Practical Implementation and Effectiveness of Machine Tool Spatial Accuracy Compensation
Overview
Spatial accuracy volumetric error compensation technology is regarded as a core solution for improving machining quality. This technique systematically analyzes and corrects the comprehensive errors of machine tools within a three-dimensional workspace, significantly reducing deviations caused by structural defects, environmental interference, or machining loads. It enables strict tolerance requirements for high-end workpieces such as aerospace components, medical instruments, and optical molds. In practice, spatial accuracy compensation can reduce volumetric errors by 50% to 90%.
This study focuses on a TYPE B five-axis machine, using an Etalon laser tracker for measurement and the Heidenhain TNC 640 controller with option 52 for spatial accuracy compensation. For example, the five-axis machining center initially had a spatial error of 20 μm, which was reduced to under 10 μm after compensation. This article details the research process and results.
21 Geometric Errors of Machine Tools
Machine tool errors include single-axis geometric errors and inter-axis squareness errors, totaling 21 items that significantly affect accuracy. Each linear axis (X/Y/Z) has six degrees of freedom errors (3 translational + 3 rotational), making 18 items for three axes, plus 3 squareness errors.
Examples of errors:
- Linear positioning error
- Horizontal straightness error
- Vertical straightness error
- Pitch error
- Yaw error
- Roll error
- Squareness error
ISO 230-1 defines these as component errors (6 DOF) and positional errors (squareness).
Spatial Accuracy Definition
Spatial accuracy refers to volumetric error, representing the combined geometric accuracy. It is defined as the worst-case deviation between target and actual positions within the machine’s volume, calculated as the vector length of maximum errors in X, Y, and Z directions.
Example: DMG Mori claims its 2.7 m travel machine achieves volumetric error below 60 μm through precision scraping processes.
Etalon Laser Tracker Measurement and Planning
The Etalon LaserTracer-NG is a high-precision device for measuring volumetric errors, with a resolution of 0.001 μm and a range up to 20 m. It is suitable for medium and large machines and also used in CMM applications.
Measurement principle: Similar to GPS, it measures relative lengths (1D laser) and calculates positions via multilateration.
Measurement and Compensation Process
Steps:
- Select a five-axis machine with spatial compensation capability
- Measure original geometric and volumetric errors
- Use laser tracker for measurement
- Compare results
- Apply compensation and verify using DBB (Ballbar)
Results: Original vs. Compensated Accuracy
After compensation, errors were significantly reduced, improving accuracy by 76%. Original volumetric error was ~30 μm, reduced to 9 μm.
Diagonal simulation tests showed 50% improvement. Actual diagonal measurement (ISO 230-6) confirmed D1 diagonal error reduced from 15.8 μm to 5.3 μm.
Ballbar tests on XY, YZ, and XZ planes showed roundness error improvements:
- XY: 3.7 μm → 2.6 μm (30% improvement)
- YZ: 6.8 μm → 4.9 μm
- XZ: 11.5 μm → 6.4 μm (44% improvement)
Conclusion and Future Outlook
Key findings:
- Compensation reduced 21 geometric errors by 76%
- Volumetric error improved from 30 μm to 9 μm
- Diagonal path accuracy improved by 50%
- Ballbar tests confirmed dynamic accuracy improvements
Future directions:
- Automating and smartifying error compensation using sensors and machine learning
- Integrating thermal, load, and dynamic errors into models
- Extending to multi-axis and complex machining centers
- Standardizing and modularizing compensation processes
- Integrating with digital twin platforms for real-time monitoring and prediction
This technology is poised to become a key enabler for high-precision machining and smart manufacturing.
References
- ISO 230-1 (2012), ISO 230-6 (2002)
- Renishaw, Hexagon, DMG Mori websites
- Chapman, M.A.V., “Limitations of laser diagonal measurements”, Precision Engineering 27 (2003)
- Renishaw technical white paper: TE334
