Autonomous Landing of Fixed-Wing UAV in a Stationary Net - Path and Navigation System
Kjetil Hope Sørbø · BIBSYS Brage (BIBSYS (Norway)) · 2016
This thesis present a path and navigation system, used in a autonomous net landing system for a fixed wing Unmanned Aerial Vehicle (UAV). A landing path of a UAV can be constructed as a straight line path, but in order for a UAV to follow the landing path it must be in a position from which it has a feasible path to the start position of the landing path. This motivates the development of a approach path logic towards the landing path entry position from any initial start position in the air space. In addition to a path generation system the UAV require a robust high accurate navigation system. This is accomplished by applying Real Time Kinematic GNSS (RTK-GNSS), which can provide centimeter level position accuracy. A shortcoming of the RTK-GNSS system is that it may loose its lock on satellites leading to loss of functionality. In this work this is compensated for by introducing a secondary Global Navigation Satellite System (GNSS) system. To handle a RTK-GNSS drop out a robust RTK-GNSS system is proposed, where previous valid RTK-GNSS position solutions are fused together with the secondary GNSS system, to be used as a compensator for the external navigation system. The compensator is designed to enable the external navigation system to achieve the same position accuracy level as the RTK-GNSS system for a short duration, until the RTK-GNSS is either reconnected or completely disconnected. With the compensator the UAV navigation system becomes robust against short drop out of the RTK-GNSS, and the availability of the RTK-GNSS is prolonged. Experimental testing, in addition to Software In the Loop (SIL) verification, of the ability of UAV to land in a stationary arbitrary placed net has been performed. For improved navigation and performance, an mobile sensor unit have been utilized to provide the required position data of the net. This sensor unit was used during testing, where it showed to provide the intended contribution.