Control Systems

William Bolton

• Publisher: Newnes
• Year: 2002
• Print ISBN: 9780750654616
• eBook ISBN: 9780080529981
• Topic: Technology & Engineering
• Subtopic: Calculus
• Index: Technology & Engineering

Working through this student-centred text readers will be brought up to speed with the modelling of control systems using Laplace, and given a solid grounding of the pivotal role of control systems across the spectrum of modern engineering. A clear, readable text is supported by numerous worked example and problems.* Key concepts and techniques introduced through applications* Introduces mathematical techniques without assuming prior knowledge* Written for the latest vocational and undergraduate courses

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Control systems

1.1 Introduction

The term automation is used to describe the automatic operation or control of a process. In modern manufacturing there is an ever increasing use of automation, e.g. automatically operating machinery, perhaps in a production line with robots, which can be used to produce components with virtually no human intervention. Also, in appliances around the home and in the office there is an ever increasing use of automation. Automation involves carrying out operations in the required sequence and controlling outputs to required values.

The following are some of the key historical points in the development of automation, the first three being concerned with developments in the organisation of manufacturing which permitted the development of automated production:

1. Modern manufacturing began in England in the 18th century when the use of water wheels and steam engines meant that it became more efficient to organise work to take place in factories, rather than it occurring in the home of a multitude of small workshops. The impetus was thus provided for the development of machinery.

2. The development of powered machinery in the early 1900s meant improved accuracy in the production of components so that instead of making each individual component to fit a particular product, components were fabricated in identical batches with an accuracy which ensured that they could fit any one of a batch of a product. Think of the problem of a nut and bolt if each nut has to be individually made so that it fitted the bolt and the advantages that are gained by the accuracy of manufacturing nuts and bolts being high enough for any of a batch of a nuts to fit a bolt.

3. The idea of production lines followed from this with Henry Ford, in 1909, developing them for the production of motor cars. In such a line, the production process is broken up into a sequence of set tasks with the potential for automating tasks and so developing an automated production line.

4. In the 1920s developments occurred in the theoretical principles of control systems and the use of feedback for exercising control. A particular task of concern was the development of control systems to steer ships and aircraft automatically.

5. In the 1940s, during the Second World War, developments occurred in the application of control systems to military tasks, e.g. radar tracking and gun control.

6. The development of the analysis and design of feedback amplifiers, e.g. the paper by Bode in 1945 on Network Analysis and Feedback Amplifier design, was instrumental in further developing control system theory.

7. Numerical control was developed in 1952 whereby tool positioning was achieved by a sequence of instructions provided by a program of punched paper tape, these directing the motion of the motors driving the axes of the machine tool. There was no feedback of positional data in these early control systems to indicate whether the tool was in the correct position, the system being open-loop control.

8. The invention of the transistor in 1948 in the United States led to the development of integrated circuits, and, in the 1970s, microprocessors and computers which enabled control systems to be developed which were cheap and able to be used to control a wide range of processes. As a consequence, automation has spread to common everyday processes such as the domestic washing machine and the automatic focusing, automatic exposure, camera.

This book is an introduction to the basic ideas involved in designing control systems with this chapter being an introduction to the basic idea of a control system and the elements used.

1.2 Systems

A car gear box can be thought of as a system with an input shaft and an output shaft (Figure 1.1(a)). We supply a rotation to the input shaft and the system then provides a rotation of the output shaft with the rotational speed of the output shaft being related in some way to the rotational speed of the input shaft. Likewise we can think of an amplifier as a system to which we can supply an input signal and from which we can obtain an output signal which is related in some way to the input signal (Figure 1.1(b)). Thus, we can think of a system as being like a closed box in which the workings of the system are enclosed and to which we can apply an input, or inputs, and obtain an output, or outputs, with the output being related to the input.

Figure 1.1 Systems: (a) a gear box, (b) an amplifier, (c) the formal picture defining a system

A system can be defined as an arrangement of parts within some boundary which work together to provide some form of output from a specified input or inputs (Figure 1.1(c)). The boundary divides the system from the environment and the system interacts with the environment by means of signals crossing the boundary from the environment to the system, i.e. inputs, and signals crossing the boundary from the system to the environment, i.e. outputs.

With an engineering system an engineer is more interested in the inputs and outputs of a system than the internal workings of the component elements of that system. By considering devices as systems we can concentrate on what they do rather than their internal workings. Thus if we know the relationship between the output and the input of a system we can work out how it will behave whether it be a mechanical, pneumatic, hydraulic, electrical or electronic system. We can see the overall picture without becoming bo...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Chapter 1: Control systems
• Chapter 2: System models
• Chapter 3: System response
• Chapter 4: System parameters
• Chapter 5: Frequency response
• Chapter 6: Nyquist diagrams
• Chapter 7: Controllers
• Appendix A: Differential equations
• Appendix B: Laplace transform
• Answers
• Index