Study On Optimization Of NC Machining Tool-path And Interpolation Algorithm

Interpolation of CNC system performance is closely related to acceleration anddeceleration control and algorithm,and a small line segments approximate machiningtool-path surface with small segment length,feedrate fluctuations and large interpolationerrors.NURBS curve due to high degree and offset problem in CAM is difficult to directlyas a tool-path, and as there is no direct and explicit relationship between the interpolationdata and arc parameter, it is hard to achieve high-speed real-timecomputing.Implementation of the cutter location point fitted spline curve with trajectoryoptimization purpose not only reduces the discretization error, but provides a reliabletool-path for spline interpolation.NURBS interpolation with arc parameter is proposedwith light interpolation computation and feedrate fluctuation by establishing parameterand arc length mapping. Tool-path optimization and its interpolation algorithms give anurgent need to improve machining accuracy and interpolation performance of CNC system,which is great significance.Analysis of the existing processing shortage of small line interpolation for CNC, thetool-path optimization and fitting spline by cutter location points are proposed, andtool-path optimization model is established.Aim at isolated and unrelated cutter points,mathematical modeling is built by geometry information of distance, curvature anddeviation space,and cutter location points preprocessing is propoesd, including therecognition and correction of the defective points in the cutter location point, the waveletsmoothing based on cutter location point coordinate components, the cutter location pointsparameter corner estimates and redundant the cutter location points algorithm ofeliminating.Ferguson and NURBS spline fitting method as tool-path optimization,by calculatingtangent vector with the tangent direction of vector rotation and the tangent sizeproportional to chord length, fast fitting Ferguson curve algorithm for calculating vectorrotation quickly is developed,least squares and constraints of NURBS spline fittingmethod are proposed;to classify possible situations for the S-shaped acceleration anddeceleration as the acceleration and deceleration curves library,the corresponding actual interpolating acceleration and deceleration curve is selected,on this basis, the trapezoidalJerk is mapped to the sine curve, infinitely differentiable acceleration and decelerationmethod is proposed.As the nonlinear relationship of NURBS parameter and arc length,parameter and arclength mapping model with accurate and analytical relation is built;parametercompensation NURBS interpolation with small feedrate fluctuation is proposed, forreal-time requirement, fast NURBS interpolation is proposed by generating guide curvewith arc and parameter relation of NURBS curve,which makes light real-time computationand small feedrate fluctuation.Proper five-axis machining tool-path model is proposed: simple and reliable mappingof cutter location and tool axis trajectory,smooth the cutter axis interpolation trajectory,and easy to control speed requirements etc.,based on this model with the blade shaft fittedNURBS curve,dual NURBS interpolation technology is developed; between programmingpoint to ensure the tool axis in the plane arc, large circle interpolation is realized withrotation proportional to displacement, and tool axis is smooth by quaternion rotation.Win32simulation platform is developed to simulate the generated NURBS program,while dual NURBS curves simulation is operated in the Machineworks software.Theproposed interpolation method is integrated into the CNC system, the trident curve andfive-hill shape surface machining are finished by comparison with NURBS interpolationand small segmentmachining. The double NURBS interpolation of S-shaped workpiece ismachined in a hybrid machine tool.