Research And Implementation Of Key Algori-Thms Of NURBS Curve Look-Ahead Direct Interpolation For High-Speed NC System

The traditional interpolation method based on continuous micro-segments has encountered its bottleneck in the high speed machining of complex curves and surfaces.With the increasing requirements of accuracy and efficiency in modern manufacturing industry,The Non-Uniform Rational B-Spline(NURBS)curve direct interpolation technology has been born.NURBS curve direct interpolation technology can not only improve the surface quality and machining efficiency effectively,but also reduce the burden of data transmission and storage.Thus it is an advanced technology in the field of NC machining.In this paper,the key algorithm of NURBS curve direct interpolation for high speed NC system is studied.The main contents of the study are as follows:First of all,the mathematical basis of NURBS curve is studied.Two representations of NURBS curve are given.In order to meet the real-time requirements of numerical control system,the preprocessing matrix method is used to solve the value and derivations of the NURBS curve.In order to solve the interpolation point parameter,a NURBS curve interpolation point parameter predictor-corrector algorithm based on FV iteration is proposed,which effectively controls the velocity volatility and reduces the amount of computation.Then,a speed constraint model for NURBS curve direct interpolation is established.The constraint of NURBS curve curvature on speed is deduced,and the acceleration and deceleration control algorithm is deeply studied.In order to balance the flexibility and the real-time performance of acceleration and deceleration,the S-shaped acceleration and deceleration control algorithm is used.The solution flow of the algorithm is deduced.On this basis,the relationship between the two constraints is discussed,and a speed constraint model in high speed machining of NURBS curve is established.Next,a NURBS curve look-ahead pre-interpolation algorithm with continuous constraint of curvature is proposed.The algorithm adaptively divides NURBS curve into segments based on the constraint of curvature on speed,which ensures the continuous constraint of curve curvature on speed and reduces the difficulty of subsequent processing.A reverse implicative speed solving algorithm facing S-shaped acceleration and deceleration bidirectional look-ahead speed planning is proposed.The algorithm effectively eliminates the sudden change of velocity caused by S-shaped acceleration and deceleration in bidirectional look-ahead speed planning,and ensures the safety of speed planning.Finally,the theory and algorithm proposed in this paper are verified.The results of experiments show that the proposed NURBS curve look-ahead direct interpolation algorithm can effectively control the chord error,kinematic parameters and velocity volatility,and thus is suitable for high speed machining of NURBS curve.