Gauge Artefact for Coordinate Measuring Machine Deviation Calibration
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Solution Overview
Problem
Coordinate positioning machines face challenges in accurately measuring small deviations in geometric properties of parts, as existing calibration methods require extensive linear calibration across the entire measurement volume, which is inefficient and prone to errors.
Innovation Solution
A gauge artefact with a base and platform featuring cooperating mounting formations that define multiple positions, allowing the platform to present nominally identical geometric properties at a common location, enabling the machine to check and correct for deviations comparable to those in the parts being measured, using a calibrated gauge artefact with known deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If extensive linear calibration is performed across the entire measurement volume, then measurement accuracy is improved, but calibration time and complexity increase
Solution Approach 1:
The calibration process is segmented into two distinct phases: (1) a comprehensive linear calibration performed once on a reference coordinate measuring machine to establish baseline accuracy, and (2) a focused deviation calibration performed repeatedly on the positioning machine only in the specific measurement volume where parts are actually measured. This segmentation eliminates the need to perform full-volume calibration repeatedly, significantly reducing calibration time while maintaining measurement accuracy.
Solution Approach 2:
The linear calibration of the reference CMM is performed in advance as a preliminary action, establishing a master map of the measurement volume. This pre-established reference data allows subsequent calibrations to focus only on detecting deviations from the master map, rather than recalibrating the entire measurement system from scratch each time.
2Measurement precision
If full-volume linear calibration is performed, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The calibration system is segmented into a reference CMM component that performs comprehensive linear calibration, and a positioning machine component that performs focused deviation detection. The calibration artifact serves as an independent reference segment with known geometric properties. This segmentation simplifies the positioning machine's calibration task to only detecting deviations from the master map, reducing overall system complexity.
Solution Approach 2:
A calibration artifact with precisely known geometric properties serves as an intermediary between the reference CMM and the positioning machine. The artifact provides a common reference framework that allows the two machines to be correlated without requiring complex direct calibration procedures. The artifact's master map acts as an intermediary data structure that mediates the calibration relationship.
3Reliability
If calibration is performed across the entire measurement volume, then measurement reliability is improved, but productivity decreases
Solution Approach 1:
The calibration approach applies local quality by focusing calibration efforts only on the specific measurement volume where parts are actually measured, rather than uniformly calibrating the entire machine capability. The master map is created only for the relevant measurement volume, and deviation calibrations are performed only in this local region. This localized approach maintains measurement reliability for the actual application while improving productivity by eliminating unnecessary calibration of unused measurement volumes.
4Measurement precision
If the coordinate positioning machine is calibrated to be linear across the entire volume, then measurement accuracy is improved, but the requirement for machine linearity becomes overly stringent
Solution Approach 1:
The requirement for overall machine linearity is extracted and replaced with a requirement for accurate deviation detection from a master map. Instead of demanding that the positioning machine be linear across its entire travel range, the system only requires that the machine can accurately detect deviations from the master map in the specific measurement volume. This extraction of the linearity requirement from the global machine performance to a local deviation-detection capability reduces the stringency of manufacturing requirements.
Solution Approach 2:
The reference CMM creates a digital copy (master map) of the calibration artifact's geometry with high accuracy. This master map copy is then used as the reference for all subsequent measurements. The positioning machine needs to accurately reproduce this copied geometry, but doesn't need to be inherently linear. The linearity requirement is transferred to the master map creation process rather than the positioning machine itself, allowing the positioning machine to be manufactured with relaxed tolerances.
Data Source
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AI summary
This invention concerns a gauge artefact (100) comprising a base (102) for mounting on a table of a coordinate positioning machine and a platform (108) comprising at least two portions having a nominally identical geometric property. The platform (108) is locatable relative to the base (102) in at least two positions such that each of the at least two portions having the nominally identical geometric property can be presented at a common location relative to the base (102). The platform (108) may be arranged such that the positions of the portions having a nominally identical geometric property can be interchanged by movement of the platform (108) between at least two distinct positions. The positions may be interchanged through rotation of the platform (108). The invention also concerns a method of checking a coordinate measuring machine.