Question

In a four-bar linkage, S denotes the shortest link length, L is the longest link length, P and Q are the lengths of other two links. At least one of the three moving links will rotate by 360^0 if

(a) S + L < P + Q

(b) S + L > P + Q

(c) S + P < L + Q

(d) S + P > L + Q

The question was posed to me in class test.

This intriguing question originated from Velocity of a point Link on a Link By Instanteneous Centre Method in portion Velocity in Mechanisms of Machine Kinematics

Answer 1

Correct choice is (a) S + L < P + Q

The explanation is: Here P,Q,R, & S are the lengths of the links.

According to Grashof’s law : “For a four bar mechanism, the sum of the shortest and longest link lengths should not be greater than the sum of remaining two link lengths, if there is to be continuous relative motion between the two links

S + L < P + Q.