Air entrapment in piezo-driven inkjet printheads

The stability of inkjet printers is a major requirement for high-quality-printing. However, in piezo-driven inkjet printheads, air entrapment can lead to malfunctioning of the jet formation. The piezoactuator is employed to actively monitor the channel acoustics and to identify distortions at an early stage. Modifications of the response of the piezoactuator indicate entrapped air bubbles and these allow us to investigate them. When we employ the signal as a trigger for high-speed imaging, we can visualize the consequences of the entrained bubbles on the droplet formation. Two mechanisms are found to cause air entrapment: First, a distorted droplet formation caused by small particles, and, second, an accumulation of ink on the nozzle plate, which favors void formation once the meniscus is pulled back.