Understanding Kinematic Pairs: Cam and Follower

In the study of mechanisms, connections between two links are called kinematic pairs. These pairs allow relative motion between the links. Kinematic pairs are classified based on the nature of contact between the two elements forming the pair.

Types of Kinematic Pairs Based on Contact

There are two main types of kinematic pairs based on how the two surfaces are in contact:

• Lower Pair: A lower pair is formed when the two elements have surface contact with each other. The contact is over an area. Examples include a sliding pair (like a piston in a cylinder), a turning pair (like a shaft in a bearing), a screw pair, and a spherical pair (like a ball and socket joint).
• Higher Pair: A higher pair is formed when the two elements have line or point contact with each other. The contact is not over an area, but theoretically along a line or at a point. When there is motion, the point or line of contact changes continuously.

Classifying the Cam and Follower

Let's consider the cam and follower mechanism. A cam is a rotating or oscillating element that imparts a desired motion to a follower, which is another element that moves in contact with the cam.

The contact between the surface of the cam and the surface of the follower is typically point contact (for a flat-faced or knife-edge follower) or line contact (for a roller follower) at any given instant. As the cam rotates, this point or line of contact shifts along the surfaces of both the cam and the follower.

Since the contact between the cam and the follower is theoretically a point or a line at any instant, it fits the definition of a higher pair.

Conclusion

Based on the analysis of the contact type between the cam and its follower, the combination belongs to the category of a higher pair. The contact is not a surface contact over an area but rather a point or line contact that changes during motion.