Assessments of Vibratory Handheld Tools and Handle Interactions

There has been a broad history of injuries occurring as the result of vibratory hand-tool use. Following these findings, three human safety standards have been proposed. These standards declare that the dynamic properties with respect to acceleration frequency spectra must be determined for vibratory hand tools. These properties must meet specific tolerances in order to be considered acceptable for use.

The standards, however, do not recognize the significance of the coupling characteristics and the energy transfer between the user and vibrating handle. This interaction reveals the amount of vibratory energy that enters the user's hands. Epidemiological data for VWF shows that certain zones of the hand are first affected causing the onset of disease. Hence vibration is most severe at specific locations on the hand.

The aim of this study was to measure the coupling forces on the hand during the operation of several tool types in real-world working conditions. Simultaneous measurements of force and acceleration were examined in order to determine similarities and differences of the resulting frequency spectra. Transfer functions were used to validate these relationships although non-linearity of the hand system may reduce the values of coherence. In addition, force variations at the finger and palm with respect to coupling dynamics and hand geometry were assessed. Finally, the reliability of the resistive-based force instrumentation system used in this study to produce accurate and repeatable measurements was assessed.