第6次课--Ch4 Planar Linkage Mechanisms课件.ppt

Chapter 4 Planar Linkage Mechanisms (平面连杆机构);4.1 Characteristics(特性) of Planar Linkage Mechanisms;A planar four-bar(杆) mechanism is the simplest planar linkage mechanism with one degree of freedom. Four-bar mechanisms are extremely(极端地) versatile(万能的) and useful devices(装置). For the sake(缘故) of simplicity(简单), designers should always first try to solve their problem with this device.;Chapter 4 Planar Linkage Mechanisms (平面连杆机构);4.2 The Types of Four-bar Mechanisms（四杆机构的类型）;In a revolute four-bar mechanism: The links connected to the frame are called side links(连架杆). Usually, one of the side links is an input link, and the other side link is an output link. The floating(漂浮的) link couples(连接) the input to the output. The floating link is therefore called the coupler(连杆). ;Fully rotating revolute (整周转动副): If two links connected by a revolute can rotate 360o relative to each other, the revolute is called a fully rotating revolute. otherwise, a partially rotating revolute(摆动副). The revolutes A and B are fully rotating revolutes, while the revolutes C and D are partially(部分地) rotating revolutes.;Crank(曲柄): If a side link can rotate continuously(连续地) through 360o relative to the frame, it is called a crank(曲柄); otherwise, a rocker(摇杆). ;According to the types of the two side links, the types of the revolute four-bar mechanisms can be divided into Crank-rocker mechanism(曲柄摇杆机构): one side link AB can rotate continuously through 360o relative to the frame while the other side link DC just rocks(摇摆). Therefore, AB is a crank while DC is a rocker. This mechanism is called a crank-rocker mechanism. ;Applications of crank-rocker mechanism;Applications of crank-rocker mechanism;In the foot-operated sewing(缝纫) machine, the oscillation(摆动) of the driving rocker is transformed into the continuous rotation of the driven crank.;(b) Double-crank mechanism (双曲柄机构) : Both of side links AD and BC can make complete revolutions relative to the frame AB. Thus,