The purpose of this investigation was to examine the vibration characteristics of the hand-arm-power tool interaction. For this study the power tool that was examined was a chain saw. The analysis of this problem was divided into two parts. One part consisted of analyzing the vibration characteristics of the human hand-arm system. This was done in a qualitative sense by investigating the influence of arm position and grip type upon the response of the hand and arm and in a quantitative sense by identifying an equivalent system for the hand and arm for a specific a m position and grip type. The other part of this investigation consisted of analyzing the vibration characteristics of a chain saw. This was done both experimentally and analytically. First, tests were conducted to identify the vibration sources of the saw, to determine the vibration response of the saw, and to determine the structural characteristics of the saw. Following this an analytical model of the saw was developed which can be used to predict the vibration response of a saw due to the forcing functions identified from the experimental part of the investigation.

With respect to the hand-arm system, normal a m position haH little influence upon the response characteristics of the hand and am, while the grip type had a significant influence. By using experimental results, it was possible to model the hand-arm system as a highly damped, threedegree-of-freedom, mass-spring-damper system. For the type of grip used for developing the model, the size of the individual had little influence upon the response of the hand-arm system.

The results of this investigation also yielded information necessary for determining meaningful hand vibration limit standards. To establish acceptable standards, it is necessary to monitor both the vibration limit levels as a function of forcing frequency and the tightness of grip for the tests used to determine these levels. For, eventhough the vibration levels may decrease with a tighter grip, the amplitude of the force transmitted through the hand may increase, resulting in an increased probability for injury.

With regard to the chain saw, the primary forcing functions causing the saw to vibrate were the shaking forces, including the fundamental shaking force and its higher harmonics and the forces due to an unbalanced clutch and flywheel, and the pulses that were caused by the exploding gas-air mixtures of the internal combustion engine. The structural characteristics of the saw amplified the response amplitudes of the saw due to the above forcing functions at frequencies above the frequency of the fundamental shaking force. The rotational vibration of the saw can be reduced by minimizing the magnitudes of the moments generated as a result of the unbalanced clutch and flywheel and as a result of the magnitude of the mass moment of inertia of the connecting rod.

Finally, an analytical model of the saw, treating the saw as a sixdegree-of-freedom system, was developed which yielded results very close to the experimentally obtained results at the fundamental forcing frequency. Because of the structural characteristics of the saw, it was not possible to get good correlation between the analytical and experimental results at higher frequencies.