Optimal strategy for fabrication of large aperture aspheric surfaces

Abstract

Aspheric surfaces are widely used because of their desirable characteristics. Such a surface can obtain nearly perfect imaging quality with fewer optical elements and reduce the size and mass of optical systems. Various machine systems have been developed based on modern deterministic polishing technologies for large aperture aspheric surfaces. Several factors affect the final precision of large aperture aspheric surfaces, such as the velocity limit of the machine and the path design. Excess velocity, which will be truncated automatically by the computer numerical control system, may cause the dwell time to deviate from the desired time. When a path designed on a two-dimensional surface map with equidistant pitch is projected onto an aspheric surface, the pitch changes as a result of the varied curvature of the aspheric surface. This may affect the removal map and cause some ripple errors. A multiregion distribution strategy, which includes velocity checking, is proposed in this study to avoid exceeding the velocity limits. The strategy can be used to modify local errors and edge effects. A three-dimensional spiral path generation method is also presented using an iterative method to ensure uniformity in the space length of the adjacent circle of the spiral path. This process can reduce the ripple error caused by the overlapping of tool paths. A polishing experiment was conducted, and the results proved the validity of the proposed strategies.

Modified subaperture tool influence functions of a flat-pitch polisher with reverse-calculated material removal rate

“…In a polishing run, the TIF serves as a removal block on the optical surfaces to achieve the target removal by block accumulating along the spatial polishing path. A powerful TIF should have (1) high stability of removal shape and removal rate in both time and position scale [23]; (2) large working span in material removal rate and removal size; (3) central peak removal for deterministic figure (preferred, but not always needed); (4) excellent smoothening effect to raise the surface roughness; and (5) no subsurface damage to optical material [24]. To achieve these rigorous demands, researchers have invented numerous polishing tools as mentioned in the last section, and novel tools would appear in front of us every few years in the future.…”

Polishing path generation for physical uniform coverage of the aspheric surface based on the Archimedes spiral in bonnet polishing

“…Thus, the physical uniform coverage of the polishing path can be easily achieved by the traditional Archimedes spiral with the same interval. Feng et al 27 proposed a three-dimensional spiral path generation method that uses an iterative method to ensure uniformity in the space length of the adjacent circle of the spiral path. However, when a flexible bonnet polishing tool is used, the contact state varies along the tool path due to the curvature variation of the curved surface, thus the polishing paths proposed by Guo and Cheng et al are not suitable for bonnet polishing.…”

Tool removal function modeling and processing parameters optimization for bonnet polishing

“…Since computer controlled polishing (CCP) processes were developed in the 1960s [1][2][3][4][5][6][7] , there have been a number of emerging technologies that are enabling the cost-effective manufacture of precision surfaces, particularly subaperture polishing. Subaperture polishing technologies have radically changed the landscape of precision optics manufacturing and enabled the production of components with higher accuracies and increasingly difficult figure requirements, including ion beam figuring [8] , plasma-assisted chemical etching [9] , magnetorheological finishing [10] , magnetorheological jet polishing [11,12] , even a fiber-based tool polishing [13] .…”

“…Subaperture polishing technologies have radically changed the landscape of precision optics manufacturing and enabled the production of components with higher accuracies and increasingly difficult figure requirements, including ion beam figuring [8] , plasma-assisted chemical etching [9] , magnetorheological finishing [10] , magnetorheological jet polishing [11,12] , even a fiber-based tool polishing [13] . Although these processes have radically different polishing mechanisms, many large aspheric even off-axis segments have been successfully fabricated using them [4][5][6] .…”