Design of an anthropomorphic finger using shape memory alloy springs

Abstract

We present the design of an anthropomorphic finger prototype. In this artificial finger, the actuators are electric pistons, whose main component is a shape memory alloy (SMA) spring. The artificial finger presents three independent degrees of freedom (DOF) for the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints, respectively. The paper outlines the kinematic and structural characteristics of the finger. The main goal pursued during the development of the finger has been that of designing a small and lightweight dextrous gripper with anthropomorphic kinematics, which could be easily ported and installed even on small robot hands. We propose to use a physical anthropomorphic finger to demonstrate and validate a neural controller based on biological models. The neural controller applies a strategy of trajectory control using the vector integration to endpoint (VITE) model, which exhibits key kinematic properties of human movements, including asymmetric bell-shaped velocity profiles. The VITE model is used to compute the desired joint movement trajectories by smoothly interpolating between initial and final muscle length commands for the antagonist muscles involved in the movement. The rate of interpolation is controlled by the product of a difference vector which continuously computes the difference between the desired and present position of the finger, and a volitional movement gating signal. Experimental performance results in the time domain are presented, and directions for future research are discussed.