Patent GB-669356-A (GB)
Title: Method and apparatus for the examination of the profiles of articles
IPC: G02B21/00
Filed: 1949-05-04
Abstract: 669,356. Optical gauging - apparatus. DUNLOP RUBBER CO.; Ltd., GOUGH, V. E., MORTON, G. F., and POWELL, E. F. April 5, 1950 [May 4, 1949], No. 11847/49. Class 106 (ii). [Also in Group XX] A method for the optical examination of the form and dimensions of the surface profile of an article of approximately constant crosssection comprises locating a portion of the article with the surface to be examined regularly spaced apart from the edge of an opening in an opaque shield, illuminating a strip adjacent one side of the shield, whereby light reflected from the strip passes through the space between the shield and the article, projecting an image of the strip on to a screen and examining the image so produced. As shown diagrammatically in Fig. 1, a length of tubing to be examined is drawn through a bore 3 in a stud 2 and is supported thereby so as to pass centrally through a hole 8 in an extension 6 of a shield 7. Light from lamps 4 is reflected from the exposed surface of the tube between the tube and the edge of the hole 8 and is focused by a lens 9 to form an image on a screen 11 at the end of a tunnel 10, the screen preferably bearing high- and low-limit circles between which the image should fall to lie within prescribed tolerances. If the tubing is flexible it may be drawn away from the optical axis by passing over a roller 12 at a point within the focal length of the lens. If the tubing is rigid it may pass through centrally bored holes in the lens and screen or through a hole in a mirror set to reflect the light along the optical axis of a system at an angle to the tube. Apparatus for carrying out the method comprises a flanged bush 49, Fig. 4, in an end plate 48, into which fits a flanged slidable plunger 50, the flanges being pressed apart by a spring 51. A ring lens 58 of polymethyl methacrylate is seated on shoulders 57, 54 of a cap 52 screwed on the bush 49 and of an extension 56 of a shield 55 carried by an annular plate 47. A ring fluorescent lamp concentric with the ring lens 58 illuminates a strip of a flexible tube 83 which is drawn through the plunger 50, over rollers 66, 67 carried by a cranked arm 64 and out through a funnel 68, by motor driven rollers, not shown. A composite lens is carried coaxially with the bore of the plunger 50 by a sleeve 62, adjustable on a boss 43 of a plate 42, with locking collar 63. The composite lens throws an image of the gap between the illuminated strip and the shield on a translucent ground glass screen 73 which covers an aperture in a flange 71 terminating a sheet metal tunnel 72 and is suspended from four equally spaced tension springs 74 stretched between studs 75 on the flange 71 and studs 75A attached to the screen so as to be adjustable in all directions when moved by setting screws 76 acting against stops 77 riveted to the screen, tolerance circles marked on the screen can thus be centred with respect to the image. As a safety device, an enlarged portion of tube or a portion with impurities adhering would press the flange of the plunger 50 inward so that a pin 80 would close contacts 79A, 79B to stop the feed mechanism. A pen controlled by a lever system is operable by a person viewing the screen to mark the tyre at any cross-section not in conformity with requirements. An embodiment adapted for ascertaining the wear on a tyre tread comprises means for rotating the tyre, a source of light to illuminate a strip running transversely across the crown and optical means for projecting an image of the strip on to a screen.