Theory of machine:
It is a branch of engg. Which deals with study of relative motion between the various parts of machine & forces which acts on them.
Application or scope:
It is very essential for an engineer in designing the various parts of a machine.
Mechanism:
o It is like skeleton & has definite motion between various links.
o It is model of machine.
o It is related to the motion.
o It may be many links e.g. Engine indicator, typewriter etc.
Link or kinematics page link or element:
Each part of machine which moves relative to some other part is known as cinematic page link or element. A page link may have consisted of several parts which are manufactured as separate unit.
Characteristic of link:
o It must be a resistance body.
o It should have relative motion.
Types of links:
o Flexible link
o Rigid page link

Kinematics pair:
Kinematics pair has two elements or page link together which have relative motion between them. The motion between them completely or successfully constrained.
Classification of Kinematics pair:
1. On the basis of contact:
§ Lower pair
§ Higher pair
2. On the basis of type of constraint:
§ Closed pair
§ Unclosed pair
3. On the basis of type of relative motion:
§ Sliding pair
§ Screw pair
§ Turning pair
§ Spherical pair
§ Rolling pair
Inversion of mechanism:
When of the links is fixed in a kinematics chain ,it is called mechanism .so we can obtain as many mechanisms as the number of page link in a kinematic chain by fixing ,in turn , different page link in a kinematics chain . This method of obtaining different mechanism by fixing different links in a kinematic chain.
Types of inversion:
1. Four bar chain or quadric cycle chain:
o Beam engine
o Coupling rod of locomotive
o Watt’s indicator mechanism
2. Single slider crank chain:
o Bull engine or pendulum engine
o Oscillating cylinder engine
o Rotary engine
o Crank & slotted quick return mechanism
o Whitworth quick return mechanism
3. Double slider crank

o Elliptical trammels
o Scotch yoke mechanism
o Oldham’s coupling
Scotch yoke mechanism
When of the links is fixed in a kinematics chain ,it is called mechanism .so we can obtain as many mechanisms as the number of page link in a kinematics chain by fixing ,in turn , different page link in a kinematics chain . This method of obtaining different mechanism by fixing different links in a kinematic chain.

This mechanism is used for converting rotary motion into a reciprocating motion. The inversion is obtained by fixing either the page link 1 or page link 3. In figure page link 1 is fixed. In this mechanism, when the page link 2 (which corresponds to crank) rotates about B as center, the page link 4 (which corresponds to a frame) reciprocates.