The Generating Approximation Of B-spline Curve And Its NC Programming Machining

Since the 1950 s,many industrial powers have carried out research on numerical control systems one after another.The numerical control system,as the brain of the numerical machine tool,controls the movement of the entire numerical machine tool automatically,and its performance directly affects the accuracy of the workpiece.The B-spline curve is applied to the numerical control system due to the high precision of fitting and convenient control.So the CNC system with spline interpolation function significantly improves the machining accuracy of CNC machine tools.But general-purpose machines do not have this function because of the confidentiality of the technology.Therefor the B-spline curve interpolation function,especially the NC system with NURBS curve interpolation function,has become a hot spot in various countries.Based on the advantages of B-spline curve fitting algorithm such as locality,continuity,and convex hulliness,the B-spline curve fitting algorithm of homogeneous and inhomogeneous was selected to compare and study.It is found that the non-uniform B-spline curve is more complex and accurate than the uniform B-spline curve.Therefore,the non-uniform B-spline curve is selected to be applied to a two-dimensional numerical control machining system.The NC macro program was written by hand and Vericut CNC simulation software was used to verify and estimate the routing,processing accuracy and processing time.At the same time,in order to facilitate the subsequent call of the NC program,the VB programming language is used to write the design program that can automatically generate the NC program.If the parameters are reasonably set,the NC macro program of the required non-uniform B-spline curve fitting algorithm can be obtained.Since the traditional B-spline curve cannot pass all the original value points,an improved B-spline curve fitting algorithm is obtained by adding new value points on both sides of the original value point to improve the fitting accuracy,the improved B-spline curve fitting algorithm replaces the traditional algorithm applied to the two-dimensional numerical control engraving technology.Manually edit the NC macro program of improved the B-spline curve fitting algorithm and use Vericut CNC simulation software to verify.In order to short the processing time and improve the processing efficiency,the VB language can be used to automatically create a design program for the NC program.The design program can automatically generate the NC macro program corresponding the required processing parameters.Comparing the error of the NURBS curve fitting algorithm and the improved B-spline curve fitting,it is found that the error of the improved B-spline curve fitting algorithm is larger than the NURBS curve fitting algorithm.So the NURBS curve fitting algorithm replaces the improved B-spline curve fitting algorithm applied to two-dimensional numerical control processing,even for the control of the entitlement factor can also be applied to the three-dimensional numerically controlled processing.Hand-written NURBS curve fitting algorithm of CNC machining macro program is verified by CNC simulation software.Based on the NURBS curve fitting algorithm,the NURBS curve swept surface method was used for 3D engraving and NC machining.In order to improve the accuracy of three-dimensional numerical control machining,reasonable plan the NC machining path,calculate the tool location,calculate the tool’s actual machining radius,generate of tool path,reasonable select the tool location,reasonable design tool radius compensation.The NC machining macro program of the NURBS curve sweep surface is written by hand and verified by the Vericut numerical control simulation software.The design program was written in VB language,which can automatically generate the NC macro program of the NURBS curve sweeping surface.