DEVELOPABILITY SENSOR HAVING AMBIENT LIGHT COMPENSATION

Publishing Venue

Xerox Disclosure Journal

Abstract

Disclosed is an improvement upon a developability sensor to provide stability of the sensor in the presence of stray or ambient light. A diffuse reflection based developability sensor is used to monitor the developed toner mass per unit of area on a control patch that is part of a xerographic process controls development stabilization system. The disclosed method uses means to compensate a light sensitive detector for measurement errors arising from ambient light present in the measuring environment. The method also uses means to measure and store the sensor response to the ambient light. Stored information is later used during the measurement of the sample to derive an accurate sensor signal when using the sensor illumination source.

XEROX DISCLOSURE JOURNAL

DEVELOPABILITY SENSOR HAVING AMBIENT LIGHT COMPENSATION
Michael A. Butler
John Buranicz
Darrel R. Rathbun

Proposed Classification

US. C1.355/208 Int. C1. G03g 21/00

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 LED DRIVE 8

^OSCILLATOR 8 CIRCUIT

Q' LIGHT S/H GATE -

'LEDPULSE

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I

-

Q DARK S/H GATE I

9

7

3

 SAMPLE AND HOLD

CORRECTED SIGNAL

I

DETECT OR

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NG. I

XEROX DISCLOSURE JOURNAL - Vol. 18, NO. 4 July/August 1993 389

DEVELOPABILITY SENSOR HAVING AMBIENT LIGHT COMPENSATION (Cont'd)

Q

- _Q

LED PULSE

DETECTOR SIGNAL

 LIGHT S/H GATE

 DARK S/H GATE

CORRECTED SIGNAL

FIG. 2

390 XEROX DISCLOSURE JOURNAL - VO~. 18, NO. 4 July/August 1993

DEVELOPABILITY SENSOR HAVING AMBIENT LIGHT COMPENSATION (Cont'd)

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7.8.9.12

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XEROX DISCLOSURE JOURNAL - VO~. 18, NO. 4 July/August 1993 391

DEVELOPABILITY SENSOR HAVING AMBIENT LIGHT COMPENSATION (Cont'd)

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P16

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FIG 3

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392 XEROX DISCLOSURE JOURNAL - VO~. 18, NO. 4 July/August 1993

DEVELOPABILITY SENSOR HAVING AMBIENT LIGHT COMPENSATION (Cont'd)

Disclosed is an improvement upon a developability sensor to provide stability of the sensor in the presence of stray or ambient light. A diffuse reflection based developability sensor is used to monitor the developed toner mass per unit of area on a control patch that is part of a xerographic process controls development stabilization system. The disclosed method uses means to compensate a light sensitive detector for measurement errors arising from ambient light present in the measuring environment. The method also uses means to measure and store the sensor response to the ambient light. Stored information is later used during the measurement of the sample to derive an accurate sensor signal when using the sensor illumination source.

A fundamental problem with light detection schemes is their intrinsic sensitivity to ambient light, either of continuous or fluctuating intensity. The disclosed method eliminates ambient light as a source of measurement error, and in particular the method is adapted to permit operation of the sensor next to a pretransfer erase lamp, as well as to permit operation of the sensor on a laboratory fixture in the presence of fluorescent lighting. The problem of ambient light is, however, a rather general one for the developability sensors that are required to span a large range of light spectra. Current techniques that result in deficiencies have'relied upon optical filters to exclude light frequencies that do not correspond to the illumination source frequencies. First, optical filters do not have a transmissivity of zero in the un...