南京理工大学机械原理chapter2.pptVIP

Types of kinematic pairs:（根据两构件接触方式的不同） Revolute pair(转动副) Sliding pair or Prismatic pair(移动副) Screw pair(螺旋副) Spherical pair(球面副) Gear pair(齿轮副) Cam pair(凸轮副) A pair that permits only relative rotation is called a revolute pair (转动副). Gear pair （齿轮副） Cam pair （凸轮副） 2.2.2. Kinematic Chain(运动链) and Mechanism If every link in a kinematic chain has at least two pair elements, all links form a closed chain.闭链 If one or more links in a kinematic chain have only one pair element, then the kinematic chain will be an open chain.开链 After the mechanism is redrawn,F=3n-2PL-Ph=3?7 -2?9 -1=2。Needs two drivers. The END of Chapter 2 2.5.2 Passive DOF ( 局部自由度 ) 2 1 A C B 4 3 2 1 A C B 3 Delete the passive DOF by welding the roller to the follower, then calculate the DOF of mechanism. 将滚子“焊接”在从动件上，消除局部自由度，再计算机构自由度。 2.5.3 Redundant Constraints 在特殊的几何条件下，有些约束所起的限制作用是重复的，这种不起独立限制作用的约束称为虚约束。 Delete the redundant constraints during the calculation of DOF. 去除虚约束，再计算机构自由度。 虚约束常出现的场合 (1) Two links are connected by more than one parallel sliding pairs Two links are connected by more than one revolute pair whose axes coincide（重合）。 Two links are connected by more than one higher pair whose common normals passing through the points of contact coincide. A revolute is conveniently(方便地) represented by a small circle placed at the centre of the revolute no matter how large its radius(半径) is. 移动副 sliding pair (关键画出相对移动的方向，导路 ) The shaded(带阴影线) links represent the frame The actual shape and dimensions of the cross section(横截面) of the sliding pair has no influence (影响) on the kinematics of the mechanism. Attention： The centerline of the sliding pair in the kinematic diagram must be parallel(平行) to the pathway(导路) in the mechanism. Any one link can be drawn as a sliding block while the other is drawn as a guide bar(导杆). The following five diagrams are equivalent. 齿轮副gear pair： 凸轮副cam： Need actual cam contour (轮廓) and end profile (外形)of fol