A Method of Measuring a 3-Dimensional Curve on a Surface with a CMM

Abstract

In order to examine and evaluate the characteristics of a mechanical component, a 3-dimensional curve on the surface of the component needs to be measured on a coordinate measuring machine (CMM). A method of measuring a 3-dimensional curve on a surface with a CMM was put forward in this paper. The measuring method of each point of the curve on the surface is divided into three steps. The first step is to select some grid points of the surface near the measured point of the curve. Actually the measuring results are the coordinates of the center of the spherical probe and all of the grid points locate in the offset surface of the measured surface. So the probe radius should be compensated. In order to make the compensation reliable, easy and simply, some regular grid points where the probe center should be set are selected and a corresponding method of calculating the normal vector of the surface is used. A small surface patch of the actual surface is measured in the second step. In the last step, some new grid points are obtained after probe radius compensation. The real coordinates of the measured point is determined by using the interpolation method and the theoretical equation of the curve. The measuring method was used to examine the modification curve of a worm generated by linear cutter edge with two degrees of freedom and the results showed the coherence of the actual modification curve to the theoretical one.