JPH02191414A - Rice cooker - Google Patents

Abstract

PURPOSE:To accurately control the completion time of rice cooking by a method wherein the temperature information detected by a temperature sensible element are converted to digital signals, and an electric heater is controlled to specified control states in two or more time steps according to the digital signals. CONSTITUTION:When a switch is operated, a microcomputer 15 issues a gate signal to a two-way three-contact thyristor 9. Thereby, an electric heater 8 starts rice-cooking at a medium calorific capacity. A thermistor 10 detects voltage V corresponding to the changes in the temperature of a pot. The voltage V are sent to an analog-to-digital converting circuit 13, and the computer 15 detects the digital signals as a function of time and detects the temperatures of the pot. When the heat exchange of rice and water is vigorously carried out in the pot and the temperature of the pot rapidly rises, the electric heater 8 carries out rice-cooking at a high calorific capacity. When it reaches dry-up state, the electric heater 8 is operated at a medium or low calorific capacity. When the temperature reaches a set temperature for the dry-up state, the electric heater 8 is interrupted. Thereby, the completion time of rice cooking is accurately controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to a rice cooker that heats a pot using an electric heater to perform a rice cooking operation.

(Prior art) In conventional rice cookers, in order to control the end time of rice cooking,
Mechanical switching devices that combine magnetic shunt steel, permanent magnets, operating levers, microswitches, etc. as temperature detection elements are widely used, and such switching devices are generally constructed as follows.

In other words, a heat-sensitive cap is provided that presses against the bottom of the outer surface of the rice-cooking pot when the rice-cooking pot is installed in a predetermined position. The temperature of the rice to be cooked is detected as the temperature of the pot using the magnetic shunt steel.

At this time, the Curie point temperature of the magnetic shunt steel is selected to be approximately equal to the cooking temperature of rice (generally around 130° C.). Further, a permanent magnet is attached to the tip of an operating lever that is rotatable between three positions, and this operating lever attracts the permanent magnet to the magnetic shunt steel in response to an external operation. The permanent magnet is rotated to the first position, and is rotated back to the second position in response to the release of the permanent magnet as the magnetic shunt steel loses its magnetism. The microswitch is turned on when the control lever is rotated to the first position and turned off when the control lever is rotated to the second position. It is configured to be formed.

Therefore, in a rice cooker equipped with the switch device configured as described above, when the operating lever is rotated to the first position,
The rotating state is maintained by the attraction between the permanent magnet and the magnetic shunt steel, and the microswitch is turned on, in response to which the rice cooking operation by the electric heater is started. After this, as the rice cooking continues, the inside of the pot exhibits a so-called dry-up state, and the temperature (detected temperature) of the magnetic shunt steel becomes higher than the rice cooking temperature and its magnetism disappears, causing the permanent magnet to be attracted. Upon release, the operating lever is rotated back to the second position and the microswitch is turned off, so that the electric heater is cut off and the rice cooking operation is completed.

(Problem to be Solved by the Invention) Thermal conductivity between the bottom of the outer surface of the pot and the heat-sensitive cap and between the heat-sensitive cap and the magnetic shunt steel depends on the processing accuracy and assembly accuracy of each of these parts. Since there is some variation due to various factors, it is inevitable that an error will occur between the actual temperature of the pot and the temperature detected by the magnetic shunt steel. On the other hand, since the Curie point temperature of magnetic shunt steel is constant, the temperature of the pot when the magnetic shunt steel loses its magnetism, that is, the temperature of the pot when the rice cooking operation is ended by the switch device, is the temperature of the pot when the rice cooking operation is terminated by the switch device. It will vary depending on the device. Moreover, since magnetic shunt steel has a heat capacity, it has poor response to sudden temperature increases such as dry-up. As a result, in the conventional rice cooker, there is a problem in that the timing at which the rice cooking operation ends is inaccurately controlled.

In addition, in a rice cooker, delicious rice can be cooked by changing the heat generation capacity of the air heater to 7 degrees during the rice cooking operation, such as 7 medium heat, 1 high heat, 1 low heat, but with the above conventional configuration. It is impossible to perform such control at multiple points in time by temperature detection.

Furthermore, since conventional rice cookers require mechanical contacts such as microswitches to detect the temperature of the pot, they also have problems such as shortened service life due to wear of the contacts.

The present invention has been made in view of the above-mentioned 11f circumstances, and its purpose is to make it possible to accurately control the timing at which the rice cooking operation ends, and to control the electric heater at multiple points in time. It is an object of the present invention to provide a rice cooker that exhibits effects such as being able to improve reliability over its lifespan.

[Structure of the Invention] (Means for Solving the Problems) The rice cooker of the present invention is provided with a temperature sensing element that converts temperature information of a pot heated by an electric heater into an electric signal, a converting means for converting an electric signal corresponding to the temperature information into a digital signal, and a control section for controlling the electric heater in a predetermined control mode at a plurality of points in time according to the temperature information supplied by the converting means. It is characterized by its composition.

(Function) According to the rice cooker of the present invention, temperature information from the temperature sensing element is processed as an electrical signal, and based on this electrical signal, the electric heater is controlled by the control section in a predetermined control mode at a plurality of points in time. Therefore, a conventional mechanical switch device is not required.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

First, the electrical configuration will be described according to FIG. 1 and 2 are power terminals connected to an AC power source (not shown), one power terminal 1 is connected to a bus 3, the other power terminal 2 is connected to a bus 4, and the bus 3 is connected to a rectifier diode 5. and is connected to a bus bar 7 via a voltage dividing resistor 6. 8 is an electric heater that heats a pot (not shown);
It is connected between the busbars 3.4 via a bidirectional three-terminal thyristor 9 in series. Reference numeral 10 denotes a thermistor, which is a temperature sensing element, arranged to sense the temperature of, for example, the bottom of the outer surface of the pot (not shown), and this is connected between bus bars 7 and 4 through a resistor 11 in series. 12 is a constant voltage diode connected between the busbars 7.4. 13 is the bus bar 7.
4 is an analog-to-digital conversion circuit serving as a conversion means, and its input terminals are connected to a resistor 11 and a thermistor 1.
The temperature detection unit 14 is connected to the common connection point of 0. Reference numeral 15 denotes a microcomputer serving as a control unit connected between the busbars 7 and 4. Its input terminal is connected to the output terminal of the analog-to-digital conversion circuit 13, and the output terminal is connected to the bidirectional three-way converter via a buffer circuit 16. The terminal is connected to the gate terminal of the thyristor 9.

Next, the operation of this embodiment will be explained with reference to the temperature characteristic diagram in FIG. 2, the voltage characteristic diagram in FIG. 3, and the flowchart in FIG. 4.

The AC power supply voltage between power supply terminals 1 and 2 is connected to the rectifier diode 5.
The voltage is rectified by the voltage dividing resistor 6, and the voltage is divided by the voltage dividing resistor 6 and applied between the busbars 7 and 4.

When the microcomputer 15 is started by operating a start switch (not shown), the microcomputer 15 is first set to "low heat generation capacity".
The gate signal is given to the bidirectional three-terminal thyristor 9 so that its conduction angle becomes intermediate. As a result, the electric heater 8 generates heat with a small heat generating capacity that is a predetermined heat generating capacity to heat the pot, and rice cooking starts at a so-called medium heat. At the beginning of rice cooking, the temperature of the pot is low as shown by the characteristic curve C shown in FIG. The detected voltage V, which is the inter-voltage voltage, increases as shown in FIG. In this case, the voltage V detected by the thermistor 10 due to a change in the temperature of the pot is given to the analog-to-digital conversion circuit 13, and the analog-to-digital conversion circuit 13 outputs a digital signal according to the change in the detected voltage V. Microcomputer 1
5 detects the temperature of the pot by taking this digital signal as a function of time, and performs the operations described below. That is, after the electric heater 8 starts heating the pot, when heat exchange with the rice water in the pot becomes relatively active, the temperature of the pot rapidly increases toward a predetermined temperature (for example, 100° C.). (shown as the first rising edge Ia in FIG. 2) (at time (1), the detection voltage V sharply drops accordingly. The microcomputer] 5 outputs "1" after the output step (A). The process moves to the judgment step (b) of ``Is it .a?'', here it is judged as rNOJ, and returns to the judgment step (b), but as mentioned above, when the temperature of the pot reaches the first rise 1. When it comes to indicate a, it is judged as rYESJ in the judgment step (b) and the process moves to the output step (11) of "setting to large heat generation capacity".Then, the microcomputer 15 determines that A gate signal is given to the bidirectional three-terminal thyristor 9 so that its conduction angle becomes large.As a result, the electric heater 8 comes to generate heat with a large heat generation capacity, so that rice is cooked with so-called high heat. The temperature of the pot becomes approximately constant at a predetermined temperature due to active heat exchange with the rice water.In this state, the detection voltage V also becomes approximately constant.After that, when the rice cooking is approximately completed, the temperature of the pot becomes approximately constant. When the temperature reaches the so-called dry-up state where the water in the pot disappears (time t2), the temperature of the pot starts to rise again rapidly (indicated by a second rise (b) in FIG. 2), and the detection voltage V The microcomputer 15 starts the output step (
After c), the process moves to judgment step (d) of ``(b?)'', here it is judged as ``NO'', and returns to judgment step (d), which is repeated. The rise of b
When it comes to show rYE in the judgment step (d)
It is determined to be SJ and the process moves to the output step (e) of "setting to medium or small heat generation capacity". In this output step (e), the microcomputer 15 gives a gate signal to the bidirectional three-terminal thyristor 9 so that its conduction angle becomes medium or small. Thereby, the electric heater 8 comes to generate heat with a medium or small heat generation capacity, and the pot is heated with a medium or low heat. After that, the microcomputer 15 moves to the judgment step (to) of "Is it the set temperature?", and initially judges it to be rNOJ and returns to the judgment step (to) repeatedly, but the temperature of the pot is in the dry-up state. When the set temperature (for example, 130°C) is reached (time t3)
In the determination step (g), it is determined that rYEsJ, and the process proceeds to the next output step (g) of "setting the heat generation capacity to zero". Then, the microcomputer 15 stops applying the gate signal to the bidirectional three-terminal thyristor 9 in this output step (g). As a result, the bidirectional three-terminal thyristor 9 becomes non-conductive, the electric heater 8 is cut off, and the rice cooking ends. As a result, the second
As shown in the figure, time t! A three-step predetermined control form: a first area A with previous medium heat; a second area B with high heat between times t1 and t2; and a third area C with medium or low heat after time t2. The rice will be cooked.

As described above, according to the embodiment, the thermistor 10 is provided which senses the temperature of the pot and detects it as an analog signal (detection voltage ■) which is an electrical signal, and the detection voltage V indicating the sensed temperature information of the thermistor 10 is converted into an analog-digital signal. It is converted into a digital signal by the conversion circuit 13 and sent to the microcomputer 15.
Since the rice cooking operation is controlled based on the temperature information provided by the microcomputer 15 as a digital signal, unlike conventional mechanical switch devices, it is possible to process parts such as heat-sensitive caps and magnetic shunt steel. There is no problem of an error occurring between the actual temperature of the pot and the temperature detected by the magnetic shunt steel due to variations in thermal conductivity due to accuracy and assembly precision, and there is no problem such as an error caused by the heat capacity of the magnetic shunt steel. Therefore, the temperature of the pot can be detected with good responsiveness and without variation, and the timing of completion of the rice cooking operation can be accurately controlled, eliminating problems such as burning rice. There isn't. Moreover, since the thermistor 10 is provided to detect the temperature information of the pot,
Unlike conventional mechanical contacts such as microswitches, there is no reduction in lifespan due to wear, and the reliability of lifespan can be improved.

In particular, in this embodiment, the rise in the temperature of the pot is detected by the temperature detection section 14 and the microcomputer 15, and the electric heater 8 is controlled in a predetermined control mode at a plurality of points in time. Specifically, at the beginning of rice cooking, the microcomputer 15 causes the electric heater 8 to generate heat with a small heat generating capacity to cook rice over medium heat, and when the first rise signal a is detected, the microcomputer 1
5 causes the electric heater 8 to generate heat with a large heat generating capacity to cook rice over high heat, and then when the rising edge b of node 2 is detected, the microcomputer 15 causes the electric heater 8 to generate heat with a medium or small heat generating capacity to cook rice over medium heat. Alternatively, the rice is cooked over low heat, and therefore, the first area A
The rice can be cooked in a three-stage control mode consisting of the second region B and the third region C, and delicious rice can be cooked.

In the above embodiment, the first rising shear a of the pot temperature is detected and the heat generating capacity of the electric heater 8 is switched so that the temperature of the pot changes from the first region A to the second region B. However, when switching from the first region A to the second region B, the absolute value of the temperature of the pot is detected and, for example, the temperature of the pot is determined to be a predetermined value (
For example, even if it is carried out when the temperature reaches 60° C., it can be sufficiently put into practical use.

In addition, the present invention is not limited to the embodiments shown in the drawings as described above, and it goes without saying that the present invention can be implemented with appropriate modifications within the scope of the gist.

[Effects of the Invention] As explained above, the rice cooker of the present invention includes a plurality of electric heaters that detect temperature information of the pot as an electric signal using a temperature sensing element and heat the pot by a control unit based on this electric signal. Since the control mode is set to a predetermined control mode at the point of This has excellent effects such as improving reliability.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is an electrical configuration diagram, FIG. 2 is a temperature characteristic diagram, FIG. 3 is a voltage characteristic diagram, and FIG. 4 is a flow chart. In the drawings, 8 is an electric heater, 10 is a thermistor (temperature sensing element), 3 is an analog-to-digital converter circuit, and 5 is a microcomputer (control unit).

Claims (1)

[Claims] 1. A pot heated by an electric heater, a thermosensor that converts temperature information of the pot into an electrical signal, and a conversion means that converts the electrical signal corresponding to the temperature information detected by the thermosensor into a digital signal. and a control section that controls the electric heater in a predetermined control mode at a plurality of points in time according to the temperature information supplied by the conversion means.