b lecture1 introduction automatic control system

Automatic Control Theory

Please Note:

Two broad categories of control:

Manual Control

Automatic Control --- A machine(or system) works by machine-self, not by manual operation.

Please Note:

This course introduces analyzing and designing of automatic control systems .

Topics include the properties and advantages of automatic control systems, time-domain and frequency-domain performance measures, stability and degree of stability, the Root locus method and frequency-domain design.

Please Note:

Matlab will be required extensively. If you have not used it before,then start practicing. We suggest that everyone become familiar with the use of MATLAB

Reasons for Using Automatic Control:

Reduce workload

Perform tasks people cant

Reduce the effects of disturbances

Reduce the effects of plant variations

Stabilize an unstable system

Improve the performance of a system (time response)

Improve the linearity of the system

Many vehicles (spacecraft, aircraft, rockets) and aerospace processes (propulsion) need to be controlled just to function.

Example: the F-117 does not even fly without computer control, and the X-29 is unstable.

There are also many stable systems that simply require better performance in some sense (e.g., faster, less oscillatory), and we can use control to modify this behavior.

Reasons for Using Automatic Control:

Examples of Automatic Control Systems

* Operating principle

* Feedback control A water-level control system

Example #1

x2

x3

Signal(variable)

xxxComponents(devices)

+-

+x1 eAdders (comparison)

e=x1+x3-x2

x

The block diagram description for a control system : Convenience


amplifier Motor Gearing Valve

Actuator

Water

container

Process controller

Float

measurement

(Sensor)

Error

Feedback

signal

resistance comparator

Desired

water level

Input

Actual

water level

Output


Example #1

The block diagram discription of a water-level control system


A DC-Motor control system

Example #2

* Operating principle

* Feedback control

M

M

+

-

+

regulator

trigger

rectifier

DCmotor

techometer

load

e

Uf (Feedback)

ur

Fig. 1.4

ua

Uk=k(ur-uf)


The block diagram discription of the DC-motor control system

Desired rotate speed n

Regulator Trigger Rectifier DCmotor

Techometer

Actuator

Processcontroller

measurement (Sensor)

comparator

Actual rotate speed n

Error

Feedback signal

Referenceinput ur

Output n

Fig. 1.9

auk ua

uf

e

Example #2

Identify the control goal:

Identify the variables to control:

Position the reader head to read the date stored on a track on the disk.

The position of the read head.


Actuator

motor

Arm

Spindle Track a

Track b

Head slider

Rotation

of arm Dis

k

A disk drive read system

Example #3

It is obvious :

a closed loop system

not a open loop system

Control

device

Actuator

motor

Read

arm

sensor

Desired

head

position

error Actual

head

position

Block diagram of a disk drive read system


Actuator

motor

Arm

Spindle Track a

Track b

Head slider

Rotation

of arm Dis

k Example #3

Automatic control systems can be designed to hold an output steady or to track a desired reference signal.

Regulator: keep output at a steady, known value.

Tracking or servo system: Make output track a reference system.

Fundamental Structure of Control Systems

We can further categorize control systems as either open-loop or closed-loop.

Closed-loop controllers(or feedback controllers) compute the control action based on the measured output of the system being controlled.


Open loop control systems

Features: Only there is a forward action from the input to the output.


Controller Actuator Process

Disturbance(Noise)

Input r(t)

Reference desired output

Output c(t)(actual output)

Controlsignal

Actuatingsignal

uk uact

Fig. 1.10

Closed loop (feedback) control systems

Features:

1) measuring the output (controlled variable) . 2) Feedback.

not only there is a forward action , also a backward action between the output and the input (measuring the output and comparing it with the input).


Controller Actuator Process

Disturbance(Noise)

Input r(t)

Reference desired output

Output c(t)(actual output)

Controlsignal

Actuatingsignal

uk uact

Fig. 1.11

measurementFeedback signal b(t)

+-

(+)

e(t)=r(t)-b(t)

Notes: 1) Positive feedback; 2) Negative feedbackFeedback.

Please Note:

Typically think of closed-loop control

so we would analyze the closed-loop dynamics.

Note that a typical control system includes the sensors, actuators, and the control law.

Feedback Control System

Comparison between the reference input and the feedback signal results in an actuating signal that is the difference between these two quantities.

The actuating signal acts to maintain the output at the desired value.

This system is called a closed-loop control system.

Measurement

Dynamic process

Disturbance

Controller Output

Sensor

Actuator Reference

Control

signal

Sensor noise

Plant

Components in a typical control system

Measurement

Dynamic process

Disturbance

Controller

Output

Sensor

Actuator

Reference Control

signal

Sensor noise

Plant

Typically, we are interested in cases where the plant and

controller are linear and time-invariant, or can be modeled

as such. Then we can represent components as transfer

functions.(We will learn this later)

Feedback Control of Dynamic System

types of control systems

1) linear systems versus Nonlinear systems.

2) Time-invariant systems vs. Time-varying systems.

3) Continuous systems vs. Discrete (data) systems.

4) Constant input modulation vs. Servo control systems.

Basic performance requirements of control systems

1) Stability. 2) Rapidness (instantaneous characteristic).

3) Accuracy (steady state performance).

Please Note:

Stability

Please Note:

0 1 2 3 4 5 6-0.5

0

0.5

1

1.5

2

2.5

Rapidness (instantaneous characteristic)

Please Note:

0 1 2 3 4 5 6 7 80

0.2

0.4

0.6

0.8

1

1.2

1.4

Accuracy (steady state performance).

Please Note:

0 1 2 3 4 5 6 7 80

0.2

0.4

0.6

0.8

1

1.2

1.4

Main Content

1. Introduction to Control Systems

2. Mathematical Models of Systems

3. Time-Domain Analysis of Control Systems

4. The Root Locus Analysis

5. Frequency-Domain Analysis

6. Design of Feedback Control Systems

This Course Credit 3

Teaching methods are composed of lecture in class and exercises/experiment after class.

Grading

Homework 20% (Due on Mondays at class)

Participation 10%

Midterm exam 30% (at approximately week8)

Final exam 40%

Pre-request Course

Calculas

Engineering Mathmatics (Complex Variables Functions)

Teaching and Grading

References

1. Farid Golnarahi ,Benjamin C. KuoAutomatic Control Systems, Ninth edition, John Wiley & Sons Inc,2009.

2. Prof. Steven Hall, course materials for 16.06 Principles of Automatic Control, Fall 2012. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology.

References

3. Richard C. Dorf, Robert H. Bishop, Modern Control Systems, 12th Edition, Prentice Hall,2010.

(you can use an old edition)

4. Robert H. Bishop, Modern Control System Analysis and Design Using Matlab and Simulink,Tsinghua University Press,2003

Classroom NMB F205

Time Monday 16:00PM - 17:45PM every week

Thursday 8:00AM 9:45AM biweekly

Please Note:

b lecture1 introduction automatic control system

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