Evaluating Variable Transmissions in Body-Powered Prosthetic Grasping

Body-powered prostheses remain popular for those with upper limb absence in part due to their inherent haptic feedback, but they still face low adoption rates due to the high forces required from the user and associated discomfort. Recent work on a desktop haptics testbed demonstrates potential benefits from including variable transmissions in simulated body-powered devices, reducing physical demands on the user and improving grasp success for a wide variety of object types. However, real-world grasping tests have yet to be performed with an embodied wearable system. In this work, we evaluate five different transmission modes, including fixed and multiple variable modes, on a body-powered wearable prosthetic device in a grasp and lift task. We demonstrate how variable transmissions can reduce actuation loads on the user with negligible changes to required motion inputs and find that abrupt, autonomous changes in transmission state can increase the risk of overgrasping and crushing fragile objects.