Patent ID: 7549716

Claim:
A method of ejecting microdroplets of ink by driving an inkjet head comprising a plate formed with a plurality of nozzles for ejecting ink droplets and a plurality of pressure chambers in fluid communication with the plurality of nozzles, respectively, and a pressure generating member for applying pressure to ink in each ink pressure chamber in response to electric signals applied to the pressure generating member, the plate having an outside surface, on which the nozzle is opened, the method comprising: a first step for generating one ink column on the outside of the nozzle and for separating a tip end of the one ink column from a remaining part of the one ink column to form a microdroplet of ink on the outside of one nozzle; and a second step for controlling an ink volume velocity in the ink pressure chamber that is connected to the nozzle to generate another ink column and to push the another ink column out of the nozzle, thereby causing the another ink column to overtake and merge with the remaining part of the one ink column and to return into the nozzle while pulling the remaining part of the one ink column back into the nozzle.