The Humanoid Robot ARMAR: Design and Control - …mindtrans.narod.ru/pdfs/ARMAR_I_robot.pdf · The...
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The Humanoid Robot ARMAR: Design and Control Tamim Asfour, Karsten Berns, and R¨ udiger Dillmann Forschungszentrum Informatik Karlsruhe, Haid-und-Neu-Str. 10-14 D-76131 Karlsruhe, Germany asfour,dillmann @ira.uka.de, [email protected] http://wwwipr.ira.uka.de/ asfour/armar Abstract. This paper addresses the mechanism design methodologies, specification, and control strategies of a mobile manipulation system for the humanoid robot ARMAR, that has to work autonomously or interactively in cooperation with humans in dynamic unstructured environments such as workshops or homes. 1 Introduction Robots of the current generation have been used in fields isolated from the human society. They suffer major shortcomings because of their limited abilities for manipulation and interaction with humans. Humanoid robots are expected to exist and work together with human beings in the everyday world such as hospitals, offices and homes and to serve the needs of elderly and disabled people [1]. These robots must be able to cope with the wide variety of tasks and objects encountered in dynamic unstructured environments. In cooperation with human beings humanoid robots should share the same working space and should react human friendly. Therefore, they need a light-weight body, high flexibility, many kinds of sensors and high intelligence. They have to be adaptive to new situations and capable of performing tasks in dynamic environments. Their design requires also a high extent of integration of mechanical, electronical and computational technologies. Since very ancient time, humans have been trying to replicate humans. Between 1495 and 1497 Leonardo da Vinci designed and possibly built the first articulated anthropomorphic robot [2]. Recently, humanoid robotics has received much interest in the robotic research community, and many significant results have been achieved world- wide [3–11]. The manipulation capabilities and intelligence of these robots are still far away from the human capability in solving complex service tasks. At the Forschungszentrum Informatik Karlsruhe (FZI) the humanoid robot ARMAR is developed for applications like assistance in workshops or home environment [12] (see figure 1). Main focus of our research is the programming and execution of manipulation tasks of ARMAR by a direct and real-time mapping between the robot and the person, which demonstrates the task. 2 The Mechatronics of ARMAR The humanoid robot has twenty-five mechanical degrees-of-freedom (DOF). It consists of an autonomous mobile wheel-driven platform, a body with 4 DOF, two anthropomorphic redundant arms each having 7 DOFs, two simple gripper and a head with 3 DOF. The total weight of the upper-body of ARMAR is about 45kg. This section describes the mechanics, sensor system and computer architecture of the robot. 2.1 Arms and Hand In order to achieve a high degree of mobility and to allow the simple and direct cooperation with humans, the structure (size, shape and kinematics) of the arm and of the torso should be similar to that of a human. We designed two anthropomorphic arms, each having 7 DOF and a length of 65 cm (including the gripper). Details about the mechanics of the arm of ARMAR are reported in [13]. Currently, a simple parallel jaw gripper is implemented, however a new humanoid five-fingered lightweight hand with only one actuator and 21 DOF is under construction [14]. The new hand is designed for anatomical consistency with the human hand. This includes the number of fingers, the placement and motion of the thumb, the proportions of the link lengths and the shape of the palm. The new hand accommodate automatically to the shape of grasped objects. It has also the ability of performing most of human hand grasping types.
Transcript of The Humanoid Robot ARMAR: Design and Control - …mindtrans.narod.ru/pdfs/ARMAR_I_robot.pdf · The...
The Humanoid Robot ARMAR: Designand Control
TamimAsfour,KarstenBerns,andRudigerDillmann
ForschungszentrumInformatikKarlsruhe,Haid-und-Neu-Str. 10-14D-76131Karlsruhe,Germany�
asfour,dillmann � @ira.uka.de,[email protected]://wwwipr.ira.uka.de/ � asfour/armar
Abstract. Thispaperaddressesthemechanismdesignmethodologies,specification,andcontrolstrategiesof amobilemanipulationsystemfor thehumanoidrobotARMAR, thathasto work autonomouslyor interactivelyin cooperationwith humansin dynamicunstructuredenvironmentssuchasworkshopsor homes.
1 Intr oduction
Robotsof the currentgenerationhave beenusedin fields isolatedfrom the humansociety. They suffer majorshortcomingsbecauseof their limited abilities for manipulationandinteractionwith humans.Humanoidrobotsareexpectedto exist andwork togetherwith humanbeingsin the everydayworld suchashospitals,officesandhomesandto serve theneedsof elderlyanddisabledpeople[1]. Theserobotsmustbeableto copewith thewidevarietyof tasksandobjectsencounteredin dynamicunstructuredenvironments.In cooperationwith humanbeingshumanoidrobotsshouldsharethe sameworking spaceandshouldreacthumanfriendly. Therefore,they needalight-weightbody, high flexibility , many kindsof sensorsandhigh intelligence.They have to beadaptive to newsituationsandcapableof performingtasksin dynamicenvironments.Their designrequiresalsoa high extentofintegrationof mechanical,electronicalandcomputationaltechnologies.
Sincevery ancienttime, humanshave beentrying to replicatehumans.Between1495and1497LeonardodaVinci designedandpossiblybuilt thefirst articulatedanthropomorphicrobot[2]. Recently, humanoidroboticshasreceivedmuchinterestin theroboticresearchcommunity, andmany significantresultshavebeenachievedworld-wide [3–11]. The manipulationcapabilitiesand intelligenceof theserobotsare still far away from the humancapabilityin solvingcomplex servicetasks.At theForschungszentrumInformatik Karlsruhe(FZI) thehumanoidrobotARMAR is developedfor applicationslikeassistancein workshopsor homeenvironment[12] (seefigure1).Main focusof our researchis theprogrammingandexecutionof manipulationtasksof ARMAR by a directandreal-timemappingbetweentherobotandtheperson,whichdemonstratesthetask.
2 The Mechatronicsof ARMAR
Thehumanoidrobothastwenty-fivemechanicaldegrees-of-freedom(DOF). It consistsof anautonomousmobilewheel-drivenplatform,abodywith 4 DOF, two anthropomorphicredundantarmseachhaving 7 DOFs,two simplegripper and a headwith 3 DOF. The total weight of the upper-body of ARMAR is about45kg. This sectiondescribesthemechanics,sensorsystemandcomputerarchitectureof therobot.
2.1 Arms and Hand
In order to achieve a high degreeof mobility andto allow the simpleanddirect cooperationwith humans,thestructure(size,shapeandkinematics)of thearmandof thetorsoshouldbesimilar to thatof ahuman.Wedesignedtwo anthropomorphicarms,eachhaving 7 DOF anda lengthof 65 cm (including thegripper).Detailsaboutthemechanicsof the arm of ARMAR arereportedin [13]. Currently, a simpleparallel jaw gripperis implemented,howevera new humanoidfive-fingeredlightweighthandwith only oneactuatorand21 DOFis underconstruction[14]. The new handis designedfor anatomicalconsistency with the humanhand.This includesthe numberoffingers,theplacementandmotionof thethumb,theproportionsof thelink lengthsandtheshapeof thepalm.Thenew handaccommodateautomaticallyto theshapeof graspedobjects.It hasalsotheability of performingmostofhumanhandgraspingtypes.
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Fig.1. ThehumanoidrobotARMAR andits kinematicsmodel.The joint variables��� – ��� arethearmDOFs. �� – �� corre-spondto thedifferentjointsof thetorso: ��� describestherotation,while �� and ��� specifytheforward,backwardandsidewardbendingof of theupperbody. � representsthetelescopicjoint of thebody.
2.2 Mobil Platform
Thereareseveralrequirementsfor thelocomotionsystemof ahumanoidrobotto dealwith adynamicunstructuredenvironment.Mobility is necessaryto extendworkingspaceandto performcooperativetaskswith humans.Stabil-ity of themobilesystemis themostessentialto insurehuman’ssafety. Fromthis remarks,we useanautonomousmobilewheel-drivenplatform. It hasanoctagonalground-planwith a diameterof 70 cm anda differentialdriveconceptwith two activedrivenwheelsonthesides.Two passive,freerotatingwheelsarealsoused.Themaximumvelocityof theplatformis about1 � � . Theplatformis equippedwith ultrasonicsensors,aplanarlaser-scanner(seesection2.4), andsufficient batterypower to allow for autonomousoperation.Up to now it is not plannedto uselegs for the locomotionof the robot,sincein a workshopenvironmentit is not necessaryto have sucha flexiblelocomotionsystem.In factonefunctionnormallysupportedby legs is thechangeof the total height.This influ-encesthe workspaceof the robot.However, we installeda telescopicjoint ( ��� ) in the torsoof ARMAR to havethis degreeof freedomtoo.
2.3 Torso and Neck
Theupperbodyof ARMAR has4 DOF (figure1). It is placedon themobileplatformandsupportsa rotationofabout������� . It alsocanbebentforward,backwardandsideward(circa ������� ). To adapttheheightof therobot(180cm), a telescopicjoint is includedin the body. With this joint the total heightof the robot canbe increasedby40cm.TheNeckof ARMAR has3 DOF.
2.4 Sensors
The sensorsystemconsistsof angleencodersfor eachjoint with a resolutionof ������� . The currentas well asthe voltageof eachmotor aremeasuredanddeterminedby specialpower electroniccard.For gripping variouskindsof objectsanartificial skin is placedontheinnersideof thegripper. It is realizedby measuringtheelectricalresistanceof theconductingrubberthatis dividedinto severalfieldsof anarray. To detecttheenvironment,astereocamerasystemis fixed on the headof ARMAR. Additionally, it is plannedto includestaingaugeson different
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partsof ARMAR, gyroscopesandaccelerationsensorsfor collision measurements,andfor the determinationofthe positionandorientationof the body of ARMAR. The sensorsystemof the mobile platform includeseightultrasonicsensorsanda planarlaser-scanner. Both typesof sensorsareusedfor a collision freenavigationof therobot.
2.5 Computer Ar chitecture
Thecomputerarchitectureof therobothasbeendesignedto bemodular. It is hierarchicallyorganizedanddividedinto computerarchitectureandsoftwarearchitecture.Thecomputerarchitectureconsistsof threelevels:themicro-controller level, the PC level andthe PC-network level. Currently, the robot is controlledby a clusterof C-167micro-controllersanda standardPC.The micro-controllersarecoupledwith specialpower cards,which controlfour motors.Themicro-controllerboardsareconnectedvia CAN-Buswith a maximumtransferrateof 1 Mbit/sto thePC.For real-timerequirementsa modularcontrolarchitectureis developed.As operatingsystemLinux aswell asReal-Time Linux areused.Thechoicewasmotivatedby theavailability of a high numberof devicesandof sourcecodes.The standardLinux kernelrunswith a lower priority asa taskof the RT-Linux kernel.For theefficient implementationof thedifferentcontrol levels,theobjectorientedmoduleMCA is implemented,sinceitenablesrapiddevelopmentandtheexchangeof controlalgorithmsat differentcontrol levels[16]. Figure2 showsthehardwareandsoftwarearchitecturesappliedto thehumanoidrobot.
C167 C167 C167 C167C167 C167
PC104Linux
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Fig.2. Thehardware(left) andsoftware(right) architectures.
3 Control
Manipulatorsareoneof themostimportanthardwarecomponentsof humanoidrobots.So,safetyandrobustcontrolis essentialrequirementfor successfulexecutionof cooperative manipulationtaskswith humans.Robustness,stability andsafetyareof greatestdegreeof importancein the caseof humanoidrobots.The implementationoffull dynamiccontrolon a robotstill remainsa challengeto robotscientistsandresearcherstoday. It is known thattheperformanceof a robotcanbeimprovedwith theincludingof therobotdynamicsinto its controller. However,thecomplexity and,moreimportant,thelackof knowledgeaboutthedynamicparametersof therobot,leadrobotsto becontrolledmostlyby PID control,wherethecontrolis doneindependentlyfor eachjoint.
SinceARMAR’s tasksarecurrentlylimited to thoserequiringlow speed,thedynamicseffectsfrom high-speedmotionscanbeneglected.Therefore,positionjoint controllersareused,becausethey canbetterdealwith nonlinearfriction. The purposeof a positioncontrolleris to drive themotor so that the actualangulardisplacementof thejoint will trackthedesiredangulardisplacementspecifiedby apreplanedtrajectory. Thejoint-anglemeasurementsof thearmsandbodyof ARMAR areobtainedby accurateencoders.A robustrobotcontrolrequiringonly positionmeasurementsis easyto implementandincreasesthedynamicperformanceof therobotmanipulator. Nevertheless,whenvelocity andforce sensorsareavailable,feedbackof the velocity andforcescanbe addedto improve theperformanceof thesystem.Figure3 shows thestructureof thecontrollerwe use.Thefuzzy-like modulechoosesa setof parameterof a classicalpositionjoint controllerdependingon the configurationof the arm.The setsofparameterareestablishedthroughexperiments.
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+
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set of parameter n
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Fig.3. Thestructureof thecontroller
For the control problemof the dual arm systemof ARMAR only the kinematiccontrol is considered.Thecontrol problemis solved in two stages:first, an inversekinematicproblemis solvedto transformtaskvariablesinto the correspondingjoint variablesfor the armsandbody of the robot.The obtainedjoint variablesareinputof a suitablejoint control scheme.The coordinationis thensolvedat the inversekinematicslevel while the arminteractioncanbeconsideredat joint controllevel.
4 Programming of manipulation tasks
Theprogrammingof manipulationtasksis doneby a directmappingof thehumanarmmovementsto the robot.Firstly, tasksaredemonstratedbyahumanoperatorandthemanipulationtrajectoriesarerecorded.In thefollowing,theprogrammingapproachof themanipulationtasksis described.
4.1 Motion Capturing
Many motioncapturingdevicesarecommerciallyavailablethesedaysanddifferenttechniquesareusedin orderto track the body motionof a person.Most of themsuffer drawbackssuchas:low updateratedueto the sensorcharacteristicsand pretty low communicationbandwidth.We usetwo commerciallyavailable position sensorscalledFasTraks.Thepositionsandorientationsof theelbow andthewrist aredirectly provided.Thehumanarmmovementsareonly kinematicallyrepresented,andthedynamicsfor humanmanipulationtaskscanbetakenintoaccountasapost-processingstep.It is notnecessaryto considerthedynamicsunlessrealisticvelocitydistributionfor manipulationmotionsis required.
4.2 Determination of the Arm Configuration
The transferof demonstratedmovementsto ARMAR is provided by an inversekinematicsalgorithm.This isnecessarybecausemost manipulationtasksare specifiedin termsof the object trajectories.The presenceof aredundantjoint in thearmof ARMAR resultsin infinite distinctarmconfigurationswith thesamehandpositionandorientation.Theredundancy of thearmcanbedescribedby therotationof thecenterof theelbow joint aboutthe axis, that passesthroughthe wrist andthe shoulderjoint (seefigure 4). The feasiblepositionsof the elbowaroundthis axisaredefinedby a curve.This curvecanbederivedfrom thefact that theendingpoint of theupperarm describesan ellipsoid centeredon the shoulderjoint and that the startingpoint of the forearmdescribesaspherecenteredon thewrist. Sincebothof thesepointshaveto bethesame,theredundancy curveresultsfrom theintersectionof theellipsoidandthesphere.Theelbow position,togetherwith thehandposition,formsa completerepresentationof thepostureof thearm.
For a givenpositionandorientationof theendeffectorandbasedon thearmgeometry, we calculatea possi-ble positionof the elbow, which is optimalwith respectto somecriteria (joint movementtime, mechanicaljointconstraints,singularityavoidance,redundancy resolutionresultingin human-likemotionsof therobotand”com-fortable” joint movements).Oncehaving theelbow position,theremainingjoint anglesaretheneasyto determine.For a completedescriptionof thealgorithmreferto [15]. So,insteadof usingtimeconsumingiterativesolutionofinversekinematics,ananalytical,geometrical,closedform solutionis provided.
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Startingfrom the humanarm movementdetectedby the above mentionedtrackingsystem,the arm config-urationcanthenbe computedfrom the sensordatausingthe inversekinematicsalgorithm.In orderto computethe joint anglesof the robot arm correspondingto the operator’s currentarm configuration,we assumethat theshoulderpositionsarefixed.
Shoulder
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f
s
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Fig.4. Determinationof thearmconfiguration:Theelbow position,togetherwith thehandposition,formsa completerepre-sentationof thepostureof thearm.Theredundancy of thearmis describedby a curve in thecartesianspace.
4.3 Motion Mapping to ARMAR
Basedon theelbow andwrist trajectoriesof thehumanarm,eachjoint angleof thearmof ARMAR is calculatedvia inversekinematics.The arm motion is mappeddirectly to the correspondinghumanoidarm motion: verticalmotion of the humanarm aremappedto the elbow joint andvertical shoulderjoint of the robot arm, whereashorizontalmotionsaremappedto thehorizontalshoulderjoint1. This mappingstrategy caneasilybeextendedtorealizealsoneckandtorsomotions.Thefinal stepof theprogrammingapproachwill beto adjustall joint anglesaccordingto thedescriptionof theobjectto bemanipulatedandtherobotenvironment.
5 Conclusionand Further Work
In this paper, the mechanismsand control schemeof the mobile manipulationsystemfor the humanoidrobotARMAR aredescribed.A closedform solutionof the inversekinematicsof the redundantarm of the robot isprovidedandan approachto transferthe humanarm movementsof typical manipulationtasksto the humanoidrobotARMAR is alsoproposed.Singlearmmotionplannersaredevelopedfor point-to-pointmotionandcurve-trackingmotion.TheInputsof themotionplannerarespecifiedby a humanoperator. TheOutputsof themotionplannersaresequencesof joint angles,andareexecutedin the simulationand thenwith the real robot via thecontrollerswe used.A simpledual-armmotionplannerfor coordinatedmotionis developed.Thismotionplannerconsiderstheclosedkinematicchainof botharmsandtheobject.Wealsoimplementedanobject-orientedsoftwaresystemthat allows a fastdebuggingof behavior-basedcontrol in a graphicalsimulationenvironment.It canbeusedsimultaneouslyto the controlof the real robot.Early manipulationtasksarealsoperformedto demonstratethe capabilitiesof the manipulationsystemof the humanoidrobot. Figure5 shows a typical manipulationtaskperformedby therobot.
Furtherwork will concentrateon the extensionof the sensorsystem,the integration of a humanoperator,the recognitionof the environment,the integrationof knowledgebasesandhuman-friendlyinterfaces,and the
1 Thevertical shoulderjoint allows theshoulderto move in thesagittalplane(forward/backward direction).Thehorizontalshoulderjoint allows theshoulderto move in thetransverseplane(outward/inwarddirection).
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Fig.5. ARMAR is performinga manipulationtask,whichwasdemonstratedby a humansupervisor.
implementationof servicetasks.For the control system,intelligent controllersable to performtasksinvolvingmultiple sensorinformationareto develop.Controlstrategiesfor thecoordinatedmotionof thewholehumanoidrobot (platform, torso,armsandhead)are also requiredfor the successfulexecutionof complex manipulationtasks.In addition,the control systemfor the navigation of the mobile platform will be implementedin ordertoprovideacollision freenavigationandto integratemobility in manipulationtasks.
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