The ACT Hand: design of the skeletal structure

Robotic hands built for manipulation are often anthropomorphic but not anatomically accurate. We are constructing an anatomically-correct testbed (ACT) of the human hand to understand its mechanisms, function, and control. We have previously demonstrated that an accurate model of the extensor mechanism in the ACT Hand is crucial in realizing human-like finger movements. Here, we present the design of the bones and joints that form the skeletal structure for the ACT Hand. The bones are machined from human bone data, and are accurate in surface shape, mass, and center-of-gravity, while the joints have been designed to match both degrees-of-freedom and passive stiffness. Our evaluation of the assembled index finger confirms the anatomic properties, and reveals the function of some of the peculiar shapes of the finger bones, the necessity of matching the joint passive stiffness properties, and the connections of the extensor mechanism.