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Automatic Control
Introduction
Dr. Aly Mousaad Aly
Department of Mechanical Engineering
Faculty of Engineering, Alexandria University
Instructor
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Instructor: Dr. Aly Mousaad Aly
Classes and office hours: every Tuesday
Email: [email protected]
Teaching assistants:
Eng. Khaled Hassib (ME221)
Eng. Nermine E. Shehata (EE290)
Eng. Sherif Omar (EE290)
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Course Materials
Slides: Will be available online .
Text Books: K. Ogata, Modern Control Engineering,
3rd edition, Prentice Hall, 1997.
References:
• N. Nise, Control Systems Engineering, John Wiley
& Sons, Inc., 2011.
• R.C. Dorf and R.H. Bishop, Modern Control
Systems, 11th ed. Pearson Education Inc., 2008.
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Grading
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Class participation, quizzes and assignments
First midterm exam
Second midterm exam
Final examination
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Why to study “Automatic Control”?
• The study of automatic control is essential for
students pursuing degrees in many engineering
disciplines (mechanical, electrical, structural,
aerospace, biomedical, or chemical).
• Applications of automatic control include, but not
limited to, aircraft, robots, civil engineering
structures, process control, …., etc.
• Automatic control has played a vital role in the
advance of engineering and science.
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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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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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Example: temple doors opened by fire
on an altar
Hero (or Heron) of Alexandria (10–70 AD)
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Example: vending machine
Heron's COIN automat
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Example: laundry machine
A laundry machine washes clothes, by setting a
program.
Program setting
(Input)
Laundry
Machine
Washed clothes
(Output)
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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Open-loop control systems
Advantages:
• Simple construction and ease of maintenance.
• 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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Closed-loop (feedback) control
In this approach, the quantity to be controlled, say
C, is measured, compared with the desired value, R,
and the error between the two, E = R - C used to
adjust C. This means that the control action is
somehow dependent on the output.
.
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Example: autopilot mechanism
Its purpose is to maintain a specified
airplane heading, despite atmospheric
changes. It performs this task by
continuously measuring the actual
airplane heading, and automatically
adjusting the airplane control surfaces
(rudder, ailerons, etc.) so as to bring
the actual airplane heading into
correspondence with the specified
heading.
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Example: antenna azimuth
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Example: antenna azimuth
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Feedback and Feedforward
• Feedback mechanism: Ability of a machine to
self-correct its operation by using some part of its
output as input.
• Feedforward mechanism: Ability of a machine to
examine the raw materials that come to it and
then decide what operations to perform. Lettersorting machines in post offices are of this type.
The machine sorts a letter by reading the zip code
on the address and then sending the letter to the
appropriate subsystem. (other examples include,
metro gate, automatic coin machine, etc.).
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Basic elements of control loop
Ref.
Disturbance
Error
Controller
Actuator
Input
Plant
Output
Sensor
The role of the controller is to make the output
following the reference in a “satisfactory” manner even
under disturbances.
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Example: playing sport
Better Sensors
Provide better Vision
Better Actuators
Provide more Muscle
Better Control Provides more finesse by combining sensors and
actuators in more intelligent ways
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Course goals
Ref.
Disturbance
Error
Controller
Actuator
Input
Plant
Output
Sensor
Implementation
Modeling
Controller
Design
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Mathematical
model
Analysis
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Procedure
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Summary
• Introduction:
Control essentiality
Examples of control systems
Open loop versus closed loop control systems
• Next Lecture:
Laplace Transformation Review
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