Circular electrographic touch sensor with orthogonal fields and linear

Abstract

A circular touch sensor having very linear response in a two coordinate system. This circular sensor has four substantially identical and symmetrical quadrants, with points for the introduction of potentials being located at polar and equatorial points on the sensor. The sensor has a uniform electrical sheet resistivity, and each quadrant has a resistance element to distribute the potentials to electrodes connected thereto which are positioned along the perimeter of the circular resistive surface. Individual ends of the resistance element in each quadrant are connected to their respective 'tie points' through a resistor of a size to adjust for a proper resistance value between the quadrants at these points. The size (effective length along the position path) of the electrodes in each quadrant generally increases, and the spacing between electrodes generally decreases, symmetrically from the edges of each quadrant toward the center of that quadrant. In this manner, voltage gradients are produced at each of the electrodes to compensate for any cumulative voltage drop along the resistance element due to current flow into the resistive surface and due to the circular geometric configuration. In the preferred embodiment, a 'floating' conductive element is placed on the path of the electrodes proximate the tie points to further enhance linearity of the sensor near these points. A typical sensor of this type is described in detail.