Montreal, June 7, 2016 – An inexpensive system for measuring the forces exerted between a user’s hand and the handle of a vibrating portable power tool was developed, and the results of usability testing with real vibrating tools in a context simulating field conditions were positive. This hand-handle coupling-force measurement system uses thin, flexible, resistive (FlexiForce^®) sensors that can be adjusted to the size of different power tool handles. “These inexpensive sensors can measure the forces exerted by the palm and fingers of the hand, provided each one is carefully calibrated to the subject before the measurements are taken. Regardless of the size of the hand and the handle, FlexiForce sensors have shown good linearity with push (up to 75 N) and grip (up to 50 N) forces and provide reproducible results on both flat and curved surfaces,” says Subhash Rakheja, coauthor and professor at Concordia University.

The new system was first tested in the lab under static and vibrating conditions. It was validated by repeated measurements on seven subjects and five different handles, three cylindrical and two elliptical. Each subject had to grasp an instrumented handle in 12 different coupling-force combinations and with two levels of vibration in the 4 to 1,000 Hz frequency range. The sensors produced “very good estimates of the push and coupling forces.” Estimate discrepancies were less than 10% in all combinations of grip and push forces investigated.

In the second stage of the study, six subjects grasped a 38 mm-diameter handle in nine combinations and with two levels of broadband vibration. The results showed that the system could also be used in the field with real tools to estimate the biodynamic response of the hand-arm system.

In the third and last stage, the validity of the system was assessed by having three subjects grasp a stationary or vibrating tool handle in different combinations of push and grip forces. The results revealed a very good correlation between the forces exerted by the hand and measured by the sensors, and the reference values, both for a stationary tool and a vibrating one.

According to the researchers, this advance will make it easier to assess the risk of injury associated with the use of various types of tools. The results of the study are freely available at http://www.irsst.qc.ca/publications-et-outils/publication/i/100861/n/low-cost-system-for-measuring-coupling-forces. To keep up with research at the IRSST, follow us on the Web, Twitter, Facebook, LinkedIn or YouTube.

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Source
Jacques Millette
Public Affairs Officer
IRSST