Detection and removal of antipersonnel landmines in infested fields is an important
worldwide problem. Around 100 million landmines have been deployed over the last two
decades, and demining will take several more decades, even if no more mines were deployed
in future. A high mine-clearance rate can only be accomplished by using new technologies
such as improved sensors, efficient manipulators and mobile robots. This paper presents some
basic ideas on the configuration and controller of a mobile system for detecting and locating
antipersonnel landmines in an efficient and effective way. The whole system has been
configured to work in a semi-autonomous mode with a view also to robot mobility and
energy efficiency. The paper outlines the main features of the overall system and focuses on
some aspects of the controller.This work has been funded by the Spanish Ministry of Science and Technology under
Grant CICYT DPI2001-1595.Peer reviewe

Cobano, José A.

García Armada, Elena

González de Santos, Pablo

Ramírez, Adriana

Digital.CSIC

ISORA043                                                     Main Menu                                                                                                            World Automation Congress  Tenth International Symposium on Robotics  with Applications   Seville, Spain  June 28th-July 1st, 2004    SILO6: A Six-Legged Robot For Humanitarian De-Mining Tasks    P. Gonzalez De Santos, E. Garcia, J.A. Cobano  and A. Ramirez  Equation Section 1SILO6: A SIX-LEGGED ROBOT FOR HUMANITARIAN DE-MININGTASKSP. GONZALEZ DE SANTOS, IAI-CSIC, SPAIN, pgds@iai.csic.esE. GARCIA, IAI-CSIC, SPAIN, egarcia@iai.csic.esJ.A. COBANO, IAI-CSIC, SPAIN, jacobano@iai.csic.esA. RAMIREZ, IAI-CSIC, SPAIN, aramirez@iai.csic.esABSTRACTDetection and removal of antipersonnel landmines in infested fields is an importantworldwide problem. Around 100 million landmines have been deployed over the last twodecades, and demining will take several more decades, even if no more mines were deployedin future. A high mine-clearance rate can only be accomplished by using new technologiessuch as improved sensors, efficient manipulators and mobile robots. This paper presents somebasic ideas on the configuration and controller of a mobile system for detecting and locatingantipersonnel landmines in an efficient and effective way. The whole system has beenconfigured to work in a semi-autonomous mode with a view also to robot mobility andenergy efficiency. The paper outlines the main features of the overall system and focuses onsome aspects of the controller.1. INTRODUCTIONFull clearance of antipersonnel-landmine infested fields is at present a serious political,economic, environmental and humanitarian problem. Politicians have shown a real interest insolving this problem, and solutions are being studied in different engineering fields. The bestsolution, albeit perhaps not the quickest, would be to apply a fully automatic system to solvethis problem. However, any such solution still appears to remain a long way from succeeding.First of all, efficient sensors, detectors and positioning systems would be needed to detect,locate and, if possible, identify different mines. Then, adequate vehicles would have to beprovided to carry the sensors over the infested fields.There are many potential vehicles that can carry sensors over infested fields; wheeled,tracked and even legged vehicles can accomplish demining tasks effectively. Wheeled robotsare the simplest and cheapest, and tracked robots are very good for moving over almost allkinds of terrain, but legged robots also exhibit interesting potential advantages in demining[2].The idea of using legged mechanisms for humanitarian demining has been underdevelopment for at least the last five years, and some prototypes have been already tested.TITAN VIII, a four-legged robot developed for general purposes at the Tokyo Institute ofTechnology, Japan [4], was one of the first walking robots adapted for demining tasks.AMRU-2, an electropneumatic hexapod developed by the Free University of Brussels and theRoyal Military Academy, Belgium [1] is one more example of walking robots used as testbeds for humanitarian demining tasks. COMET-1 was perhaps the first legged robotdeveloped on purpose for demining tasks [7]. It is a six-legged robot developed by a Japaneseconsortium, and it incorporates different sensors and location systems. The COMET team iscurrently engaged in developing the third version of its robot [5]. These four robots are basedon insect configurations, but there are also different legged robot configurations, such assliding-frame systems, being tested as humanitarian demining robots [3]. To sum up, there isa great amount of activity in developing walking robots for this specific application field.The IAI-CSIC holds experience in the design, development and control of walking robots,gait generation, terrain adaptation, robot teleoperation, collaborative control and other fields.All these technologies are mature enough to be merged in order to produce efficient roboticsystems. This paper, thus, presents the SILO6 walking robot’s ongoing results underdevelopment at IAI-CSIC, which has been configure on purpose for demining tasks.2. SYSTEM DESCRIPTION AND MAIN REQUIREMENTSThe SILO6 whole system has been configured with the aim of putting together differentsubsystem. These subsystems are (see Figure 1):1. Sensor head. The sensor head is configured to detect potential alarms but also toallow the controller to maintain the sensor head at a given height over the groundusing simple range sensors. It is based in a commercial metal detector (see Figure 2).2. Scanning manipulator. The sensor head is basically a local sensor and so the systemneeds to use a manipulator to move the sensor head and to adapt it to terrainirregularities (see Figure 2).3. Locator. After detecting a suspect object, the system has to mark the object’s exactlocation in a database for subsequent analysis and deactivation. We considered that anaccuracy of about ±2 centimetres is adequate for locating landmines. This accuracycan be obtained with commercial systems such as DGPS (Differential GlobalPositioning Systems).4. Mobile robot. A mobile platform to carry the different subsystems across infectedfields is of vital importance for thorough demining. In our case, the platform is basedon a legged robot. The following requirements are the starting point for configuringthe walking robot:· The legged robot was based on a hexapod configuration. Section 3 explains why thischoice was made.· The legged robot should belightweight enough to be handledby two adults. This requirement isimportant so the robot can berescued from technical o logisticproblems.· The robot should beautonomous from the energy pointof view. Tethers should beavoided.· The robot should be semi-autonomous from the controlpoint of view. Thus, a remoteoperator should be in the loop tocontrol the system throughteleoperation and collaborativecontrol.The robot is being configuredto optimise power consumption,mobility and stability. These areantagonistic conditions which arebeing balanced through detailed design.5. Controller. The global control system will be distributed into two main computers,the onboard computer and the operator station. The onboard computer is in charge ofcontrolling and co-ordinating the manipulator and leg joints, communicating with theDGPS, the detector and the operator station via radio Ethernet. The operator station isa remote computer in charge of defining the mobile robot’s main task and managingthe potential-alarm database.Hence, the walking robot is to be configured as a six-legged autonomous robot carrying ascanning manipulator, which handles the sensor head. The system will be controlled throughteleoperation and collaborative techniques. The sections below give an overall view of therobot’s configuration.Figure 1. DYLEMA systemRadio Ethernet aerialDGPS antennaOperator stationWalking robotSensor headScanner(manipulator)3. WALKING ROBOT CONFIGURATIONWalking robots are intrinsically slow machines, and machine speed is well known todepend theoretically on the number of legs the machine has. Therefore, a hexapod canachieve higher speed than a quadruped, and a hexapod achieves its highest speed when usinga wave gait with a duty factor of b = 1/2, that is, using alternating tripods [8]. Althoughstability is not the optimum when using alternating tripods, a hexapod configuration has beenchosen just to try to increase the machine’s speed.3.1 Body structureThe main tasks of a walking robot’s body are to support legs and to accommodatesubsystems. Therefore, the body must be big enough to contain the required subsystems, suchas an onboard computer, electronics, drivers, a DGPS and batteries.“Alternating tripods” means that two non-adjacent legs on one side and the central leg onthe opposite side alternate in supporting the robot. That means that, for a given foot position,the central leg in its support phase is carrying about half the robot’s weight, whilst the twocollateral legs in their support phase are carrying about one-fourth of the robot’s weight. Thisis especially significant in traditional hexapod configurations, where legs are placed at thesame distance from the longitudinal axis of the body. If the robot has similar legs, then thenon-central legs will be over-sized, and to optimise the mechanism the central leg’s designshould differ from that of the rest of the legs. However, using just one leg design has manyadvantages in terms of design cost, replacements, modularity and so on. A satisfactory forcedistribution and homogenisation of the system can be accomplished by displacing the centralleg a little bit from the longitudinal body axis.  In this case the central legs support a lowerweight and the corner legs increase their contribution in supporting the body (see [2] forfurther details).3.2 Leg structureWalking robots need leg configurations that provide just contact points with the ground,so a 3-DOF device is sufficient to accomplish motion. Legs have to be designed to belightweight mechanisms and have to support the robot's weight. Therefore, the load carriedby each leg is very heavy and must be supported with the leg in different configurations. Amammal configuration is the most efficient leg configuration from the energy point of view(lower torques are required). However, it is not very efficient in terms of stability. Insect-likelegs seem to be more efficient stability-wise, but power consumption increasesextraordinarily in an insect-like configuration. The idea is to provide a leg configuration thatcan accomplish its job with both stability and energy efficiency (a very important factor forFigure 2. Scanning manipulator and sensorheadFigure 3. Leg configurationFootJoint 3Joint 2Joint 1Differential systemJoint 1Joint 2Infra-red sensorsJoint 3Joints 4 and 5Sensor headAttachment torobot’s bodyoutdoor mobile robots). Development has therefore been focused on a leg that can be used inboth the mammal and the insect configuration.Feet can be designed in two basic configurations, a ball fixed to the ankle or a flat solewith articulated passive joints. The first design is the simplest and can work for applicationsin loose terrain if the radius of the ball is big enough.4. CONTROL SYSTEMThe control system is distributed between the operator station and the onboard controller.Both of them are based on PC-based computers (see Figure 1). The operator station runsunder the Windows XP operating system, and the onboard controller (the robot's controller)runs under QNX, a UNIX-like real-time multitasking operating system. Communicationbetween operator station and onboard computer is performed by radio Ethernet. The mainhardware and software aspects are discussed below.4.1 Operator stationThe operator station consists of the following modules:1. Man-machine interface.2. Alarm database manager.3. Station-robot communication.4.1.1 Man-machine interfaceThis module is a Java-based program intended to fulfil three main requirements: (a) robot-state monitoring, (b) robot teleoperation and (c) task definition. The user will have the abilityto govern robot motion remotely, with real-time visual information on what the robot isdoing. The man-machine interface also allows the user to define the task, a process thatinvolves the definition of mine-field features (field dimensions, roughness, etc.), robot pathand autonomous navigation strategies.4.1.2 Alarm-database managerEach time the robot detects an alarm, thespatial position of the suspect object isstored in a relational database. Thisdatabase will enable mines to be removedby a specialist team in a posterior step. Theuser can access every alarm location foundin a given field of a given country. Fieldand available mine features are also stored.4.1.3 Station-robot communicationCommunication between the operatorcomputer and the onboard computer isconducted by means of a radio Ethernetcard. The operator computer runs under theWindows XP operating system, whilst theonboard controller runs under the QNXoperating system. Because differentoperating systems are used, thecommunications protocol has to becompatible with any operating system. Onesuch protocol is the TCP/IP (TransmissionControl Protocol/Internet Protocol) usedworld-wide for Internet connection. Aclient-server architecture was chosen forinter-process communications, where theoperator computer is the server and theonboard computer is the client.Figure 4. SILO6 hardware architecture.DGPSantennaHost ComputerInclinometersPC busAnalogue toDigitalConverterRadioEthernetDGPSRS232AerialMetal detector3-AxisController(Axes 1-3)DDDDD...DC Motor + Encoder3-AxisController(Axes 21-23)Driver4.2 Onboard computer4.2.1 Hardware architectureThe onboard controller is a distributedhierarchical system comprising a PC-based computer, a data-acquisition boardand eight three-axis control boards basedon the LM629 microcontrollers,interconnected through an ISA bus. TheLM629 microcontrollers include digitalPID filters provided with a trajectorygenerator used to execute closed-loopcontrol for position and velocity in eachjoint. Every microcontroller commands aDC motor-joint driver based on thePWM technique. An analogue data-acquisition board is used to acquiresensorial data from the range of externalequipment (sensors, locators, etc.). Aradio Ethernet card is provided fornetwork communication with theoperator station. Additional electroniccards for interfacing with the detector arealso provided, as well as communicationwith the DGPS systems via RS232. Ageneral diagram of the SILO6 hardwarearchitecture is shown in Figure 4.4.2.2 Software architectureThe onboard computer is in charge ofthe walking robot’s gait and trajectorygeneration, manipulator control, signalprocessing and communications, as wellas coordination of the microcontrollers.These tasks are distributed in a softwarearchitecture that consists of layersdeveloped on a bottom-up basis. Theselayers can be mainly divided into:· Hardware interfaces: These layers contain the software drivers for both the walking robotand its manipulator.· Axis-control layers: These layers control the individual joints for both the walking robotand its manipulator. Individual joints are controlled through a dedicated microcontroller,which runs a PID control algorithm.· Leg control: This layer is in charge of coordinating all three joints in a leg to performcoordinated motions.· Leg kinematics: This layer contains the direct and inverse kinematic functions of a leg.· Trajectory control: This module is in charge of coordinating the simultaneous motion ofall four legs to perform straight-line or circular motions.· Stability module: This layer determines whether a given foot-position configuration isstable or not.· Gait generator: This layer generates the sequence of leg lifting and foot placement tomove the robot in a stable manner. Dynamic stability is guaranteed by the stabilitymodule. The SILO6 gait generator will be based on three gaits: a tripod gait, a spinninggait and a turning gait.· Communications: This layer handles communications with the operator interface throughradio Ethernet via the TCP/IP protocol.Figure 5. Software architectureGait GenerationandStability MonitorCommunicationsWalking robotParametersTrajectoriesManipulatorParametersTrajectories Motion ProcessesTerrain AdaptationAltitude ControlAttitude ControlTrajectory ControlRobot Kinematics(WALK library)Leg Kinematics(KIN library)Leg Control(LEG library)Axis Control(LINK library)Hardware Interface(ROB and LM libraries)Equipment andSensor DataAcquisitionManipulator KinematicsTrajectory Generation(KIN library)Axis Control(LINK library)Hardware Interface(ROB and LM libraries)· Manipulator kinematics: This layer is in charge of solving the manipulator kinematics.· Equipment and sensor-data acquisition layer: This layer provides interfaces with externalequipment.Figure 5 diagrams the different software modules and their interconnections.5. CONCLUSIONSHuman operators handling manual equipment are, at present, detecting and locatingantipersonnel landmines. However, human community can obtain many benefits by therobotization of this activity. There is international interest in eradicating landmines, andsolutions are coming from new, emerging engineering fields.New sensors are required in order to detect landmines efficiently, but existing sensors canbe carried by mobile robots over infested fields. Legged locomotion provides manyadvantages for moving on natural terrain and appears to be a good solution for carrying minesensors efficiently.Some preliminary work has been done to study the potential of using walking robots fordemining. This paper addresses the development of a walking robot endowed with amanipulator able to scan areas with a sensor head based on a metal detector. This paperintroduces the main system and provides some details of the configuration of the walkingrobot and the manipulator, and it outlines the hardware and software architecture as well.6. ACKNOWLEDGEMENTThis work has been funded by the Spanish Ministry of Science and Technology underGrant CICYT DPI2001-1595.7. REFERENCES[1] Baudoin, Y. Acheroy, M., Piette, M., and Salmon, J.P., “Humanitarian demining androbotics”, Mine Action Information Center Journal. Vol. 3, No. 2, 1999.[2] Gonzalez de Santos, P., Garcia, E., Cobano, J.A. and Guardabrazo, T., “UsingWalking Robots for Humanitarian De-mining Tasks”, Proceedings of the 35thInternational Symposium on Robotics, Paris, France, March 23-26, 2004.[3] Habumuremyi, J.C., “Rational designing of an electropneumatic robot for minedetection”, Proceedings of the 1st International Conference on Climbing and WalkingRobots, pp. 267-273, Brussels, Belgium, 1998.[4] Hirose, S. and Kato, K., “Quadruped walking robot to perform mine detection andremoval task”, Proceedings of the 1st International Conference on Climbing andWalking Robots, pp. 261-266, Brussels, Belgium, 1998.[5] Huang, Q.J and Nonami, K., “Humanitarian mine detecting six-legged walking robotand hybrid neuro walking control with position/force control”, Mechatronics, 13, pp.773-790, 2003.[6] Marques, L., Rachkov, M. and Almeida, A.T., “Control system of a demining robot”,Proceedings of the 10 th Mediterranean Conference on Control and Automation,Lisbon, Portugal, July 9-12, 2002.[7] Nonami, K., Huang, Q.J., Komizo, D., Shimoi, N. and Uchida, H., “Humanitarianmine detection six-legged walking robot”, Proceedings of the 3rd InternationalConference on Climbing and Walking Robots, pp. 861-868, Madrid, Spain, 2000.[8] Song, S.M. and Waldron, K.J., MACHINES THAT WALK: The AdaptiveSuspension Vehicle. 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SILO6: A six-legged robot for humanitarian de-mining tasks

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