农用无人机移动补给平台自主降落算法与试验

Investigation and Experiment on Autonomous Landing Algorithm of Agricultural Unmanned Aerial Vehicle Movable Supply Platform

为实现根据无人机作业位置改变中途补充能源或喷洒物的起降地点,增加无人机有效作业时间,提高无人机作业效率,设计了无人机移动补给平台。通过研究农用无人机自主降落过程,提出一种基于模糊逻辑和比例积分微分(Proportional-integral and derivative,PID)分段控制的农用无人机跟踪降落算法,该算法既拥有PID算法的高精度,又兼顾模糊控制算法响应速度快、超调量小、鲁棒性强的优点。目标轨迹跟踪预测由粒子滤波器跟踪算法和轨迹拟合算法相结合进行求解。仿真和现场试验表明,与单一的PID算法和模糊逻辑算法相比,分段控制算法能够把农用无人机对移动补给平台的跟踪误差缩小到6.7 cm以内,在移动补给平台上的降落精度控制在7.2 cm以内。

The movable supply platform of agricultural unmanned aerial vehicles(UAVs)can change the landing site of midway supplying according to the variation of the UAVs location.It was mainly focused on the autonomous landing of agricultural UAVs on movable supply platform.The main novelty was that a piecewise control algorithm which combined the fuzzy logic control and PID control was proposed to control the landing process.When the distance error between the agricultural UAV and the movable supply platform was larger than the preset threshold,the fuzzy logic control was used to control the landing process due to its quick response character.When the distance error was smaller than the preset threshold,the PID control was used due to its high precision character.The detailed control process was as follows,firstly,in order to increase the recognition accuracy of UAV on movable platform,the upper part of the movable platform was designed to be a structure symmetry“H”pattern and the lower part was designed to be a contrasting QR code pattern.The UAV could use the optical flow algorithm to detect the black and white points,such that the relative speed between UAV and the platform could be calculated.Secondly,the dynamic model of UAV was constructed and then transformed its coordinates to the global coordinates to calculate the position error between agricultural UAV and the platform.Thirdly,the particle filter tracking algorithm and fitting function was used to fit the movement path of the UAV.At last,the proposed control method was used to control the UAV move along the fitted path.Using correlation coefficient index the Matlab simulation results proved the superiority of the proposed control method in tracking step signal and sinusoidal signal compared with individual fuzzy control method and PID control method.Furthermore,field test proved the control method could reduce the tracking error between UAV and movable supply platform to no more than 6.7 cm and the landing accuracy on movable supply to no more than 7.2 cm.