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针对常规光栅条纹反射三维形貌测量方法中对实际参考面的需求,提出了基于虚拟参考面方法。在系统标定阶段,通过向标定用平面镜投射一幅特殊标记的棋盘格图像,将其在平面镜另一侧成的虚拟像所在的平面定义为虚拟参考面。根据虚拟参考面上各点与编码光栅条纹相位间的对应关系,经计算可直接得到测量所需的两垂直方向的参考相位分布,从而无需在工件测量前首先对实际参考面进行相位提取操作。与常规光栅条纹反射三维形貌测量方法相比,由于避免了对参考平面测量的需求,本文方法获得的参考相位分布,在保证测量精度的同时提高了测量速度,降低了测量的复杂性,有利于系统的集成化。搭建了光栅条纹反射三维形貌测量系统,采用基于虚拟参考面的光栅条纹反射方法对超精密加工平面镜和组合台阶的表面形貌进行测量,建立相位偏移与被测工件表面梯度的对应关系,由梯度恢复工件表面高度,测量精度达到50μm左右。
Aiming at the demand of actual reference plane in the method of measuring three-dimensional topography by conventional grating fringe reflection, a virtual reference plane method is proposed. In the stage of system calibration, the plane of the virtual image which is formed on the other side of the plane mirror is defined as a virtual reference plane by projecting a specially marked checkerboard image to the calibration plane mirror. According to the correspondence between the points on the virtual reference plane and the phases of the encoder grating stripes, the two perpendicular reference phase distributions required for measurement can be calculated directly, so that it is not necessary to perform the phase extraction operation on the actual reference plane before measuring the workpiece. Compared with the conventional grating fringe reflection three-dimensional topography measurement method, the reference phase distribution obtained in this method avoids the need for reference plane measurement, which improves the measurement speed and reduces the complexity of measurement while ensuring the measurement accuracy. Conducive to the system integration. The grating fringe reflection 3D topography measurement system is established. The surface topography of the ultra-precision machining mirror and combination step is measured by the grating reference reflection method based on the virtual reference surface. The corresponding relationship between the phase offset and the surface gradient of the workpiece is established. By the gradient to restore the workpiece surface height, the measurement accuracy of about 50μm.