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Intelligent Mobile ROBOTNavigation Technique UsingRFID Technique
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* I N D E X *
Abstract..3Introduction..4RFID technology..5Using RFID for Accurate Positioning .7
RFID BackgroundRFID Positining
Microprocessors..Driving relaysEncoder HT 12 EDecoder HT 12 DRF TransmitterRF ReceiverAtmel 89C2051 MicroController
System ArchitectureRFID communication ModuleFLC Navigation Module
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# A B S T R A C T #
The mobile robot is controlled using mobile and wireless RF
communication. In this method controlling is done depending on thefeedbackprovided by the sensor. This contains different modules
such as
Wireless unit module
Sensing and controlling module
When no prior knowledge of the environment is available, the problem
becomes even more challenging, since the robot has to build aMap of
Its Surroundingsas it moves. These three tasks ought to be solvedin conjunction due to their interdependency.
In the sensing module when thePIC micro controller is powered upby the high-speed dc motors. The sensor is mounted on the robot.
The encoder mounted on the robot transmitting the data continuously
And a number of standard RFID tags attached in robots environment
to define its path. Here the robot consists of Transmitter and
receiver. Here thefrequency used is 433 kHz.
Here we show that using RF signals from the RFID tags as an analog
feedback signals can be promising strategy to navigate a mobile robotwithin an unknown or uncertain environment.
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# INTRODUCTION #
This method is computationally simpler and more cost effective than
many of its counterparts in the state-of-the-art. It is also modular
and easy to implement since it isindependent of the robots
architectureand its work space. The main idea is toexploit the
ability of a mobile robotto navigate a priori unknown environments
without a vision system and without building an approximate map of the
robot
workspace, as is the case in most other navigation algorithms. The
suggested algorithm iscapable of reaching a target point in its a
priori unknown workspace, as well as tracking a desired trajectory
with a high precision.
The proposed algorithm takes advantage of the emerging Radio
Frequency Identification (RFID) technology and a Fuzzy Logic
Controller (FLC) to guide the robot to navigate in its working volume.
This navigation method is based on continuous encoder readings that
provide the position, orientations and linear and angular velocities of
robot.
Several modules are involved in operating mobile platforms, such as,for example, the localization, navigation, obstacle avoidance, and path
planning modules.
The most common and popular navigation methods proposed in the
literature to date rely on dead-reckoning based, landmark-based,
vision-based, and behavior-based techniques.
(dia : fig 1 of 65 pdf)
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# RFID TECHNOLOGY #
RFID is an automatic identification method that relies on storing and
remotely retrieving data.
A basic RFID system consists of three components:
An antenna or coil
A transceiver (with decoder)
A transponder (RF tag) electronically programmed with unique
information
TheAntennaemits radio signals to activate the tag and to read and
write to it.Thereaderemits radio waves in ranges of anywhere from one inch to
100 feet or more, depending upon its power output and the Radio
Frequency used. When an RFID tag passes through the
electromagnetic zone,it detects the readers activation signal.
The reader decodes the data encoded in the tags integrated circuit(silicon chip) and the data is passed to thehost computerfor
processing
The purpose of an RFID system is to enable data to be transmitted by
a portable device, called a tag, which is read by an RFID reader and
processed according to the needs of a particular application. The data
transmitted by the tag may provide identification or location
information, or specifics about the product tagged, such as price,
color, date of purchase, etc. RFID quickly gained attention because of
its ability to track moving objects.
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Using RFID for Accurate Positioning
The RFID positioning can be divided into four steps: in the first step, install RFID
tags on roads in a certain way, store very accurate location information along with
other necessary information to the tags, add an RFID reader module to thenavigation system, and use this new location information. Apart from the RFID
system, we also propose to use a tag database. Due to the memory constraint on
the tag and the data size that needs be written in a tag, the use of a database for
tags is a necessary condition. In addition, the speed of the RFID communication
also makes the use of the tag database indispensable.
RFID BACKGROUND:
In this section a brief overview of RFID technology in general is given. An RFID
system consists of tags, a reader with an antenna, and software such as a driver
and middleware. The main function of the RFID system is to retrieve information
(ID) from a tag (also known as a transponder). Tags are usually affixed to objects
such as goods or animals so that it becomes possible to locate where the goods and
animals are without line-of-sight. A tag can include additional information other
than the ID, which opens up opportunities to new application areas.
An RFID reader together with an antenna reads (or interrogates) the tags. An
antenna is sometimes treated as a separate part of an RFID system. It is,
however, more appropriate to consider it as an integral feature in both readers
and tags since it is essential for communication between them. There are two
methods to communicate between readers and tags; inductive coupling and
electromagnetic waves. In the former case, the antenna coil of the reader induces
a magnetic field in the antenna coil of the tag. The tag then uses the induced field
energy to communicate data back to the reader. Due to this reason inductive
coupling only applies in a few tens of centimeter communication. In the latter case,the reader radiates the energy in the form of electromagnetic waves. Some
portion of the energy is absorbed by the tag to turn on the tags circuit. After the
tag wake up, some of the energy is reflected back to the reader. The reflected
energy can be modulated to transfer the data contained in the tag.
Three frequency ranges are generally used for RFID systems: low (100~500 kHz),
intermediate (10~15 MHz), and high (850~950 MHz, 2.4~5.8 GHz). The
communication range in an RFID system is mainly determined by the output power
of the reader to communicate with the tags. The field from an antenna extendsinto the space and its strength diminishes with respect to the distance to tags.
The antenna desi n determines the shape f the field s that the ran e is als
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More data decreases the communication speed and requires more memory,
which leads to high cost.
In summary, there are issues to be addressed before full-fledged deployment of
RFID tags nationwide.
Making RFID tags that can withstand a harsh environment.
Fast communication speed between readers and tags. The data size
Figure 1. RFID Tags on a Road
Tag Database
While there would be location information in a tag, it would be almost impossible to
embed all the necessary information in a tag due to memory constraints and the
dynamic nature of some information. Information such as absolute coordinates of
the location will not be changed. On the contrary, relative coordinates and the
property of the road on which the tag is could change some time (unlikely, though).
Moreover, we can embed more useful information such as nearest museums,
restraints, and gas stations.
However, the contents of the information vary all the time. Thedata size as well
as the dynamic nature of it prevents from writing all the information at theinstallation time. To address this issue, wedevise a tag database which stores
information corresponding to the tagsavailable on the roads in a region (country
for instance). The information stored in the tag database is whatever information
on real tags and more such as point
of interests.
Another reason for the necessity of the tag database comes from the speed of
the RFID communication. It may not be fast enough to get all the information
from a tag while driving at, for instance, 150km/h. However, getting only
identification (ID) is very feasible even at such a high velocity. Once the ID isretrieved, it can be efficiently searched the tag database and extracted whatever
inf m ti n n c ss
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The tag database is a collection of tags and a part of the digital map that a
navigation system may carry. Generally, a digital map consists of cells each of
which contains network information for route guidance. The network information is
a graph with nodes and links.
Figure 2 shows a class diagram of the digital map. In the diagram, TagDB is an
aggregation of Tag objects which represent tags in a real world. Each cell has linksto the collections of nodes, links, and tags. For simplicity, we only show the
attributes of the Tag object. As in the diagram, a Tag object includes ID, absolute
coordinates X and Y, relative coordinates RX and RY, link ID where the tag is, and
the property field. This last field is for the number of lanes of the link, type of
the road (highway, local, etc), and so on. In Java language and most of other
programming languages, type long is 8 bytes, type float and int are 4 bytes, and
type short is 2 bytes.
F igure 2. Tag Database Class Diagram
The data size of a tag is 30 bytes. Therefore even with a million tags on the roads,thereby in the database, the size of the tag database is approximately 30MB.
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# MICROPROCESSORS #
Driving Relays:Using the outputs of the HT-12D or HT-648L decoder ICs to drive relays is quitesimple. Here are schematics showing how to drive relays directly from the data-
output pins of the decoder.
ENCODER HT12E :HT12Eis anencoder integrated circuitof 2
12
series of encoders. They are paired with212series of decoders for use in remote control system applications. It is mainly used in
interfacing RF and infrared circuits. The chosen pair of encoder/decoder should have
same number of addresses and data format.
Simply put, HT12E converts the parallel inputs into serial output. It encodes the 12 bit
parallel data into serial for transmission through an RF transmitter. These 12 bits are
divided into 8 address bits and 4 data bits.
HT12E has a transmission enable pin which is active low. When a trigger signal is received
TE i th d dd /d t t itt d t th ith th h d bit
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upon receipt of a transmission enable. This cycle is repeated as long as TE is kept low. As
soon as TE returns to high, the encoder output completes its final cycle and then stops.
FEATURESOperating voltage 2.4V~12V for the HT12E
Low power and high noise immunity CMOS technology
Low standby current: 0.1_A (typ.) at VDD=5V
HT12A with a 38kHz carrier for infrared transmission mediumMinimum transmission word Four words for the HT12E
Built-in oscillator needs only 5% resistor
Data code has positive polarity
Minimal external components
HT12A/E: 18-pin DIP SOP package
Pin Diagram:
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FLOW CHART
TIMING DIAGRAM
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HT12Dis adecoder integrated circuitthat belongs to 212series of decoders. This series
of decoders are mainly used for remote control system applications, like burglar alarm,
car door controller, security system etc. It is mainly provided to interface RF and
infrared circuits. They are paired with 212series of encoders. The chosen pair of
encoder/decoder should have same number of addresses and data format.
In simple terms, HT12D converts the serial input into parallel outputs. It decodes theserial addresses and data received by, say, an RF receiver, into parallel data and sends
them to output data pins. The serial input data is compared with the local addresses three
times continuously. The input data code is decoded when no error or unmatched codes are
found. A valid transmission in indicated by a high signal at VT pin.
HT12D is capable of decoding 12 bits, of which 8 are address bits and 4 are data bits. The
data on 4 bit latch type output pins remain unchanged until new is received.
FEATURESOperating voltage 2.4V~12V
Low power and high noise immunity CMOS Technology
Low standby current
Capable of decoding 12 bits of information Pair with Holteks 2 Series of encoders
Received codes are checked 3 times
Address/Data number combination
HT12D: 8 address bits and 4 data bits
HT12F: 12 address bits only
Built-in oscillator needs only 5% resistor
Easy interface with an RF or an infrared transmission medium
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Or Pdf (dia)
PIN DESCRIPTIONPORT 1
The Port 1 is an 8-bit bi-directional I/O port.
Port pins P1.2 to P1.7 provide internal pull-ups.
P1.0 and P1.1 require external pull-ups. P1.0 and P1.1 also serve as the positive input (AIN0)
and the negative input (AIN1), respectively, of the on-chip precision analog comparator.
The Port 1 out-put buffers can sink 20 mA and can drive LED displays directly.
When 1s are written to Port 1 pins, they can be used as inputs.
When pins P1.2 to P1.7 are used as inputs and are externally pulled low, they will source
current (IIL) because of the internal pull-ups.
Port 1 also receives code data during Flash programming and verification.
PORT 3 Port 3 pins P3.0 to P3.5, P3.7 are seven bi-directional I/O pins with internal pull-ups.
P3.6 is hard-wired as an input to the output of the on-chip comparator and is not
accessible as a general-purpose I/O pin.
The Port 3 output buffers can sink 20 mA.
When 1s are written to Port 3 pins they are pulled high by the internal pull-ups and can be
used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL)
because of the pull-ups.
Port 3 also serves the functions of various special features of the AT89C2051 as listedbelow: Port 3 also receives some control signals for Flash programming and verification.
RSTReset input. All I/O pins are reset to 1s as soon as RST goes high. Holding the RST pin
high for two machine cycles while the oscillator is running resets the device. Each machine
cycle takes 12 oscillator or clock cycles.XTAL1
Input t th in tin scill t mplifi nd input t th int n l cl ck p tin ci cuit
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OSCILLATOR CHARACTERISTICSThe XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier
which can be configured for use as an on-chip oscillator, as shown in Figure. Either a
quartz crystal or ceramic resonator may be used.
To drive the device from an external clock source, XTAL2 should be left unconnected
while XTAL1 is driven as shown in Figure.(dia)
Or
Pin
No
Function Name
1
8 bit Address pins for input
A0
2
A1
3 A2
4 A3
5 A4
6 A5
7 A6
8 A7
9 Ground (0V) Ground
10
4 bit Data/Address pins for output
D0
11 D1
12 D2
13 D3
14 Serial data input Input
15 Oscillator output Osc2
16 Oscillator input Osc1
17 Valid transmission; active high VT
18 Supply voltage; 5V (2.4V-12V) Vcc
Block Diagram of HT 12D
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19
FLOW CHART
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TIMING DIAGRAM
Applications of HT 12E & HT 12D:
Burglar Alarm, Smoke Alarm, Fire Alarm, Car Alarm, Security System
Garage Door and Car Door Controllers Cordless telephone
Other Remote Control System
RF TRANSMITTER:The RF Transmitter used is TLP434A.It has frequency range of 315 MHz to
433MHz.It operates at a voltage range of 2-12VDC.
(dia)
RF RECEIVER:The RF Receiver used is RLP434A. It has frequency range of 315MHZ to
433MHZ.it operates at a voltage range of 3.3-6 VDC
(dia)
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ATMEL 89C2051 MICROCONTROLLER:The AT89C2051 is a low-voltage, high-performance CMOS 8-bit microcomputer
with 2K bytes of Flash programmable and erasable read-only memory (PEROM).
The device ismanufactured using Atmels high-density nonvolatile memorytechnology and is compatible with the industry-standard MCS-51 instruction
set.
The AT89C2051 provides the following standard features:
2K bytes of Flash
128 bytes of RAM
15 I/O lines
two 16-bit timer/counters
a five vector two-level interrupt architecture
a full duplex serial port
a precision analog comparatoron-chip oscillator and clock circuitry
In addition, the AT89C2051 is designed with static logic for operation down to
zero frequency and supports two software selectable power saving modes.
The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial
port and interrupt system to continue functioning. The power-down mode saves
the RAM contents but freezes the oscillator disabling all other chip functions
until the next hardware reset.
PIC16F877 MICROCONTROLLER:
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# SYSTEM ARCHITECTURE #
The proposed navigation system consists of two fundamental modules:an RFID communication module and
a Fuzzy Logic Controller (FLC) navigation module.
TheRFID communication moduleis responsible for communicating with the
tags (or transponders) through an RFID reader with two receiving antennas
mounted on the robot. A high level system configuration setup of the current
navigation technique is depicted in Fig. 2, where two RFID tags, T1 and T2, are
attached on the ceiling. The robots desired trajectory is the straight-line
segment connecting the orthogonal projection points, A and B, of tags T1 and
T2, respectively.Therobot employs the FLC modulein order to provide the necessary control
action to its actuators, which is required to move the robot from one point to
another in its workspace.
Consider a scenario where the robot is presented with a desired trajectory
defined by an ordered sequence of tag IDs, like (00, 01), for instance, then it
first navigates to the orthogonal projection point of the tag with ID 00, then it
moves along the virtual straight line linking the orthogonal projection points of
tag IDs 00 and 01, where it will stop. The
Novelty in this navigation scheme is that it is independent of the tag positions,
odometry information, and structure of the working environment.
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A. RFID Communication ModuleBefore starting the mission, the robot sendstime multiplexed single-tone
sinusoidal signalswith different frequencies, and then listens to thebackscattered signals from the RFID tags. The high level architecture of the
custom-designed RFID communication module is depicted in Fig 3. Preliminary
studies were conducted to confirm the fact that using a custom-built RFID
reader with two receiving antennas can determine the relative position of the
tag (left or right) with respect to the reader mounted on the robot.
Let1 and2 be the phase angles of the signal received by the readers
receiving antennas 1 and 2, respectively.
The phase difference, , is then defined by
=12. ....(1)
This phase difference is then passed to the FLC in order to decide on the
robots direction
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B. Fuzzy Logic Controller
The purpose of FLC is to provide intelligent actions to be taken by the robot.In the current work, we use asingle-input single-outputMamdani-type FLC as
shown in Fig. 4. The aim of the FLC is to decide on the amount of tune-up
that the robot has to apply to its current directionto converge to its targetposition. The FLCs input isthe phase differenceprovided by the two
directional antennas mounted to the RFID reader on the robot. The robot then
uses this information to update its direction following the update rule (2).
(new) =(old)+ (2)
The fuzzification and defuzzification membership functions are taken as linear
triangular and trapezoidal membership functions for their higher computationalefficiency [19], as depicted in Fig. 5. An empirical analysis was performed to
optimize these membership functionparameters to improve the FLCs
performance. The minand max operators are adopted as the t-norm and s-
norm operators, while the defuzzification method is set to be the center of
area.
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Three fuzzy rules are defined to reflect the fact that the phase difference of
the signal is positive when the transmitting transponder is on the left side of
the receiving
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antenna and vice versa. These rules are:If is NegThen is CCWIf is Zero Then is ZeroIf is Pos Then is CW
The rationale behind these rules is that the robot is supposed to turn
left/right (CCW/CW, for counter-clock wise and clock-wise, respectively) ifthe RFID tag is on the left/right of the receiving antenna, whereis
negative and positive, respectively.
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# PROPOSED NAVIGATION
ALGORITHM #This section explains how the modules described above fit into the overallnavigation framework. The efficient coordination among the RFID
communication module, FLC, and different actuators of the robot allows it to
hav less computational overhead while being executed on therobots processor.
The following is a description of the different steps of the algorithm.
Step 1:The robot is pre-programmed with an ordered list of tag ID numbers
defining its desired path.
Step 2:The target tag of the current navigation phase is determined from the
ordered list of tags defining thecomplete robots desired path.
Step 3:Once the target tag is known, the robot scans through the signalsbackscattered from all the tags within its communication range and records the
phase angles1 and2 of the signal coming from the tag representing the
target tag at that time instant.
Step 4:The phase difference, , of the destination tagssignal is calculated
as defined in (1). is then passed to the FLC to quantize the tuneup the robot
has to apply to its direction to better direct itself towards its destination. The
robot updates its heading as in (2) and dispatches the required control action
to its relevant actuators.
Step 6:Once the robot reaches the destination tag, it checks for more
available destination tag IDs in the desired path. If the current destination tagis the last tag, then the robot simply stops. If not, the algorithm restarts
fromStep 2.
A thorough evaluation ofthis algorithms performanceis provided in the
following section.
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CONCLUSIONA novel RFID-based robot navigation system is proposed
in this paper. The robot is first presented with a
sequence of tag IDs defining its desired trajectory. This
sequence is then broken into a sequence of ordered
pairs of IDs each of which represents a line segment of
the overall trajectory. The mobile robot tracks each
segment by continuously assessing the phase
difference of the RF signals at the readers two
receiving antennas coming from the current segments
target tag. An FLC is adopted to compute the control
effort necessary for the robot actuators to tune its
orientation appropriately. Computer simulations were
run to demonstrate the algorithms efficiency in
tracking various paths of different complexities despite
the noise in the RF feedback signal. The proposed
algorithm is very modular as it can be easily
implemented on virtually any type of robotic systemsand working environments. It is computationally
inexpensive as it is free of any visual data processing.
With the help of sensor feedback mechanism with RF
communication the mobile robot can be controlled from
a far distance, which is desirable fact when the robot is
working in hazardous environment.
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