Patent GB-1208943-A (GB)
Title: Method and apparatus for generating a lens
IPC: C03B23/22
Filed: 1968-03-11
Abstract: 1,208,943. Grinding; casting composite joints; jointing. TEXTRON Inc. 11 March, 1968 [6 April, 1967; 1 May, 1967],No. 11699/68. Headings B3D, B3F and B3V. [Also in Division C1] A lens block for securing at one end to a glass or plastics lens blank comprises at its other end a plurality of spaced recesses 5, 36, Fig. 7, for receiving driving members of a machine for generating a surface of the lens blank secured to the block, one of the recesses being disposed centrally of the block, the axes of the recesses being in a common plane extending between opposite ends of the block, and reference means 3<SP>1</SP> on the block for locating the block in a predetermined position on the spindle of an edge grinding machine. The block may be formed of one piece of soft metal in a mould so as to adhere to one surface of the lens blank and have formed therein a pair of conical recesses 36 for use in generating the other surface of the lens blank and a central recess in which a plug 17 may be fitted and is removable to permit optical checking of the surfaces during the generating operation, the plug being formed with a conical recess 5 which is used if the surface to be ground is to be spherical. The block is also formed with notches 3<SP>1</SP>, holes 19, Fig. 8, or a flat, which act as the reference means during the edge grinding of the lens block. If the edge shape of the finished lens is such that part of the block will be machined away, an adaptor having means for engaging the notches, or flat surface, may be fitted on to the lens block, the adaptor being formed with projections 19<SP>1</SP>, Fig. 4, or recesses for engagement by the driving means of the edge grinding machine. In other embodiments, a permanent, hard metal lens block is secured to the blank (possibly with a plastic or tape coating) by adhesive, such as pitch, resin or alloy (Bi-Pb-Sn-In-Cd), poured through a hole 4, Fig. 11, into the space between the blank and the block, the block having a series of projections to support the blank. The hard metal block may be formed in two parts, 1<SP>11</SP>, 211, Fig. 3, one part having the recesses 6<SP>1</SP>, 8<SP>1</SP> for receiving the driving means of the machine for generating the surface on the lens blank, and the other part having a flat comprising the reference means for the edge finishing machine, the parts being relatively adjustable to determine the cylinder axis of the lens and securable in position by a screw 14. As shown in Fig. 14, the block 22<SP>1</SP> may be relatively thin and held by vacuum applied at an opening 88 on a vacuum chuck 84 for rough grinding, the block then being mounted in a second part with a precise fit for finish grinding, the block being accurately positioned by a key 83. The soft metal lens block may be cast in a mould, Fig. 9, with coolant grooves 78 and having a piston 48 which is non-rotatable and carries pins 105 for forming the reference means for the edge-grinding machine. A collar 28 is disposed around the piston and carries projections (cores) 36 for forming the recesses for the driving means of the surface generating means, the collar being connected by bevel gears 50, 57 to a handle 55 whereby the projections can be positioned according to the cylinder axis of the lens to be produced. The lens blank, possibly coated with plastic material or a tape, is supported on a seat 64 which can be tilted by a cam to the desired prism setting of the lens. A shield plug 17 is located in a central recess in the piston and molten metal is allowed to flow up into the mould cavity 30 from a melting- hopper. The piston 48 can be raised by a cam 92 to eject the block from the mould. Reference has been directed by the Comptroller to Specification 1,148,138.