Singularity-free 3-D path following control for model-scaled autonomous helicopters

This paper presents a singularity-free controller for 3-D path following of model-scaled autonomous helicopters. The reference path is expressed by a parameterized regular curve. The system is stratified as the inner-outer loop. Each loop is designed independently based on time-scale separation principle. During the outer position loop, the controller is constructed with saturation function to realize path following and obviate singularity in deriving desired attitude by suitable parameter selection, and the time evolution along path is designed such that the flight speed converges to desired value. The inner attitude loop is represented by Euler angle, and the controller is constructed with backstepping technique and barrier Lyapunov function to realize attitude tracking meanwhile obviating the singularity when pitch reaches ±
^π
. The simulation is provided to confirm the theoretical results.