1. Technical Field of the Invention
This invention relates to a method of generating a cutting path on a complex curved surface and, more particularly, to a cutting path generating method through which a complex curved surface can be cut along any path.
2. Description of the Related Art
A curved surface of a three-dimensional metal mold or the like on a design drawing is generally expressed by a plurality of section curves, but no profile data is shown for the shape of the area lying between a certain section curve and the next adjacent section curve. In numerically controlled machining it is essential that machining be carried out so as to smoothly connect these two section curves despite the fact that the profile between them is not given. In other words, this means that machining must be performed by generating the curved surface between the two section curves from such data as that indicative of the section curves, storing on an NC tape the data concerning the generated curved surface, and carrying out machining in accordance with commands from the NC tape. To this end, there has been developed and put into practical use a method comprising generating a plurality of intermediate sections in accordance with predetermined rules from data specifying several sections and section curves of a three-dimensional curved body, finding a section curve (intermediate section curve) on the curved body based on the intermediate sections, and generating a curved surface of the three-dimensional body based on the plurality of generated intermediate section curves. (For example, see the specification of U.S. Pat. No. 4,491,906.) This method is useful in generating a smooth curved surface from section data.
Recently, a method of creating a complex curved surface obtained by combining two or more three-dimensional curved surfaces has also been proposed. For example, refer to U.S. Ser. No. 928,288 (filing date: Oct. 23, 1986, U.S. Pat. No. 4,825,377, entitled "Complex Curved Surface Creation Method"). The proposed method of creating complex curved surfaces includes:
(i) previously inputting data specifying each of the three-dimensional curved surfaces 12a, 12b, 12c constituting a complex curved surface 11 (see FIG. 5), inputting data specifying one line of intersection CL1 (see FIG. 6) corresponding to a predetermined plane (e.g. an X-Y plane) as well as a rule (distance d, Vx, VY, etc.) for specifying a number of lines of intersection CLi (i=1, 2, . . . );
(ii) finding section curves 13 (the set of 13a, 13b, 13c) obtained when the complex curved surface 11 is cut by a section plane SSi having an i-th line of intersection CLi, among the number of lines of intersection,
(iii) and thereafter obtaining, in a similar manner, section curves based on sections corresponding to respective ones of the lines of intersection, and generating a complex curved surface by assembling the section curves.
When NC data for curved surface machining are generated using the curved surface created by the foregoing conventional method, the cutting path of the tool is one which will cause the tool to move along the obtained section curves in the order of these section curves.
More specifically, the conventional cutting path is determined in such a manner that the curved surface is machined by repeating one-way cutting or two-way cutting along the section curves that have been obtained.
Accordingly, when it is desired to perform edge cutting by moving the tool along the contour of a complex curved surface (i.e. in the directions of the solid arrows in FIG. 5), such cutting is impossible with the conventional method.
With the conventional method, moreover, surface machining generally cannot be performed by moving a tool along an arbitrary cutting path. For example, cutting cannot be performed by moving a tool successively along a number of closed paths similar to the contour lines of a complex curved surface.