JPH0368303B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to automatic cooking detection of a cooking appliance having an infrared sensor, and particularly relates to the detection cycle of the sensor.

Conventional configurations and their problems Microwave ovens equipped with pyroelectric sensors have been put into practical use as cooking appliances with infrared sensors. This sensor utilizes the phenomenon that when light hits a pyroelectric element, charges collect on its surface. Since this charge quickly saturates and disappears, a rotating shutter mechanism called a chopper is provided to interrupt the light.
It was customary to rotate the shutter at a speed of about 10 revolutions per second and alternately measure the radiation from both the shutter surface and the heat source. This amount of charge (that is, voltage) is then passed through a transistor with high input impedance such as an FET transistor, and the voltage is amplified by an amplifier circuit installed at the subsequent stage.
Take it out as a DC voltage and input it to the A/D converter,
Input the output of the A/D converter to the microcomputer to know the state of the heat source (heated object) at that time.
The idea was to control the output.

However, in this method, the output signal is small, the amplification circuit is complicated, and it is necessary to add several adjustment functions such as volume to the circuit, making it expensive. Since the original voltage was weak, it had the disadvantage of being susceptible to noise. On the other hand, there are other infrared sensors that use surface acoustic waves. This sensor is an infrared sensor that utilizes the fact that the speed of sound traveling on a piezoelectric single crystal of lithium niobate (LiNbO ₃ ) changes as the surface temperature changes, and has the following characteristics.

(1) Using the element itself as a delay element, the phase conditions,
By simply adjusting the amplitude conditions, an oscillation circuit can be easily constructed and the amount of detected infrared rays can be extracted as a frequency. Therefore, the sensor circuit can be created with a simple electric circuit configuration.

(2) Temperature measurement detects the rise in temperature of the element, so there is no need for a high-speed chopper mechanism like when using a pyroelectric element. A gentle movement with a cycle of about 5 seconds is sufficient.

However, the temperature T (〓) of the heat source and the radiant energy E are determined by E = σT ⁴ (σ is a constant, Stephan Boltzmann's law), so when the temperature of the heat source increases, the radiant energy increases by the fourth power, and accordingly. As a result, the output frequency will also increase dramatically. It is not desirable for the frequency to increase too much due to constraints on the output frequency counting method or control method. Therefore, when the sensor detects a pulse of a certain level or higher, it is conceivable to shorten the shutter cycle to suppress the infrared energy incident on the sensor and keep the detection frequency low. An object of the present invention is to control the opening/closing period of the shutter stepwise as described above to regulate the upper limit of incident energy, thereby keeping the output frequency below a certain level and accurately measuring food temperature.

Purpose of the Invention The present invention solves the above-mentioned conventional drawbacks, and makes it possible to adjust the amount of infrared radiation incident on the sensor by changing the opening/closing cycle of the shutter depending on the amount of energy from the heat source. This makes it possible to measure temperature or the configuration of the measurement system in an optimal state at all times.

Structure of the Invention In order to achieve the above object, the cooking appliance with an infrared sensor of the present invention has an infrared sensor made of an elastic surface element and a shutter mechanism whose cycle can be varied.
It has a configuration that includes a microcomputer that counts the output from the sensor and controls the external mechanism.The microcomputer selects the optimal value of the shutter cycle, and the effect is that the detection method can be selected according to the type and heating form of the heated object. It has the following.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, microwaves excited by a magnetron 1 are guided into a heating chamber 3 by a waveguide 2 and absorbed by the food. After cooling the magnetron 1, the air generated by the fan 4 enters the heating chamber 3 through the punching 8 on the side of the heating chamber 3, carries steam from the food, and guides the exhaust through the punching 9 on the opposite wall of the heating chamber 3. 10 and is exhausted to the outside of 6.

Further, as shown in FIG. 2, the infrared sensor 12 is configured to view the food inside the heating chamber through an opening 11 in the ceiling of the heating chamber 3, detect the amount of infrared radiation from the food surface, and determine the food temperature. . opening 11
There is a shutter 13 between the infrared sensor 12 and the infrared sensor 12, and the shutter 13 moves in response to commands from the control unit 14, and periodically blocks the path for radiant energy from the food to enter the infrared sensor 12 through the opening 11. ing. Therefore, the infrared sensor 12 looks at the food surface and the shutter surface alternately.

FIG. 3 shows one embodiment of an electronic circuit that controls the above mechanism. The microcomputer 15 (hereinafter referred to as microcomputer) sequentially sends the scanning pulses shown in Fig. 4 to the output terminals _S0 to _S4 , and determines which output terminal
It determines which key has been pressed by determining whether the output is High and which input terminal among the input terminals I ₀ to _{I 3} the High signal appears.
Corresponding numbers and characters are displayed on the display section 16.
At this time, the scanning pulse specifies the display digit, and segment data of numbers and characters is sent to the display section from the parallel output terminals _D0 to _D7 . Display section 16
is shown in FIG.

In FIG. 3, the individual output terminal _R1 of the microcomputer 15 is a terminal that outputs a buzzer signal to a buzzer circuit 16 that generates a confirmation sound when a key is pressed or when cooking is completed. R ₂ is the main relay switch 17 that opens and closes the 100V circuit, R ³ is the magnetron circuit 1
Relay switch 19 that controls the on/off of energization of 8.
These terminals are respectively controlled via the driver IC 20. Further, the fan motor 21 is a motor for energizing the fan 4, and the turntable motor 22 is a motor for driving a turntable 27 for rotating food in the heating chamber 3 and improving radio wave distribution.

The infrared sensor 12 and the oscillation circuit 23 send an oscillation pulse to the microcomputer 1 at a frequency corresponding to the magnitude of the input.
Send to ^R4 terminal of 5. The microcomputer 15 counts the number of oscillation pulses and learns the temperature state of the surface of the object. Also, the opening/closing signal for the shutter 13 is provided by the microcomputer 1.
The shutter ¹³ blocks the field of view of the infrared sensor 12 according to its output cycle.

FIG. 6 is a diagram showing the frequency change of the signal sent to the oscillation circuit 23 or the R4 terminal of the microcomputer ¹⁵ . In this example, the shutter on/off cycle is set to 5 seconds (2.5 seconds on - 2.5 seconds off). Moreover, the heat source temperature is constant.

Here, the food surface temperature T and the amount of infrared energy E
There is a relationship of E=σT ⁴ (σ is a constant), so
As the food surface temperature rises, the amount of infrared energy E increases dramatically (Figure 7 shows the relationship between the temperature T and the relative amount of energy Er).Therefore, the frequency f sent from the oscillation circuit 23 to the microcomputer 15 increases.
also becomes larger. However, if f becomes too large, (1) the microcomputer 15 loses its counting ability; (2) The oscillation circuit becomes saturated and cannot oscillate correctly. (3) If excessive energy is incident on the infrared sensor, the temperature detection ability of the sensor will be lost due to the thermal time constant. Such shortcomings appear. Therefore, when the temperature of the food increases and exceeds a certain value, at that point the operating cycle of the shutter 13 is shortened to keep the input frequency below a certain value. Microcomputer 15 is the current shutter 1
The food temperature is known from the opening/closing cycle of step 3 and the value of the input frequency f. At the time of detection, the output level of the R ₂ or R ₃ terminal is controlled and the magnetron circuit 18
control.

FIG. 8 shows changes in the shutter cycle and the resulting changes in the output of the oscillation circuit. In this example, the frequency is measured by moving the shutter at a cycle of 5 seconds, and when the frequency exceeds the switching level H _HZ , the cycle of the shutter 13 is switched to 2.5 seconds. On the other hand, the shutter 13 is moved at a 5 second cycle and the frequency is measured, and when the frequency falls below the switching level L _HZ , the shutter cycle is switched to 10 seconds (Figure 9).

FIG. 11 shows a flowchart of temperature conversion processing by the microcomputer 15.

First, turn on the _R5 terminal of microcomputer 15 for 2.5 seconds, and then turn on the R5 terminal for 2.5 seconds.
A 5 second period off signal is sent, and the frequency f is counted in that state. When f is greater than switching level H, the _R5 terminal of microcomputer 15 is connected for 1.75 seconds.
A signal with a 2.5 second cycle of ON and 1.75 seconds OFF is sent, the frequency f is counted, and the temperature is converted from the frequency f. If the target temperature has not been reached, the shutter cycle remains 2.5 seconds and the frequency f is counted. be done.
When f is smaller than the switching level L, a signal with a 10 second cycle of 5 seconds ON and 5 seconds OFF is sent to the _R5 terminal of the microcomputer 15, the frequency f is counted, and the temperature is converted from the frequency f. If the target temperature has not been reached, the shutter cycle remains at 10 seconds and the frequency f is counted. If f is between switching level L and H, the shutter cycle remains 5 seconds and the frequency f is counted, the temperature is converted from the frequency f, and if the target temperature has not been reached, the frequency f count and the frequency f A judgment is made.

Further, FIG. 10 shows a conceptual diagram of a sensor circuit using the surface acoustic wave element 26 as an infrared sensor. When infrared rays hit the surface 24 of the sensor, the surface 2
The speed of sound that travels through 4 changes, and the oscillation frequency changes.
When the incident energy is blocked by the shutter, the heat of the sensor is dissipated through the heat radiation path 25.
Since the amount of heat dissipation is limited, if a large amount of thermal energy is incident on the surface 24, the heat cannot be dissipated even when the shutter is closed, resulting in measurement errors, so it is necessary to shorten the opening and closing cycle of the shutter. Therefore, such a situation can be avoided.

It is also possible to set the shutter cycle to an optimal cycle from the start of cooking depending on the key.

As described above, according to this embodiment, the cycle of the shutter operation is changed and the amount of energy incident on the infrared sensor 12 during one measurement is limited when the food is at a high temperature, thereby preventing saturation of the oscillation circuit and preventing the food from becoming saturated. Accurate measurements can be made by increasing the incidence when the temperature is low.

It is also possible to set an input value that matches the counting ability of the microcomputer 15.

Since the opening/closing cycle of the shutter is output from the microcomputer 15, it can be set arbitrarily.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained.

(1) The oscillation frequency of the sensor system can be controlled to a frequency that can be counted by a microcomputer.

(2) Resolution during low temperature measurements can be improved.

(3) The shutter cycle can be set according to the type of food.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view of a microwave oven, which is a cooking device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of the same.
Fig. 3 is the electronic circuit diagram, Fig. 4 is a scanning pulse waveform diagram of the microcomputer, Fig. 5 is a front view of the display tube of the microwave oven, Fig. 6 is an output waveform diagram of the sensor oscillation system, and Fig. 7 8 and 9 are diagrams showing the relationship between the shutter cycle and the output of the sensor oscillation system, respectively.
FIG. 10 is a conceptual diagram of a surface acoustic wave infrared sensor, and FIG. 11 is a flowchart of temperature conversion processing by a microcomputer. 1... Magnetron, 3... Heating chamber, 11...
Hole, 12... Infrared sensor, 13... Shutter,
15... Microcomputer, 26... Surface acoustic wave element, 23... Oscillation circuit.

Claims (1)

[Claims] 1. A heating chamber in which food is placed, a heat source for heating the food in the heating chamber, and an infrared sensor using a surface acoustic wave element installed outside a hole bored in the wall of the heating chamber, It has an oscillation circuit that extracts the output of the infrared sensor as a continuous pulse, and a shutter mechanism is provided between the infrared sensor and the hole to periodically block the path of radiant energy that enters the infrared sensor from the heating chamber. A cooking appliance with an infrared sensor, comprising means for counting the number of oscillation pulses during the opening period of the shutter mechanism and the number of oscillation pulses during the closing period of the shutter mechanism, and means for controlling the opening and closing cycle of the shutter mechanism. 2 When opening and closing the shutter under the standard shutter opening/closing cycle, when the difference between the number of oscillation pulses during the shutter opening period and the number of oscillation pulses during the shutter closing period becomes larger than a certain value, the shutter opening/closing period changes. is made smaller than the standard time, and when the difference in the number of oscillation pulses becomes smaller than a certain value, the shutter opening/closing cycle is made larger than the standard time and the oscillation frequency is detected, and the shutter opening/closing cycle is continued until the detection ends. A cooking appliance with an infrared sensor according to claim 1, wherein the infrared sensor is fixed.