Research

My research is about multi-contact locomotion for humanoid robots. The goal is to make robots walk around robustly on uneven terrains: bricks, stairs, rubble, earth, etc. For this purpose, they will need to learn a few tricks compared to what they currently do: using their upper body to balance themselves, make sliding contacts on extra surfaces to increase their stability margin, etc.

Selected items

  • Dynamic Walking over Rough Terrains by Nonlinear Predictive Control of the Floating-base Inverted Pendulum
    Stéphane Caron, Abderrahmane Kheddar. Submitted 1 March 2017. (pdf)

    We present a real-time rough-terrain dynamic walking pattern generator. Our method automatically finds step durations, which is a critical issue over rough terrains where they depend on terrain topology. To achieve this level of generality, we introduce the Floating-base Inverted Pendulum (FIP) model where the center of mass can translate freely and the zero-tilting moment point is allowed to leave the contact surface. We show that this model is equivalent to the linear-inverted pendulum mode with variable center of mass height, aside from the fact that its equations of motion remain linear. Our design then follows three steps: (i) we characterize the FIP contact-stability condition; (ii) we compute feedforward controls by solving a nonlinear optimization over receding-horizon FIP trajectories. Despite running at 30 Hz in a model-predictive fashion, simulations show that ...

  • ZMP Support Areas for Multi-contact Mobility Under Frictional Constraints
    Stéphane Caron, Quang-Cuong Pham, Yoshihiko Nakamura. IEEE Transactions on Robotics. Submitted 12 October 2015. Accepted 6 September 2016. Published 14 December 2016. (pdf)

    We propose a method for checking and enforcing multi-contact stability based on the Zero-tilting Moment Point (ZMP). The key to our development is the generalization of ZMP support areas to take into account (a) frictional constraints and (b) multiple non-coplanar contacts. We introduce and investigate two kinds of ZMP support areas. First, we characterize and provide a fast geometric construction for the support area generated by valid contact forces, with no other constraint on the robot motion. We call this set the full support area. Next, we consider the control of humanoid robots using the Linear Pendulum Mode (LPM). We observe that the constraints stemming from the LPM induce a shrinking of the support area, even for ...

  • Multi-contact Walking Pattern Generation based on Model Preview Control of 3D COM Accelerations
    Stéphane Caron, Abderrahmane Kheddar. The 2016 IEEE-RAS International Conference on Humanoid Robots, Cancun, Mexico, November 2016. (pdf)

    We present a multi-contact walking pattern generator based on preview-control of the 3D acceleration of the center of mass (COM). A key point in the design of our algorithm is the calculation of contact-stability constraints. Thanks to a mathematical observation on the algebraic nature of the frictional wrench cone, we show that the 3D volume of feasible COM accelerations is a always an upward-pointing cone. We reduce its computation to a convex hull of (dual) 2D points, for which optimal \({\cal O}(n \log n)\) algorithms are readily available. This reformulation brings a significant speedup compared to previous methods, which allows us to compute time-varying contact-stability criteria fast enough for the control loop. Next, we propose a conservative trajectory-wide contact-stability criterion, which can ...

Pre-prints

  • Dynamic Walking over Rough Terrains by Nonlinear Predictive Control of the Floating-base Inverted Pendulum
    Stéphane Caron, Abderrahmane Kheddar. Submitted 1 March 2017. (pdf)

    We present a real-time rough-terrain dynamic walking pattern generator. Our method automatically finds step durations, which is a critical issue over rough terrains where they depend on terrain topology. To achieve this level of generality, we introduce the Floating-base Inverted Pendulum (FIP) model where the center of mass can translate freely and the zero-tilting moment point is allowed to leave the contact surface. We show that this model is equivalent to the linear-inverted pendulum mode with variable center of mass height, aside from the fact that its equations of motion remain linear. Our design then follows three steps: (i) we characterize the FIP contact-stability condition; (ii) we compute feedforward controls by solving a nonlinear optimization over receding-horizon FIP trajectories. Despite running at 30 Hz in a model-predictive fashion, simulations show that ...

  • When to make a step? Tackling the timing problem in multi-contact locomotion by TOPP-MPC
    Stéphane Caron, Quang-Cuong Pham. (pdf)

    We present a Model-Predictive Controller (MPC) for multi-contact locomotion where predictive optimizations are realized by Time-Optimal Path Parameterization (TOPP). The key feature of this design is that, contrary to existing planners where step timings are provided as inputs, here the timing between contact switches is computed as output to a linear optimization problem based on a dynamic model of the robot. This is particularly appealing to multi-contact locomotion, where proper timings depend on the terrain topology and suitable heuristics are unknown. Thanks to recent advances in multi-contact stability computations, we improve the performance of TOPP for COM trajectories, which allows us to integrate it into a fast control loop. We implement the complete control pipeline and showcase it in simulations where a model of the HRP-4 humanoid climbs up and down a series of hills ...

Journal articles

  • ZMP Support Areas for Multi-contact Mobility Under Frictional Constraints
    Stéphane Caron, Quang-Cuong Pham, Yoshihiko Nakamura. IEEE Transactions on Robotics. Submitted 12 October 2015. Accepted 6 September 2016. Published 14 December 2016. (pdf)

    We propose a method for checking and enforcing multi-contact stability based on the Zero-tilting Moment Point (ZMP). The key to our development is the generalization of ZMP support areas to take into account (a) frictional constraints and (b) multiple non-coplanar contacts. We introduce and investigate two kinds of ZMP support areas. First, we characterize and provide a fast geometric construction for the support area generated by valid contact forces, with no other constraint on the robot motion. We call this set the full support area. Next, we consider the control of humanoid robots using the Linear Pendulum Mode (LPM). We observe that the constraints stemming from the LPM induce a shrinking of the support area, even for ...

  • Completeness of Randomized Kinodynamic Planners with State-based Steering
    Stéphane Caron, Quang-Cuong Pham, Yoshihiko Nakamura. Robotics and Autonomous Systems. Submitted 17 November 2015. Accepted 11 December 2016. Published 19 December 2016. (pdf)

    Probabilistic completeness is an important property in motion planning. Although it has been established with clear assumptions for geometric planners, the panorama of completeness results for kinodynamic planners is still incomplete, as most existing proofs rely on strong assumptions that are difficult, if not impossible, to verify on practical systems. In this paper, we focus on an important class of kinodynamic planners, namely those that interpolate trajectories in the state space. We provide a proof of probabilistic completeness for these planners under assumptions that can be readily verified from the system’s equations of motion and the user-defined interpolation function. Our proof relies crucially on a property of interpolated trajectories, termed second-order continuity (SOC), which we show ...

  • Admissible Velocity Propagation: Beyond Quasi-Static Path Planning for High-Dimensional Robots
    Quang-Cuong Pham, Stéphane Caron, Puttichai Lertkultanon, Yoshihiko Nakamura. International Journal of Robotics Research. Submitted 14 November 2014. Accepted 29 September 2016. Published 1 November 2016. (pdf)

    Path-velocity decomposition is an intuitive yet powerful approach to address the complexity of kinodynamic motion planning. The difficult trajectory planning problem is solved in two separate adn simpler steps: first, find a path in the configuration space that satisfies the geometric constraints (path planning), and second, find a time-parameterization of that path satisfying the kinodynamic constraints. A fundamental requirement is that the path found in the first step should be time-parameterizable. Most existing works fulfill this requirement by enforcing quasi-static constraints in the path planning step, resulting in an important loss in completeness. We propose a method that enables path-velocity decomposition to discover truly dynamic motions, i.e. motions that are not quasi-statically executable ...

  • Supervoxel Plane Segmentation and Multi-Contact Motion Generation for Humanoid Stair Climbing
    Tianwei Zhang, Stéphane Caron, Yoshihiko Nakamura. International Journal of Humanoid Robotics. 29 August 2016. (pdf)

    Stair climbing is still a challenging task for humanoid robots, especially in unknown environments. In this paper, we address this problem from perception to execution. Our first contribution is a real-time plane segment estimation method using unorganized lidar data without prior models of the staircase. We then integrate this solution with humanoid motion planning. Our second contribution is a stair-climbing motion generator where estimated plane segments are used to compute footholds and stability polygons. We evaluate our method on various staircases. We also demonstrate the feasibility of the generated trajectories in a real-life experiment with the humanoid robot HRP-4.

  • P2P Storage Systems: Study of Different Placement Policies
    Stéphane Caron, Frédéric Giroire, Dorian Mazauric, Julian Monteiro, Stéphane Pérennes. Peer-to-Peer Networking and Applications, Springer, March 2013. (pdf)

    In a P2P storage system using erasure codes, a data block is encoded in many redundancy fragments. These fragments are then sent to distinct peers of the network. In this work, we study the impact of different placement policies of these fragments on the performance of storage systems. Several practical factors (easier control, software reuse, latency) tend to favor data placement strategies that preserve some degree of locality. We compare three policies: two of them are local, in which the data are stored in logical neighbors, and the other one, global, in which the data are spread randomly in the whole system. We focus on the study of the probability to lose a data block and the bandwidth consumption to maintain such ...

  • A model of network neutrality with usage-based prices
    Eitan Altman, Pierre Bernhard, Stéphane Caron, George Kesidis, Julio Rojas-Mora, Sulan Wong. Telecommunication Systems, Springer, June 2011. (pdf)

    Hahn and Wallsten (Econ. Voice 3(6):1–7, 2006) wrote that network neutrality “usually means that broadband service providers charge consumers only once for Internet access, do not favor one content provider over another, and do not charge content providers for sending information over broadband lines to end users.” In this paper we study the implications of non-neutral behaviors under a simple model of linear demand-response to usage-based prices. We take into account advertising revenues for the content provider and consider both cooperative and non-cooperative scenarios. In particular, we model the: impact of side-payments between service and content providers, consider an access provider that offers multiple service classes, and model leader-follower (Stackelberg game) dynamics. We finally study the additional option for ...

Conference articles

  • Whole-Body Contact Force Sensing From Motion Capture
    Tu-Hoa Pham, Adrien Bufort, Stéphane Caron, Abderrahmane Kheddar. The 2016 IEEE/SICE International Symposium on System Integration, Sapporo, Japan, December 2016. Best Paper Award. (pdf)

    In this paper, we challenge the estimation of contact forces backed with ground-truth sensing in human whole-body interaction with the environment, from motion capture only. Our novel method makes it possible to get rid of cumbersome force sensors in monitoring multi-contact motion together with force data. This problem is very challenging. Indeed, while a given force distribution uniquely determines the resulting kinematics, the converse is generally not true in multi-contact. In such scenarios, physics-based optimization alone may only capture force distributions that are physically compatible with a given motion rather than the actual forces being applied. We address this indeterminacy by collecting a large-scale dataset on whole-body motion and contact forces humans apply in multi-contact ...

  • Multi-contact Walking Pattern Generation based on Model Preview Control of 3D COM Accelerations
    Stéphane Caron, Abderrahmane Kheddar. The 2016 IEEE-RAS International Conference on Humanoid Robots, Cancun, Mexico, November 2016. (pdf)

    We present a multi-contact walking pattern generator based on preview-control of the 3D acceleration of the center of mass (COM). A key point in the design of our algorithm is the calculation of contact-stability constraints. Thanks to a mathematical observation on the algebraic nature of the frictional wrench cone, we show that the 3D volume of feasible COM accelerations is a always an upward-pointing cone. We reduce its computation to a convex hull of (dual) 2D points, for which optimal \({\cal O}(n \log n)\) algorithms are readily available. This reformulation brings a significant speedup compared to previous methods, which allows us to compute time-varying contact-stability criteria fast enough for the control loop. Next, we propose a conservative trajectory-wide contact-stability criterion, which can ...

  • Planning with the Center-of-Mass rather than Stances for Humanoids Walking on Uneven Terrains
    Stéphane Caron, Yoshihiko Nakamura. 14th World Congress in Mechanism and Machine Science, Taipei, Taiwan, 25-30 October 2015. (pdf)

    In the current literature for non-gaited humanoid motion planning, stances (i.e., contact locations) are usually planned in a first step, after which joint-angle trajectories are interpolated or planned themselves. In this paper, we propose an alternative where planning is driven by center-of-mass motions rather than stances. Our approach uses a randomized motion planner as its first layer to explore the space of horizontal CoM coordinates. At a lower level, we propose a custom method to extend stances based on a desired CoM position. We evaluate the ability of the resulting planner in a rubble-field 3D environment with a model of the HYDRA humanoid robot.

  • Teleoperation System Design of Valve Turning Motions in Degraded Communication Conditions
    Stéphane Caron, Yoshihiko Nakamura. The 33rd Annual Conference of the Robotics Society of Japan (RSJ), Tokyo, Japan, September 2015. (pdf)

    During the DARPA Robotics Challenge (DRC), robots were expected to solve a number of tasks under teleoperation by a human operator. Limits in execution time and teleoperation bandwidth required teams to implement some level of autonomy on their robots, yet meaningful input could still be provided by the operator on a regular basis via the team’s Operator Control System (OCS). The purpose of the present paper is to report on the development of Team Hydra’s OCS for the DRC in the context of the valve-turning task. We describe the design of the system as well as the technical choices made, meanwhile pointing out the underlying research questions and directions for future work.

  • Leveraging Cone Double Description for Multi-contact Stability of Humanoids with Applications to Statics and Dynamics
    Stéphane Caron, Quang-Cuong Pham, Yoshihiko Nakamura. Robotics: Science and Systems (RSS), Roma, Italy, July 2015. (pdf)

    We build on previous works advocating the use of the Gravito-Inertial Wrench Cone (GIWC) as a general contact stability criterion (a "ZMP for non-coplanar contacts"). We show how to compute this wrench cone from the friction cones of contact forces by using an intermediate representation, the surface contact wrench cone, which is the minimal representation of contact stability for each surface contact. The observation that the GIWC needs to be computed only once per stance leads to particularly efficient algorithms, as we illustrate in two important problems for humanoids : "testing robust static equilibrium" and "time-optimal path parameterization". We show, through theoretical analysis and in physical simulations, that our method is more general and/or outperforms existing ones.

  • Stability of Surface Contacts for Humanoid Robots Closed-Form Formulae of the Contact Wrench Cone for Rectangular Support Areas
    Stéphane Caron, Quang-Cuong Pham, Yoshihiko Nakamura. The 2015 IEEE International Conference on Robotics and Automation (ICRA), Seattle, USA, May 2015. (pdf)

    Humanoids locomote by making and breaking contacts with their environment. Thus, a crucial question for them is to anticipate whether a contact will hold or break under effort. For rigid surface contacts, existing methods usually consider several point-contact forces, which has some drawbacks due to the underlying redundancy. We derive a criterion, the Contact Wrench Cone (CWC), which is equivalent to any number of applied forces on the contact surface, and for which we provide a closed-form formula.

  • Kinodynamic Motion Retiming for Humanoid Robots
    Stéphane Caron, Quang-Cuong Pham, Yoshihiko Nakamura. The 32nd Annual Conference of the Robotics Society of Japan (RSJ), Fukuoka, Japan, September 2014. (pdf)

    In this paper, we advocate the use of Time-Optimal Path Parameterization (TOPP) to enable planning of dynamic motions for humanoid robots. We extend the existing formulation of ZMP constraints to arbitrary polygonal areas and provide an original approach to incorporate frictional contact constraints in TOPP. We evaluate our algorithm experimentally with the HRP-4 robot performing a stepping motion. Given a slow and quasi-static input motion, our method automatically produces a 2x-faster dynamic motion successfully executed on the real robot (4x faster in simulation).

  • Completeness of Randomized Kinodynamic Planners with State-based Steering
    Stéphane Caron, Quang-Cuong Pham, Yoshihiko Nakamura. The 2014 IEEE International Conference on Robotics and Automation (ICRA), Hong-Kong, China, June 2014. (pdf)

    The panorama of probabilistic completeness results for kinodynamic planners is still confusing. Most existing completeness proofs require strong assumptions that are difficult, if not impossible, to verify in practice. To make completeness results more useful, it is thus sensible to estabish a classification of the various types of constraints and planning methods, and then attack each class with specific proofs and hypotheses that can be verified in practice. We propose such a classification, and provide a proof of probabilistic completeness for an important class of planners, namely those whose steering method is based on the interpolation of system trajectories in the state space. We also provide design guidelines for the interpolation function and discuss two criteria arising from our ...

  • Kinodynamic Motion Planners based on Velocity Interval Propagation
    Stéphane Caron, Yoshihiko Nakamura, Quang-Cuong Pham. The 31st Annual Conference of the Robotics Society of Japan (RSJ), Tokyo, Japan, September 2013. (pdf)

    Humanoid robotics has spawned several fields of active research. When it comes to dynamic motion control, three lines of work stand out: reduced models (combined with inverse kinematics), local controllers and global planning. In the present paper, we present and further develop a motion planning approach recently proposed in [10], which allows planning with dynamics constraints while staying in the configuration space; thus avoiding the complexity explosion mentioned above. We briefly discuss how this approach can be extended to handle ZMP constraints, which may give rise to a new family of efficient motion planners for humanoid robots.

  • Kinodynamic planning in the configuration space via Admissible Velocity Propagation
    Quang-Cuong Pham, Stéphane Caron, Yoshihiko Nakamura. Robotics: Science and Systems (RSS), Berlin, Germany, June 2013. (pdf)

    We propose a method that enables kinodynamic planning in the configuration space (of dimension n) instead of the state space (of dimension 2n), thereby potentially cutting down the complexity of usual kinodynamic planning algorithms by an exponential factor. At the heart of this method is a new technique – called Velocity Interval Propagation – which, given a path in the configuration space and an interval of reachable velocities at the beginning of that path, computes exactly and efficiently the interval of all the velocities the system can reach after traversing the path while respecting the system kinodynamic constraints. Combining this technique with usual sampling-based methods gives rise to a family of new motion planners that can appropriately handle kinodynamic constraints while avoiding the complexity explosion and ...

  • Leveraging Side Observations in Stochastic Bandits
    Stéphane Caron, Branislav Kveton, Marc Lelarge, Smriti Bhagat. The 28th Conference on Uncertainty in Artificial Intelligence, 2012. (pdf)

    This paper considers stochastic bandits with side observations, a model that accounts for both the exploration/exploitation dilemma and relationships between arms. In this setting, after pulling an arm i, the decision maker also observes the rewards for some other actions related to i. We will see that this model is suited to content recommendation in social networks, where users' reactions may be endorsed or not by their friends. We provide efficient algorithms based on upper confidence bounds (UCBs) to leverage this additional information and derive new bounds improving on standard regret guarantees. We also evaluate these policies in the context of movie recommendation in social networks: experiments on real datasets show substantial learning rate speedups ranging from 2.2x to 14x ...

  • Application Neutrality and a Paradox of Side Payments
    Stéphane Caron, George Kesidis, Eitan Altman. The Re-Architecting the Internet Workshop (ReARCH), 2010. (pdf)

    The ongoing debate over net neutrality covers a broad set of issues related to the regulation of public networks. In two ways, we extend an idealized usage-priced game-theoretic framework based on a common linear demand-response model. First, we study the impact of "side payments" among a plurality of Internet service (access) providers and content providers. In the non-monopolistic case, our analysis reveals an interesting "paradox" of side payments in that overall revenues are reduced for those that receive them. Second, assuming different application types (e.g., HTTP web traffic, peer-to-peer file sharing, media streaming, interactive VoIP), we extend this model to accommodate differential pricing among them in order to study the issue of application neutrality. Revenues for neutral and non-neutral pricing are compared for the case ...

  • Incentive-based Energy Consumption Scheduling Algorithms for the Smart Grid
    Stéphane Caron, George Kesidis. IEEE SmartGridComm, 2010. (pdf)

    In this paper, we study Demand Response (DR) problematics for different levels of information sharing in a smart grid. We propose a dynamic pricing scheme incentivizing consumers to achieve an aggregate load profile suitable for utilities, and study how close they can get to an ideal flat profile depending on how much information they share. When customers can share all their load profiles, we provide a distributed algorithm, set up as a cooperative game between consumers, which significantly reduces the total cost and peak-to-average ratio (PAR) of the system. In the absence of full information sharing (for reasons of privacy), when users have only access to the instantaneous total load on the grid, we provide distributed stochastic strategies that successfully exploit this information to improve the overall load profile. Simulation results confirm ...

  • A Study of Non-neutral Networks with Usage-Based Prices
    Eitan Altman, Pierre Bernhard, Stéphane Caron, George Kesidis, Julian Rojas-Mora, Sulan Wong. The Third International Workshop on Economic Traffic Management (ETM), 2010. (pdf)

    Hahn and Wallsten wrote that network neutrality "usually means that broadband service providers charge consumers only once for Internet access, do not favor one content provider over another, and do not charge content providers for sending information over broadband lines to end users." In this paper we study the implications of non-neutral behaviors under a simple model of linear demand-response to usage-based prices. We take into account advertising revenues and consider both cooperative and non-cooperative scenarios. In particular, we model the impact of side-payments between service and content providers. We also consider the effect of service discrimination by access providers, as well as an extension of our model to non-monopolistic content providers.

  • Data Life Time for Different Placement Policies in P2P Storage Systems
    Stéphane Caron, Frédéric Giroire, Dorian Mazauric, Julian Monteiro, Stéphane Pérennes. The 3rd International Conference on Data Management in Grid and P2P Systems (Globe), 2010. (pdf)

    Peer-to-peer systems are foreseen as an efficient solution to achieve reliable data storage at low cost. To deal with common P2P problems such as peer failures or churn, such systems encode the user data into redundant fragments and distribute them among peers. The way they distribute it, known as placement policy, has a significant impact on their behavior and reliability. In this paper, we study the impact of different placement policies on the data life time. More precisely, we describe methods to compute and approximate the mean time before the system loses data (Mean Time to Data Loss). We compare this metric for three placement policies: two of them local, in which the data is ...

  • P2P Storage Systems Data Life Time for Different Placement Policies
    Stéphane Caron, Frédéric Giroire, Dorian Mazauric, Julian Monteiro, Stéphane Pérennes. 12emes Rencontres Francophones sur les Aspects Algorithmiques de Télécommunications (AlgoTel), 2010. (pdf)

    Peer-to-peer systems are foreseen as an efficient solution to achieve reliable data storage at low cost. To deal with common P2P problems such as peer failures or churn, such systems encode the user data into redundant fragments and distribute them among peers. The way they distribute it, known as placement policy, has a significant impact on their behavior and reliability. In this report, after a brief state-of-the-art of the technology used in P2P storage systems, we compare three different placement policies: two of them local, in which the data is stored in logical peer neighborhoods, and on of them global in which fragments are parted at random among the different peers. For each policy, we give either Markov ...

Talks

  • Locomotion humanoïde : du sol plat au tout-terrain
    Présentation donnée à SoftBank Robotics Europe, Paris, le 8 mars 2017. (pdf)

    Cette présentation retrace les étapes importantes du développement des contrôleurs de marche pour les robots humanoïdes, depuis la démonstration publique du Honda P2 en 1997 jusqu'aux récents développements en marche tout-terrain. Elle n'aborde que des résultats partagés dans le monde ouvert, chaque slide étant associé à un article de recherche. La première partie revisite les concepts majeurs qui ont permis de résoudre la locomotion sur sol plat. La seconde décrit plusieurs développements récents en marche tout-terrain.

  • Time-Optimal Parameterization: a tool for Humanoid Motion Planning and Predictive Control
    Talk given at Humanoids 2016, workshop W3 on The use of dynamics in the field of humanoid robotics: identification, planning, perception and control, 15 November 2016.

    Numerical optimization and dynamic models have given roboticists the tools to implement instantaneous whole-body control (e.g. finding joint torques at time t to track at best a reference trajectory). However, it provided no turnkey solution as to whole-body planning, where successful planners were historically grounded on stochastic sampling and state-space discretization rather than active sets and gradient descents. Yet, this does not mean that the two fields are hermetically separated. In this talk, we will go through the recent history of Time-Optimal Path Parameterization (TOPP), an optimization routine that has been successfully applied to both motion planning and predictive control. A key feature of TOPP is its ability to return not only ...

  • Support Areas and Volumes for Humanoid Locomotion under Frictional Contacts
    Talk given at the Max Planck Institute on 19 September 2016.

    Humanoid locomotion on horizontal floors was solved by closing the feedback loop on the Zero-tiling Moment Point (ZMP), a measurable dynamic point that needs to stay inside the foot contact area to prevent the robot from falling (contact stability criterion). However, this criterion does not apply to general multi-contact settings, the "new frontier" in humanoid locomotion.

  • ZMP support areas for multi-contact locomotion
    Talk given at LAAS-CNRS (30 May 2016), at the Journées Nationales de la Robotique Humanoïde (22 June 2016), and at the Journée Scientifique du Département Robotique du LIRMM (23 June 2016).

    The Zero-tilting Moment Point (ZMP) and its support polygon are the two notions thanks to which roboticitsts solved the problem of walking on horizontal floor. Its historic definition presents two major limitations: all contacts between the robot and the environment need to be coplanar, and frictional effects (such as sliding or yaw rotations) are not taken into account. We present here a generalization of the ZMP "support area" that overcomes these two limitations. We show how to apply it with a linear-pendulum control law to generate stable multi-contact locomoting motions for humanoids in general environments.

  • Perspectives on Motion Planning and Control for Humanoid Robots in Multi-contact Scenarios
    Talk given at the School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore. 7 March 2016.

    When today's robots move around, the motion that you observe is the result of two software stages: planning and control. Planning is the part that computes a trajectory from the initial state of the system to some goal state. Control is the part that deals with perturbations or modelling errors, and stabilizes the system at best while it performs the trajectory output by the planner.

  • Modèles simplifiés pour la locomotion des robots humanoïdes en terrain accidenté
    Présentation donnée à la Journée Francophone de la Recherche au Japon, qui s'est déroulée le vendredi 13 novembre 2015 à la Maison Franco-Japonaise de Tokyo.

    La robotique humanoïde distingue deux domaines : planification et locomotion. Tous deux servent le même objectif, qui est de permettre au robot de se déplacer d'un endroit à un autre. La locomotion repose sur des mouvements répétés (comme les pas d'une démarche) ou générés par des modèles simplifiés du robot (comme le pendule inversé, que nous allons voir). Elle nécessite généralement un sol plat ou peu accidenté. La planification fait moins d'hypothèses, ce qui la rend adaptée aux déplacements dans les environnements encombrés. Toutefois, elle nécessite d'avantage de calculs et a tendance à produire des mouvements peu naturels. Marcher en forêt relève par exemple de la locomotion, tandis qu'escalader ...

Workshops

  • Mixing bandits A recipe for improved cold-start recommendations in a social network
    Stéphane Caron, Smriti Bhagat. The 7th Workshop on Social Network Mining and Analysis, 2013. (pdf)

    Recommending items to new or “cold-start” users is a challenging problem for recommender systems. Collaborative filtering approaches fail when the preference history of users is not available. A promising direction that has been explored recently [12] is to utilize the information in the social networks of users to improve the quality of cold-start recommendations. That is, given that users are part of a social network, a new user shows up in the network with no preference history and limited social links, the recommender system tries to learn the user’s tastes as fast as possible. In this work, we model the learning of preferences of cold-start users using multi-armed bandits [5] embedded in a social network. We propose two novel strategies leveraging neighborhood estimates to ...

  • 3d hardware canaries
    Sébastien Briais, Stéphane Caron, Jean-Michel Cioranesco, Jean-Luc Danger, Sylvain Guilley, Jacques-Henri Jourdan, Arthur Milchior, David Naccache, and Thibault Porteboeuf. In Cryptographic Hardware and Embedded Systems, pages 1–22. Springer, 2012. (pdf)

    3D integration is a promising advanced manufacturing process offering a variety of new hardware security protection opportunities. This paper presents a way of securing 3D ICs using Hamiltonian paths as hardware integrity verification sensors. As 3D integration consists in the stacking of many metal layers, one can consider surrounding a security-sensitive circuit part by a wire cage. After exploring and comparing different cage construction strategies (and reporting preliminary implementation results on silicon), we introduce a "hardware canary". The canary is a spatially distributed chain of functions Fi positioned at the vertices of a 3D cage surrounding a protected circuit. A correct answer (Fn ∘ … ∘ F1)(m) to ...

Thesis

Patents

  • System and method for recommending items in a social network
    Stéphane Caron, Branislav Kveton, Marc Lelarge, Smriti Bhagat. US Patent Application US-20150199715-A1.

    The present principles consider stochastic bandits with side observations, a model that accounts for both the exploration/exploitation dilemma and relationships between arms. In this setting, after pulling an arm i, the decision maker also observes the rewards for some other actions related to i. The present principles provide a method and a system for efficiently leveraging additional information based on the responses provided by other users connected to the user via a computerized social network and derive new bounds improving on standard regret guarantees. We will see that this model is suited to content recommendation in social networks, where users' reactions may be endorsed or not by their friends.

  • Method for cold start of a multi-armed bandit in a recommender system
    Smriti Bhagat, Stéphane Caron. US Patent Application US-20150012345-A1. (pdf)

    A method performed by a recommender system to recommend items to a new user includes calculating reward estimates from multiple multi-armed bandit models of a user and her social network friends. The new user's social network friends have multi-armed bandit models that are well established. The mixed multi-armed bandit estimates are processed to select the arm that maximizes the estimated reward to the new user. The multi-armed bandit arm of the greatest reward estimate is played and the new user responds by providing feedback so that the new user's multi-armed bandit model is updated as time progresses.

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