JPH0518645Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial field of application] The present invention relates to a strain gauge mounting jig, and more specifically, to a strain gauge mounting jig, and more specifically, to a strain gauge mounting jig that has an extremely small diameter and is drilled to a predetermined depth from one end surface of a measured object. When installing a strain gauge on the inner peripheral wall between the opening end of the hole and the bottom, a tube is inserted into the installation hole, pressurized fluid is fed into the tube, and the strain gauge is installed using the expansion force. This relates to a strain gauge mounting jig.

[Conventional technology]

For example, as a conventional strain gauge mounting jig,
The ones shown in Figures 3 and 4 were published in JP-A-62.
-Disclosed in Publication No. 194430.

That is, in the strain gauge mounting jig shown in FIGS. 3 and 4, a center hole 51 is pre-drilled on the head side of the bolt 50, and a hole 51 for measuring the tightening force is formed in the center hole 51. This is for bonding the strain gauge 52.

To describe the installation of the strain gauge 52 in detail, after the strain gauge 52 made of an ordinary foil gauge is attached to the center hole 51 by adhesive, a hollow tube 53 is inserted as shown in the figure. The tube 53 has its root portion held by a holder 54, and the holder 54 is coupled to the entrance portion of the center hole 51 of the bolt 50. A holding ring 55 for holding the tube 53 is fitted into the holder 54, and a connecting fitting 56 is connected to the holding ring 55.
Further, the connecting fitting 56 is adapted to be connected to an air tube 57.

Therefore, by introducing compressed air into the tube 53 through the air tube 57, the internal pressure of the tube 53 increases, and this pressure causes the strain gauge 52 to press against the inner peripheral surface of the center hole 51. It will be crimped. Therefore, the surface of the strain gauge 52 coated with adhesive is pressed against the inner circumferential surface of the center hole 51 under uniform pressure.

[The problem that the idea attempts to solve]

However, the above-mentioned conventional example has several problems. In other words, the center hole 51 usually has an extremely small diameter of about 2 mm, and the tube 53 has no rigidity. There is a problem that it is not known whether or not the position has been reached, and for example, there is a problem that the tube 53 may be bent within the center hole 51 due to insufficient insertion or excessive insertion.
That is, when the tube 53 is pressurized in such a state, there is a problem that even pressure is not applied to the strain gauge (for example, the strain gauge 52) bonded to the inner periphery of the center hole 51.

In addition, the gauge lead 58 of the strain gauge 52
is guided out of the holder 54 between the inner periphery of the holder 54 and the outer periphery of the tube 53, but an accident occurred in which the gauge lead 58 was cut when the presser ring 55 was press-fitted into the holder 54. There was a problem with how easy it was.

Furthermore, when press-fitting the retainer ring 55 into the holder 54, the opening end of the tube 53 is first expanded against the elastic force in the contraction direction, and the retainer ring 55 is inserted into the opening end of the tube. 53 is in close contact with the outer periphery of the presser ring 55, but due to this expansion, the portion that is in close contact with the presser ring 55 becomes thinner, and in order to further improve the airtightness between the presser ring 55 and the holder 54, Since the space between the outer periphery of the holder 54 and the inner periphery of the holder 54 is extremely small, unreasonable force is applied to the thin part.
There was a problem that the tube 53 (its opening) was easily damaged.

Further, even with this arrangement, there is still a problem that the compressed air tends to leak unless the space between the opening of the tube 53 and the presser ring 55 is sealed with an adhesive or the like.

The present invention was developed in view of the above-mentioned circumstances, and its purpose is to have a simple structure at low cost, to allow the tube to be inserted into the mounting hole easily and at an accurate position, and to allow the tube to be inserted into the mounting hole at an accurate position. To provide a strain gauge mounting jig with good workability, without leakage of pressurized fluid to the outside, and without the risk of disconnection of gauge leads.

[Means to solve the problem]

In order to achieve the above object, the present invention has been developed to provide a strain gauge for mounting strain gauges on the inner circumferential wall between the open end and the bottom of an extremely small-diameter mounting hole that is drilled from one end surface of the object to be measured to a predetermined depth. In the strain gauge mounting jig, a tube is inserted into the above-mentioned mounting hole, and a strain gauge is attached by force-feeding pressurized fluid into the tube and using its expansion force. The tube is hollow with openings at both ends and has an outer diameter that can be inserted into the mounting hole, and an outer diameter that is longer than the depth and has appropriate rigidity, and an outer circumferential surface. a hollow pipe with a through hole drilled through the inner circumferential surface thereof and closed at one end; a sealing locking portion provided in the circumferential direction at a position slightly longer than the depth from one end of the pipe; and a tightening member for tightening the locking portion, and by tightly fixing the tube to the outer periphery of one end side of the pipe inserted into the tube, one end of the tube is sealed, and the tightening member tightens the locking portion. The other end of the tube is sealed by tightening the sealing locking portion while the tube is inserted through the outer periphery of the tube, and the pressurized fluid can be pumped from the open end of the tube. This is a characteristic feature.

[Effect]

According to the strain gauge mounting jig configured as described above, since the pipe has rigidity and is inserted into the tube, the pipe has a guiding function when the tube is inserted into the mounting hole. As a result, the tube can be easily inserted into the mounting hole, and the insertion position can be accurately controlled.

In addition, since a pipe with one end sealed with a stopper is inserted into the tube and the tube is sealed with the sealed end and the sealing locking part, the pressurized fluid that expands the tube is transferred to the outside of the tube. There is no leakage.

Further, since a slight gap is formed between the position of the opening surface of the mounting hole and the sealing locking portion, the opening is not blocked and an accident of cutting the gauge lead does not occur.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

1 and 2 show the overall structure of an embodiment in which a strain gauge mounting jig according to the present invention is applied to a bolt, and FIG. 1 is a front view partially shown in longitudinal section, and FIG. The figure is a sectional view taken along the - arrow in FIG. 1.

1 and 2, 1 is a bolt as an object to be measured, 1a is a threaded portion of this bolt 1, and 1
b is the head of this bolt 1, 2 is a large diameter head hole drilled in the head of this bolt 1, 2a is the bottom surface of this head hole 2, and 3 is a predetermined hole with this bottom surface 2a as one end surface. A hole for attaching a strain gauge as an installation hole of extremely small diameter (for example, about 2 mm in diameter) drilled at depth L0 with a drill, reamer, etc., 3a is the bottom of this hole 3 for attaching a strain gauge, and 3b is a strain gauge. This is the opening of the pasting hole 3. Here, this opening 3b
Of these, the surface that is equal to the bottom surface 2a will be referred to as an opening surface.

4 is a hollow pipe which is sufficiently longer than the depth L0 and has rigidity and is open at both ends, and 4a, 4a, . be.

5 is a stopper that closes the opening at the lower end of the pipe 4; 6 is a hollow tube made of silicon, for example, longer than the depth L0, with openings at both ends into which the pipe 4 is inserted; 6a is the opening at the lower end of the tube 6; 6b is formed near the upper end of the opening of the tube 6 and above the opening surface of the opening 3b by a distance L1. A tightened portion, 7 is an annular tightening member made of rubber or the like for tightening the tightened portion 6b, and 8 is a ring-shaped tightening member made by solidifying a molding agent or the like in the circumferential direction of the pipe 4 adjacent to the upper side of the tightened portion 6b. This stopper 8 and the tightened portion 6b constitute a sealing locking portion. 9 is a strain gauge attached to the inner peripheral wall of the strain gauge attachment hole 3 with adhesive; 9a;
is a gauge lead whose one end is connected to the gauge tab of this strain gauge 9, and whose other end is led out from the opening 3b of the strain gauge attachment hole 3 along the inner circumferential wall.

10 is a hose for introducing pressurized fluid such as compressed air, and 11 is a connecting portion that connects the output end of this hose 10 and the input end (opening upper end) of the pipe 4.

Note that FIGS. 1 and 2 show the tube 6 in an expanded state, and before the tube 6 is expanded, the sealing portion 6 is
The tube 6 is in a retracted state (hereinafter referred to as a "closed state") in which the inner circumference of the tube 6 is substantially in contact with the outer circumference of the pipe 4 between the portion a and the tightened portion 6b.

The operation and effect of this embodiment configured in this way will be explained.

First, the tube 6 is in the closed state, and the strain gauge 9 is placed outside the strain gauge pasting hole 3.
An adhesive is applied in advance to the attachment surface of the tube 6, and the surface opposite to the attachment surface is temporarily fixed at a predetermined position on the outer periphery of the tube 6. In this state, this jig is inserted into the strain gauge attachment hole 3. When the stopper 5 comes into contact with the bottom surface 3a of the strain gauge attachment hole 3, it is known that the intended position has been reached, and the pressurized fluid is then pumped into the pipe 4 via the hose 10 and the connection part 11. Since the lower end opening of the pipe 4 is sealed with a plug 5,
The pressurized fluid transmits pressure into the tube 6 through the communication holes 4a, 4a, . The internal pressure of 6 increases and it begins to expand. In this way, the expansion force of the tube 6 presses the strain gauge 9 to the predetermined position on the inner circumferential wall of the strain gauge attachment hole 3, and the adhesive applied in advance ensures that the attachment surface is firmly attached to the inner circumferential wall. is crimped.

In this way, according to this embodiment, since the rigid pipe 4 is inserted into the tube 6,
When inserting the tube 6 into the strain gauge pasting hole 3, the pipe 4 acts as a guide, so there is an advantage that a reliable insertion position can be realized.

Therefore, there is an advantage that when the tube 6 is expanded, the strain gauge 9 can be crimped with uniform pressure.

Further, the stopper 8 is made of a solidified molding agent, and the tightening member 7 is made of rubber, and both have a predetermined elasticity, so they fit well together, and have the advantage of being able to prevent leakage of pressurized fluid despite having a simple structure. be.

Furthermore, as the tube 6 expands, the tightening member 7 is subjected to a force that displaces it upward in the figure, but the stopper 8 prevents this displacement, and the tightening member 7 presses the stopper. This has the advantage of improved sealing performance.

Despite the high airtightness at the sealing locking portion, the opening 3b is secured, so there is no risk of damaging the gauge lead 9a, and there is an advantage that workability is good.

Further, when the strain gauge 9 is generally attached with an adhesive, air bubbles in the adhesive are pushed out during pressure bonding (crimping), but there is an advantage that the air bubbles can be expelled to the outside from the opening 3b.

Furthermore, both the pipe 4 and the tube 6 may be open at both ends; therefore, commercially available long pipes and tubes can be cut and used as long as conditions such as material, diameter, and length are met. There is an advantage.

In other words, there is an advantage that no special dedicated member is required.

It should be noted that the present invention is not limited to the above-described embodiments, but can be modified in various ways without departing from the gist thereof.

For example, the sealing engagement portion is not limited to the stopper 8, and instead may be formed as a constriction on the outer periphery of the pipe 4 corresponding to the position of the tightened portion 6b.

In addition, the head hole 2 is connected to the pipe 4 and the tube 6.
May be omitted depending on the length. In other words, the strain gauge attachment hole 3 is extended to the upper end surface of the head 1b of the bolt 1, and the space above the upper end surface of the head 1b is L1.
The above-mentioned sealing locking portion may be formed at the position.

Moreover, the pipe 4 of the above-mentioned embodiment has the communication hole 4a.
Although an example has been shown in which a large number of holes are drilled in four directions in the circumferential direction, since the pressurized fluid has isotropy, at least one hole may be drilled.

[Effect of idea]

As described in detail above, according to the present invention, a rigid pipe is inserted into a tube, one end of the pipe is closed, and both open ends of the tube are connected to the closed end and the sealing part. Since the structure is sealed, the tube can be easily inserted deep into the mounting hole with a low cost and simple structure, and the strain gauge can be mounted in an accurate position, providing good airtightness. It is possible to provide a strain gauge mounting jig that does not cause disconnection of strain gauge leads and has extremely good workability.

[Brief explanation of drawings]

1 and 2 show the overall configuration of an embodiment in which a strain gauge mounting jig according to the present invention is applied to a bolt, of which FIG. 1 is a front view partially shown in longitudinal section; Fig. 2 is a sectional view taken along the - arrow in Fig. 1, and Figs. 3 and 4 are views showing the configuration of a conventional example, of which Fig. 3 shows a part in longitudinal section. The front view and FIG. 4 are cross-sectional views taken along the - arrow in FIG. 3. 1... Bolt, 2... Head hole, 2a... Bottom,
3...Hole for strain gauge attachment, L0...Depth, 3
a...Bottom surface of the hole for attaching the strain gauge, 3b...Opening, 4...Pipe, 4a...Communication hole, 5...
Plug, 6...Tube, 6a...Sealing part, 6b...
Part to be tightened, L1... between, 7... tightening member, 8...
...stopper, 9...strain gauge, 9a...gauge lead, 10...hose.

Claims (1)

[Scope of utility model registration request] When installing a strain gauge on the inner peripheral wall between the open end and the bottom of an extremely small-diameter mounting hole drilled from one end surface of the object to be measured to a predetermined depth, a tube is inserted into the mounting hole, and the tube is inserted into the mounting hole. A strain gauge mounting jig that mounts a strain gauge by force-feeding pressurized fluid inside and using its expansion force has an outer diameter that can be inserted into the mounting hole longer than the depth of the small-diameter mounting hole. The tube is hollow with openings at both ends, and has an outer diameter longer than the depth so as to be inserted into the tube, has appropriate rigidity, and has a through hole penetrating from the outer circumferential surface to the inner circumferential surface. The device includes a hollow pipe with one end closed, a sealing locking portion provided in the circumferential direction at a position slightly longer than the depth from one end of the pipe, and a tightening member tightening the sealing locking portion. , one end of the tube is sealed by closely fixing the tube to the outer periphery of one end of the pipe inserted into the tube, and when the tightening member is inserted through the outer periphery of the tube, the sealing member is closed. A strain gauge mounting jig, characterized in that the other end of the tube is sealed by tightening the stopper, and the pressurized fluid can be pumped from the open end of the pipe.