Research On Smooth Motion Control Algorithms And Software Development Methods For CNC Systems

Manufacturing industry plays a significant strategic role in the whole national economy as its foundation. The informatization, flexibility and globalization trends of manufacturing technology promote rapid development of modern numerical control machine toward high speed, high precision, multi-functions and intelligence. Considering practical requirements of new high-performance numerical control system, to accomplish high-precision and high-efficiency motion control, this dissertation does thorough research on some key technical problems of high performance numerical control system such as flexible acceleration and deceleration feedrate planning, high-speed short blocks machining, interpolation of parametric curve, output of smooth motion instruction and software system structure from the view of both theoretical research and engineering realization with the clue of improving motion stability. The innovations of this dissertation are as follows:(1) To overcome heavy computation and poor real-time capability of existing look-ahead algorithm in S-shaped acceleration and deceleration which is currently under wide research, a nested self-adaptive look-ahead algorithm is devised. Analytical solutions are given in the two main stages: profile construction and verification of S-shaped velocity planning, which promots the application to mid- and low-cost numerical control system.(2) For the high-speed machining of short-blocks, transition algorithms of arc and Ferguson spline are proposed to avoid impacts caused by direct transition of machining paths, which can increase machining efficiency, reduce vibration and improve surface quality of work piece with the premise of ensuring machining precision. For its simplity and generity, the arc transition algorithm can be easily applied in low-cost numerical control systems by using the proposed arc interpolation algorithm in arbitrary spaces. The Ferguson spline transition algorithm improves continuity of paths which leads to higher precision and smoother transition, but it can only be used with a parametric curve interpolator. As a result, the Ferguson spline transition algorithm is more suitable for full-functional numerical control systems.(3) A variable period interpolator for parametric curve is proposed to realize real-time look-ahead and smooth interpolation using S-shaped acceleration and deceleration by nested and recursive methods. Adaptive variable period ensures the accordance of look-ahead paths and interpolation trajectory and solves problems existing in parametric curve interpolation as federate fluctuation, control of precision and difficulty in look-ahead, accomplished smooth motion control of parametric curve like NURBS. (4) Stability of motion control in pulse-driving systems is studied. On the basis of interpolation model the essence of stability is analyzed in time domain and frequency domain. It is found that there are restrictive relations among precision, efficiency and smoothness. A new smooth motion control scheme–interpolating with adaptive random period in separated-axis is proposed by means of changing interpolation period and interactive mode of multi-axes. This scheme breaks traditional interpolation models, and further more finds a new way for improving motion stability of numerical control equipments.(5) A system structure of numerical control engine based on modules, frames and scripts is proposed for reference to software engine concept by abstracting functions, algorithms and structures of numerical control systems. Furthermore, engineering application methods of numerical control engine are studied from the aspects of constructing fundamental systems, enhancement systems, innovation systems and professional motion control systems. Even consideration of execution efficiency, openness and sustainable development is given by applying the structure.The proposed smooth motion control algorithms can be used generally in high-grade CNC systems and situations with special requirements of stability. The algorithms and software engine system presented are verified to be effective and feasible on the platform of metal and nonmetal Numerical Engraving Machine which has special requirements of motion control. The achievements of this dissertation establish a solid foundation of theoretical research and engineering development for high-performance CNC systems.