Laser Tracker Kinematic Error Model Formulation and Subsequent Verification under Real Working Conditions

Abstract

A kinematic model of the Laser Tracker (LT) based on the Denavit-Hartenberg method has been developed. In this model, error matrices have been included with error parameters for linear and rotary joints. The calibration method is based on the measurement of a mesh of reflectors measured by a LT from different positions. Error parameters are calculated knowing that distances between every pair of reflectors is the same regardless the LT position. The absence of nominal data prevents us from knowing the calibration behaviour and its suitability. Although synthetic data tests show a good accuracy improvement, it is not possible to know if this will work with under real working conditions. An experiment has been made to check the calibration procedure. A set of 17 reflectors have been placed on a Coordinate Measuring Machine (CMM) and have been measured by a LT from 5 different positions. Reflector positions have also been measured with the CMM to calculate the initial errors. With LT measurements we calculate the error parameters. LT measurements are recalculated considering the kinematic error model and compared with the CMM measurements to get the residual error. Two errors have been calculated; distances error between reflectors and their position error compared with CMM data.