NX9 center of irregular 2D shape 1

[Karlis]

Hi everyone,
I have a problem that I am unable to find a solution by myself.
I have a planar sketch, that contains 4 points and a closed spline drawn through all of these points, forming something close to ellipse or circle, but not quite. What I would like to do, is to create a point, that would sit right in the center of this shape and regenerate automatically, every time I change the shape. I have tried to use "bounded plane surface" command on the spline, to create a section, then plant a "point on face" on it, and tried messing with the settings for "U and V" to locate the point in the mass center of this surface, but with no luck.
Basically I have a lot of these irregular shapes (cross-sections) and I would like to draw a centerline through them all. But the trick is to have it automatically updating after every change in the cross-sections.
Is that possible in NX9?
Thanks in advance

 

[Xwheelguy]

Do those 4 points lie at the peaks of the shape (for ellipsoid, the major and minor) and is each point 90° apart?

Tim Flater
NX Designer
NX 9.0.3.4 Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB

 

[Karlis]

Yes, they lie on the peaks, but they are not 90 degrees apart. And I'm afraid that the shapes could change so that the points would lose their peak status.
I think a better way would be locating a point in the mass center of a two-dimensional shape..

 

[cowski]

Create an extrusion from the curves (using the symmetric distance option) then use an associative "measure body" feature to measure the solid body (use the option to create a point at the CoG). Hide the body and the point will show the "center" of the curves.

www.nxjournaling.com

 

[Karlis]

That sounds very appealing Cowski!
The only thing I cant figure out is:
When using measure bodies, where exactly is the option to create a point at center of gravity? (CoG)

 

[cowski]

A point at the CoG will be created as long as the "associative" option is turned on.

I was going from memory and thought that the "create principle axes" option had to be turned on to get the point, but this is not the case. Sorry for any confusion.

www.nxjournaling.com

 

[Karlis]

It worked!!
Thanks a lot Cowski. And thank you Xwheelguy for the help too.

 

[Karlis]

Alright now I'm into another problem with the method Cowski suggested.
Everything works fine until I change my cross sections.
The symmetric extrude updates,
The body measurement also updates,
But the principal axes (center of gravity) stays right where it was.
And when I try to edit the body measurement, to recreate the axes, the option "create principal axes" is greyed out.
Any ideas on how can I make this update properly?
Thanks.

 

[JohnRBaker]

In NX 9.0, only the 'Point' at the mass center is associative. However, in NX 10.0 this function was enhanced so that both the 'Point' and the 'Principle Axis' objects update when the shape/size of the measured body is modified.

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

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

 

[cowski]

The point object that represents the center of gravity of the extrusion will update with the body measurement feature. The principal axes are not associative and will not update when the model does. If you want/need to update the axes, delete the current "principal axes" csys object and use the "measure bodies" function again; turn off the associative option or you will end up with another measure body feature in the part navigator tree.

www.nxjournaling.com

 

[Karlis]

Well since the CoG point is all I need really, is there a way how to attach anything to it? For example a spline, representing a centerline through a set of irregular sections.
Since I will have 8 of these sections, it would seem a bit tiring to recreate the "measure body" feature every time I change the sections.
I will change the sections very often in order to meet a specific goal. Is there a way? Or should I think of upgrading to NX10?

 

[cowski]

Well since the CoG point is all I need really, is there a way how to attach anything to it? For example a spline, representing a centerline through a set of irregular sections.

Easy; start the studio spline command, choose the "through points" type option, pick the degree of the spline you want to create (if you are not sure, set it to degree 3), pick the points, press OK when done.

www.nxjournaling.com

 

[Karlis]

Sorry, I guess I didnt explain myself clearly.
These points, you just referred to - I can not generate them. Either I do not know how, or the only thing I can generate is the "principal axes" which are coordinate systems and do not contain any points.
Basically, I do not know how to create a point which is CoG and updates every time I change the section.

 

[Karlis]

And for some reason, they just appeared now.
Thats a good thing I tried that again!!
Alright mates, it works. Thank you for the help

 

[JohnRBaker]

Keep in mind that the 'Point' created at the mass center IS the Measurement feature. Selecting the 'Point' on the screen IS selecting the Measurement feature. That being said, this 'Point' is also a valid object for any other function that requires the selection of a point object.

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

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