Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2002-05-02
2004-03-02
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06698298
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a torque wrench for additional tightening inspection.
BACKGROUND ART
Among inspection methods for inspecting a tightened bolt (screw) for a torque value, there is an additional tightening torque method in which the bolt in the tightened state is further tightened with a torque wrench and the torque value at which the bolt starts rotating again is read from the above-mentioned torque wrench. Incidentally, the bolt is left as it is after the inspection.
This additional tightening torque method uses such torque wrenches as a scaled torque wrench. Upon the restart of rotation, the torque value is read from the scale to check the tightening torque value of the bolt.
In this additional tightening torque method of checking the tightening torque value of a tightening bolt by using a scaled torque wrench, as shown in
FIG. 5
, a force in the tightening direction is applied to the torque wrench, and the bolt to be inspected (hereinafter, referred to as inspection bolt) undergoes a torque. The torque increases as shown by the broken line E.
On the other hand, in order for the inspection bolt in a stationary state to be rotated again, a torque must be applied beyond the one resulting from the static frictional resistance of the inspection bolt. Accordingly, when the tightening torque increases as shown by the broken line E to exceed the point A and the integral rotation of the torque wrench and the inspection bolt is sensed and confirmed at an additional tightening point B, the additional tightening torque measurement T
2
corresponding to that point is read from the scale on the torque wrench. Based on this additional tightening torque measurement T
2
, the torque value (T
1
) at the point A is calculated, for example, by using a predetermined factor. Then, it is determined if this torque value T
1
calculated equals to a desired torque value (T
0
) specified.
In such a conventional additional tightening torque method, the additional tightening torque measurement T
2
has a difference in value with respect to the actual tightening torque value T
1
. Besides, the torque measurement in additional tightening at the foregoing additional tightening point B may vary. For example, when the bearing surfaces of the tightening bolt and the member to be tightened by the tightening bolt are in close contact, the additional tightening point B rises in torque indicating position on the characteristic chart of FIG.
5
. This causes an increase in the additional tightening torque measurement T
2
.
When lubricating oil, a washer, or the like is interposed between the bearing surfaces of the member to be tightened and the tightening bolt so that the member to be tightened and the tightening bolt are in loose contact, the additional tightening point B falls in torque indicating position. The additional tightening torque measurement T
2
then approaches the tightening torque value T
1
.
In addition, the torque indicating position of the additional tightening point B also fluctuates up and down due to variations in the rotational speed of the torque wrench depending on persons to be measured, the degrees of thermal expansion of the member to be tightened and the tightening bolt depending on air temperature, and so on. These factors also cause variations in the torque measurement T
2
in additional tightening.
For this reason, the present applicant has already proposed the invention described in Japanese Patent Laid-Open Publication No. 2000-778 as a method of measuring a tightening torque which resolves such variations in the measurement T
2
.
This method of measuring a tightening torque is based on the assumption that in
FIG. 5
, when tightening is started and a stable rotating state is reached beyond the point A where the inspection bolt starts rotating again, the rotation angle and the torque value of the inspection bolt (torque wrench, in fact) trace a linear characteristic line and this characteristic line crosses the point A. At and after the point C where the rotating state is stable, the torque value corresponding to a rotation angle of the torque wrench is measured on a plurality of points. The measurement start position (&thgr;
0
) of the rotation angle is set at the point A so that the torque value at the point A can be obtained by calculation.
DISCLOSURE OF THE INVENTION
The torque wrench for additional tightening inspection described above, capable of measuring the rotation angle of the torque wrench to inspect the tightening torque, is based on the theory assuming that the rotation angle of the torque wrench is 0° until the point A shown in
FIG. 5
is exceeded.
Nevertheless, it is impossible for the entire torque wrench including the torque wrench body and the socket to be made into a perfect rigid body. For example, when a force is applied to the torque wrench, the torque wrench itself bends because of distortion. It follows that a certain angle of rotation is detected before the point A shown in
FIG. 5
is reached.
Moreover, torque wrenches to be used for measuring a tightening torque by applying an additional tightening torque to a tightening bolt already tightened as described above vary greatly in type and characteristic.
For example, in a torque wrench such as a torque wrench for additional tightening inspection shown in
FIG. 1
, as an embodiment of the invention, a wrench body
2
is provided with torque detecting means and a processor
1
including a display unit for displaying the torque value detected, and is selectively combined with ratchet type replaceable heads
3
, spanner type replaceable heads
4
, various kinds of sockets of different lengths (not shown), or the like to measure a tightening screw for a screw tightening torque. Here, variations in the torsion angles and play angles inherent to the above-mentioned attachments to be selected in use, or the various kinds of replaceable heads and sockets, cause differences in the torsion angle characteristics and play angle characteristics of the respective measuring wrenches in use.
For example, the maker side of the torque wrench ships to the user side a predetermined wrench body
2
and attachments specified by a predetermined torsion characteristic or the like in combination as intended for the measurement of the tightening torque of a tightening screw. When the user measures the tightening torque of a tightening screw, any change will not occur in the characteristic of the wrench and the tightening torque value can be easily detected (measured) on the basis of the torsion characteristic of the torque wrench specified at the time of the shipment so long as the attachments are combined and used with the wrench body
2
as they are shipped from the maker. Depending on the working environment and the like for the tightening torque measurement, however, attachments other than those shipped might have to be substituted and used with the wrench body in measurement from sheer necessity.
In such cases, a difference can occur between the torsion characteristic etc. of the attachments substituted and used by the measurer to measure the tightening screw torque value and the torsion characteristic of the attachments mounted on the wrench body upon the shipment from the maker. Then, as shown in
FIG. 6
, for example, the torque wrench may start rotating at the rotation start point &thgr;
0
before the inspection bolt actually starts rotation, thereby causing a difference in angle from the rotation start position &thgr;
1
where the inspection bolt actually rotates again (starts additional tightening).
Consequently, an error Ts appeared in the torque value calculated corresponding to this difference in angle, and it was impossible to obtain a tightening torque value with high precision.
An object of the invention according to the present application is to provide a torque wrench for additional tightening inspection which corrects an error resulting from the rotation of a torque wrench before the rotation of an inspection bolt so that a tightening torque of the bolt can be obtained with pr
Kobayashi Nobuyoshi
Tsuji Hiroshi
Kanesaka & Takeuchi
Lefkowitz Edward
Thompson Jewel V.
Tohnichi MFG. Co., Ltd.
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