Cam and follower

KOM
CAM AND FOLLOWER
kinematics

1. Kinematics of machine CAM and FOLLOWER

2. Sub Topics Classification and terminology of cams and followers, Different motions of the follower. Displacement Diagrams, Cam profiles for radial and offset followers, Cams with specified contours - tangent cam with reciprocating roller follower, Circular arc cam with flat faced follower, Graphical construction of cam profile.

3. INTRODUCTION A cam is a mechanical device used to transmit motion to a follower by direct contact. The driver is called the cam and the driven member is called the follower. In a cam follower pair, the cam normally rotates while the follower may translate or oscillate. A familiar example is the cam shaft of an automobile engine, where the cams drive the push rods (the followers) to open and close the inlet exhaust valves in synchronization with the motion of the pistons.

4. CAM Follower

5. Question 1: Discuss Terminology Used In Cam

6. ANSWER: Fig. shows a radial cam with reciprocating roller follower. (1) Base Circle: It is the smallest circle that can be drawn to then cam profile.

7. (2) Trace Point: It is a reference point on the follower and is used to generate the pitch curve (3) Pitch curve: It is the curve generated by the trace point as the follower moves relative to the cam

8. (4) Prime circle: It is the smallest circle that can be drawn from the center of the cam and tangent in the pitch curve Prime circle radius = Base circle radius for knife edge and flat faced follower Prime circle radius = Base circle radius + radius of roller for roller follower

9. (5) Lift or stroke: It is the maximum of the travel follower from its lowest position to the topmost position. (6) Pitch point: It is a point on the curve having maximum pressure angle (7) Pitch circle: It is a circle drawn from the centre of the cam though the pitch points. (8) Pressure angle: It is the angle between the direction of the follower motion and a normal to the pitch curve (9) Cam Profile: The contour of the working surface of the cam

10. Question 2: CLASSIFICATION OF THE FOLLOWER: (A) ACCORDING TO SHAPE: - The follower is classified as, (1) Knife edge follower (2) Roller follower (3) Flat faced or mushroom follower (4) Spherical follower.

11. Knife- edge follower: When the end of a follower which is in contact with cam has a sharp knife-edge , it called a knife edge follower The sliding motion takes place between the contacting surfaces i.e. the knife-edge and the cam surface. This cam is not of much use as excessive wear occurs at the contacting surface. Roller follower: When the end of the follower is a roller the follower is termed as roller follower. Here notice to be made that at the contact surface the rolling motion is taking place; hence rate of wear is reduced . In both the knife edge & roller follower side thrust exists between the follower and the guide. Roller follower is extremely used where more space is available such as in stationary gas engines Oil engines and also in Aircraft engines.

12. Flat faced or mushroom follower: When the contacting end of the follower is a perfectly flat face, it is called a flat-faced follower .Side thrust between the follower & the guide is much .reduced in case of flat-faced follower. Relative motion between the contacting surfaces is mostly of sliding nature but wear may be reduced by offsetting the axis of the follower. They are generally used where space is limited such as in cams used in valve mechanism of automobile engines.   Spherical faced follower: When the shape of a surface which is in contact with the cam is spherical , the follower is known as Spherical faced follower .The flat end of the follower is machined to a spherical shape in order to minimize high surface stresses produced during operation.

13. (B) ACCORDING TO THE MOTION OF THE FOLLOWER:- The follower are classified as, (1) Reciprocating translating follower (2) Oscillating or rotating follower.

14. (C) ACCORDING TO LOCATION OF LINE OF MOVEMENT:- (1) Redial follower: If the line movement of the follower passes through the centre of rotation of the cam, the follower is known as a radial follower.

15. (2) Offset follower: If the line of movement of the roller follower is offset from the center of rotation of the cam, the follower is known as an offset follower

16. TYPES OF MOTION OF THE FOLLOWER: (1) Simple harmonic motion. (2) Constant acceleration and deceleration. (3) Constant velocity. (4) Cyclonical motion.

17. Outstroke= Rise Of Follower 1. Simple harmonic motion.

18. 2. Uniform velocity

19. Problem 1 Draw the cam profile for following conditions :  For Radial follower, Follower type = Knife edged, in-line; lift = 50mm; base circle radius = 50mm; out stroke with SHM for 60  cam rotation; dwell for 45 cam rotation; return stroke with SHM for 90 o cam rotation; dwell for the remaining period.  

20. X axis: 1 cm = 20 Y Axis: 1 cm = 10 mm Solution: Follower rise return with Simple Harmonic Motion

21. Problem 2: Draw the cam profile for following conditions: Follower type=knife edge d follower, in line; lift=30mm; base circle radius =20mm; outstroke with uniform velocity in 120°of cam rotation; dwell for 60°; return stroke with uniform velocity during 90°of cam rotation; dwell for the remaining period.

22. X axis: 1 cm = 20 Y Axis: 1 cm = 10 mm Solution: Follower rise return with Uniform Velocity

23. Problem 3: Draw the cam profile for following conditions :  For Radial follower, Follower type = Knife edged, in-line; Stroke of follower = 40mm; base circle radius = 50mm; Follower rise with Uniform Velocity for 60  cam rotation; dwell for 30 cam rotation; return stroke with Uniform Velocity for 60 o cam rotation; dwell for the remaining 210 period. Axis of the follower offset by 20 mm to the right of cam center .  

24. X axis: 1 cm = 20 Y Axis: 1 cm = 10 mm Solution: 40 mm 60 30 60 210 Rise Return Follower rise return with Uniform Velocity

25. 20mm offset 60 30 60

26. Problem 4: Draw the cam profile for following conditions:   Follower type = roller follower, in-line; lift = 25mm; base circle radius = 20mm; roller radius = 5mm; out stroke with Uniform acceleration and retardation, for 120  cam rotation; dwell for 60  cam rotation; return stroke with Uniform acceleration and retardation , for 90  cam rotation; dwell for the remaining period.

27. Displacement Diagram

28. CAM Profile

29. Problem 5: Follower type = flat faced follower, inline; follower rises by 20mm with SHM in 120° of cam rotation, dwells for 30° of cam rotation; returns with SHM in 120° of cam rotation and dwells during the remaining period. Base circle radius =25mm.

30. Cam displacement diagram for cycloidal motion