GB1386007A - Optical distance measuring methods and apparatus - Google Patents

Abstract

1386007 Photo-electric distance measurement COMPTEURS SCHLUMBERGER 22 Feb 1972 [22 Feb 1971] 8078/72 Heading G1A [Also in Divisions G2 and H4] A distance measuring apparatus uses a device responsive to the amount of light received thereby and includes a first optical light guide arrangement which transfers light from a coherent light source and directs it towards a reflecting surface at a non- zero angle of incidence and a second light guide for transferring light reflected from the surface to the light responsive device which thus produces a signal corresponding to the distance between the reflecting surface and the emitting surface of the first light guide. In a system measuring the thickness of a sheet of float glass in a manufacturing process Fig. 11, a laser produces a parallel beam of light 54 which enters optical fibre bundle 50 at face 50Y with an incident angle #. The light emerges from surface 50Z as a hollow cone-shaped beam of half-angle #. See Figs. 4 and 4A (not shown). Receiving optical fibres 52 can only receive light reflected from the surface of the glass 70 while the fibres 62 receive only light reflected from the surface 73 of the molten tin 71 See Fig. 13 (not shown). The difference in the output signals from photodiodes 53, 63 is a linear function of the thickness of the glass sheet. The displacement of the receiving fibres from the transmitting fibres predetermines the distance from the glass at which the received light intensity is a maximum. Thus by arranging a series of annular receiving surfaces adjacent one another a wide range of thicknesses can be measured. The response of the receiver to varying distance from the reflector Fig. 8 shows a sharp peak with positive and negative slopes either side, these slopes are equal in magnitude for equally sensitive receivers (determined by cross-section of receiver bundle, gain of receiving amplifier etc.) Thus if the negative portion of one receiver coincides with the positive portion of a slightly displaced receiver, the sum of their outputs remains constant if the reflectivity of the surface remains constant. The summed output can be used to measure the reflectivity directly or to adjust the thickness measuring receivers. The optical fibre bundles may be arranged side-by-side in a circular or rectangular tube, concentrically, sandwiched or the individual receiving elements may surround the transmitting bundle Figs. 6A and 6E (not shown).