Method for detecting printing nozzle errors in an inkjet printing machine

A method for detecting printing nozzle errors caused by failed nozzles in an inkjet printing machine by using a computer, the method comprising the following steps:

• printing a nozzle test pattern having a specific number of horizontal rows of periodically vertically printed, equidistant lines, the rows being disposed below one another and limited by horizontal lines, and in each row of the nozzle test pattern, the printing nozzles corresponding to a specific number of the horizontal rows contributing only periodically to the nozzle test pattern;
• determining precise positions of individual components of the nozzle test pattern;
• using at least one camera to acquire and record the nozzle test pattern;
• producing an actual signal from the printed and acquired nozzle test pattern;
• using the generated actual signal to carry out a Fourier analysis;
• generating a reference signal with a location frequency of the Fourier-transformed actual signal;
• generating a correlation signal from the reference and actual signals, the correlation signal describing valid setpoint positions for specific points of the nozzle test pattern, the specific points being the vertically printed equidistant lines;
• eliminating all positions at edges of the correlation signal not corresponding to any setpoint positions;
• displacing the reference signal to each of the setpoint positions, resulting in a working point at an average extreme value of the reference signal;
• calculating at least one of amplitude or phase or variance errors caused by the failed nozzles from an evaluation of a signal course of the actual signal around the respective working point;
• and
• evaluating printing nozzle quality from the calculated amplitude, phase and variance errors caused by the failed nozzles.