Liquid ejection apparatus, liquid ejection method and image forming apparatus

1. A liquid ejection apparatus, comprising:

a pressure chamber which contains liquid;

a nozzle which is connected to the pressure chamber, the liquid being ejected in an ejection direction through the nozzle;

a piezoelectric element which applies pressure change to the liquid in the pressure chamber, a part of the liquid protruding from the nozzle upon the pressure change and growing into a column of the liquid having a longitudinal direction parallel with the ejection direction;

an electrode which induces a charge on a surface of the column of the liquid; and

a voltage control device which controls voltage applied to the electrode, the voltage control device reversing polarity of the electrode when the column of the liquid has grown to a prescribed length.

2. The liquid ejection apparatus as defined in claim 1 , wherein the electrode is composed of a plate arranged over the nozzle and having a hole in a position corresponding to the nozzle, the hole having a tapered shape becoming gradually narrower along the ejection direction.

3. An image forming apparatus comprising the liquid ejection apparatus as defined in claim 2 .

4. An image forming apparatus comprising the liquid ejection apparatus as defined in claim 1 .

5. A liquid ejection method comprising the steps of:

applying pressure change to liquid in a pressure chamber by using displacement of a piezoelectric element, a part of the liquid protruding from a nozzle connected to the pressure chamber upon the pressure change and growing into a column of the liquid having a longitudinal direction parallel with an ejection direction in which the liquid is ejected through the nozzle;

applying a prescribed voltage to an electrode to induce a charge on a surface of the column of the liquid; and

reversing polarity of the electrode when the column of the liquid has grown to a prescribed length.