Influence of coupling forces on the mechanical impedance of the hand-arm system during rotational vibration excitation around the xh-axis

The research presented in this paper focuses on the determination of the rotational mechanical impedance of the human hand-arm system under rotational vibration excitation, applied via the knob-shaped handle. During the development of power tools, the interaction between the power tool and the hand-arm system must be simulated. This requires accurate models of the hand-arm system's biodynamics. The current state of research provides such models for translational vibrations, but are limited when also considering rotational vibrations. To enable the development of such models, the study investigates the biodynamics of the hand-arm system for rotational vibration excitation. Therefore, the rotational impedance of 21 subjects was measured in a study. In the study, a knob-shaped measuring handle, whereby the subjects applied different combinations of gripping and push forces to the handle, vibrated the hand-arm system of the subjects rotationally. The results show that a higher gripping force results in a higher magnitude of rotational mechanical impedance, while the push force does not seem to influence the rotational impedance. The missing influence of the push force on the rotational impedance may be caused by the alignment between hand position, force direction, and excitation axis. The findings of this study extend the overall knowledge of rotational mechanical impedance for simulating the hand-arm system in power tool development. In regards to the rotational vibration exposure when performing sanding tasks, the results suggest that a frictional connection between the hand and the power tool handle reduces the vibration exposure of the hand-arm system.