Abstract
This paper presents a semirigid (SR) bonnet tool which has the advantages of high efficiency and determinacy for material removal on optical elements and also has the potential to be used on aspheric optics. It consists of three layers: a metal sheet, a rubber membrane, and a polishing pad, from inside to outside. It inherits the flexibility of a normal bonnet but has a higher stiffness. Finite element analysis was performed to determine that the stainless steel is the best-suited material for use as the metal sheet. An SR bonnet with a stainless-steel metal sheet was fabricated and tested. Its tool influence function (TIF) is Gaussian-like, and the TIF stability is more than 90%. The peak-to-valley of its uniform removal area is less than 0.1λ. Tool ripples are highly depressed and the surface profile is well preserved in the prepolishing test. In 12 min, ∼36 mm3 of material is removed.
Highlights
When used in an optical system, aspheric optics can increase the degrees-of-freedom (DOF) in a design, reduce the system’s weight and size, and provide a significant advantage for correcting system aberrations.[1]
A normal bonnet tool can conform to the aspheric or freeform surface, but its material removal rate is not that high due to low contact pressure
The average material removal rate of an R80 SR bonnet reaches 3.002 mm3∕ min as shown in Fig. 9(b), which is much higher than the rate of the normal bonnet.[27,28]
Summary
When used in an optical system, aspheric optics can increase the degrees-of-freedom (DOF) in a design, reduce the system’s weight and size, and provide a significant advantage for correcting system aberrations.[1]. Various computer-controlled optical surfacing (CCOS) processes have been developed since the 1960s.2–7. Jones[8] successfully adopted a small-pitch-tool approach with their CCOS facility for large optics, but its removal efficiency remained low and there was an obvious edge effect. Kodak[9,10] reported results on ion beam figuring (IBF) technology, which can achieve an extra-high-precision surface. It is well known that this technology’s material removal efficiency is low. Fluid jet polishing, which is similar to IBF, was developed by Fähnle et al.[11] In the 1990s, Kordonski et al.[12] proposed a magnetorheological finishing process, which demonstrates a high level of predictability but is not effective for removing mid-spatial frequency errors
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