| Polymer optical lens is a kind of optical element which is made of polymer by the way such as mold compression and inj ection molding,among which precision inj ection molding is the most widely used molding method.However,the manufacturing of high-end polymer optical lenses of precision level still faces the following problems to be solved:to reveal the influence law between geometric accuracy and optical performance;to improve the balance of volume shrinkage rate and design precise mold cavity;to introduce auxiliary means to reduce the birefringence and improve the quality of precision replication of surface microstaucture for lens;to adopt intelligent algorithm for multi-quality objective optimization to obtain the best combination of process parameters.The research on these key problems,which is of great significance to the formation of high-end polymer optical lenses,will help to improve the geometric accuracy and optical performance of polyner optical lenses comprehensively.This paper has firstly studied the relationship between the surface geometrie accuracy of polymer optical lens and its optical performance,and then studied the optimization design method of precision mold cavity,injection-assisted molding technology and injection process parameters optimization method.Finally,the effectiveness is verified by a comprehensive experiment of lens molding.The main research work of this paper is as follows:(l)The relationship has been studied between geonetric accuracy and optical performance of polymer aspheric optical lens.By means of simulation and experimental verification,an accurate model has been established in surface error and wavefront aberration based on Zemike polynomial.It has been found thatuunder a certain RMS value of surface error,the optical performance have better performance with the symmetrical distribution near the geometric center of rotation.It has also been found that,under a certain di stribution form of surface error,the greater the RMS value of surface error,the worse the optical performaice,and the distortion rate is highly sensitive to the RMS value at the bottom of the lens edge with a relative height less than 0.2.(2)A precise mold cavity design method based on non-linear shrinkage prediction has been proposed.The control algorithm based on the unified heat conduction model was adopted,and the standard deviation of the volume shrinkage of all mesh nodes was taken as the optimization objective.On this basis,the matrix operation of differential amplification was carried out on the coordinates of each node.Finally,the reverse modeling of precision mold cavity was carried out to point clouds in transformed node coordinates.The experimental results showed that the maximum surface deviation of aspheric optical lens sample is reduced by 56.5%and the average deviation is reduced by 32%compared with the traditional mold cavity design in method of uniform amplification.(3)The compression optimization structure of the automatic calibration function has been proposed,and the inffluence of the process parameters of injection compression mold on birefringence was studied,which pointed out the direction for reducing the influence of birefringence of lens.In addition,in order to improve the replication quality of polymer lens with microstructures,an injection ultrasound assisted forming technology was designed.Because of the instantaneous high temperature and high pressure on the polymer caused by the the core,the average height of the surface microstructures of optical lenses was increased by about 14.6%.(4)Taking haze HR and peak-valley value PV20 as quality objectives,a multi-objective optimization method of injection process parmeters based on improved genetic algorithm was proposed,and the best combination of process paraneters was obtained.Aiming at the problem that the classical NSGA-? genetic algorithm is not robust in diversity,an improved algorithm based on congestion distance elimination strategy has been proposed,which could effectively improve the diversity of the algorithm and the convergence speed.It was found that the process parameters which had an important impact on the two quality objectives were the holding pressure and the mold temperature.The comprehensive quality of the lens has been significantly improved by the improved NSGA-? algorithm,and the optimization results of HR and PV20 were only 4.226%and 0.532 ?m.(5)Taking an infrared Fresnel lens as an example,the experimental verification of the full text method is carried out After analyzing the design prindple and optical performance requirements,the precise mold cavity was designed based on the method of non-linear shrinkage prediction,and the precision injection ultrasonic mold is manufactured.Finally,the injection ultrasonic process paraneters are optimized based on the improved genetic algorithm.Compared with the traditional injection moulding process,the synthetic quality of the infrared Fresnel lens produced by this method has been effectively improved.The average groove height h has increased by 15.6%,and the MTF value is larger at the same spatial frequency. |
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