Patent GB-813917-A (GB)
Title: Ophthalmic lenses and process and apparatus for producing same
IPC: G02C7/06
Filed: 1956-02-24
Abstract: 813,917. Grinding and polishing lenses. PHILLIPS, B. M., PHILLIPS, E. H., PHILLIPS, E. D., and PHILLIPS, J. B. Feb. 24, 1956, No. 5838/56. Class 60. [Also in Group XX] A one-piece, multifocal, monocentric-axis lens is produced from a preformed blank having its concave face subdivided into two portions lying in different arcuate planes and separated by an arcuate shoulder extending entirely across the face of the blank by generating a distance field a<SP>1</SP>, Fig. 28, on one of the portions of the blank and simultaneously undercutting the shoulder by grinding to form an optical jump-eliminating ledge c<SP>1</SP> overhanging the distance field, polishing this field and ledge, generating a reading field b<SP>1</SP> on the other portion of the blank and simultaneously eliminating the end portions of the ledge and reducing such other portion adjacent the side edges of the blank by grinding to form walls w directed towards the reading field. The lens so formed may be completed by polishing the reading field, or triangular intermediate fields n may be ground as shown in Fig. 30 so as to eliminate the ledges w and remove the ledge c<SP>1</SP> except near the centre of the lens, followed by successive polishing of the reading field and intermediate fields. The arcuate shoulder in the blank is pre-formed so that it slopes downwardly and outwardly from what is to be the reading field to what is to be the distance field. The grinding operation is carried out in a machine comprising three units 17, 18,19, Fig. 1, each consisting of a grinder head co-operating with the faces of six blanks set radially in a cup 56 as shown in Fig. 6. Each of the three cups 56, Figs. 1 and 3, is held by a rubber gasket 58 in a cup 55 carried on a spindle 48 which is mounted in a yoke 53 carrying a disc 52 through which the spindle passes ; the spindle is rotated through a pulley-drive from a motor 45, and the yoke 53, which is resiliently mounted on a supporting structure 61 by springs 68, can be tilted by means of adjusting screws 60 with or without an interposed wedge 71 (Fig. 1) to set the cup 56 and blanks therein at a desired angle in relation to the grinder. Each of the grinder heads mounts a vertical spindle 20 which is rotated by a pulley-drive from a motor-driven shaft 9 common to all the heads and carries at its lower end a cup-shaped grinder 35 having a bevelled edge operative upon the blanks ; the grinder head may be of the selective manual or power fed type or, as shown, it may be carried by a manually-adjustable arm for positioning purposes and be provided with hand-operated rack-and-pinion gearing for feeding the grinder into the work, the limit of feed being set when an adjustable member 44 movable with the spindle engages a stop 43. A mixture of oil and water is introduced into each cup 56 through a flexible pipe S and overflows therefrom into a pan P surrounding the cup ; the mixture passes from the pans through pipes into a trough T for re-circulation. The blanks are set radially in a cup 56 by positioning them on the convex face of a blocking fixture 72, Fig. 10, placing the cup over the fixture, and injecting pitch into the space between the cup and blanks ; the face of the fixture 72 has a ledge 74 to engage the ledges on the blanks and is of a curvature corresponding to that of the field to be ground. The three grinding units shown in Fig. 1 are intended, respectively, for grinding the distance field and ledge, the reading field, and the intermediate fields (in the case when these are to be formed), and for this purpose the operative faces of the grinders 35 are of appropriate diameter, extent and inclination. The unit at the left-hand end of Fig. 1, carries out the first operation as shown in Fig. 3, the grinder 35 then generating the distance field and undercut ledge on all the blanks in the cup 56 ; the cup 56 is, for this purpose, set at the necessary inclination by the screw 60 and the blanks are blocked in the cup 56 at the appropriate curvature. The central and third units of Fig. 1, generate, respectively, the reading and intermediate fields with appropriate grinders 35 and the blanks re-blocked in another cup 56 at the necessary curvature ; the inclination of the cup 56 for both these operations is set by the screw 60, the wedge 71 also being introduced beneath the disc 52 for the third operation. The blanks are polished in a three-unit polishing machine comprising three holders 87, each of which is mounted on a motor-driven spindle 88 in a yoke and, as shown in Fig. 19, is adapted to receive a set of blanks in one of the cups 56. Resting upon each set of blanks in a cup is a polisher 108 having a ball- and-socket connection 106 with a shaft 103 mounted adjustably in a bracket 101 on an arm 98 which is journalled on an inclined shaft 97. Rotation of the cup 56 therefore results in a wobbling motion of the polisher. Rouge or other compound is fed to the cups 56 by tubing 92 from a header 93, and a trough 91 surrounds the three holders 87 for receiving overflow and draining it away, if desired for re-circulation. The polisher 108 are each formed with an annular bevelled surface effective over a desired field. The first of these units is used for polishing the distance field of a set of blanks immediately after the grinding of this field in the first grinder unit and the second unit for then polishing the reading field after grinding of this field in the second grinder unit if lenses of the kind shown in Fig. 28 are to be produced. Should lenses of the kind shown in Fig. 30 be required, grinding of the reading and intermediate fields in the second and third grinder units is followed by polishing of the reading field in the second polishing unit and the intermediate fields in the third polishing unit.