A singularity-free approach for safe interaction of robot assisted rehabilitation, based on model-free impedance control

In this paper, using a hybrid control technique for robotic rehabilitation, a singularity-free control algorithm for the safe robot-human interaction is proposed. With the use of max-plus algebra, a hybrid controller is designed to guarantee feasible robot motion in the vicinity of the kinematic singularities or going through and staying at the singular configuration. The approach taken in this paper uses a model-free impedance control and hence it does not require any information about the model except the upper bounds on the system matrix. The stability of the approach is investigated using multiple Lyapunov function theory. The proposed control algorithm is applied to a six-axis industrial robot arm, namely PUMA 560 and the results demonstrate the validity of the proposed control scheme.