Liquid jetting head, liquid jetting apparatus incorporating the same, method and apparatus for measuring natural vibration period of the same

An apparatus for measuring a natural vibration period of a liquid jetting head provided with a nozzle orifice, a pressure chamber communicated with the nozzle orifice, a liquid supply port which supplies liquid into the pressure chamber, and a pressure generation element which causes pressure fluctuation in the liquid contained in the pressure chamber, the apparatus comprising:

• a first evaluation signal generator, which generates a first evaluation signal including a first excitation element adapted to excite pressure fluctuation in liquid contained in the pressure chamber and a first ejection element which follows the excitation element after a first time period to eject a first liquid droplet from the nozzle;
• a second evaluation signal generator, which generates a second evaluation signal including a second excitation element adapted to excite pressure fluctuation in liquid contained in the pressure chamber and a second ejection element which follows the excitation element after a second time period to eject a second liquid droplet from the nozzle;
• a first evaluation signal supplier, which supplies the first evaluation signal to the pressure generating element to measure a first ejected amount of the first liquid droplet;
• a second evaluation signal supplier, which supplies the second evaluation signal to the pressure generating element to measure a second ejected amount of the second liquid droplet;
• a calculator, which calculates an ejected amount ratio of the first ejected amount and the second ejected amount;
• and
• a natural vibration period determinant, which determines the natural vibration period of the liquid jetting head based on the ejected amount ratio.