GB681311A - Improvements relating to the shaping of the periphery of an article such as a lens - Google Patents

Abstract

681,311. Grinding. E.C.S. (COVENTRY), Ltd. April 30, 1951 [May 22, 1950], No. 12718/50. Class 60. In apparatus for grinding the periphery of an article to a predetermined size and shape wherein the article is mounted to revolve coaxially with a cam of the predetermined shape, the two being pressed in unison by a substantially constant force into contact with a uniformly rotating grinding wheel and a platen respectively, the platen is movably mounted and connected to actuate means controlling a friction clutch in the drive for revolving the article and cam, such that the clutch will be engaged when the cam engages the platen with a predetermined force, a lessening of that force causing the clutch to slip or to disengage, whereby the angular movement of the article and cam will be slowed down or stopped. The apparatus comprises a grinding wheel 13 driven by belt 11 from an electric motor 10 which also drives, through friction clutch 14, belt 15 and reduction gear in casing 17, a shaft 18 carrying a former or cam 19. A lens or other work-piece 20 is clamped against a rubber disc 21 at the end of the shaft 18 by a coaxial shaft 22 movable axially to allow insertion and removal of the work-piece. The shafts 18, 22 are supported by the casing 17 and a bracket 25 which are pivotally mounted upon a fixed shaft 26. A tension spring 27 biasses the shafts angularly about the fixed shaft 26 so that the workpiece 20 will be engaged with the grinding wheel; the shafts can be manually moved angularly in the other direction till a spring-pressed ball 28 engages a depression in a collar 29 fast on the shaft 26 lightly to hold the coaxial shafts in an inoperative position. A platen 32, comprising a block with a curved convex surface to engage the periphery of the cam, is mounted upon a spindle 33 slidable in a sleeve 34, the inner end of the spindle operating, through bell crank lever 35, a thrust rod 39 which acts on the clutch actuating mechanism. The clutch comprises an axially-fast disc 43 on the driving shaft 44 and a coacting disc 45 which is fast with the adjacent pulley for the belt 15 and which is axially slidable; the thrust rod 39 acts upon a ball 46 in the end of the disc 45 through the bell crank lever 40. The clutch is normally free to move to the disengaged position, but when the shafts are manually moved fully in the feeding direction, the force applied by the cam upon the platen (when the engagement of the work-piece and grinding wheel allows) serves to effect engagement of the clutch, and, while that force is being exerted, the cam and the work-piece will rotate at a uniform slow speed, which should be dependent upon the grinding ability of the grinding wheel. For adjustment of the platen 32 the sleeve 34 is slidable in the machine frame and biassed by a spring 49 away from the cam 19; the end of the sleeve away from the cam engages a lever 50 acted upon by a micrometer adjustment 51 through a thrust rod 52.