Transcript Lever and Linkage Systems - apolloteched / FrontPage

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Lever and Linkage Systems
Methods of Power Transmission
The 3 Classes of Levers
• Each class has the fulcrum, effort and
load arranged in a different way.
• The three classes are:
Class 1 Lever
• Fulcrum between the load and the effort
Class 2 Lever
• Load between the fulcrum and the effort
Class 3 Lever
• Effort is between load and fulcrum
ROCKER ARM
• Has an input and output
arm which rock around
a fulcrum point
• Acts as a link which
transmit force or motion
between moving parts
• Operate usually as a
first class lever
• Change linear input
motion to an opposed
linear motion
BELL CRANK
• A bent first class lever
that pivots at the bent
point or elbow
• Used to change the
direction of force or
motion 90 degrees or
less
• Used to convert rotary
motion to straight line or
reciprocating motion
BELL CRANK
• Reciprocating motion
Top
– pin A moves slider to
right
– pin B moves bell
crank which moves
slider to left
Bottom
– pins move crank;
spring returns to start
position
DOUBLE BELL CRANK
• PUSH, PULL TYPE
PUSH
– requires stiff
connecting rods
PULL
– can use flexible
wires,cables, ropes
DIFFERENTIAL LINKAGE
• Used to combine several
motion inputs into a
resulting output
• Three pivot points, none
of which are fixed but are
free to float within limits
• Any pivot can function as
an input
• A motion control
mechanism rather than a
means of transmitting
force or power
FOUR-BAR LINKAGES
(Whatever the motion, each point on a moving link
must move in the same PLANE, and all the links
must be parallel)
Types of four-bar linkages:
•PARALLEL LINKAGE
•SCISSOR LINKAGE
FOUR-BAR LINKAGES
• To make a four-bar
linkage a usable device,
one of the four links, or
one of the pivots, must be
fixed
• Depending on the fixed
pivot or link different
motion outputs will occur
FOUR-BAR LINKAGES
• Fixed link
– links pivoting from
the ends of the fixed
link are either input
links or input and
output links
– the moving link
opposite the fixed
link is the connecting
link
FOUR-BAR LINKAGES
• FIXED PIVOT
– the point opposite
the the fixed point is
normally the output
point
– the remaining two
pivot points are
usually the input
points
PARALLEL LINKAGE
• To provide parallel
motion of a line or a
surface as the linkage
moves about two
controlled pivot points
• The arms remain
parallel through the
operation of the
connecting link
Eg: man lift, robot gripper
SCISSOR LINKAGE
• To change the direction
of a linear motion input
to a linear motion output
that is perpendicular to
the input
• Large motion output
(distance advantage)
with a small motion
input
• Especially true of a
series of connecting
linkages
• One fixed pivot point
SCISSOR LINKAGE
• Two pair of links of
different length
– Less force at input
pivot point - close to
pivot point
– output is identical
SCISSOR LINKAGE
• Two pair of links of
different length
– More force at input
pivot point - farther
from pivot point
– output is identical
WATT STRAIGHT LINE
MOTION
• Does not form a
parallelogram but
consists of two equal
length pivoting links and
a connecting link
• Produces a straight line
motion in the
connecting link
TOGGLE LINKAGE
•Latching
•Non-latching
TOGGLE LINKAGE
• LATCHING
– capable of snap
action from one state
to an alternate state
– arm length may be
different
– may have a toggle
stop to produce
latched condition
TOGGLE LINKAGE
• NON-LATCHING
– operated so that the
two toggle arms never
quite straighten
– may have a toggle
stop to produce
latched condition
e.g.
rock crushers
hay balers