Passive and active gravity-compensation of LIGHTarm, an exoskeleton for the upper-limb rehabilitation

This paper presents LIGHTarm, an exoskeleton for the upper-limb neuro-rehabilitation, characterized by a peculiar kinematic structure, expressly conceived to face shoulder rhythm and elbow singularity issues. The device is developed in two versions. The first prototype of this rehabilitation device is unactuated, achieving gravity compensation through a passively mechanically compensated mechanism obtaining a cost-effective and intrinsically safe solution for semi-autonomous training at home. A limitation of passively gravity-compensated devices is that they lack a dynamically and on-line tunable weight-support. Actuated devices, in respect to non-actuated ones, allow "a step further" in the real-time control of tuning the gravity-compensation feature. Starting from its unactuated version, the actuated version is presented, together with the kinematics and dynamics analyses of the mechanism.