Iterative Algorithm for Radius Stylus Compensation of Touch Sensor When Measured on CMMs of Complex Surfaces

When measuring on the Coordinate Measuring Machines by a contact method, an error arises in determining the touch point of the probe and the actual surface. Therefore, the obligatory stage of mathematical processing of results is the compensation of the touch probe radius. The efficiency of the known compensation algorithms is characterized by the measurement error and the processing time of the information. Algorithms, that take into account data on neighboring points of tangency or calculate the equidistant surfaces of the centers of a spherical probe, will be the most accurate. Therefore, they are used in the measurement of complex surfaces. The authors propose an iterative algorithm of probe radius compensation through successive refinement of the touch point coordinates. The algorithm minimizes the angle between the normals at each measured point to the nominal and actual surfaces. Comparison of the probe radius compensation results for the developed algorithm with known showed the advantage of the iterative algorithm. The above calculation example for the compressor turbine blade confirms a 25% reduction in the measurement error. The greatest effect on increasing accuracy is achieved with a small number of measured points and their uneven location on a complex surface with variable curvature.