Contact Probe Scanning for Low-Uncertainty Part Measurement
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Solution Overview
Problem
Existing methods for measuring parts using contact probes in machine tools face inaccuracies due to errors from probe straightness, part off-centre errors, and runout, especially when measuring cylindrical parts, as they struggle to directly determine the center of rotation and separate circularity from axis center drift or off-centre errors.
Innovation Solution
The method involves multiple scans of the same scan path with the contact probe moving along different paths relative to the coordinate measuring machine, allowing points close together on the part to be measured at far-apart locations, and using analytical curve fitting to account for errors, including a multi-axis contact probe that measures deflections in various directions and rotates the part within the machine, transforming measurements into a part coordinate system to minimize systematic errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple measurements are taken at the same point during different traverses of the scan path, then measurement uncertainty falls with the square root of the number of measurements, but the measurements must be considered independent which requires far-apart locations in the machine
Solution Approach 1:
The invention utilizes the spatial dimension of the machine tool by positioning measurement points far apart in the machine coordinate system while measuring the same physical locations on the part. This dimensional separation ensures measurement independence while maintaining the ability to reduce uncertainty through multiple measurements.
Data Source
Figure 1a~1c
Figure 2
Figure 3a~3b
AI summary
This invention concerns a method and apparatus for measuring a part 4 with a contact probe 3 mounted on a coordinate positioning machine 1. The method comprises measuring a plurality of points PC on the part 4 when both the part 3 and contact probe 3 are moving continuously between different positions within the coordinate positioning machine 1.The probe 3 moves, relative to the part 4, along a scan path 20 such that substantially coincident points that are closely located together along a curve or surface being measured are measured at relatively far apart positions in the machine 1 and at relatively far apart positions along the scan path SC.