EP0433593A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Bar code symbol readers with edge enhancement
Assignee: Symbol Technologies LLC
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Filing: 1990-10-12
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Granted: —
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Expires: 2010-10-12
Abstract
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 anaiog 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 signai. The output of the comparator is a digital output signai having a logical levei dependent on the amplitude of the enhanced analog signai at each zero crossing of the second derivative signal. The digital output signal is a closer representation of the code read by the scanner.
Inventors
- 👤 Boris Metlitsky
- 👤 Edward Barkan
- 👤 Jerome Swartz
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 00:39
CPC Classifications
G; G06; G06K; G06K7/00; G06K7/10; G06K7/10544; G06K7/10821; G06K7/10851; G06K7/10881
Claims Analysis
Total Claims: 34
Claim 1
Independent Claim
172 words
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 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 resoective 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 signal.
Claim 2
Independent Claim
172 words
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 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 resoective 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 signal.
Claim 3
Dependent Claim
42 words
The system as recited in claim 1, wherein the enhancement means is a filter circuit having a gain versus frequency transmission characteristic wherein the high frequency components are amplified to a greater extent than the low frequency components of the modulation-degraded signal.
Claim 4
Dependent Claim
13 words
The system as recited in claim 2, wherein the transmission characteristic is fixed.
Claim 5
Dependent Claim
40 words
The system as recited in claim 2, wherein the transmission characteristic is variable; and wherein the enhancement means includes sensor means for sensing a system characteristic, and for varying the transmission characteristic as a function of the sensed system characteristic.
Claim 6
Dependent Claim
51 words
The system as recited in claim 4, wherein the sensor means is a system characteristic-to-voltage converter operative for generating an output control voltage proportional to the sensed system characteristic; and wherein the filter circuit is operatively connected to the converter, and has its transmission characteristic varied by the output control voltage.
Claim 7
Dependent Claim
65 words
The system as recited in claim 5, wherein the transmission characteristic has a low gain from a first frequency to a higher second frequency, a high gain from a third frequency to a higher fourth frequency, and an intermediate gain from said second frequency to said third frequency, and wherein the output control voltage shifts at least one of the second, third and fourth frequencies.
Claim 8
Dependent Claim
151 words
The system as recited in claim 6, wherein the filter circuit includes a dual input operational amplifier having an output, one of the inputs of the amplifier being grounded; a first stage including a first resistor and a first capacitor connected in parallel with each other and also connected in parallel across the other input and the output of the amplifier; a second stage including a second resistor and a second capacitor connected in parallel with each other and connected in series with the other input of the amplifier; and a third resistor connected in series with the second stage and the other input of the amplifier; and a control component operatively connected to one of the resistors and the capacitors, said control component having an input control terminal for receiving the output control voltage, and for shifting said at least one frequency as a function of the output control voltage.
Claim 9
Dependent Claim
40 words
The system as recited in claim 7, wherein the control component is a field effect transistor having a gate terminal for receiving the output control voltage, and a pair of output terminals connected in parallel across one of the resistors.
Claim 10
Dependent Claim
43 words
The system as recited in claim 5, wherein the sensor means is a frequency-to-voltage converter operatively connected to the detector means for sensing the frequency of the modulation-degraded signal, and for generating the output control voltage as a function of the sensed frequency.
Claim 11
Dependent Claim
43 words
The system as recited in claim 5, wherein the sensor means is a temperature-to-voltage converter located in the vicinity of the light directing means for sensing the temperature thereof, and for generating the output control voltage as a function of the sensed temperature.
Claim 12
Dependent Claim
43 words
The system as recited in claim 10, wherein the light directing means includes a focusing lens for forming the dimension of the sampling aperture along the scan direction, and wherein the sensor means is located in the circumabient region of the focusing lens.
Claim 13
Dependent Claim
39 words
The system as recited in claim 5, wherein the sensor means is a distance-to-voltage converter for sensing the distance between the system and the indicia, and for generating the output control voltage as a function of the sensed distance.
Claim 14
Dependent Claim
78 words
The system as recited in claim 1, wherein the system is a moving beam laser scanner for reading bar code symbols on a real-time basis; and wherein the light directing means includes means for generating and directing a laser beam to each symbol, and means for optically modifying the laser beam to have a beam spot whose dimension along the scan direction constitutes the sampling aperture; and wherein the scanning means sweeps the beam spot across each symbol.
Claim 15
Dependent Claim
34 words
The system as recited in claim 1, wherein the detector means is a photosensor having a field of view which constitutes the sampling aperture, and wherein the scanning means scans the field of view.
Claim 16
Dependent Claim
97 words
The system as recited in claim 1, wherein the system is a retro-reflective laser scanner for reading bar code symbols on a real-time basis; and wherein the light directing means includes means for generating and directing a laser beam to each symbol, and means for optically modifying the laser beam to form a beam spot in cross-section; and wherein the detector means is a photosensor having a field of view which overlaps the beam spot on each symbol; and wherein the scanning means scans both the laser beam spot and the field of view across each symbol.
Claim 17
Dependent Claim
177 words
A laser scanner for reading bar code symbols having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising: (a) means for directing laser light to each symbol for reflection therefrom; (b) means for scanning each symbol 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 laser light of variable intensity reflected off each symbol 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 signal.
Claim 18
Dependent Claim
177 words
A laser scanner for reading bar code symbols having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising: (a) means for directing laser light to each symbol for reflection therefrom; (b) means for scanning each symbol 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 laser light of variable intensity reflected off each symbol 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 signal.
Claim 19
Independent Claim
163 words
A method of reading indicia having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising the steps of: (a) directing 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 coresponding 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 converting the modulationdegraded 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 modulationdegraded signal.
Claim 20
Independent Claim
163 words
A method of reading indicia having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising the steps of: (a) directing 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 coresponding 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 converting the modulationdegraded 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 modulationdegraded signal.
Claim 21
Dependent Claim
32 words
The method as recited in claim 17, wherein the increasing step is performed by amplifying the high frequency components to a greater extent than the low frequency components of the modulation-degraded signal.
Claim 22
Dependent Claim
34 words
The method as recited in claim 18, wherein the increasing step is performed by sensing the frequency of the modulation-degraded signal, and amplifying the high frequency components as a function of the sensed frequency.
Claim 23
Dependent Claim
30 words
The method as recited in claim 18, wherein the increasing step is performed by sensing ambient temperature, and amplifying the high frequency components as a function of the sensed temperature.
Claim 24
Dependent Claim
33 words
The method as recited in claim 18, wherein the amplifying step is performed by sensing the location of the indicia, and amplifying the high frequency components as a function of the sensed location.
Claim 25
Independent Claim
200 words
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 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) means for detecting light of variable intensity reflected off the indicia along the scan direction, and for generating a modulation-degraded, unenhanced 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) means for increasing the low amplitudes of the high frequency components, and for converting the modulation-degraded unenhanced analog signal to a modulation-enhanced analog signal having low and high frequency components whose respective low and high amplitudes are closer in magnitude to each other as considered with respect to the low and high amplitudes of the modulation-degraded unenhanced analog signal, obtaining a second derivative signal which is the second derivative of the unenhanced analog signal, and comparing the enhanced analog signal and the second derivative signal.
Claim 26
Independent Claim
200 words
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 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) means for detecting light of variable intensity reflected off the indicia along the scan direction, and for generating a modulation-degraded, unenhanced 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) means for increasing the low amplitudes of the high frequency components, and for converting the modulation-degraded unenhanced analog signal to a modulation-enhanced analog signal having low and high frequency components whose respective low and high amplitudes are closer in magnitude to each other as considered with respect to the low and high amplitudes of the modulation-degraded unenhanced analog signal, obtaining a second derivative signal which is the second derivative of the unenhanced analog signal, and comparing the enhanced analog signal and the second derivative signal.
Claim 27
Dependent Claim
129 words
The system as recited in claim 22, wherein the means (d) comprises a filter circuit and a comparator circuit, the filter circuit having two signal paths, the first path through which the unenhanced analog signal is differentiated by a first differentiator to produce a first derivative signal, the first derivative signal is further differentiated by a second differentiator to produce the second derivative signai, the second path through which the unenhanced analog signal is converted into an enhanced analog signal in the filter, the second derivative signal and the enhanced analog signal are compared by the comparator circuit for generating a digitized output signal having a logical level dependent on the amplitude of the enhanced analog signal at the time of each zero crossing of the second derivative signal.
Claim 28
Dependent Claim
199 words
A laser scanner for reading bar code symbols having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising: (a) means for directing laser light to each symbol for reflection therefrom; (b) means for scanning each symbol along a scan direction with a sampling aperture whose dimension along the scan direction is larger than the widths of at least one of the narrow elements, (c) means for detecting laser light of variable intensity reflected off each symbol along the scan direction, and for generating a modulation-degraded, unenhanced 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) means for increasing the low amplitudes of the high frequency components, and for converting the modulation-degradee, unenhanced analog-signal to a modulation-enhanced analog signal having low and high frequency components whose respective low and high amplitudes are closer in magnitude to each other as considered with respect to the low and high amplitudes of the modulation-degraded, unenhanced analog signal, and comparing the enhanced analog signal with a second derivative signal which is a second derivative of the unenhanced analog signal.
Claim 29
Dependent Claim
199 words
A laser scanner for reading bar code symbols having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising: (a) means for directing laser light to each symbol for reflection therefrom; (b) means for scanning each symbol along a scan direction with a sampling aperture whose dimension along the scan direction is larger than the widths of at least one of the narrow elements, (c) means for detecting laser light of variable intensity reflected off each symbol along the scan direction, and for generating a modulation-degraded, unenhanced 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) means for increasing the low amplitudes of the high frequency components, and for converting the modulation-degradee, unenhanced analog-signal to a modulation-enhanced analog signal having low and high frequency components whose respective low and high amplitudes are closer in magnitude to each other as considered with respect to the low and high amplitudes of the modulation-degraded, unenhanced analog signal, and comparing the enhanced analog signal with a second derivative signal which is a second derivative of the unenhanced analog signal.
Claim 30
Dependent Claim
128 words
The system as recited in claim 24, wherein the means (d) comprises a filter circuit and a comparator circuit, the filter circuit having two signal paths, the first path having a first differentiator in which the unenhanced analog signal is differentiated to produce a first derivative signal and a second differentiator in which the first derivative signal is further differentiated to produce the second derivative signal, the second path including an enhancement circuit through which the unenhanced analog signal is converted into an enhanced analog signal, said comparator circuit comparing the second derivative and enhanced analog signals for generating a digitized output signal having a logical level dependent on the amplitude of the enhanced analog signal at the time of each zero crossing of the second derivative signal.
Claim 31
Independent Claim
226 words
A method of operating a scanner for reading indicia having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising the steps of: directing light to the indicia for reflection therefrom; 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; detecting light of variable intensity reflected off the indicia along the scan direction; generating a modulation-degraded unenhanced 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; increasing the amplitudes of the high frequency components; converting the modulation-degraded unenhanced signal to a modulation-enhanced analog signal having low and high frequency components whose respective low and high amplitudes are closer in magnitude to each other as considered with respect to the low and high amplitudes of the modulation-degraded unenhanced analog signal; differentiating the unenhanced analog signal to form a first-derivative signal, differentiating the first derivative signal, to form a second derivative signal having zero crossings, comparing the modulation-enhanced analog signal with the second derivative signal; and, in response, generating a digitized output signal having a logical level dependent on the amplitude of the enhanced analog signal at each zero crossing of the second derivative signal.
Claim 32
Independent Claim
226 words
A method of operating a scanner for reading indicia having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising the steps of: directing light to the indicia for reflection therefrom; 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; detecting light of variable intensity reflected off the indicia along the scan direction; generating a modulation-degraded unenhanced 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; increasing the amplitudes of the high frequency components; converting the modulation-degraded unenhanced signal to a modulation-enhanced analog signal having low and high frequency components whose respective low and high amplitudes are closer in magnitude to each other as considered with respect to the low and high amplitudes of the modulation-degraded unenhanced analog signal; differentiating the unenhanced analog signal to form a first-derivative signal, differentiating the first derivative signal, to form a second derivative signal having zero crossings, comparing the modulation-enhanced analog signal with the second derivative signal; and, in response, generating a digitized output signal having a logical level dependent on the amplitude of the enhanced analog signal at each zero crossing of the second derivative signal.
Claim 33
Independent Claim
235 words
A method of operating a laser scanner for reading bar cooe symbols having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising the steps of; directing laser light to each symbol for reflection therefrom; scanning each symbol along a scan direction with a sampling aperture whose dimension along the scan direction is larger than the widths of at least one of the narrow elements; detecting iaser light of variable intensity reflected off each symbol along the scan direction; generating a modulation-degraded unenhanced 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; increasing the amplitudes of the higher frequency components; converting the modulation degraded unenhanced analog signal to a modulation-enhanced analog signal having low and high frequency components whose respective low and high amplitudes are closer in magnitude to each other as considered with respect to the low and high amplitudes of the modulation-degraded unenhanced analog signal; differentiating the unenhanced analog signal to form a first derivative signal; differentiating the first derivative signal, to form a second derivative signal having zero crossings; comparing the modulation-enhanced analog signal with the second derivative signal; and generating a digitized output signal having a logical level dependent on the amplitude of the enhanced analog signal at the time of each zero crossing of the second derivative signal.
Claim 34
Independent Claim
235 words
A method of operating a laser scanner for reading bar cooe symbols having spatially adjacent elements of narrow and wider widths and of different light reflectivity, comprising the steps of; directing laser light to each symbol for reflection therefrom; scanning each symbol along a scan direction with a sampling aperture whose dimension along the scan direction is larger than the widths of at least one of the narrow elements; detecting iaser light of variable intensity reflected off each symbol along the scan direction; generating a modulation-degraded unenhanced 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; increasing the amplitudes of the higher frequency components; converting the modulation degraded unenhanced analog signal to a modulation-enhanced analog signal having low and high frequency components whose respective low and high amplitudes are closer in magnitude to each other as considered with respect to the low and high amplitudes of the modulation-degraded unenhanced analog signal; differentiating the unenhanced analog signal to form a first derivative signal; differentiating the first derivative signal, to form a second derivative signal having zero crossings; comparing the modulation-enhanced analog signal with the second derivative signal; and generating a digitized output signal having a logical level dependent on the amplitude of the enhanced analog signal at the time of each zero crossing of the second derivative signal.
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