Question

A four - bar mechanism is made up of links of length 100, 200, 300 and 350 mm. If the 350 mm link is fixed, the number of links that can rotate fully is __________.

Answer 1

Concept:

According to Grashof’s Law:

(1) S + L ≤ P + Q (Class I mechanism)

There will be at least one complete revolution between the two links.

• If the shortest link is fixed: Double Crank Mechanism
• If any of the adjacent links of the shortest link if fixed: Crank rocker mechanism
• If the link opposite to shortest link is fixed: Double Rocker Mechanism

(2) S + L > P + Q (Class II mechanism)

• Only double rocker mechanism is possible

Calculation:

S = 100 mm, L = 350 mm, P = 200 mm, Q = 300 mm

100 + 350 < 200 + 300

S + L ≤ P + Q ⇒ Class I mechanism ⇒ There will be at least one complete revolution between the two links

Here the longest link is fixed which is adjacent to the shortest link so it will results into a crank-rocker chain. So number of links that can rotate fully is 1.