Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Patent
1997-11-10
1999-11-16
Le, N.
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
347236, 347249, 358443, H04N 1405
Patent
active
059866870
ABSTRACT:
The optical intensity of laser light from a laser diode of a laser scanning apparatus having a polygonal mirror is detected with a monitoring photodiode. The detected output is delivered to a first switching end of a selector. The optical intensity of laser light reflected from the polygonal mirror is detected with a photosensor and the detection output is delivered to a second switching end of the selector. The selector selects either one of the switching ends in accordance with the timing of a laser scan. The associated detection signal is fed to a comparator, where it is compared with a reference voltage to produce a comparison voltage, which in turn is fed to a laser drive circuit to control the emission output of the laser diode. Despite variation in the reflectance of laser light from each reflecting surface of the polygonal mirror, a constant optical intensity is obtained on the basis of the reference voltage. In addition, even if the photosensor fails to detect the laser light, laser power control is ensured by the monitoring of the photodiode to prevent the laser diode from being overdriven.
REFERENCES:
patent: 4201944 (1980-05-01), Beunders
patent: 4888647 (1989-12-01), Wada
patent: 5001341 (1991-03-01), Negishi
patent: 5136160 (1992-08-01), Nakane et al.
patent: 5264871 (1993-11-01), Tsukada
patent: 5461414 (1995-10-01), Honda et al.
Asahi Kogaku Kogyo Kabushiki Kaisha
Le N.
Pham Hai C.
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