Mechanisms and their classification

Classification & Basis:

In the previous two posts the definitions of mechanisms and the types of motion related to the mechanisms were outlined. It is necessary for us to classify based upon the functions i.e. the use of mechanism to convert the following:

1. Continuous rotation into continuous rotation e.g. pulleys 
2. Continuous rotation into reciprocating motion or the reverse e.g. a crank
3. Any combination of reciprocation or oscillation into reciprocation or oscillation

You can achieve infinite types of motions by making use of the above mentioned basic motion and combination of several mechanisms is known as compound mechanism. We will examine some of the linkages and mechanisms in the foregoing text.

The simplest complete kinematic chain consists of 4 links as per the diagram. 

Names of some of the most commonly used linkages or mechanisms are cranks for a link which rotated, rocker for the links that oscillate and coupler for the link which connects which connects a crank to a rocker

 Four Bar Linkage:

As per the diagram the four-bar Linkage consists of 4 linkages in which Link No. 1 will be the fixed link the No. 2 will be the Driver and the No. 3 the connecting link and No. 4 will be the follower.









2. Slider Crank Mechanism: 

 When we make an arrangement as shown in the Sketch, alongside, where there are 4 linkages namely 1, 2 ,3 & 4 the link 2 rotates, since one end of 3 is attached to it by a pin at b, it moves with link 2, thereby dragging the link 4 back in half its rotation and pushes it forward in its the second half of the rotation.