A globally smooth tool path reconstruction method for the ultra-precision diamond turning of microlens arrays

Microlens arrays have been widely used in industry and extensively researched in academia over the years. Lens arrays machined by slow and fast tool servo technologies commonly suffer from vibration marks near lens edges, which undermine surface finish and from accuracy. The vibration marks are caused by the machine tool's nonlinear response to abnormally large local tool path accelerations at lens edges. In this study, a globally smooth tool path reconstruction method based on frame line guided cubic spline interpolation is proposed. The incorporation of globally continuous frame lines is demonstrated to significantly improve both tangential and radial tool path smoothness. Comparative theoretical analysis and experimental investigation are conducted together with direct strategy and tangentially smooth strategy. Experimental results show significant suppression in vibration marks, a 43.8 % decrease in surface roughness Sa, and a 63.0 % decrease in form error PV compared to the direct strategy. And equal results are acquired using the proposed method with twice the efficiency of the direct method. Moreover, the nonuniformity of surface topography in a single lens resulting from the periodic cutting-in motions is also observed, explained and effectively reduced in this study.