Pressure mapping system with capacitive measuring pad

摘要

A capacitive measuring pad is constructed of transverse conductive strips separated by a compressible insulator to form a matrix of pressure sensitive capacitive nodes. The nodes are repetitively scanned in sequence by a microcomputer to measure their respective capacitances, from which measurements a pressure map is then derived. The resulting pressure map may be displayed on a color graphics monitor with different colors representing diffrent pressures. Node capacitance is found by measuring the response of the mode to a driving signal of a known voltage. This measurement is accomplished by connecting one of the node's transverse conductive strips to the driving source and the node's other conductive strips to a sense amplifier. In order to isolate the node of interest from the influence of surrounding nodes, all of the conductive strips except the two intersecting the selected node are connected to ground. Furthermore, the input impedance to ground of the sense amplifier is made negligibly small with respect to the other system impedance. In this way, only the conductive strip connected to the driving source has a voltage impressed on it, and the conductive strips of all other nodes in the system are maintained at ground potential, thus allowing an accurate measurement of the one capacitance.