JPS634128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a microwave oven equipped with an infrared detection device that detects infrared rays emitted from an object to be heated and controls high frequency output.

In order to operate a microwave oven effectively, it is important to know the heating temperature of the object to be heated and adjust the heating conditions. In order to achieve this purpose, attempts have been made to detect temperature without contacting the object to be heated using an infrared detection device, but various problems have been encountered. For example, since the intensity of received infrared rays decreases in inverse proportion to the square of the distance between the detector and the object to be heated, it is necessary to correct this, but there is a problem in that this correction means becomes complicated. Attempts have also been made to focus infrared rays using a lens system, but this complicates the configuration and increases costs.Furthermore, the detector often malfunctions due to the radio wave energy from the microwave oven. Therefore, reliable temperature detection could not be expected.

The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to prevent the infrared detector and the object to be heated from being affected by distance fluctuations and high frequencies without complicating the structure. It is an object of the present invention to provide a microwave oven that can always perform highly reliable and accurate temperature detection without causing any problems, and can perform good heating cooking with a simple configuration.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing the external shape of the microwave oven, and numeral 1 in the figure is the main body of the microwave oven. A door 2 is provided on the front surface of the microwave oven main body 1 so as to be openable and closable, and a heating chamber 3 is formed inside the main body 1 which is opened and closed by the door 2. A rotary table 4 on which an object to be heated is placed is provided at the bottom of the heating chamber 3, and the rotary table 4 is driven to rotate by a motor (not shown) in response to the operation of a magnetron (not shown). The object to be heated placed on the table 4 is irradiated with radio wave (microwave) energy from the magnetron, and is heated by the excitation of water molecules of the object by the radio wave energy. Further, an operation panel 5 is provided on the front side of the main body 1, and heating conditions are set by selectively operating various operation switches 6 disposed on the operation panel 5. Further, the display device 7 provided on the operation panel 5 is configured to display the heating temperature of the object to be heated, etc.

An infrared detection device is incorporated in the upper wall of the heating chamber 3, and this infrared detection device is constructed as shown in FIG. 2, for example. That is, the outer member 1 is bent into a U-shaped cross section.
1 is attached with a motor 12 and an infrared detector 14 fixed to a holder 13. Above motor 1
Reference numeral 2 has a rotary shaft inserted through the outer member 11, and an optical chopper body 15 fixed to the end thereof. The optical chopper body 15 consists of a rotating disk body whose inner surface is a black body with an infrared emissivity of "1" and whose outer surface is an infrared reflector, and has slit holes arranged at equal intervals in the circumferential direction. The infrared rays are rotated by the motor 12 and intermittent at a duty ratio of 50%. The window 1 provided in the outer member 11 receives infrared rays which are interrupted by the light chopper body 15 and converted into alternating current.
The light is guided to the infrared detector 14 via 1a.

On the other hand, as shown in FIG. 3, the holder 13 has a receiving part 16 inside thereof that abuts the light receiving window surface 14a of the infrared detector 14 to prevent the infrared detector 14 from shifting in the direction of the window 11a. And this receiving part 1
6 holds the infrared detector 14 in position,
A portion located in front of the light receiving window surface 14a of the infrared detector 14 communicates with the light receiving window surface 14a and widens as it moves away from the light receiving window surface 14a,
It is formed of a resin horn body having a conical hole 17 located on the side of the light receiving window surface 14a and having an opening diameter smaller than the diameter of the light receiving window surface 14a. Specifically, the hole 17 is formed in a cross-sectional shape such that as the distance from the infrared detector 4 to the object to be heated increases, the field of view seen from the infrared detector 14 similarly expands. . And holder 13
is fixed to the periphery of the window 11a coaxially with the window 11a, with the large-diameter opening of the hole 17 facing the window 11a, and thereby faces the optical chopper body 15. Further, the surface of the holder 13 is coated with a radio wave shielding body, so that high frequency waves such as microwaves are shielded. Thus, the outer member 11 to which the holder 13 and the like are attached is fixed from the back side of the ceiling plate of the heating chamber 3, and the detector 14 passes through the infrared detection transmission window 3a of the ceiling plate to the heated object housed in the heating chamber 3. It's starting to look out over the area.

Thus, in the microwave oven with the above structure,
The angle of divergence of the conical hole 17 of the holder 13 effectively defines the detection viewing angle of the infrared detector 14, as shown in FIG. That is, infrared rays incident from within the range of the above-mentioned divergence angle reach the light-receiving surface of the detector 14 while being reflected by the inner wall surface of the horn, as shown in FIG. As shown in FIG. 3b, the infrared rays outside the above range do not reach the infrared detector 14 because they are reflected toward the opening in the middle of the reflected optical path.
Furthermore, as long as this opening is set to a size smaller than the wavelength of the microwave, it is possible to easily prevent microwaves from entering through this opening.

Therefore, in a general microwave oven for cooking, when the diameter of the light-receiving surface of the detector 14 is set to 3 mmφ or less, and the minimum diameter of the object to be heated is 60 mmφ, when detecting this,
Good detection can be achieved by setting the spread angle (viewing angle) to about 4 to 10 degrees. In other words, in the case of a fixed table type microwave oven, if the approximate center of the heated object storage area is set as the detection field of view A as shown in Fig. 4a, the temperature of the heated object can be detected with almost no background noise. It becomes possible to detect without including it. In addition, in the case of a rotary table type microwave oven, as shown in FIG. It becomes possible to detect.

Here, the intensity F of the infrared rays incident on the infrared detector 14 is as follows. That is, as shown in FIG. 3, the heated object 18 emits infrared radiation proportional to the fourth power of its absolute temperature per unit area. Further, the amount of infrared rays reaching the infrared detector 14 is attenuated in inverse proportion to the square of the distance b between the detector 14 and the object to be heated 18 . Furthermore, since the cross-sectional shape of the hole 17 is set in the above relationship, the area of the heated object 18 that falls within the viewing angle of the detector 14 increases in proportion to the square of the distance b. Therefore, if the above-mentioned viewing angle is set to an appropriate condition, the infrared intensity F received by the detector 14 will be determined by the aperture distance of the light beam of the detector 14 as a, the radius of the aperture as r, and the amount of infrared radiation per unit area. When dw is expressed as follows.

F=π(r/a) ² ·dw As can be seen from this equation, the distance b does not affect the received infrared light intensity F. In other words, when such a detection method is adopted, the decrease in infrared radiation intensity that is inversely proportional to the square of the distance b can be compensated for by increasing the detection field of view in proportion to the square of the distance b. ,
The dependence on distance b can be eliminated. In the case of this embodiment, the aperture diameter of the infrared detector 14 located on the light receiving window surface 14a side is
Since the hole 17 is provided to have a diameter smaller than the diameter of the hole 4a, all of the infrared rays arriving from within the field of view can be incident on the infrared detector 14, and the presence of the receiving portion 16 allows the infrared detector 14 to be Misalignment can be prevented, and the designed dimension a can always be maintained. Therefore, the infrared rays emitted from the object to be heated 18 can be made to enter the infrared detector 14 according to the above-mentioned formula. Moreover, although it exhibits the above-mentioned effect, it does not require a complicated optical system such as a lens system or a reflecting mirror as in the conventional structure, so it can be easily realized and manufactured.

Further, since the holder 13 is provided with a radio wave shield, high frequency waves from the magnetron will not reach the light receiving surface of the detector 14, and no adverse effects will be caused by the high frequencies. Therefore, stable and highly reliable operation can be expected at all times.

FIG. 5 is a schematic diagram of a signal processing circuit attached to the infrared detection device shown in FIG. 2. In the figure, 21 is a detection element that receives infrared rays converted into alternating current by the optical chopper body 15, and a photoelectric conversion element 21a.
and a buffer 21b consisting of an FET that stabilizes and outputs the electrical output. Usually, these are integrated together in one package and configured as one cell. Therefore, the AC output of the detection element 21 is amplified to a predetermined level via an AC amplifier 22 consisting of an OP amplifier, and then a full-wave rectifier circuit 2
I am guided by 3. This full-wave rectifier circuit 23 is composed of an OP amplifier and a diode inserted into its feedback circuit, and outputs a DC voltage signal corresponding to the amplitude level of the AC output. The output of this full-wave rectifier circuit 23 is led to a DC amplifier 24 consisting of a variable resistor, an OP amplifier, etc., and is then subjected to gain compensation and input to an adder 25. That is, the DC amplifier 24 performs zero compensation in order to compensate for background noise, etc. included in the detection output.
In addition, the gain is matched with the temperature detection circuit of the optical chopper body 15, which will be described below. The temperature detection circuit 26 directly amplifies the detected temperature (electrical signal) of the optical chopper body 15 detected by the temperature sensor 27 and guides it to the adder 25. The adder 25 inputs each of the detection signals to an inverted signal input terminal and a non-inverted signal input terminal, calculates a difference between them, and outputs this as the detected temperature of the object to be heated 18 . That is, since the infrared detectors 21 and 14 detect infrared rays interrupted by the optical chopper body 15, their detection output V is Vαδ|ε ₁ T ₁ ⁴ −ε ₂ T ₂ ⁴ | However, δ: Stephan Boltzmann's constant T ₁ : Temperature of the object to be heated T ₂ : Temperature of the optical chopper body ε ₁ : Infrared emissivity of the heated object ε ₂ : Infrared emissivity of the optical chopper body. Therefore, by subtracting the temperature of the optical chopper body 15 detected by the infrared detection circuit 26 from the detection output V in the adder 25, the temperature value of the object to be heated 18 can be obtained here. This temperature value controls the output of the magnetron. Further, the temperature value is converted into a digital code and displayed on the display device 7 described above.

As described above, according to the present invention, without complicating the configuration and without being affected by high frequencies,
In addition, it has the ability to accurately detect the temperature of the heated object without being affected by distance fluctuations between the infrared detector and the heated object, making it possible to create a microwave oven that can effectively control the heating of the heated object. provide.

Note that the present invention is not limited to the above embodiments. For example, the angle of expansion of the hole in the horn body and its length may be determined as appropriate depending on the specifications.
Furthermore, there are no particular limitations on the type of microwave oven to be applied. Furthermore, various modifications can be made to the structure of the optical chopper body, and in other words, various modifications can be made without departing from the gist of the invention.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention. Fig. 1 is a perspective view showing the external appearance of the microwave oven, Fig. 2 is a schematic configuration diagram of the main parts of the microwave oven, and Fig. 3 a and b are visual fields. FIG. 4 is a schematic optical diagram for explaining angle and distance correction, FIGS. 4a and 4b are diagrams showing visual field areas, and FIG. 5 is a configuration diagram of a detection signal processing circuit. 11... Board, 12... Motor, 13... Holder (horn body), 14... Infrared detector, 15...
...Light chiyotsupa body.

Claims (1)

[Claims] 1. An infrared transmitting section is provided on the wall of the heating chamber containing the object to be heated, and an infrared detecting device is provided to detect the infrared rays transmitted through the infrared transmitting section among the infrared rays emitted by the object to be heated, and the infrared detecting device In a microwave oven that controls high frequency output based on output, the infrared detection device includes:
an infrared detector disposed with a light receiving window surface facing the infrared transmitting section; and a position of the infrared detector in a lateral direction of the infrared transmitting section with the light receiving window surface of the infrared detector in contact with the interior thereof. It has a receiving part for regulating displacement, and the receiving part holds the infrared detector in position, and a part located in front of the light receiving window surface is provided with a receiving part for controlling displacement as the distance from the infrared detector to the object to be heated increases. Therefore, the cross-sectional shape is such that the field of view seen by the infrared detector is similarly expanded, and the infrared rays emitted from the object to be heated in the field of view are focused and incident on the light receiving window surface, and the light receiving window is A microwave oven characterized by having a hole located on the window surface side and having an opening diameter smaller than the diameter of the light receiving window surface, and a horn body having at least a surface portion formed of a high frequency shielding material. .