由杠杆原理,得:=2x b A 1-cosΦ+ASn2d d rasin p+-72sin dcos opal rasin p+n-sin 2pO rO[sinΦ+-sn2d由杠杆原理，得： A B x b a s = sin 2 ] 2 [sin sin 2 ] 2 1 [ sin 2sin cos ] 2 1 [ sin sin ] 2 1 [1 cos 2 =  +  =  +  =  +   = = −  +           r b a r b a r b a d t d s v r b a s A A A