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BMFA 2413Introduction To Control
Systems
Lecturer
Silah Hayati binti KamsaniFaculty of Manufacturing Engineering
Department of Robotics and AutomationEmail: [email protected] Phone: 06-
3316401
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Learning Outcomes
At the end of this course, students should be ableto:
Identify basic control system theory such as transferfunction, Laplace Transform, stability analysis, linearequation, time respond and others.
Model linear and time invariant system using frequencydomain and state space method.
Model linear and time invariant system for mechanicaland electromechanical systems by manipulating block
diagrams and signal flow diagram. Apply commercially available mathematical software to
solve control theory problems.
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References
Text books: Nise, S Norman, Control Systems Engineering, 5th Edition, John
Wiley & Sons Inc., United State of America, 2008.
Ogata, Katsuhiko, Modern Control Engineering, 4th Edition,
Prentice Hall, 2002
Palm W. J, Control System Engineering, John Wiley, 2002
Bishop, Dorf, Modern Control Systems, 10th Edition, PrenticeHall, 2005.
Ogata, Katsuhiko, MATLAB for Control Engineers, Prentice Hall,
2008.
Computer Usage:
MATLAB and Simulink Programming
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Course EvaluationsNO. COURSE WORK PERCENTAGE, %
1 Laboratory activities x 6Laboratory work basis in maximum 2 persons/group withindividual short lab report
10
2 Project x 1Group activities with maximum 4 persons/groupTo measure the students understanding and analysis on aproblem-based task
15
3 Test x 2Test on students knowledge and understanding about therecent topic.
20
4 Practical Assessment x 1Hands-on test on students knowledge and understandingabout the laboratory and practical activities.
10
5 Assignment x 1Critical review on any journal/article regarding controlsystem (max. 2 persons/group)
5
6 Final ExamUnderstanding, applications, problem solving and decision
making.
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TOTAL 100
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Introduction
Control systems are important and are present almost everywhere in our
daily lives.
Examples of man-made control systems: CD player, radio antenna,
rockets/missiles, robots, oven, room air condition.
Examples of God-created control systems : level of adrenalin in the human
body, entry of light through the human eye, holding and carrying things
using hand, human riding a bicycle.
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Introduction
Generally, control system can be classified into threecategories;
nature control system created by God (example human body immunization, etc.)
automatic / modern control system created by human(example auto pilot flight operation, satellite system,space shuttle, robotic system and etc.)
combination between nature and automatic controlsystem (example human driving of car)
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What are the advantages ofcontrol system?
Advantages of control systems - 4 primary reasons:
Power amplification Radar rotation.
Remote control Robot for picking material in
hazardous environment.
Convenience of input form Any type of input -
mechanical, electrical, air etc.
Compensation of disturbance - Measure thedisplacement of the antenna cause by wind and return
the antenna to the position commanded by the input.
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The earliest complete control systems are water clock invented and a double
acting pump by al-Jazari, 1206.
History of Control Systems
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a. Early elevators were
controlled by hand ropes or
an elevator operator. Here, a
rope is cut to demonstrate
the safety brake, an
innovation in earlyelevators;
b. Modern Duo-lift elevators
make their way up the
Grande Arche in Paris,
driven by one motor, witheach car counterbalancing
the other. Today, elevators
are fully automatic, using
control systems to regulate
position and velocity.Photos courtesy of UnitedTechnologies Otis Elevator.
History of Control Systems
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What is SystemA system might be considered as an assemblage of
components that provide interactions.
M
f (t) Input
Spring
(K)
ViscousDamper
(C)
x (t)Output
Mass spring damper system
Disassembly system
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What is Control SystemA control system consists ofsubsystems and processes (orplants) assembled for the purpose ofcontrolling theoutputs of the processes.
Input Sensing DevicesInput Sensing Devices Output Load DevicesOutput Load Devices
Visual &Sound
Signals
Visual &Sound
Signals
Local PLC
cont rol ler
Local
Process
Cont rol
System
Local PC
Central
PLC
cont roller
Comput er
System
Other part
of indus try
Indus trial
network
(high level)
Indus trial
network
(middl e level)
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What are the areas of applicationof control engineering?
Examples of application:
Home appliances: microwave, telephone, computer, VCD player, clocketc..
Industry: CNC machine tool, robot, conveyor, AGV etc..
Biological: Animals, plants, ants, human ..etc
Social: Country, districts, society, etc.
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Controlled variable the quantity/condition that is measured andcontrolled (normally controlled variable is the output of the system)
Manipulated variable the quantity/condition that is varied by thecontroller so as affect the value of the controlled variable
Plants a piece of equipment/set of a machine functioning together,which perform a particular operation
Process progressively continuously operation that consists of aseries of controlled action to achieve a particular result.
Systems a combination of components that act together andperform a certain objective
Definitions of Terms in
Control Systems
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Disturbance a signal that tends to adversely affect the valueof the output of the system. There are two types ofdisturbance; internal disturbance generated within the system external disturbance generated outside the system and is
an input
Automatic control system a control system that is self-
regulating without human intervention
Process control system an automatic regulating system in
which the output is a variable such as temperature, pressure,
flow, liquid level or pH is called process control system
Definitions of Terms in
Control Systems
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Fundamental blocks
Represents components or subsystems such as controller, amplifier, etc.
Each block may have one or more inputs which affects the output of the
components.
The input and output signals may have the same form or they may be
changed into a different form depending on the function of the component or
subsystem.
System Representation
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Take-off point
V V
V
-allows a signal to be taken from any
components output. Assume that it does not
load any components output (the signals are not
changed).
Summing junction V=V1-V2+
-
V1
V2
-allows 2 or more signals to beadded/subtracted. The +, - sign indicates
whether the signals are added or
subtracted.
Components/subsystems
System Representation
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Components/subsystems (others)Controllers, plants
Actuators
Sensors
Amplifiers
Signals in Control Systems
Input/reference [u(t),r(t),R(s)] represented by an arrow pointing into
the block, can be manipulated or controlled
Output [y(t), c(t), C(s)] represented by an arrow pointing away from theblock, the needed signal
Error [e(t)=r(t)-c(t)]
Feedback
Disturbances/noise is also an input signal that cannot be controlled
System Representation
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Input
Transducer
Input
R(s)+ Plant+
Noise 1 Noise 2
++ Output
C(s)
+ Controller
Summer
Output
Transducer
-
Error (E(s))
Plant
System Representation
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Examples of system
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Examples of systemrepresentation
A motorcycle can be considered as a system.
The main input to the system is the throttle angle and the main output is the motorcycle speed.
This system can be represented as follow:
Fuel flow rate, q Motorcycle speed, n
The arrows represent variable while the components arerepresented by blocks.
Each blockhas an input and an output variable.
The output variables of a component can bethe input variable for another component ! !!
Throttle Engine Gear Wheel
Throttle angle, Engine speed, N Wheel speed, n
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This control function or the interference to the process is introduced by an
organization of parts (including operators in manual control) that, when
connected together is called the Control System.
Depending on whether a human body (the operator) is physically involved in
the control system, they are divided into Manual Control and Automatic
Control. Due to its efficiency, accuracy and reliability, automatic control is
widely used in chemical processed.
Control Systems Categories
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It can be seen that this control system, completed by theoperator, possesses
the following functions:
Measurement
This is essentially an estimate or appraisal of the process
being controlled by the system. In this example, this is
achieved by the right hand of the operator.Comparison
This is an examination of the likeness of the measured
values and the desired values. This is carried out in the
brain of the operator.
Control Systems Functions
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Computation
This is a calculated judgment that indicates how much the measuredvalue and the desired values differ and what action and how much
should be taken. In this example, the operator will calculate thedifference between the desired temperature and the actual one.Accordingly the direction and amount of the adjustment of the valveare worked out and the order for this adjustment is sent to the lefthand from the brain of the operator. If the outlet water temperatureis lower, then the brain of the operator will tell the left hand to open
the steam valve wider. If there is any disturbance, or variation of flowrate in water to the shower inlet, some adjustment must be made tokeep the outlet water temperature at a desired value.
Control Systems Functions
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Correction
This is ultimately the materialization of the order for the adjustment.
The left hand of the operator takes the necessary actions following
the order from brain.
Therefore, for a control system to operate satisfactorily, it must have
the abilities of measurement, comparison, computation and
correction.
Of course, the manual operation has obvious disadvantages e.g. the
accuracy and the continuous involvement of operators. Althoughaccuracy of the measurement could be improved by using an
indicator, automatic control must be used to replace the operator. In
industry, it is automatic control that is widely used.
Control Systems Functions
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Firstly, we can use a temperature measurement device to measure the
water temperature, which replaces the right hand of the operator. This
addition to the system would have improved accuracy.
Instead of manual valves, we use a special kind of valve, called a
control valve, which is driven by compressed air or electricity. This will
replace the left hand of the operator.
We put a device called a controller, in this case a temperature
controller, to replace the brain of the operator. This has the functions
of comparison and computation and can give orders to the control
valve.
The signal and order connections between the measurement device,
control valve and controller are transferred through cables and wires,
which replace the nerve system in the operator.
Automatic Control Systems
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Examining the automatic control system, it is found that it
contains the following hardware.
Sensor - a piece of equipment to measure system variables.
It serves as the signal source in automatic control.
Controller - a piece of equipment to perform the functions of
comparison and computation.
Control Element - a piece of equipment to perform the control
action or to exert direct influence on the process. This element
receives signals from the controller and performs some type of
operation on the process. Generally the control element is
simply a control valve.
Control Systems Hardware
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Associated with a control system are a number of different types of variables.
First we have the Controlled Variable. This is the basic process value being regulated by
the system. It is the one variable that we are specially interested in - the outlet water
temperature in the example above.
An important concept related to the controlled variable is the Setpoint. This is the
predetermined desired value for the controlled variable. The objective of the control
system is to regulate the controlled variable at its setpoint.
To achieve the control objective there must be one or more variables we can alter or
adjust. These are called the Manipulated Variables. In the above example this was the
input hot water flow rate.
Conclusively, in the control system we adjust the manipulated variable to maintain thecontrolled variable at its setpoint. This meets the requirement of keeping the stability of
the process and suppressing the influence of disturbances.
Control Systems Principle
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What is the objective of control
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What is the objective of controlsystems?
Objective of Control System
A control system provides an output or response for a given input orstimulus.
It is designed such that the output variable equals to the desired variable.
(Example: Air-Conditioning System desire temperature is 16C,so the output temperature of air-conditioner system should be16C)
A controlled variable normally determines the inputand outputof a controlsystem.
Control strategies are needed to achieve this objective.
Basically there are two control strategies open loop control and closed
loop control.34
Ex.: Elevator buttons and the desired level (Input), actual level ofelevator (Output), elevator level -> controlled variable.
O L C l S
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Open Loop Control Systems (OLCS):The output signal of an OLCS is not fed back to influence
the control action.
Inputtransducer
Input
R(s)
+ Plant+
Noise 1 Noise 2
++ Output
C(s)Controller
The control action of an OLCS depends only on the input
signal. OLCS are not capable of filtering disturbances/noise.
Examples: toaster, washing machine, studying time, electric
fan, traffic light, ceiling fan and oven.
Open Loop Control Systems
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Open loop control system a control system in which thecontrol/regulating action is independent of the output (output has no
effect on the control action)
In other words; the output of open loop control system is not
compared with the reference input
Input transduceris functioning to converts the form of the input tothat used by controller.
The controlleris functioning to drives the process/plant
The inputcan be called reference/set pointand the outputcan be
called controlled variable
Disturbances also called as input to the system and affect theoutput/controlled variable. Open loop controlled system cannot
compensate the disturbance and do not correct for the disturbance
signal .
Example : Washing machine operated on time basis, does not
measure the output signal (cleanliness of the clothes)
Open Loop Control Systems
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In general, any control systems that operated on a time basis isopen loop control system
Open loop control system is easier to build because systemstability is not a major problem
Advantages & Disadvantages of open loop control system; Advantages:
simple construction
easy maintenance no stability problem convenient when output is hard to measured & not economy
to produced
Disadvantages: the output may different from desired input if there is
calibration error causes by disturbance/changes re-calibration is required from time to time to maintain the
required output
Open Loop Control Systems
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Example of oven open
loop systemSWITCH
1
21
3
1 ~10000C2 ~
20000C3 ~30000C
CONTROLLER
PROCESS
OVEN
Oven system
Example of oven open loop
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Example of oven open loopsystem
Open Loop System:
The temperature of the oven is controlled by setting the switch toposition 1, 2 and 3.The controller is designed such that for each setting differentelectrical current is supplied to the heating element whichcorrespondingly generating the heat to the oven and set thetemperature 1000C, 2000C and 3000C response.If the desired temperature by user is 2000C the user will set theswitch to position 2. The performance of this system will dependon the accuracy of the controlled designed .
Switch Controller Oven
Set point Temp (T)
Current (i)
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Closed loop control system control system in which the
control/regulating action is influence by the output
In other word; the output is fed back to the input reference for
comparison The actuating error signal (differential between input and the
output signal) is fed back to the controller to reduce the error
and bring the output of the system to desired value
Input transduceris functioning to converts the form of the
input to that used by controller.
Output transducer/sensoris functioning to measure the
controlled variable/output response and convert into the form
used by controller (example ; potentiometer, thermistor,
tachometer, and etc.)
Closed Loop Control Systems
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At the 1st summing junction, the output and disturbance
which fed back via feedback path is compared with the
input reference where the output signal is subtracted from
the input signal. The result called actuating signal/error.
The controller will make correction and drive theplant/process if any error/actuating signal generated. If no
error, plants response is already the desired response.
Example : Room temperature control by measuring the
actual room temperature and comparing it with reference
temperature (desired temperature), the thermostat turns
the heating/cooling equipment on/off in such way to ensure
the room temperature at comfortable level.
Closed Loop Control Systems
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Feedback control systems are often referred to as closed
loop control system. A system that maintains a prescribed
relationship between output and input and using the
difference by comparing them is called feedback controlsystem.
There are numerous example of closed loop/feedback control
system and not limited to engineering but can be found in
various non-engineering fields.
Feedback Control Systems
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Examples of oven closed
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Examples of oven closedloop system
Switch Controller Oven
Set point
Operator
Sensor
Manually
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OLCS vs CLCS
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Open Loop System Closed Loop System
Does not have the feedback path. Have the feedback path.
Low accuracy. Greater accuracy
Sensitive to noise, disturbances andchanges in the environment.
Less sensitive to noise, disturbances andchanges in the environment.
The system cannot compensate and
correct disturbance
The system can compare the output
response with the input and make acorrection if there is any difference
Simple and inexpensive Complex and expensive
The differences between open and closed-loop system are
shown in table below;
OLCS vs. CLCS
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Car Speed Control
The car speed is controlled by pressed or depressed theaccelerator pedal, which is, controls the fuel quantity to carengine.
Figure below shows the equivalent block diagram for car speed
controller(humandriver)
carengine
transducer(speedometer
)
i/p reference(desiredspeed)
o/p response(actualspeed)
Control Systems Example
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The following term can identify from the block diagram;
Process/plant engine car
Controller human driver
Sensor/transducer speedometerInput reference desired speed (example: 110 km/h)
Controlled variable actual speed
Manipulated variable fuel quantity
The controller (human driver) is measure the car speed through speedometer.
If the speed of the car exceed than desire speed (example 110 km/h), thedriver will depressed the accelerator pedal.
Car speed control is classified as closed loop/feedback control system
Control Systems Example
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Liquid Level Control
Figure below shows the block diagram of simple liquid levelcontrol
The objective of this control system is to maintain/controlthe liquid level in the tank at desire value
controlvalve
liquid tank
level sensor
error /actuating signal
actual level
actual level
controller
Control Systems Example
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From the block diagram, the following term can be identifying;
Controlled variable liquid level
Manipulated variable liquid flow
Transducer level sensor
Process/plant liquid tank
The fluid level in the tank cannot be directly controlled. It can be controlled
only by changing/manipulating the water flow into the tank
The differences between input reference (set point) and output signal
generate an error / actuating signal.
If the error signal is positive, it indicates to controller that actual level is lower
than desired level. Than its drive controller to open the control valve to allow ahigher flow rate into the tank
If the actual level is higher than desired level, the control valve turn close to
reduce the inflow rate
The liquid level control can classify as closed loop/feedback control system.
Control Systems Example
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Analysis and Design
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Objectives
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Control systems are dynamic: it responds to the input by going through atransient phase before settling to the steady state phase. Normally, we would
like the steady state signal to be the same as the input signal.
transient response steady state
Three major analysis and design objectives are:
1. Producing the desired transient response: Transient response is the case when the plant is
changing from one steady state to another, when there are changes in the input signal.
Example: elevator.
2. Achieving stability: A system that can produce a consistent/steady output is a stable
system. An unstable system is harmful to the plant and may cause serious accidents.
3. Reducing steady state error: Steady state response only exists for stable systems. An
important characteristic for design is the steady state error. Example: an elevator that
does not stop at the same level at the floor may cause serious accidents to its passengers.
Control Systems Response
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Characteristics
Response Characteristics of elevator:
Transient response Gradual increase from 1st floor to 4th floor.Steady state response When the elevator reaches to the desiredfloor.
Steady state error The accuracy of the elevators leveling with thefloor.
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Input:desiredlevelOutput: actualelevator level(control variable)
Control Systems Design:
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Time,s
Floor
G
1
2
3
4
5
6
7
y g
Analysis & Objectives
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Control Systems Design:
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Draw aschematic.
Step 3
Simplify theblock
diagrams.
Step 5 Step 4
Determine aphysical
system from
requirements.
Step 1 Step 2
Analysis anddesign.
Step 6
Build aprototype.
Step 7
Draw afunctional
block
diagram.
Draw aschematic.
Form themathematical
model andblock
diagrams.
Step 4
Simplify the
blockdiagrams.
Step 5
Analysis and
design.
Step 6
Process
54
Design Process of Control
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System HOW TO START THE ANALYSIS OF DESIGN PROCES:
1.Transform requirements into physical system2.Draw a functional block diagram
3.Create a schematic4.Develop a mathematical model (Block Diagram)
1.Kirchhoffs voltage law2.Kirchhoffs current law3.Newtons laws
5.Reduce the block diagram6.Analyze and design
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MathematicalModel
Mathematical model of Spring Damper System:K, C and M are spring constant, damping coefficient and massresponse. The variables are force, f (t) and displacement x (t).
We would like to develop a mathematical model relating f (t) as inputand x (t) as the output.
f (t) Input
x (t) Output
f (t) Input x (t) Output
?=f
x
K C
M
Spring damper
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Mathematical
Model
Free Body Diagram of Spring Damper System:
K, C and M are spring constant, damping coefficient and massresponse. The variables are force, f (t) and displacement x (t).We would like to develop a mathematical model relating f (t) as inputand x (t) as the output.
f s (t)
Spring damper
M
f d (t)
f (t)
x(t)
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Testwaveforms
used in
controlsystems
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The End
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