FIXED AND PROGRAMMABLE AUTOMATION




 

Automated production lines

An automated production line consists of a series of workstations connected by a transfer system to move parts between the stations. This is an example of fixed automation, since these lines are set up for long produc­tion runs, making large number of product units and running for several years between changeovers. Each station is designed to perform a specific processing op­eration, so that the part or product is constructed stepwise as it progresses along the line. A raw work part enters at one end of the line, proceeds through each workstation and appears at the other end as a completed product. In the normal operation of the line, there is a work part being processed at each station, so that many parts are being processed simultaneously and a finished part is produced with each cycle of the line. The various opera­tions, part transfers, and other activities taking place on an automated transfer line must all be sequenced and co­ordinated properly for the line to operate efficiently.

Modern automated lines are controlled by program­mable logic controllers, which are special computers that can perform timing and sequencing functions required to operate such equipment. Automated production lines are utilized in many industries, mostly automobile, where they are used for processes such as machining and pressworking.

Machining is a manufacturing process in which metal is removed by a cutting or shaping tool, so that the remain­ing work part is the desired shape. Machinery and motor components are usually made by this process. In many cases, multiple operations are required to completely shape the part. If the part is mass-produced, an automated transfer line is often the most economical method of pro­duction. Many separate operations are divided among the workstations.

Pressworking operations involve the cutting and forming of parts from sheet metal. Examples of such parts include automobile body panels, outer shells of laundry machines and metal furniture More than one processing step is often required to complete a compli­cated part. Several presses are connected together in se­quence by handling mechanisms that transfer the par­tially completed parts from one press to the next, thus creating an automated pressworking line.

Numerical control

Numerical control is a form of programmable auto­mation in which a machine is controlled by numbers (and other symbols) that have been coded on punched paper tape or an alternative storage medium. The initial appli­cation of numerical control was in the machine tool in­dustry, to control the position of a cutting tool relative to the work part being machined. The NC part program represents the set of machining instructions for the par­ticular part. The coded numbers in the program specify x-y-z coordinates in a Cartesian axis system, defining the various positions of the cutting tool in relation to the work part. By sequencing these positions in the program, the machine tool is directed to accomplish the machining of the part. A position feedback control system is used in most NC machines to verify that the coded instruc­tions have been correctly performed. Today a small com­puter is used as the controller in an NC machine tool. Since this form of numerical control is implemented by computer, it is called computer numerical control, or CNC. Another variation in the implementation of nu­merical control involves sending part programs over tel­ecommunications lines from a central computer to indi­vidual machine tools in the factory. This form of numeri­cal control is called direct numerical control, or DNC.

Many applications of numerical control have been de­veloped since its initial use to control machine .tools. Other machines using numerical control include compo­nent-insertion machines used in electronics assembly, drafting machines that prepare engineering drawings, coordinate measuring machines that perform accurate inspections of parts. In these applications coded numeri­cal data are employed to control the position of a tool or workhead relative to some object. Such machines are used to position electronic components (e.g., semiconductor chip modules) onto a printed circuit board (PCB). It is basically an x-y positioning table that moves the printed circuit board relative to the part-insertion head, which then places the individual component into position on the board. A typical printed circuit board has dozens of in­dividual components that must be placed on its surface; in many cases, the lead wires of the components must be inserted into small holes in the board, requiring great precision by the insertion machine. The program that controls the machine indicates which components are to be placed on the board and their locations. This informa­tion is contained in the product-design database and is typically communicated directly from the computer to the insertion machine.

Automated assembly

Assembly operations have traditionally been per­formed manually, either at single assembly workstations or on assembly lines with multiple stations. Owing to the high labour content and high cost of manual labour, greater attention has been given in recent years to the use of automation for assembly work. Assembly opera­tions can be automated using production line principles if the quantities are large, the product is small, and the design is simple (e.g., mechanical pencils, pens, and ciga­rette lighters). For products that do not satisfy these conditions, manual assembly is generally required.

Automated assembly machines have been developed that operate in a manner similar to machining transfer lines, with the difference being that assembly operations, instead of machining, are performed at the workstations. A typical assembly machine consists of several stations, each equipped with a supply of components and a mecha­nism for delivering the components into position for as­sembly. A workhead at each station performs the actual attachment of the component. Typical workheads include automatic screwdrivers, welding heads and other join­ing devices. A new component is added to the partially completed product at each workstation, thus building up the product gradually as it proceeds through the line. Assembly machines of this type are considered to be ex­amples of fixed automation, because they are generally configured for a particular product made in high volume. Programmable assembly machines are represented by the component-insertion machines employed in the electron­ics industry.


HISTORY OF ROBOTICS

The concept of robots dates back to ancient times, when some myths told of mechanical beings brought to life. Suchautomata also appeared in the clockwork fig­ures of medieval churches, and in the 18th century some clockmakers gained fame for the clever mechanical fig­ures that they constructed. Today the termautomatonis usually applied to these handcrafted, mechanical (rather than electromechanical) devices that imitate the motions of living creatures. Some of the «robots» used in advertising and entertainment are actually automata, even with the addition of remote radio control.

The term robot itself is derived from the Czech word robota, meaning «compulsory labour». It was first used by the Czech novelist and playwright Karel Chapek, to describe a mechanical device that looks like a human but, lacking human sensibility, can perform only automatic, mechanical operations. Robots as they are known today do not only imitate human or other living forms. True robots did not become possible, however, until the inven­tion of the computer in the 1940s and the miniaturiza­tion of computer parts. One of the first true robots was an experimental model designed by researchers at the Stanford Research Institute in the late 1960s. It was ca­pable of arranging blocks into stacks through the use of a television camera as a visual sensor, processing this information in a small computer.

Computers today are equipped with microprocessors that can handle the data being fed to them by various sensors of the surrounding environment. Making use of the principle of feedback, robots can change their opera­tions to some degree in response to changes in that envi­ronment. The commercial use of robots is spreading, with the increasing automation of factories, and they have become essential to many laboratory procedures. Japan is the most advanced nation exploring robot technology. Nowadays robots continue to expand their applications. The home-made robots (горничная) available today may be one sign of the future

 


MEASUREMENTS

Metric System is a decimal system of physical units, named after its unit of length, the metre, the metric sys­tem is adopted as the common system of weights and measures by the majority of countries, and by all coun­tries as the system used in scientific work.

Weights and Measures

Length, capacity, and weight can be measured using standard units. The principal early standards of length were the palm or hand breadth, the foot, and the cubit, which is the length from the elbow to the tip of the mid­dle finger. Such standards were not accurate and defi­nite. Unchanging standards of measurement have been adopted only in modern time.

In the English-speaking world, the everyday units of linear measurement were traditionally the inch, foot, yard and mile. In Great Britain, until recently, these units of length were defined in terms of the imperial standard yard, which was the distance between two lines on a bronze bar made in 1845.

In Britain units of weight (ounces, pounds, and tons) are now also derived from the metric standard — kilogram. This is a solid cylinder of platinum-iridium alloy main­tained at constant temperature at Sevres, near Paris. Cop­ies, as exact as possible, of this standard are maintained by national standards laboratories in many countries.

International System of Units is a system of meas­urement units based on the MKS (metre-kilogram-second) system. This international system is commonly re­ferred to as SI.

At the Eleventh General Conference on Weights and Measures, held in Paris in 1960 standards were defined for six base units and two supplementary units:

Length

The metre had its origin in the metric system. By in­ternational agreement, the standard metre had been de­fined as the distance between two fine lines on a bar of platinum-iridium alloy. The 1960 conference redefined the metre as 1,650,763.73 wavelengths of the reddish-orange light emitted by the isotope krypton-86. The metre was again redefined in 1983 as the length of the path travelled by light in a vacuum during a time inter­val of 1/299,792,458 of a second.

Mass

When the metric system was created, the kilogram was defined as the mass of 1 cubic decimetre of pure water at the temperature of its maximum density or at 4.0 °C.

Time

For centuries, time has been universally measured in terms of the rotation of the earth. The second, the basic unit of time, was defined as 1/86,400 of a mean solar day or one complete rotation of the earth on its axis in relation to the sun. Scientists discovered, however, that the rotation of the earth was not constant enough to serve as the basis of the time standard. As a result, the second was redefined in 1967 in terms of the resonant frequency of the caesium atom, that is, the frequency at which this atom absorbs en­ergy: 9,192,631,770 Hz (hertz, or cycles per second).

Temperature

The temperature scale is based on a fixed temperature, that of the triple point of water at which it's solid, liquid and gaseous. The freezing point of water was designated as 273.15 К, equaling exactly 0° on the Celsius tempera­ture scale. The Celsius scale, which is identical to the centigrade scale, is named after the 18th-century Swed­ish astronomer Anders Celsius, who first proposed the use of a scale in which the interval between the freezing and boiling points of water is divided into 100 degrees. By international agreement, the term Celsius has offi­cially replaced centigrade.

One feature of SI is that some units are too large for ordinary use and others too small. To compensate, the prefixes developed for the metric system have been bor­rowed and expanded. These prefixes are used with all three types of units: base, supplementary, and derived. Examples are millimetre (mm), kilometre/hour (km/h), megawatt (MW), and picofarad (pF). Because double pre­fixes are not used, and because the base unit name kilo­gram already contains a prefix, prefixes are used not with kilogram but with gram. The prefixes hecto, deka, deci, and centi are used only rarely, and then usually with metre to express areas and volumes. In accordance with established usage, the centimetre is retained for body measurements and clothing.

In cases where their usage is already well estab­lished, certain other units are allowed for a limited time, subject to future review. These include the nau­tical mile, knot, angstrom, standard atmosphere, hec­tare, and bar.

 


17. COMPUTERS

Computer is an electronic device that can receive a program (a set of instructions) and then carry out this program by calculating numerical information.

The modern world of high technology is possible mainly due to the development of the computer. Com­puters have opened up a new era in manufacturing by means of automation, and they have enhanced modern communication systems.

Personal computers

Personal computers are also called microcomputers or home computer. The most compact are called laptops. They are portable and work on built-in batteries.

Personal computers are designed for use at homes, schools, and offices. At home they can be used for home management (balancing the family finances, for exam­ple) and for playing computer games, watching films or listening to music. Schoolchildren can use computers for doing their homework and many schools now have com­puters for independent learning and computer-literacy studies. In the office personal computers may be used for word processing, bookkeeping, storage and handling of necessary information.

Personal computers were made possible by two tech­nical innovations in the field of microelectronics: the integrated circuit, or IС, which was developed in 1959 and the microprocessor that first appeared in 1971. The IС permitted the miniaturization of computer-memory circuits, and the microprocessor reduced the size of a computer's CPU to the size of a single silicon chip.

Because a CPU calculates, performs logical opera­tions, contains operating instructions, and manages data flows, a complete microcomputer as a separate system was designed and developed in 1974.

In 1981, IBM Company offered its own microcomputer model, the IBM PC that became a necessary tool for al­most every business. The PC's use of a 16-bit microproc­essor initiated the development of faster and more pow­erful personal computers, and its use of an operating system that was available to all other computer makers led to a standardisation of the industry.

In the mid-1980s, a number of other developments were especially important for the growth of personal com­puters. One of these was the introduction of a powerful 32-bit CPU capable of running advanced operating sys­tems at high speeds.

Another innovation was the use of conventional oper­ating systems, such as UNIX, OS/2 and Windows. The Apple Macintosh computers were the first to allow the user to select icons — graphic symbols of computer func­tions — from a display screen instead of typing com­mands. New voice-controlled systems are now available, and users are able to use the words and syntax of spoken language to operate their personal computers.

 


18. HISTORY AND FUTURE OF THE INTERNET

The Internet technology was created by Vinton Cerf in early 1973 as part of a project headed by Robert Kahn and conducted by the Advanced Research Projects Agency, part of the United States Department of De­fence. Later Cerf made many efforts to build and stand­ardise the Internet. In 1984 the technology and the net­work were turned over to the private sector and to gov­ernment scientific agencies for further development. The growth has continued exponentially. Service-provider companies that make «gateways» to the Internet avail­able to home and business users enter the market in ever-increasing numbers. By early 1995, access was available in 180 countries and more than 30 million users used the Internet. The Internet and its technology continue to have a profound effect in promoting the exchange of in­formation, making possible rapid transactions among businesses, and supporting global collaboration among individuals and organisations. More than 100 million computers are connected via the global Internet in 2000, and even more are attached to enterprise internets. The development of the World Wide Web leads to the rapid introduction of new business tools and activities that may lead to annual business transactions on the Internet worth hundreds of billions of dollars.

 


19. AGRICULTURAL MACHINERY

Agricultural machines are used to till soil and to plant, cultivate, and harvest crops. Since ancient times, when cultures first began cultivating plants, people have used tools to help them grow and harvest crops. They used pointed tools to dig and keep soil loosened, and sharp, knife-like objects to harvest ripened crops. Modifications of these early implements led to the development of small hand tools that are still used in gardening, such as the spade, hoe, rake and trowel, and larger implements, such as ploughs and larger rakes that are drawn by humans, animals, or simple machines.

Modern machinery is used extensively in Western Europe, Australia, the United States, the Russian Fede­ration and Canada.

Modern large agricultural implements, adapted to large-scale farming methods, are usually powered by diesel- or petrol-fuelled internal-combustion engines. The most important implement of modern agriculture is the tractor. It provides locomotion for many other implements and can furnish power, via its power shaft, for the opera­tion of machines drawn behind the tractor. The power shafts of tractors can also be set up to drive belts that op­erate equipment such as feed grinders, pumps, and elec­tric-power generators. Small implements, such as port­able irrigators, may be powered by individual motors.

Implements for Growing Crops

Many types of implements have been developed for the activities involved in growing crops. These activities include breaking ground, planting, weeding, fertilizing, and combating pests.

Ground is broken by ploughs to prepare the seed-bed. A plough consists of a blade-like ploughshare that cuts under, then lifts, turns, and pulverizes the soil. Modern tractor ploughs are usually equipped with two or more ploughshares so that a wide area of ground can be bro­ken at a single sweep. Harrows are used to smooth the ploughed land and sometimes to cover seeds and ferti­lizer with earth. The disc harrow, which has curved, sharp-edged steel discs, is used mainly to cut up crop residues before ploughing and to bury weeds during seed­bed preparation. Rollers with V-shaped wheels break up clods of soil to improve the aeration of the soil and its capacity for taking in water.

Some cereal crops are still planted by broadcasting seeds—that is, by scattering the seeds over a wide area. Machines for broadcasting usually consist of a long seed-box mounted on wheels and equipped with an agitator to distribute the seeds. Broadcast seeds are not always cov­ered by a uniform or sufficient depth of soil, so seeding is more often done with drills, which produce continu­ous furrows of uniform depth. Specialized implements called planters are necessary for sowing crops that are planted in rows, such as maize. Maize planters and other similar machines have a special feed wheel that picks up small quantities of grain or separate kernels and places them in the ground.

Fertilizer can be distributed during the winter or shortly before seeding time. Commercial fertilizers are commonly distributed, along with seeds, by drills and planters. Manure is distributed most efficiently by a manure spreader, which is a wagon equipped with a bot­tom conveyor to carry the fertilizer back to a beater attachment, which disintegrates it and then scatters it on the ground.

After crops have begun to grow, a cultivator is used to destroy weeds and loosen and aerate the soil. A flame weeder, which produces a hot-air blast, can be used to de­stroy weeds growing around crops, such as cotton, that have stems of tough bark. The weeds are vulnerable to the hot air, but the tough stems protect the crops from dam­age. Chemical herbicides applied in the form of a spray or as granules are used extensively for weed control.

Insecticides for pest control are applied to soil and crops in the form of granules, dust, or liquid sprays. A variety of mechanical spraying and dusting equipment is used to spread chemicals on crops and fields; the ma­chinery may be self-powered, or drawn and powered by a tractor. In areas where large crops of vegetables and grain are grown, aircraft are sometimes used to dust or spray pesticides.

Chemical pesticides are used in nearly all farming op­erations undertaken in developed countries. However, increasing concern over the harmful effects that pesticides may have on the environment has led to the use of alter­native forms of pest control. For example, farmers use crop rotation to prevent pests that feed on a certain crop. Also, certain pests are controlled by introducing an or­ganism that damages or kills the pests, but leaves the crops unharmed. Finally, some crops are being genetically engineered to be more resistant to pests.

Implements for Harvesting Crops

Most cereal crops are harvested by using a combine— a machine that removes the fruiting heads, beats off the grain kernels, and cleans the grain as the combine moves through the fields. The cleaned grain is accumulated in an attached grain tank.

Wheat and other cereal crops are harvested by a com­bine which, as it moves along the rows, picks the ears from the stalks and husks them. The ears are then trans­ferred either to a sheller, which removes the kernels from the ear, or to a vehicle trailing behind the machine.

Hay harvesting usually requires several steps. First, the hay is cut close to the ground with a mower. After drying in the sun, most hay is baled. In baling, the pick­up baler lifts the hay to a conveyor that carries it to a baling chamber, which compresses the hay into bales weighing up to 57 kg or more and ties each bale with heavy twine or wire. A machine called a field chopper cuts down green hay or field-cured hay for use as animal feed. After being cut down, the hay is stored in a silo and allowed to ferment; this type of animal feed is nutritious and resistant to spoilage.

Specialized machinery is also used to harvest large root crops such as potatoes and sugar beet and to harvest fruits and vegetables. Some mechanical fruit-pickers that are used to harvest tree fruits, such as plums, cher­ries, and apricots shake the fruit tree, causing the fruit to fall on to a raised catching frame that surrounds the tree. Nut crops can also be harvested in this manner.

Use of agricultural machinery substantially reduces the amount of human labour needed for growing crops. The average amount of labour required per hectare to produce and harvest corn, hay, and cereal crops has fallen to less than a quarter of what was required only a few decades ago.

 


Предлоги, обозначающие движение

to движение по направлению к предмету (лицу), про­текающему процессу:

Come to me. — Подойдите ко мне.

from движение от предмета (лица), удаление от протека­ющего процесса:

Take this book from the table.— Убери книгу со стола. '

I come from Russia. — Я из России.

into движение внутрь ограниченного пространства:

Put the book into the bag. — Положи книгу в портфель.

out of движение из ограниченного пространства:

Take the book out of the table. — Достань книгу из стола.

on(to) /onto движение на поверхность:

Snow fell onto the ground. — Снег падал на землю.

through через, сквозь: Не went in through the door. — Он вошел через дверь.

 

Предлоги, обозначающие место

at местонахождение у предмета (лица), а также там, где протекает определенный процесс:

I am sitting at the table. — Я сижу у стола.

I study at school. — Я учусь в школе.

The pupils are at the lesson. —Ученики на уроке.

in местонахождение внутри ограниченного простран­ства:

Не is in the office. — Он в офисе.

The books are in the bag. — Книги в портфеле.

on местонахождение на поверхности:

The book is on the desk. — Книга на столе.

under местонахождение под другим предметом:

The book is under the table. — Книга под столом.

across через: My school is across the street. — Моя школа нахо­дится через дорогу.

above Местонахождение над другим предметом:

There is a lamp above the table. — Над столом висит лампа.

between между: Between us. — Между нами.

in front of местонахождение предмета (лица) впереди другого предмета (лица)

There is a telephone in front of him. — Перед ним стоит телефон.

behind местонахождение предмета (лица) позади другого предмета (лица),

There is a sport ground behind our school. — За нашей школой спортплощадка.

around местонахождение одного предмета вокруг другого предмета:

We are sitting around the table. — Мы сидим вокруг стола.

beyond по ту сторону: Beyond the limits of the city. — За пределами города.

over над, через, сверх: There is a bridge over the river. — Над рекой мост.

near вблизи, около, рядом с, возле, за:

She is sitting near the table. — Она сидит за столом.

up вверх: Up the river. — Вверх по реке.

down вниз: Down the river. — Вниз по реке.

 

Предлоги времени

in внутри временного отрезка: In April, in 1999. — В апреле, в 1999 году.

in через некоторое время: in an hour, in two days через час, через два дня

at в (точка во времени) at 5 o’clock, at midnight – в 5 часов, в полночь

on в (с названием дней недели, датами): on Monday, on the 10th of February - в понедельник, 10 февраля

by к определенному моменту: by 8 o'clock tomorrow — к 8 часам завтра

from... till / from... to... от... до: from 5 till 6 o'clock/from 5 to 60' clock — с 5-ти до 6-ти

for в течение (отрезок времени): for an hour — в течение часа

during во время (чего-либо): during the lesson— во время урока

after после (чего-либо): after work — после работы

before перед (чем-либо): before the lesson- перед уроком

within внутри, в рамках: within a month — в течение месяца

 

Прочие предлоги

при, около, посредством: by the window, by plane — около окна, самолетом

with вместе с: with a friend– с другом

for для: I'll do it for you. - Я сделаю это для тебя.

 





©2015-2017 poisk-ru.ru
Все права принадлежать их авторам. Данный сайт не претендует на авторства, а предоставляет бесплатное использование.
Нарушение авторских прав и Нарушение персональных данных

Обратная связь

ТОП 5 активных страниц!