Abstract:
A system and method are presented for improving the performance of code scanners in the extended and far ranges. At these distances, the intensity of the laser beam reflected off the code symbol can be markedly decreased, thereby decreasing the likelihood of a successful reading of the code symbol by the code scanner. The system provides for dynamic power increases to the laser source to generate a greater dynamic range.

Description:
FIELD OF THE INVENTION 
       [0001]    The disclosure relates generally to improvements in reading code symbols, and more particularly, to a system and method for reading code symbols at long range using source power control. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    A code symbol reading device (e.g., barcode scanner, barcode reader, RFID reader) is a specialized input device for certain data systems commonly used by retailers, industrial businesses, and other businesses having a need to manage large amounts of inventory. Code symbol reading devices are often employed to read barcodes. A barcode is a machine-readable representation of information in a graphic format. The most familiar of these graphic symbols is a series of parallel bars and spaces of varying widths, which format gave rise to the term “barcode.” The adoption of the Universal Product Code (UPC) version of barcode technology 1973 quickly led to a revolution in logistics by obviating the need for manual retry of long number strings. 
         [0003]    Most barcode scanners operate by projecting light from an LED or a laser onto the printed barcode, and then detecting the level of reflected light as the light beam sweeps across the barcode. Using this technique, the barcode scanner is able to distinguish between dark areas and light areas on the barcode. More light is reflected from the light areas on the barcode than the dark areas, so the optical energy reflected back to the barcode scanner will be a signal containing a series of peaks corresponding to the light areas and valleys corresponding to the dark areas. A processor converts the received optical signal into an electrical signal. The processor decodes the peaks and valleys of the signal to decode the information (e.g., product number) represented by the code symbol. 
         [0004]    Typically, barcode scanners have been designed to read barcodes in the near range (e.g., barcodes located less than about three feet from the barcode scanner). Recently, advancements have been made in developing barcode scanners capable of reading barcodes in the far range (e.g., barcodes located about 30 feet or more from the barcode scanner). Attempting to gather readings from a barcode located at these greater distances from the barcode scanner presents significant challenges. In particular, the further away that the barcode is from the barcode scanner, the weaker the return laser light signal will be at the time of signal detection at the photodetector. For barcode scanners having a substantially large scanning range (e.g., working range), in particular, this potentially dramatic variation in signal intensity strength at the photodetector places great demands on the electronic signal processing circuitry, and its ability to deliver sufficient signal-to-noise ratio (SNR) performance over broad dynamic ranges of input signal operation. 
         [0005]    Consequently, great efforts have been made over the past few decades to provide laser scanning type barcode scanners, in particular, with automatic gain control (AGC) capabilities that aim to control the gain of the various analog scan data signal processing stages, regardless of input laser return signal strength. In general, feedback control is implemented in the analog domain, and the gain of an amplified stage is adjusted according to a controller. The controller could be, but is not limited to, proportional control, PID control or fuzzy logic control, etc. Also, the amplifier refers to, but is not limited to preamplifier or gain stages along the signal path. 
         [0006]    The ability of these techniques of applying gain control to the received signal to achieve greater dynamic range is limited, for example, by the existence of laser noise. Increasing the gain of the received signal also results in proportional increases to signal noise (e.g., laser noise), which can significantly interfere with the ability to decode the scanned barcode. 
         [0007]    Therefore, a need exists for a system for reading code symbols in a scanning field that increases the strength of the signal received by the photodetector without resulting in an increase in the strength of signal noise, thereby reducing the overall signal-to-noise ratio of the signal. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect, the present disclosure embraces a system for reading code symbols in a laser scanning field. The system includes a laser scanning module for scanning a laser beam across a laser scanning field. The laser scanning module includes a laser source. A photodetector detects the intensity of the light reflected from the laser scanning field and generates a first signal corresponding to the detected light intensity. A source power control module controls the supply of power to the laser source in response to the first signal. Typically, the source power control module controls the power to maintain the intensity of the light reflected from the laser scanning field within a predetermined intensity range. 
         [0009]    In an exemplary embodiment, the source power control module is an automatic gain control circuit. In another exemplary embodiment, the source power control module is a microprocessor. In another exemplary embodiment of the system, the source power control module controls the gain of the first signal. Typically, the source power control module controls the gain of the first signal to maintain the first signal&#39;s amplitude within a predetermined amplitude range. 
         [0010]    In another aspect, the disclosure embraces a method for reading code symbols at long range. Power is supplied to a laser source to generate a laser beam. The laser beam is scanned across a laser scanning field. The intensity of the light reflected from the laser scanning field is detected. A first signal is generated that corresponds to the detected intensity of light reflected from the scanning field. The power supply is controlled in response to the first signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of an exemplary embodiment of a code symbol reading system according to the present invention. 
           [0012]      FIG. 2  is a schematic block diagram describing the major system components of an exemplary code symbol reading system according to the present invention. 
           [0013]      FIG. 3  is block diagram depicting the interaction between selected components of an exemplary code symbol reading system according to the present invention. 
           [0014]      FIG. 4  is block diagram depicting the interaction between selected components of an exemplary code symbol reading system according to the present invention. 
           [0015]      FIG. 5  is block diagram depicting the interaction between selected components of another exemplary code symbol reading system according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to the figures in the accompanying drawings, the illustrative embodiments of the code symbol reading system according to the present invention will be described in great detail, where like elements will be indicated using like reference numerals. Turning now to the drawings,  FIGS. 1 and 2  depict an exemplary code symbol reading system according to the present invention. The code symbol reading system  100  has a housing  102  having a head portion and a handle portion supporting the head portion. A light transmission window  103  is integrated with the head portion of the housing  102 . A trigger switch  104  is integrated with the handle portion of the housing  102 . The trigger switch  104  is for generating a trigger event signal to activate a scanning module  105 . The scanning module  105  repeatedly scans across its scanning field  115  a light beam (e.g., a visible laser beam) generated by light source  112  (e.g., a laser source). The laser source  112  has optics to produce a laser scanning beam focused in the scanning field  115  in response to control signals generated by a controller  150 . The scanning module  105  also includes a laser driver  151  for receiving control signals from the controller  150 , and in response thereto, generating and delivering laser (diode) drive current signals to the laser source  112 . A start of scan/end of scan (SOS/EOS) detector  109  generates timing signals indicating the start of a laser beam sweep and the end of a laser beam sweep, and sends those timing signals to the controller  150  and a decode processor  108 . Light collection optics collect light that has been reflected or scattered from a scanned object in the scanning field  115 , and a photodetector  106  detects the intensity of the collected light. The photodetector  106  generates an analog scan data signal (e.g., a first signal) corresponding to the detected light intensity during scanning operations. An analog scan data signal processor/digitizer  107  processes the analog scan data signals and converts the processed analog scan data signals into digital scan data signals (e.g., a second signal). The digital scan data signals are converted into digital words representative of the relative width of the bars and spaces in the scanned code symbol. The digital words are transmitted to a decode processor  108  via lines  142 . The decode processor  108  generates symbol character data representative of each code symbol scanned by the laser beam. An input/output (IO) communication interface module  140  interfaces with a host device  154 . It is through this IO communication module  140  that the symbol character data is transmitted to the host device  154 , which transmission may be done through wired (e.g., USB, RS-232) or wireless (e.g., Bluetooth) communication links  155  between the code symbol reading system  100  and the host device  154 . 
         [0017]    The controller  150  generates control signals to control operations within the code symbol reading system  100 . The controller  150  includes a source power control module  160 . The source power control module  160  is adapted to, under certain conditions, direct the laser driver  151  to adjust the power or intensity of the laser beam generated by the laser source  112 . 
         [0018]    The laser scanning module  105  includes several subcomponents. A laser scanning assembly  110  has an electromagnetic coil  128  and rotatable scanning element (e.g., mirror)  134  supporting a lightweight reflective element (e.g., mirror)  134 A. A coil drive circuit  111  generates an electrical drive symbol to drive the electromagnetic coil  128  in the laser scanning assembly  110 . The laser source  112  generates a visible laser beam  113 . A beam deflecting mirror  114  deflects the laser beam  113  as an incident beam  114 A towards the mirror component of the laser scanning assembly  110 , which sweeps the deflected laser beam  114 B across the laser scanning field  115  containing a code symbol  16  (e.g., barcode). 
         [0019]    As shown in  FIG. 2 , the laser scanning module  105  is typically mounted on an optical bench, printed circuit (PC) board or other surface where the laser scanning assembly is also, and includes a coil support portion  110  for supporting the electromagnetic coil  128  (in the vicinity of the permanent magnet  135 ) and which is driven by a scanner drive circuit  111  so that it generates magnetic forces on opposite poles of the permanent magnet  135 , during scanning assembly operation. Assuming the properties of the permanent magnet  135  are substantially constant, as well as the distance between the permanent magnet  135  and the electromagnetic coil  128 , the force exerted on the permanent magnet  135  and its associated scanning element is a function of the electrical drive current I DC (t) supplied to the electromagnetic coil  128  during scanning operations. In general, the greater the level of drive current I DC (t) produced by scanner drive circuit  111 , the greater the forces exerted on permanent magnet  135  and its associated scanning element. Thus, scan sweep angle α(t) of the scanning module  105  can be directly controlled by controlling the level of drive current I DC (t) supplied to the coil  128  by the scanner drive circuit  111  under the control of controller  150 , shown in  FIG. 2 . 
         [0020]    In response to the manual actuation of trigger switch  104 , the laser scanning module  105  generates and projects a laser scanning beam through the light transmission window  103 , and across the laser scanning field  115  external to the housing  102 , for scanning an object in the scanning field  115 . The laser scanning beam is generated by the laser source  112  in response to control signals generated by the controller  150 . The scanning element (i.e., mechanism)  134  repeatedly scans the laser beam across the object in the laser scanning field at the constant scan sweep angle α(t) set by the controller  150  during scanning operation. Then, the light collection optics  106  collect light reflected/scattered from scanned code symbols on the object in the scanning field, and the photo-detector  106  automatically detects the intensity of collected light (i.e., photonic energy) and generates an analog scan data signal (e.g., a first signal) corresponding to the light intensity detected during scanning operations. 
         [0021]    Typically, when the object bearing the code symbol  16  is in the near field of the code symbol reading system&#39;s  100  working distance (e.g., when the code symbol  16  is less than about seventeen feet from the code symbol reading system  100 ) the intensity of the collected light (e.g., the laser beam reflected off the code symbol  16 ) will be adequate to allow the system  100  to decode (e.g., read) the code symbol  16 . When the code symbol  16  is at the far range (e.g., greater than about seventeen feet from the system  100 ) of the working area, the intensity of the collected light can be significantly reduced from intensity levels in the near range (e.g., 1600 times less than intensity levels in the near range). The resulting analog scan data signal corresponding to the light intensity is often too weak to be decoded by the system  100 . The practical result is that the user of the system  100  attempting to scan code symbols  16  in or near the far range often encounters significant read delays or misreads. 
         [0022]    As shown in  FIGS. 3 through 5 , to combat this problem, the source power control module  160  monitors the analog scan digital signal corresponding to the detected light intensity. When the intensity of the reflected laser beam drops below a predefined intensity level, the source power control module  160  causes the laser source  112  to increase the power of its emitted laser beam. As a result of the increased power, the intensity of the reflected light is also increased. The source power control module  160  continues to cause the laser source  112  to increase the intensity of its emitted laser beam until the source power control module  160  detects that the reflected laser beam&#39;s intensity is above the level of the predefined threshold. 
         [0023]    The source power control module  160  may similarly be adapted to decrease the intensity of the laser beam emitted by the laser source  112 . This may be advantageous in that it allows for reduced power use by the laser source  112 , thereby decreasing heat output and degradation of the laser source  112 . 
         [0024]    The source power control module  160  may comprise an automatic gain control circuit  160 A or a microprocessor  160 B configured to regulate the reflected laser beam&#39;s intensity within a predefined intensity range. 
         [0025]    As shown in  FIGS. 4 and 5 , the source power control module  160  may combine the novel technique of adjusting the power of the laser source  112  with the technique of adjusting the gain of the first signal (i.e., adjusting the first signal after processing by the photodetector  106 ). Typically, the first signal&#39;s gain is adjusted via an analog gain control circuit  160 A, though it may be adjusted through a microprocessor  160 B. Gain adjustments may be made at various stages of the processing of the first signal, including during processing by the analog scan data processor  107  or during amplifier stages  170 . This novel approach of adjusting the signal on both the emitting side and the receiving side of the code symbol reading system  100  allows the two techniques to complement each other, potentially resulting in greatly improved performance. By combining power control techniques with gain control techniques, the maximum dynamic range of the system  100  can be greatly improved. For example, if the dynamic range using gain control is M:1, and the dynamic range using power control is N:1, then the maximal dynamic range resulting from employment of both techniques could be (M*N):1. 
         [0026]    The foregoing exemplary embodiments typically refer to a 1-D barcode but may be used to scan and read other symbols, such as 2-D barcodes, 2-D stacked linear barcodes, and 2D matrix codes. As used herein, the term “code symbol” includes such symbols and any symbol used to store information. 
         [0027]    To supplement the present disclosure, this application incorporates entirely by reference the following patents, patent application publications, and patent applications: U.S. Pat. No. 6,832,725; U.S. Pat. No. 7,159,783; U.S. Pat. No. 7,413,127; U.S. Pat. No. 8,390,909; U.S. Pat. No. 8,294,969; U.S. Pat. No. 8,408,469; U.S. Pat. No. 8,408,468; U.S. Pat. No. 8,381,979; U.S. Pat. No. 8,408,464; U.S. Pat. No. 8,317,105; U.S. Pat. No. 8,366,005; U.S. Pat. No. 8,424,768; U.S. Pat. No. 8,322,622; U.S. Pat. No. 8,371,507; U.S. Pat. No. 8,376,233; U.S. Pat. No. 8,457,013; U.S. Pat. No. 8,448,863; U.S. Pat. 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         [0028]    In the specification and figures, typical embodiments of the invention have been disclosed. The present invention is not limited to such exemplary embodiments. Unless otherwise noted, specific terms have been used in a generic and descriptive sense and not for purposes of limitation.