A Viewpoint Planning Algorithm Based on 7 Degree of Freedom Optical 3D Measurement System for the Turbine Blade Measurement

Optical three-dimensional (3D) measurement is an essential method for improving the efficiency of surface detection for blades in steam turbines, gas turbines, and aircraft engines. The combination of a scanner, a robot, and a turntable provides a flexible and accurate optical 3D measurement scheme. This article proposes a viewpoint planning method for a 7-degrees-of-freedom (DOF) optical 3D measurement system based on measurement feature extraction, which addresses problems such as a large number of ineffective and unreachable viewpoints, a low coverage rate, and viewpoint sequences with long motion time. It reduces the number of invalid viewpoints by extracting measurement features from blades. In addition, viewpoints within a 6 DOF space are sampled by rotating the optical axis of the scanner to improve the coverage rate. Then, the reachability of viewpoints is verified by using equivalent viewpoints for the measurement system with redundant DOF, and many invalid viewpoints are removed to reduce the time cost of the viewpoint visibility evaluation. A generalized traveling salesman problem is constructed by rotating the turntable uniformly, and a collision-free path planning algorithm based on backup solvers is designed. Finally, a third-stage rotating blade of a heavy-duty gas turbine is used as the measurement object for the experiment. The experimental results show that the proposed method improves the measurement coverage by an average of 14.75%, removes an average of 27.97% of unreachable viewpoints, and reduces the time required for viewpoint visibility evaluation time by an average of 153.84 seconds compared to traditional viewpoint sampling methods. Compared to traditional solutions to the traveling salesman problem solutions, it reduces scanning time by an average of 27.44% .