Patent ID: 7520581

Claim:
An ink droplet ejection device comprising: a plurality of nozzles; a plurality of pressure chambers held in communication with the respective nozzles; a common ink chamber held in communication with said pressure chambers so as to distribute an ink into said pressure chambers; a plurality of actuators each operable to apply an ejection pressure to the ink stored in a corresponding one of said pressure chambers, for causing an ink ejection from said corresponding one of said pressure chambers through one of said nozzles that is held in communication with said corresponding pressure chamber, whereby an image formed as a result of the ink ejection is produced on a medium; and a controller operable to supply a control signal to each of said plurality of actuators, and including (a) a composite-dot forming command portion operable to incorporate a composite-dot forming pulse train into said control signal supplied to each of said plurality of actuators, for causing the corresponding pressure chamber to successively eject a plurality of ink droplets that cooperate with each other to form a composite dot of the image, and (b) a non-composite-dot forming command portion operable to incorporate a non-composite-dot forming pulse train into said control signal, for causing the corresponding pressure chamber to eject a single ink droplet that forms a non-composite dot of the image, wherein said composite-dot forming pulse train and said non-composite-dot forming pulse train have respective waveforms that are configured such that an ejection velocity of said single ink droplet forming the non-composite dot is lower than an ejection velocity of said plurality of ink droplets cooperating to form the composite dot.