Abstract:
A machine-readable symbol reader for reading machine-readable symbols such as barcode symbols employs a first reflective surface having a first perimeter to create a pointer beam, and a movable second reflective surface with a second perimeter small than the first perimeter to create a scanning beam. The pointer and scanner beams may exist simultaneously and may be formed from a same illumination beam.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/583,406, filed Jun. 25, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This disclosure generally relates to the field of automatic data collection (ADC), and more particularly to machine-readable symbol readers for reading machine-readable symbols, for example bar code symbols, area or matrix code symbols, and/or stack code symbols.  
         [0004]     2. Description of the Related Art  
         [0005]     A variety of machine-readable symbol readers for reading machine-readable symbols are known. Such readers typically employ one of two fundamental approaches, scanning or imaging.  
         [0006]     In scanning, a focused beam of light is scanned across the machine-readable symbol, and modulated light returned from the machine-readable symbol is received by the reader and demodulated. With some scanning-type machine-readable symbol readers, the machine-readable symbol is moved past the reader. With others, the reader is moved past the machine-readable symbol. More commonly, the reader moves a beam of light across the machine-readable symbol, while the reader and machine-readable symbol remain approximately fixed with respect to one another. Demodulation typically includes an analog-to-digital conversion and a decoding of the resulting digital signal.  
         [0007]     Typically, scanning-type machine-readable symbol readers employ a light source that produces a scanning beam that may not be visible in the human range of visual perception. For example, the machine-readable symbol reader may employ a source such as a laser diode, which emits electromagnetic radiation in the infrared range. Even where the light source is in the visible range, the scanning beam is often difficult or impossible to see, for example in bright light conditions and/or at long read ranges. This makes it difficult for the user to properly aim the machine-readable symbol reader at a desired target. It is particularly difficult where targets are closely spaced, for example where carried on items stacked on a pallet or in a warehouse.  
         [0008]     Previous attempts to solve this problem have included using a brighter scanning beam. A brighter scanning beam, however, has a number of disadvantages, including high power consumption and limits placed on the power of lasers by various administrative agencies such as the Occupational Safety and Health Administration (OSHA). Another approach has been to provide a separate light source that emits a highly visible beam of light, commonly referred to as a pointer beam. This approach typically includes the use of a multi-function trigger, allowing a user to illuminate a target with the pointer beam, and then turning the pointer beam OFF and turning the scanning beam ON. This prevents the pointer beam from interfering with the reception of the scanning beam reflected or backscattered by the machine-readable symbol. Again, this approach has a number of disadvantages including high power consumption, and may lead to inaccurate scanning since the pointer beam and scanning beam are not on at the same time.  
         [0009]     There is a need for a low-cost machine-readable symbol reader with an aiming mechanism that ensures reliable aiming. There is also a need for a low-cost machine-readable symbol reader that does not require a multi-position or multi-function trigger. There is a further need for a low-cost solid state machine-readable symbol reader. Further, there is a need for a low-cost machine-readable symbol reader where the pointer beam and the scanning beam are on at the same time to allow accurate aiming and scanning.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     In one aspect, a device to scan machine-readable symbols comprises: a first reflective surface having an outer perimeter; a second reflective surface having an outer perimeter, the outer perimeter of the second reflective surface being smaller than the outer perimeter of the first reflective surface, the perimeter of the second reflective surface disposed in a volume formed by a normal projection of the perimeter of the first reflective surface such that at least a portion of the second reflective surface is exposable to illumination of the first reflective surface, and wherein the second reflective surface is mounted for movement about at least a first axis to produce a scanning motion.  
         [0011]     In another aspect a device to scan a machine-readable symbols comprises: pointer beam means for directing a pointer beam externally from the device; scanner beam means for directing a scanner beam externally from the device while the pointer beam is directed externally from the device, the scanner beam scanning along at least one axis perpendicular to the direction in which the scanner beam is directed externally from the device; and illumination means for illuminating at least a portion of the pointer beam means at a same time as at least a portion of the scanner beam means.  
         [0012]     In a further aspect, a method of scanning a machine-readable symbol comprises: oscillating a scanner reflective surface having a first outer perimeter with respect to an illumination source and a fixed reflective surface being a second outer perimeter greater than the first outer perimeter; and illuminating the scanner reflective surface and at least a portion of the fixed reflective surface exposed beyond the first perimeter at a same time with a same illumination beam.  
         [0013]     In yet a further aspect, a method of manufacturing an optical system for a machine-readable symbol reader comprises: forming a reflective surface on a substrate; positioning the reflective surface into a first reflective surface having a first outer diameter and a second reflective surface having a second outer diameter, the second diameter concentrically disposed within the first outer diameter and the second reflective surface rotationally supported from the substrate by at least a pair of torsion arms. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING(S)  
       [0014]     In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.  
         [0015]      FIG. 1  is a functional block diagram of a machine-readable symbol reader including a reflective assembly operable to produce both a pointer beam and a scanning beam according to one illustrated embodiment.  
         [0016]      FIG. 2  is a front elevational view of a micro-electro-mechanical system (MEMS) reflector assembly according to one illustrated embodiment, suitable for use in the machine-readable symbol reader of  FIG. 1 .  
         [0017]      FIG. 3  is a cross-sectional view of the MEMS reflector assembly according to another illustrated embodiment, where a second reflective surface is recessed with respect to a first reflective surface.  
         [0018]      FIG. 4  is a cross-sectional view of a MEMS reflector assembly according to still a further illustrated embodiment, where a first reflective surface is recessed with respect to a second reflective surface.  
         [0019]      FIG. 5  is a graph illustrating the cross-sectional power distribution of a focused laser beam, a width of a moving second reflective surface with respect to that power distribution, and further illustrating the portion of power reflected from a non-moving first reflective surface, according to one illustrated embodiment.  
         [0020]      FIG. 6  is a cross-sectional view of a set of light-emitting diodes suitable for use in one illustrated embodiment.  
         [0021]      FIGS. 7-11  are schematic views showing the relative positions of the scanning beam and the pointer beam at a number of successive intervals, according to one illustrated embodiment.  
         [0022]      FIG. 12  is a flow diagram showing a method of operating a machine-readable symbol reader employing a reflective assembly according to one illustrated embodiment.  
         [0023]      FIG. 13  is a flow diagram showing a method of manufacturing a machine-readable symbol reader including a reflective assembly according to one illustrated embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with machine-readable symbol readers, light sources such as laser and light emitting diodes, optics such as lens assemblies, and control subsystems have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments.  
         [0025]     Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” 
         [0026]     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Further more, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. As used herein and in the claims, the term “light” refers to electromagnetic radiation in the visible and non-visible portions of the electromagnetic spectrum, for example the infrared portion of the spectrum.  
         [0027]     The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.  
         [0028]      FIG. 1  shows a machine-readable symbol reader  10  including a housing  12 . The machine-readable symbol reader  10  may take any of a variety of forms including fixed forms such as those commonly found at supermarket checkout stands, or hand-held forms such as that illustrated in  FIG. 1 . The housing  12  typically includes an aperture  14  which may include a lens assembly  16  that allows light to leave and/or enter the housing  12 . The lens assembly  16  may focus the light leaving and/or entering the housing  12 .  
         [0029]     The machine-readable symbol reader  10  includes a illumination source  18  and a photo sensor or detector  20 , for example one or more photodiodes, which may be mounted on one or more printed circuit boards  22 . The machine-readable symbol reader  10  may also include a reflective assembly  24  positioned to reflect an illumination beam  26  produced by the illumination source  18 , out the aperture  14 . The machine-readable symbol reader  10  may also include a return light reflector  32  positioned to reflect a return beam of light  34 , returned from a target to the detector  20  as illustrated by arrows  36 . The target may take the form of a machine-readable symbol, for example a barcode symbol, area or matrix code symbol or stack code symbol.  
         [0030]     The machine-readable symbol reader  10  may further include a control subsystem  40  which may be mounted on one or more circuit boards  42 . The control subsystem  40  may include an analog-to-digital (A/D) converter  44 , digital signal processor (DSP)  46 , microprocessor  48 , random access memory (RAM)  50 , read only memory (ROM)  52 , and optionally driver  54 , all coupled by one or more buses  56 . The A/D converter  44  may convert an analog signal produced by the detector  20  into a digital signal. The control subsystem  40  may optionally include a buffer (not shown), that buffers data from the detector  20  to the A/D converter  44  or DSP  46 . The DSP  46  may receive digital data from the A/D converter  44  and decode the data according to any known or future developed decoding algorithms. The microprocessor  48  controls overall operation of the machine-readable symbol reader  10  based on instructions stored in ROM  52  and using the RAM  50  for dynamic storage. The microprocessor  48  may receive user selections from a user input device, such as the trigger  58 . The microprocessor  48  may control the reflective assembly  24 , for example via a driver  54 . While illustrated with a single line, the buses  56  may include separate control, communications and/or power buses.  
         [0031]     The reflective assembly  24  is shown in cross-section in  FIG. 1  to better illustrate the functional components thereof. As illustrated, the reflective assembly  24  includes a substrate  60 , a first reflective face or surface  62   a ,  62   b , a second reflective face  64 , and torsion arms  66   a ,  66   b  movably attaching the second reflective face  64  to the substrate  60 . The torsion arms  66   a ,  66   b  allow the second reflective surface  64  to move with respect to the first reflective surface  62   a ,  62   b . In particular, the second surface  64   a  may rotationally move about an axis defined by the torsion arms  66   a ,  66   b  with respect to the first reflective surface  62   a ,  62   b . For example, the second reflective surface  64   a  may rotationally oscillate or pivot with respect to the first reflective surface  62   a ,  62   b . Alternatively, the second reflective surface  64   a  may continuously rotate with respect to the first reflective surface  62   a ,  62   b . In the embodiment illustrated in  FIG. 1 , the second reflective surface  64  is approximately flush or planar with the first reflective surface  62   a ,  62   b.    
         [0032]     The reflective assembly may employ standard or conventional reflectors, mirrors and/or prisms, or may employ one or more micro-electro-mechanical systems (MEMS) reflector or micro-mirror, as explained in detail below.  
         [0033]     The illumination source  18  produces an illumination beam with sufficient cross-sectional area to cover an area that includes at least a portion of the first reflective surface  62   a ,  62   b , as well as the second reflective surface  64 . While illustrated as a diverging beam in  FIG. 1 , the illumination beam  26  may have a Gaussian profile similar to that commonly associated with typical laser beams. The first reflecting surface  62   a ,  62   b  reflects the illumination beam  26  out of the housing  12  to form a pointer beam  28 , while the second reflective surface  64  reflects the illumination beam  26  out of the housing  18  to create a scanning beam  30 . The return light reflector  32  may selectively pass the outwardly projecting beams  28 ,  30 , while reflecting the inwardly received return beam  34  which is returned from the target.  
         [0034]      FIG. 2  shows a front view of a reflective assembly  24  in the form of a MEMS reflective assembly according to one illustrated embodiment. Generic MEMS fabrication techniques are known in the art and may be applied to create the reflective assembly  24 , as are generic techniques for driving MEMS structures. Such techniques will not be discussed further, in the interest of brevity and clarity.  
         [0035]      FIG. 3  shows another embodiment of the reflective assembly  24 . In particular, in the embodiment of  FIG. 3  the second reflective surface  64  is recessed with respect to the first reflective surface  62   a ,  62   b . This is in contrast to the embodiment shown in  FIG. 1 , where the second reflective surface  64  is flush or planar with the first reflective surface  62   a ,  62   b.    
         [0036]      FIG. 4  shows a reflective assembly  24  according to yet another embodiment. In the embodiment of  FIG. 4 , the first reflective surface  62   a ,  62   b  comprises a recessed portion of the substrate  60 . Consequently, the first reflective surface  62   a ,  62   b  is recessed with respect to the second reflective surface  64 . From the above teachings, one of skill in the art will appreciate that other variations and/or combinations for the reflective assembly  24  are possible.  
         [0037]      FIG. 5  shows a power profile  80  for a typical laser beam. The profile  80  has a near-Gaussian shape, with an effective aperture width where the power drops as  
       1   ⅇ         
 of the maximum power. Because of the Gaussian shape, there is considerable power located outside the central density of the beam, in the fringe or wings  84   a ,  84   b . The width of the second reflective surface  64  is also illustrated in  FIG. 5 . In particular, the power in the wings  84   a ,  84   b  of the Gaussian power distribution is used to create the pointer beam  28 . 
 
         [0038]      FIG. 6  shows an alternative embodiment. For example, the machine-readable symbol reader  10  may employ an alternative illumination source, comprising a set of light-emitting diodes LEDS  90   a - 90   d  mounted on the circuit board  22 . Such can be employed in place of the laser source  18 . The machine-readable symbol reader  10  may employ a conventional mirror, for example a polygonal mirror  92 , with multiple reflective surfaces  64 . The polygonal mirror  92  may be mounted in the substrate  60  of continuous rotation about one or more axles  94 , and driven by a motor  96  controlled via driver  54  ( FIG. 1 ).  
         [0039]      FIGS. 7-11  show the relative positions of the pointer beam  28  and scanning beam  30  at successive intervals. In each instance, the illumination beam  26  illuminates the second reflective surface  64  and at least a portion of the first reflective surface  62 . The first reflective surface reflects a portion of the light to create the pointer beam  28 , which remains approximately fixed throughout the intervals represented by  FIGS. 7-11 . As the second reflective surface  64  rotates, for example oscillatingly rotating, the light reflected from the second reflective surface  64  scans across the target. For example, the scanning beam  30  moves from a position illustrated as scanning beam  30   a  in  FIG. 7 , to a position illustrated as scanning beam  30   b  in  FIG. 8 . The scanning beam  30  continues to move, to a position illustrated as scanning beam  30   c  in  FIG. 9 , then to a position illustrated as scanning beam  30   d  in  FIG. 10 , followed by a position illustrated as scanning beam  30   e  in  FIG. 11 .  
         [0040]      FIG. 12  shows a method  100  of operating a machine-readable symbol reader  10  according to one illustrated embodiment. At  102 , the second reflective surface  64  is moved with respect to the first reflective surface  62   a ,  62   b . At  104 , the illumination source  18  illuminates at least a portion of the first reflective surface  62   a ,  62   b  and the moving second reflective surface  64  to create the pointer beam  28  and scanning beam  30 , respectively. At  106 , the machine-readable symbol reader  10  receives light returned from the target symbol. At  108 , the A/D converter  44  converts the analog signal produced by the detector  20  into a digital signal. At  110 , the DSP  46  or, alternately microprocessor  48 , decodes the digital signal.  
         [0041]      FIG. 13  shows a method  120  of manufacturing a machine-readable symbol reader  10  according to one illustrated embodiment. At  122 , reflective surfaces  62   a ,  62   b ,  64  are formed on the substrate  60  using standard MEMS techniques. At  124 , the reflective surface is partitioned into the first reflective surface  62   a ,  62   b  and the second reflective surface  64  along with forming the torsion arms  66   a ,  66   b , again using standard MEMS techniques. At  126 , the reflective assembly  24  is communicatively coupled to the control subsystem  40 . At  128 , the reflective assembly  24  is positioned with respect to the illumination source  18 .  
         [0042]     The method  120  may be performed in a different order, include additional acts or omit some acts. For example, the first and second reflective surfaces  62   a ,  62   b ,  64  may be formed at the same time. In such a situation act  122  will proceed at  124 . Alternatively, first and second reflective surfaces  62   a ,  62   b ,  64  may be formed separately from one another. In such a situation act  124  may proceed act  122 .  
         [0043]     The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the invention, as will be recognized by those skilled in the relevant art. The teachings provided herein can be applied to other machine-readable symbol, not necessarily the exemplary machine-readable symbol reader  10  employing the MEMS based reflective assembly  24  generally described above. For example, the machine-readable symbol reader  10  may employ standard reflectors and mirrors, such as those typically found in current machine-readable symbol readers, so long as the reflectors or mirrors employ a similar topology as that illustrated herein.  
         [0044]     Additionally, the foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, schematics, and examples. Insofar as such block diagrams, schematics, and examples contain one or more functions and/or operations, it will be understood by those skilled in the art that each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, the present subject matter may be implemented via Application Specific Integrated Circuits (ASICs). However, those skilled in the art will recognize that the embodiments disclosed herein, in whole or in part, can be equivalently implemented in standard integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more controllers (e.g., microcontrollers) as one or more programs running on one or more processors (e.g., microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of ordinary skill in the art in light of this disclosure.  
         [0045]     In addition, those skilled in the art will appreciate that the certain mechanisms of taught herein are capable of being distributed as a program product in a variety of forms, and that an illustrative embodiment applies equally regardless of the particular type of signal bearing media used to actually carry out the distribution. Examples of signal bearing media include, but are not limited to, the following: recordable type media such as floppy disks, hard disk drives, CD ROMs, digital tape, and computer memory; and transmission type media such as digital and analog communication links using TDM or IP based communication links (e.g., packet links).  
         [0046]     The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, including U.S. provisional patent application Ser. No. 60/583,406, filed Jun. 25, 2004, are incorporated herein by reference in their entirety. Aspects of the invention can be modified, if necessary, to employ systems, circuits and concepts of the various patents, applications and publications to provide yet further embodiments of the invention.  
         [0047]     These and other changes can be made in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all machine-readable symbol readers and methods of manufacturing and/or operating the same that accord with the claims. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined entirely by the following claims.