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5. Mechanisms
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Analyse
30.
Think of more examples of machines that use cranks, rods or crankshaft
mechanisms. Describe the location and motion of the various parts.
31.
Study the camshaft on this page. Howmany switches could this camshaft
operate at the same time? How do you know?
Analyse
32.
Many bicycle seats have
a quick release clamp.
What mechanisms do
these clamps include?
Describe their movements
and functions. What
forces are applied? Why
are these clamps useful?
Analyse
29.
Study the cam mechanism above. What motion will the follower make?
Cam mechanisms
A
cam
is an irregularly shaped device that rotates on a shaft. When the cam rotates,
it pushes a special bar called a follower. The
follower
can move other parts or it
can turn a switch on and off. In some mechanisms, a spring pushes the follower
back to its original position.
cam
follower
roller
d
1
2
spring
Quick release clamp
Applications
:
we can find camshafts in toys, automatic tools and combustion
motors.
Some cams are circular, but with an axis of rotation that is off-centre. These are
called
eccentric cams
because they rotate in an irregular or eccentric way.
Applications
:
there are often eccentric cams in sewing machines and other devices
that transform rotary motion to linear motion.
eccentric
cam
follower
roller
axis of
rotation
We can put multiple cams on one shaft, called a camshaft. We can use a
camshaft to synchronize the movements of various parts, such as the valves
of an internal combustion motor. A clockwork music box also has a camshaft
mechanism.
There is a metal roller with many tiny bumps. When the roller turns, the bumps act
like cams, moving a series of metal teeth that play musical notes.
camshaft
❚
There are two types of
mechanisms that can
transform motion: rotary-
linear mechanisms (wheels,
rack and pinion, nut and
bolt, winch and crank) and
reciprocating rotary-linear
mechanisms (crank and rod,
crankshaft, camandeccentric
cam).
Key concept
ADVANCE
EDITION
