Mobility / Grashof's Condition and Barker's Classification
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Mobility of Mechanism
Degrees of freedom for planar linkages joined with common joints can be calculated through Gruebler’s equation.
Gruebler’s equation is given by the formula:
M = 3(L-1) - 2J1 - J2
where:
- M is degree of freedom or Mobility
- L is number of links
- J1 is number of full joints
- J2 is number of half joints
Grashof Condition
Grashof’s Law states that for a four-bar linkage system, if the sum of length of shortest and longest of a planar quadrilateral linkage is less than or equal to the sum of the remaining two links , then the shortest link can rotate freely with respect to neighbouring link.
Let denote the smallest link of four bar linkage with S and the longest link by L and the other two links by P and Q.
The necessary condition to satisfy Grashof’s Law is :
S + L ≤ P + Q
Barker's Classification
