CAM&FOLLOWER.ppt

Content
Introduction
Types of Cam
Classification of Follower
Cam Terminology
Types of Follower Motions

Introduction
• A cam is a mechanical member used to impart desired motion to a follower by
direct contact.
• The cam may be rotating or reciprocating whereas the follower may be rotating,
reciprocating or oscillating.
• Complicated output motions which are otherwise difficult to achieve can easily be
produced with the help of cams.
• Cams are widely used in automatic machines, internal combustion engines,
machine tools, printing control mechanisms, and so on.
• They are manufactured usually by die-casting, milling or by punch-presses.
• A cam and the follower combination belong to the category of higher pairs.
• Necessary elements of a cam mechanism are
– A driver member known as the cam
– A driven member called the follower
– A frame which supports the cam and guides the follower

Types of Cam
1.Radial or Disc Cams
• A cam in which the follower moves radially from the centre of
rotation of the cam is known as a radial or a disc cam (Fig. (a) and
(b)].
• Radial cams are very popular due to their simplicity and
compactness.

2. Cylindrical Cams
• In a cylindrical cam, a cylinder which has a circumferential contour cut in the
surface, rotates about its axis.
• The follower motion can be of two types as follows: In the first type, a groove is
cut on the surface of the cam and a roller follower has a constrained (or
positive) oscillating motion [Fig.(a)].
• Another type is an end cam in which the end of the cylinder is the working
surface (b).
• A spring-loaded follower translates along or parallel to the axis of the rotating
cylinder.

Classification of Followers
1. According to the surface in contact.
a) Knife edge follower.
When the contacting end of the follower has a sharp knife edge,
it is called a knife edge follower, as shown in Fig.(a).
The sliding motion takes place between the contacting surfaces
(i.e. the knife edge and the cam surface).
It is seldom used in practice because the small area of
contacting surface results in excessive wear.

(b) Roller follower.
• When the contacting end of the follower is a roller, it is called a
roller follower, as shown in Fig. (b).
• Since the rolling motion takes place between the contacting
surfaces (i.e. the roller and the cam), therefore the rate of wear is
greatly reduced.
• In roller followers also the side thrust exists between the follower
and the guide.
• The roller followers are extensively used where more space is
available such as in stationary gas and oil engines and aircraft
engines.

(c) Flat faced or mushroom follower.
• When the contacting end of the follower is a perfectly flat face, it is
called a flat-faced follower, as shown in Fig. 20.1 (c).
• It may be noted that the side thrust between the follower and the
guide is much reduced in case of flat faced followers.
• The only side thrust is due to friction between the contact surfaces
of the follower and the cam.
•The flat faced followers are generally
used where space is limited such as in
cams which operate the valves of
automobile engines.
• 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 is called a spherical
faced follower, as shown in Fig. (d).
• It may be noted that when a flat-faced follower is used in automobile engines, high
surface stresses are produced.
• In order to minimise these stresses, the flat end of the follower is machined to a
spherical shape.

2. According to the motion of the follower
(a) Reciprocating or translating follower.
• When the follower reciprocates in guides as the cam rotates
uniformly, it is known as reciprocating or translating follower.
• The followers as shown in Fig. (a) to (d) are all reciprocating or
translating followers.

(b) Oscillating or rotating follower.
• When the uniform rotary motion of the cam is converted into
predetermined oscillatory motion of the follower, it is called
oscillating or rotating follower.
• The follower, as shown in (e), is an oscillating or rotating follower.

3. According to the path of motion of the follower.
(a) Radial follower. When the motion of the follower is along an axis
passing through the centre of the cam, it is known as radial
follower. The followers, as shown in Fig. (a) to (c), are all radial
followers.

(b) Off-set follower.
• When the motion of the follower is along an axis away from
the axis of the cam centre, it is called off-set follower. The
follower, as shown in Fig. ( f ), is an off-set follower.

Terms Used in Radial Cams
1. Base circle. It is the smallest circle that can be drawn to the cam profile.
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. 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.
4. Pitch point. It is a point on the pitch curve having the maximum pressure
angle.
5. Pitch circle. It is a circle drawn
from the centre of the cam
through the pitch points.
6. 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.

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 of the roller.
8. Lift or stroke. It is the maximum travel of the follower from its lowest position to the
topmost position.

Motion of the Follower
• The follower, during its travel, may have one of the
following motions.
– Uniform velocity
– Simple harmonic motion
– Uniform acceleration and retardation
– Cycloidal motion

Displacement, Velocity and Acceleration Diagrams when the
Follower Moves with Uniform Velocity
• The displacement, velocity and acceleration diagrams when a knife-edged follower
moves with uniform velocity are shown in Fig. (a), (b) and (c) respectively.
• The abscissa (base) represents the time (i.e. the number of seconds required for the
cam to complete one revolution) or it may represent the angular displacement of
the cam in degrees. The ordinate represents the displacement, or velocity or
acceleration of the follower.

CAM&FOLLOWER.ppt

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