JPH09218080A - Tuning fork type load cell and weighing instrument using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tuning fork type load cell and a weighing instrument using the load cell capable of improving the accuracy insusceptible of the temperature variation. SOLUTION: A load detection mechanism 3 is attached between upper and lower beam sections 2c, 2d of a strain induction body 2. Since a tuning fork vibrator element 6 is fixed between the upper and lower beam sections 2c, 2d wherein each of temperatures is roughly the central value of the temperatures of a fixing section 2a and a movable section 2b of the strain induction body 2 and the temperatures are slightly different from each other, the influence by the temperature of the fixing section 2a or movable section 2b is reduced even when there exists a temperature gradient between the fixing section 2a and movable section 2b and a zero point shift with respect to the temperature variation is small, then it is superior in zero point stability, thereby improving the accuracy of the load detection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuning fork type load cell and a weighing device using the same, and more particularly to improvement of load detection accuracy.

[0002]

2. Description of the Related Art Generally, when an external force is applied to a tuning fork vibrator that vibrates at a natural frequency, the natural frequency changes in response to the external force, and the external force F applied to the tuning fork vibrator and the natural fork of the tuning fork vibrator. Regarding the frequency f, the relationship of the following expression (1) is established. ^{F = C1 · f 2 -C2 (} C1, C2; constant) (1) thus to vary the natural frequency, rather than changing the shape of the tuning fork vibrator, dynamic state of a vibrating object ( Since the tuning fork vibrator is sensitive to the input, the load detection mechanism using the tuning fork vibrator that is sensitive to this input has conventionally detected a small amount of mass (mg unit). It has been used in weighing devices such as electronic balance scales that measure with high accuracy.

Here, in order to achieve a high degree of load detection accuracy, a load is added to the tuning fork vibrator so that an external force is applied to the tuning fork vibrator only in one predetermined direction. The mechanism needs to be configured. A two-beam type strain element is conceivable as such a load applying mechanism.

[0004]

However, in the weighing device using the strain-generating body, the fixed portion of the strain-generating body is fixed to the base, and the weighing pan for supporting the object to be weighed is fixed to the movable portion. However, in the two-beam type strain element, heat is transferred from the fixed part to the movable part due to heat generation of the motor and the like from the movable part to the fixed part through the weighing pan on which a high or low temperature object is placed. And has a temperature gradient between the moving parts. Therefore, if a tuning fork vibrator is attached between the fixed part and the movable part of such a strain generating body, the zero point variation is large with respect to the temperature change and the zero point stability is poor, so that there is a problem that high accuracy cannot be secured. there were.

Further, when the load detecting mechanism is incorporated into the flexure element, there is a problem that a load detection error occurs due to a difference in thermal expansion coefficient between the load detecting mechanism and the flexure element to which the load detecting mechanism is attached.
For example, an integrated strain element in which a fixed portion, a movable portion, and a beam portion are integrally formed is considered in terms of workability and material cost.
Normally, aluminum alloy or steel is used, but the load detection mechanism including the tuning fork vibrator uses a constant elastic alloy such as Elinvar having a small Young's modulus temperature coefficient so that the spring constant does not change with temperature. Therefore, the coefficient of thermal expansion of the material of the strain generating body is larger than the coefficient of thermal expansion of the material of the tuning fork vibrator, and the change in the size of the strain generating body with temperature is larger than that of the tuning fork vibrator. For example, when the material of the flexure element is an aluminum alloy, the coefficient of thermal expansion of the flexure element is about three times that of the tuning fork vibrator. When a load cell is constructed with such a strain element and a tuning fork vibrator, when the ambient temperature changes, slippage occurs in the bolt tightening parts of both materials due to the difference in the thermal expansion coefficient of both materials, and the reproducibility of the zero point is improved. Since it becomes worse, it becomes difficult to secure the load detection accuracy.

An object of the present invention is to solve the above problems and provide a tuning fork type load cell capable of achieving high accuracy without being affected by temperature changes, and a weighing device using the same. .

[0007]

In order to achieve the above object, a tuning fork type load cell according to a first aspect of the present invention has a fixed portion and a movable portion to which a load is applied on the left and right, and the movable portion is an upper and lower beam portion. The flexure element is supported by the fixed part via the, and the load detection mechanism attached to the flexure element. The load detection mechanism is mounted and added between a base portion attached to either one of the upper and lower beam portions, a lever portion supported by the base portion via a fulcrum, and the base portion and the lever portion. A tuning fork vibrator whose natural frequency changes according to the load, and the load point of the lever portion is connected to the other of the upper and lower beam portions.

According to the above construction, the load detecting mechanism is mounted between the upper and lower beam portions of the strain-generating body. Therefore,
Since the tuning fork vibrator is fixed between the upper and lower beams where the temperature of the fixed part and the movable part of the flexure element is approximately the intermediate value and the temperature difference between them is small, the temperature gradient between the fixed part and the movable part is small. Even if there is, reduce the effect of heat from the fixed and movable parts,
Since the zero point variation is small with respect to the temperature change and the zero point stability is excellent, the load detection accuracy can be improved.

In the load cell according to the second aspect, an intermediate material made of a material having a coefficient of thermal expansion between the beam portion and the base portion is further inserted between the beam portion and the base portion. Therefore, since the hysteresis due to the thermal history between the two is reduced, it is possible to prevent slippage due to temperature change, improve reproducibility, and improve load detection accuracy.

According to a third aspect of the present invention, there is provided a weighing device according to the first aspect.
Alternatively, the load cell according to claim 2 and a weighing value generation circuit for obtaining a weighing value from a signal obtained by a load detection mechanism of the load cell, wherein a fixed portion of the load cell is fixed to a base, and a movable portion is to be weighed. The weighing platform that supports the object is fixed. Therefore, it is possible to reduce the size and cost of the weighing device, and it is possible to accurately measure a minute mass.

A load cell according to a fourth aspect is a differential type load cell having the flexure element and a first load detection mechanism and a second load detection mechanism mounted on the flexure element.
That is, each of the first load detection mechanism and the second load detection mechanism includes a base portion attached to either one of the upper and lower beam portions of the flexure element, and a lever portion supported by the base portion via a fulcrum. A tuning fork vibrator whose natural frequency changes according to an applied load, which is attached between the base portion and the lever portion, and the load point of the lever portion is connected to the other of the upper and lower beam portions. When a load is applied to the movable part, a tensile force acts on the tuning fork vibrator of one load detection mechanism, and a compression force acts on the tuning fork vibrator of the other load detection mechanism.

A load cell according to a fifth aspect of the present invention is the load cell according to the fourth aspect, wherein the both load detecting mechanisms are attached to one of the front and rear surfaces of the flexure element.

According to a sixth aspect of the present invention, in the load cell according to the fourth aspect, the first load detecting mechanism is mounted on a front surface of the flexure element, and the second load detecting mechanism is attached on a rear surface of the flexure element. ing.

According to the load cell of the fourth to sixth aspects, since the first and second load detecting mechanisms are mounted between the upper and lower beam portions of the flexure element, the first and second load detecting mechanisms are fixed from the fixed portion and the movable portion. By reducing the influence of heat and improving the zero point stability against temperature changes, one of the tuning fork vibrators of both load detection mechanisms is a tension type and the other is a compression type, so
By calculating the load differentially from the frequency changes of both tuning fork vibrators, even if the thermal expansion coefficient of the flexure element is different from that of the tuning fork vibrator when the temperature around the flexure element changes. Since the temperature deformation is canceled out, it is not affected by the temperature change, so that high load detection accuracy can be obtained.

According to a seventh aspect of the present invention, there is provided a weighing device according to the fourth aspect.
The load cell according to any one of claims 1 to 6 and a weighing value generation circuit for obtaining a weighing value from a difference between signals obtained by both load detection mechanisms of the load cell, wherein a fixed portion of the load cell is provided on a base. The weighing table, which is fixed and supports the object to be weighed, is fixed to the movable portion. Therefore, the zero-point stability of the weighing device can be improved, and the minute mass can be weighed with high accuracy.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a perspective view of a tuning fork type load cell according to an embodiment of the present invention, and FIG. 2 shows a configuration diagram of a weighing device using the load cell of FIG. This device comprises a tuning fork type load cell 1 having a flexure element 2 shown in FIG. 1 and a load detecting mechanism 3 attached to the flexure element 2, and FIG.
The oscillator circuit 14, the cycle counter 16, and the weighing value generating circuit 15 including the digital signal processing circuit (DSP) 18 shown in FIG.

The flexure element 2 has a fixed part 2a and a movable part 2b to which a load is applied on the left and right, and the movable part 2b is supported by the fixed part 2a via upper and lower beam parts 2c and 2d. The fixed portion 2a is fixed to the base F shown by the chain double-dashed line, and the weighing platform K shown by the chain double-dashed line is fixed to the movable part 2b. Left and right fixed part 2a, movable part 2
Hollow portions 9 each having four semi-circles at the four corners are formed in a portion surrounded by b and the upper and lower beam portions 2c and 2d. The first attachment flange 8A extends from the upper beam portion 2c toward the center of the hollow portion 9, and the second beam portion 2d extends from the lower beam portion 2d.
The mounting flange 8B extends and these mounting flanges 8B
A and 8B are formed at positions recessed from the front surface M of the flexure element 2. This is because the load detection mechanism 3 is housed in this recess without traveling forward from the flexure element 2.
Further, two elliptic holes H1 reaching the hollow portion 9 are formed on the upper surface and the bottom surface of the flexure element 2 to reduce the spring constant of the flexure element 2 as a whole.

The flexure element 2 has a parallelogram (parallelogram) structure integrally formed of, for example, an aluminum alloy material or an iron material. The load cell 1 in which the load detecting mechanism 3 is attached to the flexure element 2 receives the applied load and transmits the force to the tuning fork vibrator 6 in only one predetermined direction.

The base 4A of the load detecting mechanism 3 is
In this embodiment, it is attached to the second attachment flange 8B extending from the lower beam portion 2d by a fastening means such as a screw B1 and is provided on the right side of the base portion 4A via the fulcrum P1 and the lever portion 5.
A is supported.

The lever portion 5A extends in the vertical direction, and the load point P2 of the lever portion 5A is connected to the upper beam portion 2 at the left position of the lever portion 5A via the connecting piece 7B extending in the horizontal direction.
It is connected to the first mounting flange 8A extending from c by a fastening means such as a screw B2. The tuning fork vibrator 6 located to the left of the lever portion 5A is attached between the base portion 4A and the lever portion 5A via horizontal support pieces 7A. The natural frequency of the tuning fork vibrator 6 changes according to the applied external force.

FIG. 3 shows a load detecting mechanism 3 showing an actual shape.
The front view of is shown. As shown in this figure, the support piece 7A (fixed end) and each portion forming the fulcrum P1 (α to γ in the figure) and a part of the connecting piece 7B (load end) (δ and ε in the figure) are finely processed. , The constraint due to the bending moment when the external force Y is applied to the load cell 1 is removed.

The load detecting mechanism 3 shown in FIG. 1 is turned upside down to attach the base 4A to the first mounting flange 8A and the load point P2 to the second mounting flange 8B via the connecting piece 7B.
Alternatively, the lever portion 5A may be positioned on the left side of the base portion 4A and the tuning fork vibrator 6 may be positioned on the right side of the lever portion 5A by reversing the left and right sides. . However, in these cases, a compressive force acts on the tuning fork vibrator 6.

In FIG. 2, the tuning fork vibrator 6 of the load detecting mechanism 3 includes two vibrating reeds 10 symmetrically and parallel to the central axis, and two vibrating reeds 10 respectively connecting both ends thereof. The piezoelectric element 12a, 12b is attached to both side surfaces of the coupling portion 11 by adhesion or vapor deposition. Each of the piezoelectric elements 12a and 12b is connected to an oscillation circuit 14 installed outside. Before the external force is applied, the piezoelectric element 12a is excited by the oscillation circuit 14 to oscillate the two vibrating reeds 10 at the natural frequency, and the natural frequency is input to the oscillation circuit 14. When an external force is applied in this state, the vibrating piece 10 vibrates at a natural frequency changed according to the external force (tensile force Fp or compressive force Fc) applied in the axial direction, and the natural frequency is from the piezoelectric element 12b. It is output to the oscillation circuit 14 and taken out.

Further, as shown in FIG. 4, an intermediate member 36 is provided between the flexure element 2 and the base portion 4A. As the intermediate material 36, a material such as an iron-based material having an intermediate value of the coefficient of thermal expansion of the load detecting mechanism 3 made of a constant elastic alloy such as Elinvar and the strain generating element 2 made of an aluminum alloy is used. . The intermediate material 36 is preferably made of a material having a coefficient of thermal expansion close to that of the load detection mechanism 3. This is because by sandwiching a material having a coefficient of thermal expansion close to that of a constant temperature material between the flexure element 2 and the base portion 4A, hysteresis due to the thermal history between the two is reduced, reproducibility is improved, and temperature correction becomes possible and load detection accuracy is improved. This is because it helps improve. The intermediate member 36 may not be provided depending on the degree of influence on the temperature change between them.

Further, the second mounting flange 8B has a groove 8C.
have. This reduces the contact area between the intermediate member 36 and the second mounting flange 8B. That is, the second mounting flange 8B extending from the beam portion 2d of the flexure element 2
The heat receiving area from the load detecting mechanism 3 to the base portion 4A is reduced to reduce the influence on the temperature change. The groove 8C may not be provided depending on the degree of influence of heat on the flexure element 2.

The operation of this weighing device will be described below. In FIG. 1, when the object to be weighed is placed on the weighing platform K and its load W is applied, the movable portion 2b is displaced in the arrow Y direction. Then, since the connecting piece 7B of the load detecting mechanism 3 is pulled leftward by the relative displacement of the upper and lower beam portions 2c and 2d, the pulling force Fp by the load W is applied to the tuning fork vibrator 6 rightward by the lever principle. Works. Here, heat is transmitted from the fixed portion 2a to the movable portion 2b by heat generated by a motor or the like, and from the movable portion 2b to the fixed portion 2a through a weighing pan on which a high or low temperature object is placed. A temperature gradient is generated between the fixed portion 2a and the movable portion 2b. Therefore, when the tuning fork vibrator 6 of the load detection mechanism 3 is mounted between the fixed portion 2a and the movable portion 2b, the zero point variation is large with respect to the temperature change due to the temperature gradient between them, and the zero point stability is poor, so that high accuracy is achieved. Cannot be secured. On the other hand, according to the present invention, the load detecting mechanism 3 is provided between the beam portion 2c and the beam portion 2d, which have an intermediate temperature between the fixed portion 2a and the movable portion 2b and a small temperature difference between the upper and lower portions. It is fixed. Therefore, the influence of heat from the left and right fixed portions 2a and the movable portion 2b on the tuning fork vibrator 6 is reduced, and the zero point variation is small with respect to the temperature change of the flexure element 2, and the zero point stability is excellent. The tensile force Fp acts accurately according to the load W.

When the resonator element 10 shown in FIG. 2 vibrates at the natural frequency f1 increased in accordance with the tensile force Fp, the natural frequency f1 is output to the oscillation circuit 14 and taken out. The natural frequency f1 is input to the DSP 18 by inputting the clock input C to the cycle counter 16 for counting in order to measure its period T1. Then, by the linearization means 22 of the DSP 18, F = C1 · f1 ² −C2 in the equation (1).
Natural frequency f1 to satisfy (f1 = 1 / T1)
The square of (cycle T1) and the tensile force Fp are linearly related, and unnecessary portions such as the natural frequency of the load cell 1 are removed by filtering means 24 and 25 such as low-pass filters provided in two stages. In this way, DSP18
Is output as a measured value corresponding to the load W of the object to be measured.

In this way, the tuning fork type load cell 1 is
Since the tuning fork vibrator 6 of the load detection mechanism 3 is attached between the upper and lower beams 2c and 2d of the strain body 2, the zero point fluctuation is small with respect to the temperature change of the fixed portion 2a and the movable portion 2b. Therefore, the load detection accuracy can be improved. Further, since the intermediate member 36 and the groove portion 8c are provided, the zero point variation with respect to the temperature change is further reduced, and the load detection accuracy is further improved.

Further, by making the flexure element 2 integral, there are the following advantages. That is, if a beam consisting of two leaf springs, which are separate parts, is used, and two connecting and supporting parts are used to connect them in parallel, the load adding mechanism is composed of a total of four parts. Is sensitive to input, in order to make use of this sensitive characteristic, in order to incorporate it and manufacture a load applying mechanism, the above components are precisely processed, assembled accurately, and fine adjustment is made. It required a high degree of skill such as performing. For this reason, manufacturing is complicated and a connecting component is also required, so that it is difficult to reduce the size and cost. On the other hand, since the flexure element 2 is an integral type, it is easy to assemble with the load detection mechanism, and the dimensional accuracy is built in during machining, so that the load cell 1 with high accuracy can be easily manufactured at low cost. it can. Further, since the integrated structure eliminates the connecting parts, the load cell 1 can be downsized.

Next, the weighing device of the second embodiment will be described. FIG. 5 shows a perspective view of a tuning fork type load cell according to the second embodiment, and FIG. 6 shows a signal processing unit of a weighing device using the load cell of FIG. In order to solve the problem of the decrease in load detection accuracy due to the difference in the coefficient of thermal expansion between the material of the strain generating element 2 and the tuning fork vibrator 6, the measuring device is used in this measuring device.
Two load detecting mechanisms are provided in a differential type on one of the front and rear surfaces.

That is, the weighing device is provided with a tuning fork type load cell 1 shown in FIG. 5, which comprises a strain-generating body 2 and first and second load detecting mechanisms 3A and 3B mounted on the strain-generating body 2, and FIG. The oscillator circuit 14, the counter 16, the digital signal processing circuit 18, and the weighing value generating circuit 35 including the subtracter 20 are provided. Further, a fixed portion 2a of the flexure element is fixed to a base F shown by a chain double-dashed line in FIG. 5, and a weighing platform K similarly shown by a chain double-dashed line is fixed to a movable part 2b. . In addition, the first and second load detection mechanisms 3A and 3B
Is the fixed portion 2a or the movable portion 2 as in the first embodiment.
In order to reduce the effect of heat from b, the beams 2c, 2
It is arranged between d.

The load cell of this embodiment includes the first and second load cells.
The load detecting mechanisms 3A and 3B are formed in an integral structure so as to have the same shape and the same size and the same frequency change due to the same external force, and the first load detecting mechanism 3A is provided above the front surface M of the flexure element 2. Attached, and the second load detection mechanism 3B at the bottom
By mounting the above and making both load detection mechanisms 3A and 3B differential, the temperature dependence of the zero point due to the difference in the thermal expansion coefficient of both materials is compensated.

The first load detecting mechanism 3A is mounted below the front surface M of the flexure element 2, and the base portion 4A of the first load detecting mechanism 3A extends from the beam portion 2d in this embodiment.
Is attached to the base portion 4A by a fastening means such as a screw B1 and a lever portion 5A extending vertically is supported to the right of the base portion 4A via a fulcrum P1. The load point P2 of the lever 5A is
A first mounting flange 8A extending from the beam portion 2c at a position to the left of the lever portion 5A via a connecting piece 7B extending in the horizontal direction.
To each other by fastening means such as a screw B2. The tuning fork vibrator 6 located on the left side of the lever portion 5A is attached between the base portion 4A and the lever portion 5A via support pieces 7A extending in the horizontal direction. The natural frequency of the tuning fork vibrator 6 changes according to the applied external force (tensile force Fp).

The second load detecting mechanism 3B is mounted above the front surface M of the flexure element 2, and its base portion 4B is connected to a second mounting flange 8B extending from the beam portion 2d by a fastening means such as a screw B1. And a lever portion 5B extending in the vertical direction is supported on the left side of the base portion 4B via a fulcrum P1. The load point P2 of the lever portion 5B is connected to the first mounting flange 8A extending from the beam portion 2c at the right side position of the lever portion 5B through a connecting piece 7B extending in the horizontal direction by a fastening means such as a screw B2. ing. The tuning fork vibrator 6 located on the right side of the lever portion 5B is attached between the base portion 4B and the lever portion 5B via support pieces 7A extending in the horizontal direction. The natural frequency of the tuning fork vibrator 6 changes according to the applied external force (compressive force Fc).

Both the first load detecting mechanism 3A and the second load detecting mechanism 3B are turned upside down, that is, the bases 4A and 4B of both detecting mechanisms are attached to the first mounting flange 8A of the upper beam portion 2c. , Load points P of both levers 5A and 5B
2 through the connecting piece 7B to the second beam portion 2d of the lower beam portion 2d.
You may make it attach to the attachment flange 8B.

The first load detecting mechanism 3A and the second load detecting mechanism 3B are turned upside down, that is, the base portion 4A of the first load detecting mechanism 3A is attached to the second mounting flange 8B of the lower beam portion 2d. The base portion 4B of the two-load detection mechanism 3B can also be attached to the first attachment flange 8A of the upper beam portion 2c. In that case, for example, both lever parts 5A,
5B together, to the right of the bases 4A, 4B (may be left)
And the base 4A of the first detection mechanism 3A.
Is attached to the second mounting flange 8B extending from the beam portion 2d, and the load point P2 of the lever portion 5A located on the right side of the base 4A is attached to the first mounting portion extending from the beam portion 2c via the connecting piece 7B. While being attached to the flange 8A, the base 4B of the second detection mechanism 3B is attached to the first attachment flange 8A extending from the beam portion 2c, and the load point P2 of the lever portion 5B located to the right of the base 4B is connected. You may make it attach to the 2nd attachment flange 8B extended from the beam part 2d via the piece 7B.

The operation of this weighing device will be described below. First, the object to be weighed is placed on the weighing platform K in FIG.
When is added, the movable portion 2b is displaced in the arrow direction. Then, the tensile force Fp due to the load W acts upward on the tuning fork vibrator 6 of the first load detecting mechanism 3A mounted on the front surface side of the flexure element 2 by the lever principle. On the other hand, the piezoelectric element 12a in FIG. 6 is excited by the oscillation circuit 14,
When the vibrating element 10 vibrates at the natural frequency f1 increased according to the tensile force Fp, the natural frequency f1 is changed to the piezoelectric element 1
It is output from 2b to the oscillation circuit 14 and taken out.

This natural frequency f1 has a period T1 (1
In order to measure / f1), the clock input C is input to the cycle counter 16 for counting and input to the DSP 18. The natural frequency f1 (cycle T1) and the tensile force Fp are F = C1f1 ² -C2 (f1 =
1 / T1), the linearizing means 22 of the DSP 18 causes the natural frequency f1 to satisfy the equation (1).
The square of (cycle T1) and the tensile force Fp are linearly related to each other, and the load cell 1 is provided by filtering means 24 and 25 such as low-pass filters provided in two stages.
Unnecessary components such as natural frequency of are removed. Then, the tensile force Fp corresponding to the squared value of the increased natural frequency f1 (cycle T1) of the tuning fork vibrator 6 is output to one input of the subtractor 20.

On the other hand, when the object to be weighed is placed on the weighing platform K and the movable portion 2b is displaced in the direction of the arrow, the tuning fork vibrator 6 of the second load detecting mechanism 3B mounted on the rear surface side is operated by the lever principle. A compressive force Fc due to the load W acts in the upward direction. When the vibrating element 10 vibrates with the natural frequency f2 reduced according to the compression force Fc while the piezoelectric element 12a is excited, the natural frequency f2 is output from the piezoelectric element 12b to the oscillation circuit 14. Taken out. Next, similarly to the above, the compression force −Fc corresponding to the squared value of the reduced natural frequency f2 (cycle T2) of the tuning fork vibrator 6 is applied to the other side of the subtractor 20 via the counter 16 and the DSP 18. It is output to the input.

In the subtractor 20, the first load detecting mechanism 3
From the tensile force Fp corresponding to the squared value of the increased natural frequency f1 from A, the compressive force -Fc corresponding to the squared value of the decreased natural frequency f2 from the second load detection mechanism 3B is subtracted. , (Fp + Fc). Therefore, the subtractor 20 outputs the measured value corresponding to the load W of the object to be measured.

Here, the difference in temperature change between the flexure element 2 and the tuning fork vibrator 6 caused by the difference in the coefficient of thermal expansion of the material is
Since the second load detection mechanisms 3A and 3B are of the differential type,
It is canceled as follows, and the temperature dependence of the zero point of the load cell 1 is compensated.

That is, when the ambient temperature of the load cell 1 changes, thermal stress is generated in the load cell 1 due to the difference in thermal expansion coefficient between the materials of the strain generating body 2 and the tuning fork vibrator 6, and the two strains are generated. Tuning fork vibrators 6 mounted on the front and rear surfaces of the body 2
Is transmitted as an external force to. However, since the external force is a force having the same direction and the same magnitude with respect to the two tuning fork vibrators 6, the change amount and the changing direction of the natural frequency of each tuning fork vibrator 6 due to the force are the same. become. Therefore, the subtractor 20 causes the changed natural frequency from the tuning fork vibrator 6 of the second load detection mechanism 3B from the force corresponding to the changed natural frequency from the tuning fork vibrator 6 of the first load detection mechanism 3A. When the force corresponding to the frequency is subtracted, the change due to this temperature change is canceled and does not appear in the final output. Therefore,
The temperature dependence of the zero point of the load cell 1 can be sufficiently reduced, and high accuracy can be achieved.

As another form of this differential type, FIG. 7 shows a third type in which two load detection mechanisms are provided on both sides of the flexure element in a differential type.
1 shows a tuning fork type load cell of an embodiment. Again, the second
Similar to the embodiment, both load detecting mechanisms are arranged between the beams 2c and 2d in order to reduce the influence of heat from the movable portion 2b or the fixed portion 2a.

In this tuning fork type load cell, the flexure element 2 is symmetrical in the front-rear direction and also in the upper-lower symmetrical shape, and like the second embodiment, the first and second load detecting mechanisms 3A, 3B are provided. They have the same shape and the same size, and are formed as an integral structure so that the same frequency change is generated by the same external force. The first load detection mechanism 3A is attached to one of the front and rear surfaces of the flexure element 2 and the other to this. By mounting the second load detection mechanism 3B which is upside down and making both the load detection mechanisms 3A and 3B differential, the temperature dependence of the zero point due to the difference in thermal expansion coefficient between the two materials is compensated. There is. In the load cell of the third embodiment, since both load detection mechanisms 3A and 3B are provided on both sides of the strain generating element 2, the zero point variation with respect to temperature change is smaller than that of the load cell provided on one side. The influence of heat on the body 2 is smaller than that of the load cell of the second embodiment. The circuit that processes the signal from the load cell is the same as that in FIG. 6, and thus detailed description thereof is omitted.

In FIG. 7A, the first load detection mechanism 3
A is attached to the front surface M side of the flexure element 2, and its base portion 4A has a second mounting flange 8B extending from the beam portion 2d.
It is attached to the base portion 4A by a fastening means such as a screw B1, and a lever portion 5A extending vertically is supported to the right of the base portion 4A via a fulcrum P1. The load point P2 of the lever 5A is
A first mounting flange 8A extending from the beam portion 2c at a position to the left of the lever portion 5A via a connecting piece 7B extending in the horizontal direction.
Are connected to each other by fastening means such as a screw B2. The tuning fork vibrator 6 located on the left side of the lever portion 5A is attached between the base portion 4A and the lever portion 5A via the support pieces 7A extending in the horizontal direction. The natural frequency of the tuning fork vibrator 6 changes according to the applied external force (tensile force Fp).

In FIG. 7B, the second load detecting mechanism 3
B is attached to the rear surface N side of the flexure element 2. Base 4B
Is attached to the second mounting flange 8B at a position almost opposite to the screw B1 fastening position on the front surface by screw fastening or the like in the same manner as described above, and to the right of the base 4B via the fulcrum P1 in the vertical direction. The lever portion 5B extending in the direction of is supported. The load point P2 of the lever portion 5B has a horizontally extending connecting piece 7B.
The right side of the lever 5B through the first
It is connected to the mounting flange 8A by screw fastening or the like. Then, the tuning fork vibrator 6 located on the left side of the lever portion 5B is attached between the base portion 4B and the lever portion 5B via the support pieces 7A extending in the horizontal direction. The natural frequency of the tuning fork vibrator 6 changes according to the applied external force (compressive force Fc).

The first load detecting mechanism 3A and the second load detecting mechanism 3B are turned upside down, that is, the bases 4A and 4B of both detecting mechanisms are attached to the first mounting flange 8A extending from the beam portion 2c. Load point P2 of both levers 5A and 5B
A second portion extending from the beam portion 2d through the connecting piece 7B.
You may make it attach to the attachment flange 8B.

The first load detecting mechanism 3A is shown in FIG. 7 (a).
And the second load detection mechanism 3B of (b), the lever portion 5B is to the left of the base portion 4B, and the base 4
B may be attached to the first attachment flange 8A extending from the beam portion 2c, and the load point P2 of the lever portion 5B may be attached to the second attachment flange 8B extending from the beam portion 2d via the connecting piece 7B. .

With this measuring device, for example, an object to be weighed of several tens to several hundreds mg can be weighed at a high speed of 100 to 300 times / minute and with a high accuracy of 1/5000 to 1/10000. it can.

In the present invention, the weighing device is applied to a weight sorter or a combination weighing machine for sorting the weight of objects to be weighed, but it may be applied to a weighing device for static weighing.

[0051]

According to one aspect of the present invention, the load detecting mechanism is mounted between the upper and lower beam portions of the strain generating element. Therefore, the tuning fork vibrator is fixed between the upper and lower beams, where the temperature of the fixed part and the movable part of the flexure element is approximately the intermediate value, and the temperature difference between them is small. Even if there is a temperature gradient, the influence of heat from the fixed portion and the movable portion is reduced, the zero point variation is small with respect to the temperature change, and the zero point stability is excellent, so that the load detection accuracy can be improved.

According to another configuration, the first and second
Since the load detection mechanism is installed between the upper and lower beam parts of the flexure element, it reduces the influence of heat from the fixed part and the movable part, improves the zero point stability against temperature changes, and reduces the load. Since one of the tuning fork vibrators of the detection mechanism is a tension type and the other is a compression type, by determining the load with the differential type from the frequency change of both tuning fork vibrators, when the temperature around the flexure element changes. Even if the flexure element and the tuning fork vibrator have different thermal expansion coefficients, the temperature deformations of the two elements are canceled, so that they are not affected by the temperature change, so that high load detection accuracy can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a tuning fork type load cell according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a signal processing unit of a weighing device using the above load cell.

FIG. 3 is a front view showing a load detection mechanism.

4 is a partially enlarged view showing the tuning fork type load cell of FIG. 1. FIG.

FIG. 5 is a perspective view showing a tuning fork type load cell according to another embodiment.

FIG. 6 is a configuration diagram showing a signal processing unit of a weighing device using the load cell.

FIG. 7 is a side view showing a tuning fork load cell according to another embodiment.

[Explanation of symbols]

1 ... Tuning fork type load cell, 2 ... Strain element, 2a ... Fixed part, 2
b ... movable part, 2c ... beam part, 3 ... load detection mechanism, 3A
... first load detection mechanism, 3B ... second load detection mechanism, 4A,
4B ... Base, 5A, 5B ... Lever, 6 ... Tuning fork vibrator, 3
6 ... Intermediate material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Miyamoto One share company, Ishida Shiga Plant, 959 Shimoho, Ritto-cho, Kurita-gun, Shiga Prefecture

Claims (7)

[Claims] 1. A strain-generating body in which a fixed portion and a movable portion to which a load is applied are arranged on the left and right sides, and the movable portion is supported by the fixed portion via upper and lower beam portions, and mounted on the strain-generating body. A load cell having a load detection mechanism, wherein the load detection mechanism includes a base portion attached to one of the upper and lower beam portions, a lever portion supported by a fulcrum on the base portion, and the base portion. And a tuning fork vibrator mounted between the lever and a tuning fork whose natural frequency changes according to an applied load, and the load point of the lever is connected to the other of the upper and lower beam parts. Load cell. 2. The tuning fork load cell according to claim 1, wherein an intermediate material made of a material having a coefficient of thermal expansion between the beam portion and the base portion is inserted between the beam portion and the base portion. 3. The load cell according to claim 1 or 2, and a weighing value generation circuit for obtaining a weighing value from a signal obtained by a load detection mechanism of the load cell, wherein a fixed portion of the load cell is fixed to a base. , A weighing device in which a weighing platform for supporting an object to be weighed is fixed to a movable part. 4. A flexure body in which a fixed part and a movable part to which a load is applied are arranged on the left and right, and the movable part is supported by the fixed part via upper and lower beam parts, and the flexure body is attached to the flexure body. First
A load cell having a load detection mechanism and a second load detection mechanism, wherein each of the first load detection mechanism and the second load detection mechanism includes a base portion attached to either one of the upper and lower beam portions of the flexure element. A lever fork supported on the base via a fulcrum, and a tuning fork vibrator attached between the base and the lever, the natural frequency of which changes according to an applied load. Load point is connected to the other of the upper and lower beam parts, and when a load is applied to the movable part, a tensile force acts on the tuning fork vibrator of one load detection mechanism and the tuning fork of the other load detection mechanism. A tuning fork load cell that is set so that a compressive force acts on the vibrator. 5. The tuning fork type load cell according to claim 4, wherein the both load detection mechanisms are mounted on one of the front and rear surfaces of the flexure element. 6. The tuning fork type load cell according to claim 4, wherein the first load detection mechanism is mounted on the front surface of the flexure element, and the second load detection mechanism is mounted on the rear surface of the flexure element. 7. A load cell according to any one of claims 4 to 6, and a weighing value generating circuit for obtaining a weighing value from a difference between signals obtained by both load detecting mechanisms of the load cell. A weighing device in which a fixed portion is fixed, and a weighing platform that supports an object to be weighed is fixed to a movable portion.