Abstract: Considering feedrate and precision requirements for contouring NURBS curve characterizing large curvature corner, the interpolation algorithm by corner splitting with modifying means is proposed. Critical curvature of NURBS meeting both interpolation precision and dynamical properties of the CNC tools is defined according to chord height limit, centripetal acceleration and its derivative limits. In terms of the local maximal curvature greater than critical curvature and critical curvature of the NURBS curve, the whole NURBS curve is split into several sub-segments including sharp corner or not. For each sub-segments the feedrate are planned with S curve acc/dec, and then conforming to the compatibility relationship of feedrate and displacement between two adjacent ones, the acceleration and its derivative of each sub-segments are adjusted to ensure the integer multiple ac/dec duration to sampling time for each acc/dec phases. Under the same feed planning constraints. The feed for processing a piece of NURBS curve with large local curvature corner is planned on curvature monotonicity without modifying measure:Corner splitting without modifying method and corner splitting with modifying means. Then it is interpolated with first Taylor series expansion respectively. The comparison results indicate higher interpolation precision can be ensured by corner splitting with modifying means stably. So the proposed algorithm can be applied in high speed and high precision machining NURBS curve with large curvature corner.

Key words: coordination equation, critical curvature, curve corner, S curve acceleration/deceleration