Abstract
The fully autonomous operation of multirotor unmanned air vehicles (UAVs) in many applications requires support of precision landing. Onboard camera and fiducial marker have been widely used for this critical phase due to its low cost and high effectiveness. This paper proposes a six-degrees-of-freedom (DoF) pose estimation solution for UAV landing based on an artificial marker and a micro-electromechanical system (MEMS) inertial measurement unit (IMU). The position and orientation of the landing maker are measured in advance. The absolute position and heading of the UAV are estimated by detecting the marker and extracting corner points with the onboard monocular camera. To achieve continuous and reliable positioning when the marker is occasionally shadowed, IMU data is fused by an extended Kalman filter (EKF). The error terms of the IMU sensor are modeled and estimated. Field experiments show that the positioning accuracy of the proposed system is at centimeter level, and the heading error is less than 0.1 degrees. Comparing to the marker-based approach, the roll and pitch angle errors decreased by 33% and 54% on average. Within five seconds of vision outage, the average drifts of the horizontal and vertical position were 0.41 and 0.09 m, respectively.
Highlights
With the rapid development of micro-electromechanical systems (MEMSs) and high-performance flight control processors, applications and research of multirotor unmanned air vehicles (UAVs) have received increasing attention worldwide
GNSS and high-precision fiber-optic inertial measurement unit (IMU) (POS320, MAP Space Time Navigation Technology Co., LTD, Wuhan, China) integrated navigation systems were used as references for the pose
The camera and consumer grade MEMS IMU (ICM20602)-integrated navigation system was the system under test
Summary
With the rapid development of micro-electromechanical systems (MEMSs) and high-performance flight control processors, applications and research of multirotor unmanned air vehicles (UAVs) have received increasing attention worldwide. Due to the unique structure and stability, multirotor UAVs are widely used in precision agriculture [1,2], rescue [3], surveillance [4,5], etc These applications pose new challenges for the precision landing of UAVs [6]. Decimeter-level positioning results can be obtained by a consumer-grade dual-frequency GNSS receiver with sufficient satellites [10,11], in areas with low satellite observation such as city canyons and forests, positioning errors will increase. It is totally unavailable for indoor applications. E.g., precision agriculture, we Sensors 2019, 19, 5428; doi:10.3390/s19245428 www.mdpi.com/journal/sensors
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