Motion Control of a 4-DOF Cable-Driven Upper Limb Exoskeleton

This paper presents the motion control of a 4-DOF cable-driven upper limb exoskeleton. The exoskeleton consists of a 3-DOF shoulder module and a 1-DOF elbow module, with six cables are routed through the exoskeleton cuffs to drive the whole upper limb motion, each module can be controlled independently. This design preserves the advantages with cable-driven parallel mechanisms, and introduces the advantages in having a serial kinematic structure. To control the motion of the exoskeleton along desired trajectories in space, nonlinear feedforward control laws hi the cable length coordinates are used. Taking account of the effect of redundancy on actuation, optimal tension distribution is considered in the control laws. Trajectories tracking capability was demonstrated through experiments with the prototype of exoskeleton.