JP3428474B2 - bolt - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bolt, and more particularly, to a bolt suitable for measuring axial force by ultrasonic waves. Here, the axial force refers to a tightening force generated in the axial direction when a bolt is tightened. 2. Description of the Related Art Conventionally, in order to securely tighten a bolt, the axial force generated on the bolt has been measured using ultrasonic waves. To measure the axial force, an ultrasonic wave is incident from one end surface of the bolt, a reflected wave (echo) reflected at the other axial end surface of the bolt is detected, and the axial force generated on the bolt is determined based on the detection result. It is to be measured.
As shown in FIG. 2, before tightening the bolt (Fig. 2 A) and after (Fig. 2 B) and at the time of association with the axial force generated in the bolt from the incident ultrasonic wave to the detection of the reflected wave , And the time difference t changes in proportion to the axial force. Therefore, in order to measure the axial force, generally, the time from when the ultrasonic wave is incident to when the reflected wave is detected is measured. An axial force measuring device for detecting an axial force is generally provided with a piezoelectric element mounted on the head of a bolt to input an ultrasonic wave to the bolt and detect a reflected wave. The present invention is applied to a bolt tightening device such as a nut runner that rotationally drives a socket engaged with a head. While measuring the axial force generated on the bolt by the axial force measuring device,
When the bolt tightening device is driven and it is detected that the axial force has reached a target value, the bolt tightening device is stopped. As a result, the bolt is tightened so as to generate a constant axial force. As shown in FIG. 3 , a bolt 21 conventionally used usually reflects an end face 22a of a head 22, which is an end face on which ultrasonic waves are incident from a piezoelectric element 31, and an ultrasonic wave. The distal end surface 23a of the shaft portion 23, which is the other axial end surface of the bolt 21 to be formed, is formed substantially flat. Therefore, the propagation path of the ultrasonic wave and its reflected wave in the shaft portion 23 is diffused (the arrow Uwa in FIG. 4).
See). The time of the diffused reflected wave reaching the piezoelectric element 31 varies depending on the propagation path, and a plurality of reflected waves are detected. Further, as shown in FIG. 3 , a bolt 21 conventionally used usually has a size (diameter) d2 of a sectional area of a head 22 engaged with a socket or the like (not shown) of a bolt tightening device. However, it is formed larger than the diameter d3 of the shaft portion 23 on which the screw is formed. Therefore, head 2
The whole of the ultrasonic wave incident from 2 is the tip surface 23 of the shaft portion 23.
a, the reflected wave detected by the shaft-side end face 22b of the head 22 (see FIG.
3 (see arrow Uwb). In such a case, as shown in FIG. 5 , it is not clear which of the plurality of detected reflected waves Uwa is a reflected wave reflected by the tip end surface 23 a of the shaft portion 23, The reflected wave Uwb generated by the end face 22b on the opposite side of the portion 22 causes noise, for example, and causes the measurement accuracy of the axial force to decrease. Under such circumstances, as disclosed in Japanese Utility Model Laid-Open Publication No. Sho 60-194473, the ultrasonic wave enters the bolt closely through the end face of the bolt head and through the end face of the bolt. In a bolt axial force detection device provided with an ultrasonic vibrator to be incident, an ultrasonic lens that converges ultrasonic waves from the ultrasonic vibrator toward an end surface of the bolt is provided between the ultrasonic vibrator and an end surface of the bolt. An installed bolt axial force detecting device is known. In this device, a concave surface having a relatively large radius of curvature is formed on the lower end surface of the cap to which the ultrasonic vibrator is adhered, and a convex lens-like space having a flat surface on one side is formed between the cap and the head of the bolt. . It is described that a convex ultrasonic lens is constituted by oil filled in the space. Thus, in this bolt axial force detecting device, the ultrasonic wave directed from the ultrasonic transducer toward the end face of the bolt is converged by the action of the ultrasonic lens, so that the ultrasonic wave incident on the bolt head is applied to the bolt head. As the light propagates to the subsequent bolt shaft, it concentrates on the cross section of the bolt shaft, and the ultrasonic wave incident on the bolt head is efficiently propagated in the bolt shaft. As a result, a relatively strong ultrasonic wave is propagated in the bolt shaft portion for detecting the propagation time of the ultrasonic wave. As a result, the signal level when receiving the ultrasonic wave is raised to a higher level than other noises. As a result, a highly accurate bolt axial force can be detected. In addition, regarding the ultrasonic lens that acts to converge the ultrasonic waves, it is described that the shape of the space is changed according to the speed of sound (ultrasonic propagation characteristics) between the material filling the space and the material forming the cap. Have been. [0006] However, the length of the bolt for measuring the axial force is not always constant. Therefore, in the bolt axial force detection device disclosed in Japanese Utility Model Laid-Open No. 60-194473, the ultrasonic lens converges the ultrasonic wave from the ultrasonic vibrator toward the end face of the bolt, but the ultrasonic vibrator The convergence of the ultrasonic waves from the head to the end face of the bolt is different, and the concave or convex of the ultrasonic lens (concave surface formed on the lower end face of the cap to which the ultrasonic vibrator is adhered) varies depending on the length of the bolt. It is necessary to select the shape including the curvature or the like, and the ultrasonic wave propagation characteristics of the substance or the like to be filled in the space. Further, in this device, although it is considered to converge the ultrasonic wave directed from the ultrasonic transducer toward the end face of the bolt, the ultrasonic wave reflected on the tip end face of the bolt converges the ultrasonic wave. That is not taken into account. Therefore, the propagation path of the reflected wave becomes complicated, and the reflected wave at the time of detection may be in a diffused state. The present invention has been made in view of the above problems, and a bolt and an axial force measuring device for the bolt capable of accurately measuring an axial force without changing various settings of an axial force detecting device. The purpose is to provide. According to the present invention, in order to achieve the above-mentioned object, opposed end faces of a head and a tip are curved.
A bolt whose axial force is measured by ultrasonic waves, wherein the curved surface is formed by a base end and a tip of a shaft part of the bolt.
Head of the bolt, centered on the diagonal intersection
It is characterized in that it is formed with a curvature in which the distance to the portion and the tip is a radius . According to the present invention, opposing ends of the head and the tip are provided.
The curved surface formed on each surface functions as an ultrasonic lens . Then, fit this curved surface to the base end of the bolt shaft
Centering on the diagonal intersection of the ends,
The radius of curvature is the distance to the head and the tip, respectively.
By forming, the ultrasonic wave enters from the end face of the bolt head.
If it is Isa, ultrasound, viewed in the bolt advance while being converged toward the shank distal end face, it is reflected by the axial front edge surface
It returns again in a state of being converged toward the head end face as a reflected wave . An embodiment of a bolt according to the present invention will be described in detail with reference to FIGS. 1 and 2. The same reference numerals in the drawings denote the same or corresponding parts. The bolt of the present invention is a bolt whose axial force is measured by ultrasonic waves. As shown in FIG. 1, the head 2 of the bolt 1 and the end faces 2 of the tip of the shaft 3 oppose each other.
a and 3a are formed on curved surfaces having predetermined curvatures r 5 and r 4 . Then, a shape is formed on the end face 2a of the head 2 of the bolt 1.
The curvature r5 to be formed and the tip surface 3a of the shaft portion 3 are formed.
A curved surface is formed by making the curvature r4 different. The curvature of the curved surfaces formed on the end surface 2a of the head 2 of the bolt 1 r 5
Is determined so that an ultrasonic wave oscillated from an ultrasonic oscillator (described later) converges on the end face 3 a of the shaft portion 3.
Curvature r 4 of the curved surfaces formed on the front end surface 3a of the shaft portion 3, be reflected a reflected wave in a state of being focused ultrasound emitted from the ultrasonic oscillator to the ultrasonic detection means (to be described later) Determined to be able to. How to determine the curvature is as follows
Will be described. With the head 2 of the bolt 1 sitting on the fastening target S
The base ends of the shaft portion 3 in the state where
If the tip of 3 is G and H, a virtual link between F and H
The point where the line intersects the virtual line connecting I and G is defined as the center C2.
You. The tip end of the shaft 3 has a center C2 to G
A curved surface with a curvature r4 is formed with the distance as the radius. Ma
At the tip of the head 2 of the bolt 1, pass F from the center C2.
And a portion E where the tip surface of the bolt 1 intersects the extension line
A curved surface with a curvature r5 is formed with the distance to the radius as the radius.
You. The end faces 2a, 3a of the head 2 and the tip of the shaft 3
Can be formed by cutting, grinding, or the like at the same time that the bolt 1 is manufactured or at the same time that the screw is formed on the shaft portion 3. Bolt 1 thus formed
The head 2 is engaged with a socket (not shown) of a tightening device such as a nut runner, and is screwed into a female screw of the fastening target S by rotating the socket to be tightened.
Then, the axial force at that time is measured by the axial force measuring device 10, and the fastening device can be controlled based on the measurement result. The axial force measuring device 10 includes an ultrasonic oscillator that oscillates ultrasonic waves from the end face 2a of the head 2 of the bolt 1 and detects a reflected wave, and a piezoelectric element 11 that functions as ultrasonic detecting means, An ultrasonic oscillation / detection device 12 is provided for causing the element 11 to oscillate ultrasonic waves and for processing signals output by detecting reflected waves from the piezoelectric elements. Here, what functions as the ultrasonic oscillator and the ultrasonic detecting means is not limited to the piezoelectric element, but may be an electrostrictive vibrator. The piezoelectric element 11 is mounted in a socket of the tightening device or in a contact 13 provided so as to be able to come into contact with and retract from the bolt 1 separate from the tightening device. It is provided so as to be in close contact with the end face 2 a of the portion 2. The piezoelectric element 11 is connected to the ultrasonic oscillation / detection device 12 by a cable 14. The piezoelectric element 11 is directly fixed to the end face 2a of the head 2 of the bolt 1, and the piezoelectric element 11 and the cable 14 of the ultrasonic oscillation / detection device 12 can be detachably connected via a connector or the like. It can also be configured as follows. The ultrasonic oscillation / detection device 12 includes the piezoelectric element 1
1 is supplied with a high-frequency pulse of a predetermined voltage so as to oscillate the ultrasonic wave, and amplifies the output signal from the piezoelectric element 11 generated by the reflected wave, and oscillates the ultrasonic wave to detect the reflected wave. The time difference t (see FIG. 2 ) is measured. Cable 1 from ultrasonic oscillation / detection device 12
When a high-frequency pulse of a predetermined voltage is supplied to the piezoelectric element 11 via 4, ultrasonic waves are incident from the end face 2 a of the head 2 of the bolt 1 by the piezoelectric effect of the piezoelectric element 11. Since the end surface 2a of the head 2 of the bolt 1 is formed as a curved surface, it functions as an ultrasonic lens .
The light propagates in the bolt 1 while being converged toward the distal end surface 3a of the shaft portion 3. Further, since the distal end surface 3a of the shaft portion 3 functions as an ultrasonic lens by being formed as a curved surface, the reflected wave reflected by the distal end surface 3a of the shaft portion 3 is again converged and converged. The light propagates back toward the piezoelectric element 11. in this way,
The propagation path of the ultrasonic wave in the bolt 1 is not diffused,
Since the ultrasonic wave is reliably reflected by the tip end surface 3a of the shaft portion 3 and detected by the piezoelectric element 11, the axial force can be measured with high accuracy. Further, various settings such as the shape and material of the constituent members such as the contact 13 of the axial force detecting device 10 are changed according to the length L of the bolt 1 for measuring the axial force, the ultrasonic propagation characteristics of the constituent members, and the like. No need . [0017] Note that the curved surface of curvature r5 that is formed on the end surface 2a of the head 2, since having different curvature r4 of the curved surfaces formed on the front end surface 3a of the shaft portion 3, by the end face 2a of the head 2 Ultra The curved surface 2 of the head 2 depends on the degree of convergence of the sound wave, the diameter D3 of the shaft 3 and the degree of convergence of the reflected wave from the tip surface 3a.
The extension of a from the center C2 through the base ends F and I of the shaft is
The diameter of the piezoelectric element 11 in a plan view can be determined within the range D4 of the intersecting positions J and K. In this embodiment, the curved surface of the curvature r5 formed at the tip 2a of the head 2 of the bolt 1 serves as an ultrasonic lens to converge the ultrasonic waves oscillated from the piezoelectric element 11, and insertion hole end portion of the bolt 1 (in FIG. 1 F,
(Corresponding to the I portion) and propagates in the shaft portion 3 of the bolt 1 without interference. Also, the reflected wave reflected by the curved surface having the curvature r4 formed at the tip 3a of the shaft 3 is similarly converged, and the end of the insertion hole of the bolt 1 of the fastening target S (F, I in FIG. 1 ).
And propagates back toward the piezoelectric element 11 again without interference. Therefore, finally, the piezoelectric element 1
The reflected wave detected at 1 becomes more converged, so that the measurement accuracy of the axial force can be improved, and the curvature of both end faces can be changed by the length of the shaft 3 of the bolt 1 and the height of the head 2. Since it can be determined, the degree of freedom in design increases. According to the present invention, a bolt formed on a curved surface is formed.
The curvature of the end face facing each of the head and the tip, the bolt
The intersection of the diagonal line between the base and tip of the shaft
As a heart, the distance to the head and tip of the bolt
By setting the radius, the ultrasonic wave propagates in a converged state without interfering with the end of the insertion hole of the bolt to be fastened, so that the measurement accuracy of the axial force can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view showing an embodiment of a bolt and an axial force detecting device according to the present invention. FIG. 2 is an explanatory diagram showing a state in which ultrasonic waves incident from the head of a bolt are reflected by a tip end surface of a shaft portion by a piezoelectric element of the axial force detecting device, and reflected waves are detected by the piezoelectric element. FIG. 3 is an explanatory view showing a state in which incident ultrasonic waves of a conventional bolt are reflected by a shaft-side end surface of a head of the bolt. FIG. 4 is an explanatory view showing a state in which a propagation path of an ultrasonic wave and a reflected wave of the conventional bolt is diffused. FIG. 5 clearly shows which of the plurality of detected reflected waves is the reflected wave reflected by the shaft tip when the end face of the head of the conventional bolt and the tip face of the shaft are formed flat. FIG. 5 is an explanatory diagram showing a state in which noise is generated by a reflected wave reflected by the shaft-side end surface of the head instead of the head. FIG. 6 is an explanatory view showing a state in which a propagation path of an ultrasonic wave and a reflected wave of a conventional bolt is diffused. FIG. 7 is a diagram showing a state in which one of a plurality of detected reflected waves is a reflected wave reflected by the shaft tip when the end face of the head of the conventional bolt and the tip of the shaft are formed flat. FIG. 5 is an explanatory diagram showing a state in which noise is generated by a reflected wave reflected by the shaft-side end surface of the head instead of the head. [Description of Signs] 1 Bolt 2 Head 2a End face 3 Shaft 3a Tip face r4 Curvature r5 of shaft tip face R5 Curvature of head end face

──────────────────────────────────────────────────続 き Continuation of the front page (56) References WO 97/044644 (WO, A1) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01L 5/00 103

Claims (1)

(57) [Claims 1] Opposite end faces of a head and a tip are curved surfaces
Are formed on, a bolt axial force is measured by ultrasound, the curved surface, the base end portion of the shaft portion and the distal end portion of the bolt diagonally
The head and tip of the bolt around the point of intersection
A bolt formed with a radius of curvature each of which has a distance to the bolt.