Design Of Controllers For Tracking Performance Of XY Table Ball Screw Drive System.

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

DESIGN OF CONTROLLERS FOR TRACKING

PERFORMANCE OF XY TABLE BALL SCREW DRIVE

SYSTEM

This report submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Robotics and Automation) (Hons.)

NUR AMIRA BINTI ANANG B051110037

920219-01-5576

FACULTY OF MANUFACTURING ENGINEERING 2015

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

TAJUK: Design of Controllers for Tracking Performance of XY Table Ball Screw Drive System

SESI PENGAJIAN: 2014/15 Semester 2

Saya NUR AMIRA BINTI ANANG

mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut: 1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

untuk tujuan pengajian sahaja dengan izin penulis.

3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan pertukaran antara institusi pengajian tinggi.

4. **Sila tandakan ( )

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia sebagaimana yang termaktub dalam AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)

Alamat Tetap: No 11, Jln Murni 4, Tmn Murni,

83000 Batu Pahat, Johor

Tarikh: ________________________

Disahkan oleh:

Cop Rasmi:

Tarikh: _______________________

** Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai SULIT atau TERHAD.

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DECLARATION

I hereby, declared this report entitled “Design of Controllers for Tracking Performance of XY Table Ball Screw Drive System” is the results of my own

research except as cited in references.

Signature : ……….

Author’s Name : Nur Amira binti Anang

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APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (Robotics and Automation) (Hons.). The member of the supervisory is as follow:

……… (Dr. Ir. Lokman bin Abdullah)

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ABSTRAK

Laporan ini membincangkan hasil kerja perekaan pengawal untuk prestasi XY bola meja sistem pemaju skru. Terdapat tiga tuntutan penting dalam merekabentuk pengawal bagi pemesinan operasi dalam persekitaran pembuatan. Komponen tersebut termasuk ketepatan pengesanan yang tinggi, ketepatan pengesanan tinggi dan keteguhan. Evolusi peralatan mesin teknologi melalui kemajuan pengawal peralatan mesin menyebabkan permintaan yang berterusan dengan ketepatan pengesanan yang lebih baik dalam industri alat mesin. Objektif projek ini adalah untuk merekabentuk pengawal PID dan lata P / PI untuk prestasi XY bola meja sistem pemacu skru menjejaki dan bandingkan pengawal tersebut melalui simulasi dan eksperimen. Perbandingan keputusan antara simulasi menggunakan perisian Matlab manakala keputusan eksperimen menggunakan Googol Tech XY sistem bola meja memandu skru untuk membuktikan kejayaan pengawal yang direka. Pengawal ini direka berdasarkan analisis terhadap margin keuntungan, margin fasa, kadar lebar, kestabilan dan sensitiviti. Pengawal direka telah memenuhi peraturan kebiasaan untuk margin keuntungan dan margin fasa. Untuk margin keuntungan, peraturan kebiasaan adalah 4-10 dB manakala margin fasa adalah 30-90˚. Lata pengawal P/PI yang direka berjaya mengurangkan ralat penjejakan sistem berbanding dengan pengawal PID ketika eksperimen. Penambahbaikan dengan menambah satu lagi kaedah menganalisis pengawal yang direka oleh visualisasi menggunakan pemprosesan imej amat disyorkan. Ini membantu untuk mengesan kesilapan dengan mudah.

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ABSTRACT

This report presents the work done on designing controllers for tracking performance of XY table ball screw drive system. There are three critical demands in designing controller for machining operation in many manufacturing environment. The components include high tracking accuracy, high tracking precision and robustness. The evolution of machine tools technology through advancement of the machine tools controller causes the persistent demand of better tracking accuracy in industry of machine tool. The objectives of this project are to design PID and cascade P/PI controllers for tracking performance of XY table ball screw drive system and to compare the controllers through simulation and experimental process. The comparison of the results between the simulation using Matlab software and experimental using absolute plant of Googol Tech XY table ball screw drive system shows the success of the designed controllers in terms of the tracking performance. The controllers are designed based on the analysis of gain margin, phase margin, bandwidth, stability and sensitivity. The designed controllers have fulfilled the rule of thumb for the gain margin and phase margin. For gain margin, the rule of thumb is 4-10dB while phase margin is 30-90º. Cascade P/PI controller designed successfully lowering the tracking error of the system compared to PID controller for experimental work. It is recommended to add another method of analysing the designed controller by visualization using image processing which helps to detect the tracking error of the system easily.

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DEDICATION

To my beloved parents,

Anang bin Mohamad and Norriza binti Kasah

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ACKNOWLEDGEMENT

First and foremost, all praise to The Almighty, who made this accomplishment possible. I seek his mercy, favor and forgiveness.

Thousands of thanks to my great supervisor, Dr. Ir. Lokman bin Abdullah for the help, encouragement and guidance from the beginning until end of this writing project.

For my parents, Anang bin Mohamad and Norriza binti Kasah and my family who are always provides me with love and support all the time in order for me to complete this work. Their enthusiastic caring is valuable for me.

My thanks and appreciations also go to my colleagues in developing the project and people who have willingly helped me out with their abilities.

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TABLE OF CONTENT

Declaration Approval

Abstrak i

Abstract ii

Dedication iii

Acknowledgement iv

Table of Content v

List of Tables viii

List of Figures ix

List of Abbreviations xi

CHAPTER 1: INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 2

1.3 Objectives 3

1.4 Scope of Work 3

1.5 Structure of Report 4

CHAPTER 2: LITERATURE REVIEW 5

2.1 Introduction 5

2.2 Motion Control in Machine Tool 6

2.2.1 Mechanical Drive System 6

2.3 A Good Tracking Performance – A Controller Design Approach 9

2.3.1 Controller Design 9

2.3.2 PID Controller 10

2.3.3 Cascade P/PI Controller 12

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CHAPTER 3: METHODOLOGY 15

3.1 Introduction 15

3.2 Experimental Setup 18

3.3 Software Requirement 19

3.4 System Identification 19

3.5 Summary 22

CHAPTER 4: RESULTS AND DISCUSSIONS 23

4.1 Introduction 23

4.2 PID Controller 23

4.2.1 General Structure and Configuration of PID Controller 23

4.2.2 Design and Analysis of PID Controller 26

4.3 Cascade P/PI Controller 31

4.3.1 Cascade Control Structure and Configuration based on 31 Ideal System

4.3.2 Design and Analysis of the PI Controller based on 33 Measured FRF

4.3.3 Design and Analysis of the Position Loop based on 39 Measured FRF

4.4 Maximum Tracking Error 44

4.4.1 PID Controller 44

4.4.1.1 Simulation Results 44

4.4.1.2 Experimental Results 49

4.4.2 Cascade P/PI Controller 47

4.4.2.1 Simulation Results 47

4.4.2.2 Experimental Results 49

4.5 Root Mean Square Error (RMSE) 52 4.6 Experimental Comparison between Two Amplitudes 53

4.6.1 Maximum Tracking Error 53

4.6.1.1 Amplitude 1mm 53

i) PID Controller 53

ii) Cascade P/PI Controller 54

4.6.1.2 Amplitude 15mm 55

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vii

ii) Cascade P/PI Controller 56

4.6.2 Root Mean Square Error (RMSE) 57

4.7 Summary 57

CHAPTER 5: CONCLUSION AND RECOMMENDATION FOR

FUTURE IMPROVEMENT 58

5.1 Conclusion 58

5.2 Recommendation for Future Improvement 60

REFERENCES 61

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viii

LIST OF TABLES

3.1 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 5.1

System Model Parameters for Y- axis

Gain Values of PID Controller for Y-axis

Rule of Thumb of Gain Margin and Phase Margin Gain Margin and Phase Margin of Open Loop Position Speed Loop PI Controller for Y-axis

Gain Margin and Phase Margin of Open Loop

Gain Margin and Phase Margin of Open Loop Position Comparison of Maximum Tracking Error of Simulation and Experimental for PID Controller

Comparison of Maximum Tracking Error of Simulation and Experimental for Cascade P/PI Controller

Comparison of Maximum Tracking Error of Simulation and Experimental for Both Controllers

Comparison of RMSE of Simulation and Experimental for Both Controllers

Experimental Tracking Error with 1mm Amplitude Experimental Tracking Error with 15mm Amplitude Comparison of RMSE of Different Amplitudes for Both Controllers

Summary of the Project Objectives and Project Conclusion

21 25 26 27 34 35 41 46 49 50 52 54 56 57 59

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LIST OF FIGURES

2.1 2.2 2.3 2.4 2.5 2.6

Linear and Ball Screw Mechanism Rack and Pinion Drive System Structure of Ball Screw System Ball Screw Drive System Unity Feedback System

Ideal Cascade Control Structure for Ball Screw Drive Motor

7 7 8 8 12 13

3.1 Flowchart of the Project Methodology 17

3.2 Googol Tech XY Table Ball Screw Drive System 18

3.3 Schematic Diagram of the Overall System 19

3.4 Flowchart of System Identification 20

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 4.15

Control Structure of PID Controller

Bode Diagram of Open Loop Transfer Function for Y-axis Nyquist Plot of the Y-axis Position Open Loop Transfer Function Bode Magnitude Diagram of Sensitivity when the Magnitude is -3dB

Bode Magnitude Diagram of Sensitivity at Peak Response Bode Diagram of Position Closed Loop via PID Controller General Control Structure of Cascade Controller

General Control Scheme of Speed Loop with PI Controller Ideal Cascade for Position Controller

Cascade P/PI Control Structure

Open Loop Bode Diagram of the Speed Loop

Nyquist Plot of the Y-axis Speed Open Loop Transfer Function Bode Magnitude Diagram of Sensitivity when the Magnitude is -3 dB

Bode Magnitude Diagram of Sensitivity at Peak Response Bode Diagram of Speed Closed Loop via Cascade P/PI Controller 25 27 28 29 30 31 32 32 32 33 35 36 37 38 39

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x 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27 4.28 4.29 4.30

Open Loop Bode Diagram of the Position Loop

Nyquist Plot of the Y-axis Position Open Loop Transfer Function Bode Magnitude Diagram of Sensitivity in Absolute

Sensitivity Function for the Position Loop

Simulation Diagram for PID Controller in Simulink Simulated Tracking Error for PID Controller

Experimental Tracking Error for PID Controller

Simulation Diagram for Cascade P/PI Controller in Simulink Simulated Tracking Error for Cascade P/PI Controller

Experimental Tracking Error for Cascade P/PI Controller Mathematical Error for Cascade P/PI Controller

Experimental Tracking Error for PID Controller Experimental Tracking Error for Cascade P/PI

40 41 42 43 45 45 46 47 48 49 51 53 54 55 56

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LIST OF ABBREVIATIONS

P - Proportional

I - Integral

D - Derivative

VAV - Variable Air Volume

DSMC - Decoupled Discrete-Time-Sliding-Mode SISO - Single - Input Single - Output

GUI - Graphical User Interface FRF - Frequency Response Function LTI - Linear Time Invariant

mm - millimetre

NLLS - Non-Linear Least Square DSP - Digital Signal Processor CNC - Computer Numerical Control RMSE - Root Mean Square Error

GM - Gain Margin

PM - Phase Margin

dB - Decibels

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CHAPTER 1 INTRODUCTION

This chapter gives an overview about the project entitled, “Design of Controllers for Tracking Performance of XY Table Ball Screw Drive System. Problem statement, objectives, scopes of work and outline of the project are presented in this chapter.

1.1 Background

Machining is a process to change size from bigger to smaller and surface finish of a material through removal of materials that could be achieved by straining the material to fracture or by thermal evaporation (“SMEDA - Engineering and Manufacturing,” n.d.). Machining system consists of machine tool, cutting tool and the part to be machined. A good machining is defined as a process that can constantly perform faster with high accuracy. It is crucial for the machine tools industry in parallel with the advanced of technology today. In general, it is important for the tracking performance to be accurate and precise. Tracking accuracy is concessional by the effect that comes from the dead zones and the huge friction forces that are generated in a high stiffness electromechanical ball screw and bearing structure (Jamaludin, 2008). The purpose of the feed drive is to locate the component to the machine tool and to the work piece to the desired position.

Accuracy in position and speed lead to the quality and productivity of the machine tools. The common pattern of machine tool axes includes the rotary motor and a ball screw transmission which is finite in speed, acceleration, stroke and accuracy

(Wang, Brussel, & Swever, n.d.). The issues can be visibly rectified by using linear motors. However, the advantage of linear motors is it lead to the insistence of a controller design to solve the problems.

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2 In general, machining processes in machine tools are affected by disturbance force. Disturbance force is divided into two types which are friction force and cutting force. There are three cutting parameters that will affect the behavior of the cutting force. The parameters are feed rate, depth of cut and spindle speed (Gokkaya, 2010).

1.2 Problem Statement

Nowadays, the demand for high speed and accuracy of machine tools are needed in machine tools industry. Thus, a good controller design is crucial in order to obtain good tracking performance of a machine tool.

Unnecessary vibration will lead to inaccuracy and poor surface quality. The compensation of cutting force disturbance is desired in order to obtain good tracking performance.

In order to design controllers for XY table ball screw drive system, it requires knowledge and understanding about the machining parameters and knowledge on controller design. A threaded shaft that provides a helical raceway which role as a precision screw is the essential prerequisite for the ball screw drive with conditions of enduring high trust load and low in-house friction. The dependence of the system on the ball screw drive to run from one position to another position is the result of the requirement. The main problem is to design controllers which are PID and cascade P/PI controller with comparison of simulation and experimental in order to obtain an accurate tracking performance of the system.

The controllers are made based on the design analysis where include the gain margin and phase margin analysis and stability analysis. Besides that, the tracking performances of the designed controllers are being compared using two different amplitudes which are 1 mm and 15 mm through experimental work. The controllers are compared with the simulation based on the tracking errors and Root Mean Square Error (RMSE). The realistic and comparatively simple controllers are applicable for the machine tool industry.

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1.3 Objectives

The objectives of the project are:

i. To design PID and cascade P/PI controller for enhancement of tracking performance of XY table ball screw drive system.

ii. To compare the tracking performance of the designed controllers through simulation using Matlab software and experimental work using real plant of Googol Tech XY table ball screw drive system.

iii. To compare the tracking performance of the designed controllers using different amplitudes through experimental work.

1.4 Scope of Work The scopes of this project are:

i. The axis involved of the Googol Tech XY table ball drive screw system is Y-axis only in order to improve the tracking performance in a vertical direction. ii. The controllers are designed by simulation using Simulink of Matlab

software.

iii. The performance of controller is determined based on tracking error and RMS error.

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4 1.5 Structure of Report

This report consists of five chapters that will be explained briefly about this project. The first chapter is about an introduction which contains the project background, problem statement, objectives and scopes of the project. Second chapter supplies a literature review on the previous researchers on tracking performance of table ball screw drive system as well as the application and control system approaches. The approaches of the model and different type of controller for cutting force compensation are reviewed in chapter two. After that, Chapter 3 is the methodology of the project that provides the process and descriptions of the project. Next is Chapter 4 where the designed controller, simulation of the model results and tracking performance of the designed controllers using different amplitudes will be presented and discussed in details. Lastly, the outcome of the project will be concluded in Chapter 5. The recommendation for future improvement of the project also will be included in this chapter.

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CHAPTER 2 LITERATURE REVIEW

2.1 Introduction

Traditional machining processes consist of turning, boring, drilling, reaming, milling, threading, shaping, planing and broaching as well as abrasive processes such as grinding, ultrasonic machining, lapping and honing while advanced processes include electrical and chemical means of material removal as well as the use of abrasive jets, water jets, laser beams and electron beams (Gutowski, 2009). Milling can be defined as a process of removing materials which covers variety of operation in manufacturing industry.

It is a demand for the machining process to get higher tracking accuracy at faster speed. However, the presence of disturbance forces in the process obstruct in achieving the goal. There are two disturbance forces that might occur during machining. The disturbances are friction force and cutting force. In order to track these disturbances forces, a motion tracking controller can be made. Motion tracking controllers are designed with the objective of achieving maximum tracking accuracy and robustness against disturbance and plant uncertainties. The size of the tracking errors and actuator input signals are important indicators to validate a control system (Jamaludin, 2008).

The implementation of classical cascade controller for the purpose of controlling various types of engineering appliances has been vastly utilized by control engineer community.

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6 PID or Proportional Integral and Derivative controller is a conventional controller where the controller is the most common used in the world of control system. The factors of PID controller which are the simplicity, transparent design and ability of solving many practical control problems have contributed to its wide acceptance (Wang, 2004). Cascade controller provides a simple structure of controller but yet functional and have the ability to satisfy the control design requirement. In general, the controller consists of two loops, namely velocity loop and position loop .One of the best motion tracking controllers is Cascade P/PI controller. Velocity loop consists of Proportional (P) and Integral (I) controller which is at the inner loop while position loop is at the outer loop that consist of a Proportional (P) controller.

This chapter describes information of tracking performance of XY table ball screw drive system. Motion Control in Machine Tool is discussed in Subchapter 2.2 which including the mechanical and disturbances in drive system. Subchapter 2.3 is the controller design. This is where the controller design, cascade design based on PID and controller design based on cascade PID controller is discussed and lastly is the summary of this chapter is discussed in Subchapter 2.4.

2.2 Motion Control in Machine Tool

Machine tool is one of mechanical system that is required to perform faster in high accuracy to increase the productivity of manufacturing. This shows that processes with faster speed of processing, low time consume and high accuracy become important factors of good machine tools.

2.2.1 Mechanical Drive System

Cutting tool and work piece are two components that are used by feed drives to locate their position to the required location. When the desired location is far, rack and pinion drive is used and the other two types of power of feed drives that are mostly used in industry are linear motor drives and ball screw drive as shown in Figure 2.1 (Altintas, Verl, Brecher, Uriarte, & Pritschow, 2011).

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7 For rack and pinion drive, the straight rack can be considered as a segment of a gear having infinite pitch radius. The rotary motion of the pinion is converted into linear motion of the straight rack in this arrangement and may be manufactured with either straight spur or helical teeth (Collins, Busby, & Staab, 2010). The rack and pinion drive system is suitable for machine tools with long working path. This is because the rack and pinion drive system produced high torque with low revolution in power transfer (Altintas, 2011). Figure 2.1 shows the movement of rack and pinion in producing linear movement (“CR4 - Thread: Rack and Gear Design,” n.d.).

The drive system that will be discussed is ball screw drive system. It is commonly used in many machine tools in providing linear motion for high speed machine tools. The ball-screw drive consists of a screw supported by thrust bearings at the two ends, and a nut with recirculating balls. The nut is connected to the table. One end of the ball-screw is either attached to a rotary motor directly or through gear or belt speed

Figure 2.1: Linear and Ball Screw Mechanism (Source: Altintas, Verl, Brecher, Uriarte, & Pritschow)

Figure 2.2: Rack and Pinion Drive System (Source: Altintas, Verl, Brecher, Uriarte, & Pritschow, n.d)

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8 reduction mechanisms as shown in Figure 2.3. The nuts are preloaded to avoid backlash by adjusting the spacer, creating offset between the leads or using oversized balls. It is rather difficult to grind the pitch at uniform intervals, and the pitch errors are transmitted as position errors unless they are compensated (Altintas et al., 2011).

Figure 2.3: Structure of Ball Screw System (Source: Altintas et al, 2011)

This drive system can be described as a mechanical system that converts rotary motion to linear motion where the rotary motion comes from the rotation of the ball screw before change into linear movement. Basic structure of ball screw mechanism is shown in Figure 2.4 (“Manufacturing Automation Laboratory ( MAL ) UBC,” n.d.).

Figure 2.4: Ball Screw Drive System (Source: http://mal.mech.ubc.ca/, n.d)

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9 Last drive system that will discussed in this chapter is linear motor drive. This drive is different from the ball screw drive system as it is drives the machine tool feed axis in linear and does not need a mechanical transmission mechanism. The moving part of the liner motor is always attached directly to the load and the system can be appropriately described as having only one degree of freedom (Moscrop, 2008). Besides that, linear motors also described as special class of synchronous brushless servo motors as their function just like torque motors but are opened up and rolled out flat. Electrical energy is converted into linear mechanical energy with high level of efficiency through the interaction of the electromagnetic between the primary part which is the coil assembly and permanent magnet assembly as the secondary part. (“Direct drive linear motor principle - ETEL Innovative motion control,” n.d.).

2.3 A Good Tracking Performance – A Controller Design Approach 2.3.1 Controller Design

Previous researchers have done many researches in tracking performance of machine tools either from Computer Numerical Control (CNC) machine or the basic structure of CNC machine which is XY Table. Based on literature review, there several controllers that can be used in motion control especially in tracking performance of XY Table. The controllers include traditional Cascade, Sliding Mode Control, Gain Scheduling, Proportional Integral Derivative (PID), Cascade Proportional Integral (P/PI), Non-PID and Non Cascade controllers. Characteristics of simple, transparent design and practical made PID controller as the conventional controller that proposed by past researchers. In the next two subchapters which is Subchapter 2.3.2 and Subchapter 2.3.3 will touch about controller design based on PID and controller design based on cascade PID controller respectively.

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1.5 Structure of Report

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

The implementation of classical cascade controller for the purpose of controlling various types of engineering appliances has been vastly utilized by control engineer community.

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2.2 Motion Control in Machine Tool

2.2.1 Mechanical Drive System

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Figure 2.1: Linear and Ball Screw Mechanism (Source: Altintas, Verl, Brecher, Uriarte, & Pritschow)

Figure 2.2: Rack and Pinion Drive System (Source: Altintas, Verl, Brecher, Uriarte, & Pritschow, n.d)

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Figure 2.3: Structure of Ball Screw System (Source: Altintas et al, 2011)

Figure 2.4: Ball Screw Drive System (Source: http://mal.mech.ubc.ca/, n.d)

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2.3 A Good Tracking Performance – A Controller Design Approach 2.3.1 Controller Design

Design Of Controllers For Tracking Performance Of XY Table Ball Screw Drive System.

UNIVERSITI TEKNIKAL MALAYSIA MELAKA