Comparing Feed forward and Feedback Controllers

by David M. Koenig

 

The feed forward controller can act on a measured event (such as the drain value position) before it shows up as a disturbance in the process output (such as the tank level). Unfortunately, the feed forward controller has no idea how well it did. Furthermore, it is often rather difficult to measure the disturbance-causing event. Sometimes there will be many disturbance-causing events, some of which cannot be measured. Also, it is not always clear how the algorithm should react to the measured disturbance-causing event. Often, each feed forward control algorithm is a special custom application. Finally, if perchance, the feed forward control algorithm acts mistakenly on a perceived disturbance-causing event it can actually generate a more severe disturbance.

The feedback controller cannot anticipate the disturbance. It can only react “after the damage has been done.” If the disturbance is relatively constant there may be a good chance that the feedback controller can slowly compensate for it and perhaps even remove it. As we will show in the next couple of pages, there are some disturbances that simply should be left alone. The feedback controller can tell how well it has been done and it can often react appropriately. Unlike the case with feed forward control algorithms, there are a few well-known, easily applied feedback control algorithms that, under appropriate conditions can deal quite effectively with disturbances.

 

Koenig D. Practical Control Engineering: Guide for Engineers, Managers, and Practitioners. – McGraw-Hill, 2009. – 538 p. (P. 7-8).

17. Translate the text in the written form:

Types of Feedback Control Systems

by B. Kuo & F. Golnaraghi

 

Feedback control systems may be classified in a number of ways, depending upon the purpose of the classification. For instance, according to the method of analysis and design, control systems are classified as linear or nonlinear, and time-varying or time-invariant. According to the types of signal found in the system, reference is often made to continuous-data or discrete-data systems, and modulated or unmodulated systems. Control systems are often classified according to the main purpose of the system. For instance, a position-control system and a velocity-control system control the output variables just as the names imply. In a particular case, the type of control system is defined according to the form of the open-loop transfer function. In general, there are many other ways of identifying control systems according to some special features of the system. It is important to know some of the more common ways of classifying control systems before embarking on the analysis and design of these systems.

 

Kuo, B., Golnaraghi, F. Automatic Control Systems. – 9^th Ed. – Wiley, 2010. – 944 p. (P. 11).

18. Make a sentence out of the two parts:

 

1) Feedback -

 

2) Driver -

 

3) Transducer -

 

 

a) a defect in a circuit, which prevents the current from following the intended course.

b) an electromagnetic device controlling a larger current or activating other devices in the same or another electric circuit.

c) an instrument for measuring, comparing or controlling electric voltage.

 

4) Potentiometer

 

5) Relay –

 

6) Detector -

 

7) Amplifier -

 

 

8) Regulator –

 

9) Fault -

 

10) Assembly -

 

d) a device used to increase the strength of an electric signal.

e) any machine part that communicates motion to another part.

f) any device that transmits energy from one system to another or converts the energy in form.

g) a mechanism for controlling the movement of machinery, the flow of liquids, gases, electricity, steam, etc.

h) an apparatus for indicating the presence of smth., as electric waves.

i) a fitting together of parts to make the whole.

 

j) a transfer of [part of the output of an active circuit or device back to the input.

UNIT THREE

Texts: History of the word “cybernetics”; The History of Cybernetics; Cybernetics; The Heritage and Revival of Cybernetics; Сфера кибернетики; Обратнаясвязь

Grammar: The Complex Subject and the Complex Object; the Construction for + infinitive

1. Memorize the words:

Rudder – руль

to assure – убеждать; уверять; обеспечивать; гарантировать

root – корень

to denote – обозначать, означать

to manage – управлять

 

2. Translate the text and tell what the word “cybernetics” stands for:

History of the word "cybernetics"

Cybernetics is the discipline that studies communication and control in living beings and the machines built by man. A more philosophical definition, suggested by Louis Couffignal in 1958, considers cybernetics as "the art of assuring efficiency of action". The word cybernetics was reinvented by Norbert Wiener in 1948 from the Greek kubernetes, pilot, or rudder. The word was first used by Plato in the sense of "the art of steering" or "the art of government ". Ampère used the word cybernetics to denote "the study of ways of governing." One of the very first cybernetics mechanisms to control the speed of the steam engine, invented by James Watt and Matthew Boulton in 1788, was called a governor, or a ball regulator. Cybernetics has in fact the same root as government: the art of managing and directing highly complex systems.

 

3. Memorize the words:

a cone shaped float – конусообразный поплавок

to run dry – работать всухую

self-regulatory device – саморегулирующееся устройство

knowledge management – управление знаниями

to keep great minds busy – занимать умы великий людей

a holding tank – бак-сборник

 

4. Translate the text and speak about the history of cybernetics:

The History of Cybernetics

As it is known, the first artificial automatic regulatory system, a water clock, was invented by the mechanic Ktesibios (2-1 century BC) from ancient Greece. In his water clocks water flowed from a source such as a holding tank into a reservoir, then from the reservoir to the mechanisms of the clock. The device used a cone shaped float to monitor the level of the water in its reservoir and adjust the rate of flow of the water accordingly to maintain a constant level of water in the reservoir, so that it neither overflowed nor was allowed to run dry. This was the first artificial truly automatic self-regulatory device that required no outside intervention between the feedback and the control of the mechanism.

The word cybernetics was first used in the context of self-governance by Plato (428-348 BC) in the Laws to signify the governance of people. In 1834 Andre Marie Ampere, the French physicist and mathematician, systematized the human knowledge of that time under different numbers. Under number 83 he listed a science that was to deal with the methods of regulating society. Ampere termed this science “cybernetics” from the Greek word “kubernetes” meaning “steersman” or “pilot”. This literal translation embodies much of the modern relevance of the cybernetics principles.

After Ampere, however, the term “cybernetic” was forgotten until it appeared again in 1948 in a book of the well-known American mathematician Norbert Wiener (1894-1964). His book was entitled “Cybernetics or Control and Communication in the Animal and the Machine” The name ‘cybernetics’ was coined by N. Wiener to denote the study of “teleological mechanisms”, that is machines with corrective feedback. Wiener was part of a group of very brainy people of various specialties – psychology, mathematics, sociology, philosophy, knowledge management. So, the modern study of cybernetics began at the intersection of neurology, electronic network theory and logic modeling. Wiener popularized the social implications of cybernetics, drawing analogies between automatic systems such as a regulated steam engine and human institutions. The laws described by N. Wiener as the basis if cybernetics greatly interested scientists of many specialties.

The foundations of cybernetics were laid and its basic principles were formulated in the works of mathematicians, physicists, physicians and engineers. The works of American scientists Claude Shannon and John von Neumann were of outstanding importance.

Thus, the study of control and response to complex systems has been keeping great minds busy for thousands of years, and Wiener seems to be regarded as the chief modern architect.

5. Answer the questions using the information from these texts:

1) When did the first automatic regulatory system appear? 2) How did Ktesibios’s system operate? 3) When was the word ‘cybernetics’ first used? 4) Who used it and how? 5) What kind of classification did Ampere do? 6) What does the word ‘cybernetics’ mean? 7) Who is considered to be the founder of cybernetics? 8) What did Wiener denote by the word ‘cybernetics’? 9) What sciences contributed to its development?

 

6. Translate and memorize the following word combinations:

The first artificial automatic regulatory system; a water clock; ancient Greece; a holding tank; to use a cone shaped float; to monitor the level of the water; to overflow; to run dry; self-regulatory device; to adjust the rate of flow of the water; accordingly; to maintain a constant level of water; to require no outside intervention; feedback; self-governance; to systemize the human knowledge; the methods of regulating society; to term the science; steersman; literal translation; to embody relevance of the cybernetics principles; very brainy people; knowledge management; intersection of sciences; electronic network theory; the social implications of cybernetics; to draw analogies; a regulated steam engine; to lay the foundation; to formulate the basic principles; to be of outstanding importance; control and response to complex systems; to keep great minds busy.

 

7. Translate the following sentences paying attention to the Complex Object:

1) We want the information to be measured in bits. 2) They supposed the system to be out of order. 3) They believe the data to be reliable. 4) I should like this reaction to be repeated. 5) In this case we may suppose the chain of symbols to be endless. 6) The computing equipment enabled investigators to process the received data much quicker. 7) I have never heard anyone give so much interesting information in one report. 8) The students observed the liquid change. 9)Scientists make new electronic machines store information, handle calculations and even control production process.

8. Translate into English using the Complex Object:

1) М. Фарадей предполагал, что луч света меняет свою полярность, проходя через намагниченный кристалл. 2) Мы наблюдали, как работает этот прибор. 3) Ампер полагал, что ток течет от положительного полюса к отрицательному. 4) Теперь мы знаем, что тепло это форма энергии. 5) Я чувствую, что эта проблема – трудная. 6) Никто не ожидал, что он станет физиком. 7) Мы бы хотели, чтобы вы рассказали нам об автономном управлении. 8) Мы знаем, что Белл был учителем. 9) Никто не заметил, как двигатель остановился из-за того, что выключили ток.

 

9. Translate the following sentences paying attention to the Complex Subject:

1 ) The water seems to be boiling. 2) The new power plant is expected to have been put onto operation and it proved to be of great practical importance. 3) Coal is considered to be a valuable fuel. 4) The electrolytes appear to change greatly when the current passes through them. 5) Light and radio waves are said to be of similar nature. 6) The application of this device is unlikely to give better results. 7) This new approach to the problem discussed appears to be the most satisfactory.

10. Translate into English using the Complex Subject:

1) Они, наверняка, уже проанализировали результаты эксперимента. 2) Чувствительность прибора оказалась слабой. (poor). 3) Сообщили, что оптический эквивалент транзистора уже изобрели. 4) Известно, что тела расширяются при нагревании. 5) Кажется, что это легкая задача. 6) Оказалось, что изменения температуры были вызваны (affect) работой компьютера. 7) Говорят, что пластик используется вместо металлов. 8) Мы, конечно, решим эти задачи. 9) Было обнаружено, что сопротивление ртутного провода исчезает при охлаждении до - 269°С. 10) Он, наверное, не понимает это правило. 11) Вряд ли мы проведем этот эксперимент. 12) По-видимому, этот компьютер вышел из строя. 13) Они, вероятно, примут участие в конференции. 14) Он, кажется, изучил вопрос очень хорошо. 15) Несомненно, новый метод будет очень эффективным. 16) Оказывается, свойства этих металлов гораздо лучше.

 

11.Translate the following sentences:

1) It is very good for this engine to have been repaired before the experiment began. 2) This is a good possibility for us to utilize the electronic equipment for speeding up the process of calculation. 3) It required some more experiments for the engineers to prove the precision of the results obtained. 4) It was for our engineer to decide what kind of computer to utilize for such calculations. 5) Much more heat is required for the water to boil than for the needle to become white-hot. 6) Electromotive force is necessary for the current to flow along the circuit.

12. Translate into English:

1) Мы ожидали, пока установят новое оборудование. 2) Необходимо огромное количество энергии для того, чтобы эта реакция произошла. 3) Для того, чтобы этот процесс произошел, температура должна быть очень высокой. 4) Нам очень трудно получить эту информацию.

 

13. Memorize the words:

behavioral responses – поведенческий отклик (реакция)

self-determination – самоопределение

principles of regulating and responding – принцип регулирования и реакции

the way we relate to our world – то, как мы соотносимся с нашим миром

tolerance and variety of responses – допуск и разнообразие откликов

the subject matter – предмет (кибернетики)

the controlled object – объект управления

feed-forward and feedback – прямая и обратная связь

the applied cybernetics – прикладная кибернетика

power supply – источник питания

 

14. Read the text and say what the science cybernetics studies:

Cybernetics

I. As we know, contemporary cybernetics began as an interdisciplinary study connecting the fields of control systems, electrical network theory, mechanical engineering, logic modeling, evolutionary biology and neuroscience in the 1940s. It was N. Wienner who has combined the main cybernetics perspectives which have been developed by many and various people over the past two thousand years. He defined the principles of regulating and responding to mechanical and electrical systems, social and governmental systems, human and animal nervous systems, and human and animal social systems. The cybernetics concept is relevant to the modern development of management and one’s own role and potential within systems of all kinds. The organization in which we work, the world in which we live, the people around us – these are all systems. Cybernetics is central to our understanding of life, organizations and the way we relate to our world.

The first law of cybernetics is considered to be the following: “The unit within the system with the most behavioral responses available to it, controls the system”. This law has great significance especially in understanding and developing greater individual self-determination; and greater understanding, tolerance and variety of responses to situations and people around us. And this all is essential for our ability to interact and respond effectively within work and beyond. The first law of cybernetics is one of the most powerful maxims for living a happy productive and successful life. And while ‘successful’ is of course a matter of individual interpretation, cybernetics provides the key to achieving it, whatever your interpretation might be. It’s a very powerful concept – in a way cybernetics is the source of thoughtful choice over unquestioning instinct.

II. Thus, as we see, cybernetics is the science of general principles of control, means of control and human society. The subject matter of cybernetics is a cybernetic system, including a variety of interconnected elements which are able to store, process and exchange information. The examples of cybernetic systems may serve an automatic regulator, a computer, a human brain and the human society.

Any control process, to be used on a cybernetic system, implies continuous information exchange between the controlled object (a machine or a human muscle) and the control unit (an automatic regulator or the brain of a living organism. The control process represented on the scheme below involves the transmission, accumulation, storage and processing of information about the controlled object. The laws governing control processes are based on such fundamental concepts as feed-forward and feedback. The controlled object receives information from the control unit through the feed-forward and modifies its behavior. The information transmitting process about the effects or results of the control operations is achieved through the feedback.

 

Feed-forward

 

Feedback

 

Cybernetics can be subdivided into theoretical cybernetics and technical one. The cornerstones of theoretical cybernetics are information theory, the theory of algorithms and the theory of automatic systems which investigates the methods of building data-processing systems. Technological cybernetics is concerned with design and operation of technical control systems and computer hardware. The applied cybernetics is associated with the use of theoretical and technological cybernetics for solving specific control tasks to be found in industry, power supply, transport, communication, etc.

Cybernetics studies human thinking to create algorithms for computer programming. It also studies the automata design principles and investigates the possibilities of using them to mechanize human mental processes. The main goal of cybernetics is to achieve maximum automation of control processes in various spheres of human activity.

 

15. Look through the text and answer the questions using the information from the text:

1) Why can cybernetics be called an interdisciplinary science? 2) What fields does contemporary cybernetics connect? 3) Who is considered the founder of cybernetics? 4) What did he do to develop the science? 5) What kind of science is cybernetics? 6) What is the main law of cybernetics? 7) What is the subject matter of cybernetics? 8) What does any control process used in a cybernetic system imply? 9) What fundamental concepts govern control processes in cybernetics? 10) What do theoretical and technological cybernetic deal with?

16. Find in the previous texts the English equivalents for:

Саморегулирующееся устройство; следить за уровнем воды; искусственная система автоматического регулирования; бак-сборник; водяные часы; регулировать скорость потока воды; соответственно; поддерживать постоянный уровень воды; работать всухую; обратная связь; самоуправление; рулевой; буквальный перевод; социальная причастность; регулируемый паровой двигатель; заложить основу; иметь значение; занимать умы великих умов; нельзя не упомянуть.

Понятие «кибернетика»; теория электрических сетей; междисциплинарная наука; машиностроение; правительственные системы; определять принципы регулирования и отклика; в пределах возможных систем; понимание жизни; самоопределение; процесс передачи информации; разнообразие реакций; взаимодействовать; эффективно реагировать; мощные (сильнодействующие) правила; плодотворная и успешная жизнь; средства управления; предмет «кибернетика»; запоминать и обрабатывать информацию; человеческий мозг; человеческое общество; непрерывный обмен информацией; объект управления; управляющее устройство; прямая связь; обратная связь; модифицировать поведение.

 

17. Translate the text and think of its title:

There are many definitions of cybernetics and many individuals who have influenced the definition and direction of cybernetics. Norbert Wiener, a mathematician, engineer and social philosopher, coined the word "cybernetics" from the Greek word meaning "steersman." He defined it as the science of control and communication in the animal and the machine. Ampere, before him, wanted cybernetics to be the science of government. For philosopher Warren McCulloch, cybernetics was an experimental epistemology concerned with the communication within an observer and between the observer and his environment. Stafford Beer, a management consultant, defined cybernetics as the science of effective organization. Anthropologist Gregory Bateson noted that whereas previous sciences dealt with matter and energy, the new science of cybernetics focuses on form and pattern. For educational theorist Gordon Pask, cybernetics is the art of manipulating defensible metaphors, showing how they may be constructed and what can be inferred as a result of their existence.

Cybernetics takes as its domain the design or discovery and application of principles of regulation and communication. Cybernetics treats not things but ways of behaving. It does not ask "what is this thing?" but "what does it do?" and "what can it do?" Because numerous systems in the living, social and technological world may be understood in this way, cybernetics cuts across many traditional disciplinary boundaries. The concepts which cyberneticians develop thus form a metadisciplinary language by which we may better understand and modify our world.

Several traditions in cybernetics have existed side by side since its beginning. One is concerned with circular causality, manifest in technological developments--notably in the design of computers and automata--and finds its intellectual expression in theories of computation, regulation and control. Another tradition, which emerged from human and social concerns, emphasizes epistemology--how we come to know-- and explores theories of self-reference to understand such phenomena as autonomy, identity, and purpose. Some cyberneticians seek to create a more humane world, while others seek merely to understand how people and their environment have co-evolved. Some are interested in systems as we observe them, others in systems that do the observing. Some seek to develop methods for modeling the relationships among measurable variables. Others aim to understand the dialogue that occurs between models or theories and social systems. Early work sought to define and apply principles by which systems may be controlled. More recent work has attempted to understand how systems describe themselves, control themselves, and organize themselves. Despite its short history, cybernetics has developed a concern with a wide range of processes involving people as active organizers, as sharing communicators, and as autonomous, responsible individuals.

18. Translate the text into English in the written form:

Сфера кибернетики

from Wikipedia

 

Объектом кибернетики являются все управляемые системы. Системы, не поддающиеся управлению, в принципе, не являются объектами изучения кибернетики. Кибернетика вводит такие понятия, как кибернетический подход, кибернетическая система. Кибернетические системы рассматриваются абстрактно, вне зависимости от их материальной природы. Примеры кибернетических систем—автоматические регуляторы в технике, ЭВМ, человеческий мозг, биологические популяции, человеческое общество. Каждая такая система представляет собой множество взаимосвязанных объектов (элементов системы), способных воспринимать, запоминать и перерабатывать информацию, а также обмениваться ею. Кибернетика разрабатывает общие принципы создания систем управления и систем для автоматизации умственного труда. Основные технические средства для решения задач кибернетики— ЭВМ. Поэтому возникновение кибернетики как самостоятельной науки (Н. Винер, 1948) связано с созданием в 40-х гг. XX века этих машин, а развитие кибернетики в теоретических и практических аспектах— с прогрессом электронной вычислительной техники.

Кибернетика является междисциплинарной наукой. Она возникла на стыке математики, логики, семиотики, физиологии, биологии, социологии. Ей присущ анализ и выявление общих принципов и подходов в процессе научного познания. Наиболее весомыми теориями, объединяемыми кибернетикой, можно назвать следующие:

- теория передачи сигналов;

- теория управления;

- теория автоматов;

- теория принятия решений;

- синергетика;

- теория алгоритмов;

- распознавание образов;

- теория оптимального управления.

19. Translate the text and define the main problems touched upon in it: