Lifting Equipment - Uneven lift

[UGMENTALCASE]

Afternoon,

I have a 3 leg lifting device which will lift a component in two states. Open state is a straight foward lift. The component could also carry a unit on one side of it, which would affect the lift. So my 3 leg lifter has an offset lifting hole to cater for the offset weight. My question is what function can I use in NX 7.5 to determine where the C of G would be when lifted from each lifting point? I've tried a few things but don't have a license for it.

Thanks in advance

 

[jerry1423]

THe CG will never change, no matter what the orientation of the part is.

 

[capnhook]

The CG of the assembly WILL change, when this assembly carries "a unit on one side of it".

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[jerry1423]

oh yea, that's right
Yes, you can use NX to find the CG.
In the model:
analysis -> measure bodies -> asoociative (toggle on) -> pick the bodies in the assembly that you need for the lift
The CG will show as a point in the assembly model. In very large assemblies it may be hard to find. Naturally look close to where you think the CG will be.
There will be a Body measurement feature in you Part Navigator. By highlighting that you may find the point easier.

 

[KhimaniMohiki]

Under Measure bodies>Annotation you can create principal axes, then create a CSYS on the principal axes which can be used to locate lifting points

Khimani Mohiki
Design Engineer - Aston Martin
NX8.5

 

[UGMENTALCASE]

Cheers Guys, yes I have got this far no problem. What I have is the point where there is extra weight added to the assembly there is another lifting hole to use when the extra weight is on the assembly, but when I have the new c of g when the extra weight is applied, is there an easier way of checking where the hole should be? Or would it be a case of measuring the error between the two CSYS and that's how much I move the hole? Or is there a way where you can simulate out if being lifted on the 3 points? What I'm saying is, when I have positioned my hole for lifting the tool with the extra weight, how would I know how it will react once lifted?

Or am I talking about something that doesn't exist?!?!?!

 

[jerry1423]

so what you want to know how much tension is on each of the three cables ?

 

[UGMENTALCASE]

Well, if you pick something up with an even lift, the part will be horizontal (so to speak). Then you add the weight on the side, and pick it up from the same 3 lifting points it will be an uneven lift. So is there anything in NX where you can check that when I move the lifting hole to cater for the uneven lift (to make it an even lift again) it will show you whether or not it will lift horizontal?

Does that make sense?

 

[JohnRBaker]

What you do is use the Measure Body to create the CG of the original assembly which will include an associative Point object (as described above by several posters). If you position your lift point so that the vector formed by the main lifting cable passes through this Point the load will not move when lifted.

Now add your additional Component(s) and then go back and edit the 'Body Measurement' feature, that you will find in the Part Naviagtor' and while in the Edit dialog, select the newly added Component(s) which will add them to the measurement feature. After selecting OK the CG Point will move to it's new location. Now all that you have to do is move the arrangement of cables so that the main lifting cabled is again aligned with the location of the Point and your load will still be stable when lifted.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
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