Effects of body-powered prosthesis prehensor stiffness on performance in an object stiffness discrimination task

In this paper, we present results from two human subject experiments focusing on effect of prehensor stiffness on object stiffness discrimination task performance in a body-powered prosthesis. Humans have the ability to alter the directional endpoint stiffness of their arms through co-contraction of agonist/antagonist muscle pairs. In the area of prosthesis design, while the need for position and force control has long been recognized, the concept of end effector stiffness modulation has been mostly ignored. In this study we attempt to broaden the existing knowledge base by (1) using an experimental setup which mimics the control inputs of a shoulder-driven body-powered prosthesis operated in voluntary closing (VC) mode, and (2) exploring the impact of end effector stiffness modulation on the quality of haptic feedback the user receives about the environment. Results of the first experiment indicated that tuning of prehensor stiffness in a body-powered prosthesis can increase the performance of the user in correctly and more easily identifying objects with varying stiffness.