Presentation board digitizer systems

Abstract

A presentation board digitizer system for large boards preferably employs at least three spaced-apart ultrasound receivers assemblies. A current position of an ultrasound transmitter is assigned as a weighted centroid of time-of-flight position measurements based on at least two pairs of receiver assemblies. The weighting used varies as a function of the position of the transmitter across the board. A preferred structure of an ultrasound receiver assembly for use in the system employs a pair of ultrasound receivers arranged side-by-side in a line perpendicular to the surface of the presentation board. The receivers are connected so as to generate a total output signal corresponding to the instantaneous sum of the ultrasound signals received at each, such that the receiver assembly is most sensitive to ultrasound signals incident from a plane adjacent to the presentation board. Also described are a transmitter device for use with a conventional pen in which the ultrasound transmitter is a cylindrical element lying coaxial with the pen and adjacent to its tip, and a jointed eraser structure.

1 . A system for use with a surface, comprising: 
 a plurality of receiver assemblies comprising a first ultrasound receiver located adjacent to the surface, and a second ultrasound receiver displaced from the first ultrasound receiver in a direction substantially perpendicular to the surface, the first and second ultrasound receivers being connected to generate a total output signal corresponding to the instantaneous sum of the ultrasound signals received at each of the first and second ultrasound receivers;    an attachable strip, wherein the plurality of receiver assemblies are mounted to the strip; and    a movable transmitter device comprising an ultrasound transmitter.    
     
     
         2 . The system of    claim 1   , further comprising: 
 an infrared receiver mounted on the strip; and    wherein the movable transmitter device further comprises an infrared transmitter.    
     
     
         3 . The system of    claim 1   , wherein the first and second ultrasound receivers within each of the plurality of receiver assemblies are connected in series.  
     
     
         4 . The system of    claim 1   , wherein the movable transmitter device further comprises a housing having a substantially cylindrical opening terminating at a first end comprising an inner housing surface having a central bore, the housing receiving a portion of the body of a drawing implement comprising a body, a back end, and a front end opposite the back end comprising an operative tip, wherein the operative tip of the drawing implement extends through the central bore, a retainer attachable to a second end of the opening to retain the drawing implement within the housing, the retainer having a spring element for biasing the drawing implement towards the inner housing surface, wherein the ultrasound transmitter is mounted relative to the housing proximal towards the central bore.  
     
     
         5 . The system of    claim 4   , wherein the inner housing surface comprises an annular wedge surface.  
     
     
         6 . The system of    claim 4   , wherein the spring further comprises a shaped abutment surface for centering the back end of the drawing implement.  
     
     
         7 . The system of    claim 6   , wherein the shaped abutment surface comprises an axial conical projection.  
     
     
         8 . The system of    claim 6   , wherein the shaped abutment surface comprises a conical recess.  
     
     
         9 . The system of    claim 4   , wherein the ultrasound transmitter is a substantially cylindrical piezoelectric transmitter attached to the housing around the central bore.  
     
     
         10 . The system of    claim 4   , wherein the housing further comprises: 
 a microswitch actuated by changes in pressure exerted on the surface so as to be responsive to a force exerted on the operative tip of the drawing implement towards the housing; and    electronic circuitry responsive to the microswitch to affect operation of the ultrasonic transmitter at least when the microswitch indicates a force exerted on the operative tip of the drawing implement towards the housing.    
     
     
         11 . The system of    claim 10   , wherein the electronic circuitry is battery powered.  
     
     
         12 . The system of    claim 10   , wherein the electronic circuitry operates the ultrasonic transmitter for a given time interval after the microswitch ceases to indicate a force exerted on the outer housing towards the operative tip of the drawing implement.  
     
     
         13 . The system of    claim 12   , wherein the given time interval is at least about half a second.  
     
     
         14 . The system of    claim 12   , wherein the ultrasound transmitter transmits continuously, and wherein the electronic circuitry is responsive to the microswitch to change a signal transmitted by the transmitter while the microswitch indicates a force exerted on the operative tip of the drawing implement towards the housing.  
     
     
         15 . A process for use with a surface, comprising: 
 providing at least three ultrasound receivers associated with the surface;    transmitting an ultrasound signal from an element movable relative to the surface;    receiving the ultrasound signal at the plurality of ultrasound receivers; and    analyzing outputs from the ultrasound receivers comprising the step of identifying as a current position a weighted centroid of at least a first calculated position derived from the outputs of a first pair of the receivers and a second calculated position derived from the outputs of a second pair of receivers, wherein the weighting varies as a function of approximate position relative to the ultrasound receivers.    
     
     
         16 . The process of    claim 15   , further comprising: 
 transmitting an infrared signal from the element.    
     
     
         17 . The process of    claim 16   , wherein the infrared signal comprises synchronization information.  
     
     
         18 . The process of    claim 16   , wherein the infrared signal comprises pen color information.  
     
     
         19 . The process of    claim 15   , wherein the ultrasound receivers are substantially collinear, and wherein the weighting varies linearly with distance in the direction of alignment of the ultrasound receivers over at least a given switch-over zone.  
     
     
         20 . The process    claim 19   , wherein the weighted centroid approximates to the first calculated value when the movable element is within a first given region of the surface.  
     
     
         21 . A digitizer system for digitizing operative strokes of a drawing implement comprising a body, a back end, and a front end opposite the back end against a board, the system comprising: 
 a movable transmitter device comprising a housing and a central bore, the central bore receiving a portion of the body of the drawing implement with its operative tip extending through the central bore, and an ultrasound transmitter mounted relative to the housing proximal towards the central bore;    at least two ultrasound receivers mounted relative to the board for receiving air-borne ultrasound signals;    a transducer associated with the board so as to detect vibrations from the transmitter device conducted through the board; and    a processor responsive to outputs from the at least two ultrasound receivers to calculate a current position of the transmitter, the processor being additionally responsive to an output from the transducer to identify contact between the drawing implement and the board, thereby identifying operative strokes of the drawing implement.    
     
     
         22 . A system for digitizing operative strokes of a drawing implement comprising a body, a back end, and a front end opposite the back end comprising an operative tip, the system comprising: 
 at least one ultrasound receiver assembly; and    a transmitter device comprising a housing having a substantially cylindrical opening terminating at a first end comprising a surface with a central bore, the housing receiving a portion of the body of the drawing implement with its operative tip extending through the central bore, a retainer attachable to a second end of the opening to retain the drawing implement within the housing, the retainer having a spring element for biasing the drawing implement towards the surface, and an ultrasound transmitter mounted relative to the housing proximal towards the central bore.    
     
     
         23 . The system of    claim 22   , wherein the surface comprises an annular wedge surface.  
     
     
         24 . The system of    claim 22   , wherein the spring further comprises a shaped abutment surface for centering the back end of the drawing implement.  
     
     
         25 . The system of    claim 24   , wherein the shaped abutment surface comprises an axial conical projection.  
     
     
         26 . The system of    claim 24   , wherein the shaped abutment surface comprises a conical recess.  
     
     
         27 . The system of    claim 26   , wherein the transmitter is a substantially cylindrical piezoelectric transmitter attached to the housing around the central bore.  
     
     
         28 . The system of    claim 26   , wherein the housing further comprises: 
 a microswitch actuated by changes in pressure exerted on the surface so as to be responsive to a force exerted on the operative tip of the drawing implement towards the housing; and    electronic circuitry responsive to the microswitch to affect operation of the ultrasonic transmitter at least when the microswitch indicates a force exerted on the operative tip of the drawing implement towards the housing.    
     
     
         29 . The system of    claim 28   , wherein the electronic circuitry is battery powered.  
     
     
         30 . The system of    claim 28   , wherein the electronic circuitry operates the transmitter for a given time interval after the microswitch ceases to indicate a force exerted on the outer housing towards the operative tip of the drawing implement.  
     
     
         31 . The system of    claim 31   , wherein the given time interval is at least about half a second.  
     
     
         32 . The system of    claim 28   , wherein the transmitter transmits continuously, and wherein the electronic circuitry is responsive to the microswitch to change a signal transmitted by the transmitter while the microswitch indicates a force exerted on the operative tip of the drawing implement towards the housing.  
     
     
         33 . The system of    claim 28   , wherein the ultrasound transmitter comprises a piezoelectric ultrasound transmitter.  
     
     
         34 . The system of    claim 33   , further comprising at least one element of an electromagnetic: communications link, the at least one element being associated with the electronics circuitry.  
     
     
         35 . The system of    claim 34   , wherein each of the at least one element of the electromagnetic communications link comprises an infrared transmitter.  
     
     
         36 . The system of    claim 34   , wherein each of the at least one element of the electromagnetic communications link are spaced around the first end of the housing.  
     
     
         37 . A system for digitizing the position of a drawing implement in relation to a presentation board, the drawing implement comprising a central axis and an operative tip, the system comprising: 
 at least one receiver assembly; and    a transmitter device comprising a substantially cylindrical piezoelectric transmitter element positioned coaxially with the drawing implement so as to circumscribe a part of the drawing implement proximal to the operative tip.    
     
     
         38 . The system of    claim 37   , further comprising: 
 an eraser device comprising a handle, an eraser element comprising a substantially flat eraser surface, and a pivot joint connecting between the handle and the eraser element, the pivot joint having two degrees of rotational freedom such that, in use, the eraser element assumes an orientation with the eraser surface parallel to the presentation board substantially independent of the orientation at which the handle is held.    
     
     
         39 . The system of    claim 37   , further comprising: 
 a narrow-band eraser device comprising a handle, an eraser element having a substantially flat eraser surface, and a plurality of contact microswitches located on the eraser surface, such that when a portion of the eraser surface contacts the presentation board, at least one microswitch corresponding to the portion is activated and such that when substantially an entirety of the eraser surface contacts the presentation board, substantially all of the microswitches are activated.    
     
     
         40 . The system of    claim 39   , wherein the narrow-band eraser device further comprises a plurality of ultrasound transmitters and a plurality of infrared transmitters for identifying contact with a presentation board.  
     
     
         41 . The system of    claim 40   , wherein the narrow-band eraser device further comprises at least one reflector for each of the transmitters.  
     
     
         42 . The system of    claim 39   , wherein the narrow-band eraser device further comprises a pressure-sensitive element for identifying contact with the presentation board.