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Winch/Crane; Motion Compensation Control

Winch/Crane; Motion Compensation Control

Winch/Crane; Motion Compensation Control

(OP)
Hi! I'm currently seeking for any material related to motion control systems using acceleration sensors/clinometers. The problem is to compensate roll/heave and pitch movement of small vessels during subsea deployment of sensors. Due to my information this can be done by fast automatic pay-in/out of certain winch cable length or moving a hydraulic crane jib up and down. Any hint's concerning publications or further contacts about motion control systems and control software are very welcome.  

RE: Winch/Crane; Motion Compensation Control

Dark,

How big is the vessel?  A purely mechanical solution might be something along the lines of "rocker stoppers" used to stablize boats at anchor.

These are large surface area dampers that resist motion through the water - they could be placed all along your cable's depth without too much trouble, and they would stabilize it passively.  All bets are off if you are towing cables though.

Your choice of vessel configuration could be important too.  There are some smaller SWATH types, or even catamarans that are far more stable than small boats.

Submarines (even something you tow) are of course very stable in the Sea.

It would seem to me that if you want to go the dynamic compensation route, then the simplest place to mount your 3 axis sensor would be on the end of the boom, right near the exit of the cable.  Any other location will involve a lot of unnecessary calculations in real time.  If you locate the end of the boom near the vessel's roll axis (pitch too?) then you also negate these factors too.

Simplify the mechanical system and geometry as much as possible, because sea states are not simple problems, and require a huge margin of safety and overload considerations.

The Brittish were developing a "sky-hook" crane to recover their Sea Harrier attack aircraft back to their carriers.  The thing would reach over the side of the rolling ship and "gracefully" grab the damn plane "by the scruff of the neck" and swing it onto the deck.  Note that the arm would have to gracefully transition from it's end being motionless in space to motionless in relation to the deck...

I haven't seen anything on this since about 1989 - check Avaition Week.

If you can orient your cable pay-out placement to reduce the effects of pitch and roll, you should be able to rig something very simple with an accelerometer.

Hey!  I just thought of this - if you rig the accelerometer in a way that it's always tangent to the cable as it exits, you could do this with a single axis !

Of course, at that point you could just monitor tension in the cable too.

Fair Winds and following seas!
Larry

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