Abstract
A Computer Controlled Optical Surfacing (CCOS) system has been developed for correcting form errors on aspheric surfaces. Experiments were carried out to find the correlation between different polishing parameters and polishing metrics such as removal rate, uniformity etc. Based on established polishing parameters, polishing process is developed to correct surface errors on planar, spherical and aspheric surfaces. A convolution model between TIF and dwell times was developed to simulate and solve for correction polishing. Surface accuracies of peak-to-valley (PV) 141 nm and root-mean-squared (RMS) 22 nm has been achieved for planar surface. For aspheric surface, current accuracy of 662 nm PV and of 115 nm RMS is achieved with further development ongoing.
Highlights
The global market is moving towards tighter and tighter specifications on aspheres, while at the same time pushing for a reduction in unit price
The process is characterised by the “Tool Influence Function”, the removal per unit of time as a function of the position within the working area of the process
If the process is linear in time, the removal at a point on the surface, R(x), depends on where the process is held on the surface, xp, how long it is held there, the dwell time d(xp), and the influence function of the process, f (u), R(x) = d(xp) · f x − xp
Summary
The global market is moving towards tighter and tighter specifications on aspheres, while at the same time pushing for a reduction in unit price. To improve the accuracy of a CNC polished asphere, it is typically ‘finished’ on a much more expensive, corrective polishing platform (such as Magneto-Rheological Finishing [1], Precessed Bonnet Polishing [2] or Ion-Beam Figuring [3]) These so-called Computer Controlled Optical Surfacing (CCOS) platforms are commercially available and in widespread use around the world, and are being installed more and more in low-cost countries. Using these platforms on the lower-end of their capability scale will become a very competitive and uneconomical use of our machine park. We achieve this by using proven, of-the-shelf components, flexible processes and existing industry standards
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