Patent GB-1062967-A (GB)
Title: A proximity detector
IPC: G01D5/26
Filed: 1964-08-13
Abstract: 1,062,967. Photo-electric position determination. MECHANICAL TECHNOLOGY Inc. Aug. 13, 1964 [Sept.9, 1963], No. 33097/64. Heading G1A. A device for determining the position of a test object comprises a light source and a photoelectric detector each associated with an optical path passing through solid light-conducting media and means associated with the detector for indicating the space between adjacent end faces of the media and the test object. Fig. 5 shows an optical fibre bundle 1 divided in a random manner into two portions 10 and 12 towards one end thereof and having its other end disposed opposite a test object 14 the spacing of a reflecting surface of which it is required to determine. A light source 32 feeds light into the fibres of portion 10 and a detector 20 receives light reflected by the object from portion 12. The detector is associated with an indicating meter 24. It is explained that there is a relationship between the light received by the detector and the spacing. As the latter increases so does the cell output up to a certain amount after which it falls off again, Fig. 6 (not shown). Instead of a random distribution of fibres in the bundle 1 the transmitting fibres may be arranged in a central bundle and the receiving fibres in an annulus or plurality of groups round it. Fig. 10 shows an arrangement in which light transmitted through central bundle 152 and reflected from the test object 168 to bundle 154 leading to detector 166 is compared with light forming a reference beam and travelling by fixed reflector 170 through bundle 158 to detector 164. In a modification of this arrangement the reflector 170 is not used and the reference path is simply a bundle of fibres leading from the source alongside the transmitting bundle to the end face and then bent back on itself to the reference signal detector, Fig. 12 (not shown). The test object may be a diaphragm attached to, but spaced from, the end face of the optical fibre bundle and affected by external pressure. Two systems as shown in Fig. 5 may be arranged with the end faces of their optical fibre bundles at different distances from the same test object and the two results obtained from them combined to prevent the system being affected by changes in test object reflectivity. Instead of two completely independent optical systems a single light source feeding to the nearer end face may be used and the second set of receiving fibres arranged in an annulus round the fibres of the first system and with their ends spaced back from the end thereof. Instead of using bundle end faces spaced from the test object by different amounts a plurality of receiving bundles having a common end face but different fibre diameters is suggested. Fig. 17 shows a central transmitting fibre bundle 302 surrounded by a three annular receiving bundles 304, 306 and 308 each associated with a separate photo-electric detector. The maximum amount of light is received by bundles 304, 306 and 308 in turn as a reflecting test object 322 is moved further away. The composite system may be used to compensate, as in the arrangements described above, for reflectivity variations. It is also possible to obtain the distance information in digital form by associating the detectors with trigger arrangements.