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Validation of the network method for evaluating uncertainty and improvement of geometric error parameters of a laser tracker

Published

Author(s)

Octavio Icasio Hernandez, Diego A. Bellelli, Luiz H. Vieira, Daniel Cano, Bala Muralikrishnan

Abstract

Five national metrology institutes (NMIs) worked together to develop a standard method to evaluate a laser tracker's (LT) measurement uncertainty and LT geometrical errors, and the validation of that uncertainty and geometric errors for large scale dimensional metrology in subsequent measurements. For these evaluations and validations, the NMIs used the network method which consists of measurement of a set of fixed 3D points (targets) from different LT positions. All NMIs realized the network of targets that included 19 fixed 3D points within a defined volume, which were measured by the LT's from five different positions. We use commercial and custom self-developed software for the LT measurement uncertainty evaluation for the data obtained from each NMI. Both software uses the bundled adjustment method. This method can transform the 19 measured 3D points from five different LT positions to a unique reference coordinate system, in our case, the first LT position. From the unique coordinate system, a new composite group of 3D points can be calculated, and residuals (differences) between these composite 3D points and the 3D points in the bundled adjusted positions of each LT can be evaluated. The standard deviation of residuals is considered as the uncertainty of every LT variable, in this case, range, horizontal, and vertical angles. Then, with Monte Carlo simulation, we can propagate the uncertainty of each LT variable to the position of every 3D point in the network. Also, by fitting the composite points to an LT geometrical error model, we can identify the geometrical error parameter of each NMI's LT. This means that we can partially identify a poor LT performance; then, in a real measurement, the user can be provided a warning recommending that they perform an LT compensation.
Citation
Precision Engineering-Journal of the International Societies for Precision Engineering and Nanotechnology
Volume
72

Keywords

bundled adjustment, geometrical errors, laser trackers, network of points, uncertainty

Citation

, O. , Bellelli, D. , Vieira, L. , Cano, D. and Muralikrishnan, B. (2021), Validation of the network method for evaluating uncertainty and improvement of geometric error parameters of a laser tracker, Precision Engineering-Journal of the International Societies for Precision Engineering and Nanotechnology (Accessed September 20, 2021)
Created July 23, 2021