Systems and Sensors for Tracking Radiation Blocking Objects on a Surface

Abstract

Several systems for tracking one or more radiation blocking objects on a surface are disclosed. A pair of radiation sensors are provided adjacent the surface and a plurality of radiation sources are provided adjacent the surface. Radiation from at least some of the radiation sources travels across the surface to reach each of the radiation sensors. One or more radiation blocking objects on the surface attenuate radiation from one or more radiation sources from reaching each of the sensors. The position of the one or more radiation blocking objects is estimates and may be tracked based on the position of the one or more attenuated radiation sources relative to each radiation sensor.

1 . A system for sensing the position of a radiation blocking object, the system comprising:
 a frame;   a first radiation sensor mounted to the frame;   a second radiation sensor mounted to the frame, wherein the first and second radiation sensors are spaced by a distance;   a plurality of radiation sources mounted to the frame, wherein at least some of the radiation sources are visible to each of the radiation sensors;   a controller coupled to radiation sources and the radiation sensors.   
     
     
         2 . The system of  claim 1  wherein each of the radiation sensors is sensitive to radiation emitted by the radiation sources and provides a radiation intensity level to the controller corresponding to the intensity of radiation incident on the sensor. 
     
     
         3 . The system of  claim 1  wherein each of the radiation sensors is selected from the group consisting of:
 a photosensor; 
 a photodiode; 
 a photocell, 
 a solar cell; and 
 a photovoltaic cell. 
 
     
     
         4 . The system of  claim 1  wherein the frame at least partially surrounds a surface. 
     
     
         5 . The system of  claim 1  wherein the surface is selected from the group consisting of: a writing surface; and the surface of a display screen. 
     
     
         6 . (canceled) 
     
     
         7 . The system of  claim 1  further including a bezel and wherein the radiation sources and radiation sensors are mounted within the bezel. 
     
     
         8 . (canceled) 
     
     
         9 . The system of  claim 1  further including one or more diffusers for diffusing radiation emitted by at least some of the radiation sources. 
     
     
         10 . The system of  claim 9  wherein the diffusers are selected from the group consisting of:
 translucent sheet material; 
 translucent plastic; 
 translucent glass; 
 lenticular diffusers; 
 diffraction gratings; and 
 lenticular diffraction gratings. 
 
     
     
         11 . The system of  claim 1  wherein:
 the frame has first, second, third and fourth sides; 
 the first radiation sensor is mounted between the first and second sides; 
 the second radiation sensor is mounted between the first and fourth sides; 
 radiation sources are mounted on second, third and fourth sides. 
 
     
     
         12 . The system of  claim 1  further including an interface coupled to the controller for providing a position of the radiation blocking object to an external device. 
     
     
         13 . A method of estimating the position of a radiation blocking object on a surface, the method comprising:
 providing a first sensor and a second sensor;   providing a plurality of radiation sources, wherein:
 radiation emitted by at least some of the radiation sources passes across the surface and is incident on the first sensor; and 
 radiation emitted by at least some of the radiation sources passes across the surface and is incident on the second sensor; 
   assembling a first radiation intensity signal corresponding to the first radiation sensor;   assembling a second radiation intensity signal corresponding to the second radiation sensor; and   estimating the position of the radiation blocking object based on the radiation intensity signals.   
     
     
         14 . The method of  claim 13  wherein each radiation intensity signal corresponding to a radiation sensor is assembled by sequentially sampling a radiation intensity level from the radiation sensor while at least some of the radiation sources are sequentially activated. 
     
     
         15 . The method of  claim 14  wherein the radiation intensity signals are assembled contemporaneously. 
     
     
         16 . The method of  claim 15  wherein at least one of the radiation sources is activated separately at different intensities to generate a radiation intensity signal corresponding to a first radiation sensor and a radiation intensity signal corresponding to the second radiation sensor. 
     
     
         17 . The method of  claim 14  wherein the radiation intensity signals are assembled sequentially. 
     
     
         18 . The method of  claim 17  wherein a first radiation intensity signal corresponding to the first radiation sensor is assembled and then a second radiation intensity signal corresponding to the second radiation sensor. 
     
     
         19 . The method of  claim 13  wherein estimating the position of the radiation blocking object includes:
 identifying a first group of one or more attenuated radiation sources in the first radiation intensity signal; 
 identifying a second group of one or more attenuated radiation sources in the second radiation intensity signal; 
 estimating the position of the radiation blocking object based on the position of the first group of attenuated radiation sources relative to first radiation sensor and the position of the second group of attenuated radiation sources relative to the second radiation sensor. 
 
     
     
         20 . The method of  claim 19  wherein:
 identifying a first group of one or more attenuated radiation sources includes, for at least some of the radiation sources, comparing a radiation intensity level in the radiation intensity signal to a baseline level for the radiation source at the first radiation sensor; and 
 identifying a second group of one or more attenuated radiation sources includes, for at least some of the radiation sources, comparing a radiation intensity level in the radiation intensity signal to a baseline level for the radiation source at the second radiation sensor. 
 
     
     
         21 . The method of  claim 20  wherein:
 a radiation source is only included in the first group if the radiation intensity level for the radiation source is below the baseline level for the radiation source at the first radiation sensor by a threshold; and 
 a radiation source is only included in the second group if the radiation intensity level for the radiation source is below the baseline level for the radiation source at the second radiation sensor by a threshold. 
 
     
     
         22 . The method of  claim 19  wherein the estimating the position of the radiation blocking object includes:
 identifying a first center radiation source based on the first group; 
 identifying a second center radiation source based on the second group; and 
 estimating the position of the radiation blocking object based on the first center radiation source, the second center radiation source. 
 
     
     
         23 .- 35 . (canceled)