Kinematic Pair: Lower Pair and Higher Pair

On the basis of nature of contact between mating elements kinematic pairs are classified in two groups
  • Lower Pair
  • Higher Pair

kinematic pair

1. Lower Pair

If there is area/surface contact between mating elements the pair is known as lower pair.

The elements has sliding motion mutually in a lower pair because of surface contact. Basic kinematic pair like prismatic pair, revolute pair, screw pair, are some examples of lower pair. 

Note: lower pair permits sliding motion between elements

Lower pairs are further classified in two groups (on the basis of Degree of Freedom - DOF 

Degree of Freedom(DOF)=1
  • Prismatic pair or Sliding pair (P)
  • Revolute pair (R)
  • Screw Pair or Helix pair (H)
Degree of Freedom(DOF)>1
  • Cylindrical pair (C)
  • Spherical Pair or Globular pair (G)
  • Planar pair or Ebony (E)

2. Higher Pair

If there is point or line contact between mating elements the pair is known as higher pair. Example: Cam & follower, Gear & Pinion

Special case of higher Pair: Wrapping pair is formed whenever there is a flexible link involved. one link is wrapped over another link. Example: Belt & Pulley, chain and sprocket mechanism

Note: Rolling with slipping motion is permitted by higher pair.

In Belt and Pulley Mechanism at each point of entry and exit there will be one higher pair.

>> According to Hartenberg the pair which can be inverted are lower pairs, whereas the inversion of higher pair is not possible.