Slow tool servo diamond turning of optical freeform surface for astigmatic contact lens

Abstract

ABSTRACT Three ultra-precision machinin g processes namely fast tool servo, slow tool servo and diamond milling, are frequently used to produce optical freeform surface. Slow tool servo machining has the advantages of no extra attachment and fast setting-up, however the three dimensional tool shape compensation and tool-path generation must be conducted carefully for getting high form accuracy and fine su rface finish. This research aimed to deve lop a model of three dimensional tool shape compensation for generating 3D tool path in slow tool servo diamond turning of asym metrically toric surface for astigmatic contact lens. The form accuracy of freeform surface was measured by ultra-high accuracy 3D profilometer (UA3P) with user define function. After co rrection, the form error is less than 0.5 m both in X- and Y-direction and the surface roughness is less than 5nm. Keywords: astigmatic contact lens, slow tool servo diamond turning, optical freeform surface 1. INTRODUCTION The manufacturing method of contact lenses includes direct lathing, spin casting and cast molding. In traditional, the toric surface used to correct the astigmatism has been inefficien tly fabricated by direct lathing. The disposable astigmatic contact lens can’t be made with this process due to the high cost of produc tion. Because of the pr ogress of the freeform optics machining technology, the astigmatic contact lens could be manufactured by casting method recently. For the casting method, the plastic optical mould made by plastic injection method is used to generate the contact lens. And the