JPS6311566B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a microwave oven having an automatic finishing control function using a gas sensor as a detection element. <Conventional technology and its problems> Conventional microwave ovens that automatically control the finish of food by detecting gas generated as food is heated with a gas sensor have the following problems. It was hot. Here, before explaining the above problem, let us assume that the sensor resistance value of the gas sensor when the gas concentration reaches 30 (PPm) is R30 (Ω), and the gas concentration reaches 30 (PPm).
(PPm), the sensor resistance value is R300 (Ω)
and β=R300/R30 is the sensor sensitivity, which is used below. The finished state of food is expressed using this sensor sensitivity β as a parameter. As shown in FIG. 5, the voltage V _S across the gas sensor changes as shown in the figure, depending on the gas generated as the food is heated with respect to the heating time. That is, when the value of sensor sensitivity β is small, the time required for the voltage V _S across the gas sensor to reach the detection voltage becomes short. Next, the above problems will be listed. Problem (1): Due to variations in sensor sensitivity, the finished state of the food varied and there was a large difference in performance between products. When the sensor sensitivity β and the finished food temperature were measured for the same detection voltage, the finished temperature changed depending on the sensor sensitivity β, as shown in FIG. 6a. That is, the finishing temperature of the sensor with low sensor sensitivity β was low. Problem (2): In order to reduce the variation in problem (1) above, sensors were classified by sensitivity value and a correction circuit corresponding to the sensitivity was added, but the cost required for sensor selection and the external The price increased due to the addition of a correction circuit. Problem (3): The sensitivity of the gas sensor changed due to gases such as dimethylsiloxane generated when the oven was air-baked, which affected the finish of the food.
In addition, when a special aging process was performed to prevent changes in sensor sensitivity, the price increased due to the labor involved. All of these problems are caused by the fact that the sensor sensitivity is not a constant value. The above problem will be explained in more detail with reference to a conventional microwave oven control circuit shown in FIG. When you press the cook switch 11 on the microwave oven to start cooking,
The voltage V across the sensor 16 at that time is the memory circuit 1
2 is stored. Based on the voltage V across the sensor 16 at the start of heating output from the memory circuit 12, a finish detection level smaller than this is set. In other words, this finish detection level is determined by sensor 1 for detecting the end of main heating other than additional heat.
6, and the initial voltage of the sensor 16 is V
It is obtained by multiplying by a constant k, which is a finish detection level coefficient. This constant k is the ratio of the voltage across the sensor when the end of heating is detected to the initial voltage V, and is determined experimentally in advance.
In the control circuit shown in FIG. 7, a constant k (<1) is set by the voltage dividing ratio of the two voltage dividing resistors _RA and _RB .
Therefore, the finish detection level obtained by dividing the output of the memory circuit 12 by the resistors R _A and R _B
kV is input to one input end of the detector 14 and heating of the food is started. Gas is generated from the food heated by the heating device 13, and the voltage V _S across the sensor gradually decreases from the initial voltage V.
When the finish detection level kV is reached, the detector 14
The output of is reversed, relay coil L and relay contact 15 are turned off, and heating device 13 is turned off.
It turns OFF. However, the value of constant k is fixed,
That is, since the detection voltage kV is constant, when the sensor sensitivity β deteriorates, the finished temperature increases as shown in FIG. 6a. <Purpose of the Invention> The present invention was made in view of such conventional problems, and it is possible to utilize the characteristics of a sensor in an electric circuit even when the sensor sensitivity varies or changes and is not a constant value. The object of the present invention is to provide a microwave oven that can always obtain a uniform finished state of food to be processed by setting a finish detection level corresponding to sensor sensitivity. <Means for Solving the Problems> In order to achieve the above object, the microwave oven of the present invention calculates a finished detection level of a smaller value from the initial output value of the gas sensor, and compares the output of the gas sensor with the finished detection level. In a microwave oven that controls the power supply to the food heating means by comparing the above-mentioned finish detection level, the heater voltage of the above-mentioned gas sensor is set to the rated value V _A and a non-rated value lower than this rated value.
A switching means for switching to V _B and a switching means for controlling this switching means to switch from the rated value V _A to a non-rated value V _B and then return to the rated value V _A when setting the finish detection level at the start of heating. control means and each stable output of the gas sensor when the heater voltage is at the rated value V _A and at a value outside the rated value V _B ;
A first storage means and a second storage means for storing V _SA and V _SB, respectively, and an initial output value V ₀ of the gas sensor at the rated value obtained by returning the heater voltage from the non-rated value V _B. a third storage means and an arithmetic means for calculating a value obtained by multiplying the value of (V _SB /V _SA )·V ₀ by a finish detection level coefficient k by introducing the outputs of the first to third storage means; The present invention is characterized in that the calculated value of the calculating means is set as the finish detection level. <Function> With the above configuration, when setting the finish detection level at the start of heating, k(V _SB /
The value of (V _SB / _{V SA} ) among the values of V SA ) and Vo is equivalent to the voltage dependence of the sensor, and this voltage dependence has an equivalent relationship to the sensor sensitivity. Therefore, the calculated finish detection level changes depending on the sensor sensitivity; if the sensor sensitivity is poor, the finish detection level will be high, and conversely, if the sensor sensitivity is good, the finish detection level will be correspondingly small. As a result, no matter how the sensor sensitivity changes, the finish detection level changes accordingly, so the finish will always be the same. <Examples> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. First, the focus of this invention will be explained. That is, the present invention is based on the facts obtained through detailed experiments on gas sensors as described below. Here, the voltage dependence Q of the sensor is defined as follows and will be used below. When the heater voltage of the sensor changes from the rated voltage V _A , e.g. 5V, to a voltage V _B of 90 to 98% of the rated voltage, e.g. 4.8V, the resistance value of the sensor in the air changes from R _C to R _D. do.
At that time, let Q=R _D /R _C be the voltage dependence of the sensor. Therefore, with the sensor heater voltage on the horizontal axis,
The experimental data shown in FIG. 2, in which the vertical axis is the voltage dependence Q that changes in response to changes in the sensor sensitivity β, was obtained. Furthermore, when the heater voltage is, for example, 4.8V, the relationship between the voltage dependence Q and the sensor sensitivity β is graphed as shown in FIG. From FIG. 3, it was found that the sensor sensitivity β and the voltage dependence Q are in a proportional relationship. In other words, β=CQ, where C is a proportionality constant... (1) Therefore, from this equation (1), the voltage dependence Q corresponding to the sensor sensitivity β is determined from the change in the sensor heater voltage, and the voltage dependence Q is By correspondingly changing the finish detection voltage level, the finished temperature of the food can be kept constant regardless of the sensor characteristics, that is, the sensor sensitivity β. This invention was made with attention to such points. Next, in FIG. 1 showing the block configuration of the present invention, the voltage switching device 3 of the heater 1 is connected to the sensor 1.
It is provided on the power supply side of the heater 1 of No. 6 and switches the voltage value applied to the heater 1. Switching device 3 is rated value
a normally closed relay contact A ₁ giving V _A , e.g. 5V;
It consists of relay contacts B ₁ and C ₁ for switching to a value V _B smaller than V _A , for example 4.8V. Memory circuit M ₁ ,
M ₂ and M ₃ are provided on the output side of the sensor 16 via relay contacts A ₂ , B ₂ and C ₂ , respectively. The memory circuit M ₁ stores the voltage V _SA across the sensor when the heater voltage is _VA . The memory circuit _M2 stores the voltage _VSB across the sensor when the heater voltage is _VB .
The memory circuit _M3 stores the initial value Vo at both ends of the sensor. Relay coil A is interlocked with relay contacts A ₁ and A ₂ by a timer T _A . Relay coil B
is interlocked with relay contacts B ₁ and B ₂ by timer T _B. Relay coil C is interlocked with relay contacts C ₁ and C ₂ by timer T _C. Divider 4
introduces the outputs of memory circuits M ₁ and M ₂ and calculates the voltage ratio
Calculate V _SB /V _SA . The k-constant multiplier 5 introduces the output of the divider 4 and multiplies V _SB /V _SA by a coefficient k (<1) obtained experimentally in advance, similar to that explained in FIG. Multiplier 6 outputs Vo and k of memory circuit _M3 .
The output of the constant multiplier 5 is introduced to calculate the finish detection level k·(V _SB /V _SA )·V ₀ and output it to the detector 7. The detector 7 introduces the voltage V _S across the sensor, outputs a signal level that is inverted depending on whether the voltage V _S across the sensor reaches k・(V _SB /V _SA )・V ₀ , and activates the relay coil D. Instructs to turn on and off. Relay coil D controls power supply to heating device 13 in conjunction with relay switch _D1 . Note that the memory circuits M ₁ , M ₂ ,
The _M3 divider 4, the k-constant multiplier 5, the multiplier 6, etc. can be more easily configured by a microcomputer. Next, the operation of the above embodiment will be explained according to the following steps. Step 1: The power supply voltage V _C is divided between the sensor 16 and the load resistor R _L. The relay contact A ₁ is set to the normally closed side by the timer T _A before cooking starts, and the voltage V _A is always applied to the sensor heater 1 . Step 2: Press the cook switch 11 to start cooking. The voltage V _SA across the sensor immediately after the start is stored in the memory circuit _M1 . Step 3: After the time τA shown in FIG. 4 has elapsed, relay coil A is turned off by timer T _A , timer T _B begins to operate, and relay coil B is turned on. Also, relay contact B ₁ closes,
The heater voltage is switched from V _A to V _B. As the heater voltage changes, the _fourth
It fluctuates for several seconds as shown in the figure. Step 4: After a τB time (several seconds) has elapsed after switching the heater voltage, the relay contact _B2 closes, and the stable voltage across the sensor _VSB is stored in the memory circuit _M2 . Furthermore, relay coil B is turned off, timer T _C is activated, and relay coil C is turned on. Therefore, the heater voltage
Returned from V _B to V _A. i.e. relay contacts
By closing _C1 , the heater voltage is switched to V _A , and after a few seconds, relay contact _C2 closes and the stable initial value Vo of the voltage across the sensor is stored in memory circuit _M3 . Step 5: The divider 4 and the k-constant multiplier 5 calculate k・(V _SB /V _SA ), and the multiplier 5 further calculates the finish detection level k・(V _SB /
V _SA )·Vo is calculated and set in the detector 7.
Thereafter, power is supplied to the heating device 13 until the voltage V _S across the sensor reaches the finish detection level. Step 6: When the voltage V _S across the sensor reaches the finish detection level after a time τC after returning the heater voltage to V _A , the detector 7 is inverted from the H level to the L level and the relay coil D is turned OFF. Then, the relay contact _D1 turns OFF and the heating device 13 stops. Next, an experiment was conducted using this example, and the above-mentioned finish detection level was determined, and the data obtained by measuring the finished state are shown in the table.

[Table] In this first table, Vo=5 and k=0.6. Also, in this experiment, the voltage across the sensor V _B
changed as shown in Figure 4. Here, the finish detection level set in step 5 will be described in more detail. In FIG. 1, the gas sensor 2 is connected in series with a load resistor R _L and connected to a DC power supply V _C. The gas sensor 2 is made of a semiconductor, and the value of the load resistor R _L is selected to be much larger than its resistance value, so even if the resistance value of the gas sensor 2 changes somewhat, the current value remains constant. It's okay to think about it. As mentioned above, the heater voltage of sensor 2 is
When the sensor resistance values at rated voltage V _A and lower voltage V _B are R _C and R _D , sensor 2
The voltage dependence Q of is defined as Q=R _D /R _C. Also, the voltage across the sensor when the heater voltage is V _A
V _SA and the voltage V _SB across the sensor when the heater voltage is V _B are stored as measured values in the first and second storage means, respectively. Therefore, in the constant current circuit, V _SB /V _SA =R _D /R _C =Q (2) holds true. Furthermore, since Q∝β from the above equation (1), the finish detection level calculated by the multiplier 6 is k・(V _SB /V _SA )・Vo=kQV ₀ ∝β・Vo ...(3) Become. That is, even if the sensor sensitivity β changes, the finish detection level automatically changes accordingly, so the finishing time is always the same, or in other words, the finishing state is always the same. In fact, as can be seen from the above table and FIG. 4, when the sensor sensitivity β is poor, that is, when the value V _SB /V _SA corresponding to the voltage dependence Q is large, as in the case of β = 0.6,
The finish detection level k·(V _SB /V _SA )·Vo also increases correspondingly, and the finished state is reached quickly even if the voltage across the sensor V _S falls slowly. On the other hand, when the sensor sensitivity β is good, that is, when the voltage dependence Q is small, the finished state detection level becomes small, and the finished state is reached slowly with respect to the rapid fall of the voltage V _S across the sensor. As a result, the same finishing time (τA + τB + τC) can always be obtained regardless of whether the sensor sensitivity is good or not, and therefore the finishing temperature of the food becomes constant as shown in Fig. 6b. In the above example, approximately 10 of (τA + τB) time
Change heater voltage from 5V to 4.8V to 4.8V in a few seconds
However, since the food is not heated suddenly, the amount of gas generated is small, and it can be said that there is no effect on the voltage V _S across the sensor during that time. In addition, when applied to a microwave oven configured to perform cleaning for ventilation without oscillating microwaves for a few seconds from the start of cooking, such effects need not be taken into consideration at all. <Effects of the Invention> As described above, the microwave oven of the present invention has a configuration in which the heater voltage of the gas sensor is changed and the finish detection level is varied in accordance with the rate of change in the voltage across the gas sensor corresponding to the change. Therefore, the finishing temperature can be set accurately regardless of variations in the sensor sensitivity of the gas sensor, and it can be automatically controlled to achieve a good finished state. In addition, since no external correction circuit or special aging process is required, the present invention is inexpensive and has great effects on microwave ovens that perform automatic food finish control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention.
Figures 2 and 3 are a diagram of the relationship between the heater voltage and sensor voltage dependence, and a diagram of the relationship between sensor sensitivity and sensor voltage dependency, respectively, which were shown to explain the operation of Figure 1. Action explanatory diagram, 5th
The figure is an output characteristic diagram of the voltage across the sensor shown to explain the problems with the conventional method. Figure 6 is a relationship diagram between sensor sensitivity and finished food temperature to explain the above problems. Figure 7 is the conventional example. FIG. 2 is a block diagram of a microwave oven. DESCRIPTION OF SYMBOLS 1... Heater, 2... Gas sensor, 3... Heater voltage switching device, 4... Divider, 5... K constant multiplier, 6... Multiplier, 7... Detector, 11...
Cook switch, 13...Heating device.

Claims (1)

[Claims] 1. In a microwave oven that calculates a finish detection level of a smaller value from an initial output value of a gas sensor, and compares the output of the gas sensor with the finish detection level to control power supply to a food heating means, The heater voltage of the above gas sensor is set to the rated value V _A and the non-rated value V _B that is lower than this rated value.
and a switching control means that controls the switching means to switch from the rated value V _A to a non-rated value V _B and then return to the rated value V _A when setting the finish detection level at the start of heating. and,
The above heater voltage is the rated value V _A and the non-rated value V _B
Each stable output V _SA of the above gas sensor at
A first storage means and a second storage means each store V _SB , and the heater voltage is set to a value other than the rated value.
third storage means for storing the initial output value V ₀ of the gas sensor at the rated value returned from V _B ;
a calculation means for introducing the outputs of the first to third storage means and calculating a value obtained by multiplying the value of (V _SB /V _SA )·V ₀ by a finish detection level coefficient k; A microwave oven configured to set a calculated value of as the finish detection level.