GB1464466A - Scanner - Google Patents

Abstract

1464466 Scanning apparatus for photo-electric detection of objects POST OFFICE 30 April 1974 18886/74 Heading G1A A scanning arrangement for use in detecting the presence or absence or measuring the dimension of objects, e.g. parcels on a conveyer belt, comprises a light source, located on one side of the path of movement of the objects, and on the other side a fixed sensor in association with focusing means for focusing light on to the sensor, the focusing means including at least one aperture in a rotatable member, the scanning arrangement having means by which the effective angular extent of the sensing field may be limited so that e.g. false identification of the absence of radiation as being due to presence of an object, is prevented. The focusing means comprises a plurality of lenses 11 mounted in a rotatable cylinder 12 as in Figs. 2 and 4. The objects to be sensed interrupt light from an elongated source 18, Fig. 4, as they pass. The limitation of the angular field may be by means of a mirror 26, Fig. 4, the additional extent of the angular field defined by the distance between two lenses being illuminated by additional source 24 and accurate adjustment being with the aid of shield 27. Alternatively, an additional source 14, Fig. 2, illuminates additional detector 13 via scanning lenses, the walls of box 15 being adjustable to define the angular field since the output of sensor 13 is used to gate the inverted output of the main detector 10. This detector may be a photodiode associated with a trigger circuit. The source may be underrun to match its omission wavelengths more suitably to the detector spectral sensitivity. The rotatable housing may be replaced by a rotatable disc. The observed field may be divided into sectors by appropriate construction and sectoring of box 15 of Fig. 2.