等 倾 角 线 快 速 跟 焦 的 激 光 差 动 共 焦 自 由 曲 面 测 量 方 法

To address the issue of measurement accuracy degradation caused by varying nonlinear errors induced by normal inclination angle changes during point-by-point scanning of freeform surfaces, an isoclinic line-based rapid focusing differential confocal method for freeform surface measurement was proposed. The method utilizes an improved Coherent Point Drift（CPD）registration algorithm to calculate the precise pose of the Freeform Surface Under Test（FSUT）. Based on the precise pose of the FSUT, multiple isoclinic lines are planned. By performing axial scanning with the sensor, the relationship between light intensity and defocus amount on different isoclinic lines is obtained. The axial response light intensity is used as feedback to track the contour of the FSUT along the isoclinic lines. Leveraging the characteristic that the non-linear error between the normalized differential confocal axial response light intensity and defocus amount is insensitive to small angle changes, fast scanning measurement of freeform surfaces is realized by focusing along isoclinic lines. Experimental results show that the tracking error of the isoclinic lines in the proposed method is ±70 nm, which has a negligible impact on the calculation accuracy of defocus amount compared with the differential confocal measurement resolution. Compared with the traditional differential confocal measurement method, the efficiency is increased to at least 5 times higher; the Peak-to-Valley （PV）value of the surface profile obtained by point-to-point subtraction with ZYGO interferometer data is 9 nm, and the Root Mean Square（RMS）value is 1 nm, achieving high-precision and fast measurement of freeform surfaces.