Patent ID: 6825675
Filing Date: 2004-11-30
Classification: B41J

Abstract:
A method for detecting at least one possibly shorted printhead in a printer having first and second printheads in parallel which are supplied a voltage from the output of a voltage source, wherein the method comprises the steps of:a) obtaining a calibration resistor having a resistance which, when placed in parallel to the voltage source, is equivalent to a predetermined maximum leakage current of a single non-shorted printhead in a quiescent state; b) disposing the calibration resistor and a capacitance load in parallel across the output of the voltage source to define a first circuit; c) with the first and second printheads electrically isolated from the first circuit, determining a first decay time for the first-circuit voltage across the capacitance load to reach a second voltage from a first voltage after the voltage source is disconnected from the first circuit; d) determining a second decay time which is shorter than the first decay time; d) disposing the first and second printheads and the capacitance load in parallel across the output of the voltage source to define a second circuit; e) with the calibration resistor electrically isolated from the second circuit and with the first and second printheads in a quiescent state, determining the second-circuit voltage across the capacitance load at the second decay time after the voltage source is disconnected from the second circuit; and g) indicating at least one possibly shorted printhead of the first and second printheads when the second-circuit voltage at the second decay time is less than the second voltage.