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POSITION CONTROL STRATEGIES OF DC SERVO MOTOR
By
ERNY AZNIDA ALWI
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of the Requirements for the Degree of Master of Science
June 2003
Abstract of thesis presented to the Senate ofUniversiti Putra Malaysia in fulfilment of the requirements for the degree of Master of Science
POSITION CONTROL STRATEGIES OF DC SERVO MOTOR
By
ERNY AZNIDA ALWI
June 2003
Chairman: Samsul Bahari Mohd Noor, Ph.D.
Faculty: Engineering
Direct Current (DC) servo motor is mainly studied for its speed and position control.
This study however, concentrated only on the position control part. The technology of
position control of DC servo motor has evolved considerably over the past few years.
To date, various types of DC servo motor position control scheme have been developed.
To name some, there are microcontroller�based control, PC based control, adaptive
control and optimal control.
In this study, a simulation and a real time implementation of DC servo motor position
control are presented. The types of controller designed and tested are the proportional
integral derivative (PID) controller and the adaptive controller. PID control scheme is
chosen mainly because of its simplicity advantage while the adaptive scheme is chosen
due to its ability to adapt.
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With some modification and adaptation, these two designed schemes have been
interfaced via MA TLAB Real Time Toolbox to a servo trainer as the plant for real time
implementation. This toolbox contains a library of blocks with real time input and
output support. Following the design part, the modeling and simulation part are done.
The mathematical design or model of the controller then has been simulated in
MATLAB before being interfaced to the real plant. The PID and adaptive controller
have been successfully implemented to the plant with satisfactory results. Analysis has
been done to compare the performance of the two controllers from the simulation and
real time results.
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PERPUSTAKAAt>J SULTAN ABDUL SAMAD UNIVERSfTl PUmA MAlAYSIA
Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk Ijazah Master Sains
STRA TEGI KA WALAN KEDUDUKAN MOTOR SERVO ARUS TERUS
Oleh
ERNY AZNIDA ALWI
Jun 2003
Pengerusi: Samsul Bahari Mohd Noor, Ph.D.
Fakulti: Kejuruteraan
Kajian berkenaan motor servo arus terns (DC) kebiasaannya tertumpu kepada kawalan
kelajuan dan kedudukannya. Walaubagaimanapun, dalam kajian ini, hanya kawalan
kedudukan sahaja akan diberi tumpuan. Teknologi kawalan kedudukan motor arus terus
telah berkembang pesat sejak beberapa tahun kebelakangan ini. Sehingga ke hari ini,
pelbagai jenis sistem kawalan kedudukan motor arus terns telah dibangunkan. Di
antaranya, kawalan berasaskan pengawal mikro, kawalan berasaskan komputer,
kawalan adaptasi dan kawalan optimal.
Dalam kajian ini, simulasi dan implementasi masa nyata dibentangkan. Jenis pengawal
yang direkabentuk dan diuji adalah pengawal terbitan kamiran perkadaran (PID) dan
pengawal adaptasi. Skima pengawal PID dipilih disebabkan kelebihannya yang mudah
manakala pengawal adaptasi dipilih kerana kebolehannya untuk menyesuaikan diri.
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Dengan sedikit pengubahsuaian dan penyesualan, kedua-dua sistem yang telah
direkabentuk disambungkan ke servo trainer yang merupakan loji untuk implementasi
masa nyata melalui antaramuka MA TLAB Real Time Toolbox. Perisian ini mengandungi
himpunan blok-blok dengan masukan dan keluaran masa sebenar. Selepas rekabentuk,
permodelan dan simulasi dilakukan. Rekabentuk matematik atau model pengawal
kemudiannya disimulasikan di dalam MATLAB sebelum diantaramukakan dengan loji
sebenar. Pengawal PID dan adaptasi telah berjaya diimplementasikan ke loji dengan
keputusan yang memuaskan. Analisa ke atas keputusan simulasi dan masa nyata
dijalankan untuk membandingkan prestasi kedua-dua pengawal.
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ACKNOWLEDGEMENTS
I would like to express my appreciation especially to my project supervisor, Dr. Samsul
Bahari Mohd Noor and all the supervisory committee for the given guidance and time
spent. Many thanks also go to my loving family, my parents, husband and my beautiful
daughter for their unconditional support and love which without it this work would not
have been possible. Finally special thanks to my friends and all who have contributed in
making my research a success.
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I certify that an Examination Committee met on 4th June 2003 to conduct the final examination of Emy Aznida Alwi on her Master of Science thesis entitled "Position Control Strategies of DC Servo Motor" in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1 980 and Universiti Pertanian Malaysia (Higher Degree) Regulation 1 98 1. The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows:
Syed Javaid Iqbal, Ph.D. Lecturer Faculty of Engineering
Universiti Putra Malaysia (Chairman)
Samsul Bahari Mohd Noor, Ph.D. Lecturer Faculty of Engineering
Universiti Putra Malaysia (Member)
Sen an Mahmood, Ph.D Lecturer Faculty of Engineering Universiti Putra Malaysia (Member)
Jasronita Jasni Lecturer Faculty of Engineering
Universiti Putra Malaysia (Member)
GULAM HMAT ALI, Ph.D. ProfessorlDeputy Dean School of Graduate Studies
Universiti Putra Malaysia
Date: 0 4 DEC 2fXB
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This thesis submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirements for the degree of Master of Science. The members of the Supervisory Committee are as follows:
Samsul Bahari Mohd Noor, Ph.D. Lecturer Faculty of Engineering Universiti Putra Malaysia (Chairman)
Senan Mahmood, Ph.D Lecturer Faculty of Engineering Universiti Putra Malaysia (Member)
Jasronita Jasni Lecturer Faculty of Engineering Universiti Putra Malaysia (Member)
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AINI IDERIS, Ph.D. ProfessorlDean School of Graduate Studies Universiti Putra Malaysia
DECLARATION
I hereby declare that the thesis is based on my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institutions.
x
ERNY AZNIDA AL WI
Date: %t2-�S &')
TABLE OF CONTENTS
DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL DECLARATION LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS
CHAPTER
1
2
INTRODUCTION 1 . 1 Importance of Servo Position Control 1 .2 Objectives 1 .3 Thesis Organization
LITERATURE REVIEW 2.1 Introduction 2.2 Position Controller Development for Different Types
of Motor 2.2. 1 The Optimal Position Controller 2 .2.2 The Robust Position Controller
2.3 The PID Controller 2.3 . 1 Tuning the PID Controller
2.4 Adaptive Control Scheme 2.4.1 Gain Scheduling 2.4.2 Model Reference Adaptive Systems 2.4.3 Self-Tuning Regulators 2.4.4 Dual Control
2.5 Recursive Least Square Estimator 2.6 System Representation 2.7 System Stability 2.8 Servo Motor
2.8. 1 Definition of Servo System 2.8.2 Types of Motor 2.8.3 Motor Amplifier Dead-zone
2.9 Summary
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Page
ii 1ll V Vll viii x xiii XIV XVll
1 1 2 3
4 4
5 6 7 8 10 12 13 14 15 16 16 1 7 1 9 1 9 20 21 21 22
3 METHODOLOGY 23 3 . 1 Introduction 23 3 .2 Description of Servo System 24 3 .3 Method of System Representation 25 3.4 Determination of Servo System Model 26
3.4.1 Actuator and Sensor Characteristics 27 3.4.2 Motor and Sensor Characteristics 29 3.4.3 Measurement of kj• km and ke 29
3 .5 Constructing the SIMULINK Model 35 3.5 . 1 Designing Model o f Servo System with
Controllers 35 3.5 .2 Designing Model of Controller with Real
Time Feature 41 3 .6 Hardware Configuration 42 3 .7 Summary 44
4 RESULTS AND DISCUSSION 45 4. 1 Introduction 45 4.2 Experimental Results 46 4.3 Mathematical Solution of System Model 49 4.4 SIMULINK Model Designs 52
4.4. 1 Model of Servo System with Controller 52 4.4.2 Model of Controllers for Real Time
Implementation 53 4.5 SIMULINK Simulation Results 54 4.6 Real Time Implementation Results 64 4.7 Discussion 72
5 CONCLUSION AND FUTURE WORKS 74 5.1 Conclusion 74 5 .2 Future Works 76
REFERENCES 77 APPENDICES
A Experimental Data 8 1 B SIMULINK S-Function Files 84 C Matlab M-Files for SIMULINK Model 87 D Data Sheets 127
BIODATA OF THE AUTHOR 1 30
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Table 4. 1 : Data of Experiment 1
Table 4.2 : Data of Experiment 2
Table 4.3 : Data of Experiment 3
LIST OF TABLES
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Page
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LIST OF FIGURES
Page
Figure 2. 1 : A servo system 20
Figure 3 . 1 : The servo trainer 24
Figure 3 .2 : Servo control system: clutch engaged 26
Figure 3 .3 : Block diagram representation of servo control system 27
Figure 3 .4 : Block diagram of overall transfer function for servo control 29 system
Figure 3 .5 : Connection for Experiment 1 , to determine the value of motor 32 gain constant, k;
Figure 3 .6 : Connection for Experiment 2, to determine the value of velocity 33 sensor gain constant, kw
Figure 3 .7 : Connection for Experiment 3, to determine the value of angle 34
sensor gain constant, ko
Figure 3 .8 : Opening a new model window 36
Figure 3 .9 : SIMULINK Library Browser and a blank model window 37
Figure 3 . 1 0 : Using the SIMULINK Library Browser 37
Figure 3 . 1 1 : Example of a complete model 39
Figure 3 . 1 2: To reveal the masked block 39
Figure 3 . 1 3 : Underneath the masked PID block 40
Figure 3 . 1 4 : Setting the parameter value 40
Figure 3 . 1 5 : Selecting the hardware driver 43
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Figure 3 . 1 6 : Hardware driver parameter setting
Figure 4. 1 : Result of Experiment 1 , to determine the value of k{
Figure 4.2 : Result of Experiment 2, to determine the value of km
Figure 4.3 : Result of Experiment 3, to determine the value of k{)
Figure 4.4 : PID controller
Figure 4.5 : Adaptive controller
Figure 4.6 : Real time PID controller
Figure 4.7 : Real time adaptive controller
Figure 4.8 : Output ofPID controller
Figure 4.9 : Output of adaptive controller
Figure 4. 10 : Control signal for adaptive controller
Figure 4. 1 1 : Control signal for PID controller
Figure 4. 12 : Square wave output for adaptive controller
Figure 4. 1 3 : Sawtooth output for adaptive controller
Figure 4. 1 4 : Square wave output for PID controller
Figure 4. 1 5 : Sawtooth output for PID controller
Figure 4. 16 : Input signal of square wave input Vs the output for adaptive controller
Figure 4. 17 : Input signal of sawtooth input V s the output for adaptive controller
Figure 4. 1 8 : Control signal for square input of the adaptive controller
Figure 4. 1 9 : Control signal for sawtooth input of the adaptive controller
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6 1
6 1
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Figure 4.20 : Output of P ID controller for square input
Figure 4.2 1 : Output of P ID controller for sawtooth input
Figure 4.22 : Control signal of P ID controller for sawtooth input
Figure 4.23 : Control signal of P ID controller for square input
Figure 4 .24 : Real time output for PID controller
Figure 4.25 : Real time output for adaptive controller
Figure 4.26 : Real time control signal for PID controller
Figure 4 .27 : Real time control signal for adaptive controller
Figure 4.28 : Step input Vs real time output for PID controller
Figure 4.29 : Step input Vs real time output for adaptive controller
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LIST OF ABBREVIATIONS
e(t) Parameter estimates
A Forgetting factor
e Output shaft position (0)
OJ Shaft velocity / speed (rpm)
cp State vector
crt) Prediction error
b Friction coefficient of rotating component
DC Direct current
hp Horse power
ko Angle sensor gain (volts/rev)
kw Velocity sensor gain (volt.sec/rev)
K(t) Weighting factor vector
Kd Derivative gain
K, Integral gain
ki Motor sensor gain (rev/sec. volt)
k{, kt' Gain constant of load
km,km' Motor constant
Kp Proportional gain
LQ Linear quadratic
L Motor armature inductance (H)
pet) Covariance matrix
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PI Proportional-integral
PID Proportional-integral-derivative
R Motor armature resistance (0 )
rev Revolution
RLS Recursive least square
rpm Rotation per minute
T Time constant (sec)
v Input drive voltage (volts)
v Motor drive amplifier voltage (volts)
VI Load control voltage (volts)
VSC Variable structure control
Yo Position output (volts)
Yro Velocity output (volts)
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CHAPTER 1
INTRODUCTION
1.1 Importance of Servo Position Control
The rapid development of electronics world has not left the area of motor control
deserted. The initiation of motors has brought about profound changes in everyday life
for over a century. At present, there are numerous system topologies for motor control
depending on the motor type and application as to be discussed in the following chapter.
Servo motors have replaced traditional gears, belts, and pulleys, thereby eliminating the
wear and failure problems associated with the use of these older technologies. These
servo motors are used in applications that require position and speed or torque control,
and these range from robotics and semiconductor equipment to packaging, food and
beverage, and printing. Use of servo motors in factory machines and equipment are
helping to improve productivity in a wide array of processes.
DC motor systems are also used widely in various fields of technology. They are used
in power plants to generate electrical power and in industrial occupancies to furnish the
required mechanical motive power to drive mechanical machinery and control various
industrial processes. Ranging from robotics manipulators to the disk drive of a
computer, DC motor acts as one of the vital part. For both applications, the position
control of the motor is the major part to be given attention. Efforts made on controlling
the position of DC motor result in so many types of control scheme for the mentioned
purpose. For instance, there are micro controller-based control, PC based control,
adaptive control, optimal control, etc. Some of these control schemes will be explained
and discussed briefly in this study. More detailed discussions will be centered upon the
studied controllers, which are the PID and adaptive controllers.
1.2 Objectives
The main intention of this project is to implement the designed position control
strategies of DC servo to the real plant, via newly introduced real time software, the
MATLAB Real Time Toolbox. Among other objectives to be achieved through out the
study are:
(i) To describe in detail how to develop the plant model, plus description
on how to design the two types of controller, the PID and the adaptive
controller by means of SIMULINK and by making use of MATLAB
Real Time Toolbox.
(ii) To apply the developed or established control strategies to real DC servo
motor based on simulation done in SIMULINK, MATLAB.
(iii) To analyze the stability and to compare the simulation performance of
the two designed controllers of DC servo position.
(iv) To analyze the stability of adaptive control system, plus to compare the
performance between adaptive controller and conventional PID
controller in real time implementation.
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1.3 Thesis Organization
This thesis describes the development of real time implementation of DC servo position
control schemes. The first chapter introduces the background and the aim of this study.
Subsequently, the second chapter reviews the present and past works on various means
of position control of a DC motor. Previous research examples on related topic will be
unleashed. It also includes brief descriptions of methods to be used in this study. The
third chapter discusses the way and the flow of works towards realizing the project
designs and simulations. Detailed explanation on designing the controller via
SIMULINK also presented in this chapter. This includes the hardware configurations
and software designs. The fourth chapter reveals the simulations and experimentations
results obtained. Analysis and discussions upon the achieved results are featured in this
chapter. Finally, the last chapter concludes the study with a few suggestions of future
works, to further develop the design.
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2.1 Introduction
CHAPTER 2
LITERATURE REVIEW
Various importance of position control in the industry and research fields has been
explained in the first paragraph of the previous chapter. It is imperative for the user to
understand the performance specification of different motor types when designing a
product for position control. For position control systems, three major motor types are
most commonly used: stepper motors; DC servo motors, in which the current�carrying
windings move and the second field is stationary and usually comes from a permanent
magnet; and brushless DC motors with a moving permanent magnet and stationary
current-carrying windings [30] .
Most motion control systems today make use of either stepper or DC servo motors.
Both motor types offer precise positioning and speed control but they differ in a number
of ways [30] . For DC motors, stator field is produced by either a field winding or by
permanent magnets while rotor field is set up by passing current through a commutator
and into the rotor assembly. Their rotational speed is dependant on the strength of the
rotor field.
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Whereas, the stepper motors are electromechanical actuators which convert digital
inputs to analog motion. They are particularly well suited to applications where the
controller signals appear as pulse train. Also, they are limited to about one horsepower
and 2000 rpm, therefore limiting them in many applications [ 1 ] . Due to these reasons,
the DC motor is found more suitable and has been chosen for this study.
To date, lots of other controller types [2,4,6] have been implemented for the same
purpose, position control of motors. However this study differs in a way that it is
realized using the Real Time Toolbox, which is a new tool applied for position control
of DC servo. A couple of previous designs of various controllers for motor position
control purpose will be featured further in section 2.2 of this chapter.
2.2 Position Controller Development for Different Types of Motor
Researchers designed different types of controllers to suit different types of motors.
Despite the latest emphasis of the ever-evolving fuzzy logic control technology, the
conventional controllers are not lagging in terms of efficiency and simplicity
advantages. Many engineering problems demand automatic control in the presence of
uncertainties and unforeseen large changes in system parameters and input signal. To
obtain robustness to uncertainties, a lot of adaptive control approaches have been
proposed in recent years. A few approaches of position control techniques done in
previous researches [2,3,5] will be presented briefly in this section.
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2.2.1 The Optimal Position Controller
Even though the designed techniques for the sliding mode are well established [8], it is
not easy to shape the dynamics of the reaching phase. Some process may require an
optimal performance. Hence to comply with this reason to be considered, the linear
quadratic (LQ) method is an easy way to design the control law. This proposed method
has the fully flexibility of shaping the dynamics of the closed loop system to meet the
desired specification. An optimal controller has been designed via combining the
classical state feedback control and variable structure control (VSC) and demonstrated
on a synchronous reluctance motor to meet this purpose [2]. This new method fully
matches the merits of the easy design of the linear quadratic method and the strong
robustness of the variable structure control. This method has proven that the
synchronous reluctance motor can be used in position control and the designed
performance can be easily obtained regardless of the disturbance and uncertainty.
While Morris, et. al. [3] has addressed the problem of controlling a two flexible link
manipulator system, and proposed a quadratic optimal control and a computed-torque
controller as the solutions. The study initially explained the necessity for having an
accurate static and dynamic model of the two flexible link manipulator, which properly
represents the coupling and interaction between links . The functions to be fulfilled by
the controller of a flexible manipulator system were to compensate for the static
deflection of the flexible links under gravity forces and also to reduce both the
magnitUde and the time duration of link oscillations, which arise naturally out of its
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