针对四旋翼飞行器在依靠地标导航完成动平台自主降落任务中存在的目标易丢失、地标定位死区大和降落可靠性差等问题，设计了一种基于复合地标导航的动平台四旋翼飞行器自主优化降落系统。该系统以圆环地标和二维码构成复合地标来解决仅用单一地标定位时存在的定位死区大和定位范围小等问题。针对地标识别丢失、动平台车轮打滑和码盘标定不精确等问题，建立动平台的精确运动模型同时考虑码盘包含未知测量偏差，基于扩展卡尔曼滤波器实现了对动平台连续位姿的在线估计。最终，基于动平台位姿估计结果以最小Jerk指标设计降落轨迹和降落策略，实现了四旋翼飞行器在动平台上高效平稳的降落。为验证所提系统的有效性，设计了仿真和实际降落实验，验证了所提复合地标实现摄像头距离在0.5~6.0 m内的综合完整定位；所设计的动平台状态估计器能在码盘存在未知测量偏差的情况下准确估计出平台的实时位姿，同时所提自主优化降落策略和轨迹规划算法保证了可靠的动平台降落。
To address visual loss, big dead zone, and low landing reliability in marker-based localization, a moving platform landing system based on hybrid landmark is proposed. The circular ring tag and two-dimensional tag are combined together to provide precise localization of camera in large space. An estimator based on extended Kalman filter is proposed to estimate the pose of moving platform online. Meanwhile, the unknown measurement bias of encoder is considered in the system model to improve the robustness of estimator under wheel-clip and reduce the calibration error from encoders. Finally, based on the statement estimation, an optimal landing strategy is designed using the minimum Jerk trajectory, and the efficient and stable landing of the quadrotor on the moving platform is realized. To verify the effectiveness of the proposed landing system, several simulation and actual landing experiments are given. The experimental results show that the hybrid landmark has small dead zone and realizes the complete and comprehensive localization from 0.5 m to 6.0 m, the estimator can obtain accurate pose of the moving platform under the unknown measurement bias of encoder, and the proposed optimal landing strategy can realize reliable landing on the moving platform.
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