JPH02146972A - Piezoelectric element applying sensor device - Google Patents

Abstract

PURPOSE:To finish food optically by discriminating food by the time intervals of a vapor signal detected by a piezoelectric element. CONSTITUTION:A piezoelectric element is installed into an electronic oven, and the pulses of a pressure change by boiling vapor are detected. Synchronizing pulses are prepared from a commercial power supply, and a magnetron is not oscillated and the signal of the piezoelectric element is sampled and detected while being synchronized with timing having no noise. When sampling timing when the signal of the piezoelectric element is brought to a prescribed value or more is continued for a specified period, the pressure change by boiling vapor is decided, and a counter is counted up. The intervals of the counting time are measured and the kinds of foods are discriminated, and the additional heating time is set in response to the kinds.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to signal detection using a piezoelectric element, particularly when applied to a microwave oven.

2. Description of the Related Art A conventional piezoelectric sensor of this kind will be described using an example in which it is applied to reheating food in a microwave oven as a signal detection means. FIG. 5 is a block diagram of the main body of the microwave oven. 1 is a piezoelectric element, 31 is a heating chamber, 32 is a magnetron that generates microwaves, 33 is a cooling fan that cools the magnetron 32, 34 is a turntable, 35 is a turntable drive motor, and 36 is a heating chamber that directs the air from the cooling fan. 31 is an air passage leading to the food, 38 is the steam generated from the food, 39 is an exhaust passage, 40 is the steam generated from the food 37, and the piezoelectric element 1
The air guiding path 41 is a control means for controlling the magnetron 32, the cooling fan 33, and the turntable drive motor 35 based on the signal from the piezoelectric element 1, and these constitute the microwave oven 15.

FIGS. 6a and 6s are diagrams showing the operating principle of vapor detection by the piezoelectric element 1.

When the piezoelectric element 1 whose components are lead titanate and zirconia is polarized in a strong electric field to form a ferroelectric material, as shown in FIG. It is electrically neutral, and no current flows through the ammeter 43.However, when hot boiling steam from the food imparts a thermal change ΔT'C to the piezoelectric element 1, the piezoelectric element 1. 1 is unable to follow the rapid temperature change, resulting in an unbalanced state of charge.Therefore, the ammeter 43
The current caused by the imbalance can be observed in the form of a pulse. When the boiling steam applies thermal changes to the piezoelectric element 1 one after another, such pulsed currents can be observed one after another.

Next, when we examine the frequency components of this pulsed current, we find that in the low frequency region (0 to 47 bands), the frequency component of the current generated in a pulsed manner is 40 dB in A before boiling steam generation and B after boiling steam generation, as shown in Figure 7. It was found that there was a change in signal level.

Therefore, the signal from the piezoelectric element 1 has been detected using a circuit configuration as shown in FIG. 2 is a resistor that converts the current generated by thermal changes in the piezoelectric element 1 into voltage, 3 is a capacitor, and 4 is a resistor, which prevents direct current from being applied to the bypass filter and the piezoelectric element 1. 5 is a low-pass filter that has a pass characteristic up to the 4th frequency band according to the frequency characteristics shown in FIG. 7, 6 is an amplifier that amplifies the signal, 7 is a diode, 12 is a smoothing circuit that smoothes the signal, and 15 is a device. A microwave oven 17 is a comparing means for comparing the smoothed signals and stopping the device 15.

FIG. 9 is a diagram showing signal changes after smoothing when configured as shown in FIG. 8. In the figure, A is a pulse-like voltage due to thermal changes.
The mouth shows a smoothed pulsed voltage. Therefore, when the control means 41 detects in the comparison means 17 that the smoothed signal level exceeds the set level 18, the apparatus is stopped.

Problems to be Solved by the Invention However, in the case of the above configuration, as shown in FIGS. Since there are a wide variety of steam components and amounts generated from foods, such as types of food products, it was necessary to create a key for each type of food. Alternatively, there is a method of identifying food based on changes in the signal level after smoothing, but when high frequency noise from a microwave oven magnetron, vibration shock, etc. are applied to the piezoelectric element 1, they are applied to the smoothing circuit 12. Therefore, increasing the noise tolerance requires increasing the smoothing time constant, which slows down the detection time of food finish.
A situation of overcooking of food occurs.

On the other hand, if the noise tolerance is lowered, unnecessary noise may exceed the set level 18, causing a misjudgment that the food is finished.

The present invention solves these conventional problems by accurately detecting boiling steam from food using a piezoelectric element, and by providing a 0' control algorithm within the heating chamber.

Means for Solving the Problems In order to solve the above problems, the piezoelectric element applied sensor of the present invention includes a detection means for sampling and detecting the signal level from the piezoelectric element at an appropriate timing for detecting a steam signal; a signal width detection means for detecting the signal width when the signal level of the piezoelectric element is equal to or higher than a predetermined signal level; a counter for counting signals equal to or higher than a set level for each predetermined signal width; and a count of the counter. It is composed of a control means that controls the equipment based on the time interval.

Operation With the above configuration, the present invention has an operation of discriminating food based on the time interval of steam signals detected by the piezoelectric element.

Example FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

To explain the differences from the conventional circuit configuration diagram, the signal of the piezoelectric element 1 is input to the control means 41 (in the present invention, a microcomputer) as a pulse voltage through the resistor 8 without being smoothed, and the commercial power supply 9 through transformer 10 to 11
A clock pulse synchronized with the commercial power supply 9 is inputted to the control means 41 by the power supply synchronization circuit. 13
14 is a detection means for detecting the signal level of the piezoelectric element 1 inputted to the control means 41; 14 is a signal width detection means for detecting the signal width when the signal level of the piezoelectric element 1 is higher than a predetermined signal level; 16 29 is a counter that counts signals equal to or higher than the signal level every predetermined signal width, and 29 is a timer that measures the time interval of the counter.

Next, the second reason why the control algorithm of the present invention can be realized is explained.
This will be explained using figures.

The piezoelectric element 1 has vibrations 19 caused by the door shock of the microwave oven as described in the prior art section, radio wave noise 20 caused by the magnetron, and a signal 21 caused by thermal changes in boiling steam as a real signal. Looking at these waveform diagrams, it can be seen that the pulse width of the boiling steam signal is significantly different from the pulse widths of other noise sources, and that the magnetron 32 oscillates for only half a cycle of the power supply.

This is because the noise is due to high frequency components, and the signal component due to thermal change due to boiling steam is a low frequency component signal as explained in Section 7, so this difference in pulse width appears.

To explain this using the waveform diagram shown in FIG. 3 and the control flowchart shown in FIG. 4, the piezoelectric element 1 is The signal level is detected by the detection means 13 (25), and the signal width detection means 14 is configured to count the counter 16 (27) if a signal with a set level of 18 or more is detected at every sampling time 24, for example four times or more in a row. 28), the time interval 29 counted by the counter 16 is measured with a timer 30), for example, it is determined whether the food 37 in the heating chamber 31 is watery or oily, and the time interval is determined based on the time interval. Control means 4 so that the food 37 is finished optimally
1 is for additional heating control.

For example, foods with high viscosity like curry stew,
As shown in FIG. 10(b), the time interval measured by the counter becomes longer. That is, since the food 37 has not yet been sufficiently heated and steam is sparsely generated due to partial heating, the control means further continues the radio wave heating. However, when steam is generated in a concentrated manner as the heating progresses, such as with rice, the time interval measured by the counter is naturally short.

Therefore, the control means 41 is for stopping the radio wave heating.

In one embodiment of the present invention, the signal width detection means detects the number of samples of the piezoelectric element signal that is equal to or higher than the set level, but the signal width itself that is equal to or higher than the set level may also be detected using a timer or the like. Effects of the invention which are not limited to one embodiment of the invention As described above, according to the invention, the following effects can be obtained.

1. Compared to conventional analog circuits that identify food based on changes in smooth signal levels, this system identifies food based on the amount and timing of steam that is applied to the piezoelectric element as food heats up, and also detects the heating state. Since the detection is performed, the food will be finished to the optimum level.

2. There is no need to provide multiple special keys for food discrimination, and only one key is required, which simplifies the configuration of the device.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a piezoelectric element application sensor device according to an embodiment of the present invention, and FIG. 2 is a signal waveform diagram generated in the same piezoelectric element.
Fig. 3 is a waveform diagram of each part of the circuit, Fig. 4 is a flowchart of the control algorithm, Fig. 5 is a main body configuration diagram of the microwave oven, Fig. 6 is an explanatory diagram showing the operating principle of the piezoelectric element, Fig. 7
The figure is a characteristic diagram showing frequency components due to boiling steam of the same piezoelectric element, FIG. 8 is a conventional circuit configuration diagram, and FIGS. 9 and 10 are signal waveform diagrams of the same circuit. 1...Pressure! Element, 5...Low pass filter, 6...Amplifier, 13...Detection means, 14...Signal width detection means, 15...
...Equipment, 16...Counter, 18...
・Predetermined signal level (setting level),
24...Sampling time, 29...
・Time interval, 32...High frequency radiation means, 41.
...control means. Name of agent Patent attorney Shigetaka Awano 1 person Fig. 9' Tshi ΔT)"t3t, plan number 10 picture right

Claims (1)

[Claims] a piezoelectric element that detects the progress of heating the food; a filter that appropriately filters the signal of the piezoelectric element; and an amplifier;
detection means for sampling and detecting the signal level of the signal; signal width detection means for detecting the signal width when the signal level is equal to or higher than a predetermined signal level;
A piezoelectric element application comprising a counter that counts signals equal to or higher than the signal level for each predetermined signal width, and a control means that discriminates the food based on the time interval counted by the counter and controls the high-frequency heating device. sensor device.