# PLANER MECHANISM

A link is defined as a single part which can be a resistant body or a combination of resistant bodies having inflexible connections and having a relative motion with respect to other parts of the machine. A link is also known as kinematic link or element. Links should not be confused with the parts of the mechanism. Different parts of the mechanism can be considered as single link if there is no relative motion between them.

Example: The frame of any machine is considered as single link as there is no relative motion between the various parts of the frame. As shown in slider crank mechanism shown below, the frame is considered as one link (link 1) as there is no relative motion in frame itself. The crank here is link 2 & connecting rod is again single link (link 3). The slider or piston is link 4 as there is no relative motion it. In this way, many complex mechanisms can be describe by simple configuration diagram by considering the definition of a link.

 Slider crank mechanism

Links can be classified into Binary, Ternary, and Quaternary etc. depending upon its ends on which revolute or turning pairs can be placed.

The links can also be classified into Rigid, Flexible, Fluid according to its nature such as

Rigid link is the link which do not deform while transmitting the motion

Flexible link is the link which deform while transmitting the motion but does not affect its function of transmitting motion such as belts, chains etc.

Fluid link is the link which uses the fluid pressure to transmit the motion such as hydraulics jack, brakes and lifts.

## RIGID BODY

A rigid body is a body in which the distance between the two points on the body remains constant or it does not deform under the action of applied force. In actual practice no body is perfectly rigid but we assume it to be rigid to simplify our analysis.

## RESISITANT BODY

A Resistant body is a body which is not a rigid body but acts like a rigid body whiles its functioning in the machine. In actual practice, no body is the rigid body as there is always some kind of deformation while transmitting motion or force. So, the body should be resistant one to transmit motion or force.

Examples: The cycle chain is the resistant body as it acts like rigid body while transmitting motion to the rear wheel of the cycle, Belt in belt and pulley arrangement.