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![Page 1: Mechanisms](https://reader038.fdocuments.net/reader038/viewer/2022110402/56812a44550346895d8d73e8/html5/thumbnails/1.jpg)
Mechanisms
Dean Hackett March 2012
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Types of motion
• Linear
• Rotary
• Reciprocating
• Oscillating
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Simple (Basic) Machines
• Two ‘families’– Inclined plane– lever
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Simple Machines
• Inclined plane
• Wedge
• Screw
• Lever
• Wheel and axle
• Pulley
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Work = Force x distance
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Classes of Lever
• Class 1
• Class 2
• Class 3
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Types of Linkage
• Parallel
• Reverse motion
• Bell crank
• Treadle
• Crank slider
bellCrank.swf
CrankSlider.swf
parallelLinkage.swf
reverseLinkage.swf
treadle.swf
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Have a think...
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Lever Mechanisms
Fulcrum
4 m 1 m
Effort 10N
Load xN
Fulcrum
4 m1 m
Effort 10N
Load yN
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Mechanical Advantage = Load
Effort
4 m 1 m
Effort 10N
Load 40N
Mechanical Advantage
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Velocity Ratio
4 m 1 m
Effort 10N
Load 40N
50mm
200mm
Velocity Ratio =
Distance moved by Effort
Distance moved by Load
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Efficiency
4 m 1 m
Effort 10N
Load 40N
50mm
200mm
Efficiency = M.A.
V.R.x
100%
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Lever Mechanism
What load can this person lift?
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Rotary Motion
A Pulley Mechanism uses rotary motion to transmit rotary motion between two parallel shafts.
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Discuss...
• How do you attach a pulley to a shaft?
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Mechanisms using Rotary Motion
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Pulley mechanisms can be used to increase or decrease rotary velocity
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Velocity Ratio Velocity Ratio =
Distance moved by Effort
Distance moved by Load
Velocity Ratio =
Distance moved by the driver pulley
Distance moved by the driven pulley
Velocity Ratio = Diameter of Driven Pulley
Diameter of Driver Pulley
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Velocity RatioPulley Shaft Rotary Velocities can be calculated using the
following formula
rotary velocity of driven pulley x diameter of driven pulley =
rotary velocity of driver pulley x diameter of driver pulley
rotary velocity of driven = diameter of driver pulley
diameter of driven pulley
rotary velocity of driver x
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What is the rotary velocity of the driven pulley shaft?
rotary velocity of driven = diameter of driver pulley
diameter of driven pulley
= 30
90
revs/min
= 150 revs/min
rotary velocity of driver x
450 x
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Pulleys and Belts
A section through a grooved pulley and
round belt
Vee pulley and section through a vee pulley and belt
Stepped cone pulleys provide a range of shaft speeds
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Flat belts and
pulleys
A section through a flat pulley and belt
Flat belt in use on a threshing
machine
Jockey pulley in use
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Chains and sprockets
Bicycle chain and sprockets
Graphical symbols
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Velocity Ratio = number of teeth on the driven
sprocket number of teeth on the driver sprocket
= 12
36
= 1 : 3
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Example
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Pulleys and Lifting Devices
The pulley
is a form of Class 1 lever
11pulley.swf
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Movable single pulley
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Pulleys
Velocity Ratio =
Distance moved by Effort
Distance moved by Load
Velocity Ratio = the number of rope sections that support the load
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Two Pulley System
Velocity Ratio
=
Distance moved by
Effort
Distance moved by
Load
Velocity Ratio
=
2x
x
Velocity Ratio = 2:1
21pulley.swf
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Four Pulley System
Velocity Ratio
=
Distance moved by
Effort
Distance moved by
Load
Velocity Ratio
=
4x
x
Velocity Ratio = 4:1
41pulley.swf
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Cams
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Cams
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Uses
Pear shaped cams are used in valve control mechanisms
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Cams used in a four cylinder engine
http://www.youtube.com/watch?v=OXd1PlGur8M&feature=related
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Cam motions
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Types of cam follower
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Types of cam follower
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Springs are used to keep the follower in contact with the cam
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Cam Profiles camSystems.swf
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Displacement graph for a pear shaped cam
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Displacement Graphs
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Bearings
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Thrust Bearings
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Bearings
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Bearings
• Bronze
• Nylon
• PTFE
• Air
• White metal
• Cast Iron
• Sintered
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Gears
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Gears
Gears are not only used to transmit motion.
They are also used to transmit force.
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Gears
Mechanical Advantage =
Number of teeth on the driven gear
Number of teeth on the driver gear
Velocity Ratio = Gear Ratio =
Number of teeth on the driven gear
Number of teeth on the driver gear
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Gears
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Gears
Gear Ratio =Product of teeth on the driven gearsProduct of teeth on the driver gears
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Gears
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Gears
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Gears
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Gears
http://www.youtube.com/watch?v=9NoQm0wnK_c&feature=related
http://www.youtube.com/watch?v=K4JhruinbWc&NR=1
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Basic Gear Geometry
http://www.sdp-si.com/D190/PDF/D190T25.PDF
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The inclined plane
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The inclined plane
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The inclined plane
Effort required to pull trolley up slope
F = effort E
F = 1000 x sin
F = 1000 x 0.01
F = 10N
E = 10N
sin = 1/100 = 0.01
M.A. = 1000/10
= 100
Follow link to see effects of steeper incline:http://lectureonline.cl.msu.edu/~mmp/applist/si/plane.htm
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The screw thread
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Screw thread terms
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Screw thread forms
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Screw thread forms
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Screw thread forms
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B.S. PD7308
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Newton’s Laws
• First Law– A body continues in its state of rest or uniform
motion in a straight line unless compelled by some external forces to change that state.
(sometimes know as the law of inertia)
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Newton’s Laws
• Second Law– Rate of change of momentum is proportional
to the applied force and takes place in the direction in which the force acts.
(Continued force means continued acceleration)
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Newton’s Laws
• Third Law– To every action there is an equal and
opposite reaction