1. IOT
POLY ENGINEERING
4-09
A 4-bar linkage mechanism has a crank that rotates at a
constant angular speed. The crank is connected to the
coupler which is connected to the follower. The frame does
not move.
crank
coupler
follower
frame
KINEMATICS is the branch of physics that
studies the motion of a body or a system of
bodies without consideration given to its mass
or the forces acting on it.

2. IOT
POLY ENGINEERING
4-09
A Grashof linkage is a planar four-bar linkage with
S + L < P + Q
where S = length of the shortest link
L = length of longest link
P and Q are the lengths of the two remaining links.
1. Crank-Rocker : a Grashof linkage where the shortest link is the
input link (crank).
2. Double-Rocker: a Grashof linkage where the shortest link is the
floating link (coupler).
3. Rocker-Crank : a Grashof linkage where the shortest link is the
output link (follower).
4. Crank-Crank : a Grashof linkage where the shortest link is the
ground link (frame).

3. IOT
POLY ENGINEERING
4-09
1. Crank-Rocker : a Grashof linkage where the shortest link is the
input link (crank).

4. IOT
POLY ENGINEERING
4-09
2. Double-Rocker: a Grashof linkage where the shortest link is the
floating link (coupler).

5. IOT
POLY ENGINEERING
4-09
4. Crank-Crank : a Grashof linkage where the shortest link is the
ground link (frame).

6. IOT
POLY ENGINEERING
4-09
A pantograph is a mechanism that is
used to create a drawing that is larger
or smaller than an original drawing.
The pantograph simulation below creates a drawing that
is larger than the original drawing.

7. IOT
POLY ENGINEERING
4-09
A parallel bar mechanism is a mechanism that
retains parallelism in its members.

8. IOT
POLY ENGINEERING
4-09
A straight line mechanism is a mechanism that is
used to create straight lines. The examples below
are Peaucellier mechanisms.

9. IOT
POLY ENGINEERING
4-09
Two more examples of a straight line mechanism are
shown below. These are the Tchebicheff mechanism.

10. IOT
POLY ENGINEERING
4-09
Example of a nearly straight line mechanism is shown
below. This is the Watt mechanism, invented by
James Watt of steam engine fame. If you look
closely, you will see that the path deviates from a
straight line at the top and the bottom of motion.

11. IOT
POLY ENGINEERING
4-09
This is a SCOTCH YOKE. As the yellow knob rotates, it
causes the light gray yoke to move side to side.
Thus, rotational motion has been converted to linear
motion.

12. IOT
POLY ENGINEERING
4-09
This is a GENEVA MECHANISM. As the small black knob
rotates at a constant rate, it causes the dark gray mechanism
to rotate one-sixth of a turn and stop, rotate one-sixth of a
turn and stop, etc. The Geneva mechanism on the right side
causes one-fourth of a turn movements.
Rotational motion has been converted to sporadic rotational
motion.