Estimation of biodynamic forces distributed on the fingers and the palm exposed to vibration.

The hand-tool coupling force in the operation of a vibrating tool is generally composed of applied force (AF) and biodynamic force (BF). There is wide interest in quantifying the coupling force. The objectives of this study are to develop an effective method for estimating the BF and to investigate its fundamental characteristics. Using the biodynamic response of the hand-arm system, such as apparent mass or mechanical impedance, and the acceleration that can be measured on vibrating tools, this study proposed an indirect method for the BF estimation. The BFs distributed on the fingers and the palm of the hand along the forearm direction (z(h)-axis) in the operations of eighteen types of tool were estimated and used to identify the distributed BF characteristics. The results indicate that the BFs depend on both the tool vibration spectrum and the biodynamic properties of the hand-arm system. The dominant BF frequency component is usually at the same frequency as the dominant vibration frequency of each tool. The BF distributed on the palm (2-98 N) is much higher than that distributed on the fingers (1-30 N) at frequencies less than 100 Hz, but these biodynamic forces (2-22 N) are comparable at higher frequencies. The palm BF on several tools with relatively low dominant frequencies (< or = 40 Hz), especially in the resonant frequency range (16-40 Hz), is comparable with the applied palm force (50-100 N). Since the resonant frequency of the palm BF is also in the range of the dominant vibration frequencies of many percussive tools, the palm BF may be related to the disorders in the wrist-arm system. The BF on the fingers is likely to be closely related to the dynamic stresses and deformations in the fingers and it may thus be used to quantify the finger vibration exposure.