Design Method Of Single Diamond Turning Progressive Addition Lenses And Its Realization

Compared with traditional rotational symmetric optical elements,freeform surface elements have the characteristics of small size and high design freedom However,the design and processing of such components are difficult,which limits their wide application in the optical field.In recent years,single point diamond turning has been regarded as an effective method for machining optical freeform surfaces.The advantage of this machining method is that it can be formed in a single clamping and can often obtain high-precision components.Progressive addition lens(PAL)is a typical optical freeform surface,which is widely used to correct people’s vision problems.In this paper,single point diamond turning is used as a PAL processing method,and its key technologies in optical design,turning principles,and tool path planning are studiedThe design method of PAL can be divided into direct method and indirect method.This study uses direct method,the design of the surface can be divided into solving the power addition curve and constructing the surface.The change in vertex power along the meridian line is called the power addition curve.The design of this part needs to ensure that the optical change on the whole curve is continuous to provide a smooth visual effect.After explaining the design principle of the addition power curve,this article focuses on analyzing the change law of the curve when different design parameters are used.The results show that when the order of the nonzero derivative of the curve at the distant-sighted and near-sighted points is larger,the transition of the curve is smoother and the area of the far-view and near-view zones increases correspondingly.Then the optical variation on the meridian is extended to the whole surface and a design example is given.Finally,the performance evaluation criteria of the lens are briefly described,and the iso-sphericity and iso-cylindrical degree change diagrams of the design surface are obtained by using optical analysis software.Single point diamond turning has a different trajectory generation principle than traditional turning,and the expression of machining instructions is also different.Starting from the configuration of single point diamond lathe,this thesis discusses the basic principle of single point diamond turning,and briefly describes the method of coordinate system transformation.Then,the selection criteria of geometric parameters of diamond tools are discussed.In order to avoid interference and overcut which affect the quality of the surface to the greatest extent,it is necessary to reasonably select the rake angle,clearance angle,tool nose radius and included angle of the turning tool according to the characteristics of the surface.For the convenience of explanation,a sine surface with a large change in curvature of the surface is taken as an example,and the method of selecting the geometric parameters of the tool is explained in detail.Precise planning of tool path during turning is the basic requirement of ultra-precision machining.The tool path planning principle of single point diamond turning is as follows:firstly,a series of discrete points are selected from the two-dimensional plane,and then these points are mapped to the three-dimensional surface to obtain the turning track.After comparative analysis,an optimized tool path generation method is proposed,which selects discrete points by equal angle method and compensates tool radius in Z direction.The simulation results show that this method can avoid the over-cutting caused by the position of the tool tip,and at the same time ensure that the rotation of the spindle and the transverse feed are uniform,avoid unnecessary vibration,and is beneficial to the cutting quality.A 250UPL single point diamond lathe from Moore was used for turning experiments,and a PAL surface with a roughness of 0.087 um was obtained.FFV lens optical analyzer was used to measure the vertex power and cylinder distribution of the lens surface,which verified the rationality of the optical design and processing methods.