EP0240767A2
Expired / Lapsed
EP
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Digital bar code slot reader
Assignee: HP Inc
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Filing: 1987-03-12
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Granted: —
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Expires: 2007-03-12
Abstract
Abstract A digital bar code slot reader provides low first bar error rates and a wide scan speed range for bar codes on laminated badges and tags, and is also capable of reading bar codes on paper. The reflectance waveform from the bar code is differentiated in order to find the regions of high slope. The differentiated signal is peak detected to find the amplitude of the slope occurring at the initial card edge. This peak detected value is used to generate thresholds to be compared to the differentiated reflectance signal during the rest of the scan. When the slope of the reflectance signal is above the positive threshold or below the negative threshold, a switching signal is produced. To compensate for the lower amplitude output of the differentiator (33) at low scan speeds, one of the amplifiers (34) in the circuit produces a higher gain at low frequencies than at high frequencies.
Inventors
- 👤 Michael Brosnan
- 👤 Ronald Quan
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 02:44
CPC Classifications
G; G06; G06K; G06K7/00; G06K7/10; G06K7/10544; G06K7/10821; G06K7/10851
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
166 words
Apparatus for digitizing a reflectance signal obtained from scanning a bar code, comprising: a differentiator responsive to the reflectance signal from the bar code to produce a first signal proportional to the slope of the reflectance signal; a peak detector responsive to the first signal to produce a second signal proportional to the peak amplitude of the first signal; means for inverting the second signal to produce a third signal; a positive threshold comparator responsive to the first signal and to the second signal to produce a first digital output signal when the amplitude of the first signal goes above the amplitude of the second signal; a negative threshold comparator responsive to the first signal and to the third signal to produce a second digital output signal when the amplitude of the first signal goes below the amplitude of the third signal; and means for combining the first and second digital output signals to produce a third digital output signal corresponding to the input reflectance signal.
Claim 2
Dependent Claim
166 words
Apparatus for digitizing a reflectance signal obtained from scanning a bar code, comprising: a differentiator responsive to the reflectance signal from the bar code to produce a first signal proportional to the slope of the reflectance signal; a peak detector responsive to the first signal to produce a second signal proportional to the peak amplitude of the first signal; means for inverting the second signal to produce a third signal; a positive threshold comparator responsive to the first signal and to the second signal to produce a first digital output signal when the amplitude of the first signal goes above the amplitude of the second signal; a negative threshold comparator responsive to the first signal and to the third signal to produce a second digital output signal when the amplitude of the first signal goes below the amplitude of the third signal; and means for combining the first and second digital output signals to produce a third digital output signal corresponding to the input reflectance signal.
Claim 3
Dependent Claim
36 words
The apparatus of claim 1 further comprising an amplifier connected between the differentiator and the peak detector for amplifying said first signal, said amplifier having higher gain for low frequency signals than for high frequency signals.
Claim 4
Independent Claim
160 words
A method for digitizing a reflectance signal obtained from scanning a bar code, comprising the following steps: differentiating the reflectance signal from the bar code to produce a first signal proportional to the slope of the reflectance signal; peak detecting the first signal to produce a second signal proportional to the peak amplitude of the first signal; inverting the second signal to produce a third signal; comparing the amplitude of the first signal to the amplitude of the second signal and producing a first digital output signal when the amplitude of the first signal goes above the amplitude of the second signal; comparing the amplitude of the first signal to the amplitude of the third signal and producing a second digital output signal when the amplitude of the first signal goes below the amplitude of the third signal; and combining the first and second digital output signals to produce a third digital output signal corresponding to the input reflectance signal.
Claim 5
Independent Claim
160 words
A method for digitizing a reflectance signal obtained from scanning a bar code, comprising the following steps: differentiating the reflectance signal from the bar code to produce a first signal proportional to the slope of the reflectance signal; peak detecting the first signal to produce a second signal proportional to the peak amplitude of the first signal; inverting the second signal to produce a third signal; comparing the amplitude of the first signal to the amplitude of the second signal and producing a first digital output signal when the amplitude of the first signal goes above the amplitude of the second signal; comparing the amplitude of the first signal to the amplitude of the third signal and producing a second digital output signal when the amplitude of the first signal goes below the amplitude of the third signal; and combining the first and second digital output signals to produce a third digital output signal corresponding to the input reflectance signal.
Claim 6
Dependent Claim
41 words
The method of claim 1 further comprising the step of amplifying said first signal before the peak detecting step is performed wherein the amplifying is done by an amplifier having higher gain for low frequency signals than for high frequency signals.
References Cited (Backward Citations)
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