Muscle Actuator Design for the ACT Hand

Abstract

We are constructing an anatomically-correct testbed (ACT) of the human hand to understand its mechanisms, function, and neural control. As a part of this effort, we created an actuator that mimics both the active and passive behaviors of the human muscles. To use it as the actuator of the ACT Hand, it must conserve the tendon-driven structure so that the size or the weight of the hand do not have to be compromised. A custom-made spring composite was used to simulate the human's nonlinear passive muscle stiffness closely (R2 = 0.99). A coreless DC motor was used to siumulate the active contraction. The passive and active components interacted in parallel and they were attached to a cable tendon that inserted into the bones. In order to study the neural control of hand movements, we incorporated Hill's model in the active contraction component. Therefore, the computer program could simply specify the muscle activation level, and the appropriate tendon tension could be provided given the current muscle length. This muscle actuator allowed an accurate realization of neural activation based control of ACT Hand, and it provides a foundation for intimate brain-machine interface.