Patent ID: 7328961

Claim:
A droplet ejection apparatus comprising: a plurality of droplet ejection heads, each of the droplet ejection heads including: a diaphragm; an actuator which displaces the diaphragm; a cavity filled with a liquid, an internal pressure of the cavity being increased and decreased in response to displacement of the diaphragm; and a nozzle communicated with the cavity through which the liquid is ejected in the form of droplets in response to the increase and decrease of the internal pressure of the cavity; a driving circuit which drives the actuator of each droplet ejection head; an oscillator unit which generates a signal on the basis of a residual vibration of the diaphragm displaced by the actuator after driving the actuator by the driving circuit; a subtracting unit which subtracts the number of pulses, which are included in the signal generated by the oscillator unit for a predetermined time period, from a predetermined reference value; and a judging unit for judging whether or not an ejection failure is occurring in the droplet ejection heads on the basis of the subtraction result by the subtracting unit; wherein the judging unit judges a cause of the ejection failure when it is judged that the ejection failure is occurring; the judging unit judges that an air bubble has intruded into the cavity in the case where the subtraction result is smaller than a first threshold; the judging unit judges that the liquid in the vicinity of the nozzle has thickened due to drying in the case where the subtraction result is larger than a second threshold; and the judging unit judges that paper dust is adhering in the vicinity of the outlet of the nozzle in the case where the subtraction result is smaller than the second threshold and larger than a third threshold.