Investigating the jettability of toluene in a piezo inkjet

This report starts by introducing the working principles of a single nozzle piezo inkjet system. The current voltage waveform calibration process for a piezo inkjet is time consuming and subsequently a cause for material waste. Recent research has demonstrated that the use of real-time imaging of in-flight drops integrated with genetic algorithms (GAs) can lead to improved waveforms that provide enhanced system performance. In this work, the same imaging system is used to reproduce known results for simple fluids such as water, and manual waveform tuning was used instead. This framework was then extended to nonpolar solvents. The experiments presented in this project investigated the jettability of toluene. Toluene is a nonpolar liquid that has raised interest about its viability as an ink used in piezo inkjets. The manual waveform tuning process was centered around adjusting key parameters such as dwell time and dwell voltage. As these parameters were tweaked, real-time imaging was used to observe the drop formation at the orifice of the inkjet nozzle. Once the key parameters were optimized, a droplet of toluene was generated. Unipolar, bipolar, and tripolar actuation waveforms were investigated to determine if a droplet of toluene was able to be dispensed. Bipolar and tripolar waveforms produced droplets that were dispensed at irregular frequencies along with physical deformities. This work found that using a unipolar actuation waveform produced the best results, generating consistent spherical toluene droplets with an average drop volume of 30.2 pL. The optimal waveform parameters were as follows: a rise time of 11 µs, a dwell time of 36 µs, a fall time of 9 µs, and a dwell voltage of 60 V.