JP2002286538A - Load cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To support a strain gage 2 having strain piece parts 2a to 2d disposed at a 90 degree angle from each other so as not to restrain the deformation of the strain piece parts 2a to 2d when a load is imposed on them. SOLUTION: Among the strain piece parts 2a to 2d forming four legs, one leg 2a is fixedly supported and the remaining three legs 2b to 2d are fixed in a longitudinally displaceable manner. This prevents the deformation of the piece parts 2a to 2d from being restrained, thereby providing this load cell with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a load cell for measuring weight using a strain gauge.

[0002]

2. Description of the Related Art In general, a load cell of this type generates a strain in a flexure element when a measurement load is applied, and the electric resistance of a strain gauge provided in the flexure element changes according to the distortion. The load cell is configured to perform weight measurement by utilizing the load cell. As such a load cell, a load cell of a type in which a load of an object to be measured is intensively received at one point of a strain body is known.
In such a method, in order to reduce a measurement error due to an eccentric load generated when an object to be measured is eccentrically placed on the load receiving portion, a large distance between the load receiving portion and the strain body may be employed. desirable.

[0003]

However, when a flat-type load cell having a low height is to be manufactured, the distance between the load receiving portion and the strain body cannot be made large. For this reason, the area of the load receiving portion must be reduced in order to reduce the measurement error due to the eccentric load as much as possible, and there is a problem that it is difficult to measure the weight of the bulky measured object. On the other hand, it is possible to increase the area of the load receiving portion by adopting a method of receiving a load with a plurality of load cells, but in this case, there is a problem that the cost increases because a plurality of load cells are required. Therefore, the inventor of the present invention disclosed in Japanese Patent Application No. 2000-166280 that a four-legged flexure element provided with a strain gauge was radially stretched radially around a fixed portion fixedly supported on a base. The measurement load is dispersed and received at the distal end of the flexure element, and the fixed part is supported and fixed on the lower surface to the base, and the load receiver that receives the measurement load on the upper surface of the distal end of each flexure element serves as a support member. In other words, a strain gauge is provided on one side of each strain-generating piece, and the gauge output from each strain-generating piece when a load is applied is evenly distributed to displace the load. In addition to reducing the measurement error, the measurement load can be dispersed and received by the plurality of strain-generating pieces, and the strain due to the tensile stress and the strain due to the compressive stress can be applied to one surface of the strain-generating piece. To cause the strain gauge Be provided only on one surface of the strain body can form a bridge circuit capable of temperature compensation, the productivity of the strain gauges formed Thus is so improved.

However, in this structure, since all the tips of the plurality of strain-generating pieces are supported and fixed, a load is applied to the upper surface of the strain-generating body to generate tensile and compressive stress in the strain-generating pieces. When deformed to the extent necessary, the deformation of the strain-generating piece portion is restrained. As a result, the deformation of the strain-generating piece portion with respect to the load change is not linear, but is curved as shown by a solid line in FIG. Therefore, there is a problem that a load cell with high accuracy cannot be obtained, and there is a problem to be solved by the present invention.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been made for the purpose of solving these problems, and comprises a plurality of strain-generating pieces provided with strain gauges. In providing a flexure element that is radially extended and receives a load of the measured object in a dispersed manner by deformation of the plurality of flexure pieces, at least one of the distal ends of the flexure pieces is provided. One is a load cell, which is fixedly supported, and the strain-flexing piece portion having a diagonal relationship with the fixedly-supported strain-generating piece portion is a support that can be displaced. By doing so, one of the strain-generating pieces having a diagonal relationship can be displaced, so that the deformation of the two strain-generating pieces is not restricted, and as a result, the strain caused by the load change is reduced. The deformation of the distorted piece portion becomes linear, resulting in a highly accurate load cell. In this case, the strain-flexing piece portion is 9
When a quadruped with an angle of 0 degrees is used, one or two adjacent strain-flexing pieces are fixedly supported at the tip, and the rest is a support that can be displaced. Can be. In these devices, the strain gauge may be characterized in that the strain gauge is attached to the surface of the strain-generating piece opposite to the surface on which the load of the measured object is applied.

[0006]

Next, an embodiment of the present invention will be described with reference to the drawings. In the drawings, reference numeral 1 denotes a base which constitutes a load cell. The base 1 has a square plate shape, and the upper surface of the base 1 has a flexure element 2a to 2d of a quadruple of a flexure element 2 described later. Four support parts 1a corresponding to each tip
To 1d are formed to protrude in a pin shape. On the other hand, the flexure element 2 is formed of a central portion 2e and four-legged flexure pieces 2a to 2d extending radially in the horizontal direction around the central portion 2e. Distortion pieces 2a to 2d
Are provided at equal intervals of 90 degrees from each other. Then, the strain-flexing pieces 2a to 2d and the supports 1a to 1
The connection with d is as described later.

Reference numeral 3 denotes a rectangular load receiving plate on which an object to be measured is placed, and the center of the load receiving plate 3 is connected to the center of the strain body 2 via a connecting pin 4.
e is supported and fixed on the upper surface of the load receiving plate 3 so that the load of the object placed on the load receiving plate 3 is dispersed and received by the distal ends of the strain-flexing pieces 2a to 2d of the four legs. Is configured.

When an object to be measured is placed on the load receiving plate 3, compressive stress acts on each of the strain-generating pieces 2a to 2d at a portion adjacent to the central portion 2e as shown in FIG. While a strain is generated, a tensile stress acts on a portion adjacent to the support portion of the supports 1a to 1d to generate a strain, and strain gauges R1 to R8 are formed at the portions where the strains are generated by the respective generated stresses. Have been.

In other words, the strain gauges R1 to R8 are formed at two locations on the lower surface of each of the strain-generating pieces 2a to 2d, that is, at two locations on the opposite side to the side on which the load receiving plate 3 described later is arranged, for convenience. However, these strain gauges R1 to R8 are
Are formed to form a Wheatstone bridge circuit shown in FIG. In this case, the strain gauges R1-
Two of R4 are connected in series to form two sides serving as a compressive stress detecting unit, and two of strain gauges R5 to R8 on which a tensile stress acts are connected in series and a tensile stress detecting unit is formed. Are formed, and the sides serving as the tensile stress detecting section and the sides serving as the compressive stress detecting section are wired so as to face each other. With such wiring, the strain caused by the temperature change of the strain gauges R1 to R8 can be canceled out by the tensile stress detecting section and the compressive stress detecting section, that is, the temperature can be corrected. Here, in this embodiment, the strain body 2 is formed of phosphor bronze (excellent in heat resistance and small in elastic modulus), and the strain gauges R1 to R8 are formed of copper-nickel alloy with manganese added. Have been.

The supporting portions 1a to 1d and the strain generating pieces 2a to 2
The support at four places with d is performed by tightening with the screw 5, and the tightening strength is as follows. That is, in the case of the first embodiment shown in FIG.
a and the strain-flexing piece 2a are securely tightened (fixed).
However, the remaining three supporting portions 1b to 1d and the strain generating pieces 2b to 2d are in a loose temporary fixing state, and these strain generating pieces 2b to 2d are displaced in the extending direction (the plate length direction). I can do it. This displacement is caused by the strain element 2b.
The screw holes 2f formed in the holes 2d to 2d may be formed as stupid holes with respect to the screws 5, but are preferably elongated in the plate length direction in order to avoid positional deviation in the circumferential direction. still,
Since the upper surfaces of the strain-generating pieces 2b to 2d are in a state where the lower surfaces of the screw heads of the screws 5 are in surface contact, the strain-generating pieces 2b to 2d are displaced in the above-described plate length direction. As a result, the flat support of the distal end portions of the strain generating pieces 2b to 2d by the screws 5 is maintained, and when a load is applied,
It is possible to prevent the distal ends of the strain-generating pieces 2b to 2d from being lifted up, thereby not affecting the uniform deformation of the strain-generating pieces 2a to 2d.

In the present embodiment, the base 1 has a rectangular shape, and a strain generating body 2 is disposed so as to be diagonal in a state of being deflected to one side, and the adjacent strain generating piece portions 2a to 2a. 2d
The analog circuits 6, 7, and 8 are disposed in three of the four spaces between them, and two of the analog circuits 6, 7 facing each other are provided with external circuits for adjusting the resistance of the strain gauges R1 to R8. Spaces 9 and 10 are provided for mounting resistors. On the other hand, in the space on the opposite side of the base 1 from which the flexure element 2 is provided, a digital circuit installation space 11 including a liquid crystal display unit 12 is secured, whereby an analog circuit unit and a digital circuit unit are provided. And the separation from
The influence of noise is reduced by shortening the distance between the strain gauges R1 to R8 and the analog circuit including the amplifier circuit.
By doing so, the base 1 is connected to the flexure element 2
This makes it possible to provide a space-saving, compact, and thin load cell.

In the structure constructed as described above, since the measured load is distributed and received by the four-legged strain-generating pieces 2a to 2d, the load applied to one strain-generating piece 2a to 2d is reduced. The maximum measurable load amount can be increased as a whole. And, this is the strain generating piece portion 2a to 2d
Has a strained portion due to tensile stress and a strained portion due to compressive stress on one surface, so that even if strain gauges R1 to R8 are provided only on one surface, the strain gauges R1 to R8 allow the Wheatstone bridge circuit to be connected to the tensile stress detection unit and the compression unit. Can form a stress detector
Temperature correction can be performed. As a result, pretreatment such as polishing of the gauge forming surface of the strain generating element 2 and formation of an insulating layer, sputter deposition of a gauge film and a wiring pattern, formation of a gauge pattern, and the like need only be performed on one surface of the strain generating element 2. become,
A plurality of strain gauges R1 to R8 can be simultaneously formed with high positional accuracy, and productivity is improved.

Moreover, in this case, one strain-generating piece 2a
Are fixed so as not to be displaced, and the remaining three strain-generating pieces 2b to 2d have a loose supporting structure so that they can be displaced in the longitudinal direction of the strain-generating pieces.
When the member is to be deformed by receiving a measured load, the strain-generating pieces 2a to 2d are displaced in the longitudinal direction and are not restrained by deformation. The deformation of the distorted body becomes linear, so that a load cell with high accuracy can be obtained. In addition, since the displacement of the strain-generating pieces 2b to 2d is performed in a state where one portion of the strain-generating piece 2a is fixed, the displacement is stable, and the stability of the load cell is not impaired. . Further, since the strain gauges R1 to R8 are provided on the lower side opposite to the side on which the load receiving plate 3 is provided and are in a protected state, they are careless when loading and unloading the object to be measured. It is possible to avoid a problem that an object hits or is damaged by being hit.

Incidentally, when supporting the strain-generating pieces 2a to 2d, when fixing the strain-forming pieces 2a to 2d,
All quadruples, tripods, opposing bipods, adjacent bipods,
Then, a case where only one leg is used as in the previous embodiment can be considered. So we actually created these fixed structures,
0-200.6 which is the range of the rated load for each
gf, the reference level is compared with the actually measured output value, and an error (straightness (%) =
(Difference between a reference output value and an actually measured output value when an arbitrary load is applied / the arbitrary load) × 100), the error is 1.40% in the above case and 1 in the above case. .3
8%, which was as large as 1.67%, whereas the case where the present invention was implemented was as small as 0.045%, and as much as 0.051% in the case where the present invention was implemented. 2
It is confirmed that the error is increased in the case where the strain-generating pieces having a diagonal relationship are fixed with respect to each other with respect to the center of the center, and the present invention has been completed here. It is confirmed whether there is.

[Brief description of the drawings]

FIG. 1 is a schematic side view, partially cut away, showing a structure of a load cell.

FIG. 2 is a schematic plan view of a flexure element.

FIG. 3 is an explanatory diagram showing stress acting on a strain body.

FIG. 4 is a Wheatstone bridge circuit diagram.

FIG. 5 is a graph showing a relationship between a load and a deformation of a flexure element when a load is changed.

FIG. 6 is a plan view showing an arrangement state of a load cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base 2 Strain-generating body 2a Strain-flexing piece part fixed 2b-2d Strain-flexing piece part which can be displaced 3 Load receiving plate 4 Support pin R1-R8 Strain gauge

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shingo Nakano 1-268, Hirosawa-cho, Kiryu-shi, Gunma F-term (reference) 2F049 AA12 AA16 BA13 CA01 CA05

Claims (3)

[Claims] A plurality of strain-generating pieces provided with strain gauges are radially extended in a radial direction to receive a load of a measured object dispersedly by deformation of the plurality of strain-generating pieces. In providing, at least one of the distal end portions of the strain-generating piece portion is fixedly supported, and the strain-generating piece portion having a diagonal relationship with the fixedly supported strain-generating piece portion can be displaced. A load cell characterized by high support. 2. The strain generating element according to claim 1, wherein when the strain generating element is a quadruped having an angle of 90 degrees, the tip of the strain generating element is fixedly supported by one leg or two adjacent legs. A load cell characterized in that the remaining strain-flexing pieces are supported so as to be misaligned. 3. The load cell according to claim 1, wherein the strain gauge is attached to a surface of the strain generating piece opposite to a surface on which a load of the measured object is applied.