Curvilinear interpolation system and method

Abstract

A curvilinear interpolation system and method for use in a numerical control apparatus such as a machine tool or a robot having two or more drive axes and movable while effecting linear interpolation on a given curve with a plurality of line segments. For each line segment a curvature K.sub.p of the curve is calculated at a current curve interpolating point P.sub.p, and a curvature K.sub.n calculated at a point P.sub.n on the curve spaced a given search length l.sub.S from the point P.sub.p along the curve. Then, a curvature K.sub.s is set equal to K.sub.p when K.sub.p .gtoreq.K.sub.n and set equal to K.sub.n when K.sub.p <K.sub.n. The curvature K.sub.s is compared with a limit curvature K.sub.L established for determining whether a curve portion is a straight line or an arc for establishing the curve portion as an arc having the curvature K.sub.s when K.sub.s .gtoreq.K.sub.L to approximate the curve portion with a line segment so as to fall within an allowable error t and for establishing the curved portion as a straight line when K.sub.s <K.sub.L to approximate the curve portion with a line segment of a prescribed length. An operative member such as a robot arm is then moved along a path defined by the plurality of line segments thereby calculated.