DESIGN AND IMPLEMENTATION OF MULTIPLE USER MOBILE ROBOT

FOLLOWING SYSTEM

ZAHARI BIN HASAN

A project report submitted in partial

fulfilment of the requirement for the award of the

Master of Electrical Engineering

Faculty of Electrical and Electronic Engineering

Universiti Tun Hussein Onn Malaysia

JUNE 2015

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ABSTRACT

Recently automation product for intelligent robot is increasingly getting very

common. By the help of intelligent robot technologies that increased comfort,

greater safety and security, life has been becoming easier [1]. With this system,

mobile robot can be controlled from any target. It is desirable in many

applications for a mobile robot to track and follow a person. The purpose of this

thesis is to detail the design and implementation of a mobile robot following

system through the use of beacons and remote control encoder decoder. This

project entailed the design and construction of a mobile robot with the capability

of determining its location in reference to know reference points and correct

address. The implementation involved the use of ultrasound to determine the

distance between the robot and known reference points and infrared decoder and

decoder to determine the correct leader. From the distance, the Cartesian

coordinates for the robot’s location along the horizontal plane where determined.

The produced robot was capable of navigating within a 2m by 2m square area

successfully. Possible source of error can be attributing to round of error due to

conversion from floating point to integer as well as errors within the reflection of

ultrasound frequency used to synchronize beacon transmission.

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ABSTRAK

Pada masa ini produk automasi untuk robot pintar semakin mendapat sambutan.

Dengan bantuan teknologi robot pintar yang dapat meningkatkan keselesaan,

keselamatan dan keselamatan , kehidupan telah menjadi lebih mudah [1]. Dengan

sistem ini, robot mudah alih dapat dikawal dari mana-mana sasaran. Ia adalah wajar

kerana dalam banyak aplikasi, robot mudah alih dapat mengesan dan mengikuti

seseorang. Tujuan tesis ini adalah untuk menerangkan dengan lebih jelas tentang

reka bentuk dan pelaksanaan sistem ikutan robot mudah alih dengan menggunakan

‘beacon’ dan pengkod serta penyahkod kawalan jauh. Projek ini melibatkan reka

bentuk dan pembinaan sebuah robot mudah alih dengan keupayaan menentukan

lokasinya dengan merujuk titik rujukan dan alamat yang betul. Pelaksanaan ini

melibatkan penggunaan isyarat ultrasonik untuk menentukan jarak antara robot dan

rujukan yang dikenalpasti untuk diikuti dan pengkod serta penyahkod inframerah

untuk menentukan bahawa sasaran untuk diikuti adalah betul. Dari jarak tersebut,

koordinat Cartesian untuk lokasi robot sepanjang satah mendatar dapat ditentukan.

Robot yang dihasilkan mampu bergerak dalam kawasan 2m x 2m dengan jayanya.

Kesalahan yang mungkin berlaku adalah disebabkan oleh penukaran nilai titik

perpuluhan ke nilai integer, juga boleh disebabkan oleh pantulan frekuensi

ultrasound yang digunakan untuk menyegerakkan isyarat pengeluar dari ‘beacon’ .

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CONTENTS

CHAPTER CONTENTS PAGE NO.

TITLE i

STUDENT DECLARATION ii

ACKNOWLEDGEMENT iii

ABSTRACT iv

ABSTRAK v

CONTENTS vi

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOL AND ABBREVIATIONS xvi

LIST OF APPENDICES xviii

CHAPTER 1 INTRODUCTION

1.1 Project Overview 1

1.2 Introduction 2

1.3 Problem Statement 3

1.4 Objective 4

1.5 Scope of Work 4

1.6 Flow Chart 5

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CHAPTER 2 LITERATURE REVIEW

2.1 Background of the chapter 7

2.2 Literature related to area of study 8

2.2.1 Sensor Based Approach 8

2.2.2. Transmitter and receiver Based 8

Approach

2.2.3 Following System Using Infrared based 9

Approach

2.2.4 Following System Using Blinking LED 10

Devices

2.2.5. Following System Using an Ultrasonic 11

Positioning System

2.2.6 Following System using Intelligent Space 11

Approach

2.2.7 Following Systems Using 12

Combined/Multi-Mode Approach

2.2.8 Microcontroller 12

2.2.9 Gps 14

2.2.9.1 Position Solution 15

2.2.9.2 Accuracy and Update Rate 15

2.2.10 Beacon Based Positioning System 16

CHAPTER 3 METHODOLOGY

3.1 Background 18

3.2 Ultrasonic, encoder and detector 19

3.2.1 Ultrasonic principle 19

3.2.2 Encoder design 22

3.2.3 Decoder design 22

3.3 Ultrasonic Transmitter design 23

3.4 Ultrasonic Receiver design 26

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3.5 Detection Circuit 27

3.6 Positioning System 28

3.7 Algorithm 32

3.7.1 Triangulation and Trialation 34

3.8 IFC (Interface Free Controller). 35

3.8.1 IFC-MB00 (Main Board) 36

3.8.2 IFC-PC00 (Power Card) 37

3.8.3 IFC-CP04 (Control Panel Card) 38

3.8.3 (a) Communication Address 38

3.8.4 IFC-BL002(Brushless Motor Card) 39

3.8.5 IFC-DI08 (Digital Input Card) 39

3.8.6 IFC-AI08 (Analogl Input Card) 40

3.9 Brushless DC Motor 41

3.10 Block Diagram 42

3.11 MPLAB® C Compiler for PIC18 MCUs (C18) 42

3.12 MPLAB®

X Integrated Development 43

Environment (IDE)

3.13 Basic Control System Concepts 44

3.13.1 The open loop system 44

3.13.2 The closed loop system 45

3.13.3 On/Off Controller 45

3.13.4 PID Controller 46

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3.13.4.1 The proportional term 48

3.13.4.2 The integral term 49

3.13.4.3 The derivative term 50

3.13.4.4 PID Control Loop Tuning 51

3.14 Software Implementation 51

3.14.1 Leader and the Follower Robot interaction 51

3.14.2 Software Implementation for the Follower 52

Robot

CHAPTER 4 RESULT

4.1 Background 55

4.1.1 Specification 55

4.1.2 Robot requirement 56

4.2. Ultrasonic Transmitter 57

4.2.1 Output Testing result 59

4.3 Ultrasound Receiver 61

4.4 Infrared Encoder 64

4.5 IR Decoder 71

4.6 Sensor Assembly Testing 76

4.6.1 ADC Conversion formula 76

4. 7 PID Tuning 80

4.7.1 P Controller 83

4.7.2 Integral Controller 84

4.7.3 Derivative Controller 85

4.8 The implemented Hardware 87

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CHAPTER 5 CONCLUSION AND RECOMMENDATION

5.1 Background 89

5.2 Conclusion 89

REFERENCES 91

APPENDIX A 94

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

Table 4.1

Table 4.2

Table 4. 3

Table 4. 4

Table 4. 5

Table 4. 6

Expected Result

Checking Digital Value for Ultrasonic Receiver (RX)

Sensor detection testing

P controller Test Result

PI Controller Test Result

PID Controller Test result

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

Figure 1.1

Figure 2.1

Figure 2.2

Figure 2.3

Figure 2.4

Figure 2.5

Figure 2.6

Figure 3.1

Figure 3.2

Figure 3.3

Figure 3.4

Figure 3.5

Figure 3.6

Figure 3.7

Project Flow Chart

Configuration of nine ultrasonic range finders installed on

the follower.

Configuration where the threshold configuration where the

threshold determined and the values ofhe thresholds.

The robot follows the human using a camera and the image

of LEDs obtained from camera mounted on the robot.

Typical structures of a microcontroller and personal

computer system

Global Position System Illustration

Beacon Based Positioning for office equipment

The flow chart of project implementation

Ultrasonic principles

Ultrasonic Tx and Rx Principles

(a) Ultrasonic wave propagation (b)ultrasonic sensor

frequency (c) ultrasonic sensor directivity

IR encoder.

Remote control Decoder

Control Pulse Generator

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Figure 3.8

Figure 3.9

Figure 3.10

Figure 3.11

Figure 3.12

Figure 3.13

Figure 3.14

Figure 3.15

Figure 3.16

Figure 3.17

Figure 3.18

Figure 3.19

Figure 3.20

Figure 3.21

Figure 3.22

Figure 3.23

Figure 3.24

Figure 3.25

Figure 3.26

Figure 3.27

Figure 3.28

Figure 3.29

Figure 3.30

Figure 3.31

Figure 3.32

Figure 3.33

Figure 3.34

40Khz Pulse Generator

Ultrasonic driver Circuit

Ultrasonic driver Circuit

Inverting Amplifier

Detection Circuit

Sensor positioning

(a) middle sensor ON, (b) right sensor ON, (c) Left

sensor ON ,(d) Robot turn until middle sensor ON

Detection Algorithm

Trialation

Triangulation

IFC Card

IFC-MB00

IFC-PC00

IFC-CP04

IFC-BL02

IFC-DI08

IFC-AI08

Brusless DC Motor.

Mobile Robot Following System.

Block Diagram of 2 Basic Control system

on/off Controller

Block Diagram of a PID control system

step response waveforms of a system with high and low Kp

gain constants

step response waveforms of a system with tuned Kp value

and Ki Constant.

Following robot signal interaction

Flow Chart for Follower Robot

Flow chart of following robot movementUltrasonic

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Figure 4.1

Figure 4.2

Figure 4.3

Figure 4.4

Figure 4.5

Figure 4.6

Figure 4.7

Figure 4.8

Figure 4.9

Figure 4.10

Figure 4.11

Figure 4.12

Figure 4.13

Figure 4.14

Figure 4.15

Figure 4.16

Figure 4.17

Figure 4.18

Figure 4.19

Figure 4.20

Figure 4.21

Figure 4.22

Figure 4.23

Figure 4.24

Figure 4.25

Figure 4.26

Figure 4.27

Figure 4.28

Figure 4.29

Transmitter circuit

PCB layout for Ultrasonic Transmitter Beacon

Result for Ultrasonic TX Output

40 Khz sonic Burst

Operating region of transistor

Ultrasonic Receiver Circuit Diagram

Time Domain(Transient) simulation in Proteus

Simulation Result in Proteu

(a)Output before rectifier

(b) Output After rectifier

HT 12E block diagram

Transmission timing for the HT12E

Flow chart fot HT12E

Oscillator Frequency vs. Supply Voltage

IR Encoder Schematic Diagram

Simulation result on astable timer output 38KHz

PCB layout fo IR Encoder

Address testing for IR encoder

Address Carried by 38KHz Carrier Frequency

HT 12D block diagram

Timing diagram for HT12D

Flow chart for HT12D

IR Decoder Schematic Diagram

PCB layout fo IR Decoder

Address Carried by 38KHz Carrier Frequency

Signal Received at HT12D

Graph for Sensor detection testing

Source code for Sensor comparasion

Graph for Sensor detection testing

Source code for PID variable selection

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Figure4.30

Figure 4.31

Figure 4.32

Figure 4.33

Program for PID updated value

IR and Ultrasonic Transmitter

Receiver sensors front View

Overall system

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LIST OF ABBREVIATION

A Ampere

B Binary

CPU Central Processing Unit

D Decimal

GPS Global Positioning System

I Current

IFC Interface Free Card

LED Light Emitting Diode

MC Microcontroller

PC Personal Computer

R Resistance

RF Radio Frequency

RAM Random Access Memory

ROM Read Only Memory

V Volt

H Hexadecimal

AC Alternating Current

DC Direct Current

PIC Programmable Interface Controller

PID Proportional Integral Derivative

IFC Interface free Card

TOF Time of Flight

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IR Infrared

IRR Infrared Receiver

TX Transmitter

RX Receiver

xviii

LIST OF APPENDICES

A C-18 Program For Multi User Mobile Robot Following

System

PAGE

94

CHAPTER I

INTRODUCTION

1.1 Project Overview

This paper presents the result of efforts to design and implement a mobile robot

following system in part to fulfill the requirement for the UTHM. The Mobile robot

following system incorporates the use of encoder and decoder device with ultrasonic

sensors as a following system. This project is a two-semester endeavor and this paper

presents the hardware and software design and a detail description of testing and

building of the system. This lays the framework for the rest of the robotics

development platform while thoroughly exploring the behavior of a human following

robot system.

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1.2 Introduction

In recent years, mobile robot has become autonomous enough to suite the application

in our life. Navigation within local environments may be comprised of various

methods however this report addresses the use of navigation relative to beacons.

Navigation relative to beacons utilizes the distance or direction between the robot and

beacon utilizes the distance or direction between the mobile robot and several beacons

in order to determine the position of the mobile robot relative to the beacon. If the

beacon positions are known, the robot will be able to recognize its own position

within its operational environment. Active beacon has been used in this project. In

order to determine location relative to beacons the robot may utilize either

triangulation or trialation. Triangulation refers to the use of the angle measurements

between the robot and the various beacons while trialation uses distance

measurements. An active beacon is a system where the beacon transmits its location,

through a signal, to the robot. This usually consists of ultrasound or radio transmitters,

which are synchronized either by a single beacon controller or by the robot itself. The

mobile robot detects the transmissions of these beacons and uses either the distance

(calculated through DTOF measurements) or angle measurements to determine its

position. An IFC Mobile Robot with an additional encoder and decoder with

ultrasonic positioning system have been adopted to implement specific human-

following system. The first stage is human positioning. Encoded signals and

ultrasonic signal are transmitted from beacon located on a specially made casing,

which the target leader wears. The signals will be received by ultrasonic receivers

and IR decoder located on the Mobile Robot, this coded address can be change in the

controller to match it with the transmitter, five(5) ultrasonic sensors will be use to

control the robot algorithm. Finally, with the readings from the ultrasonic positioning

system, a potential field based motion algorithm is formed [1]. Basically, the leader

in leader/follower behavior is the target that is followed by the other robot (follower).

The leader (target) can be either human or robot. The follower, which is a robot, need

to follow the leader autonomously. The task of this behavior is called task following.

When a follower robot performs a task following, the most important thing for the

follower is to be able to obtain the position of the leader. The follower must be able to

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obtain its current position relative to the target before it makes decision on how to

follow the target. “Localization” or knowledge of its current location is calculated by

one or more means, using sensors such as motor encoder, vision, laser or sonar

sensors. There are many vision systems being built to track and follow the target

effectively. The method can be seen in [11], [12] and [13].

1.3 Problem Statement:

The idea to invents and develops the Mobile Robot Following System begin when

Few applications of cooperative robotics have been reported, and supporting theory is

still in its formative stages [14]. One of the main tasks for cooperative wheeled

mobilerobots [15] is the object (target) following task, which usually represents to

follow another robot. Also, the following task is important for the wheeled mobile

robots in [9], [10] and the target can be static or a dynamic object. There are many

problems arise when designing a robot to perform a following task. These problems

include robot may looses or hits the target being followed. Besides, the robot may also

choose not to follow the desired object and goes after another detected object from the

environment in a dynamic environment. Current human-tracking mobile robots also

are not capable of operating in unstructured environments. Because several main

approaches, such as vision and infrared sensors, are not fully reliable in all situations

and it cannot give a condition to differentiate which target to follow, it is necessary to

explore other methods. The main objective of this research is to investigate the

feasibility of developing an intelligent human-following robot system so that it can

support human in everyday life by interacting with specific human. In this research

the positioning system using a encoder/decoder with ultrasonic will be consider.

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1.4 Objective

The main objective is to design and implement the mobile robot following system

using an IR encoder/decoder/ and ultrasonic beacon positioning system, equipped on

the IFC mobile robot. There are 3 main objectives, at least to be achieved during the

time frame of the project as follows:-

1. To design and construct an autonomous following robot system.

2. To integrate the concept of selected leader/follower behavior.

3. To improve the capability of the mobile robot in performing the

following task smoothly by Programming a PID controller in the

system.

1.5 Scope of work

The project will be done by limiting the scopes into four (4). The scopes are as

follows:

1. The working model will only use IR encoder/decoder channel.

2. This mobile robot can be only move in linear platform.

3. Detection of target distance is 0 to 3 meters.

4. Mobile Robot is control by using PIC microcontroller and program the PIC via

MPLAB programming software with C-18 compiler.

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1.6 Flow chart

Figure 1.1 : Project Flow Chart

If decoder= encoder

Set decoder

Address (robot)

Follow target (Ultrasonic Beacon)

Start

If distance <x

If target move Right

If target move Left

If distance >x

Check

Algorithm

Stop

Calculate the

different

Calculate the

different

Calculate the

different

Move towards

Target

Turn until sensor facing

the target

Turn until sensor facing

the target

Yes

Yes

Yes

Yes

No

No

No

No

Target send

encoded Signal

Yes

Stop No

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The flow chart of the project is shown in figure 1.1, From the flowchart, IFC Mobile

robot must be set for certain channel address. First the target must send channel data

(encode) through IR frequency carrier that is 38Khz, the receiver at the Mobile Robot

will decode the data, if the address code did not match it will stop, and when it find its

match address code, the mobile robot will follow the target that have the same

channel with it by calculating the different from ultrasonic TX and ultrasonic RX .

When it find an obstacle it will try to find the target according its algorithm program.

This Mobile robot will be equipped with five (5) 40Khz ultrasonic distance sensor

that will check the status of the target movement itself. The Ultrasonic sensor will be

use to determine whether the target move left, right or stop.

CHAPTER 2

LITERATURE REVIEW

2.1 Background

A literature review was done to identify the main problems those are affect on this

project. For this research it is necessary to identify which part are related to the

project. This chapter will present background information about several position

systems that are conventionally used for autonomous robot following system and

review some of the robots that were built to perform the task following. Position and

orientation information can be relative or global. The knowledge of the global or

relative orientation and position of a robot provides the ability to create advanced

control strategies and can be used to improve the overall perception of a following

environment.

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2.2 Literature related to area of study

2.2.1 Sensor Based Approach

A non-vision based approach uses several kinds of rangefinders, such as sonar

sensors, infrared sensors, and others. Each rangefinder on the robot can determine the

distance between the nearest object and the rangefinder itself. Because the robot is not

able to distinguish between object and target person, this approach can only be

adopted to implement either obstacle avoidance when regarding all the objects as

obstacles or person-tracking when the target person is always the nearest object to the

robot without any obstacle in between [1-10].

2.2.2. Transmitter and receiver Based Approach

Using a transmitter and receiver approach, the transmitters located on the target

person transmit signals, such as ultrasonic waves or blinking LED. The receivers

located on the mobile robot receive these signals. After computing the distance and

the angle of the target from those signals, the robot knows where to move in order to

turn itself toward the target person and decrease the distance in between. In [1], [5],

[6] a transmitter and receiver based approaches have been discussed.

2.2.3 Following System Using Infrared based Approach

The main method in following system is potential field method, where the follower

was “attracted” to the target and was “pushed away” from the obstacles [7]. Using an

Infrared approach, IR receiver is installed inside a black hollow cylinder , the IR

receiver can receive the signal emitted from the IR transmitter only when the

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transmitter is placed in front and along with the axis of the cylinder, which confirms

the directional property of the light. The detection range of the receiver can be

adjusted by placing the side walls around the receiver. One of the simplest methods to

deploy several receivers to cover the front 180-degree detection range is to equally

divide the detection range by the number of the utilized receivers, just like slicing the

cake [1] as shown in figure 2.1 and 2.2.

Figure 2.1 Configuration of nine ultrasonic range finders installed on the follower

Figure 2.2 :Configuration where the threshold configuration where the threshold

determined and the values ofhe thresholds

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2.2.4 Following System Using Blinking LED Devices

This approach requires equipping the target person with two infrared LED devices

with fixed distance between them and using a camera on the robot to detect the two

devices. This is similar to the vision-based approach. The main difference is that the

signals from infrared LED devices should be firmer and not affected by the

disturbance in the environment, as long as they are not blocked by any obstacle. The

camera is able to rotate to keep the target person in the middle of the image. By

computing the distance between two LED lights and the deviation of the two lights

from the central vertical axis in the image, the range and the bearing of the target

person can be obtained respectively by the robot [8] as shown in figure 2.3.

Figure 2.3: The robot follows the human using a camera and the image of LEDs

obtained from camera mounted on the robot.

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2.2.5. Following System Using an Ultrasonic Positioning System

This approach is to equipped the ultrasonic transmitters on the target person and the

receivers on the robot. By computing the time interval between transmitting and

receiving the ultrasonic signal, the distance between the target person and the robot

will be determined. The angle can also be computed from the time delay between

several receivers. These approaches are straight-forward for person-tracking, but they

are not suitable when there are obstacles between the target person and the robot. The

detection of obstacles will be a problem using these approaches. Without any

additional mechanism, the robot is not able to implement obstacle avoidance. [2]

2.2.6 Following System using Intelligent Space Approach

The intelligent space approach [9], [10] utilizes several sensors, such as visual or non-

visual sensors that are located in the environment to detect both the robot and the

target person. Therefore, the position information of the robot and target person will

be in the global coordinate and determined by the sensors in the intelligent space.

From the relative positions of the robot and the target person, the robot motion will be

planned by this intelligent space and controlled through the network. However, the

desired approach in this research is to design an autonomous robot that implements

tasks in unstructured environments. This approach then becomes unsuitable although

it well function.

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2.2.7 Following Systems Using Combined/Multi-Mode Approach

A combined/multi-modal approach is made of a combination of several approaches. It

is able to gather the advantages of each single approach. This is also the key subject in

this thesis. By using an ultrasonic positioning system along with the IR decoders, this

research combines the transmitter-and-receiver based approach with the non-vision

based approach. A suitable algorithm also will be designed to adapt the robot to

several situations that may happen in the implementation of person-tracking. The

robot can then accomplish the person-tracking tasks, which include person-following

and obstacle avoidance in unstructured environments [6].

2.2.8 Microcontroller

Like most computers, microcontrollers (MCs) are simply general-purpose instruction

executors. Like the computer, the effectiveness of an MC depends amongst other

things upon the program of instructions provided to it and hence the skill of the

programmer. A program is a series of instructions that step the computer through a

sequence of simple data manipulations to accomplish useful tasks. In all cases MCs

are small stand-alone computer systems designed for the purpose of control whereas a

personal computer (PC) is primarily designed to process large amounts of data

quickly. An MC has all of the components on a single chip, such as CPU, RAM,

ROM, inputs and outputs. A microprocessor is simply a CPU and needs the RAM,

ROM, inputs and outputs to be added to the system. Shown in figure 2.4.

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Following are the reasons why microcontrollers are incorporated in this control

systems:

a. Cost: Microcontrollers with the supplemantary circuit components are much

cheaper than a computer with an analog and digital I/O.

b. Size and Weight: Microcontrollers are compact and light compared to

computers.

c. Simple applications: If the application requires very few number of I/O and

the code is relatively small, which do not require extended amount of memory

and a simple LCD display is sufficient as a user interface, a microcontroller

would be suitable for this application.

d. Reliability: Since the architecture is much simpler than a computer it is less

likely to fail.

e. Speed: All the components on the microcontroller are located on a singe piece

of silicon. Hence, the applications run much faster than it does on a computer.

Figure 2.4: Typical structures of a microcontroller and personal computer system

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2.2.9 GPS

Global Position Systems are widely becoming the position system of choice for

autonomous navigation. This technology allows for an agent to determine its location

using broadcasted signals from satellites overhead. The Global Positioning System

associated with the United States is maintained by the Department of Defense to

providea positioning service for use by the US military [17]. Since its creation, the

service hasbeen used for commercial purposes such as nautical, aeronautical, and

ground based navigation, and land surveying. The current US based GPS satellite

constellation system consists of a 24-satellite system. The number of satellites for this

system can vary due to satellites being taken in and out of service. Other countries are

leading efforts to developalternative satellite systems for their own GPS systems. A

similar GPS systems is the GLONASS constructed by Russia [17]. Each satellite

maintains its own specific orbit and circumnavigates earth once every 12 hours. The

orbit of each satellite is timed and coordinated so that five to eight satellites are above

the horizon of any location on the surface of earth at any time. Figure 2.5 illustrates

the manner by which an autonomous vehicle determines its’ position using GPS.

Fig. 2.5: Global Position System Illustration

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2.2.9.1 Position Solution

A GPS receiver calculates position by first receiving the microwave RF signals

broadcast by each visible satellite [17]. The signals broadcasted by the satellites are

complex high frequency signals with encoded binary information. The encoded binary

data contains a large amount of information but mainly contains information about the

time that the data was sent and location of the satellite in orbit. The GPS receiver

processes this information to solve for its position and current time.

2.2.9.2 Accuracy and Update Rate

GPS receivers typically provide position solutions at 1Hz but GPS receivers can be

purchased that output position solutions up to 20Hz. The accuracy of a commercial

GPS system without any augmentation is approximately 15 meters [19]. Differential

GPS is an alternative method by which GPS signals from multiple receivers can be

used to obtain higher accuracy position solutions. Differential GPS operates by

placing a specialized GPS receiver in a known location and measuring the errors in

the position solution and the associated satellite data. The information is then

broadcast in the form of correction data so that other GPS receivers in the area can

calculate a more accurate position solution. This system is based on the fact that there

are inherent delays as the satellite signals are transmitted through the atmosphere.

Localized atmospheric conditions cause the satellite signals within that area to have

the same delays. By calculating and broadcasting the correction values for each

visible satellite the differential GPS system can attain accuracy from 1mm to 1cm

[17]. Recently a new type of GPS correction system has been integrated so that a land

based correction signal is not required to improve position solutions. The Wide Area

Augmentation System sends localized correction signals from orbiting satellites [18].

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Currently this system only covers most of North America. This type of system has

been used in research and position solutions with errors of less than three meters have

been observed.

2.2.10 Beacon Based Position Systems

This type of position system is based on determining the position of a mobile agent by

actively or passively communicating with devices in the environment. These devices

can range from RF and ultrasonic transmitters to signal reflectors similar to those used

for Radar. This system typically relies on knowledge of beacon positions apriority.

With an accurate locations of the various beacons in the environment, a mobile agent

can calculate its’ position and orientation by using the perceived geometric

relationship between the beacons. Shown below in Figure 2.6 is an illustration of a

typical beacon configuration for determining the position and orientation of a mobile

agent. GPS is a form of space based beacon position system. Typically an

autonomous agent determines the distances and or angles from its position and

orientation to the specified beacon and combines this information with that of other

beacons. Beacon based position systems can be used for many types of navigation but

have limitations dependent on their configurations. Historically, aircraft used to

perform navigation by receiving land based beacon signals [16]. Each beacon had a

specific broadcast frequency. An aircraft would tune into the broadcast frequencies of

the beacons located at the departure and arrival destinations. Using the information

derived from relative angles of the beacons, an aircraft could maintain a direct flight

path. This system caused problems due to the constraint and inefficiency of direct

flight paths. This system also required large numbers of beacons to be placed across

the country to accommodate typical flight paths. The system also presented problems

when traveling across large oceans where intermediate beacons could not be placed.

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Fig. 2.6: Beacon Based Positioning for office equipment

CHAPTER 3

METHODOLOGY

3.1 Background

This part of section is mainly to shown the flow of methods used in this project.

Predetermine the steps involved in any project can predict on the instruments,

procedures, results, cost and others. This is very important to researcher because, time

frames of dividing the research part can save time and deliver optimum results. The

method in form of flow chart that involved in this project is discussed as shown in

figure 3.1.:

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Figure 3.1: The flow chart of project implementation

3.2 Ultrasonic, encoder and detector :

3.2.1 Ultrasonic principle:

Ultrasonic sensors emit short, high-frequency sound pulses at regular intervals. These

propagate in the air at the velocity of sound. If they strike an object, then they are

reflected back as echo signals to the sensor, which itself computes the distance to the

target based on the time-span between emitting the signal and receiving the echo,

refer to figure 3.2.

Documentation

and Thesis

writing

Literature

review

Problem Statement

Design Ultrasonic Transmitter

and Receiver

Design IR encoder and decoder

Design Mobile Robot Using IFC

Card

Software

Decoder

Design Target Positioning and

algorithm software

START

Start

END End

20

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Figure 3.2 Ultrasonic principle

As the distance to an object is determined by measuring the time of flight (TOF) and

not by the intensity of the sound, ultrasonic sensors are excellent at suppressing

background interference. Virtually all materials which reflect sound can be detected,

regardless of their color. Even transparent materials or thin foils represent no problem

for an ultrasonic sensor. Ultrasonic sensors are suitable for target distances from 20

mm to 10 m and as they measure the time of flight they can ascertain a measurement

with pinpoint accuracy. Some of ultrasonic sensors can even resolve the signal to an

accuracy of 0.025 mm. Ultrasonic sensors can see through dust-laden air and ink

mists. Even thin deposits on the sensor membrane do not impair its function. Sensors

with a blind zone of only 20 mm and an extremely thin beam spread are making

entirely new applications possible today. Fill level measurement in wells of micro

titer plates and test tubes, as well as the detection of small bottles in the packaging

industry, can be implemented with ease. Even thin wires are reliably detected. Sound

is our inner ear's ability to detect the variations in air pressure caused by vibration.

The rate of these variations determines the pitch of the tone. Higher frequency tones

result in higher pitch sounds and lower frequency tones result in lower pitch tones.

Most people can hear tones that range from 20 Hz, which is very low pitch, to 20 kHz,

which is very high pitch. Subsonic is sound with frequencies below 20 Hz, and

ultrasonic is sound with frequencies above 20 kHz. Since the sensor's are at 40 kHz,

they are definitely ultrasonic, and not audible as shown in figure 3.3 and 3.4.

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Figure 3.3 Ultrasonic Tx and Rx Principles

(a) (b)

(c)

Figure 3.4 (a) Ultrasonic wave propagation (b)ultrasonic sensor frequency,

(c) ultrasonic sensor directivity

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3.2.2 Encoder design:

An encoder is a circuit that accepts an active level on one of its inputs, representing

digit, such as a decimal or octal digits, and converts it to a coded output such as BCD

or binary. Encoders can also be devised to encode various symbols and alphabetic

characters. The process of converting from familiar symbols or numbers to a coded

format is called encoding. Figure 3,5 shows the IR encoder.

Figure 3.5 IR encoder

3.2.3 Decoder design:

A decoder is combinational logic circuit that essentially performs a “reverse” of

encoder functions. A decoder is a logic circuit that accepts a set of inputs that

represents a binary number and activates only the output that corresponds to the input

number. In other words, a decoder circuit looks at its inputs, determines which binary

number is present there, and activates the one output that corresponds to that number

23

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; all other outputs remain inactive. In its general form, a decoder has N input lines to

handle N bits and form one to 2 N address lines to indicate the presence of one or

more N-bit combinations. Fig 3.6 shows the IR decoder.

Figure 3.6 Remote control Decoder

3.3 Ultrasonic Transmitter design

Figure 3.7:Control Pulse Generator

IC1 inFigure 3.7 is the oscillation circuit to control the sending-out time of the

ultrasonic pulse, fi. The circuit is the same as the ultrasonic range meter but the value

of the resistors and the capacitors are changed. The oscillation frequency is the same.

24

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The time of the oscillation pulse can be calculated by the following formula. Actually,

with the error of the parts, it is different from the calculation a little.

The condition : RA = 1M-ohm, RB = 15K-ohm, C = 0.1µF

TL = 0.69 x RB x C

= 0.69 x 15 x 103 x 0.1 x 10-6

= 1 x 10-3

= 1 msec

TH = 0.69 x ( RA + RB ) x C

= 0.69 x 1015 x 103 x 0.1 x 10-6

= 70.0 x 10-3

= 70 msec

Figure 3.8: 40Khz Pulse Generator

IC2 in figure 3.8 is the circuit to make oscillate the ultrasonic frequency of 40KHz.

Oscillation's operation is same as IC1 and makes oscillate at the frequency of about

40 KHz. It makes RB>RA to bring the duty(Ratio of ON/OFF) of the oscillation wave

close to 50%. The frequency of the ultrasonic must be adjusted to the resonant

frequency of the ultrasonic sensor. Therefore, I am made to be able to adjust the

oscillation frequency by making the RB the variable resistor (VR1). The output of IC1

is connected with the reset terminal of IC2 through the inverter. When the reset

91

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