Inkjet head

An inkjet head, comprising:

• a pressure chamber for storing ink;
• a nozzle communicating with the pressure chamber;
• an actuator configured to eject the ink through the nozzle by changing a volume of the pressure chamber;
• and
• an actuator drive circuit configured to output to the actuator a drive signal that has a drive waveform having a predetermined cycle based on a number of gradation levels being used for printing, wherein
• when printing is performed using three or more gradation levels, the drive circuit outputs the drive signal having a multi-drop drive waveform including:
• two or more first waveforms for ejecting first to (n−1)-th droplets of the ink, where n is equal to or greater than 3,
• a second waveform for ejecting an n-th droplet of the ink, and
• an intermediate time between the first waveform for ejecting the (n−1)-th droplet and the second waveform for ejecting the n-th droplet, the intermediate time being longer than a time between two of the first waveforms that are adjacent to each other, wherein
• wherein a boost pulse by which a first voltage is applied to the actuator is applied in the intermediate time,
• a second voltage lower than the first voltage is applied to the actuator before the boost pulse, and
• the second waveform includes an expansion pulse following the boost pulse and by which a third voltage lower than the second voltage is applied to the actuator.

An inkjet printer, comprising:

• an inkjet head including:
• a pressure chamber for storing ink;
• a nozzle communicating with the pressure chamber;
• an actuator configured to eject the ink through the nozzle by changing a volume of the pressure chamber;
• and
• an actuator drive circuit configured to output to the actuator a drive signal that has a particular drive waveform having a predetermined cycle based on a number of gradation levels being used for printing, wherein
• when printing is performed using three or more gradation levels, the drive circuit outputs the drive signal having a multi-drop drive waveform including:
• two or more first waveforms for ejecting first to (n−1)-th droplets, where n is equal to or greater than 3,
• a second waveform for ejecting an n-th droplet,
• an intermediate time between the first waveform for ejecting the (n−1-th droplet and the second waveform for ejecting the n-th droplet, the intermediate time being longer than a time between two of the first waveforms that are adjacent to each other, and
• a boost pulse by which a first voltage is applied to the actuator before the second waveform, wherein
• a second voltage lower than the first voltage is applied to the actuator before the boost pulse during the intermediate time, and
• the second waveform includes an expansion pulse following the boost pulse and by which a third voltage lower than the second voltage is applied to the actuator;
• and
• a control circuit configured to control the inkjet head to print an image on a sheet.