Anthropomorphic and Linear Arm Models for Mechanical Power Tool Testing

Vibrational dynamics of hand-held power tools are relevant for ergonomics and system performance. In application of these tools, the human user is in the force flow, thus has a relevant influence on the vibrations occurring in the human body. For development purpose and valid comparison between tools, reproducible testing is needed. The testing is most useful if it simulates different user types, working poses and muscle activation states, as observed in the tools’ application. The admittance of an anthropomorphic two link arm system strongly depends on the arm pose angles. This work examines how well this angle dependent behaviour can be approximated by a linear mass-spring-damper system, which is easier to build for test rigs. Parameter optimization under the assumption of fixed masses in the linear replacement system showed unsatisfactory fitting of the system dynamics for some arm poses. Therefore the authors recommend to consider building future test rigs in an anthropomorphic arm setup. The work further reveals the importance of implementing adjustable stiffness and damping in test rigs.