Measurement of complex surfaces using precision coordinate measuring machine with Zernike algorithms

Abstract

The paper introduces an innovative approach called Zernike-based CMM Surface Metrology (ZCSM) to enhance the accuracy of measuring large optical surfaces using coordinate measuring machines (CMMs). Traditional methods like laser interferometry and deflectometry, while precise, face limitations such as restricted dynamic range and sensitivity to specific surface properties. CMMs offer a promising alternative but are susceptible to systematic errors, particularly due to probe deflection when scanning, which can introduce geometric errors not present on the test surface. ZCSM addresses this challenge by fitting the surface form using Zernike polynomials, decomposing form errors into wavefront aberrations. A notable feature of the ZCSM method is the dual-parameter error compensation, which iteratively removes errors by correcting wavefront aberrations and verifying surface profiles until within the tolerance range. The feasibility of ZCSM was validated by measuring an astronomical mirror using a ZEISS XENOS CMM. The results showed that ZCSM’s accuracy is comparable to interferometry, underscoring its potential as a viable alternative for precision metrology. The research indicates that ZCSM significantly improves the measurement accuracy of CMMs for large optical surfaces. Future research could focus on refining the method to eliminate higher-order residual aberrations and angular offsets, further enhancing its precision and applicability.