In cutter-path genertation for sculptured surface machining (SSM), cutter-location (CL) points are usually generated as a sequence of "planar" points defined on horizontal planes (during contouring) or vertical planes (during area scanning) which are parallel with the xz-plane or yz-plane. A simple method of obtaining NC-codes for SSM is to connect adjacent CL-points with a line segment. The main disadvantages of this linear interpolation method are 1) excessive NC-file sizes with too small line segments and 2) tangential discontinuity between linear movements (G01) commands, both of which affect the quality of surface finish as well as machining productivity. Thus, it is a recent trend that circular interpolations (and NURBS interpolation), which are free from the above drawbacks, are widely used in SSM.
Presented in the thesis is a biarc curve fitting method for circular interpolation. In the proposed biarc-fitting method which is termed the "flexible biarc-fitting method", the input point sequence is first preprocessed so that "break points" (or tangent discontinuity points), linear regions and circular regions are identified. And then a search rule is applied to each "freeform" curve segment so that minimum-deviation biarcs can be fitted. For this purpose, a handle or decision variable defining the shape of a biarc is introduced. The effectiveness of the proposed method is demonstrated by a number of illustrative examples.
