Specially shaped mounting rings keep lenses precisely centered, regardless of temperature, in the lens housings of cameras and other optical systems. These rings feature (1) well-defined contact spots for alignment, plus (2) relieved surfaces that form flexures to accommodate small manufacturing tolerances and differences among the thermal expansions of lenses, lens housings, and the rings themselves. These rings are made by numerically controlled machining of recently developed clean, strong, machinable plastics.
The figure illustrates a prototype ring of this type, made from a commercial polyimide. First, the inner and outer cylindrical surfaces were machined to established precise inner and outer diameters. Next, with the ring mounted in a bracing fixture, three flats were machined on the outside and relieved surfaces were cut on the inside. Thus, the three remaining convex arcs on the outer surface of the ring would make contact with the inner surface of the lens housing, the three remaining concave arcs on the inner surface of the ring would make contact with the lens, and the outer flats and the inner relief cuts would provide the required small amount of flexibility to accommodate thermal-expansion mismatches while keeping the lens centered.
The Elastomeric Ring Holds the Lens with its three inner concave arced stubs and engages the lens housing with its three outer convex arced stubs. Thermal expansion and/or contraction of the lens, the housing, and/or the ring itself are absorbed by flexure of the ring. For greater precision, a ring could be made with six inner and six outer stubs.
This work was done by Virginia G. Ford of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Mechanics category.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, NASA Management Office–JPL; (818) 354-7770. Refer to NPO-19518.