Bar code reading systems having electrical power conservation and laser radiation power limiting means
First Claim
1. In a bar code reader having means for providing pulsed light beam adapted to be incident upon a bar code and which is returned therefrom, and means for providing an electrical bar code signal corresponding to such bar code in response to light returned from said bar code so as to enable decoding thereof, the improvement wherein said producing means comprises a light source having an optical power output (P) vs. electrical current (I) characteristic having a slope efficiency Δ
- P/Δ
I which is non-linear and characterized by an abrupt positive change between an initial region of low slope efficiency and a subsequent region of higher slope efficiency, and means for applying repetitive current pulses to said source to operate said source at a point on said characteristic in said region of higher slope efficiency and with a duty cycle such that the average optical power output is no greater than a certain level which does not exceed radiological health restrictions, and said electrical signal providing means comprises means for removing signal components of said electrical signal at the repetition rate of said current pulses.
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Accused Products
Abstract
Bar code readers using laser diodes conserve electrical power and limit output laser radiation to levels required by governmental regulation (1 milliwatt average power) by utilizing a laser diode having a output optical power vs laser current characteristic which has a slope efficiency (the ratio of the change in power to the change in current, ΔP/ΔI, which is less than 1 in the region where stimulated (laser) emission occurs. The laser is operated with current pulses having a duty cycle less than 100%, and preferably in the range from 50% to 20% in the stimulated emission region of its characteristic, such that the average output laser power does not exceed the level required by government regulations (1 mw) while the laser output during the pulses is greater than 1 mw. Upon detection after reflection or scattering (return of light) from the bar code, the optical signal is photodetected to provide an electrical signal which is envelope detected and components of the signal at the repetition rate of the current pulses are removed, as by filtering. The filtered signal is digitized to provide a digital signal from which the bar code may be decoded.
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Citations
8 Claims
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1. In a bar code reader having means for providing pulsed light beam adapted to be incident upon a bar code and which is returned therefrom, and means for providing an electrical bar code signal corresponding to such bar code in response to light returned from said bar code so as to enable decoding thereof, the improvement wherein said producing means comprises a light source having an optical power output (P) vs. electrical current (I) characteristic having a slope efficiency Δ
- P/Δ
I which is non-linear and characterized by an abrupt positive change between an initial region of low slope efficiency and a subsequent region of higher slope efficiency, and means for applying repetitive current pulses to said source to operate said source at a point on said characteristic in said region of higher slope efficiency and with a duty cycle such that the average optical power output is no greater than a certain level which does not exceed radiological health restrictions, and said electrical signal providing means comprises means for removing signal components of said electrical signal at the repetition rate of said current pulses. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
- P/Δ
Specification