A NURBS interpolation method with minimal feedrate fluctuation for CNC machine tools

Abstract

To reduce the feedrate fluctuation in non-uniform rational B-spline (NURBS) interpolation caused by approximation errors of interpolation methods, a new NURBS interpolation method with minimal feedrate fluctuation for CNC machine tools is proposed to obtain the sampling curve parameter by solving a quartic equation with respect to the curve parameter increment according to the scheduled feedrate using Ferrari’s formulas and Shengjin’s formulas. Firstly, the second-order Taylor expansion is applied on the numerator and denominator in the NURBS representation separately with unknown curve parameter increment. Then, a quartic equation with respect to the curve parameter increment is formed and solved by Ferrari’s formulas and Shengjin’s formulas efficiently, which can achieve minimal feedrate fluctuation in real-time interpolation. In principle, the proposed method can totally eliminate the feedrate fluctuation for second-degree NURBS curves and can reduce it to a satisfied value for other high-degree NURBS curves. Finally, numerical simulations and experiments are conducted to verify the feasibility and applicability of the proposed method.