MOTOR CONTROL SYSTEM DEVELOPMENT USING MICROCONTROLLER BASED ON PID CONTROLLER

SITI NUR WAHIDAH BINTI ABDUL WAHAB

A project report submitted infulfillment of the requirement for the award of the

Master Degree of Electrical Engineering

Faculty of Electrical and Electronic EngineeringUniversiti Tun Hussein Onn Malaysia

JULY 2014

v

ABSTRACT

PID controllers which are one of the algorithms that can adjust the input values based

on historical data and the emergence rate of differences, in order to make the system

more accurate and stable. This project is focused mainly on designing and

implementing PID controller for a Dc servo motor. The PID controller are used to

control position of the Dc servo motor, while the speed motor are control by

manually run with a specified performance requirement. PID controller are designed

based on MATLAB/Simulink software to obtain the optimum position control of

PID controller parameters and realized by using microcontroller to the real Dc servo

motor. All codes in microcontroller are developed on MPLAB X IDE software

program for embedded system.

vi

ABSTRAK

Pengawal PID yang merupakan salah satu algoritma yang boleh menyesuaikan nilai-

nilai input berdasarkan data sejarah dan kadar pengeluaran di perbezaan, untuk

membuat sistem yang lebih tepat dan stabil. Projek ini menumpukan kepada bentuk

dan melaksanakan pengawal PID untuk Dc servo motor. Pengawal PID digunakan

untuk mengawal kedudukan Dc servo motor, semasa motor kelajuan adalah kawalan

secara manual dengan keperluan prestasi yang ditetapkan. PID pengawal direka

berdasarkan perisian MATLAB / Simulink untuk mendapatkan kawalan kedudukan

optimum parameter pengawal PID dan menggunakan mikro pengawal sebenar Dc

servo motor. Semua kod dalam mikropengawal dibangunkan dengan menggunakan

program perisian MPLAB X IDE untuk sistem terbenam.

vii

CONTENTS

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACK v

ABSTRAK vi

CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xiv

LIST OF APPENDICES xvi

CHAPTER 1 INTRODUCTION

1.1 Introduction 1

1.2 Problem Statement 2

1.3 Objectives 3

1.4 Project Scope 3

1.5 Thesis Structure 3

viii

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction 5

2.2 Dc Servo Motor 5

2.3 PID Controller 6

2.3.1 Introduction of PID Controller 7

2.3.2 Proportional Action, 7

2.3.3 Integral Action, 8

2.3.4 Derivative Action 9

2.4 Hardware Description 9

2.4.1 Microcontroller (PIC18F46K22) 9

2.4.2 Motor (ID23005) 11

2.4.3 Two Channel Optical Encoders 12

2.4.4 MD10C (Motor Driver) 13

2.4.5 Nokia 3310 LCD 14

2.4.6 Potentiometer 16

2.4.7 Linear Axis Model 16

2.5 Previous Case Study 17

2.5.1 Performance Comparison Between

PID and Fuzzy Logic Controller in

Position Control System of DC

Servomotor 17

2.5.2 Controller design for servo motor using

MATLAB 18

2.5.3 PID Controller Design For Controlling

DC Motor Speed Using MATLAB

Application 18

2.5.4 DC Motor speed and position control

using analog PID controller 19

2.5.5 Real –Time DC Servo Motor Position

Control by PID Controllers Using Labview 19

2.6 Conclusion 20

ix

CHAPTER 3 METHODOLOGY

3.1 System Overview 21

3.2 Flowchart of PID Controller Design For

Dc Servo Motor 22

3.3 Methods and Approach 24

3.3.1 Digital Servo Motor Control 24

3.3.2 Servo Motor Modeling 24

3.3.3 Transfer Function Block Diagram 28

3.3.4 State Space Representation 29

3.4 Block Diagram 33

3.5 PID controller Design 33

3.5.1 Manual Tuning 34

3.5.2 Setting PID Parameter Using Simulink 35

3.6 Developing software and hardware 37

3.6.1 MPLAB X IDE software 37

3.6.2 Schematic circuit diagram 38

3.7 Hardware development 39

3.8 Conclusion 40

CHAPTER 4 RESULT AND ANALYSIS

4.1 Introduction 41

4.2 Simulation from MATLAB 42

4.2.1 PID Controller for Position Control 42

4.3 Result From Hardware 45

4.3.1 Output Response for Speed Control 45

4.3.2 Output responses for Position Control 48

4.4 Conclusion 50

CHAPTER 5 CONCLUSION AND RECOMMENDATION

5.1 Conclusion 51

5.2 Recommendation and Future Work 52

x

REFERENCES 53

APPENDICES 55

xi

LIST OF TABLES

3.1 DC Motor Parameter 25

3.2 Effect of Increasing a Parameter Independently 34

xii

LIST OF FIGURE

2.1 Digital DC Servomotor 6

2.2 Block diagram of PID controller 7

2.3 PIC18F46K22 10

2.4 Motor (ID23005) 11

2.5 Two Channel Optical Encoder 13

2.6 Motor driver (MD10C) 14

2.7 LCD Nokia 3310 15

2.8 Pin Connections of LCD Nokia 3310 15

2.9 Potentiometer 16

2.10 Linear Axis Model 16

3.1 Sequences of PID Controller Implementation on the

DC Servomotor 22

3.2 The PID controller design for position control project

methodology 23

3.3 A Dc motor wiring diagram 25

3.4 Block Diagram an Armature Controller of Speed

Dc Servo Motor 28

3.5 Block Diagram an Armature Controller of Position

Dc Servo Motor 29

3.6 Block Diagram of Project 33

3.7 Block diagram PID controller with motor 34

3.8 Block Diagram of PID Controller with

DC Servo Motor System 35

3.9 Method tuning of PID values 36

3.10 PID tuner parameter window 36

xiii

3.11 MPLAB X IDE software program 37

3.12 MPLAB X IDE Start Page 37

3.13 Schematic circuit diagram 38

3.14 Implementing with hardware 39

3.15 Hardware connection 39

4.1 PID Controller For Position Dc Servo Motor 43

4.2 Step response for the closed-loop system with

PID controller 44

4.3 Command display for speed control 45

4.4 Speed control at 50% duty cycle 46

4.5 Output response at 50% duty cycle 46

4.6 Speed control at 25% duty cycle 47

4.7 Output response at 25% duty cycle 47

4.8 Select PID Setting 48

4.9 Selection of PID value 49

4.10 Select PID Run 49

4.11 Output of speed, position and error 49

xiv

LIST OF SYMBOLS

Symbol Description

PID

Dc

Proportional Integral Derivative Controller

Direct Current

Ra Armature resistance

La Armature inductance

Va(t) Armature input voltage

Ia(t) Armature current

ωm(t) Motor Angular Velocity

θm(t)

(t)

Motor Angular Displacement

Back emf

T(t) Motor torque

Jm Motor of inertia of motor + load

B Viscous frictional constant of motor + load

KT Torque constant

KB Voltage constant

Kp Proportional gain

xv

Ki Integral gain

Kd Derivative gain

Tp Peak time

Tr Rise time

Ts Settling time

Os% Percentage of overshoot

ess Steady state error

PS1

PS2

Projek Sarjana 1

Projek Sarjana 2

xvi

LIST OF APPENDICES

APPENDIX TITLE PAGE

A MPLAB Coding ( PID Controller ) 55

B Gantt chart for Master Project 1 (PS 1) 66

C Gantt chart for Master Project 2 (PS 2) 67

CHAPTER 1

INTRODUCTION

This chapter introduces the project that has been carried out. The important overview

or description including the problem statement, project objectives, project scopes and

expected result are also emphasized in this chapter.

1.1 Introduction

Nowadays, several control system algorithm have been applied in control system

engineering including position controls. Position control for digital servo motor

exists in a great variety of automatic processes. However, the system does contain

nonlinearities which have an obstructive influence on system response, such as the

load effect[1].

From a practical point of view, complete information about uncertainties is

difficult to acquire in advance. To deal with these uncertainties, much research has

been carried out in recent years to apply various approaches in the position control

[2]. When uncertainties occur, the fuzzy control method is used instead of the PID

control method [3].

2

As a very good method, a fuzzy controller method can convert expert

knowledge into regulations of control system, and the regulations can be used to

determine the output value by logical inference. So it also does not need precision

system model and has high robust ability. In recent years, fuzzy controllers have

been widely developed, and a variety of methods have been proposed to improve the

performance of fuzzy controller [4]-[6].

In this project, digital servo motor control is used to investigate the feedback

control systems. This system has facilitated us to investigate different kind of control

techniques and implement simple Proportional-Integral-Derivative (PID) controller

with the aid of MATLAB/ Simulink which are performed by controlling the states of

the system, which might be position.

1.2 Problem Statement

In industries, there are some of control techniques that can be applied to solve the

problems such as DC motor speed, water tank and others. In designing a control

system, factors such as the nonlinearity systems, time response, cost and reliability

have to be taken into account.

Many controller have been proposed to control digital servo motors including

Optimal Control, Sliding Mode Control, Adaptive Control, Neural Network, Fuzzy

Logic etc., however, these controllers are complex hence difficult to implement.

On the other hand, proportional derivative integral (PID) controller is widely

used in feedback control of industrial processes and is simple in both structure and

principles.

In this project, the PID controller will be implemented to control the position

of a digital servo motor. The advantage of use the PID controller is to obtain the

output that follows the input in a short time, with minimal overshoot, and while little

error.

3

1.3 Objectives

The main objectives of the project are:

1) To investigate the application of PID controller in digital servo motor

control.

2) To design the PID controller in order to control the position of a

digital servo motor.

3) To analyze the performance of the designed PID controller in terms of

settling time, rise time and overshoot percentage.

1.4 Project Scope

The scopes of this project are:

1) Find the mathematical model of the digital servo motor.

2) Design and simulate the PID controller using Matlab software.

3) Implement the designed PID controller on the digital servo motor

controlled by using PIC as a microcontroller.

1.5 Thesis Structure

This report consists of five main chapters. The contents of each chapter are explained

as the state below.

Chapter 1 introduces the project and its objectives. It also states the problem

statement of the project, project scopes as well as the thesis structure.

In Chapter 2, the theory and literature study about the DC motor system is

explored and discussed. They serve as the foundation to execute the project. Besides

that, several control approaches such as PID controller, as the proposed controller,

4

are also discussed. Lastly, the components that are used in this project and previous

study related to this project are also introduced.

In Chapter 3, the mathematical modeling of DC motor is discussed. It can be

represented in state space equation and transfer function. The principle and physical

criteria has also been studied in detail. The design requirement of the Dc motor

system is set to design the controller. The PID controller used to control the speed

and position of Dc motor system is also explained in this chapter.

Chapter 4 shows and discusses the result of the speed control Dc motor

system using PID controller.

Chapter 5 concludes and discusses the project finding. A few commendations

is also included for the future work.

5

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

This chapter discusses about the DC motor, PID controller as well as the

microcontroller used to realize designed controller. It also highlights some previous

case studies that are related to this project from reference books, thesis, conference

papers and journal.

2.2 Dc Servo Motor

Dc motor has good speed control response and wide speed control range. It is widely

used in industries whose systems need high control requirements, such as rolling

mill, double-hulled tanker, high precision digital tools and etc [8]. Basically, the

hardware of this digital servo motor system consists of DC brush-type servo motor,

motor shaft encoder and rail encoder, platform, belt drives and pulleys for moving

the platform, flywheel, and friction break [10].

6

Dc servo motor consists of magnetic field and electrical field that interact

with each other to produce a mechanical force. To correct the performance of a

mechanism, error sensing feedback was used as an automatic device. The main

purpose of feedback signal is to control mechanical position and speed or other

parameters.

The Dc servo motor, as shown in Figure 2.1, is paired with some type of

encoder to provide position and speed feedback. In the simplest case, only the

position is measured. The measured position of the output is compared to the

command position, the external input to the controller. An error signal is generated

if the output position differs from that required. It causes the motor to rotate in either

direction and needed to bring the output shaft to the appropriate position. As the

positions approach, the error signal reduces to zero and the motor stops.

Figure 2.1: Digital DC Servomotor

2.3 PID Controller

In recent years, new modern methods of control have been used, such as fuzzy

control, neural networks and neuro-fuzzy controllers among others. However,

about over 90% of control loops still use industrial PID controllers [9]. But it is

known that the majority of these loops operate poorly tuned, creating additional

costs that could be minimized. This justifies the importance of the tune of

controllers[9].

7

2.3.1 Introduction to PID Controller

The PID controller combines the proportional, integral and derivative components

obtaining the classical equation which can be seen below:

where is the proportional gain, is the integration time constant, is the

derivation time constant, is the controller input and is the controller

output. Figure 2.2 shows the block diagram that represent PID controller.

Figure 2.2 : Block diagram of PID controller

2.3.2 Proportional Action, Kp

The proportional term produces an output value that is proportional to the current

error value. The proportional response can be represents as per equation below:

8

where Pout: Proportional term of output Kp: Proportional gain, a tuning parameter

e: Error = SP − PV

t: Time or instantaneous time (the present)

2.3.3 Integral Action, Ki

The contribution from the integral term is proportional to both the magnitude of

the error and the duration of the error. Summing the instantaneous error over

time (integrating the error) gives the accumulated offset that should have been

corrected previously. The accumulated error is then multiplied by the integral gain

and added to the controller output[9]. The magnitude of the contribution of

the integral term to the overall control action is determined by the integral gain, Ki.

The integral term is given by:

where

Iout : Integral term of output Ki: Integral gain, a tuning parameter e: Error = SP − PV : Time in the past contributing to the integral response

9

2.3.4 Derivative Action, Kd

The rate of change of the error is calculated with respect to time, multiplied by

another constant D, and added to the output. The derivative term is used to determine

a controller's response to a change or disturbance of the process. The derivative term

is given by:

where

Dout: Derivative term of output

Kd: Derivative gain, a tuning parameter

e: Error = SP − PV

t: Time or instantaneous time (the present)

2.4 Hardware Description

This section discusses the hardware used in this project such as PIC18F46K22

microcontroller, motor driver (MD10C), Dc motor (ID23005) and encoder.

2.4.1 Microcontroller (PIC18F46K22)

In this project, PIC18F46K22 microcontroller, as shown in Figure 2.3, was used as

the microcontroller. PIC18F46K22 can be easily programmed using MPLAB

software. MPLAB also serves as a single, unified graphical user interface for

10

additional Microchip and third-party software and hardware development tools. In

MPLAB, the language that was used are C programming languages and assembly

language.

Figure 2.3 : PIC18F46K22

The following are the specifications for PIC18F46K22:

Full 5.5V operation

Low voltage option available for 1.8V-3.6V operation

Self-reprogrammable under software control

Power-on Reset (POR), Power-up Timer (PWRT) and Oscillator

Start-up Timer (OST)

Programmable Brown-out Reset (BOR)

Extended Watchdog Timer (WDT) with on-chip oscillator and

software enable

Programmable code protection

In-Circuit Serial Programming™ (ICSP™) via two pins

In-Circuit Debug via two pins

Precision 16 MHz internal oscillator block:

11

- Factory calibrated to ± 1%

- Software selectable frequencies range of 31 kHz to 16 MHz

- 64 MHz performance available using PLL

- No external components required

Four Crystal modes up to 64 MHz.

Two external Clock modes up to 64 MHz

2.4.2 Motor ( ID23005)

The ID23005 series are ideal motors for applications using a simple Dc brush drive

for cost sensitive applications. In addition, the higher inertia armatures provide

improved motor to load inertia matching for medium to high inertia loads. This

motor as shown in Figure 2.4 is used for this project for control speed and position.

Combination motor, motor encoder and rail encoder created Linear Axis

Motor[10].

Figure 2.4 : Motor (ID23005)

12

Below are specifications for this motor.

Continuous Stall Torque : 0.402 Nm

Peak Stall Torque : 2.825 Nm

No Load Max. Speed : 6000 RPM

Continuous Rated Torque : 0.360Nm

Peak Rated Torque : 0.72 Nm

Rated Speed : 3400 RPM

Rated Power : 128Watts /0.17HP

Inductance : 6.40 mH

Resistance : 2.23 ohms

Max. Terminal Voltage : 60 Vdc

Torque Constant : 0.121 Nm/A

Voltage Constant : 0.121 V/rad/sec

Motor Inertia : 0.00006286 Kg-m²

Motor Weight : 1.588Kg

2.4.3 Two Channel Optical Encoders

While the velocity can be determined from position measurements, encoders are able

to provide a separate output which is proportional to the velocity[10]. Encoders are

widely used as position transducers in robotics and machine tools. Two channnel

optical encoder is a rail encoder. The encoder connected with motor. These encoders

may be quickly and easily mounted in a motor. Figure 2.5 shows the two channel

optical encoder.

13

Figure 2.5 : Two Channel Optical Encoder

Features of two channel optical encoder:

• Two Channel Quadrature Output with Optional Index Pulse

• Quick and Easy Assembly

• No Signal Adjustment Required

• External Mounting Ears Available

• Low Cost

• Resolutions Up to 1024 Counts Per Revolution

• Small Size

• -40°C to 100°C Operating Temperature

• TTL Compatible

• Single 5 V Supply

2.4.4 MD10C (Motor Driver)

MD10C, as shown in Figure 2.6, is designed to drive high current brushed DC motor

up to 10A continuously. This is to support for both locked-ant phase and sign-

magnitude PWM signal as well as using full solid state components which result in

faster response time and eliminate the wear and tear of the mechanical relay.

14

Figure 2.6 : Motor driver (MD10C)

Specification of MD10C:

Bi-directional control for 1 brushed DC motor.

Support motor voltage ranges from 5V to 25V.

Maximum current up to 13A continuous and 30A peak (10 seconds).

3.3V and 5V logic level input.

Solid state components provide faster response time and eliminate the

wear and tear of mechanical relay.

Fully NMOS H-Bridge for better efficiency and no heat sink is

required.

Speed control PWM frequency up to 20KHz.

Support both locked-anti phase and sign-magnitude PWM operation.

Dimension: 75mm x 43mm.

2.4.5 Nokia 3310 LCD

The LCD of Nokia 3310 consists of 84x84 pixel monochrome LCD display can use

it for graphics, text or bitmaps. These displays are small only about 1.5" diameter but

15

very readable due and comes with a backlight. These displays are inexpensive, easy

to use, require only a few digital I/O pins and are fairly low power as well. To drive

the display it need 3 to 5 digital output pins (depending on whether to manually

control the chip select and reset lines). Another pin can be used to control (via on/off

or PWM) the backlight. The front view and pin connection of LCD Nokia 3310 was

shown in Figure 2.7 and Figure 2.8.

Figure 2.7 : LCD Nokia 3310

Power requiments:

The display uses the PCD8544 controller chip from Philips.

This chip is designed to run only at 3.3V.

Can draw up to 80mA (4 white LEDs at 20mA each) if want to use

the backlight. The backlight pin is connected to a transistor so all 4

LEDs can PWM at once from a microcontroller pin.

Figure 2.8 : Pin Connections of LCD Nokia 3310

16

2.4.6 Potentiometer

Potentiometers as shown in Figure 2.9 are rarely used to directly control significant

amounts of power. Instead they are used to adjust the level of analog signals and as

control inputs for electronic circuits. Potentiometers can be used as position feedback

devices in order to create closed loop control, such as in a servomechanism. This

method of motion control used in the DC Motor is the simplest method of measuring

the angle or speed.

Figure 2.9 : Potentiometer

2.4.7 Linear Axis Model

Figure 2.10 shows the model linear axis. The Linear Axis positioning system

includes a Dc brush servo motor (ID23005), a belt mechanism, and two optical

encoders (one on the motor and the other on the travel cart)[10]. This model was

used in this project to measure the speed and position of motor.

Figure 2.10 : Linear Axis Model

17

2.5 Previous Case Studies

There are a number of researchers done similar with this project, mostly by foreign

manufacturers, university and colleges.

2.5.1 Title : Performance Comparison Between PID and Fuzzy Logic

Controller in Position Control System of DC Servomotor. [11]

This paper investigated and compared the performance between PID and fuzzy logic

controller. In this study, the design and development of a GUI software using

Microsoft Visual Basic 6.0 for position control system were implemented. The

techniques used was direct digital control (DDC) technique.

DDC is basically a microprocessor based technology in which a controller

performs closed loop function via sophisticated algorithms and strategies. The

controller function handles inputs and outputs while the software provides the logic.

Within the controller, the analogue signal enters the system where it is

converted to a digital form so that the data can be acted upon according to a set

of parameters or formulas. DDC control brings speed, precision, flexibility to

control functions at low cost.

From the DDC, the waveform was obtained by combination of PID and

fuzzy logic controller and the results were analyzed. The output response of PID and

fuzzy logic controller were then compared. The results showed that PID performs

better compared to fuzzy logic in term of percentage overshoot which is 0%

overshoot compared to fuzzy logic with an overshoot of 16%. However, when

comparing both of the rise time and settling time of both controllers, the fuzzy

logic controller performs better, with a Tr of 400.00 ms and Ts of 100 ms.

18

2.5.2 Title : Controller design for servo motor using MATLAB. [12]

In this paper, the controller for servo motor was designed using MATLAB software

by simulink model block diagram. Some ideas to create block diagram is shown in

this report based on their project. The comparison between three case studies was

discussed in this paper. Simulations are performed for three different values of the

armature resistance in order to investigate effect of armature current [12]. To make

an expression controller design, this article is generating the design by using

MATLAB/SIMULINK. This new design method gives us a simple way to design a

speed controller for a servo motor and design in discrete time systems. The

experimental is used to obtain the transfer function to design PID controller [12].

This reference is denoting how to design the PID controller. A PID feedback loop

can maintain the system stability because it can eliminate the error, reduce the

overshoot and reduce the settling time. The basic concept of PID control can be

generalized within the same structure PID controller design method was proposed to

deal with both performance and robust stability specifications for multivariable

processes in order to give the best performance for servo motor controller in the

future [12].

2.5.3 Title : PID Controller Design For Controlling DC Motor Speed Using

MATLAB Application. [13]

This project was about the development of a PID controller design for DC motor

using MATLAB. IN this project, firstly, a PID controller was designed using

MATLAB/ Simulink software. The mathematical mode of Dc motor was then

developed using Ziegler-Nichols method and trial and error method. Next, the control

algorithm was built in the Matlab/ Simulink software and compiled with Real-Time

Window Target. The Real-Time Window Target Toolbox includes an analog input

and analog output that provide connection between the data acquisition card (PCI-

19

1710HG) and the simulink model. The system used Litton - Clifton Precision Servo

DC Motor JDH-2250.

2.5.4 Title : DC Motor speed and position control using analog PID controller.

[14]

This paper presented the real time DC motor speed and position control in order to

know the function of PID controller as an operational amplifier. DC motor control

has been used for variable speed and position applications for many decades and

historically were the first choices for speed control applications requiring accurate

speed control, controllable torque, reliability and simplicity. The PID controller was

designed by using MATLAB/ Simulink to obtain the best coefficients that could

achieve the performance requirement of the DC motor. Then, the estimated

parameters was transfered to the hardware part that executed the PID controller. The

graphical user interfaces (GUI) was developed using Microsoft Visual Basic 6.0 to

plot and monitor the system response in real time [13]. Based on the concept that

showed in this paper, the output from the control system could be connected with

personal computer through DAQ that showed the response of the system. In this part,

analog signal from plant was converted to digital signal and transfer to personal

computer to plot and analyze the response during operation. During the experiment,

the PID controller corrected the error by calculating and analyzing it that resulted in

increasing transient response between the command and actual movement.

2.5.5 Title : Real –Time DC Servo Motor Position Control by PID Controllers

Using Labview. [15]

This paper was about the design of a position control of a DC servo motor using PID

Control algorithms. The controller was designed based on Labview program and the

real - time position control of the DC servo motor was realized by using DAQ

20

device. All the codes were developed in the Labview Real-Time Development

System and then downloaded the real-time code to run embedded applications on a

PXI. The servo systems are generally controlled by conventional Proportional

Integral Derivative (PID) controllers. This system aimed to achieve some of the

criteria when applied PID controller such as less steady state error, minimum settling

time, minimum rising time and less overshoot at the system. To achieve the aims,

the authors adjusted the PID controller parameters by using some other tuning

techniques. The system provided output position in real time in order to obtain

system responses of PID controller.

2.6 Conclusion

All the references for this project’s literature review have helped the author to focus

on preparation of the project and generate ideas to execute this project successfully.

The PID controllers used by those papers prove that they are efficient in controlling a

DC motor.

21

CHAPTER 3

METHODOLOGY

In this chapter, method and alternatives that have been used for designing the

controller are discussed and explained in detail, including steps for getting the state-

space model of the Dc motor, PID design, hardware configuration and the

implementation of PID controller on microcontroller, PIC.

3.1 System Overview

Proportional -Integral-Derivative (PID) controller design for servo motor consists of

two main parts in designing mathematical model for controller (PID) and servo

motor. In this project, PID controller is designed using MATLAB software then

compared with the designed system generated. This PID controller can compare the

results by using simulation and hardware result.

22

3.2 Flowchart of PID Controller Design For Dc Servo Motor.

Figure 3.1 shows the flowchart used as a guideline in completing the project.

Figure 3.1: Sequences of PID Controller Implementation on the DC

Servomotor

Mathematical Model of Controller (PID)

Design Block Diagram

Implement the Design in MATLAB

Simulation and Analysis

Find the best value

of PID

Output and Result

ERROR?

END

YES

YES

NO

NO

Interface with hardware

Simulation and Analysis

ERROR?

23

Figure 3.2 illustrates the flowchart to implement the PID controller.

Figure 3.2: The PID controller design for position control project methodology.

Start

General Literature Review

Research on the Potential of Digital Servo Motor Control

Available

Modeling of Digital Servo Motor Control

Design PID Controller

Debug and Troubleshooting

Use MPLAB X IDE for the Software

Development

Error

Thesis Writing

End

Yes

No

No

Yes

Test performance of PID Controller

24

3.3 Methods and Approach

3.3.1 Digital Servo Motor Control

The hardware of the servo system consists of the mechanical unit containing the Dc

brush-type servo motor, motor shaft encoder, rail encoder, platform, belt drives and

pulleys for moving the platform, flywheel and friction brake.

The digital servo system uses a brush-type permanent-magnet dc motor. As

with conventional Dc motors that employ a field winding, permanent-magnet Dc

motors create mechanical energy by the interaction between the magnetic field

created by current flowing through the armature windings and the magnetic field

created by the permanent magnet [8].

The interaction between these two magnetic fields produces a force (called

the torque) that causes the rotor/armature to rotate. The connections to the armature

windings are made through brushes, which commutate or switch the current to the

armature winding loops in order to produce a torque that causes the rotor/armature

assembly to rotate continuously. Reversing the polarity of the dc power supply to the

armature results in a current flow to the armature windings that produces a torque

causing the rotor/armature to rotate in the opposite direction.

3.3.2 Servo Motor Modeling

Servo motor is used for position or speed control in closed loop control systems. The

equivalent circuit diagram of servo motor is presented in Figure 3.3. The armature is

modelled as a circuit with resistance, Ra connected in series with an inductance, La

and a voltage source, Vb(t) representing the back emf in the armature when the rotor

rotates.

53

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