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VIBRATION SUPPRESSION OF HARD DISK DRIVE MECHANISM USING INTELLIGENT ACTIVE FORCE CONTROL

NUR SAFWATI BINTI MOHD NOR

A project report submitted in partial fulfilment of the requirements of the award of the

Master of Engineering (Mechanical)

Faculty of Mechanical Engineering Universiti Teknologi Malaysia

JUNE 2011

iii

ACKNOWLEDGEMENT

Alhamdulillah, all praise is due to Allah SWT, the most beneficent and the

most merciful, who has taught me what I knew not and for His guidance, blessing for

granting me patience and perseverance to accomplish this master’s thesis

successfully.

I would like to further extend my gratitude towards my supervisor, Professor

Dr. Musa bin Mailah who has guided, assisted and contributed his time and effort to

ensure that I get it right. I also like to give my sincere thanks to all the academic and

non-academic staff members of Faculty of Mechanical Engineering especially at

Department of System Dynamics and Control as well as doctoral students at System

and Control Laboratory for their cooperation, kindness and assistant throughout this

project. Also, I would like to thank the Universiti Teknologi Malaysia for providing

financial support for my master study.

Lastly, I also wish to extend my thanks to everyone who have helped directly

or indirectly in executing this master’s project. My deep gratitude goes to my

beloved family for their constant love, unlimited support and understanding.

iv

ABSTRACT

One of the key performances of a Hard Disk Drive (HDD) system is its

ability to control or suppress the vibration occurred. The fast development of HDD

technology such as in the aspect of high transfer rate, large amount of stored data and

the emerging of portable HDD have giving a great challenge to researchers to come

up with new solutions and effective techniques to control such a non-linear

mechanical system accurately and robustly. This study focuses on the

implementation of Active Force Control (AFC) scheme together with intelligent

control technique which employing Fuzzy Logic (FL) and Iterative Learning Control

(ILC) applied to the linear Voice Coil Motor (VCM) actuator in the HDD dynamics.

This type of active control technique and vibration model was done through

simulation study using MATLAB and Simulink. The performance of the Intelligent

Active Force Control (IAFC) system was compared to the traditional proportional-

integral-derivative (PID) control system in terms of tracking performance and system

robustness in countering the disturbances, particularly the vibration and friction. The

external vibration was modeled as sinusoidal and random form whereas the friction

was modeled based on Coulomb friction. Sensitivity analysis of the system output

response was conducted with respect to some variations in operating and loading

parameters involved in the HDD system dynamics. The simulation results for each

type of proposed controllers as well as from what had been discussed in comparative

study part affirm the superiority of the proposed control techniques over its

counterpart.

v

ABSTRAK

Salah satu kunci prestasi sistem ‘Hard Disk Drive (HDD)’ adalah

kemampuannya untuk mengendalikan getaran yang berlaku. Perkembangan pesat

teknologi HDD seperti dalam aspek kadar pemprosesan data yang cepat, sejumlah

data yang besar yang disimpan dan munculnya HDD mudah alih telah memberikan

cabaran besar kepada penyelidik-penyelidik untuk datang dengan penyelesaian-

penyelesaian baru dan teknik yang berkesan untuk mengawal sistem mekanik dengan

tepat dan kukuh. Penelitian ini memfokuskan pada pelaksanaan ‘Active Force

Control (AFC)’ skim bersama-sama dengan teknik kawalan bijak yang menggunakan

‘Fuzzy Logic (FL)’ dan ‘Iterative Learning Control (ILC)’ diterapkan pada aktuator

‘Voice Coil Motor (VCM)’ dalam dinamik HDD. Jenis teknik kawalan aktif dan

model getaran dilakukan melalui kajian simulasi menggunakan MATLAB dan

Simulink. Prestasi ‘Intelligent Active Force Control (IAFC)’ adalah sistem yang

dibandingkan dengan sistem kawalan tradisional ‘Proportional-Integral-Derivative

(PID)’ dalam hal pelacakan prestasi dan ketahanan sistem dalam melawan gangguan,

khususnya getaran dan geseran.Getaran luaran dimodelkan sebagai bentuk sinusoidal

dan rawak sedangkan gesekan dimodelkan berdasarkan geseran ‘Coulomb’. Analisis

sensitiviti respon sistem telah dilakukan dengan memperhatikan beberapa variasi

dalam pelaksanaan dan ‘loading parameter’ yang terlibat dalam sistem

HDD. Keputusan simulasi untuk setiap jenis kawalan dicadangkan daripada apa yang

telah dibincangkan dalam bahagian kajian perbandingan seterusnya menegaskan

keunggulan teknik kawalan yang dicadangkan berbanding teknik kawalan yang lain.

vi

TABLE OF CONTENTS

CHAPTER TITLE

TITLE PAGE

DECLARATION

ACKNOWLEDGEMENTS

ABSTRACT

ABSTRAK

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF ABBREVIATIONS

1 INTRODUCTION

1.1 General Introduction

1.2 Research Background and Contribution

1.3 Problem Statement

1.4 Research Objective

1.5 Research Scope

1.6 Research Methodology

1.7 Outline of Project Report

2 LITERATURE REVIEW

2.1 Introduction

2.2 Critical Review on Previous Studies

PAGE

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ii

iii

iv

v

vi

x

xi

xv

1

1

2

3

4

4

5

6

8

8

9

vii

2.2.1 Anti-Windup Compensator

2.2.2 H2 and Blending Control Method

2.2.3 Neural Networks for Disturbance and Friction

Compensation

2.2.4 Comparison of The Critical Literature Review

2.3 Mechanism Of HDD And Vibration

2.3.1 Vibration Suppression Control Of HDD

2.4 Active Force Control

2.4.1 Estimated Mass

2.5 Intelligent Control Adopting Fuzzy Logic

2.5.1 Fuzzy Controller Architecture

2.5.2 Fuzzy Set And Membership Function

2.5.3 Linguistic Variables And Fuzzy Rules

2.5.4 Defuzzification

2.6 Intelligent Control Adopting Iterative Learning

2.7 Conclusion

3 MATHEMATICAL MODEL AND DESIGN OF THE

CONTROLLER

3.1 Introduction

3.2 Mathematical Model Of Linear VCM

3.3 Design Of The Controller

3.4 Tuning Of Controller’s Parameters

3.5 Vibration Model

3.6 Friction Model

3.7 Conclusion

4 SIMULATION OF HDD ACTUATION MECHANISM BY

USING LINEAR VCM (PID CONTROL AND AFC)

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4.1 Introduction

4.2 PID Controller

4.2.1 Simulation Parameters

4.3 AFC Algorithm By Crude Approximation (AFC)

4.3.1 AFC Parameters

4.4 Results And Discussion

4.5 Conclusion

5 SIMULATION OF HDD ACTUATION MECHANISM BY

USING LINEAR VCM (INTELLIGENT CONTROL)

5.1 Introduction

5.2 AFC Algorithm And Fuzzy Logic Controller (AFCAFL)

5.2.1 Linguistic Variables

5.2.2 Determination Of Membership Function

5.2.3 Fuzzy Rules Design

5.3 AFC Algorithm And Iterative Learning (AFCAIL)

5.3.1 Iterative Learning Parameters

5.4 Results And Discussion

5.5 Conclusion

6 COMPARATIVE STUDY

6.1 Introduction

6.2 The Effect Of Estimated Mass

6.3 The Effect Of Frequency’s Amplitude

6.4 The Effect Of Fuzzy Logic Variable

6.5 The Effect Of Friction

6.6 The Effect Of Reference Input

6.7 Conclusion

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7 CONCLUSION AND FUTURE WORKS

7.1 Conclusion

7.2 Recommendations For Future Works

REFERENCES

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x

LIST OF TABLE

TABLE NO.

2.1

5.1

5.2

5.3

5.4

TITLE

Comparison of the control methods

Error (μm)

Change of Error (μm)

Estimated Mass (kg)

Fuzzy rules

PAGE

15

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64

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LIST OF FIGURE

FIGURE NO.

1.1

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

2.10

2.11

2.12

2.13

2.14

2.15

2.16

2.17

2.18

2.19

TITLE

Research methodology

AW compensation applied to PZT control loop

PZT micro-actuator control without AW compensator

PZT micro-actuator control with AW compensator

System response without AW compensator

System response with AW compensator

The structure of controller’s design to the VCM actuator.

Frequnecy response with vibration suppession at 650 Hz

and 2 kHz.

Neural network control scheme applied to HDD positioning

system.

Tracking error of the VCM actuator

Output response of the HDD positioning mechanism by

neural network

The schematic diagram of hard disk drives.[20]

Mechanical structure of a typical linear VCM actuator.[23]

The AFC scheme applied to a dynamic system.

Fuzzy controller architecture

Membership function of a fuzzy set

Linguistic variables and its quantifier

Center of gravity method

The simplest ILC scheme

Control principle of ILC to VCM actuator of HDD

PAGE

7

10

10

11

11

12

13

14

15

16

16

20

21

26

29

30

31

33

34

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xii

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

3.10

3.11

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4.10

4.11

4.12

4.13

4.14

positioning system

Mechanical structure of linear VCM of HDD positioning

mechanism

PID control block diagram of HDD positioning system

PID control incorporating AFC scheme

Incorporating FL technique to estimate the mass matrix

Incorporating ILC technique to estimate the mass matrix

Sinusoidal vibration model

Random vibration model

Simulink diagram of HDD positioning mechanism with a

friction model

Coulomb friction model

Hang-off effect of Coulomb friction

Limit cycling effect of Coulomb friction

The Simulink diagram of PID controller

The Simulink diagram of PID controller + AFC

Tracking of the HDD system without controller

Output response of HDD system without controller in

frequency domain

Acceleration of HDD system without controller

Tracking of PID control scheme without disturbance

Output response of PID control without disturbance in

frequency domain

Tracking of PID control scheme with disturbance

Output response of PID control with disturbance in

frequency domain

Acceleration of PID control with disturbance

Tracking of AFC scheme

Output response of AFC in frequency domain

Acceleration of AFC scheme

Tracking performance of PID control and AFC

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46

46

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52

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57

xiii

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

5.10

5.11

5.12

5.13

5.14

5.15

6.1

6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

AFC and Fuzzy Logic Scheme

Membership function for error

Membership function for change of error

Membership function for estimated mass

Rule Editor

Surface Viewer

The Simulink diagram of AFCAIL

Iterative learning subsystem

Tracking of AFCAFL scheme

Output response of AFCAFL in frequency domain

Acceleration of AFCAFL

Tracking of AFCAIL scheme

Output response of AFCAIL in frequency domain

Acceleration of AFCAIL

Comparison of tracking performance

The effect of changing estimated mass of 0.0001 kg (left)

and 0.2 kg (right)

Comparison of estimated mass in determining the

appropriate value.

PID controller with vibration frequency’s amplitude 10

times greater

AFC with vibration frequency’s amplitude 10 times greater

AFCAFL with vibration frequency’s amplitude 10 times

greater

AFCAIL with vibration frequency’s amplitude 10 times

greater

The effect of changing the range of membership function

Effect of friction alone (left) and friction with external

vibration (right)

Effect of friction alone (left) and friction with external

vibration (right)

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63

65

65

66

67

68

68

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69

69

70

70

73

73

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74

75

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6.10

6.11

6.12

6.13

Comparison of PID controller and AFC scheme due to

friction

Performance of PID and AFC with respect to pulse input

signal

Performance of PID and AFCAFL with respect to pulse

input signal

Performance of PID and AFCAIL with respect to pulse

input signal

79

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81

81

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LIST OF ABBREVIATIONS

AFC Active force control

AFCAFL Active force control and fuzzy logic

AFCAIL Active force control and iterative learning

FL Fuzzy logic

HDD Hard disk drive

ILC Iterative learning control

PCB Printed circuit board

PID Proportional-Integral-Derivative

PZT Piezoelectric

VCM Voice coil motor

1  

CHAPTER 1

INTRODUCTION

1.1 General Introduction

The development of Hard Disk Drive (HDD) is getting faster nowadays. The

industry competes with each other to produce a HDD which is able to store up to

Gigabytes of data, transfer the data faster as well as to make the HDD portable and

light in weight. Consequently, these factors have created numerous engineering

studies such as academic research in order to investigate and improve the

performance of HDD. One of the big areas in this research is to study on the

vibration affect to HDD and its effective method to suppress the vibration occurred

so that the performance can be increased. Vibration is one type of disturbance which

is common to any mechanical system like HDD. In HDD, vibration may comes from

the contact of its mechanical components during the read and write operation of data.

Besides, the air gap between the end of the suspension (head slider) and disk during

writing data onto the very high speed spinning disk also create the vibration in HDD.

In addition, some external vibrations such as shock to a fixed or portable HDD may

cause failure to the positioning mechanism of HDD. As a result, these sources of

vibration will degrade the performance of HDD and cause significant error during its

data track registration. To solve this discrepancy, the design development of each

2  

electromechanical component and control techniques applicable to HDD have been

studied through various research.

1.2 Research Background and Contribution

Vibration suppression control in HDD becomes a significant area to be solved

these several years. Research done to reject disturbance either internal or external

vibration can be found in many literatures [1-6]. Through literatures, the controller’s

design has been the most important part to be developed and improved. The common

control techniques used by others are servo control, feedforward control and optimal

control. Many research also incorporated smart device like PZT as the actuator and

sensor to enhance the servo performance of HDD. However, PZT does have some

limitations for certain applications. For instance, it may produce error in reading the

signal when the PCB where PZT is mounted deflected [7-9]. This could happen due

to strain sensitivity of PZT. Hence, in this study, the research work was focussed on

the implementation of new control algorithm to HDD positioning system. A novel

control method known as AFC which never been applied to HDD system was

proposed. The advantages of AFC method which is robust to disturbance of a

dynamics system is expected to eliminate vibrations occur in HDD. The most

challenging part of this research was to tune the value of estimated mass in the AFC

loop. This estimation need to be properly approximated since the estimated mass will

determine the estimated disturbance force to the system that is significant in

achieving disturbance rejection [10]. Therefore, two control methods which AFC and

ILC were embedded to the AFC loop in order to indentify the appropriate estimated

mass of the system. On the other hand, comparative study with Anti Wind-up

vibration control in HDD done by Hermann et. al [11] was conducted for validation

purpose of the simulation results.

3  

1.3 Problem Statements

In this study, the importance of vibration suppression is highlighted to ensure

accurate positioning of head slider during read and write of data in HDD. There are

two major things which going to be solved in this study. In the first part of this

research, the AFC method is implemented to HDD positioning system. AFC is

widely used in robotics system where research was done for trajectory of robot’s

arm. The implementation of this AFC has been improved the trajectory of the robot’s

arm successfully. One new area which using AFC technique was vehicle active

suspension system done by Priyandoko et. al [10]. His work was to isolate the

disturbances experienced by a vehicle suspension system. Thus, this study is

important to use this advantageous AFC method to another new application that is

HDD positioning mechanism system.

Secondly, this study focuses on one of the important criteria of AFC loop which

is the estimation of mass matrix. A good estimation of the estimated mass is crucial

when the system dynamics keep changing. As in HDD positioning system, this

problem need to be solve since it involves with highly non-linear system. The

dynamics of this system change whenever the loading parameters vary and hence

produce different operating parameters. In this case, the crude approximation

technique is not practical and effective to be applied to the HDD system.

Thus, other control method using fuzzy logic and iterative learning are embedded

to the AFC loop in order to estimate the mass matrix intelligently.

4  

1.4 Research Objective

The main objective of this study is to suppress the vibration phenomenon

generated in HDD mechanism using intelligent AFC technique.

1.5 Research Scope

The scope of this study is:

i. Theoretical study on head positioning mechanism of HDD,

control methods and Artificial Intelligence (AI) technique.

ii. Consider one degree of freedom (DOF) HDD mechanism

actuated using linear Voice Coil Motor (VCM).

iii. Implement Proportional-Integral-Derivative (PID) controller and

AFC methods in simulation by using Simulink.

iv. Consider Fuzzy Logic (FL) method and Iterative Learning

Control (ILC) to be embedded into the AFC loop.

v. The main disturbance element considered is at low frequency

vibration of the mechanism.

vi. Comparative study.

5  

1.6 Research Methodology

This research is divided into several parts of study. Initially, some critical

literature reviews were done related to HDD actuation system and find out the

gap of knowledge in the previous research. After done with the literature, the

dynamics of the HDD actuation mechanism was modelled based on linear VCM.

Next, it was followed by the controller design stage and tested the controller by

giving disturbance with variation in its parameters. The simulation part was

applied in MATLAB/Simulink to obtain the response of the system. Finally, the

results were analysed and validated by conducting comparative study.

Figure 1.1: Research methodology

 

6  

1.7 Outline of The Project Report

This thesis is organized into seven chapters. The critical literature reviews of

related previous studies and all the theoretical frameworks used in this study are

explained in Chapter 2. It also included the comparison of some related studies

by previous researchers in vibration control of HDD system and the fundamental

knowledge of control strategies to be used in this study. In Chapter 3, the

significant starting part of this research is discussed which are the mathematical

modelling and design of the controller. The modelling of linear VCM actuator as

the dynamics system of HDD positioning mechanism is illustrated as it is

required for the simulation of the control system. Besides, the control system

block diagram of each proposed control methods is also represented in this

chapter.

Meanwhile, Chapter 4 and 5 are dedicated for the simulation of HDD

actuation mechanism by using the modelled linear VCM. Chapter four covers the

simulation part of the conventional PID control and AFC whereas chapter five

covers the simulation part of the intelligent control techniques embedded to the

AFC loop. The intelligent control techniques applied in this study are the fuzzy

controller and iterative learning control. In both chapters, the MATLAB

Simulink models are shown together with the list of the control parameters used.

The graphical approach of the parameters tuning followed by the simulation

results are finally end the chapters.

The comparative study of all the simulation results is presented in Chapter 6.

This comparative study is important due to the validation of the simulated results.

The simulated results are discussed with respect to several operating and loading

parameter conditions in order to meet the objective of this study. The transient

performance characteristics and its frequency response are explained in detail

which lies on the control techniques to estimate the mass matrix and trajectory

track performance of proposed control schemes.

7  

Lastly, Chapter 7 summarizes the research done and provides some possible

future works that can be explored to improve and validate this study on vibration

control of HDD positioning system.

87  

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