MULTI-FOCAL LASER SCANNING BAR CODE SYMBOL READING SYSTEM EMPLOYING A SCAN DATA SIGNAL PROCESSOR HAVING A VARIABLE PASS-BAND FILTER STRUCTURE WITH FREQUENCY CHARACTERISTICS CONTROLLED BY MEASURING THE BEAM SPOT SPEED OF THE LASER SCANNING BEAM PRODUCING THE ANALOG SCAN DATA SIGNAL BEING PROCESSED BY SAID SCAN DATA SIGNAL PROCESSOR

• US 6,588,663 B1
• Filed: 02/10/2000
• Issued: 07/08/2003
• Est. Priority Date: 12/18/1995
• Status: Expired due to Fees

• Current Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Original Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Inventors: Zhu, Xiaoxun, Knowles, C. Harry, Dickson, LeRoy, Check, Frank, Lucera, Mark
• Primary Examiner(s): Lee, Michael G.
• Assistant Examiner(s): Kim, Ahshik
• Application Number:
  US09/501,903
• Time in Patent Office: 1,244 Days
• Field of Search: 235/462.01, 235/462.12, 235/462.22, 235/472.01, 235/462.34
• US Class Current: 235/462.01
• CPC Class Codes: G02B 26/106 having diffraction gratings as scanning elements, e.g. holographic scanners holographic optical elements G02B5/32, holography G03H
• CPC Class Codes: G06K 17/0022 arrangements or provisious for transferring data to distant stations, e.g. from a sensing device "transfer between computer elements G06F13/00 "; data-transmission H04L
• CPC Class Codes: G06K 2207/1013 Multi-focal
• CPC Class Codes: G06K 7/10 by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
• CPC Class Codes: G06K 7/10564 Light sources
• CPC Class Codes: G06K 7/10584 Source control
• CPC Class Codes: G06K 7/10594 Beam path
• CPC Class Codes: G06K 7/10603 Basic scanning using moving elements
• CPC Class Codes: G06K 7/10663 using hologram
• CPC Class Codes: G06K 7/10673 Parallel lines
• CPC Class Codes: G06K 7/10693 for omnidirectional scanning
• CPC Class Codes: G06K 7/10702 Particularities of propagating elements, e.g. lenses, mirrors G06K7/10831 takes precedence
• CPC Class Codes: G06K 7/10792 Special measures in relation to the object to be scanned
• CPC Class Codes: G06K 7/10801 Multidistance reading
• CPC Class Codes: G06K 7/10811 Focalisation
• CPC Class Codes: G06K 7/10851 Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device basic electronic circuitry H03
• CPC Class Codes: G06K 7/10861 sensing of data fields affixed to objects or articles, e.g. coded labels postal sorting B07C3/14, conveying articles B65G47/48
• CPC Class Codes: G06K 7/10871 randomly oriented data-fields, code-marks therefore, e.g. concentric circles-code
• CPC Class Codes: G06K 7/10881 constructional details of hand-held scanners
• CPC Class Codes: G06K 7/10891 the scanner to be worn on a finger or on a wrist
• CPC Class Codes: G06K 7/109 : adaptations to make the hand-held scanner useable as a fixed scanner
• CPC Class Codes: G06K 7/14 : using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence
• CPC Class Codes: G07F 9/002 : Vending machines being part of a centrally controlled network of vending machines
• CPC Class Codes: G07G 1/0054 : with control of supplementary check-parameters, e.g. weight or number of articles

Abstract

The zone laser scanning systems by processing analog scan data signals with a scan data signal processor having a plurality of pass-band filters and amplifiers that are automatically selected for passing only the spectral components of an analog scan data signal produced when a bar code symbol is scanned at a particular focal zone in the laser scanning system. Two or more different pass band filter structures can be provided for use in the scan data signal processor, wherein each pass-band filter structure is: tuned to the spectral band associated with a particular focal zone in the laser scanning system. When a bar code, symbol is scanned by a laser beam focused within the first focal zone or scanning range of the system, the pass-band filter structure associated with this focal zone or scanning range is automatically switched into operation using a control signal produced by determining the spot speed of the laser scanning beam producing the analog scan data signal being processed. Only spectral components associated with the produced analog scan data signal and noise existing over this pass-band are allowed within the analog signal processor. By virtue of the present invention, first and second derivative signals can be generated and processed to produce a corresponding digital scan data signal for use in subsequent digitizing and decode processing operations, without compromising system performance due to the destructive effects of thermal and substrate noise outside the spectral pass-band of interest for the bar code symbol being scanned.

Claims

1. A multi-focal zone laser scanning system comprising:

a system controller;

a visible laser diode for generating a laser beam of sufficient power;

a variable focus lens subsystem, realizable using movable optical components translated relative to each other in a real-time manner in response to control signals produced by said system controller so as to vary the focal distance of the laser beam at different focal planes within said system during laser scanning operations;

a laser beam scanning mechanism for scanning the variably focused laser beam along a predefined scanning pattern during laser scanning operations;

a photodetector for detecting the intensity of laser light reflected off a scanned bar code symbol and producing an electrical analog scan data signal corresponding to the structure of the scanned bar code symbol;

a preamplification circuit for preamplifying the analog scan data signal produced by said photodetector, so as to produce a preamplified analog scan data signal D₁;

a scan data signal processor, containing first and second derivative signal band-pass filters and amplifiers, for processing said preamplified analog scan data signal D₁ and generating a digital scan data signal D₂ corresponding to the analog scan data signal provided as input thereto;

a digitizer circuit for producing digital words D₃ representative of the time duration of the first and second signal levels in the digital scan data signal D₂ a decode processor for processing the digital words D₃ produced from said digitizer circuit so as to decode the digital scan data signal D₂ and produce a symbol character data string representative of the corresponding scanned bar code symbol;

a real-time bar code element width measurement processor for real-time measurement of the time duration of the first and second binary signal levels occurring in the digital scan data signal D₂ as a bar code symbol is scanned at different focal planes within the system, and real-time comparison of the measured time durations of the first and second binary signal levels with predetermined time duration measures stored in a memory structure, so as to determine the corresponding spot speed of the laser scanning beam that would produce such measured time durations for a bar code symbol of a particular resolution, scanned at a particular focal plane in the system; and

a pass-band filter control signal generator for producing variable pass-band (VPB) control signals based on the determined beam spot speed of the laser scanning beam at each particular instant in time, and providing such VPB control signals to at least one of said preamplirication circuit, and said first and second derivative signal band-pass filters and amplifiers employed in said scan data signal processor.

2. The multi-focal zone laser scanning system of claim 1, wherein said decode processor uses decode tables and bar code stitching techniques.

3. The multi-focal zone laser scanning system of claim 1, wherein said laser beam scanning mechanism is a mechanism selected from the group consisting of a holographic scanning mechanism, a polygon-type scanning mechanism, and any other electro-mechanical or electro-acoustical scanning mechanism capable of scanning one or more focused laser beams within said system.

4. The multi-focal zone laser scanning system of claim 1, wherein said memory structure comprises a beam spot speed table containing data for n-number of bar code symbol resolutions unspecified by the predetermined minimum element width (x) in the bar code symbol, wherein a predetermined digital time-duration measure for each minimum bar code element (x) is provided in said table according to scanning distance (di) away from said laser beam scanning mechanism.

5. The multi-focal zone laser scanning system of claim 4, wherein for each scanning distance d_i, there is a predetermined laser beam spot speed associated with the laser scanning system.

6. The multi-focal zone laser scanning system of claim 4, wherein said beam spot speed table is constructed by measuring the time duration of the signal levels of minimum bar code elements scanned at predetermined focal planes in said system, converting these time duration measures in to digital words, and recording these digital words in the column of a table, assigned to a particular bar code element width.

7. The multi-focal zone laser scanning system of claim 4, wherein during system operation, said real-time bar code element width measurement processor produces digital time counts which are compared with the digital time counts stored in the columns of said beam spot speed table;

the output of this count comparison process is a corresponding beam spot speed value which produces such a time count when a bar code symbol of a particular resolution is scanned at the corresponding scanning distance; and

said VPB filter control signal generator uses the produced beam spot speed value to determine the appropriate VPB control signal so that the pass-band frequency characteristics are set for each preamplifier, filter and amplifier in said scan data signal processor.

8. A multi-focal zone laser scanning system comprising:

a visible laser diode for generating a laser beam of sufficient power;

a fixed lens focusing system, adapted to focus said laser beam over a single predetermined focal region determined by the beam waist characteristics and maximum beam spot size requirements in said system, during laser scanning operations;

a laser scanning mechanism for scanning the focused laser beam along a predefined scanning pattern during laser scanning operations;

a photodetector for detecting the intensity of laser light reflected off a scanned bar code symbol and producing an electrical analog scan data signal corresponding to the structure of the scanned bar code symbol;

a preamplification circuit for preamplifying the analog scan data signal produced by said photodetector, so as to produce a preamplified analog scan data signal D_I;

a scan data signal processor, containing first and second derivative signal band-pass filters and amplifiers, for processing said preamplified analog scan data signal D₁ and generating a digital scan data signal D₂ corresponding to the analog scan data signal provided as input thereto;

a digitizer circuit for producing digital words D₃ representative of the time duration of the first and second signal levels in the digital scan data signal D₂ a decode processor for processing the digital words D₃ produced from said digitizer circuit so as to decode the digital scan data signal D₂ and produce a symbol character data string representative of the corresponding scanned bar code symbol;

a real-time bar code element width measurement processor for real-time measurement of the time durations of the first and second binary signal levels occurring in the digital scan data signal D₂, as a bar code symbol is scanned within said single predetermined focal region, and real-time comparison of the measured time durations of the first and second binary signal levels with predetermined time duration measures stored in a memory structure, so as to determine the corresponding laser beam spot speed that would produce such measured time durations for a bar code symbol of a particular resolution, scanned within said single predetermined focal region;

a pass-band filter control signal generator for producing variable pass-band (VPB) control signals based on the determined beam spot speed value of the laser scanning beam at each particular instant in time, and providing such VPB control signals to at least one of said preamplification circuit, and said first and second derivative signal band-pass filters and amplifiers employed in said scan data signal processor.

9. The multi-focal zone laser scanning system of claim 8, wherein said decode processor uses decode tables and bar code stitching techniques.

10. The multi-focal zone laser scanning system of claim 8, wherein said laser beam scanning mechanism is a mechanism selected from the group consisting of a holographic scanning mechanism, a polygon-type scanning mechanism, and any other electro-mechanical or electro acoustical scanning mechanism capable of scanning one or more focused laser beams within said system.

11. The multi-focal zone laser scanning system of claim 8, wherein said memory. structure comprises a beam spot speed table containing data for n-number of bar code symbol resolutions specified by the predetermined minimum element width (x) in the bar code symbol, wherein a predetermined digital time-duration measure for each minimum bar code element (x) is provided in said table according to scanning distance (d_i) away from said laser scanning mechanism.

12. The multi-focal zone laser scanning system of claim 8, for each scanning distance d_i, there is a predetermined laser beam spot speed associated with the laser scanning system.

13. The multi-focal zone laser scanning system of claim 12, wherein said beam spot speed table is constructed by measuring the time duration of the signal levels of minimum bar code elements scanned at predetermined focal planes in said system, converting these time duration measures pinto digital words, and recording these digital words in the column of a table, assigned to a particular bar code element width.

14. The multi-focal zone laser scanning system of claim 8, wherein during system operation, said bar code element width measurement processor produces digital time counts which are compared with the digital time counts stored in the columns of said beam spot speed table;

the output of this count comparison process is a corresponding beam spot speed value which produces such a time count when a bar code symbol of a particular resolution is scanned at the corresponding scanning distance; and

said VPB filter control signal generator uses the produced beam spot speed value to determine the appropriate VPB control signal so that the pass-band frequency characteristics are set for each preamplifier, filter and amplifier in said scan data signal processor.

15. The laser scanning system comprising:

a laser scanning mechanism for producing a laser beam within a plurality of focal zones and scanning said laser beam over a bar code symbol, and producing an analog scan data signal indicative of the intensity of light reflected from said scanned bar code symbol;

a control signal producing mechanism for producing a control signal indicative of the spot speed of the laser scanning beam at the focal zone in which the bar code symbol is being scanned and at the instant in time said analog scan data signal is being generated; and

a scan data signal processor for processing said analog scan data signal;

wherein said scan data signal processor includes a plurality of first derivative signal pass-band filter structures that are electronically-switched into operation in response to said control signal at each instant in time of laser scanning operation.

16. A multi-focal zone laser scanning system comprising:

a laser beam scanning mechanism for (i) producing a laser beam, (ii) focusing said produced laser beam within a scanning volume having a depth of field and a plurality of predefined focal zones, (iii) scanning said focused laser beam across a bar code symbol within said depth of field, (iv) collecting a laser light signal produced by said scanned laser beam (reflecting off said bar code symbol, (v) detecting said collected laser light signal, and (vi) producing an analog scan data signal corresponding to the detected laser light intensity and having a frequency bandwidth determined by the speed of the laser beam across the scanned bar code symbol and the structure of said scanned bar code symbol;

a control signal generator for dynamically generating a control signal indicative of the spot speed of the laser scanning beam scanning the bar code symbol at the instant said analog scan data signal is being produced; and

an analog scan data signal processor including a first derivative signal generator for receiving said analog scan data signal and generating a first derivative signal representative of the first time-derivative of said analog scan data signal;

a plurality of pass-band filter structures, each one of said plurality of pass-band filter structures being preassigned to one of said predefined focal zones and having frequency response characteristics for optimally filtering the first derivative signal produced when scanning said bar code symbol within said predefined focal zone; and

control circuitry, responsive to the control signal generated by said control signal generator, for dynamically switching one of said plurality of pass-band filter structures into operation so that the first derivative signal produced in response to said laser beam scanning a bar code symbol within one of said predefined focal zones is optimally filtered by said dynamically-switched pass-band filter structure preassigned to said predefined focal zone.

17. The multi-focal laser scanning system of claim 16, wherein at instant in time said dynamically switched pass-band filter structure filters out the spectral components of paper noise residing outside the frequency bandwidth of said first time-derivative signal, produced by said a laser beam when scanning said bar code symbol within said predefined focal zone.

18. The multi-focal laser scanning system of claim 16, wherein said laser beam scanning mechanism comprises a holographic scanning disc for supporting a plurality of holographic scanning facets for scanning said laser beam during laser scanning operations, wherein each said holographic scanning facet has focal length which falls within one of said predefined focal zones, and wherein said control signal generator comprises a holographic scanning facet detector for detecting the holographic scanning facet which generates said laser beam at any instant in time, and automatically produces said control signal.

19. The multi-focal laser scanning system of claim 16, wherein said laser beam scanning mechanism comprises:

a polygonal-type laser beam-scanning element for scanning said laser beam during laser scanning operations, and

a variable laser beam focusing mechanism for focusing said produced laser beam to one of said predefined focal zones in response to said control signal; and

wherein said control signal generator comprises an object measurement device for automatically measuring a physical dimension of the object on which said bar code symbol resides, and automatically generating said control signal.

20. The multi-focal laser scanning system of claim 19, wherein said physical dimension is the height of said object measured relative to a surface on which said object is supported during laser scanning operations.