GB1298457A - Improvements in or relating to optical scanning systems - Google Patents

Abstract

1298457 Optical scanning systems NATIONAL RESEARCH DEVELOPMENT CORP 26 Feb 1970 [28 Feb 1969 8 May 1969] 11007/69 23624/69 Heading G2J [Also in Division H4] An optical scanner comprises a drum 1 of imaging elements 3 such as lenses or mirrors, a faceted mirror 4 which is small relative to the drum diameter and fixed relative to the drum, each facet facing a respective element 3 and being inclined to the drum axis so that the reflection of the optical axis of the element 3 in the facet extends parallel to the drum axis, and a motor 2 for rotating the drum 1 and mirror 4 together so that each such reflection of the optical axes of the elements 3 in turn coincides with a given axis. As shown, infra red radiation from an image 8 is passed by a plane mirror periscope 9, 10 to a mirror element 3<SP>1</SP>, which may be spherical but is preferably of conic section, and is thereby focused at or near the surface of the corresponding mirror facets and passed via relay mirrors 5, 6 to a detector 7. Such a system is said to minimize vignetting by the facet edges. Rotation of the drum and mirror 4 thus scans a line 12 of points 13 and vertical scanning is performed by deflecting the mirror 10 by a cam driven by the motor 2. If the elements 3 are lenses, mirrors 9 and 10 may be omitted, and the mirrors 5, 6 may also be replaced by a lens system. In the embodiment shown, the mirror 4 is coaxial with the drum and the "given axis" is therefore displaced from the drum axis. In Fig.5 (not shown), the mirror 4 is mounted eccentrically of the drum and geared thereto, so that the "given axis" and the drum axis are coincident, which is preferred. Also the drum is mounted horizontally and mirror 9 omitted. Each element 3 and the cam driving the mirror 10 are provided with reflective facets which co-operate with respective light sources and photo-diodes to provide line and frame sync. pulses respectively. Alternatively a peg or flag on each mirror 3 may interrupt a light beam. To provide upper and lower reference levels e.g. in infrared thermography:- (a) a solenoid may insert a fixed temperature source between the drum and the mirror 4 once per frame (b) the facets of mirror 4 may be separated by slots through which a reference source is visible once per line (c) black vanes may be disposed between the facets of mirror 4 to emit at the ambient temperature, or (d) reflective vanes between the mirror facets and at an angle thereto may reflect light from a fixed reference source to the detector 7, Fig.2 (not shown). The signal from the detector 7 may be converted to a digital signal supplied to circuits generating characters from the digital values which are displayed in the relevant position on a television screen. Such circuitry may be operable only for a selected area of the image 8. A rangefinder producing two visible light beams resting in the plane 8 may be provided. The detector may be replaced by a light source for display purposes.