GB1484996A - Measurement of the position of a surface - Google Patents

Abstract

1484996 Measuring position of a surface UNITED BISCUITS (UK) Ltd 6 Sept 1974 [24 Aug 1973] 40262/73 Heading G1A The variations in level of a surface across its area, are monitored photo-electrically by projecting a pattern or area of light on to the surface and sensing the transverse shift of the reflected pattern by a strip array of photodiodes which is repetitively electronically scanned. The source of light may be a conventional tungsten filament or a tungsten-halogen lamp, a laser, and may be associated with a slit, straight edge &c. and a lens to produce a sharp outline image on the surface. The image may be a wide area, a thin line or two discrete linear areas, Fig. 4 (not shown). Light may be directed by mirrors on to the surface and reflected light may be magnified, x4, on to the photodiode array. The output of the photodiode array, which is repetitively electronically scanned is, in one arrangement, fed to a level detector which produces a squarewave output varying in mark-space ratio in dependence upon the instant of time in each scan that a datum level is reached, i.e. a level representing illumination of a diode. The squarewave is smoothed to obtain a voltage proportional to the average pulse duration which is displayed on a meter and is proportional to the level of the surface. When this is referred to a reference plane, the thickness of the object the top surface of which is being monitored, is given. Other circuit facilities could include a C.R.T. display or a computer. When two sides of the object are monitored e.g. by use an additional complete system or of extra mirrors and lenses and a further photoelectric arrangement, thickness is measured from the combined, summed, signals. The objects may be biscuits moving on a conveyer belt.