Study and experimentation for a procedure for the evaluation of measurement uncertainty in hand-arm transmitted vibrations

Hand transmitted vibrations are a critical parameter for health and safety of operators. When dealing with widespread machine tools such as impact hammers, drills and so on, maximum acceptable levels of vibration transmitted to the hand are defined. The general aim is to protect the users from the most common diseases, which are recognised to be caused by hand transmitted vibration. There is a set of national and international directives, norms and laws, which deal with the definition of acceptable vibration levels and with minimum requirements for their measurement. Such measurements are subjected to the influence of various factors, including operator position, hand pressure on the handle, activation force and so on, which are difficult to control and to evaluate. On the other hand, evaluation of uncertainty is highly recommended, since measurement results are used to establish conformance with requirements. So the aim of this work is to perform a two-side investigation on the effects of such influence quantities on the measured vibration value. From one side a numerical model of the mechanical behaviour of the hand arm system, was developed and used to evaluate the variations in the mechanical properties due to the hand-arm position, muscle activation muscle mass and so on. On the other side an experimental campaign was designed and performed to investigate the effects of such quantities on the measured value. Such indications are considered in a procedure for uncertainty evaluation, that gives suggestions to the operator for the formal uncertainty evaluation, when measurement are carried out, as usual, in weakly controlled conditions, and provides a numerical indication of the various effects.