Constant tension load-transferring apparatus and method
AssigneeWestern Gear Corporation
InventorsDuncan Bell, Donald A. Swanson, John P. Veale
Life of this patent
Estimating the term…
Abstract
An elongated pipe is held in a first constant tension mechanism and then, while the tension is maintained, the pipe load is shifted to a second constant tension mechanism by automatically correlating the declining tension force of the first constant tension mechanism with the increasing tension force of the second constant tension mechanism until the pipe is completely shifted to the second constant tension mechanism.
Claims11
Control apparatus for shifting tensioned loads between two load-transporting mechanisms, comprising;
- a first load-transporting mechanism including first means for holding a load, first powered means for moving the first load-holding means along a path to move the load, and first control means for varying the velocity and direction of the first load-holding means in order to maintain a desired tension in the load,
- a second load-transporting mechanism including second means for holding a load, second powered means for moving the second load-holding means along a path to move the load, and second control means for varying the velocity and direction of the second load-holding means in order to maintain a desired tension in the load, and
- transfer control means operative for shifting the load exclusively from said first load-transporting mechanism to said second load-transporting mechanism without substantially varying the desired tension in the load.
A method for shifting tension loads between two load-transporting mechanisms, comprising;
- gradually reducing the load forces on a first load-transporting mechanism;
- and
- gradually increasing the load forces on a second load-transporting mechanism at a rate which causes the total forces on said first and second load-transporting mechanisms to be substantially constant.
A constant tension load-transferring apparatus comprising:
- a first load-supporting mechanism connected to said load including means for exerting a first axial force on said load for alternately paying out and retracting said load;
- a second load-supporting mechanism connected to said load including means for exerting a second axial force on said load for alternately paying out and retracting said load;
- and
- tension control means for gradually increasing said first force while gradually decreasing said second force and for maintaining the sum of said first and second forces substantially constant, whereby the tension in the load is substantially constant during the transfer.
An apparatus for transferring a length of conduit from a first conduit-supporting mechanism to a second conduit-supporting mechanism while maintaining the tension of said conduit substantially constant while the conduit is suspended from a vessel and is subjected to wave action and other dynamic forces, said apparatus comprising:
- transfer control means including means for generating a first desired tension signal which changes as a function of time from a value indicative of a preset tension in the conduit to a value indicative of substantially zero tension in the conduit, said transfer control means further including means for generating a second desired tension signal indicative of the present tension minus the tension indicated by said first desired tension signal;
- first tension sensing means for measuring the axial force exerted on said conduit by said first conduit-supporting mechanism and generating a first actual tension signal indicative thereof;
- second tension sensing means for measuring the axial force exerted on said conduit by said second conduit-supporting means and generating a second actual signal indicative thereof;
- first comparator means for comparing said first actual tension signal to said first desired tension signal;
- second comparator means for comparing said second actual tension signal to said second desired tension signal;
- first powered means associated with said first conduit-supporting mechanism and responsive to said first comparator means for paying out said conduit when said first actual tension signal is greater than said first desired tension signal and for retracting said conduit when said first actual tension signal is less than said first desired tension signal;
- and
- second powered means associated with said second conduit-supporting mechanism and responsive to said second comparator means for paying out said conduit when said second actual tension signal is greater than said second desired tension signal and for retracting said conduit when said second actual tension signal is less than said second desired tension signal, whereby said conduit-supporting mechanisms pay out and retract conduit in response to said wave action and other dynamic forces, thereby maintaining the tension of said conduit substantially constant during the transfer.
Dependencies are inferred from the claim text.