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

• US 7,207,492 B2
• Filed: 05/09/2003
• Issued: 04/24/2007
• 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): Kim; Ahshik
• Application Number:
  US10/435,606
• Publication Number:
  US 20040074968A1
• Time in Patent Office: 1,446 Days
• Field of Search: 235/462.01, 235/462.22, 235/462.23, 235/462.25, 235/462.29, 235/462.14
• US Class Current: 235/462.14
• 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 decoe 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 bar code reading system having multiple focal planes, comprising:

a visible laser diode for generating a laser beam;

a focusing subsystem for varying the focal distance of the laser beam at different focal planes within said system during laser scanning operations;

a laser 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 scan data signal processor having first and second derivative signal band-pass filters and amplifiers, for processing the analog scan data signal and generating a digital scan data signal corresponding to the analog scan data signal, said digital scan data signal having first and second signal levels;

a digitizer circuit for producing digital words representative of the time duration of the first and second signal levels in the digital scan data signal;

a bar code element width measurement processor for real-time measurement of the first and second binary signal levels occurring in the digital scan data signal, as a bar code symbol is scanned at different focal planes within said system, and real-time comparison with predetermined time duration measures stored in a non-volatile 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 at a particular focal plane in said system;

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

a decode processor for processing the digital words produced from said digitizer circuit so as to decode the digital scan data signal and produce symbol character data representative of the corresponding laser-scanned bar code symbol.