Browse Prior Art Database

REFLECTANCE SENSORS FOR COPY QUALITY OPTIMIZATION

IP.com Disclosure Number: IPCOM000027854D
Original Publication Date: 2001-Apr-30
Included in the Prior Art Database: 2004-Apr-09
Document File: 4 page(s) / 152K

Publishing Venue

Xerox Disclosure Journal

Abstract

Disclosed are paper brightness sensors located in each paper tray and original document tray of an electrophotographic printing machine. The sensors measure reflectance of sheets being fed with output signals being used to control the halftone image density to make a copy look like the original or make the contrast of an extended print run appear consistent.

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XEROX DISCLOSURE JOURNAL

              b
Paper Sensor A

REFLECTANCE SENSORS FOR COPY QUALITY OPTIMIZATION
Thomas Acquaviva
Jan Bares

Proposed Classification
U. S. C1. 399/023 Int. C1. G03g 15/00

74 Figure 1

Xerox Disclosure Journal - Vol. 25, No. 2 MarcWApril2001 79

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REFLECTANCE SENSORS FOR COPY QUALITY OPTIMIZATION (Cont'd)

Disclosed are paper brightness sensors located in each paper tray and original document tray of an electrophotographic printing machine. The sensors measure reflectance of sheets being fed with output signals being used to control the halftone image density to make a copy look like the original or make the contrast of an extended print run appear consistent.

Previous methods for improving system performance were accomplished by measuring paper properties and using acquired information to alter machine parameters. One example might be a paper sensor that monitors basis weight so that feed actuators can be adjusted to reduce the occurrence of misfeeds and multifeeds. The sensors disclosed herein instead monitor the reflectance of "white" paper in the document scanner and in each paper feed tray. Knowing the ratio of the two reflectances, the image density can be adjusted on a copy-by-copy basis to optimize the perceived image contrast or density range. Thus, a sensor and algorithm that adjust image density by varying the number of dots and or size of a dot pattern through image processing is disclosed.

As shown in Fig. 1, the method of achieving copy quality optimization places an optical sensor 10 (original paper sensor A) just downstream of the feedhead in a paper feeder (not shown) and aimed at sheet 12 as it feeds. A calibrated white backing 14 ensures uniformity of the reflected light. The sensor is of the type shown in Fig. 1 and consists of a light source such as a Light Emitting Diode (LED 16), which directs a light beam perpendicular to the paper surface. Sensor 10 receives the reflected light illustrated by arrows 18. A similar sensor (paper sensor B) placed in the document feeder of the electronic scanner (both not shown) looks at the document as it is fed. A similar white backing would also be used.

As copy sheets feed, referring to Fig. 2, sensor signals 20 and 22 from the original paper sensor A (sensor 10 in Fig. 1) and copy paper sensor B pass through sample and hold circuits 24 and 26 to record the highest reflectance level and compensate for timing differences. A simple divider circuit 28 monitors the ratio of the signals coming from the original paper and the copy paper. If the reflected light from the original is greater than that reflected off the copy paper, then the of ratio A/B on output co...