国 上泽克通大学 e-国b口 Covered LECTURE 9 Cha8 in Design of Machinery CAM DESIGN 凸轮机构设计 国 上泽充通大学 Lectures Power/Energy Conversion Power/Energy (Electrical Motors) Transmission (Gears,Cam,Linkage, Belt Drives Power Serews) Joints Transmission (Fasteners, Support (Bearings) Structural Connectors) Support (Frames) Tools Statics,Dynamics, Stress Analysis,etc. 1
1 CAM DESIGN 凸轮机构设计 LECTURE 9 Covered : Cha8 in Design of Machinery Lectures Power/Energy Conversion (Electrical Motors) Transmission Support (Bearings) Joints (Fasteners, Connectors) Structural Support (Frames) Tools Statics, Dynamics, Stress Analysis, etc. Power/Energy Transmission (Gears, Cam, Linkage, Belt Drives, Power Screws)
上泽文廷大学 CAM Design ©Topics What is a cam mechanism How does a cam mechanism work? Classification and construction of a cam mechanism Timing diagram and motion program How to design a cam according to the motion program? What are kinematic characteristics of a cam mechanism? Reading---Chapter 8 in Design of Machinery Handouts---Dynacam software students'edition 圆上泽大华 What is a cam mechanism? .Where can we find cams? >Convenient device for transforming one motion into another >Has a curved or grooved surface that mates with a follower =Imparts motion to follower Follower oscillation.translation,or both 2
2 CAM Design Topics • What is a cam mechanism • How does a cam mechanism work? • Classification and construction of a cam mechanism • Timing diagram and motion program • How to design a cam according to the motion program? • What are kinematic characteristics of a cam mechanism? Reading --- Chapter 8 in Design of Machinery Handouts--- Dynacam software students’ edition •Where can we find cams? Convenient device for transforming one motion into another Has a curved or grooved surface that mates with a follower =Imparts motion to follower Follower oscillation, translation, or both What is a cam mechanism?
上活成大峰 What is a cam mechanism? Pitch curve Cam surface Prime circle Roller follower Base circle WWWWW 国 上泽充通大警 What is a cam mechanism? Reciprocating roller follower Trace point Total follower travel Maximum pressure Pitch circle angle 2 Follower motion Cam shaft Pitch point 3/ Base. circle Pitch point Prime circle Pitch curve Cam profile 3
3 What is a cam mechanism? What is a cam mechanism?
园 上活我大峰 What is a cam mechanism? 1.Base circle.It is the smallest circle that can be drawn to the cam profile 2.Trace point.It is a reference point on the follower and is used to generate the pitch curve. In case of knife edge follower,the knife edge represents the trace point and the pitch curve corresponds to the cam profile.In a roller follower,the centre of the roller represents the trace point. 3.Pressure angle.It is the angle between the direction of the follower motion and a normal to the pitch curve.This angle is very important in designing a cam profile.If the pressure angle is too large,a reciprocating follower will jam in its bearings. 4.Pifch point.It is a point on the pitch curve having the maximum pressure angle. 5.Pitch circle.It is a circle drawn from the centre of the cam through the pitch points. 6.Pifch curve.It is the curve generated by the trace point as the follower moves relative to the cam.For a knife edge follower,the pitch curve and the cam profile are same whereas for a roller follower,they are separated by the radius of the roller. 7.Prime circle.It is the smallest circle that can be drawn from the centre of the cam and tangent to the pitch curve.For a knife edge and a flat face follower.the prime circle and the base circle are identical.For a roller follower.the prime circle is larger than the base circle by the radius of the roller. 8.Lif or stroke.It is the maximum travel of the follower from its lowest position to the opmost position. 圈上清庆大坐 Cams compare with linkages .Linkage advantages >Reliability >Ease of construction >Lower cost .Cam-follower systems more compact than linkages >For same output motion >Can generate a true dwell >Intermittent motion ME371 Design Manufacturing ll 4
4 What is a cam mechanism? ME371 Design & Manufacturing II Cams compare with linkages •Linkage advantages Reliability Ease of construction Lower cost •Cam-follower systems more compact than linkages For same output motion Can generate a true dwell Intermittent motion
国 上游充通大学 Classifications of Cam Mechanisms D TONG Type of follower motion(rotation,translation) Type of joint closure(force,form) © Surface of contact(roller,mushroom,flat) Path of the motion of the follower(radial,axial) Type of the cam(radial and cylindrical) Type of motion constraints(critical extreme position(CEP)and critical path motion(CPM)) Type of motion program(rise-fall(RF),rise-fall- dwell(RFD),rise-dwell-fall-dwell(RDFD) ME371 Design Manufacturing ll 圈上清支大学 Classifications of Cam Mechanisms Type of Follower Motion Follower- Half joint Translating and oscillating followers Cam Spring Depends on motion required 02 Half joint Cam h2aaad4 02 Spring Follower 5
5 ME371 Design & Manufacturing II Classifications of Cam Mechanisms Type of follower motion (rotation, translation) Type of joint closure (force, form) Surface of contact (roller, mushroom, flat) Path of the motion of the follower (radial, axial) Type of the cam(radial and cylindrical) Type of motion constraints (critical extreme position(CEP) and critical path motion (CPM)) Type of motion program (rise-fall (RF), rise-falldwell (RFD), rise-dwell-fall-dwell (RDFD) ME371 Design & Manufacturing II Type of Follower Motion Translating and oscillating followers Depends on motion required Classifications of Cam Mechanisms
圈上洋文大学 Classifications of Cam Mechanisms Type of Joint Closure ⑧Force closed cams Follower Half joint require an external force to keep the cam in contact Cam Spring with the follower A spring usually supplies this force Half joint Cam haa四4 02 Spring Follower- 圈上清支大学 Classifications of Cam Mechanisms Type of Joint Closure Form closed cams are closed by joint geometry Slot milled out of the cam Half joint Follower Conjugate 2 4 Track cr goove Cam ME371 Design Manufacturing ll 6
6 ME371 Design & Manufacturing II Type of Joint Closure Force closed cams require an external force to keep the cam in contact with the follower A spring usually supplies this force Classifications of Cam Mechanisms ME371 Design & Manufacturing II Form closed cams are closed by joint geometry Slot milled out of the cam Type of Joint Closure Classifications of Cam Mechanisms
国 上游充通大￥ Classifications of Cam Mechanisms Surface of contact Roller Mushroom Flat-Faced Follower Follower Follower V follower Follower Follower Follower Spring Spring Spring Cam Cam cam cam ME371 Design Manufacturing ll 圈上泽庆大坐 Classifications of Cam Mechanisms Path of the motion of the follower Radial,offset or Axia D Radial follower offset follower Axial Cam 对心凸轮 偏置凸轮 ME371 Design Manufacturing ll 7
7 ME371 Design & Manufacturing II Roller Follower Mushroom Follower Flat-Faced Follower Flat-Faced Follower Mushroom Follower Roller Follower Surface of contact Classifications of Cam Mechanisms ME371 Design & Manufacturing II Radial, offset or Axial Radial follower offset follower 对心凸轮 偏置凸轮 Axial Cam Classifications of Cam Mechanisms Path of the motion of the follower
圈上游通大￥ Classifications of Cam Mechanisms Type of the cam (c)Cam v ced tollowe d Com with sphencal 仍Cam with offset faced follower. follower. disc cam cylindrical or barrel 盘型 圆柱凸轮 国 上泽充通大警 Cams from the industry 8
8 Type of the cam Classifications of Cam Mechanisms disc cam cylindrical or barrel 盘型 圆柱凸轮 Cams from the industry
图 上活大等 Cam Design Procedure ©Type Synthesis Selection of cam and follower type based on basic motion requirements Geometric,environmental,and economic considerations ©Follower Motion: from timing diagram->motion program · Based on specified rise,return,dwell Dimensional Synthesis of Cam Profile ."Wrapping around"follower profile onto cam ©Analysis Pressure Angle,Radius of Curvature,Dimensional Constraints... ME371 Design Manufacturing ll 国 上净文通大学 Cam Design Procedure Selection of cam and follower type Type Synthesis based on basic motion requirements Geometric.environmental.and economic considerations Follower Motion Based on specified rise,return,dwell Dimensional Wrapping around' follower profile Synthesis onto cam Analysis Pressure Angle,Radius of Curvature,Dimensional Constraints. 9
9 ME371 Design & Manufacturing II Cam Design Procedure Type Synthesis • Selection of cam and follower type based on basic motion requirements • Geometric, environmental, and economic considerations Follower Motion: from timing diagram->motion program • Based on specified rise, return, dwell Dimensional Synthesis of Cam Profile • “Wrapping around” follower profile onto cam Analysis • Pressure Angle, Radius of Curvature, Dimensional Constraints... Cam Design Procedure • Selection of cam and follower type based on basic motion requirements • Geometric, environmental, and economic considerations • Based on specified rise, return, dwell • “Wrapping around” follower profile onto cam • Pressure Angle, Radius of Curvature, Dimensional Constraints... Type Synthesis Follower Motion Dimensional Synthesis Analysis
® 上浒充通大￥ 5 3 7177n777 3 77 国 上泽文大粤 Motion mm or in High dwell 1 Low dwell Rise Fall 0 0 90 180 270 360 Cam angle日deg 0 0.25 0.50 0.75 1.0 Time t sec timing diagram-运动时序/运动循环图 10
10 timing diagram-运动时序/运动循环图