A part of a machine or a member of a mechanism, connecting other parts or members and having a relative motion with one another.
- It can be a binary (2 joints), ternary (3 joints) or Quaternary (4 joints)
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 (combination of two links), is made fix the chain can be called as a mechanism.
- 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 number of links forming a mechanism is four, is a case of Simple Mechanism whereas a mechanism consisting more than four links is regarded as Compound mechanism.
- Four bar mechanism (4 links & 4 turning pairs), 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.
- Two links or elements when in contact have constrained motion (successfully or completely).
Types of Kinematic Pair
Based on 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.
- Spherical Pair- spherical shaped link turning inside a fixed link.
- Screw (Helical) – having turning as well as sliding motion. e.g., lead screw
Based on 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.