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.