Ultra high-speed 3D shape measurement technology for specular surfaces based on μPMD

Area of Science:

• Optical Metrology
• Surface Metrology
• 3D Reconstruction

Background:

• Phase Measuring Deflectometry (PMD) is a non-contact, high-precision technique for specular surface measurement.
• Traditional PMD using Liquid Crystal Displays (LCDs) is limited to ~100 fps due to slow liquid crystal response times, hindering dynamic surface measurement.
• Measuring rapidly moving surfaces requires significantly higher frame rates than currently achievable with standard PMD.

Purpose of the Study:

• To develop a novel 3D dynamic sensing technique, microsecond-PMD (µPMD), capable of measuring rapidly moving specular surfaces.
• To achieve high-speed fringe acquisition at kHz or 100kHz levels for dynamic 3D reconstruction.
• To enable real-time monitoring applications in manufacturing.

Main Methods:

• Proposed µPMD utilizes a high-frame-rate sinusoidal fringe display (HSFD) with sub-microsecond fringe pattern switching times.
• HSFD employs a specialized LED array and two-step optical expansion, leveraging LED's fast switching characteristics.
• Superior sinusoidal fringe properties are achieved through a combination of a discrete sinusoidal LED array, orthogonal gratings, and a light diffuser, optimized using swarm optimization.

Main Results:

• The µPMD system achieved a superfast fringe acquisition rate of 4000 frames per second (fps).
• Sub-micrometer precision was attained in three-dimensional (3D) reconstruction of specular surfaces.
• Demonstrated feasibility for dynamic measurement of moving surfaces, overcoming limitations of traditional PMD.

Conclusions:

• The proposed µPMD technique successfully enables high-speed, high-precision 3D reconstruction of dynamic specular surfaces.
• This advancement overcomes the frame rate limitations of conventional PMD systems.
• µPMD holds significant potential for real-time monitoring and quality control in advanced manufacturing processes.