Optical Flat Calibration for CMM Error Correction
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Solution Overview
Problem
Existing coordinate measuring machines (CMMs) face challenges in calibrating and correcting errors, particularly for smaller machines, as conventional laser interferometry is complex and not suited for measuring errors in smaller working spaces, and requires additional equipment for squareness errors.
Innovation Solution
The use of an optical flat with a recognizable pattern, such as a grating, in combination with a 3-D optical probe like a white-light interferometric objective, allows for the calibration of CMMs by taking optical measurements to determine linear positioning, straightness, pitch, yaw, and roll errors, providing 18 of the 21 error parameters required for correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser interferometry is used for CMM calibration, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the calibration function from complex laser interferometer systems and implements it using a simple optical flat with integrated gratings that can be measured by the CMM's own optical probe, eliminating the need for external calibration equipment
Solution Approach 2:
The optical flat serves multiple functions: it provides both the measurement surface and the reference grating scale, allowing the CMM to calibrate itself using its existing optical measurement capabilities without requiring separate calibration instruments
2Measurement precision
If laser interferometers are used for calibration, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The CMM performs self-calibration by measuring the optical flat with its own optical probe, eliminating the need for external operators to set up and operate complex laser interferometer equipment
Solution Approach 2:
The calibration standards (optical flat with gratings) are integrated into a single component that can be measured directly by the CMM, merging the calibration reference and measurement process into one unified operation
3Measurement precision
If laser interferometry is used for calibration, then measurement precision is improved, but adaptability deteriorates
Solution Approach 1:
The optical flat provides localized reference gratings that can be positioned within the limited working space of small CMMs, allowing high-precision calibration adapted to compact machine geometries where laser interferometers cannot be accommodated
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise and cost-effective calibration of CMMs, particularly for smaller machines, by providing a self-contained system for error correction without the need for bulky laser interferometers, allowing for on-site calibration by users and reducing the complexity of the process.
Implementation Method 1
optical measurements are taken of the flat while translating the objective in the coordinate direction subject to calibration
Data Source
AI summary
A coordinate measuring machine is calibrated by taking optical measurements of an optical flat that includes a grating placed on its surface. The arm of the CMM capable of multi-directional translation in relation to an object is fitted with a white-light interferometric objective and optical measurements are taken of the flat while translating the objective (or the flat) in the coordinate direction subject to calibration. The objective may serve also as the probe of the CMM.