To accurately characterize the geometric form of key components in industrial products, many profile measuring instruments have been developed to date. However, there are some special components, such as the hemispherical resonators featuring thin curved transparent surfaces, which are difficult to be measured using general instruments. The chromatic confocal technology was introduced in this paper to conduct the bilateral form characterization of this type of surfaces. Based on the assumption of tilted plate approximation, a modified ray tracing model was presented to correct the errors produced by the curved surfaces. The experiment of measurement on tilted, fused silica plates was conducted to demonstrate the effectiveness of the proposed model. Results show that the developed model improves the measurement accuracy of plates with large tilt angle. A three-axis motion stage was built with self-developed chromatic confocal sensor to obtain the bilateral profiles of the resonator. By fitting the spheres with the scanning profiles, the form error between the measurement points and the fitted spheres can be calculated. Partial form errors along the circumferential and axial directions of the resonator are evaluated, and an intuitive assessment of its thickness variation along the circumferential direction was made.
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.
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