Characterization of the NEURARM bio-inspired joint position and stiffness open loop controller

This paper presents the characterization of the position and stiffness open loop controller for the NEURARM bio-inspired joint. A novel antagonistic non-linear actuation scheme is proposed for the NEURARM platform, a 2 DoF planar robotic arm that has been developed to imitate the principal functional features of the human arm for planar movements. The NEURARM joint has the actuation scheme based on a contractile element (a hydraulic piston) in series with a non-linear elastic element, able to mimic the force-elongation characteristic of the muscle-tendon complex. The non-linear spring is obtained by a linear tension spring rendered non-linear by means of a specifically designed mechanism. Such actuation scheme allows the implementation of control strategies based on equilibrium point and impedance control hypotheses of human motor behavior. The preliminary results of the characterization of the open loop joint stiffness and position controller are presented.