Please
Do Not Use This Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
Title: Cam and follower
Radial
Aim: To record the kinematics properties of various
radial cams
Apparatus:
Cam:
1.
SHM
2.
Uniform motion
3.
Constant acceleration
4.
Tangent
Follower:
1.
Roller
2.
Lever
3.
Knife-edge
4.
Flat –footed
5.
Offset roller
Please
Do Not Use This Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
THEORY:
*GENERAL KNOWLEDGE*
·
A cam is a rotating machine
element which gives reciprocating or oscillating motion to another element
known as follower. The cam and follower have a point or line contact
constituting a higher pair.
·
The contact between them is
maintained by an external force which is generally provided by a spring or
sometimes by the weight of the follower itself when it is sufficient.
·
The cam converts rotary motion
of one element into reciprocating (linear) motion or into oscillatory motion.
The cam is the driver member and the follower is the driven member
Classification of Cams
Cams
may be classified in many ways. The most important classification is based on
the motion and displacement of the follower with respect to the axis of
rotation or oscillation of the cams. Based on this, the types of cams are as
follows:
·
Radial or Disc Cam: In
the radial cams, the working surface of the cam is designed such that follower
moves in a plane perpendicular to the axis of the cam performing a
reciprocating or oscillating motion.
·
Cylindrical Cam: In this type of cam,
the follower either reciprocates or oscillates in a plane parallel to the axis
of the cam. In this a circumferential contour is cut in the surface of the
cylinder which rotates about its own axis. The follower rides in the groove of
the cylinder surface and it reciprocates in the plane parallel to the axis of
rotation.
Wedge Cam: Here the cam has
translatory motion and the profile of the cam is formed on one side of the cam.
Classification of Cam Followers
According
to the Surface Contact:
·
Knife edged followers:
These are simple in construction. The contacting end of the follower with the
cam has a sharp knife edged hence it is called so. The motion between the cam
and follower is sliding. It is not used in practice because small area of
contact surface results in high rate of wear at the edges due to which the
transmission of motion may not be accurate as desired.
·
Roller follower:
The contact end of the follower is roller and the rolling motion exists between
the cam and follower. Compared to knife edge followers, the rate of wear and
tear is less due to less friction. These are used in aircraft engines and oil
engines.
·
Flat face or mushroom follower:
These are used where space is limited to operate valve of automobile engine.
The contact surface is perfectly flat. The side thrust between guide and
follower is much reduced. It is called a mushroom follower when the flat face
is circular.
·
Spherical follower:
When the contact end of the follower is of spherical shape.
According
to the Path of the Motion of the Follower:
·
Radial follower:
In a radial follower the follower translates along an axis passing through the
center of the cam.
·
Offset follower:
The axis movement of the follower is away from the axis of the centre of
rotation of the cam.
THEORY 1.
A cam is a rotating or sliding piece
in a mechanical
linkage used especially in transforming rotary motion into linear
motion or vice versa. It is often a part of a rotating wheel (e.g. an eccentric wheel) or shaft (e.g.
a cylinder with an irregular shape) that strikes a lever at one or more points on its circular
path. The cam can be a simple tooth, as is used to deliver pulses of power to a
steam hammer, for example,
or an eccentric
disc or other shape that produces a smooth reciprocating (back and forth)
motion in the follower,
which is a lever making contact with the cam
Displacement
diagram
Fig. 2 Basic displacement diagram
Certain cams
can be characterized by their displacement diagrams, which reflect the changing
position a roller follower (a shaft with a rotating wheel at the end) would
make as the cam rotates about an axis. These diagrams relate angular position,
usually in degrees, to the radial displacement experienced at that position.
Displacement diagrams are traditionally presented as graphs with non-negative
values. A simple displacement diagram illustrates the follower motion at a
constant velocity rise followed by a similar return with a dwell in between as
depicted in figure 2.[4] The rise is
the motion of the follower away from the cam center, dwell is the motion where
the follower is at rest, and return is the motion of the follower toward the
cam center.[5]However, the most common type is in the valve actuators in internal combustion engines. Here, the cam profile is commonly symmetric and at rotational speeds generally met with, very high acceleration forces develop. Ideally, a convex curve between the onset and maximum position of lift reduces acceleration, but this requires impractically large shaft diameters relative to lift.
CAM & FOLLOWER :-
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. A cam and the follower combination belongs to
the category of
higher pairs.
1. A driver member
known as the cam.
2. A driven member
called the follower
Types of Cams :
I. According to
shape
1. wedge and flat Cams :- A
wedge cam has a wedge W which, in general, has a
translational motion. The follower.
The follower F can either translate or oscilate.
2. 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.
3. Spiral cams :- A spiral
cam is a face cam in which a groove is cut in the form of a
spiral as shown in fig. the
spiral spiral groove consists of teeth which mesh with a
pin gear follower.
4. Cylindrical cams :- In
a cylindrical cam, a cylinder which has a circumferential
contour cut in the surface,
rotate about its axis.
5. Conjugate cams: - A conjugate cam is a double – disc cam, the
two discs being
Keyed together and are in
constant touch with the two rollers of a follower. It is
used for low noise, high speed
and dynamic loads.
6. Globoidal cams :- A
globoidal cam can have two types of surfaces, convex or Concave. A
circumferential contour is cut on the surface of rotation of the cam to Impart
motion to the follower which has an oscillatory motion.
7. Spherical cams:- In a
spherical cam, the follower oscillates
About an axis perpendicular
to the axis of rotation of the cam.
II. According to
Follower Movement
1. Rise-Return-Rise (R-R-R) :- In
this, there is alternate rise and return of the
follower with no periods of dwells. Its
use is very limited in the industry. The
follower has a linear or an angular
displacement.
2. Dwell-Rise-Return-Dwell (D-R-R-D) :- In
such a type of cam, there is rise and
return of the follower after a dwell.
This type is used more frequently than the R-
R type
of cam
3. Dwell-Rise-Dwell-Return (D-R-D-R) :- It is most widely
used type of cam. The
dwelling of the cam is followed by rise
and dwell and subsequently by return and
dwell
III. According to
Manner of Constraint of the Follower
1. Pre-loaded Spring Cam
2. Positive-Drive Cam
3. Gravity Cam
Types of Followers :-
I. According to shape
1. Knife-edge Follower
2. Roller Follower
3. Mushroom Follower
IV. According to
Movement
1. Reciprocating Follower
2. Oscillating Follower
V. According to
Locating of Line of Movement
1. Radial Follower
2. Offset Follower
For Procedures, See your Mechanical Laboratory Manual.
Please
Do Not Use This Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
Observations :-
1.
Comparison between Cam & Follower
2.
Type of Motion to be named
Applications:-
1. Cams are used in
Automatic machines
2. In internal
combustion engine
3. In machine tools
4. Printing Control mechanisms
PRECAUTIONS:
For
Precautions, See General Laboratory Precautions
Please
Do Not Use This Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
Blogger Comment
Facebook Comment