Method and apparatus for the electronic detection of air inside a thermal inkjet printhead

摘要

A detection circuit for detecting the existence of non-collapsing bubbles in the ink cells of a thermal inkjet printhead is connected to a heater element of an ink containing cell. The detection circuit has a sensing element of low resistance when compared to the resistance of the heater element so that printing and detecting operations can proceed simultaneously. Current in the heater element is proportional to the potential drop across the sensing element. An amplifier is used to measure the potential drop and is connected to a blocking capacitor. Non-collapsing bubbles are detected if the voltage drop across the sensing element varies from a reference level.