JP3925645B2 - Load cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a load cell, and more particularly to a load cell suitable for use as a load sensor for an electronic balance or an electronic balance.
[0002]
[Prior art]
In a load cell used as a load sensor for an electronic balance or an electronic balance, generally, as illustrated in FIG. 3, a fixed column portion 311 and a movable column portion 312 are provided at both ends, and flexible portions e are provided at both ends. The first and second parallel beam portions 313a and 313b connected to each other are used, and the strain gauges S1 to S4 are attached to the respective flexible portions e. It is used a lot. The strain generating body 31 has a fixed column portion 311 fixed to a scale base or the like, and a measurement plate is placed on the movable column portion 312 via a plate receiver (see, for example, Patent Document 1).
[0003]
The strain gauges S <b> 1 to S <b> 4 are connected to each other to form a Wheatstone bridge as shown in FIG. 4, and are caused by distortion of each flexible portion e caused by the measured load W acting on the movable column portion 312. Due to the change in resistance value of each strain gauge S1 to S4, the output of the Wheatstone bridge becomes a value proportional to the load to be measured, and is used for the calculation of the measured value. That is, due to the load to be measured, compressive strain is generated in the strain gauges S1 and S2, and tensile strain is generated in the strain gauges S3 and S4. The compressive strain and the tensile strain are almost the same value, and the measured load W is detected as a change in resistance value by the Wheatstone bridge shown in FIG.
[0004]
In such a load cell, in order to widen the measurement range of the load, in order to increase the deformation allowable amount of the strain generating body 31, more specifically, the elastic deformation allowable amount of each flexible portion e, each flexible portion e is thinned. Measures such as doing are taken.
[0005]
[Patent Document 1]
JP 2001-343294 A (2nd page, 4th page, FIG. 1)
[0006]
[Problems to be solved by the invention]
By the way, even if the elastic deformation allowable amount of the flexible portion is increased as described above, there is a restriction on the allowable strain amount of the strain gauge attached to the flexible portion. Due to the existence of the allowable strain amount of the strain gauge, there was a limit in extending the load measurement range.
[0007]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a load cell capable of obtaining a wider load measurement range without increasing the allowable strain amount of the strain gauge.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the load cell of the present invention has a plurality of strain gauges attached to a strain generating body deformed by a load to be measured, and the resistance value of each strain gauge based on the unloaded state of the strain generating body. In the load cell that detects the magnitude of the load to be measured from the change, the load generating direction of the load to be measured is determined by the elastic member having the same load-elastic deformation linearity as the strain generating body in the unloaded state. A predetermined deformation is given in the opposite direction, and the magnitude of the measured load is detected based on the resistance value of each strain gauge in the predetermined deformation state in the opposite direction. (Claim 1).
[0009]
Here, in this invention, the structure (Claim 2) using the same material and the same shape as the said strain body as the said elastic member can be employ | adopted suitably.
[0010]
In the present invention, a configuration in which the elastic member is integrally formed with the strain body (Claim 3) can also be adopted.
[0011]
The present invention applies strain to the strain generating body in a direction opposite to the load direction of the load to be measured and distorts it, and detects the load to be measured with reference to the resistance value of the strain gauge in the applied state of the preload. , Trying to achieve the intended purpose.
[0012]
In other words, if the strain body is deformed in the direction opposite to the load direction of the load to be measured, each strain gauge is in a state of being distorted in the direction opposite to that at the load of the load to be measured. Is opposite in polarity to the measurement of the load to be measured. Such deformation in the reverse direction is applied by an elastic member having linearity of load-elastic deformation equivalent to that of the strain generating body, for example, by an amount equivalent to the allowable strain amount of each strain gauge. For example, if the output of the bridge is -v, by increasing the load to be measured, the output changes from -v to + through 0, and when it reaches + v, each strain gauge has an allowable strain amount. To reach. That is, a load measurement range twice as large as that of the conventional one can be obtained within the allowable strain amount of the strain gauge.
[0013]
Here, since the elastic member that applies a preload to the strain generating body has the same load-elastic deformation linearity as the strain generating body, the linearity of the load detection output is also predicted only by the strain generating body. This is equivalent to the case where no load is applied, and no problem occurs.
[0014]
Then, if the elastic member for applying the preload is made of the same shape and material as the strain generating body as in the invention according to claim 2, the required load-linearity of elastic deformation can be easily obtained. And there is an advantage that a member with a different design is not required and the cost is advantageous.
[0015]
Further, if the elastic member is formed integrally with the strain body as in the invention according to claim 3, the required space can be reduced.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a front view of an embodiment of the present invention. In FIG. 1, the deformation amounts of the strain body 1 and the elastic member 2 are exaggerated.
[0017]
The strain body 1 is of the same Robertal type as in the prior art, wherein the fixed column portion 11 and the movable column portion 12 are connected by two upper and lower beam portions 13a, 13b, and both end portions of each beam portion 13a, 13b. Each has a structure in which a flexible portion e is formed. In addition, strain gauges S1 to S4 are attached to each flexible portion e. These strain gauges S1 to S4 are connected to each other so as to form a Wheatstone bridge exactly the same as that in FIG.
[0018]
The elastic member 2 has the same material and shape as the strain body 1, and includes a fixed column portion 21, a movable column portion 22, two upper and lower beam portions 23a and 23b, and both end portions of each beam portion 23a and 23b. Each is formed with a flexible portion e. Accordingly, the linearity of load-elastic deformation of the elastic member 2 is the same as that of the strain body 1.
[0019]
In the strain body 1 and the elastic member 2, the lower surfaces of the fixed column portions 11 and 21 are fixed to, for example, the base B of the electronic scale, and the movable column of the elastic member 2 is disposed on the lower surface of the movable column portion 12 of the strain body 1. The upper surface of the portion 22 comes into contact with a predetermined preload, whereby the strain body 1 is deformed so that the movable column portion 12 is lifted upward. The preload is set so that the strain amount of each of the strain gauges S1 to S4 becomes an allowable strain amount due to the deformation of the strain generating body 1 due to the contact of the elastic member 2.
[0020]
The measurement pan P for placing the load to be measured is supported on the movable column portion 12 of the strain body 1 via the tray receiver PS.
[0021]
In the above embodiment, in a no-load state where nothing is placed on the measurement pan P, tensile strain is generated in the strain gauges S1 and S2, and compressive strain is generated in the strain gauges S3 and S4. In this state, assuming that the output of the Wheatstone bridge by the strain gauges S1 to S4 is −v, if the load to be measured is gradually increased from 0 on the measurement dish P, the strain of each strain gauge S1 to S4 is increased. The amount gradually decreases and eventually reverse distortion occurs. During this time, the output of the Wheatstone bridge gradually approaches 0 from −v, and turns to + after exceeding 0. When the output of the Wheatstone bridge reaches + v, each of the strain gauges S1 to S4 reaches an allowable strain amount opposite to the no-load state.
[0022]
Therefore, according to the embodiment of the present invention described above, the load measurement range is doubled even if the allowable strain amount of each strain gauge S1 to S4 is the same as that of the conventional load cell shown in FIG. can do.
[0023]
Here, in the above-mentioned embodiment, although the example which formed the strain body 1 and the elastic member 2 by another member was shown, these can also be formed integrally.
FIG. 2A is a front view showing an example thereof, and FIG. 2B is a right side view thereof. In FIG. 2 as well, the deformation amounts of the strain body 10 and the elastic member 20 are exaggerated.
[0024]
In this example, the basic structure of the strain body 10 includes a fixed column portion 101, a movable column portion 102, and two upper and lower beam portions 103a and 103b, as in the previous example, and each of the beam portions 103a and 103b. The flexible portions e are provided at both ends. Moreover, the point by which the strain gauges S1-S4 are each affixed on each flexible part e is also equivalent.
[0025]
The same applies to the basic structure of the elastic member 20. The elastic member 20 includes a fixed column part 201, a movable column part 202, and two upper and lower beam parts 203a and 203b that connect the fixed column part 201, the movable column part 202, and the beam parts 203a and 203b. Flexible portions e are formed at both ends.
[0026]
The feature of this example is that the strain body 10 and the fixed column portions 101 and 201 of the elastic member 20 are integrated with each other. The beam portions 203a and 204b and the movable column portion 202 of the elastic member 20 are They are located on both sides of the beam portions 103 a and 103 b and the movable column portion 102 of the strain body 10. In other words, in practice, after a plate-shaped base material having a required thickness is processed in the same manner as a Robert-type strain body, the thickness of the plate-shaped base material is divided into three parts, except for the fixed column portion. A slit in the direction to be formed is formed, and the central portion is the strain body 10 and the both side portions are the elastic members 20.
[0027]
Then, both end portions of the convex strain applicator 30 are screwed to the lower surfaces of the movable column portions 202 of the elastic members 20 on both sides, and the movable column portion of the strain generating body 10 is formed by the central projecting portion of the strain applier 30. By pressing the lower surface of 102, the deformation body 10 is deformed in the direction opposite to the load direction of the load to be measured.
[0028]
In this embodiment, by making the total thickness of the elastic members 20 on both sides the same as the thickness of the strain body 10, the same effects as those of the previous embodiment can be achieved. In addition, this embodiment has an advantage that the required dimension in the longitudinal direction may be the same as that of the conventional load cell shown in FIG.
[0029]
【The invention's effect】
As described above, according to the present invention, the resistance value of the strain gauge in the state where the elastic member is deformed in the direction opposite to the load direction of the load to be measured is set to the unloaded state. As a reference, the load to be measured is detected, so that the load measuring range can be doubled at most even if a strain gauge having the same allowable strain amount is used as compared with the conventional load cell.
[Brief description of the drawings]
FIG. 1 is a front view of an embodiment of the present invention, and shows an exaggerated amount of deformation of each part.
FIG. 2 is a front view (A) and a right side view (B) of another embodiment of the present invention, and is also a diagram exaggerating the amount of deformation of each part.
FIG. 3 is a front view showing a configuration example of a conventional load cell.
FIG. 4 is an explanatory diagram of a Wheatstone bridge formed by strain gauges S1 to S4 attached to a load cell.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,10 Strain body 11,101 Fixed column part 12,102 Movable column part 13a, 13b, 103a, 103b Beam part 2,20 Elastic member 21,201 Fixed column part 22,202 Movable column part 23a, 23b, 203a, 203b Beam part 30 Strain imparting tool e Flexible part S1-S4 Strain gauge

Claims (3)

In a load cell that attaches a plurality of strain gauges to a strain generating body that is deformed by a measured load, and detects the magnitude of the measured load from the resistance value change of each strain gauge based on the unloaded state of the strain generating body,
The strain body in the unloaded state is given a predetermined deformation in the direction opposite to the load direction of the load to be measured by the elastic member having the same load-elastic deformation linearity as the strain body, and the reverse direction. A load cell configured to detect the magnitude of a load to be measured on the basis of a resistance value of each strain gauge in a predetermined deformation state. The load cell according to claim 1, wherein the elastic member is a member having the same material and shape as the strain body. The load cell according to claim 1, wherein the elastic member is formed integrally with the strain generating body.

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