Patent ID: 7150517

Claim:
A method for driving a piezoelectric ink jet head composed of: a pressure chamber filled with an ink; a nozzle that communicates with the pressure chamber and has an ink meniscus formed therein from the ink that fills the pressure chamber; a piezoelectric element of transverse vibration mode that contracts in the direction of plane when subjected to a drive voltage applied thereto; and an oscillator plate that is stacked on the piezoelectric element so as to constitute a drive section and deflects so as to decrease the volume of the pressure chamber as the piezoelectric element contracts in the direction of plane when a voltage is applied thereto, so as to pressurize the ink in the pressure chamber and discharge an ink droplet from the tip of the nozzle, and wherein the piezoelectric ink jet head is operated by combining (A) the step of applying a drive voltage to the piezoelectric element so that the piezoelectric element contracts in the direction of plane and the oscillator plate deflects, thereby decreasing the volume of the pressure chamber, and (B) the step of removing the drive voltage applied to the piezoelectric element so that the contraction of the piezoelectric element in the direction of plane is canceled and consequently the deflection of the oscillator plate is canceled, thereby increasing the volume of the pressure chamber, thereby to discharge an ink droplet from the tip of the nozzle, characterized in that the piezoelectric element is driven with a drive voltage waveform that has at least one of the following settings: (a) time constant τ UP of rise of the drive voltage in the process (A) is set in a range that satisfies the relation of the expression (i): Ta /(− ln 0.01)≦τ UP ≦Ta /(− ln 0.25) (i) with respect to the period Ta of the ensuing vibration of the drive section which is superposed on the vibration waveform of the volumetric velocity of ink in the head, (b) time constant τ DN of fall of the drive voltage in the process (B) is set in a range that satisfies the relation of the expression (ii): Ta /(− ln 0.01)≦ρ DN ≦Ta /(− ln 0.25) (ii) with respect to the period Ta.