Research On Processing Technology Of Progressive Multifocal Lens Based On Fast Tool Servo

Optical free-form surface elements can not only realize some special optical functions,but also effectively reduce the volume and weight of optical systems and greatly improve imaging quality.Currently,they have been widely used in various frontier fields and daily life.Progressive multifocal lens is a typical optical free-form surface element.Compared with the traditional spherical lens,the diopter of the far-view area and the near-view area of the lens are different,and the diopter gradually changes smoothly in the intermediate transition area.The wearer can see objects at different distances continuously and clearly.However,due to the complex surface structure of the lens,the processing cost is high and the marketing is difficult.Single-point diamond ultra-precision turning technology based on fast tool servo system can process progressive multifocal lens,and the processed lens has high surface quality and low manufacturing cost.This paper attempts to design and manufacture a set of fast tool servo device according to the surface shape characteristics of progressive multifocal lens,and use it in the turning experiment of progressive multifocal lens,and to study the influence of different processing parameters on the surface quality and surface roughness of lens through the processing experiment.The geometric profile of progressive multifocal lens is relatively complex,and the lens profile corresponding to different initial parameters is also different.In this paper,the surface shape characteristics of progressive multifocal lens are studied.According to the set initial parameters,the meridian of lens is designed by Winthrop method,and on this basis,the rise equation of lens surface shape is solved.Three-dimensional geometric modeling of lens surface shape is carried out in MATLAB,and the evaluation method of lens surface shape is studied by using the concepts of sphericity and cylindricity.According to the rise equation of the lens surface shape and the geometric relation of the cutting part shape of the cutter,the geometric parameters of the diamond cutter are solved.Combined with the turning principle of non-rotational symmetric curved surface,the lens three-dimensional geometric model is discretized into equidistant spiral lines,and a series of tool tip position points for numerical control programming are obtained by using equal angle division method.The fast tool servo device that can be used to process progressive multifocal lenses is the basis of experimental research.According to the obtained lens surface equation and the characteristics of tool tip motion trajectory,this paper calculates the overall parameters of the fast cutter servo device,the overall structure of the fast tool device is designed.Some standard parts are selected,and some non-standard parts are designed and simulated by finite element method.Furthermore,an experimental platform for the fast tool servo system is built on ultra-precision machine tools.According to the working principle of the fast-cutting servo closed-loop control system,the hardware circuit connection and numerical control program debugging of the fast tool device are carried out to realize the three-axis linkage of the machine tool spindle,the X axis and the motion axis where the fast tool is located.The design experiment tests the working stroke,system static stiffness,positioning accuracy and repeated positioning accuracy of the fast tool device.The processing of progressive multifocal lens not only needs to process the correct surface shape,but also needs to ensure that the processed surface quality meets the requirement that the surface roughness is less than 0.1μm.There are many factors that affect the surface quality.The main influencing factors are spindle speed,feed rate and back feed rate.The quality of lens processing surface can be characterized by the three-dimensional surface morphology and surface roughness of the processing area detected by a white light interferometer.Through the method of controlling variables,the effects of spindle speed,feed rate and back feed rate on the surface quality of lens processing are studied separately.According to the detection results of the white light interferometer,the reason is analyzed.By changing the numerical control program,the processing parameters are optimized to improve the surface quality of lens processing.