Patent ID: 6858860

Claim:
An apparatus for measuring a natural period of liquid in a pressure chamber formed in a head device which is provided with a nozzle orifice communicated with the pressure chamber and an actuator which varies pressure of the liquid contained in the pressure chamber, the apparatus comprising: a driver, which generates a plurality of drive signals, each of which drives the actuator to eject a liquid droplet from the nozzle orifice under a condition different from the conditions established by the other drive signals; a light emitter, which emits a light beam so as to intersect a space through which the liquid droplet passes; a light receiver, which receives the light beam which has been passed through the space; a first calculator, which calculates an ejection velocity of the liquid droplet based on a timing at which the actuator is driven and a change in a photo-receiving state of the light receiver, with regard to every drive signal; and a second calculator, which calculates the natural period based on a change in the ejection velocity which is obtained from the plural drive signals, wherein; each of the drive signals has a first waveform element which decompresses the pressure chamber, a second waveform element which holds a decompressed state of the pressure chamber, and a third waveform element which compress the pressure chamber; each condition is defined by varying a duration of the second waveform element; each condition is determined such that the change the ejection velocity has at least two peak values; and the natural period is determined as a time period represented by an interval-of the peak values.