Island cutting method

An area cutting method for cutting an area delimited by a curve of an external shape and at least two closed curves which lie within said curve of the external shape, comprising the steps of:

• moving a tool relative to a workpiece along a first cutting path to perform cutting;
• moving the tool to a machining starting point on a second cutting path, which is shifted from the first cutting path by a predetermined amount, after the completion of cutting along the first cutting path;
• moving the tool relative to the workpiece along the second cutting path to perform cutting;
• calculating first and second offset curves obtained by outwardly offsetting respective closed curves by an amount dependent upon tool diameter;
• moving the tool, while the tool performs cutting, along with second cutting path to a first point of intersection R.sub.i of two points of intersection between said second cutting path and the first offset curve;
• checking, after cutting along said first cutting path, before moving the tool, without the tool performing cutting, to that point of intersection U.sub.i of two points of intersection T.sub.i and U.sub.i between the second offset curve and the second cutting path which does not lie inside the first offset curve, whether a second point of intersection S.sub.i lies between the two points of intersection T.sub.i and U.sub.i between the second cutting path and the second offset curve to determined whether said second point of intersection lies inside the second offset curve;
• moving the tool, without the tool performing cutting, to that point of intersection U.sub.i of two points of intersection T.sub.i and U.sub.i between the second offset curve and the second cutting path which does not lie inside the first offset curve when a second point of intersection S.sub.i between the first offset curve and the second cutting path lies inside the second offset curve;
• and
• moving the tool, while the tool performs cutting, along the second cutting path from said point of intersection U.sub.i to a machining end point on the cutting path.

An area cutting method for cutting an area bounded by an external shape curve and including two closed curves inside the external shape curve, comprising the steps of:

• (a) producing an external offset curve;
• (b) producing first and second offset curves for the two closed curves;
• (c) beginning machining path processing;
• (d) obtaining, after beginning machining path processing, first through sixth points of intersection between a straight line and the two offset curves and the external offset curve where the first and sixth points are for the intersection with the external offset curve, the second and third points are for the intersection with the first offset curve and the fourth and fifth points are for the intersection with the second offset curve;
• (e) determining whether the two offset curves intersect along the straight line using the points of intersection;
• (f) machining along the straight line between the first and second points, moving without machining between the second and third points, machining along the straight line between the third and fourth points, moving without machining between the fourth and fifth points and machining along the straight line between the fifth and sixth points when the two offset curves do not intersect along the straight line;
• and
• (g) machining along the straight line between the first and second points, moving without machining between the second and fifth points, and machining along the straight line between the fifth and sixth points when the two offset curves intersect along the straight line.