welcom to kom lecture
Myself P.Senthilkumar, Faculty in mechanical Engineering
In this lecture , we are going to discuss about four bar mechanism
The main objective of this lecture is
To understand the working methodology of four bar mechanism
The specific objectives are
1. To explain the working of four bar mechanism
2. To classify the various types of four bar mechanism
3. To show the application of fourbar mechanism in beam engine & coupled rod of locomotive
4. Finally, to find the velocity component of four bar mechanism
Let me explain the application of fourbar mechanism in a car.
when i press wiper lever,it actuates motor
which create oscillating motion on windshied
Now my question is How does it work?
I mean the motor create rotary motion but at the output we are getting oscillating motion
There is an arrangement between the motor and wiper
That arrangement converts rotary motion of motor into oscillating motion of wiper at the output
That arrangement is noting but four bar mechanism
The purpose of four bar mechanism is
to convert rotary motion of motor into oscillating motion of wiper at the output.
Specific objective 1
To explain the working of four bar mechanism
This is an arrangement of four bar mechanism
This is the working model of four bar mechanism
Here the rotary motion of crank converted into
oscillating motion of rocker at the output
with the help of connecting rod
Link 1 frame which is fixed
Link 2 crank
Link 3 connecting rod
Link 4 rocker
The simplest and basic kinematic chain is four bar chain.
Here the degree of freedom is n=1
Thats why it is called simple mechanism
Grashofs law states that
Sum of the shortest and longest link
should not be greater than sum of remaining link
Let us consider a four bar diagram
shortest link AD
Longest link BC
This is the condition to be satisfied for four bar mechanism
Specific objective 2
To find various inversion of four bar mechanism
Inversion is an process of obtaining
different mechanism by fixing different link
There are 3 possible inversion
The name itself give meaning ' crank lever
crank act as input, lever act as output
two crank make complete rotation
here two link act as lever
let me show the simulation of four bar mechanism
& its inversion
In this arrangement, add pin joint and motor on respective place
Fix link1
This is the simulation of four bar mechanism
Fix green link instead of blue link
You can see an double crankmechanism
i mean two link will make complete rotation
like this
Similarly you can fix link3
when you fix link 4
you can see rocker rocker motion
i mean two link will make oscillating motion
These are the 3 possible inversion in four bar mechanism
specific objective 3
To show the application of four bar mechanism in beam engine and locomotive
This is the arrangement of beam engine
Let me show you the working model of beam engine
in this model,this is link1,and this is link 2.
link3,link 4
when i rotate crank about fixed point
the lever oscillate about this point
Meanwhile slider slide inside the cylinder
This is the working of crank lever mechanism
i mean beam engine
The purpose of this mechanism is
to convert the rotary motion of crank into sliding motion of slider inside the cylinder.
Coupled rodof locomotive
This is an arrangement of coupled rod of locomotive
when crank1 at wheel 1 rotates about fixed point
the crank2 at wheel 2 will also rotate with the help of
connecting rod
The purpose of this mechanism is to
convert roary motion of one crank into another crank
The distance between two point is fixed,
in order to maintain a constant distance between wheel
thats why this mechanism is commonly used in locomotive
specific objective 4 is
to resolve velcotiy component for four bar mechanism
Let us consider a four bar mechanism like this
ABCD
Now apply law of relative velocity
velocity always perpendicular to link
Draw Vba
Perpendicular to BA
Draw Vcb
Perpendicular to CB
Finally draw Vcd
Perpendicular to CD
first move blue color line
next move
green colorline
finally move orange color line
by measuring length of these line
we canfind velocity of individual component
stimulating question
Identify the type of mechanism used in following toys
The answer is double crank mechanism
it act as double crank
oscillating body
The floor act as fixed link
link1
link 2
link 3&4
when i fix oscilating body
it simply make rotary motion
you can see it simply make rotary motion like this
let me show you once again
double crank mechanism
a type of four bar mechanism
There are lot of mechanism used in toys
This is one example for walking mechanism
used in toys
i will show you one more example
walking mechanism using cam
In real world,you can find lot of mechanism like this in toys.
let me conclude todays lecture
today we discussed about four bar mechanism
in that ,first we discussed about different terminology
along with grashof law
then we disccused about
inversion of four bar mechanism
crank rocker
rocker rocker
and douple crank mechanism
then we discussed about
application like
bema engine and coupled rod of locomotive
finally we discussed about
kinematic analysis of four bar mechanism
Next class, we are going to discuss about slider crank mechanism
Thank you
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