Electrographic tough sensor having reduced bow of equipotential field

Abstract

A resistor electrode type touch sensor having enhanced area of linear response by reducing the bow in perimeters of the sensor. Within a resistive layer of substantially uniform resistivity orthogonal electrical fields are produced to give coordinates of a selected position. Overlying, but spaced from, the resistive layer is an optional flexible conductive pick-off sheet facing the resistive layer which will contact the resistive layer when touched at a selected position. Other elements are described to obtain signals corresponding to the coordinates of a selected point. A resistance element is positioned proximate the perimeter of the resistive layer made up of discontinuous conductive lines applied to the resistive layer. For a given value of the resistive layer, the value of the resistance element is determined by the length and width of any gaps between the conductive lines. Electrodes of a selected effective length and spacing are located along selected paths proximate the edges of the resistive layer and attached thereto. Each electrode is connected to selected positions along the resistance element to provide selected voltages to the resistive layer. The effective length and spacing of the electrodes, and the positions of connection to the resistance element, are selected to produce an effective voltage gradient at the electrodes that progressively decreases from corners of the sensor to the center line of each edge of the sensor to counteract any voltage drop along the resistance element when voltages are applied thereto so as to substantially eliminate the bow of electrical fields produced in the resistive layer.