MULTI-FOCAL LASER SCANNING BAR CODE SYMBOL READING SYSTEM EMPLOYING A VARIABLE SECOND DERIVATIVE SIGNAL PASS-BAND FILTER STRUCTURE HAVING FREQUENCY CHARACTERISTICS THAT ARE CONTROLLED IN A REAL-TIME MANNER BY DETECTING BAR CODE ELEMENTS IN ANALOG SCAN DATA SIGNALS PRODUCED BY SAID SYSTEM

• US 6,540,139 B1
• Filed: 02/10/2000
• Issued: 04/01/2003
• 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:
  US09/499,530
• Time in Patent Office: 1,146 Days
• Field of Search: 235/462.01, 235/462.16, 235/462.28, 235/472.01
• 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

A scan data signal processor is disclosed for use with a laser scanning system having a plurality of different focal zones within which a laser scanning beam is scanned across one or more bar code symbols and an analog scan data signal is automatically produced. The scan data signal processor comprises a first and second derivative signal generation stages, a second-derivative zero-crossing detector, a real-time bar code element detector, and a control logic circuitry. The first derivative signal generation stage derives a first derivative signal from the analog scan data signal. The second derivative signal generation stage derives a second derivative signal from the first derivative signal. The second-derivative zero-crossing detector detects zero crossings in said second derivative signal. The real-time bar code element detector automatically detects the presence and absence of bar code element data encoded within said analog scan data signal. The control logic circuitry automatically activates the second-derivative zero-crossing detector in response to the detection of the presence of bar code element data encoded within said analog scan data signal, and automatically deactivates the second-derivative zero-crossing detector, in response to the detection of the absence of bar code element data encoded within the analog scan data signal. By virtue of the present invention, it is now possible to enable the detection of zero-crossings occurring in the second derivative of the analog scan data signals only when bar code element data has been detected, indicative that a bar code symbol has been scanned. This results in more accurate generation of digital output signals from the scan data signal processor.

Claims

1. A multi-focal 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; and

a scan data signal processor for receiving and processing said analog scan data signal in response to the scanning of a bar code symbol by said scanned laser beam, said scan data signal processor including

a first derivative signal generation circuit for deriving a first derivative signal from said analog scan data 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 analog scan data 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, and

a bar code element detection circuit for activating and deactivating said second derivative signal zero-crossing detection circuit in response to detecting the absence and presence of bar code element data in said analog scan data signal.

2. The multi-focal laser scanning system of claim 1, wherein said first derivative signal generation circuit comprises

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

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

3. The multi-focal laser scanning system of claim 1, wherein the second derivative signal generation circuit comprises

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

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

4. The multi-focal laser scanning system of claim 1, wherein said second derivative zero-crossing detector comprises a comparator and a high-input/low-output impedance amplifier.

5. The multi-focal laser scanning system 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.

6. The multi-focal laser scanning system of claim 1, wherein said bar code element detection circuit comprises a zero-reference signal generator, an analog signal level shifting circuit, a comparator circuit, and a second-derivative zero-crossing detector enable circuit.

7. A multi-focal 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; and

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

a first derivative signal generation stage for deriving a first derivative signal from said analog scan data signal,

a second derivative signal generation stage for deriving a second derivative signal from said first derivative signal,

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

a real-time bar code element detector for automatically detecting the presence and absence of bar code element data encoded within said analog scan data signal, and

control logic circuitry for automatically activating the second-derivative zero-crossing detector in response to the detection of the presence of bar code element data encoded within said analog scan data signal, and automatically deactivating the second-derivative zero-crossing detector in response to the detection of the absence of bar code element data encoded within said analog scan data signal.

8. A method of scanning bar code symbols comprising the steps of:

(a) producing a laser beam within a plurality of focal zones and scanning said laser beam over a bar code symbol;

(B) producing an analog scan data signal indicative of the intensity of light reflected from said scanned bar code symbol;

(C) generating an analog scan data signal from the scanned bar code symbol;

(D) differentiating said analog scan data signal twice to produce a second derivative signal from said analog scan data signal;

(E) processing said analog scan data signal so as to detect the presence of a bar code element encoded within said analog scan data signal; and

(F) automatically detecting the zero-crossings within said second derivative signal in response to the detection of said bar code element encoded within said analog scan data signal.

9. The method of claim 8, which further comprises after step (F):

(G) automatically deactivating the detection of zero-crossings within said second derivative signal in response to the absence of a bar code element detected within said analog scan data signal.

11. The multi-focal laser scanning system of claim 8 which further comprises:

control circuitry for automatically deactivating the detection of zero-crossings within said second derivative signal in response to the absence of a bar code element detected within said analog scan data signal.

10. A multi-focal 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; and

a scan data signal processor for receiving said analog scan data signal corresponding to a scanned bar code symbol, and processing said analog scan data signal, said scan data signal processor including

differentiation circuitry for differentiating said analog scan data signal twice to produce a second derivative signal from said analog scan data signal,

bar code element detection circuitry for automatically processing said analog scan data signal so as to detect the presence of a bar code element encoded within said analog scan data signal, and

zero-crossing detection circuitry for automatically detecting the zero-crossings within said second derivative signal in response to the detection of each bar code element encoded within said analog scan data signal.

12. A multi-focal 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; and

a scan data signal processor for receiving and processing said analog scan data signal in response to the scanning of the bar code symbol by said laser beam, said scan data signal processor including

a first derivative signal generation circuit for deriving a first derivative signal from said analog scan data 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 analog scan data 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, and

a bar code element detection circuit for activating and deactivating said second derivative signal zero-crossing detection circuit in response to detecting the absence and presence of bar code element data in said analog scan data signal.

13. The multi-focal laser scanning system of claim 12, wherein said first derivative signal generation circuit comprises

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

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

14. The multi-focal laser scanning system of claim 12, wherein the second derivative signal generation circuit comprises

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

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

15. The multi-focal laser scanning system of claim 12, wherein said second derivative zero-crossing detector comprises a comparator and a high-input/low-output impedance amplifier.

16. The multi-focal laser scanning system of claim 12, 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.

17. The multi-focal laser scanning system of claim 12, wherein said bar code element detection circuit comprises a zero-reference signal generator, an analog signal level shifting circuit, a comparator circuit, and a second-derivative zero-crossing detector enable circuit.

18. A multi-focal laser scanning system comprising:

a laser scanning mechanism for producing a laser scanning 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; and

a scan data signal processor for 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 including

an analog scan data preamplification circuit for deriving a preamplified analog scan data signal from said analog scan data signal, said analog scan data preamplification circuit including a plurality of focal-zone controlled scan data signal pass-band filters and amplifiers integrated therewith,

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

a bar code element detection circuit for activating and deactivating said second derivative signal zero-crossing detection circuit in response to detecting the absence and presence of bar code element data in said analog scan data signal.

19. The multi-focal laser scanning system of claim 18, wherein said scan data signal preamplification circuit comprises

a first scan-range controlled scan data signal pass-band filter and amplifier arranged along the first channel (A) of the circuit corresponding to a first scan range of the system, and

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

20. The multi-focal laser scanning system of claim 18, wherein said first derivative signal generation circuit comprises

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

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

21. The multi-focal laser scanning system of claim 18, wherein the second derivative signal generation circuit comprises

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

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