• SUBJECT-THEORY OF MACHINES.�BRANCH- MECHANICAL ENGINEERING.�SEMESTER- 4^th.�CHAPTER- ONE.�FACULTY- Er. BARENDRA NATH MOHANTA.�

TOPIC- SIMPLE MECHANISM OF MACHINE

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INTRODUCTION

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A machine is a device by means of which available energy can be converted into derived form of useful work. It is the assembly of resistant bodies or links whose relative motions are successfully constrained so that available energy can be converted into useful work. Machines are used to transmit both motion and force.

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A machine is device which receives energy and transforms it into some useful work. Example: Lathe, Shaper, Scooter etc.. ·

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Theory of machine is the branch of engineering which deals with the relative motion and force between various machine elements.

KINEMATIC LINK..

Each part of a machine, which moves relative to some other part, is known as link or element.

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Links in reciprocating engine

• Link-1 : piston, piston rod and cross head
• Link-2 : crank, crankshaft and flywheel
• Link-3 : cylinder, engine frame and main bearings

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Link should have two characters.

• 1. It should have relative motion.
• 2. It should be a resistant body.

Figure of link.

Types of link..

• Rigid link : A rigid link is on which does not undergo any deformation while transmitting motion. Example : Deformation of a connecting rod, crank etc.. is not appreciable

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• Flexible link : A flexible link in one which is partly deformed in a manner not to affect the transmission of motion. Example : belts, ropes, chains and wires

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• Fluid link : A fluid link is one which is formed by having a fluid in a reciprocal and the motion is transmitted through the fluid by pressure or compression only as in the case of hydraulic presses, jacks and brakes.

Kinetic pair

The two links or elements of a machine, when in contact with each other are said to form a pair. When two elements or links are connected in such a way that their relative motion is constrained they form a kinematic pair and the process of connecting them is called pairing.

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• Lower pair : When the two elements of a pair have a surface contact while relative motion takes place and the surface of one element slides over the surface of the other, the pair formed is known as lower pair. Example : sliding pair, turning pair, piston cross head, tailstock on the leather bed, shaft revolting in a bearing, steering gear, universal joint. The relative motion is purely sliding or turning.

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• Higher pair: When the two elements of a pair have a line or point contact while in motion, the pair so formed is known as a higher pair. The relative motion being the combination of sliding and turning, thus it is complex. Example : belt, rope and chain drives, gears, cam and follower, ball and roller bearing.

mechanism

When one element or link of a kinematic chain is fixed, the arrangement may be used for transmitting or transforming motion. It is termed as mechanism.

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Types of mechanism

• Simple mechanism: Mechanism having four links. Example: Coupling rod mechanism of a locomotive beam engine etc.

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• Compound mechanism: Mechanism having more than four lines. It may be formed combining two or more simple mechanism.

inversion

• Different mechanisms can be obtained by fixing different links in a kinematic chain. It is known as inversion of the original kinematic chain.

• Suppose number of links of a kinematic chain = L

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• So L different mechanisms may be obtained by fixing each of the lines in turn. Each mechanism is termed as inversion.

Cam and followers

• Definition: A cam may be defined as a rotating, oscillating or reciprocating body which imparts a reciprocating or oscillating motion to another body, called a follower.

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• The cam and the follower constitute a higher pair.

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• Application: Used in clocks, printing machines, internal combustion engines for operating valves, paper cutting machines, automatic screw cutting machines, shoe making machinery, feed mechanism of automatic lathe.

Classification follower

Surface in contact follower

• (i) Knife edge follower
• (ii) Roller follower
• (iii)Spherical faced follower

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Motion of the follower

• (i) Reciprocating or translating follower
• (ii) Oscillating or rotating follower

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Path of motion of the follower

• (i) Radial follower
• (ii) Offset follower

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Classification of cam

Radial or Disc cam

1.Reciprocating cam

2.Tangent cam

3.Circular cam

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Cylindrical cam

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