Laser differential confocal interference surface automatic measurement method

Abstract

Considering the low accuracy, slow speed and small adjustment range of measuring an object with a spherical surface using traditional interferometry owing to adjusting the posture of the object, an automatic laser differential confocal interferometric measurement method is proposed to measure the surface shapes, which achieves the high-precision confocal axial positioning of the measured object through a precise differential confocal fixed-focus technology. The posture of the measured object is adjusted through a five-dimensional adjustment workbench. Subsequently, the Zernike fitting is used to reduce the defocus and tilt errors, and a zero-order fringe adjustment of the interferometric surface shape is achieved, automatically determining the surface shape. A laser differential confocal interferometric measurement system for surface shapes was constructed. Experiments demonstrate that the difference between the automatic interference measurement results and the Zygo interferometer measurement results is 0.0004 λ, the repeated measurement accuracy of this method can reach 0.0019 λ, the average measurement time of a single interferometric surface shape is 20.1 s, and the measurement efficiency is improved by 1.5 times compared to the manual adjustment to the zero-order fringe. Compared with the traditional adjustment based on Zernike fitting, this method has increased the lateral adjustment range by 11.5 times and the axial adjustment range by 1.5 times. This method provides an effective measurement method for the rapid and high-precision measurement of interferometric surface shapes.