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Types of Kinematic pairs
Entry posted by Tania Alam
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When two links (or elements) in a machine are in contact with each other, they form a pair. When the relative motion between these two links is completely or partially constrained, then the links are said to form a kinematic pair.
In simple words, a kinematic pair or simply a pair is a joint of two links having relative motion between them.
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Kinematic pairs can be classified on the basis of:
1) Nature of contact between the pairing elements
(a) Lower pair – surface or area contact between the members of the pair
There are 6 types of lower pairs
I. Revolute pair (R)
II. Prismatic pair (P)
III. Screw or helix pair (H)
IV. Cylindrical pair (C)
V. Spherical or globular pair (G)
VI. Planar pair or Ebony (E)
(b) Higher pair – point or line contact between the members of the pair
Examples of line contact –
I. Tooth gears
II. Ball and roller bearings
III. Wheel rolling on a surface
Examples of point contact –
I. Cam and follower pair
(c) Wrapping pair – similar to higher pair, but there are multiple point contacts, one body wraps over the other, comprises of belts, chains, etc.
Examples – A belt driven pulley
2) Nature of mechanical constraint
(a) Form or Self closed pair – the contact between the two bodies is maintained by geometric form
Examples – Screw pair (lower pair)
(b) Forced closed pair – the contact between the two bodies is maintained by application of external force
Examples – Ball and roller bearings
(c) Open pair – links are not help together mechanically, contact due to the force gravity or some spring action.
Examples – Cam and follower pair
3) Nature of relative motion of one link to the other in the pair
(a) Sliding pair – sliding motion
Examples – Rectangular rod in a rectangular hole in a prism
(b) Turning pair – turning or revolving motion
Examples – Circular shaft revolving inside a bearing
(c) Rolling pair – rolling motion
Examples – Ball and roller bearings
(d) Screw or Helical pair – both turning and sliding motion
Examples – Lead screw and nut of a lathe
(e) Spherical pair – one link is in the form of a sphere and can turn inside a fixed link
Examples – Ball and socket joint
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