Scanner navigation system with variable aperture

Abstract

A portable scanner for document imaging includes at least one position detector. The position detector has an optical detector and an aperture assembly adjacent the optical detector. The aperture assembly has a first aperture size and a second aperture size. The aperture assembly is adjustable between the first aperture size and the second aperture size.

I claim:  
     
         1 . A portable scanner for document imaging, comprising at least one position detector in said portable scanner, said at least one position detector comprising an optical detector and an aperture assembly adjacent said optical detector, said aperture assembly having a first aperture size and a second aperture size, said aperture assembly being adjustable between said first aperture size and said second aperture size.  
     
     
         2 . The portable scanner of  claim 1 , wherein said aperture assembly is adjusted to said first aperture size when said portable scanner is imaging a substantially light target, and wherein said aperture assembly is adjusted to said second aperture size when said portable scanner is imaging a substantially dark target.  
     
     
         3 . The portable scanner of  claim 1 , wherein said at least one position detector further comprises a lens, and wherein said aperture assembly is located between said optical detector and said lens.  
     
     
         4 . The portable scanner of  claim 1 , further comprising an actuator attached to said aperture assembly to adjust said aperture assembly between said first aperture size and said second aperture size.  
     
     
         5 . The portable scanner of  claim 4 , wherein said actuator comprises a piezoelectric element.  
     
     
         6 . The portable scanner of  claim 4 , wherein said actuator comprises a solenoid.  
     
     
         7 . The portable scanner of  claim 4 , wherein said actuator comprises a motor.  
     
     
         8 . The portable scanner of  claim 1 , further comprising a lever attached to said aperture assembly to adjust said aperture assembly between said first aperture size and said second aperture size, said lever extending to an exterior of said portable scanner so that said aperture assembly may be manually adjusted by moving said lever.  
     
     
         9 . The portable scanner of  claim 1 , wherein said first aperture size is between about 0.5 mm 2  and about 0.6 mm 2 .  
     
     
         10 . The portable scanner of  claim 1 , wherein said second aperture size is between about 1.1 mm 2  and about 1.8 mm 2 .  
     
     
         11 . The portable scanner of  claim 1 , wherein said aperture assembly comprises a plate with a plurality of apertures with fixed sizes, wherein said plurality of apertures each have a different fixed aperture size, and wherein said aperture assembly is adjustable to position each of said plurality of apertures adjacent said optical detector.  
     
     
         12 . The portable scanner of  claim 11 , further comprising a moveable rod operatively attached to said aperture assembly, said moveable rod adjusting said aperture assembly to position each of said plurality of apertures adjacent said optical detector.  
     
     
         13 . The portable scanner of  claim 1 , wherein said aperture assembly comprises a plurality of moveable plates, each of said plurality of moveable plates comprising an opening, said plurality of moveable plates overlapping so that a portion of each of said openings are aligned to form a variable aperture in said aperture assembly, wherein said plurality of moveable plates may be slid apart or together to smoothly vary a size of said variable aperture.  
     
     
         14 . The portable scanner of  claim 13 , wherein said variable aperture has a substantially oblong shape.  
     
     
         15 . The portable scanner of  claim 13 , wherein said variable aperture has a substantially rectangular shape.  
     
     
         16 . The portable scanner of  claim 13 , wherein said variable aperture has a substantially rectangular shape when said plurality of moveable plates are proximate and a substantially cruciform shape when said plurality of moveable plates are distant.  
     
     
         17 . The portable scanner of  claim 13 , wherein said plurality of moveable plates are attached to a pivot pin, and wherein said plurality of moveable plates are rotated about said pivot pin to slide apart or together to vary said size of said variable aperture.  
     
     
         18 . The portable scanner of  claim 13 , wherein said plurality of moveable plates are attached to a plurality of mounting arms, and wherein said plurality of mounting arms move away from or toward each other to slide said plurality of moveable plates apart or together to vary said size of said variable aperture.  
     
     
         19 . The portable scanner of  claim 18 , wherein said plurality of moveable plates comprises two plates.  
     
     
         20 . The portable scanner of  claim 18 , wherein said plurality of moveable plates comprises four plates.  
     
     
         21 . The portable scanner of  claim 1 , wherein said aperture assembly comprises a substantially transparent substrate with an electro-chromic coating thereon, said electro-chromic coating forming an aperture having a variable size when an electric current is applied to said electro-chromic coating.  
     
     
         22 . A method for varying the intensity of light incident on a navigator photodetector in a portable scanner, comprising: 
 providing an aperture assembly adjacent said navigator photodetector in said portable scanner, wherein said aperture assembly has a variable aperture size which may be adjusted to vary the intensity of light incident on said navigator photodetector;    determining an optimal aperture size which best enables said navigator photodetector to detect a position of said portable scanner; and    adjusting said aperture assembly so that said variable aperture size is set substantially at said optimal aperture size.    
     
     
         23 . The method of  claim 22 , wherein determining said optimal aperture size comprises: 
 combining a current image frame produced by said navigator photodetector with a plurality of previous image frames, said plurality of previous image frames being captured by said navigator photodetector simultaneously, all but one of said plurality of previous image frames being shifted in a plurality of directions;    producing a plurality of correlation coefficients indicating a degree of correlation between said current image frame and said plurality of previous image frames, said plurality of correlation coefficients indicating a direction and magnitude of movement between a time when said previous image frames were captured and current time when said current image frame was captured;    fitting a surface to a plot of said plurality of correlation coefficients;    calculating a bowl depth corresponding to a variation in a height between a highest point and a lowest point on said surface; and    selecting a larger optimal aperture size if said bowl depth is small, and selecting a smaller optimal aperture size if said bowl depth is large.    
     
     
         24 . The method of  claim 22 , wherein determining said optimal aperture size comprises measuring an amount of light incident on said navigator photodetector, and providing a small optimal aperture size if a large amount of light is incident on said navigator photodetector and providing a large optimal aperture size if a small amount of light is incident on said navigator photodetector.  
     
     
         25 . A portable scanner for document imaging, comprising: 
 at least one position detector;    an optical detector located in said position detector; and    means for varying a cross-sectional area of a light path to said optical detector.