Saturday, January 24, 2009

What's Shaking - A Convenient Measurement of Vibration Could be Used for Standards

International Journal of Industrial Ergonomics
Volume 39, Issue 1, January 2009, Pages 174-184

An investigation on characteristics of the vibration transmitted to wrist and elbow in the operation of impact wrenches

X.S. Xu, a, , D.E. Welcomea, T.W. McDowella, C. Warrena and R.G. Donga

aEngineering & Control Technology Branch, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA

To help assess the risk of the vibration exposure during impact wrench operation and to develop a convenient and effective method to monitor and control the exposure, this study aims to investigate the characteristics of the vibrations transmitted to the wrist and elbow in the operation and to evaluate the on-the-wrist and on-the-elbow vibration measurement methods. Six subjects participated in the experiment. Each of them used 15 impact wrenches on a simulated workstation. Tri-axial accelerations at three locations (tool handle, wrist, and elbow) and the tool effective torques were measured and used in the evaluations. Results confirm that the severity of the vibration exposure generally depends on tool and individual, and that the vibrations measured at wrist and elbow reflect the influences of both factors. This study also found that the accelerations measured at the wrist and elbow are correlated with the ISO frequency-weighted tool acceleration. The fundamental resonance of the hand-arm system in the range of 16–50 Hz is well reflected in the vibration measured at the wrist. The results also demonstrate that vibration exposure duration can be reliably detected from the wrist vibration data. Moreover, the wrist vibration is suggestively correlated with the torque of the pneumatic impact wrenches. These findings suggest that the measurement of the wrist vibration can be used as an alternative approach to perform the exposure risk assessment and to monitor and control the exposures in the operation of the impact wrenches.
BrooklynDodger(s) comment: An unacceptable fraction of people who use powered hand tools in routine assembly operations suffer cumulative trauma disorders. Most quantitative standards for limiting exposure are unprotective because they are aimed at event windows of a year or so - the most anyone is in an unchanged work station - rather than a 30 to 45 year career. Standards also suffer from the variety of features of exposure that may be measured, usually measuring some features means omitting others. Then, investigators compete incomplete exposure schemes against retrospective short term outcomes. European standards for tools exist, based on acceleration. A large fraction of current tools violate these standards, which limits the ability to see exposure response.

This investigation proposes a method of measuring the interaction of force with worker characteristics. Laboratory studies generate a lot of numbers - 6 workers x 15 tools x however many parameters measured.

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