Precision trajectory generation for CNC milling of arbitrary contours and surfaces

Abstract

In an effort to improve cutter path tracking for high precision milling of spatial contours and sculptured surfaces, a new CNC trajectory generation approach is presented. Linking the CAD part design with control motion execution, command generation has traditionally been limited to the issues of coordinated motion kinematics and interpolation function design. Unlike sample interpolators commonly used in practice today, the proposed trajectory generator accounts for the nonlinear effects of the machine dynamics and tool cutting forces. The new trajectory commands are obtained by solving the inverse dynamics problem enhanced with a cutting load predictor. Also, the algorithm utilizes efficient machine dynamics formulation in a parameterized space. Using three- and five-axis CNC machines as demonstration examples, the coordinated trajectories generated by the new algorithm were fed into the machine nonlinear closed loop simulator and the response was compared with that based on conventional interpolators. The results demonstrate superior tracking performance over a wide range of operational speeds—low, medium, and high—when new coordinated trajectories are employed.