Position control of a flexible cable gantry crane: theory and experiment

Cranes are commonly used at construction sites and shipyards to transport heavy payloads. The swinging of the payload during and after transit poses a major safety and site efficiency problem. The objective of this research is to design implementable stabilizing controllers for a distributed model of the crane system. The governing partial differential equations of a horizontally-translating gantry, flexible cable, and payload are derived. A control law, based on Lyapunov theory, is developed to dampen the vibrations of the payload using the gantry motor, gantry position and velocity sensors, and a cable departure angle sensor. An exact modal analysis of the closed loop system is performed assuming constant tension and no damping. A Galerkin approach is used to incorporate spatially varying tension and damping. Design of the control gains is demonstrated using a root locus approach. The theory is successfully tested on an experimental mockup of the gantry crane system. The controller significantly reduces the time required for the payload oscillations to damp out.