Fabrication of polygonal Fresnel lenses with a rotating cutting tool on three-axis ultraprecision lathes

Abstract

Fresnel lenses are gaining wider applications due to their advantages of being lighter, thinner and suitable for increasingly complex and miniaturized optical systems. To increase the fill factor when combining multiple Fresnel lenses to form an array, polygonal Fresnel lenses have been designed and machined with the ultra-precision machine tools in industry. However, for the three-axis machine tool equipped with the X-, Z-, and C-axes, it is difficult to machine the straight edges of the polygonal Fresnel lens due to the lack of a Y-axis. Although the synchronized servo motions of the linear axis and the spindle can be utilized to fit the relative motion trajectory of the tool to a straight line, the cutting tool rotates relative to the workpiece and thus the tool rake face is not always perpendicular to the direction of the relative motion during machining. In this paper, a high-precision rotating platform is integrated into the three-axis ultra-precision machine tool to make the cutting tool track the rotation of the spindle and keep the tool rake face perpendicular to the direction of the relative motion at all times. Then the tool trajectory is generated and the influence of the tool nose radius is compensated. Finally, an experiment of cutting the hexagonal Fresnel lens is performed on a three-axis ultra-precision lathe, and the machined workpiece is inspected with a white light interferometer. The experimental results show that the profile accuracy of the machined polygonal Fresnel lens satisfies the requirements in industrial applications.