JPH0749263A - Weight sensor for microwave oven - Google Patents

Abstract

(57) [Summary] [Object] The present invention aims to improve a weight sensor used in a microwave oven. [Structure] A turntable shaft 3 which is driven by a motor 2 and is movable in the axial direction is biased upward by a spring 7, and a buzzer 9 interlocked with the vertical displacement of the turntable shaft is fixed to face the buzzer 9. The configuration is such that the oscillator 13 and the phase difference detection circuit 15 detect a change in the distance between the buzzer 10 and the buzzer 10. [Effect] A weight sensor for a microwave oven having the accuracy and reliability of a spring balance can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a weight sensor which is indispensable for automatic cooking of a microwave oven.

[0002]

2. Description of the Related Art Among microwave ovens currently on the market in Japan, weight sensors are mounted on all models of intermediate level or higher, but it may be due to a structural limitation that a turntable drive shaft is used. Most of them use a kind of pressure sensor that utilizes changes in electrostatic capacity. Therefore, even if compared with a general inexpensive spring balance, not only the basic performance such as weight accuracy and resolution is inferior, but also the structure and the electric circuit are complicated, resulting in a high price.

In order to adopt this inexpensive and high-performance spring balance for detecting the weight of food in a microwave oven, a means for converting the displacement of the spring into an electric signal is necessary, but a highly reliable and inexpensive conversion means has been conventionally used. I couldn't find it.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art by providing a highly reliable and inexpensive means for converting the displacement of a spring into an electric signal. The purpose is to realize an inexpensive weight sensor for a microwave oven.

[0005]

In order to solve the above problems, a weight sensor for a microwave oven according to the present invention includes a turntable shaft that is driven by a motor and is movable in the axial direction.
A spring and a sound wave oscillating element and a sound wave receiving element having substantially the same resonance frequency are provided, the turntable shaft is biased upward by a spring, and one of the sound wave oscillating element and the sound wave receiving element is the turntable. The shaft is interlocked with the vertical movement of the shaft, and the other is fixed at a position facing it, and means for detecting a change in distance between the sound wave oscillating element and the sound wave receiving element is provided.

As the distance change detecting means, an oscillator having substantially the same frequency as the resonance frequency of the sound wave oscillating and receiving element and a phase difference detecting circuit are provided, and the output of the oscillator is branched into two, one of which is the sound wave. The oscillator is connected to the other, the other is connected to one of the two inputs of the phase difference detecting circuit, and the other of the two inputs of the phase difference detecting circuit is connected to the output of the sound wave receiving element.

[0007]

[Function] Since the turntable shaft is vertically movable and is biased upward by a spring, when food is placed on the turntable mounted on this shaft, a distance corresponding to the weight of the food is placed. Only the turntable shaft moves downward. One of the sound wave oscillating element and the sound wave receiving element is interlocked with the vertical movement of the turntable shaft,
Since the other is fixed at the opposite position, and the means for detecting the distance between both elements is provided, the output of the means for detecting the distance between both elements is a value corresponding to the weight of the food placed on the turntable. Show. That is, it functions as a weight sensor.

An oscillator having the same frequency as that of both elements and a phase difference detection circuit are provided as means for detecting the distance between both elements, the output of the oscillator is branched into two, one is connected to a sound wave oscillating element, and the other is detected as a phase difference. Since it is connected to one of the two inputs of the circuit and the other input is connected to the output of the acoustic wave receiving element, the two inputs of the phase difference detection circuit when the distance between the two elements decreases corresponding to the food weight. Among these, the phase of the oscillator that is one input does not change at all, whereas the input of the one that connects the output of the sound wave receiving element changes the phase corresponding to both element intervals,
As a result, the output of the phase difference detection circuit corresponds to the food weight.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a turntable of a microwave oven equipped with a weight sensor according to an embodiment of the present invention and its drive motor and its vicinity. A turntable 1 made of an enamel iron plate is mounted on a ceramic turntable shaft 3 of a drive motor 2 and rotated. The turntable shaft 3 is rotated at a speed of about 10 revolutions per minute by a speed reducing means provided inside the drive motor 2 and is slightly movable in the vertical direction. The drive motor 2 is fixed to a motor mounting bracket 4 made of a slightly thick iron plate, and the motor mounting bracket 4 has two metal plates of the same degree, a short Z-shaped bracket 5 and a tall Z-shaped bracket. 6 and 6 are welded. The turntable shaft 3 is attached to the short Z-shaped metal fitting 5.
A circular hole that penetrates without touching is opened, and one end of the coil spring 7 is fixed around the circular hole. A movable piece 8 also made of an iron plate is fixed to the other end of the coil spring 7.

The movable piece 8 has a substantially circular shape and has four claws extending in the axial direction of a circle on its outer circumference, and the tip of the claw has a disk shape.
The outer periphery of the ceramic buzzer 9 that emits a sound of kHz is fixed by adhesion. The short Z-shaped metal fitting 5 and the tall Z-shaped metal fitting 6 are fixed such that their lower sides are parallel to each other, but the coil spring 7 and the movable piece 8 are arranged between the two parallel sides. Position it. Therefore, the movable piece 8 and the ceramic buzzer 9 are also parallel to them, and are coaxial with the turntable shaft 3 and the round hole of the short Z-shaped metal fitting 5. A coaxial circular hole is also formed in the tall Z-shaped metal fitting 6, and a ceramic buzzer 10 having the same specifications as the ceramic buzzer 9 is adhered and fixed around the hole in the direction facing the buzzer 9.

Below the turntable 1, what is drawn by a chain double-dashed line is an oven bottom wall 11 of the microwave oven. A mounting member 12 is welded under this, and the motor mounting member 4 is screwed thereto. The lower end of the turntable shaft 3 has a surface-lubricated hemispherical shape and rotates in contact with the movable piece 8.

FIG. 2 is a perspective view of the ceramic buzzers 9 and 10. Although not drawn in FIG. 1 to avoid making it complicated, two thin lead wires are connected.

FIG. 3 is an electric circuit diagram and a voltage waveform diagram of each part of the circuit diagram. The output of the 6 kHz oscillator 13 having the same resonance frequency as the ceramic buzzers 9 and 10 is branched into two, one of which is connected to the ceramic buzzer 10. The other is connected to one of the two inputs of the phase difference detection circuit 15 via the attenuator 14. A ceramic buzzer 9 is connected to the other of the two inputs. Phase difference detection circuit 15
Is composed of two comparators 16 and 17 and one exclusive OR gate 18. The output of the exclusive OR gate 18 is output as a weight sensor via an integrating circuit 21 including a resistor 19 and a capacitor 20.

V ₁ and V ₂ are voltage waveforms applied to the inputs of the two comparators 16 and 17, and V ₃ and V 2
₄ is the output waveform, V ₅ is the output waveform of the exclusive OR gate 18, and V ₆ is the output waveform of the integrating circuit 21.

The operation of this embodiment will be described below. The turntable shaft 3 driven by the motor 2 is movable up and down, and is biased upward by a coil spring 7 via a movable piece 8. When food is placed on the turntable 1, a load is applied to the coil spring 7 via the turntable shaft 3 and the movable piece 8. The coil spring extends by an amount corresponding to this load, and between the two ceramic buzzers (sound wave transmitting element and sound wave receiving element) 9 and 10 provided to face the movable piece 8 and the tall Z-shaped metal fitting 6, respectively. Distance becomes shorter.

When the output of the oscillator 13 having a frequency of 6 kHz is added to the ceramic buzzer (sound wave emitting element) 10 having a resonance frequency of 6 kHz, the buzzer generates a sound of 6 kHz. The ceramic buzzer (sound wave receiving element) 9 provided facing this receives this sound wave and generates an electric signal of 6 kHz although weak. This is the V ₂ waveform of FIG. The output of oscillator 13 is applied to comparator 17 via attenuator 14, which is the V ₁ waveform.

When the distance between the two ceramic buzzers becomes shorter, the V ₂ waveform moves to the left side of the figure. This is because the time for propagating as sound in the space is shortened and the phase of the received signal waveform advances. 6kHz when the speed of sound is 340m / s
Since the wavelength of z is about 57 mm, if the distance between buzzers decreases by 1 mm, the phase advances by about 6 degrees. The advanced waveform is shown by a dashed line.

Two AC waveforms V₁, V₂Is the comparator
-V as output when applied to 16 and 17₃, V_Four
The square wave of is obtained. These two square waves are exclusive
V when added to Shibua Gate 18_FiveIs obtained. V
_FiveIs two AC waveforms V₁, V ₂Rectangle whose width is the phase difference of
It's a wave. When this is added to the integration circuit 21, a rectangular wave V_Fiveof
DC waveform V of voltage almost proportional to width₆Is obtained. Obey
Lever V₆Is the weight of the food on the turntable
The corresponding voltage value is shown. In other words, a weight sensor can be realized
It is a translation.

In this embodiment, a separately excited ceramic buzzer having a resonance frequency of 6 kHz is used as a sound wave transmitting and receiving element. This is because it also has the function of receiving. There is no problem in using a frequency other than 6 kHz. However, the setting of the distance between two elements and the determination of this frequency are important issues in terms of design. Some people may find it annoying because 6 kHz is audible to the human ear. To prevent this, for example, there are methods such as (1) using an ultrasonic element, (2) providing a sound absorbing material in the surroundings, or (3) sounding in a pulse shape for a short time. All of these methods of use are known and will not be discussed here.

An oscillator and a phase difference detection circuit were used to detect a distance change between two acoustic wave elements, but the invention is not limited to this. For example, a commercially available 400 kHz ultrasonic wave for detecting a distance with a resolution of 1 mm is used. It is also possible to use an element.

The attenuator 14 is used to make the input levels of the two comparators approximately the same, and a combination of resistors is generally used.

[0023]

As described above, according to the weight sensor for a microwave oven of the present invention, the axial displacement of the turntable corresponding to the food weight is detected by utilizing the difference in the arrival time of sound waves. Therefore, a weight sensor having the same accuracy and reliability as a spring balance can be realized with a simple configuration and a simple electric circuit, and this is effective in reducing the price of a microwave oven and improving cooking performance.

[Brief description of drawings]

FIG. 1 is a sectional view of a weight sensor of the present invention.

FIG. 2 is a perspective view of a sound wave transmitting element or a sound wave receiving element.

FIG. 3 is an electric circuit diagram of the weight sensor of the present invention.

[Explanation of symbols]

 3 Turntable Shaft 7 Coil Spring 9 Ceramic Buzzer (Sound Wave Transmission Element) 10 Ceramic Buzzer (Sound Wave Reception Element) 13 Oscillator 15 Phase Difference Detector

Claims (2)

[Claims] 1. A turntable shaft driven by a motor and movable in an axial direction, a spring, and a sound wave transmitting element and a sound wave receiving element having substantially the same resonance frequency, the turntable shaft comprising: The sound wave transmitting element and the sound wave receiving element are urged upward by a spring, and one of the sound wave transmitting element and the sound wave receiving element is interlocked with the vertical movement of the turntable shaft, and the other is fixed at a position facing this, and the sound wave transmitting element and the sound wave receiving element A weight sensor for a microwave oven, which is provided with means for detecting a change in distance between the two. 2. The distance change detecting means is provided with an oscillator having a frequency substantially the same as the resonance frequency of the sound wave transmitting and receiving elements and a phase difference detection circuit, and the output of the oscillator is branched into two, one of which is 2. The sound wave transmitting element, the other of which is connected to one of the two inputs of the phase difference detection circuit, and the other of the two inputs of the phase difference detection circuit is connected to the output of the sound wave receiving element. Weight sensor for microwave oven.