DeepFunction: Deep Metric Learning-based Imbalanced Classification for Diagnosing Threaded Pipe Connection Defects using Functional Data

In modern manufacturing, most of the product lines are conforming. Few products are nonconforming but with different defect types. The identification of defect types can help further root cause diagnosis of production lines. With the sensing development, signals of process variables can be collected in high resolution, which can be regarded as multichannel functional data. They have abundant information to characterize the process and help identify the defect types. Motivated by a real example from the pipe tightening process, we focus on defect classification where each sample is a multichannel functional data. However, the available samples for each defect type are limited and imbalanced. Moreover, the functions are incomplete since the pre-tightening process before the pipe tightening process is unobserved. To classify the defect samples based on imbalanced, multichannel, and incomplete functional data is very important but challenging. Thus, we propose an innovative classification framework based on deep metric learning using functional data (DeepFunction). The framework leverages the power of deep metric learning to train on imbalanced datasets. A neural network specially crafted for processing functional data is also proposed to handle multichannel and incomplete functional data. The results from a real-world case study demonstrate the superior accuracy of our framework when compared to existing benchmarks.