In-situ Monitoring Methods for Electrohydrodynamic Inkjet Printing towards Autonomous In-space Manufacturing

In-space manufacturing is a promising solution to mitigate uncertainties and unexpected failures during long-duration or long-distance space missions. Electrohydrodynamic (EHD) inkjet printing is a high-resolution technology that has demonstrated its capability for electronics manufacturing under microgravity conditions. Given the autonomous operational requirements of in-space platforms, such as the International Space Station (ISS), automation of the printing process, including control and inspection for high stability and quality, is essential. Vision-based solutions are among the most widely used methods for process monitoring. However, traditional camera and lens setups have several limitations: they require significant space, offer limited resolution for micron-scale features, and experience delays in data collection, transmission, and analysis due to large data sizes. In this paper, we propose an in-situ monitoring system based on laser diffraction to replace conventional camera/lens setups for monitoring the EHD printing process. We evaluate its capability to identify jetting modes and capture key jetting features, such as jetting diameter and jetting direction, by comparing its performance with traditional vision-based methods. Our results demonstrate that the laser diffraction system can accurately identify different jetting modes and achieve approximately 45× magnification by converting jetting patterns into diffraction patterns. This significantly improves the measurement accuracy of the jetting diameter. Based on this monitoring system, we developed a Statistical Process Control (SPC) chart to track the transition from unstable jetting to stable cone-jetting conditions, thereby validating the feasibility of the proposed concept.