Patent GB-865450-A (GB)
Title: Improvements in grinding and polishing machines
Inventor: DARGIE ROBERT EDWARD
IPC: B24B13/02
Filed: 1959-10-16
Abstract: 865,450. Grinding and polishing lenses. AMERICAN OPTICAL CO. Oct. 16, 1959, No. 35167 /59. Class 60. [Also in Group XXVI] A surfacing apparatus for abrading or polishing lenses of simple or complex curvature comprises in combination a lens holder 62, Figs. 1 and 2, a lap holder 30, means for rotating the latter about its central axis, means for moving the lens holder in a circular path around the lap, means for oscillating the lens holder transversely relative to the lap during the orbital movement of the lens holder, resilient means rotatable with the lap holder for maintaining a predetermined axial alignment of the lens in relation to the lap during simultaneous movement of the two holders, a container for liquefied abrasive medium and a pump for supplying a controlled amount of such medium intermittently to the lens during each revolution of the lap, the pump having a stationary part and part rotatable with the lap. In a modified construction, the lens holder may be rotated about its central axis, and the lap holder moved orbitally and transversely over the lens. As described, the apparatus comprises two surfacing units A and B, Figs. 1 and 2 of identical construction each in the form of a rotatable abrading portion 12 and an oscillating head part 13, the former including means for aligning and supporting the lens blank L. The two units may be operated either independently or simultaneously; in the latter case, they may perform similar or different surfacing operations. In the part 12, a lap 35, accurately centred over an adaptor 30 driven by an extension 20 of a drive-shaft 14, is clamped between plates 39, 40, Fig. 6; when the required coaxial alignment between the shaft and lap axes has been obtained. A disc 22, drivingly secured to the member 20, is flanged and grooved to provide an annular channel in which a flexible hose 118, forming the rotating part of the abrasive fluid pump, is carried. On the disc 22 is mounted a flexible harness, 42, Fig. 4, comprising pairs of flat spring members forming flexible arms 43, 48, 51, of which the arms 51 flex only in a direction normal to that of the other pairs of arms and at their free ends are provided with a part 52 comprising a socket of resilient rubber-like material receiving the ball-ends of a yoke 54 extending between the said free ends and having its horizontal axis intersecting the vertical axis of the lap 35 and shaft 14. An enlargement 56 at the centre of the yoke 54 has a centrally-disposed cavity 57, Fig. 6, bottomed by a wear-resistant conical seat 58 which is engaged by a drive pin 59 secured to an adjustable rotating crank arm 81 driven by the head mechanism 13 to actuate the yoke and the lens holder 62 over the lap 35 in the required circular path during grinding or polishing. The drive between the holder 62 and yoke centre 56 is affected by two further pins 60 extending from the yoke into recesses 61 formed in the holder 62. The head part 13 is swingably mounted over the base 10 by a bracket 65, Fig. 2, attached to the upper end of a vertical shaft 67. A spindle 72, which is clamped to the bracket 65 at its outer ends pivotally supports the end of an arm 77. The forward end of the arm 77 carries a tiltable support 79 for a spindle 80 which is driven from an electric motor 85 and drives through the crank arm 81 the drive pin 59 referred to above. Also carried by the bracket 65 is an arm 75 supporting means 76 for raising or lowering the head 13. The pressure between the lens blank L and lap surface is controlled by a spring 94 secured to the arm 77 and attached at its other end to a lever 93 pivoted in the upper end of the arm 75. The lever 93 is actuated by an operating arm 90 to set the desired tension of the spring, anti-clockwise movement of the lever 90, Fig. 2, increasing tension and clockwise movement raising the the head 13 and drive pin 59 clear of the abrading portion 12. While the spindle 80, crank arm 81, and pin 59 are driven in the required circular path from the motor 85, the arm 77 and head 13 are oscillated transversely of the axis of the lap and shaft 14 through the action of an arm 106 rigidly secured to the lower end of the shaft 67. The laps of both surfacing units A and B are rotated continuously through a belt drive 16 from a motor 18, which also drives through a second belt drive 101 a pair of adjustable arms pivotally and eccentrically connected to the upper ends of vertical shafts 104 driven by the drive 101 to provide the oscillatory motions of the arms 106, the shafts 67, and the heads 13, the initial setting of the latter relative to their associated laps is adjustable. The lateral adjustment of the support 79 of the spindle 80 relative to the arm 77 is so effected that the drive pin 59 is directed towards the surface of the lap along an axis which is approximately normal to the tangent of the curved surface at the point of intersection of the axis of the pin and the surface. A scale 109, Fig. 1, indicates the extent of adjustment required for various lap curvatures. Abrasive medium contained in a container 115 is distributed over the surface of the lap 35 by a pump in the form of. the flexible hose pipe 118, Figs. 1 and 2, which is clamped around the periphery of the disc 22 and is so arranged for engagement by an adjustablymounted roller 127 that during each rotation of the lap the pipe sucks up abrasive medium and discharges it over the lap ; a portion of the periphery of the disc 22 encircled by the hose pipe is flattened to provide the necessary intermittent action of the roller 127. If a sperical form of lap is used, the flexible harness 42 may be removed, since axis-aligning means are unnecessary, the drive pin 59 then directly engaging the block 62 on which the lens blank L is mounted. For grinding steeply curved convex surfaces, the blocked lens blank is fixed to the adaptor 30 with its convex side uppermost, the concave lap being placed over the lens and supported in alignment therewith by the yoke 54 of the harness 42.