液滴塗布ヘッド内の気泡検出に関する研究
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概要
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The stability of jetting is a major requirement for industrial inkjet heads. Air bubbles entrapped in a piezo-driven inkjet head can occasionally cause jetting failures. The piezo actuators can be used as sensors to detect the acoustic influence caused by air bubbles. As in our previous paper, we developed a controllable bubble generation method by focused THG Nd:YVO4 laser with the secondary Bjerknes forces and could intentionally generate bubbles from about 5 micron to 150 micron in radius at the designated point near the nozzle inside the inkjet heads.In this paper, experimental results on the relationship between the electric signal from the piezo actuators and bubbles are presented. We find the existence of a kind of a dead zone where the emitted sound pressure from a bubble is insensitive to the bubble size. Our numerical study shows this phenomenon is attributed to the increase of the radiation impedance with an increasing bubble size in reverberant sound fields as in the inkjet heads. We also present CFD simulation results using models with a bubble inside an inkjet head in order to make an estimate of the bubble size and position to cause jetting failures.