Dynamics, Control, and Estimation for Aerial Robots Tethered by Cables or Bars
This work addresses control and estimation challenges for tethered aerial robots, which is an incremental advancement in robotics with potential applications in inspection, surveillance, or payload delivery.
The paper tackles the problem of controlling an aerial robot tethered to the ground by a passive cable or rigid link, providing a thorough characterization of its nonlinear dynamics and designing globally convergent nonlinear observers and controllers for trajectory tracking, with numerical tests showing robustness under various non-ideal conditions.
We consider the problem of controlling an aerial robot connected to the ground by a passive cable or a passive rigid link. We provide a thorough characterization of this nonlinear dynamical robotic system in terms of fundamental properties such as differential flatness, controllability, and observability. We prove that the robotic system is differentially flat with respect to two output pairs: elevation of the link and attitude of the vehicle; elevation of the link and longitudinal link force (e.g., cable tension, or bar compression). We show the design of an almost globally convergent nonlinear observer of the full state that resorts only to an onboard accelerometer and a gyroscope. We also design two almost globally convergent nonlinear controllers to track any sufficiently smooth time-varying trajectory of the two output pairs. Finally we numerically test the robustness of the proposed method in several far-from-nominal conditions: nonlinear cross-coupling effects, parameter deviations, measurements noise and non ideal actuators.