A practical evaluation approach towards form deviation for two-dimensionalcontours based on coordinate measurement data

A precise evaluation of the form deviations of two-dimensional (2D) enginee ring contours is of essential importance in precision manufacturing. In thi s paper, we propose a practical approach towards evaluating form deviations of 2D contour profiles based on coordinate measurement data. Using this ap proach, a 2D contour is divided into straight and curved parts. Each straig ht part is directly presented by the original definition of the part; and e ach curved part is further represented by its optimal interpolation circula r are segments whose interpolation accuracy can be specified arbitrarily. T he approximate contour curve consisting of the straight and circular are se gments has the fewest interpolation segments under the condition of satisfy ing the pre-specified interpolation accuracy. The form deviation of a measu red point is defined as the distance from the point to its corresponding st raight or circular segment. The geometrical form deviation of the contour p rofile is evaluated using the least square method. It has been demonstrated that the difference between the deviation definitions, relative to the ori ginal contour or to the approximate contour, is not larger than the pre-spe cified accuracy value for circular are interpolation. Therefore, the evalua tion precision of the form deviation can be sufficiently guaranteed. The ap proach is easy and convenient for engineering applications. The effectivene ss and the efficiency of the approach are verified with a practical example of a planar cam contour in the paper. (C) 1999 Elsevier Science Ltd. All r ights reserved.