JPH0127723B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rice cooker that uses a microcomputer to control the amount of power of a heater.

In this type of rice cooker, the characteristics of the temperature rise of cooked rice during cooking vary depending on the amount of rice cooked and the amount of electric power of the heater, and are not uniform and have large differences in parts. In particular, there is a big difference in the time it takes for rice to boil when cooking a small amount of rice and cooking a large amount of rice, even with the same amount of electricity.
It is affected by how well the rice is cooked.

In other words, in the conventional method of detecting the amount of cooked rice by detecting the temperature rise rate of the inner pot and decreasing the amount of power of the heater from the middle of heating up the rice, the amount of rice cooked is the same, but the amount of power of the heater is reduced due to the voltage difference. Due to external fluctuation factors such as temperature differences, differences in room temperature and water temperature, variations in temperature detection, and differences in heat transfer due to differences in structure, the position at which the amount of electricity is reduced shifts significantly, affecting the cooking time and causing overcooking. Uniform cooking cannot be achieved due to insufficient boiling time.

In addition, due to the external fluctuation factors mentioned above, it is difficult to accurately determine the amount of cooked rice, and when the amount of cooked rice is large,
If the temperature is detected as medium, the power is switched to medium heat before the rice has sufficiently boiled, and as a result, the temperature of the rice rises unevenly, resulting in uneven cooking.

On the other hand, if the amount of rice to be cooked is small, more electricity than necessary will be used to boil the rice, resulting in overcooking or
The water in the inner pot evaporates in a short period of time, resulting in insufficient boiling time and problems such as insufficient gelatinization of rice starch.

Furthermore, the cooking time varies depending on the amount of rice cooked.
This is inconvenient for the user.

Therefore, in view of the above-mentioned conventional circumstances, the present invention detects the weight of the main body or inner pot, determines the amount of rice to be cooked, and controls the heat by supplying the optimum power at the start of cooking, and also controls the heating power by controlling the heat due to external fluctuation factors. On the other hand, the present invention provides a rice cooker with further improved rice cooking performance by correcting the amount of power of the heater.

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

In Figures 1 and 2, 1 is the rice cooker main body;
Reference numeral 2 denotes an outer pot disposed within the main body 1; 3 an inner pot detachably housed within the outer pot; 4 a heater provided at the inner bottom of the outer pot 2; and 5 above the inner pot 3. The outer lid of the completed body is equipped with an inner lid 5a that closes the opening, 6 is a temperature sensor provided so as to be in close contact with the bottom wall of the inner pot 3, and 7 is a temperature sensor that is attached to the main body 1 so as to cover the lower opening of the main body 1.
A synthetic resin bottom frame 9 with a mounting plate 8 attached to the top surface is inserted into the inside of the bottom frame 7,
A synthetic resin bottom lid on which a microcomputer 18 (to be described later) is disposed, and the inner flange 7a of the bottom frame 7
A compression spring 10 is installed between the outer flange 9a of the bottom cover 9 and
is installed. Reference numeral 11 denotes an adjustment screw that connects the bottom frame 7 and the bottom cover 9, and also serves to adjust the facing distance between a pair of electrodes 17' and 17'', which will be described later.

Reference numeral 12 is an operation panel attached to the rice cooker main body 1 and has a power switch 13, a rice cooking switch 14, a double cooking selection switch 15, a display section 16 for displaying the rice cooking process, etc.; 17 is a weight sensor; It is composed of a pair of electrode plates 17' and 17'' attached to the frame 7 and the bottom cover 9, and the compression spring 10.

Reference numeral 19 denotes a bottom plate that closes the bottom opening of the bottom cover 9.

Next, the block diagram of the control circuit shown in FIG. 3 will be explained. 20 is a heater 4, a weight sensor 1
7 is the power source for driving the electrodes 17', 17'' and the microcomputer 18; 21 is the power source 20 and the heater 4;
When a signal is input to the gate terminal G, it turns on (conductivity), but when no signal is input, it turns off (cut off) and controls the energization rate to the heater 4. .

22 inputs the signal from the temperature sensor 6,
The target value and temperature sensor 6 stored in advance in the memory 18a of the microcomputer 18
A comparator 23 is an oscillation circuit that performs comparison with the measured value of , and a part of the capacitor constituting this oscillation circuit is replaced with an electrode capacitance. That is, the electrode capacitance changes as the distance between the pair of electrodes 17' and 17'' increases or decreases in proportion to the total weight of the inner pot 3 containing rice and water and the main body 1, and this change The amount of cooked rice is detected as a change in the oscillation state, and the input circuit 18c of the microcomputer 18
It is input as an input signal to. Note that 18b and 18d are microcomputers 18
24 is a warning and notification buzzer.

In the above configuration, when the inner pot 3 containing rice and water is installed in the main body 1, the main body 1 including the outer lid 5, the outer pot 2, the heater 4, the bottom frame 7, the mounting plate 8, the temperature detection sensor 6, etc. The weight W ₁ (hereinafter referred to as product weight),
The total weight W ₀ of the rice and the inner pot 3 containing water is added to the compression spring 10, and the compression spring 10 is the total weight
It is displaced in the compression direction in proportion to W ₀ .

At this time, one of the pair of electrode plates 17', 17'', which is attached to the bottom frame 7, moves downward by the displacement of the compression spring 10. The capacitance C changes in inverse proportion to the distance between the electrodes. (FIG. 5) That is, if the dielectric constant of air is ε, the area of the electrode plate is S, and the distance between the electrode plates is d, the capacitance C is expressed by the following equation.

C=εS/d...(ε and S are constants) This change in capacitance C is converted into a change in the oscillation frequency f of the oscillation circuit 23, but at this time, the oscillation frequency f is inversely proportional to the capacitance C. do. (Fig. 6) f∝1/C (However, the resistance R is constant.) Therefore, from both equations, the oscillation frequency f is proportional to the distance d between the electrodes. (Fig. 7) f∝d... On the other hand, it is clear from the characteristics of the compression spring 10 that the distance d between the electrodes and the weight W ₀ applied to the compression spring 10 are proportional. (Fig. 8) W ₀ ∝d... From the equation, it can be seen that the weight W ₀ and the oscillation frequency f have a linear linear relationship. (Figure 9) f∝W ₀ ... Furthermore, as shown in Figure 4, the weight of rice and water
Rice cooking amount determination weight W ₀ which is the sum of W ₂ and product weight W ₁
Since the amount of cooked rice V is proportional to (W ₀ ∝V), it can be concluded that the oscillation frequency f is proportional to the amount of cooked rice V, as shown in FIG.

f∝V... Also, due to the difference in weight detection structure, the weight detected by the weight sensor 17 consisting of the bottom frame 7, compression spring 10, electrode plates 17', 17'', bottom cover 9, etc. Instead of the sum of weight W ₂ and product weight W ₁ (W ₀ ), it is the weight of rice and water W ₂ plus inner pot 3, or the weight of rice, water, and inner pot 3 plus outer pot 2 and heater 4. It goes without saying that if the weight of rice and water (W ₂ ) is included, such as the weight of the temperature sensor 6, etc., then the above equation holds true regardless of the weight of any block.

As an example, the rice cooking process will be specifically explained below.

When the inner pot 3 containing rice and water is placed inside the main body 1 and the power switch 13 is turned on, the microcomputer 18 is powered up and starts operating.

When the change in the capacitance C of the weight sensor 17 is converted into a change in the oscillation frequency f via the oscillation circuit 23 and inputted to the input circuit 18c of the microcomputer 18, the microcomputer 18 receives the change programmed in the memory 18a in advance. Fixed time T
Count pulse signals of oscillation frequency f during
Based on data set in advance through experiments,
The amount of rice in the installed inner pot 3 is automatically determined from the above-mentioned count number.

In this manner, with the inner pot 3 installed, the amount of rice to be cooked can be determined before the heater 4 is energized.

Next, when the rice cooker switch 16 is pressed, power is started to be applied to the heater 4, and the rice and water in the inner pot 3 begin to be heated. Here, with reference to FIG. 11, the difference between the rice cooking method according to the conventional method of determining the amount of cooked rice based on the temperature rise gradient of a temperature sensor and the rice cooking method of the present invention will be explained.

In the conventional method, the amount of rice to be cooked is determined based on the temperature rise gradient after rice cooking starts, so it is impossible to control the heat power at the beginning of rice cooking. That is, in FIG. 11, _TR is the room temperature, and _t6 is the time required for the preset temperature Td to Te. In the conventional method, the amount of cooked rice is determined based on this _t6 . Therefore, it is not possible to control the heat until the temperature sensor reaches Te and determines the amount of rice to be cooked, and if the room temperature T _R exceeds Td, an error will occur in the data at _t6 , making it impossible to determine the amount of rice to be cooked. It has shortcomings.

However, according to the present invention, which determines the amount of cooked rice based on weight, regardless of the room temperature _TR at the time of starting rice cooking,
In addition, the amount of rice to be cooked can be determined at the same time as rice cooking starts, and the firepower can be controlled immediately to match the amount of rice being cooked. Problems such as rice that only the surface becomes gelatinized and the core remains can be solved. Further, unlike the conventional method, errors in determining the amount of rice to be cooked due to voltage fluctuations and variations in the wattage of the heater 4 are no longer caused.

As described above, according to the present invention, when rice cooking is started and the heating power is turned on high, the cooked rice in the inner pot 3 boils, as can be seen from the control example [ ] (5 cups) shown in FIG. If the temperature of the temperature sensor 6 at the point Ta is the temperature of the temperature sensor ₆ at the point
From the point that the temperature Ta has been reached, the heating can be reduced to medium heat.

When the water in the inner pot 3 runs out, the temperature at the bottom of the inner pot rises rapidly, and when the temperature sensor 6 reaches the temperature Tb, the heater 4 is turned off and the rice cooking mode is switched from rice cooking to uneven cooking.

Instead of this temperature sensor 6, the boiling point Ta of cooked rice is determined by changes in the output of the weight sensor 17, that is, changes in the amount of water evaporated from the inner pot 3 during rice cooking.
Needless to say, it is possible to detect the dry-up temperature point Tb. Various methods can be considered to detect the boiling point where the heat decreases from high heat to medium heat and the dry-up temperature point where the heat changes from cooking rice to unevenness due to changes in evaporation during rice cooking.One example is shown in FIG. 12.

As shown in FIG. 12, the characteristics of the amount of evaporation of water in the inner pot 3 are that the amount of evaporation is small up to point A, where the cooked rice in the inner pot 3 boils, and increases almost linearly after point A. After the dry-up point B, where the water in the cooked rice in the inner pot 3 is almost gone, the amount of evaporation decreases again.

Therefore, a certain amount (for example, 10 in Figure 12)
The point A of evaporation is regarded as the point at which the cooked rice in the inner pot 3 boils, and can be detected by the microcomputer 18 as the point at which the heat decreases from high to medium.

Also, if the point where water evaporates to the extent that the rice in the inner pot 3 has an appropriate moisture content is point B, where a certain amount (80 g in Figure 12) evaporates from point A, then Similarly to point A, microcomputer 1
8, the point B is considered to be almost the dry-up point, and at this point, the electricity supply to the heater 4 is stopped, and it becomes possible to switch from rice cooking to uneven cooking.

Here, the amount of evaporation of a certain amount of water at point A and point B is detected as standard data (however, the data value must be calculated as an experimental value by controlling the heater differently depending on the amount of rice cooked). ), but it goes without saying that the thermal power can also be controlled by other methods, such as using a change in the slope of the amount of evaporation (△W/△T).

According to the above, since the conventional temperature sensor 6 is unnecessary, the firepower control sensor only needs one weight sensor 17, and can be realized at a very low cost.

On the other hand, if the outer lid 5 is closed without the inner pot 3 installed in the main body 1 and the rice cooking switch 14 is pressed, no signal is output from the weight sensor 17, so the microcomputer 18 immediately detects that the inner pot 3 is It can detect that the inner pot 3 is not installed, and alert the user with the buzzer 24 that the inner pot 3 is not installed.
You can also take safety measures such as not accepting cooked rice.

Conventionally, separate parts such as a safety switch for detecting the inner pot 3 were required, but according to the present invention, the weight sensor 17 can also be used to detect the inner pot 3, making it possible to reduce costs. .

In addition, the inner pot 3 is installed in the main body 1, the outer lid 5 is closed,
The rice cooking switch 14 is pressed to start cooking rice, but if there is no rice or water in the inner pot 3, that is, if the rice is cooked empty, there is obviously no change in the signal from the weight sensor 17.

At this time, if it is programmed in advance in the memory 18a of the microcomputer 18 that if there is no change in the weight of the inner pot 3 for a certain period of time, it is empty cooking, then the inner pot 3 will be empty in a relatively short time (for example, about 3 minutes). It is possible to perform safety processing such as determining whether the rice is cooked and displaying the information to the user or turning off the heater 4.

Therefore, the weight sensor 17 can detect empty cooking without providing a separate temperature sensor.

Furthermore, in FIG. 12, since the area from point A to point B is a region where the amount of evaporation changes almost linearly, the slope of this straight line can be considered to be almost constant as long as the room temperature, amount of rice cooked, and power consumption are constant.

Therefore, even if the amount of rice to be cooked is detected by the weight sensor 17 and the rice cooking is started by controlling the heating power of the heater 4 according to the amount of rice stored in advance in the memory 18a of the microcomputer 18, the room temperature, heater wattage, and voltage will not change. It is conceivable that deviations from the original slope may occur due to external fluctuation factors such as.

Even in this case, since the amount of cooked rice has already been detected when the inner pot 3 is installed in the main body 1, the points A-B corresponding to each amount of cooked rice programmed in the memory 18a of the microcomputer 18 in advance Compare the slope data of the straight line with the gradient of the actual evaporation amount, and if the slope of the evaporation amount is large compared to the data, reduce the energization rate of the heater 4, and conversely, if it is small, increase the energization rate of the heater 4. By doing so, correction can be made to obtain an appropriate rice cooking curve.

As described above, the present invention detects the weight of the main body or the inner pot to determine the amount of rice to be cooked and controls the control circuit that controls the amount of electricity for the heater. It is possible to control the heat power, supply optimal power throughout the rice cooking process, and also correct the amount of power in response to external fluctuation factors, making it possible to further improve rice cooking performance.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a rice cooker showing an embodiment of the present invention, and FIG. 2 is a front view of an example of the operation panel thereof.
FIG. 3 is a block diagram showing an example of the control circuit, and FIG. 4 is an explanatory diagram showing the relationship between the amount of rice cooked and the weight.
Figures 5 to 10 are characteristic diagrams of each displacement constant of the weight sensor, Figure 11 is a rice cooking control diagram showing examples of rice cooking with a conventional rice cooker and a rice cooker according to the present invention, and Figure 12 is a rice cooking control diagram. It is a characteristic diagram of the evaporation amount of water. In the diagram, 1...Main body, 2...Outer pot, 3...Inner pot,
4... Heater, 6... Temperature sensor, 17... Weight sensor, 17', 17''... Electrode, 18... Microcomputer.

Claims (1)

[Claims] 1. A weight detection means for detecting the weight of the main body or the inner pot, and determining the amount of rice cooked based on the weight detected by the weight detection means, and controlling the heater to supply the amount of electricity corresponding to the determined amount of rice cooked. a control means for controlling energization; after the start of rice cooking, detecting the amount of water evaporation in the inner pot; and determining fluctuations in external fluctuation factors such as room temperature, voltage, and power consumption based on the detected amount of evaporation; A rice cooker comprising a correction means for correcting so as to supply an appropriate amount of electric power.