Planning and Control of Aircraft Ground Movement Operations With Towbarless Robotic Tractors

This article studies the automation of aircraft ground movement operations using towbarless robotic tractors. The tractor-aircraft system is modeled as a car-like mobile robot with an off-hooked trailer, in which an accurate dynamic model of the tractor-aircraft system is employed. The primary objective of this study is to determine the control inputs and the resulting collision-free trajectories to steer the aircraft from the initial to the final position, under the assumption that the model of the system and the positions of the obstacles are known. This trajectory planning problem is formulated as an energy-time optimal control problem, which is solved using a pseudospectral knotting numerical method. The effects of the uncertainty in the weight of the aircraft on the solution of the planning problem are also quantified. Since, in general, the tractor-aircraft system moves backwards during ground movement operations, the issue of jackknifing is also addressed. Therefore, the secondary objective of this article is to deal with the problem of tracking the planned trajectory while preventing jackknifing. The trajectory tracking problem is solved using a Jacobian linearization of the offset dynamics about the planned trajectory, in which the optimal control inputs are used as feedforward terms to improve tracking precision.