Mechanisms unit 6
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Transcript of Mechanisms unit 6
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They have many different uses:
Raising or lowering a water bucket.
Telling the time by moving its cogwheels or gears.
Moving people from one place to another.
Entertaining children in a park by swinging.
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All of them are made of mechanisms
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Mechanisms are devices that transmit and/or
convert forces and motions from an input
element to an output element.
The aim of a mechanism is to make the tasks
easier with less effort and more comfort.
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Input motion
Input force
Mechanism Output motion
Output force
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Classification of mechanisms
To transmit motion
Linear Rotary
To transform motion
From rotary to linear
From rotary to reciprocating
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Linear
Lever
Pulley
Rotary
Friction drives or wheels
Pulleys with belts
Gear mechanisms
Gear mechanisms with chain
Worm gear
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A lever is the simplest kind of mechanism. Common
examples of each type are the crowbar, the
wheelbarrow and the pair of tweezers.
Parts: The load is the object you are trying to move.
The effort is the force applied to move the load.
The fulcrum (or pivot) is the point where the load is pivoted.
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M.A. = Effort
Load
Load
Effort
Fulcrum
d1
d2
Law of the lever
L·d1 = E·d2
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The longer the distance is, the less effort you have to do1
Balanced lever
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1st class
M.A.?
2nd class
M.A.
3rd class
All levers are one of three types, usually called
classes. The class of a lever depends on the
relative position of the load, effort and fulcrum T
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http://www.youtube.com/watch?v=Us2KfO_yrPA
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It is a wheel that turns when a rope, belt or chain passes through a channel.
It rotates around an axle that is fixed
when you apply a force (F) to move up a load (R).
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Fixed pulley
E=R
No mechanical advantage
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Moveable pulley
E=R/2
Mechanical advantage=2
The force you apply is multiplied
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Compound pulleys
Mechanical advantage=R/F
The force you apply is multiplied
4:1
6:1
It is a set of fixed and
movable pulleys.
The more movable
pulleys, you have the
less effort you have to
apply
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https://www.youtube.com/watch?v=9T7tGosXM58&feature=related
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This mechanism is made up (consists) of at least
two wheels or pulleys in contact.T
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Driver wheel
Driven wheel
Shaft
•If the number of wheels is odd, the drivenwheel rotates in the same direction than thedriver wheel.•If the number of wheels is even, the drivenwheel rotates in the opposite direction thanthe driver wheel.
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A pulley system is made up of two pulley wheels each
on a shaft, connected by a belt. This transmits rotary
motion and force from the driver pulley to the driven
pulley.
driven pulley rotates in the same direction driven pulley rotates in the opposite direction
BeltAndPulley
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Gears are wheels with teeth. Gears consist of
toothed wheels fixed to shafts. The teeth
interlock with each other, and as the first shaft
(the driver shaft) rotates, the motion is
transmitted to the second or driven shaft so they
are used to transmit movement between two
shafts.
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A number of gears connected together are called a
gear system or gear train
They can also be moved with a chain. It´s also
called sprocket.
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It’s a mechanism made up
(composed) of a gear and a worm
(threaded shaft). It’s a method of
making large speed reductions.
Each time the shaft spins one
revolution, the gear turns forward
by only one tooth.
The worm can drive the worm gear
round, but the worm gear cannot
drive the worm, so it’s used as a
breaking system. Worm gear, worm
gear (video)
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The quotient of the speed/velocity is called the gear ratio.
The gear ratio also determines the amount of turning force or torque transmitted.
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Rotary into Linear
Rack and Pinion
Nut and bolt
Winch with a crank handle
Rotary into Reciprocating
Cam
Crank link slider
Crankshaft
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The pinion is a round gear and the rack is a flat
bar with teeth.
It is a reversible mechanism.
Rack and pinion
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It’s a reversible mechanism
you can spin both, the nut
or the bolt.
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The longer the crank handle is, the less force you
need to move the load.
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The cam is a flat piece of metal that has a
specific shape that pushes the follower.
Different types of cams
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It’s made up of a circularcrank, a link (connectingrod) and a slider.
It is a reversible mechanism.
Crank link slide
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The crankshaft is the red part of the figure.
It is a reversible mechanism.
Crankshaft video
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