Ink jet head and ink jet apparatus having the same

An ink jet head, comprising:

• a pressure chamber connected to a nozzle;
• an actuator configured to cause liquid in the pressure chamber to be ejected from the nozzle by deforming a wall of the pressure chamber;
• and
• a drive circuit configured to apply voltage to the actuator to drive the actuator, wherein
• when a predetermined number of droplets of the liquid is ejected from the nozzle, the voltage applied to the actuator is changed from a first value to a second value that causes the pressure chamber to expand, repeatedly changed from a third value that is between the first value and the second value to the second value each time period λ the predetermined number of times, and then changed from the third value to the first value, the time period λ being a primary natural oscillation period of the actuator when the pressure chamber and the nozzle are filled with the liquid.

An ink jet apparatus, comprising:

• an ink jet head configured to eject ink;
• and
• a conveying device configured to convey a sheet as the ink jet head ejects the ink, to form an image on the sheet, wherein
• the ink jet head includes:
• a pressure chamber connected to a nozzle;
• an actuator configured to cause liquid in the pressure chamber to be ejected from the nozzle by deforming a wall of the pressure chamber;
• and
• a drive circuit configured to apply voltage to the actuator to drive the actuator, wherein
• when a droplet of the liquid is ejected from the nozzle, the voltage applied to the actuator is changed from a first value to a second value that causes the pressure chamber to expand, and then changed from a third value that is equal to the second value or between the first value and the second value to the first value after a time period λ, which is a primary natural oscillation period of the actuator when the pressure chamber and the nozzle are filled with the liquid.