JPH0127725B2 - - 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 the heater.

The temperature rise characteristics of rice during cooking in this type of rice cooker vary depending on the amount of rice cooked and the amount of electricity used by the heater.
It is not uniform and there are large differences in parts. In particular, there is a large difference in the time it takes for rice to boil when cooking a small amount of rice and when cooking a large amount of rice even when using the same amount of electricity, which affects 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 power is reduced will shift significantly, affecting the cooking time and causing overcooking or boiling. Even cooking cannot be achieved due to insufficient maintenance 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 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 optimal power at the start of rice cooking, thereby further improving rice cooking performance. The present invention provides an improved rice cooker.

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 bottom 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 inner 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.

12 is attached to the main body 1 and is a power switch 1
3. Rice cooking switch 14, 2-degree cooking selection switch 1
5 and an operation panel each having a display section 16 for displaying the rice cooking process, and 17 a weight sensor;
It is composed of a pair of electrode plates 17' and 17'' attached to the bottom 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, electrodes 17',
7'' and a power supply for driving the microcomputer 18, and 21 is a triax connected in series with the power supply 20 and the heater 4. When a signal is input to its gate terminal G, it turns on (conducts), but when no signal is input, it is turned on (conducting). If not, it is turned off (cut off) and the energization rate to the heater 4 is controlled.

22 is a memory 18a of a microcomputer 18 which receives the signal from the temperature sensor 6 and will be described later.
a comparator that compares a target value stored in advance with the measured value of the temperature sensor 16;
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 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 is input as an input signal to the input circuit 18c of the microcomputer 18. 18b and 18d are the control circuit and output circuit of the microcomputer 18, and 24 is a warning signal. It is also a buzzer for notification.

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

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), 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 rice cooker 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., 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, as can be seen from the control example [] (5 cups) shown in Fig. 11,
Temperature sensor 6 at the boiling point of rice in the inner pot 3
Assuming that the temperature of is Ta, the heating can be reduced to medium heat after t ₁ has elapsed and the temperature sensor 6 reaches the temperature Ta.

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.

Also, the inner pot 3 is placed inside the main body 1, the outer lid 5 is closed, and the rice cooking switch 14 is pressed to start rice cooking, but if there is no rice and water in the inner pot 3, that is, it is empty cooking. In this case, there is clearly no change in the signal from the weight sensor 17.

At this time, if the processing information indicating that if there is no change in the weight of the inner pot 3 for a certain period of time is empty cooking is programmed in the memory 18a of the microcomputer 18 in advance, it can be done in a relatively short time (for example, about 3 minutes). It is judged as empty cooking and a buzzer 24 is sent to the user.
It becomes possible to carry out safety processing such as giving a notification or turning off the heater 4.

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

As described above, according to the present invention, the amount of rice to be cooked is determined by detecting the weight of the main body or the inner pot, and the heater is energized so that a preset amount of electricity is supplied corresponding to the determined amount of cooked rice. Since it is controlled, it is possible to control the heating power by supplying the optimum amount of electric power commensurate with the amount of rice to be cooked from the start of rice cooking, and the rice cooking performance can be further improved. In particular, since the present invention comprises a non-contact capacitive weight detection means, it is less likely to fail, has a long life, and can accurately detect the amount of cooked rice.

In addition, empty cooking is automatically detected by detecting changes in the weight of the main body or inner pot after rice cooking starts, so there is no need to install a separate temperature sensor to detect empty cooking as in the past, and the number of parts can be reduced. It has the effect of being able to reduce costs and provide products 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.
5 to 10 are characteristic diagrams of each displacement constant of the weight sensor, and FIG. 11 is a rice cooking control diagram showing an example of rice cooking using a conventional rice cooker and a rice cooker according to the present invention. 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)

[Scope of Claims] 1. A main body, an outer pot disposed within the main body, an inner pot removably housed in the outer pot, an outer lid that closes an opening of the inner pot, and the outer pot. A heater provided at the inner bottom, a compression spring provided between the bottom frame and the bottom cover that are integrated with the main body, and which expands and contracts according to the weight of the main body, and a compression spring that expands and contracts according to the weight of the main body, and a A rice cooker comprising a weight detecting means for detecting weight, and controlling the amount of cooked rice by determining the amount of cooked rice based on the weight detected by the weight detecting means and supplying a preset amount of electric power to the heater, the rice cooker comprising: The detection means is constructed of a capacitance type consisting of a pair of electrode plates attached to the bottom frame and the bottom cover, respectively, and further detects empty cooking of the inner pot from a change in the capacitance of the weight detection means. A rice cooker characterized by being equipped with an empty cooking detection means that cuts off power supplied to the heater.