JPH0451735B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a microwave oven equipped with a piezoelectric element sensor that detects and controls the state of gas generated from food as the food is heated.

Prior Art As shown in FIG. 4, a conventional microwave oven with a sensor detects a change in the resistance value of a humidity sensor 36 by dividing the voltage of a reference voltage power source 37 with a resistor 38 to control the device. . (For example, Jikai 53-
77365 Publication) Problems to be Solved by the Invention In this conventional method, the voltage across the resistor 38 is used as a control signal, so when producing a large number of 38, variations in the voltage of the power supply 37 lead to variations in the control voltage signal, making management difficult. In addition, since humidity sensors essentially utilize grain boundary phenomena for detection, in order to ensure detection accuracy and prevent clogging of grain boundaries, humidity sensors are kept warm with a heater or periodically heated. Various efforts were required in terms of maintenance, such as burning off dirt.

The present invention has been made in view of such problems, and it is an object of the present invention to detect the heating state of food with a simple configuration.

Means for Solving the Problems The present invention provides a piezoelectric element sensor in the exhaust section of the gas discharged from the heating chamber, and a controller that controls the operation of the notification means based on the signal from the piezoelectric element sensor. A piezoelectric element sensor has electrodes arranged on both sides of a piezoelectric element, and the surfaces of the piezoelectric element and the electrodes are covered with synthetic resin.

The apparatus also includes a controller that controls the operation of the heating means based on a signal from the piezoelectric element sensor.

Effects According to the present invention, when gas containing moisture generated from the food is discharged from the exhaust section as heating progresses, the piezoelectric sensor detects a change in the temperature of the exhaust flow and adjusts the temperature according to the temperature. Because it oscillates a signal,
The operation of the notification means or heating means is controlled based on the signal from this piezoelectric element sensor.

Embodiment FIGS. 1a and 1b are perspective views of a piezoelectric element sensor of the present invention and a diagram showing a state in which the piezoelectric element sensor is attached. In FIG. 1, a piezoelectric element sensor is constructed by sandwiching and fixing a piezoelectric element 1 made of lead titanate or the like between lead wires 3 and 5 having electrodes 2 and 4, and dipping with epoxy resin 8 or the like. The sensor is fixed to an insulating plate 6 with a fixing material 7 and attached to a metal plate 10 of an exhaust section 9 of the heating chamber with screws 11 or the like.

FIG. 2 shows an embodiment of a microwave oven equipped with a piezoelectric sensor according to the present invention. In FIG. 2, the output of the piezoelectric element sensor 12 is configured to prevent changes in polarization characteristics due to ion conduction due to the application of a DC component to the sensor, and to block the DC component of the sensor voltage output. It is connected to an amplifier 13 for voltage amplification, a comparator 14 for voltage comparison, and a controller 15.

A food product 17 is placed in the heating chamber 16 , and a portion of the cooling air from the magnetron 18 is guided into the heating chamber 16 through a duct 20 by a fan 19 . A portion of the cooling air is shown by a solid arrow line 21, and a portion of gas such as moisture generated from the food is shown by a dotted arrow line 22. The cooling air and the gas containing moisture generated from the food are removed from the exhaust section 2.
3 and is sent out from the heating chamber 16 to the outside.

A piezoelectric sensor 12 is attached to the exhaust section 23. In this embodiment, a winding 27 is wound around the core 24 of the motor that drives the fan 19 together with the winding 26 from the power plug via the power switch 25. , resistor 30, constant voltage diode 31
It constitutes a constant voltage power supply section consisting of the following, eliminating the need for a transformer for the control circuit. Further, the buzzer 32 is
It is configured to operate according to a signal from the controller 15 when the amplified signal voltage becomes larger than a set threshold voltage ΔV _T .

FIG. 3 shows an example of the output voltage characteristics of the sensor 12 of the microwave oven having the configuration shown in FIG. FIG. 3a shows an example of how the output voltage changes over time when water boils inside the refrigerator. (b) in FIG. 3 is the frequency spectrum of the output voltage in the same state. () in figure b
If the water temperature is low after turning on the microwave oven,
() is an example of the output voltage before turning on the power.

This characteristic indicates that the boiling state of water in the refrigerator can be detected by looking at voltage change components in a frequency range smaller than 50Hz. That is,
When the food 17 in the refrigerator interior 16 is heated, the gas passing through the exhaust section 23 becomes a mixture of high-calorific exhaust due to warm water vapor 22 and cooling air 21.

The mixing ratio of both changes over time. Therefore, the heat transmitted to the piezoelectric element through the microphone case changes, and the mechanical stress caused by this thermal change generates a polarization voltage. With such an output voltage,
By amplifying the voltage with the amplifier 13 and comparing the signal voltage with the threshold voltage ΔV _T in the comparator 14 shown in FIG. 2, the controller 15 issues a buzzer when the signal voltage becomes larger than ΔV _T. For example, you can tell when your food has reached its boiling point. It is also possible to have a configuration in which heating is stopped by turning off the power supply voltage using a controller. Furthermore, if the detection sensitivity is increased by increasing the amplification degree of the amplification device or by devising the mounting method of the piezoelectric element sensor, it is possible to detect not only the boiling point but also water temperatures of around 60°C, where the water vapor pressure rapidly increases. . In this case, if the threshold voltage can be manually set variably, many effects can be expected, such as making it possible to adjust the cooking quality.

Effects of the Invention As described above, according to the present invention, a microwave oven with a food heating state detection function can be realized with an extremely simple configuration.

Humidity sensors and gas sensors essentially utilize the grain boundary phenomenon of the sensing element, so to prevent clogging of the grain boundaries, they are kept warm with a heater or periodically burned off to remove dirt. Although many complicated measures are required in terms of maintenance, the present invention does not require such measures. Therefore, there is no need for electricity for heat retention or for grilling, making it a power-saving type.

Furthermore, there is no need for control parts for maintaining the accuracy of the heat-retaining heater power or a special transformer for the heater power, and the cost is low. Furthermore, as is clear from FIG. 3b, since the signal is large, stable control can be achieved with respect to the noise level caused by electromagnetic noise within the microwave oven and wind noise from the cooling fan. In addition, piezoelectric sensors have electrodes placed on both sides of the piezoelectric element, and the surfaces of the piezoelectric element and electrodes are covered with synthetic resin. Even when used in the exhaust part of a microwave oven, which is constantly exposed, insulation between electrodes can be ensured over a long period of time.

[Brief explanation of the drawing]

1A and 1B are a perspective view and a sectional view of a piezoelectric element sensor of a microwave oven equipped with a piezoelectric element sensor according to an embodiment of the present invention, FIG. 2 is a block diagram of a microwave oven equipped with the same piezoelectric element sensor, Figures a and b are output characteristic diagrams of the same piezoelectric element sensor, and Figure 4 is a block diagram of a conventional example. 1... Piezoelectric element, 2, 4... Electrode, 3, 5...
Lead wire, 8...Resin, 11...Exhaust part, 13...
…Amplifier.

Claims (1)

[Scope of Claims] 1. A heating chamber for storing food, a heating means for heating the food, a notification means for notifying the heating state of the food, and an exhaust section for gas discharged from the heating chamber. The piezoelectric element sensor includes a piezoelectric element sensor that detects a temperature change of the discharged gas, and a controller that controls the operation of the notification means based on a signal from the piezoelectric element sensor, and the piezoelectric element sensor has electrodes on both sides of the piezoelectric element. A microwave oven equipped with a piezoelectric sensor, in which the surfaces of the piezoelectric element and electrode are covered with synthetic resin. 2. A heating chamber that accommodates food, a heating means that heats the food, a piezoelectric element sensor that is provided in an exhaust section for gas discharged from the heating chamber and detects temperature changes of the discharged gas, and a controller that controls the operation of the heating means based on a signal from an element sensor, and the piezoelectric element sensor has electrodes arranged on both sides of the piezoelectric element, and the surfaces of the piezoelectric element and the electrodes are covered with synthetic resin. Microwave oven with piezoelectric sensor.