Highly efficient machining of non-circular freeform optics using fast tool servo assisted ultra-precision turning

Abstract

Freeform optics has been regarded as the next generation of the optical components, especially those with non-circular apertures are playing an increasingly significant role in scanning field and specialized optical system. However, there still exist challenges to machine non-circular optical freeform surface. This paper is focused on highly efficiently generating freeform surfaces with optical surface quality by ultra-precision turning using a fast tool servo (FTS). A systematic strategy of machining smooth freeform surfaces with rectangular aperture is proposed in this paper. The contour of freeform optics is decomposed and assigned to the motions of slide and FTS back-and-forth. An optimized model is established for deriving the profile of the rotational component to cater for the capacity of FTS. Tool path reconstruction is carried out to generate a smooth tool trajectory and modified the contour to cater for the stroke of FTS. Simulation is adopted to analyze the machining property of a typical rectangular freeform surface. A rectangular freeform surface is efficiently machined via the proposed method, where a micron level profile error and nanometric finish in Ra are realized. Characteristics of reflection are analyzed via experiment and simulation. Prospects of such machining approach are discussed to provide guidance to future study.

RBF Interpolation Algorithm for FTS Tool Path Generation

“…Tian et al used ultraprecision diamond turning machining technology based on an FTS system to realize 3D surface generation of a rear-view mirror, which is a typical optical freeform surface [10]. Li et al fabricated a rectangular freeform surface on germanium using FTS, satisfying designing targets of the freeform surface [11].…”

“…However, neither the accuracy nor the smoothness requirement could be fulfilled. Li and Zhou both used Hermite interpolators to regenerate the surface [11,23]. However, all points on the surface could not achieve a determined solution due to the characteristics of the Hermite interpolant.…”

Novel Approach to Improve the Optical Performance by Machining Process Without Surface Finishing

“…Conventionally, surface finishing process [10][11][12] followed by machining process is considered as one of the standard procedures to improve the surface quality of optical elements. Further, the ultraprecision machining technology has been rapidly developed through numerous studies, such as parameter optimization [13][14][15][16][17] and random path generation [18,19]. Although the surface finishing process has been developed as a way to indisputably improve the quality of optical surfaces, it is time-consuming and less economical owing to the additional efforts that are required after the machining process.…”

Mechanically Enabled Two-Axis Ultrasonic-Assisted System for Ultra-Precision Machining

“…Complex surfaces are widely demanded in various applications including optics, bioengineering, and advanced manufacturing [1][2][3]. Ultra-precision diamond cutting is normally used for the fabrication of complex surfaces because it allows a high degree of freedom for the structural design [4,5]. However, the diamond tool is not applicable for the cutting of ferrous materials, e.g., steel, due to the graphitization of the tool and massive tool wears in high pressure and temperature [6,7].…”