Patent ID: 7887151

Claim:
A method for adjusting uniformity of liquid ejection from a liquid ejection head, comprising: determining a first polarization voltage and a second polarization voltage based on polarization degrees for a set of piezoelectric elements corresponding to nozzles of the liquid ejection head; and adjusting polarization degrees selectively for each one of the set of the piezoelectric elements in parallel based on the determined first polarization voltage of said set of the piezoelectric elements, wherein adjusting comprises: applying the first polarization voltage to the piezoelectric elements; evaluating first polarization degrees of the piezoelectric elements a predetermined time after application of said first polarization voltage; and applying the second polarization voltage to selected ones of the piezoelectric elements; evaluating second polarization degrees of said ones of the piezoelectric elements after application of the second polarization voltage; and determining if further polarization adjustment is required; wherein further polarization adjustment comprises: calculating a next polarization voltage from said first and second polarization voltages and said first and second polarization degrees; and applying the next polarization voltage to selected ones of the piezoelectric elements in parallel.