南京理工大学机械原理chapter2ppt课件.ppt

《南京理工大学机械原理chapter2ppt课件.ppt》由会员分享，可在线阅读，更多相关《南京理工大学机械原理chapter2ppt课件.ppt（83页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、南京理工大学机械原理chapter2ppt课件 Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望Chapter1 IntroductionChapter2 Structural Analysis of Planar MechanismsChapter3 Kinematic Analysis of MechanismsChapter4 Planar Linkage MechanismsChapter 5 Cam MechanismsChapter 6 Gear Mec

2、hanismsChapter 7 Gear TrainsChapter 8 Other Mechanisms in Common UseChapter 9 Balancing of MachineryChapter 10 Motion of Mechanical Systems and Its RegulationChapter 11 Efficiency of Machine2Chapter 2 Structural Analysis(结构分析结构分析)of Planar Mechanisms(平面机构平面机构)3Planar mechanism平面机构平面机构：Spatial mechan

3、ism空间机构空间机构：All links of a mechanism move in planes that remains parallel to each other各构件的相对运动各构件的相对运动各构件的相对运动各构件的相对运动平面互相平行（常用的机构大多数为平面机构）。平面互相平行（常用的机构大多数为平面机构）。平面互相平行（常用的机构大多数为平面机构）。平面互相平行（常用的机构大多数为平面机构）。至少有两个构件能在三维空间中相对运动。至少有两个构件能在三维空间中相对运动。至少有两个构件能在三维空间中相对运动。至少有两个构件能在三维空间中相对运动。452.1 Purpose of

4、Structural Analysis2.2 Planar Kinematic Pairs(平面运动副平面运动副)and Planar Mechanisms2.3 The Kinematic Diagram of a Mechanism(机机构运动简图构运动简图)2.4 Degree of Freedom of a Mechanism2.5 Points for Attention during the Calculation of DOF6机构结构分析的目的机构结构分析的目的 探讨机构具有确定运动的条件探讨机构具有确定运动的条件机构的分类机构的分类画机构的运动简图画机构的运动简图2.1 Pu

5、rpose of Structural Analysis72.2 Planar Kinematic Pairs(平面运动副平面运动副)and Planar Mechanisms2.2.1 Kinematic Pairs2.2.2.Kinematic Chain(运动链运动链)and Mechanism82.2.1 Kinematic Pairs机构的组成要素机构的组成要素Link构件构件Kinematic Pairs运动副运动副In order to transmit(传输传输)and transform(转换转换)motion,every link must be kept permanen

6、tly(永久永久地地)in contact(接触接触)with other links by some kind of connection and have motion relative to them.Such a mobile connection(可动连接可动连接)is called a kinematic pair.9Types of kinematic pairs:（根据两构件接触方式的不同根据两构件接触方式的不同）Revolute pair(转动副转动副)Sliding pair or Prismatic pair(移动副移动副)Screw pair(螺旋副螺旋副)Spheri

7、cal pair(球面副球面副)Gear pair(齿轮副齿轮副)Cam pair(凸轮副凸轮副)面接触lower pair点、线接触higher pair 10A pair that permits only relative rotation is called a revolute pair(转动副转动副).面接触lower pair低副低副11A pair that allows only relative rectilineal(直线的直线的)translation(平移平移)is called a sliding pair or prismatic pair(移动副移动副).12点

8、、线接触高副higher pair 13Gear pair（齿轮副）（齿轮副）14Cam pair（凸轮副）（凸轮副）15A pair element运动副元素运动副元素the part of the link surface Which make contact with another linkAttention:（1）One kinematic pair can connect only two links.（2）Those connections that join two machine elements firmly(牢固地牢固地)and do not allow the conn

9、ected machine elements(零件零件)to move relative to each other,such as welds(焊接焊接),rivets(铆钉铆钉),or nuts(螺母螺母)and bolts(螺栓螺栓),are not kinematic pairs.16按两构件间按两构件间相对运动相对运动 Planar kinematic pair(平面平面)Spatial kinematic pair(空间空间)面接触面接触(surface contact)：lower pair sliding revolute screw spherical 如：移动副、转动副如：

10、移动副、转动副；螺旋副、球副点、线接触点、线接触(point,line contact)：higher pair 如：齿轮副，凸轮副如：齿轮副，凸轮副gearcamConclusion：Types of kinematic pairs按两按两构件构件接触接触方式方式 17螺旋副screw球副spherical18DOF of a Link构件的构件的自由度自由度 构件含有独立运动的数目构件含有独立运动的数目刚体作空间运动时，则刚体作空间运动时，则有有6 6个自由度。个自由度。an unconstrained link on a plane would have 3 DOF（刚体作平面运动时，有

11、刚体作平面运动时，有3 3个自由度）个自由度）19Constraint（约束）：对独立运动的限制约束）：对独立运动的限制one planar lower pairs（低副）（低副）sets two constraints（2个约束，个约束，1个自由度）个自由度）20one planar higher pairs（高副）（高副）sets one constraints（1个约束，个约束，2个自由度）个自由度）212.2.2.Kinematic Chain(运动链运动链)and Mechanism When a number of links are connected by means of k

12、inematic pairs,the resulting mobile system is a kinematic chain.22 If every link in a kinematic chain has at least two pair elements,all links form a closed chain.闭链闭链23If one or more links in a kinematic chain have only one pair element,then the kinematic chain will be an open chain.开链开链24Kinematic

13、 chain Closed chain:（闭链）（闭链）每一构件至少含有两个运动每一构件至少含有两个运动副元素副元素,动其中几杆，其余各动其中几杆，其余各杆便于传递运动，广泛使用杆便于传递运动，广泛使用 Open chain:（开链）（开链）一个以上的构件只有一个运动副一个以上的构件只有一个运动副元素应用于机械手，挖掘机，机元素应用于机械手，挖掘机，机器人，多自由度器人，多自由度 Conclusion：Types of kinematic chain25 If a link of the kinematic chain is fixed as the frame机架机架,then the ki

14、nematic chain becomes mechanism.26mechanism driving links:have their own independent motion driven links:generate the expected output motion(output links)27 2.3 The Kinematic Diagram of a Mechanism 2.3.1 Definition2.3.2 Representation of a Kinematic Pair 2.3.3 The representation of a link in the kin

15、ematic Diagram 2.3.4 Procedures for Drawing the Kinematic Diagram of a Mechanism 282.3.1 Definition不考虑与运动无关的因素（外形，尺寸，具体构造），不考虑与运动无关的因素（外形，尺寸，具体构造），仅用简单线条，符号，按一定比例表示各运动副的相对仅用简单线条，符号，按一定比例表示各运动副的相对位置位置.This diagram is used only to express the relationship between the motions of links,it should be simp

16、le but provide all necessary(but not redundant多余的多余的)information determining the relative motion of all links.The Kinematic Diagram of the Mechanism 机构运动简图机构运动简图29Attention：It should be simple but provide all necessary (but not redundant)information determining the relative motion of all links.Accor

17、ding to specified symbols(符号符号).The kinematic diagram should be drawn to scale(按比例按比例).If not,such a diagram is called the schematic diagram(机构示意图)of the mechanism.302.3.2 Representation of a Kinematic Pair 转动副转动副 revolute pair：(关键画出转轴位置关键画出转轴位置)The shaded(带阴影线带阴影线)links represent the frame.31A revo

18、lute is conveniently(方便地方便地)represented by a small circle placed at the centre of the revolute no matter how large its radius(半径半径)is.32移动副移动副 sliding pair(关键画出相对移动的方向，导路关键画出相对移动的方向，导路)The shaded(带阴影带阴影线线)links represent the frame33 The actual shape and dimensions of the cross section(横截面横截面)of the

19、sliding pair has no influence(影响影响)on the kinematics of the mechanism.34Attention：The centerline of the sliding pair in the kinematic diagram must be parallel(平行平行)to the pathway(导路导路)in the mechanism.Any one link can be drawn as a sliding block while the other is drawn as a guide bar(导杆导杆).The foll

20、owing five diagrams are equivalent.35齿轮副齿轮副gear pair：凸轮副凸轮副cam：Need actual cam contour(轮廓轮廓)and end profile(外形外形)of follower(从动件从动件).362.3.3 The representation of a link in the kinematic Diagram The kinematic function of the link to keep the distance.Straight line can be used links with two pair ele

21、ments(双副构件双副构件)：37A link with more than two pair elements can be represented by a hatched(阴影线的阴影线的)or welded(焊焊接的接的)polygon(多边形多边形)with pair elements at corners.38Note the differences between the following two groups of figures：39The special representative(有代表性的有代表性的)symbols(符符号号)used in a kinematic

22、 diagram for some common mechanisms are listed in Table 2-1（P9）.402.3.4 Procedures for Drawing the Kinematic Diagram of a Mechanism 1)Run the mechanism slowly,study the structure of the mechanism.How many links?Types of all kinematic pairs?2)stop at a suitable position,Chose a drawing plane3)Draw th

23、e schematic diagram机构示意图机构示意图4)Measure kinematic dimensions415)Select scale=6)Draw the kinematic diagram of the mechanism.42Oscillating Guide-bar Mechanism43摆动导杆机构Oscillating Guide-bar Mechanism44Oscillating Guide-bar Mechanism45Crank and Oscillating Block Mechanism46摇块机构Crank and Oscillating Block

24、Mechanism47Crank and Oscillating Block Mechanism48Ex.：Circular disk 1 rotates relative to the frame 4 about a fixed axis(轴轴)A.The link 3oscillates(摆动摆动)about a fixed axis D.The circular disk 1 matches(配合配合)with a hole on circular disk 2.The circular disk 2 matches with a large hole on the link 3.495

25、02.4 Degree of Freedom of a Mechanism2.4.1 the definition of DOF2.4.2 Structural Formula of a planar Mechanism2.4.3 Condition for a mechanism to have a determined motion51 2.4.1 Definition机构中各构件相对于机架所能有的独立运动的数目机构中各构件相对于机架所能有的独立运动的数目 the DOF of the mechanism ORDOF:The number of independent coordinate

26、s required to define its position.522.4.2 Structural Formula of a Planar MechanismN:the number of moving links(does not include the frame!)PL:the number of planar lower pairs Ph:the number of planar higher pairs The DOF of a Planar Mechanism F=3N-2PL-Ph53Example1:2.4.3 Condition for a mechanism to h

27、ave a determined motion54如果有两个原动件，那么该机构会从最弱构件处损坏。如果有两个原动件，那么该机构会从最弱构件处损坏。The number of the driving linksthe DOF of Mechanism,it will be broken 55Example2:铰链五杆机构：铰链五杆机构：56如果只给一个如果只给一个原动件，机构原动件，机构运动不确定运动不确定 The number of the driving links 0,F0,原动件数原动件数=F=F，运动确定，运动确定原动件数原动件数FFF，机构破坏，机构破坏Conclusion:602.

28、5.1 Compound Hinge 2.5.2 Passive DOF(局部自由度局部自由度)2.5.3 Redundant Constraints2.5 Points for Attention during the Calculation of DOF612.5.1 Compound Hinge The number of revolutes in a compound hinge=one less than the number of links joined at that hinge.由由m个构件组成的复合铰链应按照个构件组成的复合铰链应按照 m-1个转个转动副计算。动副计算。Mu

29、ltiple joints(compound hinge)62Example:A AB BD DC CE EF F632.5.2 Passive DOF(局部自由度局部自由度)2 21 1A AC CB B4 43 32 21 1A AC CB B3 364 Delete the passive DOF by welding the roller to the follower,then calculate the DOF of mechanism.将滚子将滚子“焊接焊接”在从动件上，消除局部自由在从动件上，消除局部自由度，再计算机构自由度。度，再计算机构自由度。652.5.3 Redunda

30、nt Constraints在在特特殊殊的的几几何何条条件件下下，有有些些约约束束所所起起的的限限制制作作用用是是重重复的，这种不起独立限制作用的约束称为虚约束。复的，这种不起独立限制作用的约束称为虚约束。66 Delete the redundant constraints during the calculation of DOF.去除虚约束，再计算机构自由度。去除虚约束，再计算机构自由度。67虚约束常出现的场合虚约束常出现的场合(1)Two links are connected by more than one parallel sliding pairs68(2)Two links

31、are connected by more than one revolute pair whose axes coincide（重合）。（重合）。69(3)Two links are connected by more than one higher pair whose common normals passing through the points of contact coincide.70 However,if their common normals(公法线公法线)do not coincide(重合重合),then both higher pairs should be cou

32、nted.71(4)The distance between two points on two links remains constant during the motion of the mechanism,adding one link and two revolutes create a redundant constraints.72(5)The locus of a point is a straight line,adding one link with one fixed guide way parallel to the line and one revolute with

33、 its centre at that point will create a redundant constraint.F=3n-2PL-Ph=33-24=173(6)Symmetrical or duplicated structureIn order to transmit(传输传输)more power,many pinions(小齿轮小齿轮)are distributed(分布分布)symmetrically in space.Only one pinion should be counted.Note：gear 1,gear 3,and link 4 constitute(组成组成

34、)a compound hinge(复合铰链复合铰链).74Example2 n=7，pl=9，ph=1 F=3n-2pl-ph=37-29-1=2 n=5，pl=7，ph=0 F=3n-2pl-ph=35-27-0=1 n=5，pl=6，ph=2 F=3n-2pl-ph=35-26-21=1 75Attention：(1)Redundant constraints can improve the rigidity(刚度刚度)of a mechanism,improve the force condition in links,etc.and are widely used.(2)Deleti

35、ng the redundant constraints during the calculation of DOF does not mean that the redundant constraints should be omitted(省略省略)from real mechanisms.虚约束不影响机构的运动，但可改善构件的受力状况和刚度虚约束不影响机构的运动，但可改善构件的受力状况和刚度虚约束在计算虚约束在计算DOFDOF时去掉，但实际应用不能去掉时去掉，但实际应用不能去掉76(3)All redundant constraints require some special dime

36、nsions.Therefore,attention should be paid to manufacturing(制造制造)accuracy(精度精度)when any redundant constraint is used.虚约束需要满足准确的几何关系，否则便成了实约束虚约束需要满足准确的几何关系，否则便成了实约束77Example1：Calculate the DOF of a Mechanism（先看有无注意事项，复合铰链先看有无注意事项，复合铰链，再看有几个构件，再看有几个构件）78(1)The spring(弹簧弹簧)should not be counted.(2)C is

37、a compound hinge of links 2、3、4。(3)The roller has a passive DOF(局部自由度局部自由度).(4)There are two parallel(平行平行)sliding pairs E and E between the frame 8 and the slider 6.One of the sliding pairs is redundant(多余的多余的).Solution:79After the mechanism is redrawn,F=3n-2PL-Ph=3 7-2 9-1=2。Needs two drivers.80At

38、tentions(this chapter):Planar Kinematic PairsPlanar MechanismsThe Kinematic Diagram of a MechanismCalculate the DOF of the mechanismCompound Hinge,Passive DOF,Redundant Constraints.81Homework1.Read book p4-23.2.Exercise p23,2-6:Fig2-43,2-44,2-45,2-463.Calculate the DOF p23,2-7:Fig2-47,2-50,2-51,2-5282The END of Chapter 283