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
First Claim
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.
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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.
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Citations
15 Claims
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1. A laser scanning system comprising:
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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.
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2. A laser scanning system comprising:
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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. - View Dependent Claims (3)
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4. A laser scanning system comprising:
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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. - View Dependent Claims (5)
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6. A multi-focal zone laser scanning system comprising:
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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. - View Dependent Claims (7, 8, 9, 10)
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.
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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.
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11. A multi-focal zone laser scanning system comprising:
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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. - View Dependent Claims (12, 13, 14, 15)
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.
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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.
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Specification