Abstract:
Optical systems and methods of data reading with collection systems having improved depth of field. One configuration is directed to an image-based optical reading system with a plurality of sensor arrays, such as a charge coupled device (CCD) arranged in a compact configuration to minimize the overall package size while providing extended read range. In an example configuration, two CCD arrays are placed back to back to minimize height and overall package size with fold mirrors providing the optical path to a backward facing array.

Description:
BACKGROUND  
       [0001]     The field of the present invention relates to data capture devices, such as scanners and optical code reading devices. In particular, optical readers and methods of reading are described herein which employ imaging technology to capture optical codes.  
         [0002]     A common type of optical code is a barcode such as the omnipresent UPC label. A barcode label comprises a series of parallel dark bars of varying widths with intervening light spaces, also of varying widths. The information encoded in the barcode is represented by the specific sequence of bar and space widths, the precise nature of this representation depending on which particular barcode symbology is in use. Typical methods for reading barcodes comprise generation of an electronic signal wherein a signal voltage alternates between two preset voltage levels, one representing a dark bar and the other representing a light space. The temporal widths of these alternating pulses of high and low voltage levels correspond to the spatial widths of the bars and spaces. It is this temporal sequence of alternating voltage pulses of varying widths which is presented to an electronic decoding apparatus for decoding.  
         [0003]     In one method of reading, referred to as a “scanning,” an illumination beam is moved (i.e., scanned) across the barcode while a photodetector monitors the reflected or backscattered light. For example, the photodetector may generate a high voltage when a large amount of light scattered from the barcode impinges on the detector, as from a light space, and likewise may produce a low voltage when a small amount of light scattered from the barcode impinges on the photodetector, as from a dark bar. The illumination source in spot scanners is a typically a laser, but may comprise a coherent light source (such as a laser or laser diode) or non-coherent light source (such as light emitting diode). A laser illumination source may offer advantages of higher intensity illumination which may allow barcodes to be read over a larger range of distances from the barcode scanner (large depth of field) and under a wider range of background illumination conditions.  
         [0004]     Another method of reading is referred to as the “imaging” method whereby light reflecting off a surface is detected by an array of optical detectors, commonly a charge-coupled device (CCD) or CMOS. The scan surface is typically illuminated by some uniform light source, such as a light-emitting diode (LED), incandescent light, or laser illumination. Alternately, the illumination may be provided by ambient light such as disclosed in U.S. Pat. No. 5,814,803 hereby incorporated by reference. In such an imaging technique, as with a scanning laser, an electrical signal is generated having an amplitude determined by the intensity of the collected light.  
         [0005]     In either the scanning laser or imaging technique, the amplitude of the electrical signal has one level for dark bars and a second level for light spaces. As the label is scanned, positive-going and negative-going transitions in the electrical signal occur, signifying transitions between bars and spaces. Techniques are known for detecting edges of bars and spaces by detecting the transitions of the electrical signal. Techniques are also known for determining the widths of bars and spaces based on the relative location of the detected edges and decoding the information represented by the bar code.  
         [0006]     In data reading devices, a return light signal from the object or symbol being read is focused onto a detector or detector array. In the example of a data reader reading the bars and spaces of a typical bar code, there needs to be sufficient difference in signal intensity between the signal corresponding to the light space and the signal corresponding to the dark bar in order for the processor to differentiate therebetween. In either type of data reading system, depth of field plays an important role in effectively detecting the an image at the sensor. Thus in data reading applications there has been demand for increased depth of field, i.e., the range of distance over which the scanner can effectively scan.  
         [0007]     There are several methods for improving depth of field, but there are essentially two areas which may be controlled, namely (1) outgoing beam generation and (2) collection. This application focuses on methods for improving depth of field and signal differentiation from the collection side.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is directed to data readers and methods of data reading with collection systems having improved depth of field.  
         [0009]     A preferred embodiment is directed to an image-based optical reading system with a plurality of sensor arrays, such as a CCD or CMOS, arranged in a compact configuration to minimize the overall package size while providing extended read range. In one configuration, a data reader includes two separate CCD or CMOS arrays and optical paths produce the extended read range. In one arrangement, the CCD or CMOS arrays are placed back to back to minimize height and overall package size with fold mirrors providing the optical path to the backward facing array.  
         [0010]     The foregoing and other objects, features, and advantages will become apparent from the following more detailed description set forth in conjunction with the accompanying drawings. It is intended that each of these disclosed embodiments may be implemented individually or in combination with other of the embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic diagram showing a typical optical code scanning system.  
         [0012]      FIG. 2  is a cut-away view of a handheld data reader suitable for the systems of the preferred embodiments.  
         [0013]      FIG. 3  is a schematic diagram illustrating an imaging system according to a preferred embodiment.  
         [0014]      FIG. 4  is a schematic diagram illustrating an imaging system according to a alternate embodiment.  
         [0015]      FIG. 5  is a schematic diagram illustrating an imaging system according to another alternate embodiment.  
         [0016]      FIG. 6  is a schematic diagram illustrating an imaging system according to another alternate embodiment.  
         [0017]      FIG. 7  is a schematic diagram illustrating an imaging system according to another alternate embodiment.  
         [0018]      FIG. 8  is a schematic diagram illustrating an imaging system according to another alternate embodiment.  
         [0019]      FIG. 9  is a schematic diagram illustrating an imaging system according to another alternate embodiment.  
         [0020]      FIGS. 10-11  are schematic diagrams illustrating an imaging system according to another alternate embodiment,  FIG. 10  being a top view and  FIG. 11  being a perspective view.  
         [0021]      FIG. 12-14  are schematic diagrams illustrating an imaging system according to another alternate embodiment,  FIG. 12  being a side view,  FIG. 13  being a perspective view, and  FIG. 14  being a rear view. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     The preferred embodiments will now be described with reference to the drawings. For conciseness of description, the detector arrays are described as CCD arrays, but other suitable detectors may be implemented such as CMOS.  
         [0023]      FIG. 1  illustrates a typical imaging system  100  comprised of an optical collection system or lens  103 , a CCD detector  104 , a pre-amplification block  105 , a signal processing block  106 , and a decoding block  107 . The optical collection system  103  operates in the presence of ambient illumination  101 , gathering ambient light reflecting off a target (such as a bar code label  102 ) and focusing the gathered light on the CCD detector  104 . Alternately, the system may be provided with an illumination system, such as one or more LED&#39;s (light emitting diodes). The CCD detector  104  interacts with the pre-amplification block  105  to obtain a CCD input signal comprised of imaging data. The CCD input signal may be processed by the signal processing block  106  and provided to the decoding block  107  for decoding.  
         [0024]     Although the imaging region of the CCD detector  13  may be various shapes, a planar imaging surface is preferred. In contrast to a conventional retrodirective multi-line laser scanner having a laser and mirrors, the optical sensing portion of an area imaging system may be quite small because of the relatively small size of the CCD array.  
         [0025]      FIG. 2  is a cut-away view of a handheld data reader  150  of suitable configuration according to a preferred embodiment. The handheld data reader  150  comprises a head section  151  encasing most or all of the optical system and electronics, a digital board  153  on which is mounted an optics chassis  156 , and an analog board  154  connected to the back of the optics chassis  156  and also connected to the digital board  153 . The data reader  150  also includes a handle board  155  encased in a portion of the housing formed as a handle section  152  below the scan head section  151 .  
         [0026]     The left sections of the housing head section  151  and handle section  152  are removed and thus not shown in the figure. The data reader  150  may also include a window dispose in a front portion of the head section  151  for sealing off the interior space of the data reader where the various components are disposed but allowing light to pass therethrough.  
         [0027]     The data reader may also be provided with an aiming mechanism. For example two pointer LED assemblies  157   a ,  157   b  are mounted on or in the optical chassis  156 , each containing a pointer LED with suitable focusing/diffusing optics for projecting an aiming pattern into the read volume. The pointer LED projects an aiming pattern comprised of a spot, line segment, or image to assist the operator in aiming the reader so as to position the target being read at a desired location relative to the reader.  
         [0028]     The data reader  150  preferably comprises an imaging system having a relatively large depth of field that can operate solely in ambient light. Alternately, the data reader  150  may employ illumination source(s) such as LED&#39;s  158   a ,  158   b  mounted on the PCB  153 . Alternately, the illumination LED&#39;s may be mounted to some other suitable location such as the chassis  156  or the housing.  
         [0029]     The data reader includes inlets  159   a ,  159   b  for the two CCD arrays that are arranged in a compact arrangement to minimize the overall package size. The two separate CCD arrays, arranged along separate optical paths produce the extended read range.  
         [0030]     Preferably, each of the CCD arrays is two-dimensional array capable of acquiring a two-dimensional image. Such a imaging array is useful for reading one-dimensional codes such as UPC/EAN and Code 39, but is particularly useful for reading two-dimensional codes such as PDF-417, Maxicode, Datamatrix, Datastrip, RSS (Reduced Space Symbol), and Code 49.  
         [0031]      FIG. 3  illustrates a first embodiment of an optical system  160  having a first collection system, shown as a lens  170 , that focuses an image along first incoming optical path  172  and onto the first CCD array  174 . A second collection system, shown as a lens  180 , focuses an image along a second incoming optical path  182  and toward a first fold mirror  184 , then to second fold mirror  186 , and then onto a second CCD array  188 . The back-to-back arrangement of the first CCD array  174  and second CCD array  188  may minimize height and overall package size. The first and second CCD arrays  174 ,  188  may be mounted on a common substrate such as a chassis, or on opposite sides of a common printed circuit board  190  simplifying both mechanical construction and electrical connection.  
         [0032]     The two optical paths  172 ,  182  and lens designs for the lens systems  170 ,  180  provide for two overlapping read ranges with both a wide angle and narrow angle field of view. The back-to-back placement shortens the overall length and provides some height reduction. The height reduction also minimizes the optical path offset, which should enhance smooth overlap between the two read ranges.  
         [0033]     The two incoming optical paths  172 ,  182  are generally parallel, but offset from each other. The offset may be lateral, such as the configuration of  FIG. 2 , or may be some other arrangement such as vertical or diagonal.  
         [0034]     In the back-to-back arrangement illustrated in  FIG. 3 , the respective sensors arrays  174 ,  188  face in opposite directions. In another configuration, the respective sensors arrays  174 ,  188  may be arranged to face in the same direction. In such a system, the first fold mirror  184  would reflect the incoming light  182  between the sensors arrays  174 ,  188  and second fold mirror  186  would be positioned between the sensors arrays  174 ,  188  for reflecting the incoming light  182  onto the second sensor array  188 .  
         [0035]      FIG. 4  illustrates an alternate embodiment of an optical system  200  having a first collection system, shown as a lens  210 , that focuses an image along optical path  212  and onto the first CCD array  214 . A second collection system, shown as a lens  220 , focuses an image along optical path  222  and onto a second CCD array  224 . The first CCD array  214  and second CCD array  224  are constructed in a side-by-side or in a stacked arrangement to provide for common mounting such as on a common PCB  230 .  
         [0036]     The back-to-back arrangement of two CCD arrays may be more compact than a stacked or side-by-side arrangement.  
         [0037]      FIG. 5  illustrates another embodiment of an optical system  250  having a first collection system, shown as a lens  260 , that focuses an image along first incoming optical path  262  and toward a first fold mirror  264  which in turn reflects the image onto the first CCD array  266 . A second collection system, shown as a lens  270 , focuses an image along a second incoming optical path  272  and toward a first fold mirror  274 , which in turn reflects the image onto a second CCD array  276 . The first CCD array  266  and second CCD array  276  are arranged facing in opposite directions perpendicular to the axes  262 ,  272  of the lenses  260 ,  270  to minimize height and overall package size. The first and second CCD arrays  266 ,  276  may be mounted on a common substrate such as a chassis, or on opposite sides of a common printed circuit board  280  simplifying both mechanical construction and electrical connection. The CCD arrays  266 ,  276  may aligned back-to-back or, as illustrated in  FIG. 5 , laterally offset. Further, the arrays may be disposed in offset, parallel planes as in  FIG. 5 , or may be configured in a common plane.  
         [0038]      FIG. 6  illustrates another embodiment of an optical system  300  having a first collection system, shown as a lens  310 , that focuses an image along first incoming optical path  312  and onto the first CCD array  314 . A second collection system, shown as a lens  320 , focuses an image along a second incoming optical path  322  and toward a first fold mirror  324 , then to second fold mirror  326 , and then onto a second CCD array  328 . The first CCD array  314  and second CCD array  328  are arranged back-to-back separated by a gap within which the second fold mirror  326  is disposed. Such a configuration may minimize height and overall package size. The first and second CCD arrays  314 ,  328  may be mounted on a common substrate such as a chassis, or on a common printed circuit board  330  simplifying both mechanical construction and electrical connection.  
         [0039]      FIG. 7  illustrates another embodiment of an optical system  350  having a first collection system, shown as a lens  360 , that focuses an image along first incoming optical path  362 , and toward a fold mirror  364  which reflects the image and onto the first CCD array  366 . A second collection system, shown as a lens  370 , focuses an image along a second incoming optical path  372  and toward a fold mirror  374 , and then onto a second CCD array  376 . The first CCD array  366  and second CCD array  376  are arranged facing in opposite directions, separated by a gap within which the fold mirrors  364 ,  374  are disposed. Such a configuration may minimize height and overall package size. The first and second CCD arrays  364 ,  374  may be mounted on a common substrate such as a chassis, or on a common printed circuit board  380  simplifying both mechanical construction and electrical connection.  
         [0040]      FIG. 8  illustrates another embodiment of an optical system  400  having a first collection system, shown as a lens  410 , that focuses an image along first incoming optical path  412 , and toward a fold mirror  414  which reflects the image and onto the first CCD array  416 . A second collection system, shown as a lens  420 , focuses an image along a second incoming optical path  422  and toward a fold mirror  424 , and then onto a second CCD array  426 . The first CCD array  416  and second CCD array  426  are arranged facing in opposite directions, with offset axes providing different distances from the respective lenses  410 ,  420 . The first and second CCD arrays  364 ,  374  may be mounted on a common substrate such as a chassis, or on a common printed circuit board (not shown) for simplifying both mechanical construction and electrical connection.  
         [0041]      FIG. 9  illustrates another embodiment of an optical system  450  having a first collection system, shown as a lens  460 , that focuses an image passing through aperture  462  along first incoming optical path  464  and toward a first fold mirror  466  which in turn reflects the image onto the first CCD array  468 . A second collection system, shown as a lens  470 , that focuses an image passing through aperture  472  along first incoming optical path  474  and toward a first fold mirror  476  which in turn reflects the image onto the first CCD array  478 . The first CCD array  468  and second CCD array  478  are arranged facing in the same direction perpendicular to the axes  464 ,  474  of the lenses  460 ,  470  to minimize height and overall package size. The first and second CCD arrays  468 ,  478  may be mounted on a common substrate such as a chassis, or on opposite sides of a common printed circuit board  480  simplifying both mechanical construction and electrical connection. The CCD arrays  468 ,  478  may aligned side-by-side in a common plane.  
         [0042]     Typically the arrays illustrated in the previous embodiments are linear in geometry such as the arrays  516 ,  526  illustrated in  FIGS. 10 and 11 .  
         [0043]     Another alternate multiple sensor imaging collection system  500  is illustrated in  FIGS. 10-11 . An incoming image of a barcode for example is passed through a slit or aperture  512  and is focused via a first collection system, shown as a lens  510 , along an incoming optical path toward a fold mirror  514  which reflects the image and onto the first CCD array  516 . Another image of that same barcode is passed though slit or aperture  522  and is collected by a second collection system, shown as a lens  520 , which focuses the image along an incoming optical path and toward a second fold mirror  524 , and then onto a second CCD array  526 . The lenses  510 ,  520  are vertically offset (as shown in  FIG. 11 ) and longitudinally offset (as shown in  FIG. 10 ). The lenses  510 ,  520  focus a linear image of the barcode toward the elongated fold mirrors  514 ,  524  so that a section of an entire width of the bar code is imaged onto the detectors  516 ,  526 . As in previous embodiments, the lens systems  520 ,  520  focus to different fields due to differing axial position (e.g. lens  510  is nearer to the target) and/or different optical lens power. The lenses  510 ,  524  may have the same optical power (and preferably are the same for ease of manufacture) but may provide different focal fields due to the differing axial location. The fold mirrors  514  and  524  are elongated corresponding to a section of a barcode being imaged onto the linear CCD arrays  516 ,  526 . The mirrors  514 ,  524  are arranged generally perpendicular and stacked vertically. The first CCD array  516  and second CCD array  526  are arranged facing in opposite directions, but may be offset vertically for alignment with respective fold mirrors  514 ,  524 .  
         [0044]     Yet another alternate multiple sensor imaging collection system  550  is illustrated in  FIGS. 12-14 . An incoming image of a barcode for example is first reflected off a common fold mirror  560  toward the multiple collection systems. The first collection system  570  comprises a wide field imager, including lens sections  572  and  574 , focusing an image reflecting off fold mirror  560  onto sensor array  576 . The second collection system comprised of lens  580  is a more standard field imager with a longer focal length, focusing an image reflecting off the fold mirror  560  and onto the sensor array  586 . As shown in the figures, the first collection system  570  produces a wide field of view  578  and  579  in the near fields. The second collection system  580  has a longer focal length and produces a more narrow field of view  588  for the near field reading and a more narrow field of view  589  for far field reading.  
         [0045]     The collection lens systems  570 ,  580  have axes which are offset but aligned as shown in the rear view of  FIG. 14 . The axes of the lenses  570 ,  580  are not necessarily parallel, each axis being oriented to achieve a desired overlapping image fields.  
         [0046]     In each of the embodiments, the collection systems may comprise a lens system comprised of one or more optical elements such as lenses, prisms, mirrors, holographic elements, apertures, gratings. The lens elements may be single focal or multifocal such as described in Pat. No. 5,814,803 incorporated by reference, or may include active focusing mechanism such as a movable focusing lens element.  
         [0047]     The data reading systems may be implemented for a handheld reader  150  as illustrated in  FIG. 2  for portable operation, or may comprise a fixed reader such as may be used for presentation scanning. Alternately, the reader may comprises a portable unit operable for multi-mode operation being operable in either a fixed mode and a handheld mode. The switch may comprise either a manually actuated switch on the housing or alternately a sensor which senses when the reader is moved (using a motion sensor or accelerometer) or is grasped by the operator (such as a contact sensor). Upon sensing that the reader has been moved or grasped, the reader may switch into handheld mode.  
         [0048]     The aiming mechanism may apply to either handheld or fixed mode. When operating in handheld mode, the operator uses the aiming pattern to assist in moving the data reader to position the aiming pattern onto the optical code. In the fixed mode of operation, the operator moves the item to place the optical code into the scan region and thereby positions the aiming pattern onto the optical code.  
         [0049]     While the invention has been particularly shown and described with reference to certain embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.