Lecture1 Introduction

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Page : 1EE406 Control Systems Lecture 1 : Introduction to Control Engineering

UCSI University Faculty of EngineeringKuala Lumpur, Malaysia Department of Mechatronics

Lecture 1Introduction to Control Engineering

Mohd Sulhi bin Azman

Lecturer

Department of Mechatronics

UCSI University

[email protected]

1 August 2011


Contents

Definitions

Open & closed loop systems

Dynamic vs static systems

Linear systems

Stable systems

Control system design process

Mathematical modelling


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Definitions

Control system is a device or set of devicesused to manage, command, direct or regulatethe behaviour of other devices or systems.

This field is wide. It is also applied in economy,finance, political science, physics, mathematicsand biological sciences.

There are three things that define controlsystems: input, systems and output.


Control System Representation

We can represent a control system in block diagrams, interms of input, system and output.

The output may or may not be equal to the specifiedresponse by the input.

Thus, the purpose of control system is regulate thesystem to produce the desired output.

PROCESSInput Output


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Types of Control System

Broadly speaking, there are three major type ofcontrol systems: Man made control system

Natural control system

Mixed (combination) control system


Man Made Control System

The system (technology) is created by human.

Example : electrical switch


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Natural Control System

Also called biological control. The type of control is available in nature.

Example : pointing a finger.

Input : precise direction of the object

Output : actual pointed direction


Mixed (Combination) Control System

The system is controlled by nature (human)through man-made technology.

Example : driving a car


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Application Examples

Home heating or air-conditioning,controlled by a thermostat.

Home entertainment system withbuilt-in control.

Cruise (speed) control of anautomobile.

Electronic voltage regulator.

Automatic bread toaster.

Photographic automatic focus control.

Altitude control of space vehicle. Automatic washing machine.

Law and order.


Type of Control System

Two types : open loop and closed loop.

Open loop : systems that utilizes a device tocontrol the process without using feedback.

Closed loop : systems that uses a measurementof the output (usually a sensor) and compares itwith the desired input.


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Open Loop System

Also known as feed-forward controlsystem.

Characteristics: Simplest (and cheap too!) type of

control

Contains no feedback

The output is not affected by the input

Application examples: Simple electric switch

Kettle or water heating devices Mobile phone

Word processor

Alarm clock


Typical Open Loop Block Diagram

We can generally design or draw a block diagram for anysystem provided that we know the input and the output.

Contains no feedback.

Sometimes, the input is also called the desired input orthe reference input.

The output is sometimes called the actual output oractual response.

ControllerInput OutputPlant


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Example 1 : Kettle

It is a merely an on-off device.

Block diagram:

Source : Warwick, An Introduction to Control Systems


Example 2 : Mobile Phone

It is an open loop system.

Why?1. Phone received call/signals.

2. As the phone is turned on, it will make connection withsatellite until the signal (call) is terminated by the phoneoperator (human).

3. The phone is unable to turn itself off even after aconversation between humans have ended.

4. Hence, it is an open loop system.


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Example 3 : Word Processor

Control type : open loop system

Why? The monitor continues to display output characters

on the computer monitor if the human give suitableinput via keyboard.

No input, then no output.


Closed Loop System

Also known as the feedback system.

The system uses the measurement of the actual outputto compare with the input, hence producing a veryeffective output.

The block diagram representation is given as follows:

ControllerInput OutputPlant

Measurement


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Example Application of Closed-Loop System

Example applications: Washing machine

Oven

Driving an automobile

Law and order

Why are the above example falls in the categoryof closed-loop system?


Example 4 : Air Conditioner Control

Control type : Closed loop.

Why? It is a self-regulating machine

performing the operation with and

without the need of the human. This machine will keep the

surrounding temperature to that ofthe preset value.

Sensor is used to maintain thetemperature in which the air-conditioner is placed.


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Example 5 : Driving a Car

Control Type : Closed Loop.

A person steering an automobile,assuming his or her eyes are wideopen, by looking at the autoslocation on the road and makingthe appropriate adjustments.

Block diagram:

Source : Dorf & Bishop, 2007.


Example 6 : Law & Order

Control type : closed loop, because it has a feedback mechanism.

Block diagram:

HUMAN SOCIALBEHAVIOUR

CONTROLLERPolice, Army, Media, Judiciary, Public

Opinion, Education, Peer, Friends,Parents

ETHICSLaws, Regulations, Rules, Ordinances, Orders,

Statutes, Constitution, By-Laws, Codes,Manners, Etiquette

INPUT OUTPUT

Source : Spier (2001)


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Example 7 : Jogging System

BrainInput

(joggingdirection)

Output (actualjogging direction)Feet & Leg

Visual sensory(eyes)


Example 8 : Water Level System


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Example 9 : Traffic Light Control System

The idea is to minimize the waiting time.Furthermore, it is also intended to make thetraffic flow smooth.

Many control techniques

can be used: intelligent

control system is one of

them.


Input and Output System

Sometimes, we might have one input and oneoutput, but there are cases where we mighthave multiple input and multiple output.

The one (single) input and one (single) output issometimes called the SISO system.

On the other hand, the multiple input andmultiple output is sometimes called the MIMOsystem.


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Example 10 : SISO and MIMO system

The following example illustrates the application intelecommunication engineering.

SISO system:

MIMO system:


Classes of Control Systems

We can also categorize a control system in two(2) classes: servomechanism and regulators.

Servomechanism is a power amplifying feedback

device in which the controlled variable is amechanical position or time derivative ofposition such as velocity or acceleration.

A regulator is a system where the referenceinput is constant for a long period of time.


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Servomechanism

Usually, we use servo motors forservomechanism applications.

Characteristics: Closed loop system.

The control action is dependent on the desired result.

Automatic (intelligent) control.

Measures position (displacement), velocity and/oracceleration.

Application example: (speed) cruise control of cars.

Water level system.


Servomechanism

Purpose of servomechanism: (1) accurate control of motion without the need for human

attendants (automatic control);

(2) maintenance of accuracy with mechanical load variations,changes in the environment, power supply fluctuations, and agingand deterioration of components (regulation and self-calibration);

(3) control of a high-power load from a low-power commandsignal (power amplification);

(4) control of an output from a remotely located input, withoutthe use of mechanical linkages (remote control, shaft repeater).


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Servomechanism

A servomechanism is typically a feedback system. The followingblock diagram illustrates the effect of servomechanism.

The constant speed control system of a DC motor is aservomechanism that monitors any variations in the motor's speedso that it can quickly and automatically return the speed to itscorrect value. Servomechanisms are also used for the controlsystems of guided missiles, aircraft, and manufacturing machinery.


Example 11 : Remote Antenna Positioning System

One example using a servomechanism is the positioning system for aradar antenna.

In this case, the controlled variable is the antenna position. Theantenna is rotated with an electric motor connected to thecontroller that is located some distance away. The user selects adirection, and the controller directs the antenna to rotate to aspecific position.


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Example 12 : Industrial Robot

Sophisticated robots use closed-loopposition systems for all joints.

An example is the industrial robot.

The robot has six independently

controlled axes (known as six degrees of freedom) allowing it to getto difficult-to-reach places. The robot comes with and is controlledby a dedicated computer-based controller.

This unit is also capable of translating human instructions into therobot program during the teaching phase. The arm can move frompoint to point at a specified velocity and arrive within a fewthousandths of an inch.


Example 13 : Regulators

Characteristics : closed loop system.

The input (setpoint) is heldconstant.

Application example: Car (power) window.

Human body temperature.

Automatic temperatureregulated over.

Human perspiration system.


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Static System

A static system is a deterministic system. The effects of inertia isignored.

Statics is branch of mechanics dealing with analysis of behaviour(usually in terms of displacements, strains, stresses and forces) ofbodies (mechanical systems, structures) while neglecting inertiaeffects. It is based on equilibrium conditions and the quantity timeplays no role in the analysis.

For a static system, the output response to an input that does notchange with time i.e. the input is held constant. Mathematically:

The output signal, y(t), at time t, depends on the value of input at time t.


Dynamic System

Dynamics is a branch of mechanics where due emphasis is paid toinertial effects as opposed to statics where such effects areignored.

A dynamic system may or may not be a deterministic andpredictable system. It is a system that evolve or change with

respect to time.

Generally, this particular system is described by differentialequations. Mathematically:

The output signal y(t), at time t, depends on past values of the input.


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Static vs Dynamic

Consider Figures (a) and (b) below:

For the resistor in Figure (a), the output e(t) is given as e(t)=R i(t).This output depends only upon the input at that time so the resistorrepresents memory-less or static system.

In the case of the capacitor, the output is expressed as:

It is evidently clear that a capacitor is a dynamic system. Theoutput depends on all past inputs.

1( ) ( )

t

e t i d C

=


Stable and Unstable System

If a system is brought to any particular initial condition(or state) and its response decays continuously to zerostate, the system is said to be stable of a particularkind called asymptotically stable.

If a system grows out of bound without any limit, thenthe system is an unstable system.

A stable system Unstable system Analogy


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Quiz

Classify on the stability of the following system:

t

f(t)

t

f(t)

t

f(t)

t

f(t)

System I

System II

System III

System IV


Linear vs Non-linear System

Linear system is a type of system that satisfies the principle ofsuperposition and homogeneity.

A non-linear system is not a linear system. Mathematically, it is aset of non-linear equations where the variables to be solved cannotbe written as a linear combination of independent components.


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Analysis of Control System

The main objective of a control system is toproduce a desired system, reducing errors andachieving systems stability.

What do we analyze in control system? Transient (temporary) response

Steady-state response

Stability


Transient Response

Also known as the natural response(remember differential equations?) it is the homogeneous solution.

Example : consider an elevator

going from the first floor to thefourth floor.

If a transient response is: Too slow passenger would be angry

Too fast you would be scared


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Steady State Response

An approximation to the desired response.

It is also the response that exist for a long timefollowing the given input signal.

In the previous lift example, the steady stateresponse is when the lift is about to reach thefourth floor.

We will also examine the steady state error,which is how accurately the system performs.


Output Response of Control System

Consider an example of an elevator going from the first floor to thefourth floor.

The output of the elevator can be represented as follows (Nise,2007)


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Analogy

Transient time thetime for your to searchfor your life.(soul searching process)

Steady state thestate where you areold, happy, attainsfinancial freedomand waiting to diepeacefully.

Baby (infant)

Adolescent

Adult

Old/mature/senior

Steady stateerror the

regrets that youhave. Have youachieved your

desired goal, oncedreamt when you

were younger?

God, friends, money, education, ambition etc.


Stability

It is a performance measure of a system.

If a system is stable, then it should operate properly.

An unstable system would lead to self-destruction or chaos. For example, inflight control system, if it is unstable, it would crash.

The total response of the system is given by:

For a particular control system to be useful, we want the natural responseto either approach to zero or oscillate. Sometimes, the natural responsewill go out of bound, hence the system would be unstable.

We can use mathematical techniques to analyze and control the stability ofa particular control system.

natural response forced response

h p

x

x x x

= +

= +


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Control System Design Process

The following are the steps as outlined by Nise(2007) in his book:


Control System Design Process

An alternative version is provided by Dorf &Bishop in his textbook:


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Mathematical Modeling

It uses mathematical language to describe a particular system.

Why? Important to gain understanding and further insight to the system,

hence enabling us to perform analysis.

Useful for prediction, formulation and simulation.

Useful for estimation and prediction of unforeseeable event that couldsomehow affect the system.

Type of mathematical model studied in control engineering: Classical form : representation of nth order differential equations

Transfer functions : the ratio between the output to the input, found aftertaking the Laplace transform of differential equations.

State space : a representation of a set of nth order simultaneous first-orderdifferential equations.


How to Start Modeling

Uses conservation laws a set of principlesdescribing certain quantities within an isolatedsystem that does not change with time.

It is a preserved (conserved) quantity.

Among the aspects conserved : mass,momentums, energy, charges etc.

Example : Kirchoffs Voltage and Current Laws.


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Control System Design Example

Antenna Azimuth Positioning System

Figure (a) : System Concept [source: Nise, 2007]



Figure (b) : Detailed System layout [source: Nise, 2007]


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Figure (c) : System Schematic [Source : Nise, 2007]



Figure (d) : Functional Block Diagram [source : Nise, 2007]


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Next Step

Textbook reference : Chapter 1.

Reading: Wu Hejun & Miao Changyun (2010) Design of intelligent traffic

light control system based on traffic flow. Proceedings of the201O International Conference on Computer and CommunicationTechnologies in Agriculture Engineering.

Homework 1 has been posted on the course website.Attempt them. You do not have to submit Homework 1 as

it will not be graded.

Thank You.


Wise Word

"The difference between a successful person and

others is not a lack of strength, not a lack ofknowledge, but rather in a lack of will.

Vincent T. Lombardi

Lecture1 Introduction

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