Browse Prior Art Database

Automatic Zeroing of Force-Sensitive Touch Screen

IP.com Disclosure Number: IPCOM000100422D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Levine, J: AUTHOR

Abstract

An improved method is disclosed to automatically zero the force sensors of a force-sensing touch screen, thereby compensating for electrical and mechanical drift and for mechanical offsets which occur when the display is tilted or moved.

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Automatic Zeroing of Force-Sensitive Touch Screen

       An improved method is disclosed to automatically zero the
force sensors of a force-sensing touch screen, thereby compensating
for electrical and mechanical drift and for mechanical offsets which
occur when the display is tilted or moved.

      One type of touch screen uses force sensors to measure the
force and moments applied to a display surface by a finger or stylus.
 The location of the stylus can be calculated from such information,
as in U.S. Patent 4,745,565.  Errors in calculated position can be
introduced by amplifier offset voltages.  If the sensors respond to a
steady force, additional errors will be introduced by mechanical
deformation and creep, and by changes in the orientation of the
screen with respect to the vertical.  All of these errors can be much
reduced by frequently measuring the offset voltages and subtracting
them from the raw data. Such measurements are best done automatically
rather than on demand of the user.  For this to work, it is essential
to avoid measuring for compensation at a time when a user is actually
touching the screen, either to enter data or to reorient the screen
for better viewing.

      One way to determine that the screen is being touched is to
compare the measured force (including compensation) with some
threshold.  The compensation reset measurements would be discontinued
when the force exceeds the threshold. This method will introduce
erroneous compensation if a user presses lightly, so that the force
is significant but still below threshold.  In this case, the system
will recover after the user lifts his finger.  It will fail
permanently if a static force greater than threshold is applied, for
example, by tilting or defor...