A Combined 3D Linear and Circular Interpolation Technique for Multi-Axis CNC Machining

In multi-axis CNC machining of sculptured surfaces, a linear interpolation technique has been used to generate the command signals for positions along the straight line segments that connect each consecutive data point. Due to the rotational movements superimposed on the translational movements in multi-axis CNC machining, the actual cutter contact (CC) point moves along a space curve path, while the linear interpolation technique generates positions along the straight line path. The nonlinear curve segments deviate from the linearly interpolated line segments resulting in nonlinearity errors, which in turn, commonly cause difficulties to ensure high precision machining. An interpolator design technique for solving the nonlinearity errors problem in multi-axis CNC machining is presented. A combined 3D linear and circular interpolation principle is developed on the basis of the 3D linear and circular interpolation principles. The new designed interpolator is capable of driving the rotation movement pivot along a predesigned 3D curve path, so that the CC point motion trajectory is via a straight line connecting machining data points. Therefore, the proposed interpolator design technique on-line eliminates nonlinearity errors, and provides a solution to the nonlinearity errors problem for multi-axis CNC machining.