20 May 2017

Types of kinematic pairs

Types of kinematic pair :

Kinematic pair can be classified according to :
  • The nature of the contact.
  • The nature of mechanical constraint.
  • The nature of relative motion.
Kinematics pairs according to nature of contact :

Lower pair: A pair of links having surface area contact between the member is known as a lower pair.
In the lower pair, the contact surfaces of the two links are similar.

For example : 
  • Nut turning on a screw shaft.
  • Shaft rotating in a bearing.
  • All pairs of slider-crank mechanism.
  • Universal joint.
Higher pair: A pair has a point or line contact between the links is known as a higher pair.
In the higher pair, the contact surfaces of the two links are dissimilar.

For example : 
  • Rotating on a surface 
  • Cam and follower pair 
  • Tooth gear 
  • Ball-bearing  
  • Roller bearings 
Kinematic pairs according to the nature of mechanical constraint :

Closed pair: When the elements of a pair are held together mechanically it is known as a closed pair.
The two elements are geometrically identical one is solid and full and other is hollow or open. The letter not only envelops the former but also and closed it. 
All the lower pairs and some of the higher pairs are closed pair.
A screw pair belong to the closed pair category also. 
Closed pair

Unclosed pair: When two links of a pair are in contact but due to some spring action or force of gravity, they constitute an unclosed pair.
In this, the links are not held together mechanically. 

Unclosed pair

Kinematics pair according to nature of relative motion :

Sliding pair: If two links have a sliding motion related to each other, they form the sliding pair. 

For example - A rectangular rod in a rectangular hole in a prism

Sliding pair

Turning pair: When one link has a turning on revolving motion relative to others, they constituted a turning pair.
They also called revolving pair.

For example - In a slider-crank mechanism all pairs except the slider and guide pair are turning pair.
A circular shaft revolving inside a bearing.

Turning pair

Rolling pair: When the link of a pair has a rolling motion relative to each other, they form a rolling pair.

For example - Rolling wheel on a flat surface
Ball and roller bearing in a ball bearing 
The ball and shaft constitutive and rolling pair where is the ball and the bearing is a second rolling pair.

Rolling pair

Screw pair : If two mating links have a turning as well as sliding motion between them, they form of screw pair. This can be achieved by cutting matching threads on the two links.

For example - The lead screw and the nut of a late is a screw pair.

Screw pair

Spherical pair : When one link in the form of sphere turn inside a fixed link, it is a spherical pair.

For example - The ball and socket joint

Spherical pair