Machine Tool Axis Error Identification Using a Rotating Sphere Calibrator
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Solution Overview
Problem
Existing methods for identifying geometric errors in four-axis-control horizontal machining centers face challenges such as interference issues with touch trigger probes, expensive and complex installation jigs, and inaccurate measurements due to deformation under gravity, particularly when trying to measure single axis and inter-axis geometric errors.
Innovation Solution
The method involves using a calibrator with linearly aligned spheres on a machine tool table, where a position measurement sensor on the spindle measures sphere positions while the calibrator is rotated to various angles, allowing for accurate identification of translational axis errors, including positioning and squareness errors, without the need for an inclination mechanism, thus simplifying the process and reducing operator burden.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If a touch trigger probe is used to measure geometric errors, then measurement capability is provided, but interference with the measurement object occurs and measurement accuracy deteriorates
Solution Approach 1:
The patent replaces the mechanical touch trigger probe with a laser interferometer-based measurement system. The laser interferometer measures the positions of spheres on the calibration object optically without mechanical contact, eliminating interference while maintaining high measurement capability and accuracy.
2Adaptability or versatility
If an inclination mechanism is added to change measurement directions, then measurement versatility is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the calibration object rotatable about the vertical axis, allowing dynamic change of measurement directions. The rotation mechanism enables the same calibration object to be measured from multiple angular positions, providing measurement versatility without requiring a complex fixed inclination mechanism.
Solution Approach 2:
The patent designs a universal measurement method that can identify all inter-axis geometric errors (squareness errors between X-Y, Y-Z, and Z-X axes) using the same calibration object and measurement procedure, regardless of the specific error type. This multi-functional approach eliminates the need for different specialized jigs for different measurement scenarios.
3Measurement precision
If multiple measurement directions are required, then comprehensive error identification is enabled, but operator burden and measurement time increase
Solution Approach 1:
The patent employs periodic rotation of the calibration object to multiple predetermined angular positions (e.g., 0°, 90°, 180°, 270°). At each position, the laser interferometer automatically measures sphere positions, and the control unit processes all data to identify geometric errors. This periodic measurement approach comprehensively captures errors in all directions while automating the process to reduce operator burden and total measurement time.
4Measurement precision
If expensive precision jigs are used for calibration, then measurement accuracy is improved, but manufacturing cost increases
Solution Approach 1:
The patent uses a calibration object with spheres that can be manufactured at low cost using conventional machining. The spheres are positioned on a plate or block that does not require ultra-precise manufacturing, unlike traditional laser calibration jigs. This approach achieves high measurement accuracy for geometric errors while significantly reducing the cost of the calibration system.
Solution Approach 2:
The patent creates a simplified calibration model using spheres on a plate that replicates the essential measurement function of expensive precision jigs. The sphere centers serve as reference points that can be measured with high accuracy using the laser interferometer, without requiring the calibration object itself to be manufactured with ultra-precise geometries.
Data Source
AI summary
An error identification method includes: installing a calibrator including a sphere row A and a sphere row B in which a plurality of spheres are linearly aligned in a direction perpendicular to the sphere row A on a table such that the sphere row A and the sphere row B are approximately parallel to respective two of the translational axes and measuring positions of a plurality of spheres of the sphere row A and the sphere row B using a position measurement sensor tool; rotating the calibrator to a plurality of angles around a normal direction on the upper surface of the table to install on the table and measuring each position of the plurality of spheres of the sphere row A and the sphere row B; and identifying an error of the translational axis based on measured values in the installing and the rotating.