High-precision estimation and double-loop compensation of contouring errors in five-axis dual-NURBS toolpath following tasks

Five-axis machine tools are commonly adopted in machining of complex parts with sculptured surfaces. However, the contouring error in five-axis dual-NURBS (Non-Uniform Rational B-Spline) toolpath following will be formed due to the existence of servo lag and dynamics mismatch, which is adverse to the machining precision. The five-axis contouring error includes coupled tool-tip and tool-orientation errors, which makes it difficult to control. This paper proposes a high-precision five-axis contouring-error estimation algorithm based on the reasonable definition of the five-axis contouring error, followed by a double-loop error compensation method. In order to estimate both the tool-tip and tool-orientation contouring errors accurately, an initial-value regeneration based Newton method is presented for fast and precise approximation of the two error items. Furthermore, a double-loop five-axis contouring error compensation approach, featured an inner-loop predictive compensation and an outer-loop feedback compensation, is provided to control the incoming errors and existing errors simultaneously. From the verification testing results, it can be seen that the proposed error-estimation algorithm possesses an excellent estimation accuracy, and the double-loop compensation method performs better than the existing single-loop compensation approach.