Surface bilateral profile measurement of curved transparent components based on chromatic confocal sensor

Abstract

The system performance of many industrial products is dominated by the surface profile accuracy of their primary component, thus it is of great essence to achieve high precision profile characterization. The chromatic confocal technology provides an effective means for precise measurement of surface profile, yet there exists non-negligible errors when measuring transparent curved component. The aim of this paper is to investigate the effects of the curvature of component on the confocal rays and obtain its bilateral surface profile by chromatic confocal technology simultaneously.The assumption of tilted plate approximation for curved specimen was made. By adopting the optical ray tracing analysis, a modified model was then proposed to correct the measurement error existed in the traditional one. The validity of the proposed model is conducted by 2D bilateral profile measurements of the hemispherical shells after the calibration with tilted fused silica plates. Experimental results show that the proposed model significantly improves the measurement accuracy of bilateral profile of curved transparent components at large equivalent tilt angle. This method overcomes the drawbacks of other spatial coordinate based profile measurement methods, and achieves high accuracy simultaneous measurement of bilateral profile of transparent components.

Bilateral form characterization of curved transparent components using chromatic confocal sensor

“…To address above challenges and difficulties, by employing chromatic confocal measurement approach, a modification model based on the assumption of plane-parallel plate approximation is proposed to correct the errors caused by the surface curvature of curved transparent components. 23 This allows accurate form measurement merely by linear scanning without swinging motion for surface normal tracking, which reduces the scanning degrees of freedom in a certain range. Using a hemispherical resonator sample as the typical component, we simultaneously measured the bilateral circumferential and axial profiles of the resonator and its circumferential thickness variation as well.…”