Research Of Optical Lenses Assembling Apparatus Based On Measurement Of Lens Thicknesses, Airgap Distances And Centering Errors

Optical lenses have been widely used in civil, industrial inspection, nationaldefense and military, aerospace and other fields. Demands for the overallperformance of optical lenses are highly increased in many fields. Traditionalmethods now are unable to meet the precision requirements in assemblinghigh-performance optical lenses. The optical lenses assembling apparatus, mentionedin this paper, is designed to achieve high accuracy. Due to the integratedmeasurement of lens centering errors, lens centre thicknesses and airgap distances,the apparatus finishes the assembly work of the optical lenses on one table, whichensures the reference axes consistency and improves the precision and efficiency inthe optical lenses assembly.This paper’s main research work is as follow:1. Taking into consideration the current technology and the future developmenttrends of optical lenses assembling apparatus, the paper studies the technical solutionof one device combining the measurements of lens centering errors, lens centrethicknesses and airgap distances. Research shows technical solution of theintegration of optical lenses assembling apparatus is feasible. 2. By comparing the advantages and disadvantages of various optical structuresin measuring lens centering errors, the paper brings up an optimal optical structurewhich combines the focusing method and lens-switching method. The optimalstructure not only ensures the measurement precision but also avoids problems ofblind measuring area. The paper designs the optical structure and analyzes theimaging quality of the optical system. The results of the analysis demonstrate thatthe design can satisfy the requirements and ensures the image quality on the basis ofa reasonable allocation of the optical lenses tolerances. The ray tracing modelestablished in the paper also analyzes the effects of stray light on the imaging quality,which turns out to be little.3. The lens centering errors calculation model is established to calculate theimage position of every sphere center and the paraxial magnification in the imagingprocess. The model can also calculate centering errors of the lenses according to thediameter of trajectory by the moving of the center of the cross target and the paraxialmagnification. The model provides a method to calculate centering errors for themain control software.4. The paper brings up the method of optical coherent measurement, whichmeasures optical lens thicknesses and airgap distances without contacting the lenses.Based on the Michelson interferometer, it is easy to operate the apparatus whenoptical fiber is used to conduct light. In order to locate the reflection intensity fromall surfaces of lenses in the dynamic range of photoelectric detector, a lens in themeasurement arm is designed to change the focus position continuously in a range. Amathematical model between material dispersion and coherence signal is establishedto calculate lens centre thicknesses and airgap distances.5. The software of the optical lenses assembling apparatus is programmed. Inthe module of measurement of lens centering errors. The paper also researches thealgorithms to seek the coordinates of the cross target’s centre and to fit the optimalaxes of all sphere centres. In the module of measurement of lens thicknesses andairgap distances, an algorithm of seeking the peak of coherence signal is researched. 6. The measurement accuracy of the apparatus is analyzed according to thetheory of errors. The results show that the total line centering errors of optical lensesis0.77μm, and that the total angle centering errors of optical lenses is1.6arc-seconds, and that the total errors of lens centre thicknesses and airgap distancesis2.30μm.7. Experiments are made to measure the lens centering errors, lens centrethicknesses and airgap distances of known lenses using the apparatus. During theseexperiments, the measurement accuracy can be obtained. The results show that themeasurement accuracy of line centering errors of sphere surface is better than1μm,and the measurement accuracy of angle centering errors of plane surface is betterthan2.4arc-seconds, and the measurement accuracy of lens centre thicknesses andairgap distances is better than3μm.