Method of fast nozzle failure detection

A method of nozzle failure detection in an ink jet printer having a plurality of ejection units each of which comprises a nozzle and an associated liquid chamber with an electromechanical transducer for energizing a pressure wave in the liquid chamber so as to expel an ink droplet from the nozzle, the method comprising steps of nozzle failure detection to be performed, for each ejection unit, with a given minimum detection frequency, wherein each nozzle failure detection step comprises:

• energizing the transducer with a waveform that does not lead to the ejection of a droplet but creates a pressure fluctuation that is sensitive to whether or not the ejection unit is in a malfunction state;
• measuring the pressure fluctuation in order to detect the malfunction state,
• defining a mask pattern that is independent of image contents to be printed, said mask pattern defining positions of blank pixels on a dark background such that the blank pixels are distributed over an area of an image so finely that they are hardly perceptible to the human eye;
• and
• when an image is being printed, performing the nozzle failure detection steps for each ejection unit at timings at which the respective nozzles are in pixel positions that belong to the mask pattern.