JPS6349359B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control mechanism for a microwave oven cooking device using a microcomputer.

In recent years, with the introduction of microcomputers, the cooking software of cooking appliances has expanded, and the ways to use them are becoming more diverse.
A large number of operation keys are lined up, and the operation procedures can even be complicated. For this reason, poor operability has been pointed out as a drawback of systems incorporating microcomputers.

Therefore, in order to eliminate the above-mentioned drawbacks, cookers with good operability using temperature sensors and humidity sensors have been developed. The present invention relates to a cooking appliance using these sensors, and particularly to simplifying a control circuit for a cooking appliance using a temperature sensor and a humidity sensor, and providing a flexible control system.

Figure 1 shows a conventional microwave oven control circuit using a microcomputer. 1 is the cooking oven body, 2 is the magnetron device, 3 is the humidity sensor installed at the exhaust port, and 4 is the humidity sensor 3. a first amplifier that amplifies the resulting detection signal;
5 is a second amplifier that amplifies and rectifies the signal from the first amplifier 4 and outputs only the positive half cycle portion as a converted voltage; 6 is a polarity inversion amplification that smoothes the output signal of the second amplifier 5; 7 is a level shift circuit that adds an additional voltage to the smoothed voltage from the smoothing circuit 6 to turn the negative voltage into a positive voltage, 8
9 is a peak hold circuit, 9 is a comparator that compares the added output of the peak hold circuit 8 and level shift circuit 7 with a reference level ΔV, and generates an output when this level is exceeded; 10 is a central processor that controls the magnetron driver 11; It is a device.

FIG. 2 shows operating waveforms for explaining the outline of the operation of the above circuit. Curves A to B show the output waveforms of the level shift circuit 7, and curves H to D show the outputs of the peak hold circuit 8. . Curve E is the summed output of curves A to B and curves H to D, and is the input voltage waveform of input terminal A of comparator 9.

FIG. 3 is a characteristic curve of the humidity sensor 3, showing the relationship between relative humidity RH% and sensor resistance R _S.

When you start cooking now, the temperature inside the oven starts to rise and the relative humidity around the sensor starts to drop. The output of the level shift circuit 7 in this case is curve A in FIG. At time t=t _p after the start of cooking,
Steam is blown out from the food to be cooked, and the relative humidity around the sensor 3 provided at the exhaust port increases, so that the output increases to the positive side as shown by curve B in FIG. On the other hand, the output of the peak hold circuit 8 holds the potential at time t _p in FIG. 2, and becomes as shown by curve D. As a result, the comparator 9 compares the potential V _A at point A in FIG. 1 with the reference potential V _R , and if V _A > V _R , the central processing unit 10 determines that steam has blown out from the object to be heated. do. This controls the output mode of the magnetron device 2 and executes cooking.

Although the outline of the operation has been explained above, the disadvantage of this method is that a smoothing circuit 6, a level shift circuit 7, and a peak hold circuit 8 are required, and the circuit configuration is complicated and the number of parts is large. In particular, the peak hold circuit 8 requires a large capacitor with excellent characteristics. This is because, as shown by the smooth level curve B' in FIG. 2, when the amount of steam from the food to be cooked is small, it takes a long time (first (indicated by T' in Figure 2), and the peak hold circuit 8 is
This is because it is necessary to hold the potential during that time. The next problem is that the resistance of sensor 3 is greatly affected by steam noise from the food being cooked, so the output signal of sensor 3 is smoothed and the detection circuit is given a time constant characteristic to prevent malfunctions. It is necessary to prevent it. In other words, the system must detect only the continuous generation of steam. However, this equivalently reduces the vapor detection ability of the detection circuit, and has the disadvantage that the detection ability is lost especially when the amount of vapor generated from the object to be heated is small.

The present invention has been made in view of the above-mentioned conventional drawbacks, and embodiments of the present invention will be described below with reference to FIGS. 4 to 8. Figure 4 shows the circuit configuration.
21 is the oven body, 22 is the magnetron device,
23 is a humidity sensor provided at the exhaust port of the oven body 21, 24 is an amplifier circuit, 25 is a comparator, 2
6 is a digital-to-analog converter (hereinafter referred to as a D/A converter), 27 is a central processing unit, and 28 is a driver circuit that controls the oscillation of the magnetron device 22.

FIG. 5 shows the characteristics of the amplifier circuit 24, FIG. 6 shows the characteristics of the D/A converter 26, and FIG. 7 shows the output waveform of the amplifier circuit 24 during actual cooking operation. It is.

Next, the operation will be described with reference to FIGS. 4 and 7. The central processing unit 27 drives the magnetron device 22 in accordance with the operator's KEY input signal to start cooking. Further, a scan pulse from the sensor 23 is applied, and the signal is amplified by the amplifier circuit 24 and used as one input signal of the comparator 25. In this case, the output pulse of the amplifier circuit 24 generally shows a decreasing tendency until time t=t _p as shown in FIG. This is because the temperature inside the oven increases due to the oscillation of the magnetron device 22, the relative humidity around the humidity sensor 23 attached to the exhaust port decreases, and the electrical resistance of the sensor increases as shown in FIG. . Next, during a period of time t> _tp , the relative humidity increases due to the blowing of steam from the food to be cooked, and the sensor resistance increases, so that the output pulse of the amplifier circuit 24 increases. On the other hand, the central processing unit 27 applies the digital code to the D/A converter 26 and uses the analog voltage having the characteristics shown in FIG. The central processing unit 27 stores the magnitude of the output signal of the sensor 23 in an internal register as a digital code D _o . in this case,
The central processing unit 27 has a lowest value storage register,
The lowest value of the output signal D _o of the sensor is stored as D _nio . In Figure 7, the lowest value D _nio until time t = t _p
is updated, but when t>t _p the lowest value becomes D _nio (t _p ) and remains constant.

Since the sensor output D _o changes from a decreasing trend to an increasing trend after time t = t _p , the central processing unit 27
Even at this time, it is possible to detect that steam has started to come out from the food to be cooked. However, in reality, in order to prevent false detection due to noise, it is the output of the sensor that determines that steam has blown out from the food being cooked.
The method is such that it is determined that steam has been generated from the food only when D _o becomes greater than the value D _nio stored in the lowest value register by ΔD or more and this state continues for a certain period of time. In this method, the central processing unit 2
The peak value (or minimum value) can be detected and held only by the calculation processing of D _o and D _nio according to 7. Further, the threshold level voltage ΔV of the conventional circuit example shown in FIG. 2 can be set as a digital amount ΔD. Further, since an arbitrary time interval can be easily created by counting pulses synchronized with the power supply waveform by the central processing unit 27, there is no need for a large-capacity capacitor for a peak value hold circuit as in the prior art. In addition, this allows the determination to be made any number of times at arbitrary time intervals, thereby reducing the possibility that the central processing unit 27 will mistakenly detect the boiling point due to changes in air volume or minute steam noise from the surface of the food to be cooked before the boiling point is reached. be able to. Furthermore, this method does not require a hardware smoothing circuit as in the conventional example, and it is possible to reduce the amount of change in the sensor output, thereby reducing the disadvantage of the conventional method of reducing the steam detection ability of the circuit.

Next, measures to prevent malfunction of vapor detection according to the present invention will be explained with reference to FIG. FIG. 8 is a diagram showing the output of the amplifier circuit 24 of the humidity sensor 23 with respect to the cooking time. In Figure 8, curve A is the humidity sensor 23.
The initial relative humidity around is high, e.g. RH=90%
In the case of , curves B and C are characteristic curves when the initial relative humidity is lower than that, for example, 60% and 20%. As is clear from the R _S -R _H characteristics in Figure 3, R _H
At 90% the sensor resistance R _S is on the order of 10 ³ to 10 ⁴ Ω, R _H
=20%, R _S is on the order of 10 ⁷ -10 ⁸ Ω. Therefore, in the case of characteristic curve C where R _H is low, it is more susceptible to the influence of external noise than in the case of characteristic curve B, which causes malfunction. For example, when R _H is as high as 90%, the sensor resistance R _S is on the order of 10 ³ to ^{10 4} Ω,
As an analog amplifier circuit, it is possible to detect a stable signal, but when R _H is as low as 20%, the sensor resistance R _S becomes 10 ⁷ to 10 ⁸ Ω, which is a high impedance for an analog amplifier circuit. It becomes extremely susceptible to electrical (including electromagnetic waves) noise from power sources such as the microwave's magnetron oscillator and heater. The output waveform at this time becomes a largely wavy output as shown in characteristic curve C in FIG.

On the other hand, when the impedance is low, the characteristic curve A shows a relatively linear output, and the influence of external noise is small.
The difference in the increase in the output of 4 becomes smaller. Therefore, in the case of characteristic curve C, the threshold voltage ΔV ₃ should be increased as much as possible, and in the case of characteristic curve A, the threshold voltage ΔV ₁ should be increased.
must be made as small as possible. Therefore, by switching the digital amount ΔD of the threshold level ΔV in several stages as a function of the output D _o of the sensor amplifier circuit 24 and making a decision, stable operation is possible over a wide operating range. For example, if the output level D _o immediately after starting cooking is 10V, ΔV is 0.5V,
If D _o is 5V, ΔV is 1V, and if D _o is 1V, ΔV is 1.5V. Further, the D/A converter can be easily configured with a ladder circuit using resistive elements.

As is clear from the above description, according to the present invention, the number of circuit components is small and stable control can be obtained.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the circuit configuration of a conventional microwave oven equipped with a microcomputer.
The figure is an operation waveform diagram for explaining the operation in Figure 1.
Figure 3 is a characteristic diagram showing the characteristics of the humidity sensor.
The figure is a block diagram showing the circuit configuration of a microwave oven according to an embodiment of the present invention, FIG. 5 is a diagram showing the characteristics of the amplification circuit for the sensor output signal of FIG. 4, and FIG. Diagram showing the characteristics of /A converter, No. 7
8 are diagrams showing operating waveforms of the circuit of FIG. 4. 22...Magnetron device, 23...Humidity sensor, 24...Amplification circuit, 25...Comparator, 26...Digital analog converter, 27...Central processing unit.

Claims (1)

[Claims] 1 A heating means for heating the food to be cooked, a humidity sensor for detecting the relative humidity that changes due to water vapor emitted from the food to be cooked, an amplifier circuit for amplifying the output of this humidity sensor, and an amplifier circuit for amplifying the output pulse of this amplifier circuit. a comparator that compares the level with the analog output of the digital-to-analog converter, outputs a pulse voltage that scans the humidity sensor, outputs a digital code to the digital-to-analog converter, and outputs a digital code to the digital-to-analog converter; A register for storing the output level of the digital value D as a digital value D, and a minimum value D _nio of the digital value D.
and a central processing unit having a built-in register for storing a threshold value ΔD corresponding to the humidity sensor output D _O corresponding to the initial relative humidity.
(However, ΔD is a monotonically decreasing function of D _O. ), and the value at the n (however, n is 1, 2, 3, ...) sensor output detection by the central processing unit is set as D _o , when the n+1st time is D _o+1 ,
If D _o+1 < D _o , update and store D _o+1 as D _nio in the lowest value register, and if D _o+1 ≧D _o , D _o+1 −D _nio ≧ΔD
A cooking device configured to determine that steam has been generated from an object to be cooked only when , and to select a cooking mode based on the determination result.