Vertical motion compensation for a crane's load
AssigneeThe United States of America as represented by the Secretary of the Navy
InventorsSteven F. Naud, Max D. Weber, Lei Lani Lucero, J. Dexter Bird, III, Martin D. Fink, Christoph Hyder
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Abstract
A method and system are provided for reducing sea state induced vertical motion of a shipboard crane's load. Sea state induced vertical velocity of the crane's suspended load is determined as a function of: i) the horizontal radial distance the load extends from the crane's axis of rotation, and ii) motion of the ship at the crane's axis of rotation. The load is then moved vertically at a speed that is defined as being equal to the vertical velocity in a direction that is opposite that of the vertical velocity.
Claims8
A method of reducing sea state induced vertical motion of a shipboard crane's load, comprising the steps of:
- providing a crane mounted on a ship and pivotable about an axis of rotation, said crane suspending a load at a horizontal radial distance from said axis of rotation;
- determining sea state induced vertical velocity of said load as a function of vector components of said horizontal radial distance and motion of said ship at said axis of rotation wherein said motion includes pitch, roll and heave rates of said ship at said axis of rotation;
- and
- moving said load vertically at a speed that is defined as being equal to said vertical velocity in a direction that is opposite that of said vertical velocity.
A method of reducing sea state induced vertical motion of a shipboard crane's load, comprising the steps of:
- providing a crane mounted on a ship and pivotable about an axis of rotation, said crane suspending a load at a radial distance r from said axis of rotation;
- determining sea state induced vertical velocity v of said load where
- v=y(dφ/dt)−x(dθ/dt)+(dz/dt)
- where y is a first vector component of said radial distance r along a horizontal longitudinal axis of said ship passing through said axis of rotation, x is a second vector component of said radial distance r along a horizontal athwartship axis of said ship passing through said axis of rotation, dφ/dt is a pitch rate of said ship about said horizontal athwartship axis, dθ/dt is a roll rate of said ship about said horizontal longitudinal axis, and dz/dt is a heave rate of said ship at said axis of rotation;
- and
- moving said load vertically at a speed that is defined as being equal to said vertical velocity in a direction that is opposite that of said vertical velocity.
A system for reducing sea state induced vertical motion of a load suspended a radial distance from an axis of rotation of a pivotable crane mounted on a ship, said system comprising:
- means for determining sea state induced vertical velocity of said load as a function of vector components of said radial distance and motion of said ship at said axis of rotation wherein said motion includes pitch, roll and heave rates of said ship at said axis of rotation;
- and
- means for moving said load vertically at a speed that is defined as being equal to said vertical velocity in a direction that is opposite that of said vertical velocity.
Dependencies are inferred from the claim text.