ME 0208 Machines and Mechanisms II.pptx

7/27/2019 ME 0208 Machines and Mechanisms II.pptx

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ME 0208 Machines and Mechanisms

Unit II

ADVANCED MECHANISMS AND CAMS

II Year III Sem

Department of Mechanical Engineering

SRM UNIVERSITY


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PANTOGRAPH

A pantograph is an instrumentused to reproduce to an enlarged or

reduced scale and as exactly as possible

the path described by a given point.

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Department of Mechanical Engineering


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A pantograph (or "pan") is an apparatusmounted on the roof of an electric train or

tram to collect power through contact with an

overhead wire.


Pantograph in rail


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The steering gear mechanism is used forchanging the direction of two or more of the

wheel axles with reference to the chassis, so

as to move the automobile in any desired

path.


Steering Gear Mechanism


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In order to avoid skidding, the two front

wheels must turn about the sameinstantaneous center I which lies in the axis of

the back wheels.

Davis Steering gear

Ackerman steering gear



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It is used to connect two non-parallel &intersecting axes shafts, having small angle

between two axes.

Single Hooke's joint

Double Hooke's joint


Hooke's joint


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Applications


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Double Hooke's joint


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A cam is a rotating machine element whichgives reciprocating or oscillating motion to

another element known as follower.

The cam and follower have a line contact andconstitute a higher pair.


Cams and followers


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Types of radial and disk cams

Pear Circular Drop



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Swash Cam



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Radial or Disc Cam

In radial cams, the follower reciprocates or

oscillates in a direction perpendicular to the

cam axis.


Classification of CAMS


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Cylindrical Cam

In cylindrical cams, the followers reciprocates or

oscillates in a direction parallel to the cam axis.


Cylindrical cam with reciprocatingfollower

Cylindrical cam with oscillatingfollower


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According to the surface in contact.

According to the motion of the follower.

According to the path of motion of the

follower.


Classification of Followers


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According to the surface in contact.

1.Knife edge follower



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2. Roller follower

3. Flat faced or

Mushroom follower



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4. Spherical faced follower


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According to the motion of the follower.

1. Reciprocating or translating follower.

2. Oscillating or rotating follower.



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According to the path of motion of the

follower

1. Radial follower

2.Off-set follower



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Application of CAM


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1. Base circle

2. Trace point

3. Pressure angle

4. Pitch point

5. Pitch circle

6. Pitch curve

7. Prime circle8. Lift or Stroke


Terms Used in Radial Cams


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Base Circle

It is the smallest circle

that can be drawn tothe cam profile

Cam profile

Cam shaft


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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.

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Pressure angle

It is the angle between the

direction of the follower

movement and a normal to

the pitch curve.

This angle is very importantin designing a cam profile. If

the pressure angle is too

large, a reciprocating follower

will jam in its bearing.



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Pitch point

It is point on the pitch curve

having the maximum pressure

angle

Pitch circle

it is a circle drawn from thecenter of the cam through the

pitch points.



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Prime circle

It is the smallest circle that can be

drawn from the center of the camand tangent to the pitch curve.

For a knife edge and flat face

follower, the prime circle and thebase circle are identical.

For a roller follower the prime

circle is larger than the base circleby the radius of the roller



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Lift of the stroke

It is the maximum travel of the follower from its

lower position to the topmost position



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Motion of the follower

1. Uniform velocity

2. Simple harmonic motion

3. Uniform acceleration and retardation

4. Cycloidal motion.



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Displacement, velocity and acceleration diagram

when the follower moves with uniform velocity



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when the follower moves with SHM

Displacement velocity and acceleration diagram when the


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Displacement, velocity and acceleration diagram when the

follower moves with uniform acceleration and retardation


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when the follower moves with cycloidal motion


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Steering Gear Mechanism

Davis Steering gear


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Davis Steering gear



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Ackerman steering gear



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ME 0208 Machines and Mechanisms II.pptx

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