Clément, Brice

Hoffman, Enrico,

Ivaldi, Serena

Mouret, Jean-Baptiste

Tsagarakis, Nikos,

Zhou, Chengxu

Hoffman, Enrico, Mingo

Tsagarakis, Nikos, G

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HAL Id: hal-01790597https://hal.archives-ouvertes.fr/hal-01790597Submitted on 13 May 2018HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestinée au dépôt et à la diffusion de documentsscientifiques de niveau recherche, publiés ou non,émanant des établissements d’enseignement et derecherche français ou étrangers, des laboratoirespublics ou privés.Whole-Body Compliant Control of iCub: first resultswith OpenSoTEnrico Hoffman, Brice Clément, Chengxu Zhou, Nikos Tsagarakis,Jean-Baptiste Mouret, Serena IvaldiTo cite this version:Enrico Hoffman, Brice Clément, Chengxu Zhou, Nikos Tsagarakis, Jean-Baptiste Mouret, et al..Whole-Body Compliant Control of iCub: first results with OpenSoT. IEEE/RAS ICRA Workshop onDynamic Legged Locomotion in Realistic Terrains, May 2018, Brisbane, Australia. ￿hal-01790597￿Whole-Body Compliant Control of iCub: firstresults with OpenSoTEnrico Mingo Hoffman1, Brice Clement2, Chengxu Zhou1,Nikos G. Tsagarakis1, Jean-Baptiste Mouret2 and Serena Ivaldi2I. INTRODUCTIONHumanoid bipedal robots are becoming more and morepopular among the research community thanks to their ver-satility in terms of locomotion and manipulation capabilities.On the other side, these platforms are, in general, morecomplex to control than other robotics platforms: locomotionin open and cluttered environments, balancing, whole-bodycontrol, redundancy resolution and perception are some ofthe still open topics in this field. Furthermore, it is verydifficult to find mature hardware platforms to perform exper-iments. Several small-sized humanoids are actually availablefor purchasing but, for what concern medium (children-like)and large (adult-like) sizes, there are very few companiesproviding such products [1], [2]. Among the medium sizeplatforms, the iCub [3] is the one with the highest numberof working units in the world. iCub is a humanoid robotwith 53 degrees of freedom (DoF), originally conceived forresearch in cognitive and developmental robotics [3]. Afterbeing equipped with force/torque and tactile sensors it becamea central platform for whole-body dynamics estimation [4],torque control and physical interaction [5], enabling researchin human-robot collaboration and assistance-oriented tasks [6].In these applications, locomotion, balancing and manipulationare complex and, in general, uncertainties are present due tothe unstructured scenario and the presence of human agents. Itis well known that such uncertainties can be handled with com-pliant controllers that permits to manipulate the environmentor interact with humans in a safe way and without breakingthe robot. In particular, it was shown that compliance playsa crucial role for the stabilization of bipeds when subject toexternal pushes [7].In this work we present the integration of a simple compliantstabilizer [8], which acts at the level of the Center of Mass(CoM), together with a whole-body controller [9], in the iCubrobot. This integration effort has been made in order to provideiCub with a simple but effective module which can handlewhole-body tasks and stabilization at the same time.This research was supported by European Union Horizon 2020 roboticsprogram [ICT-23-2014], grant agreement n.731540 AnDy and grant agreementn.644727 CogIMon, by the European Research Council (grant agreementn.637972 ResiBots, and by the Region Grand Est (project “LocoLearn”).1 Advanced Robotics Department, Italian Institute of Technology, Italy,Genoa, {enrico.mingo, chengxu.zhou, nikos.tsagarakis}@iit.it2 Inria, CNRS, Université de Lorraine, LORIA, France, Nancy,{brice.clement, jean-baptiste.mouret, serena.ivaldi}@inria.frII. COMPLIANT WHOLE-BODY CONTROLLERThe compliant whole-body controller is divided in two maincomponents: the Compliant Stabilizer and the Whole-BodyInverse Kinematics (IK) Engine. The Compliant Stabilizeris based on the work in [8] and uses a simplified modelto stabilize the robot at the CoM. The stabilization is donecomputing a control input, consisting in a correction of thereference of the CoM, based on the desired vs actual Zero Mo-ment Point (ZMP) position as well as its velocity. Equivalentstiffness and damping gains are used to tune the controller. Theactual position of the ZMP is measured using the force/torquesensors at the ankles of iCub. This well known solution isvery effective because when the robot has the feet in contactwith the environment, the force/torque sensors measure all thepossible interactions which the robot is subject to.Fig. 1: Proposed control scheme: xd contains all the desired refer-ences from the user side. The CoM reference is modified by theCompliant Stabilizer which generates a ∆xCoM according to thedesired position of the ZMP (namely ZMPd) and the measuredwrenches from the feet wLF and wRF. The updated references x∗d aresent to the Whole-Body IK Engine and converted to joint velocitiesq̇d. The output joint velocities are integrated and sent to the jointposition PID controllers.The corrections at the level of the CoM are added tothe CoM reference and sent, with all the other Cartesianreferences, to the Whole-Body IK Engine. This componentis based on the work in [9] and permits to handle prioritiesbetween tasks as well as constraints in form of equalitiesand inequalities. In particular, the Whole-Body IK Enginecomputes, from the Cartesian references, joint level velocitieswhich are integrated and sent to the robot low level PID con-trollers. OpenSoT permits to easily customize the controller interms of formulation, tasks/constraints organization and solver.In particular in this wok we have chosen the velocity controlformulation, the tasks are organized in the following priorities(a) Tele-Operation(b) Squats(c) Empty glass stabilizationFig. 2: Experiments performed on iCub using the proposed whole-body control structure.(in particular we are considering a floating-base robot):(WorldTRFoot +World TLFoot) /(WorldT XYCoM +World T ZOWaits + TNeck) /(WorldTRArm +World TLArm) /TPosture<<(C JointLimits+ CJoint VelocityLimits)(1)where aT Xb represents the X component of a velocity task from framea to frame b expressed in frame a (if frame a is missing, the task isintended in joint space), and C represents a constraint. the formulationin (1) shows how the tasks and constraints are organized. In particularthe symbol ”\” is used to set HARD priority (in terms of null-space projection) relation between tasks while the ”+” symbols isused to set SOFT priority (in terms of augmentation) between them.Such ”stack” enables to move the arms ensuring that the CoM willnot change its position, the stabilizer behaves in order to track adesired ZMP reference changing the reference of the CoM. Despitein this work a fixed position for the ZMP is considered, the samecontrol architecture has been used in other robots to realize walkingbehaviours. Figure 1 shows the implemented control scheme.III. EXPERIMENTSWe consider three set of experiments where a human appliesexternal forces to various parts of the body of the robot.In the first experiment the robot is balancing while an operatortele-operates the hand end-effectors. The level of compliance isgiven primarily by the equivalent stiffness and damping gains of thestabilizer. On the other side, the motion behaviour is given by theparameters of the IK engine. The second task consists in squattingmotions: here we observed that high compliance along the X axisgenerates high oscillatory motions, therefore we reduced the gainsin the X direction of the stabilizer (which correspond to increasingthe stiffness). Finally we consider a typical service task: carrying anempty plastic cup on a tray. Here, we want that the robot to be able tostabilize the object while being subject to external perturbations. Themotion behaviour given by (1) permits to stabilize the end-effectors.Of course, considering the order of priority in (1), the arms willmove in a way to do not disturb the CoM tracking from the previoustask. This is compatible with human-like behaviours: if the robot issubject to very high external perturbation, the main task to satisfy isthe balancing (with any limb) than the stability of the plastic cup.Figure 2 shows the setup of the aforementioned experiments, a videois available at https://www.youtube.com/watch?v=W6ug-wtAfTk.IV. CONCLUSIONIn this work a simple, yet effective, whole-body compliant stabi-lizer for the humanoid robot iCub has been presented. The control ar-chitecture is based on the feed-back controller in [cite ChenXue] andthe whole-body IK in [9]. Experiments of such control architectureshave been demonstrated for squatting motions, tele-operation andbimanual-manipulation, all taking into account rejection of externaldisturbances. An open-source implementation of the compliant stabi-lizer is available at https://github.com/ADVRHumanoids/compliantstabilizer, the OpenSoT library is available at https://github.com/robotology/OpenSoT. Future works will integrate walking with ma-nipulation and tele-operation with learning [10].REFERENCES[1] K. Kaneko, F. Kanehiro, M. Morisawa, K. Akachi, G. Miyamori,A. Hayashi, and N. Kanehira, “Humanoid robot hrp-4-humanoid roboticsplatform with lightweight and slim body,” in Intelligent Robots andSystems (IROS), IEEE/RSJ Int. Conf. on, 2011, pp. 4400–4407.[2] O. Stasse, T. Flayols, R. Budhiraja, K. Giraud-Esclasse, J. Carpentier,A. Del Prete, P. Soueres, N. Mansard, F. Lamiraux, J.-P. Laumondet al., “Talos: A new humanoid research platform targeted for industrialapplications,” 2017.[3] L. Natale, F. Nori, G. Metta, M. Fumagalli, S. Ivaldi, U. Pattacini,M. Randazzo, A. Schmitz, and G. Sandini, “The icub platform: a toolfor studying intrinsically motivated learning,” in Intrinsically motivatedlearning in natural and artificial systems. Springer, 2013, pp. 433–458.[4] M. Fumagalli, S. Ivaldi, M. Randazzo, L. Natale, G. Metta, G. Sandini,and F. Nori, “Force feedback exploiting tactile and proximal force/torquesensing,” Autonomous Robots, vol. 33, no. 4, pp. 381–398, 2012.[5] F. Romano, G. Nava, M. Azad, J. Čamernik, S. Dafarra, O. Dermy,C. Latella, M. Lazzaroni, R. Lober, M. Lorenzini et al., “The CoDyCoproject achievements and beyond: Toward human aware whole-bodycontrollers for physical human robot interaction,” IEEE Robotics andAutomation Letters, vol. 3, no. 1, pp. 516–523, 2018.[6] S. Ivaldi, L. Fritzsche, J. Babič, F. Stulp, M. Damsgaard, B. Graimann,G. Bellusci, and F. Nori, “Anticipatory models of human movementsand dynamics: the roadmap of the AnDy project,” in Digital HumanModels (DHM), 2017.[7] Z. Li, B. Vanderborght, N. G. Tsagarakis, L. Colasanto, and D. G. Cald-well, “Stabilization for the compliant humanoid robot coman exploitingintrinsic and controlled compliance,” in Robotics and Automation, IEEEInt. Conf. on, 2012, pp. 2000–2006.[8] C. Zhou, Z. Li, X. Wang, N. Tsagarakis, and D. Caldwell, “Stabilizationof bipedal walking based on compliance control,” Autonomous Robots,vol. 40, no. 6, pp. 1041–1057, 2016.[9] E. M. Hoffman, A. Rocchi, A. Laurenzi, and N. G. Tsagarakis, “Robotcontrol for dummies: Insights and examples using opensot,” in Hu-manoid Robotics, IEEE-RAS Int. Conf. on, 2017, pp. 736–741.[10] J. Spitz, K. Bouyarmane, S. Ivaldi, and J.-B. Mouret, “Trial-and-errorlearning of repulsors for humanoid qp-based whole-body control,” inHumanoid Robotics, 2017 IEEE-RAS Int. Conf. on, 2017.

Whole-Body Compliant Control of iCub: first results with OpenSoT

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Whole-Body Compliant Control of iCub: first results with OpenSoT

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