Liquid injection device and inkjet recording device including the same

1. A liquid injection device, comprising:

a liquid injection head injecting a liquid drop; and

a controller controlling the liquid injection head; wherein

the liquid injection 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 so as to be in communication with the pressure chamber, the nozzle allowing a liquid to flow out therefrom;

the controller includes:

a driving signal generator generating a driving signal including, in one liquid drop injection period, a first driving pulse to expand and contract the pressure chamber to inject a first liquid drop, a second driving pulse to expand and contract the pressure chamber to inject a second liquid drop; a third driving pulse to expand and contract the pressure chamber to inject a third liquid drop, and a fourth driving pulse to expand and contract the pressure chamber to inject a fourth liquid drop; and

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

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

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

the second driving pulse starts at a timing that is about m×Tc after a start of the first driving pulse, m being an integer of 1 or greater, to maintain the pressure chamber in the expanded state for the time period of about (½)×Tc, and to inject the second liquid drop at a speed higher than, or equal to, a speed at which the first liquid drop is injected;

the third driving pulse starts at a timing that is about (n+(½))×Tc after a start of the second driving pulse, n being an integer of 1 or greater; and

the fourth driving pulse starts at a timing that is about p×Tc after a start of the third driving pulse, p being an integer of 2 or greater, and to inject the fourth liquid drop at a speed higher than, or equal to, a speed at which the third liquid drop is injected.

2. The liquid injection device according to claim 1 , wherein

the first driving pulse includes:

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;

the second driving pulse includes:

a second potential decreasing waveform decreasing from the intermediate potential to a second minimum potential during a third time period; and

a second minimum potential maintaining waveform maintained at the second minimum potential for a fourth time period; wherein

the first driving pulse results in a sum of the first time period and the second time period being equal to about (½)×Tc; and

the second driving pulse results in a sum of the third time period and the fourth time period being equal to about (½)×Tc.

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

an amount of potential change provided by the first driving pulse from the intermediate potential to the first minimum potential is ΔV 1 ;

an amount of potential change provided by the second driving pulse from the intermediate potential to the second minimum potential is ΔV 2 ; and

ΔV 1 and ΔV 2 satisfy ΔV 1 ≦ΔV 2 .

4. The liquid injection device according to claim 3 , wherein

the third driving pulse includes a third potential decreasing waveform decreasing from the intermediate potential to a third minimum potential during a fifth time period;

the fourth driving pulse includes a fourth potential decreasing waveform decreasing from the intermediate potential to a fourth minimum potential during a sixth time period;

an amount of potential change provided by the third driving pulse from the intermediate potential to the third minimum potential is ΔV 3 ;

an amount of potential change provided by the fourth driving pulse from the intermediate potential to the fourth minimum potential is ΔV 4 ; and

ΔV 3 and ΔV 4 satisfy ΔV 3 ≦ΔV 4 .

5. The liquid injection device according to claim 4 , wherein ΔV 1 and ΔV 3 satisfy ΔV 1 <ΔV 3 ≦1.3×Δv 1 .

6. The liquid injection device according to claim 1 , wherein the fourth ink drop is injected at a speed higher than, or equal to, and at most about 1.2 times as high as, the speed at which the first ink drop is injected.

7. The liquid injection device according to claim 1 , wherein the third driving pulse maintains the pressure chamber in an expanded state for a time period of about (½)×Tc.

8. The liquid injection device according to claim 1 , wherein the fourth driving pulse maintains the pressure chamber in an expanded state for a time period of about (½)×Tc.

9. The liquid injection device according to claim 1 , wherein m is 1.

10. The liquid injection device according to claim 1 , wherein n is 2.

11. The liquid injection device according to claim 1 , wherein p is 2.

12. An inkjet recording device, comprising the liquid injection device according to claim 1 .