1-Mobility.pptVIP

Homework Calculate mobility of mechanisms shown in P. 25, Fig. 2-53 to Fig. 2-58 Due in one week; Do homework by yourself; Draw draft with ruler, compass, protractor, and drafting triangle; Indicate local DOF and redundant constraints. Homework * Composition and mobility of planar mechanisms * Contents Composition of mechanisms How to draw kinematic diagram Mobility of planar mechanisms * Word list Planar mechanism 平面机构 Gear pair 齿轮副 Mobility 可动性 Frame (base) 机架 Links 构件 Driving links 原动件 Kinematic pairs 运动副 Driven links 从动件 Joints 运动副 Output links 输出件 Elements 零件 Scale 比例尺 Revolute 转动副 Degree of freedom 自由度 Hinge 铰链 Coordinate 坐标（系） Slider 移动副 constraint 约束 Cam pair 凸轮副 Lower pair 低副 Compound hinge 复合绞链 Higher pair 高副 Local DOF 局部自由度 Redundant constraint 虚约束 * Composition of mechanisms A mechanism is a combination of links which can transform or transmit a determined motion. Every link must be kept permanently in contact with other links by a mobile connection, which is called a kinematic pair (joint). * Links Links: one or a group of elements that have independent motion. * 1: shank of connecting rod 2: bolt 3: nut 4: cap of connecting rod 1 2 3 4 Kinematic pairs (joints) A pair element: the part of the link surface which makes contact with another link and forms a kinematic pair. A lower pair: if two pair elements of a kinematic pair have surface contact or its equivalent. A higher pair: if the connection takes place only at a point or along a line. Revolute, slider, cam pair, gear pair * Lower pairs higher pairs * Terms A kinematic chain: a mobile system composed of a number of links connected by kinematic pairs. A closed chain: if every link in a kinematic chain has at least two pair-elements An open chain: if one or more links haves only one pair-element Frame: links fixed to the base of the machine Driving links: some moving links have their own independent motion Driven links: the other moving links Output links: one or more driven links are