Winch/Crane; Motion Compensation Control 1

[DarkWater]

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.  

 

[LTD]

Dark,<br><br>How big is the vessel?&nbsp;&nbsp;A purely mechanical solution might be something along the lines of &quot;rocker stoppers&quot; used to stablize boats at anchor.<br><br>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.&nbsp;&nbsp;All bets are off if you are towing cables though.<br><br>Your choice of vessel configuration could be important too.&nbsp;&nbsp;There are some smaller SWATH types, or even catamarans that are far more stable than small boats.<br><br>Submarines (even something you tow) are of course very stable in the Sea.<br><br>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.&nbsp;&nbsp;Any other location will involve a lot of unnecessary calculations in real time.&nbsp;&nbsp;If you locate the end of the boom near the vessel's roll axis (pitch too?) then you also negate these factors too.<br><br>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.<br><br>The Brittish were developing a &quot;sky-hook&quot; crane to recover their Sea Harrier attack aircraft back to their carriers.&nbsp;&nbsp;The thing would reach over the side of the rolling ship and &quot;gracefully&quot; grab the damn plane &quot;by the scruff of the neck&quot; and swing it onto the deck.&nbsp;&nbsp;Note that the arm would have to gracefully transition from it's end being motionless in space to motionless in relation to the deck...<br><br>I haven't seen anything on this since about 1989 - check Avaition Week.<br><br>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.<br><br>Hey!&nbsp;&nbsp;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 !<br><br>Of course, at that point you could just monitor tension in the cable too.<br><br>Fair Winds and following seas!<br>Larry<br><br>