Question

The minimum number of links in a single degree-of-freedom planar mechanism with both higher and lower kinematic pairs is

(a) 2

(b) 3

(c) 4

(d) 5

The question was asked in an online quiz.

This interesting question is from Velocity of a point Link on a Link By Instanteneous Centre Method in division Velocity in Mechanisms of Machine Kinematics

Answer 1

Correct choice is (c) 4

Explanation: From the Kutzbach criterion the degree of freedom,

n = 3(l − 1) − 2j − h

For single degree of Freedom (n = 1),

1 = 3(l − 1) − 2j − h

3l − 2j − 4 − h = 0                   …(i)

The simplest possible mechanisms of single degree of freedom is four-bar mechanism. For this mechanism j = 4, h = 0

From equation (i), we have

3l − 2 x 4 − 4 − 0 = 0

or, l = 4.