JPH0127726B2 - - Google Patents

Description

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

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

In other words, in the conventional method of detecting the amount of rice cooked by detecting the temperature rise rate of the inner pot and controlling the amount of power of the heater from the middle of heating up the rice, the difference in power of the heater due to the voltage difference even when the amount of rice cooked is the same. Due to fluctuation factors such as 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 power is reduced has shifted significantly, affecting the cooking time, resulting in overcooking or maintaining boiling. Uniform cooking cannot be achieved due to lack of time.

In addition, due to the above fluctuation factors, it is difficult to accurately detect the amount of cooked rice, and if the amount of cooked rice is detected at the temperature of a medium amount when a large amount of rice is being cooked, turn the heat from high to medium before the rice has sufficiently boiled. 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 insufficient gelatinization of rice starch.

Furthermore, the cooking time varies depending on the amount of rice to be cooked, which 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 heat by controlling the amount of water in the cooked rice. To provide a rice cooker which is inexpensive and whose rice cooking performance is further improved by detecting the dry-up point at which water disappears from the amount of evaporation of water in an inner pot.

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. an outer lid of the completed body including an inner lid 6 that closes the opening; 7 is a bottom frame made of synthetic resin that is press-fitted into the main body 1 so as to cover the lower opening of the main body 1; and a mounting plate 8 is attached; 9
is a bottom lid made of synthetic resin that is inserted inside the bottom frame 7 and has a microcomputer 18 (to be described later) disposed therebetween, and is located between the inside flange 7a of the bottom frame 7 and the outside flange 9a of the bottom lid 9. A compression spring 10 is provided. 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.

12 is an operation panel attached to the rice cooker 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; 7, a pair of electrode plates 17' and 17'' attached to 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, electrodes 17',
7″, power supply for driving the microcomputer 18;
21 is a triax connected in series to the power supply 20 and the heater 4; it is turned on when a signal is input from the output circuit 18d of the microcomputer 18 to its gate terminal G; it is turned off when no signal is input. The energization rate to the heater 4 is controlled.

23 is an oscillation circuit in which a part of the capacitor constituting this oscillation circuit is replaced with an electrode capacitance.

That is, 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 the electrode capacitance changes.
This amount of change is replaced as a change in the oscillation state, and is inputted to the input circuit 18c of the microcomputer 18 as an input signal. In addition, 1
8a and 18b are the memory and control circuit of the microcomputer 18, and 24 is a warning/notification buzzer.

In the above configuration, when the inner pot 3 containing rice and water is installed inside the rice cooker main body 1, the outer lid 5, the outer pot 2,
The weight W ₁ of the main body 1 including the heater 4, bottom frame 7, mounting plate 8, etc. (hereinafter referred to as product weight) and the total weight W ₀ of the inner pot 3 containing rice and water are added to the compression spring 10, The compression spring 10 is displaced in the compression direction in proportion to the total weight 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, so the static The capacitance C changes in inverse proportion to the distance between the electrodes. (Fig. 5) 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 inter-electrode distance d. (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), the conclusion is 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.
Weight of rice and water (W ₂ ), etc.
It goes without saying that if the weight of the block is included, the above equation holds true regardless of the weight of the block.

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

When the inner pot 3 containing rice and water is placed in 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.

With the inner pot 3 installed in this manner, the amount of rice to be cooked is 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 . For this reason, it is not possible to control the heat until the temperature sensor reaches Te and determines whether the rice is 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 being cooked. It has

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,
Moreover, the amount of rice to be cooked can be determined at the same time as the rice cooking starts, and the heat power can be controlled immediately in accordance with the amount of rice to be cooked.
For this reason, conventional problems such as rice boiling too quickly, especially when cooking a small amount of rice, resulting in insufficient water absorption time, and only the surface of the rice grains becoming gelatinized, resulting in rice with cores remaining, can be solved. Further, unlike the conventional method, errors in determining the amount of cooked rice do not occur due to voltage fluctuations or variations in heater wattage.

As described above, according to the present invention, when rice cooking is started and the heating power is turned on high, as in the control example [] (5 cups) and the control example [] (10 cups) shown in FIG. Let T _R be the temperature at which the rice in the inner pot 3 boils, then in either case, heating can be reduced to medium heat from the point at which temperature Ta is reached after _t1 .

When the water in the inner pot 3 runs out, the temperature at the bottom of the inner pot rises rapidly, and when it reaches the temperature Tb, the microcomputer 18 turns off the triator 21 and the heater 4, so that the rice is cooked unevenly. Change.

Here, the present invention detects the boiling point Ta and dry-up temperature point Tb of cooked rice based on a change in the output of the weight sensor 17, that is, a change in the amount of water evaporated from the inner pot 3 during rice cooking. Various methods can be used to detect the boiling point when the heat decreases from high to medium due to changes in evaporation during cooking, and the dry-up temperature point when the rice changes from cooking to unevenly.
An example is shown using Figure 2.

In other words, the characteristic of the amount of water evaporation in the inner pot 3 is the first
As shown in Figure 2, the rice in the inner pot 3 is boiling A.
The amount of evaporation is small up to this point, increases almost linearly after point A, and decreases again after point B, which is the dry-up point at which the water in the cooked rice in the inner pot 3 is almost gone.

Therefore, a certain amount (for example, 10 in Figure 12)
The microcomputer 18 regards the evaporated point A as the point at which the cooked rice in the inner pot 3 boils, and determines the point at which the heat is reduced from high heat to medium heat.
is stored in advance in the memory 18a of
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, the microcomputer 18
The above control is possible by storing in the memory 18a that the point B is regarded as almost the dry-up point, the triax 21 is turned off at this point, the power supply to the heater 4 is stopped, and rice cooking is switched from rice cooking to uneven cooking.

Note that here, the amount of evaporation of a certain amount of water at point A and point B is detected as reference 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).

As described above, the present invention detects the weight of the main body or inner pot, converts this into an electric signal to determine the amount of rice to be cooked, and controls the heating power from the start of rice cooking with the amount of power of the heater commensurate with the amount of rice to be cooked. Therefore, the rice cooking performance can be further improved regardless of the amount of rice cooked or the room temperature.

In addition, the amount of water evaporated in the inner pot is detected to detect the dry-up point where the water in the cooked rice disappears, and the rice is cooked unevenly, so there is no need for conventional parts such as temperature sensors. The structure can also be simplified and can be provided at low cost.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a rice cooker showing an embodiment of the present invention, FIG. 2 is a front view of an example of the operation panel section,
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 using a conventional rice cooker and a rice cooker according to the present invention;
Figure 2 is a characteristic diagram of the amount of water evaporated during rice cooking. In the diagram, 1...Main body, 2...Outer pot, 3...Inner pot,
4... Heater, 17... Weight sensor, 17',
17″... Electrode, 18... Microcomputer.

Claims (1)

[Claims] 1. A main body, an outer pot disposed within the main body, an inner pot removably housed within the outer pot, an outer lid that closes the opening of the inner pot, and a heater provided at the inner bottom of the outer pot. a weight detecting means for detecting the weight of the main body or the inner pot; a converting means for converting the weight detected by the weight detecting means into an electric signal; and an amount of rice to be cooked based on the electric signal input from the converting means. a control means for determining the amount of rice to be cooked and controlling the electric power of the heater according to the amount of rice to be cooked; A rice cooker comprising a switching means for switching from Karamurashi to Karamurashi.