Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1999-06-09
2001-08-28
Frech, Karl (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S454000
Reexamination Certificate
active
06279829
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to reducing bandwidth limited noise in an optical scanner; in particular, in a bar code scanner.
2. Description of the Related Art
U.S. Pat. No. 5,852,286, which issued to Ed Coleman, and which is assigned to PSC Inc., and which is incorporated in its entirety herein by reference, discloses a system and method for reducing bandwidth limited noise in a bar code scanning system.
FIGS. 1 through 10
provide details of such a system and method. In such a system and method, a duty cycle of a laser light source is controlled such that it repeatedly is “on” for a certain period of time, and then “off” for a certain period of time. Furthermore, positive and negative gains of a demodulator circuit at a receive side are controlled in accordance with the duty cycle. As a result, the elements of a received signal that are contributed by the ambient light are substantially canceled out.
Thus, the system and method described above reduces bandwidth limited noise by modulating the light and then synchronously controlling the demodulation in the signal processing of the photodetector signal. Also, the duty cycle of the pulsing can be varied, along with the gains in the demodulation portion.
While the system and method described above is useful for reducing the noise caused by ambient light, such a system and method may not be so useful when other optical scanners are utilized in a same environment, for systems that do not operate in a pulsed manner, or for systems operating in an environment where the ambient light characteristics are unknown or varying.
SUMMARY OF THE INVENTION
An object of the invention is to provide a system and method for optical scanning of an object, using a multiple scanner system in which a laser pulser of a first system operates at a first frequency and where a laser pulser of a second system operates at a second frequency different from the first frequency.
Another object of the invention is to provide a single scanner with multiple light sources, where the single scanner includes a first light source and a first laser pulser, and a second light source that may contain a second laser pulser. The single scanner has one photodetector for receiving light from the first and second light sources. The first and second pursers operate and a rate f
1
and a rate f
2
, respectively, where f
1
is not equal to f
2
, and f
2
may equal zero Hertz, corresponding to a non-pulsed source.
Yet another object of the invention is to provide a single scanner with a single light source, and where the modulation frequency of the laser pulser can be adjusted via hardware or software. The adjusting of the modulation frequency would also result in a commensurate adjustment of a bandwidth of a filter stage in a receive portion of the system. This system works well when noise frequencies are known and unchanging.
Still another object of the invention is to provide a single scanner with a single light source at multiple modulation frequencies, and where the modulation frequency varies in a predetermined manner. The filter stage bandwidth also varies in a corresponding manner. This system works well when noise frequencies are not known or change frequently.
Still yet another object of the invention is to provide a single light source with closed loop control of modulation frequencies, and where the modulation frequency of the laser pulser is varied based on frequency analysis and measurement of the ambient noise signal. The scanner is configured to optimize the modulation frequency to yield an optimal signal-to-noise ratio, and the scanner is configured to respond in real time to changes in the ambient noise frequency.
REFERENCES:
patent: 3774014 (1973-11-01), Berier
patent: 4591242 (1986-05-01), Broockman et al.
patent: 5281800 (1994-01-01), Pelton et al.
patent: 5333045 (1994-07-01), Gusmeroli et al.
patent: 5778016 (1998-07-01), Sucha et al.
patent: 5821978 (1998-10-01), Yamamoto et al.
patent: 5852286 (1998-12-01), Coleman
patent: 6072921 (2000-06-01), Frederick et al.
patent: 6078390 (2000-06-01), Bengtsson
Hems Randall K.
Rudeen Robert W.
Foley & Lardner
Frech Karl
PSC Scanning Inc.
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