Monocular Structured-Light Sensing for 3D Metallic Hole Measurement

Area of Science:

• Metrology and Inspection
• Optical Measurement Systems
• Computer Vision

Background:

• Non-contact inspection of metallic circular holes is critical for quality control but challenging due to reflective surfaces.
• Existing methods like 2D vision lack depth accuracy, while 3D systems incur high costs.
• Conventional structured-light approaches often fail with combined reflection and edge defects.

Purpose of the Study:

• To develop a robust monocular structured-light framework for accurate metric inspection of metallic circular holes.
• To integrate sensing geometry, radiometric reliability, and robust hole estimation into a unified measurement chain.
• To overcome challenges posed by reflective surfaces and edge defects in hole inspection.

Main Methods:

• A monocular structured-light system using a single calibrated camera and an obliquely projected line laser.
• Multi-exposure high-dynamic-range (HDR) fusion and adaptive Gaussian regularization for stable stripe centerlines.
• Geometry-aware contour screening and probabilistic multi-stage RANSAC for outlier-robust circle parameter estimation.

Main Results:

• The system successfully performed non-contact metric inspection on steel and aluminum alloy workpieces.
• Accurate diameter and center-position measurements were achieved, with mean optical-CMM diameter differences as low as 0.096 mm for aluminum holes.
• The framework demonstrated stability under challenging conditions like local saturation and uneven illumination.

Conclusions:

• The proposed monocular structured-light framework provides a feasible and accurate solution for inspecting metallic circular holes.
• The integrated approach effectively addresses challenges from reflective surfaces and edge defects.
• The system's performance is validated on specific workpieces and measurement volumes.