A Comparison of Workspace and Force Capabilities between Classes of Underactuated Mechanisms

We propose a novel approach to study the ability of an underactuated mechanism, or a mechanism that has fewer actuators than degrees of freedom, to passively adapt to environmental constraints. While prior work in underactuated robotic hands has primarily focused on the mechanism's ability to curl its distal degrees of freedom inward even after the proximal degrees of freedom are constrained by contact with the environment, this paper explores the mechanism's adaptability in terms of both motion and force-application capabilities in the presence of external constraints. Specifically, using four different transmissions for a novel singly-actuated linear three degree-of-freedom mechanism, this paper analyzes how the system's ability to reconfigure joints and apply new contact forces varies as a function of the transmission configuration and object geometry. We show that with more extensive rerouting of a single actuator to multiple joints, the mechanism exhibits greater motion and force adaptability at the cost of decreased maximum joint travel and contact forces.