Phase-dependent control of an upper-limb exoskeleton for assistance in self-feeding

In this paper, a phase-dependent trajectory planning methodology is proposed and employed to control a 7 DOF redundant exoskeleton to help the elderly and the disabled in performing a self-feeding task. The feeding task is divided into five different phases and trajectories. For a particular phase in which the shoulder flexion angle is small, inverse kinematic is solved in closed-form by constraining the shoulder rotation. For all the other phases, a redundancy resolution method named Sensorimotor Transformation Model (STM) is employed to obtain a unique natural elbow position which in turn is used to obtain closed-form inverse kinematic solution. Discontinuity between two successive trajectories arising from the proposed method is compensated for. The experiment results show that the proposed method can drive the exoskeleton naturally and smoothly to reach the target and subsequently near to the user´s mouth for feeding/drinking.