Wireless Controlled Laser Tracking Based

Hovering Mine DetectorMujtaba Hussain

Electrical Engineering DepartmentComsats Institute of Information Technology CIIT Lahore

smhussain(ciitlahore.edu.pk

Abstract: The main methods used for demining on land aremanual detection using metal detectors and prodders,detection by specially trained dogs and mechanicalclearance using armored vehicles fitted with frails, tillers orsimilar devices, however in all the methods the position ofmine prior to detection is unknown A lot of causalitiesoccur during demining operation. Existing mechanicalsystems are expensive and very difficult to deploy speciallyin those areas where it is not possible to take heavymachinery. Due to the advancement in tracking systems, anintegrated system employing latest tracking techniquesusing laser range finder as tracker can be used to detect theexact location of mine in the minefield. Radio frequencytransmitter controls the aerospace vehicle. This new idea ofdetecting mines by integrating the above-mentionedtechnologies is implemented on a home made hovercraftusing laser range finder System as a tracking tool thusproviding a fixed reference point.

1. INTRODUCTION

An estimated 110 million landmines are strewn across ourplanet in more than 70 countries. Landmines kill and woundover 20,000 people each year [1]. The process of mineremoval is referred as demining.. In manual as well asmechanical detection knowing the position of mine prior todemining operation is a big challenge.The first step is manual demining is to scan the area withmetal detectors which is sensitive enough to pick up mostmines landmines with very low metal content. The metaldetectors are carried by trained personals. Most of the minesare pressure sensitive. Any small mistake in taking next stepmay cost them their own lives. More sophisticated sensors areneeded to detect mine that are buried under the deep soil andare made up of material other than metal like wood, plastic.Mechanical assets consist of Mine rollers, mine flails, Mineplows and modified long armed demining bull dozers. Indemining they are driven through minefield, deliberatelydetonating the mines it drives over. These vehicles aredesigned to withstand the explosions with little damage.Different sensors are used to detect the mines in the minefield. Ground penetration Radars employ higher frequencysignals of the order of 1GHz to detect plastic or wooden minebodies. Similarly hybrid sensors consisting of both GPR andmetal detectors in a single instrument is also been used.

In both manual or mechanical case, a sensor has to bedeployed in the mine field. Similarly the mechanical system isvery expensive and large to deploy in each part of the world.Apart from aerospace vehicles like helicopters, which have anability to hover in air, hovercrafts provide an excellentapproach to solve our problem [3]. Hovercrafts, as we knoware vehicles capable of flying few inches above the groundirrespective of nature of surface on which it is hovering [2].The surface can be land or sea or river. Placing a minedetector over it can help us to locate the mine by creating anRF link between the source and station. Integration of laserrange finder with PC based software can help us to know theexact position of mines. At the same time a wirelesscontroller controls the land marine vehicle. The RF linktransmits the acknowledgement detected by mine sensor tothe base station. This minimizes the presence of humans intothe minefield.The present work addresses the development of a newtechnique of finding the position of mine through theintegration of land marine vehicle with embedded systems,mine detector, RF link and a tracking module consisting oflaser range finder integrated with tracking software used onPC.The remaining organization of paper is as follows. In section2. Laser range finder as a position finding tool is discussed.The hovercraft vehicle dynamics are discussed in section 3.Transmission side integration along with software involved isdiscussed in Section 4.The modules involved at vehicle sideare discussed in section 5. Limitations and improvements ofthis prototype are outlined in section 6. Section 7 concludesthe paper.

II. OVERVIEW OF TRACKING TECHNIQUES

The function of the tracker is to search for moving or brightcolored objects and report the position of the targets. Targettracking in a rapidly changing dynamic environment is a well-studied problem in engineering disciplines. Our challenge isto know the position of mine in a minefield.There are different sensors or systems, which exist todetermine the position of various objects with respect to afixed reference point.

A. Ultrasonic Sensors

1-4244-1553-5/07/$25.00 ©2007 IEEE

These sensors produce sound waves. The sound waves arereflected back from an object. The sound receiver receives thesound. The time taken by the sensor is measured and by thisprincipal the distance of an object from a fixed referenceposition is known. Ultrasonic sensors can effectively give thedistance of objects ranging from 1 to 2 meters.In our case we need to track hovercraft carrying mine detectorin the mine field. Since the distance to hovercraft is the rangeof several hundred meters so this technique is not useful.

B. Global Positioning System (GPS)

GPS system consists of the constellation of 24 satellitesorbiting earth. GPS receivers are commercially available.These receivers give its position in terms of Longitude andLatitude. Placing a GPS receiver on the moving hovercraftcan solve our problem to some extent. The coordinates can betransmitted to base station through RF link. However the GPSreceiver has an error of 10 meters in giving the position of anobject. This error is extremely fatal in a sense that duringmine searching operation, position of many mines becomesunknown.

C. Laser Range Finder

A laser range finder is a device, which uses a laser beam inorder to determine the distance to a reflective object.The most common form of laser range finder operates on thetime of flight principal by sending a laser pulse in a narrowbeam towards the object and measuring the time taken by thepulse to be reflected off the target and returned to the sender.The pulse may be coded in order to reduce the chance that therange finder can be jammed. It is possible to use Dopplereffect techniques to judge whether the object is movingtowards or away from the range finder. One that uses veryshort, sharp laser pulses and has a very fast detector can rangeon object to within a few centimeters.Most laser range finder devices have serial output. The outputof these devices is attached to PC and all the data can besaved on PC.

D. Laser Range Finder as Position FindingTool

A major problem in any demining position is the location ofmine in minefield. When the RC hovercraft is deployed in theminefield, its position can be determined by pointing the laserrange finder at the vehicle. The output of the device gives itsposition relative to a fixed reference point.In this way, an accurate position of the vehicle can be known.

The LMV (Land marine Vehicles) or hovercraft travels closeto but above ground or water as shown in Fig. 1.[5].hovercraft, the air takes the shape of the bottom of thehovercraft, the inside edges of the skirt, and the surface it'shovering above. The fan that blows air under the bottom ofthe hovercraft keeps pushing more and more air below thehovercraft, thus increasing the pressure in the air cushion. [6].Air-cushion vehicles can attain higher speeds than ships ormost land vehicles and use much less power than helicoptersof the same weight. Much like a standard automobile, thehovercraft contains four control perimeters (x, y, and z-coordinates and orientation angle) which must be controlledwith vertical and horizontal thrust and orientation iscontrolled by motion of rudders. .Different perimeters likespeed, direction, heading of hovercraft can easily beperformed.

Fig. 1. Hovercraft vehicle diagram

A. Hovercraft Vehicle Dynamics and Working

When the hovercraft is finally able to move, it will mostdefinitely require steering capabilities [7]. This is achievedthrough the use of rudders. The shape of the rudder dictateshow well it will be able to move air. Servomotors usuallymove the rudders. A hovercraft may be fitted with singlethruster or double thruster to control its height from theground. For this project a double thruster hovercraft isselected [8]. The double thrust system provides stability butrequires more power. Fig.2 shows the hovercraft type vehiclemodel and its coordinate system where

1 angle of vehicle with heading0 angle between gravity positions and fans;1 distance between gravity positions and fansFr Force generated by right side fanFl Force generated by left side fan

III. INTRODUCTION TO HOVERCRAFT

IV. TRANSMISSION SIDE

Fig]2.HTmol iiLs c kdirme gysnm

B. Thrust calculationfor mine detection

The anti personal mines detonate at a pressure of 25 pounds.Anti tank mines are detonated at a pressure of 60 pounds. Sothe thrust generated must be less than 25 pounds so that themine may not explode with pressure of thrust.Pressure is defined as the force exerted on a surface per unitarea of the surface.

Pressure = Force AreaP=F A

In order to calculate the lift force of a hovercraft, we solvethis equation for the force.

F =P AIn order to have a lift force of 16 lbs, following calculationshave to be performed.

Lift force=9Lbs

Lift Force=Pressure x Area

9 = (3 lbs / ft2)(A ft2)A=3 ft2Therefore Length=2ft and Width=1.5ftSince we using a double thruster fans with output Fl and FrthereforeFl +Fr=9+9= 8lbsThis 1 8lbs of thrust is sufficient to generate thrust so that mineis not exploded by its pressure.

C. Hovercraft as Mine Detection Vehicle

As discussed in the above section hovercrafts can fly fewinches above the ground. As a result they don't exert pressure

on pressure sensitive mines. Similarly because of theircapability to carry load, an array of mine sensors can easily bedeployed as pay load. Different mine sensors like metaldetector, GPR (Ground Penetration Radar), or their hybridcan easily be kept as a payload on the vehicle.Unlike other mechanical techniques of detecting mines likeHydrema mine clearing vehicle, Mine rollers, mine flails andMine plows, hovercrafts are very cheap, easy to handle andcan be employed on short notice in a field.

Keeping in view the tracking and control features thedescription of the system has been divided into two parts.

A. Control Signals Transmission Module

In order to control different perimeters of hovercraft, a RFtransmitter has been used.The objective of this work is to create a hardware that canreceive byte patterns from PC based software and directs theRC transmitter to send signals to hovercraft to perform aparticular task.The transmission side consists of RF joystick based remotecontrol, microcontrollers and PC. The transmitter iscommercially available RC transmitter with built in joysticks.It has a RC receiver with PWM outputs RI and R2 from arange of Ims to 2ms.Transmitter's block diagram is shown inFig. 3.

B. Working ofRF remote control

A standard RC joystick transmitter is shown in Fig. 4.As seenin the Fig. 4, the transmitter has 2 Joysticks AI and B 1. Eachjoystick can be moved manually from fingers by 0 to 180degrees. The output ofjoystick is analogue.The internal block diagram is shown in Fig. 3.From Fig. 3 it is observed that this analogue output isconverted to digital format from A/D converter. This digitaloutput is sent to Pulse generator IC to produce pulses of thepattern shown in Fig. 5. Joystick Al controls the pulse widthofA and joystick BI controls pulse width of D.

FIg.i.CmpoenLisarm ofRtar_ansmit[,cmddo s nFig, 4 l

Fig. 3. Component Level diagram ofRC transmitter

Stick Al

*1 0 180

Fig. 4. Standard commercially available RC transmitters

PUISE FRAMEA=L= Cel (500-50Os)B=C=F=1~E=1]m

Fig. 5: Pulses Generated

C. Pattern Generation Technique

As seen in Fig. 3, the output A/D converter is given to Signalgenerator IC that changes the pulse widths of its output bydepending upon the analogue signals received from joystick.The idea is to generate these signals shown in Fig. 5artificially through microcontroller. The microcontroller willproduce PWM signals of pattern and range shown in Fig. 5.This RC transmitter has been modified to receive pulses frommicrocontroller as shown in Fig. 6.

MY ROC OlqTROLLEPC BbSiED BrfScEDaSInd

IPORTlrERFAsC

J OYSTICK IO|BASED C STHlC OlqTROL|

R|FTX|

Fig. 6: TmmssJmi

The user has an option to control the vehicle by two ways(Fig. 6). One way is through PC based interface and otherway is by joystick [6]. The user has an option to switch toeither PC mode or joystick mode by this selection switch.A parallel port link has been placed between the PC and themicrocontroller based frame generator. The user from PCsends a byte pattern to microcontroller and themicrocontroller in turn sends the corresponding signal frameto RC transmitter. Our basic aim is to generate pulses as

shown in Fig. 5. This pulse frame is generated bymicrocontroller and is sent to the transmitter [9].. Table 1 shows the byte pattern which microcontroller shouldreceive from parallel port ofPC to perform a particular task.The receiver on hovercraft has two PWM outputs. Pulse Acontrols the PWM output from Receiver RI and pulse widthD controls the PWM output of Receiver R2 The range ofPulse A and D is shown in Fig. 5.

TABLE 1

THE BYTE PATTERN RECEIVED FROM MICROCONTROLLER ANDPULSES PRODUCED AT RECEIVER SIDE

Byte Patten Pulse Pulse RI R2No (A) (D) (ms) (ms)

1 0000 500 500 1 12 0001 500 1000 1 1.53 0010 500 1500 1 2.04 0011 1000 500 1.5 15 0100 1500 500 2.0 16 0101 1000 1000 1.5 1.57 0110 1500 1500 2.0 2.08 0111 1500 1000 2.0 1.59 1000 1000 1500 1.5 2.010 1001 600 600 1.1 1.111 1010 700 700 1.2 1.212 1011 800 800 1.3 1.3

Different physical actions performed by hovercraft upon

receiving of particular byte pattern is shown in Table 2.Thedetails of receiving side will be briefly discussed in nextsection 5.

TABLE 2THE PHYSICAL ACTION PERFORMED BY HOVERCRAFT

BYTE ACTION PERFORMEDPATTERN0000 Turn OFF motors and bring rudders to neutral

position0001 Turn on vertical thrusters0010 Turn on horizontal thruster in forward direction0011 Turn on horizontal thruster in reverse direction0100 Move rudders to the right0101 Move rudders to the left0110 Turn on vertical thrusters+ Turn on horizontal

thruster in forward direction+ Move rudders to theright

0111 Turn on vertical thrusters+ Turn on horizontalthruster in forward direction+ Move rudders to theleft

1000 Turn on vertical thrusters+ Turn on horizontalthruster in reverse direction+ Move rudders to theright

1001 Turn on vertical thrusters+ Turn on horizontalthruster in reverse direction+ Move rudders to theleft

1010 Turn on vertical thrusters+ Turn on horizontalthruster in forward direction+ Move rudders toneutral position

D. Tracking Module

A laser range finder with a RS232 output is connected to themicrocontroller through its UART as shown in Fig. 7.At the same time a RF receiver is also connected to themicrocontroller. The purpose of this RF receiver is to indicatethat a mine has been detected on the mine field. Themicrocontroller is connected to serial port of PC through itsUART.

NICROCONTOLL PC BASED SOFTTJJAREERBAED SINALrWIThTR AT

RF TRACKE IfCNRO C MMONTOLLE R

CONTR~OL

SIGNAL

LASER RANGE RF|FTDER

Fig. 7 Base Station Side

When mine sensors detects the mine, it sends the signal tobase station through RF transmitter. At base station when RFreceiver receives the signals, it gives high output. This highoutput is detected by the microcontroller. The microcontrolleralso receives signals from the laser range finder through itsUART. When the microcontroller senses that the output ofRFreceiver is high, it sends the position through its UART to PCwhere it is saved in data abase.

E. Software Description

The algorithm of the software running in the PC as well as inmicrocontroller is shown in Fig. 8 and Fig. 9 respectively.

INITIALIZE THE PORTS AND PREPARE THE UART FORSERIAL DATA RECEPTION AND TRANSMISSION

RECEIVE THE DATA FROM LASER RANGEFINDER AND SAVE IT IN BUFFER

IL WAIT FOR THE HIGH OUTPUT FROM RFDATA RECEIVER

IF ()IJTPIJT IS LOW

INITIALIZE THE DATABASE, VARIABLES ANDPORTS

WAIT FORINPUT FROMUSER TOACTIVATE THECONTROLSYSTEM OFHOVERCRAFT

WHEN THE UI BUTTON IS PRESSEND THENSEND THE CORRESPONDING BYTE FRAMETHOUGH PARALLEL PORT TOMICROCONTROLLER BASED SIGNALGENERATOR

Fig. 9 Flow Diagram of PC based Software

V. VEHICKE SIDE

A double thruster hovercraft fitted with DC electric motorshas been selected. The vertical thrusters Fr and Fl are used toprovide lift to the vehicle.. The motor direction is controlledby H-bridge circuit, which is controlled by microcontroller.H Bridge is an electronic circuit consisting of transistors or

MOSFET's, which is used to control the direction of motor[10].The motion along x-axis is controlled by horizontal electricmotor. Double thrusters producing force Fr and Fl control themotion along vertical or z-axis. A single servomotor is usedto control the rudders, which coordinate and y-axis controlof hovercraft.To control the low level operation of the hovercraft, an

embedded circuit has been designed to receive PWM signalsfrom RC receiver and control the position of servomotor,vertical and horizontal thrusters' movements.A two channel PWM output RC receiver has been used withoutputs RI and R2 shown in Fig. IO.Each output RI and R2has a range of 1 millisecond to 2-millisecond pulse width.A microcontroller has been used to interpret data fromchannels RI and R2 to implement the actions as mentioned inTable t, Table2.Fig. 10 shows the block diagram of thereceiver side system.

Fig. 8 Flow Diagram of Tracking Microcontroller

IF THE OUTPUT IS HIGHTHEN SEND TRACKINGDATA TO PC

A

r I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

4

Fig. 10. Vehicle side control module

Channel 2

Fig. 11 RC Two-channel receiver

As shown in Fig. 10, the microcontroller takes input from thetwo channels of RC receiver and controls the servo motor,horizontal and vertical thrusters.The H-bridge circuit is PWM controlled so that the bothforward and reverse thrust of the motor can be controlled thusincreasing the maneuverability of the hovercraft.

Fig. 12: Transmission Side

On Vehicle side as shown in Fig. 12 the microcontrollerreceives signal from mine detector and after processing thatmine has been detected it sends the digital stream of requiredformat to the RF transmitter. Any input from the minedetector will change the format of data transmitted and this

changed data stream will enable the receiver side to takerequired action.

VI. PRACTICAL RESULTS

Initial tests procedures were conducted by using metaldetector and mines with metal casing. About twenty mineswere laid in the ground. The vehicle managed to detect thenine teen mines. In any de mining standard the system that isdeveloped should have a reliability of 98%. The prototypesystem achieved this standard by missing only one mine. Thismine was missed because the speed of the hovering vehiclewas a little bit faster so as a result it missed the mine. Thisproblem was easily overcome by reducing the speed of thevehicle. The data in the log files was confirmed by manualdetection of mines. Both the results matched each other.

A. System limitations

DC Electric motors create the vertical thrust in this LandMarine vehicle. The thrust motor consumes approximately20A (amperes) of current. Due to the limited availability ofresources, instead of petrol engine, electric motor is used.Since the battery capable of producing 20A current occupies alarge volume and weight, it cannot be placed on the landmarine vehicle. Wires connected to thrust motor have to bestretched out of the vehicle and connected to the off boardbattery. This limits the long-range control of vehicle. This isone of the major limitations in this prototype system.

B. Suggested improvements:

One of the major upgrade or improvement required by thisprototype system is to change its thruster's module, whichhave DC motor and its external supply. For practical and fielduse, the vertical thruster system should be replaced by petrolengine used in hobby aircrafts. This will make the systemmore practical and feasible.

VII. CONCLUSION

In order to protect the de-mining specialists and to guaranteeuniform search strategies a low cost and lightweight robot isneeded. Ideally mine detection systems should have followingfeatures

* Low power consumption (<2W) single supply* Simple interface and local pre-processing* Low cost (<$500)* Reliability above 98%* False alarms below 20%

The prototype system developed met the above-mentionedcriteria [1]-[4] False alarms can easily be overcome by usinga more powerful and accurate sensor. Initial testing showedthat reliability of the system was approximately 98%. The

system was cheap as compared to the other de miningtechniques, which are dangerous and expensive. It was foundthat this project would have a profound effect on humansafety in the de-mining process. It will also help to detectlarge number of mines planted in war-devastated areas aroundthe world where they are danger to civilians.

A. Military Applications

The prototype system developed is capable of providinginformation to help the commander to have an upper edge onthe enemy. If the enemy's line of defense is based upon minefield then by using the prototype system on the mine field andperforming the tactical analysis of the region, coordinates ofmine in terms of coordinates or distance determined by laserrange finder from fixed reference position is received. Thedata collected can enable the field commander to chalk outstrategy to neutralize the enemy's line of defense.Instead of sending humans in to the minefield to detect themines, the prototype system is equally capable of doing thisjob without having a fear of loosing human life while in theprocess of searching the mines.The prototype vehicle can be used for patrolling the areas. Bysetting the vehicle to autopilot mode, it can be used as asurveillance vehicle.At the same time it can be used as a pilot vehicle creating asafe passage for vehicles or persons moving through theminefield.

REFRENCES

[1] M. Draper and T. Kocak, "Performance ofEMI based mine detectionusing back propagation neutral networks", Proc. ofthe European Sympon Artificial Neural Networks, Bruges, Belgium, April 2005

[2] Rappaport, C., Stephen Azevedo, Tom Rosenbury, And Jamie Gouch andArnold Dean, "Detecting Anti personnal mines with a HandHeldParabolic Reflector Transmitter / Multistatic Receiver Impulses GPR",2000 UXO/Countermine ForumMay,2000

[3] Rappaport, C., Silevitch, M., McKnight, S., "Multi-mode SubsurfaceLand Sensing and Imaging for Mine Detection", accepted forpublication iSPIE 45th Annual Meeting and Exhibition, San Diego CA,July 2000

[4] [AV/MCM95] "Autonomous Vehicles in Mine Counter-MeasuresSymposium", Monterey, April 2005

[5] A. Suluh, T. Sugar and M.Mcbeath,"Spatial Navigation PrincApplicationsto Mobile Robotics," Proceedings of the International, Conference onRobotics and Automation, 2001

[6] Walker, Daniel."Remote Manipulation of Mobile Robots Using StockRadio Components,"GRASP Lab, University ofPennsylvania. March 23, 2001

[7] Yih, Paul. "Radio Controlled Car Model as a Vehicle Dynamics TestBed". Dynamic Design Laboratory. Stanford Universityhttp: www-cdr.stanford.edu/dynamics/rccar/ April 200 1.

[8 Mujtaba Hussain "RF Controlled GPS based Hovering Mine Detector"Final year Undergraduate thesis, University of Engineering andTechnology,Lahore, 2004