Abstract:
A method for reading symbols having data identifying characteristics is provided. The method includes the steps of: providing a nose portion that forms part of a symbol capture device. The nose portion has a plurality of spaced apart light sources that are adapted to put images on a surface. The images can be used to ascertain proper positioning and focal plane of the device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to symbol capture devices, and more particularly, relates to a symbol capture device or other symbol capture device with guiding light beams for ascertaining the focal length and field of view at that focal length of an image capture device.  
         [0003]     2. Description of the Related Art  
         [0004]     Symbol capture devices used for reading symbols having data identifying characteristics such as barcodes are known. Typically, a symbol capture device has guiding light beams for suitable positioning including the positioning of focal length and field of view. That is to say, the symbol capture device needs to be positioned relative to the symbol located at a distance at an optimal position. Known methods to determine the optimum position include using laser light sources or light emitting diodes (LED). It is important to position the device correctly, because it operates as a CCD camera or the like, and the clarity of the image and effectiveness of reading is decreased if the position is incorrect.  
         [0005]      FIG. 1  shows three prior art LED projection schemes on to a surface for use in positioning the surface to be read relative to the device. The drawbacks of prior art LED schemes are that the projections do not provide a clear field of view, and there is no indication of the focal plane at which the surface to be read should be positioned.  
         [0006]      FIG. 2  is an alternative prior art arrangement using lasers. The laser provides the same visual display to a user regardless of distance between the device and the surface of the image. While it clearly shows the field of view, the cost is relatively high. Additionally, it is difficult to ascertain the focal length. It is desirable to have a system wherein the user can easily determine the proper focal length as well as the field of view of the image capture device at that focal length. The solution should have minimal cost.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention generally provides a symbol capture device with guiding light beams for focal length and field of view determination.  
         [0008]     The present invention further provides a symbol capture device with a set of light sources for both field of view and focal length adjustments.  
         [0009]     The present invention further provides a symbol capture device with a light source comprising light emitting diodes (LED), without the cost of laser sources.  
         [0010]     A method for reading symbols having data identifying characteristics is provided. The method includes the steps of: providing a nose portion that forms part of a symbol capture device. The nose portion has a plurality of spaced apart light sources that are adapted to casue a viewable image on a surface having an image to be captured. A plurality of images are generated on the surface. The focal length and the field of view of optically discernable from characteristics of the provided images.  
         [0011]     A system for reading symbols having data identifying characteristics is provided. The system includes: a nose portion that forms part of a symbol capture device a plurality of spaced apart light sources is provided for the nose portion. The light sources are adapted to place images on a surface having the symbols formed thereon. A plurality of images are generated upon said surface as the result of the light source, and the images convey information sufficient to readily ascertain the focal plane and the field of view. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.  
         [0013]     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0014]      FIG. 1  depicts a set of three prior art scan projections.  
         [0015]      FIG. 2  depicts an alternative prior art scan projection using laser.  
         [0016]      FIG. 3  depicts an optimal positioning including focal length and field of view of the present invention.  
         [0017]      FIG. 4  is a first detailed depiction of  FIG. 3 .  
         [0018]      FIG. 5  is a second detailed depiction of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     The present invention relates to using light emitting diodes (LEDs) and their associated lenses in a scan system for defining or adjusting to an optimal focal length and a balanced field of view. Referring to  FIGS. 3-5 , a preferred embodiment of the present invention is described.  
         [0020]     Referring now to  FIG. 3 , an optimal positioning including focal length and field of view is shown. A symbol capture device nose portion  10  having two light emitting diodes, LED  12 , LED  12 ′ that are positioned on a top surface is provided. LED  12  and LED  12 ′ are spaced apart in that a distance having a non-zero value exists between LED  12  and LED  12 ′. Light generated out of LED  12  radiates through lense  14  and lens  15  to form an image on any suitable surface. Similarly, light generated out of LED  12 ′ radiates through lense  16  and lens  17  for forming similar reflections. An imaginary assumed center axis  18  is used as a reference line. Substantially perpendicular to center axis  18  is the imaginary first surface  20 . It is imaginary in that if a suitable surface is placed there, an image of the light will occur. Similarly a second surface  22 , a third surface, and a fourth or optimal surface may be imagined to exist and form images thereupon. The images that would be formed on these surfaces are shown in  FIG. 4 , although the structure of each individual image may not be the perfect squares that are shown for explanatory purposes in  FIG. 4 .  
         [0021]     As can be seen, one of the differences among first surface  20 , second surface  22 , third surface  24 , and fourth surface or optimal reflection surface  26  is that a different distance exists between a pair center points within image  30  and image  30 ′. The distances are respectively d 1 , d 2 , d 3  and d 4  relating to first surface  20 , second surface  22 , third surface  24 , and fourth surface or optimal reflection surface  26  respectively. As can be seen, the value of d 1 , is greater than that of d 2 , which is greater than that of d 3  and d 4  is zero in that the center points of image  30  and image  30 ′ coincide (d 1 &gt;d 2 &gt;d 3  and d 4 =0). The optimal focal length is known to be achieved when image  30  and image  30 ′ are adjusted to coincide (d 4 =0).  
         [0022]     Because of the images  28  and  28 ′, the user will know the exact field of view of the device at its optimal focal plane, and can appropriately position the surface having the images to be scanned so that the image is within the field of view defined by the images  28  and  28 ′ and at the focal plane. In other words, the invention provides a simple method for determining both field of view and appropriate focal distance from a set of two LEDs and four lenses. The user simply places the surface to be read in front of the image capture device, and moves the surface closer to or further from the device. When images  30  and  30 ′ completely overlap, the surface is positioned at the focal plane for optimum image capture, and the field of view at that surface is shown by the images  28  and  28 ′. Those of skill in the art will recognize how to choose the lenses needed to convey the proper images.  
         [0023]     As can be seen, in the preferred embodiment two LEDs are used. Specifically, LED  12 , LED  12 ′ and four lenses  14 - 17  are used in conjunction with the two LEDs. An extra focusing lens  38  may or may not be provided for processing reflected light beam  36 ,  36 ′ and feeding the same to a light receiver  40 . Light receiver  40  converts the light signal into some other type of signals such as electric signal. Light receiver  40  may comprise charge coupled device (CCD), complementary metal oxide semiconductor sensor (CMOS), or any other suitable receiver. Two beams  36 ,  36 ′ are used to define the field of view a. The two beams  32 ,  32 ′ generated by different LEDs may be concentrated by two different lenses, i.e. lens  14 , lens  16  respectively. Two more beams  34 ,  34 ′ through different lenses  15 ,  17  but preferably from the different LEDs, i.e. LED  12 , LED  12 ′ are used to define focal length. Furthermore, the present invention contemplates the reading of one dimensional as well as two dimensional commonly known barcode systems, and other types of images as well.  
         [0024]     Although the foregoing description of this invention makes reference to bar code symbol capture devices, by way of example, the invention itself is equally applicable to other methods and systems for data reading and forms of encoded data (indicia) other than bar codes.  
         [0025]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.