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Fundamental and Types of Mechanisms
Content-
1.1 Kinematics of Machines: - Definition of Kinematics, Dynamics, Statics, Kinetics, Kinematic link, Kinematic Pair and its types, constrained motion and its types, Kinematic chain and its types, Mechanism, inversion, machine and structure.
1.2 Inversions of Kinematic Chain.
1.2.1 Inversion of four bar chain, coupled wheels of Locomotive & Pantograph.
1.2.2 Inversion of Single Slider Crank chain- Rotary I.C. Engines mechanism, Whitworth quick return mechanism, Crank and Slotted lever quick return mechanism.
1.2.3 Inversion of Double Slider Crank Chain- Scotch Yoke Mechanism & Oldham’s coupling.
1.3 Common Mechanisms
1.3.1 Bicycle free wheel Sprocket mechanism.
1.3.2 Geneva Mechanism.
1.3.3 Ackerman’s Steering gear mechanism.
1.3.4 Foot operated air pump mechanism.
Introduction
The subject Theory of Machines is an applied science. Theory of Machines takes care of motion and strength aspect of a machine and uses principles from physics, kinematics, static and kinetics.
Machines are mechanical devices used to accomplish work. A mechanism is a heart of a machine. It is the mechanical portion of the machine that has the function of transferring motion and forces from a power source to an output.
Mechanism is a system of rigid elements (linkages) arranged and connected to transmit motion in a predetermined fashion.
Mechanism consists of linkages and joints.
Kinematics of Machines:-
Kinematics is the branch of Theory of Machines which deals with relative motion between the various parts of the machine. It is related with study of motion characteristics i.e. velocity and acceleration.
Dynamics-
Dynamics is the branch of Theory of Machines which deals with forces acting on the machine parts while in motion.
Force in a machine part can be either from outside or from within the body.
Statics-
Statics is the branch of Theory of Machines which deals with forces and their effect while the machine parts are at rest. When dynamics of machine neglects mass effect and studies only external forces that branch of Dynamics is known as Statics i.e. mass of the part is assumed to be negligible
Kinetics
When Dynamics of machine neglects external forces and studies forces only on account of mass of the machine components, then the force study is known as Kinetics.
Kinematic link-
Each part of the machine which moves relative to some other part is known as page link or Kinematic page link or Element. The page link element need not to be a rigid body but must be a resistant body.
Types of links-
i) Rigid link- Rigid page link is one which does not undergo any deformation while transmitting motion. Rigid page link do not exists. But deformation of connecting rod or other element is negligible, so it is considered as rigid link
ii) Flexible link- A flexible page link is one which is partly deformed in a manner not to affect the transmission of motion
Example-Belts, ropes, Wires & Chains
iii) Fluid link- A fluid page link is one which is formed by having a fluid in a receptable and the motion is transmitted through fluid by pressure or compression only.
Example- Hydraulic press, jack etc
Kinematic Pair
There is always a relative motion between existing between two links. If this relative motion between the pair of links is constrained type then the pair is called as Kinematic pair.
Types of Kinematic Pair
1. According to type of relative motion between parts
i) Sliding Pair-When two elements of pair are connected in such a way that one can only slide relative to other the pair is known as sliding pair...
Example- Piston & Cylinder, Tailstock.
ii) Turning Pair- When the two elements of pair are connected in such a way that one can only turn or revolve about a fixed axis of another page link the pair is known as turning pair.
iii) Rolling pair- When the two elements of pair are connected in such a way that one roll over another fixed link, the pair is known as rolling pair.
iv) Screw Pair- When the two elements of pair are connected in such a way that one element can turn about the other by screw threads, pair is known as screw pair.
Example- Nut and Bolt
v) Spherical Pair- When the two elements of pair are connected in such a way that only one element (with spherical shape) turns or swivels about other fixed element the pair formed is called as Spherical pair.
2. According to type of contact between Elements-
i) Lower pair- When the two elements of pair have surface contact when relative motion takes place and surface of one element slides over surface of another the pair formed is Lower pair.
Example- Sliding pair, turning Pair
ii) Higher pair- When the two elements of pair have a line or point contact when relative motion takes place and the motion between two elements is partly turning and partly sliding then the pair formed is known as higher pair.
3. According to the type of closure
i) Self Closed pair- When the two elements of pair are connected together mechanically in such a way that only required kind of relative motion occur, it is known as self closed pair.
ii) Force closed pair- When the two elements of pair are connected mechanically but are kept in contact by the action of external forces the pair is said to be force closed pair.
Constrained motion and its types-
Two links are connected with each other by various means and this method of connection decides the type of relative motion between the links. If this relative motion is one and only type then it is said to be constrained motion.