Position responsive apparatus, system and method having electrographic

Abstract

A position responsive apparatus, system and method which employs a position responsive surface formed of two orthogonally disposed arrays of grid elements which in one embodiment, the elements are coupled along one border with a resistor chain or the equivalent which is excited with an a.c. source at terminal locations. Capacitive coupling between the orthogonally disposed arrays at the cross-over locations of grid elements is significantly reduced by reducing the area of the grid elements at the cross-over positions. Further, intermediate grounding terminals serve to minimize disruptive potentials caused by the capacitive coupling. The control for the system employs a procedure wherein a correction look-up table is developed as part of the manufacture of the apparatus wherein readings are taken at the nodal points of communication between the grid array and the resistor chain and which then are treated to provide a regularly incremented sequence of address values developed from a signal domain computation. Physical domain coordinate values are correspondingly derived and are located in the table with each address value. The control for the embodiment accesses this memory for purpose of developing corrected coordinate outputs, thus eliminating the need for precise calibration of each resistor within the resistor chain. The invention further contemplates the employment of transparent grid array elements. Significant improvements to performance are achieved by exciting these elements from resistor chains located and coupled therewith at oppositely disposed ends of the grid elements. An improved switching approach is provided wherein excitation currents are employed at the switching stage which then are applied to voltage follower stages for coupling with the grid array terminal.