Winches: Drive unit

Winch drive

The winch drive controls the winch wire in one of two control mode classes: length control or force control. Which is appropriate depends largely on the nature of the winch being modelled:

• Length control is appropriate for a constant speed winch. The winch tension then depends simply on the unstretched length of winch wire out, and the wire stiffness and damping properties.
• Force control mode is for modelling a (nominally) constant tension winch. Because such winches often deviate quite seriously from the constant tension ideal, facilities are provided for modelling winch deadband, stiffness, damping, and drag.

Deadband

A deadband of +/- this value is applied to the winch drive force between hauling in and paying out the winch.

Stiffness

This can be used to model, for example, winch hydraulic accumulators. It is the rate at which the zero-velocity winch force (the drive force applied when the winch is neither hauling in nor paying out) varies with the total unstretched length of winch wire paid out.

Damping

These terms can be used to represent damping in a winch's hydraulic drive system. They are linear damping coefficients $c\urm{i}$, $c\urm{o}$, giving rise to a damping force proportional to haul-in or payout velocity respectively.

Drag

These terms can be used to represent drag in a winch's hydraulic drive system. They are quadratic drag coefficients $d\urm{i}$, $d\urm{o}$, giving a drag force proportional to haul-in/payout velocity squared respectively.