CMM Sphere Calibration via Surface Topography Mapping
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Solution Overview
Problem
High-precision coordinate measuring machines (CMMs) face accuracy uncertainties due to spherical shape errors in calibration spheres and probe spheres, which are not adequately addressed by existing calibration methods, leading to increased manufacturing costs and reduced measurement accuracy.
Innovation Solution
Measuring the calibration sphere and/or probe sphere separately using a surface measuring device and transferring the measurement results to the CMM, allowing for precise determination of roundness deviations and surface topography, thereby reducing tolerance errors and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration spheres and probe spheres are used with standard roundness tolerances, then the calibration process is simple and cost-effective, but measurement accuracy is reduced due to uncertainty from spherical shape errors
Solution Approach 1:
The patent applies preliminary action by measuring the calibration sphere and probe sphere in advance using a surface measuring device to determine their actual surface topography and roundness deviations. This pre-measurement data is then transferred to the CMM controller to create correction maps, eliminating the need for complex real-time compensation during calibration operations.
Solution Approach 2:
The patent introduces an intermediary approach by using a surface measuring device as a mediator between the spherical components and the CMM. The surface measuring device captures precise geometric data that is then processed and applied as correction factors in the CMM software, serving as an intermediate step that bridges the gap between standard manufacturing tolerances and high-precision measurement requirements.
2Reliability
If standard calibration spheres with manufacturing tolerances are used, then manufacturing costs are reduced, but uncertainty in measurement results increases
Solution Approach 1:
The patent applies parameter changes by transforming the measurement parameters through mathematical correction models. The actual surface topography data obtained from surface measurement is processed to generate correction maps that adjust the nominal sphere parameters (radius, center position, roundness) to reflect the true geometric characteristics, thereby compensating for manufacturing tolerances.
Solution Approach 2:
The patent uses copying by creating a digital replica or model of the actual sphere surface topography. The correction map is essentially a digital copy of the sphere's real geometry that is stored in the CMM controller and applied during measurements, allowing the system to account for manufacturing deviations without requiring physically perfect spheres.
3Measurement precision
If separate surface measurement of calibration spheres is performed, then roundness deviation determination is improved, but the preparation time and process complexity increase
Solution Approach 1:
The patent applies preliminary action by performing surface measurement of the calibration sphere before it is used in the CMM. This pre-measurement captures the sphere's actual geometry, and the correction data is prepared in advance and stored in the CMM controller, so that during actual measurement operations, the system can immediately apply the corrections without additional measurement time.
Data Source
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AI summary
The invention relates to a method and a corresponding system for preparing to operate a tactile probing coordinate measuring machine (1), more particularly for preparing to calibrate a coordinate measuring machine (1) by tactile probing of a calibrating element (2, 4) by means of a probing device (3, 8) arranged on the coordinate measuring machine (1), said method comprising the following steps: measuring the surface of a probing ball (3) that deviates from an ideal shape of a ball as a probing element of the coordinate measuring machine (1), or measuring the surface of a calibrating ball (2, 4) that deviates from an ideal shape of a ball as a calibration normal, by means a surface measuring device (21), and determining coordinates of a plurality of real surface points on the probing ball or calibrating ball (2, 4) in a coordinate system of the probing ball or calibrating ball (2, 4); placing a reference feature (14; 15; 16) of the probing ball (3) or the calibrating ball (2, 4) in relation to the coordinate system of the probing ball (3) or the calibrating ball (2, 4); mounting the probing ball (3) on a tactile probing coordinate measuring machine (1) or arranging the calibrating ball (2, 4) in the measuring range of the tactile probing coordinate measuring machine (1); and placing the coordinate system of the probing ball (3) or the calibrating ball (2, 4) in relation to a coordinate system of the coordinate measuring machine (1) in such a manner that information about positions of the real surface points on the probing ball (3) or calibrating ball (2, 4) is available or can be determined in the coordinate system of the coordinate measuring machine (1).