US 8,297,597 B2 · Method for lift compensation

Abstract

A method for lift compensation of an item (12) which is connected to a vessel (1) by means of a rope (4) which is coiled around the rope drum (6) of a lifting device (2), the lifting device (2) being provided with a heave compensator (20), a controller (30) of the heave compensator (20) controlling the effect of the driving device (32, 34, 42) of the rope drum (6) on the basis of a heave term and a deviation term, the method comprising: —bringing a correction term into the heave compensation when, because of environmental forces, the force on the rope (4) falls outside a first limit (d, e); and—leaving the correction term out when the force on the rope (4) is within a second limit (c, f), the second limit (c, f) being equal to or different from the first limit (d, e).

Claims17

Dependent claims

A method for lift compensation of an item connected by a rope to a lifting device disposed on a vessel, wherein the lifting device comprises a heave compensator arranged to control a speed of a rope drum, the method comprising:

with the heave compensator, controlling the rope drum of the lifting device according to a calculated contribution comprising a heave term and a deviation term, wherein the deviation term is calculated from a difference between a current position of the item and a selected position of the item;
monitoring a force on the rope;
and
bringing in a correction term into the calculated contribution for the heave compensator when the force is above a first upper limit or below a first lower limit, wherein the correction term is determined to feed rope faster from the rope drum when the force is above the first upper limit and to tighten the rope when the force is below the first lower limit.

1 more element

Dependencies are inferred from the claim text.

Method for lift compensation

Life of this patent

Method for lift compensation

Life of this patent

Abstract

Claims17