JPS58150816A - Strain detector - Google Patents

Abstract

PURPOSE:To facilitate the attachment of strain gauges and to prevent the generation of measuring error due to flexural force or torsion force, by providing every four strain gauges to the front and the back surfaces of a wafer like strain generating plate so as to cross the same at right angles in line symmetry to form bridge connection. CONSTITUTION:A narrow strain generating part 1a is provided to the central part of a strain generating plate 1 comprising a wafer material and circular perforations 1a, 1b for attachment are provided in the vicinity of both ends thereof in a longitudinal direction (load direction). To the front side of the strain generating part 1a, four strain gauges A, A', C, C' are adhered so as to be crossed at right angles in symmetric relation to central lines 1c, 1d. In opposed relation to these strain gauges, four strain gauges B, B', D, D' are adhered to the back side of said strain generating plate 1. These strain gauges are subjected to bridge connection so as to include A, A', B, B' or C, C', D, D' in a pair of opposed sides. Synthesized resistances of the strain gauges in each opposed sides are cancelled against flexion or distortion and measuring error is not generated. In addition, the attachment thereof is made easy.

Description

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

For example, when a compressive strain is detected by this type of strain detector and measured by a strain measuring device, a buckling phenomenon may occur in the strain-generating plate, particularly in the strain-generating portion, and accurate strain measurement may not be possible. Therefore, in some conventional strain detectors, the strain-generating part (sensing part) of the strain-generating plate is formed into a hollow thick-walled cylinder shape or a square cross-section to increase the cross-sectional shape. There are some that are designed to prevent bending.

However, in such conventional strain detectors, the cross section of the strain-generating part is large, so if there are irregularities on the mounting surface of the object to be measured (for example, a rough surface such as the so-called black surface of a casting), strain detection becomes difficult. When the strain detector is installed, bending force acts on the strain detector, and the output from that bending force is considerably affected, making it impossible to accurately measure the tensile strain or compressive strain of the object to be measured. In extreme cases, the measurement range could be significantly exceeded during the installation stage, making measurement impossible.

In order to avoid such a situation, in the past, the mounting surface of the strain detector on the object to be measured was finished to be a smooth flat surface, and the bolt hole or thread allowance was precisely finished using a reamer or precision tap. This kind of work requires special jigs and tools, and takes a lot of time.
This was a contributing factor to the increase in jig and tool costs and labor costs.

In addition, Kamimachi's conventional strain detector has a large cross-section of the sensing part to prevent buckling, which increases the rigidity of the object to be measured. Since strain is supported by the rigidity of the strain detector itself, accurate strain detection has been difficult.

Furthermore, in manufacturing the above-mentioned conventional strain detector, the strain-generating part is formed by cutting a round bar or square material.
Processing costs also had to rise.

Therefore, in order to eliminate the influence of bending or torsion on the compression and tension of the object to be measured, the present invention provides four thin strain plates arranged symmetrically and perpendicularly on the front and back sides of the thin strain plate. Each strain gauge is provided with a bridge connection to cancel the effects of bending or twisting.

Furthermore, in addition to the above configuration, the present invention includes two thin reinforcing plates having reinforcing ribs to prevent buckling.
The strain plate is sandwiched between both sides, and a hard filler is filled and solidified on the outer surface of the reinforcing plate.

The present invention will be described in detail below based on embodiments shown in the accompanying drawings. Note that the same members are given the same reference numerals.

FIG. 1 is a perspective view showing an embodiment of the present invention.

A narrow strain-generating portion 1a is provided in the center of the strain-generating plate 1 made of a thin plate material, and circular through-holes 1b, 1b for attachment are bored near both ends in the longitudinal direction (load direction). It is set up. Four strain gauges A are attached to the strain-generating portion 1a on the front side (top side in the figure) of the strain-generating plate 1.

A' and C2C' are attached by means such as adhesive. Strain gauges A are attached at almost symmetrical positions with respect to the center line IC in the longitudinal direction, and in the same direction, and strain gauges C9σ are attached at approximately symmetrical positions with respect to the center line 1d, which is approximately perpendicular to the longitudinal direction. Moreover, they are attached to each other in the same direction.In addition, four strain gauges a, B', and
D and D' are attached. These four strain gauges B, B', D, and rj are provided on the back side of the four strain gauges A on the front side in substantially the same direction and at the same position so as to correspond to each of C2σ. . That is, the strain gauges B and B' are located at approximately symmetrical positions with respect to the longitudinal center line IC, and in the same direction,
The strain gauges D and ff are attached in the same direction as the strain gauges A, and the strain gauges D and ff are attached in substantially symmetrical positions with respect to the center line 1d, and in the same direction, and in the same direction as the strain gauge C20'.

FIG. 2 is a circuit diagram showing the connection of the strain gauges in the above embodiment. Four strain gauges At A HO+ O' attached to the front side of the strain plate 1 constitute a bridge circuit, and one strain gauge on the front side and a strain gauge on the back side located axially symmetrically thereto constitute the bridge circuit. are connected in series with the same sending direction. That is, the four strain gauges A attached to the front side of the strain plate 1, O, O
' are included in each side of the bridge circuit. And for example, with a strain gauge person, 180° to the axis IC
The strain gauge on the back side located on the opposite side (that is, located axially symmetrically) is connected in series to the same side of the bridge circuit, and the strain gauge on the back side located 180° opposite to the axis IC is connected in series to the same side of the bridge circuit. The gauge and the gauge are connected in series on the same side of the bridge circuit.

Furthermore, the relationships between the strain gauges C and U, and between σ and D are the same as above, and in this case, they are located axially symmetrically with respect to the axis 1d. Note that l is a power supply and e is an output signal.

Next, the operation of the above embodiment will be explained.

The strain plate 1 is attached to the object to be measured by inserting, for example, a mounting screw (not shown) into the circular through-holes 1b and 1b drilled in the strain plate 1 and screwing it into a screw hole formed in the object to be measured. Attach to something. It is assumed that the strain plate 1 is bent during this installation. In this case, assume that strain gauges A and 2 have expanded, and strain gauges B and B' have contracted. In the case of simple bending, strain gauges A and B have the same amount of expansion, strain gauges B and B' have the same amount of contraction, and the amount of expansion and contraction are the same. Therefore, strain gauge A
``The combined resistance, and the combined resistance of the strain gauge and B, remains unchanged from before the target occurred.''

Even if the direction of bending deviates from the above by 90°, the amount of bending will be canceled in the same way as above, and the combined resistance of strain gauges 0 and U, and the combined resistance of strain gauges σ and D will be the same as before the bending occurs. There is no change.

On the other hand, assume that twisting occurs regarding the axis 11Il.

In this case, if strain gauge C2σ expands, strain gauges D and ff contract. In case of simple twist, use b strain gauge 0. The amount of elongation of σ is the same, the amount of contraction of strain gauges D and ff is the same, and the amount of elongation and the amount of contraction are the same. Therefore, the combined resistance of strain gauge 0 and the shore, and the combined resistance of strain gauges σ and D do not change before and after this twisting. Likewise, even if the wire is twisted in the opposite direction, the combined resistance will not change.

Even if simple bending or twisting occurs, it can be canceled, so even if both bending and twisting occur,
TJ cancels the effects of bending and torsion. Therefore, even if there are irregularities on the mounting surface of the object to be measured, measurement errors due to bending or twisting forces will not occur.

3 is an exploded perspective view showing another embodiment of the present invention, FIG. 4 is a plan view, FIG. 5 is a sectional view taken along the line V-V in FIG. 4, FIG. 6 is a front view, and FIG. The figure is a sectional view in the direction of arrows ``--'' in FIG. 4.

3 to 7, reference numeral 1 denotes a strain plate made of a thin plate material, and this strain plate 1 is provided with a strain part 1a formed narrowly in the center. There are circular through holes 1b near both ends of the direction (direction).

1b are drilled in each case, and four strain gauges are attached to each of the front and back sides of the strain-generating portion 1a by means of adhesive or the like in the same manner as shown in FIG.

2 is a reinforcing plate, and at the center of this reinforcing plate 2 is a strain gauge attached to the strain plate 1.

A rectangular through hole 2a larger than the attached area of C9σ is bored, and near both ends of the reinforcing plate 2 in the longitudinal direction, the hole 2a has the same spacing and the same diameter as the two through holes lb provided in the strain plate l. A circular hole 2b is drilled at both ends of the reinforcing plate 2 in the short side direction (direction perpendicular to the load direction), and a circular hole 2b is formed at 90° to the same side.
A reinforcing rib 2C that is bent to prevent buckling is provided. This reinforcing plate 2 is made of a thin plate material, and the through holes 2a and 2b are punched out using, for example, a press machine, and the reinforcing ribs 2c are formed by bending.

Reference numeral 3 designates a fixing member, which includes a cylindrical body 3a with a flange having a circular hole 3c in the center, and a ring having an inner diameter that fits into the cylindrical portion of the cylindrical portion of the cylindrical flanged body 3a and the same outer diameter as the flange. It consists of a body 3b and serves to fix the strain plate 1 and the reinforcing plate 2 as described below. In FIGS. 5 and 7, 4 is a molded body for buckling prevention made by hardening a hard filler such as epoxy resin or synthetic rubber, and the elastic modulus is, for example, the strain plate 1.
Those with a value of 1/10 or less are selected.

The strain detector 5 having such a configuration is assembled as follows.

First, as can be inferred from FIG. 3, the surfaces of the two reinforcing plates 2 opposite to the surfaces with the reinforcing ribs 2c are brought into contact with the strain plate 1, and the strain plate 1 is The cylindrical portion of the flanged cylindrical body 3, which is one of the fixing members 3, is inserted into the through hole 2b of the reinforcing plate 2 and the through hole 1b of the strain plate 1,
The reinforcing plate 2 on the opposite side is made to protrude outward, and then the ring body 3b
After fitting into this protruding cylindrical portion, the cylindrical portion is caulked, and the strain plate 1 and the two reinforcing plates 2 are fixed together near both ends thereof to be integrated.

Filler material such as the epoxy resin is placed on the surface of the two reinforcing plates 2 of the integrated strain detector 5 on which the reinforcing ribs 2C are provided, at a height that is approximately the same as the height of the reinforcing ribs 2C. The mold body 4 is filled by filling it to the extent that it is solid and solidifying it.
form. At this time, the filler is the strain-generating portion 1 of the strain-generating plate 1.
a, strain gauge A, C9σj B? ” )
D? It also flows into the peripheral part of the fixing member 3, and these parts are integrated via the molded body 5, so to speak.

This state is shown in FIGS. 4 to 7.

To explain the operation of the present invention configured in this way, first, a hole or a screw hole for a bolt (not shown) for attaching the strain detector 5 to the object to be measured is formed, and the bolt is attached to the fixing member. The strain detector 5 is attached to the object to be measured by inserting it into the circular hole 3C provided in the object to be measured and screwing it into, for example, the screw 6 provided in the object to be measured.

If a compressive load is applied to this object to be measured,
Mounting bolt (not shown), fixing member 3 of strain detector 5
The strain plate 1, two reinforcing plates 2 and the molded body 4 are
These are compressed in the longitudinal direction (load direction)
It contracts in the width direction (direction perpendicular to the load direction).

As a result, jC1σl"l" is applied to each of the four strain gauges A attached to the front and back surfaces of the strain plate portion 1a of the strain plate 1.
ID and υ also deform according to the contraction or expansion of the strain-generating portion 1a. Also, strain gauge A, C2σtB+B', D,
As shown in FIG. 1, Ilf is attached to the front and back surfaces of the strain-generating portion 1a in the load direction and in a direction orthogonal thereto, and these eight strain gauges create a Wheatstone bridge as shown in FIG. configured. Therefore, the amount of strain can be measured from the output of this bridge using a strain measuring device (not shown). When this compressive strain is detected by the strain detector 5 according to the above-described embodiment, since the compressive force applied to the strain detector 5 is also received by the reinforcing plate 2, the reinforcing ribs 2C of the reinforcing plate 2 Buckling can be prevented. Also,
Since the molded body 4 forms a large compressive and tensile cross section of the strain detector 5, this molded body 4 also acts effectively against buckling. Therefore, even when a large compressive strain occurs, there is no buckling, and the amount of compressive strain can be accurately detected.

On the other hand, tensile strain can be measured in a similar manner (although buckling is not involved).

Furthermore, the strain-generating portion 1a is formed narrowly, and the reinforcing plate 2 is made of a thin plate material, and a through-hole 2a is formed in the center (although this through-hole 2a can separate the reinforcing plate 2 and the strain-generating plate 1). When superimposed, strain gauge people.

To, 0. The molded body 4 has a much smaller elastic modulus than the strain-generating plate 1 (
For example, since the strain detector 5 is made of a filler made of a material (for example, 1/10 or less), the rigidity of the strain detector 5 as a whole is small.
Therefore, it is possible to detect the compressive strain of objects to be measured with low rigidity, such as thin plates and plastics.

Furthermore, when installing the strain detector 5 on the object to be measured, it is possible that the mounting surface is rough to some extent or that the two bolt mounting holes provided in the object to be measured are not properly drilled in parallel. If not, bending acts on the strain detector 5, and the strain plate 1 is also bent, but the strain gauge A p A
s OHσ, n, rf are the strain-generating portion 1 in the center of the strain-generating plate 1
a, and this strain plate 1 is attached to two reinforcing plates 2.
. Even if the bending stress is applied, the bending stress is close to zero, so almost no bending output is sent out from the strain gauge. Furthermore, the installation and connection of these strain gauges are shown in Figure 17.
As shown in FIG. 2, the bending output is canceled.

Therefore, for example, the strain detector can be directly attached to the object to be measured, which has a somewhat rough surface, and the attachment operation becomes extremely easy.

Also, the strain gauge is 0. σt Bt' *D
, rf are covered by the molded body 4, so they are cut off from the outside air and insulation deterioration due to moisture absorption can be prevented.

Furthermore, the strain plate 1 and the reinforcing plate 2 are made by punching a thin plate material,
Since it is only necessary to bend and form, it can be easily processed using a press machine and manufacturing costs can be reduced.

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

For example, the shape of the reinforcing ribs of the reinforcing plate, the fixing member, etc. can be changed as appropriate.

Further, the strain detector 5 itself can be used by being housed in a case 6 made of plastic, for example, as shown in FIGS. 8 and 9. In this case, the case 6 has a thickness that allows the strain detector 5 to be accommodated with ample space, and a circular through hole 6a from which a part of the fixing member 3 can protrude is formed, and one end is provided with a circular through hole 6a through which a part of the fixing member 3 can protrude. Derive the strain output,
A cable 7 is connected to transmit the strain to the strain measuring instrument.

As described in detail above, according to the present invention, it is easy to manufacture and attach to the object to be measured, and the rigidity against compression and tension is small, and buckling does not occur under compression, so the range in which compressive strain can be detected is It is possible to propose a strain detector that has a large amount of strain and can suppress the effects of bending and torsion to a negligible degree.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing one embodiment of the present invention, Fig. 2 is a circuit diagram showing the connection of strain and strain gauges, and Figs. 3 to 7 are configurations of other embodiments of the present invention. Figure 3 is an exploded perspective view, Figure 4 is a plan view, and Figure 5 is a diagram taken from Figure 4 V-V.
Cross-sectional view in the direction of line arrows, Figure 6 is a front view, Figure 7 is Figure 4 ■
8 and 9 are a sectional view in the direction of the -■ line, and a plan view and a front view showing the strain detector according to the present invention housed in a case. A, t Bt Ffl C1σ, D, Tj...
・Strain gauge, 1...Strain plate, 1a...
...Strain part, lb, 2a, 2b...Through hole,
2...Reinforcement plate, 2C...Reinforcement lip,
3... Fixed member, 4... Molded body, 5... Strain detector. Fig. 1 b Fig. 2 Fig. 3 N Fig. 4 Fig. 5 Fig. 6 Fig. 7 ``4 81st section 1

Claims (2)

[Claims] (1) It has a thin strain-generating plate having a strain-generating part in the center formed narrowly, and four strain gauges each attached to the front side and the back side of the strain-generating part, Of the four strain gauges attached to the front side of the strain part, two strain gauges are attached in substantially the same direction and symmetrically with respect to the center line in one direction of the strain generating plate, and the remaining two strain gauges The four strain gauges attached to the back side of the strain plate are attached in substantially the same direction and symmetrically with respect to a center line that is substantially perpendicular to the one direction, and the four strain gauges attached to the back side of the strain plate are in contact with each of the four strain gauges on the front side. A bridge circuit is constructed with four strain gauges attached to the front side of the strain plate, which are installed on the back side in almost the same direction and at the same position, and are axially symmetrical to the one strain gauge on the front side. and a strain gauge located on the back side of the bridge circuit, the strain gauge being connected in series within the same side of the bridge circuit. (2) A thin strain-generating plate having a strain-generating part in a narrowly formed central part, four strain gauges each attached to the front side and the back side of the strain-generating part, and at least the strain gauges attached to the central part of each Two thin reinforcing plates, each having a through hole larger than the attachment area of the strain gauge and reinforcing ribs formed on both sides to prevent buckling, are stacked so as to sandwich the strain plate from both sides; A fixing member that fixes the two reinforcing plates and the strain plate together at both ends thereof and has an attachment part to the object to be measured in the fixing part; At least the outer plate surface and the peripheral part of the fixing member are provided with a molded body for preventing buckling, which is made by filling and solidifying a hard filler, and one of the four strain gauges attached to the front side of the strain generating part is provided. Two strain gauges are affixed in substantially the same direction and symmetrically to a center line in one direction of the strain plate, and the remaining two strain gauges are attached substantially symmetrically to a center line that is substantially perpendicular to the one direction. The four strain gauges attached in substantially the same direction and attached to the back side of the strain plate are provided on the back side in substantially the same direction and at the same position so as to correspond to the four strain gauges on the front side, respectively. A bridge circuit is constructed with four strain gauges attached to the front side of the strain plate, and one strain gauge on the front side and a strain gauge on the back side located axially symmetrically to the strain gauge are connected to the same transmission line of the bridge circuit. A strain detector characterized by being connected in series in the direction.