JPH049526A - Heating cooker - Google Patents

Abstract

PURPOSE:To improve the reliability and reduce the cost by controlling operation of a magnetron based upon the fluctuation of hot air dissipated from food undergoing high frequency heating detected by first and second temperature detector elements of different thermal responses. CONSTITUTION:As food 3 undergoing high frequency heating gets enough high temperature, temperature of air involved in hot air dissipated from the food 3 begins to fluctuate. First and second thermistors are provided as first and second temperature detection elements each serving to detect the temperature of the air dissipated from the food 3 undergoing the high frequency heating, and operation of a magnetron 5 is controlled on the basis of the temperature fluctuation decided by the thermistors. Further, since the temperature fluctuation is detected on the basis of an output level difference between temperature detection signals outputted from the first and second thermistors of different thermal responses, high and low variations of ambient temperature are cancelled out even though the ambient temperature is severely varied. Thus, temperature fluctuation detection accuracy due to the variations of the ambient temperature is prevented from being lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a cooking device that can automatically perform cooking using high-frequency heating.

(Prior art) Conventionally, this type of heating cooker uses a humidity sensor to detect moisture (steam) emanating from food during high-frequency heating.
Alternatively, a gas sensor detects gas components such as alcohol, and a microcomputer controls the operation of the magnetron (particularly the timing of heating completion) based on the detection results.

Recently, as shown in Japanese Patent Application Laid-Open No. 61-269890, a system has been put into practical use that uses a microphone to detect the sound waves generated when the food is boiling and controls the operation of the magnetron. .

(Problem to be Solved by the Invention) By the way, in a device configured using a humidity sensor, if oil, etc. in oil smoke generated from food adheres to the surface of the humidity sensor and the surface becomes dirty, the influence of the dirt will be reduced. As a result, the sensitivity of the humidity sensor tends to decrease, resulting in low operational reliability. In order to overcome this drawback, some devices periodically heat the humidity sensor with a heater to periodically remove dirt from the humidity sensor, but this makes the circuit configuration complicated and increases the cost. It ends up.

Further, in a configuration using a gas sensor, the gas sensor must be kept at a high temperature of about 300° C. in order to function, so the circuit configuration becomes complicated and the cost increases.

On the other hand, devices configured to use a microphone to detect sound waves generated when the food being cooked boils have the drawback of being susceptible to noise such as motor vibrations and external noise, and having low operational reliability.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a heating cooker that can improve the reliability of its operation, and that can be simplified in structure and reduced in cost.

[Structure of the Invention] (Means for Solving the Problems) The heating cooker of the present invention is equipped with a magnetron for high-frequency heating food stored in a heating cooking chamber. a first temperature sensing element that detects the temperature of air containing hot air; Equipped with a temperature detection element,
The present invention is characterized in that it includes a control means for controlling the operation of the magnetron based on temperature fluctuations detected by the difference in the output levels of the temperature detection signals output from the first and second temperature detection elements.

In this case, the first temperature sensing element and the second temperature sensing element may be configured to have different thermal responses by covering the second temperature sensing element with a cover.

(Function) During high-frequency heating, the temperature of the air containing hot air emanating from the food is detected by the first and second temperature sensing elements. Then, when the food reaches a sufficiently high temperature, a large amount of hot air such as food steam begins to be generated, and the fluctuations of the hot air around the temperature detection means become large, causing the first and second temperature detection Fluctuations in the detected temperature also increase due to differences in the output levels of the temperature detection signals output from the elements. The control means detects such temperature fluctuations and controls the operation of the magnetron to perform automatic cooking. In this case, a temperature sensor such as a thermistor, which is cheaper and more reliable than conventional ones, can be used as the temperature detection element, so reliability can be improved and costs can be reduced. By the way, when detecting temperature fluctuations, if the configuration is such that detection is performed based on a temperature detection signal output from one temperature detection element, when the ambient temperature of the temperature detection element fluctuates greatly,
The temperature detection accuracy may decrease due to the fluctuation. On the other hand, since temperature fluctuations are detected based on the difference in the output level of the temperature detection signals output from the first and second temperature sensing elements that have different thermal responses, the fluctuations in the ambient temperature are offset. can do.

In addition, when making the thermal responsiveness of the first and second temperature sensing elements different, it is possible to use temperature sensing elements with the same configuration and the second temperature sensing element.
By simply covering the temperature sensing element with the cover, it is possible to make the thermal responses of both temperature sensing elements different with a simple configuration.

(Example) Hereinafter, a first example of the present invention will be described based on FIGS. 1 to 8.

First, in FIG. 2, a rotating plate 2 is provided at the bottom of the cooking chamber 1, and a food 3 is placed on the rotating plate 2.

A magnetron 5 is provided in the upper part of the heating cooking chamber 1 via a waveguide 4, and the food 3 is irradiated with high frequency waves generated by the magnetron 5.
is heated with high frequency.

On the other hand, an exhaust duct la is provided at the upper side of the heating cooking chamber 1, and a temperature detection means 6 is provided within the exhaust duct la. As shown in FIGS. 3 and 4, the temperature detection means 6 includes a substrate 7, a first temperature detection element such as a first thermistor 8 having negative temperature characteristics, and a second temperature detection element such as a negative temperature characteristic. It consists of a second thermistor 9 with a characteristic. In this case, the first and second thermistors 8 and 9 are provided on the substrate 7, and the second thermistor 9 is covered with a cover 10 made of resin. As a result, as shown in FIG. 5, the thermal responsiveness of the first and second thermistors 8 and 9 to temperature changes is different. Specifically, the thermal responsiveness of the second thermistor 9 is different from that of the first thermistor 9. The thermal response of the thermistor 8 is worse than that of the thermistor 8. In addition, in FIG. 5, the solid line P indicates the change in ambient temperature, and the solid line Q
indicates the change in the temperature detected by the first thermistor 8, and the solid line R
indicates a change in the temperature detected by the second thermistor 9. During high-frequency heating, a blower fan (not shown) blows air into the cooking chamber 1 to exhaust the air inside the cooking chamber 1 through the exhaust duct 1a, thereby ventilating the inside of the cooking chamber 1.

Thus, each temperature detection signal output from the first and second thermistors 8 and 9 is input to the AC amplifier circuit 11.

In this AC amplifier circuit 11, a fluctuation component of the detected temperature is detected based on the difference in output level of the temperature detection signals of the first and second thermistors 8 and 9, and only this fluctuation component is amplified. This AC amplifier circuit 11 has a circuit configuration as shown in FIG. That is, the first and second thermistors 8 and 9 and the two resistors 12 and 13 constitute a bridge circuit 14, and a DC power supply voltage (+V) is applied to this bridge circuit 14.

In this case, the relationship between the resistance values R, , R2 of the first and second thermistors 8 and 9 at room temperature and the resistance values R, , R4 of the other two resistors 12.13 is set as follows. ing.

R1・R4−R2・R5 Then, the potential difference between both output terminals 15° and 16 of the bridge circuit 14 is detected by the differential amplifier circuit 17, and the output signal of the differential amplifier circuit 17 is converted into a low frequency component as the detected temperature signal Vt. The signal is input to the blocking circuit 18.

The low frequency component blocking circuit 18 is constructed by connecting two capacitors 19 and 20 in series between its input and output, and connecting the capacitors 19 and 20 to a ground terminal via a resistor 21. Therefore, this low frequency component blocking circuit 18 suppresses the fluctuation component (
When the AC component (AC component) is not included (when only the DC component is included), the passage of the signal Vt is
On the other hand, when fluctuation (alternating current component) occurs in the signal Vt, the signal Vt is allowed to pass. This low frequency component blocking circuit 1
The signal VtO output from the operational amplifier 22 is input to the inverting input terminal (-) of the operational amplifier 22 and amplified. A feedback resistor 23 is connected between the output terminal and the inverting input terminal (-) of the operational amplifier 22, while the non-inverting input terminal (+) side of the operational amplifier 22 is connected to a ground terminal.

Operational amplifier 22 of AC amplifier circuit 11 configured as described above
The output terminal of the comparator 2 forming the comparison circuit 23
It is connected to the inverting input terminal (-) of No. 4. The non-inverting input terminal (+) of this comparator 24 has two resistors 2
A reference voltage V rer divided by 5.26 is input.

On the other hand, the comparator 24 which is the output terminal of the comparison circuit 23
The output terminal of is connected to a control circuit 27 (see FIG. 2). This control circuit 27 is constituted by a microcomputer or the like, and controls the operation of the magnetron 5 as will be described later.

In this case, the control means 28 is composed of the AC amplifier circuit 11, the comparison circuit 23, and the control circuit 27.

Next, the operation of the above configuration will be explained. Heating cooking chamber 1
When food 3 is placed inside and high frequency heating cooking starts,
The magnetron 5 operates in oscillation to generate high frequency waves, and the food 3 is irradiated with the high frequency waves to heat the food 3 with high frequency waves.

- During this high-frequency heating, a blower fan (not shown) sends air into the heating cooking chamber 1 to exhaust the air in the heating cooking chamber 1 through the exhaust duct 1a, and the temperature of the exhaust air is adjusted to the first and second It is detected by the thermistors 8 and 9 of 2.

As the cooking progresses, the temperature of the food 3 gradually rises, and the hot air gradually emanates from the food 3, and the hot air flows as shown by arrow A in Figure 1 and is included in the exhaust gas. By this, the temperature of the exhaust gas (the first and second thermistors 8
and the ambient temperature at 9) gradually rises as shown in FIG. With this temperature rise, the voltage level of the detected temperature signal Vj output from the bridge circuit 14 having the first and second thermistors 8 and 9 to the low frequency component blocking circuit 18 via the differential amplifier circuit 17 gradually decreases. However, the change in the signal Vt is gradual, and the signal Vt
Since it contains almost no fluctuation component (AC component),
The signal Vt may pass through a low frequency component blocking circuit 18;
Therefore, the output of the operational amplifier 22 (the output of the AC amplifier circuit 11) maintains approximately OV (see FIG. 7). After that, when the temperature of the food 3 rises to a sufficiently high temperature (approximately 100 degrees Celsius or close to it), a large amount of hot air such as steam starts to be generated from the food 3, and the hot air is fanned by the exhaust wind, causing the first And the ambient temperature of the second thermistors 8 and 9 begins to fluctuate.

When such a state occurs, the second thermistor 9 is covered with a cover 10 made of resin, and the first and second thermistors 8 and 9 have different thermal responses to temperature changes. The detected temperature signal Vt output from the bridge circuit 14 having the second thermistors 8 and 9 to the low frequency component blocking circuit 18 via the differential amplifier circuit 17 includes a fluctuation component (AC component). Therefore, the detected temperature signal V
t is the low frequency component blocking circuit 18 i! Incidentally, it is amplified by the operational amplifier 22, and the operational amplifier 22 outputs a relatively large amplitude fluctuation signal Vs as shown in FIG. This fluctuation signal Vs is compared with the reference voltage V ref in the comparator 24 of the comparison circuit 23,
When this reference voltage V rer is exceeded, the comparator 24 sends a high level signal Vh (eighth
(see figure) is output.

In this control circuit 27, it is determined whether the pulse width of the high level signal h output from the comparator 24 is greater than or equal to a certain time width Tw, and if it is not greater than Tw, the signal vh is caused by electrical noise. Ignore this and continue high-frequency heating. This enables highly reliable control. Then, when the pulse width of the high-level signal Vh becomes equal to or greater than Tv, the operation of the magnetron 5 is stopped to end the high-frequency heating.

According to the first embodiment, focusing on the fact that when the food 3 being high-frequency heated reaches a sufficiently high temperature, the temperature of the air containing hot air emanating from the food 3 begins to fluctuate, First and second thermistors 8 and 9 are provided as first and second temperature sensing elements for detecting the temperature of the air containing hot air emanating from the thermistor 8.
Since the operation of the magnetron 5 is controlled based on the temperature fluctuations detected by and 9, high-frequency heating cooking can be automated without using a conventional humidity sensor, gas sensor, or microphone.

In this case, as the first and second temperature sensing elements, temperature sensors such as thermistor 8.9, which are simpler and more reliable than conventional ones, can be used, so the circuit configuration can be simplified and costs can be reduced. In addition, it is possible to perform highly reliable automatic cooking with little aging and no risk of malfunction due to external noise.

Further, in the first embodiment, when detecting temperature fluctuation, the first and second thermistors 8 having different thermal responses are used.
Temperature fluctuations are detected based on the difference in the output levels of the temperature detection signals output from thermistors 8 and 9, so even if the ambient temperature fluctuates greatly, the resistance values of both thermistors 8 and 9 will fluctuate in the same way. , it is possible to offset fluctuations in the ambient temperature, and it is possible to prevent a decrease in temperature fluctuation detection accuracy due to fluctuations in the ambient temperature. Furthermore, in the above embodiment, by configuring the bridge circuit 14, fluctuations in the DC power supply voltage (+V) can be offset, and a decrease in temperature detection accuracy due to fluctuations in the DC power supply voltage (+V) can be prevented. There are advantages.

Furthermore, in the embodiment described above, in order to make the thermal responses of the first and second thermistors 8 and 9 different, since thermistors having the same configuration are used and the second thermistor 9 is simply covered with the cover 10, both thermistors are It is possible to make the thermal responses of 8 and 9 different with a simple configuration. Furthermore, in the above embodiment, two thermistors 8 and 9 are provided on one substrate 7.
Since the structure is such that the parts are arranged and integrated, handling of parts becomes easy during assembly, and assembly work efficiency can be improved.

In the first embodiment, the operation of the magnetron 5 is immediately stopped when the pulse width of the high-level signal Vh outputted from the comparator 24 becomes equal to or greater than the predetermined time width Tw. However, the present invention is not limited to this. For example, from the time when the pulse width of the high level signal vh exceeds a certain time width Tv, additional heating may be performed for a predetermined time, and then the operation of the magnetron 5 may be stopped. Alternatively, the output of the magnetron 5 may be reduced during this additional heating.

Further, in the above embodiment, the second thermistor 9 is covered with the cover 10 made of resin, but it is not limited to this, and may be covered with a cover made of metal or ceramic, for example. Furthermore, instead of covering the second thermistor 9 with the cover 10, the second thermistor may be molded with resin or the like.

On the other hand, FIGS. 9 and 10 show a second embodiment of the present invention. In this second embodiment, an oven heater is installed on the upper surface of the heating cooking chamber 1 in the first embodiment described above. 2
A control means 28 controls whether the heater 29 is turned on or off based on the temperature detected by the first thermistor 8. In this case, the first thermistor 8 is arranged so as to face the inside of the heating cooking chamber 1, and as shown in FIG.
Jl is input to the control circuit 27 as well as the differential amplifier circuit 17, and the control circuit 27 is input based on this detected temperature signal ■t8.
controls whether the heater 29 is turned on or off.

That is, when the heater 29 is energized to perform oven cooking, when the temperature in the heating cooking chamber 1 rises, the thermistor 8
The voltage level of the detected temperature signal Vt1l outputted from the sensor decreases. Therefore, when the voltage level of the detected temperature signal Vt8 falls below the set level (that is, when the temperature inside the heating cooking chamber 1 rises above the set temperature), the control circuit 27 turns off the heater 29, and then The temperature in the cooking chamber 1 is set by repeating the operation of re-energizing the heater 29 when the temperature in the cooking chamber 1 decreases and the voltage level of the detected temperature signal vt8 exceeds the set level. Perform oven cooking by keeping the temperature close to that of the oven.

Note that even if high-frequency heating is started immediately after the completion of oven cooking, the temperature in the heating cooking chamber 1 is too high and cannot be controlled by temperature detection by the first and second thermistors 8 and 9. In such a case, the control circuit 27 notifies the user by a buzzer or display, and
Prevents the initiation of high frequency heating.

According to the second embodiment, even during oven cooking, the energization and disconnection of the heater 29 can be controlled based on the temperature detected by the thermistor 8, so one thermistor 8 can be used for high-frequency heating control and for oven heating control. It can be used for both purposes, and the thermistor 8 can be used effectively.

In addition, in the second embodiment, the heater 29 for heating the oven is
Although the energization/disconnection of the heater is controlled based on the temperature detected by the thermistor 8, it is also possible to control the energization/disconnection of the heater for heating the grill.

Further, in each of the above embodiments, the thermistor 8.9 was used as the temperature detection element, but the present invention is not limited to this.
For example, a silicon diode may be used, and the temperature may be detected by utilizing the temperature dependence of the forward voltage drop of this silicon diode.

In addition, the present invention can be modified in various ways such as, for example, a transistor temperature sensor may be used as the temperature sensing element.

[Effects of the Invention] As is clear from the above description, the present invention detects the temperature of air containing hot air emanating from food being heated by high frequency using first and second temperature sensing elements having different thermal responses. death,
Since the structure is such that the operation of the magnetron is controlled based on the temperature fluctuation detected by the difference in the output level of the temperature detection signals output from these first and second temperature detection elements, All the drawbacks of using a microphone can be eliminated, the reliability of operation can be improved, the configuration can be simplified and costs can be reduced, and the first and second temperature detection can be performed even if the ambient temperature fluctuates greatly. By taking the difference between the temperature detection signals output from the elements, fluctuations in ambient temperature can be offset and detection accuracy can be increased.

In this case, by covering the second temperature sensing element with a cover, the thermal responsiveness of the first temperature sensing element and the second temperature sensing element is made different, so that the thermal responsiveness of both temperature sensing elements is It has the advantage of being able to realize different values with a simple configuration.

[Brief explanation of drawings]

1 to 8 show a first embodiment of the present invention, in which FIG. 1 is an electrical circuit diagram of the main part, FIG. 2 is a schematic diagram of the overall configuration, and FIG. 3 is a temperature detection means. 4 is a top view of the same, FIG. 5 is a characteristic diagram showing the thermal response of the first and second thermistors 8 and 9, and FIG. 6 is a graph of the ambient temperature of the thermistor over time after the start of high-frequency heating. FIG. 7 is an output waveform diagram of the operational amplifier of the AC amplifier circuit, and FIG. 8 is an output waveform diagram of the comparator of the comparison concave path. 9 and 10 are a diagram corresponding to FIG. 2 and a diagram corresponding to FIG. 1, respectively, showing a second embodiment of the present invention. In the drawing, 1 is a heating cooking chamber, ]a is an exhaust duct, 3 is a food product, 5 is a magnetron, 6 is a temperature detection means, 8 is a first thermistor (first temperature detection element), and 9 is a second thermistor (second temperature sensing element), 11 is an AC amplifier circuit, 14
17 is a bridge circuit, 17 is a differential amplifier circuit, 18 is a low frequency component blocking circuit, 23 is a comparison circuit, 27 is a # control circuit, and 28 is a control means. Applicant: Toshiba Corporation

Claims (1)

[Scope of Claims] 1. In a heating cooker equipped with a magnetron that heats food stored in a heating cooking chamber with high frequency, a first device detects the temperature of air containing hot air emanating from the food being heated with high frequency. A temperature sensing element, a second temperature sensing element that has a thermal response different from that of the first temperature sensing element and detects the temperature of the air, and from these first and second temperature sensing elements. A heating cooker comprising: control means for controlling the operation of the magnetron based on temperature fluctuations detected by a difference in output level of output temperature detection signals. 2. The cooking device according to claim 1, wherein the second temperature sensing element has different thermal response from the first temperature sensing element by being covered with a cover.