Machine Dynamics, Solved Problems, Linkages, Mobility of a mechanism, Problem 5

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Published on January 15, 2022 3:56:59 PM ● Video Link: https://www.youtube.com/watch?v=zi261-0O7Aw

Duration: 1:53

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#Theory_of_Machines #Mechanical_Engineering #Kinematics

This video is part of a series of videos presenting solutions of problems related to the machine dynamics topic.

In this video, we will calculate mobility of a double-cam mechanism.


In this problem we are asked to determine the mobility of the mechanism shown here.



First, we need to determine, L, the number of links or the number of mechanical parts, in the mechanism,

Second, we need to determine, j 1, the number of lower pairs, or the number of joints allowing each, one degree of freedom,

Third, we need to determine, j 2, the number of higher pairs, or the number of joints allowing each, two degrees of freedom,

Finally, we will calculate mobility M, as 3 times L minus 1, minus 2 j 1, minus j 2.


This mechanism is built from,

The ground

Three bars,

And, two cams.

Thus, L is equal to 6


The cams are connected to the ground using two rotating kinematic pairs, or two pin joints.

Also bar 4 is connected to bar 2 and 3 using two other pin joints.

The bars 2 and 3, the cam followers, are connected to the ground using two translating or prismatic kinematic pairs.

In all 4 pin joints and 2 prismatic joints are used.

Thus, j 1 is equal to 6.

We have two cam connections, between each cam and its follower.
These two cam kinematic pairs are considered as higher pairs.

Hence, j 2 is equal to 2.


Substituting the value of L, j 1 and j 2 in the equation of mobility gives M is equal to 1