Browse Prior Art Database

Variable Threshold Document Sensing

IP.com Disclosure Number: IPCOM000108778D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Fortenberry, RS: AUTHOR [+4]

Abstract

This article discloses a design that assures high reliability in an optical sensor used to sense the presence of a document inserted into a printer. The concepts disclosed could apply to non-optical sensors that provide an analog output and could also be used in applications other than paper sensing.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Variable Threshold Document Sensing

       This article discloses a design that assures high
reliability in an optical sensor used to sense the presence of a
document inserted into a printer.  The concepts disclosed could apply
to non-optical sensors that provide an analog output and could also
be used in applications other than paper sensing.

      The sensor includes a light-emitting diode (LED) and detector
mounted side-by-side, an analog-to-digital (A/D) converter that
digitizes the output of the detector circuit, and a microprocessor
algorithm that analyzes the A/D signal and flags the presence of a
document.  The A/D converter and algorithm enable an optical sensor
to function over a broader range of operating conditions than is
possible with the fixed threshold circuitry commonly seen in such
applications.  The extended operation range is important in a
printer, accounting for:
 .   The presence of paper dust, which falls on the face of the
sensor and on the background of the paper path, creating a false
signal.
 .   Continuous, long-lifetime service of the printer, which leads to
LED degradation.
 .   The variation in reflectivity of common documents that must be
sensed.
 .   Variation in the power supply voltage that drives the sensor.

      To achieve the improved operating range, the thresholding
algorithm maintains a continuously varying threshold level.  Starting
from a state where no document is present:
 .   The sensor voltage is read and compared to the threshold level.
 .   If greater than the threshold level, a document is present and
the printer responds appropriately.
 .   If less than...