Drive method and drive apparatus for ink jet head

1. A drive method for an ink jet head, comprising:

as a drive pulse, applying a first pulse for increasing and then restoring the volume of a pressure chamber and giving pressure vibration to the chamber in which ink are accommodated,

and then a second pulse for reducing and then restoring the volume of the pressure chamber to an actuator arranged corresponding to the pressure chamber wherein

the second pulse is turned on at first point of time causing the pressure vibration amplitude at second point of time to be the same with that of generated by the first pulse when the first pulse is turned on,

wherein the second point of time is the time when flow velocity of the ink nearby the nozzle inside the pressure chamber becomes 0 after the first point of time, and the second pulse is turned off at the second point of time.

2. The drive method for an ink jet head according to claim 1 , wherein a third pulse is applied between the first pulse and the second pulse as the drive pulse to reduce and then restore the volume of the pressure chamber.

3. The drive method for an ink jet head according to claim 2 , wherein the third pulse is turned on when the pressure of the pressure chamber becomes 0 and turned off when the pressure of the pressure chamber becomes 0 again.

4. The drive method for an ink jet head according to claim 2 , wherein the third pulse is turned on when an ink liquid column is to be separated from the nozzle and turned off when the ink liquid column is completely separated from the nozzle later.

5. A drive apparatus for an ink jet head which ejects ink drops out from a nozzle connected with a pressure chamber, comprising:

a drive signal generation section configured to apply, as a drive pulse,

a first pulse for increasing and then restoring the volume of the pressure chamber and giving pressure vibration to the chamber in which ink are accommodated, and then a second pulse for reducing and then restoring the volume of the pressure chamber to an actuator arranged corresponding to the pressure chamber, wherein

the drive signal generation section turns on the second pulse at first point of time causing the pressure vibration amplitude at second point of time to be the same with that of generated by the first pulse when the first pulse is turned on,

wherein the second point of time is the time when flow velocity of the ink nearby the nozzle inside the pressure chamber becomes 0 after the first point of time,

and turns off the second pulse at the second point of time.

6. The drive apparatus for an ink jet head according to claim 5 , wherein

the drive signal generation section applies a third pulse between the first pulse and the second pulse as the drive pulse to reduce and then restore the volume of the pressure chamber.

7. The drive apparatus for an ink jet head according to claim 6 , wherein

the drive signal generation section turns on the third pulse when the pressure of the pressure chamber becomes 0 and turns off the third pulse when the pressure of the pressure chamber becomes 0 again.

8. The drive apparatus for an ink jet head according to claim 6 , wherein

the drive signal generation section turns on the third pulse when an ink liquid column is to be separated from the nozzle and turns off the third pulse when the ink liquid column is completely separated from the nozzle later.

9. A drive apparatus for an ink jet head which ejects ink drops out from a nozzle connected with a pressure chamber, comprising:

a drive signal generation section configured to apply, as a drive pulse,

a first pulse for increasing and then restoring the volume of a pressure chamber and giving pressure vibration to the chamber in which ink are accommodated;

a second pulse for reducing and then restoring the volume of the pressure chamber cancelling the pressure vibration of a pressure chamber; and

a third pulse for reducing and then restoring the volume of the pressure chamber, to an actuator arranged corresponding to the pressure chamber,

wherein

when carrying out a gradation printing by changing a number of the ink drops ejected out from the nozzle of the ink jet head according to a number of drive pulses,

the drive pulse includes a DRP waveform and a DRCRP waveform, the DRP waveform being formed by orderly combining the first pulse and the second pulse, the DRCRP waveform being formed by orderly combining the first pulse, the third pulse, and the second pulse by applying the third pulse for reducing and then restoring the volume of the pressure chamber, between the first pulse and the second pulse, and

the drive pulse for the ejection of the last ink drop is the DRCRP waveform.

10. The drive apparatus for an ink jet head according to claim 9 , wherein

the waveform for the ejection of an ink drop prior to the last ink drop is the first waveform.

11. The drive method for an ink jet head according to claim 9 , wherein

the waveform for the ejection of the last ink drop is applied at predetermined base timing,

and waveform(s) are additionally applied prior to the base timing if the number of ink drops is more than 1.

12. The drive apparatus for an ink jet head according to claim 9 , wherein

the drive signal generation section comprises a reference drive waveform generation portion configured to generate a waveform for the formation of pixels of a maximum gradation including the first waveform and the second waveform; and

passing range selection circuits configured to select a passing range for the waveform generated by the reference drive waveform generation section according to the number of the ink drops ejected out from the nozzle.