Free-form surface measurement with laser differential confocal precise positioning

For free-form surfaces with multiple degrees of freedom, conventional interferometric detection methods face challenges in achieving dynamic detection during the machining process, primarily owing to continuous variations in the unknown surface topography. This study proposes a free-form surface measurement method with laser differential confocal precise positioning, enabling high-precision zero-point positioning, position tracking, and single-point contour scanning of the free-form surface topography. The proposed method addresses the challenge of high-precision and large-range measurements through non-contact and rapid surface shape detection. In this study, a free-form surface measurement system with precise differential confocal positioning was developed. Theoretical analysis and preliminary experiments show that the axial resolution of the differential confocal sensor and laser interferometer was 1 nm; the measurement angle ranges of the laser interferometer and the phase-sensitive demodulator were ± 4° and ± 20°, respectively. The composite uncertainty of the sensor using this method was 12.4 nm. This offers a new approach for high-precision, automatic, and rapid measurement of free-form surfaces, with potential applications in the field of optical manufacturing.