An adaptive on-machine sampling strategy for blades based on modified equal chord height method

In the context of the aeronautics industry, the parts of the aircraft should be machined precisely and efficiently, for which an appropriate on-machine measurement technique is indispensable. The blade is a core part in an aeroengine, and its surface topography has a freeform with complex geometrical configuration and dramatic curvature change from the pressure side or suction side to the leading edge or trailing edge. Given the problem that the allocation of checkpoints determined by the traditional equal chord height method fails to properly follow the curvature variation of the blade surface and then results in measurement error, an adaptive sampling strategy with the modified equal chord height method is proposed. The second-order derivative of curvature is introduced to accurately describe the shape change of the blade surface for the purpose of providing a better consistency between the measurement point assignment and the profile shape. A set of control factors is defined and used to adjust the distribution of measurement points adaptively. The significant advantages of the method in sampling time and reconstruction performance are validated by the case studies with the results that MAE and RMSE of the reconstructed surface are 1.6 µm and 3.5 µm, respectively, and on-machine measurement experiment with the results that MAE and RMSE are 13.1 µm and 15.7 µm, respectively, which are far less than those of the other three classical sampling methods. In addition, on the premise of guaranteeing accuracy, the efficiency can be improved by nearly 50%, which meets the production requirements on efficiency and accuracy of the on-machine measurement.