Geometrical Characterisation of a 2D Laser System and Calibration of a Cross-Grid Encoder by Means of a Self-Calibration Methodology

• Published in: Sensors (Basel, Switzerland) Switzerland), 2017-08, Vol.17 (9), p.1992
• Main Authors: Torralba, Marta, Díaz-Pérez, Lucía C, Valenzuela, Margarita, Albajez, José A, Yagüe-Fabra, José A
• Format: Article
• Language: English
• Subjects: 2D-stage; Axes (reference lines); Calibration; grid encoder; Lasers; Measuring instruments; nanopositioning; plane mirror laser interferometer; self-calibration; Uncertainty
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s17091992

This article presents a self-calibration procedure and the experimental results for the geometrical characterisation of a 2D laser system operating along a large working range (50 mm × 50 mm) with submicrometre uncertainty. Its purpose is to correct the geometric errors of the 2D laser system setup generated when positioning the two laser heads and the plane mirrors used as reflectors. The non-calibrated artefact used in this procedure is a commercial grid encoder that is also a measuring instrument. Therefore, the self-calibration procedure also allows the determination of the geometrical errors of the grid encoder, including its squareness error. The precision of the proposed algorithm is tested using virtual data. Actual measurements are subsequently registered, and the algorithm is applied. Once the laser system is characterised, the error of the grid encoder is calculated along the working range, resulting in an expanded submicrometre calibration uncertainty (k = 2) for the X and Y axes. The results of the grid encoder calibration are comparable to the errors provided by the calibration certificate for its main central axes. It is, therefore, possible to confirm the suitability of the self-calibration methodology proposed in this article.