THEORY OF MACHINE AND MACHINE ELEMENTS DESIGNUNIT 2 CAM AND FOLLOWER.
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The document is a detailed educational resource focused on the theory of machines, specifically cam and follower mechanisms. It describes various types of followers and cams, their classifications based on contact surface and motion, and the motions of followers. Additionally, it includes technical aspects such as pressure angles and the nomenclature related to cam profiles.
THEORY OF MACHINE AND MACHINE ELEMENTS DESIGNUNIT 2 CAM AND FOLLOWER.
- 1. 1 KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY (AUTONOMOUS) (Approved by AICTE, New Delhi, Affiliated to Anna University, Chennai, Accredited by NAAC B++ Grade, Accredited by NBA, Recognized by UGC with 2(f) & 12(B) An ISO 9001:2015 certified Institution) Namakkal - Trichy Main Road, Thottiam, Trichy - 621215 20AG403 THEORY OF MACHINE AND MACHINE ELEMENTS DESIGN Prepared by, Dr. P. DINESHKUMAR, M.E., Ph.D., Assistant Professor, Department of Agricultural Engineering, Kongunadu College of Engineering and Technology, Trichy.
- 2. Dr. P. Dineshkumar / AP / AGE / KNCET 2 UNIT 2 CAM, FOLLOWER AND GEARTRAINS Cam and follower - types - application – displacement diagrams - profile layout for uniform velocity - Uniform acceleration and retardation - simple harmonic and cycloidal motion. Gears - classification - terminology -law of gearing - tooth profile - interference between rack and pinion. Gear trains - simple - compound reverted - epicyclic gear trains.
- 3. Dr. P. Dineshkumar / AP / AGE / KNCET 3 INTRODUCTION A cam is a rotating machine element which gives reciprocating or oscillating motion to another element known as follower. The cam and the follower have a line contact and constitute a higher pair. The cams are usually rotated at uniform speed by a shaft, but the follower motion is predetermined and will be according to the shape of the cam.
- 4. Dr. P. Dineshkumar / AP / AGE / KNCET 4 Classification of Followers
- 5. Dr. P. Dineshkumar / AP / AGE / KNCET 5 According to the surface in contact
- 6. Dr. P. Dineshkumar / AP / AGE / KNCET 6 KNIFE EDGE FOLLOWER The contacting end of the follower has a sharp knife edge, it is called a knife edge follower, as shown in figure. The sliding motion takes place between the contacting surfaces (i.e. the knife edge and the cam surface). It is seldom used in practice because the small area of contacting surface results in excessive wear.
- 7. Dr. P. Dineshkumar / AP / AGE / KNCET 7 ROLLER FOLLOWER The contacting end of the follower is a roller, it is called a roller follower, as shown in figure since the rolling motion takes place between the contacting surfaces (i.e. the roller and the cam), therefore the rate of wear is greatly reduced. In roller followers also the side thrust exists between the follower and the guide. The roller followers are extensively used where more space is available such as in stationary Gas and oil engines and aircraft engines.
- 8. Dr. P. Dineshkumar / AP / AGE / KNCET 8 FLAT FACED OR MUSHROOM FOLLOWER The contacting end of the follower is a perfectly flat face, it is called a flat-faced follower, as shown in figure. It may be noted that the side thrust between the follower and the guide is much reduced in case of flat faced followers. The flat faced followers are generally used where space is limited such as in cams which operate the valves of automobile engines.
- 9. Dr. P. Dineshkumar / AP / AGE / KNCET 9 SPHERICAL FACED FOLLOWER The contacting end of the follower is of spherical shape, it is called a spherical faced follower, as shown in figure. It may be noted that when a flat-faced follower is used in automobile engines, high surface stresses are produced. In order to minimise these stresses, the flat end of the follower is machined to a spherical shape.
- 10. Dr. P. Dineshkumar / AP / AGE / KNCET 10 According to the motion of the follower
- 11. Dr. P. Dineshkumar / AP / AGE / KNCET 11 1. Reciprocating or translating follower When the follower reciprocates in guides as the cam rotates uniformly, it is known as reciprocating or translating follower. 2. Oscillating or rotating follower. When the uniform rotary motion of the cam is converted into predetermined oscillatory motion of the follower, it is called oscillating or rotating follower.
- 12. Dr. P. Dineshkumar / AP / AGE / KNCET 12 ANIMATION
- 13. Dr. P. Dineshkumar / AP / AGE / KNCET 13 According to the path of motion of the follower
- 14. Dr. P. Dineshkumar / AP / AGE / KNCET 14 Radial follower When the motion of the follower is along an axis passing through the centre of the cam, it is known as radial follower. Off-set follower When the motion of the follower is along an axis away from the axis of the cam centre, it is called off-set follower.
- 15. Dr. P. Dineshkumar / AP / AGE / KNCET 15 Classification of Cams 1. Radial (or disc or plate) cams 2. Wedge (or flat) cams 3. Cylindrical (or barrel) cams 4. Conical Cams 5. Globoidal Cams 6. End (or face) Cams
- 16. Dr. P. Dineshkumar / AP / AGE / KNCET 16 Radial (or disc or plate) cams In the radial cams, the follower reciprocates (i.e., translates) in a plane perpendicular to the axis of cam, as shown in figure.
- 17. Dr. P. Dineshkumar / AP / AGE / KNCET 17 Wedge (or flat) cams A wedge cam has wedge shape which imparts translator motion to the follower, as shown in figure.The wedge do not rotate, it only translates in forward and backward directions. But the follower may have translator motion or oscillatory motion
- 18. Dr. P. Dineshkumar / AP / AGE / KNCET 18 Cylindrical (or barrel) cams In the cylindrical cam, a cylinder which has a circumferential contour cut in the surface, rotates about its axis.The follower rides at the groove cut on the periphery of the cylinder.
- 19. Dr. P. Dineshkumar / AP / AGE / KNCET 19 Conical Cams If the cylindrical surface in the cylindrical cam is replaced by a conical surface, a conical cam is obtained. In conical cams, the follower rides along a groove cut on the conical surface, as shown in figure. In this, the follower reciprocates in a direction parallel to an end-generation.
- 20. Dr. P. Dineshkumar / AP / AGE / KNCET 20 Globoidal Cams Globoidal cams are similar to the cylindrical cams, but they have either a convex surface or a concave surface. The circumferential contour is cut on the surface of the cam and the cam imparts motion to the follower by rotating about its axis.
- 21. Dr. P. Dineshkumar / AP / AGE / KNCET 21 End (or face) Cams The end cam has a rotating portion of a cylinder, a cone, or a sphere, which oscillates a follower having its perpendicular to the cam axis, as shown in figure. In end cam, the follower translates or oscillates, whereas the cam usually rotates.
- 22. Dr. P. Dineshkumar / AP / AGE / KNCET 22 RADIAL CAM NOMENCLATURE 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.
- 23. Dr. P. Dineshkumar / AP / AGE / KNCET 23 4. Pitch 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. Pitch 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. 8. Lift or stroke: It is the maximum travel of the follower from its lowest position to the topmost position.
- 24. Dr. P. Dineshkumar / AP / AGE / KNCET 24
- 25. Dr. P. Dineshkumar / AP / AGE / KNCET 25 MOTION OF THE FOLLOWER The follower, during its travel, may have one of the following motions. 1. Uniform velocity 2. Simple harmonic motion 3. Uniform acceleration and retardation 4. Cycloidal motion.