Patent GB-933640-A (GB)
Title: Improvements in or relating to methods and apparatus for surfacing articles
IPC: B24B13/02
Filed: 1962-04-17
Abstract: 933,640. Grinding and polishing lenses. AMERICAN OPTICAL CO. April 17, 1962 [July 3, 1961], No. 14946/62. Class 60. A device for use in finishing a compound curvature on a surface of a work member comprises a tool member having a working surface thereon of of the shape desired to be finished on said surface of said work member, a rotatable base, supporting means on said base adapted to receive and support a first of said members fixedly for rotation therewith, a resilient coupler encircling said supporting means and first member, said coupler having one of its ends fixed to said base for rotation in unison therewith and holding means on the opposite end of said coupler for receiving and supporting the second of said members in adjacent relation with the first of said members and with given meridians of the respective surfaces of said members retained substantially parallel to each other at all times during rotation of said base and coupler carried thereby. A machine for surfacing a toric lens L comprises a base 24, preferably hollow. Links 28, 30 are pivotally connected to the base 24 and to blocks 32 forming part of a head 26. The blocks 32 are interconnected by rods 38, 40. An overhanging portion 50 of the head 26 is mounted to pivot about the rod 38, the portion 50 embodying a casting 52 having a pair of depending split bearings 54 fitted to the rod 38. The portion 50 is located axially of the rod 38 by a collar 51 secured on the rod 38 between the bearings 54. Attached to the forward end of the casting 52 is a spindle housing 56 in which is journalled a spindle 58 belt-driven at about 60 r.p.m. from a motor 60 mounted on the casting 52. The spindle housing 56 has an integral mounting bracket 68 provided with a slot 72 receiving a bolt 70 mounted in the casting 52. The contacting surfaces of the casting 52 and mounting bracket 68 are curved so that the spindle housing axis can be tilted from the vertical, the centre of curvature of the surfaces being approximately at the average centre of curvature of a lens blank surface being worked. The link 30 has a lateral extension 200 connected by a link 202 to a crank-pin adjustable in a slot of a plate 208 driven by a motor 210, whereby the head 26 is oscillated. For lifting the head portion 50 to permit insertion or removal of workpieces, an air cylinder 78 secured to the base 24 has its piston-rod 82 connected to the head casting 52 by a flexible cable or cord 84. For exerting pressure on the workpiece during surfacing a spring 86 is connected under tension between the base 24 and a member 88 adjustable in the casting 52 whereby the pressure can be varied. A housing 100 attached to, and extending upwardly through, the top of the base 24 has journalled therein a lower spindle 102 beltdriven at about 600 r.p.m. from a motor 104. A first adaptor 116 is threadedly connected to the upper end of the spindle 102. A second adaptor 118 has a tapered upper section for receiving a tool 120, an intermediate annular shoulder and a lower cylindrical portion fitting in a recess formed in the upper end of the spindle 102. The tool adaptor 118 is held on the spindle 102 by a bolt 130. A locating pin 132 fixed in the spindle 102 enters an opening 134 in the tool adaptor 118. A keying pin 136 is secured in a lateral opening in the tapered section of the tool adaptor 118; the tool 120 has a tapered opening interfitting with the tapered upper section of the adaptor 118 and has a key slot 140 fitting over the pin 136. A plate 142 fits on a shoulder of the first adaptor 116 and is secured thereto. The plate has an annular portion 147 carrying an upstanding coupler 148 which supports and resiliently connects an upper work-holding assembly 150 to the plate 142. The coupler 148 is a coil spring of such rigidity that it tends naturally to support the work-holding assembly 150 at a desired level relatively to the tool 120 while also being relatively freely and substantially evenly flexible in all meridians to permit its uppermost end to move laterally and tilt as required during surfacing; it is relatively easily compressible to permit the workpiece to remain in engagement with the tool at all times during surfacing; it is substantially immune to torsional forces tending to wind or unwind its convolutions as a result of pressures applied between the workpiece and tool or forces caused by rotation of the fixture at relatively high speeds. The lowermost convolution of the coupler 148 is secured to the annnular portion 147. The uppermost convolution of the coupler 148 is secured to an annulus 162 having a recess into which isfitted a rotatable adjustable collar 166. Locking studs 168 threaded into the annulus pass through arcuate slots 170 in the collar 166. The latter has diametricallyopposed raised sections 172 between which a yoke 176 is pivotally mounted by studs 178. The mid-portion of the yoke 176 has a ballsocket 184 receiving the ball-shaped end of a crank-pin 186 carried eccentrically by the upper spindle 58. Pins 190 in the yoke 172 engage sockets 192 in a block 188 to which the lens L is attached, e.g. by pitch; alternatively, the block may be of low melting-point alloy and cast directly on the lens. In blocking, the cylinder meridian c of the lens is aligned parallel to a line passing centrally through the sockets 192, so that when the lens is mounted in the fixture the cylinder meridian c is at right angles to the axis of the yoke arms 175 and the base meridian b is parallel to the axis of the arms 175. The working surface of the finishing tool 120 has base and cylinder meridians b<SP>1</SP>, c<SP>1</SP>, the curvatures of which match the base and cylinder curvatures of the lens blank. The location of the cylinder meridian c<SP>1</SP> is indicated by a notch 196; the key slot 140 in the tool is located in parallel alignment with the cylinder meridian c<SP>1</SP> so that when the tool 120 is applied to the tool adaptor 118 its key slot 140, in fitting over the pin 136, aligns the cylinder meridians c, c<SP>1</SP>. For polishing a gloss or plastic lens, a thin polishing pad 198 of felt or plastics is attached to the surface of the tool, e.g. by pressuresensitive adhesive or by cement. A liquidpolishing medium is supplied continuously during the operation by a pump 220 througha flexible tube 216 attached to the housing 56 or other part of the head 26. A splash covering 224 collects used polishing medium and directs it through tube 226 to the container 222 in which the pump is situated. In a modification, Fig. 12, the fixture and adjacent associated parts are contained in a bowl 228 carrying the fixture and mounted on the lower spindle 102 so as to be rotated thereby; liquid polishing medium in the bowl is delivered by a stationary collector 230 through a tube 234. For fine grinding, the lens blank is in direct engagement with the tool surface and a liquid abrasive medium, e.g. emery suspended in water, is used. Thin coverings of screening material, e.g. wire mesh conformable accurately to the tool surface may be used to protect the tool surface. For surfacing the convex side of a lens the tool has a concave working surface; alternatively, the lens is blocked upon a work-holder which resembles and replaces the tool 120 and a tool is used which resembles and replaces the block 188. Modified constructions of the coupler 148 are described.