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Automatic Control



Introduction

Dr. Aly Mousaad Aly

Department of Mechanical Engineering

Faculty of Engineering, Alexandria University

Instructor


Instructor: Dr. Aly Mousaad Aly


Classes and office hours: every Tuesday


Email:
aly.mousaad@pua.edu.eg



Teaching assistants:

Eng.
Khaled

Hassib

(ME221)

Eng.
Nermine

E.
Shehata

(EE290)

Eng.
Sherif

Omar (EE290)



Slides 1: Introduction

2

Course Materials

Slides:
Will be available online .


Text Books:

K. Ogata, Modern Control Engineering,
3
rd

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, 11
th

ed. Pearson Education Inc., 2008.

Slides 1: Introduction

3

Grading


Class participation, quizzes and assignments


First midterm exam


Second midterm exam


Final examination


Slides 1: Introduction

4

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
.

Slides 1: Introduction

5

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.


Slides 1: Introduction

6

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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7

Example: temple doors opened by fire
on an altar

Hero

(or
Heron
)
of Alexandria

(10

70 AD)




Slides 1: Introduction

8

Example: vending machine

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9

Heron's COIN automat

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
.


Slides 1: Introduction

10

Laundry

Machine

Program setting

(Input)

Washed clothes

(Output)

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.

Slides 1: Introduction

11

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.




.


Slides 1: Introduction

12

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.

Slides 1: Introduction

13

Example: antenna azimuth

Slides 1: Introduction

14

Example: antenna azimuth

Slides 1: Introduction

15

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. Letter
-
sorting 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.).


Slides 1: Introduction

16

Basic elements of control loop










The role of the controller is to make the output
following the reference in a “satisfactory” manner even
under disturbances.


Slides 1: Introduction

17

Controller

Actuator

Plant

Sensor

Ref.

Input

Output

Error

Disturbance

playing sport

Slides 1: Introduction

18

Better Sensors

Provide
better
Vision

Better
Control

Provides
more finesse by combining
sensors

and



actuators

in more intelligent ways

Example:

Better Actuators

Provide
more
Muscle

Course goals











Slides 1: Introduction

19

Controller

Actuator

Plant

Sensor

Ref.

Input

Output

Error

Disturbance

Mathematical
model

Modeling

Controller

Design

Implementation

Analysis

Procedure

Slides 1: Introduction

20

Summary


Introduction:

Control essentiality

Examples of control systems

Open loop versus closed loop control systems


Next Lecture:

Laplace Transformation Review

Slides 1: Introduction

21