Bar code symbol reader with modulation enhancement
First Claim
1. A system for reading indicia having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising:
- (a) means for directing light from a source of light to the indicia for reflection therefrom;
(b) means for scanning the indicia along a scan direction with a sampling aperture whose dimension along the scan direction is larger than the width of at least one of the narrow elements;
(c) detector means for detecting light of variable intensity reflected off the indicia along the scan direction, and for generating a modulation-degraded, analog electrical signal having high frequency components of low amplitudes corresponding to the narrow elements, and low frequency components of higher amplitudes corresponding to the wider elements; and
(d) enhancement means for increasing the low amplitudes of the high frequency components, and for converting the modulation-degraded signal to a modulation-enhanced, analog electrical signal having low and high frequency components whose respective low and higher amplitudes are closer in magnitude to each other as considered with respect to the low and higher amplitudes of the modulation-degraded, analog electrical signal;
whereinthe enhancement means includes sensor means for sensing a system characteristic and a filter circuit having a gain versus frequency transmission characteristic such that the high frequency components are amplified to a greater extent than the low frequency components of the modulation-degraded, analog electrical signal, the sensor means varying the transmission characteristic as a function of the sensed system characteristic.
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Accused Products
Abstract
The depth of modulation of an analog electrical signal generated by a photodetector during scanning of a bar code symbol in the field of bar code scanning is enhanced under circumstances where the modulation of the analog signal has been degraded, for example, by an oversized sampling aperture in relation to the widths of the symbol elements. The analog signal has high frequency components whose low amplitudes are increased in magnitude prior to being conducted to a digitizer. The effect of noise introduced during reading of the bar code is cancelled by comparing in the comparator, the modulation-enhanced analog signal with the second derivative signal derived from the modulation-degraded unenhanced analog signal. The output of the comparator is a digital output signal having a logical level dependent on the amplitude of the enhanced analog signal at each zero crossing of the second derivative signal. The digital output signal is a closer representation of the code read by the scanner.
75 Citations
15 Claims
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1. A system for reading indicia having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising:
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(a) means for directing light from a source of light to the indicia for reflection therefrom; (b) means for scanning the indicia along a scan direction with a sampling aperture whose dimension along the scan direction is larger than the width of at least one of the narrow elements; (c) detector means for detecting light of variable intensity reflected off the indicia along the scan direction, and for generating a modulation-degraded, analog electrical signal having high frequency components of low amplitudes corresponding to the narrow elements, and low frequency components of higher amplitudes corresponding to the wider elements; and (d) enhancement means for increasing the low amplitudes of the high frequency components, and for converting the modulation-degraded signal to a modulation-enhanced, analog electrical signal having low and high frequency components whose respective low and higher amplitudes are closer in magnitude to each other as considered with respect to the low and higher amplitudes of the modulation-degraded, analog electrical signal;
whereinthe enhancement means includes sensor means for sensing a system characteristic and a filter circuit having a gain versus frequency transmission characteristic such that the high frequency components are amplified to a greater extent than the low frequency components of the modulation-degraded, analog electrical signal, the sensor means varying the transmission characteristic as a function of the sensed system characteristic. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of reading indicia having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising the steps of:
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(a) directing light from a source of light to the indicia for reflection therefrom; (b) scanning the indicia along a scan direction with a sampling aperture whose dimension along the scan direction is larger than the width of at least one of the narrow elements; (c) detecting light of variable intensity reflected off the indicia along the scan direction, and generating a modulation-degraded, analog electrical signal having high frequency components of low amplitudes corresponding to the narrow elements, and low frequency components of higher amplitudes corresponding to the wider elements; and (d) increasing the low amplitudes of the high frequency components, and for converting the modulation-degraded signal to a modulation-enhanced, analog electrical signal having low and high frequency components whose respective low and higher amplitudes are closer in magnitude to each other as considered with respect to the low and higher amplitudes of the modulation-degraded, analog electrical signal;
whereinthe step of increasing includes amplifying the high frequncy components to a greater extent than the low frequency components of the modulation-degraded, analog electrical signal, sensing the frequency of the modulation-degraded signal, and amplifying the high frequency components as a function of the sensed frequency.
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14. A method of reading indicia having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising the steps of:
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(a) directing light from a source of light to the indicia for reflection therefrom; (b) scanning the indicia along a scan direction with a sampling aperture whose dimension along the scan direction is larger than the width of at least one of the narrow elements; (c) detecting light of variable intensity reflected off the indicia along the scan direction, and generating a modulation-degraded, analog electrical signal having high frequency components of low amplitudes corresponding to the narrow elements, and low frequency components of higher amplitudes corresponding to the wider elements; and (d) increasing the low amplitudes of the high frequency components, and for converting the modulation-degraded signal to a modulation-enhanced, analog electrical signal having low and high frequency components whose respective low and higher amplitudes are closer in magnitude to each other as considered with respect to the low and higher amplitudes of the modulation-degraded, analog electrical signal;
whereinthe step of increasing includes amplifying the high frequency components to a greater extent than the low frequency components of the modulation-degraded, analog electrical signal, sensing the ambient temperature, and amplifying the high frequency components as a function of the sensed temperature.
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15. A method of reading indicia having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising the steps of:
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(a) directing light from a source of light to the indicia for reflection therefrom; (b) scanning the indicia along a scan direction with a sampling aperture whose dimension along the scan direction is larger than the width of at least one of the narrow elements; (c) detecting light of variable intensity reflected off the indicia along the scan direction, and generating a modulation-degraded, analog electrical signal having high frequency components of low amplitudes corresponding to the narrow elements, and low frequency components of higher amplitudes corresponding to the wider elements; and (d) increasing the low amplitudes of the high frequency components, and for converting the modulation-degraded signal to a modulation-enhanced, analog electrical signal having low and high frequency components whose respective low and higher amplitudes are closer in magnitude to each other as considered with respect to the low and higher amplitudes of the modulation-degraded, analog electrical signal;
whereinthe step of increasing includes amplifying the high frequency components to a greater extent than the low frequency components of the modulation-degraded, analog electrical signal, sensing a distance between the indicia and a scanning head, and amplifying the high frequency components as a function of the sensed distance.
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Specification