Abstract:
An optical text scanning device compatible with a small handheld computer such as a personal digital assistant (PDA). The scanning device allows for a clear view of the text that is scanned simultaneous to the scanning process so that the operator can continuously align the device to the text. The scanned images of the text are converted in real-time to standard byte or word characters for subsequent display on the computer&#39;s viewing screen. The operator can quickly verify the accuracy of the conversion by comparing the displayed character with the actual character of text on the surface that is being scanned. Scanned text characters are stored in standard digital text files for ease of manipulation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part claiming priority to U.S. patent application Ser. No. 12/070,803 filed Feb. 21, 2008 now U.S. Pat. No. 8,056,805 which was a continuation-in-part claiming priority to U.S. patent application Ser. No. 11/156,814 filed Jun. 17, 2005, now U.S. Pat. No. 7,364,077. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The invention relates to an optical text scanning device integrated with a small handheld computer such as a personal digital assistant (PDA). In particular, it teaches hardware and software concepts that allow simultaneous optical viewing of the text as it is scanned and real-time conversion of the scanned images to a standard text character stream for subsequent display on a viewing screen. 
     BACKGROUND OF THE INVENTION 
     The small handheld computer or personal digital assistant (PDA) has become a popular tool in the business world and more recently in personal communications. These devices have incorporated wireless functions, cellular phone functions, personal audio, camera and video functions so that the market for such devices have expanded well beyond the business person to the individual. The modern PDA operates as a multifunction device that many individuals carry with them at all times. 
     The PDA performs as a technology platform for the development of many new value-added portable devices that can be integrated as hardware or software add-ons to the PDA or linked through wireless functions. There is an ever growing market for PDA add-ons as the penetration of users continues to expand from business applications to personal applications. 
     A relevant class of PDA add-on devices has been developed to improve the means of getting information into and out of the device. Cameras based PDA add-ons are particularly effective because a large volume of data, typically 1 Megabyte to 10 Megabytes, can be collected optically and electronically in a sub-second period of time. Closely related to optical imaging is the field of optical scanning of documents. With the addition of an optical scanner to a PDA, especially a PDA that has wireless or cellular capabilities, one can perform such tasks as, for example, portable faxing of documents from the field, or, the scanning and uploading of a serial number from the field so that useful product information could be rapidly and accurately downloaded to a technician during a repair process. 
     With respect to the prior art, there are examples of optical scanning devices that could be used in conjunction with a PDA. One example is an optical wand. Optical wands are currently commercially available and may communicate with PDAs via an external cable, but these are not seamlessly integrated and require an extra hand-held device. For example, Faulkerson, U.S. Pat. No. 4,804,949 discloses a scanning device in combination with a computer mouse connected via an umbilical cord to an external computer for OCR processing and text display. Faulkerson does not teach the on-board integration of optical scanning functions directly into a PDA. 
     Liao, U.S. Patent application No. 2004/0093444 A1 shows a PDA converted into an optical scanning device by adding an optical scanner assembly onto the back surface. Liao also discloses the application of scanning business card data into a PDA as bit-mapped images. Liao does not include a mechanism for illuminating the object to be scanned nor does he provide for simultaneous viewing of the object during the scan nor does he provide a mechanism for real-time image conversion to digital characters. 
     A similar disclosure is read in Huang, U.S. Patent Application No. 2002/0169509 A1 in which the author discloses a handheld device, such as a PDA, capable of optical scanning. Huang discusses a feeder scanner design in which the PDA is situated inside a base housing and the documents are fed through a scanner channel via a set of rollers. Huang&#39;s design limits the scanned document sizes to those that can fit through the housing and otherwise suffers from similar limitations as Liao. 
     In Tsai, U.S. Patent Application No. 2003/0151780, a scanning device is disclosed which includes a chassis for housing a PDA. Tsai also discloses an optical sensing assembly engaged with the transmission assembly so as to transfer the speed signal of the movement of the scanning device. Tsai&#39;s invention, while not limited by the document size, suffers from some of the same general limitations as the other designs, namely that the viewing of the document is limited to a bit-mapped image of the scanned input and that there is no immediate conversion to a standard digital character format. Real-time scanning of text directly into standard byte or word character format would realize a significant improvement in portability over the prior art, since text files composed of standard digital characters have much smaller file sizes compared to image file formats. 
     SUMMARY OF THE INVENTION 
     The current invention is a PDA compatible text scanner with certain novel features. The text scanner is incorporated into the PDA via physical, electronic, optical and software functions and can be used in a portable fashion as the combined unit is battery powered and handheld in size and weight. The text scanner can be a permanent fixture of the PDA or easily removable. The invention need not be limited to using a PDA platform: any type of portable handheld computer could be substituted for the PDA, such as a handheld calculator, portable audio player or cell phone. 
     An objective of the invention is to allow text to be scanned easily from a variety of sources. The scanning function is not constrained to the size or type of document. For example, but not by way of limitation, the document may be the size of a business card or the document may be part or all of the text in a large architectural scale blueprint. The invention does not constrain the geometry of the scanned text to a flat surface but may be employed to scan text on curved surfaces such as medicine containers or other product containers. 
     A feature of the preferred embodiment of this invention is that the text scanner assembly is constructed of optically transparent material and designed in such a way that the user can clearly view the text as it is scanned. The invention also incorporates a set of horizontal and vertical alignment marks that combine functionally with the clear view of the scanned text allowing for ease of alignment and scanning accuracy. The invention further discloses an illumination light guide that not only eases the viewing of text, but also increases the signal to noise level of the electronic image capture and subsequent character recognition process. Another feature of the invention is that it converts the scanned image of the text characters to standard byte or word digital character format in real time, for example to ASCII format, storing the digital character in memory and displaying the digital character on the PDA viewing screen. The invention incorporates the use of optical character recognition (OCR) processes in conjunction with the scan process. 
     The PDA compatible text scanner in the present invention utilizes known electronic interfaces found on PDAs such as a module expansion slot or memory expansion slot (e.g. SecureDigital, MMC, compact flash, etc.). Modern PDAs may incorporate a built-in camera and light source. The preferred embodiment teaches a means of using camera devices that are built-in to the PDA to accomplish the image acquisition. However, built-in PDA cameras are not a general requirement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the features and advantages, reference is now made to the detailed description along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
         FIG. 1  is a perspective drawing of one embodiment. 
         FIG. 2  (A, B) show two views of a preferred embodiment showing (A) the top view, and (B) the bottom view. 
         FIG. 3  is a partial cross-sectional view of a preferred embodiment showing the detail of a camera unit and optical assembly. 
         FIG. 4  (A-C) are drawings of a second embodiment showing views: (A) a top view, (B) a cross-sectional view AA showing the optical components, and (C) a bottom view. 
         FIG. 5  is block diagram of the electronic architecture. 
         FIG. 6  is a flow diagram. 
         FIG. 7(A-D)  are drawings of a third embodiment showing views: (A) top view, (B) side view, (C) first cross-section view of an optical reader assembly attached to a PDA indicating the optical cavity and optical components, (D) second cross-section view of an optical reader assembly attached to a PDA indicating the illuminator light guide. 
         FIG. 8(A-C)  are drawings of a fourth embodiment showing views: (A) top view, (B) bottom view, (C) cross-section view of an optical reader assembly attached to a PDA indicating the optical cavity and optical components. 
         FIG. 9  is a drawing of a fifth embodiment showing a perspective view of a rotatably attached optical reader assembly. 
         FIGS. 10A-10C  are drawings of the fifth embodiment showing a side view, a non-rotated cross-section view and a rotated cross-section view of the optical reader assembly and a mounting assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1  is shown a front perspective view of the preferred embodiment of a PDA text scanner device comprised of an optical reader assembly  200  mechanically attached to a rectangular shaped PDA unit  100  by four screws  140   a ,  140   b ,  140   c  and  140   d  secured from the rear via holes  240   a ,  240   b ,  240   c  and  240   d . The top surface of reader assembly  200  is approximately co-planar with and faces the same direction as the front surface of the PDA unit  100 . Text print, printed figures or written objects form an optical target  180  that lies on a surface  181  that is beneath the bottom surface of optical reader assembly  200 . The surface  181  is located ideally from 0 to 2 cm below the bottom surface of the optical reader assembly. The top and bottom surfaces of optical reader assembly  200  are approximately parallel. The optical reader assembly is further shown in  FIG. 2 . 
     Those familiar with PDA devices will realize that the mechanical means by which the optical reader assembly attaches to the PDA unit is dependent upon the specific geometry of the PDA unit and that the invention may easily encompass other means of attachment. For example, in other embodiments it may be beneficial to include a spring-loaded ball-and-detent attachment mechanism (not shown) or a molded plastic form that releasably connects to the body of the PDA to allow for rapid and easy removal of the optical reader assembly when it is not in use or where access to certain features of the PDA (such as the camera) is required. 
     PDA unit  100  has a viewing screen  120  and control buttons  130  situated on the front surface just below the viewing screen  120  and a built-in camera unit  151  on the rear surface. In use, scanned characters  185  appear on the PDA viewing screen  120  as the optical target  180  is scanned into the device. An acquire button  220  is mounted on the top surface of the optical reader assembly as shown along with an optical reader indicator LED  225 , also mounted on the optical reader assembly&#39;s top surface. 
     Referring to  FIG. 2 , the optical reader assembly  200  includes an optical block  210  that is transparent and made of clear acrylic material  210  in the preferred embodiment. Other materials such as glass or crystal can be used in alternated embodiments. Colored transparent materials may also be used for special applications of the invention (such as in a low light embodiment or for aesthetic appeal such as in a children&#39;s toy). 
     The electrical connection between the optical reader assembly  200  and the PDA unit  100  is accomplished using PDA electrical interface  150 . Acquire button  220  and optical reader indicator LED  225  are connected by electrical traces (not shown) to the electrical connector  250  which mates with PDA electrical interface  150 . In other embodiments, the optical reader assembly  200  may incorporate the use of driver electronics between the PDA electrical interface and said components to accomplish electronic connections. 
     Continuing with  FIGS. 2A and 2B , optical reader assembly  200  incorporates alignment marks. In particular, there are a set of horizontal alignment marks  231   a  and  231   b  inscribed on the bottom surface of optical reader assembly  200  and a vertical alignment mark  232  inscribed on the top surface of the optical reader assembly  200 . 
     Mirrors  270   a  and  270   b  and Lens  280  guide light from the bottom of the optical reader assembly  200  to the back of the PDA unit  100 . Further details of the optical components are disclosed in  FIG. 3 . 
     As shown in  FIG. 3 , a rhomboid shape optical cavity  252  is included in the optical reader. The cavity forms a void in optical block  210  and is defined by parallel surfaces  253  and  254 , inner surface  255 , outer surface  257  and lens mount  256 . PDA camera unit  151  is typically recessed into PDA unit  100  behind the PDA viewing screen  120 . Mirror  270   a  is affixed with adhesive to surface  254  of the cavity with its reflective surface facing optical target  180  at an angle of about 45 degrees from the optical axis  274 . Optical axis  274  is the axis defined by a line on which the centers of the optical components lie and is approximately perpendicular to the back of the PDA as it exits optical reader assembly  200 . Mirror  270   b  is adhered to surface  253  of the cavity with its reflective surface facing PDA camera unit  151  at an angle of about 45 degrees from optical axis  274 . PDA camera unit  151  incorporates a first optical lens  280 , aperture stop  285  and optical image detector  290  as shown and it is built-in to the PDA unit  100 . The first optical lens  280  is positioned such that an optical image of optical target  180  is formed on the surface of optical image detector  290 . Aperture stop  285  serves to define the field of view and depth of field of the camera unit. In the preferred embodiment, optical reader assembly  200  incorporates a second optical lens  281  which is centered on optical axis  274  and located just inside the bottom surface of optical reader assembly  200  attached to lens mount  256 . Mirrors  270   a  and  270   b  are fixed in such a way as to define optical ray paths  275  from the surface of optical detector  290  to mirrors  270  to optical target  180  thereby allowing optical target  180  to be imaged on optical detector  290 . 
     In the preferred embodiment the lenses are made of glass or plastic substrate and assembled as separate elements. In an alternate embodiment, at least one of the lenses may be molded as a part of the block  210 . In other embodiments, at least one of the optical lens functions may be combined with the mirror function by using a curved mirror surface; the lens positions and overall magnification may vary as long as the object is imaged onto the detector surface. The equations for determining lens position relative to the object and detector are well known in the art. 
     In the preferred embodiment, the mirrors are front silvered flat glass substrates inserted into optical reader assembly  200  and fixed in place by an adhesive. There are other means of accomplishing the function of the mirrors such as using multiple silvered substrates, silvering one or more surfaces of the optical reader assembly  200  or inserting one or more prisms into the optical cavity  252 . 
     In the preferred embodiment, optical image detector  290  is a charge-coupled device (CCD) having approximately 500 by 500 pixels and lateral dimensions of one-half inch or less. The invention comprehends that other technology may be deployed in the PDA to accomplish the optical to electronic conversion of the image—for example, a CMOS imaging device may be deployed in other embodiments. In the preferred embodiment, camera unit  151  is integral to the PDA unit  100  and may accomplish functions known in the art such as autofocus and zoom in conjunction with software resident on the host PDA. For example, the autofocus function will allow the optical target  180  to be placed at different distances from the scanning unit. The resident software may also operate the integrated camera in a “black and white” mode whereby the color information is discarded, thereby creating further efficiencies in the scanning process. Within the scope, it is envisioned that the user can quickly remove the optical reader assembly so that optical images of text or other material could be taken in photographic mode and processed accordingly. 
     In an alternate embodiment shown in  FIG. 4A , optical reader assembly  300  is shown. The optical reader assembly  300  has optical body  310  made of clear acrylic and has two mounting tabs  342   a  and  342   b  for mounting the device on the PDA unit. The mounting is accomplished by inserting the mounting tabs into matching recesses into the PDA unit  100  and utilizing set screws to hold the mounting tabs  342  in place. Those familiar with PDA devices will realize that the mechanical means by which the optical reader assembly attaches to the PDA unit is dependent upon the specific geometry of the PDA unit and that the invention may easily encompass other means of attachment. For example, in other embodiments it may be beneficial to include a spring-loaded ball-and-detent attachment mechanism or a molded plastic form that snaps to the body of the PDA to allow for rapid and easy removal of the optical reader assembly when it is not in use. 
     Optical body  310  includes an acquire button  320 , indicator LED  325  attached to the top surface and an electrical connector  350  that mates with PDA electrical interface  150  to connect said devices with PDA unit  100 . 
     Horizontal alignment marks  331   a ,  331   b  and vertical alignment mark  332  are inscribed into the main body  310 : the horizontal and vertical marks indicate the position of optical target  180  placement relative to the main body  310 . 
     An optical cavity  352  is included in the optical body generally centered at the horizontal midpoint marked by vertical alignment mark  332  as shown in  FIG. 4A  and  FIG. 4C . Referring to  FIG. 4B , optical cavity  352  is defined by reflector support surface  353 , inner surface  354 , camera housing  355 , lens mount  356 , illuminator light guide  360  and illuminator housing  358 . The reflector support surface, inner surface, camera housing, illuminator light guide and illuminator housing form a void in the main body and comprise a housing for the optical components of the system. Mirror  370 , in the preferred embodiment, is a front silvered partially reflecting mirror of about 50% reflectivity attached by its non-reflective surface to reflector support surface  353  using an adhesive. The reflective surface of mirror  370  is facing optical target  378  at an angle of about 45 degrees from the optical axis  374 . Optical axis  374  is a line through the centers of the optical components and is approximately perpendicular to the bottom face of the PDA unit as it exits optical reader assembly  300 . 
     In other embodiments, mirror  370  may be replaced by a back silvered mirror or a triangular prism positioned to reflect light from optical target  378  into the other optical components of the system. In other embodiments, where the illuminator light guide is not directly behind the mirror surface  353 , the function of the mirror  370  can also be performed by a reflective coating applied directly to reflector surface  353 . 
     Optical reader assembly  300  incorporates an optical lens  380  fixed to lens mount  356 , aperture stop  385  which is fixed to and supported by camera housing  355 , and optical image detector  390  affixed to camera housing  355 . The optical lens  380  is centered on the optical axis  374  and located just inside the bottom surface of optical reader assembly  300 ; it is positioned approximately mid-way between the optical target  378  and the optical detector  390  at about twice its focal distance from optical target  378  so that an image of optical target  378  is formed on the surface of optical detector  390  with approximately unit magnification. Aperture stop  385  serves to define the field of view and depth of field. Optical ray paths  375  trace light from optical target  378  to lens  380  to mirror  370  to optical detector  390 , thereby allowing optical target  378  to be imaged by optical detector  390 . Optical lens  380  may incorporate an anti-reflection coating to reduce stray light reflections. 
     In the present embodiment the lens is made of glass or plastic substrate and assembled as a distinct element. In another embodiment, the lens may be molded as a part of optical block  310 . In other embodiments, the optical lens function may be combined with the mirror function by using a curved mirror surface; the lens position and overall magnification may vary as long as the object is imaged onto the detector surface. The equations for determining lens position relative to the object and detector are well known in the art. 
     Optical reader assembly  300  has an illuminator light guide  360  which is a tapered hole situated just behind partially silvered mirror  370 . Illuminator housing  358  is a hole connecting to illuminator light guide  360  both of which are generally centered on the optical axis  374  as projected through the mirror  370 . Light source  340  is fixed inside illuminator housing  358  so that it protrudes into the illuminator light guide  360  at approximately the rear focal plane of lens  380 . Light from light source  340  propagates through the partially silvered mirror  370 , through the lens  380  and exits optical reader assembly  300  approximately collimated to illuminate the optical target  378 . Light source  340  is typically a light emitting diode (LED) chosen to match the spectral response of the optical detector  390 , but other sources of illumination are possible within the scope of the invention. Light source  340  is powered by current received from PDA unit  100  via electrical interface  150  and flexible wires (not shown) which interconnect to electrical connector  350 . Electrical connector  350  provides a mating interface with PDA electrical interface  150 . 
     In alternate embodiments of the invention the illumination guide is accomplished by the insertion of one or more optical waveguides such as a void in the optical block or optical fibers. The illuminator light spectrum and optical waveguide may be chosen to match the wavelength peak sensitivity of the optical detector, such as in the infrared range so as to illuminate a large area of text in the vicinity of the optical reader. The illumination light spectrum may also be chosen in the visible spectrum to enhance the user&#39;s ability to see the material to be scanned, especially in the absence of ambient light. In such embodiments where an optical waveguide is deployed, the partially silvered mirror may be replaced by a fully reflecting mirror or prism. 
     Optical image detector  390  is a charge-coupled device (CCD) having approximately 500 by 500 pixels and lateral dimensions of one-half inch or less. Optical detector  390  can be model TC237 680×500 pixel monochrome CCD made by Texas Instruments of Dallas, Tex. The invention comprehends that other technology may be used to accomplish the optical to electronic conversion of the image—for example, a CMOS imaging device may be deployed in other embodiments. The camera may accomplish functions known in the art such as autofocus and zoom in conjunction with software resident on the host PDA. For example, the autofocus function will allow the optical target  378  to be placed at different distances from the optical reader assembly. The resident software may also operate the integrated camera in a “black and white” mode whereby the color information is discarded, thereby creating further efficiencies in the scanning process. Within the scope, it is envisioned that the user can easily remove the optical reader assembly so that optical images of text or other material could be taken in photographic mode and processed accordingly. 
     Optical detector  390  is physically connected to control circuit board  395 . Control circuit board  395  provides on-board memory, clocking, electrical buffering and computer interface functions. Control circuit board  395  is electronically connected to the PDA unit  100  via flexible cabling (not shown) which interconnects to electrical connector  350  which mates with PDA electrical interface  150 . 
     Optical reader assembly  300  may incorporate the use of other driver electronics (not shown) between the PDA electrical interface  150 , light source  340 , acquire button  320  or indicator LED  325  to accomplish electronic connection. 
     In a third embodiment shown in  FIGS. 7A-7D , optical reader assembly  700  is shown. The optical reader assembly  700  includes optical body  710  made of clear acrylic and has two mounting tabs  742   a  and  742   b  for mounting the device on PDA unit. The mounting is accomplished by inserting the mounting tabs into matching recesses into PDA unit  100  and utilizing set screws to hold mounting tabs  742   a  and  742   b  in place. Those familiar with PDA devices will realize that the mechanical means by which the optical reader assembly attaches to the PDA unit is dependent upon the specific geometry of the PDA unit and that the invention may easily encompass other means of attachment. For example, in other embodiments it may be beneficial to include a spring-loaded ball-and-detent attachment mechanism or a molded plastic form that snaps to the body of the PDA to allow for rapid and easy removal of the optical reader assembly when it is not in use. 
     Optical reader assembly  700  includes an optical body made of clear acrylic material  710 , an acquire button  720 , indicator LED  725  attached to the top surface and an electrical connector  750  that mates with PDA electrical interface  150  to connect said devices with the PDA unit  100 . 
     Horizontal alignment marks  731   a ,  731   b  and vertical alignment mark  732  are inscribed into the optical body  710 : the horizontal and vertical marks indicate the position of optical target  180  placement relative to the optical body  710 . 
     Optical cavity  752  is included in optical body  710  and centered at generally the horizontal midpoint marked by vertical alignment mark  732  as shown in  FIG. 7A . Referring to  FIG. 7C , the optical cavity  752  is defined by reflector support surface  753 , inner surface  754  and lens mount  756 . The reflector support surface and inner surface form a void in the main body and comprise a housing  755  for the optical components of the system. Mirror  770 , in the present embodiment, is a front silvered mirror of high reflectivity attached by its non-reflective surface to reflector support surface  753 . The reflective surface of mirror  770  faces optical target  180  at an angle of about 45 degrees from the optical axis  774  which is a line generally through the centers of the optical components and is approximately perpendicular to the bottom face of the PDA unit as it exits the optical reader assembly  700 . 
     In other embodiments, mirror  770  may be replaced by a back silvered mirror or a triangular prism positioned to reflect light from the optical target  180  into the other optical components of the system. In other embodiments, the function of the mirror  770  can also be performed by a reflective coating applied directly to reflector surface  753 . 
     Optical reader assembly  700  incorporates a primary optical lens  780  fixed to lens mount  756 . The primary optical lens  780  is centered on the optical axis  774  and located just inside the bottom surface of optical reader assembly  700 . 
     Continuing with  FIG. 7C  and  FIG. 1 , PDA camera unit  151  faces the vertical and is recessed into the PDA unit  100  at the upper end of the PDA. PDA camera unit  151  incorporates a camera lens  781 , aperture stop  785  and optical image detector  790  mounted to support  755  as shown. Primary optical lens  780  is positioned approximately its focal distance away from optical target  180  such that optical rays  775  are rendered nearly parallel as they enter PDA camera unit  151  resulting in an optical image of optical target  180  on the surface of optical image detector  790 . The aperture stop  785  serves to define the field of view and depth of field of the camera unit. 
     In the third embodiment, lens  180  is made of glass or plastic substrate and assembled as a distinct element. In an alternate embodiment, the lens may be molded as a part of optical block  710 . In other embodiments, the optical lens function may be combined with the mirror function by using a curved mirror surface; the lens position and overall magnification may vary as long as the object is imaged onto the detector surface. The equations for determining lens position relative to the object and detector are well known in the art. 
     Also in the third embodiment, the mirror is a front silvered flat glass substrate inserted into optical reader assembly  700  and fixed in place by an adhesive. There are other means of accomplishing the function of the mirrors such as using multiple silvered substrates, silvering one or more surfaces of optical reader assembly  700  or inserting one or more prisms into optical cavity  752 . 
     In the third embodiment, optical image detector  790  is a charge-coupled device (CCD) having approximately 500 by 500 pixels and lateral dimensions of one-half inch or less. The invention comprehends that other technology may be used to accomplish the optical to electronic conversion of the image—for example, a CMOS imaging device may be deployed. The camera unit  151  is integral to the PDA unit  100  and may accomplish functions known in the art such as autofocus and zoom in conjunction with software resident on the host PDA. For example, the autofocus function will allow the optical target  180  to be placed at different distances from the scanning unit. The resident software may also allow the integrated camera to operate in a “black and white” mode whereby the color information is discarded, thereby creating further efficiencies in the scanning process. Within the scope, it is envisioned that the user can easily remove the optical reader assembly so that optical images of text or other material could be taken in photographic mode and processed accordingly. 
     As shown in  FIG. 7D , optical reader assembly  700  has an illuminator light guide  760  which is a hole in optical block  710  from the interface surface  744  to the bottom surface  743 .  FIGS. 7A and 7B  show top and side views of the illuminator light guide  760 . A light source  740  with it collimating lens  741  is a part of the PDA unit  100 . The position and angle of the illuminator light guide  760  is made to match the positions of the collimating lens  741  and optical target position  180 . Light from light source  740  propagates through the illuminator light guide  760  along optical rays  776  and exits the optical reader assembly  700  to illuminate the optical target  180 . 
     Other embodiments of the invention are conceived in which the illumination light guide is accomplished using different shaped voids than the present embodiment or optical fibers inserted into the optical block  710 . The illuminator light spectrum and optical waveguide may also be chosen so as to illuminate a large area of text in the vicinity of the optical reader to enhance the user&#39;s ability to see the material to be scanned, especially in the absence of ambient light. The illumination light spectrum may also be chosen to match the peak sensitivity of the optical detector. 
     In a fourth embodiment shown in  FIG. 8 , optical reader assembly  800  is shown. The optical reader assembly  800  is made of clear acrylic and has two mounting tabs  842   a  and  842   b  for mounting the device on PDA unit  100 . The mounting is accomplished by inserting the mounting tabs into matching recesses into PDA unit  100  and utilizing set screws to hold mounting tabs  842  in place. Those familiar with PDA devices will realize that the mechanical means by which the optical reader assembly attaches to the PDA unit is dependent upon the specific geometry of the PDA unit and that the invention may easily encompass other means of attachment. For example, in other embodiments it may be beneficial to include a spring-loaded ball-and-detent attachment mechanism or a molded plastic form that snaps to the body of the PDA to allow for rapid and easy removal of the optical reader assembly when it is not in use. 
     Optical reader assembly  800  includes an optical body made of clear acrylic material  810 , an acquire button  820 , indicator LED  825  attached to the top surface and an electrical connector  850  that mates with PDA electrical interface  151  to connect said devices with PDA unit  100 . 
     Horizontal alignment marks  831   a ,  831   b  and vertical alignment mark  832  are inscribed into optical body  810 : the horizontal and vertical marks indicate the position of optical target  180  placement relative to the optical body  810 . 
     A cylindrical optical cavity  852  is included in optical body  810  and generally centered at the horizontal midpoint marked by vertical alignment mark  832  as shown in  FIG. 8A  and  FIG. 8B . Referring to  FIG. 8C , optical cavity  852  includes a threaded inner surface  854  and bottom opening  886  forming a void in the optical body and comprising a housing for the optical components of the system. The optical components are mounted and threaded into the cylindrical optical cavity  852  in inner surface  854  and held in place by adhesive. Optical axis  874  is a line generally through the centers of the optical components and is approximately perpendicular to the PDA unit as it exits optical reader assembly  800 . 
     Reader assembly  800  incorporates an optical lens  880  fixed to lens mount  856  which is threaded into optical cavity  852 . Aperture stop  885  is fixed to and supported by optical cavity  852 . Optical image detector  890  is affixed to camera electronics  895  which abuts electronics mount  897  and is held in place by cap  896  threaded into the top of optical cavity  852 . Optical lens  880  is positioned approximately mid-way between optical target  180  and optical detector  890  at about twice its focal distance from optical target  180  so that an image of optical target  180  is formed on the surface of optical detector  890  with approximately unit magnification. Aperture stop  885  serves to define the field of view and depth of field. Optical ray paths  875  trace light from optical target  180  to lens  880  to optical detector  890 , thereby allowing optical target  180  to be imaged by optical detector  890 . Optical lens  880  may incorporate an anti-reflection coating to reduce stray light reflections. 
     In the present embodiment the lens is made of glass or plastic substrate and assembled as a separate element. In another embodiment, the lens may be molded as a part of optical block  810 . The equations for determining lens position relative to the object and detector are well known in the art. 
     Optical image detector  890  is a charge-coupled device (CCD) having approximately 500 by 500 pixels and lateral dimensions of one-half inch or less. The invention comprehends that other technology may be used to accomplish the optical to electronic conversion of the image—for example, a CMOS imaging device may be deployed in other embodiments. The camera may accomplish functions known in the art such as autofocus and zoom in conjunction with software resident on the host PDA. For example, the autofocus function will allow optical target  180  to be placed at different distances from the optical reader assembly. The resident software may also operate the integrated camera in a “black and white” mode whereby the color information is discarded, thereby creating further efficiencies in the scanning process. 
     Optical detector  890  is physically and electrically connected to camera electronics  895 . Camera electronics  895  provides on-board memory, clocking, electrical buffering and computer interface functions. Camera electronics  895  is electronically connected to PDA unit  100  via cabling  892  which interconnects to the electrical connector  850  which mates with PDA electrical interface  150 . 
     Optical reader assembly  800  may incorporate the use of other driver electronics (not shown) between PDA electrical interface  150 , acquire button  820  or indicator LED  825  to accomplish electronic connection. 
     In a fifth embodiment shown in FIGS.  9  and  10 A- 10 C, optical reader assembly  800  is rotatably attached to PDA unit  100  by a hinge  905  attached to the optical reader assembly and a mounting assembly  906 . Mounting assembly  906  includes a frame and a cavity  908 . Mounting assembly  906  is attached to PDA unit  100  by a releasable friction fit between cavity  907  and PDA Unit  100 . Optical reader assembly  800  is electrically connected to flexible connector  910 . Flexible connector  910  is electrically connected to connector  850 . Connector  850  is, in turn, connected to the PDA. Optical reader assembly  800  includes a pocket  930  to store excess flexible connector material. 
     In use, hinge  905  enables the PDA to be held at a different angle than the optical reader assembly. The angle allows a more comfortable and natural angle for scanning lengthy text subjects and therefore accommodates the user. 
     The electronic architecture of the invention is shown in  FIG. 5 . PDA unit  100  includes a microprocessor  110  and electronic memory  115 . Certain software programs may be stored in memory  115  and executed by microprocessor  110  to operate on PDA unit  100  to accomplish tasks that will be described. The type of microprocessor  110  and the storage capability of the electronic memory  115  are not critical to the invention except that they should be chosen to efficiently accomplish the tasks that will be described. For example, in another embodiment, microprocessor  110  may be composed of two processors, one processor dedicated to the user interface and normal functioning of the PDA; the other processor dedicated to image and OCR processing. Either or both processors could be a RISC class processor. 
     Microprocessor  110  accepts user stimulus electronically from the acquire button  220  and PDA buttons  130  to control the scanning process. As the optical target  180  is scanned, microprocessor  110  displays text characters  185  on PDA viewing screen  120 . During the scan process, certain states and conditions of the process may be indicated by PDA viewing screen  120  or the indicator LED  225 . In the alternate embodiments, the acquire buttons and indicator LEDs interact with the microprocessor in a similar way to the preferred embodiment. 
     To scan text, PDA camera unit  151  acquires an electronic image  155  of a character of text in optical target  180 . The electronic image  155  is a bit-mapped pixilated representation of the optical image that exists on the surface of optical detector  290  and would typically contain 500 by 500 bytes i.e. 250 kbytes total. That image is stored momentarily in the on-board memory of camera unit  151  until the PDA microprocessor  110  extracts the electronic image  155  from the camera unit  151  and stores it in electronic memory  115 . 
     Microprocessor  110  then acts on the electronic image  155  stored in memory  115  to convert the electronic image  155  into a byte or word digital character representation, such as the ASCII representation. The byte or word representing the digital character, which in turn represents the character of text in optical target  180  that was scanned, is then stored into an available location in memory  115 . The portion of memory  115  that holds the electronic image  155  is then freed to be used for the next character in the scan. 
       FIG. 6  is a flow chart of a scan process that accomplishes the overall text scanning task. The process begins with step  501  when a text scanning application software program  500  residing in the electronic memory  115  of the PDA unit  100  is initiated. Once the program starts, it performs the step  505  of activating the acquire button  220  and camera unit  151 , then step  508  of verifying the electronic integrity of the optical reader assembly  200  and lighting indicator  225 , thereby signaling the operator that the PDA unit  100  is ready to scan text. Upon ready signal, step  510  is performed where the optical reader assembly  200  is placed over optical target  180  and aligned with alignment marks  231  and  232 . After alignment the software program  500  waits to take further action until the acquire button is pressed in step  512 . When acquire button  220  is pressed down, the software program  500  leaves step  512  and moves to step  513  in which it sets scanning state to “ON”. In subsequent step  516 , the electronic image data  155  is acquired from camera unit  151  and this image represents the current character situated in the optical path  275 . Microprocessor  110  processes the electronic data  155  utilizing optical character recognition (OCR) software code in step  519 . If the OCR process is successful, a valid byte or word digital character within the available character set will be selected and in step  522  the OCR process will return a valid character to the microprocessor  110  signaling that it was successful. If the OCR process is unable to match a valid character, it will return a flag to the microprocessor  110  indicating failure. OCR algorithms are well known in the art such that commercially available software code may be utilized to accomplish this task. 
     If OCR step  522  indicates success, then software program  500  proceeds to step  525  in which microprocessor  110  stores the character in memory  115  and on to step  526  in which the microprocessor  110  displays the character on the PDA viewing screen  120 . Moving to step  528  then, the microprocessor  110  checks the state of the acquire button  220 : if the button is still pressed down, then the software program  500  flows back to step  516  to repeat. If acquire button  220  is released, then the scanning state is changed to “OFF” in step  550  and the operator is queried in step  555  to scan again or to stop. If the operator selects to continue scanning, the scanning process is repeated beginning with step  510 . If the operator selects to stop scanning then the process moves to step  560 . In step  560  and subsequent steps  563  and  565 , the scanned and processed text is edited if the operator chooses to, is saved to a text file and the program exits, respectively. 
     If OCR step  522  indicates failure, then the scan process proceeds immediately to step  545  in which the microprocessor  110  displays an error condition on the PDA viewing screen  120  indicating to the operator that the last character was not valid and that the operator must rescan. The software program proceeds to check that the acquire button is still depressed in step  528 . If the button is depressed, then the device acquires a new image and the conversion process repeats. If the acquire button is released, the scanning state is switched to “OFF” in step  550  and the scan process moves to step  555  to query the user to continue scanning or not. The software program  500  proceeds as described before from that point. In other embodiments, the PDA may signal the operator with the indicator LED  225  or with audio sounds instead of or in concert with the visual signals on the PDA viewing screen. 
     In another embodiment of the invention, the scan process is altered by inserting a step between step  516  and step  519 . The new software step deconvolves and transforms the electronic image data  155  using the known transfer function for the optical components so as to remove the distortion effects of optical aberrations. 
     While this invention has been described in reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.