High-Precision Trajectory Tracking Control for Free-Flying Space Manipulators With Multiple Constraints and System Uncertainties

Precise motion control for free-flying space manipulators (FFSMs) plays an important role in space missions. However, system uncertainties and various physical constraints severely degrade the trajectory tracking performance. In order to tackle these difficulties, a fully actuated system approach (FASA)-based composite controller is developed, which consists of a nonlinear disturbance observer (NDO) in the inner loop and a high-precision trajectory controller in the outer loop. More specifically, the NDO is designed for tackling system uncertainties. Moreover, a gradient-based optimal parameter tuning method is developed for tuning the control gains of the composite controller. The satisfaction of physical constraints, which include angular constraints and actuator constraints can be guaranteed by the gradient-based optimal parameter tuning method. Therefore, the high-precision trajectory tracking performance, optimal control gains, angular constraints, and actuator constraints can be ensured simultaneously. Simulation results are presented to demonstrate the effectiveness of the proposed method.