Image-based Machine Learning Applications in Nitrate Sensor Quality Assessment and Inkjet Print Quality Stability

An on-line quality assessment system in the industry is essential to prevent artifacts and guide manufacturing processes. Some well-developed systems can diagnose problems and help control the output qualities. However, some of the conventional methods are limited in time consumption and cost of expensive human labor. So, more efficient solutions are needed to guide future decisions and improve productivity. This thesis focuses on developing two image-based machine learning systems to accelerate the manufacturing process: one is to benefit nitrate sensor fabrication, and the other is to help image quality control for inkjet printers.

In the first work, we propose a system for predicting the nitrate sensor's performance based on non-contact images. Nitrate sensors are commonly used to reflect the nitrate levels of soil conditions in agriculture. In a roll-to-roll system, for manufacturing thin-film nitrate sensors, varying characteristics of the ion-selective membrane on screen-printed electrodes are inevitable and affect sensor performance. It is essential to monitor the sensor performance in real-time to guarantee the quality of the sensor. We also develop a system for predicting the sensor performance in on-line scenarios and making the neural networks efficiently adapt to the new data.

Streaks are the number one image quality problem in inkjet printers. In the second work, we focus on developing an efficient method to model and predict missing jets, which is the main contributor to streaks. In inkjet printing, the missing jets typically increase over printing time, and the print head needs to be purged frequently to recover missing jets and maintain print quality. We leverage machine learning techniques for developing spatio-temporal models to predict when and where the missing jets are likely to occur. The prediction system helps the inkjet printers make more intelligent decisions during customer jobs. In addition, we propose another system that will automatically identify missing jet patterns from a large-scale database that can be used in a diagnostic system to identify potential failures.