Global Positioning of Robot Manipulators via NPID-like Regulators with Two Nonlinear Integral Actions

This paper deals with the position control of robot manipulators with uncertain and varying-time payload. Proposed is a set of novel NPID-like regulators consisting of a linear combination of the proportional control mode, derivative control mode, nonlinear control mode shaped by a nonlinear function of position errors, and two nonlinear integral control modes driven by a nonlinear function of position errors and its derivative, respectively. By using Lyapunov's direct method and LaSalle's invariance principle, the simple explicit conditions on the regulator gains to ensure global asymptotic stability are provided. The theoretical analysis and simulation results show that: an attractive feature of our scheme is that this kind of NPID-like regulators has the faster convergence, better flexibility and stronger robustness with respect to uncertain and varying-time payload, and then the optimum response can be achieved by a set of control parameters in the whole control domain of interest, even under the case that the payload is changed abruptly.