JPH028188Y2 - - Google Patents

Description

[Detailed description of the invention] <Technical field> The present invention is a device for measuring the axial force of a fastening element, more specifically, a fastening axial force that acts on a fastening bolt when fastening elements such as bolts and nuts are used to measure the fastening axial force. Related to measuring instruments for measuring force.

<Prior art> Conventionally, devices for measuring the fastening axial force (tensile axial force) acting on fastening bolts when fastening elements such as bolts and nuts are used have, for example, It has been proposed that a small diameter portion (notch) is formed and a strain gauge is attached to the outer circumferential surface of this small diameter portion.

However, in such a known measuring device, since bending stress acts on the fastening bolt in addition to the fastening axial force (tensile axial force) after fastening, it is greatly influenced by this bending stress to accurately measure the fastening axial force. (b) In relation to the above, in order to measure the fastening axial force relatively accurately, at least two or four strain gauges must be attached to the outer circumferential surface of the fastening bolt. (c) The lead wire of the strain gauge is guided through a groove formed in a part of the outer circumferential surface of the fastening bolt, but the surface of the washer or fastening body is attracted by this groove during fastening, so the actual In addition, since the friction conditions are different from those in other cases, it is not possible to accurately measure the fastening axial force. (2) Also, since the groove for passing the lead wire through the fastening bolt is formed, this groove deteriorates the symmetry of bending. , it is not possible to sufficiently reduce the influence of bending stress, and it is not possible to accurately measure the fastening axial force.

Furthermore, as a bolt stress measurement method, for example, a technique disclosed in Japanese Patent Application Laid-Open No. 137171/1980 is known. In this method, a thin plate or rod equipped with a strain gauge is inserted into a through hole provided in a bolt and fixed to the bolt, and the stress in the bolt is measured from the strain value of the thin plate or rod when the bolt is loaded. It is what it is.

However, this method has the following problems to be solved.

(1) Since the thin plate or rod (hereinafter referred to as the core) is not fixed to the bolt with a tensile preload applied, machining strain (residual stress) in the core itself or discontinuity in the threaded joint may occur. Due to the presence of boundary surfaces, etc., a large axial force loss occurs, making it impossible to accurately measure the axial force of the bolt from an initial small value.

(2) Since the core and the bolt are connected by screws, they tend to loosen under conditions of high vibration or repeated use, resulting in poor reliability.

On the other hand, the technology of applying an axial preload load to the load detector in the case by tightening a nut into the case via a bracket and a disc spring was disclosed in Japanese Patent Application Laid-Open No. 49-1999.
It is disclosed in Publication No. 40966. The technique of this preload device can be applied to the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 137171/1983. However, in this application example, there are the following serious problems to be solved.

(1) Preload is applied by tightening a nut onto the bolt via a disc spring. As described above, there is a discontinuous boundary surface on this threaded joint surface (fitting surface), and surface yield occurs at this boundary surface, resulting in loss of axial force. For this reason, accurate measurement of axial force becomes virtually impossible.

(2) When applied to members under high vibration, in addition to the above-mentioned surface yield, loosening is likely to occur on the threaded joint surface.
Poor reliability.

<Purpose of the invention> The present invention was made in view of the above facts, and its main purpose is to solve the above-mentioned conventional problems and to accurately measure the bolt fastening axial force from an initial small value. It is an object of the present invention to provide a fastening axial force measuring instrument that can be used.

Another object of the present invention is to provide a fastening axial force measuring tool that can accurately measure the dynamic axial force of a bolt under high vibration conditions without being adversely affected by vibration.

<Summary of the invention> According to the invention, there is provided a bolt having a head at one end and an axial through hole formed in the shaft center, and a core body having a large-diameter head formed at one end of the shaft. Consisting of
The core is assembled to the bolt by inserting the shaft into the through hole of the bolt and engaging the large diameter head with the head of the bolt, and the core has at least One strain gauge is pasted on the core,
A fastening axial force measuring tool is provided, characterized in that both ends of the bolt are fixed by welding while a tensile preload is applied to the bolt.

<Preferred Specific Example of the Invention> Hereinafter, a specific example of the fastening axial force measuring instrument constructed according to the present invention will be described with reference to the accompanying drawings.

In FIGS. 1 to 4 showing a specific example of a fastening axial force measuring instrument according to the present invention, the illustrated fastening axial force measuring instrument 2 is composed of a fastening bolt 4 and a core body 6. As shown in FIG. 2, this fastening bolt 4 is a normal bolt having a head 8 and a screw 10, and has a through hole 12 extending axially through the center of the bolt.
It is formed by drilling. Through hole 12
is a large diameter recess 14 located at the upper end of the fastening bolt 4.
and a main portion 16 extending from the large diameter recess 14 to the lower end of the fastening bolt 4.

As shown in FIGS. 3 and 4, the core body 6 has a large-diameter head 18 and a shaft portion 20 extending downward from the large-diameter head 18. The large diameter head 18 of this core body 6 has a shape corresponding to the shape of the large diameter recess 14 formed in the head 8 of the fastening bolt 4,
The axial length of this large diameter head 18 is the length of the through hole 1.
The length in the axial direction of the large diameter recess 14 of No. 2 is substantially the same, and the outer diameter of the large diameter head 18 is substantially the same as the length of the large diameter recess 14 of No.
The inner diameter of the large-diameter recess 14 is substantially the same as that of the large-diameter recess 14 . As shown in FIGS. 3 and 4, a guide groove 24 extending radially outward is formed on the lower surface of the large-diameter head 18 of the core 6, and on the outer peripheral surface of the large-diameter head. A groove 26 is formed extending upwardly from the outer end of groove 24. The shaft portion 20 of the core body 6 is formed with a small diameter portion (notch) 22 having a slightly smaller outer diameter than other portions in order to generate stress concentration. The axial length of this shaft portion 20 is substantially the same as the axial length of the main portion 16 of the through hole 12, but the outer diameter of the other portion of the shaft portion 20 other than the small diameter portion 22 is It is slightly smaller than the inner diameter of the main portion 16 of.

Two strain gauges 28 (one shown in the drawing) are attached to the outer circumferential surface of the small diameter portion 22 of the shaft portion 20 of the core body 6, which are located diametrically opposed to each other. The lead wire 30 of this strain gauge 28 is connected to the shaft portion 2 of the core body 6.
0 along the circumferential surface of the large-diameter head 18, and then extends upward through the guide groove 24 and the groove 26 formed in the large-diameter head 18, and is connected to the connection terminal 32 provided on the upper surface of the large-diameter head 18. has been done.

As shown in FIG. 1, the shaft portion 20 of the core body 6 is inserted into the through hole 12 (inside the main portion 16) of the fastening bolt 4, and the large diameter of the through hole 12 of the large diameter head portion 18 of the core body 6 is It is inserted (engaged) into the recess 14 . Then, with the bottom surface of the large-diameter recess 14 of the through-hole 12 and the lower surface of the large-diameter head 18 of the core body 6 in contact with each other, the lower end of the shaft portion 20 of the core body 6 is penetrated by welding as indicated by numeral 34. The core body 6 is assembled into the through hole 12 of the fastening bolt 4 by fixing it to the lower end of the main part 16 of the hole 12 and fixing the large diameter head 18 to the head 8 of the fastening bolt 4 by welding. . By combining the core bodies 6 in this manner, the large-diameter head 18 of the core body 6 and the shaft portion 20 are fixed to the fastening bolt 4 by welding to form an integral structure therewith.

In such a fastening axial force measuring instrument 2, the core body 6 is assembled so that a tensile preload is applied thereto. That is, in the specific example, when assembling the core body 6 to the fastening bolt 4, the head of the core body 6 is 18 and the shaft portion 20 are fastened by welding to the bolt 4.
By doing so, an appropriate tensile preload is applied in advance to the core body 6 to which the strain gauge 28 is attached.

The fastening axial force measuring device 2 thus assembled is used for fastening a fastening body (not shown) in place of a normal bolt. By detecting the change in resistance of the strain gauge 28 affixed to the outer surface of the small diameter portion 22 of the core body 6 that is pulled together with the fastening bolt 4, the core body 6 is The tensile axial stress acting on the fastening axial force is measured, and the fastening axial force (tensile axial force) acting on the fastening axial force measuring tool 2 is measured accordingly.

FIG. 5 shows a modification of the fastening axial force measuring instrument constructed according to the present invention. A fastening axial force measuring instrument 2' shown in FIG. 5 is composed of a fastening bolt 4 and a core body 6. This fastening bolt 4 has a head 8 and a threaded portion 10, and a through hole 12 is bored through the center thereof in the axial direction and has substantially the same inner diameter over its entire length. There is. Further, a groove 36 is formed on the upper surface of the head 8 and extends radially outward from the center thereof.

The core body 6 has a large diameter head 18 and a shaft portion 20 extending downward from the large diameter head 18. The outer diameter of the large-diameter head 18 of the core body 6 is larger than the inner diameter of the through hole 12, and the outer diameter of the shaft portion 20 of the core body 6 is slightly smaller than the inner diameter of the through hole 12. The axial length of the shaft portion 20 of the core body 6 is the same as that of the through hole 12.
A small diameter portion (notch) 22 is formed at a predetermined portion of the shaft portion 20, and has a slightly smaller outer diameter than other portions.

Two strain gauges 28 (one is shown in the drawing) are attached to the small diameter portion 22 of the shaft portion 20 of the core body 6, as in the specific example shown in FIGS. 1 to 4. The lead wire 30 of 28 is connected to the fastening bolt 4 and the core body 6
It is connected to a connecting terminal 32 provided on the large-diameter head 18 of the core body 6 through a gap between the two and a groove 36 formed in the head 8 of the fastening bolt 4 .

In this case, the shaft portion 20 of the core body 6 is inserted into the through hole 12 of the fastening bolt 4, and the large diameter head portion 18 of the core body 6 is inserted into the through hole 12 of the fastening bolt 4.
The lower surface of the bolt 4 is engaged with the upper surface of the head 8 of the fastening bolt 4, and the shaft portion 20 of the core body 6 is positioned within the through hole 12. Then, the large diameter head 1 of the core body 6
It is assembled into the through hole 12 of the fastening bolt 4 as required with the lower surface of the fastening bolt 8 engaged with the top surface of the head 8 of the fastening bolt 4. That is, by fixing the lower end of the shaft portion 20 of the core body 6 to the lower end of the through hole 12 by welding 34, and by fixing the large diameter head 18 to the head part 8 by welding, the core body 6 are combined as required.

Even in such a modified example, the core body 6 is assembled so that a tensile preload is applied to the core body 6, and when the core body 6 is assembled to the fastening bolt 4, the large diameter head 18 of the core body 6 or the lower end of the fastening bolt 4 is With a predetermined compressive load applied to the core body 6, the large-diameter head portion 18 and the shaft portion 20 are fixed to both ends of the fastening bolt 4 by welding.

In the specific examples and modifications described above, a compressive load is applied to the large-diameter head 18 of the core body 6 or the lower end of the fastening bolt 4 during assembly, but instead of these, a configuration as shown in FIG. Alternatively, a tensile preload may be applied to the core body 6.

In Fig. 6 showing a part of the fastening axial force measuring instrument,
A male thread 3 is provided at the lower end of the shaft portion 20 of the core body 6 in the modified example.
8 is formed, and a nut 40 is screwed onto this male thread 38. Other configurations may be substantially the same as the specific example shown in FIGS. 1 to 4 or the modified example shown in FIG. 5.

When the modification shown in FIG. 6 is applied, the shaft portion 20 of the core body 6 is pulled by rotating the nut 40, thereby applying a tensile preload to the shaft portion 20.

In the modification shown in FIG. 6, in order to prevent stress concentration from occurring in the male thread 38 of the shaft portion 20 of the core body 6 and the strength of the core body 6 decreasing, the male thread of the core body 6 is Preferably, the inner diameter of the thread 38 is at least larger than the diameter of the shaft portion 20.

Further, the shaft portion 20 of the core body 6 is also fixed using the nut 40.
After tightening, the nut 40 may be fixed to the fastening bolt 4 by welding.

In these embodiments and modifications, it is further preferred that the core body 6 be made of a material that is substantially the same as the material of the fastening bolt 4 or a material that has a greater tensile strength.

In specific examples and modifications, it is also possible to select a material for the core body 6 that is stronger than the tensile strength of the fastening bolt 4 and has a higher yield point than the fastening bolt 4, such as spring steel.

<Effects of the invention> According to the invention described above based on preferred specific examples, the following effects can be obtained.

(1) The core is assembled into the bolt with a tensile preload applied, and both ends are fixed to the bolt by welding, creating a welded structure as a whole, and there is no space between the core and the bolt. , there is no discontinuous boundary surface as in the prior art. Therefore,
Loss of axial force due to machining distortion of the core body, surface yield at discontinuous interfaces, etc. is substantially eliminated, and the axial force of the bolt can be accurately measured from an initial small value.

(2) The core and bolt are completely fixed by welding at both ends, so when used under high vibration as in the past, there is no chance of loosening or discontinuity between the core and bolt. Problems such as surface yield at the interface can be completely eliminated. Therefore, it has become possible to accurately measure dynamic axial force under high vibration conditions. Moreover, the repeated durability is also significantly improved.

(3) Both ends of the core are fixed to the bolt by welding, so even though a through hole is formed in the bolt, the strength of the bolt hardly decreases and the strength as a bolt component is maintained. . Moreover, since the appearance of the bolt is not impaired in any way, it can be easily put to practical use as a bolt component that can monitor axial force.

Furthermore, when measuring axial force, the present invention can be applied to the bolt itself that is actually used, thereby making it possible to use it as a fastening axial force measuring tool. Therefore, all of the fastening conditions, such as thread surface, bearing surface friction, fastening length, load bearing area, strength, etc., can be maintained virtually the same, making it possible to perform completely simulated axial force measurements. can. This can be said to have significantly improved the reproducibility of the measured axial force.

(4) If the core is made of a material with a tensile strength greater than that of the bolt, such as spring steel, the axial force can be measured within the elastic range of the core, even if the tightening axial force exceeds the yield point of the bolt body. The measurement range can be expanded.

(5) When a nut is used at the joint end of the core and bolt, the required tensile preload can be easily obtained. Moreover, in this state, the core body and nut, and the nut and bolt are fixed by welding, so as a result, there is no discontinuous interface between the core body and bolt (the axial force of the bolt is (The axial force is transmitted to the core body through the threaded part, and no axial force acts on the screw fitting surface.) Therefore, the axial force loss due to surface yielding of the same part after assembly is completely eliminated, and therefore the shaft Force can be measured accurately from an initial small value.

(6) If a small diameter part is provided in the shaft of the core and a strain gauge is pasted there, stress concentration will occur in the small diameter part, making it possible to improve the sensitivity of axial force measurement.

Although specific examples and modifications of the fastening axial force measuring device according to the present invention have been described above, the present invention is not limited to such specific examples and modifications, and various modifications can be made without departing from the scope of the present invention. It is possible to modify it.

For example, although two strain gauges 28 are used in the illustrated example and modified example, one or four strain gauges 28 (each attached 90 degrees apart) may be used, if desired.

In addition, in order to prevent the adverse effects of oil, water, etc. from acting on the strain gauge 28, a strain gauge coating agent or a strain gauge coating agent is applied to the gap between the fastening bolt 4 and the core body 6 when assembling the fastening axial force measuring device. A welding material having the same effect as this may be enclosed.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view showing a specific example of a fastening axial force measuring instrument constructed according to the present invention. 2 is a partially cutaway front view showing a fastening bolt of the fastening axial force measuring instrument shown in FIG. 1; FIG. FIG. 3 is a front view showing the core of the fastening axial force measuring instrument shown in FIG. 1. Fourth
The figure is a sectional view taken along the - line in FIG. 3. FIG. 5 is a partially cutaway front view showing a modification of the fastening axial force measuring instrument constructed according to the present invention. FIG. 6 is a partially cutaway view showing a part of a modified example of the core body in the fastening axial force measuring instrument. 2 and 2'... fastening axial force measuring device, 4... fastening bolt, 6... core body, 12... through hole, 28... strain gauge, 32... connecting terminal.

Claims (1)

[Claims for Utility Model Registration] 1. Consisting of a bolt with a head at one end and an axial through hole formed in the shaft center, and a core body with a large diameter head formed at one end of the shaft. , the core body is
The shaft portion is inserted into the through hole of the bolt, and the large diameter head is engaged with the head of the bolt to be combined with the bolt, and the core body has at least one strain gauge. A fastening axial force measuring instrument, characterized in that the core body is fixed by welding at both ends while a tensile preload is applied to the bolt. 2. The scope of the utility model registration claim in which the large-diameter head of the core body is fixed to the upper surface of the head of the bolt by welding, and the tip of the shaft part is fixed to the other end of the bolt by welding. The fastening axial force measuring device described in item 1. 3. A recess with a shape corresponding to the large-diameter head of the core is formed in the head of the bolt, and the large-diameter head of the core is positioned within the recess and welded. The fastening axial force measuring instrument according to claim 1 of the utility model registration claim, which is fixed. 4. The outer diameter of the shaft portion of the core body is slightly smaller than the inner diameter of the through hole, and the lead wire of the strain gauge extends along the outer peripheral surface of the shaft portion to the lower surface of the large diameter head, and then extends to the lower surface of the large diameter head. The groove extends to the upper surface of the large-diameter head through a guide groove formed on the lower surface of the large-diameter head and a groove formed on the outer peripheral surface of the large-diameter head, and is provided on the upper surface of the large-diameter head. A fastening axial force measuring instrument according to claim 1 or 3 of the utility model registration claim, which is connected to a connecting terminal. 5. A small diameter portion is formed in the shaft portion of the core, and the strain gauge is attached to the outer peripheral surface of the small diameter portion. The stated fastening axial force measuring device. 6. The fastening shaft according to any one of claims 1 to 5, wherein the core body is made of a material that is substantially the same as the material of the bolt or a material that has a higher tensile strength than the material of the bolt. Force measuring instrument.