Development of a human-friendly visual inspection method for painted vehicle bodies

Visual inspections performed in the final stage of the vehicle manufacturing process are crucial for assuring the quality of painted vehicle bodies. However, lengthy visual inspections can cause fatigue and discomfort of the eyes, which may adversely affect inspection accuracy and efficiency. This study developed a new human-friendly visual inspection method for the detection of defects (e.g., scar and dent) on vehicle bodies, and compared its performance to a conventional inspection method in terms of critical fusion frequency (Hz, indirect measure of eye fatigue), defect detectability (%), and subjective satisfaction score (7-point Likert scale). The new method was devised to project bright-dark linear stripes onto the surface of the vehicle body and created emergent features (distorted stripes) where a defect existed. The critical fusion frequency of the new method decreased slightly (3.7%) after a 30-minute visual inspection task, whereas that of the conventional method dropped substantially (11.0%), which implied more severe eye fatigue. Additionally, the new method had significantly higher defect detectability (92.1%) and satisfaction score (5.8 points) than those (73.4% and 3.5 points) of the conventional method.