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Small-Tool Polishing
Small-tool polishing technology polishes parts to remove subsurface damage caused by optical grinding and then deterministically figures the optical surface to meet the optical requirements. For glass and glass-ceramic components, this process is used prior to ion figuring to achieve the surface micro-roughness requirements and minimize overall process cycle time. For other optical materials, small-tool polishing can be used to finish optical surface to their final requirement. Optimized with special motion control software and tooling, the computer-controlled process gives ITT precise, consistent control of the motion and forces that shape and figure complex optical surfaces. High Departure Optics ITT's small-tool technology, a sub-diameter orbital lap polisher, can produce optics ranging from 10 to 96in. (0.25 to 2.4m) in diameter, with over 1000 waves (633 microns) of departure even on small optics. The process is used extensively for initial figuring of high-departure aspheric and off-axis optics with rectangular, hexagonal and other aperture shapes. Applications include optics for remote sensing cameras, laser amplifier slabs, lightweighted satellite optics, and primary and secondary mirrors for astronomical telescopes. The polisher also is used to polish optics that cannot be ion figured, such as those used in laser-based nuclear fusion programs. Superior Convergence Control Specially-written control software and custom-formulated polishing pads allow ITT to converge optics quickly and accurately with a high degree of determinism. Control software: By accurately modeling the polishing pad's interaction with the optical surface, the control software can accurately remove surface errors. Pad construction: Polishing pads formulated from a proprietary composite material further optimize the process by tightly controlling removal rates and shapes. Accurate motion control of a precisely-known polishing pad results in highly repeatable operating conditions. It allows ITT to remove glass predictably, and remove errors deterministically. As a result, ITT can remove up to 80 percent of the surface errors in a single polishing cycle. Fewer Production Cycles Determinism of this magnitude reduces the number of test iterations, enabling rapid correction of the optical figure. Just how rapid is demonstrated by comparing our advanced small-tool polishing process with conventional polishing techniques still practiced by many optical engineering firms. In 1979-80, when manual polishing was still state-of-the art, ITT devoted 18 polish and test cycles over five months to figure the 97.5in. (2.5m) diameter backup primary mirror for the Hubble Space Telescope. Today, using small-tool polishing, the processing time for this optic would be dramatically reduced. |
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