Anti-Sway Crane.

strantor

Joined Oct 3, 2010
6,782
I use a gantry crane like that here in my shop, and I don't have any problems with the load swinging when I lift, except when I do not have the crane centered over the object's center of gravity.

When you lift something from a position not over it's center of gravity (or even worse, not even directly over the object at all), as soon as it's free of the friction force of the ground, it immediately seeks to center itself under the crane. The result, as we all know, is positive overshoot, followed by negative overshoot, followed by positive, and so on... (swinging).

So, just get your crane centered properly before you lift.

EDIT:
if I am lifting something that I cannot identify it's COG; for example your 1m cube, which may be a box of unknown, unevenly loaded contents, I lift from the visual center, just little bit of upward motion but not all the way off the ground. When the box just barely begins to lift up, it will start to slide a bit on the ground (one corner will drag). This partially-engaged friction on the ground greatly dampens the oscillations compared to had I just quickly lifted it up off the ground. This brief period need only last a second or two, then you can start lifting up. Once you've got the technique down, it does not add any appreciable time to your routine.
 

strantor

Joined Oct 3, 2010
6,782
There is many links on Google 'crane anti-sway control' see Images.
It is the same or similar principle to the inverted pendulum I mentioned.
It will definitely require some motor controller of some kind as the on/off of the normal contactor will not be precise enough.
Here is one.
http://www.smartcrane.com/SmartCrane/About_Anti-Sway.html
Max.
That's talking about sway while traversing, and particularly at the end of traverse. That's what I expected OP to be talking about when I read the title of the thread, but as I read it, he hasn't even mentioned traversing yet; his issue is upon lifting from the ground.

The sway while traversing, and upon stopping, is also a human technique. It is not hard to manage the sway.
  • start traversing in a given direction at the max speed you intend to traverse. the load will fall behind the crane block.
  • When the load stops falling behind the crane block, and starts to speed up, stop the crane.
  • just as the swinging load passes under the crane block, start the crane again and go full speed.
  • Now the crane block and load speed will be the same, and will remain the same indefinitely, all the way across the shop.
  • just before you reach your destination, stop the crane. the load will continue.
  • when the load gets just over the destination spot, quickly advance the crane block to be directly over the top of the load.
  • time all this right (it's easy after some practice) and you will have zero sway during starting, traversing, and stopping. No automatic control needed whatsoever.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
That's talking about sway while traversing, and particularly at the end of traverse. That's what I expected OP to be talking about when I read the title of the thread, but as I read it, he hasn't even mentioned traversing yet; his issue is upon lifting from the ground.
The examples i show would work on lifting or traveling pretty much the same principle involved. The load is swinging.
Max.
 

crutschow

Joined Mar 14, 2008
34,285
Obviously if the load sways sideways because the load was off-center to the side when initially lifted, then there is no way to compensate for that.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619

strantor

Joined Oct 3, 2010
6,782
Obviously if the load sways sideways because the load was off-center to the side when initially lifted, then there is no way to compensate for that.
Yes there is; I described it already, the method by which I compensate for it:
if I am lifting something that I cannot identify it's COG; for example your 1m cube, which may be a box of unknown, unevenly loaded contents, I lift from the visual center, just little bit of upward motion but not all the way off the ground. When the box just barely begins to lift up, it will start to slide a bit on the ground (one corner will drag). This partially-engaged friction on the ground greatly dampens the oscillations compared to had I just quickly lifted it up off the ground. This brief period need only last a second or two, then you can start lifting up. Once you've got the technique down, it does not add any appreciable time to your routine.
 

strantor

Joined Oct 3, 2010
6,782
I think the idea is to do this function, without need of skill.

Fast turnover.
If you're right, then I see that as all the more reason to go out into the shop and play with the crane for a few hours. That's all the time it took me to master the art of humanoid anti sway crane control.

Personally, i got the impression he was trying to automate some process involving the crane; ex: "pick up from conveyor #1, travel to conveyor #2, deposit, travel to conveyor #1, repeat"
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
I do not really see prevention of load sway with a crane with On/Off motor control when stopping, especially H.S. gantry's unless rapid stop start jabs by the operator, a VFD slow down would cure this to some extent.
There would be no need for the fixes shown in #24.
Max.
 

BR-549

Joined Sep 22, 2013
4,928
That's true Max...for electronic control. But like strantor says....if a human plays with moving mass for a while, he can do that and smoke at the same time.

And when you restore smoking rights, no more turn over.
 
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