Capacitive Head Gap Measurement for Printers
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Apparatus for measuring the print head to platen gap on matrix printers is disclosed using a capacitive gap technique. Accurate distance measurements can be made between adjacent parts in locations which are difficult to reach using the capacitance vs. displacement method. As shown in the figure, the head 10 and the platen 12 of the printer comprise a variable capacitor in the circuit shown, where: V1 = source potential Va = amplifier output R = resistance of amplifier input stage Cs = standard capacitance (reactance Xs) Cu = unknown capacitance (reactance Xu) i1 = current passed by standard capacitance Cs i2 = current fed back by probe test structure capacitance e = input voltage to amplifier, i.e.