Classifications

• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
  • G06K7/10544—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum
  • G06K7/10554—Moving beam scanning
  • G06K7/10594—Beam path
  • G06K7/10683—Arrangement of fixed elements
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
  • G06K7/10544—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum
  • G06K7/10821—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum further details of bar or optical code scanning devices
  • G06K7/10831—Arrangement of optical elements, e.g. lenses, mirrors, prisms

Definitions

• the present invention generally relates to electro-optical readers, such as laser
• indicia such as bar code symbols
• UPC Universal Product Code
• the bar code symbol itself is a coded pattern of graphic indicia
• processing system for applications in point-of-sale processing, inventory control, and the like.
• a scanning laser light beam at a targeted symbol to be read.
• the light source in a laser scanning bar code reader is typically a semiconductor
• the laser beam is optically
• the laser light beam is directed
• the moving-beam reader operates by repetitively scanning the light beam in a
• the scanning component may either sweep the
• Bar code readers also include a sensor or photodetector which detects light
• the photodetector or sensor is positioned in the reader
• the light which is reflected or scattered off the symbol.
• the light is detected and converted into
• Some bar code readers are "retro-reflective". In a retro-reflective reader, a
• moving optical element such as a mirror is used to transmit the outgoing beam and receive the
• Non-retro-reflective readers typically employ a moving mirror to transmit the
• analog electrical signal generated by the photodetector is converted by a digitizer into a pulse
• width modulated digitized signal with the widths corresponding to the physical widths of the bars and spaces.
• Such a digitized signal is then decoded, based on the specific symbology used
• the density of a bar code symbol can be expressed in terms of the
• minimum bar/space width also called “module size”, or as a “spatial frequency” of the code
• a bar code reader typically will have a specified resolution, often expressed by
• the module size that is detectable by its effective sensing spot.
• the beam spot size is the module size that is detectable by its effective sensing spot.
• the spot size is such as to produce
• Gaussian beams typically have a profile along their axis of propagation exhibiting a waist
• collimated zone determines a depth of field (focusing range) for maximum bar code density.
• an axicon optical element for example, a conical lens
• Such a non-diverging beam can provide two
• the conical axicon by itself, produces a generally circular beam spot, which
• Ellipticity of the beam spot can be introduced in an axicon-based reader by
• the conical axicon is sensitive to pointing error of the laser.
• Still another object of the present invention is to introduce ellipticity of a beam
• a still further object of the present invention is to increase the depth of focus
• This asymmetric optical element also known herein as a "rooftop” element, has a pair
• lens surfaces preferably planar, meeting along a line that intersects along an optical axis
• Another feature of this invention resides in a novel aperture stop for reducing
• aperture stop includes an optical aperture, and a support bounding the optical aperture along
• optical aperture in accordance with the prior art, may be circular,
• the optical aperture has a plurality of light-passing areas spaced apart along the
• a light-obstructing area is located between a pair of light-passing areas.
• the border is configured to have a periodic shape at opposite sides of the optical
• the periodic shape may be sinusoidal or
• this invention proposes
• aperture is not a vertical linear edge, or a curved edge as in the case of a circular or elliptical
• each edge has a plurality of light-passing areas and light-blocking areas so that the light intensity change is continuous and gradual. Since the opposite sides of the
• the soft edge aperture reduces the effect of the wiggles in the
• FIG. 1 is a broken-away, perspective view of a handheld device used in a reader
• the device for electro-optically reading indicia located in a working range of distances, the device
• FIG. 2 is an enlarged perspective view of the rooftop element embodiment of
• FIG. 1 A first figure.
• FIG. 3 is a graph of a line spread function over two axes showing an undesirable
• FIG. 4 is an enlarged, elevational view of the aperture stop embodiment of FIG.
• FIG. 5a is a rectangular aperture stop in accordance with the prior art
• FIGS. 5b, 5c are line spread functions over two axes for close-in and far-out
• FIG. 6a is a soft edge aperture stop having a first set of design parameters in accordance with this invention.
• FIGS. 6b, 6c are analogous to FIGS. 5b, 5c, but for the aperture stop of FIG. 6a;
• FIG. 7a is a soft edge aperture stop having a second set of design parameters in accordance with this invention.
• FIGS. 7b, 7c are analogous to FIGS. 5b, 5c, but for the aperture stop of FIG.
• FIGS. 8a, 8b are elevational views of the aperture stop of FIG. 4, but with a
• FIG. 9 is a perspective view of another embodiment of a rooftop element in
• FIG. 10 is an enlarged sectional view of a detail of the surfaces of FIG. 9;
• FIG. 11 is a perspective view of another embodiment of a rooftop element in
• FIG. 12 is a diagrammatic, perspective view of an imaging reader employing
• FIG. 13 is a diagrammatic view of an axicon-based optical assembly in
• FIG. 14 is a view of a non-axicon-based optical assembly for extending working
• FIG. 15 is a view of another non-axicon-based optical assembly for extending
• symbol broadly encompasses not only symbol
• bar code symbols but also other one- or two-dimensional graphic patterns, as well as
• symbol may apply to any type of pattern or
• indicia which may be recognized or identified either by scanning a light beam and detecting
• FIG. 1 shows an indicia 15 as one example of a "symbol" which
• the present invention can read.
• FIG. 1 depicts a handheld laser scanner device 10 for reading symbols.
• laser scanner device 10 includes a housing that is generally of the type shown in the above-
• the invention may also be implemented in other types of
• housings such as a desk-top workstation or a stationary scanner.
• a desk-top workstation or a stationary scanner.
• the barrel portion 11 of the housing includes an exit port or window 13 through which an
• outgoing laser light beam 14 passes to impinge on, and scan across, a bar code symbol 15
• the laser beam 14 moves across the symbol 15 to create a scan pattern.
• the scanning pattern is one-dimensional or linear, as shown by line 16. This linear
• a manually-actuated trigger 19 or similar means permit an operator to initiate the
• the scanner device 10 includes a laser source 20, e.g. , a gas laser tube or a
• the laser source 20 generates the
• a photodetector 21 is positioned within the housing to receive at least a portion
• the photodetector 21 may face toward the
• a convex portion of the scan mirror 17 may focus reflected light
• the photodetector 21 faces toward the scan mirror.
• the photodetector 21 detects the light reflected from the
• a digitizer typically converts the analog signal into a pulse width modulated
• a decoder typically comprising
• the laser source 20 directs the laser beam through an optical assembly
• the mirror 17 mounted on a vertical shaft and
• the laser source 20 activates the laser source 20 and the motor 18.
• the laser source 20 generates the laser beam
• aperture 23 modify the beam to create an intense beam spot of a given size which extends
• the modified laser beam outwardly from the scanner housing 11 and toward the bar code
• the photodetector could also be mounted in a retroreflective
• the system circuitry then converts the analog signal to a
• the surfaces 25, 26 could also be used as front surfaces, and the surface 24 can also be used
• exit surfaces 25, 26 meet along a line 27 that intersects and is
• the optical element 22 has a length L and a width W, both of these mutually orthogonal dimensions being independently selectable.
• the optical element 22 bends the light beam 14 coming from the
• FIG. 3 depicts the line spread
• line spread function is a function obtained by integrating the light intensity distribution of the
• wiggle 30 is identified by wiggle 30.
• the presence of the wiggle leads to decoding degradation or
• the aperture stop 23 is
• the aperture stop 23 has a "soft" edge
• the aperture stop 23 has an optical aperture 31 , and a support 32 bounding the aperture 31 along a border 33 that shapes the aperture with variable
• the soft edge is characterized by at least two, and preferably a succession of,
• the light-passing areas alternate with the light-
• one light-obstructing area is located between a pair of adjacent light-passing areas.
• FIG. 4 depicts a preferred embodiment in which the soft edge is a sinusoidal
• FIG. 5a depicts a standard rectangular aperture 46;
• FIG. 5b depicts the
• FIG. 5c depicts the corresponding line spread
• FIG. 6b depicts the corresponding line spread functions 53, 54 at the close-in target planes; and FIG. 6c depicts the corresponding line spread functions 55, 56
• shoulders 51, 52 have in degrading reader performance for both close-in and far-out symbols
• the period T is chosen to be smaller than the
• the beam profile preserves its consistency even with a significant pointing error
• FIGS. 8a, 8b depict a beam spot shift or pointing error, and the beam profile is not
• the asymmetric rooftop element 22 extends the working range whose effect is
• the aperture stop enables the horizontal and vertical dimensions of the
• the vertical size of the beam spot can be any shape.
• the front surface 24 need not be planar, but can be configured as a cylindrical surface 61 to
• the aperture stop could be formed integrally with the
• rooftop element 22 by forming a series of grooves 62, 63 on each planar surface 25, 26.
• the grooves of each series can be spaced apart with variable distance, thereby
• FIG. 11 Still another embodiment of the rooftop element 64 is depicted in FIG. 11 and
• each exit surface is curved, rather than flat.
• each curved exit surface 65, 66 is a parabola.
• FIG. 12 schematically depicts components of an imaging reader including a
• imaging readers having a linear array typically have a lower depth of focus than moving beam
• imaging reader more available for use in high throughput environments.
• the new system has the same working range as the one without the axicon-aperture
• the sensor array which, in turn, enables the sensor's exposure time to be reduced. By reducing the exposure time, the handheld reader's immunity to hand motion is increased.
• invention is to deliberately form a negative spherical aberration on a surface of a positive
• FIG. 13 depicts an axicon-based prior art arrangement in which the laser diode
• conical axicon 71 to focus the beam to multiple focal points, e.g., all points between Pl and
• the focusing lens 69 is
• FIG. 14 depicts, according to this invention, an additional optical component
• the beam wavefront is aspherical, as schematically represented by reference numeral 75.
• negative spherical aberration refracts outer marginal light rays (i.e. , the rays Rl which are
• Negative spherical aberration just like positive spherical aberration, is an
• the focusing lens is deliberately overcorrected.
• the sag (W) of a wavefront at the plane of the exit pupil can be described as:
• A is the coefficient of defocus
• B is the coefficient of spherical aberration
• R is the
• B is zero.
• B is selected to be a negative value.
• the optical assembly is less sensitive to diode pointing errors and laser
• spot can be made elliptical to a greater extent than can be achieved with axicon-bases
• the negative spherical aberration can be introduced by application of plastic
• the negative spherical aberration can be introduced by
• a separate optical component i.e., a phase plate 76, as shown in FIG. 15.
• a phase plate 76 a separate optical component
• plano-covex lens 69 collimates the laser beam.
• the plastic phase plate 76 has a first surface that combines two zones: a beam modifying zone and a conical zone. The beam modifying
• the effective aperture is formed by the intersection
• the conical zone deflects the rays outside
• the phase plate 76 for generating the negative spherical aberration can be also
• phase plate 76 is useful for extending the working range in imaging applications. Therefore, the phase plate 76

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Electromagnetism (AREA)
• Artificial Intelligence (AREA)
• Toxicology (AREA)
• General Health & Medical Sciences (AREA)
• Health & Medical Sciences (AREA)
• Computer Vision & Pattern Recognition (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Mechanical Optical Scanning Systems (AREA)
• Facsimile Scanning Arrangements (AREA)
• Lenses (AREA)

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Applications Claiming Priority (2)

Publications (1)

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Citations (12)

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• 2004
  • 2004-07-23 US US10/897,724 patent/US7063261B2/en not_active Expired - Fee Related
• 2005
  • 2005-06-30 JP JP2007522523A patent/JP4643644B2/ja not_active Expired - Lifetime
  • 2005-06-30 EP EP05764402A patent/EP1771803B1/en not_active Expired - Lifetime
  • 2005-06-30 CN CNB2005800248769A patent/CN100517364C/zh not_active Expired - Lifetime
  • 2005-06-30 WO PCT/US2005/023825 patent/WO2006023111A1/en not_active Ceased
  • 2005-07-13 TW TW094123712A patent/TWI378261B/zh not_active IP Right Cessation
• 2006
  • 2006-03-06 US US11/369,130 patent/US7224538B2/en not_active Expired - Lifetime

Patent Citations (13)

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