Light emitting diode scanner
First Claim
Patent Images
1. A system for reading symbols, comprising:
- (a) light source means for generating a light beam;
(b) focusing means for focusing the light beam to a scan spot of predetermined area at scan plane and for positioning the scan spot on a symbol located in a working distance range in the vicinity of the scan plane;
(c) scanning means for sweeping the scan spot across the symbol in a scan, thereby reflecting off the symbol reflected light, at least a returning portion of which travels away from the symbol back in the direction of the light source, the returning portion of the reflected light having a variable intensity over the scan;
(d) a sensor for viewing and detecting the variable intensity of the returning portion of the reflected light over a field of view, and for generating an electrical signal indicative of the detected variable light intensity;
(e) a signal processor for processing the electrical signal and generating therefrom data descriptive of the symbol, the signal processor including(i) a converter for receiving the electrical signal and developing an amplified, filtered, and inverted first voltage signal relative to the electrical signal,(ii) a delay circuit for developing a delayed version of the first voltage signal(iii) a peak-locating comparator for receiving the first voltage signal and the delayed version of the first voltage signal, the peak locating comparator changing state whenever the first voltage signal and the delayed version of the first voltage signal are equal, and the peak-locating comparator generating an output,(iv) a gating comparator for receiving the first voltage signal, for changing state on pulses of the first voltage signal that are greater than positive and negative noise thresholds, and for generating an output, and(v) a latch comparator for receiving the outputs of the peak-locating comparator and the gating comparator, the latch comparator changing state only if the gating comparator has changed state since the last change of state of the peak-locating comparator, the latch comparator providing data descriptive of the symbol; and
(f) imaging means for imaging a viewing window of the sensor means, said viewing window having an area smaller than that of the scan spot, and for positioning the viewing window at a viewing plane that is spaced away from the scan plane.
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Abstract
A portable scanning head emits and receives light from a light emitting diode to read symbols, such as bar-code symbols. The optics within the scanner are operative for focusing a light beam and the view of a light sensor in different planes exteriorly of a scanner housing. Imaging means are provided in the unit for imaging a viewing window. The viewing window has an area smaller than that of the scan spot. The system can employ an LED as a light source and tolerate the relatively large-sized (on the order of millimeters) scan spot without sacrificing reading performance since the photodiode "sees" only that portion of the scan spot visible through the viewing window.
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Citations
21 Claims
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1. A system for reading symbols, comprising:
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(a) light source means for generating a light beam; (b) focusing means for focusing the light beam to a scan spot of predetermined area at scan plane and for positioning the scan spot on a symbol located in a working distance range in the vicinity of the scan plane; (c) scanning means for sweeping the scan spot across the symbol in a scan, thereby reflecting off the symbol reflected light, at least a returning portion of which travels away from the symbol back in the direction of the light source, the returning portion of the reflected light having a variable intensity over the scan; (d) a sensor for viewing and detecting the variable intensity of the returning portion of the reflected light over a field of view, and for generating an electrical signal indicative of the detected variable light intensity; (e) a signal processor for processing the electrical signal and generating therefrom data descriptive of the symbol, the signal processor including (i) a converter for receiving the electrical signal and developing an amplified, filtered, and inverted first voltage signal relative to the electrical signal, (ii) a delay circuit for developing a delayed version of the first voltage signal (iii) a peak-locating comparator for receiving the first voltage signal and the delayed version of the first voltage signal, the peak locating comparator changing state whenever the first voltage signal and the delayed version of the first voltage signal are equal, and the peak-locating comparator generating an output, (iv) a gating comparator for receiving the first voltage signal, for changing state on pulses of the first voltage signal that are greater than positive and negative noise thresholds, and for generating an output, and (v) a latch comparator for receiving the outputs of the peak-locating comparator and the gating comparator, the latch comparator changing state only if the gating comparator has changed state since the last change of state of the peak-locating comparator, the latch comparator providing data descriptive of the symbol; and (f) imaging means for imaging a viewing window of the sensor means, said viewing window having an area smaller than that of the scan spot, and for positioning the viewing window at a viewing plane that is spaced away from the scan plane. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of reading symbols, comprising the steps of:
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(a) generating a light beam; (b) focusing the light beam to a scan spot of predetermined area at a scan plane, the scan spot being positioned on a symbol located in a working distance range in the vicinity of the scan plane; (c) sweeping the scan spot across the symbol in a scan, at least a returning portion of light being reflected back from the symbol, said returning portion of the reflected light having a variable intensity over the scan; (d) viewing and detecting the variable intensity of said returning portion of the reflected light over a field of view by sensor means, and generating an electrical signal indicative of the detected variable light intensity; (e) processing the electrical signal and generating therefrom data representative of the symbol, the step of processing including (i) converting the electrical signal into an amplified, filtered, and inverted first voltage relative to the electrical signal, (ii) developing a delayed version of the first voltage signal, (iii) comparing the first voltage signal and the delayed version of the first voltage signal in a peak-locating comparator, the peak locating comparator changing state when the first voltage signal and the delayed version of the first voltage signal are equal, (iv) receiving the first voltage signal in a gating comparator, the gating comparator changing state when the first voltage signal exceeds positive and negative noise thresholds, and (v) receiving the outputs of the peak-locating comparator and gating comparator, the latch comparator changing state only if the gating comparator has changed state since the last change of state of the peak-locating comparator, the latch comparator providing data descriptive of the symbol; and (f) imaging a viewing window of the sensor means, the viewing window having an area much smaller than that of the scan spot, and positioning the viewing window at a viewing plane that is spaced away from the scan plane. - View Dependent Claims (18, 19, 20, 21)
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Specification