A new method to minimize the five-axis CNC machining error around singular points based on NC program interpolation

Singularity in five-axis machining is a series of positions where the rotation axis is parallel to the tool direction. At the singularity points, the rotary axis is unpredictable and might rotate abruptly, which causes a large nonlinear error and damages the machine tool. For the machining at singularity points, it is desirable first to reduce the nonlinear error to avoid gouge and then limit the axis velocity to protect the machine tools. This paper presents a novel approach to avoid gouge and limit the axis velocity at singularity. In the gouge avoiding, an inverse kinematic function around singularity (IKS) is proposed, and the NC program is optimized by the G-code blocks interpolating, which preserves the original G-code and reduces the nonlinear errors. In the limitation of the axis velocity, a concept of maximum allowed feedrate (MAF) is introduced, and the angular velocity of each axis at the singularity point is limited by interpolating the F-code (feedrate command) to each G-code block. In the end, simulations and experiments' results demonstrate the effectiveness of the NC program interpolation method.