NX 8 COnstraining Assemblies to other Assemblies

[dabiz7]

Hello all,

new user to NX, like all other CAD jobs I have ever started, the boss said, "here's the machine, go to it !" No training budget, right !!!!!!!!!!!!!!!
Anyway, I do have about 13 years experience with Catia v4 and v5, so I have been picking NX 8 up pretty quickly.

One point I am having trouble with. Constraining asseblies to other assemblies. Consider an example, Assembly1 is a drive shaft with a U joint constrained in the yoke at the end of the shaft. Assembly2 is a transmissin with the yoke at the output end of the trans. Of course, the output yoke of the trans is constrained to the transmission, but is not fixed, it can spin about the output shaft axis.

Now what I would like to do is constrain these two assemblies together so that the combined assembly will maintain the correct kinematic relationship that I define with the constraints and will move in a correct manner based on the individual constraints of the seperate assemblies. Every time I try to do this now, I get a red constrain sysmbol and the parts do not move to the correct location.

If someone can point me to a good tutorial discussing constraining assemblies to other assemblies in NX 8, that would be great. Maybe I am just missing
a button to select. I can't believe this functionality does not exist in this level of software, I'm sure I am just not selecting something correctly.

Thanks, I hope I described my question correctly.

 

[JohnRBaker]

What you're looking for is referred to in NX as 'Overriding a sub-Assembly Component's position in a higher level Assembly'.

To learn more about what this can be used to do and how one would go about overriding the Components of a sub-Assembly in some higher level Assembly, simply open your NX Help document and do a search on 'Position Override'.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
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To an Engineer, the glass is twice as big as it needs to be.

 

[dabiz7]

Thank you for the reply

I did open the Help, it gave a minimal description of Position override
The instructions were that as a pre-requisite to Position Override, to go to Preferences --> Assemblies --> Interaction to Assembly Constraints
When I go to Preferences --> Assemblies, Interaction to Assembly Constraints is not in the list of options.
There are a bunch of options to select, but that isn't one of them. Any suggestions?
Is there an online source that describes this functionality in more detail?

 

[dabiz7]

Also, the instructions for Position override say that you can right click on the component assembly node
in Assembly navigator and select 'Override Position"....When I do this, that is not an option that shows up in the list
of commands to select

 

[JohnRBaker]

First let me apologize, the item which instructs you to...

"...go to Preferences --> Assemblies --> Interaction to Assembly Constraints"

...is incorrect as this was a left over from the pre-NX 7.5 era when you could still use either the older Mating Conditions or the then newer Assembly Constraints, and so this was simply making sure that you were in the correct positioning scheme. Note that starting with NX 7.5 the only positioning scheme available to you is to use Assembly Constraints, therefore this NX Help file entry is both obsolete and meaningless (this has been corrected for NX 8.5).

However, the ability to select a Component, either within the graphics window or from the Assembly Naviagtor and indicate that you wish to override its position, that is still what it is that you need to do. That being said, I suspect that I know why you're not seeing this option.

Perhaps we should start at the beginning. You need to understand that Component positions are being overridden in the CONTEXT of the higher-level assembly. This Component option is NOT defined inside of the owning Assembly, the assembly in which the parts were added as Components. What you have to do is to have the top-level Assembly set as your Work Part and the Components which you're selecting must be members of a sub-Assembly in that higher-level Assembly. Only then will you see the override option. And once you've designated a Component as having it's position 'overridden' then you can create a new Constraint, at that higher-level assembly, which will now be used to define that Components new position IN THAT ASSEMBLY ONLY. That is, this will have NO impact whatsoever on the Assembly which actually contains the original Component. In fact, you don't even need WRITE access to the sub-Assembly file in order to override the position of components in THAT sub-Assembly, but they will only be seen as overridden in that higher-level Assembly.

Anyway, I hope this helps clear-up why what you saw appeared to be misleading and why you didn't see what you should have seen all along.

One other thing that you must be aware of, in order to override a Component you must actually have the Assemblies module active. That is, if you go to the 'NX Start' pull-down menu, that there should be a checkmark next to the 'Assemblies' item on that pull-down menu.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[dabiz7]

I ma still checking on this, I got a simple example I made to Overide position, but I need to try it on a more complicated model.
My next problem, how do I constrain the assembly to stop moving when it detects an interference or clash with another part?
In Catia, this was easy, you could set your assembly to recognize interfernce and clash and your assembly would not move if it detected such a problem...How do i do this in NX 8 Assemblies???

What I have ia a multi-segment hydraulic cylinder that is extending and I would like to simulate the correct motion of the intermediate segments during the cylinder extension and retraction...

 

[JohnRBaker]

Once you've overridden the Component's position, but BEFORE you assign any new constraint try going to...

Assemblies -> Component Position -> Move Component...

...and at the bottom of the dialog, in the 'Settings' section, set the 'Collision Detection' option to 'Stop Before Collision'. Now when you drag the overridden Component you not be able to drag it past point where a collision would occur (you may have to acknowledge an initial 'collision' before you can actually move the cylinder, similar to what I did in the video below:

http://www.youtube.com/watch?v=M_2laN615vE

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.