JPH049525A - High frequency heating device - Google Patents

Abstract

PURPOSE:To ensure the reliability improvement and the reduce cost by detecting increased fluctuation of surrounding hot air when food gets high temperature with the advance of cooking and controlling operation of a magnetron by control means. CONSTITUTION:As food 3 undergoing high frequency heating gets enough high temperature, temperature of air including hot air disposed from the food 3 begins to fluctuate. A thermistor 6 is provided as temperature detector means for detecting the temperature of air included in the hot air dispersed from the food 3 undergoing the high frequency heating, and operation of a magnetron 5 is controlled on the basis of the detected temperature fluctuation. Automation of high frequency cooking by the thermistor 6 is intended without use of a humidity sensor, a gas sensor, an a microphone. Further, operation states of loads such as the magnetron 5 are changed over to interrupt the control based upon the temperature fluctuation until a predetermined time is elapsed, and the operation of the magnetron 5 is controlled as such temperature fluctuation being not produced. Thus, detection of fluctuation due to variations of DC supply voltage upon the loading state being changed over is prevented from being operated erroneously.

Description

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

(Prior art) Conventionally, this type of high-frequency heating device 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, a microcomputer controlled the operation of the magnetron (especially when heating ended).

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 food rises during cooking to control the operation of a magnetron. There is.

(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. 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.

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 these circumstances, and an object of the present invention is to provide a high-frequency heating device that can improve the reliability of operation and can be simplified in structure and reduced in cost.

[Configuration of the Invention (Means for Solving the Problems) The high-frequency heating device of the present invention is equipped with a magnetron for high-frequency heating food stored in a heating cooking chamber. temperature detection means for detecting the temperature of the air containing air; and control means for controlling the operation of the magnetron based on the temperature fluctuation detected by the temperature detection means. When the operating state of the load is switched, the control based on the temperature fluctuation is suspended until a predetermined period of time has elapsed since the switching.

(Function) 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 amount of hot air emitted from the food increases as the cooking progresses (as the temperature of the food rises). After that, 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 becomes large, and the fluctuation of the detected temperature output from the temperature detection means also becomes large. . The control means detects such temperature fluctuations and controls the operation of the magnetron 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.

By the way, when the operating state of a load such as a magnetron that receives power from the power supply is switched at the start of cooking or as cooking progresses, the power supply voltage changes at the time of switching, causing the output of the temperature detection means to change. It causes the signal to fluctuate,
There is a risk that signal fluctuations during this switching may be mistaken for temperature fluctuations.

To deal with this, when the operating state of a load such as a magnetron is switched, the control means suspends control based on temperature fluctuations until a predetermined period of time has elapsed from the time of switching, and during that time, the control means suspends control based on temperature fluctuations. The operation of the magnetron is controlled on the assumption that it will not occur. This prevents erroneous operation of fluctuation detection due to fluctuations in the power supply voltage when switching the operating state of the load.

(Example) Hereinafter, one embodiment of the present invention will be described based on the drawings.

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 heated by high frequency by irradiating the food 3 with high frequency waves generated by the magnetron 5.

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, the cooling fan 31 cools the magnetron 5 while blowing air into the heating cooking chamber 1 to exhaust the air inside the heating cooking chamber 1 through the exhaust duct 1a to ventilate the inside of the heating cooking chamber 1. .

Thus, 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 a voltage dividing resistor 8 and the thermistor 6 is connected between the output terminal (+V) of a DC power supply circuit 32 to be described later and a ground terminal, and a connection point 9 between the voltage dividing resistor 8 and the thermistor 6 is connected between the output terminal (+V) and the ground terminal. The output detected temperature signal Vt is input to the low frequency component blocking circuit 10. This 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 the ground terminal via a resistor 13. Therefore,
This low frequency component blocking circuit 10 prevents the signal Vt from passing through both capacitors 11 and 12 when the input detected temperature signal Vt does not include a fluctuation component (AC component) (when it contains only a DC component). On the other hand, when fluctuations (AC component) occur in the signal Vt, the signal Vt
t 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. Note that a feedback resistor 15 is connected between the output terminal and the inverting input terminal (-) of this operational amplifier 14;
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 comparator 17 that constitutes the comparison circuit 16.
is connected to the inverting input terminal (-) of Two resistors 18 are connected to the non-inverting input terminal (+) of this comparator 17.
．． The reference voltage V rer divided by 19 is input.

On the other hand, a comparator 17 which is an output terminal of the comparison circuit 16
The output terminal of the magnetron 5 is connected to a control circuit 20 (see FIG. 1), and the control circuit 20 controls the operation of the magnetron 5 as described later. In this case, the control means 21 is composed of the AC amplifier circuit 7, the comparison circuit 16, and the control circuit 20.

The control circuit 20 operates using a DC power supply circuit 32 connected to a commercial AC power supply 33 via a power transformer 34 as a DC power supply. In this case, the control circuit 20 includes, for example, a microcomputer, and controls energization/disconnection of the relay coils 35 to 37 according to its control program, thereby controlling the cooling fans 31 . A drive circuit 5a of the magnetron 5,
The ON/OFF state of the relay switches 38 to 40 provided in each energizing path of the motor 2a of the rotary plate 2 is controlled as follows.

That is, when food 3 is placed in heating cooking chamber 1 and high-frequency heating cooking is started, relay coil 3 is activated by control circuit 20.
5 to 37 to turn on relay switches 38 to 40, the magnetron 5 oscillates and generates high frequency waves, and the food 3 is irradiated with the high frequency waves, thereby heating the food 3 with high frequency waves. At the same time, relay switch 38
When turned on, the cooling fan 31 is driven and the heating cooking chamber 1 is heated.
Exhaust duct 1a blows air inside heating cooking chamber 1
The temperature of the exhaust gas is detected by a thermistor 6. Furthermore, during cooking, relay switch 4
0 turns on, the motor 2a is energized to rotate the rotating plate 2, and the food 3 on the rotating plate 2 is uniformly heated.

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. As a result, the temperature of the exhaust gas (the ambient temperature around the thermistor 6) gradually rises as shown in FIG. With this temperature rise, the voltage level of the detected temperature signal Vt outputted from the thermistor 6 to the low frequency component blocking circuit 10 gradually decreases, but the change in the signal Vt is gradual; Since Vt contains almost no fluctuation component (AC component), the signal Vt is passed through the low frequency component blocking circuit 10.
Therefore, the output of the operational amplifier 14 (the output of the AC amplifier circuit 7) maintains approximately Oy (see Fig. 4).
. 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 agitated by the exhaust air, causing the thermistor 6 This causes fluctuations in the ambient temperature. In such a state, the detected temperature signal Vj output from the thermistor 6 includes a fluctuation component (AC component), so the detected temperature signal Vt passes through the low frequency component blocking circuit 10 and is output by the operational amplifier 14. The signal is amplified, and the operational amplifier 14 outputs a relatively large amplitude fluctuation signal Vs as shown in FIG. This fluctuation signal Vs is compared with a reference voltage V ref in a comparator 17 of the comparison circuit 16, and when it exceeds this reference voltage V ref', a high level signal vh is sent from the comparator 17 to the control circuit 20 (see Figure 15). is output. Then, in this control circuit 20, it is determined whether the pulse width of the noise level signal vh outputted from the comparator 17 is equal to or larger than a certain time width TV, and Tw
Otherwise, the signal vh is ignored as electrical noise and high-frequency heating is continued. This enables highly reliable control. Then, the high level signal v
When the pulse width of h becomes equal to or greater than Tw, the operation of the magnetron 5 is stopped to end the high-frequency heating.

By the way, at the start of cooking, loads such as the magnetron 5° cooling fan 312 and the motor 2a of the rotating plate 2 start operating at the same time, so the DC power supply voltage (+V), which is the output voltage of the DC power supply circuit 32, fluctuates at the start of cooking. (See Figure 4). Also, as the cooking progresses, for example, the magnetron 5
The DC power supply voltage (+V) also fluctuates when the operating state (output state) is automatically switched. In this way, when the DC power supply voltage (+V) changes at the start of cooking or during cooking, the output voltage of the thermistor 6 (detected temperature signal Vt)
The voltage also fluctuates and fluctuates, which is amplified by the operational amplifier 14, and as shown in FIG. 4, the operational amplifier 14 outputs a spurious fluctuation signal VSn due to fluctuations in the DC power supply voltage (+V). If this false fluctuation signal Vsn is processed in the same way as the original fluctuation signal Vs, there is a risk that the false fluctuation signal Vsn will be mistaken for temperature fluctuation, causing malfunction.

Therefore, in this embodiment, when the operating state of the load such as the magnetron 5 is switched and the DC power supply voltage (+V) fluctuates, the predetermined time T from the switching until the output state of the operational amplifier 14 becomes stable is set. The control circuit 20 interrupts the control based on the temperature fluctuation (output signal of the operational amplifier 14) until the time elapses, and controls the operation of the magnetron 5 on the assumption that no temperature fluctuation occurs.
A control program for the internal microcomputer has been created. This prevents malfunction of fluctuation detection due to fluctuations in the DC power supply voltage (+V) when switching the operating state of the load, thereby eliminating automatic cooking failures.

According to this embodiment described above, the food 3 during high frequency heating
Focusing on the fact that when food 3 becomes sufficiently hot, the temperature of the 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, or microphone. In this case, a thermistor 6, which is cheaper and more reliable than the conventional one, is used as the temperature detection means.
Since it is sufficient to use a temperature sensor such as the above, the circuit configuration can be simplified and costs can be reduced, and highly reliable automatic cooking can be achieved with little deterioration over time and no risk of malfunction due to external noise. obtain.

Moreover, in this embodiment, when the operating state of the load such as the magnetron 5 is switched and the DC power supply voltage (+V) fluctuates, the predetermined time T from the time of switching until the output state of the operational amplifier 14 stabilizes. Based on the temperature fluctuation (output signal of the operational amplifier 14) until
During this period, the operation of the magnetron 5 is controlled on the assumption that no temperature fluctuation occurs. Therefore, fluctuations caused by fluctuations in the DC power supply voltage (+V) when switching the operating state of the load are avoided. Detection errors can be prevented, and the reliability of automatic cooking can be improved from this aspect as well.

In this embodiment, the operation of the magnetron 5 is immediately stopped when the pulse width of the high-level signal vh outputted from the comparator 17 exceeds a certain time width Tw, but the control mode is different from this. The present invention is not limited to this, and for example, additional heating may be performed for a predetermined time from the time when the pulse width of the high-level signal vh exceeds a predetermined time width Tv, and then the operation of the magnetron 5 may be stopped. Good, also, during this additional heating, magnetron 5
The output may be reduced.

In addition, the present invention may employ, for example, a silicon diode or a transistor temperature sensor whose forward voltage drops as the temperature rises as the temperature detection means, or a temperature sensor such as a thermistor may be used as a temperature sensor with other three resistance elements. Various modifications are possible, such as a configuration in which a bridge circuit is configured in combination with the two output terminals of the bridge circuit, and the temperature is detected based on the potential difference between both output terminals of the bridge circuit.

[Effects of the Invention] As is clear from the above description, the present invention is provided with a temperature detection means for detecting the temperature of air containing hot air emitted from food being heated by high frequency, and the temperature detected by this temperature detection means is Since the operation of the magnetron is controlled based on the fluctuation of It can be done cheaply.

Moreover, when the operating state of a load such as a magnetron is switched, control based on temperature fluctuations is suspended until a predetermined period of time has elapsed from the time of switching, and during that time, the magnetron is operated on the assumption that no temperature fluctuations occur. Since this is controlled, it is possible to prevent erroneous operation of fluctuation detection due to fluctuations in the power supply voltage when switching the operating state of the load, and from this point of view as well, the reliability of automatic cooking can be improved.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention. Fig. 1 is a schematic diagram of the overall configuration, Fig. 2 is an electric circuit diagram of the main part, and Fig. 3 is a diagram of the ambient temperature of the thermistor after the start of high-frequency heating. Figure 4 is a diagram showing changes over time; Figure 4 is a voltage waveform diagram showing changes over time in the operational amplifier output voltage and DC power supply voltage of an AC amplifier circuit;
The figure is an output waveform diagram of the comparator of the comparison circuit. In the drawing, 1 is a heating cooking chamber, 1a is an exhaust duct, 2 is a rotating plate, 2a is a motor (load), 3 is food, 5 is a magnetron (load), 6 is a thermistor (temperature detection means), and 7 is an AC amplification 10 is a low frequency component blocking circuit, 16 is a comparison circuit, 20 is a control circuit, 21 is a control means, 31 is a cooling fan (load), and 32 is a DC power supply circuit. Temperature (C) Applicant: Toshiba Corporation Figure 3

Claims (1)

[Claims] 1. In a high-frequency heating device equipped with a magnetron for high-frequency heating of food stored in a cooking chamber, a temperature detection means for detecting the temperature of air containing hot air emanating from the food being high-frequency heated, and this temperature detection means control means for controlling the operation of the magnetron based on temperature fluctuations detected by the magnetron, and the control means controls the operation state of the magnetron or the like when a predetermined period of time has elapsed from the time of switching the operating state of the load such as the magnetron. A high-frequency heating device characterized in that the high-frequency heating device is configured to interrupt control based on the temperature fluctuation until the temperature changes.