Command shaping and closed-loop control interactions for a ship crane

This paper presents a control method for suppressing payload swing in rotary, ship-based, boom cranes. The crane configuration studied consists of a payload mass that swings on the end of a spherical pendulum of varying lift-line length (hoisting). The lift-line is attached to a boom capable of elevation (luffing). The boom is attached to a column that can rotate about an axis perpendicular to the ship's deck (slewing) Positioning of the payload is accomplished through luff, slew, and hoist commands issued in real-time by an operator. The control strategy for mitigating swing blends the operator's command shaped inputs with a coupled nonlinear controller compensating for sea-induced crane base motion and external swing disturbances. Swing angle feedback is supplied by a sensor attached at the lift-line attachment point. Sea-induced base motion is assumed to be known through the use of an inertial measuring unit on the ship. Analytical and experimental results are presented regarding the interaction of the nonlinear swing feedback controller and the command shaping control.