Research On Design And Machining Method Of Freeform Optical System Under Manufacturing Constraint

With the development of technology,various new optical systems and new industry demands have gradually emerged,surpassing the capabilities of traditional optical systems composed of conventional optical components.Consequently,new optical systems incorporating freeform surfaces have emerged and are gradually being applied in various scenarios.However,while freeform surfaces bring numerous advantages to optical systems,their complex surface shapes also pose various challenges,including design,fabrication,inspection,and adjustment.In particular,existing manufacturing methods have limited the machining accuracy and achievable aperture of freeform lenses,directly impeding the further development of freeform optics.The two main factors affecting the machining accuracy of freeform surfaces are:1)the manufacturing process of freeform surfaces,and 2)the difficulty of machining freeform mirror surfaces.This paper addresses these several aspects by studying the following methods to decline the machining error of freeform surfaces:(1)In the toolpath of single-point diamond turning for freeform surfaces,this paper analyzes the design principles of traditional toolpath methods and the sources of errors during the turning process.For the linear interpolation error during the processing,the traditional equiangular algorithm does not consider the surface representation of the freeform surface.In this paper,an adaptive toolpath algorithm is designed,which can select appropriate tool control points on the Archimedean spiral line according to the changes in the freeform surface shape.Using the adaptive algorithm for path planning can make the overall error distribution of the surface shape more uniform.At the same time,using the same tool control points can improve the processing accuracy and efficiency of the surface shape.(2)Considering the characteristics of turning methods,the difficulty of machining freeform surfaces is analyzed in relation to the deviation from a reference non-freeform surface.Therefore,the deviation root mean square(RMS)of freeform surfaces relative to the reference non-spherical surface is proposed as a measure of the difficulty of turning freeform surfaces.A large number of randomly generated freeform surfaces are used for verification.(3)The initial structural design of freeform surfaces is conducted using the principle of equal optical path length,and the RMS deviations of each freeform mirror surface are appropriately added to the ZEMAX merit function as manufacturing constraints.The initial structure is then further optimized with and without the addition of manufacturing constraints.Compared to the case without manufacturing constraints,incorporating manufacturing constraints significantly reduces the machining difficulty of individual mirror surfaces while ensuring imaging quality of the optical system.