A Pre-Measurement Device for Contour Measurement Path Planning of Complex Small Workpieces

Small overall dimensions, intricate geometries, and discontinuous local surface normals characterize complex small workpieces. These features impose stringent requirements on the alignment accuracy of the workpieces when using a profilometer for three-dimensional surface measurement. This paper presents a pre-measurement method based on a reverse projection algorithm. By capturing shadow contours from multiple viewing angles, the three-dimensional pointcloud of the workpiece can be reconstructed. The reconstructed pointcloud is then used to analyze the workpiece pose and guide the path planning of a point-scanning profilometer. Experimental results show that, for a standard sphere with a radius of 12,703 mm, the measured results of the proposed measurement device achieve a fitted radius deviation of 1.8 μm when measuring 70% of the area of the spherical surface. This accuracy meets the precision requirement for guiding the path planning of the profilometer. Furthermore, the measured results from the device are employed to correct the scanning path of a five-axis profilometer for complex workpieces, such as cross-cylinder workpieces, without the need for manual pose adjustment or high-precision fixtures.