a measurable temperature range from becoming narrow. Consequently, it is possible to measure the temperature without enlarging the device and giving discomfort due to the operating sound of the cooling fan. According to the induction heating cooker of the present embodiment, good control performance is provided by a quick response of the infrared ray sensor 7, and high performance and safety of the automatic cooking function can be realized.
An induction heating cooker according to Embodiment 2 of the present invention will be described with reference to
In the induction heating cooker according to Embodiment 2 of the present invention, the configurations other than the temperature measuring device 2 are the same as those in Embodiment 1. The temperature measuring device 2 will be described below.
In the present embodiment, the reference voltage changing unit 12 selectively switches a value of the reference voltage Vref to be inputted to the plus terminal of the operational amplifier 91 of the voltage converting unit 9, to a low voltage value V1 or high voltage value V2 (V2>V1) according to the temperature of the infrared ray sensor 7 detected by the temperature detecting unit 8.
In
In
In the present embodiment, the reference voltage changing unit 12 changes the value of the reference voltage Vref according to the temperature of the infrared ray sensor 7 detected by the temperature detecting unit 8. Accordingly, when the temperature of the infrared ray sensor 7 rises, it is possible to prevent the output voltage of the amplifying unit 10 from adhering to 0 V. Consequently, it is possible to prevent the measurable temperature range of the low temperature region from becoming narrow.
Generally, when the infrared ray sensor 7 and measurement environment are determined, the relationship between the temperature measured by the temperature detecting unit 8 and the reference voltage Vref and the measurable temperature range of the cooking container 13 are determined. The measurement environment refers to the distance between the infrared ray sensor 7 and the cooking container 13, the optical path therebetween, and optical characteristics in the surrounding of the infrared ray sensor 7. For example, when the infrared ray sensor 7 is a photodiode, the relationship between the temperature measured by the temperature detecting unit 8 and the reference voltage Vref is determined based on the parallel resistance of the photodiode and the characteristics of the operational amplifier 91 used in the current-voltage converting circuit. Further, the measurable temperature range is determined according to a sensitivity wavelength region and a sensitivity of the photodiode. When the temperature measuring device 2 is used in a predetermined measurement environment, it is possible to know what degree of the temperature of the infrared ray sensor 7 influences the measurable temperature range, and therefore when such a condition is known in advance, it is possible to prevent the measurable temperature range from becoming narrow by changing the reference voltage Vref at the time when the temperature of the infrared ray sensor 7 reaches a predetermined temperature which causes the influence (for example, the temperature at which the reference voltage Vref becomes 0 V).
Although the value of the reference voltage Vref is changed when the temperature of the infrared ray sensor 7 reaches a predetermined temperature or more in Embodiment 2, the reference voltage Vref may be changed when the output voltage Va of the amplifying unit 10 becomes lower than the reference voltage Vref. When the infrared ray sensor 7 is a photodiode, the voltage converting unit 9 operates as a current-voltage converting circuit. As illustrated in
Embodiment 1 and Embodiment 2 may be combined. Accordingly, it is possible to prevent the measurable temperature ranges of both of the high temperature region and low temperature region from becoming narrow, and the temperature of the cooking container 13 can be accurately detected.
Further, in this case, in changing the amplification factor and the reference voltage when the temperature measured by the temperature detecting unit 8 is higher than a predetermined temperature, the reference voltage may be changed preferentially over the amplification factor. As described above, when the temperature of the infrared ray sensor 7 rises, the measurable temperature range of the cooking container 13 which is the measurement target becomes narrow both on the high temperature region and low temperature region. At this time, the output voltage Va of the amplifying unit 10 at the time when the temperature of the infrared ray sensor 7 becomes high adheres to 0 V as illustrated in
When the predetermined temperature in step S503 of
Although specific embodiments have been described for the present invention, it is obvious for a person skilled in the art that various modifications, corrections and other utilizations are possible. Consequently, the present invention is not limited to the specific disclosure herein, and can be limited only by the claims attached herewith.
The induction heating cooker according to the present invention has an effect of measuring a temperature of a cooking container in a wide range even when a temperature of an infrared ray sensor rises, and is useful as a heating cooker which is used in, for example, general households, restaurants, and offices.
Number | Date | Country | Kind |
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2008-27775 | Oct 2008 | JP | national |
2009-183016 | Aug 2009 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2009/005554 | 10/22/2009 | WO | 00 | 4/20/2011 |