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TEHSEEN ARIF BHATTI

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CAMS

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CAMS DEFINITION

A CAM changes the input motion, which is usually

rotary motion (a rotating motion), to a reciprocatingmotion of the follower.

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CAMS CAM MECHANISM

The transformation of one of the simple motions, such

as rotation, into any other motions is oftenconveniently accomplished by means of a cammechanism A cam mechanism usually consists of twomoving elements, the cam and the follower, mounted

on a fixed frame. Cam devices are versatile, and almostany arbitrarily-specified motion can be obtained. Insome instances, they offer the simplest and mostcompact way to transform motions.

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CAMSAcam may be defined as a machine element having a

curved outline or a curved groove, which, by itsoscillation or rotation motion, gives a predeterminedspecified motion to another element called thefollower.

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TYPES OF CAMS

(on the basis of shapes) There are two types of cams.

RADIAL or DISC CAM

CYLINDRICAL CAM

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RADIAL or DISC CAM

In radial cams, the follower reciprocates or oscillates ina direction perpendicular to the cam axis.

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CYLINDRICAL CAM

In cylindrical cams, the follower reciprocates oroscillates in a direction parallel to the cams axis.

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TYPES OF CAM FOLLOWERSAccording to the surface in contact of the follower

a)KNIFE-EDGEFOLLOWER

In this type of follower,the contacting end issharp knife-edge. The

sliding motion takesplace between thecontact surfaces.

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TYPES OF CAM FOLLOWERS

According to the surface in contact of the follower

(b)ROLLER FOLLOWER

If the contact end of thefollower is a roller, it iscalled roller follower. Inthis type, the rollermotion takes placebetween the contactsurfaces, therefore therate of wear isconsiderably reduced.

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(c) FLAT-FACEDFOLLOWER

It is also calledmushroom follower. Inthis type the contactingend of the follower isperfectly flat surface.

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(d) SPHERICAL-FACEDFOLLOWER

In this type of follower,the contact surface isspherical-shaped.

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TYPES OF CAM FOLLOWERSAccording to the path of motion of follower

RADIAL FOLLOWER

When the motion of the follower is along an axispassing through the centre of the cam, it is knownas radial followers. Above figures are examples ofthis type.

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TYPES OF CAM FOLLOWERSAccording to the path of motion of follower

OFFSET FOLLOWERWhen the motion of the follower is along an axisaway from the axis of the cam centre, it is called off-set follower. Above figures are examples of this type

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CAM Nomenclature Cam profile: The outer

surface of the disc cam.

Base circle : The circle

with the shortest radiusfrom the cam center to anypart of the cam profile.

Trace point: It is a pointon the follower, and its

motion describes themovement of the follower.It is used to generate thepitch curve.

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CAM Nomenclature Pitch curve : The path

generated by the tracepoint as the follower is

rotated about astationery cam.

Prime circle: Thesmallest circle from thecam center through thepitch curve

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CAM Nomenclature Pressure angle: The

angle between thedirection of the follower

movement and thenormal to the pitchcurve.

Pitch point: Pitch pointcorresponds to the pointof maximum pressureangle.

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CAM Nomenclature Pitch circle:A circle

drawn from the camcenter and passes

through the pitch pointis called Pitch circle

Stroke: The greatestdistance or anglethrough which thefollower moves or rotates

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MOTION OF THE FOLLOWERAs the cam rotates the follower moves upward anddownward.

The upward movement of follower is called rise

(Outstroke) The downward movement is called fall

(Returnstroke).

When the follower is not moving upward and

downward even when the cam rotates, it is calleddwell.

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TYPES OF FOLLOWER MOTION1. Uniform motion ( constant velocity)

2. Simple harmonic motion

3. Uniform acceleration and retardation motion

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a) Uniform motion (constant

velocity) Displacement diagram: Displacement is the distance that a

follower moves during one complete revolution (or cycle)of the cam while the follower is in contact with the cam.

It is the plot of linear displacement (s) of follower V/S

angular displacement () of the cam for one full rotation ofthe cam. A period is a part of the cam cycle and it includes the

following:

Rise (Outstroke) the upward motion of the follower causedby cam motion.

Fall (Return stroke) the downward motion of the followercaused by cam motion.

Dwell the stationary position of the follower caused by cammotion.

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velocity)

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velocity)

Displacement diagramSince the follower moves with uniform velocity duringits rise and fall, the slope of the displacement curvemust be constant as shown in fig.

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b) Simple Harmonic motion

360 = ONE REVOLUTION OF CAM = 1 CYCLE

FALL

60 180120 240

RISE

300

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b) Simple harmonic motion Since the follower moves

with a simple harmonicmotion, therefore

velocity diagram consistsof a sine curve and theacceleration diagramconsists of a cosine

curve.

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c) Uniform acceleration and

retardation

Since the

acceleration andretardation areuniform, thereforethe velocity varies

directly with time.

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APPLICATIONS OF CAMSCams are widely used in:

Inlet and outlet valves of internal combustion engines.

Paper cutting machinesAutomatic machines

Textile machines

Printing control mechanism

Machine tools

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THANKS

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cams (MTR-212)