Patent ID: 7364274

Claim:
A driving method of a droplet ejection head, the droplet ejection head comprising: a plurality of channels, each of the plurality of channels being separated by a sidewall, each of the sidewalls comprising at least partially a piezoelectric material, the plurality of channels being divided into three groups comprising a first group of channels, a second group of channels, and a third group of channels, and each group of channels in the three groups of channels comprising channels physically separated from one another and between which two channels of the other groups of channels are disposed; a nozzle having an opening for ejecting liquid; and an electrode formed on a sidewall of each group of channels; wherein the driving method of the droplet ejection head comprises: applying an electric voltage pulse to the electrode of each group of channels, one group of channels at a time, for driving each of the three groups of channels sequentially in a time-sharing mode; generating a shear deformation of the sidewall of each group of channels; and ejecting liquid from a channel of the plurality of channels as a droplet from the nozzle by a pressure generated with the shear deformation of the sidewall, wherein the step of applying the electric voltage pulse to the electrodes of each group of channels, one group of channels at a time, comprises: a first step for enlarging a volume of a channel in the group of channels; a second step for keeping a state of the volume enlarged; a third step for reducing the volume of the channel to protrude a liquid pillar from the nozzle; a fourth step for keeping a status of the volume reduced; and a fifth step for enlarging the volume of the channel, wherein the third step for the second group of channels starts when a condition α/β<⅓ is satisfied for the protruded pillar at a nozzle of an adjoining channel in the first group of channels previously driven, and separates the protruded pillar from a meniscus to eject the protruded pillar as a droplet, and wherein α denotes a width of the protruded liquid pillar at a front edge of the opening in the nozzle, and β denotes a maximum width of the protruded liquid pillar.