| OCR Text |
Show 92 or a secondary source such as the reflected light of a lase beam. In most cases, the light source is one of severa] light-emitting diodes. The light-emitting diodes are easily distinguished from one another by flashing them on and off in sequence under computer control. The position of a light source is measured by four scanner boxes. contains a spinning disk, two light assemblies, and a reference assembly. Each scanner box source sensing The disks contain several narrow radial slits cut near the edge. One-dimensional scans of the environment are made when the slits pass through the light source sensing assemblies. The disks easily withstand the stresses resulting from the high angular velocity of thirty-five hundred revolutions per minute at which they are spun. A light source sensing assembly contains an objective lens to gather photons from a light source and focus them onto the plane of the moving slit. Photons which pass through the slit are gathered by a Fresnel lens and a condensing lens, and are directed toward a photomultiplier tube. The time of excitation of the photomultiplier tube, relative to a reference time, indicates the position of the slit and hence a plane in space in which a light source lies. The light source sensing assemblies have been built to gather and respond to light within a usable volume measuring roughly 5 x 7.5 x 3 meters. A digitzer and control unit digitizes the signals from the scanner boxes and passes the asynchronously |
