Application of PH curve in CNC look-ahead function

A new method was developed to smooth the micro-line while machining in computer numerical control systems. Four rules including angle between transfer vectors with speed limitation, length and angle between the micro-lines with accuracy limitation and the monotonicity of the point were proposed to divide segments into some areas. Nonlinear least squares method was introduced to fit the lines into PH curves. Simulated annealing algorithm was used to adjust the tangent vector for getting better accuracy. The model of adjustment included both unidirectional and bidirectional adjustments by the situation of the point between the areas. Straight slope was considered as the initial value of the tangent vector in the simulated annealing algorithm. Chord error was computed by segmenting the micro-line, the error was the objective function to determine the adjustment of the vector. The results illustrate the dividing rules improve the fitting efficiency. Smooth curves with high accuracy were obtained to get better velocity profile.