GB636042A - Improved method of, and means for, grinding lenses or other articles having surfacesof compound curvature - Google Patents

Abstract

636,042. Grinding and polishing. ABBEY, A. (American Optical Co.). May 12, 1947, No. 12798. [Class 60] In a method of, and apparatus for, generating compound surfaces such as those of a toric lens, the lens 6 is rotated about a first fixed axis in contact with a rotating cup-like tool 31 and the tool is tilted about a second fixed axis normal to and intersecting the axis of rotation of the lens, the tilting movement and the lens rotation being synchronized so that the tool assumes a given angle of tilt in one major axis of the lens and assumes another given angle of tilt in the other major axis of the lens. The lens 6 is secured by an adhesive to a holder 5 on a shaft 4 splined to a gear 17, and cutting feed is applied by a weighted lever 11 engaging an adjustable stop 10 which reads against a scale 9. A motor 16 drives the gear 17 through reduction gearing and, through a belt drive 38 maintained taut by a jockey pulley 57, also rotates the shaft 32 carrying the tool 31. The shaft 32 is journalled in a bracket 35 pivoted on the machine frame, the pivot 36 being co-axial with the centre of the semicircular abrading surface of the tool and intersecting the axis of the lens shaft 4. The bracket 35 is tilted by a swash-plate 21 which is pivotable on a shaft 20 driven from the gear 17 and is engaged by a slide 52 loaded by a spring 53 and connected to a lever 41 having a link 40 joining it to the bracket. As shown in Fig. 1, the shaft 32 is vertical in one major axis of the lens and a flat surface is formed on that axis, but rotation of the swash-plate will tilt the shaft 32 to the right in the direction of arrow.56 to produce a concave surface, Fig. 8C, on the other major axis at right angles to the first axis. If the angle of the swash-plate to its shaft 20 is increased by re-setting a collar 25 against a scale 30, the shaft will tilt to the left beyond the vertical in the direction of arrow 55 and will produce a convex surface, Fig. 8B, on the first axis of the lens. By using a smaller swash-plate, the whole of the tilting movement may be made to take place to the left of the vertical position so that the surfaces in both axes are convex. The swash-plate may be circular or may be elliptical or other shape in order to vary the rate of change between the two curves. The initial tilt of the tool for any setting of the swash-plate can be adjusted to give the required basic curve by variation of the lever arm of the lever 40 through adjustment of a sliding pivot 48<SP>1</SP> against a scale 47.