GB1198907A - Machine for Generating Toric Surfaces - Google Patents

Abstract

1,198,907. Grinding lenses. TEXTRON Inc. 24 May, 1968, No. 24929/68. Heading B3D. A machine for generating toric surfaces comprises a tool 21 having an annular cutting surface rotatably supported on a base 15, a work slide 24, means 66 for supporting and pivoting the work slide on an axis perpendicular to the axis of rotation of the tool, means for holding a workpiece 23 on the slide to contact the cutting surface and to swing thereagainst when the slide is swung about the pivotal axis, means for shifting the work slide angularly in a plane perpendicular to the pivotal axis to move the axis in an arcuate path to a selected angular position relative to the axis of rotation of the tool, means for selectively adjusting the radius of the arcuate path, and means for holding the slide fixed relative to the base while the adjustment of the radius is being effected. The tool consists of a grinding-wheel which is mounted on a spindle assembly 17 driven from a motor M-5 mounted on the base 15. The base rotatably supports a spindle 28 carrying a lower trunnion 27 and connected by gearing 38 to a motor M-1. A pair of guide rods 43 on the lower trunnion slidably support an intermediate slide 26 movable along the guide rods by a lead-screw 53 driven from a motor M-3. Both the lead-screw and spindle 28 are connected to electrical resolvers which give direct analogues of the positions of the trunnion and slide. The slide 26 rotatably supports a stub shaft 66, which constitutes the pivotal axis, connected to an upper trunnion 25. A wheel 70 is yieldably connected to the stub shaft and engaged by a worm 80 driven from a motor M-2 to angularly move the trunnion 25 which is provided with bearing blocks 94, 95 engaged by guide-rods 90, 91 on the upper or work slide 24. A rack 99 is fixed to the slide and meshes with a pinion on a shaft coupled to an electric brake unit in a housing 104 for preventing the movement of the slide along the rods 90, 91 during adjustment of the radius of the arcuate path. The upper slide 24 carries a pair of guide rods 116, 117 on its top surface parallel to rods 90, 91 and a work-holding fixture 22 has blocks 118 engaging the rods 116, 117, the fixture being reciprocable along the rods by a motor M-4 driving, through a friction clutch 129, 130, an eccentric pin 132 located in a vertical slot in the housing 122 of the fixture. The forward or grinding position of the fixture is determined by a yieldable stop 134 engaged by a dog 135 on the fixture. The housing 122 supports a chucking mechanism comprising a ram 138 which is adjustable by a yoke mechanism 150 driven from a handle 155 to adjust the chuck according to the desired thickness of the lens to be ground, the lens, which is secured to a block 156 held in the chuck by vacuum, having its back surface engaged by a pin 161 coupled to a dial indicator 165. Relative movement of the upper slide on rods 90, 91 occurs as a result of movement of the upper trunnion 25 and intermediate slide 26 between the lower rods 42, 43 and the upper rods 90, 91. The upper slide is, however, connected to the base by an arm 168 which is fixed to the base and has a depending stud 169 engaging a slot in a turn-table 171 which is rotatable in the slide 24 and yieldingly urged by spring-loaded plungers engaging pins 175, 176 on the turntable to a position in which the slot is transverse to the rods 90, 91. When the slide 26 and trunnion 25 are adjusted so that the axis of stubshaft 66 is not coincident with spindle 28, the slot in the turntable 171 permits the relative movement of the stud 169 and upper slide 24. The machine is automatically controlled by an electrical relay circuit and includes dials 188, 189 operating resolvers which can be set in accordance with the base and cross curves to be produced on the lens, the resolvers co-operating with the feed back resolvers associated with the spindle 28 and slide 26. The base curve formed by swinging of the slide 24 is arcuate but the cross curve is approximate because the diameter of the wheel is constant, the cross-curve being elliptical rather than circular. The error is reduced by corrective scales marked on the dial 188. The setting of the machine and the grinding operation is controlled automatically by the circuits which includes various limit switches associated with the slides and trunnions.