Patent GB-1389982-A (GB)
Title: Manufacture of optical elements
IPC: B24B13/00
Filed: 1973-06-26
Abstract: 1389982 Grinding lenses AMERICAN OPTICAL CORP 26 June 1973 [26 June 1972] 30335/73 Heading B3D A carrier for supporting a lens blank B during surface grinding or polishing operations comprises a lens blank receiving surface on one side, referencing means 34 on the receiving surface against which one side of a lens blank can be positioned for blocking to the carrier, and a mounting surface 36 opposite the receiving surface and adapted to engage carrier supporting means in lens blank grinding and polishing apparatus. The mounting surface has a flat outer member portion 36 disposed in a plane located at a fixed predetermined distance X from the referencing means 34, and a shank 38 extends away from the surface for detachably connecting the carrier to the grinding and polishing apparatus. The carrier has at least one opening 30 extending therethrough from the carrier mounting surface to the receiving surface for use in introducing a lens blocking medium 32 between the receiving surface and a lens blank positioned relative thereto. The carrier is used in the grinding and polishing of multifocal lens blanks, such as a trifocal lens blank or, as described a bifocal lens blank B, Fig. 3, having a reading portion RP separated by a cliff-like division line L having a minimum height of, say, 0À1 mm., from a distance portion DP. An unfinished blank B is engaged with the side walls 14, Fig. 4, of a blocking fixture 10 and is pulled against a seating 16 by vacuum pressure applied through a line 18. The carrier 24 is held by an adapter 20 having a recess for receiving the shank 38 which has a flat surface 40 positioned to extend in the same direction as the cliff-like dividing line of the lens and a recess 42 for engagement by a spring-pressed detent. The carrier is pressed by the adapter until the reference portion 34 engages the blank and is secured thereagainst by pitch or low-melting point alloy 32 poured through one or more of the openings 30 in the carrier. The carrier with the lens blank is removed from the blocking fixture and the shank 38 engaged with a corresponding recess 51, Fig. 6, in an adapter 50 mounted on a wheel 44 rotatable about an axis 46, the annular portion 36 abutting the adapter and being pulled thereagainst by the spring-pressed detent 54. The lens blank is thus positioned while the reading portion is milled or generated by the grinding wheel 58, the wheel 44 rotating about the axis 46. After grinding of the reading portion, the wheel 44 with the carriers and lens blank is removed from the grinding apparatus and fitted on to a shaft 62, Fig. 7, for polishing of the previouslyground reading portion RP by a wheel P having a plastic, felt or other polishing surface using rouge. Thereafter, the carrier with the blank is removed from the wheel 44 of the polishing machine and mounted in an adapter 50<SP>1</SP>, Fig. 8, on a larger wheel 66 of a grinding machine for the distance portion DP to be ground by a wheel 72, the wheel 66 then being removed and remounted in the polishing machine for polishing of the distance portion. In each case, a plurality of carriers are mounted in adapters on the wheels for simultaneous grinding or polishing of a plurality of lens blanks. In another embodiment, two blanks each on a respective carrier 24, Fig. 9, are mounted in a master carrier 78 with the distance portions of the blanks adjacent and a number of master carriers are mounted on the wheel 74 so that, during rotation of the wheel the distance portions of the blanks are ground simultaneously by a wheel T3.