UG6.0中怎样画变节距弹簧

End_pitch=0.5-------------------------------------终止卷螺距
OD=1----------------------------------------------弹簧外直径
Start_pitch=0.1075--------------------------------起始卷螺距
Turns=5-------------------------------------------弹簧圈数
Wire_dia=0.05-------------------------------------弹簧线径
height=Turns*mean_pitch---------------------------弹簧高度
mean_pitch=(Start_pitch+End_pitch)/2--------------平均螺距
[mm]p0=Wire_dia
[mm]p1=0
rad=OD/2------------------------------------------弹簧外半径
t=1-----------------------------------------------规律曲线
x=t*height
x1=0
x2=mean_pitch
x3=height-mean_pitch
x4=height
xt=cos(360*Turns*t)*rad---------------------------X规律
yt=sin(360*Turns*t)*rad---------------------------Y规律
z1=0
z2=Start_pitch
z3=height-End_pitch
z4=height
zt=zt1+zt2+zt3+zt4--------------------------------Z规律
zt1=(((x-x2)*(x-x3)*(x-x4)/((x1-x2)*(x1-x3)*(x1-x4))))*z1
zt2=(((x-x1)*(x-x3)*(x-x4)/((x2-x1)*(x2-x3)*(x2-x4))))*z2
zt3=(((x-x1)*(x-x2)*(x-x4)/((x3-x1)*(x3-x2)*(x3-x4))))*z3
zt4=(((x-x1)*(x-x2)*(x-x3)/((x4-x1)*(x4-x2)*(x4-x3))))*z4

变螺距弹簧在已知起始螺距和终止螺距、圈数条件下利用拉格朗日插值法确定Z值变化规律

用表达式，构建你要的曲线！