The Selection of Radius Correction Method in the Case of Coordinate Measurements of a Turbine Blade

The objective of the research presented in the paper is the selection of suitable probe radius correction method in the case of coordinate measurements of a turbine blade. The investigations are based on theoretical analysis of geometric data and on further computer simulation of measurements and data processing. In the paper two methods for computing coordinates of corrected measured points are verified. Those so-called local methods of probe radius correction are based on the 2 degree and the 4 degree Bézier curves. They are dedicated first of all to coordinate measurements of free-form surfaces which are characterized by big values of curvature, e.g. those surrounding the leading and trailing edges of a turbine blade. Numerical simulations are done for several models of the transverse sections of turbine blades with diversified magnitudes of radii of curvature. There are considered both manufacturing deviations and coordinate measurement errors of each examined profile of turbine blade. Moreover, the paper presents an algorithm concerning computations of data which extends the set of standard algorithms used for the analysis of coordinate measurements of a turbine blade developed by Carl Zeiss for its coordinate measuring machines and coded within the measurement software Calypso and Blade Pro. The paper shows how to implement the developed algorithms of probe radius correction within the standard CMM software by using parametric programming option PCM available in the measurement software Calypso.