Post on 02-Apr-2018
7/27/2019 Session 23 Notes
1/28
KINEMATICS OF CAM
1
7/27/2019 Session 23 Notes
2/28
CAM Definition- Cam is a mechanical member used for transmitting desired motion to a
follower by direct contact.
Cam may be rotating, reciprocating or oscillating where as the follower may be
reciprocating or oscillating.
Complicated output motions which are otherwise difficult to achieve can be easily
produced with the help of cam
The cam and follower have line or point contact
and coming under higher pair
Application: IC engine, automatic machines,
machine tools, paper cutting machine& textile machine
Necessary elements of cam mechanism are:
1. Cam: The driving member is known as cam
2. Follower: The driven member is known as follower
3. Frame: It supports the cam and guides the follower 2
7/27/2019 Session 23 Notes
3/28
Examples for cam
In IC engines to operate the inlet and exhaust valves
7/27/2019 Session 23 Notes
4/28
Classification of Cams
Cams are classified according to :
(a) Shape
(b) Follower movement (c) manner of constraint of the follower
4
7/27/2019 Session 23 Notes
5/28
(a)According to Shape
1. Wedge and Flat Cams 2. Radial or Disc Cams 3. Spiral Cams
4. Cylindrical Cams 5. Conjugate Cams 6. Globoidal Cams
7. Spherical Cams
5
(b)According to Follower movement1. Rise-return-rise (RRR) 2. Dwell Rise-return Dwell (DRRD)
3. Dwell-rise-dwell-return-Dwell (DRDRD) 4. Dwell-rise-dwell (DRD)
(c)According manner of constraint of the follower1. Pre-loaded Spring Cam 2. Gravity Drive Cam
3. Positive Drive Cam
7/27/2019 Session 23 Notes
6/28
1.Wedge and Flat Cams
6
(a)According to Shape
2. Radial or disc cams
7/27/2019 Session 23 Notes
7/28
7/27/2019 Session 23 Notes
8/28
6. Globoidal Cams
8
7.Spherical cams
7/27/2019 Session 23 Notes
9/28
9
(b)According to Follower movement1. Rise-return-rise (RRR) 2. Dwell Rise-return Dwell (DRRD)
3. Dwell-rise-dwell-return-Dwell (DRDRD) 4. Dwell-rise-dwell (DRD)
7/27/2019 Session 23 Notes
10/28
10
(c)According manner of constraint of the follower1. Pre-loaded Spring Cam 2.Gravity Drive Cam
7/27/2019 Session 23 Notes
11/28
11
3. Positive-drive cam
7/27/2019 Session 23 Notes
12/28
Types of Follower
Cams are classified according to :
(a) Shape
(b) movement
(c) location of line of movement
12
7/27/2019 Session 23 Notes
13/28
(a)According to Shape
1.Knife edge follower
2. roller follower
3. mushroom follower
13
(b)According to movement1. Reciprocating follower
2. oscillating follower
(c)According to location of line of movement1. Radial follower
2. offset follower
7/27/2019 Session 23 Notes
14/28
14
(a)according to shape:1. Knife-edge Follower 2. Roller Follower
3. Flat or Mushroom Follower
7/27/2019 Session 23 Notes
15/28
15
(b) according to movement
1. Reciprocating follower 2. oscillating follower
7/27/2019 Session 23 Notes
16/28
7/27/2019 Session 23 Notes
17/28
17
Follower
Trace
point
Pressure angle()
(maximum)
Radial cam nomenclature
7/27/2019 Session 23 Notes
18/28
18
Follower
Trace
point
Pressure angle()
(maximum)
Radial cam nomenclature
7/27/2019 Session 23 Notes
19/28
Terminology of a radial cam with reciprocating follower is shown.
1. Cam profile
Surface of cam which comes into contact with follower is known as cam profile
2. Base circle
Smallest circle that can be drawn to the cam profile. Radius of base circle known
as least radius of cam
3. Trace pointIt is reference point of follower to trace the cam profile. In knife edge follower
knife edge itself is tracing point. In roller follower, centre of roller is the tracing
point.
4. Pitch curveLocus of path of tracing point. For the purpose of drawing cam profile, it is
assumed that cam is fixed and the follower rotates around it.
5. Prime circle
The smallest circle drawn tangent to the pitch curve.19
7/27/2019 Session 23 Notes
20/28
6. Pressure angle ()
It is angle between the direction of follower motion and a normal to the pitch
curve. This angle is very important. It represent steepness of cam profile.
7. Pitch point
It is the point on the pitch curve at which the pressure angle is maximum
8. Pitch circle
It is the circle passing through the pitch point and concentric with base circle.
9. Cam angle
It is the angle of rotation of cam for a defined displacement of follower
10.Lift or stroke
It is the maximum displacement of the follower from the base circle of the cam.
Also called as throw of the cam
20
Di l t Di
7/27/2019 Session 23 Notes
21/28
Displacement Diagram
Movement of the trace point against the rotation of cam through an angle is called
displacement diagram.
21
It represents angular displacement of cam and represents the corresponding angular
or linear displacement of follower from its initial position
X-axis displacement of cam
Y-axis displacement of follower
Angle of cam rotation () ((one full rotation3600 ))
Followerd
isplacement(h)
7/27/2019 Session 23 Notes
22/28
22
1. Angle of ascent (or) out stroke angle (or) rise (0)
Angle of rotation of cam from the position when follower begins to rise till it
reaches its highest position.
2. Angle of dwell(d)
It is angle through which the cam rotates while follower remains stationary at
the highest or lowest position.
3. Angle of descent (or) return stroke angle (or) fall (R)
It is angle through which the cam rotates during the time the follower return to
initial position
4. Angle of action
It is the total angle moved by the cam during its rotation, between the beginning
of rise of follower and end of return of follower.
7/27/2019 Session 23 Notes
23/28
Displacement Diagram for follower motion
Motion of the fol lower
During its travel follower may have one of the following motion
1. Uniform velocity motion
2. Simple harmonic motion (SHM)
3. Uniform acceleration and retardation (or) parabolic motion
4. Cycloidal motion
23
7/27/2019 Session 23 Notes
24/28
1. Uniform velocity motion
The follower moves with uniform
velocity during its rise and fall, the
slope of the displacement curve
must be constant.
Velocity , v= constant
Acceleration,
a=0 (constant velocity),
a=dv/dt =0
24
S (S )
7/27/2019 Session 23 Notes
25/28
2. Simple harmonic motion (SHM)
When a body rotates on a circular
path with uniform angular
velocity, its projection on the
diameter will have simple
harmonic motion.
25
h
3
7/27/2019 Session 23 Notes
26/28
3. Uniform acceleration and retardation (or) parabolic motion
There is a acceleration in the first
half of follower motion where it is
deceleration during second half.
26
4 C l id l ti
7/27/2019 Session 23 Notes
27/28
4. Cycloidal motion
There is a acceleration in the first half of
follower motion where it is deceleration during
second half.
27
h
4 C l id l ti
7/27/2019 Session 23 Notes
28/28
4. Cycloidal motion
28
h