Abstract
A safe and rapid formation generation is of great importance for the cooperation performance of the multiple unmanned helicopters. The trajectory optimization and control is the key problem in the process of the formation generation. To achieve this goal, a novel safe formation generation strategy is proposed through trajectory optimization and tracking control. First, the rapidly-exploring random tree (RRT) algorithm is applied to obtain the initial guess to satisfy the requirement of rapid solution. Then, the Gauss pseudospectral method is used to transform the optimal control problem to the nonlinear programming (NLP) problem and the sequence quadratic programming (SQP) method is utilized to gain the optimal trajectory combined with the initial guess. Second, a finite-time sliding mode controller is proposed to ensure the finite time trajectory tracking in the presence of model parameter uncertainties and unknown external disturbances. Finally, the numerical simulation is provided to show the effectiveness of the proposed formation generation strategy for unmanned helicopters formation.
Highlights
With the vertical takeoff, landing, air hovering and flexible flight characteristics, unmanned helicopter has been widely used in military and civilian fields, such as target reconnaissance, disaster relief, strike power patrols and agricultural plant protection [1]–[4]
Considering the unmanned helicopters formation control problem, since the control frequency of the attitude inner loop is much shorter than the position outer loop, the principle of multi-time scale can be used to prove the finite time stability for the entire closed-loop system
The optimal path point computation time of rapidly-exploring random tree (RRT) algorithm is about 0.1s, and the time for the pseudospectral method to solve the optimal trajectory of 10 unmanned helicopters formation is about 0.9s
Summary
With the vertical takeoff, landing, air hovering and flexible flight characteristics, unmanned helicopter has been widely used in military and civilian fields, such as target reconnaissance, disaster relief, strike power patrols and agricultural plant protection [1]–[4]. B. Zhang et al.: Trajectory Optimization and Finite-Time Control for Unmanned Helicopters Formation. A controller design method using nonsingular terminal sliding mode surface and extended state observers (ESOs) was proposed to solve the finite-time convergence problem of system states in course of the transition flight control for a small tilt rotor UAV [37]. In the past few years, many collision avoidance algorithms have been designed of the formation generation process for spacecraft and UAVs. A hybrid particle swarm optimization and genetic algorithm was proposed to solve formation reconfiguration problem by Duan [39]. A new finite-time tracking controller based on sliding mode method combined with the potential function method is designed to achieve the high precision control performance.
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