Ink jet head driving method and apparatus

1. An ink jet head driving method for applying a drive pulse to an actuator to change capacities of a plurality of pressure chambers in which ink has been filled, ejecting an ink droplet from a nozzle formed in communication with the pressure chamber to print onto a printing medium, and moreover, continuously ejecting a plurality of liquid droplets to carry out gradation printing according to the number of liquid droplets, the method comprising:

making control so as to, in the case where the number of the liquid droplets is smaller than a predetermined number, apply a boost pulse to amplify a pressure vibration of the pressure chamber prior to a drive pulse for ejecting a first liquid droplet; and in the case where the number of liquid droplets is equal to or greater than the predetermined number, disable applying of the boost pulse.

2. The ink jet head driving method according to claim 1 , wherein an ejection speed of ink from the nozzle in the case where no boost pulse is applied for the number of liquid droplets and the ejection speed in the case where the boost pulse is applied are measured, and the number of liquid droplets when a difference therebetween hardly occurs is set as the predetermined number.

3. An ink jet head driving apparatus comprising:

a plurality of pressure chambers in which ink has been filled;

an ink jet head which applies a drive pulse to an actuator to change the capacity of each of the pressure chambers, ejects an ink droplet from a nozzle formed in communication with the pressure chamber to carry out printing onto a printing medium, and moreover, continuously ejects a plurality of liquid droplets to carry out gradation printing according to the number of liquid droplets, and

drive signal generating section configured, in the case where the number of the liquid droplets is smaller than a predetermined number, to apply a boost pulse to amplify a pressure vibration of the pressure chamber prior to a drive pulse for ejecting a first liquid droplet; and in the case where the number of liquid droplets is equal to or greater than the predetermined number, to disable applying of the boost pulse.

4. The ink jet head driving apparatus according to claim 3 , wherein an ejection speed of ink from the nozzle in the case where no boost pulse is applied for the number of liquid droplets and the ejection speed in the case where the boost pulse is applied are measured, and the number of liquid droplets when a difference therebetween hardly occurs is set as the predetermined number.

5. An ink jet head driving apparatus comprising:

a plurality of pressure chambers in which ink has been filled;

an ink jet head which applies a drive pulse to an actuator to change the capacity of each of the pressure chambers, ejects an ink droplet from a nozzle formed in communication with the pressure chamber to carry out printing onto a printing medium, and moreover, continuously ejects a plurality of liquid droplets to carry out gradation printing according to the number of liquid droplets,

drive pulse number generating section configured to generate the number of the drive pulses;

judging section configured to judge whether or not the number of drive pulses generated from the drive pulse number generating section is equal to or greater than a predetermined number which has been stored in advance;

pulse applying section configured, in the case where it has been judged that the number of drive pulses is smaller than the predetermined number by the judging means, to apply a drive pulse that follows a boost pulse to the actuator by the number of drive pulses, and, in the case where it has been judged that the number of drive pulses is equal to or greater than the predetermined number by the judging means, to apply a drive pulse to the actuator by the number of drive pulses.

6. The inkjet head driving apparatus according to claim 5 , wherein the predetermined number stored in advance in the judging section can be externally changed.