This article presents an offshore-simulated loading and unloading of a payload from a floating platform to a fixed structure. The experiments are performed in a dry-lab, where a Stewart platform is used to simulate the motion of the vessel. A hydraulically actuated vehicle loader crane is used to perform the tasks of payload transfer. The crane includes a hydraulic winch where the wire force is measured by a load cell. A mathematical model of the winch is derived and is experimentally verified. The control strategies include a heave compensation and a constant tension mode. A motion reference unit is used to generate the reference motion of the moving platform. Experimental results show the wire force while performing the load cases. This paper shows the advantage of using a reference motion as a feed forward control reference, instead of only relying on the constant tension.
This paper presents the planned use of digital displacement high torque low speed motors to drive large winches in off-shore and maritime applications.
The digital displacement technology uses forced actuation of high- and low pressure valves for each cylinder chamber, i.e. valves are opened and closed by actuation forces independently of cylinder pressure and supply pressures. Motors equipped with the technology are well suited for low speed secondary controlled operation including start and stop. It also enables unloading of motor cylinders that are not needed to produce torque, whereby excellent efficiency at partial displacement is obtained.
A research project on application of multi digital motors on a winch with lifting capacity in the 150 t range is presented, and advantages of using such winch drives in off-shore and maritime lifting operations are discussed.
Positioning and metering are challenges in winch systems with traditional drives. A unique control scheme that allows very fine positioning of the motor shaft is presented. The performance of this method is shown in simulation and demonstrated with measurements on a motor.
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