中文摘要：

为了使不同的凸轮廓线具有统一的表达形式，并保证凸轮廓线的光顺性，采用NURBS曲线来逼近凸轮廓线，并结合最小二乘法构建了NURBS曲线的目标函数，建立了基于NURBS曲线的凸轮廓线表达模型。将该模型用于步行式插秧机共轭凸轮推秧装置中共轭凸轮廓线的表达，拟合得到的凸轮廓线曲率变化均匀。与传统的拟合方法对比发现，用NURBS曲线拟合后得到的凸轮廓线曲率变化均匀、误差小，需要的型值点少，从而表明采用NURBS曲线表达凸轮廓线具有明显的优势。

英文摘要：

In order to make different cam profiles have a unified expression form,and to ensure the fairness of the cam profile,a method to approximate cam contour curve by using NURBS curves was put forward,and with the least square method a target function of NURBS curves was constructured, then the expression model of cam profile based on NURBS curves was established. After using the model to express the cam profile of the conjugate cam used in the walking-type rice transplanter＇s seedling-pushing mechanism, more uniform variation of the cam contour curve can be obtained after fitting. Compared with traditional fitting methods, it can be found that fitting method based on NURBS curves has smaller error and needs less points. All these aspects indicate that the cam profile＇s expression method based on NURBS curves has obvious advantages.