  Visual defect detection is critical to ensure the quality of most products.
However, the majority of small and medium-sized manufacturing enterprises still
rely on tedious and error-prone human manual inspection. The main reasons
include: 1) the existing automated visual defect detection systems require
altering production assembly lines, which is time consuming and expensive 2)
the existing systems require manually collecting defective samples and labeling
them for a comparison-based algorithm or training a machine learning model.
This introduces a heavy burden for small and medium-sized manufacturing
enterprises as defects do not happen often and are difficult and time-consuming
to collect. Furthermore, we cannot exhaustively collect or define all defect
types as any new deviation from acceptable products are defects. In this paper,
we overcome these challenges and design a three-stage plug-and-play fully
automated unsupervised 360-degree defect detection system. In our system,
products are freely placed on an unaltered assembly line and receive 360 degree
visual inspection with multiple cameras from different angles. As such, the
images collected from real-world product assembly lines contain lots of
background noise. The products face different angles. The product sizes vary
due to the distance to cameras. All these make defect detection much more
difficult. Our system use object detection, background subtraction and
unsupervised normalizing flow-based defect detection techniques to tackle these
difficulties. Experiments show our system can achieve 0.90 AUROC in a
real-world non-altered drinkware production assembly line.
