## Kinematic Mechanism Definition

Contents

### What is Mechanism

It can be defined as when the assembly of different bodies is done in such a way that the motion of one causes constrained or predictable motion to other members.

In other words, when one of the links of a kinematic chain, a combination of kinematic pairs (a combination of two links), is made fix the chain can be called as a mechanism.

Read Also: Theory of Machine Objective Questions

• A mechanism may be used for transmitting the motion or for modifying the motion.
• A machine itself is a mechanism or a combination of mechanisms and a machine apart from imparting motion also transmits and modifies the available mechanical energy to some other desired work.
• A mechanism can be a Simple Mechanism or a Compound Mechanism.

• When the number of links forming a mechanism is four, it is a case of Simple Mechanism whereas a mechanism consisting of more than four links is regarded as a Compound mechanism.
• Four bar mechanism (4 links & 4 turning pairs), a slider-crank mechanism (4 links, 3 turning pairs and 1 sliding pair) and double slider crank mechanism (4 links, 2 turning & 2 sliding pairs) are the three types of simple mechanisms.

### Kinematic Pair

• Two links or elements when in contact have constrained motion (successfully or completely).

### Types of Kinematic Pair

#### Based on the Nature of Contact

• Lower Pair- having surface or area contact. e.g., shaft motion in bearings
• Higher Pair- point or line contact types. e.g., cam and follower pair

#### Based on Nature of Relative Motion

• Sliding Pair- relative motion is sliding.
• Turning Pair- having turning or revolving motion.
• Rolling Pair- having rolling motion relative to each other.
• Screw (Helical) – having turning as well as sliding motion. e.g., lead screw

#### Based on the type of closure or nature of Mechanical Constrain

• Closed/Self closed- elements held mechanically. e.g., all lower pairs are closed pair.
• Open/forced closed- links are made in contact by other means or some external forces like gravity, spring action. e.g., cam & follower.