Real-Time Inspection of Rod Straightness and Appearance by Non-Telecentric Camera Array

Abstract

In this paper, we propose a measurement system that employs a camera array based on a non-telecentric optical system and an accompanying measurement algorithm to measure the straightness, length, diameter, and appearance of a rod. Measurements using telecentric optical systems, which employ orthogonal projection to preserve the dimensional ratios regardless of distance, are common in image-based inspection of the dimensional or geometrical tolerances of industrial products. However, some cases depend on the size of the target or inspection item, wherein it is difficult to configure a measurement system using telecentric optical systems. As an example, this study considers the measurement of straightness of a long rod and shows that it is possible to achieve high measurement accuracy using non-telecentric optical systems by introducing methods to calibrate miniscule errors and distortions that remain uncorrected in conventional image calibration methods. We also show that the same measurement allows for the measurement of other inspection items and evaluation of their respective measurement accuracies, thereby proving that a flexible image-based inspection process can be constructed using the proposed system and method.