JPH0949751A - Weight sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple low-cost weight sensor capable of detecting and deciding the accurate weight without influence of heat and the like. SOLUTION: The weight sensor comprises a coiled spring L1 elongating or contracting in response to the weight W of a matter to be measured, an LC resonance circuit having the spring L1 formed as an inductance element, and weight deciding means for deciding the weight W of a matter to be measured based on the resonance frequency of the circuit. When the weight of the matter to be measured is loaded to the spring L1 , the spring L1 is elongated or contracted in response to the weight W, and the inductance of the coil is varied in response to the elongated or contracted amount. As a result, the resonance frequency of the circuit formed with the spring L1 as the inductance element is varied as well, and the weight W of the matter to be measured is decided by the weight deciding means based on the frequency signal responsive to the change.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weight sensor for automatically detecting the weight of an object to be weighed.

[0002]

2. Description of the Related Art For example, a cooking utensil equipped with a microcomputer such as a microwave oven is provided with a weight sensor for automatically detecting and measuring the weight of a food item placed on a turntable.

Conventionally, as this kind of weight sensor, for example, a differential transformer type, a strain gauge type, or a capacitance type is used.

[0004]

However, the above-mentioned differential transformer type is excited by a constant frequency and a constant voltage.
An electromotive force induced in the secondary coil changes depending on the position of the movable core, which includes a secondary coil, a movable iron core that moves following the descending motion of the object to be measured, and a secondary coil. Since these are connected in reverse polarity and taken out as an output, the structure is complicated and the cost is high.

The strain gauge type is also constructed by forming a bridge with a strain gauge, and detects a change in strain amount as a change in electric amount. Therefore, although the cost is comparatively lower than that of the differential transformer type, when the electric quantity output is converted into a digital signal and is taken into the microcomputer, the measured object is first placed on the turntable. The inertial load signal when placed is captured as a pulse, which may lead to erroneous measurement.

Further, the electrostatic capacitance type has a drawback that it is weak against heat, and there is a possibility that an electrostatic capacitance may change due to a temperature change due to the influence of heat, resulting in an erroneous determination. Therefore, it is not suitable for application to a device such as a microwave oven that is easily affected by heat from the heater.

An object of the present invention is to provide a weight sensor which solves the problems of the conventional weight sensor as described above and which enables simple and low cost detection and determination of weight accurately.

[0008]

In order to achieve the above object, the present invention comprises the following problem solving means.

That is, according to the present invention, a coil spring that expands and contracts according to the weight of the object to be measured, an LC resonance circuit formed by using the coil spring as an inductance element, and a change in the resonance frequency of the LC resonance circuit based on the change of the resonance frequency And a weight determining means for determining the weight.

Further, according to the present invention, in the configuration, there is provided an elevating member that supports the weight of the object to be measured and moves up and down according to the weight of the object to be measured, and the elevating member is suspended by a coil spring. .

Further, the invention of the present application is as follows.
It has an elevating member that supports the weight of the object to be measured and moves up and down according to the weight of the object to be measured, and the elevating member is supported by the coil spring.

Further, according to the present invention, the weight sensor in each of the above-mentioned configurations is configured for a microwave oven.

[0013]

The present invention has the following actions corresponding to the above-mentioned configurations.

First, as described above, the present invention is based on a coil spring that expands and contracts according to the weight of the object to be measured, an LC resonance circuit configured by using the coil spring as an inductance element, and a change in the resonance frequency of the LC resonance circuit. And a weight determination means for determining the weight of the object to be measured.

Therefore, when the weight of the object to be measured is loaded on the coil spring, the coil spring expands or contracts according to the weight, and the inductance of the coil portion changes according to the amount of expansion or contraction.

As a result, the resonance frequency of the LC resonance circuit constructed by using the coil spring as an inductance element also changes, and the weight determination means determines the weight of the object to be measured based on the frequency signal corresponding to the change.

In this case, if an elevating member such as a turntable that supports the weight of the object to be measured and that moves up and down according to the weight of the object to be measured is provided and the elevating member is suspended by a coil spring, the measurement can be performed. When an object is placed on the elevating member, the elevating member descends according to the weight of the measurement object placed on the elevating member, and the coil spring as an inductance element of the LC resonance circuit expands according to the descending amount. As a result, the resonance frequency of the LC resonance circuit becomes high.

Then, correspondingly, the weight determining means determines the weight.

Further, in the structure provided with the elevating member, when the elevating member is supported from below by a coil spring as an inductance element similar to the above, when the object to be measured is placed on the elevating member, The elevating member descends according to the weight of the measurement object placed on the elevating member, and the coil spring as the inductance element of the LC resonant circuit contracts according to the amount of processing, and the resonance frequency of the LC resonant circuit decreases. .

Then, correspondingly, the weight determining means determines the weight.

Further, when each of the above-mentioned components is constructed as a weight sensor for a microwave oven in particular, it is possible to change the inductance amount relatively easily by utilizing the raising / lowering operation of the turntable rotary shaft. .

[0022]

As a result of the above, according to the weight sensor of the present invention, the coil spring is simply expanded or contracted according to the weight of the object to be measured, and the change in the resonance frequency corresponding to the change in the length is detected. In addition, the weight of the measured object can be detected and determined at low cost.

Moreover, since the coil spring itself, which is the sensing means, is not affected by temperature and the inductance does not change due to temperature, it can be applied without any problem even when used as a weight sensor of a microwave oven, for example. Particularly in the case of a microwave oven, the resonance frequency can be changed by utilizing the raising and lowering operation of the turntable rotary shaft, which is convenient.

[0024]

【Example】

(Embodiment 1) FIGS. 1 to 3 show the configuration of a weight sensor unit of a high frequency heater such as a microwave oven according to Embodiment 1 of the present invention.

First, FIG. 1 shows the overall structure of the same sensor unit. In FIG. 1, reference numeral 1 is a bottom wall forming the bottom of the inner wall of the microwave oven heating chamber 2, for example. A support shaft insertion hole 5 for penetrating the rotation support shaft 4 of the turntable 3 is formed in a substantially central portion of the bottom wall 1, and the rotation support shaft of the turntable 3 is supported through the support shaft insertion hole 5. The shaft 4 is inserted from the lower side and is projected into the upper heating chamber 2 by a predetermined height as shown in the figure.

The rotation support shaft 4 of the turntable 3 is horizontally supported in a sensor box 11 fixedly provided in the housing of the microwave oven main body and has a predetermined thickness and width with high spring rigidity. The leaf spring 12 is elastically and rotatably supported above the leaf spring 12, and in the middle (substantially the central portion) of the leaf spring 12, a driven gear 7 is interposed via a key groove 7a and a spindle side key 4a as shown in FIG. The splines are fitted so that they can slide relative to each other in the thrust direction. The driven gear 7 is meshed with a drive gear 9a of a turntable drive motor 9 fixed to the ceiling surface of the sensor box 11.

Reference numeral 13 is a support member having a bearing portion for fixing the driven gear 7 at a predetermined position and rotatably supporting the same. The ball bearing 10 is attached to the lower boss portion of the driven gear 7. Support through. As a result, the rotary support shaft 4 can slide up and down, but stable rotation drive by the turntable drive motor 9 is also possible.

A leaf spring 12 supporting the rotary support shaft 4
A control board 15 is provided below the tip 12a side of the sensor box 11 so as to be fixed to the vertical wall portion 14a of the sensor box 11 on the bottom portion 14 side. A coil spring L ₁ having coil portions la and lb on both left and right sides is stretchably stretched between the control board 15 and the tip portion 12a of the leaf spring 12, as shown in detail in FIG. There is.

Both ends of the coil spring L ₁ which are continuous with each other are provided in the weight detection circuit of the control board 15 shown in FIG.
It is connected and fixed by screws so as to be incorporated as a first inductance element forming the sensor section. Therefore, in this structure, when an object to be heated is placed on the turntable 3, the rotary support shaft 4 moves downward by a predetermined amount against the supporting rigidity of the leaf spring 12 in accordance with the weight W of the object to be heated. Be lowered to. Then, the length of the coil portions la and lb of the coil spring L ₁ is shortened according to the descending amount, the pitch between the coil loops of the coil portions la and lb is reduced, and the inductance value is increased.

Then, the resonance frequency fo of the weight detection circuit shown in FIG. 3 changes (decreases) in response to the increase in the inductance value, and the microcomputer 2 based on the change value.
The weight W of the object to be heated is detected by 0.

That is, in the weight detection circuit of FIG. 3, first, the combined inductance component (la + lb) of the coil portions la and lb of the coil spring L ₁ is used as the first inductance element, and the capacitor C ₁ as the capacitance element is used as the first inductance element. A second high-frequency series resonance circuit (Hartley LC oscillation circuit) is formed by connecting the second inductance element L ₂ in series via {fo = 1 / (2π√L ₁ + L ₂ + C
₁ )}.

And the L₁, C₁, L₂Series resonance circuit
R on the output side of₁, C₂Emitter connection via bias circuit
A ground type amplification transistor Q is provided, and the amplification transistor
Only the AC component of the oscillation frequency output when Q is turned ON or OFF
Coupling capacitor C _ThreeTake out through the waveform
After the waveform is shaped through the shaping circuit 16, the frequency signal is sequentially received.
Signal / voltage signal conversion circuit 17 and A / D conversion circuit 18
Convert it to a digital signal and finally
Input to the control unit 20 and determined as a weight value. What
Oh, R in the figure₂Is a feedback resistance of the amplification transistor Q, C_Four
Is an AC bypass diode.

As described above, according to the weight sensor of the embodiment of the present invention, the coil spring L ₁ is extended according to the weight W of the object to be measured through the turntable 3, the rotary support shaft 4, and the leaf spring 12, and the extension thereof. By only detecting the change in the resonance frequency fo of the resonance circuit of the weight detection circuit corresponding to the change in length,
The weight W of the object to be heated can be accurately detected and determined very easily and at low cost.

Moreover, since the coil spring L ₁ itself, which is the sensing means, is not affected by temperature and does not change in inductance value due to temperature as in the electrostatic capacitance method, when used as a weight sensor for a microwave oven as described above. Can be used without any problems.

(Embodiment 2) In the above embodiment, the coil spring L ₁ is contracted according to the weight of the object to be heated to increase the inductance value and change the resonance frequency fo. As an example 2, as shown in FIG. 4, one end 19b of a support plate 19 supporting the rotary support shaft 4 of the turntable 3 is vertically rotated on a shaft 21 fixed between the left and right side walls of the sensor box 11. The other end 19a is supported and supported by a coil spring L ₁ as an inductance element similar to the above so as to be suspended and supported between the other end 19a and the support plate 13 of the driven gear 7 according to the weight W of the object to be heated. The coil spring L ₁ may be extended to reduce its inductance value (in this case, the above fo becomes higher).

In this case, the coil spring L ₁ may be shared with the support spring of the rotary support shaft 4 of the turntable 3 or may be provided separately.

(Embodiment 3) Further, in the weight detection circuit of FIG. 3 in the above-described Embodiment 1, for example, as shown in FIG. 5, a combined inductance adjusting coil L ₁ ′ is connected in series to the coil spring L _{1 of the} sensor section. It may be inserted.
By doing so, the span of inductance change can be expanded.

(Fourth Embodiment) Furthermore, in the weight detection circuit of FIG. 3 described above, for example, as shown in FIG.
It goes without saying that the _second side may be reversely configured as a sensor section.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a weight sensor section of a high-frequency heater according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a configuration of a main part of the weight sensor.

FIG. 3 is a circuit diagram showing a configuration of a weight detection circuit of the weight sensor.

FIG. 4 is a cross-sectional view showing the structure of the weight sensor section of the high-frequency heater according to the second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a weight detection circuit of the weight sensor of the high-frequency heater according to the third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a weight detection circuit of a weight sensor of a high frequency heater according to a fourth embodiment of the present invention.

[Explanation of symbols]

2 is a heating chamber, 3 is a turntable, 4 is a rotation support shaft, 7 is a driven gear, 9 is a turntable motor, 9a is a drive gear, 12 is a leaf spring, 19 is a support plate, L ₁ is a coil spring,
C ₁ is a capacitor, and 20 is a microcomputer unit.

Claims (4)

[Claims] 1. A coil spring that expands and contracts according to the weight of an object to be measured, an LC resonance circuit configured by using the coil spring as an inductance element, and the weight of the object to be measured is determined based on a change in the resonance frequency of the LC resonance circuit. A weight sensor comprising a weight determination means. 2. The weight according to claim 1, further comprising an elevating member that supports the weight of the object to be measured and moves up and down according to the weight of the object to be measured, and the elevating member is suspended by a coil spring. Sensor. 3. The weight sensor according to claim 1, further comprising an elevating member that supports the weight of the object to be measured and that moves up and down according to the weight of the object to be measured, and the elevating member is supported by a coil spring. . 4. The weight sensor according to claim 1, wherein the weight sensor is configured as a weight sensor for a microwave oven.