JPH038682B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shear type strain detector that is attached to an object to be measured, detects strain occurring in the object, and obtains an electrical signal corresponding to the strain.

Conventional strain detectors generally have a strain-generating portion formed into a hollow thick-walled cylinder or a square cross-section to increase the cross-section in order to prevent buckling. Therefore,
Not only is the stiffness high, but the strain sensitivity is low, and the strain on the object to be measured, such as a thin plate or plastic, is supported by the rigidity of the strain detector itself, making accurate strain detection difficult. Ta.

On the other hand, in order to increase the above-mentioned strain sensitivity, two offset shelf-shaped notches are provided on each side of the central axis, which reach the sides at right angles, overlap each other by d on the axis, and are parallel to each other at intervals of l. The displacement induced on the central axis of the parallelogram strain measurement plate is
A shear type strain detection method is described in JP-A-57-124203 in which the shear stress concentrated on the overlapping area ld in the middle of the notch in a book is magnified and detected using a cross-shaped gauge above it. There is.

However, the structure described in the above-mentioned publication does not take buckling into consideration at all, and has the disadvantage that it easily buckles even when a slight compressive load is applied.

Another disadvantage is that when a tensile load is applied, twisting or inclination occurs, making it impossible to obtain an output signal that accurately corresponds to the applied load.

In order to overcome this drawback, as shown in Figure 2 of the same publication, the single shear plate strain detector described above was turned over with one of its long sides as the central axis. It is necessary to provide two strain-generating parts (stress concentration parts) that are symmetrical about the central axis.

However, with this configuration, although it is possible to prevent twisting and tilting when a tensile load is applied, it is completely impossible to prevent buckling. A pair of strain detectors are formed in the side direction), which increases the size in the width direction, resulting in the problem of being restricted in the installation location, and in addition, two strain-generating parts are formed in parallel. As a result, a new problem arises in that the strain detection sensitivity is reduced by half compared to the case of only one strain-generating section, and the cost is increased.

The present invention was made in view of the above circumstances, and
It is easy to manufacture and attach to the object to be measured, has low stiffness in compression and tension, is resistant to buckling under compression, and is almost unaffected by bending, so it is easy to detect strain in the object to be measured. The purpose of the present invention is to provide a strain detector that does not require very precise finishing of the instrument mounting surface, allows the strain detector itself to be manufactured at low cost, and can also save jigs and tools and labor costs associated with installation.

That is, in order to achieve the above purpose, the first
The invention provides a strain detector that is attached to an object to be measured to detect strain occurring in the object to be measured and obtain an electric signal corresponding to the strain. A mounting portion is formed for the purpose of the present invention, and a substantially central portion thereof serves as a strain-generating portion, and a pair of mounting portions extending from opposite side edges of the strain-generating portion in a direction approximately orthogonal to the load application direction to the strain-generating portion are formed. A slit is formed, and both ends in the direction perpendicular to the load direction are bent in the same direction to form reinforcing ribs to prevent buckling, with the surface on which each reinforcing rib is formed facing outward. Two overlapping strain plates of the same shape, and these two
strain gauges attached to the strain-generating portions of the surfaces on which the reinforcing ribs are formed of the two strain-generating plates in directions that are approximately 45° and 135° with respect to the load application direction; A filler is filled and solidified so as to cover at least the surface on which the reinforcing ribs are formed and the strain gauge, and to be approximately at the same height as the reinforcing ribs. It is characterized by comprising a sufficiently smaller mold body.

Further, the second invention provides a strain detector that is attached to an object to be measured to detect strain occurring in the object to be measured and obtain an electrical signal corresponding to the strain. A mounting part for attaching to an object is formed, a substantially central part is a strain-generating part, and the strain-generating part faces in a direction approximately perpendicular to the load application direction from mutually opposite side edges across the strain-generating part. A strain-generating plate is formed with a pair of slits extending to Approximately 45 degrees and
A filler is filled and solidified so as to cover the strain gauges attached in a direction forming an angle of 135 degrees, the plate surface of the strain plate and the strain gauges, and to be at approximately the same height as the reinforcing ribs. Become,
The present invention is characterized by comprising a molded body having a sufficiently smaller elastic modulus than the strain plate.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIGS. 1A, B, and C are a plan view, a front center cross-sectional view, and a cross-sectional view taken along the line AX-X of the same figure, respectively, showing the configuration of a first embodiment of the present invention.

In the figure, reference numeral 1 denotes a strain plate made of a thin plate material, and mounting holes 2 are provided at both ends of the strain plate 1 in the longitudinal direction (load application direction) as attachment portions for attaching it to the object to be measured. , 3 are bored, and the approximately center part is the strain generating part 4, and the strain gauge
SG1 and SG2 are attached by adhesive or other means in directions that are oriented at 45° and 135° with respect to the line segment connecting the mounting holes 2 and 3, that is, the direction of load application. Side edges opposite to each other with the strain-generating portion 4 in between (here, the term "side edge" refers to a portion extending inward from the side by a certain amount).
same as below. ) are formed with two slits 6 and 7 perpendicular to the line segment 5 connecting the mounting holes 2 and 3.
In this case, the length of the slits 6 and 7 is the same as that of the strain plate 1.
The length is set to reach a portion slightly past the line segment 5 from the side edge of the strain plate 1, and furthermore, on both ends of the strain plate 1 in the short side direction (direction perpendicular to the load application direction), there are 90 Reinforcing ribs 8 and 9 bent at an angle of 8° to prevent buckling are provided. This strain plate 1 is
The attachment holes 2, 3 and the slits 6, 7 are punched out of a thin plate material using, for example, a press machine, and the reinforcing ribs 8, 9 are bent and formed. In the case of this first embodiment, two of the above-mentioned strain plates 1 are stacked back to back, that is, the surfaces on which the reinforcing ribs 8 and 9 are not formed are stacked on each other, and although not shown in the drawings, for example, The cylindrical part of the flanged cylindrical body is attached to the strain plate 1.
are fitted into each of the mounting holes 2 and 3 to protrude outward from the strain plate 1 on the opposite side.Next, after fitting a ring body (button) into the protruding cylindrical part, the cylindrical part is caulked 2. The two strain plates are fixed together near both ends thereof and integrated.

After that, strain gauges SG1,
A strain detector is constructed by attaching SG2.

Next, the operation of the first embodiment having the above configuration will be explained.

First, form holes or screw holes for bolts (not shown) to attach the strain detector to the object to be measured.
The strain detector is attached to the object to be measured by inserting the bolts into the mounting holes 2 and 3 drilled in the strain plate 1 and screwing them into, for example, the above-mentioned screw holes provided in the object to be measured. Install.

If a compressive load is applied to the object to be measured, it will be transmitted to the strain plate 1 via a mounting bolt (not shown) and compress the strain plate 1. Since the slits 6 and 7 are formed in the strain plate 1 so as to be biased to one side, it is thought that the points of action acting on the strain generating portion 4 move to G1 and G2 in FIG. 1A. Therefore, when a compressive load is applied to the mounting holes 2 and 3 as described above, shear strain is intensively generated in the strain generating portion 4. Due to this shear strain, the strain-generating portion 4
A total of four strain gauges SG1 are attached to the top in directions of 45° and 135° relative to the load direction, respectively.
SG2 contracts or expands. Generally, a Wheatstone bridge circuit is configured by four strain gauges, so an output signal corresponding to the shear strain of the strain generating section 4 is sent from the output end of the Wheatstone bridge circuit, and this is transmitted to a strain measuring device. (not shown) allows the amount of shear strain to be measured.

Here, if the mounting dimension of the strain detector is L, the compressive strain occurring between this dimension L on the object to be measured is εa, and the elongation of the strain detector is ΔL, then the elongation ΔL
is expressed by the following equation.

ΔL=εa·L (1) The shear stress σs generated in the strain-generating portion 4 when the strain detector is elongated by ΔL is expressed by the following equation.

σs＝3E・IΔl／Al ³・3/2=3E.th ³ .
L・εa/12t・h・l ³・3/2=3E・h ²・L・εa/8l ³ (
2) Here, t is the thickness of the strain-generating portion 4, h is the height of the strain-generating portion 4, E is the longitudinal elastic modulus, I is the second moment of area,
l is the length of the strain-generating portion 4.

Further, the relationship between the shear stress σs and the shear strain εa is as follows, assuming that Poisson's number is m.

σs=εa・m・E/2(m+1) (3) From equations (2) and (3) above, εs/εa=2(m+1)/E・m・
3E・h ²・L/8l ³ = (m+1)・3・h ²・L/m・4l ³ (4
) As shown in equation (4) above, it can be seen that there is a magnification relationship between the strain on the object to be measured and the strain (shear strain) generated in the strain detector.

Incidentally, try calculating by substituting specific numerical values into the above equation (4). That is, h=8mm, l=12mm, L=
40mm, m=3.3, εs/εa=(3.3+1)×3×8 ² ×40/3.3×4×12
³ = 1.448.

Next, when calculating by changing l=8 mm, the following value is obtained.

εs/εa=4.886 In this latter calculation example, a strain (shear strain) approximately five times as large as the strain (compressive or tensile strain) in the object to be measured is generated in the strain detector. In other words, it is possible to obtain a strain detector that generates a large detection output in response to a relatively small acting force (applied load) and a small amount of deformation.
Therefore, with this detector, it is possible to detect strain in objects to be measured with low rigidity such as thin plates and plastics, and it is also possible to accurately detect minute strains. According to this first embodiment, since the two strain plates 1 are symmetrically superposed, even if bending force is applied to the strain detector, it hardly affects the strain detection output. I won't give it. Further, since the reinforcing ribs 8 and 9 are configured to receive the compressive force applied to the strain detector, buckling can be prevented by the reinforcing ribs 8 and 9. Therefore, even when a large compressive strain occurs, there is no buckling, and the compressive strain can be accurately detected.

Although not shown, a hard filler such as epoxy resin or synthetic rubber is cured on the upper and lower surfaces of the embodiment shown in FIG. When a molded body is formed to prevent bending, the following advantages can be obtained.

First, as mentioned above, the molded body is formed to have approximately the same height as the reinforcing ribs 8 and 9, and is much larger than the cross section of the strain plate, so the bending rigidity is lower than that of the flat plate. Much larger than the strain plate. Therefore, despite having low tensile and compressive rigidities, it has strong properties against buckling under compression.
Therefore, in particular, it is possible to detect compressive strain of an object to be measured with low rigidity, which has been considered difficult in the past, with high precision without causing buckling.

Second, the molded body isolates the strain gauge from the outside air and protects the strain gauge from deterioration of insulation due to moisture absorption and deterioration due to oxidation.

FIGS. 2A and 2B are a plan view and a sectional view taken along the line AX-X in the same figure, showing the configuration of a second embodiment of the present invention.

This second embodiment has the following points: reinforcing ribs 8' and 9' for preventing buckling on the edge of the strain plate 1' face in opposite directions, and bushes 10 and 11 (however, 11 is not shown in the figure). (does not appear), Butsuyu 12 and 13
This embodiment differs from the first embodiment in that they are respectively attached so as to sandwich the strain plate 1' between them. In particular, in the case of the second embodiment, since only one strain plate 1' is required, strain can be detected with half the force compared to the first embodiment. In this figure, mounting hole 2',
3', strain plate 4', line segment 5', slits 6', 7',
Points of action G1', G2' are 2, 3, and 2 as shown in FIG.
4, 5, 6, 7, G1, and G2, respectively.

Note that the present invention is not limited to the above-described embodiments, but can be implemented with various modifications.

For example, in each of the above embodiments, the slits are formed in a direction perpendicular to the load application direction (line segment connecting the mounting holes 2, 3, etc.), but the slits are not necessarily orthogonal. It is not necessary to do so, and it may be formed so as to intersect the line segments 5 and 5' at a certain angle.

Furthermore, a hard filler such as epoxy resin or synthetic rubber is cured on the upper and lower surfaces of the embodiment shown in FIG.
The structure for forming the molded body to prevent buckling has been described above, but on the front and back surfaces of the strain plate 1' of the second embodiment, the reinforcing ribs 8' and 9' are provided with substantially the same height. A molded body may be formed in the same manner. In this case, the modulus of elasticity of the molded body is selected to be, for example, 1/10 or less of that of the strain plate 31.

As detailed above, according to the first invention, firstly, the two strain plates are thin plates, and the outer shape is formed, the reinforcing ribs are bent, and the slits and mounting portions are formed. Holes can be easily punched using a press machine, and therefore can be manufactured at low cost.

Second, the strain-generating plate itself has a thin plate shape, reinforcing ribs are formed only near both sides, and the strain-generating portion has slits, so the cross section is extremely small, and the molded body is Although the cross section is larger than the strain-generating portion, the elastic modulus is sufficiently lower than that of the strain-generating plate, so the rigidity against tension and compression is small.
Therefore, it is possible to detect with high sensitivity the tensile strain and compressive strain of objects to be measured with low rigidity, such as thin plates and plastics, which was impossible with conventional devices.

Thirdly, since the two strain plates are stacked on top of each other so that their reinforcing ribs are on opposite sides, the bending rigidity is much greater than that of the strain plate. As described above, the height is approximately the same as the height of the reinforcing rib of the strain plate, and it is much larger than the cross section of the strain part, so the bending rigidity is much greater than that of the strain part. Therefore, despite having low tensile and compressive rigidities, it has strong properties against buckling under compression. Therefore, especially
Compressive strain in objects with low rigidity, which has been considered difficult in the past, can be detected with high sensitivity without causing buckling.

Fourth, since the structure is such that a pair of thin strain-generating plates are stacked with their reinforcing ribs on the outside, the strain-generating part is located at the center of the cross section, that is, at the neutral plane of bending, and the bending force is The bending stress is close to zero even when the bending force is applied. Therefore, even if the strain detector is mounted on an object to be measured that has a somewhat rough surface, the output due to the bending force will be mixed into the strain detection output as in the case of conventional methods. It is possible to obtain an output that corresponds only to tensile strain or compressive strain.Therefore, there is no need to finish the strain sensor mounting surface of the object to be measured with great precision, and the labor costs associated with jigs and installation can be reduced. Significant savings can be achieved.

Fifth, since reinforcing ribs are provided on each side of the strain plate, there is no risk of twisting or tilting when a tensile load is applied, unlike the conventional example described in the above publication; Unlike the other conventional example, there is no need to provide two strain-generating parts symmetrically about the central axis.
The width dimension can be reduced, and there is no reduction in strain sensitivity, and there are fewer restrictions on the object to be measured.
Furthermore, it can be manufactured at a lower cost than the conventional example.

Moreover, according to the second invention, effects similar to the first to fifth effects of the first invention can be achieved.

[Brief explanation of drawings]

FIGS. 1A, B, and C are a plan view, a front center cross-sectional view, a sectional view taken along the line X-X in FIG. 2A, and FIG.
and B are a plan view showing the configuration of a second embodiment of the present invention, and a sectional view taken along the line X--X in FIG. 1, 1'... Strain plate, 2, 3, 2', 3'... Mounting hole, 4, 4'... Strain part, 5, 5'... Line segment,
6, 7, 6', 7'...slit, 8, 9, 8',
9'... Reinforcement rib, 10, 11, 12, 13...
Butsuyu, SG, SG1, SG2...Strain gauge.

Claims (1)

[Scope of Claims] 1. In a strain detector that is attached to an object to be measured to detect strain occurring in the object and obtain an electrical signal corresponding to the strain, the object to be measured is attached at both ends in the direction of load application. A mounting part for attaching to an object is formed, and a substantially central part is a strain-generating part. A pair of slits are formed, and both ends in the direction perpendicular to the load direction are bent in the same direction to form reinforcing ribs to prevent buckling, and the surfaces on which the reinforcing ribs are formed are on the outside. The two strain-generating plates having the same shape are stacked in this way, and the strain-generating portions of the surfaces of the two strain-generating plates on which the reinforcing ribs are formed are placed at an angle of approximately 45° with respect to the direction of load application. and
strain gauges each attached in a direction forming an angle of 135°; and a strain gauge that covers at least the surface of the two strain plates on which the reinforcing ribs are formed and the strain gauge, and has a height that is approximately the same as the height of the reinforcing ribs. 1. A shear type strain detector comprising a molded body filled with a filler and solidified so as to have a modulus of elasticity sufficiently smaller than that of the strain plate. 2 In a strain detector that is attached to an object to be measured to detect the strain occurring in the object to be measured and to obtain an electrical signal corresponding to the strain, mounting for attaching to the object to be measured at both ends in the direction of load application. A portion is formed, a substantially central portion is a strain-generating portion, and a pair of slits extending from opposite side edges of the strain-generating portion in a direction approximately perpendicular to the load application direction and extending to the strain-generating portion are formed. a strain-generating plate having reinforcing ribs formed thereon, both ends of which are bent in opposite directions in a direction perpendicular to the load direction to prevent buckling, and the front and back surfaces of the strain-generating portions of the strain-generating plate; strain gauges attached in directions that are approximately 45° and 135° with respect to the load application direction, and a strain gauge that covers the plate surface of the strain plate and the strain gauge and has a height that is approximately the same as the height of the reinforcing rib. 1. A shear type strain detector comprising: a molded body having a modulus of elasticity sufficiently smaller than that of the strain-generating plate;