Spherical Probe Calibration via Multi-Directional Spindle Rotation
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Solution Overview
Problem
Existing calibration methods for spherical measurement probes in machine tools lack precision and are cumbersome, particularly in determining the central point of a calibration sphere and reference position, especially when the sphere is not centered on the spindle axis.
Innovation Solution
A method involving four basic measurements with the measurement probe rotated by a consistent angle around the spindle axis, combined with additional measurements to account for early and late contact positions and transverse offsets, allows for precise determination of the reference position and actual radius of the measurement probe relative to the spindle axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the calibration sphere is not centered on the spindle axis, then the calibration can be performed in more practical scenarios, but the measurement precision deteriorates
Solution Approach 1:
The calibration process is divided into multiple independent basic measurements taken from different transverse directions. Each measurement is performed independently with the measurement probe rotated by a consistent angle, and the results are combined through mathematical evaluation to determine the reference position. This segmentation allows accurate calibration even when the calibration sphere is not centered on the spindle axis.
Solution Approach 2:
The calibration method extends from single-direction measurements to multi-directional measurements in three-dimensional space. By performing measurements from four different transverse directions that meet in a common point and are evenly distributed, the method captures spatial information from multiple dimensions, enabling accurate determination of the reference position regardless of the calibration sphere's lateral offset from the spindle axis.
2Measurement precision
If multiple basic measurements are performed with probe rotation, then the reference position determination accuracy improves, but the calibration time increases
Solution Approach 1:
The calibration process uses periodic rotation of the measurement probe around the spindle axis by consistent angles between measurements. This periodic action creates a systematic measurement pattern that can be efficiently evaluated mathematically. The regular angular intervals allow for optimized calculation algorithms that reduce processing time while maintaining high accuracy in reference position determination.
Solution Approach 2:
The method performs preliminary positioning of the tool spindle at identical longitudinal positions and pre-orientates the calibration sphere at the same orientation before conducting the basic measurements. This preliminary action ensures that all measurements are taken from consistent reference conditions, eliminating the need for repeated positioning adjustments during the measurement sequence and thereby reducing total calibration time.
3Measurement precision
If the measurement probe is rotated by a consistent angle matching the transverse direction angles, then the mathematical evaluation simplifies and precision improves, but the device complexity increases
Solution Approach 1:
The calibration method changes the angular parameter of the measurement probe rotation to match the angular separation between transverse measurement directions. By setting the rotation angle equal to the angle between adjacent transverse directions, the measurement data aligns with the mathematical evaluation model, simplifying the calculation of the reference position while improving precision. This parameter matching creates an optimized measurement configuration.
Data Source
AI summary
Four basic measurements are performed when calibrating a spherical measurement probe fastened to a tool spindle having a fixed longitudinal position along the spindle axis. Moving the measurement probe transversely towards the calibration sphere yields a basic position of the tool spindle relative to an element with an attached calibration sphere, when measurement probe touches the calibration sphere. The measurement probe is rotated about the spindle axis from one basic measurement to the next by the same angle, whereas the orientation of the calibration sphere is maintained for all four basic measurements. Based on the basic positions, a reference position of the tool spindle relative to the element, at which the tool spindle is located above the calibration sphere and the spindle axis goes through a central point of the calibration sphere, is determined and taken into account in further calibration of the measurement probe.