Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1993-02-26
1994-04-19
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250214R, 346140R, G01D 1516, G01N 1506
Patent
active
053048148
ABSTRACT:
A sensor circuit and method for detecting the presence of a substance having a flow that can be turned on and off, such as ink in an ink ejecting print head, has means for turning on and off the flow of the substance at a predetermined frequency. An optical sensor has a light path that is at least partially interrupted by the substance when the flow is turned on. The optical sensor is biased to operate within a range in which the sensor produces an output, even though the light path is only partially interrupted by the substance. An integrator integrates the output of the sensor, and a high gain amplifier amplifies the integrated signal to provide a sensor circuit output signal. When the substance at least partially interrupts the light path, the integrated output signal indicates its presence. The circuit is preferably used to control a heater of a thermal ink ejecting print head by adjusting the power to the heater to assure its operation with a power applied above the power threshold at which ink ejection begins.
REFERENCES:
patent: 4281332 (1981-07-01), Horike
patent: 4933684 (1990-06-01), Tasaki et al.
Allen Stephone
Nelms David C.
Xerox Corporation
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