Planar cargo control of elastic ship cranes with the "Maryland Rigging" system

This article concerns cargo pendulation control of an elastic ship-mounted crane using the Maryland Rigging system. The boom luff angle, the length of the upper cable, and the position of its lower suspension point are used as inputs to control the planar vibrations of the elastic boom and the pendulation of the payload. The disturbances acting on the ship are represented by the rolling displacement of the ship due to sea motions and the force acting directly on the payload. The dynamic of the crane is described by a multi-model problem depending on the current values of the cable length and boom luff angle. Accordingly a variable-gain observer and a variable-gain controller are designed. The controller uses the estimated states and the measured roll angle to create the required damping and to compensate for the rolling motion of the ship. Simulation and experimental results showed that the expressed control strategy per-forms very well and has a significant effect in suppressing the vibrations for different operating conditions and payload masses.