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 DETECTING THE FOCAL DISTANCE OF THE LASER SCANNING BEAM PRODUCING THE ANALOG SCAN DATA SIGNAL BEING PROCESSED BY SAID DATA SIGNAL PROCESSOR

• US 6,499,661 B1
• Filed: 02/10/2000
• Issued: 12/31/2002
• 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): Le, Thien M.
• Assistant Examiner(s): Kim, Ahshik
• Application Number:
  US09/499,529
• Time in Patent Office: 1,055 Days
• Field of Search: 235/462.01, 235/472.01, 235/462.22, 235/462.39
• 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 effects of paper/substrate noise are significantly reduced in multi-focal 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. 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 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 focal distance of the scanned laser beam at each instant in time of scanning system operation;

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 scanning system operation.

2. A 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 automatically producing an analog scan data signal indicative of the intensity of light reflected from said scanned bar code symbol; and

a scan data signal processor for processing said analog scan data signal, said scan data signal processor including

a preamplification circuit for preamplifying said analog scan data signal produced in response to scanning a bar code symbol by said scanned laser beam within one of said plurality of focal zones,

a first derivative signal generating circuit for deriving a first derivative signal from said preamplified analog scan data signal,

a variable pass-band filter having a plurality of different pass-band filter structures having different pass-band filter characteristics for processing a signal selected from the group consisting of said preamplified analog scan data signal and said first derivative signal,

a control signal generation circuit for generating a control signal indicative of the focal distance of the scanned laser beam producing said analog scan data signal provided to said preamplification circuit, and

a filter control circuit for electronically switching into operation selected pass-band filter structures using said control signal, thereby automatically tuning said scan data signal processor to an optimum setting for the focal zone being scanned at each given moment of operation of said laser scanning system.

3. The laser scanning system of claim 2, wherein an optical device is used to produce said laser beam and said control signal generation circuit comprises a mechanism for analyzing said optical device during laser scanning so as to determine the focal distance of said scanned laser beam.

4. A laser scanning system comprising:

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

a scan data signal processor for processing said analog scan data signal, said scan data signal processor including

a plurality of different pass-band filters, wherein one of said pass-band filters is dynamically switched into operation for pass-band filtering the analog scan data signal produced by said scanned laser beam scanning a bar code symbol within one of said predefined focal zones so as to filter out spectral components of paper noise residing outside the frequency spectrum of said analog scan data signal produced in response to scanning said bar code symbol within said predefined focal zone.

5. The laser scanning system of claim 4, wherein said laser scanning mechanism is selected from the group consisting of a holographic laser scanning mechanism, a polygonal-type laser scanning mechanism, and any other type laser scanning mechanism capable of generating a laser scanning pattern having multiple focal zones.

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

a laser beam scanning mechanism for (i) producing a laser scanning 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 predefined focal zone in which said scanned bar code symbol resides at any instant in time when scanned by said laser beam during said laser scanning operations; 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 by said scanned laser beam 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.

7. The multi-focal laser scanning system of claim 6, 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 derivative signal, produced by said laser beam when scanning said bar code symbol within said predefined focal zone.

8. The multi-focal laser scanning system of claim 6, wherein said laser beam scanning mechanism comprises a holographic scanning disc for supporting a plurality of holographic scanning facets for scanning said produced laser beam,

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 scanning beam at any instant in time, and automatically produces said control signal.

9. The multi-focal laser scanning system of claim 6, 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 resides, and automatically generating said control signal.

10. The multi-focal laser scanning system of claim 6, 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.

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

a laser beam scanning mechanism for (i) producing a laser scanning 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 predefined focal zone in which said scanned bar code symbol resides at any instant in time when scanned by said laser beam during said laser scanning operations;

a scan data signal processor for processing said analog scan data signal, said analog scan data signal processor including 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 analog scan data signal produced when scanning said bar code symbol by said scanned laser beam 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 analog scan data 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.

12. The multi-focal laser scanning system of claim 11, 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 derivative signal, produced by said laser beam when scanning said bar code symbol within said predefined focal zone.

13. The multi-focal laser scanning system of claim 11, wherein said laser beam scanning mechanism comprises a holographic scanning disc for supporting a plurality of holographic scanning facets for scanning said produced laser beam,

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 scanning beam at any instant in time, and automatically produces said control signal.

14. The multi-focal laser scanning system of claim 11, 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.

15. The multi-focal laser scanning system of claim 14, 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.