Retour au site du LAAS-CNRS

Laboratoire d’analyse et d’architecture des systèmes

Publications de l'équipe gepetto

Choisir la langue : FR | EN

371documents trouvés

16242
01/01/2018

Joint position and velocity bounds in discrete-time acceleration/torque control of robot manipulators

A.DEL PRETE

GEPETTO

Revue Scientifique : IEEE Robotics and Automation Letters, Vol.3, N°1, pp.281-288, Janvier 2018, DOI: 10.1109/LRA.2017.2738321 , N° 16242

Lien : https://hal.archives-ouvertes.fr/hal-01356989

Diffusable

Plus d'informations

Abstract

This letter deals with the problem of controlling a robotic system whose joints have bounded position, velocity, and acceleration/torque. Assuming a discrete-time acceleration control, we compute tight bounds on the current joint accelerations that ensure the existence of a feasible trajectory in the future. Despite the clear practical importance of this issue, no complete and exact solution has been proposed yet, and all existing control architectures rely on hand-tuned heuristics. We also extend this methodology to torque-controlled robots, for which joint accelerations are only indirectly bounded by the torque limits. Numerical simulations are presented to validate the proposed method, which is computationally efficient and hence suitable for high-frequency control.

140657
17095
28/09/2017

Online payload identification for quadruped robots

G.TOURNOIS, M.FIOCCHI, A.DEL PRETE, R.ORSOLINO, D.G.CALDWELL, C.SEMINI

IIT, Genova, GEPETTO

Manifestation avec acte : IEEE/RSJ International Conference on Intelligent Robots and Systems ( IROS ) 2017 du 24 septembre au 28 septembre 2017, Vancouver (Canada), Septembre 2017, 8p. , N° 17095

Lien : https://hal.laas.fr/hal-01575033

Diffusable

Plus d'informations

Abstract

The identification of inertial parameters is crucial to achieve high-performance model-based control of legged robots. The inertial parameters of the legs are typically not altered during expeditions and therefore are best identified offline. On the other hand, the trunk parameters depend on the modules mounted on the robot, like a motor to provide the hydraulic power, or different sets of cameras for perception. This motivates the use of recursive approaches to identify online mass and the position of the Center of Mass (CoM) of the robot trunk, when a payload change occurs. We propose two such approaches and analyze their robustness in simulation. Furthermore, experimental trials on our 80-kg quadruped robot HyQ show the applicability of our strategies during locomotion to cope with large payload changes that would otherwise severely compromise the balance of the robot.

140693
17054
24/09/2017

A Kinodynamic steering-method for legged multi-contact locomotion

P.FERNBACH, S.TONNEAU, A.DEL PRETE, M.TAIX

GEPETTO

Manifestation avec acte : IEEE/RSJ International Conference on Intelligent Robots and Systems ( IROS ) 2017 du 24 septembre au 28 septembre 2017, Vancouver (Canada), Septembre 2017, 7p. , N° 17054

Lien : https://hal.laas.fr/hal-01486933

Diffusable

Plus d'informations

Abstract

We present a novel method for synthesizing collision-free, dynamic locomotion behaviors for legged robots, including jumping, going down a very steep slope, or recovering from a push using the arms of the robot. The approach is automatic and generic: non-gaited motions, comprising arbitrary contact postures can be generated along any environment. At the core of our framework is a new steering method that generates trajectories connecting two states of the robot. These trajectories account for the state-dependent, centroidal dynamic constraints inherent to legged robots. The method, of low dimension, formulated as a Linear Program, is really efficient to compute, and can find an application in various problems related to legged locomotion. By incorporating this steering method into an existing sampling-based contact planner, we propose the first kinodynamic contact planner for legged robots.

140189
17313
21/09/2017

Modification of the spontaneous seat-to-stand transition in cycling with bodyweight and cadence variations

B.WATIER, A.COSTES, N.TURPIN

GEPETTO, Toulouse III, CRIR

Rapport LAAS N°17313, doi 10.1016/j.jbiomech.2017.08.003, Septembre 2017

Lien : https://hal.laas.fr/hal-01584024

Diffusable

Plus d'informations

Abstract

When a high power output is required in cycling, a spontaneous transition by the cyclist from a seated to a standing position generally occurs. In this study, by varying the cadence and cyclist bodyweight, we tested whether the transition is better explained by the greater power economy of a standing position or by the emergence of mechanical constraints that force cyclists to stand. Ten males participated in five experimental sessions corresponding to different bodyweights (80%, 100%, or 120%) and cadences (50 RPM, 70 RPM, or 90 RPM). In each session, we first determined the seat-to-stand transition power (SSTP) in an incremental test. The participants then cycled at 20%, 40%, 60%, 80%, 100%, or 120% of the SSTP in the seated and standing positions, for which we recorded the saddle forces and electromyogram (EMG) signals of eight lower limb muscles. We estimated the cycling cost using an EMG cost function (ECF) and the minimal saddle forces in the seated position as an indicator of the mechanical constraints. Our results show the SSTP to vary with respect to both cadence and bodyweight. The ECF was lower in the standing position above the SSTP value (i.e., at 120%) in all experimental sessions. The minimal saddle forces varied significantly with respect to both cadence and bodyweight. These results suggest that optimization of the muscular cost function, rather than mechanical constraints, explain the seat-to-stand transition in cycling.

140919
17277
06/09/2017

Experimental evaluation of simple estimators for humanoid robots

T.FLAYOLS, A.DEL PRETE, P.WENSING, A.MIFSUD, M.BENALLEGUE, O.STASSE

GEPETTO, UND, AIST

Rapport LAAS N°17277, Septembre 2017, 7p.

Lien : https://hal.archives-ouvertes.fr/hal-01574819

Diffusable

Plus d'informations

Abstract

This paper introduces and evaluates a family of new simple estimators to reconstruct the pose and velocity of the floating base. The estimation of the floating-base state is a critical challenge to whole-body control methods that rely on full-state information in high-rate feedback. Although the kinematics of grounded limbs may be used to estimate the pose and velocity of the body, modelling errors from ground irregularity, foot slip, and structural flexibilities limit the utility of estimation from kinematics alone. These difficulties have motivated the development of sensor fusion methods to augment body-mounted IMUs with kinematic measurements. Existing methods often rely on extended Kalman filtering, which lack convergence guarantees and may present difficulties in tuning. This paper proposes two new simplifications to the floating-base state estimation problem that make use of robust off-the-shelf orientation estimators to bootstrap development. Experiments for in-place balance and walking with the HRP-2 show that the simplifications yield results on par with the accuracy reported in the literature for other methods. As further benefits, the structure of the proposed estimators prevents divergence of the estimates, simplifies tuning, and admits efficient computation. These benefits are envisioned to help accelerate the development of baseline estimators in future humanoids.

140663
17249
04/09/2017

A human-inspired mechanical criterion for multi-contact locomotion in humanoids

F.BAILLY, J.CARPENTIER, B.PINET, P.SOUERES, B.WATIER

GEPETTO

Rapport LAAS N°17249, Septembre 2017, 7p.

Lien : https://hal.laas.fr/hal-01569252

Diffusable

Plus d'informations

Abstract

This work aims at experimentally identifying a mechanical principle of locomotion stability in humans and demonstrating that this principle can be used for generating stable multi-contact motions for humanoids. For this purpose, a destabilizing setup was built on which five different experiments were carried out by 15 human volunteers. We first show experimentally that when humans balance is perturbed (walking on a destabilizing setup, increasing walking speed, grasping or not a fixed element), the distance between the center of mass (CoM) and the central axis of the external contact wrench significantly increases. This result is coupled with a theoretical reasoning in mechanics in order to exhibit how lowering this distance amounts to lower the body's angular acceleration and thus constitutes a good strategy against falling. Finally, we illustrate the interest of this result for humanoid robot motion generation by embedding the minimization of the distance between the CoM and the central axis of the external contact wrench in an optimal control formulation in order generate multi-contact locomotion.

140582
17168
28/08/2017

H-RRT-C : Haptic Motion Planning with Contact

N.BLIN, M.TAIX, P.FILLATREAU, J.Y.FOURQUET

GEPETTO, LGP

Manifestation avec acte : IEEE International Symposium on Robot and Human Interactive Communication ( Ro-MAN ) 2017 du 28 août au 01 septembre 2017, Lisbonne (Portugal), Août 2017 , N° 17168

Lien : https://hal.archives-ouvertes.fr/hal-01513794

Diffusable

Plus d'informations

Abstract

This paper focuses on interactive motion planning processes intended to assist a human operator when simulating industrial tasks in Virtual Reality. Such applications need motion planning on surfaces. We propose an original haptic path planning algorithm with contact, H-RRT-C, based on a RRT planner and a real-time interactive approach involving a haptic device for computer-operator authority sharing. Force feedback allows the human operator to keep contact consistently and provides the user with the feel of the contact, and the force applied by the operator on the haptic device is used to control the roadmap extension; on the contact surface, the orientation of the manipulated part is variable. Our approach has been validated through two experimental examples, and brings significant improvement over state of the art methods in both free and contact space to solve path-planning queries and contact operations such as insertion or sliding in highly constrained environments

140233
17172
23/08/2017

Multi-contact locomotion of legged robots

J.CARPENTIER, N.MANSARD

GEPETTO

Rapport LAAS N°17172, Août 2017, 16p.

Lien : https://hal.laas.fr/hal-01520248

Diffusable

Plus d'informations

Abstract

Locomotion of legged robots on arbitrary terrain using multiple contacts is yet an open problem. To tackle it, a common approach is to rely on reduced template models (e.g. the linear inverted pendulum). However, most of existing template models are based on some restrictive hypotheses that limit their range of applications. Moreover, reduced models are generally not able to cope with the constraints of the robot complete model, like the kinematic limits. In this paper, we propose a complete solution relying on a generic template model, based on the centroidal dynamics, able to quickly compute multi-contact locomotion trajectories for any legged robot on arbitrary terrains. The template model relies on exact dynamics and is thus not limited by arbitrary assumption. We also propose a generic procedure to handle feasibility constraints due to the robot whole body as occupation measures, and a systematic way to approximate them using off-line learning in simulation. An efficient solver is finally obtained by introducing an original second-order approximation of the centroidal wrench cone. The effectiveness and the versatility of the approach is demonstrated in several multi-contact scenarios with two humanoid robots both in reality and in simulation.

140272
16241
18/08/2017

Regularized hierarchical differential dynamic programming

M.GEISERT, A.DEL PRETE, N.MANSARD, F.ROMANO, F.NORI

GEPETTO, IIT, Genova

Revue Scientifique : IEEE Transactions on Robotics, Vol.33, N°4, pp.819-833, Août 2017 , N° 16241

Lien : https://hal.archives-ouvertes.fr/hal-01356992

Diffusable

Plus d'informations

Abstract

This paper presents a new algorithm for optimal control (OC) of nonlinear dynamical systems. The main feature of this algorithm is that it allows the specification of the control objectives as a hierarchy of tasks. Each task is described by a cost function that the algorithm tries to minimize, while not affecting the tasks of higher priority. The concept of strict priority allows for an easier and more robust specification of the control objectives, without hand-tuning of task weights. The hierarchy also makes it possible to properly regularize the behavior of each task independently. For the first time, we properly define the problem of regularizing the task cost functions in the presence of a hierarchy and propose an algorithm to compute an approximate solution. Several simulated scenarios with different robots compare our solution with other state-of-the-art methods, validating the interest of the hierarchy in OC and empirically demonstrating the importance of regularization to generate safe behaviors.

140188
17133
29/07/2017

Robustness to inertial parameter errors for legged robots balancing on level ground

N.GIFTSUN, A.DEL PRETE, F.LAMIRAUX

GEPETTO

Manifestation avec acte : International Conference on Informatics in Control, Automation and Robotics ( ICINCO ) 2017 du 26 juillet au 28 juillet 2017, Madrid (Espagne), Juillet 2017, 8p. , N° 17133

Lien : https://hal.archives-ouvertes.fr/hal-01533136

Diffusable

Plus d'informations

Abstract

Model-based control has become more and more popular in the legged robots community in the last ten years. The key idea is to exploit a model of the system to compute precise motor commands that result in the desired motion. This allows to improve the quality of the motion tracking, while using lower gains, leading so to higher compliance. However, the main flaw of this approach is typically its lack of robustness to modeling errors. In this paper we focus on the robustness of inverse-dynamics control to errors in the inertial parameters of the robot. We assume these parameters to be known, but only with a certain accuracy. We then propose a computationally-efficient optimization-based controller that ensures the balance of the robot despite these uncertainties. We used the proposed controller in simulation to perform different reaching tasks with the HRP-2 humanoid robot, in the presence of various modeling errors. Comparisons against a standard inverse-dynamics controller through hundreds of simulations show the superiority of the proposed controller in ensuring the robot balance.

140788
Les informations recueillies font l’objet d’un traitement informatique destiné à des statistiques d'utilisation du formulaire de recherche dans la base de données des publications scientifiques. Les destinataires des données sont : le service de documentation du LAAS.Conformément à la loi « informatique et libertés » du 6 janvier 1978 modifiée en 2004, vous bénéficiez d’un droit d’accès et de rectification aux informations qui vous concernent, que vous pouvez exercer en vous adressant à
Pour recevoir une copie des documents, contacter doc@laas.fr en mentionnant le n° de rapport LAAS et votre adresse postale. Signalez tout problème de dysfonctionnement à sysadmin@laas.fr. http://www.laas.fr/pulman/pulman-isens/web/app.php/