2015 WINTER

Applications:

An Oldham's coupling is used for connecting two parallel shafts whose axes are at a small distance apart.

Used to transmit motion and power.

Types of Constrained Motions :

Following are the three types of constrained motions:

In an epicyclic gear train, the axes of the shafts, over which the gears are mounted, may move relative to a fixed axis. A simple epicyclic gear train is shown in Fig. where a gear A and the arm C have a common axis at 1 about which they can rotate. The gear B meshes with gear A and has its axis on the arm at O2, about which the gear B can rotate. If the arm is fixed, the gear train is simple and gear A can drive gear B or viceversa, but if gear A is fixed and the arm is rotated about the axis of gear A (i.e.

Necessity: A clutch is necessary for the transmission of power of shafts and machines which must be started and stopped frequently. Its application is also found in cases in which power is to be delivered to machines partially or fully loaded. The force of friction is used to start the driven shaft from rest and gradually brings it up to the proper speed without excessive slipping of the friction surfaces.

In automobiles, friction clutch is used to connect the engine to the driven shaft. It may be noted that -

All the rotating and reciprocating parts should be completely balanced as far as possible. If these parts are not properly balanced,

The dynamic forces are set up.

These forces increase the loads on bearings and stresses in the various members.

Also produce unpleasant and even dangerous vibrations.

Brakes : A brake is a device by means of which artificial frictional resistance is applied to a moving machine member, in order to retard or stop the motion of a machine.

Types : Hydraulic brakes

1.Electric brakes  2.Mechanical brakes.

The brake absorbs either kinetic energy of the moving member or potential energy given up by objects being lowered by hoists, elevators etc.

The energy absorbed by brakes is dissipated in the form of heat.

Stability of governor : 

A governor is said to be stable when for every speed within the working range there is a definite configuration i.e. there is only one radius of rotation of the governor balls at which the governor is in equilibrium. For a stable governor, if the equilibrium speed increases, the radius of governor balls must also increase.

Hunting of governor :

A flywheel controls the speed variations caused by the fluctuation of the engine turning moment during each cycle of operation.

A flywheel used in machines serves as a reservoir, which stores energy during the period when the supply of energy is more than the requirement, and releases it during the period when the requirement of energy is more than the supply.

Advantages -1. The V-belt drive gives compactness due to the small distance between the centres of pulleys.

2. The drive is positive, because the slip between the belt and the pulley groove is negligible.

3. Since the V-belts are made endless and there is no joint trouble, therefore the drive is smooth.

4. It provides longer life of 3 to 5 years.

5. It can be easily installed and removed.

6. The operation of the belt and pulley is quiet.

7. The belts have the ability to cushion the shock when machines are started.