Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1981-05-11
1984-01-31
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
250236, H01V 4014
Patent
active
044292180
ABSTRACT:
In a radiant energy beam scanning system, a detector, positioned at a predetermined position along the path scanned by the beam, for sensing the center position of the power distribution within the beam and generating a signal indicative thereof. When utilized in an information recording system, the detector is positioned adjacent the start position of the scan path so that the generated indicator signal provides a reference for system timing and synchronization. In such a recording environment, synchronization of the system relative to the center position of power distribution within the beam compensates for variations in beam power level and focus, assuring proper alignment of information recorded on consecutive scan lines. In a preferred form, a diode detector, partially masked in a cross-scan direction, is employed to provide an output signal when irradiated by the scanning beam. The detector output signal is amplified and filtered to provide a reference signal which represents the average total power of the beam. The reference signal is divided in half and supplied to a comparator for comparison with the detector output signal. As the beam crosses the edge of the mask, the detector output decreases rapidly towards zero. When this output signal reaches 50% of the average total power level, the comparator switches, creating the indicator signal.
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Chittum Robert A.
Mason John B.
Nelms David C.
Xerox Corporation
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