Page 25 - Analysis and Design of Machine Elements

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An Overview of Machine Design

1.1 Introduction

1.1.1 Machines and Machine Elements
A machine is a device that employs power to accomplish a desired function to benefit
humankind. It is generally composed of a power source to provide power and move-
ment, and an executive device to fulfil intended function. In between is a transmission
system and controller. Power sources can be prime movers, that is, a machine utilizes
a natural source of energy to produce power, like an internal combustion engine; or a
secondary mover, like an electric motor, which receives energy directly or indirectly
from a generator driven by a prime mover [1]. Take a car as an example; power sources,

either engines in motor vehicles or batteries in electrical vehicles, provide power
to executive devices; for example, wheels, through a transmission system (including
couplings, clutches, shafts, powertrain etc.). The control system, that is, steering
systems and brakes, control car movement. Lights, meters and windscreen wipers are
accessories that facilitate a car running properly.
Machines involve a vast variety of mechanical products in various fields of
manufacturing, transportation, aerospace, construction, agricultural, energy and many
others. ‘Products’ covers industrial robots, machine tools and automated assembly sys-
tems in manufacturing systems; automobiles, trains, ships and aircraft in transportation
vehicles; mobile cranes, dump trucks and concrete mixers in construction equipment.
Household appliances, like vacuum cleaners, washing machines and air-conditioning
systems are also machines.
A similar concept, that is, mechanism, is a combination of elements formed and con-
nected to transmit motion in a predetermined fashion. Typical mechanisms include
linkages, cams and follower systems, gears and gear trains and so on. There is no clear
division between mechanisms and machines. If the transmitted forces or power are
significant, it is considered a machine; otherwise, it is considered a mechanism [2].
Machinery is a derived term and refers to a grouping of mechanisms and machines [1].
A machine composes individual machine elements properly designed and arranged
to work together. Machine elements are the fundamental components of a machine,
and are broadly classified as universal elements, such as bolts, keys, splines, pins, belts,
chains, gears, bearings and springs that are widely used in different kinds of machines,
and special elements such as turbine blades, crankshafts and aircraft propellers, which

Analysis and Design of Machine Elements, First Edition. Wei Jiang.
© 2019 John Wiley & Sons Singapore Pte. Ltd. Published 2019 by John Wiley & Sons Singapore Pte. Ltd.
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