Optimization of fast tool servo diamond turning for enhancing geometrical accuracy and surface quality of freeform optics

Fast tool servo (FTS) diamond turning is a promising technique for high-precision generation of freeform optics with remarkable efficiency. However, the conventional constant scheme for control point sampling fails to consider the surface variation, which might lose some details of the surface profile and result in low form accuracy and non-uniform surface quality. Facing this issue, this manuscript proposes a novel optimization method for control points sampling, which restrains the deviations and contains as much of the surface details. In the optimization method, the sampling intervals between two adjacent control points are actively adjusted to adapt the surface variation of the desired surface. By adopting this method, the sampling induced interpolation error between the control points is restrained within the tolerance and eliminates lack/over-definition of control points in the machining area. The feasibility of the proposed optimization method is demonstrated by both theoretical prediction and fabrication experiment of sinusoid freeform surface. Compared with the conventional sampling method, both the predicted and measured form error of the proposed method are remarkably reduced about 35 % with the same amount of control points. This technique provides a new route to sampling control points in FTS diamond turning to achieve high accuracy and flexible fabrication of freeform surface machining.