Dimensional measurement data analysis, part 2: Minimum zone evaluation

Modern inspection systems such as coordinate measurement machines generate discrete three dimensional coordinates representing points from the surface of a manufactured part. These coordinates must be compared to a target or nominal geometry to determine if the part conforms to specification. Quite often a least squares fit or a min-max fit are employed to determine the pa rt geometry. However, as described in Part I of this paper acceptable devia tions are often specified as tolerance zones about the nominal geometry. Pa rt I of this paper presents a zone fitting algorithm having an objective of placing the sampled data points within a specified tolerance zone. If ail of the points fit within the zone, the part is passed. This pass/fail resul t does not provide information as to the quality of the part. The question that is not answered is "Did the points just fit into the tolerance zone, o r did the points fit with ample space remaining?" This question is importan t as it informs production personnel whether their processes are operating well within specifications or just barely within specifications. In this part of the paper, the zone fitting method developed in Part I of t his paper is extended to a minimum zone evaluation. This can be formulated as a one dimensional search for the critical value of the zone fitting obje ctive function. The I,minimum zone evaluation algorithm developed in this p aper can be applied to an arbitrary geometry profile evaluation. A number o f examples are presented to demonstrate its capabilities.