Research On NURBS Adaptive Interpoliation Algorithm For Short Linear Segments Machining

Interpolation is the most important core technology of CNC system. Interpolation algorithm directly affects the quality and efficiency of processing. With the development of the manufacturing industry, product modeling becomes increasingly complex, and traditional processing technology is more difficult to meet the processing requirements of modern society. Since traditional CNC system only has linear, circular and some other simple interpolation functions, complex curves have to be divided into small segments when being machined. This processing method inevitably results in discontinuity of the machining path’s first-order derivative, makes the acceleration and deceleration frequent and causes the NC code too large, etc. NURBS interpolation can not only retain the curve’s smoothness, but also can easily get higher machining speed and accuracy because of the path is continuous. Therefore, researching NURBS interpolation algorithm has important implications for improving CNC system’s performance.On the basis of existing research about NURBS interpolation, there are 2 difficult problems to solve. One is the difference between the theoretical step-length and actual arc length. The othe is how to coordinate the relationship of curve arc length, interpolation step length and ramp distance. An algorithm of NURBS interpolation is proposed in this paper to solve these problems. The main idea is:first interpolate the curve from back to forward to determine the deceleration point on the curve, and the corresponding speed information. Then interpolate the curve from front to back to determine the location of each cycle interpolation points and output infomation. The main contents of this paper are:Designed a NURBS curve fitting algorithm for existing small segments code. Include judging which small segment can be fitted into NURBS, determining the boundary conditions according to CAD model and analyzing how to calculate control points. A GM code interpreter was designed to verify the feasibility of the algorithm.Designed a NURBS interpolation algorithm to make it easier that calculate parameter, coordinate value and derivative value. Studied the feed-rate control problem, analyzed speed restrictions, proposed deceleration point prediction algorithm and optimized the path connection model. The feed-rate is limited by chord error and acceleration, and can adapt to the curve’s curvature.At last, according to experiment demand, a motion control platform based on EtherMAC was completed. Write a program on NURBS interpolation algorithm to control X-Y table move. Parse packet and get real-time interpolation data, verify the correctness and effectiveness of the algorithm proposed in this paper.