[ppt]lever and linkage systems - apolloteched /...
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Forging new generations of engineers
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
• Reciprocating motionTop
– 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
BELL CRANK
DOUBLE BELL CRANK
• PUSH, PULL TYPEPUSH
– 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
Types of four-bar linkages:•PARALLEL LINKAGE•SCISSOR LINKAGE
(Whatever the motion, each point on a moving link must move in the same PLANE, and all the links must be parallel)
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 crushershay balers