其它语言学习第次课.pptx

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,#,If the,cam,rotates an angle,B,0,OB=,counter-clockwise from the beginning,the follower will rise through a corresponding distance,BB=S,from the lowest position along its guide way.,Suppose that,the cam mechanism has been designed according the,given,motion curve S-,.,Cam Rotating,Follower Rotating,Therefore,motion curve S-,can be understood such,ways:The,cam is stationary,.The,frame and the follower rotate,in the direction,opposite,to,.,The follower will rise through a corres-ponding S along the guide-way relative to the frame.,This is the,principle of inversion,(,反转法,).,The minimum circle centred at O and tangent to the pitch circle is called the,base circle,of the cam pitch curve,or,prime circle,(,基圆,).,If offset e=0,the offset translating follower becomes an,in-line translating follower,.,What will happen if e=0?,Characteristics:,The roller is always tangent to the cam contour(,实际廓线,)at all times.,2.Graphical Synthesis of Plate Cam with Translating Roller Follower,（直动滚子从动件圆盘凸轮）,The locus of the,roller centre,relative to the cam is called the,pitch curve(,理论廓线）,of the cam.,The roller is tangent to the cam contour(,实际廓线,)at all times,and the cam contour is the envelope(,包络线）,of the family of the roller circles,.,The,pitch curve,(,理论廓线,)and the,cam,contour,(,实际廓线,)are parallel(,法向等距,).,The minimum radius of the pitch curve is called the radius r,P,of the prime circle.,Note:,the minimum radius of the,cam contour,is not r,P,.,For the knife-edge follower,the pitch curve and the cam contour are the same.,The process to design the cam contour is:,5.4 Plate Cam with Oscillating Roller Follower,（摆动滚子从动件圆盘凸轮）,In this mechanism,The angular lift(,角行程),of the follower is,max,.,The motion equations can also apply to the oscillating follower,so long as,S is replaced by,and,h,by,max,The cam contour is obtained by drawing a smooth curve tangent to the family of all roller circles.,Since,the follower arm must have some physical dimensions,the side edge of the straight arm of the follower may interfere(,干涉),with the cam contour.,It is,necessary,to check that this will not occur at all positions.To avoid interference,the arm may be designed as a bent(,弯曲),rod.,5.5 Plate Cam with Translating Flat-faced Follower,(,直动平底从动件圆盘凸轮）,This follower is used often in high-speed cam mechanisms.,The motion curve of the follower will be restricted since all sections of the cam contour must be,convex,（凸起）,.,Inline?,Offset,？,Redundant constraint,The,cam contour,may be drawn as a smooth curve,tangent to,the family of the,position lines,of the flat face.,Graphical Synthesis of Cam Mechanisms,5-3,Plate Cam with Translating Roller,(or Knife-edge)Follower,5.4,Plate Cam with Oscillating Roller Follower,（摆动滚子从动件圆盘凸轮）,5.5 Plate Cam with Translating Flat-faced Follower,(,直动平底从动件圆盘凸轮）,(1)Analytical Synthesis of the Pitch Curve,Lead to a substantial,(,显著的,),saving of time in the design process.,5.6 A Few Questions Should Be Discussed,(2)Pressure Angle,(3)The minimum radius of the prime circle,(,最小基圆半径,),Pressure Angle,Pressure angle,changes during motion so it is necessary to control the value of the maximum pressure angle,max,.,pressure angle,Return in Return in form-closed force-closed cam mech.cam mech.or rise,Translating fol.25,35,70,80,O,scillating fol.35,45,The minimum radius of the prime circle (,最小基圆半径,),When r,P,is so small that,max,is equal to,in the rise or in the return,the corresponding,r,P,is called,the minimum radius of the prime circle,denoted as,(r,P,),min,Review of Chapter 5,Characteristics of Cam Mechanisms,Classifications of Cam Mechanisms,1.,By the cam shape,2.By the motion type of the follower,3.By the shape of the follower end,4.By the manner of keeping the cam and the follower in contact,Review of Chapter 5,Basic Concepts of Cam Mechanisms,Concept of Follower Motion Curves,(,从动件运动规律,),Concept of quasi-velocity,Concept of quasi-Acceleration,Review of Chapter 5,Follower Motion Curves,1.Constant Velocity Motion Curve,2.Constant Acceleration and Deceleration Motion Curve,(,等加速等减速运动规律,),3.3-4-5 Polynomial,(,多项式,),Motion Curve,4.,Cosine Acceleration Motion Curve(or Simple Harmonic(,谐波,),Motion Curve),5.,Sine Acceleration Motion Curve(or Cycloid(,摆线,)Motion Curve),6.Combined Motion Curves,Homework,Please redo the example in slider 3.,Please analyze the characteristics of each motion curves of cam mechanisms.,