Many of our customers work with production parts that can have flat or flattish bottoms. Fuel cell plates, curved display glass, ceramic plates, etc. These tend to be brittle forms that cannot be flattened with something like a vacuum fixture - although often a three ball array fixture will employ a vacuum cup in its center.
The three ball array works well with our planar skew correct software. The three balls establish an arbitrary dispensing plane for the part and our software then automatically matches the pattern program to the part. The net result on a rigid part is a perfect plane-to-plane match. The only way to be more precise would be to rescan each individual point, a technique that while accurate is quite time consuming.
This type of fixture lends itself nicely to those types of applications that benefit from a template based periphery locating system. The operator places a template used to locate the part, places the part, turns on the vacuum, and then removes the template. Alternatively we have, in the past, mounted the vacuum and three-ball array on a riser platform which would allow the template to be clear of the part during dispensing and subsequent part offload.
As always, if you have any questions, please do not hesitate to call.