采用三次NURBS曲面构造鞋楦模型及刻楦仿真

Construction of shoe last model based on three-order NURBS surface and last machining simulation

为实现鞋楦曲面的精加工,基于复杂曲面实物的几何模型反求方法,从鞋楦实物模型得到其数字化模型,提出了一种可控精度的鞋楦曲面模型重构方法.利用三维实体激光扫描仪测量获取点数据,基于小波变换原理采用无偏似然估计对鞋楦原始测量点数据进行降噪平滑处理,采用三次非均匀有理B样条(NURBS)曲线表示鞋楦u、v向表面曲线,由此得到三次NURBS曲面并拟合鞋楦表面.建立了鞋楦数学模型,采用等残留高度法计算无干涉刀位轨迹,并基于Unigraphics平台虚拟刻楦进行数控(NC)程序仿真验证.仿真结果表明,该重构方法使鞋楦曲面精度可以调节,根据不同加工效率要求方便地计算刀具轨迹.误差分析结果表明,与设定鞋楦加工精度相比,产生的误差控制在允许范围内.

In order to improve the precision of shoe last machining, a surface model construction method for shoe last with reverse engineering method in complex surface-kind was put forward. First the point data of shoe last were acquired by 3D laser scanner. Based on wavelet transformation, Stein’s unbiased risk estimate was used to smooth and de-noise the measurement data. Three-order non-uniform rational B-spline （NURBS） curve was constructed to describe the u and v direction curves of shoe last surface, consequently three-order NURBS surface was obtained to fit the shoe last surface. A mathematical model of shoe last was built, based on which the interference-free tool path was generated according to the constant scallop height principle. The model was set up using Unigraphics software to simulate the numerical control ma- chining process of shoe last. The results show that the accuracy of shoe last surface can be adjusted with this reconstruction method. The tool path can be conveniently computed according to the acquirement of machining efficiency, and the errors compared with the given machining precision are acceptable within permissible limits.