JPS6029937Y2 - Electric rice cooker dry cooking prevention device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a device for preventing dry cooking in an electric rice cooker that controls the rice cooking operation by detecting the temperature of the pot using a temperature-sensitive electric element such as a thermistor. .

Conventionally, electric rice cookers are equipped with temperature detection means for controlling the rice cooking operation, that is, for automatically turning off the electric heater when the rice is cooked.

Conventionally, there are two methods for this temperature detection means, the first of which is a switching type temperature detection method using a combination of magnetic shunt steel or bimetal and a micro switch.
The second method is a non-switching temperature detection method in which the temperature of the pot is detected by a thermistor and the detection signal is processed by an electronic circuit.

Of both of these, the switching type temperature detection type is essentially a lever switch mechanism, and the mechanism is designed so that the power cannot be turned on when no pot is housed in the main body. Therefore, there is an advantage that empty cooking due to erroneous operation can be prevented.

However, since it is not possible to adjust the operating temperature, there is a drawback that it is not possible to perform ``cooking porridge 1'' and ``burning dates.''

On the other hand, the non-switching temperature detection method has a structure in which the temperature detection signal is processed by an electronic circuit, so it has the advantage of being able to easily perform various types of rice cooking operations such as cooking porridge and adding burnt dates. There is.

However, on the other hand, since the power can be turned on at any time, there is a drawback that it is possible to accidentally start dry cooking.

The present invention was made to address the above drawbacks,
The purpose of this system is to detect the temperature using a temperature-sensitive electric element such as a thermistor, and control the rice cooking operation based on the temperature detection hand signal.The purpose is to reliably prevent so-called dry cooking by using electrical means, which has a simpler configuration than mechanical means. The purpose of the present invention is to provide a device for preventing dry cooking of an electric rice cooker.

An embodiment of the present invention will be described below based on the drawings. First, in FIG. 1, 1 is a substantially cylindrical outer case, 2 is a bottom frame fitted to the lower part of the outer case 1, and 3 is an outer case. 4 is a heat insulating material placed between the outer case 1 and the inner case 3; 5 is a pot that is detachably attached to the inner case 3; 6 is the inner case of the inner case 3; An electric heater for cooking rice is arranged at the bottom, 7 is an electric heater for keeping warm wrapped around the upper periphery of the inner case 3, 8 is a lid rotatably supported on the outer case 1, and 9 is the lid 8 This is a locking device that keeps the device locked.

Reference numeral 10 denotes a heat transfer case that is provided in pressure contact with the outer bottom of the pot 5 by a spring 10a, and a non-switching temperature-sensitive electric element, such as a thermistor 11 with negative characteristics, is disposed inside the case for heat transfer. .

Further, 12 is a lever whose base end is rotatably supported by a pin 13 and whose other end is connected to the heat transfer case 10. Therefore, this lever 12 is used to attach and detach the pot 5. It rotates following the corresponding vertical movement of the heat transfer case 10.

Reference numeral 14 denotes a microswitch whose actuator 14a is arranged so as to face the base end side of the lever 12;
It is configured to close or open depending on the rotation of the lever 12 depending on whether the lever 12 is attached or not attached.

Next, the electrical configuration will be explained according to FIGS. 2 and 3.

First, in FIG. 2 showing the outline of an electric circuit, reference numeral 15 denotes a bidirectional three-terminal thyristor (hereinafter simply referred to as a thyristor) which is a switching means, and this and the electric heater 6 for rice cooking.
A series circuit with the plug 16 is connected to receive power from the plug 16.

In addition, the electric heater 7 for heat retention is connected in parallel with the thyristor 15.
are connected, and therefore, when the thyristor 15 is turned off, the rice cooking electric heater 6 and the warming electric heater 7 are energized in series, and each generates heat with a relatively small heat generation capacity to perform a warming operation. When the thyristor 15 is turned on, only the rice cooking electric heater 6 is energized and generates heat with a relatively large heat generation capacity to perform the rice cooking operation.

Reference numeral 17 denotes a power switch, which cuts off the power supply to the rice cooking electric heater 6 and the heat-retaining electric heater 7 when receiving a dry cooking signal, which will be described later.

18 is a control device configured by a microcomputer, which controls the thyristor 15. The power supply opening/closing unit 17 is controlled in a predetermined manner to execute rice cooking operation and warming operation.

Next, matters related to dry cooking prevention, which is the direct target of the present invention, will be explained in detail.

FIG. 3 shows the temperature detection section 19 and the dry cooking determination section 20 regarding the temperature of the pot 5.

In particular, the dry cooking determination section 20 can be achieved by a program of a microcomputer within the control device 18, but for convenience of explanation, FIG. 3 shows it in a block form as a combination of electronic functional circuits.

Now, in the temperature detecting section 19, the detection signal S1, which is determined by the change in the internal resistance of the thermistor 11, becomes the temperature detection signal Sla that is digitized by the AD converter 21.

This temperature detection section Sla is a signal obtained by detecting the temperature of the pot 5 or the heat transfer case 10 by the thermistor 11, and serves as temperature information necessary to control the rice cooking operation described above.

In the present invention, this temperature detection signal Sla is also used as temperature information for determining dry cooking.

That is, in the temperature detection section 19, 22 is a comparator, which is used to detect the reference temperature output from the reference data output section 23, for example, 14.
The reference temperature value signal S2, which is a digital value corresponding to 0°C, is constantly compared with the temperature detection signal Sla, and when the detected temperature exceeds 140°C, the comparison signal S with a logical value of "1" is generated.
Outputs 3.

On the other hand, in the dry cooking determination section 20, 24 is a reset circuit section that outputs a reset pulse P1 with a logical value of "1" in synchronization with the power being turned on and the rice cooking operation being started. R-S flip-flop 25.26 and counter 27. Timer counter 28
It is designed to be input to each reset terminal R of.

Further, 29 is an oscillator that outputs a clock pulse P2 with a period of IHz, and the clock pulse P2 is sent to the counter 27,
It is input to each of the 28 count input terminals C.

Then, the count content of the counter 27 is, for example, "30".
When the R-
triggers the S flip-flop 25 and also triggers the counter 27
outputs one pulse to trigger the R-S flip-flop 26 when the count reaches, for example, r300J, in other words, when a predetermined time of 5 minutes has elapsed after the start of the rice cooking operation.

30 is a gate section consisting of an AND circuit, each of whose input terminals are connected to the output terminal of the temperature detection section 19, the Q output terminal of the R-S flip-flop 25, and the Q output terminal of the R-S flip-flop 26. It is configured to receive a signal and provide an output from its output terminal to the control device 18 via an OR circuit 31.

Incidentally, the other input terminal of the OR circuit 31 is provided with a pot non-installation detection signal S4 having a logical value of "1" which is output in response to the opening of the microswitch 14.

Therefore, the dry cooking determination section 20 operates as described below.

That is, the R-S flip-flops 25 and 26 and the counters 27 and 28 are reset by the reset pulse P1 that is output in synchronization with the start of the rice cooking operation.
-S flip-flop 26 outputs a logic "1" signal from its Q output terminal, and R-S flip-flop 25 outputs a logic "0" signal from its Q output terminal.

Therefore, at the start of the rice cooking operation, the output from the temperature detection section 19, that is, the comparison signal S3, does not pass through the gate section 30.

After that, the counter 27 triggers the R-S flip-flop 25 after 3 hours have elapsed, so that a logic value "1" signal is output from the Q output terminal of the R-S flip-flop 25, and the gate section 30 is Passage of the comparison signal S3 from the detection section 19 is now allowed.

By the way, if the rice cooking operation is started without storing rice or water in the pot 5, that is, if the so-called dry cooking state occurs, the temperature of the pot 5 will drop to 140°C within 5 minutes after the rice cooking operation starts.
When the temperature of the pot 5 exceeds 140° C., the temperature detection section 19 outputs a comparison signal S3.

Therefore, the dry heating signal S5 with the logical value rlJ is output from the gate section 30, and the control device 18 that receives this gives the dry heating signal S5 to the power supply opening/closing section 17 to supply power to each electric heater 6゜7. cut off.

On the other hand, if rice and water are stored in the pot 5 and a through rice cooking operation is performed, the temperature of the pot 5 will not exceed 140°C within 5 minutes after starting the rice cooking operation. , and when 5 minutes have passed after the start of the rice cooking operation, the counter 27 is set to R.
- triggers the S flip-flop 26 to output its output terminal Q.
Since the logical value rOJ signal is outputted from the gate section 30, the empty cooking signal S5 is not outputted from the gate section 30, and therefore, the rice cooking operation is executed without interruption.

Incidentally, when the rice cooking operation is started without the pot 5 being attached, the pot not being attached detection signal S4 is applied from the control device 18 to the power switch section 17, and the power to each electric heater 6.7 is cut off.

In this way, even if the temperature of the pot 5 is detected by a temperature-sensitive electric element such as the thermistor 11, which is a non-heating type temperature detection means, and the rice cooking operation is controlled accordingly, so-called dry cooking can be reliably prevented. be.

Furthermore, since the prevention of dry cooking is remotely achieved by electrically processing the temperature detection signal, the structure is extremely simple compared to systems that are remotely related to mechanical means.
Furthermore, the electrical configuration is also simple because the temperature detection signal for controlling the rice cooking operation can also be used as a signal for determining if the rice is cooked dry.

In addition, the dry cooking determination unit 20 is configured to stop the dry cooking determination operation by blocking the output of the dry cooking signal S5 until a predetermined short time of 30 seconds has elapsed after the start of the rice cooking operation. When a new rice cooking operation is started immediately after the rice cooking operation is once completed, there is no possibility that the empty cooking signal S5 will be outputted by mistake.

Incidentally, in the above embodiment, when the dry cooking signal S5 is output, the dry cooking alarm may be emitted by a buzzer or the like.

As described above, the present invention is capable of reliably preventing so-called dry cooking and detecting dry cooking even in a device in which the temperature of the pot is detected by a temperature-sensitive electric element such as a thermistor, and the rice cooking operation is controlled based on the temperature detection signal. Since they are distantly related to each other by electrical signal processing means, there is no need for structural complexity.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; Fig. 1 is a partially sectional front view, Fig. 2 is an overall electrical configuration diagram, and Fig. 3 is an electrical configuration of main parts. It is a block diagram. In the figure, 5 is a pot, 6 is an electric heater for rice cooking, 11 is a thermistor (temperature sensing electric element), 19 is a temperature detection section, 20 is a dry cooking judgment section, 28 is a counter (timer), and S5 is a dry cooking signal. be.

Claims (1)

[Scope of utility model registration request] In an electric rice cooker that controls the rice cooking operation by detecting the temperature of the pot using a temperature-sensitive electric element such as a thermistor, there is a timer that executes a timer operation for a certain period of time after the rice cooking operation starts, and a timer that executes a timer operation for a certain period of time after the rice cooking operation starts, and a timer that executes a timer operation for a certain period of time after the rice cooking operation starts. In between, a dry cooking determination section is provided which determines this and outputs a dry cooking signal when the temperature detected by the temperature sensitive electric element rises to a reference temperature, and is configured to cut off the power supply in response to the dry cooking signal. A dry cooking prevention device for an electric rice cooker, which is characterized by: