Towards an effective identification strategy in volumetric error compensation of machine tools

Abstract

The influence of technical parameters for volumetric error compensation in large-volume machine tools (MTs) is presented in this paper. The techniques presented are based on characterization models using nonlinear optimization procedures. The parameters presented allow for the characterization of different errors in the MT studied and depend on the kinematics and geometry of the system, regardless of the optimization methodology. The kinematics is affected by the MT errors on the number and type of axes and movements. To relate the coordinates of the tool to the coordinates of a laser tracker, a kinematic model of the MT that includes the measurement system must be defined. Kinematic models can be realized by using homogeneous transformation matrices or independent rotation and translation arrays according to the type of machine. Chebyshev, simple or Legendre polynomial regression functions can be used to characterize the geometric errors of the MT and are presented and compared. The distribution of measurement points, mesh or cloud, and optimization constraints of polynomial regressions are factors that also affect volumetric error compensation. Therefore, these parameters were studied and presented as well. In addition to the parameters discussed above, another parameter that affects the accuracy of data capture is the measurement noise. To improve the measurement accuracy, multilateration techniques need to be applied. Each of the aforementioned parameters has been studied by using a synthetic test generated by a parametric synthetic data generator. The selected parameters constitute a package of optimization improvement regardless of the optimization methodology, which have improved the nonlinear optimization from 60–70% to 98%.

Modelling of Computer-Assisted Machine Tool Volumetric Verification Process

“…If measurement is carried out using an LT in a position, only a value of ̅̅̅̅̅ is needed. However, if the same LT is located at three different positions to apply multilateration techniques [22], four different values of , = ..…”

“… Errors of identification strategy. To obtain approximation functions the identification process can be constituted with a different optimization process according to the strategy defined by the user [22]. All the influences of errors are divided into sources of errors in which the test definition can predict their behaviour, and sources of error which influence the MT accuracy should be measured and determined in-situ.…”

“…Radial uncertainty is modelled with a constant term plus another dependent on the measurement distance, Eq. (22). Meanwhile angular uncertainties are modelled as constant terms, Eqs.…”

Protocol for machine tool volumetric verification using commercial laser tracker

“…The different verification techniques used to improve the accuracy of the machine are divided into direct measurement techniques, which uses an independent characterisation of the geometrical error of each axis of the MT, known as geometric verification [1][2][3][4][5][6] and indirect measurement, which uses the combined effect of all geometric errors through the intensive process of parameter identification, known as volumetric verification [7][8][9][10][11].…”

Development of precision measurement network of experimental advanced superconducting tokamak

“…It is widely used in measurement jobs of large-scale artifacts. In recent years, a multistation method was proposed based on the highly accurate measuring distance-to-calibration machine tool, 8 articulated CMM 9,10 or on establish the high precision measuring network. [11][12][13] However, a multistation method also cannot measure the hidden components of a large-scale and complicated structural device.…”