(3)约束方程为 rx)+(yxy)2=12 D (xrxn)2+(y4-y)2=12 B (x-xc)2+yc)2=12 (xC-x)2+(yc-y)2=12 x x 自由度为k=2×44=4广义坐标为x、y、0、q A =xi+yj rB=(+l cos0)i+(+I sine) j rc=x+l(cose -sino l i+ ly+/(sine+coso)]j rD=(r-l sin )i+ (+l coop )j 1414 (3)约束方程为 (xA-xB) 2+(yA-yB) 2 = l 2 (xA-xD) 2+(yA-yD) 2 = l 2 (xB-xC) 2+(yB-yC) 2 = l 2 自由度为: k =24 -4 = 4 广义坐标为:x、y、、 rA = x i + y j rB = (x + l cos) i + (y + l sin) j rC = [x + l (cos - sin)] i + [y + l (sin+cos)] j (xC-xD) 2+(yC-yD) 2 = l 2 rD = (x - l sin) i + (y + l cos) j   x y A B C D x y