JP4250064B2 - Strain gauge and arrangement method thereof - Google Patents

Description

  The present invention relates to a strain gauge that is inserted into a hole drilled in an object to be measured such as a bolt and measures axial strain generated in the object to be measured, and a method of arranging the strain gauge.

  Conventionally, a method is known in which a strain gauge is attached to the outer surface of an object to be measured to measure axial strain generated in the object to be measured. The strain gauge has a substantially rectangular thin plate-like base and a sensing part made of a resistor provided on the surface of the base, and the object to be measured is attached via an adhesive applied to the back surface of the base. Affixed to.

  However, when the object to be measured is a bolt screwed into the object to be fastened, a strain gauge cannot be attached to the outer surface of the object to be measured. Therefore, a small-diameter hole (for example, 2 mm in diameter and 15 mm in depth) is formed in the axial direction of the object to be measured, and a strain gauge is provided in the hole to measure the axial strain. In this case, since the strain gauge and the hole are very small, even if a thin tool such as a needle is used, it is difficult to press the strain gauge against the peripheral wall surface of the hole and attach it. The sensitive area may be damaged.

  Therefore, when installing the strain gauge in the hole drilled in the object to be measured, after filling the hole with the adhesive in advance, insert the strain gauge into the hole to cure the adhesive, and insert the strain gauge into the hole. It is made to fix in the inside (for example, refer patent document 1). For measurement, a fixed strain gauge is connected to a switch box containing a resistor, for example, so as to form one side of the Wheatstone bridge, and the switch box is connected to a strain measuring instrument in a state of being connected to the strain measuring instrument. Measure the strain. Then, the strain measuring device detects a change in the resistance value in the sensitive part of the strain gauge, and the strain value is obtained based on the change.

When a strain gauge is installed in the hole as described above, the thickness of the adhesive interposed between the back surface of the strain gauge base and the peripheral wall surface of the hole is determined by attaching the strain gauge to the outer surface of the object to be measured. When compared to the thickness of the adhesive. And as the thickness of the adhesive increases, the strain gauge becomes more susceptible to the phenomenon (creep) in which the adhesive layer deforms over time. As a result, there is a problem that the strain transmitted to the strain gauge is reduced and the measurement error is increased. In particular, since the creep becomes larger as the temperature becomes higher, it is difficult to maintain the measurement accuracy in a high temperature range of 80 ° C. or higher, and the reliability is remarkably lowered.
JP-A-6-347349

  The present invention has been made to solve the above-mentioned problems, and relates to a strain gauge that is inserted into a hole formed in a measured object and measures axial strain generated in the measured object. And providing a simple method for disposing the strain gauge inside a hole drilled in the object to be measured. It is an issue.

  The present invention has been made to solve the above-described problems, and includes a substantially rectangular plate-shaped base and a sensing part made of a resistor provided on the surface of the base, and is pierced in an object to be measured. Concerning the improvement of the strain gauge for measuring the axial strain generated in the object to be measured, which is inserted into the hole provided, a constricted portion shortened in the width direction is formed at the center in the longitudinal direction of the base, and the constricted The width of the base on both sides in the longitudinal direction of the base sandwiching the portion is half the circumference of the hole, and the width of the minimum width portion of the constricted portion is equal to or less than the diameter of the hole; A portion is provided on at least one surface of both sides in the longitudinal direction of the base sandwiching the constricted portion, and the base is folded from the constricted portion so that the surface is on the inner side. Can be inserted into a hole drilled in the object to be measured Characterized in that there.

  The strain gauge according to the present invention is disposed in a hole formed in the object to be measured, and includes a peripheral wall surface of the hole and the strain gauge. Applying an adhesive to at least one of the back surface of the base and a front end of a push rod that can be inserted into the hole against the surface of the constricted portion of the base, so that the base faces the inside. A step of pushing the strain gauge into the hole from the constricted portion while turning back at the constricted portion.

  According to the present invention, since the base width of the portions on both sides in the longitudinal direction of the base is half of the circumferential length of the hole, when the base is inserted into the hole in a folded state, The sides on both sides in the width direction of the portions on both sides in the longitudinal direction are abutted with each other. In addition, the both side portions are bent in the width direction by the peripheral wall surface of the hole, so that they are to be restored, but because they are forcedly pressed, they are curved along the peripheral wall surface of the hole and become the same shape as the hole. Touch the peripheral wall of the hole. As a result, the thickness of the adhesive interposed between the back surface of the base and the peripheral wall surface of the hole can be made as thin as possible. Therefore, it becomes difficult to be affected by the creep of the adhesive, and it is possible to measure accurately up to a high temperature range. Further, as described above, since both side portions of the base are in the same shape as the hole and come into contact with the peripheral wall surface of the hole, it is possible to prevent both side portions of the base in the hole from being inclined with respect to the axial direction of the hole. Therefore, the parallelism between the sensing part on the base surface and the axial direction of the hole can be maintained, and the axial strain can be accurately measured. Furthermore, by using the push rod, the strain gauge can be easily pushed into the hole.

  Further, the strain gauge of the present invention is provided with the sensitive parts on the surfaces of the both sides in the longitudinal direction of the base, and the conductive wire part connecting the sensitive parts provided on the both sides to the constricted part. It is characterized by providing.

  According to the present invention, even if the strain acting on the peripheral wall surface of the hole is different and uneven on both sides sandwiching the constricted part, the unevenness is averaged by the sensing parts provided on both side parts. It is possible to measure the strain in the measured state.

  Next, an example of an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a plan view showing a configuration of a strain gauge according to an embodiment of the present invention, FIG. 2 is an explanatory sectional view showing a state in which the strain gauge shown in FIG. 1 is disposed on a bolt hole, and FIG. 1 is a perspective view showing the strain gauge shown in FIG. 1, FIG. 4 is an explanatory sectional view showing a state in which the strain gauge shown in FIG. 1 is disposed in the hole of the bolt, and FIG. 5 is a line AA in FIG. It is a cross-sectional arrow view.

  With reference to FIGS. 1 and 2, the strain gauge 1 in the present embodiment is inserted into a hole 21 drilled in a bolt 2 as an object to be measured and used to measure axial strain generated in the bolt 2. And includes a base 11 having a substantially rectangular plate shape and a sensing part 12 made of a resistor provided on the surface of the base 11. The object to be measured is not limited to the bolt 2.

  The base 11 is composed of a constricted portion 11a located at the central portion in the longitudinal direction and two base main portions 11b which are portions on both sides in the longitudinal direction of the base sandwiching the constricted portion 11a. The base main part 11 b has a constant base width W that is half the circumference of the hole 21, and its back surface is attached to the peripheral wall surface of the hole 21. The width of the constricted portion 11 a is shorter than the base width W of the base main portion 11 b, and the width W ′ of the minimum width portion is equal to or smaller than the diameter of the hole 21.

  The base 11 is made of a synthetic resin insulating material such as polyimide, for example, in terms of creep resistance, heat resistance, and processability. The base 11 has an appropriate rigidity so that the base 11 can be bent elastically at the constricted portion 11a. The length of the constricted portion 11a is set to an appropriate length so that the base main portion 11b can easily come into contact with the peripheral wall surface of the hole 21.

  The sensing part 12 is provided on the surface of each of the two base main parts 11 b and is composed of a resistor whose resistance value changes according to the strain in the longitudinal direction of the base 11. The resistor is made of, for example, a Cu—Ni alloy and is formed in a foil shape by photoetching or the like. And the sensing part 12 is connected in series by the conducting wire part 13 provided in the surface of the constriction part 11a. Therefore, even if the two sensing units 12 have different resistance values and are biased, the strain can be measured with the bias averaged.

  Each sensing part 12 is connected to a lead wire 15 via a tab 14 provided on the surface of each of the two base main parts 11b. In addition, the conducting wire part 13 and the tab 14 are the same material as the resistor which comprises the sensing part 12, and are formed in foil shape similarly to this resistor.

  Next, a method of disposing the strain gauge 1 in the hole 21 will be specifically exemplified. In this embodiment, the bolt 2 has a nominal diameter of 8 mm, for example. Then, a hole 21 having a diameter of 2 mm and a depth of 15 mm is drilled in advance from the top of the bolt 2 along the axis.

  The strain gauge 1 has a base width W of 3.1 mm which is half of the circumferential length of the hole 21, a width W ′ of the minimum width portion of the constricted portion 11 a is smaller than the diameter of the hole 21, for example, 1 mm, a base length is, for example, 20 mm, and a base thickness Is, for example, 30 μm, the thickness of the sensing part 12 is, for example, 5 μm, and the length of the constricted part 11 a is, for example, 5.8 mm.

  Also, a push bar 3 that can be inserted into the hole 21 is prepared. The push rod 3 is formed so that the cross section of the portion inserted into the hole 21 is a substantially rectangular shape having a width of 0.5 mm and a length of 1.5 mm, for example. In addition, the front-end | tip part of the push rod 3 is processed into the curved surface shape so that the surface of the constriction part 11a may not be damaged.

  In order to dispose the strain gauge 1 in the hole 21, first, the adhesive 4 is applied to both the peripheral wall surface of the hole 21 and the back surface of the base 11 of the strain gauge 1. As the adhesive 4, it is desirable to use a thermosetting adhesive mainly composed of phenol having excellent heat resistance, for example, phenol having heat resistance of 200 ° C. or higher.

  Next, with the back surface of the constricted portion 11 a facing the open end of the hole 21, the tip of the push rod 3 is pressed against the surface of the constricted portion 3 as shown in FIG. 2, and the constricted portion 11 a is brought into the hole 21. Push in. According to this, the base 11 is folded back at the constricted portion 11a so that the surface is inside, and the strain gauge 1 is pushed into the hole 21 in this state. In the strain gauge 1, the base width W of the base main portion 11 b is half the circumference of the hole 21. Therefore, in the process of inserting into the hole 21, the sides on both sides in the width direction of the two base main portions 11 b Are butted together. In the hole 21, the base main portion 11 b is bent in the width direction by the peripheral wall surface of the hole 21, so that it tries to be restored by the elastic force of the base 11 itself, but is forcedly pressed by the peripheral wall surface of the hole 21. For this reason, as shown in FIG. 3, the two base main portions 11 b are curved along the peripheral wall surface of the hole 21 over the entire length to form a cylinder having the same shape as the hole 21. Therefore, the back surface of the base main portion 11 b is in contact with the peripheral wall surface of the hole 21.

  In this state, the base main portion 11b is prevented from being tilted in the hole 21, and the parallelism between the sensitive portion 12 on the surface of the base main portion 11b and the axial direction of the hole 21 is ensured, so that the axial strain can be accurately measured. It will be possible to measure.

  Next, as shown in FIG. 4, after the portion excluding the lead wire 15 of the strain gauge 1 is pushed into the hole 21 to a predetermined depth, the push rod 3 is removed. In the insertion process of the strain gauge 1, the longitudinal direction (longitudinal direction) of the cross section of the portion inserted into the hole 21 of the push rod 3 is matched with the width direction of the base 11. According to this, as shown in FIG. 5, it is possible to prevent the push rod 3 from being separated from the surface of the base main portion 11 b and to damage the sensing portion 12 provided on the surface of the base main portion 11 b by the push rod 3.

  After disposing the strain gauge 1 in the hole 21 by the above method, the adhesive 4 is reacted and cured, and the strain gauge 1 is used for measurement. The strain measurement method is well known and will not be described in detail. For example, the strain gauge 1 is connected to a switch box (not shown) with a built-in resistor so that the two sensing parts 12 of the strain gauge 1 form one side of the Wheatstone bridge. ) And the switch box is connected to a strain measuring device (not shown). Then, the strain measuring device detects a change in the resistance value of the sensing part 12 that occurs according to the axial strain of the bolt 2, and the strain value is obtained based on the change.

  As described above, the strain gauge 1 of the present embodiment can be easily arranged in the hole 21 of the bolt 2 according to the above arrangement method. In addition, since the two base main portions 11 b are abutted with each other in the hole 21 and curved along the peripheral wall surface of the hole 21, the adhesive 4 interposed between the base main portion 11 b and the peripheral wall surface of the hole 21. The thickness can be made as thin as possible. Therefore, the influence of the creep of the adhesive can be reduced and the measurement can be accurately performed up to a high temperature range.

  Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention. For example, when there is a concern that the lead wire portion 13 of the strain gauge 1 is damaged by the push rod 3, the lead wire portion 13 is provided on the back surface of the constricted portion 11a, the through hole is provided in the base 11, and the lead wire portion 13 is provided. It is good also as a structure connected to the sensing part 12 through a through hole.

  Moreover, the strain gauge of this invention can also be set as the structure which abbreviate | omitted the conducting wire part 13, when connecting each sensitive part 12 to a distortion | strain measuring device in parallel via the said switch box. In addition, the sensing part 12 may be provided only on one base main part 11b, but in this case, the balance on both sides sandwiching the constricted part 11a is lost and adversely affects the measurement. Thus, it is desirable to provide both base main parts 11b. Furthermore, in the above-described embodiment, one sensitive part 12 is provided on the surface of each base main part 11b. However, two sensitive parts 12 are provided on the surface of each base main part 11b. A total of four sensing parts 12 of the part 11b may be connected so as to form a bridge.

  Moreover, in the arrangement | positioning method of the said embodiment, although the adhesive agent 4 was apply | coated to both the back surface of the base 11 of the strain gauge 1, and the surrounding wall surface of the hole 21, it does not necessarily need to apply | coat to both. It may be applied only to.

The top view which shows the structure of the strain gauge of one Embodiment of this invention. Explanatory sectional drawing which shows the state which has arrange | positioned the strain gauge of FIG. 1 on the hole of a volt | bolt. The perspective view which shows the strain gauge of FIG. 1 in a hole. Explanatory sectional drawing which shows the state which has arrange | positioned the strain gauge of FIG. 1 in the hole of a volt | bolt. FIG. 5 is a cross-sectional view taken along line AA in FIG. 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Strain gauge, 11 ... Base, 11a ... Constriction part, 11b ... Base main part, 12 ... Sensitive part, 13 ... Conducting wire part, 2 ... Bolt, 21 ... Hole, 3 ... Push bar, 4 ... Adhesive.

Claims (3)

A substantially rectangular plate-shaped base and a sensing part made of a resistor provided on the surface of the base are provided, inserted into a hole drilled in the object to be measured, and axial strain generated in the object to be measured is measured. A strain gauge for
In the central part of the base in the longitudinal direction, a narrowed part shortened in the width direction is formed,
The width of the base on both sides in the longitudinal direction of the base sandwiching the constricted portion is half the circumference of the hole, and the width of the minimum width portion of the constricted portion is equal to or less than the diameter of the hole,
The sensing part is provided on at least one surface of both sides in the longitudinal direction of the base sandwiching the constriction part,
A strain gauge, wherein the base can be inserted into a hole drilled in the object to be measured from the constricted portion in a state where the base is folded at the constricted portion so that the surface is inside.   The base is provided with the sensing portions on the surfaces of both sides in the longitudinal direction of the base, and the constricted portion is provided with a conductor portion for connecting the sensing portions provided on the both sides. The strain gauge according to 1. A method of disposing the strain gauge according to claim 1 or 2 in a hole drilled in an object to be measured,
Applying an adhesive to at least one of the peripheral wall surface of the hole and the base back surface of the strain gauge;
The tip of a push rod that can be inserted into the hole is pressed against the surface of the constricted portion of the base, and the base is folded back at the constricted portion so that the surface is inside, while the strain gauge is moved from the constricted portion to the hole. And a step of pushing into the strain gauge.

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