New method for testing the laser tracker length measuring unit using a large-scale horizontal arm CMM and its application for assessing the accuracy of distance measurements

Abstract

The paper presents a method for determining systematic errors and variability in the readings of a laser interferometer used in laser tracking systems. The method utilizes standalone interferometers treated as references and a large-scale CMM as a system for moving the measurement point, allowing continuous measurement up to a maximum distance of 15 m. Both interferometers use the same corner cube reflector and remain stationary during measurements. The concept and assumptions of the developed method are described as well as key technical issues and their solutions. The research setup, characteristics of the tested and reference systems and the research methodology together with the measurement strategy, are presented. Results obtained with the developed methodology can be used as input data to the simulation model of the laser tracker measuring unit. This model can be used to estimate the length measurement uncertainty after a single measurement of the assessed distance. This paper presents uncertainties obtained by means of the simulation and compares them with ones estimated using statistical analysis of a series of measurements. The conducted validation proved the metrological consistency of the results with uncertainties associated to them for both considered methods. Advantages of the presented method over previously developed methods were also shown. They include faster and simpler adjustment of the tested and reference systems, the general availability of the systems used for moving a measuring mirror (corner cube reflector), use of a single corner cube reflector for both laser systems, making the measurement results independent of the influence of translation and rotation errors of the guide/system responsible for moving the corner cube reflector and considerable reduction of the impact of environmental conditions on the obtained results.