From Ellipsoids to Midair Control of Dynamic Hitches

TL;DR

This paper develops an ellipsoid-based kinematic model and a quadratic programming controller for precise, safe, and high-speed control of cable hitches created by multiple aerial vehicles, enhancing aerial cable manipulation capabilities.

Contribution

It introduces a novel ellipsoid-based kinematic model linking cable hitches to system dynamics and designs a CLF-HOCBF-QP controller for accurate and safe hitch control.

Findings

Stable high-speed tracking demonstrated in simulations

Effective enforcement of cable tension constraints

Precise control of hitch position and shape achieved

Abstract

The ability to manipulate and interlace cables using aerial vehicles can greatly improve aerial transportation tasks. Such interlacing cables create hitches by winding two or more cables around each other, which can enclose payloads or can further develop into knots. Dynamic modeling and control of such hitches are key to mastering inter-cable interactions in the context of cable-suspended aerial manipulation. This paper introduces an ellipsoid-based kinematic model to connect the geometric nature of a hitch created by two cables and the dynamics of the hitch driven by four aerial vehicles, which reveals the control-affine form of the system. As the constraint for maintaining tension of a cable is also control-affine, we design a quadratic programming-based controller that combines Control Lyapunov and High-Order Control Barrier Functions (CLF-HOCBF-QP) to precisely track a desired hitch position and system shape while enforcing safety constraints like cable tautness. We convert desired geometric reference configurations into target robot positions and introduce a composite error into the Lyapunov function to ensure a relative degree of one to the input. Numerical simulations validate our approach, demonstrating stable, high-speed tracking of dynamic references.