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Base alignment cannot be computed.


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Hello everyone,
I know I asked this question on another part but I am have the same issue on another part. Once I get my base alignment and setup clearance planes, I will do a manual alignment and try to run the part. But I always get an error message that reads. Base alignment cannot be computed. Regardless of how I setup the base alignment I always get this message. I am programming from CAD, and have tried several different parts but still the same result. What settings am I missing?
Thank you,
Lou
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On first looks, everything appears to be ok. I suspect the cylinder may be giving you a problem. When you do a manual alignment, are you only taking 5 points? If so, you should take 3 at one height and 2 at another height. Better yet, take 4 at top and 4 at bottom. Common mistake is to take 4 at top and 1 at bottom. Though technically correct for minimum number of points for a cylinder, the calculated cylinder will not be correct.

Also, when measuring the Planar plane, make sure to take point high and low, front and back. Many people will just take 3 or 4 points in a straight line. This is not good for calculating a plane.
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Tom it won't even let me do a manual alignment. Once I set that up to run so I can do a manual alignment I get the error message. Base alignment cannot be computed.
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Yes but to orientate to the way I have it mounted on the table I need to change it to -Z. When I try to run it, I can touch off on the cylinder for the first alignment then I get the Base alignment cannot be computed.
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The cylinder actuals for the X and the Y are way off of nominal. Bad probing or strategy on the cylinder? Increase the number of points on your cylinder and you will get a form value which will help you further diagnose what is going on.

Scratch that. 7 points on a cylinder and no form value? What is up with that guys?

Marc is about to make a great point about the using the correct stylus. (see what I did there)
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For the alignment, I would create an intersection of the cylinder to the top plane and use that point as X & Y, and just program a line on that flat edge for the planer that would then be either Y+ or Y- depending on your direction.
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For the sake of discussion, let's assume the model is already in the desired orientation (+Z is up, +Z is to the right, and +Y is the back). Let's say you use a plane for spatial and Z origin and a cylinder for the X and Y origin. Typically, the cylinder would have a +Z space axis, the X and Y actuals will be at bottom of the cylinder. However, where the axis of the cylinder intersects the top plane, is automatically X0 Y0. To prove my point, create an intersection of the cylinder and plane and you will see the X, Y and Z nominals and actuals are zero. So, if the actuals off, it's because the cylinder is not perpendicular to the plane. You should be able to confirm this with the deviation in A1 and/or A2. So, creating an intersection of the cylinder to the plane is really an extra unnecessary step. However, this would be a good option for a parallel cylinder that you wanted to use for a planar rotation.

In Lou's case, his actuals are way off as Chad and Marc pointed out, so I think I would start over. Not sure if Lou did this, but I would orient the model first before creating any features. (CAD > Modification, CAD Model Transformation). Get the model oriented the way you want to end up first. Don't worry about the translation, as once you Create the BA, translations should fall right in. Rotations, on the other hand, COULD end up screwing things up if you don't know what to look for.
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Only points are taken on cylinder - but sigma and form is ZERO - with 7 points it looks like bad points taken.
Other planes are not scanned.

I would try to make fresh new alignment.
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Thank you for your reply Tom. I will try this later. I did notice the cylinder actuals were way off. I haven't touched off of any features. I am programming from a CAD model, I thought I could just extract the features and choice the characteristics and setup a base alignment, then do a manual alignment and run it. I have done automatic healing and left the strategies as optimum. I have started over several times with different parts.
I can program the same part manually without the CAD model and it runs great. But once I start programming from CAD things fall apart. When I went for training everything seems easy peasy I was looking forward to program from a CAD model, but dang not sure whats going one now. I appreciate everyone's help.
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Lou, it sounds like your Part Alignment X,Y,Z is not in the same orientation as your CMM X,Y,Z. You can verify this by viewing the model from -Y and then putting your CMM sensor and probe straight down. Select your RC position list and you should see the CMM sensor pointing correctly straight down toward your part. If it is different, then the CMM axis is different than your part alignment. Unfortunately, I have experienced this myself.
I have found it best when programming from the model to use CAD/Modification/CAD model transformation, and get the part in the correct orientation/location, and then build your base alignment from the part.
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In your screenshots of the 3 feature windows the clearance group for the cylinder is CP -Z while for the two planes it is CP +Z. Could this be causing a navigation issue that forces Calypso to error out in the middle of the base alignment?
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I think Peter is right, the way he has the part set up he can't get to the cylinder from Z-. This is why it can't be computed.
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