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Moire Fringe Method of Assessing Video Display Unit Jitter

IP.com Disclosure Number: IPCOM000108227D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 116K

Publishing Venue

IBM

Related People

Beanlands, P: AUTHOR [+3]

Abstract

A Moire Fringe technique allows video display units (VDUs) on production lines to be assessed for jitter by line operators. Quantitive measurements permit data gathering for quality improvement.

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Moire Fringe Method of Assessing Video Display Unit Jitter

       A Moire Fringe technique allows video display units
(VDUs) on production lines to be assessed for jitter by line
operators.  Quantitive measurements permit data gathering for quality
improvement.

      Jitter is an undesirable instability in the positioning of an
image on a VDU which is disturbing to an operator. All cathode ray
tube (CRT) based display units are susceptible to it, and measurement
presents intractable problems especially on color CRTs.  Currently
known measurement techniques need specialised laboratory-based
equipment or skilled inspectors.  This article describes a technique
whereby small movements of the scan position are magnified between 10
to 100 times, rendering them easily visible to an untrained eye.  The
method may be used as an attribute check in production, or adapted to
yield measured variables data.  No special equipment is required and
the check is made quickly.  It is suitable for use as a high quality
manufacturing 100% test.

      Jitter is one kind of spatial instability of the CRT image
caused by visual display defects whereby the image moves periodically
over a very small distance, at a frequency of less than about 30 Hz.
Its exact definition varies between ergonomic standards, but there is
agreement that the frequencies at which the human visual system is
most disturbed are between one and three hertz, and that it is
undesirable.  Also, jitter of greater amplitude than 100 um at a
frequency of 2 Hz, viewed from 500 mm, will be so disturbing as to
render the display unit unusable to most people.

      Current legislation of standards organizations is in general
terms, that any periodic movement of the image of greater amplitude
than 0.05 mm, and frequency less than 30 Hz, will cause problems, and
may fail one or more ergonomic standards.

      Jitter cannot be eliminated entirely.  It most frequently
arises because of the displacement of the electron beam wi...