LuBan: Low-Cost and In-Situ Droplet Micro-Sensing for Inkjet 3D Printing Quality Assurance

Inkjet 3D printing is a disruptive manufacturing technology in emerging metal- and bio-printing applications. The nozzle of the printer deposits tiny liquid droplets, which are subsequently solidified on a target location. Due to the elegant concept of micro-droplet deposition, inkjet 3D printing is capable of achieving a sub-millimeter scale manufacturing resolution. However, the droplet deposition process is dynamic and uncertain which imposes a significant challenge on quality assurance of inkjet 3D printing in terms of product reproducibility and process repeatability. To this end, we present Luban as a certification tool to examine the printing quality in the inkjet printing process. Luban is a new low-cost and in-situ droplet micro-sensing system that can precisely detect, analyze and localize a droplet. Specifically, we present a novel tiny object sensing method by exploiting the computational light beam field and its sensitive interference effect. The realization of Luban is associated with two technical thrusts. First, we study integral sensing, i.e., a new scheme towards computational light beam field sensing, to efficiently extract droplet location information. This sensing scheme offers a new in-situ droplet sensing modality, which can promote the information acquisition efficiency and reduce the sensing cost compared to prior approaches. Second, we characterize interference effect of the computational light beam field and develop an efficient integration-domain droplet location estimation algorithm. We design and implement Luban in a real inkjet 3D printing system with commercially off-the-shelf devices, which costs less than a hundred dollars. Experimental results in both simulation and real-world evaluation show that Luban can reach the certification precision of a sub-millimeter scale with a 99% detection accuracy of defect droplets; furthermore, the enabled in-situ certification throughput is as high as over 700 droplets per second. Therefore, the performance of our Luban system can meet the quality assurance requirements (e.g., cost-effective, in-situ, high-accuracy and high-throughput) in general industrial applications.