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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