Multi-objective optimization of actuation waveform for high-precision drop-on-demand inkjet printing

Abstract

High-precision drop-on-demand (DOD) inkjet printing has been considered as one of the promising technologies for the fabrication of advanced functional materials. For a DOD printer, high-precision dispensing techniques for achieving satellite-free smaller droplets have long been desired for patterning thin-film structures. Optimization of an actuation waveform driving a DOD inkjet printer is one of the most versatile and effective strategies to obtain high-precision droplets. Considering the complexity of physics behind the droplet dispensing mechanisms and the large degrees of freedom in the applied waveforms, conventional trial-and-error approaches are not effective for searching the optimal waveform. The present study considers the inlet velocity of a liquid chamber located upstream of a dispensing nozzle as a control variable and aims to develop an automated waveform tuning framework to optimize its waveform using a sample-efficient Bayesian optimization (BO) algorithm. First, the droplet dispensing dynamics are numerically reproduced by using an open-source OpenFOAM solver, interFoam, and the results are passed on to another code based on PyFoam. Then, the parameters characterizing the actuation waveform driving a DOD printer are determined by the BO algorithm so as to maximize a prescribed multi-objective function expressed as the sum of two factors, i.e., the size of a primary droplet and the presence of satellite droplets. The results show that the present BO algorithm can successfully find high-precision dispensing waveforms within 150 simulations. Specifically, satellite droplets can be effectively eliminated and the droplet diameter can be significantly reduced to 24.9% of the nozzle diameter by applying the optimal waveform. Moreover, the prediction using the Gaussian process regression suggests that the size of the primal droplet is highly correlated with the period of a waveform. Finally, the criterion for achieving single-droplet dispensing is proposed based on the energy budget analysis.