JPH04230990A - Heat cooking appliance - Google Patents

Abstract

PURPOSE:To improve the reliability of the automatic cooking action by a magnetron, simplify a structure, and reduce the cost. CONSTITUTION:A temperature detecting means 6 outputting a signal at the level corresponding to the temperature of the air containing the heat radiated from the food 3 heated with a high frequency is provided, a fluctuation detecting means 20 outputting a signal at the level corresponding to the temperature fluctuation based on the temperature detection signal outputted from the temperature detecting means 6 is provided, and a control means 21 controlling the action of a magnetron 5 based on either the temperature detection signal outputted from the temperature detecting means 6 or the fluctuation detection signal outputted from the fluctuation detecting means 20 is provided.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooking device capable of automatically cooking using high-frequency heating.

0003

[Prior Art] Conventionally, this type of heating cooker uses a humidity sensor to detect moisture (steam) emitted from food during high-frequency heating, or detects gas components such as alcohol using a gas sensor. Based on the detection results, the microcomputer controls the operation of the magnetron (especially when heating ends).
was supposed to be controlled.

[0004] Also, recently, Japanese Patent Application Laid-Open No. 61-26989
As shown in Japanese Patent No. 0, a system has been put into practical use that uses a microphone to detect sound waves generated when the food being cooked boils to control the operation of a magnetron.

[0005]

[Problems 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 effects of the dirt will be reduced. As a result, the sensitivity of the humidity sensor tends to decrease, resulting in low operational reliability. To overcome this drawback, some devices have been designed to 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. Put it away.

[0006]Furthermore, 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.

[0007] On the other hand, the configuration in which the sound waves generated when the food being cooked boils is detected by a microphone has the drawback that it is easily affected by noise such as motor vibration and external noise, and its operation reliability is low. .

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a heating cooker that can improve the reliability of its operation and can be simplified in structure and reduced in cost. Another object of the present invention is to provide a heating cooker that can prevent overcooking even when food has small fluctuations in temperature at the end of cooking.

[Configuration of the invention]

0010

[Means for solving the problems] The heating cooker of the present invention includes:
A heating cooker equipped with a magnetron that heats food stored in a heating cooking chamber using high frequency waves, comprising temperature detection means that outputs a signal at a level corresponding to the temperature of air containing hot air emanating from the food being heated under high frequency waves. The temperature detection means outputs a signal at a level corresponding to the temperature fluctuation based on the temperature detection signal outputted from the temperature detection means, and the temperature detection signal outputted from the temperature detection means and the fluctuation The present invention is characterized in that it includes a control means for controlling the operation of the magnetron based on any of the fluctuation detection signals output from the detection means.

In this case, the temperature detection means may be constituted by a thermistor.

[0012] Furthermore, the control means is configured such that even before the output level of the fluctuation detection signal output from the fluctuation detection means reaches the set value for fluctuation detection, the output level of the temperature detection signal output from the temperature detection means is adjusted to the temperature. The configuration may be such that when the detection set value is reached, the magnetron is stopped and the cooking is completed.

[0013]

[Operation] According to the above means, during high-frequency heating, the temperature of the air containing hot air emitted from the food is detected by the temperature detection means, but the hot air emitted from the food is detected by the progress of cooking (the temperature of the food). Then, when the food reaches a sufficiently high temperature, a large amount of hot air such as steam starts to be generated from the food, and the fluctuation of the hot air around the temperature detection means increases, causing the detection output from the temperature detection means to increase. Temperature fluctuations also increase. Such temperature fluctuations are detected by the fluctuation detection means, and the control means controls the operation of the magnetron based on the fluctuation detection signal output from the fluctuation detection means to perform automatic cooking. In this case, as the temperature detection means, a temperature sensor such as a thermistor, which is cheaper and more reliable than conventional ones, can be used, so reliability can be improved and costs can be reduced.

On the other hand, when reheating rice by high-frequency heating, for example, it is preferable to stop the high-frequency heating before temperature fluctuations occur. In this case, the control means controls the operation of the magnetron based on the temperature detection signal output from the temperature detection means to perform automatic cooking. This allows high-frequency heating to be stopped before temperature fluctuations occur.

Furthermore, since the temperature detection means is constituted by a thermistor, reliability can be improved, costs can be reduced, and the configuration can be simplified.

By the way, depending on the type of food, even when the food is heated to a sufficiently high temperature, fluctuations in hot air such as steam generated from the food, that is, fluctuations in temperature, may not become very large. In such a case, even when it is time to finish cooking, the output level of the fluctuation detection signal output from the fluctuation detection means does not reach the set value for fluctuation detection, so the food is heated until it becomes charred. In other words, there is a risk of overcooking.

On the other hand, the control means, when the output level of the temperature detection signal from the temperature detection means reaches the temperature detection setting value even before the fluctuation detection signal reaches the fluctuation detection setting value, Since the magnetron is controlled to stop and the cooking is completed, overcooking can be prevented even if the type of food does not have large temperature fluctuations at the end of cooking.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. 1 to 7. 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.
The food 3 is heated by high frequency by irradiating the food 3 with the high frequency waves generated in the above.

On the other hand, an exhaust duct 1a is provided at the upper side of the heating cooking chamber 1, and a thermistor 6 having a negative temperature characteristic serving as temperature detection means is provided within the exhaust duct 1a. 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. Note that the magnetron 5 is cooled by the blower fan.

The output signal of the thermistor 6 is input to the AC amplifier circuit 7, and only the fluctuation component of the temperature detected by the thermistor 6 is amplified in the AC amplifier circuit 7. This AC amplifier circuit 7 has a circuit configuration as shown in FIG. That is, a series circuit of voltage dividing resistor 8 and thermistor 6 is connected between the DC power supply terminal (+V) and the ground terminal, and a temperature detection signal is output from a common connection point 9 between voltage dividing resistor 8 and thermistor 6. Vt is the low frequency component blocking circuit 10
is input.

The low frequency component blocking circuit 10 is constructed by connecting two capacitors 11 and 12 in series between its input and output, and connecting both capacitors 11 and 12 to a ground terminal via a resistor 13. There is. Therefore, when the input temperature detection signal Vt does not include a fluctuation component (AC component) (when it contains only a DC component), the low frequency component blocking circuit 10 prevents the signal Vt from passing through the capacitors 11 and 11. , 12, and on the other hand, when fluctuation (alternating current component) occurs in the signal Vt, the signal Vt is allowed to pass.

The signal Vto output from the low frequency component blocking circuit 10 is input to the inverting input terminal (-) of the operational amplifier 14 and amplified. A feedback resistor 15 is connected between the output terminal and the inverting input terminal (-) of the operational amplifier 14, while the non-inverting input terminal (+) side of the operational amplifier 14 is connected to a ground terminal.

The output terminal of the operational amplifier 14 of the AC amplifier circuit 7 configured as described above is connected to the inverting input terminal (-) of the comparator 17 constituting the comparison circuit 16. The non-inverting input terminal (+) of this comparator 17 has
Reference voltage Vref divided by two resistors 18 and 19
is input. In this case, the AC amplifier circuit 7 and the comparison circuit 1
6 constitutes a fluctuation detection means 20.

On the other hand, the output terminal of the comparator 17 which is the output terminal of the comparison circuit 16 is connected to the control circuit 2 which is the control means.
Connected to 1. This control circuit 21 is constituted by a microcomputer or the like, and controls the operation of the magnetron 5 as described later. On the other hand, the temperature detection signal Vt outputted from the thermistor 6 is inputted to the control circuit 21 as well as the low frequency component blocking circuit 10, and the control circuit 21 operates based on this temperature detection signal Vt. The operation of the magnetron 5 is controlled as described below.

Further, as shown in FIG. 1, a switch signal output from a switch input circuit 22 is input to the control circuit 21. This switch input circuit 22 selects either a course in which temperature fluctuations are detected and automatic cooking is performed, or a course in which temperature is detected and automatic cooking is performed (that is, high-frequency heating is stopped before temperature fluctuations occur). It has a course selection switch for selection. By manually operating this course selection switch, either of the above two courses is selectively executed.

Next, the operation of the above configuration will be explained. First, a case will be described in which a course is selected in which automatic cooking is performed by detecting temperature fluctuations. In this case, the control circuit 21
The input of a high level signal Vh, which is a fluctuation detection level signal outputted from the comparator 17 of the comparison circuit 16, is enabled, and the magnetron 5 is driven and controlled based on this signal Vh. Specifically, when the food 3 is placed in the cooking chamber 1 and high-frequency cooking is started, the magnetron 5 oscillates to generate high-frequency waves, and the food 3 is irradiated with the high-frequency waves, causing the food 3 to receive high-frequency waves. heated.

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 measured by the thermistor 6. Detected by. 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,
The temperature of the exhaust gas (the ambient temperature around the thermistor 6) gradually rises as shown in FIG.

With this temperature rise, the temperature detection signal Vt output from the thermistor 6 to the low frequency component blocking circuit 10
, the voltage level gradually decreases, but the change in the signal Vt is gradual, and the signal Vt contains almost no fluctuation component (AC component), so the signal Vt is processed by the low frequency component blocking circuit. Therefore, the output of the operational amplifier 14 (the output of the AC amplifier circuit 7)
maintains approximately 0V (see Figure 4).

After that, the temperature of the food 3 reaches a sufficiently high temperature (10
When the temperature rises to about 0° C. or close to 0° C., a large amount of hot air such as steam starts to be generated from the food 3, and the hot air is agitated by the exhaust air, causing fluctuations in the ambient temperature of the thermistor 6. When a situation like this occurs,
Since the temperature detection signal Vt output from the thermistor 6 includes a fluctuation component (AC component), the temperature detection signal Vt passes through the low frequency component blocking circuit 10, is amplified by the operational amplifier 14, and is output from the operational amplifier 14. Figure 4
As shown in the figure, a fluctuation signal Vs with a relatively large amplitude is output. This fluctuation signal Vs is compared with the reference voltage Vref in the comparator 17 of the comparison circuit 16, and when it exceeds this reference voltage Vref, the comparator 17 sends a high level signal Vh to the control circuit 21 (see FIG.
) is output.

In this control circuit 21, it is determined whether the pulse width of the high level signal Vh outputted from the comparator 17 is greater than or equal to a certain time width Tw.
If it is not greater than w, the signal Vh is ignored as electrical noise and high-frequency heating is continued. This enables highly reliable control. Then, when the pulse width of the high-level signal Vh becomes equal to or greater than Tw, the operation of the magnetron 5 is stopped to end the high-frequency heating. In addition, in FIG. 3, the broken line shows the temperature change when high frequency heating is continued.

Now, a case will be described in which a course is selected in which automatic cooking is performed by detecting the temperature, that is, a course in which high-frequency heating is stopped before temperature fluctuation occurs, such as when reheating rice using high-frequency heating. . In this case, the control circuit 21 enables the input of the temperature detection signal Vt output from the thermistor 6, and
The magnetron 5 is driven and controlled based on the following.

Specifically, when high-frequency cooking is started, the food 3 is heated in the same manner as described above, and the temperature of the exhaust gas, that is, the ambient temperature of the thermistor 6, gradually rises. As the temperature rises, the voltage level of the temperature detection signal Vt output from the thermistor 6 gradually decreases. Here, as shown in FIG. 6, when the temperature detection signal Vt drops by a preset voltage ΔV (that is, when the exhaust temperature rises above the set temperature), the control circuit 21 stops the operation of the magnetron 5. to end high-frequency heating.

According to this embodiment having such a configuration, attention is paid to the fact that when the food 3 being heated by high frequency reaches a sufficiently high temperature, the temperature of the air containing hot air emanating from the food 3 begins to fluctuate. A thermistor 6 is provided as a temperature detection means for detecting the temperature of air containing hot air emanating from the food 3 during high frequency heating, and the operation of the magnetron 5 is controlled based on the temperature fluctuation detected by the thermistor 6. Therefore, it is possible to automate high-frequency heating cooking using the temperature detection means (thermistor 6) without using a conventional humidity sensor, gas sensor, and microphone.

In this case, a temperature sensor such as the thermistor 6, which is cheaper and more reliable than conventional ones, can be used as the temperature detection means, so the circuit configuration can be simplified, the cost can be reduced, and the temperature can be reduced over time. It is possible to perform highly reliable automatic cooking with little change and no risk of malfunction due to external noise.

On the other hand, if it is necessary to stop the high-frequency heating before the temperature fluctuates, such as when reheating rice using high-frequency heating, a course that automatically cooks by detecting the temperature is selected. . In this case, as shown in FIG. 6, when the temperature detection signal Vt drops by a preset voltage ΔV, the operation of the magnetron 5 is stopped and the high-frequency heating is terminated. As a result, high frequency heating can be stopped before temperature fluctuations occur. Therefore, appropriate automatic cooking can be performed corresponding to various foods.

Note that in the first embodiment, the comparator 1
Although the operation of the magnetron 5 is immediately stopped when the pulse width of the high-level signal Vh outputted from the high-level signal Vh outputted from the terminal 7 becomes equal to or greater than a certain time width Tw, the control mode is not limited to this, and for example, The above high level signal V
After the pulse width of h reaches a certain time width Tw or more, additional heating may be performed for a predetermined period of time, and then the operation of the magnetron 5 may be stopped. Also, during this additional heating, the output of the magnetron 5 may be It is also possible to lower the value.

Furthermore, as shown in FIG. 3, immediately after the first cooking is finished, the temperature around the exhaust duct 1a is high, so even if high-frequency heating is started immediately, the temperature detection by the thermistor 6 is not possible. cannot be controlled by In such a case, the control circuit 21 performs control to prevent the start of high-frequency heating until the temperature falls below a predetermined temperature.

[0038] By the way, when a course is selected in which automatic cooking is performed by detecting temperature fluctuations, depending on the type of food, when the food has been heated to a sufficiently high temperature, that is, when the time has come to finish cooking. In some cases, fluctuations in hot air such as steam generated from food, that is, fluctuations in temperature, do not become very large. In such a case, Figure 7
As shown in (b), since the output level of the fluctuation signal Vs, which is the fluctuation detection signal outputted from the fluctuation detection means 20, does not reach the fluctuation detection set value ±Vs1, the food is heated until it becomes charred. In other words, there is a risk of overcooking.

In contrast, in this embodiment, even before the fluctuation signal Vs reaches the fluctuation detection set value Vs1, the temperature in the heating cooking chamber 1 is high, as shown in FIG. 7(a). When the temperature reaches the set temperature Tc, that is, as shown in FIG. 7(c).
As shown, the temperature detection signal Vt from the thermistor 6
When the output level reaches the temperature detection set value Vt1, the control circuit 21 stops the magnetron 5 and automatically ends cooking. It is possible to reliably prevent overcooking due to overcooking.

Furthermore, the temperature detection means is not limited to the thermistor 6, and for example, the temperature detection means shown in FIGS.
As in the second embodiment of the present invention shown in , a silicon diode 23 is provided in place of the thermistor 6, and the temperature is detected by utilizing the temperature dependence of the forward voltage drop of the silicon diode 23. good. That is, as shown in FIG. 9, the forward voltage Vf of the silicon diode 23 has a characteristic of decreasing linearly as the temperature rises.

As shown in FIG. 10, the advantage of using such a silicon diode 23 is that the DC power supply voltage (+
Even if the current flowing through the silicon diode 23 fluctuates due to fluctuations in V), the forward voltage drop change width ΔV is extremely small compared to the current change width ΔI, so the influence of the DC power supply voltage (+V) fluctuation is reduced. It has the advantage of being possible.

[0042] In addition, the present invention provides temperature detection means including:
For example, a transistor temperature sensor may be used, and
Various modifications are possible, such as forming a bridge circuit by combining a temperature sensor such as a thermistor with three other resistance elements, and detecting the temperature based on the potential difference between both output terminals of this bridge circuit.

[0043]

[Effects of the Invention] Since the present invention is as explained above, the following effects can be obtained.

[0044] In the heating cooker according to the first aspect, the operation of the magnetron is controlled based on either the temperature detection signal output from the temperature detection means or the fluctuation detection signal output from the fluctuation detection means. This eliminates all the shortcomings of conventional humidity sensors, gas sensors, and microphones, improves operational reliability, and simplifies the configuration to reduce costs. When reheating, automatic cooking can be performed based on the temperature detection signal output from the temperature detection means, so high-frequency heating can be stopped before temperature fluctuations occur.

[0045] In the heating cooker of the second aspect, since the temperature detecting means is constituted by a thermistor, reliability is improved and
Cost reduction and configuration simplification are possible.

In the heating cooker according to claim 3, the control means is configured such that the output level of the temperature detection signal from the temperature detection means reaches the set value for temperature detection even before the fluctuation detection signal reaches the set value for fluctuation detection. When this temperature is reached, the magnetron is stopped and the cooking is controlled to end, so that overcooking can be reliably prevented even for foods whose temperature fluctuations at the end of cooking are not very large.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic configuration diagram showing a first embodiment of the present invention.

[Figure 2] Electrical circuit diagram of main parts

[Figure 3] Diagram showing the change in ambient temperature of the thermistor over time after the start of high-frequency heating

[Figure 4] Output waveform diagram of operational amplifier of AC amplifier circuit

[Figure 5
] Comparator output waveform diagram of comparison circuit

[Figure 6] A diagram showing the output waveform of the thermistor as well as the output waveform of the operational amplifier of the AC amplifier circuit.

[Fig. 7] (a), (b), and (c) are diagrams showing changes in temperature in the cooking chamber over time, diagrams showing output waveforms of the operational amplifier of the AC amplifier circuit, and diagrams showing the output waveforms of the thermistor.

[Figure 8]
Electrical circuit diagram of a temperature detection circuit showing a second embodiment of the present invention

[Figure 9] Diagram showing the relationship between forward voltage and temperature of a silicon diode

[Figure 10] Diagram showing the relationship between forward voltage drop and current of a silicon diode

[Explanation of symbols]

1 is a heating cooking chamber, 1a is an exhaust duct, 3 is food, 5 is a magnetron, 6 is a thermistor (temperature detection means), 7 is an AC amplifier circuit, 10 is a low frequency component blocking circuit, 16 is a comparison circuit, 20 is a fluctuation 21 is a control circuit (control means), and 23 is a silicon diode (temperature detection means).

Claims (3)

[Claims] [Claim 1] A heating cooker equipped with a magnetron that heats food stored in a heating cooking chamber with high frequency, outputting a signal at a level corresponding to the temperature of air containing hot air emanating from the food being heated with high frequency. a temperature detection means; a fluctuation detection means for outputting a signal at a level corresponding to temperature fluctuation based on a temperature detection signal output from the temperature detection means; a temperature detection signal output from the temperature detection means and the fluctuation; A heating cooker comprising: control means for controlling the operation of the magnetron based on any of the fluctuation detection signals output from the detection means. 2. The cooking device according to claim 1, wherein the temperature detection means is a thermistor. 3. The control means is configured such that even before the output level of the fluctuation detection signal output from the fluctuation detection means reaches the set value for fluctuation detection, the output level of the temperature detection signal output from the temperature detection means is lower than the temperature. 2. The heating cooker according to claim 1, wherein when the detection set value is reached, the magnetron is controlled to stop and the cooking ends.