mechanisms presentation 2012

8/2/2019 Mechanisms Presentation 2012

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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


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Have a think...
http://cooler-server/Central/Documents/Uni%20Teaching/2yr/Mechanisms%20and%20Structures/balancedBeam.swf


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Lever Mechanisms

Fulcrum

4 m 1 m

Effort

10N

LoadxN

Fulcrum

4 m1 m

Effort

10N

LoadyN


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Mechanical Advantage = Load

Effort

4 m 1 m

Effort10N

Load40N

Mechanical Advantage


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Velocity Ratio

4 m 1 m

Effort10N

Load40N

50mm200mm

Velocity Ratio =

Distance moved byEffort

Distance moved byLoad


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Efficiency

4 m 1 m

Effort10N

Load40N

50mm200mm

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 rotarymotion 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 ordecrease rotary velocity


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VelocityRatio Velocity Ratio =

Distance moved byEffort


Velocity Ratio =

Distance moved bythe driver pulley

Distance moved bythe 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 agrooved pulley and

round belt

Vee pulley and section through a vee pulley andbelt

Stepped cone pulleys provide a range of shaft speeds


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Flat belts

andpulleys

A section through a flatpulley and belt

Flat belt in use on athreshing machine

Jockey pulley in use


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Chains andsprockets

Bicycle

chain andsprockets

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

Thepulley is

a formof Class1 lever


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Movable single pulley


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Pulleys

Velocity Ratio =

Distance moved by

Effort


Velocity Ratio = the number of rope sections that support theload


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Two Pulley System

Velocity Ratio =

Distancemoved byEffort

Distancemoved by

Load

Velocity Ratio =

2x

x

Velocity Ratio = 2:1


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Four Pulley System

Velocity Ratio =

Distancemoved byEffort

Distancemoved by

Load

Velocity Ratio =

4x

x

Velocity Ratio = 4:1


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Cams


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Cams


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Uses

Pear shaped cams are used in valvecontrol mechanisms


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Cams usedin a four

cylinderengine

http://www.youtube.com/watch?v=OXd1PlGur8M&feature=related
http://www.youtube.com/watch?v=OXd1PlGur8M&feature=relatedhttp://www.youtube.com/watch?v=OXd1PlGur8M&feature=relatedhttp://www.youtube.com/watch?v=OXd1PlGur8M&feature=relatedhttp://www.youtube.com/watch?v=OXd1PlGur8M&feature=relatedhttp://www.youtube.com/watch?v=OXd1PlGur8M&feature=relatedhttp://www.youtube.com/watch?v=OXd1PlGur8M&feature=relatedhttp://www.youtube.com/watch?v=OXd1PlGur8M&feature=relatedhttp://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 incontact with the cam


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Cam Profiles


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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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ThrustBearings


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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 onlyused to transmit

motion.

They are also usedto transmit force.


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Gears

Mechanical Advantage =

Number of teeth on thedriven gear

Number of teeth on thedriver gear

Velocity Ratio = Gear Ratio =Number of teeth on the

driven gear

Number of teeth on thedriver gear


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Gears


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Gears

Gear Ratio =Product of teeth on the driven gears

Product 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
http://www.youtube.com/watch?v=9NoQm0wnK_c&feature=relatedhttp://www.youtube.com/watch?v=9NoQm0wnK_c&feature=relatedhttp://www.youtube.com/watch?v=9NoQm0wnK_c&feature=relatedhttp://www.youtube.com/watch?v=9NoQm0wnK_c&feature=relatedhttp://www.youtube.com/watch?v=K4JhruinbWc&NR=1http://www.youtube.com/watch?v=K4JhruinbWc&NR=1http://www.youtube.com/watch?v=K4JhruinbWc&NR=1http://www.youtube.com/watch?v=K4JhruinbWc&NR=1http://www.youtube.com/watch?v=K4JhruinbWc&NR=1http://www.youtube.com/watch?v=K4JhruinbWc&NR=1http://www.youtube.com/watch?v=9NoQm0wnK_c&feature=relatedhttp://www.youtube.com/watch?v=9NoQm0wnK_c&feature=relatedhttp://www.youtube.com/watch?v=9NoQm0wnK_c&feature=relatedhttp://www.youtube.com/watch?v=9NoQm0wnK_c&feature=related


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Basic Gear

Geometry

http://www.sdp-

si.com/D190/PDF/D190T25.PDF


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The inclined plane

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
http://lectureonline.cl.msu.edu/~mmp/applist/si/plane.htmhttp://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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Newtons Laws

First Law

A body continues in its state of rest or uniform

motion in a straight line unless compelled bysome external forces to change that state.

(sometimes know as the law of inertia)


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Newtons Laws

Second Law

Rate of change of momentum is proportional

to the applied force and takes place in thedirection in which the force acts.

(Continued force means continuedacceleration)


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Newtons Laws

Third Law

To every action there is an equal and

opposite reaction