Development of Dummy Based on Impedance Properties of Human Soft Tissue Using a Nonlinear Viscoelastic Model

Securing human safety in a physical human–robot interaction (pHRI) has been extensively studied to allow for the expansion of robotic applications. Dummies with the same impedance properties as those of human soft tissues are suitable substitutes for the validation of the safety assurance of the pHRI experiment. This study demonstrated the development process of dummies with high biofidelity. A psychophysiological experiment was designed to replicate the clamping scenario, and the center of the palm, thenar eminence, and forefinger pad were selected as three soft tissues of the human hand to be impacted to obtain the dynamic response of the contact force. A nonlinear five-element viscoelastic model was developed to quantify the viscoelasticity of the three soft tissues through curve fitting of the contact force. Subsequently, three dummies were fabricated using a polyurethane resin material. The biofidelity of the dummies was examined via a parametric comparison with the soft tissues and curve comparisons to examine whether the steady-state force and the dynamic response of the contact force were located within the corresponding ranges enclosed by the calibration curves of the soft tissues. All three dummies showed high biofidelity in the case where the steady-state force exceeded approximately 5 N, even though they have different nonlinearity of elasticity from that of soft tissues.