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Can you split a CAD model in 2 sides and only prealign to one side?


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We have a unique threaded part and the prealignment is in love with the threads. We need the scans to prealign to the main body of the CAD model. 

I've tried many local alignments using several strategies, but I cannot get the local alignment to align correctly to the main body.

I tried to split the CAD model then when I bring the 2nd CAD in I select 'fixture', but when I use the fixture as a target for the prealignment is says there is no data. 

Is there a way to use a split CAD model and only align to one side?

 

Thanks.

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Hi,

quite not sure if i really understood your problem: You can create a PatchCompound from parts of your CAD via point selection and you can use this PatchCompound-Object for the Prealignment (and in many more functions).

A CAD which you have declared as fixture is only used as collision control object for your VMR (and some other functionalities restricted to the semantic of a fixture object). You can't use your fixture for inspection or alignment purposes.

Hope this helps?! Otherwise you must contact our professional support for your particular problem.

Regards,

Bernd

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I have a screw with a unique attachment to the top. I don't want the part to use any of the threads to prealign the part.

 

I cannot use Create Patch Compound unless the part is already prealigned, then I can click on a surface to create a patch then fit that to the mesh, and I can then use that surface for profile measurements.

 

I cannot create a patch on the CAD model using points so I don't understand what you are saying. I would love to create 3 planes on a CAD model and use only those planes for a prealignment, but I don't know how to do this without the prealignment already created and applying a fitting method to the mesh.

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Hi Tim,

again, it's quite hard without the concrete part to give you the "right" hints, for these tasks I recommend strongly to contact the professional support.

Nevertheless, you can create a PatchCompound without (!) applying the measuring principle as 'Fitting element'. Instead you can apply 'No measuring principle' (which is necessary for usage in the Prealignment) and then you can use this (only) nominal PatchCompound object as portion of the CAD in the 'Prealignment'. Hint: Usually you have to choose 'Long' if your actual data covers much more then your PatchCompound.

Hoe this helps?!

Regards,

Bernd

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Thank you, that fixed my problem. I was not using 'no measuring principle'. If you don't do this it will give you an error when trying to use a surface as a prealignment target.

This will help us out alot thanks.

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To offer another possible workaround in such situations.  Align a representative stl by any means necessary to the correct orientation .  Export , bring back in as a nominal in a different part container.  Delete all alignments used in the original part then create an initial alignment to the mesh of the part just created , then further alignments can be driven by surfaces , points etc as usual in the target part.

Hope this makes sense .

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,

It would be awesome if I could do a quick prealignment, then another prealignment to only rotate the part in Z to a specific feature of the CAD model. Is this possible?

I tried this by doing a prealignment to my main cylindrical outer body and bottom plane, so the part is perfectly aligned except for rotation/clocking.

There are a few parts with unique internal clocking features that I'd like to do a 2nd prealignment to and just let the part snap into place with only rotation in Z.

I tried a 'local alignment' to do this. There is a 'target' area which I can select my 2nd clocking surface patch, but it then has a yellow error symbol saying that I need to click on the 'actual part' to do a local alignment. 

 

I tried to force the software to do back to back prealignments with the following code, but it errors out on the  last line below and says 'can't computer the transformation':

CAD_ALIGNMENT=gom.script.alignment.create_prealignment (
	computation_mode='enhanced', 
	compute_additional_bestfit=False, 
	name_expression='Prealignment_1', 
	parent_alignment=gom.app.project.parts['Part'].original_alignment, 
	part=gom.app.project.parts['Part'], 
	target_element=gom.app.project.inspection['PREALIGN_SUR'])
	
	
CAD_ALIGNMENT=gom.script.alignment.create_prealignment (
	computation_mode='enhanced', 
	compute_additional_bestfit=False, 
	name_expression='Prealignment_2',
	parent_alignment=gom.app.project.alignments['Prealignment_1'],
	part=gom.app.project.parts['Part'], 
	target_element=gom.app.project.inspection['PREALIGN_SUR_2']

 

Any thought would be greatly appreciated, thanks.

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I just figured it out...you can use the menu drill downs to get to another 2nd prealignment.  You cannot do a 2nd prealignment using the top right 'plus' button.

Also, my code worked above, I just didn't select enough surfaces for it to work, there must be enough surfaces for it to work.

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Hi Tim,

I guess you have a rotational symmetric part but which is not completely rotational symmetric?
We have an entry in our database for parts like that and I hope that this issue is scheduled for one of the next releases. 

I guess your idea is not working very stable in the moment because the 'Prealignment' must try to find a solution for all six degrees of freedom (parameters of a transformation)? Nevertheless, as I already mentioned it is always helpful to have concrete real world data that we would be able to recheck if newly developed functions really will work. You can provide data as always via our professional support.

Regards,

Bernd

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Yes, this is a symmetrical part with a very specific clocking feature that the prealignment will not repeat 100% with a traditional prealignment.

We are experimenting with two things now that you taught me how to use CAD surfaces to prealign to:

1) prealignment with selected CAD surfaces to locate "AND" clock/rotate the part to the proper orientation in one shot

        ---the key to this strategy in my opinion is to make sure you have not selected surfaces that compete with each other for clocking/rotation

        ---I'm also running many tests over many parts if we need to use 'LONG' and 'ADDITIONAL BEST FIT' for this strategy.

2) prealignment with selected CAD surfaces to located the part without worrying about the clocking, then another 2nd prealignment to clock/rotate the part into orientation using the prealignment 1 as a Parent

 

We can send a sample file....do you have a personal upload location I can send to you personally or is there a general upload locaton I can send it to?

 

Thanks.

 

 

 

              

          

 

 

 

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