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Knowledge on computational compensation of geometrical deviations

Once geometrical deviations of a machine are determined by measurement, the data can be used for numerical compensation. For coordinate measuring machines a recorded measurement point can be corrected with a known deviation vector before evaluation or display of the measured value. For production machines, the requirement is higher: Even during the path planning of the compensation vector has to be calculated in real time for each interpolated path point.

Therefore in the past in machine tool controls the possibility for compensation was limited by the available computing power. This limitation does no longer exist in modern machine tool controls.

Today controllers offer extensive possibilities for compensation up to the complete volumetric compensation, so that the geometry information obtained through Etalon technology can be optimally utilized to improve accuracy.

Together with the major control manufacturers Etalon has developed and validated the necessary algorithms for volumetric compensation, so that a correct data flow and tested interfaces can be guaranteed when using the Etalon technology.

But Etalon also worked on the application side: In order to utilize the possibilities of volumetric compensation in the industry optimally, it was necessary to create a common language between metrologists, machine tool builders and users of machine tools. All parties should know the possibilities but also the limits of numerical compensation of machine tools.

This is why an internationally recognized document was supported, the ISO Technical Report 16907 “Numerical Compensation of Machine Tools.” This comprehensive document summarizes the basis for the application of computational compensations in machines and is a good technical foundation for anyone who deals with this topic, whether metrologist, mechanical engineer or user.

Etalon technology is now used in many applications to increase the geometric accuracy e.g. the calibration of high-precision coordinate measuring machines, for small and medium-sized machining centers with high accuracy requirements or in heavy machine: For the highest requirements customers worldwide rely on the Etalon technology for the compensation of machine deviations and reduce the spatial deviations of their machines by 50 % to 90%.

  • A compensation reduces the effect of the geometric errors and therefore leads to a higher geometric quality of the workpieces produced.
  • With a periodical compensation, the machine tool accuracy can be maintained over the life cycle of the machine. Geometric changes due to aging, wear, foundation shifting, collisions or changes in the thermal environment can be partially or fully restored.
  • By reducing the geometrical requirements on guideways, positioning and assembly accuracy of the machine components, the total cost for the production of machine tools can be reduced.
  • Measurements of components on the machine tool compensation may reduce the measurement uncertainty.
  • The reproducibility of the movement remains the limit for the achievable accuracy.
  • Thermo-elastic deformations remain an important source of geometric changes.
  • While for most of the machine tools the positioning of the TCP can be ideally compensated in the entire volume, the physical orientation of the tool may remain unchanged. Large rotational deviations in combination with very large tools can therefore still make geometric deviations visible.
  • Narrow geometrical tolerances on the machine components may also be responsible for the rigidity, the reproducibility and the stability of the machine tool. Hence they may not be reduced easily.

Etalon technology offers interfaces for compensation opportunities provided by the control manufacturers. This allows a safe operation and ensures that the machine or controller manufacturer remains responsible for the overall system. Nevertheless Etalon is supporting control manufacturers worldwide in advancing their compensation possibilities e.g. by the provision of test data sets.

For an overview on the possibilities of different controllers, please contact us at etalon.info@hexagon.com.

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