Lecture 1 Introduction, control systems
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Transcript of Lecture 1 Introduction, control systems
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IntroductionControl systemLecture 1
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Lesson Objectives:
1. To define a control system.2. Open loop and closed loop systems
Lesson
Objectives:
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Lesson Objectives 01
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To define a controlsystem
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Control System DefinitionControl System DefinitionControl System DefinitionControl System Definition
A control system consists of subsystems and processes (or plants)assembled for the purpose of obtaining a desired output with desired
performance, given a specified input.
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Systems: collections of subsystems/components
Input: reference value/actuation signal/set point
Output: measured response/actual result
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Example
Consider an elevator
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A control system inits simplest form
The inputrepresents adesired output
When the eighth-floor button is pressed on the first floor, the elevator rises to the eighthfloor with a speed and floor levelling accuracy designed for passenger comfort
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Control system
The performance of the elevator can be seen from the elevator response
curve in the figure. Two major measures of performance are apparent: (1) the transient
response and (2) the steady-state error.
In our example, passenger comfort and passenger patience are dependent
upon the transient response. If this response is too fast, passenger comfort
is sacrificed; if too slow, passenger patience is sacrificed.
The steady-state error is another important performance specification
since passenger Safety and convenience would be sacrificed if the
elevator did not properly level.
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What is a control system?
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A control system consists
of subsystems and plantassembled for the purpose
of controlling the outputs
of the plants. Norman S.Nise
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Elements of a control system?
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Any control system consist of four elements:
1. The input is the desired response of acontrol system
2. The output is the actual response of acontrol system
3. Subsystem is any system that helps
controlling the output of the controlsystem
4. A plant is a system in which its output isthe one to be controlled
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Example of a control system
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Desiredlight
ActualLightOn-Off
Switch Bulb
Control System
Room
Desiredtemp
Actual
temp
Temp
Settingknob
AirConditioned
Control System
Room
On
OffSwitch
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Lesson Objectives 02
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Open loop and closed
loop system
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Control system types
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Two types:
1. Open loop control system
2. Closed loop control system.
Also called Feedback control
system or Automatic controlsystem
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Open loop system
Open loop system is also known as non feedback system
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For example, the plant can be a furnace or air conditioning system, where the output
variable is temperature. The controller in a heating system consists of fuel valvesand the electrical system that operates the valves.
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Control System Configurationsa. Open-loop system
Examples:
Toaster
Mechanical System with Mass and Spring
Characteristics: Simple, less complicated configuration
Could not compensate for any disturbances
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Closed loop system
Closed-Loop Control Systems utilizes feedback tocompare the actual output to the desired output response.
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Closed loop system: Example
Speed control of car
Objective: To keep moving atconstant speed
Activities in controlling car
Reading speedometer
Deciding to increase or decreasespeed
Acting on the gas pedal
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(a) Automobile steeringcontrol system.
(b) The driver uses thedifference between theactual and the desired
direction of travel to generatea controlled adjustment ofthe steering wheel.
(c) Typical direction-of-travelresponse.
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Closed loop system: Example
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Control System ConfigurationsClosed-loop system
Characteristic:
Compensates disturbances to the system for greater accuracy
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Control system types
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Open-loop control system?
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Desiredlight
ActualLight
On-OffSwitch
Bulb Room
Sun Light orBlocked light
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Closed-loop control system?
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Desiredlight Actual
Light
On-Off
Switch Bulb Room
Sun Light or blocked light
Light
sensor
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Open-loop control system?
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Desiredtemp
ActualtempTemp
Settingknob
On-Offswitch
Room
People in the room
Airconditioned
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Closed-loop control system?
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Desired
temp
Actual
tempTempSettingknob
OnOff
switch
Room
People in the room
Airconditioned
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Control systems Introduction
Why Control?
Modern society have sophisticated control systems whichare crucial to their successful operation.
Reasons to build control systems: Power amplification
Remote control
Convenience of input form
Compensation for disturbance
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Control systems Introduction
Feedback
Feedback is a key tool that can be used to modify thebehavior of a system.
This behavior altering effect of feedback is a keymechanism that control engineers exploit deliberately to
achieve the objective of acting on a system to ensure that
the desired performance specifications are achieved.
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Control systems Introduction
What is the Control System
Engineer trying to achieve?
First, understand the broader picture of the
application to best apply a suitable control system.
A good control system is a system that will
generate a response quickly and without oscillation(good transient response),
have low error once settled (good steady-state response),
and will not oscillate wildly or damage that system(stability).
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Control systems Introduction
Control System DesignCycle
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Next lecture
Review of Laplace transform Modeling
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