A kinematic thumb model for the ACT hand

The thumb is essential to the hand´s function in grasping and manipulating objects. Previous anthropomorphic robot hands have thumbs that are biologically-inspired but kinematically-simplified. In order to study the biomechanics and neuromuscular control of hand function, an anatomical robotic model of the human thumb is constructed for the anatomically-correct testbed (ACT) hand. This paper presents our ACT thumb kinematic model that unifies a number of studies from biomechanical literature. We also validate the functional consistency (i.e. the nonlinear moment arm values) between the cadaveric data and the ACT thumb. This functional consistency preserves the geometric relationship between muscle length and joint angles, which allows robotic actuators to imitate human muscle functionality