Browse Prior Art Database

Method of Continuously Computing the Point of Contact on a Touch Sensitive Screen With Piezosensors

IP.com Disclosure Number: IPCOM000122670D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Gungl, KP: AUTHOR

Abstract

The point of contact on a piezoelectric screen is computed by measuring the moments of force at four points. For technological reasons, a force proportional measuring signal from a piezosensor is obtainable only with the aid of very expensive charge amplifiers. By measuring the current signal, which can be done by inexpensive transimpedance converters, a differential time signal is obtained. However, for computing the point of contact, the actual force rather than a differential time value is required. Existing computing methods are only suitable for computing single touches but not for continuous touch sensing.

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Method of Continuously Computing the Point of Contact on a Touch
Sensitive Screen With Piezosensors

      The point of contact on a piezoelectric screen is
computed by measuring the moments of force at four points.  For
technological reasons, a force proportional measuring signal from a
piezosensor is obtainable only with the aid of very expensive charge
amplifiers.  By measuring the current signal, which can be done by
inexpensive transimpedance converters, a differential time signal is
obtained. However, for computing the point of contact, the actual
force rather than a differential time value is required. Existing
computing methods are only suitable for computing single touches but
not for continuous touch sensing.

      As the hands of a human being are never absolutely steady, even
a subjectively static pressure exerted by them is subject to slight
variations.  Based on this knowledge, the proposed method measures
and numerically integrates such variations during a predetermined
interval.  This allows determining the point of contact with adequate
accuracy. The proposed algorithm
      o    computes the point of contact during dynamic and static
force application, and
      o    continuously computes the point of contact during static
force application and finger motion (continuous tracing).

      Compared with previous methods, the method described in this
article, which utilizes existing inexpensive electronic amplification
means, has the additional advantage of allowing a wider variety of
functions and computing the point of contact at much higher speed.

      The algor...