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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 Movements
Rotary
Linear
Reciprocating
Oscillating
RotaryROW - ter - ree
http://farm3.static.flickr.com/2728/4342863982_b8752b4313.jpg
Engine Crank Shaft
Crank shaft rotates (rotary movement).
Rotary Movement
Reciprocating Movement
Cams
Rotary Optical Illusion
Just look at the crosshairs (the +) in the center of the image for a few seconds and then start blinking your eyes.
You will notice the inner spiral is moving in clockwise direction while the outer spiral is moving in opposite direction.
Universal Joint
It is…
…a joint or connector in a rigid rod that allows the rod to 'bend' in any direction
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
• Tire swing
Tire Swing
Socket Wrench Universal Joint
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.
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
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