In-process Monitoring of Electrohydrodynamic Inkjet Printing using Machine Vision

Electrohydrodynamic inkjet printing (e-jet printing) is one type of micro/nano scale 3D printing techniques that automatically deposit functional materials to form 3D structures on the substrate. Unlike traditional thermal or acoustic inkjet printing, e-jet printing utilizes high electrical forces for the ink to overcome surface tension at the tip of micro needles. The droplets and filaments coming out from the needle have dimensions much smaller than the dimension of the needle, thus to print geometries in micro and nano scale. E-jet printing process parameters can affect the final quality attributes of fabricated constructs. Currently, assessment of these critical geometries and attributes information must be performed offline using optical microscopy or scanning electron microscopy. This drawback affected the efficiency of micro/nano printing from translation to industrial practice. The research in this paper focused on fundamental research to enable in situ monitoring of e-jet printing using a real-time images characterization technique. In conclusion, the study in this paper investigated using machine vision for real-time monitoring of micro/nano scale 3D printing. The method worked well for micro-filament detection in e-jet printing, and may be further implemented into feedback control system of complicated e-jet printing. However, the optical machine vision was limited to micro scale detection. One of the future research topic is to develop nano scale in situ detection mechanism for e-jet printing.