Bar code reader with enhanced sensitivity
First Claim
1. A bar code reading system comprising light source means projecting light concentrated in a givenlimited spectral band, first and second light detector means arranged forreceiving light from the light source means after reflection from a bar code, and for supplying respective first and second light responsive outputs,said first and second light detector means providing comparable outputs in response to ambient light, and providing different responses to said given limited spectral band, such that an enhanced sensitivity to the light in said given limited spectral band which is reflected from the bar code is provided by a differential between the first and second light responsive outputs,said first and second light detector means comprising first and second light sensitive means responsive to light transmitted thereto for supplying said respective first and second light responsive outputs, and optical filter means in the path of reflected light from a bar code to the first and second light sensitive means, said optical filter means transmitting a first spectral band substantially including said limited spectral band to said first light sensitive means and transmitting a second spectral band substantially excluding said limited spectral band to said second light sensitive means.
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Accused Products
Abstract
In laser bar code scanners bright sunlight tends to overpower the reflected laser light, drastically reducing the difference between bar code and background signals. In the present bar code reader, a plurality of light detectors are utilized with different spectral response characteristics at the wavelength of the incident laser beam, such that the differential response of the detectors tends to minimize the effect of background illumination. Narrowband optical filters with offset passbands may be used with conventional light sensors. As another example, filters with long wavelength transmission characteristics and offset cutoff wavelengths may be employed if necessary with a neutral density filter to provide balanced responses under broadband illumination.
53 Citations
35 Claims
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1. A bar code reading system comprising light source means projecting light concentrated in a given
limited spectral band, first and second light detector means arranged for receiving light from the light source means after reflection from a bar code, and for supplying respective first and second light responsive outputs, said first and second light detector means providing comparable outputs in response to ambient light, and providing different responses to said given limited spectral band, such that an enhanced sensitivity to the light in said given limited spectral band which is reflected from the bar code is provided by a differential between the first and second light responsive outputs, said first and second light detector means comprising first and second light sensitive means responsive to light transmitted thereto for supplying said respective first and second light responsive outputs, and optical filter means in the path of reflected light from a bar code to the first and second light sensitive means, said optical filter means transmitting a first spectral band substantially including said limited spectral band to said first light sensitive means and transmitting a second spectral band substantially excluding said limited spectral band to said second light sensitive means.
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5. An optical reading system characterized by being relatively insensitive to sunlight, said system comprising
laser light source means scanning a laser beam of a limited spectral band over successive points of a scanning path to produce reflected light of a limited spectral band which occupies a locus of reflected light paths during scanning of the laser beam, and an array of first and second light detectors having respective first and second spectral response characteristics so as to provide essentially comparable outputs in response to sunlight, while the first detectors are differentially sensitive to said limited spectral band, respective pairs of said first and secon light detectors being distributed over said locus of reflected light paths such that a reliable differential measure of the reflected light of the laser beam is provided for each successive scanning point of the laser beam along its scanning path, each pair of said first and second light detectors comprising first and second optical filter means and first and second light sensitive means, said first optical filter means transmitting a first spectral band comprising at least a portion of said limited spectral band to one of said first light sensitive means and said second optical filter means transmitting a second spectral band substantially excluding said limited spectral band to one of said second light sensitive means.
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11. An optical reading system for reading optical information in the presence of broadband ambient light, said system comprising
light source means for illuminating optical information so as to generate a light signal of limited spectral bandwidth representing the optical information, first and second optical sensor means receiving said light signal and generating first and second outputs, respectively, means causing said first and second optical sensor means to provide different spectral response characteristics for said limited spectral bandwidth, but to provide first and second outputs which are substantially balanced in the presence of broadband ambient light alone, and means coupled with said first and second optical sensor means and responsive to the differential between said first and second outputs to provide a sensitive measure of said light signal in the presence of broadband ambient light.
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21. An optical reading system comprising
light source means of limited spectral bandwidth illuminating optical information so as to generate a light signal representing the optical information, and supplying light in a scanning plane intersecting the optical information, and first and second sets of light detector means disposed respectively above and below the scanning plane, and arranged so as to intercept generally equal magnitudes of said light signal.
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25. The method of reading optical information which comprises
illuminating the optical information to produce a light signal representing the optical information, transmitting to a first photosensor means a first spectral distribution including ambient light and the light signal representing the optical information, transmitting to a second photosensor means a second spectral distribution which includes ambient light but results in substantial attenuation of the light signal, and forming an output corresponding to the differential between the outputs from the first and second photosensor means, as a sensitive measure of the optical information in the presence of ambient light.
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32. The method of reading optical information which comprises
illuminting optical information with light of a narrow spectral band so as to produce a light signal representing the optical information, collecting the light transmitted along first and second light paths from the optical information, transmitting light from the first light path to a first optical detector means having a spectral response including said narrow spectral band, transmitting light from the second light path to a second optical detector means having a spectral response such that the narrow spectral band is attenuated by at least fifty percent, and producing an output which is a function of the differential between the outputs of the first and second optical detector means.
Specification