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For example; In a slider crank mechanism the link 2 rotate relative to the link 1 and constitute a turning pair. Similarly, links 2,3 and 3,4 constitute turning pairs. Link 4 [slider] reciprocates relative to the link 1 and is a sliding pair.
Types of kinematic pairs
Kinematic pairs can be classified according to
For example- All pairs of slider crank mechanism, nut turning on a screw, shaft rotating in a bearing, universal joint etc.
b] Higher pair- when a pair has a point or line contact between the links, it is known as a higher pair. the contact surface of the two links are dissimilar.
For example- Ball and roller bearing, wheel rolling on a surface, cam and follower pair, tooth gear etc.
Kinematic pairs can be classified according to
- Nature of contact
- Nature of mechanical constraint
- Nature of relative motion
- Kinematic pairs according to nature of contact
For example- All pairs of slider crank mechanism, nut turning on a screw, shaft rotating in a bearing, universal joint etc.
b] Higher pair- when a pair has a point or line contact between the links, it is known as a higher pair. the contact surface of the two links are dissimilar.
For example- Ball and roller bearing, wheel rolling on a surface, cam and follower pair, tooth gear etc.
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Kinematic pair according to nature of mechanical constraint
a] Closed pair- When the elements of a pair held together mechanically, it is known as a closed pair. The two element are geometrically identical; one is solid and full, and the other is hollow or open. The latter not only envelops the former but also encloses it. The contact between the two can be broken only by destruction of at least one of the members.
all the lower pairs and some of the higher pairs are closed pairs. A cam and follower pair and a screw pair belong to the closed pair category.
b] Unclosed pair- When two links of a pair are in contact either due to force of gravity or some spring action, they constitute an unclosed pair. In this, the links are not held together mechanically, e.g., cam and follower pair.
Kinematic pair according to nature of relative motion-
a] Sliding pair- when the two elements of a pair are connected in such a way that, one can only slide relative to the other, the pair is known as a sliding pair.
For example- The piston and cylinder, cross head and guide of a reciprocating steam engine, ram and its guide in shaper, tail stock on the lathe bed etc. are the example of a sliding pair.
A little consideration will show that, a sliding pair has a completely constrained motion.
b] Turning pair- When two elements of a pair are connected in such a way that one can only turn or revolute about a fixed axis of another link, the pair is known as turning pair.
For example- A shaft with collars at both ends fitted into a circular hole, the crankshaft in a journal bearing in an engine, lathe spindle supported in headstock, cycle wheel turning over their axels etc. are the examples of turning pairs.
c] Rolling pair- When the two elements of a pair are connected in such a way that one rolls over another fixed link, the pair is known as rolling pair.
For example- Ball and roller bearings.
d] Screw pair- When the two elements of a pair are connected in such a way that one element can turn about the other by the screw threads, the pair is known as screw pair.
For example- The lead screw of a lathe with nut, and bolt with a nut are the examples of screw pair.
e] Spherical pair- When one link in the form of sphere turns inside a fixed link, is known as a spherical pair,
For example- The ball and socket joint is a spherical pair.
Kinematic pair according to nature of mechanical constraint
a] Closed pair- When the elements of a pair held together mechanically, it is known as a closed pair. The two element are geometrically identical; one is solid and full, and the other is hollow or open. The latter not only envelops the former but also encloses it. The contact between the two can be broken only by destruction of at least one of the members.
all the lower pairs and some of the higher pairs are closed pairs. A cam and follower pair and a screw pair belong to the closed pair category.
b] Unclosed pair- When two links of a pair are in contact either due to force of gravity or some spring action, they constitute an unclosed pair. In this, the links are not held together mechanically, e.g., cam and follower pair.
Kinematic pair according to nature of relative motion-
a] Sliding pair- when the two elements of a pair are connected in such a way that, one can only slide relative to the other, the pair is known as a sliding pair.
For example- The piston and cylinder, cross head and guide of a reciprocating steam engine, ram and its guide in shaper, tail stock on the lathe bed etc. are the example of a sliding pair.
A little consideration will show that, a sliding pair has a completely constrained motion.
b] Turning pair- When two elements of a pair are connected in such a way that one can only turn or revolute about a fixed axis of another link, the pair is known as turning pair.
For example- A shaft with collars at both ends fitted into a circular hole, the crankshaft in a journal bearing in an engine, lathe spindle supported in headstock, cycle wheel turning over their axels etc. are the examples of turning pairs.
c] Rolling pair- When the two elements of a pair are connected in such a way that one rolls over another fixed link, the pair is known as rolling pair.
For example- Ball and roller bearings.
d] Screw pair- When the two elements of a pair are connected in such a way that one element can turn about the other by the screw threads, the pair is known as screw pair.
For example- The lead screw of a lathe with nut, and bolt with a nut are the examples of screw pair.
e] Spherical pair- When one link in the form of sphere turns inside a fixed link, is known as a spherical pair,
For example- The ball and socket joint is a spherical pair.
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