The Research On Look-ahead Speed Control In Embedded Numerical Control System Based On Dual-core CPU

CNC system is the kernel of CNC machine tools to achieve high-speed and high-precision machining control.Its performance directly determines the performance of machine tool.Embedded CNC system,which is constructed by dual-core processor of ARM and DSP,can meet the needs of high-grade CNC system in terms of high performance and low cost.Look-ahead speed control can calculate and plan the machining path before interpolation,which achieves efficient and smooth operation of machine tools.Through a combination of embedded technology and look-ahead control technology,the distances of numerical control hardware technology and control software at home and abroad can be shorten,which will bring new opportunities to the development of equipment manufacturing industry in China.In this paper,the look-ahead interpolation algorithms of micro-lines and NURBS curves are carried out,simulated and ver ified by exper iments on the platform of dual-core CNC system based on OMAP3530,respectively.The main research work is as follows:(1)The acceleration and deceleration technology is an important part of the look-ahead speed control algorithm.The segmented expressions in traditional S-shaped acceleration and deceleration planning are complicated,and there are many kinds of velocity curves.For the convenience of calculation,a simplif ied method of S-shaped acceleration and deceleration planning is studied,which will be applied to the following look-ahead algorithm.(2)In the traditional micro-lines interpolation,the starting and stopping within the same line segment will lead to low machining efficiency.To solve this problem,the look-ahead speed constraints based on a composite model of corner transition are analyzed.The optimal speed at the junction of micro-line blocks is determined as well.According to the magnitude of the optimal speed,the number of look-ahead blocks is selected adaptively,which reduces the calculation time of look-ahead algorithm effectively.(3)To realize coordinated control of precision and velocity in the process of curve machining,an adaptive method of NURBS interpolation based on the look-ahead control is proposed.According to the information of preprocessing stage,the sensitive points of feederate and the feedrate on these points along the curve are searched first.The feedrate on these sensitive points is re-planned to prevent a jump in velocity afterward.Finally,the deceleration point is predicted using the symmetry of NURBS curve and bidirectional interpolation.Through feedrate planning,the Muller method and Newton iterative method are used to calculate the parameter of the next interpolation cycle in the real-time interpolation stage,which avoids the calculation of NURBS der ivative.The simulation results demonstrate that the NURBS interpolation method can meet the flexibility of machine tool and reduce the fluctuation of feederate.(4)A dual-core communication program and a look-ahead control algorithm module are designed for the platform of dual-core CNC system.The functional software modules in embedded CNC system are realized as well.The execution time test of the real-time interpolation algor ithm of NURBS verifies its real-time performance.At the same time,the simulation and experimental results of the look-ahead speed interpolation algorithm show its effectiveness.