Light-based touch screen using elliptical and parabolic reflectors
A touch screen system, including a housing, a display mounted in the housing, a plurality of light pulse emitters mounted in the housing below the display, a plurality of light pulse receivers mounted in the housing below the display, a first light guide, mounted in the housing along a first edge of the display, including a first substantially parabolic reflective surface for reflecting light pulses transmitted by the emitters, and a first substantially elliptical refractive surface, positioned substantially above the first substantially parabolic reflective surface, for refracting the reflected light pulses over the display, a second light guide, mounted in the housing along an opposite edge of the display, including a second substantially elliptical refractive surface for further refracting the light pulse refracted by the first substantially elliptical refractive surface, and a second substantially parabolic reflective surface, positioned substantially below the second substantially elliptical refractive surface, for reflecting the further refracted light pulses to the receivers, and a calculating unit, mounted in the housing and connected to the receivers, to determine a location of a pointer on the display that partially blocks the light pulses refracted by the first light guide, based on outputs of the receivers corresponding to light pulses refracted by the second light guide.
1. A touch screen comprising:
a housing;
a display mounted in said housing;
a plurality of light pulse emitters mounted in said housing below said display;
a plurality of light pulse receivers mounted in said housing below said display;
a first light guide, mounted in said housing along a first edge of said display, comprising:
a first substantially parabolic reflective surface for reflecting light pulses transmitted by said emitters; and
a first substantially elliptical refractive surface, positioned substantially above said first substantially parabolic reflective surface, for refracting the reflected light pulses over said display;
a second light guide, mounted in said housing along an opposite edge of said display, comprising:
a second substantially elliptical refractive surface for further refracting the light pulses refracted by the first substantially elliptical refractive surface; and
a second substantially parabolic reflective surface, positioned substantially below said second substantially elliptical refractive surface, for reflecting the further refracted light pulses to said receivers; and
a calculating unit, mounted in said housing and connected to said receivers, to determine a location of a pointer on said display that partially blocks the light pulses refracted by said first light guide, based on outputs of said receivers corresponding to light pulses refracted by said second light guide.
2. The touch screen of claim 1 wherein said first substantially parabolic reflective surface and said first substantially elliptical refractive surface have the same focal location, and wherein said second substantially parabolic reflective surface and said second substantially elliptical refractive surface have the same focal location.
3. The touch screen of claim 1 further comprising two additional light guides mounted in said housing and arranged along the remaining two edges of said display, the four light guides comprising a single unit surrounding said display.
4. The touch screen of claim 1 , wherein said first and second light guides comprise a portion of a screen glass covering said display.
5. The touch screen of claim 1 further comprising a screen glass covering said display, the screen glass comprising a painted frame on the screen glass inner surface, surrounding a rectangular viewing window, and wherein said first and second light guides each comprise a daylight filter sheet aligned with said painted frame.
6. The touch screen of claim 1 further comprising a screen glass covering said display, the screen glass comprising a painted frame on the screen glass inner surface, surrounding a rectangular viewing window,
wherein said first and second light guides each comprises an infra-red transparent portion that is colored like said painted frame and aligned with said painted frame.