Lecture - 6 (degrees of freedom (part - 2))

CALCULATIONS FOR ' F ' 

Let, 
'L' denotes number of links 
'J' denotes Number of binary joints 
'H' denotes Number of higher pairs 
'F' denotes Degrees of freedom
'N' denotes number of those motions which are not the part of mechanism


KUTZBACH Criteria to calculate 'F' is -
                       F = 3 (L-1) - 2J - H - N
The Kutzbach criterion is also called the mobility formula, because it computes the number of parameters that define the configuration of a linkage from the number of links and joints and the degree of freedom at each joint.
For example - 

  • In the mechanism shown below
 L = 4 ; J = 4 ; H = 0 ; N = 1
Therefore,   F = 3(L-1) - 2J - H - N 
                        = 3(4-1) - 2(4) - 0 - 1 = 0 ;     F = 0


Here sliding motion of link 3 is not the part of mechanism therefore N = 1


  • In the mechanism shown below
 L = 4 ; J = 3 ; H = 1 ; N = 1
Therefore,  F = 3(4-1) - 2(3) - 1 - 1 = 1 ;   F = 1

Here rotational motion of follower (link 3) is not the part of mechanism therefore N=1


  • In the mechanism shown below
 L=3 ; J=2 ; H=1 ; N=0
Therefore,  F = 3(3-1) -2(2) - 1 - 0 = 1 ;  F = 1

For more continue to lecture-7

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