Uncertainty estimation of an indexed metrology platform for the verification of portable coordinate measuring instruments

Abstract

This work presents the development of an uncertainty estimation procedure for an indexed metrology platform. The use of an indexed metrology platform in calibration and verification procedures for portable coordinate measuring instruments, enables the evaluation of different working volumes of the instrument that rotates with the platform in six rotating positions without moving the gauge from a fixed location, reducing in this way the testing time and test setups in comparison with the tests included in the applicable standards. The platform is able to express points in a global reference coordinate system located in the lower platform through its mathematical model. Due to the platform model complexity and according to the GUM supplement 1, the propagation of distributions using the Monte Carlo method was applied to estimate the platform measurement uncertainty. The different error sources affecting the platform uncertainty were first identified. An analysis of the dynamic behavior of the platform by means of a computational and experimental modal test was done in this work. The capacitive sensors assembled in the platform determine the position and orientation of the upper platform with respect to the lower platform and were selected as input variables of the model with their related errors. The n-homogeneous transformation matrices obtained in the simulation as output variables will allow the coordinate reference system change from the upper platform to the lower platform. In this way, it is possible to estimate the influence of the indexed metrology platform position and orientation uncertainty in the generation of points in a global reference system and as a consequence, its influence in a distance measurement.