Research On Five-Axis Linkage Dual NURBS Interpolation Technology

With the rapid development of numerical control technology,five-axis CNC machine tools play an increasingly important role in the processing of complex modeling parts due to their good applicability,high machining accuracy and high processing efficiency.As a key technology in the digital manufacturing of complex modeling parts,the NURBS curve directly affects the machining accuracy of the parts.In view of the traditional interpolation method,there is a poor fitting effect at the inflection point of the complex surface curve,and the acceleration of the traditional machine tool speed planning algorithm is repeated and abrupt,resulting in large processing error and low processing efficiency.This paper uses a five-axis CNC machine tool to carry out dual NURBS interpolation technology.The main work contents and research results are as follows:(1)A double NURBS fitting algorithm based on angle smoothing is studied.Aiming at the problem that the current machining path does not satisfy the second-order continuity,a double NURBS fitting algorithm based on angle smoothing is proposed.Firstly,the velocity sensitive point on the machining path is obtained by solving the radius of curvature of the machining path.Secondly,the data at the sensitive point of the tool path velocity is calculated,and the correspondence between the path curve parameter and the arc length information at the speed sensitive point is obtained.Then,Synchronous double NURBS model is used to obtain the tool position data.Finally,the comparison experiment with Taylor's second-order interpolation algorithm is carried out.The results show that the proposed method can obtain a tool with high precision and continuous tool trajectory information.(2)The S-shaped velocity planning algorithm based on the servo performance of CNC machine tools is studied.Aiming at the problem that the traditional speed planning method does not consider the machine structure,which causes the feed speed and acceleration of each axis of the machine tool to exceed the servo capacity range and increase the machining error,an S-shaped speed planning algorithm based on the servo performance of CNC machine tools is proposed.Firstly,the smoothed machining path is obtained by the angle-smooth double NURBS fitting algorithm.Secondly,according to the machine structure and machining path,the instantaneous velocity and acceleration range of each axis of the machine tool are calculated.Then,through the 7-segment S-shaped velocity planning algorithm,Corresponding relationship between arc length information and velocity and acceleration of machining path;finally,the comparison experiment with Taylor second-order interpolation algorithm is carried out.The results show that the speed and acceleration of the algorithm accord with the servo performance of the machine when the calculation amount is not increased.Effectively avoid the problem of speed and acceleration fluctuation caused by frequent start and stop of the machine tool,and achieve a smooth transition of machine speed and acceleration.(3)Design software and hardware for five-axis CNC machine tool processing system.The hardware modules of the system mainly include: a main processor development board,a coprocessor development board and an AC double turntable numerical control machine tool;the software modules include: a parameter setting module,a data input module,an interpolation module,a result display module and a driving module.This paper mainly builds the software running environment in the main processor,and writes the embedded software through Platform Builder software.This paper proposes a double NURBS fitting algorithm based on angle smoothing and an S-shaped velocity planning algorithm based on servo performance of CNC machine tools.Through the processing of three-dimensional five-pointed star and three-dimensional relief flower,the results show that the numerical control system embedded in this algorithm has less vibration during processing,and the surface of the work is smooth and the texture is uniform,which meets the requirements of high-speed and high-precision machining.