Mechanisms
What is a Mechanism?
A mechanism is the part of a machine
which contains two or more pieces
arranged so that the motion of one
compels the motion of the others.
Generally used to:
– Change the direction of movement
– Change the type of movement
– Change the speed of movement
– Change the amount of torque or force
available to do work
Mechanism Movement
Rotary
Oscillating
Linear
Reciprocating
Universal Joint
• Angular Range
> 90˚ and < 270˚
• Speed and Torque
constant
• Ratio 1:1
• Flow of Power
reversible
• Input & Output Shafts
same direction
Where Can You Find a
Universal Joint?
• Drive shaft of
vehicles
• Power take-off
Universal joints are
used to transmit rotary
movement at an angle
that is not 90°.
www.rqriley.com/imagespln/pattersn_ujoint.jpg
Bevel Gear
• 90˚ Angle
• Speed and Torque
constant
• Gear Ratio 1:1
• Flow of Power
reversible
Where Can You Find a
Bevel Gear?
• Hand drill
• Car differential
• Shaft-driven bicycle
• The bevel gear is
used to change
rotational motion at a
90˚ angle.
• Using gears with
differing numbers of
teeth will change the
speed and torque.
Simple Gear Train with Idler
IDLER GEAR
• Input and Output Shafts
parallel
• Speed is decreased
• Torque is increased
• Ratio 4:1
• Flow of Power
reversible
• Input and Output Gears
same direction
• Without Idler Gear
different direction
Where Do You Find a
Simple Gear Train with Idler?
Two meshed gears will rotate
in opposite directions.
An Idler Gear allows the
drive and driven gears to
rotate in the same direction.
Paper Transport Rollers
Worm and Wheel
•
•
•
•
•
90˚ Angle
Speed is decreased
Torque is increased
Gear Ratio 20:1
Flow of Power
NOT reversible
• Direction of Travel
reversible
Where Do You Find a
Worm and Wheel?
• Tuning mechanism on
string instruments
• Electric motors
• A worm is used to
• Winch
reduce speed and
increase torque.
• The motion is not
reversible; a gear
cannot drive a worm.
Crown and Pinion
•
•
•
•
•
90˚ Angle
Speed is decreased
Torque is increased
Gear Ratio 3.2:1
Flow of Power
reversible
• Direction of Travel
reversible
Where Do You Find
a Crown and Pinion?
• Watches
• Carousel
• DVD player
How many crown
and pinion gears do
you see in this
pendulum clock?
Rack and Pinion
• Input Movement
rotary
• Output Movement
linear
• Distance is
2 in.
• With a Larger Pinion Gear the rack will move a longer
distance
• Flow of Power
reversible
• Direction of Travel
reversible
Where Do You Find a
Rack and Pinion?
• Used in steering systems • Used to convert
between rotary
of cars to convert rotary
and linear
motion of steering wheel
motion.
to the side to side motion
• Provides gear
in the wheels.
reduction to
• Rack and pinion
make it easier to
steering
Pinion
turn the wheels.
Rack
Lead Screw
• Input Movement
rotary
• Output Movement
linear
• 6 Revolutions = 1 in.
• Flow of Power
NOT reversible
• Force is Increased
• Direction of Travel
reversible
Where Do You Find a
Lead Screw?
• Jack
• Vice
• Changes rotary
movement into linear
movement
• Significantly
increases force
• A person can put a
little force into
turning the handle to
move a heavy car.
Cam and Follower
FOLLOWER
CAM
• Input Movement
rotary
• Output Movement
reciprocating
• Follower moves up and
down 1 time for every
revolution of the crank
• Flow of Power
Not reversible
• Direction of Travel
reversible
Where Do You Find a
Cam and Follower?
• Cam shaft
• As a cam rotates,
the flat follower is
raised and lowered,
converting rotary
motion to
reciprocating (back
and forth) motion.
Crank and Slider
• Input Movement
rotary
• Output Movement
reciprocating
• Slider Moves
1 in. - diameter of
crank
• Increased Crank
increased
distance slider
moves
• Flow of Power
not reversible
Where Do You Find a
Crank and Slider?
• Steam train
• Internal combustion
engine
Pulley and Belt
• Input and Output Shaft
parallel
• Speed is increased
• Torque is decreased
• Ratio 1:2.5
• Flow of Power is reversible
• Open Belt wheels turn in
same direction
• Crossed Belt wheels turn
in opposite direction
Where Do You Find a
Pulley and Belt?
• Lawn mower
• Car engine
BELTS
Image Resources
Microsoft, Inc. (2008). Clip Art. Retrieved November 25, 2008, from
http://office.microsoft.com/en-us/clipart/default.aspx