Quantifying alignment effects in 3D coordinate measurement.
-
2009-10-01
-
Details:
-
Creators:
-
Corporate Creators:
-
Subject/TRT Terms:
-
Publication/ Report Number:
-
Resource Type:
-
Geographical Coverage:
-
Corporate Publisher:
-
Abstract:The use of fixtureless, non-contact coordinate measurement has become increasingly prevalent in manufacturing
problem solving. Manufacturers now routinely use measurement systems such as white light area scanners, photogrammetry,
laser trackers, and portable laser scanners to conduct studies that require measuring upstream supplier parts, tooling, or inprocess
subassemblies. For part measurements in these studies, certified fixtures with alignment features such as tooling balls
often are not available. Instead, manufacturers rely on ad hoc part-holding fixtures or measure parts without fixtures and
perform alignments mathematically. Here, advancements in software are providing operators with numerous alignment options,
and users are actively using this functionality. Naturally, these additional capabilities have led to inconsistencies in the
alignment method used across measurement studies, often affecting dimensional results.
This paper reviews several common alignment or registration methods and provides a metric to assess systematic
alignment error. To demonstrate alignment effects, we present a measurement system study of a moderately complex part
requiring an over-constrained datum scheme. We first measure the part using a conventional fixture-based method to establish a
baseline for static and dynamic repeatability. We then compare these with results from two mathematically-based iterative
alignment methods based on fixtureless measurement. Next, we assess the systematic alignment error between the different
fixture/alignment alternatives. We show that for the same basic datum scheme provided on engineering drawings, the systematic
alignment error is a far more significant issue for problem solving than the repeatability error or equipment accuracy.
-
Format:
-
Collection(s):
-
Main Document Checksum:
-
Download URL:
-
File Type: