An on-board pan-tilt controller for ground target tracking systems

For a ground target tracking system using an unmanned helicopter, an on-board pan-tilt controller is proposed to adjust the attitude of the camera, so that to keep the target staying at the center of the image plane when the target is in sight. When the target is temporarily out of view due to various reasons, the designed controller will make the camera quickly re-capture the target by estimating its state and then regulating the orientation of the camera correspondingly. Specifically, a novel state transformation is firstly introduced to make the error system independent of the target image. Subsequently, a nonlinear pan-tilt controller is designed for the transformed error system. Lyapunov techniques are then employed to prove that the target tracking error in the image plane is driven to zero exponentially fast. To facilitate the implementation of the constructed controller, a visual estimator is also utilized to obtain the state information of the target even if it is occasionally out of the view of the camera by introducing an effective nonlinear filter. Simulation results are provided to validate the performance of the presented control system.