Stability Considerations in Quaternion Attitude Control using Discontinuous Lyapunov Functions

Unit quaternions are a powerful tool for singularity free analysis and the control of arbitrary amplitude motion in a three-dimensional space. The authors present the use of proportional derivative quaternion feedback stabilisation for relative motion attitude control. Global asymptotic stability is guaranteed by defining a particular Lyapunov function and formal requirements are established. Conditions for a finite time control are also presented

Pendulation control of an offshore crane

This paper considers a control system for a crane that reduces pendulation of suspended loads in offshore lifting operations. The modelling of the ship crane is studied and an anti-pendulation arm is designed and proposed. Two different types of models are derived, one based on torque and one kinematic. For the torque model, Lyapunov analysis and non-linear control design is applied on the vertical plane. Linear control design techniques for the linearized kinematic model are applied in both vertical and horizontal planes. These techniques are based on linear quadratic Gaussian (LQG) and generalized predictive control (GPC). The advantage for the linear control designs is the explicit use of the vessel dynamics and sea wave disturbances in the control design that considerably improves the controlled pendulation of the crane. Design issues, simulation results and comparison studies are considered