Research On Motion Control System Of Free-form Curve Machining

At present, CAD system is widely used to support free curve and surface modeling. And the conventional CNC controller just offers line and arc interpolators. But it can't process free curve or surface's program data directly. The solution to this problem is to make tool path approximate in the form of line or small arc using CAM software. So it's not easy to meet the standard of high-speed precision machining for the reason that the approximation method will cause many problems, such as a larger profile error, a longer machine program, excessive transmission loads, the velocity discontinuity and the mechanical vibration, etc. Hereby, it's of great significance to study the CNC system with free curve interpolation.The objective studied in this thesis is aimed to study the real-time interpolation algorithm of NURBS (Non-uniform Rational B-spline) curve and implement it based on DSP for the Blackfin series of ADI Corporation. And experiments are carried out in a CNC machine tool for improving track function and receiving NURBS curve information directly. The main research contents are as follows.Firstly, G code compiler is designed and the three-dimensional simulation of track is implemented based on VC6.0.Secondly, the design of interpolator with free curve interpolation and the nature of NURBS curve are studied respectively. Also, the relation between feedrates and interpolating precision is considered together with the dynamic character of machine tool. The NURBS interpolation algorithm is studied and the post-processing approach of velocity planning is presented.Lastly, the hardware platform based on DSP is built. And the line and arc interpolation algorithms of minimum deviation with S-shape acceleration and deceleration capability are implemented. Also, the real-time NURBS interpolation algorithm is realized and applied into real CNC system for machining work.Results show that the interpolation algorithm could guarantee the high-speed jog, meet the standard of interpolating precision, and make the electric motor steady and shockless in operation. So it is testified to have the feasibility and high performance of interpolator with free curve interpolation designed in this dissertation.