A study on an improved direct search interpolation method for two-axis CNC thermal cutting systems

A microcomputer-based reference pulse software interpolator, which can be effectively applied for two-axis computer numerical control (CNC) systems such as those used in plasma arc cutting and laser beam cutting machines, is proposed in the present study. The proposed interpolation method is based upon searching in two or three directions for the minimum path error, while the axes of motion do not move simultaneously in the stairs approximation method and the basis for selecting an interpolating point is not related to any criteria of path error in the digital differential analyses (DDA) method. Accordingly, this method has many advantages over the other two competing methods, such as small maximum path error of only a half basic length unit (BLU), uniform velocity along the cutter path, high degree of path smoothness and maximum velocity allowable. Since the velocity of the proposed CNC system is controlled through adjusting two interrupt interval times at each interpolation step, a constant velocity can be maintained along any cutting path. The proposed interpolation algorithm is very simple and can be easily applied for the practical CNC systems, since it is based on transforming the interpolating paths in all interpolating cases to those in one typical case.