Method for detecting disturbance in droplet ejection of an inkjet print head

An inkjet printer comprising an inkjet print head and a control unit operatively coupled to the inkjet print head for controlling operation of the inkjet print head, the inkjet print head comprising an ejection unit, wherein the ejection unit comprises:

• a pressure chamber for holding an amount of liquid, said pressure chamber being in fluid communication with a nozzle orifice;
• and
• an actuator operatively coupled to the pressure chamber for generating a pressure wave in the liquid in the pressure chamber for ejecting a droplet of the liquid through the nozzle orifice upon application of a droplet ejection pulse,
• wherein the control unit is configured to supply the droplet ejection pulse to the inkjet print head for controlling the inkjet print head to expel a droplet of liquid through the nozzle orifice, and
• wherein the control unit is configured to supply a disturbance detection pulse, then to detect a residual pressure wave in the pressure chamber and to analyze the residual pressure wave for determining whether a disturbance is present in the ejection unit of the inkjet print head, the disturbance detection pulse being determined by taking into account at least one resonance frequency of the pressure chamber and having a frequency spectrum different from a frequency spectrum of the droplet ejection pulse.