有 2RI 2RI 2R R J R R LT A(o,yo) 故在终端A4的曲率为 0 C(x0,0) k R (1+y 十 4R <<1,略去二次项 R 4R2,得k~1 R2 0 2 1 0 x Rl y 有  x= x = 2 2 1 l Rl  , 2R l = 0 1 0 x Rl y x= x = l Rl 1  , 1 R = 故在终端A的曲率为 0 2 3 2 (1 ) A x x y y k = +   = 2 3 2 2 ) 4 (1 1 R l R +   1, R l  . 1 R , 得 kA  4 2 2 R l 略去二次项 x y o R ( , ) 0 0 A x y ( ,0) 0 C x l