Question

Abcd is a four link mechanism ,ad is fixed link . ab =30 ,bc=50,cd=60,ad=70.what is mechanism?

Answer 1

as the shortest link is fixed it's a double crank mechanism

Answer 2

Given,

ABCD is a 4 link mechanism,

AD: fixed,

AB = 30, BC = 50, CD = 60, AD = 70.

To find,

Type of mechanism.

Solution,

Here, it can be seen that link AD, which is the largest link (∵ AD = 70), is given to be fixed.

Now, AB = 30, which is the shortest link, will work as a crank, since it will be able to rotate completely and make full revolutions.

This can also be verified using Grashof's law, which states that, "for a four-bar linkage system, the sum of the shortest and longest link of a planar quadrilateral linkage is less than or equal to the sum of the remaining two links, then the shortest link can rotate fully with respect to a neighboring link".

That is,

(s + l) < (p + q),

where,

s = length of the shortest link,

l = length of the longest link

p and q = lengths of the remaining two links.

So, here,

(30 + 70) < (50 + 60)

100 < 110

So the condition is satisfied.

Hence,

AD is fixed, and,

AB is acting like a crank,

so, the link BC is a coupler, and,

CD will work as a rocker.

Thus, it will be a crank-rocker mechanism.

Therefore, the 4 link mechanism ABCD will be a crank-rocker mechanism.