Mechanical system
Encyclopedia
A mechanical system manages power
to accomplish a task that involves forces and movement. Mechanical is derived from the Latin
word machina, which in turn derives from the Doric Greek
μαχανά (machana), Ionic Greek
μηχανή (mechane) "contrivance, machine, engine" and that from μῆχος (mechos), "means, expedient, remedy".
The Oxford English Dictionary defines the adjective mechanical as skilled in the practical application of an art or science, of the nature of a machine or machines, and relating to or caused by movement, physical forces, properties or agents such as is dealt with by Mechanics
. Similarly Merriam-Webster Dictionary defines "mechanical" as relating to machinery or tools.
A mechanical system consists of (i) a power source and actuators that generate forces and movement, (ii) a system of mechanisms
that shape the actuator input to achieve a specific application of output forces and movement, and (iii) a controller with sensors that compares the output to a performance goal and then directs the actuator input. This can be seen in Watt's steam engine (see the illustration) in which the power is provided by steam expanding to drive the piston. The walking beam, coupler and crank transform the linear movement of the piston into rotation of the output pulley. Finally, the pulley rotation drives the flyball governor which controls the valve for the steam input to the piston cylinder.
Power flow through a mechanical system provides a way to understand the performance of devices ranging from levers and gear trains to automobiles and robotic systems.
Waterwheel: Waterwheels appeared around the world around 300 BC to use flowing water to generate rotary motion, which was applied to milling grain, and powering lumber, machining and textile operations
. Modern water turbine
s use water flowing through a dam
to drive an electric generator.
Windmill: Early windmills captured wind power to generate rotary motion for milling operations. Modern wind turbine
s also drives a generator. This electricity in turn is used to drive motor
s forming the actuators of mechanical systems.
Engine: The word engine derives from "ingenuity" and originally referred to contrivances that may or may not be physical devices. See Merriam-Webster's definition of engine. A steam engine
uses heat to boil water contained in a pressure vessel; the expanding steam drives a piston or a turbine. This principle can be seen in the aeolipile
of Hero of Alexandria. This is called an external combustion engine
.
An automobile
engine is called an internal combustion engine
because it burns fuel (an exothermic
chemical reaction) inside a cylinder and uses the expanding gases to drive a piston
. A jet engine
uses a turbine to compress air which is burned with fuel so that it expands through a nozzle to provide thrust to an aircraft
, and so is also an "internal combustion engine."
Power plant: The heat from coal and natural gas combustion in a boiler
generates steam that drives a steam turbine
to rotate an electric generator. A nuclear power plant
uses heat from a nuclear reactor
to generate steam and electric power
. This power is distributed through a network of transmission lines for industrial and individual use.
Motors: Electric motors
use either AC
or DC
electric current to generate rotational movement. Electric servomotors
are the actuators for mechanical systems ranging from robotic systems
to modern aircraft
.
Fluid Power: Hydraulic
and pneumatic
systems use electrically driven pump
s to drive water or air respectively into cylinders to power linear movement
.
. These elements provide structure for the system and control its movement.
The structural components are, generally, the frame members, bearings, splines, springs, seals, fastener
s and covers. The shape, texture and color of covers provide a styling and operational interface
between the mechanical system and its users.
The assemblies that control movement are also called "mechanisms
." Mechanisms are generally classified as gear
s and gear train
s, which includes belt drives and chain drive
s, cam
and follower
mechanisms, and linkage
s, though there are other special mechanisms such as clamping linkages, indexing mechanisms
, escapement
s and friction devices such as brake
s and clutch
es.
The number of degrees of freedom (dof) or mobility of a mechanism depends on the number of links and joints and the types of joints used to construct the mechanism. The general mobility of a mechanism is the difference between the unconstrained freedom of the links and the number of constraints imposed by the joints. It is described by the Chebychev-Grübler-Kutzbach criterion.
s, logic
, and actuator
s to maintain the performance of components of a machine. Perhaps the best known is the flyball governor
for a steam engine. Examples of these devices range from a thermostat
that as temperature rises opens a valve to cooling water to speed controllers such the cruise control
system in an automobile. The programmable logic controller
replaced relays and specialized control mechanisms with a programmable computer. Servomotors that accurately position a shaft in response to an electrical command are the actuators that make robotic systems
possible.
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
to accomplish a task that involves forces and movement. Mechanical is derived from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
word machina, which in turn derives from the Doric Greek
Doric Greek
Doric or Dorian was a dialect of ancient Greek. Its variants were spoken in the southern and eastern Peloponnese, Crete, Rhodes, some islands in the southern Aegean Sea, some cities on the coasts of Asia Minor, Southern Italy, Sicily, Epirus and Macedon. Together with Northwest Greek, it forms the...
μαχανά (machana), Ionic Greek
Ionic Greek
Ionic Greek was a subdialect of the Attic–Ionic dialect group of Ancient Greek .-History:Ionic dialect appears to have spread originally from the Greek mainland across the Aegean at the time of the Dorian invasions, around the 11th Century B.C.By the end of the Greek Dark Ages in the 5th Century...
μηχανή (mechane) "contrivance, machine, engine" and that from μῆχος (mechos), "means, expedient, remedy".
The Oxford English Dictionary defines the adjective mechanical as skilled in the practical application of an art or science, of the nature of a machine or machines, and relating to or caused by movement, physical forces, properties or agents such as is dealt with by Mechanics
Mechanics
Mechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment....
. Similarly Merriam-Webster Dictionary defines "mechanical" as relating to machinery or tools.
A mechanical system consists of (i) a power source and actuators that generate forces and movement, (ii) a system of mechanisms
Machine (mechanical)
The mechanical properties of a machine manage power to achieve desired forces and movement. Modern machines often include computers and sensors that monitor performance and plan movement, and are called mechanical systems....
that shape the actuator input to achieve a specific application of output forces and movement, and (iii) a controller with sensors that compares the output to a performance goal and then directs the actuator input. This can be seen in Watt's steam engine (see the illustration) in which the power is provided by steam expanding to drive the piston. The walking beam, coupler and crank transform the linear movement of the piston into rotation of the output pulley. Finally, the pulley rotation drives the flyball governor which controls the valve for the steam input to the piston cylinder.
Power Sources
Human and animal effort were the original power sources for early machines. Natural forces such as wind an water powered larger mechanical systems.Waterwheel: Waterwheels appeared around the world around 300 BC to use flowing water to generate rotary motion, which was applied to milling grain, and powering lumber, machining and textile operations
Watermill
A watermill is a structure that uses a water wheel or turbine to drive a mechanical process such as flour, lumber or textile production, or metal shaping .- History :...
. Modern water turbine
Water turbine
A water turbine is a rotary engine that takes energy from moving water.Water turbines were developed in the 19th century and were widely used for industrial power prior to electrical grids. Now they are mostly used for electric power generation. They harness a clean and renewable energy...
s use water flowing through a dam
Hoover Dam
Hoover Dam, once known as Boulder Dam, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the US states of Arizona and Nevada. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President...
to drive an electric generator.
Windmill: Early windmills captured wind power to generate rotary motion for milling operations. Modern wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
s also drives a generator. This electricity in turn is used to drive motor
Motor
Motor is a device that creates motion. It usually refers to an engine of some kind. It may also specifically refer to:*Electric motor, a machine that converts electricity into a mechanical motion...
s forming the actuators of mechanical systems.
Engine: The word engine derives from "ingenuity" and originally referred to contrivances that may or may not be physical devices. See Merriam-Webster's definition of engine. A steam engine
Steam engine
A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...
uses heat to boil water contained in a pressure vessel; the expanding steam drives a piston or a turbine. This principle can be seen in the aeolipile
Aeolipile
An aeolipile , also known as a Hero engine, is a rocket style jet engine which spins when heated. In the 1st century AD, Hero of Alexandria described the device, and many sources give him the credit for its invention.The aeolipile Hero described is considered to be the first recorded steam engine...
of Hero of Alexandria. This is called an external combustion engine
External combustion engine
An external combustion engine is a heat engine where an working fluid is heated by combustion in an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine, produces motion and usable work...
.
An automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
engine is called an internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
because it burns fuel (an exothermic
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...
chemical reaction) inside a cylinder and uses the expanding gases to drive a piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
. A jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
uses a turbine to compress air which is burned with fuel so that it expands through a nozzle to provide thrust to an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
, and so is also an "internal combustion engine."
Power plant: The heat from coal and natural gas combustion in a boiler
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
generates steam that drives a steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
to rotate an electric generator. A nuclear power plant
Nuclear power plant
A nuclear power plant is a thermal power station in which the heat source is one or more nuclear reactors. As in a conventional thermal power station the heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity.Nuclear power plants are usually...
uses heat from a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
to generate steam and electric power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
. This power is distributed through a network of transmission lines for industrial and individual use.
Motors: Electric motors
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
use either AC
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
or DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
electric current to generate rotational movement. Electric servomotors
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
are the actuators for mechanical systems ranging from robotic systems
Robotics
Robotics is the branch of technology that deals with the design, construction, operation, structural disposition, manufacture and application of robots...
to modern aircraft
Fly-by-wire
Fly-by-wire is a system that replaces the conventional manual flight controls of an aircraft with an electronic interface. The movements of flight controls are converted to electronic signals transmitted by wires , and flight control computers determine how to move the actuators at each control...
.
Fluid Power: Hydraulic
Hydraulic cylinder
A Hydraulic cylinder is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. It has many applications, notably in engineering vehicles.- Operation :...
and pneumatic
Pneumatic cylinder
Pneumatic cylinders are mechanical devices which utilize the power of compressed gas to produce a force in a reciprocating linear motion....
systems use electrically driven pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
s to drive water or air respectively into cylinders to power linear movement
Linear actuator
A linear actuator is an actuator that creates linear motion .Mechanical and hydraulic actuation are the most common methods of achieving the linear motion...
.
Mechanisms
The mechanism of a mechanical system is assembled from components called machine elementsMachine element
Machine elements are basic mechanical parts used as the building blocks of most machines. Most are standardized to common sizes, but customs are also common for specialized applications.-Types:*Shafts**Couplings*Keys*Splines*Bearings**Roller bearings...
. These elements provide structure for the system and control its movement.
The structural components are, generally, the frame members, bearings, splines, springs, seals, fastener
Fastener
A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...
s and covers. The shape, texture and color of covers provide a styling and operational interface
Industrial design
Industrial design is the use of a combination of applied art and applied science to improve the aesthetics, ergonomics, and usability of a product, but it may also be used to improve the product's marketability and production...
between the mechanical system and its users.
The assemblies that control movement are also called "mechanisms
Mechanism (engineering)
A mechanism is a device designed to transform input forces and movement into a desired set of output forces and movement. Mechanisms generally consist of moving components such as gears and gear trains, belt and chain drives, cam and follower mechanisms, and linkages as well as friction devices...
." Mechanisms are generally classified as gear
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
s and gear train
Gear train
A gear train is formed by mounting gears on a frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, this provides a smooth transmission of rotation from one gear to the next.The transmission of...
s, which includes belt drives and chain drive
Chain drive
Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and motorcycles...
s, cam
Cam
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path...
and follower
Cam follower
A cam follower, also known as a track follower, is a specialized type of roller or needle bearing designed to follow cams. Cam followers come in a vast array of different configurations, however the most defining characteristic is how the cam follower mounts to its mating part; stud style cam...
mechanisms, and linkage
Linkage
Linkage generally means "the manner or style of being united", and can refer to:*Genetic linkage, the tendency of certain genes to be inherited together*Flux linkage, the total flux passing through a surface formed by a closed conducting loop...
s, though there are other special mechanisms such as clamping linkages, indexing mechanisms
Geneva drive
The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotation into an intermittent rotary motion. The rotating drive wheel has a pin that reaches into a slot of the driven wheel advancing it by one step...
, escapement
Escapement
In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...
s and friction devices such as brake
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
s and clutch
Clutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...
es.
The number of degrees of freedom (dof) or mobility of a mechanism depends on the number of links and joints and the types of joints used to construct the mechanism. The general mobility of a mechanism is the difference between the unconstrained freedom of the links and the number of constraints imposed by the joints. It is described by the Chebychev-Grübler-Kutzbach criterion.
Controllers
Controllers combine sensorSensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
s, logic
Logic
In philosophy, Logic is the formal systematic study of the principles of valid inference and correct reasoning. Logic is used in most intellectual activities, but is studied primarily in the disciplines of philosophy, mathematics, semantics, and computer science...
, and actuator
Actuator
An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which...
s to maintain the performance of components of a machine. Perhaps the best known is the flyball governor
Centrifugal governor
A centrifugal governor is a specific type of governor that controls the speed of an engine by regulating the amount of fuel admitted, so as to maintain a near constant speed whatever the load or fuel supply conditions...
for a steam engine. Examples of these devices range from a thermostat
Thermostat
A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...
that as temperature rises opens a valve to cooling water to speed controllers such the cruise control
Cruise control
Cruise control is a system that automatically controls the speed of a motor vehicle. The system takes over the throttle of the car to maintain a steady speed as set by the driver.-History:...
system in an automobile. The programmable logic controller
Programmable logic controller
A programmable logic controller or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many industries and machines...
replaced relays and specialized control mechanisms with a programmable computer. Servomotors that accurately position a shaft in response to an electrical command are the actuators that make robotic systems
Robot
A robot is a mechanical or virtual intelligent agent that can perform tasks automatically or with guidance, typically by remote control. In practice a robot is usually an electro-mechanical machine that is guided by computer and electronic programming. Robots can be autonomous, semi-autonomous or...
possible.
See also
- History of technologyHistory of technologyThe history of technology is the history of the invention of tools and techniques, and is similar in many ways to the history of humanity. Background knowledge has enabled people to create new things, and conversely, many scientific endeavors have become possible through technologies which assist...
- Machine (mechanical)Machine (mechanical)The mechanical properties of a machine manage power to achieve desired forces and movement. Modern machines often include computers and sensors that monitor performance and plan movement, and are called mechanical systems....
- Linkage (mechanical)Linkage (mechanical)A mechanical linkage is an assembly of bodies connected together to manage forces and movement. The movement of a body, or link, is studied using geometry so the link is considered to be rigid. The connections between links are modeled as providing ideal movement, pure rotation or sliding for...
- Mechanism (engineering)Mechanism (engineering)A mechanism is a device designed to transform input forces and movement into a desired set of output forces and movement. Mechanisms generally consist of moving components such as gears and gear trains, belt and chain drives, cam and follower mechanisms, and linkages as well as friction devices...