基于三频外差法的异构铸件三维测量系统

惯性平台中的台体和本体均为复杂异构铸件，目前多采用人工划线法建立多个基准来进行测量，效率和精度低，易漏检误检。基于多频外差法的三维光学测量系统已广泛应用于航空、航天等制造领域，根据被测铸件异构的特点，结合双目视觉和相位光栅法较高的检测效率和精度，搭建了一套三维测量系统。首先通过平板标定法得到系统的固定参数和可变参数，然后利用数字光栅投影仪向被测零件表面投射三套不同频率的相移条纹图，相机同步采集变形条纹图，再利用四步相移和三频外差法得到周期为1的相位分布，以此为基准展开得到连续分布的绝对相位，结合极线约束和相位匹配重建出被测零件的三维点云数据，最后在三维软件中完成点云处理、曲面重构和三维测量。实验结果表明，系统的绝对测量精度小于0.1mm，能够实现异构铸件的三维尺寸测量，具有较高的检测效率。

Three-dimensional Heterogeneous Castings Measurement System Based on Tri-frequency Heterodyne Principle

The machine body and noumenon in the inertial platform are complex heterogeneous castings. At present, the manual marking method is used to establish multiple benchmarks for measuring castings. This method has low efficiency and accuracy, and is easy to miss detection and error detection. Three-dimensional optical measurement system based on multi-frequency heterodyne method is widely used in aerospace and other manufacturing fields. Based on the characteristics of the heterogeneous castings, a three-dimensional measurement system combined with high detection efficiency and precision of binocular visions and phase grating has been built. Firstly, the plate calibration method is selected to obtain the fixed and variable parameters of the system. The digital grating projector projects three sets of different frequency phase shifting stripe onto the tested surface, and the cameras acquire the deformation stripe images synchronously. Secondly, the phase distribution with a period of 1 through the principle of four-step phase shifting and three-frequency heterodyne is gotten, on the basis of this phase distribution, the absolute phase is obtained. Then, the point cloud data is reconstructed by the polar constrains and phase matching. Finally, the point cloud processing, surface reconstruction and three-dimensional measurement are completed in the 3D software. The experiment results show that the absolute accuracy of this system is less than 0.1mm, and it can realize 3D measuring of heterogeneous castings and has the high detection efficiency.