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Link  is a rigid body paired with other parts of a machine for thepurpose of transmittingforce or motion.

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Classifcation o links : Rigid link -> Which does not undergo any deformation while

transmitting motion.

Flexible link -> Which is deformed appreciably while transmittingmotion with out eecting the function.

Fluid link -> Tube or container capable of transmitting motion bypressure or compression.

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Types o constraints :  Completely constrained motion : If the constrained motion is obtained

by its own links.

 Successully partially! constrained : If the constrained motion is notcompletely constrained.

"ncomplete constrained : If the motion between the links takes place inmore than one direction.

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#inematic pair : A joint between two links that permits relativemotion. In this links are pairing elements.Classifcation o #inematic pair :

a! $ccording to nature o relati%emotion :• Sliding pair : Which permits relative sliding between its links.

•Turning pair : Which permits only turning motion between links.

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•Rolling pair : Two links are connected in such that one of the link rollsover the other.

•

 Scre& pair : The relative motion between the two links is thecombination of sliding and turning.

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rical pair : One of the link in the form of a sphere and it is rotated in a !ed li

b! $ccording to (ature o Contact :• Lo&er pair : Which permits surface contact between two links

while in motion and it is completely constrained. • )ig'er pair : Which permits only point or line contact betweentwo links while in motion and it is incompletely constrained.

"ear#.gif 

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$nlcam%.gif "ear#.gif 

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rding to (ature o *ec'anical arrangement o

• Closed pair : Which links of kinematic pair held together mechanically

so as to have a constrained motion.  Contact breaks only bydestruction o links!+

• ,pen pair : &lements of a pair that are not held together mechanically

are unclosed pairs.

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#inematic C'ain : It is an assembly of links in which the relativemotion between them e!ists and motion of each relative to the other isdenite.

' ( )p*%Where ' ( +o. of links,  p ( +o. of pairs

a! " L .p-/ condition is satised then the link is -ompletely -onstrainedand have specic relative motion.b! " L .p-0 condition is satised then the inematic chain is locked andaccept no relative motion.c! " L .p-1 condition is satised then the inematic chain is

incompletely constrained and relative motion between the links is notdenite.

Fig - a

Fig - b Fig - c

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tures : +o relative motion between the links or it is also called as 'ocked chai

2xamples : /ridges, roof truss, machine frame etc.,

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*$C)"(2 *2C)$("S*#. The arrangement of links withconstrained motion for doing useful

work.

#. The arrangement of links withone link !ed and the motion of

other links connected.

). It modies energy and doesuseful work.

). It modify and transmit motion.

0. A machine is a practicaldevelopment of any mechanism.

0. A mechanism is a working modelof any machine.

%. &!amples 1 $team engine,$haper, $crew jack etc.,

%. &!amples 1 Watch, Typewriter,$pring toys etc.,

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'ever*-rank mechanism 2 'ink 3a4 rotates and link 3c4 oscillates

ersions o a 3uadratic C'ain :

&!amples 1 4eam 2ngine 2 It is used to convert rotary motion to

reciprocating motion of the piston. 5$hown in g*)6

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basic78uickreturn.gif 

ithworth 9uick return mechanism:'ever crank mechanism 1

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0. ;ouble -rank mechanism 2 'ink 3b4 and 3d4 make completerevolutions.

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/+ 5att *ec'anism67ouble Le%er mec'anism

Watts7 linkage.gif    Watt<s7'inkage7=ear7$uspension.gif 

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ering gear mec'anism 67ouble Le%er mec'anism:

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I denotes Instantaneous centre.

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-rank and $lotted 'ever 9uick =eturn>echanism

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