Trajectory tracking for mobile manipulator based on nonlinear active disturbance rejection control

This paper designs a nonlinear active disturbance rejection control (ADRC) to solve the trajectory tracking problem of a mobile manipulator (MM) in the presence of parameters' uncertainties, and nonlinear dynamics coupling effects of the MM system. The control scheme consists of a nonlinear extended state observer (NESO) and a nonlinear proportional derivative (PD) controller. Based on the Lagrange formulation, a dynamical model of the MM is formulated, where external disturbances and modelling uncertainties are assumed to be part of the 'total disturbance' which is estimated with an observer and rejected online in the control law. Since the proposed controller cannot be performed unless the full transformed state vector of the system model is available, an NESO is designed to estimate the transformed state vector as well as the uncertainties. The nonlinear PD controller utilises the state estimated by the NESO, and the effect of uncertainties is cancelled online by the control input. Experimental results of the MM proposed tracking controller show its validity and efficiency.