Research On The Machining Mechanism In Slow Tool Servo Turning Of Microlens Array And The Evaluation Of Its Optical Performance

Microlens array is a typical kind of micro optical elements,which has the advantages of small size,light weight and easy integration.It is widely used in the optical fields such as uniformly light propagating,optical communication and optical field imaging.Slow tool servo turning(STS)is an ultra-precision machining method that can realize the machining of microlens array.In order to ensure the optical performance of the microlens array,STS machining process is usually optimized to reduce the machining error.However,the current research mainly focuses on improving the machining accuracy of parts,and is lack of research on the relationship between machining error and optical performance,which leads to the adoption of conservative control method on machining accuracy control benchmark,and increasing the machining cost and difficulty.Based on the STS machining method,this paper studies the tool locus optimization,surface generation prediction,the relationship between machining error and optical performance as well as the evaluation mechanism of the optical performance,to improve the optical performance of the microlens array.The main research work is as follows:(1)The tool locus generation method of STS machining of microlens array is studied and compared.The optimization methods of tool locus are studied to improve the precision of lens edge area,the smoothness of Z axis motion,and the efficiency of machining.Based on the analysis of the topological structure of ultra-precision machine tools,an virtual axis machining method is proposed to realize the independent machining of every cell using the XYZC axis of machine tools.Research shows that:the mixed discretization method and the Z direction offset compensation method are suitable for machining occasions where the spherical radius of lens cell is much larger than the tool tip radius,which the residues of material is small and the machining smoothness of the machine tool can be improved.The locus optimization method can reduce the machining residue of the lens edge on the radial direction of the workpiece,avoid the influence of z-axis speed jump on the boundary quality,and the optimization method of eliminating invalid locus can effectively improve the machining efficiency.(2)In view of the multi-factor effect on the surface quality of the STS machining of the microlens array,a prediction model of the surface generation of the STS machining is proposed,and used to optimize the machining parameters and predicted the error distribution of the STS.Based on the study of planar ultra-precision turning,this model considers the influence of machining parameters,tool parameters and other factors,and emphatically analyzes the influence of three-dimensional tool-work vibrations.On this basis,the mathematical description of the microlens array and the optimized locus of STS machining are introduced to complete the model establishment.The research shows that:there is an optimal value of tip radius to makes the theoretical surface roughness minimum for a certain mcrolens array cell radius.The reduction of feeding speed can effectively reduce the surface roughness on the premise of meeting the machining efficiency.The tool tip radius error and the tool alignment error change the radius of the lens and affect the distribution of the low and medium frequency error.(3)In order to evaluate the optical performance of microlens array in the application optical field imaging,and study the process optimization method to improve the optical performance,based on the theory of light transmission and diffraction,the optical characteristics of microlens array such as imaging characteristics,focal spot quality,focal length,modulation transfer function(MTF)and distortion are studied.The optical measurement platform is built according to the proposed measurement method of microlens array optical performance based on CCD vision detection technology.According to the measurement result,the influencing mechanism between the microlens array topographic error and optical performance parameters is established.The error of the microlens array cells'positions affects the positions of the microlens array's foci.The spherical radius error of the lens cell affects the focal length.The non-rotational symmetry degree of the low and medium frequency error distribution decreases the MTF value of the cell,which makes the contrast resolution of the lens to the low and medium frequencies of optical signals decreases.(4)The STS machining and optical test experiments of the microlens array are carried out.With different machining parameters are used and the tool error is introduced to the machining,microlens arrays of Al6061 were machined by STS.The transparent microlens arrays of PMMA material was produced from the microlens array of A16061 by UV curing transfer printing technology,and the optical performance was tested.Through these experiments,the effect of STS machining of microlens array on the optical performance is verified.The roughness of the microlens array can be reduced and the focusing consistency of each element can be improved by reducing the feed per workpiece revolution and choosing the optimized radius of the tool nose.By reducing the tool alignment error,the MTF value of the unit to the medium and low frequency optical signal can be improved.