Position estimation of tethered micro unmanned aerial vehicle by observing the slack tether

At disaster sites, the use of Micro Unmanned Aerial Vehicles (MUAVs) is expected for human safety. One application is to support first-phase emergency restoration work conducted by teleoperated construction machines. To extend the operation time of a MUAV, the authors proposed a powerfeeding tethered MUAV to provide an overhead view of the site to operators. The target application is to be used outdoors, so a robust and simple position estimation method for the MUAV is required. Therefore, in this paper, the authors propose a position estimation method for the MUAV by observing the slack tether instead of using the Global Positioning System (GPS), vision sensors, or a laser rangefinder. The tether shape is assumed to be a catenary curve that can be estimated by measuring the tether's length, tension, and outlet direction. To evaluate the proposed method, the authors developed a prototype of a helipad with a tether winding mechanism for the tethered MUAV, which contains a measurement function of the tether status. Some indoor experimental results proved the feasibility of the proposed method.