Liquid ejection device and inkjet recording including the same

1. A liquid ejection device, comprising:

a liquid ejection head ejecting a liquid drop; and

a controller controlling the liquid ejection head; wherein

the liquid ejection head includes:

a hollow case main body provided with an opening;

a vibration plate attached to the case main body to cover the opening, the vibration plate defining a pressure chamber together with the case main body;

a pressure generator coupled with the vibration plate and expanding and contracting the pressure chamber; and

a nozzle in the case main body and in communication with the pressure chamber, the nozzle allowing a liquid to flow out therefrom; wherein the controller includes:

a driving signal generator generating a driving signal including, in one liquid drop ejection period, a first driving pulse to expand and contract the pressure chamber to eject a first liquid drop and a second driving pulse to expand and contract the pressure chamber to eject a second liquid drop; and

a driving signal supplier supplying the driving signal to the pressure generator of the liquid ejection head;

the first driving pulse and the second driving pulse are the only driving pulses included in the one liquid drop ejection period of the driving signal;

Tc is a Helmholtz characteristic vibration period of the liquid ejection head;

the first driving pulse maintains the pressure chamber in an expanded state for a time period of (½)×Tc±(⅛)×Tc;

the second driving pulse starts at a timing that is n×Tc±(⅛)×Tc after a start of the first driving pulse, n being an integer satisfying n≥2, to maintain the pressure chamber in the expanded state for the time period of (½)×Tc±(⅛)×Tc, and to eject the second liquid drop at a speed higher than, or equal to, a speed at which the first liquid drop is ejected; and

when liquid is ejected by the liquid ejection head, the driving signal generator generates, in the driving signal, the second driving pulse subsequent to the first driving pulse with no non-ejection pulse being included between the first driving pulse and the second driving pulse.

2. The liquid ejection device according to claim 1 , wherein the first driving pulse and the second driving pulse each include:

a first potential decreasing waveform decreasing from an intermediate potential to a first minimum potential during a first time period; and

a first minimum potential maintaining waveform maintained at the first minimum potential for a second time period; and

a sum of the first time period and the second time period is equal to (½)×Tc±(⅛)×Tc.

3. The liquid ejection device according to claim 2 , wherein

the first driving pulse further includes a potential recovery waveform increasing from the first minimum potential to the intermediate potential; and

the second driving pulse further includes a first potential increasing waveform increasing from the first minimum potential via the intermediate potential to a first locally maximum potential.

4. The liquid ejection device according to claim 3 , wherein the second driving pulse further includes:

a first locally maximum potential maintaining waveform maintained at the first locally maximum potential for a predetermined time period;

a second potential increasing waveform increasing from the first locally maximum potential to a second locally maximum potential;

a second locally maximum potential maintaining waveform maintained at the second locally maximum potential for a predetermined time period; and

a potential recovery waveform decreasing from the second locally maximum potential to the intermediate potential.

5. The liquid ejection device according to claim 1 , wherein the second liquid drop is ejected at a speed higher than the speed at which the first liquid drop is ejected.

6. The liquid ejection device according to claim 1 , wherein n satisfies n≤5.

7. The liquid ejection device according to claim 6 , wherein n is 2.

8. An inkjet recording device, comprising the liquid ejection device according to claim 1 .