18-04-2014, 12:31 PM
Metrological Problem Mapping for Coordinate Measuring Machines
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Abstract
Coordinate Measuring Machines (CMM) are
widely used in industry as an inspection part where a product is
subjected to verification of the geometric features, dimensions
and tolerance specifications with respect to the product design
specifications. The most of the series standard ISO 10360 are
developed and are in developing process to assure quality and
increase accuracy of CMMs over the past 15 years. This paper
presents the importance of calibration as a key for
establishment traceability of the measurement results with
Coordinate Measuring Machines.
INTRODUCTION
The essential part for assuring and controlling quality in
industrial manufacturing is inspection process where a
product is subjected to verification of the geometric features,
dimensions and tolerance specifications with respect to the
product design specifications. One of the most interesting
topics in the automation of the inspection process is the right
fixture design realized by Coordinate Measuring Machine
(CMM) and Machine Visions which allows the automation of
the inspection fixture design process to be made easier,
reducing time and cost associated to the inspection process
and to the manufacturing process in general. The CMM is not
only a common instrument for quality control of parts but
also precise equipment on automation of production lines.
The selection of a suitable CMM therefore is a critical
decision in a company’s quality control standards. This
important selection is further complicated by the long life
expectancy of CMMs compared to machine tools and by the
wide array of CMM performance standards used in whole or
part by various CMM manufacturers.
TASK-RELATED CALIBRATION
The reliability of dimensional measurements in CMM can
be achieved by establishing the traceability to the national
standards where important roles play task-related calibration.
Based on the series standard ISO 10360 there are two basic
principles of CMM task-related calibration:
• Comparator principle
• Error synthesis principle
In comparator principle the measurement of traceable
reference objects yields directly the errors associated with
specific measurement tasks. The errors associated with the
parameters of the measured object due to the accuracy of the
CMM including its software can be determined directly and
calibrations of this kind are only valid for objects with
essentially the same geometrical form and size as the
reference object used, measured in the same location and
using the same measurement strategy. Provided that suitable
reference artefacts are available
SUMMARY AND CONCLUSIONS
Coordinate Measuring Machine is a complicated instrument
for establishment traceability of the measurement results.
CMM allow high-accuracy measurements on complex three-
dimensional components and make several measurement
tasks which are challenging or impossible using other
methods. In this study the importance of task-related
calibration is expressed carefully as an important key for
establishment traceability and getting reliable results in
CMM. Amongst the others, a task-related calibration method
as a promising tool for reliable measurement results is
described. In task-related calibration one of the main and
difficult sources of evaluating measurement uncertainty is the
number and interactions of variables that can affect a CMM
measurement.