manufacturing control technology 2_control 1

8/7/2019 Manufacturing Control Technology 2_control 1

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CHAPTER 1INTRODUCTION TO CONTROL

SYSTEMIgnatius Agung Wibowo


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DEFINITION Control: Regulate, direct or command and ability

to make something do what you want System: a group of things, pieces of equipment

that are connected and work together to perform

certain objective A control system is an interconnection of

components forming a system configuration that

will provide a desired system response


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CONTROL SYSTEM BASIC

Control system can be described by 3

components:

1. Input/ stimulus/ desired response

2. Control system3. Output/ response/ actual response

OutputInputControlsystem


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CONTROL SYSTEM

OBJECTIVE

To control the outputs in someprescribed manner by the input through

the elements of the control system


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EXAMPLE OF CONTROLSYSTEM

Controlling the temperature of a furnace

Input: desired temperature is given by adjusting theopening of the fuel valve

Control system: Fuel valve, pipes and the furnace

Output: the actual temperature of the furnace

Fuel

Actual Temperature

Desired Temperature

Control valve


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ADVANTAGES OF CONTROLSYSTEM

Doing tasks which

are impossible forhuman being tocontrol manually

Examples: Point a huge

antenna

Carry an elevatorand stop at theright floor


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ADVANTAGES OF CONTROLSYSTEM

We build control system for 4 primary reasons:

Power amplification Remote control

Convenience of input form

Compensation for disturbances

All of this primary reason is to make precisioncontrol for a system that impossible forhuman to control manually such as motor

speed, etc.


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EXAMPLES Power amplification: rotates a knob can rotate a

radar antenna Remote control: robot arm can be used to pick

up material in radioactive environment

Convenience of input form: by adjusting theposition of thermostat yields a desired thermaloutput in temperature control system

Compensation for disturbance: In antennapointing system when wind rotates the antennathe system is able to correct it


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OPEN-LOOP AND CLOSED-LOOPCONTROL SYSTEM

2 Basic categories of control system:

1. Open-loop control system

2. Closed-loop control system


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OPEN-LOOP CONTROL SYSTEM

Systems in which the output has no effect on the control

action are called open-loop control system

Desiredoutput

response, rController Controlled

process

Output /Controlledvariable, yActuating

signal, u


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OPEN-LOOP CONTROL SYSTEM (cont.)

Open loop control system also can be drawn in the following block

diagram

Thus, to each reference input there correspond fixedoperating conditions.

CONTROLLEROUTPUT

ELEMENT LOAD

Outputresponse

Input signal(reference)

ACTUATOR


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EXAMPLE OF OPEN-LOOP CONTROL

SYSTEM

1) Antenna pointing system (open loop)

AMPLIFIER MOTOR

PowerSupply

Highpower

GEARS

ANTENNA

O

Output

response

+V

-V

0V

Input

signal

Low

power


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EXAMPLE OF OPEN-LOOP CONTROL SYSTEM

(CONT.)

2. Automatic toaster: the temperature set and toasting aredetermined by a timer

CONTROLLER

(TIMER & ON-OFF SWITCH)

HEATER

Dial Setting(Desired

temperature)Actual

temperature


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EXAMPLE OF OPEN-LOOP SYSTEM

(CONT.)

3 Electronic typewriter

KEYBOARD(Desired

character)

PCONTROLLER

POWERAMP

Printwheel

(Actualcharacter)

DCMOTOR


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CLOSED-LOOP SYSTEM

A closed-loop control system utilizes and additional

measure of the actual output (feedback signal) tocompare with the desired output response.


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CLOSED-LOOP SYSTEM (cont.)

The difference between the desired output response and

feedback signal is known as actuating error signal The actuating error signal is fed to the controller to

reduce the error and bring the output of the system to adesired value

A closed-loop control system is often referred to asfeedback control system.


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CLOSED-LOOP SYSTEM (cont.)

Closed loop control system also can be drawn in the

following block diagram

CONTROLLEROUTPUT

ELEMENT LOAD

Error detector(Comparator/

Differentiator)

E

MEASUREMENTFeedback

Reference

signal(R)

Output(C)

-

+


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EXAMPLE OF CLOSED-LOOP CONTROL

SYSTEM

1. Antenna pointing system (closed loop)

CONTROLLER AMPLIFIER MOTOR

Feedback

Errordetector

Ve = Vi - Vo

Output

Input

(Vi)

180 0

+V

0

+

-

Output

sensor

Vo

180

+V

0


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EXAMPLE OF CLOSED-LOOP SYSTEM

(CONT.)

CONTROLLER AMPLIFIER LOAD

Ve = Vi - Vo

TACHOMETER

Small generator

Reference

signal(Vi)

Speed

MOTOR

Vo

Vorpm

Antenna-

-

+

Speed control block diagram


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SERVO CONTROL Position control

When the output variable is mechanical position iscalled servo-mechanism

Amplifier is called servo amplifier

Examples of servo-mechanism applications : robotics

autopilot for an aircraft

recording devices lathe and milling machines


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COMPARISON BETWEEN OPEN-LOOP AND

CLOSED-LOOP CONTROL SYSTEM

Open-loop system

The system is simple, makes: its price is cheap

it is more reliable, and

it is easy to maintain It is not accurate; accuracy depends on the calibration

of its elements. If the value of the elements changes,caused by factors like temperature, age, pressure, or

humidity, then the calibration will change. There is noerror correction by a controller


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COMPARISON BETWEEN OPEN LOOP

AND CLOSED LOOP CONTROL SYSTEM(CONT.)

Open-loop system (cont.):

It does not experience stability problem.

Its output response is slow.

Its controller action does not have any

relationship with the output.


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Closed-loop system

The system is complex, requires transducerand error detector, makes:

it is more expensive,

it is less reliable, and

it is difficult to maintain.

The system is very accurate; because there is

a correcting action by the controller.


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Closed-loop system It may experience stability problem, i.e.

when a positive feedback occurs.

Its response is fast.

Its controller action has a relationship withthe output.


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FEEDBACK AND ITS EFFECTS A system that maintains a relationship between

the output and some reference input by comparingthem and using the difference as a means ofcontrol is called a feedback control system

Feedback system = closed loop system

Feedback effects are: Reduction of system error on system Effect on performance characteristic, such as:

Stability

Bandwidth Overall gain

Impedance Sensitivity


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CONTROL SYSTEMS CLASSIFICATION

1. Single-Input-Single-Output (SISO)

CONTROL SYSTEM

Input Output


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(CONT.)

2. Multiple-Input-Multiple-Output (MIMO)

CONTROL SYSTEM

Input Output

.

.

.

.

.

.


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(CONT.)

3. Linear

Its components show linear characteristics(where superposition theorem may apply)

4. Non-Linear

Superposition theorem cannot be used. The

system is difficult to analyze, there is notheory which can be used for all conditions,e.g. amplifier.


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(CONT.)

5. Time-Invariant

The parameters of this control system do notchange with time, e.g. R, L, C.

6. Time-Variant

The parameters of this control system change

with time. It is difficult to analyze, e.g.resistance winding of a DC motor varies whenthe temperature rising, fighter aircraft


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(CONT.)

7. Analog (Continuous-Time) Control System

All signals in this system are in the form of analog (continuous)signal

8. Digital (Discrete-Time) Control System

In this system a digital computer is used as the controller in thesystem. Any control law can be applied via programming, e.g.

fly by wire

DIGITALCOMPUTER D/A

PLANT

SENSOR

Input Output

A/D


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(CONT.)

9. Process Control

Variables which are required to be controlled are temperature,

pressure, level, flowrate, pH, or viscosity.

The terminologies are different although the theories are similar.For example reference signal is called set point.

Valve B

Level detector

CONTROLLERSet point

Control Valve A

Measured variable


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(CONT.)

10. Sequential Control

The operations of this controlsystem are performed in orders

which are already set before. Forexample in an automatic washing

machine, the operations of fillingthe tube, washing the clothes,draining the tube, rinsing the

clothes, and spinning the clothesare already set. Another example is

the use of PLC (ProgrammableLogic Controller) in control system.


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(CONT.)

11. Feed Forward Control System


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CONTROL SYSTEM DESIGN

Three main objectives of control system

design are as follows:1.To produce desired transient response

2.To reduce steady state error

3.To achieve stability


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DESIGN PROCESS

Design of a control system basically follows these 5

steps:Step 1: Determine physical system andspecification from requirements

First of all, the design requirements of the systemwhich are desired transient response and steadystate error are determined.


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DESIGN PROCESS (CONT.)

Step 2: Functional block diagram and schematic

Based on the systems requirements, a functionalblock diagram is drawn. Based on the blockdiagram, a schematic of the system is obtained. Thisschematic can be in a form of electrical model,

mechanical model or both.Step 3 : Mathematical representation

A mathematical model of the system is obtainedfrom schematic using physical laws such asKirchoff's Voltage Law, Kirchoff's Current Law andNewton's Law


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DESIGN PROCESS (CONT.)Step 4: Reduction of block diagram

Initial block diagram might be too complicated.

Therefore, it is reduced to simple block in order toget simple equations that represent the system

Step 5: Analyze and design

Once the simple representation of the system isobtained, it is easier to analyze the system. Thesystem is analyzed to see whether the transient

response specification, steady state error andstability requirements are met. If the requirementsare not met, then the controller is designed to meetthe specification.

manufacturing control technology 2_control 1

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