A globally stable PD-NP-INP-D regulator for robot manipulators

This paper deals with the position control of robot manipulators with uncertain and varying-time payload. Proposed is a simple class of robot regulators consisting of a linear PD feedback plus a bounded nonlinear term of position errors plus an integral action driven by an NP-D controller, where the nonlinear terms are shaped by a continuous bounded nonlinear function of position errors. 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 PD-NP-I^NP-D controller 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, even under the case that the payload is changed abruptly.