Characterisation of the mechanical impedance of the human hand–arm system: The influence of vibration direction, hand–arm posture and muscle tension

There are several occupational illnesses related with vibration transmission from power hand tools to hand–arm system. International Standards have been developed to evaluate the risk of injury after exposure to this kind of vibrations; nevertheless, the current standards recognise that some aspects need to be investigated, such as the influence of vibration transmission direction, arm posture or hand grip force. To investigate these aspects an instrumented hand tool has been constructed by the author to measure the hand grip force and the energy transmission to the operator. The vibration applied is generated and controlled by an electro-dynamic shaker. The results of the experiment allow the authors to describe the dissipative model of hand–arm system, and therefore propose new frequency filters to weigh the accelerations obtained in tools depending on vibration transmission direction to hand–arm system.Relevant to industryThe methodology proposed in this study provides a better evaluation of health risks associated with exposure to hand-transmitted vibration from power tools. The results obtained can also be used in handle design for new tools, which is more effective than personal protective equipment solutions, in order to minimise potential harm to operator's health.