JPH0142726Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a microwave oven that detects food temperature using an infrared sensor.

(B) Prior Art Recently, microwave ovens have been commercialized that detect food temperature using an infrared sensor and perform microwave heating control based on the detected temperature.

In such a microwave oven, the infrared rays incident on the infrared sensor must be intermittent, and for this purpose, a perforated disk chopper and a motor for rotating the chopper are provided, and the infrared sensor,
The chopper and motor are housed integrally in the same housing along with a circuit for amplifying and processing the output of the infrared sensor, thereby achieving compactness. In this case, the casing is made of metal and prevents microwaves from undesirably riding on the internal infrared sensor and circuit, thereby suppressing a decrease in the SN ratio. Note that the signal amplified and processed by the above circuit is sent to other circuits outside the above case, but since such a signal has already been amplified, even if the microwave is applied to it, the SN ratio is not very high at this point. If the signal line for transmitting the signal is microwave-shielded, the reduction in the S/N ratio can be further suppressed.

However, with the above configuration, there is a limit to the miniaturization of the chopper and motor itself, and the infrared sensor and the circuit for amplifying and processing the output of the sensor are separate from the chopper and motor due to space considerations. Therefore, even if the casing is made compact, the size is not sufficiently reduced.

(c) Purpose of the invention The purpose of the invention is to make the structure surrounding an infrared sensor more compact and smaller.

(d) Structure of the invention In order to achieve the above object, the structure of the invention includes an infrared sensor having an infrared detector into which infrared rays from food enter, a plurality of infrared passing parts, and a plurality of infrared non-passing parts. , first and second facing bodies facing each other, in which the infrared passing parts and the infrared non-passing parts are arranged alternately, and a vibrating body that periodically changes the relative positional relationship of these first and second facing bodies. A printed circuit board to which the infrared sensor is directly attached, which is built in the infrared sensor and has a chopper mechanism that cuts off the infrared rays incident on the infrared detector, and a circuit that amplifies and processes the signal from the infrared sensor. The present invention is characterized by comprising a substrate and a microwave shielding housing in which the printed circuit board is disposed.

(e) Examples A microwave oven according to an embodiment of the present invention will be described below.

In FIG. 1, 1 is a heating chamber into which microwaves are supplied to heat food 2, 3 is an opening formed in the center of the upper wall of the heating chamber, and 4 is a microwave blocking ring fixed to the opening. So, the ring is food 2
It allows infrared rays from to pass through, but blocks microwaves. 5 is the above ring 4 inside
A metal case 6 is fixed to a mounting plate 7 within the case, and an infrared ray passing hole 8 is formed in the lower wall of the case, facing the ring 4. is formed.

Reference numeral 9 denotes an infrared sensor for directly receiving infrared rays from the food 2 that has passed through the ring 4 and the hole 8 to detect the temperature of the food; This is a printed circuit board on which a temperature detection circuit 11 for amplification and processing is formed. The sensor 9 is directly attached to the lower surface of the substrate by solder, and the circuit components 12, 12, . . . of the temperature detection circuit 11 are attached to the upper surface by solder. Reference numeral 13 denotes a metal lid that covers the upper part of the housing 6 with the printed circuit board 10 disposed inside the housing 6, so that the printed circuit board 10 to which the sensor 9 is attached is substantially shielded from microwave radiation.

Reference numeral 14 denotes a shutter mechanism for opening and closing the upper end opening of the ring 4. The upper end opening of the ring 4 is opened so that the sensor 9 can receive infrared rays from the food 2 during microwave heating, and when not heated by microwaves. The heating chamber 1 is closed to prevent oil smoke, food waste, etc. from rising through the ring 4 and contaminating the sensor 9 and the like.

Reference numeral 15 denotes a duct for guiding cooling air from a blower (not shown) into the case 5 to cool the sensor 9 and the like during microwave heating, and the air after cooling passes through the ring 4 into the heating chamber 1. is discharged,
This prevents oil smoke, food particles, etc. from rising during heating.

FIG. 2 shows a specific structure of the sensor 9. As shown in FIG.

16 is a pyroelectric infrared detector made of lithium tantalate (LiTaO ₃ ) single crystal and generates a charge according to the amount of change in incident infrared rays; 17 and 18 are nichrome-deposited films on the front and back surfaces of the infrared detector, respectively. The front and back electrodes 19 are made of copper, phosphor bronze, etc., and the back electrode 18 is placed on the support base so as to face the upper surface of the support base 19. The body 16 is fixed with a conductive adhesive 20 such as silver paste.

21 is an alumina substrate on which an impedance conversion circuit 22 is arranged to make the infrared sensor 9 low resistance since the infrared detector 16 has a high resistance, and 23 is a storage body consisting of a metal cap 24 and a header 25. The support stand 19 and the substrate 21 are fixed on the header 25 inside the housing. Reference numeral 26 denotes a ground terminal directly implanted in the header 25, and the terminal is electrically connected to the back electrode 18 via the support base 19 and adhesive 20. 27 and 28 are the headers 2, respectively.
5, the first implanted through the insulating materials 29 and 30,
A second lead terminal 31 is a lead wire connecting the surface electrode 17 and the impedance conversion circuit 22;
32 and 33 are lead wires that connect the impedance conversion circuit 22 and the first and second lead terminals 27 and 28.

34 is the cap 24 for allowing infrared rays to enter the infrared detector 16 from the surface electrode 17 side.
The opening 35 is an infrared transmitting body that closes the opening, and the transmitting body is made of a silicon or germanium plate having a thickness of several hundred μm and has a high transmittance for infrared rays having a wavelength of 2 to 15 μm.

36 is a shield made of aluminum or the like and covers the infrared detector 16 and the impedance conversion circuit 22, and 37 is an opening formed in a portion of the shield located above the detector 16.

38 is a planar first opposing body attached to the opening, and as shown in FIG. A plurality of first infrared non-transmissive portions 39 extending in a fan-shaped linear shape in the direction (FIG. 2) and a first infrared transmissive portion 40 located between each of the first infrared non-transmissive portions 39 are formed. has been done. and,
The widths W1 and W2 of the first infrared non-transmissive portion 39 are 100 μm and 120 μm, respectively, and the first infrared transparent portion 4
The widths W1' and W2' of 0 are the same dimensions as the above W1 and W2. Reference numeral 41 denotes a planar second opposing body arranged parallel to and close to the first opposing body 38, and the second opposing body includes the first infrared non-transmissive portion as shown in FIG. 3b. A plurality of second infrared non-transmissive portions 42 made of the same material as 39 and extending in a fan-shaped linear shape in a direction parallel to the paper surface (FIG. 2), and between each of the second infrared non-transmissive portions 42. A second infrared transmitting portion 43 is formed. The widths W1' and W2 of the second infrared non-transmissive section 43 and the widths W1' and W2' of the second infrared transmissive section 43 are the widths W1 and W2 of the first infrared non-transmissive section 39 and the widths W1' and W2 of the second infrared transmissive section 43, respectively. The dimensions are the same as the widths W1' and W2' of the transparent section 40.

44 is a vibrator formed by pasting together two piezoelectric plates made of ferroelectric material or a metal plate and a piezoelectric plate made of ferroelectric material, that is, a bimorph, which has a rectangular parallelepiped shape and its length and width W. , thickness a
(Fig. 4) are approximately 30 mm, 5 mm, and 0.5 mm, respectively. Examples of the piezoelectric plate include quartz crystal, Rothsiel salt, barium titanate, and the like. And the above bimorph 4
4 is made longer in the direction perpendicular to the infrared incident direction, that is, in the lateral direction, so that the left end 44' is connected to the header 25.
It is fixed to an insulating stand 45 provided at the right end 44''
The second opposing body 41 is attached to the. Reference numeral 46 indicates a third lead terminal embedded in the header 25 via an insulating material 47, and reference numerals 48 and 49 indicate first and second lead terminals formed on both sides of the left end 44' of the bimorph 44, as shown in FIG. A vibrating electrode, the first and second vibrating electrodes are connected to the third lead terminal 46 and the header 2, respectively.
5 (ground terminal 26). Reference numeral 50 denotes a support base made of resin such as Teflon, and a groove 51 is cut into the support base to slidably support the free end 41' of the second opposing body 41.

A predetermined alternating current voltage, that is, a periodic pulse, is applied to the first vibrating electrode 48 via the third lead terminal 46, but when such a pulse is not applied, the second vibrating electrode 48 The second non-infrared transmitting portion 45 of the opposing body 41 completely overlaps the first infrared transmitting portion 40 of the first opposing body 38 (located in the shaded area J in FIG. 3C). When the pulse is applied, the bimorph 44 is bent in the direction A, and the second infrared non-transmissive portion 42 completely overlaps the first infrared non-transmissive portion 39 (dot area I in FIG. 3C). ). Therefore, the first vibrating electrode 4
8, the bimorph 44 periodically vibrates in directions A and B, and the infrared detector 16 receives infrared rays from the food 2 outside the infrared sensor 9 periodically. incident.
When such incidence occurs, the amount of infrared rays incident on the infrared detector 16 changes periodically, and the infrared detector 16 generates a charge corresponding to this amount of change. This charge is based on the temperature difference between the temperature of the food 2 and the room temperature (the temperature of the second opposing body 41).

Here, the first and second opposing bodies 38, 41 and the bimorph 44 constitute a chopper mechanism that cuts off the infrared rays from the food 2, and this chopper mechanism is built into the infrared sensor 9.

52 is a fourth lead terminal implanted in the header 25 via an insulating material 53; 54 is a room temperature diode for outputting a DC voltage based on room temperature;
The anode of the diode is connected to the fourth lead terminal 5.
2, and its cathode is connected to the header 25 (grounded).

FIG. 5 specifically shows the temperature detection circuit 11 together with the infrared sensor 9, and the impedance conversion circuit 22 in the infrared sensor 9 includes an input/output resistor 55 of 10 ¹⁰ to 10 ¹¹ Ω, a FET 56, and an output resistor 57 of about 10 KΩ. It is formed in

The infrared sensor 9 is supplied with a DC voltage through the first lead terminal 27, and the bimorph 4
4, the sixth lead terminal 28 has an amplitude corresponding to the temperature difference between the temperature of the food 2 and the room temperature.
An alternating current signal e as shown in Figure a is output. 58 is an astable multivibrator, and 59 is an oscillator that oscillates a pulse f with a voltage V of 1 to 30 V, preferably 14 V, at a frequency of 20 Hz, as shown in FIG. 6b, and 59 vibrates the bimorph 44 based on the pulse f. a drive circuit that outputs periodic pulses for
61 and 62 are DC amplifiers, 63 is a filter amplifier, and 64 is a synchronous detector, which synchronizes the AC signal e from the infrared sensor 9 and the pulse f from the oscillator 58, and When the temperature is higher than room temperature, a positive DC signal is output according to the temperature difference, and when the temperature of the food 2 is lower than room temperature, a negative DC signal is output according to the temperature difference.

That is, as for the output AC signal e of the infrared sensor 9, when the temperature of the food 2 is higher than room temperature, the positive half cycle e+ coincides with the pulse f, and when the temperature of the food 2 is lower than room temperature, the negative half cycle e- coincides with pulse f. When the pulse f and the positive half cycle e+ match, the synchronous detector 64 outputs a positive DC signal corresponding to the temperature difference between the food 2 and the room temperature, and pulse f and the negative half cycle e+. When a match is established with e-, a negative DC signal corresponding to the temperature difference between the food 2 and the room temperature is output.

Reference numeral 65 denotes a synthesis circuit that adds together the DC signal from the synchronous detector 64 and the DC signal corresponding to the room temperature of the room temperature diode 54, and this circuit generates a signal corresponding to the temperature of the food 2 by such addition. Output. Reference numeral 66 is an output terminal for outputting the temperature signal to a predetermined circuit that controls microwave heating.

(f) Effect of the invention As is clear from the above explanation, according to the invention, the chopper mechanism that cuts off the infrared rays incident on the infrared detecting body of the infrared sensor has a plurality of infrared passing parts and a plurality of infrared non-passing parts. and periodically changing the relative positional relationship between first and second opposing bodies facing each other, in which the infrared passing parts and the infrared non-passing parts are arranged alternately, and the first and second opposing bodies. The chopper mechanism can be built into an infrared sensor, and can be made much smaller than a conventional chipper consisting of a circular plate with a hole and a motor that rotates the chopper. Furthermore, since the chopper mechanism can be made smaller, an infrared sensor can be easily integrated into a circuit that amplifies and processes signals from the sensor within the microwave shielding housing without having to take into account the spatial relationship with the chopper mechanism. It can be mounted directly onto a printed circuit board. Based on these points, we developed a configuration in which the chopper mechanism is built into an infrared sensor, the infrared sensor is directly attached to a printed circuit board, and the printed circuit board is placed inside a microwave shielding housing. Because of this, the structure around the infrared sensor can be made more compact and smaller, thereby making it possible to obtain an extremely practical microwave oven.

[Brief explanation of the drawing]

The drawings show a microwave oven according to an embodiment of the present invention, with FIG. 1 being a sectional view of the main parts, and FIG. 2 being a sectional view of an infrared sensor.
Figures 3a, b, and c are plan views of the main parts of the sensor, respectively;
4 is a plan view of FIG. 2 viewed from the direction of the arrow, FIG. 5 is a circuit diagram of the main part, and FIGS. 6a and 6b are signal waveform diagrams of the main part in FIG. 6... Housing, 9... Infrared sensor, 10... Printed circuit board, 11... Temperature detection circuit, 38... First opposing body, 41... Second opposing body, 44... Bimorph.

Claims (1)

[Scope of utility model registration request] An infrared sensor having an infrared detecting body through which infrared rays from food enter, a plurality of infrared passing parts and a plurality of infrared non-passing parts, the infrared passing parts and the infrared non-passing parts being arranged alternately and facing each other. and a vibrating body that periodically changes the relative positional relationship between the first and second opposing bodies, and is built in the infrared sensor and detects infrared rays incident on the infrared detecting body. An intermittent chopper mechanism, a printed circuit board on which a circuit for amplifying and processing signals from the infrared sensor is formed, the infrared sensor is directly attached, and a microwave shielding case in which the printed circuit board is placed. A microwave oven featuring