Investigation Of Ultra-precision Cutting Technique On Complex Microlens Array

With the rapid development of society and the profound change of science and technology,people have set higher requirements for optical performance and miniaturization of optical products.To meet the requirements,microlens array(MLA),which has compact structure and can realize complex optical performance,has been developed.Such advantages of MLA as effectively reducing the volume of optical modules and improving imaging performance of optical system make MLA be a kind of important optical parts.As development requirements increase,to realize complex optical performance,the geometric structure of MLA changes from easy-tocut conventional structure to difficult-to-cut complex structure;to adapt to complex application environment,the materials of MLA have changed from easy-to-cut materials to difficult-to-cut materials.Therefore,the MLA are gradually upgrading from conventional MLA to complex MLA.In order to meet above requirements for complex MLAs and machine such complex MLAs with high accuracy and efficiency,this dissertation focuses on studying ultra-precision cutting technology for complex MLAs.The relevant research contents are summarized as follows.To solve the problem of high-precision and high-efficiency cutting MLA with complex pattern,the scheme of slow tool servo(STS)is proposed,and a planning strategy for cutting path of STS is developed according to diversity characteristic of complex pattern.Following the process of calculating cutting path of STS for MLA,aiming at existing shortcomings of present algorithms,the algorithm for generating discrete points is optimized,a method for calculating Z-coordinates of discrete points based on filtering calculation mode is proposed,and the efficient calculation for compensating tool nose radius along Z-direction is realized according to geometric model for compensating tool nose radius along Z-direction.Therefore,a planning strategy for calculating cutting path of STS for MLA with complex pattern is developed.The experimental results of designed various MLA and microstructure array(MSA)show that the developed planning strategy not only has good computational accuracy and efficiency,but also has good applicability for complex pattern,such as the MLA with circle contour,dual-aperture and unequally spacing and the MSA with non-circle contour and variable spacing.Finally,the characteristics of MLA cut by STS method are studied,and research results show that integrated turning path of STS has restricted machinable structure range of unit surface in MLA.For the MLA with complex unit surface that cannot be cut by STS method,the off-spindle-axis rotation turning(OSART)method is proposed.Firstly,OSART technology is studied,including the kinematics of off-spindle-axis rotation,the planning strategy for turning path of OSART,and machinable geometric structure of MLA with OSART method.Then a variety of MLA and MSA with complex unit surface machining experiments are designed to demonstrate the correctness of above research conclusions,and to show machining advantages and potential of OSART from different perspectives.Subsequently,the OSART results of single crystal germanium(Ge)MLA show that although this method is able to cut Ge MLA in ductile mode,the surface roughness and cutting efficiency need to be further improved.The hardness and brittleness of Ge make above two cutting methods unable to give consideration to both machining accuracy and efficiency.To solve this problem,ultrasonic elliptical vibration cutting(UEVC)technology is introduced into above two cutting methods forming ultrasonic elliptical vibration assisted cutting(UEVAC)methods.The introduction of elliptical locus changes the cutting path of original cutting method.To prevent elliptical locus from over-cutting or under-cutting with target contour reducing the accuracy of microstructure,the algorithm for calculating cutting path of UEVAC method is studied.According to the formation of describing MLA with discrete points,the subdivision interpolation calculation mode is employed to calculate the motion path of tool tip for desired contour.According to geometric characteristics of variable curvature in elliptical trajectory,a nonequidistant offset compensation strategy is proposed.Based on above research conclusions and specific cutting methods,an algorithm for calculating cutting path of UEVAC method is proposed.The designed comparative machining experiments verify the necessity of non-equidistant offset compensation strategy,and the correctness of proposed algorithm.Meanwhile,it also shows that the UEVAC method has the advantages of machining microstructures whose sag heights are larger than the amplitude of longitudinal vibration.Finally,the machining results of two large size concave and convex MLAs demonstrate that UEVAC method has good machining accuracy.Based on improved cutting accuracy with aforementioned algorithm,highefficiency processing for cutting Ge MLA with UEVAC method is further investigated.Firstly,the influence law of UEVC technology on enhancing the critical cutting depth of brittle-plastic transition of Ge is studied by analyzing chip micro morphology of turning Ge plane experiment.Secondly,the relevant processing experiments are designed to study high-efficiency processing plan for turning Ge MLA with UEVAC method.Finally,based on above research contents,ultrasonic elliptical vibration assisted STS method and OSART method are employed to fabricate Ge MLA.The relevant machined results indicate that compared to conventional cutting method,UEVAC method not only decreases form error PV and surface roughness Sq of unit of Ge MLA by 24.35% and 12.5%,respectively,but also increases cutting efficiency of MLA by 13.5 times.Therefore,UEVAC method can be employed to achieve mass production of Ge MLAs.