Align axis to vector in NX 7.5

[DaSalo]

Has the "align axis to vector" option in the "Move Object" tool changed in NX 7.5? I have been getting an error message that says something like "Two axes do not intersect. Cannot define transformation."

Not too big of deal because I can get what I want using the "Dynamic" option just as easily. Just curious if something is different. I used to use this option a lot before I got used to the "Dynamic" option and never had any trouble with it before switching to 7.5. It could just be me.

 

[JohnRBaker]

I suspect that what's happened is that we've 'fixed' what was seen by some people as an undesired result, that is, using NX 6.0 it was possible, with the right settings, to create a 'Move Object' feature where nothing had actually moved.

But let's go back to what it is that 'Align Axis to Vector' is supposed to do. It basically allows you to move/copy an object by editing it's orientation FROM one vector to another. In essence it's a sort of 'Rotate Between Two Axis', which was one of the 'Transform' methods available before NX 6.0. Now back in the pre-NX 6.0 days it was obvious from the name that if the 'Two Axes' were parallel that this wouldn't make any sense since they would not form an angle and therefore nothing could 'Rotate'. In fact, if you selected parallel axes that's the error message that you got, 'Axes are parallel'. Well in NX 6.0 we changed this scheme to the more general 'Align Axis to Vector', but there would still be potential problems if the axes selected did prove to be parallel.

Using NX 6.0, depending on whether you were trying to create an 'Associative' Move you got two different 'results'. If the 'Associative' option was toggled OFF, and the selected vectors were parallel the error message read 'No motion has been specified. It does not make sense to move objects and their parents zero distance'. However, if the 'Associative' option was toggled ON, then you got the warning 'No motion has been specified. Is this really your intent.' with the choice to accept this or not along with the option 'Don't display this message again'. And this is where the problem was, that is; why would anyone create a 'Move Object' feature that never actually moved anything? The consensus was that this was an undesired result and so a second look was taken at what was really causing this in the first place and that's when they discovered that IF the 'Align Axis to Vector' scheme really was the replacement for 'Rotate Between Two Axis' then perhaps we needed to apply that same rule, that is that the vectors had to be non-parallel and if we had actually decided to use an error message that read that way, you probably wouldn't even be making this inquiry as to what's happened to 'Move Object' in NX 7.5.

What happened is something that often does with software, we report exactly what is that the software is having a problem with rather than simply describing what it was that the user did wrong, in this case selecting parallel vectors. Instead we report that 'Two axes do not intersect. Cannot define transformation.', which is just a programmer's way of saying that the 'axes are parallel'. And so, like with NX 6.0, if we had allowed you to proceed, nothing would have actually moved, resulting in a 'null' feature, which it has been decided was an undesirable situation.

Anyway, I hope that this explains what happened between NX 6.0 and NX 7.5, and that in in reality the interaction is much cleaner today, even if the error messages could do with a little editing to make it clearer as to exactly what it was that the user was trying to do that was not allowed.

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

http://www.siemens.com/plm

http://www.plmworld.org/museum/

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

 

[DaSalo]

That all makes sense John. Here's a little wrinkle: The two axes that I am choosing are NOT parallel. Here is a description of how I was trying use it last night when I was prompted to post the question:

I was working with an unparametized fixture model that needed to be adapted to fit a new part. I remodeled some elements and then used "Move Object" to swing the existing objects around to fit the new orientation. There were a few fasteners that were off on a hidden layer that didn't get included in the initial "Move Object" operation. I attempted to get one of these fasteners back in its hole by using the "Align Axis to Vector" option and then the "Point to Point" option. I first selected the end face of the screw as the "From Vector"; arrow was displayed normal to this face and parallel to the cylinder axis. I then selected the point in the center of that same end face as the "Rotation Point". Finally, I selected the cylindrical face of the hole that I wanted the screw to go into as the "To Vector". So far so good, all selections seem valid and I see a ghost image of the transformation with the screw moving as I expect. Then I hit "OK", it thinks for a second, and then gives me the "Axes do not intersect" message.

It is just as easy to do this by realigning the csys in the "Dynamic" option so no functionality lost. I am using 7.5.2.5 by the way. Keep forgetting to run the 7.5.3.3. update. When I do this exact same operation using "Dynamic" the screw moves exactly as expected, and exactly as was shown in the ghost preview in the "align axis to vector" option.

I'll try to post a model demonstrating this later tonight.

Thanks for your time. I like hearing about the history of how these features evolve.

 

[JohnRBaker]

It appears that the 'Parallel Axes' situation is simply a special case of the 'Axes do not intersect' problem. I suspect that in situations where the vectors do NOT actually intersect, due to the fact that they lay on different planes, the Alert message was intended to provide feedback indicating that while the system was NOT able to automatically find an intersection, the user can still go back and define one manually. Granted, perhaps we need to reword the Alert to make that more clear, but without actually talking to the developer responsible, I can't say why that was not included in the Alert (perhaps he/she was trying to keep it from becoming too verbose).

Anyway, try going back and selecting the 'Specify Pivot Point' option and manually selecting an appropriate point about which a 'rotation' would logically take place.

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

http://www.siemens.com/plm

http://www.plmworld.org/museum/

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