Laser scanning bar code symbol reader employing variable pass-band filter structures having frequency response characteristics controlled by time-measurement of laser-scanned bar code symbol

• US 6,481,625 B2
• Filed: 11/18/1999
• Issued: 11/19/2002
• 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 MINH
• Application Number:
  US09/442,718
• Publication Number:
  US 20020000466A1
• Time in Patent Office: 1,097 Days
• Field of Search: 235/462-1-4, 235/462.24, 235/462.25, 235/482.01, 235/454, 235/375, 359/890, 359/895, 359/887, 348/336, 348/337, 348/339
• US Class Current: 235/462.1
• 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 provisions 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 multi-focal zone laser scanning system comprising:

a scanner housing;

a laser scanning beam mechanism disposed within said scanner housing, for producing laser scanning beam and scanning said laser beam so as to produce laser scanning pattern that is focused along a plurality of different predefined focal zones, and automatically generating an analog scan data signal corresponding to the structure of a bar code symbol structure scanned by said scanned laser beam;

a scan data signal processor for processing said analog scan data signal, and 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 said first derivative signal produced while said scanned laser beam scans said bar code symbol structure within said predefined focal zone, and

control circuitry for dynamically switching one of said plurality of pass-band filter structures into operation so that said first derivative signal produced in response to said laser beam scanning said 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;

a bar code element width measurement processor for measuring in real-time the width of the signal levels in said analog scan data signals, and producing signal level width measurement data representative thereof; and

a data processor for converting said signal level width measurement data into control signals for use by said control circuitry so that one of said plurality of pass-band filter structures is automatically switched into operation so that said first derivative signal produced in response to said laser beam scanning said 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.

2. The multi-focal zone laser scanning system of claim 1, wherein said scanner housing is hand-supportable.

3. The multi-focal zone laser scanning system of claim 1, wherein said scanner housing is countertop-supportable.

4. The multi-focal zone laser scanning system of claim 1, wherein said scanner housing is fixed-type countertop housing.

5. The multi-focal zone laser scanning system of claim 1, wherein said laser scanning beam mechanism produces an X-bar or like scan pattern dynamically focused along said plurality of different predefined focal zones, and generates said analog scan data signal corresponding to the structure of said bar code symbol structure scanned by said scanned laser beam.

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

a scanner housing;

a laser scanning beam mechanism disposed within said scanner housing, for producing laser scanning beam and scanning said laser beam so as to produce a laser scanning pattern that is focused along a plurality of different predefined focal zones, and automatically generating an analog scan data signal corresponding to the structure of a bar code symbol structure scanned by said scanned laser beam;

a scan data signal processor for processing said analog scan data signal, and 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 said analog scan data signal produced while said scanned laser beam scans said bar code symbol structure within said predefined focal zone, and

control circuitry for dynamically switching one of said plurality of pass-band filter structures into operation so that said analog scan data signal produced in response to said laser beam scanning said 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;

a bar code element width measurement processor for measuring in real-time the width of the signal levels in said analog scan data signals, and producing signal level width measurement data representative thereof; and

a data processor for converting said signal level width measurement data into control signals for use by said control circuitry so that one of said plurality of pass-band filter structures is automatically switched into operation so that said analog scan data signal produced in response to said laser beam scanning said 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 zone laser scanning system of claim 6, wherein said scanner housing is hand-supportable.

8. The multi-focal zone laser scanning system of claim 6, wherein said scanner housing is a countertop-supportable.

9. The multi-focal zone laser scanning system of claim 6, wherein said scanner housing is a fixed-type countertop housing.

10. The multi-focal zone laser scanning system of claim 6, wherein said laser scanning beam mechanism produces an X-bar or like scan pattern dynamically focused along said plurality of different predefined focal zones, and generates said analog scan data signal corresponding to the structure of said bar code symbol structure scanned by said scanned laser beam.

11. A laser scanning bar code symbol reading system having a scanning range, comprising:

a laser scanning mechanism for laser scanning bar code symbol elements located within the scanning range of the system, and producing an analog scan data signal in response to the laser scanning of said bar code symbol elements;

a first derivative signal generation circuit for generating a first derivative signal from said analog scan data signal;

a signal conversion circuit responsive to said laser scanning mechanism for converting said analog scan data signal into a corresponding digital scan data signal having binary signal levels corresponding to the bar code symbol elements laser scanned by said laser scanning mechanism;

a time duration measurement circuit for measuring the time duration of the binary signal levels in said digital scan data signal; and

a variable pass-band filter structure for filtering the first derivative signal generated by said first derivative signal generation circuit, said variable pass-band filter structure having variable frequency characteristics that are controlled in a real-time manner by the measured time duration of the binary signal levels in the digital scan data signal produced by said signal conversion circuit in response to laser scanning said bar code symbol elements located within the scanning range of said laser scanning bar code symbol reading system.

12. The laser scanning bar code symbol reading system of claim 11, wherein said time duration measurement circuit comprises an application specific integrated circuit (ASIC) chip that compares real-time measurement of binary signal levels in said digital scan data signal with predetermined time measures of digital scan data signals, stored in a memory device, for bar code symbols having different resolutions that have been laser scanned at different scanning distances from said laser scanning bar code symbol reading system.