JPH0439553Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Technical field The present invention relates to a thin load cell, and more specifically, the invention has a thick disk-like outer shape and a circular hole protruding from the center. The present invention relates to a thin load cell in which a strain gauge is attached to a strain-generating portion of a strain-generating body that deforms elastically, and the applied load is converted into an electric signal by the strain gauge and detected.

(b) Prior Art This type of load cell is divided into those having a cylindrical strain-generating portion and those having a disc-shaped strain-generating portion.

Among these, the one having a cylindrical strain-generating part has a cylindrical load applying part 1 whose longitudinal section is formed in a substantially I-shape, as shown in FIG. A cylindrical strain generating part 2 is formed in the center, and a strain gauge 3 for detecting compressive strain (or tensile strain, the same applies hereinafter) is bonded to approximately the center of the outer peripheral surface of this strain generating part 2. Annular flange portions 4 and 5 extend from the upper and lower portions of the outer periphery of such a load cell, and a seal plate 6 is attached to the tip end of the annular flange portions 4 and 5.

When a load cell having such a configuration is used, the bottom surface opposite to the load application section 1 is placed and fixed on the immovable member 7, and the top surface side of the load application section 1 is in contact with or against an object to be measured (not shown). Fixed.
When a load is applied from the object to be measured to the upper surface of the load application section 1, compressive strain occurs in the strain generating section 2 in the direction of load application, and tensile strain occurs in the direction orthogonal to the direction of load application. The compressive strain and tensile strain at this time are detected by strain gauges 3, respectively.

The cylindrical load cell configured in this way is
When the height of the strain-generating portion 2 is reduced to make it thin, the stress distribution in the cylindrical strain-generating portion 2 becomes uneven, and the strain gauge 3 attached thereto generates an electric signal that accurately corresponds to the applied load. In addition to the drawback that the detection output cannot be obtained, there is also a drawback that the detection output varies greatly depending on the condition of the surface to which the applied load is applied.

As an example of a load cell that has been devised to overcome these drawbacks, there is a load cell having a disk-shaped strain-generating portion as shown in FIG. 6, for example.

That is, a thin disc-shaped strain generating part 12 is extended from the middle part of the outer peripheral surface of the thick disc-shaped load application part 11,
The outer peripheral end thereof is integrally connected to the inner peripheral end of a fixed base 13 in the shape of a thick plate disk. Such a strain-generating part 1
2 near the load application part 11 on the inner surface and the fixed base 1
Strain gauges 14 and 15 for detecting bending strain are connected to each of the third portions. In order to prevent outside air from entering the strain gauges 14 and 15, a disc-shaped seal plate 16 extending inward is attached to the lower end of the fixed base 13, and the inner end of the seal plate 16 is The load applying section 11 is
is connected to the bottom end of.

In such a load cell, the fixed base 13
When the lower surface of the is placed and fixed on the immovable member 7 and a load is applied in the direction of the arrow from the upper surface of the load application section 11, bending strain is generated in the strain generating section 12, and the strain gauge 1
4 and 15, resistance value changes occur in different directions. The structure is such that the value of the applied load is detected by detecting this change in resistance value using a suitable Wheatstone bridge circuit. However, in such a load cell, the strain-generating portion 1
Since this type detects bending strain (2), a large output can be obtained with a small load, but it cannot withstand large loads, and in order to use it for large loads, that is, for high capacity, the thickness of the strain-generating part 12 must be increased. I have no choice but to do it.
When the plate thickness of the strain-generating portion 12 is increased, the load applying portion 11
A large stress concentration occurs at the boundary between the strain-generating part 12 and the strain-generating part 12 and the fixed base 13, and even a moderate load can exceed the elastic limit or cause fatigue failure in a relatively short period of time. There is a risk of causing accidents such as accidents. For this reason, in this type of load cell, the value of the load actually applied must be set to a low value, and it was therefore considered that the load cell was unsuitable for high capacity applications.

(c) Purpose This invention was created in view of the above circumstances.
The objective is to provide a thin load cell that can reduce stress concentration without sacrificing substantial sensitivity and that can obtain an electrical signal that accurately corresponds to the applied load without causing fatigue failure even at high loads. be.

(d) Structure In order to achieve the above-mentioned purpose, the thin load cell according to the present invention has a thick disk-like outer shape, has a circular hole protruding in the center, and has a strain-generating structure that elastically deforms when a load is applied. In a thin load cell in which a strain gauge is attached to a strain-generating part of a body, and the applied load is converted into an electric signal and detected by the strain gauge, the strain-generating part is connected between the circular hole and the outer periphery of the strain-generating body. A narrow annular groove reaching a predetermined depth from one side of the strain body is formed, and an annular groove wider than the groove on the first side reaching a predetermined depth from the other side of the strain body. By forming a load applying part between the circular hole and both grooves of the flexure body, a fixed base between both grooves and the outer periphery of the flexure body, and a fixed base between the grooves and the outer periphery of the flexure body, and A thin strain-generating portion is provided between the bottom surface of the groove and the bottom surface of the groove on the other surface side, and a strain gauge is attached to the other surface side of the strain-generating portion.

Hereinafter, one embodiment of the present invention will be explained in detail using FIGS. 1 to 3A and 3B.

In the same figure, 21 is made of a material that elastically deforms when subjected to a load, such as nickel-chromium steel, nickel-chromium-molybdenum steel, Amber (trade name), beryllium-copper alloy, aluminum alloy, etc., and is almost thick-walled disc-shaped. It is a strain-generating body formed in This strain body 21 has a circular hole 22 protruding from the center thereof. A predetermined depth (in the case of the embodiment, the flexure element 21 is approximately halfway between the circular hole 22 and the outer periphery of the flexure element 21 from one surface side (the upper surface side in FIG. 1) of the flexure element 21 Constant width W ₁ reaching a depth of about 1/3 of the plate thickness
An annular groove 23 (concentric with the circular hole 22) is formed. On the other hand, the other surface side of the strain body 21 (lower surface side in FIG. 1) also has a width W ₂ wider than the groove 23 on the one surface side, which reaches a predetermined depth from the other surface side.
An annular groove 24 is formed. 2 like this
By forming the two annular grooves 23 and 24, a load applying portion 25 with a large thickness and high rigidity is formed between the circular hole 22 of the strain body 21 and the grooves 23 and 24. Furthermore, a rigid fixed base 26 which is similarly thickened in the thickness direction is formed between the grooves 23 and 24 and the outer periphery of the strain body 21, and the bottom surface of the groove 23 and the bottom surface of the groove 24 are A thin strain-generating portion 27 having a predetermined thickness depending on the rated capacity is formed between them.

In other words, the outer diameter D ₁ of the other surface side (lower surface side in FIG. 1) of the load application section 25, the outer diameter D ₂ of one surface side, the inner diameter D ₃ of the one surface side of the fixed base 26,
and the four diameters of the inner diameter D ₄ on the other surface side of the fixed base 26 have the following relationship: D ₁ <D ₂ <D ₃ <D ₄ .

One surface (top surface) of the load application section 25 is made to protrude somewhat from one surface (top surface) of the fixed base 26 in consideration of displacement during load application;
The other surface is retracted from the other surface of the fixed base 26.

At the bottom of the groove 24 on the other side, that is, on the other side of the strain-generating portion 27, there is a load applying portion 25 where large bending stress occurs.
4 in the area closer to the fixed base 26 and the area closer to the fixed base 26.
As shown in FIG. 2, four pairs of strain gauges SG1 to SG8 are attached at 90[deg.] intervals by bonding, vapor deposition, sputtering, or other means. Near the open end of the groove 24 on the other side to which the strain gauges SG1 to SG8 are attached, the strain gauges are attached.
In order to prevent a decrease in insulation resistance due to moisture absorption of SG1 to SG8 and deterioration due to oxidation, a disk-shaped sealing plate 28 with low rigidity is inserted and fixed.

Next, the operation of this embodiment having such a configuration will be explained.

First, the bottom surface of the fixed base 26 is placed and fixed on, for example, an immovable member of the object to be measured, and the upper surface of the load application section 25 is brought into contact with or fixedly attached to, for example, the lower part of the object to be measured.

When a load is applied in the direction from the surface (one surface) side of the load application section 25 to the lower surface (other surface) side, the load application section 25 is displaced downward, and along with this, the strain generating section 2
7, bending strain occurs.

At this time, the radial strain distribution on the strain gauge attached surface side (bottom of the groove 24) of the strain generating part 27 is the third
The curve becomes like the curve indicated by the symbol P in Figure B. That is, a large tensile strain occurs in a portion of the strain generating portion 27 closer to the load application portion 25, a large compressive strain occurs in a portion closer to the fixed base 26, and a bending strain occurs approximately at the center of the strain generating portion 27. Does not occur. Therefore, the load application section 25 of the strain generating section 27
Strain gauge SG1 attached to the closer part,
The resistance values of SG3, SG5, and SG7 increase, while
The resistance values of the strain gauges SG2, SG4, SG6, and SG8 attached to portions of the strain generating portion 27 closer to the fixed base portion 26 decrease.

The curve also indicated by the symbol Q in Fig. 3B is
When the groove width W ₁ on one surface side (upper surface side) of the flexure element 21 is the same as the groove width W ₂ on the other surface side (lower surface side), as shown by the dashed line in FIG. 3A, This is a strain distribution curve.

Comparing the strain distribution curves P and Q, it is found that the strain distribution curve Q has large peak values +εqmax,
-εqmax, whereas the strain distribution curve P has small peak values +εpmax and -εpmax on the + and - sides even though they are at the same location. What is more noteworthy is that the peak value of the strain distribution curve P according to the present invention +εpmax, -
Despite the significant decrease in εpmax, the strain value +εp in the vicinity of the load application part 25 on the strain generating part 27 to which the strain gauges SG1, SG3, SG5, and SG7 are attached is the same as the groove width of the grooves 23 and 24. W ₁ and
This value is approximately the same as the strain value +εq at the same portion of the strain-generating portion 27 when W ₂ is the same width. This means that the strain gauge SG
2. Strain part 2 with SG4, SG6, and SG8 attached
Strain value in the vicinity of the fixed base 26 on 7 -
Similarly, εp has a value comparable to the strain value -εq. In other words, as in this example, the groove width W ₁ is
By making the width narrower than W ₂ , the maximum strain εpmax and maximum stress can be significantly lowered without reducing strain sensitivity compared to a groove width W ₁ that is the same as the groove width W ₂ . It was.

This is because the groove width W ₁ of the groove 23 on the surface receiving the load (top surface) is made narrow, and the groove width W ₂ of the groove 24 on the surface opposite to the surface receiving the load (bottom surface) is made wide. This is thought to be due to the stress being distributed.
Furthermore, at the bottom of the groove 23, the strain-generating portion 27, the load applying portion 25, and the fixed base 26 are connected by a circular arc surface with a relatively large radius _R1 , which also reduces stress concentration. Contributing. In this embodiment, the radius R ₁ of the arcuate surface at the bottom of the groove 23 on one side is formed to be large (specifically, R ₁ is preferably 20% or more of the plate thickness of the strain-generating portion 27). The radius R ₂ of the circular arc surface at the bottom of the groove 24 on the other side is formed to be relatively small. this is,
The radius R ₂ of the arc surface at the bottom of the groove 24 on the other side is the radius
If it is made as large as R ₁ , it will contribute to reducing stress concentration to some extent, but on the other hand, doing so will force the strain gauges SG1 to SG8 to move toward the center of the strain-generating portion 27 where the amount of strain is small. gone,
As a result, the detection output obtained from strain gauges SG1 to SG8 will decrease.
The relationship was set as R ₁ > R ₂ .

Note that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the gist thereof.

For example, the shape of the bottom surface of the groove formed on one side does not have to be an arcuate surface. For example, as shown in FIG. 4, the shape of the groove 35 on the one side among the two grooves 35 and 36 is The inner diameter end of the strain generating part 32 of the strain generating body 31 and the load application part 33 are connected by an inclined surface l ₁ , and the outer diameter end and the fixed base 34 are connected by an inclined surface l ₂ . You can. In this case, the slope l ₁ and
It is desirable to provide a circular arc surface with a small radius at the joint at each end of l ₂ .

In addition, in the load cell of the above embodiment, one surface side of the load application section 25 is made to protrude from one surface side of the fixed base 26, but the load cell mounting surface of the object to be measured is different from the diameter D ₂ of the load application section 25. The protrusion amount may be zero or negative as long as the protrusion amount is the same.

In addition, in the case of the embodiment, strain gauges SG1 to SG8 are attached with their gauge axes aligned in the diametrical direction, but some of the strain gauges are attached with their gauge axes aligned in the circumferential direction. You can do it like this.

(e) Effects As detailed above, according to the present invention, the structure is simple and easy to manufacture, and the maximum strain due to stress concentration can be significantly reduced without reducing strain detection sensitivity. A device with a high capacity can be easily manufactured, and the load applied unevenly to the load application section can be converted into an electrical signal that accurately corresponds to the load using the strain gauge, without the need to attach many strain gauges to the strain-generating section. It is possible to provide a thin load cell that can be detected by

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a thin load cell that is an embodiment of the present invention, FIG. 2 is a sectional view taken along the line X--X in FIG. 1, and FIGS. 1 and 2 are enlarged cross-sectional views showing the details of the configuration near the strain-generating part of the thin load cell, and diagrams showing the magnitude of strain in each part of the strain-generating part, and Figure 4 are similar to those shown in Figures 1 to 2. FIG. 3 is a cross-sectional view showing the main parts of another embodiment different from the thin load cell shown in FIG. 3. FIG. 5 is a cross-sectional view showing an example of a conventional cylindrical load cell. FIG. 2 is a sectional view showing an example of a load cell. 21, 31... Strain body, 22... Circular hole, 2
3, 24, 35, 36... Groove, 25, 33... Load application section, 26, 34... Fixed base, 27, 32
...Strain part, 28...Seal plate, SG1 to SG8...
...strain gauge.

Claims (1)

[Claims for Utility Model Registration] (1) A strain gauge is attached to the strain-generating part of a strain-generating body that has a thick disk-like external shape, has a circular hole protruding from the center, and deforms elastically when a load is applied. In a thin load cell that detects the applied load by converting it into an electric signal using the strain gauge, a predetermined depth is provided between the circular hole and the outer periphery of the strain body from one side of the strain body. By forming a narrow annular groove reaching a predetermined depth from the other surface of the strain generating body and a wider annular groove wider than the groove on the one surface side reaching a predetermined depth from the other surface of the strain generating body, a load applying part between the circular hole of the body and the both grooves, a fixed base between the both grooves and the outer periphery of the strain body, and a bottom surface of the groove on the one side and a groove on the other side. A thin strain-generating portion is provided between the bottom surface of each
A thin load cell characterized in that a strain gauge is attached to the other surface of the strain generating part. (2) Claim 1 of the Utility Model Registration Claim characterized in that a plurality of strain gauges are attached to the bottom surface of the groove on the other wide side, at a portion closer to the load application portion and a portion closer to the fixed base. Thin load cell. (3) The outer circumferential surface of the load application part and the inner circumferential surface of the fixed base are connected to the inner diameter end and outer diameter end of the strain generating part via a relatively large circular arc surface on one side, and the other side is The thin load cell according to claim 1, wherein the load cell is connected to an inner diameter end and an outer diameter end of the strain-generating portion via a small circular arc surface.