Measurement of fluid continuity in a fluid carrying member

Abstract

In an inkjet printer using ink reservoirs located physically remote from the print head, tubes are used to deliver ink from the ink reservoirs to the print heads. Air initially present within the tubes can interfere with the proper operation of the print heads and cause print head reliability problems Additionally, air present within the tubes can interfere with the proper flow of ink from the ink reservoirs to the print heads through the tubes. An embodiment of a fluid continuity measurement apparatus includes current sources for each of the tubes. Each of the current sources delivers a substantially constant current to the corresponding tube. Voltage measurement circuits are coupled across each of the tubes. Each of the voltage measurement circuits generates an output corresponding to the voltage across the corresponding tube. The voltages appearing between the ends of the tubes changes as the volume of the air within the tubes changes. Increasing the volume of air within the tubes increases the resistance of the tubes there by increasing the voltages resulting from the application of a substantially constant current. A controller coupled to the output of the voltage measurement circuits compares each of the voltages output from the voltage measurement circuits to an empirically determined threshold value to determine if the volume of air within the tubes has reached an unacceptable level.