Infrared touch panel with improved sunlight rejection

• US 6,677,934 B1
• Filed: 07/30/1999
• Issued: 01/13/2004
• Est. Priority Date: 07/30/1999
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Blanchard, Randall D.
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Osorio, Ricardo
• Application Number:
  US09/364,953
• Time in Patent Office: 1,628 Days
• Field of Search: 345/173, 345/175, 345/178, 250/221
• US Class Current: 345/175
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen

Abstract

Ambient light can saturate the light detectors of a touch screen and cause unreliable operation. To address this concern, one or more filters may be placed proximate the detectors. A first filter may be a spatial filter, such as a microlouvre filter. A microlouvre filter is arranged so that it passes light transmitted by the light detectors and rejects off-axis light. Another filter may be a narrow band optical filter, such as a dichroic notch filter. Such an optical filter passes light having wavelengths within a narrow band selected to correspond to the spectral characteristics of the light emitters, while it rejects light of other wavelengths. The spatial filter and the narrow band optical filter may be used separately or in combination.

Claims

1. A touch screen system comprising:

an array of emitters and detectors, each of the emitters being arranged to transmit light along a path to one of the respective detectors, wherein the emitters transmit light of a first wavelength band and the detectors respond to light of a second wavelength band, the second wavelength band being broader than the first wavelength band;

a narrow band optical filter disposed adjacent the detectors in the path of the transmitted light, the narrow band filter passing light of a third wavelength band, the third wavelength band being narrower than the second wavelength band;

a display screen disposed adjacent the array;

a controller being coupled to the detectors, the controller delivering a position signal in response to at least one of the respective detectors failing to receive the light transmitted from its respective emitter; and

a host computer coupled to the display screen and to the controller to receive the position signal.

2. The system, as set forth in claim 1, further comprising a face plate disposed over the array and the display screen.

3. The system, as set forth in claim 1, further comprising a bezel disposed about the array, the bezel being generally transparent to light of the first wavelength band.

4. The system, as set forth in claim 3, wherein the filter is mounted onto an inner surface of the bezel.

5. The system, as set forth in claim 1, wherein the narrow band optical filter comprises a dichroic notch filter.

6. The system, as set forth in claim 1, wherein the third wavelength band is substantially equal to the first wavelength band.

7. The system, as set forth in claim 1, wherein the third wavelength band is narrower than the first wavelength band.

8. The system, as set forth in claim 1, wherein the emitters comprise infrared light emitting diodes.

9. The system, as set forth in claim 1, wherein the detectors comprises infrared photodetectors.

10. In a touch screen system comprising an array of emitters and detectors, each of the emitters being arranged to transmit light along a path to one of the respective detectors, wherein the emitters transmit light of a first wavelength band and the detectors respond to light of a second wavelength band, the second wavelength band being broader than the first wavelength band, a display screen disposed adjacent the array, a controller being coupled to the detectors, the controller delivering a position signal in response to at least one of the respective detectors failing to receive the light transmitted from its respective emitter, and a host computer coupled to the display screen and to the controller to receive the position signal, the improvement comprising:

a narrow band optical filter disposed adjacent the detectors in the path of the transmitted light, the narrow band filter passing light of a third wavelength band, the third wavelength band being narrower than the second wavelength band.

11. The system, as set forth in claim 10, wherein the narrow band optical filter comprises a dichroic notch filter.

12. The system, as set forth in claim 10, wherein the third wavelength band is substantially equal to the first wavelength band.

13. The system, as set forth in claim 10, wherein the third wavelength band is narrower than the first wavelength band.

14. In a touch screen system comprising an array of emitters and detectors, each of the emitters being arranged to transmit light along a path to one of the respective detectors, wherein the emitters transmit light of a first wavelength band and the detectors respond to light of a second wavelength band, the second wavelength band being broader than the first wavelength band, a display screen disposed adjacent the array, a controller being coupled to the detectors, the controller delivering a position signal in response to at least one of the respective detectors failing to receive the light transmitted from its respective emitter, and a host computer coupled to the display screen and to the controller to receive the position signal, the improvement comprising the act of:

disposing a narrow band optical filter adjacent the detectors in the path of the transmitted light, the narrow band filter passing light of a third wavelength band, the third wavelength band being narrower than the second wavelength band.