MET 305                                 MECHANICS OF MACHINES                              TUTORIAL .5Student Name & No.__...
MET 305                               MECHANICS OF MACHINES                             TUTORIAL .52.2.According to the mo...
MET 305                              MECHANICS OF MACHINES                              TUTORIAL .5 3. Cam Terminology    ...
MET 305                        MECHANICS OF MACHINES   TUTORIAL .54. Types of follower motions    1. Uniform velocity   2....
MET 305                            MECHANICS OF MACHINES   TUTORIAL .5   3. Uniform acceleration and retardation   4. Cycl...
MET 305                               MECHANICS OF MACHINES                          TUTORIAL .55. Objective          a. T...
MET 305                                 MECHANICS OF MACHINES                             TUTORIAL .52. Draw the cam profi...
MET 305                                MECHANICS OF MACHINES                             TUTORIAL .53.. Cam with 30 mm as ...
MET 305                               MECHANICS OF MACHINES                          TUTORIAL .54. Determine the profile o...
MET 305                                  MECHANICS OF MACHINES                              TUTORIAL .55. It is required t...
MET 305                              MECHANICS OF MACHINES                          TUTORIAL .56. It is required to set ou...
MET 305                            MECHANICS OF MACHINES                       TUTORIAL .5    10. Conclusion    This tutor...
MET 305                            MECHANICS OF MACHINES                       TUTORIAL .5    10. Conclusion    This tutor...
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Met 305 tutorial_6_cams

  1. 1. MET 305 MECHANICS OF MACHINES TUTORIAL .5Student Name & No.________________________________ Date:___________________Section: _________________________________________ Score: ___________________ Cams1. IntroductionA cam is a rotating machine element, which gives reciprocating or oscillating motion to anotherelement known as follower. The cam and the follower have a line contact and constitute ahigher pair. The cams are usually rotated at uniform speed by a shaft, but the follower motionis predetermined and will be according to the shape of the cam The cam and follower is one ofthe simplest as well as one of the most important mechanisms found in machinery today. Thecams are widely used for the inlet and exhaust valves of internal combustion engines,automatic attachment of machineries, paper cutting machines, spinning and weaving textilemachineries, feed mechanism of automatic lathes etc.2. Classification of FollowersThe followers may be classified as discussed below:2.1. According to the surface in contact.The followers, according to the surface in contact, are as follows:(a) Knife edge follower. When the contacting end of the follower has a sharp knife-edge, it isknife-edge follower, as shown in Fig. (a). The sliding motion takes place between the surfaces(i.e. the knife-edge and the cam surface). This is seldom used in practice because the small areaof contacting surface results in excessive wear. In knife-edge followers, a considerable sidethrust exists between the follower and the guide.(b) Roller follower. When the contacting end of the follower is a roller, it is called a rollerfollower, as shown in Fig.(b). Since the rolling motion takes place between the contactingsurfaces (i.e. the roller and the cam), therefore the rate of wear is greatly reduced. In roller followersalso the side thrust exists between the follower and the guide. The roller followers areextensively used where more space is available such as in stationary gas and oil engines andaircraft engines.(c) Flat faced or mushroom follower. When the contacting end of the follower is a perfectly flatface, it is called a flat-faced follower, as shown in Fig.(c). It may be noted that the side thrustbetween the follower and the guide is much reduced in case of flat-faced followers. The onlyside thrust is due to friction between the contact surfaces of the follower and the cam. Therelative motion between these surfaces is largely of sliding nature but wear may be reduced byoff-setting the axis of the follower, as shown in Fig.(f) so that when the cam rotates, thefollower also rotates about its own axis. The flat faced followers are generally used where spaceis limited such as in cams which operate the valves of automobile engines.Note : When the flat faced follower is circular, it is then called a mushroom follower.(d) Spherical faced follower. When the contacting end of the follower is of spherical shape, it iscalled a spherical faced follower, as shown in Fig.(d). It may be noted that when a flat-facedfollower is used in automobile engines, high surface stresses are produced. In order to minimizethese stresses, the flat end of the follower is machined to a spherical shape.
  2. 2. MET 305 MECHANICS OF MACHINES TUTORIAL .52.2.According to the motion of the follower. The followers, according to its motion, are of thefollowing two types(a) Reciprocating or translating follower. When the follower reciprocates in guides as the camrotates uniformly, it is known as reciprocating or translating follower. The followers as shown inFig. 20.1 (a) to (d) are all reciprocating or translating followers.(b) Oscillating or rotating follower. When the uniform rotary motion of the cam is convertedinto predetermined oscillatory motion of the follower, it is called oscillating or rotatingfollower. The follower, as shown in Fig 20.1 (e), is an oscillating or rotating follower.2.3. According to the path of motion of the follower. The followers, according to its path ofmotion, are of the following two types:(a) Radial follower. When the motion of the follower is along an axis passing through thecentre of the cam, it is known as radial follower. The followers, as shown in Fig. (a) to (e) are allradial followers.(b) Off-set follower. When the motion of the follower is along an axis away from the axis of thecam centre, it is called off-set follower. The follower, as shown in Fig. (f), is an off-set follower.Note : In all cases, the follower must be constrained to follow the cam. This may be done bysprings, gravity or hydraulic means. In some types of cams, the follower may ride in a groove. important in order to draw the cam profile.
  3. 3. MET 305 MECHANICS OF MACHINES TUTORIAL .5 3. Cam Terminology 3.1. Base circle. It is the smallest circle that can be drawn to the cam profile. 3.2. 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. 3.3. 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. 3.4. Pitch point. It is a point on the pitch curve having the maximum pressure angle. 3.5. Pitch circle. It is a circle drawn from the centre of the cam through the pitch points. 3.6. Pitch curve. It is the curve generated by the trace point as the follower moves relative to he 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. 3.7. 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 f the roller. 3.8. Lift or stroke(throw, travel). It is the maximum travel of the follower from its lowest position to the topmost position.
  4. 4. MET 305 MECHANICS OF MACHINES TUTORIAL .54. Types of follower motions 1. Uniform velocity 2. Simple harmonic motion
  5. 5. MET 305 MECHANICS OF MACHINES TUTORIAL .5 3. Uniform acceleration and retardation 4. Cycloidal Motion
  6. 6. MET 305 MECHANICS OF MACHINES TUTORIAL .55. Objective a. To understand different types of followers b. To analyze various types of follower displacements c. To analyze and draw different types of cams for different types of followers and motions6. Procedure 1. Check the type of follower. 2. Study the type of follower motion. 3. Draw the displacement diagram. 4. Construct the cam profile.7. Problems1. Draw the profile of a disc cam to give uniform motion (uniform velocity) during outstroke of 25mm to a knife edge follower during the first half of the cam revolution. The return of the cam alsotakes place with uniform motion (uniform velocity) during the remaining half of the camrevolution. Minimum radius of the cam is 25 mm. Draw the shaft on which the cam is mountedshowing the position of the key. Shaft diameter - 25 mm. The axis of the knife edge follower passesthrough the axis of the cam.
  7. 7. MET 305 MECHANICS OF MACHINES TUTORIAL .52. Draw the cam profile for cam with roller reciprocating follower. The axis of the follower passesthrough the axis of the cam and rotates anticlockwise. Particulars of the cam and the follower motionare the following: Roller diameter = 5 mm Minimum radius of the cam = 20 mm Total lift = 25 mm.The cam has to lift the follower with simple harmonic motion during 180° of cam rotation, then allowthe follower to drop suddenly halfway, and further return the follower with uniform velocityduring the remaining 180° of cam rotation. Show the position of key on the shaft to which thecam is mounted. Determine the maximum velocity and maximum acceleration on the outstroke, ifthe cam rotates at a uniform speed of 100 r.p.m.Answer
  8. 8. MET 305 MECHANICS OF MACHINES TUTORIAL .53.. Cam with 30 mm as minimum diameter is rotating clockwise at a uniform speed of 1200r.p.m. clockwise and has to give the motion to the roller follower 10 mm diameter as definedbelow : (i ) Follower to complete outward stroke of 25 mm during 120° of cam rotation with equal uniform acceleration and retardation. (ii) Follower to dwell for 60° of cam rotation. (iii) Follower to return to its initial position during 90° of cam, rotation with equal uniform acceleration and retardation (iv) Follower to dwell for the remaining 90° of cam rotation. Layout the cam profile when: (a) the roller follower axis passes through the axis of the cam ; (b) the roller follower axis is offset to right by 5 mm.Determine the uniform acceleration of the follower on the outstroke and the return stroke, andalso the maximum velocity of the follower during outstroke and the return stroke. Answer
  9. 9. MET 305 MECHANICS OF MACHINES TUTORIAL .54. Determine the profile of cam to give oscillatory motion to the follower, with uniform angularvelocity about its pivot. One oscillation is completed in one revolution of the cam. The distancebetween the cam centre and the pivot of the follower is 50 mm. The base circle diameter is 40mm. Angle of oscillation is 29°. The length of the oscillating lever = 50 mm with roller of 5 mmdiameter at the end. The cam rotates anticlockwise.Answer
  10. 10. MET 305 MECHANICS OF MACHINES TUTORIAL .55. It is required to set out the profile of a cam to give the following motion to the reciprocatingfollower with a flat mushroom contact face: (i) Follower to have a stroke of 20 mm during 120° of cam rotation; (ii) Follower to dwell for 30° of cam rotation (ii) follower to return to its initial position during 120° of cam rotation; (iv) Follower to dwell for remaining 90° of cam rotation. Cam rotates anticlockwiseAnswer
  11. 11. MET 305 MECHANICS OF MACHINES TUTORIAL .56. It is required to set out the profile of a cam to give the following motion to the follower: (i) Follower to move outwards through 31.4 mm during 180° of cam rotation, with cycloidal motion; (ii) Follower to return with cycloidal motion during 180° of cam rotation.Determine the maximum velocity and acceleration of the follower during the outstroke when thecam rotates at 2400 r.p.m. clockwise. The base circle of the cam is 30 mm diameter and the rollerdiameter of the follower is 10 mm. The axis of the roller is offset by 7.5 mm to the right.
  12. 12. MET 305 MECHANICS OF MACHINES TUTORIAL .5 10. Conclusion This tutorial enables the student to construct any type of cam profile for any mechanism design.
  13. 13. MET 305 MECHANICS OF MACHINES TUTORIAL .5 10. Conclusion This tutorial enables the student to construct any type of cam profile for any mechanism design.

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