Miao Li, Zhu Linlin, Fang Changshuai, Yan Ning, Yang Xudong, Zhang Xiaodong
State Key Laboratory of Precision Measuring Technology & Instruments, Laboratory of Micro/Nano Manufacturing Technology, Tianjin University, Tianjin 300072, China.
Sensors (Basel). 2021 Jan 14;21(2):554. doi: 10.3390/s21020554.
Profile measurement is a key technical enabler in the manufacturing of highly curved freeform surfaces due to their complex geometrical shape. A current optical probe was used to measure nearly rotary freeform surfaces with the help of one rotation axis, because the probe needs to measure along the normal vector of the surface under the limitation of the numerical aperture (NA). This kind of measuring system generally has a high cost due to the high-precision, multi-axis platform. In this paper, we propose a low-cost, dual-axis rotation scanning method for a highly curved freeform surface with an arbitrary shape. The optical probe can scan the surface profile while always keeping consistent with the normal vector of the measuring points with the help of the double rotation axis. This method can adapt to the changes in curvature in any direction for a highly curved freeform surface. In addition, the proposed method provides a system error calibration technique for the rotation axis errors. This technique can be used to avoid the dependence of the measuring system on the high-precision platform. The three key system errors that affect the measurement accuracy such as installation error of the B-axis, A-axis, and XZ perpendicularity error are first analyzed through establishing an error model. Then, the real error values are obtained by the optimal calculation in the calibration process. Finally, the feasibility of the measurement method is verified by measuring one cone mirror and an F-theta mirror and comparing the results to those obtained using commercial equipment. The maximum measurable angle of the system is ±90°, the maximum measurable diameter is 100 mm, and the measurement accuracy of the system reaches the micron level in this paper.
轮廓测量是制造高度弯曲的自由曲面的关键技术，因为其几何形状复杂。由于在数值孔径（NA）的限制下，探头需要沿曲面的法向量进行测量，因此当前的光学探头借助一个旋转轴来测量近似旋转的自由曲面。由于高精度、多轴平台，这种测量系统通常成本很高。在本文中，我们针对任意形状的高度弯曲自由曲面提出了一种低成本的双轴旋转扫描方法。光学探头可以在双旋转轴的帮助下扫描曲面轮廓，同时始终与测量点的法向量保持一致。该方法可以适应高度弯曲自由曲面在任何方向上的曲率变化。此外，所提出的方法提供了一种用于旋转轴误差的系统误差校准技术。该技术可用于避免测量系统对高精度平台的依赖。首先通过建立误差模型分析影响测量精度的三个关键系统误差，如B轴安装误差、A轴安装误差和XZ垂直度误差。然后，在校准过程中通过优化计算获得实际误差值。最后，通过测量一个锥面镜和一个F-θ镜并将结果与使用商业设备获得的结果进行比较，验证了测量方法的可行性。本文中系统的最大可测角度为±90°，最大可测直径为100mm，系统测量精度达到微米级。
