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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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.
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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.
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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
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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.
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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.
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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.
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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.
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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
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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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Displacement, velocity and acceleration diagram
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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Displacement, velocity and acceleration diagram
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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