JPH0143215B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronically controlled cooking device that detects the temperature of food by detecting infrared rays from the food and controls heating based on the detected temperature.

Generally, in this type of cooker, infrared rays from the food are periodically interrupted by a chopper, and the periodically interrupted infrared rays are detected by an infrared detector. Heating is then controlled by determining whether the temperature of the food has reached a desired temperature based on the output signal of the detector.

However, if the infrared rays of the chopper stop intermittent due to, for example, a motor failure, and the intermittent cycle becomes infinite and deviates from a predetermined value, the output signal of the infrared detector becomes undesirable. The disadvantage is that the temperature of the food cannot be detected, thus resulting in undesired cooking.

The present invention has been made in view of these points, and embodiments of the present invention will be described in detail below with reference to the drawings regarding a microwave oven.

In Fig. 1, 1 is the exterior of the microwave oven body;
2 is a heating chamber for storing the food 3; 4 is a magnetron that oscillates microwaves for heating the food 3; 5 is attached to the upper wall of the heating chamber 2;
a microwave blocking ring that allows infrared rays emitted from to pass through, but blocks microwaves from passing through, 6
2 is a chopper that rotates periodically by the drive of a synchronous motor 7 and periodically cuts off the infrared rays that have passed through the ring 5. The chopper has cut-off parts 6a, 6a, and 6a and open part 6
It consists of b, 6b, 6b. Here, when the motor 7 is connected to a commercial power supply with a frequency of 60 Hz (described later), it rotates at a rate of 300 times/minute, and at this time, the rate at which the infrared rays are intermittent is 15 times/second.

Reference numeral 8 denotes an infrared detector having a so-called pyroelectric effect that outputs a signal corresponding to the amount of change in incident infrared radiation, and the detector is made of, for example, lithium tantalate (LiTaO ₃ ) crystal. In such a case, the infrared rays from the food 3 and the infrared rays from the chopper 6 are alternately incident on the detector 8 at the same interval at a rate of 15 times/second due to the intermittent operation of the chopper 6. At this time, the amount of infrared rays incident on the detector 8 includes the infrared rays from the food 3 and the infrared rays from the chopper 6.
The detector 8 outputs a signal with a frequency of 15 Hz having an amplitude corresponding to the temperature difference between the food 3 and the chopper 6. Reference numeral 9 denotes a chopper temperature detection unit, that is, a diode, which is disposed near the chopper 6 to detect the temperature of the chopper 6 and outputs a DC signal according to the temperature of the chopper, and 10 denotes a light emitting diode 10a facing the chopper 6 via the chopper 6. and a phototransistor 10b, and is a signal generator, that is, a photointerrupter, which outputs a periodic signal related to the intermittent cycle of the chopper 6. More specifically, with the intermittent cycle of the chopper 6, the photo interrupter 10 is exposed to the open portions 6b, 6b, 6b of the chopper 6.
When the light emitting diode 10a is positioned periodically, the light from the light emitting diode 10a periodically reaches the phototransistor 10b, and at this time, the photointerrupter 10 outputs a periodic pulse.

FIG. 3 shows the circuit of the microwave oven. Reference numeral 11 denotes a filter amplifier that amplifies the output signal of the detector 8 and outputs only a signal having a frequency near the frequency of 15 Hz, and the output of this amplifier is as shown in Fig. 4a.
It is a sine wave as shown in . This output is of course food 3
It has an amplitude based on the temperature difference between the tipper 6 and the chopper 6, and its frequency is 15Hz. 12 is connected to the photo interrupter 10 via a Zener diode 13.
is a transistor to which the output of is applied. Here, if the cutoff parts 6a, 6a, 6a of the chopper 6 are located between the light emitting diode 10a of the photointerrupter 10 and the phototransistor 10b, the phototransistor 10b is not turned on, so the output of the photointerrupter 10, that is, the Zener diode The potential on the anode side of 13 becomes high level (0 potential). At this time, the Zener diode 13 is in the off state, and as a result, the transistor 12 does not turn on because no base current flows, and therefore the collector potential of the transistor 12 becomes a negative level corresponding to the negative potential of the terminal 14 -Vcc. . On the other hand, when the open portions 6b, 6b, 6b of the chopper 6 are located between the photointerrupters 10, the phototransistor 10b is turned on and the Zener diode 13 is turned on.
The anode side of is at a low level corresponding to the negative potential of the terminal 15 -Vcc. At this time, the Zener diode 13
is turned on and the transistor 12 is turned on, so the potential of the collector of the transistor 12 is at a high level (0
potential). That is, the photo interrupter 10 connects the interrupter to the openings 6b, 6 of the chopper 6.
b, 6b are located, the transistor 12 outputs a negative pulse as shown in FIG.
When a and 6a are located, a negative pulse as shown in FIG. 4c is output. In such a case, the number of pulses from the photo interrupter 10 and the transistor 12 is 15 ¹ / similar to the number of infrared interruptions by the chopper 6.
Seconds.

Reference numeral 16 denotes a rectifying section, ie, a field effect transistor (FET), which is normally on and turns off when a negative pulse is output from the transistor 12 based on the output of the photointerrupter 10. Here, when the FET is off, the filter amplifier 1
The AC output of No. 1 is a positive half cycle, and such a state occurs when the temperature of the food 3 is higher than the temperature of the chopper 6. Note that when the temperature of the food 3 is lower than the temperature of the chopper 6, the AC output of the filter amplifier 11 is in the negative half cycle when the FET 16 is off. At this time, the output of the filter amplifier 11 is 180 degrees out of phase with the signal shown in FIG. 4a, as shown in FIG. 4a'.

The FET 16 outputs a zero potential signal when it is on, and outputs the signal from the filter amplifier 11 shown in FIG. 4a only when it is off. That is, FET
The output of 16, as shown in FIG. 4d, is obtained by half-wave rectifying the signal shown in FIG. 4a. 17 is above
This detector detects the output of the FET 16, and when it receives the signal shown in FIG. 4d, it outputs a positive DC signal as shown in FIG. 4e. Reference numeral 18 denotes a first amplifier for amplifying the DC signal, and the output of this amplifier is of course a DC signal corresponding to the temperature difference between the food 3 and the chopper 6. A second amplifier 19 amplifies the output of the diode 9, and the output of this amplifier is a DC signal corresponding to the temperature of the chopper 6. Reference numeral 20 denotes a combiner for combining the outputs of the first and second amplifiers 18 and 19, which combines the outputs of the first and second amplifiers 18 and 19. A DC signal corresponding to the temperature of the food 3 is output by adding the DC signal corresponding to the temperature of the chopper 6 from the above.

If the temperature of the food 3 is lower than the temperature of the chopper 6, the FET 16 outputs a negative half cycle signal as shown in FIG. 4 d', and the detector 17 outputs a negative half cycle signal as shown in FIG. 4 e'. Outputs a negative DC signal. In this case, the synthesizer 20 subtracts such a negative signal from the signal corresponding to the temperature of the chopper 6, and thereby the synthesizer 20 outputs a signal corresponding to the temperature of the food 3.

A third amplifier 21 amplifies the output of the combiner 20. Reference numeral 22 denotes a control unit, that is, a microcomputer (hereinafter referred to as μCOM) that controls the microwave oven, and the μCOM has TEMP, TEMP ₁ ,
Storage areas for COUNT and COUNT ₁ are provided. 23 is a DA converter which converts the digital signal outputted from the μCOM into an analog signal.
That is, the μCOM 22 sequentially outputs digital signals corresponding to a plurality of temperatures, and at this time the DA converter 23 sequentially outputs analog signals corresponding to the temperatures. 24 sequentially compares the signal corresponding to the temperature of the food 3 from the third amplifier 21 and each signal corresponding to each temperature from the D-A converter 23, and outputs signal A when the two match. It is a comparator that
When μCOM 22 receives such signal A, it detects the current temperature of food 3 based on the digital signal output to DA converter 23 at this time.

25 is a keyboard equipped with a start key and numeric keys from 0 to 9 for setting the desired temperature, etc.; 26;
is a terminal for μCOM 22 to input a pulse from the transistor 12 that is output based on the output of the photo interrupter 10; 27 and 28 are first and second transistors turned on by signals B and C from μCOM 22, respectively; 29 is a buzzer that sounds when the first transistor 27 is turned on, 30 is a light emitting diode that emits light when the second transistor 28 is turned on, 31 is a commercial power supply with a frequency of 60 Hz, and 32 is a high DC voltage for applying high DC voltage to the magnetron 4. A circuit 33 is a triax, and when the triax is turned on, power from the power source 31 is supplied to the DC high voltage circuit 32 and the motor 7. 34 is a gate circuit that includes a phototransistor 35 that is turned on by light emission from the light emitting diode 30, and outputs a gate signal for turning on the triac 33 when the phototransistor is turned on.

Next, the operation of the microwave oven will be explained with reference to the flowchart of the μCOM 22 program shown in FIG.

Normally, a program cycles through steps S1 and S2 unless the start key is pressed (this process is called the first loop). In step S1, a key operation on the keyboard 25 is detected, and when a desired temperature is operated, the temperature is stored in the TEMP area in the μCOM 22. In step S2, it is determined whether or not the start key has been operated.

Therefore, when heating the food 3 until the temperature reaches 95° C., first operate keys 9 and 5 on the keyboard 25. Then, in step S1, a signal corresponding to 95°C is stored in the TEMP area. Subsequently, when the start key is operated, the key operation is also detected at step S1, but when the key is detected, the program exits the first loop and reaches step S3. In this step, a signal C is output, and therefore a high voltage is applied to the magnetron 4 to start microwave heating and the motor 7 to start rotating. The program then proceeds to step S4.
In this step, counting every second is started in the COUNT area. The program then reaches step S5. In this step, the contents of the COUNT area are
It is determined whether or not 10 seconds have been reached, but in this case, 10 seconds have not been reached since the count has just started, and therefore the program remains at step S5.
During this 10 seconds, the rotation of the motor 7 is in a steady state, that is, it rotates at a rate of 300 times/minute, and therefore the infrared rays emitted from the food 3 by the chopper 6 are interrupted at a rate of 15
times/second.

And after the above 10 seconds have passed, the program will
Leaves the S5 step and reaches the S6 step. In this step, the contents of the COUNT area are cleared to 0, and counting is therefore newly started from 0. The program then reaches step S7. In this step, it is determined whether the contents of the COUNT area have reached 2 seconds, but in this case, it has not reached 2 seconds since a new count has just started, so the program advances to step S8. . In this step
Counting of the number of pulses arriving at the terminal 26 from the transistor 12 is started in the COUNT ₁ region. The number of such pulses is 15 ₁ /sec depending on the number of interruptions of the infrared rays. The program then reaches step S9. In this step, digital signals corresponding to each temperature are sequentially output to the D-A converter 23,
Then, the digital signal when the signal A arrives, that is, the signal corresponding to the current temperature of the food 3, is stored in the TEMP ₁ area. The program then reaches step S10. In this step, the contents of each area of TEMP and TEMP ₁ are compared to determine whether or not the current temperature of food 3 has reached 95℃, but if it has not reached 95℃ in this case, the program will Return to S7 step. Then, when the temperature of food 3 is below 95℃, S7 ~ until the content of the COUNT area reaches 2 seconds
Each step of S10 is cycled through (this process is referred to as the second loop).

After 2 seconds have elapsed, the program exits the second loop at step S7 and reaches step S11.
In this step, counting in the COUNT ₁ area is stopped. The program then reaches step S12. In this step, the content of the COUNT ₁ area is 28.
It is judged whether or not it is between ~32, but in this case, 15 pulses arrive at the terminal 26 in 1 second, so 30 pulses are counted in 2 seconds in the COUNT ₁ area. Therefore the program then
Proceed to step S13. In this step, the contents of the COUNT area are cleared to 0, which causes the COUNT
Counting starts anew from 0 in the area. Furthermore, the contents of the COUNT ₁ area are cleared to 0.
Then, the program passes through steps S9 and S10 and returns to step S7, after which the temperature of food 3 is 95℃.
The second loop and the loop of steps S11 to S13 are alternately circulated until reaching the step (this process is referred to as the third loop).

When the temperature of food 3 reaches 95℃, the program exits the third loop at step S10 and returns to step S14.
Each step of S15 is reached. In step S14, the output of signal C is stopped, and therefore the microwave heating ends. Further, the motor 7 also stops rotating. At step S15, signal B is output for a few seconds and the buzzer 29
will sound to notify you that heating is complete. Further, the contents of the TEMP and TEMP ₁ areas are cleared, and if counting is in progress in the COUNT and COUNT ₁ areas, counting is stopped and the contents thereof are cleared. After that, the program returns to step S1 and enters the first loop.

During the heating process, if the infrared intermittent cycle of the chopper 6 changes due to a failure of the motor 7, or if the infrared intermittent cycle stops altogether and the intermittent cycle becomes infinite, the photointerrupter 10 and even the transistor 12 The number of pulses changes accordingly or becomes zero. This state is then detected in step S12 of the third loop. i.e. COUNT ₁
It is determined that the count content of the area is outside the range of 28 to 32. In such a case, the program exits the third loop at step S12 and reaches steps S14 and S15, heating is therefore stopped midway and this is notified.

In addition, when the motor 7 fails, the infrared intermittent cycle changes or becomes infinite, so the frequency of the output signal of the infrared detector 8 deviates significantly from 15 Hz, so even if the temperature of the food 3 rises, Regardless, almost no signal is output from the filter amplifier 11. From this, if the number of pulses from transistor 12 is not detected by μCOM 22, then
Heating continues even though the temperature of the food 3 has reached the predetermined temperature.

Furthermore, in the present invention, the photointerrupter 10 and its peripheral circuit (i.e., the transistor 1
By supplying a synchronizing pulse (ie, FIG. 4c) generated by the Zener diode 13 (2, Zener diode 13, etc.) to the FET 16, the output signal of the infrared detector 8 is rectified, and the temperature is detected. For this reason, Chiyotupa 6
Even if the infrared detector 8 operates normally and the output signal of the infrared detector 8 is normal, if the synchronization pulse fluctuates or stops generating due to a failure of the photointerrupter 10 or its peripheral circuit, the output signal of the infrared detector 8 may not be correct. Since the current cannot be rectified, correct temperature detection is impossible, and therefore, undesired cooking is performed.

However, in the present invention, the synchronization pulse is also used as a periodic pulse in a configuration in which a periodic pulse corresponding to the intermittent period of the chopper 6 is generated, the period is detected, and heating cooking is stopped in case of an abnormality.
It is also possible to detect an abnormality in the synchronization pulse due to a failure in the photo interrupter 10 or its peripheral circuits.

In this point, the synchronization pulse supplied to FET16,
If periodic pulses corresponding to the intermittent period of the chopper 6 are generated individually, the period of the synchronous pulse is not detected, so correct temperature detection becomes impossible due to fluctuations in the synchronous pulse, resulting in undesired cooking. will be done.

As is clear from the above description, according to the present invention, there is provided a heating chamber for storing food, a heating means for heating the food, a tipper that periodically intermittents infrared rays emitted from the food, and an intermittent of the tipper. A signal generation section that directly detects the operating state and outputs a periodic signal according to the intermittent operation; an infrared detection section that detects the infrared rays interrupted by the chopper; A rectifying section that rectifies the signal from the infrared detection section, a tipper temperature detection section that detects the temperature of the upper tipper, a combining section that combines the signal from the tipper temperature detection section and the signal from the rectifying section, and the combining section. a control section that controls driving of the heating means based on a signal from the signal generator, the control section detecting the output signal of the signal generating section and controlling the driving of the heating means when the period of the signal is other than a predetermined value. Since the chopper stops, for example, even if the motor that drives the chopper breaks down, undesired heating will not be performed. Moreover, since the signal generation section used for rectifying the signal from the infrared detection section is also used as described above for determining such a failure by the control section, the cost increase can be suppressed accordingly. Further, due to such dual use, an abnormal periodic signal will not be supplied to the rectifying section due to a failure of the signal generating section, and undesired heating can be reliably prevented.

[Brief explanation of drawings]

The figures show a microwave oven according to an embodiment of the present invention, Fig. 1 is a sectional view, Fig. 2 is a plan view of the chopper, Fig. 3 is a circuit diagram, Fig. 4 is a waveform diagram of the main part of the circuit in Fig. 3, and Fig. Figure 5 is a flowchart of the microcomputer program. 2...Heating chamber, 4...Magnetron, 6...Chiyotsupa, 8...Infrared detector, 10...Photo interrupter, 22...Microcomputer.

Claims (1)

[Claims] 1. A heating chamber for storing food, a heating means for heating the food, a tipper that periodically intermittents infrared rays emitted from the food, and a device that directly detects the intermittent operation state of the tipper and responds to the intermittent operation. a signal generating section that outputs a periodic signal; an infrared detecting section that detects the infrared rays interrupted by the chopper; a rectifying section that rectifies the signal from the infrared detecting section based on the periodic signal from the signal generating section; A tipper temperature detection section that detects the temperature of the tipper, a synthesis section that combines the signal from the tipper temperature detection section and a signal from the rectification section, and controls the driving of the heating means based on the signal from the synthesis section. An electronically controlled cooking appliance, comprising a control section that detects an output signal of the signal generation section and stops driving of the heating means when the period of the signal is other than a predetermined value.