Файл: Н.Н. Курпешко Английский язык Методические указания для обучения студентов II курса (III семестр) специальности 180400.pdf

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Control Engineering Practice

Control engineering is concerned with the analysis and design of goaloriented systems. Therefore the mechanization of goal-oriented policies has grown into a hierarchy of goal-oriented control systems. Modem control theory is concerned with systems with the self-organizing, adaptive, robust, learning, and optimum qualities. This interest has aroused even greater excitement among control engineers.

The control of an industrial process (manufacturing, production, and so on) by automatic rather than human means is often called automation. Automation is prevalent in the chemical, electric power, paper, automobile, and steel industries, among others. The concept of automation is central to our industrial society. Automatic machines are used to increase the production of a plant per worker in order to offset rising wages and inflationary costs. Thus industries are concerned with the productivity per worker of their plant. Productivity is defined as the ratio of physical output to physical input. In this case we are referring to labor productivity, which is real output per hour of work. In a study conducted by the U. S. Commerce Department it was determined that labor productivity grew at an average annual rate of 2.8% from 1948 to 1984. In order to continue these productivity gains, expenditures for factory automation in the United States are expected to double from 5. 0 billion dollars in 1988 to 8. 0 billion dollars in 1992. World-wide, expenditures for process control and manufacturing plant control are expected to grow from 12.0 billion dollars in 1988 to 22.0 billion dollars in 1992. The U. S. manufacturers currently supply approximately one-half of worldwide control equipment.

The transformation of the U. S. labor force in the country's brief history follows the progressive mechanization of work that attended the evolution of the agrarian republic into an industrial world power. In 1820 more than 70% of the labor force worked on the farm. By 1900 fewer than 40% were engaged in agriculture. Today, less than 5% work in agriculture.

In 1925 some 588,000 people, about 1. 3% of the nation's labor force, were needed to mine 520 million tons of bituminous coal and lignite, almost all of it from underground. By 1980 production was up to 774 million tons, but the work force had been reduced to 208,000. Furthermore, only 136,000 of that number were employed in underground mining operations. The highly mechanized and highly productive surface mines, with just 72,000 workers, produced 482 million tons, or 62% of the total .

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The easing of human labor by technology, a process that began in prehistory, is entering a new stage. The acceleration in the pace of technological innovation inaugurated by the Industrial Revolution has until recently resulted mainly in the displacement of human muscle power from the tasks of production. The current revolution in computer technology is causing an equally momentous social change: the expansion of information gathering and information processing as computers extend the reach of the human brain.

The decline in the work week in the United States is illustrated by Fig. 1.8.

Figure 1.8. The work week in U. S. manufacturing industries shortened from 67 hours in 1860 to about 39 hours in 1984.

Control systems are used to achieve (1) increased productivity and (2) improved performance of a device or system. Automation is used to improve productivity and obtain high quality products. Automation is the automatic operation or control of a process, device, or system. We utilize automatic control of machines and processes in order to produce a product within specified tolerances.

The term automation first became popular in the automobile industry. Transfer lines were coupled with automatic machine tools to create long machinery lines that could produce engine parts, such as the cylinder block, virtually without operator intervention. In body-parts manufacturing, automatic-feed mechanisms were coupled with high-speed stamping presses to increase productivity in sheet-metal forming. In many other areas where designs were relatively stable, such as radiator production, entire automated lines replaced manual operations.

With the demand for flexible, custom production emerging in the 1980s, a need for flexible automation and robots is growing.

There are about 150,000 control engineers in the United States and also in Japan, and over 100,000 control engineers in the Soviet Union. In the

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United States alone, the control industry does a business of over thirty billion dollars per year! The theory, practice, and application of automatic control is a large, exciting, and extremely useful engineering discipline. One can readily understand the motivation for a study of modern control systems.

1.3. Examples of Modern Control Systems

Feedback control is a fundamental fact of modem industry and society. Driving an automobile is a pleasant task when the auto responds rapidly to the driver's commands. Many cars have power steering and brakes, which utilize hydraulic amplifiers for amplification of the force to the brakes or the steering wheel. The desired course is compared with a measurement of the actual course in order to generate a measure of the error. This measurement is obtained by visual and tactile (body movement) feedback. There is an additional feedback from the feel of the steering wheel by the hand (sensor). This feedback system is a familiar version of the steering control system in an ocean liner or the flight controls in a large airplane. All these systems operate in a closed-loop sequence. The actual and desired outputs are compared, and a measure of the difference is used to drive the power amplifier. The power amplifier causes the actuator to modulate the process in order to reduce the error. The sequence is such that if the ship, for instance, is heading incorrectly to the right, the rudder is actuated in order to direct the ship to the left. The system is a negative feedback control system, because the output is subtracted from the input and the difference is used as the input signal to the power amplifier.

There is a basic manually controlled closed-loop system for regulating the level of fluid in a tank. The input is a reference level of fluid that the operator is instructed to maintain. (This reference is memorized by the operator.) The power amplifier is the operator and the sensor is visual. The operator compares the actual level with the desired level and opens or closes the valve (actuator) to maintain the desired level.

1.4. 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

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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-procluced, 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.

1.5. 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

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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 it's 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.

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ЛИТЕРАТУРА:

1.U.S. News and World Report, October 8, 2000.

2.The Independent Guide to Personal Computing, December 6, 1999

3.Агабекян И.П. Английский для технических вузов. – Ростов н/Д, 2000.

Famous people of science and engeneering ....……………………...45

High level programming languages:

Fortran and pl/1…………………………………….……….………. 53

UNIT V………………………………………………………………64

Computers……………………………………………………….64

UNIT VI . ……………………………………………………………73

Modern computer technologies ...............................………………...73