JPS6353444B2 - - 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 circumstances, and its purpose is to always perform highly reliable and accurate temperature detection without being affected by the distance between the infrared detector and the object to be detected. It is an object of the present invention to provide a microwave oven that can perform good 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 is provided at the bottom of the heating chamber 3 on which an object to be heated is placed and rotated, and the object to be heated is irradiated with radio wave energy. Note that the object to be heated is heated by exciting water molecules by radio wave (microwave) energy. An operation panel 5 is provided on the front side of the microwave oven main body 1. Various operation switches 6 and a display device 7 are arranged on the operation panel 5, and by selectively operating the operation switches 6, the operating conditions of the microwave oven, such as the heating energy intensity by the magnetron device and the heating The time is set. Further, the heating temperature of the object to be heated detected by an infrared detection device, which will be described later, is displayed on the display device 7. As shown in the schematic diagram of FIG. 2, the rotary table 4 is connected to a motor 9 via a rotary shaft 8 passing through the bottom wall of the heating chamber 3, and responds to the operation of the magnetron device. Rotationally driven.
Then, the object to be heated 10 is placed on this table 4 and heated. Further, the magnetron 11 is provided at the top of the main body 1, and this magnetron 1
Microwave radio waves emitted from the heating chamber 3 are guided to the upper antenna opening 12a of the heating chamber 3 via the waveguide 12. A radio stirring fan 14 rotatably driven by a motor 13 is provided near the antenna opening 12a. The radio waves guided from the opening 12a are stirred by the stirring blades 14 and radiated substantially uniformly throughout the interior of the heating chamber 3. An air introduction passage 1 is provided in the upper part of the microwave oven main body 1.
5 is provided, and external air is sent into the heating chamber 3 via an air inlet 17 by a blowing fan 16. This introduced air forms an air flow from the upper part of the heating chamber 3 downward, and the object to be heated 1 is irradiated with the radio wave energy.
Water vapor and the like released from the outlet 18 are discharged through the outlet 18. Further, the air introduction port 17 of the air introduction path 15
An infrared transmitting window 19 is provided on the upper wall opposite to the infrared transmitting window 19, and an infrared detecting device 20 is provided above the infrared transmitting window 19. The infrared detecting device 20 and the infrared transmitting window 19 are connected to the motor 13 via pulleys 21a, 21b and a belt 21c to rotate, and out of the infrared rays emitted from the object to be heated 10, the Inlet port 17
Further, an optical chopper body 22 is provided that interrupts the infrared rays that have passed through the infrared transmitting window 19 and causes the infrared rays to enter the infrared detecting device 20 . The optical chopper body 22 is a rotating disc body whose lower surface is formed of a black body with an infrared emissivity of approximately "1" and whose upper surface is formed of an infrared reflector, and is made of a rotating disc body whose lower surface is formed of a black body with an infrared emissivity of approximately "1", and whose upper surface is formed of an infrared reflector. The infrared rays are intermittent at a duty ratio of 50% using slit holes provided at intervals. The infrared rays are interrupted and converted into alternating current by the optical chopper body 22 and guided to the infrared detection device 20 . The infrared detection device 20 is constructed as shown in FIG. 3, for example. That is, the top plate 24 of the heating chamber 3 is covered and the motor 1 is
3, and a horn body 2 so as to close a hole 26 provided at a position facing the infrared transmitting window 19 in a plate member 25 having a U-shaped cross section and supporting the pulley 21b.
7 is attached, and an infrared detector 28 is attached to this horn body 27. As shown in FIG. 4, the horn body 27 has a cone-shaped cavity 29 in the center, and includes a horn member 30 made of synthetic resin such as ABS resin, and the entire surface of the horn member 30. A mirror-finished high frequency shield body 31 made of metal plating or the like is provided to cover the high frequency shield body 31. A stepped large diameter portion 32 is formed in the horn member 30 on the small diameter side of the cavity 29 and coaxially communicated therewith, and the infrared detector 28 is inserted into the stepped large diameter portion 32. ing. The infrared detecting device 20 configured in this manner has an E-tap 33 formed on the large-diameter side end surface of the cavity 29 in the horn member 30 that is fitted into a protrusion 34 protruding from the plate material 25. According to the above plate material 25
is fixed. The width of the cavity 29 is set to a viewing angle of 4 to 10 degrees when viewed from the position of the infrared detector 28. Further, numeral 35 in FIG. 4 indicates a lid body that covers the opening of the stepped large diameter portion 32. Thus, the output of the infrared detection device 20 is introduced into a processing circuit 41 provided within the microwave oven main body 1. This processing circuit 41 is configured as shown in FIG. 5, for example. That is, 28 in the figure is the infrared detector which receives the infrared rays converted into alternating current by the optical chopper body 22, and converts the impedance of the photoelectric conversion element 28a and its electrical output and outputs the same.
It is composed of a buffer amplifier 28b consisting of an FET. Usually, these are integrated together in one package and configured as one cell. Thus, the AC output of the infrared detector 28 is amplified by compensating the gain to a predetermined level via an AC amplifier 42 consisting of an OP amplifier, and then guided to full-wave rectifier circuits 43 and 44. The full-wave rectifier circuits 43 and 44 are composed of an OP amplifier and a diode inserted into its feedback circuit, and output a DC voltage signal corresponding to the amplitude level of the AC output. This output is the DC amplifier 4
5, zero compensation is performed in order to compensate for background noise, etc. contained in the detection output. On the other hand, a temperature detection circuit 46 is provided, and this circuit 4
Reference numeral 6 utilizes the fact that the forward voltage of the diode has temperature characteristics, and sends out an output capable of compensating for gain and zero level fluctuations due to temperature of the infrared detector 28. This output is then led to an adder 47. The adder 47 inputs each of the detection signals to the inverted signal input terminal and the non-inverted signal input terminal, calculates the difference between them, and applies this to the object to be heated 1.
It is output as a detected temperature of 0. That is, since the infrared detector 28 detects infrared rays interrupted by the optical chopper body 22, its detection output V is V∝σ|ε ₁ T ₁ ⁴ −ε ₂ T ₂ ⁴ | where σ: Stephan-Boltzmann 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, in the adder 47, the DC amplifier 45
The temperature value of the object to be heated 10 can be obtained by subtracting the temperature signal detected by the temperature detection circuit 46 from the output signal. This temperature value is converted into a digital code and displayed on the aforementioned display device 7, and is also given as an input control signal to the magnetron 11. On the other hand, the heated object 1 of the infrared detection transmission window 19
A cleaning mechanism 51 is provided on the opposite surface of 0. This cleaning mechanism 51 is shown in FIG.
As shown in c, a cleaning cloth body 52 is provided which is movably provided in sliding contact with the surface of the transmission window 19 facing the object to be heated 10 . That is, the cleaning cloth body 52 is provided at one end of the support body 53. This support body 53 is provided at one end of two rotating levers 54a and 54b arranged in parallel. Further, the rotating levers 54a and 54b have an operating rod 55 attached to the other end thereof, and the center portion thereof is supported by pins 56a and 56b as a center of rotation. Thus, the rotating lever 54a is biased in the direction of the arrow by the spring 57. The end of the operating rod 55 is pressed against the inner wall surface of the door 2 which is in a closed state with respect to the main body 1, and is pushed inward against the spring 57. As a result, the support body 53 is slid in the opposite direction, and the cleaning cloth body 52 is placed on the side of the transmission window 19, as shown in FIG. 6a. Further, when the door 2 is in the open state, the operation rod 55 is in a released state. This allows the support 53
is slid toward the transparent window 19 by the biasing force of the spring 57, as shown in FIG. 6b. By this sliding, the cleaning cloth body 52 moves in sliding contact with the surface of the transparent window 19. As a result, dirt on the transmission window 19 is wiped away by the cleaning cloth body 52. That is, by opening and closing the door 2, the operating rod 55 is moved back and forth, and in response to the advancing and retreating of the operating rod 55, the cleaning cloth 52 moves in sliding contact with the surface of the transparent window 19. Cleaning is done. According to the microwave oven having such a structure, it goes without saying that the object to be heated 10 is heated very effectively by the radio waves emitted substantially uniformly into the heating chamber 3 by the stirring blade 14. The temperature of the object to be heated 10 can be detected effectively and reliably by the infrared detection device 20 . That is, since the air flow is formed downward from the upper inlet 17 to the lower outlet 18 in the heating chamber 3, water vapor, oil dust, etc. from the object to be heated 10 generated by heating will flow into the heating chamber. 3. It is quickly discharged without accumulating in the tank. Therefore,
Infrared rays radiated from the heated object 10 are no longer absorbed by water vapor, and problems such as oil dust adhering to the infrared transmitting window 19 and attenuating the transmitted infrared rays do not occur. Therefore, the infrared detection device 20 can perform temperature detection with high reliability and accuracy. Moreover, since the infrared transmitting window 19 is cleaned each time the door 2 is opened or closed when the microwave oven is used, a clean surface is always maintained. Therefore, even when the microwave oven is used for a long time, there is no problem that the detection accuracy decreases. Moreover, even if the transmission window 19 becomes dirty, maintenance is easy because the cleaning cloth body 52 can be replaced as appropriate.
Easy to handle. Therefore, it is possible to operate the microwave oven while always knowing the exact heating conditions for the object to be heated 10, and it is possible to prevent overheating and the like and to operate the microwave oven effectively. Further, in the microwave oven according to the present invention, the infrared detection device 20 is connected to the heating chamber 3,
That is, it consists of a horn member 30 made of resin having a truncated cone-shaped cavity 29 that widens as it approaches the infrared transmitting window 19, and a high frequency shield body 31 provided to cover the surface of the horn member 30. It consists of a horn body 27 and an infrared detector 28 that detects infrared rays collected by the cavity 29 of the horn body 27. Therefore,
Infrared rays emitted from the object to be heated 10 can be detected satisfactorily while noise is prevented from entering. That is, the viewing angle of the infrared detector 28 is effectively defined by the divergence angle of the cavity 29, which is formed in the shape of a truncated cone, as shown in FIG. Infrared rays incident from within the range of the above-mentioned spread angle reach the light-receiving surface of the detector 28 while being reflected by the inner wall surface of the horn as shown in FIG. As shown in b, the light is reflected toward the opening in the middle of the reflected optical path. Therefore, if the field of view of the infrared detector 28 is set in the range indicated by the broken line circle Z in FIG. 8a, that is, within the surface of the object to be heated 10, the The infrared rays emitted from the hatched area of the object 10 in the figure can be detected, and the field of view Z of the infrared detector 28 is set at the center of rotation of the object 10 as shown in FIG. 8b. If this is done, infrared rays emitted from the object to be heated 10 can be detected regardless of the rotation of the rotary table, and no noise will be detected.
Note that at this time, the intensity F of the infrared rays incident on the infrared detector 28 is as follows. That is, infrared rays are emitted per unit area of the object to be heated 10 in proportion to the fourth power of the absolute temperature thereof. Further, the amount of infrared rays reaching the infrared detector 28 is attenuated in inverse proportion to the square of the distance b between the detector 28 and the object to be heated 10. Further, the area of the heated object 10 that falls within the viewing angle of the detector 28 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 28 will be determined by the aperture distance of the light beam of the detector 28 being a, the radius of the aperture being r, and the intensity per unit area per unit solid angle. When the amount of infrared radiation is dW and the receiving area of the detector is X, it is expressed as follows. F=π(r ₁ /a) ² /X ^dW Here, assuming that the height of the heating chamber 3 of a commonly used microwave oven is approximately 200 mm and the size of the heated object is approximately 60 mm in minimum diameter, then Good detection can be achieved by setting the above-mentioned viewing angle to about 4° to 10°. In addition, the horn body 27 is replaced by a resin horn member 30.
and a high frequency shield body 31 provided so as to cover the surface of this member 30, the horn member 30 can be manufactured easily and with high precision by injection molding, and the high frequency shield body 31 The horn body 27 can be easily formed into a mirror surface by plating or the like, and as a result, the horn body 27 can be manufactured easily. Note that the present invention is not limited only to the above embodiments. For example, the cleaning mechanism may be configured such that a cam mechanism is connected to the rotating shaft of the door 2, and the cleaning body is moved by this cam mechanism. It goes without saying that the transmitting film constituting the infrared transmitting window may be moved in sliding contact with a cleaning body to clean the transmitting film. Furthermore, the cleaning mechanism may be operated electrically in response to opening and closing of the door 2. Furthermore, when the present invention is applied to an apparatus without a rotary table, the infrared detection field of view Z may be set at the center of the object to be heated 10, as shown in FIG. 8b. Further, the material and structure of the cleaning cloth body may be appropriately set, and may be configured to be replaceable. Alternatively, the horn body may be divided into two parts, and the two members may be finally joined together. Furthermore, the cavity provided in the horn body is not limited to a conical shape but may be parabolic or concave. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, in which Fig. 1 is a perspective view showing the external shape, Fig. 2 is a schematic diagram showing the general configuration, and Fig. 3 is an enlarged view of the main parts in Fig. 2. 4 is an enlarged sectional view of the infrared detection device in the same embodiment, FIG. 5 is a configuration diagram of the processing circuit in the same embodiment, and FIGS. 6 a to 6 c are cleaning mechanisms in the 21st embodiment. FIGS. 7A and 7B are diagrams for explaining the infrared detection range, and FIGS. 8A and 8B are diagrams for explaining the infrared detection range on the object to be heated. 1... Microwave oven body, 2... Door, 3... Heating chamber, 4... Rotating cable, 10... Heated object, 1
9...Infrared transmission window, 20 ...Infrared detection device,
22...Chiyotsupa body, 27...Horn body, 28...
...Infrared detector, 29...Cavity, 30...Horn member, 31...High frequency shield body.

Claims (1)

[Scope of Claims] 1. An infrared transmitting section is formed on the wall of a heating chamber that houses an object to be heated, and an infrared detecting device is provided for detecting infrared rays that have passed through the transmitting section among the infrared rays emitted from the object to be heated. In the microwave oven, the high frequency output is controlled according to the output of the device, the infrared detection device includes a horn member made of a resin having a cavity that widens as it approaches the heating chamber, and the horn. It is characterized by comprising a horn body made of a high frequency shield body provided so as to cover the surface of the member, and an infrared detector that detects the infrared rays collected by the cavity of the horn body. microwave oven. 2. The microwave oven according to claim 1, wherein the front surface of the horn body is provided with an optical chopper device that cuts off infrared rays incident on the cavity of the horn body.