Cooperative Transportation Using Rotorcraft: Swing State Estimation And Control

Abstract

A cooperative transportation scenario is investigated where two rotorcraft carry a suspended payload. First, equations of motion are derived according to the Lagrangian approach, provided the coupled slung-load system is modeled as a set of three point masses and two mass-less rigid cables. It is noted that the system is underactuated, with a residual degree-of-freedom characterizing payload swing motion. An observation model is derived where the oscillation angle is directly obtained from a minimal set of measured information which include the position of both the agents and their acceleration over the local horizontal plane. Data fusion is performed by a recursive algorithm in the form of a Fading Gaussian Deterministic filter, whose theoretical background was recently investigated by one of the authors. Validation is performed in a realistic simulation scenario where multirotors are modeled as rigid bodies in the presence of linear-elastic cables, aerodynamic disturbances, and rotor forces and moments obtained by Blade Element Theory. The estimated swing angle and rate are shown to be suitable feedback variables for payload stabilization tasks. To this end, a control law is proposed to simultaneously perform minimum-swing formation-keeping and trajectory-tracking maneuvers with benefits on flying qualities and overall energy demand.