Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Threaded fastener stress
Reexamination Certificate
1998-12-15
2001-02-13
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Threaded fastener stress
C073S597000
Reexamination Certificate
active
06186010
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 9-347647 filed on Dec. 17, 1997 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bolt and, more particularly, to one adapted to ultrasonic axial tension measurement. The term “axial tension” used herein stands for a tightening force generated in the tightened bolt in its axial direction.
2. Description of the Related Art
It has been a conventional practice to conduct ultrasonic measurement of the axial tension generated in the tightened bolt in the axial direction for secure bolt tightening. The aforementioned axial tension measurement is conducted through ultrasonic radiation to one end surface of the bolt and detection of reflection (echo) from the other end surface of the bolt in the axial direction. The axial tension generated in the bolt will be measured based on the detected results. Referring to
FIG. 3
, the time taken from ultrasonic radiation to detection of the reflection before tightening the bolt (
FIG. 3A
) is shorter than that after tightening the bolt (
FIG. 3B
) by the time t owing to generation of the axial tension in the bolt. The time difference t will vary in proportion to the axial tension. Accordingly the time taken from ultrasonic radiation to reflection detection has been conventionally measured so as to measure the axial tension.
An axial tension measurement device is generally formed of a piezoelectric element which is mounted to a head of the bolt for ultrasonic radiation thereto and detection of reflection. This device has been applied to a bolt tightening device such as a nut runner which rotates a socket engaged with the bolt head for rotation. The bolt tightening device is driven while the axial tension generated in the bolt is measured by the axial tension measurement device. When it is detected that the axial tension reaches a target value, operation of the bolt tightening device is stopped. In this way, the bolt can be tightened such that a constant axial tension is generated.
Referring to
FIG. 5
, both a top surface
22
a
of a head portion
22
to which ultrasonic radiation is applied from a piezoelectric element
31
and a bottom surface
23
a
of an axial portion
23
of a generally employed bolt
21
as the other end surface thereof in an axial direction from which the ultrasonic radiation is reflected have substantially flat surfaces. As a result, each propagation path of both the ultrasonic radiation and the reflection will be diffused within the axial portion
23
(as shown by an arrow Uwa in FIG.
6
). The time taken by the diffused reflection to reach the piezoelectric element
31
may vary depending on the propagation path. As a result, a plurality of different reflections are detected.
Referring to
FIG. 5
, the generally employed bolt
21
is formed such that a sectional area (diameter) d
1
of the head portion
22
to be engaged with a socket (not shown) of the bolt tightening device is larger than the sectional area (diameter) d
3
of the axial portion
23
that has been threaded. Accordingly all the ultrasonic radiation applied to the head portion
22
is not always reflected from a bottom surface
23
a
of the axial portion
23
. That is, detected reflection may include the one reflected from the end surface
22
b
of the radially extended portion of the head portion
22
(as shown by an arrow Uwb in FIG.
5
). Referring to
FIG. 7
, it is difficult to distinguish the reflection from the bottom surface
23
a
of the axial portion
23
from those of a plurality of detected reflections Uwa. Furthermore, the reflection Uwb from the end surface
22
b
of the extended portion of the head portion
22
of the bolt
21
may be a cause of noise, thus degrading accuracy of the axial tension measurement.
On the foregoing ground, publication of Japanese Utility Model No. SHO 60-194473 discloses a device for detecting axial tension of a bolt incorporating an ultrasonic transducer disposed in close proximity to the top surface of the bolt head for ultrasonic radiation into the bolt. In the aforementioned device, an ultrasonic lens for converging ultrasonic radiation from the ultrasonic transducer to the top surf ace of the bolt head is interposed therebetween. A concavity having relatively a large radius of curvature is formed in a back surface of a cap to which the ultrasonic transducer is adhered, which may form a convex-like space having one flat surface defined by the bolt head. A convex ultrasonic lens can be defined by the space filled with oil.
In the aforementioned device for detecting axial tension of the bolt, the ultrasonic lens converges the ultrasonic radiation applied from the ultrasonic transducer to the top surface of the bolt head. The ultrasonic radiation applied into the bolt head is focused to the cross section of the axial portion of the bolt as it propagates from the bolt head to the axial portion. The ultrasonic radiation applied into the bolt head is, thus, efficiently propagated within the axial portion of the bolt. The ultrasonic radiation exhibiting relatively higher intensity can be propagated within the axial portion of the bolt for detecting the ultrasonic propagation time. As a result, the signal level upon receipt of the ultrasonic radiation is raised to a higher level compared with other noise, thus detecting the axial tension of the bolt with high accuracy. The aforementioned generally employed art discloses the description with respect to change in the shape of the space constituting the ultrasonic lens for converging the ultrasonic radiation depending on the sonic speed of propagation between the substance filled in the space and the cap-forming material(ultrasonic propagation characteristics).
However, the length of the bolt subjected to the axial tension measurement is not always constant. Accordingly, in the device for detecting the axial tension of a bolt disclosed in Publication of Japanese Utility Model SHO No. 60-194473, the ultrasonic radiation applied from the ultrasonic transducer to the top surface of the bolt head can be converged by the ultrasonic lens. However, the convergence degree of the ultrasonic radiation applied from the ultrasonic transducer to the top surface of the bolt head may vary. Therefore it is necessary to select the type of the ultrasonic lens, concave or convex (the concavity formed in the back surface of the cap to which the ultrasonic transducer is adhered), lens shape including the curvature, and ultrasonic propagation characteristics such as the material with which the lens-forming space is filled in accordance with the bolt length.
In the above-identified reference, convergence of the ultrasonic radiation applied from the ultrasonic transducer to the top surface of the bolt head is considered. However, the convergence of the ultrasonic reflection from the bottom surface of the axial portion of the bolt is not considered. As the propagation path of the reflection becomes complicated, the reflection is diffused while being detected.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a bolt adapted to measure axial tension generated therein without changing various settings of the device for detecting the axial tension and to provide an axial tension measurement device for the bolt.
The present invention provides a bolt subjected to ultrasonic axial tension measurement, in which at least one of opposite end surfaces of a head portion and an axial portion of the bolt is formed into a curved surface having a predetermined curvature.
In this invention, a curved surface formed as a top surface of a head portion or a bottom surface of an axial portion of the bolt functions as the ultrasonic lens. If the top surface of the head portion of the bolt is formed into a curved surface, the ultrasonic radiation applied thereto is converged for propagation within the bolt toward the bottom surface of the axial portion. If the bottom su
Aoki Tatsuyuki
Eguchi Takashi
Sakai Tomoji
Burns Doane , Swecker, Mathis LLP
Noori Max
Toyota Jidosha & Kabushiki Kaisha
LandOfFree
Bolt for ultrasonic axial tension measurement does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Bolt for ultrasonic axial tension measurement, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bolt for ultrasonic axial tension measurement will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2592570