Q. The link lengths of a planar four bar mechanism are AB = 100 mm, BC = 25 mm, CD = 75 mm and DA = 90 mm. For achieving the full rotation of both the input (crank) as well as the output (follower) links, the link that needs to be fixed is
Ans: BC
Sol:
S = 25 mm, L = 100 mm, P = 75 mm and Q = 90mm.
∵ L + S = 100 + 25 = 125 mm, and P + Q = 75 + 90 = 165
∴ L + S < P + Q, Grashof’s criterion satisfies..
∴ For Double-Crank Mechanism, fixed link is the shortest link i.e. link BC.
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