Hand held symbology reader illumination diffuser

Abstract

A hand held industrial identification symbol reader projects diffuse illumination onto a region of interest to produce high contrast images of symbols. The diffuse illumination is particularly well suited for producing images of symbols that are marked directly on objects. The diffuse illumination is created through the use of an optically translucent diffuser having a generally tapered shape that distributes diffuse illumination throughout the field of view of the reader. The diffuse illumination can be supplemented with dark field illumination using selectively actuated illumination sources.

What is claimed is: 
     
         1 . An apparatus for imaging a symbol on an object, the apparatus comprising:
 a hand held portable imaging system having an imager;   a lens disposed between the imager and a region of interest, the region of interest being the intended position of the symbol on the object, the lens and imager defining a field of view and an optical axis;   an illuminator adjacent to the lens, directing illumination towards the region of interest; and   a tapered translucent diffuser concentrically aligned with the optical axis, having a first distal end surrounding the field of view proximate to the lens, and a second distal end surrounding the field of view proximate to the region of interest.   
     
     
         2 . The apparatus according to  claim 1  wherein the tapered translucent diffuser is composed of polymethyl methacrylate. 
     
     
         3 . The apparatus according to  claim 2  wherein the tapered translucent diffuser is fabricated in an injection molding process. 
     
     
         4 . The apparatus according to  claim 1  wherein the tapered translucent diffuser has a conical shape. 
     
     
         5 . The apparatus according to  claim 1  wherein the tapered translucent diffuser has a cylindrical shape. 
     
     
         6 . The apparatus according to  claim 1  further comprising:
 a dark field illuminating light pipe concentrically aligned with the optical axis and surrounding the tapered translucent diffuser; and 
 a dark field illuminator directing illumination into the dark field illuminating light pipe. 
 
     
     
         7 . The apparatus according to  claim 6  wherein the tapered translucent diffuser is removably attached. 
     
     
         8 . The apparatus according to  claim 6  wherein the tapered translucent diffuser has a first color characteristic, the illuminator emits illumination having a color characteristic similar to the first color characteristic, and the dark field illuminator emits illumination having a second color characteristic. 
     
     
         9 . The apparatus according to  claim 8  wherein the first color characteristic is blue, and the second color characteristic is red. 
     
     
         10 . The apparatus according to  claim 8  wherein at least one color characteristic is infrared. 
     
     
         11 . The apparatus according to  claim 6  further comprising:
 a light absorbing filter applied to the diffuser and disposed between the diffuser and the region of interest. 
 
     
     
         12 . The apparatus according to  claim 1  wherein the illuminator further comprises a plurality of selectively actuated illuminators. 
     
     
         13 . The apparatus according to  claim 12  wherein the plurality of selectively actuated illuminators have a north-south and east-west selective actuation. 
     
     
         14 . An apparatus for imaging a symbol on an object, the apparatus comprising:
 a hand held portable imaging system having an imager;   a lens disposed between the imager and a region of interest, the region of interest being the intended position of the symbol on the object, the lens and imager defining a field of view and an optical axis;   an illuminator adjacent to the lens, directing illumination towards the region of interest;   a dark field illuminating light pipe having a first distal end surrounding the lens and the illuminator, and a second distal end surrounding the field of view proximate to the region of interest, the second distal end configured to emit a dark field illumination toward the object at a low angle; and   a tapered translucent diffuser concentrically aligned with the optical axis and disposed within the dark field illuminating light pipe, the diffuser having a first distal end surrounding the field of view proximate to the lens, and a second distal end surrounding the field of view proximate to the object.   
     
     
         15 . The apparatus according to  claim 14  wherein the tapered translucent diffuser does not diffuse the dark field illumination. 
     
     
         16 . The apparatus according to  claim 15  wherein the tapered translucent diffuser has a transparent optical property where it is disposed before the dark field illumination. 
     
     
         17 . The apparatus according to  claim 14  wherein the tapered diffuser is removable. 
     
     
         18 . The apparatus according to  claim 14  and further comprising a plurality of dark field illuminators at the second distal end of the dark field illuminating light pipe configured to provide the dark field illumination. 
     
     
         19 . An apparatus for imaging a symbol on an object, the apparatus comprising:
 a hand-held portable imaging system having an imager;   a lens disposed between the imager and a region of interest, the region of interest being the intended position of the symbol on the object, the lens and imager defining a field of view and an optical axis;   a first illuminator adjacent to the lens, directing illumination towards the region of interest;   a semi-reflecting mirror disposed in front of the lens aligned with the optical axis configured to direct at least a portion of illumination reflected from the region of interest into the lens;   a second illuminator directing illumination at the semi-reflecting mirror so that at least a portion of the illumination from the second illuminator is directed towards the region of interest;   a first diffuser disposed between the second illuminator and the semi-reflecting mirror; and   a tapered translucent diffuser concentrically aligned with the optical axis, having a first distal end surrounding the field of view proximate to the lens, and a second distal end surrounding the field of view proximate to the region of interest.   
     
     
         20 . The apparatus according to  claim 19  wherein the first illuminator has a first intensity, and the second illuminator has a second intensity, so as to configure the apparatus to produce a uniform distribution of illumination over the field of view at the region of interest.