Patent GB-720887-A (GB)
Title: Improvements in or relating to lens chucks
IPC: B24B13/005
Filed: 1953-04-16
Abstract: 720,887. Vacuum chucks. KODAK, Ltd. April 16, 1953 [April 16, 1952], No. 10459/53. Class 60  A lens, e.g. for use in lens abrading apparatus, comprises a body portion, formed with a recess adapted to receive and position a lens with its outer surface projecting beyond the chuck, a flexible member resting on the bottom of the recess and means for drawing and holding the flexible member into tight engagement with the bottom of the recess to form a fluid seal between the flexible member and the wall of the recess. A dish-shaped suction cup 30 has its lower surface 31 resting on the bottom 26 of a recess 12 in the chuck 11a; the upper surface 32 of the cup engages the moulded surface 20 of the lens near the outer periphery 33 of the cup. An annular recess 34 in the upper edge of recess 12 receives an annular ring 35 which serves as a seat and support for the lens 15 adjacent the edge 14 thereof. A stem 36 depending from the cup 30 extends into a central opening 37 in a pilot stem 38 of the chuck 11a, the stem fitting loosely in the opening and serving to position the cup 30 on the lower surface 26 of the recess. The stem may be made of the same material as the cup but is preferably of brass and secured to the cup by a threaded member 39. Since the stem 36 fits loosely in the opening 37, vacuum applied to the hole 22 by means of the vacuum pump 23 evacuates the space between the stem 36 and the wall of the opening 37; moreover, the span 40 between the lower surface 31 of the cup 30 and the bottom 26 of the recess 12 is evacuated so as to draw the cup 30 downwardly into tight sealing engagement with the bottom'of the recess to provide a seal between the cup and the recess. The cup 30 may have an aperture 41 so that when vacuum is applied, the space 42 between the lower surface 20 of lens 15 and the upper surface 32 of the cup 30 is also evacuated to draw the lens downwardly into tight engagement with the sUrface 32 of the cup 30 and also against the seating ring 35 thus providing a fluid seal which prevents coolant being drawn into the vacuum line. In addition, evacuation of the space 42 increases the holding force on the lens 15 and ensures that the latter will not rotate or spin relative to the chuck. Due to the flexible nature of the cup 30, it accommodates itself to irregularities in the surface 20. to provide the desired sealing between the lens and the cup. Instead of relying on the loose fit between the stem 36 and opening 37, the stem 36 may have a longitudinally flat section on its outer surface, or the inner surface of opening 37 may have an axially extending keyway or slot 43 which connects the hole 22 and the spaces 40, 42. To position the cup 30 in the opening 37 and to prevent rotation of the cup relative thereto, the stem 36 has a radially extending pin 44 projects into the keyway 43. For lens polishing, in which water and rouge are used, the cup 30 may be of rubber. For lens grinding, in which oil is used, the cup 30 is of oil resistant material such as polymerized 2-chlorobutadiene 1.3 (" Neoprene "). Instead of a separate seating ring 35, the periphery 33 of the cup 30 may be extended upwardly so as to form a seating ring which is integral with the cup 30.