Vector Field-Based Guidance for Planar Smooth Path Following of a Small Unmanned Helicopter

This study investigates a guidance method that will allow the small unmanned helicopter to follow the predefined horizontal smooth path. A stable nonlinear guidance law, which needs the information of the inertial position and groundspeed of the helicopter and the implicit function of the desired path, is designed to generate the reference course rate command based on the concept of the vector field. The asymptotic approximation to the desired path with bounded following errors has also been demonstrated by using the Lyapunov stability arguments. Some conditions for guaranteeing the stability have been extended. Simulations on following four types of planar paths, i.e., the square, circular, elliptic, and cubic curve paths, have verified the effectiveness of the proposed method. The predefined square path following performance of the proposed vector field-based method is compared with another two guidance laws, which are based on the PD-like and fuzzy logic control. The comparison shows that the proposed method can guide the helicopter to follow the predefined path most smoothly. The maximum overshoot by using the proposed method is less than 0.016 meters, while those by using the other two methods are all larger than 0.80 meters. Moreover, the vector field-based method will cost the least time for the vehicle to converge to the predefined path.