Patent ID: 8356885

Claim:
An inkjet printhead having a plurality of ink chambers that periodically contain ink during printing, each of the plurality of ink chambers having a respective nozzle, the printhead comprising: a heater element having a beam structure suspended in the ink chamber, the heater element formed of conductive material having a resistance that is a function of temperature, the conductive material directly contacting the ink when ink is present in the ink chamber, the heater element having electrical contacts for connection to an electrical power source for heating the heater element with an electrical signal; control circuitry for measuring a current passing through the heater element during heating of the heater element, determining a temperature of the heater element from a known applied voltage, the measured current and a known relationship between the current, resistance and temperature and comparing the temperature to a known temperature indicative of the heater element being in contact with the ink or a known temperature indicative of the heater element not being in contact with the ink, in order to generate an output signal indicative of the ink being present or absent from the ink chamber; and, the control circuitry also being configured for providing the heater element with a drive signal to heat the heater element in order to raise the temperature of part of the ink above its boiling point to form a vapor bubble that causes a drop of ink to be ejected through the nozzle.