POSITION SENSING SYSTEMS FOR USE IN TOUCH SCREENS AND PRISMATIC FILM USED THEREIN

摘要

A dual light-source position detecting system for use in touch screens is provided that utilizes parallax to determine the position of an interposing object, and a prismatic film that is brightly retroreflective over a broad entrance angle to enhance to accuracy of the parallax determination of position. The position detecting system includes at least one camera positioned to receive light radiation traversing a detection area and that generates a signal representative of an image; two spaced-apart sources of light radiation, which may be LEDs, or IR emitters positioned adjacent to the camera for outputting light radiation that overlaps over at least a portion of a detection area, and a prismatic film positioned along a periphery of at least a portion of the detection area that retroreflects the light radiation from the two sources to the camera. The prismatic film includes a plurality of triangular cube corner retroreflective elements having dihedral angle errors el7 e2, and e3 such that ex ~ e2 ? 0 and e3 ~ 0 to enhance the efficiency of the retroreflection of the light radiation from the two spaced apart LEDS or IR emitters along the sides of the detection area. If two cameras are mounted in opposing corners of a same side of the touch screen and two dual radiation sources are used in combination with these cameras, an unambiguous determination can be made of the location of two simultaneously interposing objects.