Text c Feedback

Essential to all automatic-control mechanisms is the feedback principle, which enables a designer to endow a machine with the capacity for self-correction. A feedback loop is a mechanical, pneumatic, or electronic device that senses or measures a physical quantity such as position, temperature, size, or speed, compares it with a preestablished standard, and takes whatever preprogrammed action is necessary to maintain the measured quantity within the limits of the acceptable standard. The feedback principle has been used for centuries. An outstanding early example is the flyball governor, invented in 1788 by the Scottish engineer James Watt to control the speed of the steam engine. In this device a pair of weighted balls is suspended from arms attached to a spindle, which is connected by gears to the output shaft of the engine. At the top of the spindle the arms are linked by a lever with a valve that regulates the steam input. As the engine speeds up beyond the desired rate, causing the spindle to rotate faster, the flyballs are driven upward by centrifugal force. The action of the flyballs partly closes the input valve, reducing the amount of steam delivered to the engine. The common household thermostat is another example of a feedback device. In manufacturing and production, feedback loops require that acceptable limits or tolerances be established for the process to be performed; that these physical characteristics be measured and compared with the set of limits; and, finally, that the feedback system be capable of correcting the process so that the measured items comply with the standard. Through feedback devices, machines can start, stop, speed up, slow down, count, inspect, test, compare, and measure. These operations are commonly applied to a wide variety of production operations that can include milling, boring, bottling, and refining.

Words and expressions

feedback principle - обратная связь; обратное питание

to endow - обеспечивать

feedback loop - контур обратной связи

flyball governor - центробежный маховик-регулятор

arm - рычаг, коромысло; траверса

spindle - шпиндель; палец

shaft - вал; стержень

lever - балансир; коромысло

milling - фрезерование; измельчение

boring - бурение; расточка

bottling - разливка

refining - очистка; рафинирование

Exercise 1

Ответьте на вопросы:

1. By means of what principle a machine can be provided with the capacity for self-correction?

2. What is the principle of a feedback loop operation?

3. When was the feedback principle first introduced?

4. Who was the inventor of the flyball governor and what was it used for?

5. What was the principle of flyballs operation in James Watt’s stem engine?

6. Can we consider a household thermostat as a feed back device?

7. What functions can be performed by machine using feedback devices?

8. In what production operations are feedback devices used?

Exercise 2

Составьте предложения, используя данные выражения:

Automatic-control mechanism - feedback principle - mechanical device – pneumatic device - electronic device - to measure a physical quantity - a preestablished standard – to take a preprogrammed action - limits of the acceptable standard - limits or tolerances - physical characteristics - wide variety of production operations.

Exercise 3

Переведите на русский язык следующие предложения:

1. Feedback controls are widely used in modern automated systems.

2. A feedback control system consists of five basic components.

3. The input to the system is the reference value, or set point, for the system output.

4. The sensing elements are the measuring devices used in the feedback loop to monitor the value of the output.

5. This device consists of two metal strips joined along their lengths.

6. The two metals possess different thermal expansion coefficients.

7. Bimetallic strip is capable of measuring temperature.

8. There are many different kinds of sensors used in feedback control systems for automation.

9. The purpose of the controller and actuating devices in the feedback system is to compare the measured output value with the reference input value and to reduce the difference between them.

10. In general, the controller and actuator of the system are the mechanisms by which changes in the process are accomplished to influence the output variable.

11. These mechanisms are usually designed specifically for the system and consist of devices such as motors, valves, solenoid switches, piston cylinders, gears, power screws, pulley systems, chain drives, and other mechanical and electrical components.

12. The switch connected to the bimetallic strip of the thermostat is the controller and actuating device for the heating system.

13. When the output (room temperature) is below the set point, the switch turns on the heater.

14. When the temperature exceeds the set point, the heat is turned off.

Exercise 4

Текст на самостоятельный перевод:

Computer Use

The creation of the computer has greatly facilitated the use of feedback loops in manufacturing processes. Computers and feedback loops have promoted the development of numerically controlled machines (the motions of which are controlled by punched paper or magnetic tapes) and machining centers (machine tools that can perform several different machining operations). More recently, the introduction of microprocessors and computer combinations have made possible the development of computer-aided design and computer-aided manufacture (CAD and CAM) technology. When using these systems a designer draws a part and indicates its dimensions with the aid of a special light pen on a televisionlike cathode-ray tube computer display screen. fter the sketch has been completed to the satisfaction of the designer, the computer automatically generates a magnetic or punched tape that directs a machining center in machining the part.

Another development that has further increased the use of automation is that of flexible manufacturing systems (FMS). FMS extends automation to companies in which small production runs do not make full automation economically feasible. A computer is used to monitor and govern the entire operation of the factory, from scheduling each step of production to keeping track of parts inventories and tool use. Automation has also had an influence on areas of the economy other than manufacturing. Small computers are used in systems called word processors, which are rapidly becoming a standard part of the modern office. This technology combines a small computer with a cathode-ray display screen, a typewriter keyboard, and a printer. It is used to edit texts, to type form letters tailored to the recipient, and to manipulate mailing lists and other data. The system is capable of performing many other tasks that increase office productivity.