Patent GB-332245-A (GB)
Title: Improvements in devices for grinding and polishing lenses
IPC: B24B27/00
Filed: 1929-04-17
Abstract: 332,245. Desenberg, J. April 17, 1929. Lenses, grinding and polishing; vacuum chucks. - A machine for grinding and polishing lenses consists of an intermittently rotated head carrying a number of holders for lenses which engage grinding or polishing tools, the operation of grinding &c. being completed in a number of steps performed by successive tools. The machine comprises a base 1 carrying a vertical column 2 on which is rotatably mounted a hollow shaft 5, carrying a head 8 in which are mounted, in ball bearings 11, 12, radial oscillatory horizontal axles 10, each carrying an arm 14 in which is slidably adjustable, by a screw 16, a slide 17. The slide carries a passively rotatable work holder 19 to which the lens 20 is held by suction from a suction box 21 having a pipe 24 communicating with a suction pump. Each axle 10 carries a sector 25 engaged and oscillated by a sector 27 on a pin 26, the sector carrying a pivoted arm 29 having thereon a roller 30 which may be engaged with a cam groove 32 in a drum 33 rotatable on a head 35 carried by columns 36 and rotated by a toothed wheel 39 and teeth 38 on the bottom of the drum, the wheel 39 being chain driven from an electric motor 44. The lens 20 is ground by a tool 46 interchangeably mounted on a spindle 47 slidable in, and rotatable with a sleeve 48 mounted in ball bearings 50, 55, in members carried by flanges 53, 56 of the machine frame, the sleeve being driven by a cord 59 which serves also to drive the other sleeves. The spindles are each attached by ball bearings 60 at their lower ends to a member 66 secured to the upper end of a rod 67 carrying an adjustable bush 75 engaged by the end of a lever 71 mounted on an axle 70 and carrying counterweights 72 to apply the grinding pressure. The axles 70 of all the grinding &c. stations are connected by universal joints to move together. The member 66 also carries, on columns 77, a vessel 78 surrounding the work and the grinding tool to catch dust &c. Grinding-material is fed from a container through a tube 79. Grinding is stopped at a predetermined point by means of a feeler lever 83 on an arm 82 and which has a point adapted to be engaged by the tool 46 when this has been raised a determined amount. The lever, on being lifted, closes an electrical contact 84 and energizes a solenoid 86, which moves a lever 89 to engage the top of the member 66, whereby preventing further upward movement of the grinding-tool. In order to stop the grinding action should a piece of work break or slip out, or if a work-holder has no work thereon, a weight 95 is provided supported by a piston 93 in a cylinder 92 connected by a pipe 96 to the suction box of the work-holder, breakage &c. of work breaks the vacuum and the weight 95 falls, thereby engaging an arm 98 on a lever 99 to move the end 101 thereof into the path of the bush 75 and prevent upward movement thereof. In order to give intermittent rotation to the rotary head to move the work pieces from one grinding station to the next, a motor 102 is provided driving through worm gearing 104 - - 106 a shaft 108 carrying two cams 117, 131 and a crank 109. The crank operates at intervals through a maltese cross 111 to rotate a gear wheel 115 engaging teeth 116 on the shaft 5, and the grinding-tools and associated parts are lowered out of the path of the work-holders and work during rotation thereof by the action of the cam 117, which operates through a lever 121 on an axle 70 snd an arm 160 thereon to lift all the levers 71 and thus depress the bushes 75 and the tool spindles &c. The rotary head is accurately positioned after each rotation by a pin 124 which is moved into and out of engagement with aperture 123 in the head by a bell crank lever 127 operated, through a rod 129, by a cam 131. In order to wash off abrasive from the work between its engagement by two successive grinders the movement of the head from station to station is made in two steps so that in the intermediate position a tank 132 of water can be raised by a column 133 supported on the member 66 to immerse the work. Finished work is removed from the tool-holders and the new work is supplied by a feed table which takes the place of one of the grinding spindles and is operated intermittently to receive finished work at one station in the feed table and to apply new work from the next station to the work-holder. The work thus applied to the holder is convoyed by the intermittent rotation of the head to coarse grinding, fine griuding, and polishing stations, being washed between each pair of operations. In order to polish the work uniformly the distance of the work from its oscillatory axis is altered slightly at each movement of the head to the next polishing tool by the engagement of pawls 145 with spur wheels 144 on the upper ends of the screwed spindles 16. In a modification, the grinding-spindles are horizontal and are radial to the rotary head, the work being carried on arms oscillated on horizontal axes by a rotating cam ring within the head.