Low-Coherence Measurement Methods for Industrial Parts With Large Surface Reflectance Variations.

High-precision measurement of sizes and key parameters of industrial parts is crucial to ensure manufacturing accuracy and assembly reliability. Low-coherence measurement methods offer advantages, including high precision, relatively large measuring range, and nondestructive nature. These measurement methods have shown great potential for applications in the field of industrial measurement. However, most of the current industrial low-coherence measurement methods assume that the surface reflectance of parts is constant or has little variability, resulting in poor adaptability and limited application range of these methods. To address this issue, this article proposes a low-coherence measurement method for measuring key parameters of industrial parts, which can be applied to a variety of parts with significant surface reflectance variations. To be more specific, we first establish an industrial low-coherence model that theoretically proves its feasibility in adapting to surfaces with varying reflectance levels. Based on the derived measurement model, we design a simple yet effective optical path that ensures the adaptability of the proposed system to different surfaces. Finally, we build an industrial low-coherence system to verify the effectiveness of the proposed method. We measure key parameters of a standard step and various industrial parts with different reflection conditions, and measurement results show that the proposed method achieves an optimal measurement accuracy of 0.0017 mm and a maximum range exceeding 29.0 mm. The proposed method is also demonstrated to be adaptable to industrial parts with a variety of reflection conditions, including diffuse reflection, specular reflection, and mirror-like reflection.