To study various types of kinematics links, pairs, chains & Mechanisms.
APPARATUS USED: – Kinematics links, pairs, chains & Mechanisms.
THEORY: –
1. Definitions of kinematics links, pairs, chains & Mechanisms.
2. Classifications of kinematics links, pairs, chains & Mechanisms.
3. Diagrams of kinematics links, pairs, chains & Mechanisms
4 Advantages & Disadvantages of kinematics links, Pairs, chains & Mechanisms.
5. Applications of kinematics link, Pairs, chains & Mechanism
6. Examples of kinematics link, Pairs, chains & Mechanisms.
KINEMATIC LINK: – A mechanism is made of a number of resistant bodies out of which some may have motions relative to the others. A resistant body or a group of resistant bodies with rigid connections preventing their relative movement is known as a link. A link also known as kinematic link or element.
Examples :- A slider-crank mechanism consists of four links: frame and guides, crank connecting rod and slider, the crank link may have crankshaft and flywheel also, forming one link having no relative motion of these.
CLASSIFICATIONS OF LINKS:-
1. Binary link
2. Ternary link
3. Quarternary link
KINEMATIC PAIR: – A kinematic pair or simply a pair is a joint of two links having relative motion between them.
CLASSIFICATIONS OF PAIRS:
1-Kinematics pairs according to nature of contact:-
(i) Lower pair (links having surface or area contact)
Examples- Nut turning on a screw, shaft rotating in a bearing, universal joint etc.
(ii) Higher pair (Point or line contact between the links)
Examples:- when rolling on a surface, cam and follower pair, tooth gears, ball and roller bearings etc.
2- Kinematics pairs according to nature of Mechanical Constraint:-
(a) Closed pair (when the elements of a pair are held together mechanically)
Examples :- all the lower pairs and some of the higher pair
(b) Unclosed pair (when two links of a pair are in contact either due to force of gravity or some spring action), Example :- cam and follower pair.
3-Kinematics pairs according to nature of relative motion:-
(i) Sliding pair
(ii) Turning pair
(iii) Rolling Pair
(iv) Screw pair (Helical pair)
(v) Spherical pair
KINEMATIC CHAIN :- A kinematic chain is an assembly of links in which the relative motions of the links is possible and the motion of each relative to the others is definite. If indefinite motions of other links , it is a non-kinematic chain.
Types of kinematics chains :-
(i) Four bar chain or quadric cycle chain
(ii) Single slider crank chain
(iii) Double slider crank chain
MECHANISM :- A linkage is obtained if one of the links of a kinematics chain is fixed to the ground. If motion of each link results in definite motions of the others, the linkage is known as a mechanism. If one of the links of a redundant chain is fixed, it is known as a structure. The degree of freedom of a structure is zero or less. A structure with negative degree of freedom is known as a superstructure.
OBSERVATION & CONCLUSION:-
1. Comparison between kinematics links, Pairs, chains & Mechanisms.
2. Type of Motion to be named.
VIVA-QUESTIONS :-
a) Define machine & structure.
b) Concept of kinematics links, pairs, chains & mechanism.
c) Classification & examples of all the kinematics links, pairs, chains & mechanism.
d) Grashof’s criterion.
e) Types & examples of constrained motion.