Modern Control - Lec 01 - Introduction to Control System

1. LECTURE (1)
Introduction to Control
Systems
Assist. Prof. Amr E. Mohamed

2. Objectives
 In this lecture, we lead you through a study of the basics of control
system.
 After completing the chapter, you should be able to
 Describe a general process for designing a control system.
 Understand the purpose of control engineering
 Examine examples of control systems
 Understand the principles of modern control engineering.
 Realize few design examples.
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3. What is “Control”?
 Make some object (called system, or plant) behave as we desire.
 Imagine “control” around you!
 Room temperature control
 Car driving
 Voice volume control
 Balance of bank account
 “Control” (move) the position of the pointer
 etc.
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4. Application Automatic Control
 Automatic control has played a vital role in the advance of engineering
and science.
 Applications:
 Robotic systems
 Aircraft
 Missile guidance systems
 Industrial processes
 Transportations
 … etc.
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5. What is “Automatic Control”?
 Not manual!
 Why do we need automatic control?
 Convenient (room temperature, laundry machine)
 Dangerous (hot/cold places, space, bomb removal)
 Impossible for human (nanometer scale precision positioning, work
inside the small space that human cannot enter, huge antennas
control, elevator)
 It exists in nature. (human body temperature control)
 High efficiency (engine control)
 Many examples of automatic control around us
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6. Manual Liquid-level control system
A manual Control Systems for regulating the level of fluid in a tank by adjusting the
output valve. The operator views the level of fluid through a port in the side of the tank.
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7. Automatic Liquid-level control system
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8. 8
controller
Pneumatic
Valve
Float
Water Tank
Desired
Level
Actual
Level
Plant
Controlled variableManipulated
variable
Reference input
Feedback Element
Feedback Signal

9. Example: laundry machine
 A laundry machine washes clothes, by setting a program.
 A laundry machine does not measure how clean the clothes become.
 Control without measuring devices (sensors) are called open-loop
control.
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Laundry
Machine
Program setting
(Input)
Washed clothes
(Output)

10. Open-loop control systems
 Open-loop control systems. Those systems in which the output has no
effect on the control action are called open-loop control systems.
 In other words, in an open-loop control system the output is neither
measured nor fed back for comparison with the input.
 In the presence of disturbances, an open-loop control system will not
perform the desired task.
 Open-loop control can be used, in practice, only if the relationship
between the input and output is known and if there are neither internal
nor external disturbances.
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11. Open-loop control systems
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Controller Actuator Process
output or
controlled
variable
Disturbance
Control Signal
Plant
input or
reference input filter
(transducer)
Fig. 1.2 An open-loop system

12. Open-loop control systems
Advantages:
 Simple construction, ease of maintenance, and less expensive.
 There is no stability concern.
 Convenient when output is hard to measure or measuring the output
precisely is economically not feasible. (For example, in the washer
system, it would be quite expensive to provide a device to measure the
quality of the washer's output, cleanliness of the clothes).
Disadvantages:
 Disturbances and changes in calibration cause errors, and the output
may be different from what is desired.
 Recalibration is necessary from time to time.
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13. Closed-loop control systems
 Closed-loop control systems. Feedback control systems are often
referred to as closed-loop control systems.
 In practice, the terms feedback control and closed-loop control are
used interchangeably.
 In a closed-loop control system the actuating error signal, which is the
difference between the input signal and the feedback signal , is fed to
the controller so as to reduce the error and bring the output of the
system to a desired value.
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14. Closed-loop (feedback) control
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_
+ +
sensor or
output transducer
sensor noise
summing junction
or comparator
error or
actuating signal
Controller Actuator Process
output or
controlled
variable
Disturbance
Control
Signal
Plant
input or
reference input filter
(transducer)

15. Closed-loop control systems
Advantages:
 High accuracy
 Not sensitive to disturbance
 Controllable transient response
 Controllable steady state error
Disadvantages:
 More Complex, and More Expensive.
 Possibility of instability.
 Need for output measurement.
 Recalibration is necessary from time to time.
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16. Definitions.
 Systems - A system is a combination of components that act together
and perform a certain objective.
 Control System – An interconnection of components forming a system
configuration that will provide a desired response.
 Plants – A plant may be a piece of equipment, perhaps just a set of
machine parts functioning together, the purpose of which is to perform a
particular operation.
 Process – The device, plant, or system under control. The input and
output relationship represents the cause-and-effect relationship of the
process.
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Process
OutputInput

17. Definitions.
 Disturbances - A disturbance is a signal that tends to adversely affect
the value of the output of a system. If a disturbance is generated within
the system, it is called internal, while an external disturbance is
generated outside the system and is an input.
 Controlled Variable – is the quantity or condition that is measured and
controlled. the controlled variable is the output of the system.
 The Manipulated Variable – is the quantity or condition that is varied by
the controller so as to affect the value of the controlled variable.
Normally,
 Control - means measuring the value of the controlled variable of the
system and applying the manipulated variable to the system to correct or
limit deviation of the measured value from a desired value.
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18. Definitions.
 Feedback Control - Feedback control refers to an operation that, in the
presence of disturbances, tends to reduce the difference between the
output of a system and some reference input and that does so on the
basis of this difference.
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19. CONTROL SYSTEM DESIGN
 The following table shows the control
system design process.
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20. CD player speed control: Open-Loop
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21. CD player speed control: Closed-Loop
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22. TEMPERATURE CONTROL SYSTEMS
 The temperature in the electric furnace is measured by a thermometer,
which is an analog device. The analog temperature is converted to a digital
temperature by an A/D converter. The digital temperature is fed to a
controller through an interface. This digital temperature is compared with
the programmed input temperature, and if there is any error, the
controller sends out a signal to the heater, through an interface, amplifier,
and relay, to bring the furnace temperature to a desired value.
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23. Analog Vs Digital Control Systems
 Analog
 Digital
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24. Case Study Antenna Azimuth Position Control System
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25. Case Study Antenna Azimuth Position Control System
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26. Case Study Antenna Azimuth Position Control System
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