Torque wrench with angular motion detector

Details Torque wrench with angular motion detector Torque wrench with angular motion detector

1995-06-21

1996-07-09

Chilcot, Richard

Measuring and testing

Dynamometers

Responsive to torque

7386221, B25B 2314

Patent

active

055334091

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Field of the Invention
The invention relates to the detection of angular motion, and provides an application of particular relevance and usefulness in torque measurement.
2. Background of the Invention
Many engineering applications involve tightening threaded fasteners, for example nuts and bolts, to within specified torque tolerances. This helps ensure that the performance of the fastenings is reliable and predictable. Fastenings tightened to torques that fall below their specified range can work loose and eventually come undone, whereas those tightened to torques above this range are subject to excessive stresses that can cause failure or eventually weaken the joint. When tightening fastenings, whether by hand or powered tool, means are required to give independent verifications of the applied torque.
In carrying out Quality Control testing on fastenings, it is often necessary to discover the torque to which any particular fastening has been tightened. To do this, the operator applies a gradually increasing torque to the tightened fastening. Initially there is no relative motion of nut and bolt, i.e. no further tightening of the fastening, because the torque to overcome static friction has not yet been reached. On continued application of increasing torque a point is eventually reached at which the nut begins to move relative to the bolt and further tightening of the fastening commences. This is felt by the operator as a sudden movement of the initially stationary torque wrench, and is known as the breakaway point. The torque applied to the fastening at the precise moment that this movement starts is an indication of the torque to which the fastening was originally tightened. It is known as the breakaway torque, and it is this value that is commonly recorded and used in a Quality Control Programme.
If the operator continues to apply torque after the breakaway point is reached, the fastening becomes tightened to a higher torque than it was initially. If the specified torque tolerance for the fastening is narrow, this may mean that the fastening is overtightened, and hence weakened. It is therefore desirable that the breakaway point is detected quickly and reliably if the testing of a fastening is not to degrade that fastening.
The traditional method of breakaway point detection in which the operator simply records the value of torque displayed by the torque wrench at the point when he judges movement of the wrench to commence, is subject to a number of limitations. The time at which movement is first detected depends on the sensitivity of the operator, who is required to see or feel for movement of the wrench. A particularly heavy handed operator may overtighten and therefore degrade the joint he is supposed to be testing. The nature of the joint, which may be "hard" or "soft" will influence the ability to detect breakaway point and the reliability of the peak reading achieved.
It is an object of the present invention to provide a detector which is able to sense the commencement of breakaway virtually instantaneously and to record an accurate reading of the torque applied at that breakaway point.


SUMMARY OF THE INVENTION

The invention provides apparatus for providing information relating to the angular movement of, and torque applied to, a threaded fastener comprising: flywheel axis lies in the same plane as the fastener axis: flywheel, for sensing the proximity of the indicia relative to a given point on the torque wrench to establish a pulse output when the flywheel is rotated: relating to the angular movement of the torque wrench about the axis of the fastener, and for monitoring the output of the torque sensor to provide information about the applied torque; and
The number of indicia on the flywheel generally depends on the nature of the flywheel and its intended speed of rotation. Large, high inertia flywheels are usually rotated at lower angular speeds than smaller lighter wheels, and so a greater number of indicia would be required to give a sufficiently high frequency pulse outp

REFERENCES:
patent: 4091664 (1978-05-01), Zerver
patent: 4262528 (1981-04-01), Holting et al.
patent: 4265109 (1981-05-01), Hallbauer et al.

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