Patent GB-974635-A (GB)
Title: Improvements in or relating to the detection of faults in flat glass
IPC: G01N21/896
Filed: 1962-01-19
Abstract: 974, 635. Inspecting glass photoelectrically. PILKINGTON BROS Ltd., H. BENSON, A. RICKABY, and J R. BEATTIE. Jan. 17,1963 [Jan. 19, 1962], No. 2084/62. Heading G1A. [Also in Divison G4] The invention relates to a method of and apparatus for detecting faults for example stone, bubble, ream or scratches in or on the surface of flat glass and comprises means 1 for supporting and effecting relative movement between the glass 2 and sensing means, and indicating means associated with the sensing means to indicate the presence of a fault in the glass, wherein the sensing means includes a light source 3 which illuminates the glass, an optical system 9 arranged to form an image of a strip shaped zone 8 of the glass extending transversely to the direction of the said relative movement and scanning means such as a rotating disc 11 provided with slots 16 for scanning the whole of the said image and wherein the sensing means includes light sensitive means responsive to an image of a fault in the glass. In the arrangement shown, a strip light source 3 such as a fluorescent tube mounted transversely to the direction of motion of the glass 2 illuminates a strip shaped zone 8 of the glass an image of which is produced at a photomultiplier 19 by lenses 9 and a parabolic mirror 18. As the glass moves relative to the sensing means contiguous strip shaped zones are scanned by the photomultiplier 19 by means of radial slits 16 in a rotating scanning disc 11. In an alternative arrangement (Fig. 4 not shown) surface defects only are detected, the strip light source is mounted above the surface of the glass and light reflected from the surface under investigation is investigated by sensing means and scanning means as described above. Output pulses from the photomultiplier 19 may be fed to a counter circuit which counts the number of faults which occur or alternatively they may be fed to a recording means (Figs. 2 and 3 not shown, (see Division G4) which prints out the co-ordinates of the position of each fault on the glass, using reference signals or "clock" pulses recorded on a magnetic tape 24 on the rim of the disc 11 which may be picked up by a head 26, and reference signals from a pulse generator comprising a photo-cell receiving light interrupted by peripheral teeth on a wheel geared to the rollers 1 driving the glass 2. Alternatively the reference or "clock" signals may be produced from a series of marks or teeth on the scanning disc, sensed photo-electrically. Instead of printing out the information a record may be made directly on the glass by means of an automatic marking device (not shown). In another application the information from the recording means may be fed to a computer which either marks the glass or is connected to an automatic cutter (not shown) so that the glass may be cut in the most economical way. If a width of glass larger than 12 inches is to be inspected a plurality of sensing means side by side each scanning 12 inches of glass may be used and in this case the recording means is arranged so that a prefix is added to the data output to indicate the distance in feet the fault appears from one edge of the glass. In another arrangement (not shown) for the detection of bubbles in the glass, light from.a line source is directed obliquely on to the underside of the glass and if it strikes a bubble then it is scattered thereby on to the slit 7 behind which is located the photo-electrical device 19. Ream, ream knots and surface dimples may be detected by a further embodiment (not shown) in which the underside of the glass is illuminated by a point source for example a high pressure mercury lamp and a shadowgraph of the illuminated region of the glass formed on an opalescent screen above the glass and below the slit 7, local changes in the light intensity being detected in a manner similar to that shown with respect to Fig. 1. The photomultiplier 19 may be replaced by a moving film on which light transmitted through the scanning disc is recorded. The scanning means may work in conjunction with a C.R.T.which produces on its face a roster synchronized with the scanning of the image, the brightness of the scanning spot being controlled by the output from the photomultiplier 19 and a film record being made of the roster. Alternatively in the sensing means the image may be formed on a photosensitive surface which is then electronically scanned to produce an output signal.