Patent ID: 8733898

Claim:
An ink jet head for ejecting an ink droplet to form an image on a recording medium, comprising: a pressure chamber to which ink is supplied; an actuator which applies pressure on the ink filled in the pressure chamber; a circuit which applies to the actuator a drive-waveform for sequentially ejecting one or more ink droplets to form one pixel on the recording medium, the one ink droplet having a volume V, expressed in units of a linear dimension cubed; and a nozzle plate, attached to the pressure chamber, which has a nozzle fluidly communicating with the pressure chamber to eject an ink droplet therefrom, the nozzle having a stepped inner surface shaped to include an inlet communicating with the pressure chamber and having a first sectional area in a plane orthogonal to an ink-ejecting direction, and to include an outlet communicating with the inlet and having a length Ln 1 , expressed in units of the linear dimension, in the ink-ejecting direction and a second sectional area C 1 , expressed in units of the linear dimension squared, in the orthogonal plane smaller than the first sectional area, the Ln 1 , C 1 , and V satisfying the relationship of 0.5≦Ln 1 /(V/C 1 )≦1.0.