basic mechanisms
TRANSCRIPT
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
LinearReciprocating
Oscillating
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
www.rqriley.com/imagespln/pattersn_ujoint.jpg
Universal joints are used to transmit rotary movement at an angle that is not 90°.
Bevel Gear
• 90˚ Angle
• Speed and Torque
constant
• Gear Ratio 1:1
• Flow of Power
reversible
Where Can You Find a
Bevel Gear?
• 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.
• Hand drill
• Car differential
• Shaft-driven bicycle
Simple Gear Train with Idler• 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
IDLER GEAR
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?
• A worm is used to
reduce speed and
increase torque.
• The motion is not
reversible; a gear
cannot drive a worm.
• Tuning mechanism on
string instruments
• Electric motors
• Winch
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 to convert
between rotary
and linear
motion.
• Provides gear
reduction to
make it easier to
turn the wheels.
• Used in steering systems
of cars to convert rotary
motion of steering wheel
to the side to side motion
in the wheels.
• Rack and pinion
steering
Rack
Pinion
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.
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
Cam and Follower
• 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
CAM
FOLLOWER
Where Do You Find a
Cam and Follower?
• As a cam rotates,
the flat follower is
raised and lowered,
converting rotary
motion to
reciprocating (back
and forth) motion.
• Cam shaft
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
Image Resources
Microsoft, Inc. (2008). Clip Art. Retrieved November 25, 2008, from
http://office.microsoft.com/en-us/clipart/default.aspx