ANALOG SCAN DATA SIGNAL PROCESSOR EMPLOYING A TIME-DOMAIN SUBSTRATE NOISE FILTER FOR NON-LINEARLY PROCESSING ANALOG SCAN DATA SIGNALS AND REDUCING SUBSTRATE NOISE SIGNAL LEVELS THEREIN PRIOR TO FIRST DERIVATIVE SIGNAL GENERATION AND PROCESSING OPERATIONS CARRIED OUT WITHIN SAID ANALOG SCAN DATA SIGNAL PROCESSOR

• US 6,616,040 B1
• Filed: 02/09/2000
• Issued: 09/09/2003
• 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, Check, Frank, Lucera, Mark G.
• Primary Examiner(s): Frech, Karl D.
• Assistant Examiner(s): Kim, Ahshik
• Application Number:
  US09/500,871
• Time in Patent Office: 1,308 Days
• Field of Search: 235/462.01, 235/462.22, 235/462.16, 235/472.01, 235/472.02
• 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 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
• CPC Class Codes: H01M 4/06 : Electrodes for primary cells
• CPC Class Codes: H01M 4/42 : Alloys based on zinc
• CPC Class Codes: H01M 50/109 : of button or coin shape
• CPC Class Codes: H01M 50/1243 : characterised by the internal coating on the casing
• CPC Class Codes: Y02E 60/10 : Energy storage using batteries

Abstract

An analog scan data signal processor is disclosed, in which a time-domain non-linear substrate noise filter is provided before a first derivative signal generation stage so as to produce, as output, a substantially fixed zero-reference signal level whenever a signal level indicative of a bar code substrate is detected, and the signal level analog scan data signal, whenever a signal level indicative of a bar code element is detected. By virtue of the present invention, it is now possible to reduce the level of substrate noise signals within input analog scan data signals, prior to deriving first derivative signals for subsequent signal processing. Consequently, the accuracy of binary signal level detection within such analog scan data signal processors can be significantly improved, thereby improving the performance of bar code symbol reading systems within which such analog scan data signal processors are employed.

Claims

1. A scan data signal processor for use in a laser scanning system, and capable of receiving and processing an analog scan data signal in response to the scanning of a bar code symbol by a laser scanning beam, said scan data signal processor comprising:

a non-linear time-domain substrate noise filtering circuit for processing said analog scan data signal and producing a time-domain filtered signal in which substrate noise in said analog scan data signal is smoothed or filtered out primarily during signal levels corresponding to the scanning of substrates and bar code spaces realized on the substrate, by said laser scanning beam;

a first derivative signal generation circuit for deriving a first derivative signal from said time-domain filtered signal, said first derivative signal generation circuit including a plurality of focal-zone controlled first derivative signal pass-band filters and amplifiers integrated therewith;

a second derivative signal generation circuit for deriving a second derivative signal from said time-domain filtered signal, said second derivative signal generation circuit including a plurality of focal-zone controlled second derivative signal pass-band filters and amplifiers integrated therewith;

a first derivative signal threshold-level generation circuit for generating upper and lower first derivative signal threshold levels for use in determining when said first derivative signal has attained its peak positive and negative values during signal processing operations; and

a binary A/D signal conversion circuit including

a second derivative zero-crossing detector for detecting zero-crossings in said second derivative signal,

a pair of first derivative signal comparators for comparing said first derivative signal with said upper and lower first derivative signal threshold levels so as to detect positive and negative peak values in said first derivative signal, and in response thereto, producing gating signals at the time of occurrence of said detected positive and negative peak values;

a digital output signal generating circuit for receiving detected second derivative zero-crossings provided thereto as input, and producing a digital output signal for subsequent signal processing, and

a second derivative zero-crossing gating circuit, responsive to said gating signals, for gating to said digital output signal generating circuit, only detected second derivative zero-crossings occurring between alternating positive and negative peaks in said first derivative signal detected by said pair of first derivative signal comparators;

wherein said first derivative signal generation circuit further comprises

a first scan-range controlled first derivative signal pass-band filter and amplifier arranged along a first channel (A) of said first derivative signal generation circuit corresponding to a first scan range of said laser scanning system, and

a second scan-range controlled first derivative signal pass-band filter and amplifier arranged along a second channel (B) of said first derivative signal generation circuit corresponding to a second scan range of said laser scanning system.

3. The scan data signal processor of claim 1, wherein said second derivative zero-crossing detector comprises a comparator and a high-input/low-output impedance amplifier (i.e. buffer).

4. The scan data signal processor of claim 1, wherein said digital output signal generating circuit comprises a set/reset latch circuit consisting of four NAND gates arranged to produce as output, said digital output signal corresponding to said analog scan data signal provided as input to said scan data signal processor.

5. The scan data signal processor of claim 1, wherein said non-linear time-domain substrate noise filtering circuit performs, in essence, a first multiplication operation of zero on said analog scan data signal during substrate-related signal levels and a multiplication of unity on said analog scan data signal during bar element related signal levels, whereby the form of said first and second multiplication operations is that of a digital signal having transitions that correspond approximately with the signal level transitions in said analog scan data signal.

6. The scan data signal processor of claim 1, wherein said non-linear time-domain substrate noise filtering circuit comprises an analog signal amplifier, a zero-reference signal generator, a clipping diode, a high-impedance output amplifier, and a buffer amplifier.

7. The scan data signal processor of claim 1, wherein said second derivative zero-crossing gating circuit further comprises

a bar code element detector for automatically activating and deactivating of the second-derivative zero-crossing detector.

8. The scan data signal processor of claim 7, wherein said second-derivative zero-crossing detector is automatically enabled only upon detection of bar code element data encoded within said analog scan data signal, thereby preventing the detection of zero-crossings in said second derivative signal associated with thermal and paper noise present during bar code symbol scanning operations.

9. The scan data signal processor of claim 7, wherein after automatically enabling the detection of zero-crossings in said second derivative signal, said second-derivative zero-crossing detector is automatically disabled after a predetermined time period, and automatically re-enabled after redetection of subsequent bar code element data encoded within the analog scan data signal associated with the same bar code symbol or subsequent bar code symbol.

10. The scan data signal processor of claim 7, wherein said second derivative signal zero-crossing detector is enabled only when digital scan data elements are encoded within the analog scan data input signal, as will occur when at least a portion of a bar code symbol is scanned.

11. The scan data signal processor of claim 7, wherein said second-derivative signal zero-crossing detector employs gating signals which are automatically generated only when bar code element data is detected in the analog scan data input signal, thereby substantially improving the performance of the signal processor in the presence of thermal and paper noise.

2. A scan data signal processor for use in a laser scanning system, and capable of receiving and processing an analog scan data signal in response to the scanning of a bar code symbol by a laser scanning beam, said scan data signal processor comprising:

a non-linear time-domain substrate noise filtering circuit for processing said analog scan data signal and producing a time-domain filtered signal in which substrate noise in said analog scan data signal is smoothed or filtered out primarily during signal levels corresponding to the scanning of substrates and bar code spaces realized on the substrate by said laser scanning beam;

a first derivative signal generation circuit for deriving a first derivative signal from said time-domain filtered signal, said first derivative signal generation circuit including a plurality of focal-zone controlled first derivative signal pass-band filters and amplifiers integrated therewith;

a second derivative signal generation circuit for deriving a second derivative signal from said time-domain filtered signal, said second derivative signal generation circuit including a plurality of focal-zone controlled second derivative signal pass-band filters and amplifiers integrated therewith;

a first derivative signal threshold-level generation circuit for generating upper and lower first derivative signal threshold levels for use in determining when said first derivative signal has attained its peak positive and negative values during signal processing operations; and

a binary A/D signal conversion circuit including

a second derivative zero-crossing detector for detecting zero-crossings in said second derivative signal,

a pair of first derivative signal comparators for comparing said first derivative signal with said upper and lower first derivative signal threshold levels so as to detect positive and negative peak values in said first derivative signal, and in response thereto, producing gating signals at the time of occurrence of said detected positive and negative peak values;

a digital output signal generating circuit for receiving detected second derivative zero-crossings provided thereto as input, and producing a digital output signal for subsequent signal processing, and

a second derivative zero-crossing gating circuit, responsive to said gating signals, for gating to said digital output signal generating circuit, only detected second derivative zero-crossings occurring between alternating positive and negative peaks in said first derivative signal detected by said pair of first derivative signal comparators;

wherein the second derivative signal generation circuit further comprises

a first scan-range controlled second derivative signal pass-band filter and amplifier arranged along a first channel (A) of said second derivative signal generation circuit corresponding to the first scan range of said laser scanning system, and

a second scan-range controlled second derivative signal pass-band filter and amplifier arranged along a second channel (B) of said second derivative signal generation circuit corresponding to the second scan range of said laser scanning system.

12. The scan data signal processor of claim 2, wherein said non-linear time-domain substrate noise filtering circuit performs, in essence, a first multiplication operation of zero on said analog scan data signal during substrate-related signal levels and a multiplication of unity on said analog scan data signal during bar element related signal levels, whereby the form of said first and second multiplication operations is that of a digital signal having transitions that correspond approximately with the signal level transitions in said analog scan data signal.

13. The scan data signal processor of claim 2, wherein said non-linear time-domain substrate noise filtering circuit comprises an analog signal amplifier, a zero-reference signal generator, a clipping diode, a high-impedance output amplifier, and a buffer amplifier.

14. The scan data signal processor of claim 2, wherein said second derivative zero-crossing gating circuit further comprises

a bar code element detector for automatically activating and deactivating of the second-derivative zero-crossing detector.

15. The scan data signal processor of claim 14, wherein said second-derivative zero-crossing detector is automatically enabled only upon detection of bar code element data encoded within said analog scan data signal, thereby preventing the detection of zero-crossings in said second derivative signal associated with thermal and paper noise present during bar code symbol scanning operations.

16. The scan data signal processor of claim 14, wherein after automatically enabling the detection of zero-crossings in said second derivative signal, said second-derivative zero-crossing detector is automatically disabled after a predetermined time period, and automatically re-enabled after redetection of subsequent bar code element data encoded within the analog scan data signal associated with the same bar code symbol or subsequent bar code symbol.

17. The scan data signal processor of claim 14, wherein said second derivative signal zero-crossing detector is enabled only when digital scan data elements are encoded within the analog scan data input signal, as will occur when at least a portion of a bar code symbol is scanned.

18. The scan data signal processor of claim 14, wherein said second-derivative signal zero-crossing detector employs gating signals which are automatically generated only when bar code element data is detected in the analog scan data input signal, thereby substantially improving the performance of the signal processor in the presence of thermal and paper noise.