What is Kinematic Pair?
In classical mechanics, a kinematic pair is a connection between two physical entities that impose constraints on their relative movement (kinematics). Let’s understand systematically kinematic pairs and their detailed classification.
“A kinematic pair is a connection between two adjacent links that permits a definite relative motion between them.”
Classification of Kinematic Pairs
Kinematic pairs can be classified on the premise of their nature of the contact, constraints, and the nature of relative motion between the elements in contact. Here is the complete classification of kinematic pairs with the appropriate examples.
Types of Kinematic Pair
On the basis of the nature of relative motion
Piston and cylinder
Ball and roller bearings
Crank and connecting rod
Cap and bottle
Circular bar in a circular hole
On the basis of the nature of contact
Piston and cylinder
Cam and follower
Belt and pulley
On the basis of the nature of mechanical constraints
Ball and socket joint
Cam and follower
On the Basis of the Nature of Relative Motion
In this scenario, our main focus will be the type of relative motion taking place between the elements while classifying kinematic pairs based on the nature of relative motion. There are six types of kinematic pairs on the premise of the nature of relative motion as follows-
Sliding Pair: This consists of two components connected in such a way that one is constrained to have a sliding motion relative to another component, Then the pair is known as sliding pair.
Example: Rectangular bar in a rectangular hole, Square bar in a square hole, Piston and cylinder of an IC engine, and Tail- Stock and lathe bed, etc.
Rolling Pair: This consists of two elements connected in such a way that one is constrained to roll in another element which is fixed, Then the pair is known as the rolling pair.
Example: Ball and roller bearings, Wheel rolling on a flat surface and marble rolling on a flat surface, etc.
Turning Pair: This consists of two components connected in such a way that one is constrained to turn or revolve about a fixed axis of another element, Then the pair is known as the turning pair.
Example: Shaft with a collar at both ends revolving in a circular hole, The crankshaft of an IC engine turning in a bearing, Cycle wheels revolving about their axles, etc.
Screw Pair: This consists of two elements connected in such a way that one component turns about the other component through threads. In this scenario, The motion is a combination of turning and sliding.
Example: The lead screw of a lathe and nut, Nut and bolt combination, and Screw with nut of screw jack.
Spherical Pair: Spherical Pair consists of two elements joined in such a way that one element in the form of a sphere turns about the other fixed element.
Example: Ball and socket joint, Pen stand and Minor attachment of vehicles, etc.
Cylindrical Pair: A pair in which one link has independent revolute and sliding motion relative to the other is themed as a cylindrical pair.
Example: Circular bar in a circular hole and motion of door latch etc.
On the Basis of the Nature of Contact
In this scenario, our main focus will be the type of contact taking place between the elements. Whether it is point contact or line contact while classifying kinematic pairs based on the nature of the contact. There are three types of kinematic pairs on the premise of nature of contact as follows-
Lower Pair: When the two elements are having surface contact with each other. At the time, when relative motion takes place and the surface of one element slides over the surface of another element, the pair is termed a lower pair.
Example: Nut turning in a screw, Shaft rotating in a bearing, Universal joint, and all pairs of slider-crank mechanisms.
Higher Pair: When the two elements of a pair are having line contact or point contact with each other. At the time, when relative motion takes place and the motion between the two elements is partly turning, sliding then the pair is known as the higher pair.
Example: Toothed gearing, Belt and rope drives, Ball and roller bearings, cam and follower, etc.
Wrapping Pair: A pair in which one body completely wraps over the other body is termed a wrapping pair.
Example: Rope and pulley, Belt and pulley and chain and sprocket, etc.
On the Basis of the Nature of Mechanical Constraints
In this scenario, our main focus will be the nature of mechanical constraints, whether it is because of geometry itself or due to an external means (e.g. gravity, spring) while classifying kinematic pairs based on the nature of mechanical constraints. There are two types of kinematic pairs on the premise of the nature of mechanical constraints as follows-
Closed Pair: A pair in which elements of pairs are held together mechanically, due to their geometry, is termed a closed pair. “All lower pairs are closed pairs”
Example: Screw and nut, ball and socket joint, carriage and guideways, etc.
Open Pair: A pair in which elements of pairs are not held mechanically, but due to the consequence of an externally applied force.
Example: Cam and follower mechanism, door closing mechanism, automotive clutch operating mechanism, etc.
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