Background compensating bar code readers
First Claim
1. Apparatus for reading a luminescent bar code on a background surface whose reflectance may vary over the coded area, comprisingmeans for providing light to scan, and to excite luminescence in, the bar code,means for providing light to scan, and to reflect without luminescence from the background surface of, the bar code,means responsive to the reflected nonluminescent light for providing a first signal.means responsive to the luminescence for providing a second signal, andmeans responsive to the first and second signals for providing an output that is substantially independent of background reflectance in the coded area.
1 Assignment
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Accused Products
Abstract
Methods and apparatus for reading a luminescent and substantially transparent bar code 1 on a background surface 2 whose reflectance may vary over the coded area. Light 7 scans (70), and excites luminescence 8 in, the bar code 1. The light 7 also reflects (9) without luminescence from the background surface 2 of the bar code 1. A first electrical or optical signal 11 is provided (4) responsive to the reflected nonluminescent light 9, and a second electrical or optical signal 10 is provided (4) responsive to the luminescent 8. Typically the first signal 11 is processed (5) to provide a third signal 31 that varies with background reflectance substantially as does the second signal 10; and the second and third signals 10, 31 are combined (5) to provide a fourth signal 12 that is substantially independent of background reflectance in the coded area, and which is decoded (6) to provide the desired reading.
201 Citations
27 Claims
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1. Apparatus for reading a luminescent bar code on a background surface whose reflectance may vary over the coded area, comprising
means for providing light to scan, and to excite luminescence in, the bar code, means for providing light to scan, and to reflect without luminescence from the background surface of, the bar code, means responsive to the reflected nonluminescent light for providing a first signal. means responsive to the luminescence for providing a second signal, and means responsive to the first and second signals for providing an output that is substantially independent of background reflectance in the coded area.
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25. A method for reading a luminescent bar code on a background surface whose reflectance may vary over the coded area, comprising
providing a beam of light focused to a small area and containing at least one predominant frequency band, scanning the beam across the bar code, selectively collecting reflected nonluminescent light in a first frequency band, selectively collecting light in a second frequency band predominantly resulting from luminescence of the bar code, converting the collected light in the first frequency band into a first signal responsive to the reflectance of the background surface, converting the collected light in the second frequency band into a second signal responsive to the amount of luminescent light. modifying the first signal to provide a third signal that varies with background reflectance substantially as does the second signal. combining the second and third signals to provide a fourth signal of substantially constant amplitude and substantially independent of the local background reflectance under the luminescent material of the bar code, and decoding the information in the fourth signal.
Specification