A new laser reflection-confocal thickness measurement (LRCTM) method is proposed for the reference lens central thickness calibration of the combined focal-length. LRCTM uses the reflector to reflect the convergent beam that come from the test lens to precisely identify the vertexes of test lens first and last surface, then uses ray tracing facet iterative algorithm to obtain lens central thickness. The test lens is put in the parallel light which makes its coaxality easier to adjust, and the optical path can be shortened with the reflector reflecting the convergent beam. LRCTM has high precision and concise structure, and it is suitable to be applied in the engineering. Preliminary experiments and analysis indicate that the relative measurement accuracy can be better than 0.03%.
A high precision radius automatic measurement method using laser differential confocal technology is proposed. Based on the property of an axial intensity curve that the null point precisely corresponds to the focus of the objective and the bipolar property, the method uses the composite PID (proportional-integral-derivative) control to ensure the steady movement of the motor for process of quick-trigger scanning, and uses least-squares linear fitting to obtain the position of the cat-eye and confocal positions, then calculates the radius of curvature of lens. By setting the number of measure times, precision auto-repeat measurement of the radius of curvature is achieved. The experiment indicates that the method has the measurement accuracy of better than 2 ppm, and the measuring repeatability is better than 0.05 μm. In comparison with the existing manual-single measurement, this method has a high measurement precision, a strong environment anti-interference capability, a better measuring repeatability which is only tenth of former’s.
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