9 research outputs found
FASTKIT: A Mobile Cable-Driven Parallel Robot for Logistics
International audienceThe subject of this paper is about the design, modeling, control and performance evaluation of a low cost and versatile robotic solution for logistics. The robot under study, named FASTKIT, is obtained from a combination of mobile robots and a Cable-Driven Parallel Robot (CDPR). FASTKIT addresses an industrial need for fast picking and kitting operations in existing storage facilities while being easy to install, keeping existing infrastructures and covering large areas. The FASTKIT prototype consists of two mobile bases that carry the exit points of the CDPR. The system can navigate autonomously to the area of interest. Once the desired position is attained, the system deploys the CDPR in such a way that its workspace corresponds to the current task specification. The system calculates the required mobile base position from the desired workspace and ensures the controllability of the platform during the deployment. Once the system is successfully deployed, the set of stabilizers are used to ensure the prototype structural stability. Then the prototype gripper is moved accurately by the CDPR at high velocity over a large area by controlling the cable tension
Contribution à la commande des robots parallèles à câbles à redondance d'actionnement
Cable-driven parallel robots (CDPR) are particularly well adapted for some applications such as handling of heavy payloads over large workspaces. However, in order to fully control all the degrees of freedomof the mobile platformand to obtain large workspace to footprint ratios, redundant actuation may be required, which implies the determination of feasible cable tension distributions. In this thesis, in the case of CDPR with two degrees of actuation redundancy, real-time compatible algorithms capable of efficiently calculating various continuous tension distribution are introduced. Furthermore, efficient control schemes are proposed in order to increase the CDPR tracking performances. First, an dual-space feedforward control scheme is introduced to compensate for the plate-formeand whinches dynamics. In order to deal with parametric variations and incertainties in the models, an adaptive dual-space motion control scheme for CDPR is finally presented. Experimental results validate the reel-time efficiency of the proposed tension distribution algorithmand control schemes as well as their stability along the tracked trajectory.Les Robots Parallèles à Câbles (RPC) sont particulièrement adaptés pour des applications telles que le transport de charges lourdes au travers de grands espaces de travail. Afin de contrôler l'ensemble des degrés de liberté de la plate-forme tout en optimisant la taille de l'espace de travail du robot par rapport au volume de sa structure, la redondance d'actionnement est nécessaire. Dans cette thèse, un algorithme de distribution des tensions des câbles compatible temps-réel est introduit. Il permet de calculer efficacement différentes solutions optimales au problème de la distribution des tensions des RPC à deux degrés de redondance. Des schémas de commande adaptés aux RPC, intégrant l'algorithme de distribution des tensions, sont ensuite proposés. Un schéma de commande en espace double est introduit pour compenser la dynamique de la plate-forme et des enrouleurs. Afin de pallier les incertitudes et les variations des paramètres des modèles, une commande adaptative en espace double est finalement proposée. Des résultats expérimentaux prouvent la compatibilité temps-réel des algorithmes et des lois de commande développés dans cette thèse, ainsi que leur stabilité le long de la trajectoire suivie
Contribution to the control of redundantly actuated cable-driven parallel robots
Les Robots Parallèles à Câbles (RPC) sont particulièrement adaptés pour des applications telles que le transport de charges lourdes au travers de grands espaces de travail. Afin de contrôler l'ensemble des degrés de liberté de la plate-forme tout en optimisant la taille de l'espace de travail du robot par rapport au volume de sa structure, la redondance d'actionnement est nécessaire. Dans cette thèse, un algorithme de distribution des tensions des câbles compatible temps-réel est introduit. Il permet de calculer efficacement différentes solutions optimales au problème de la distribution des tensions des RPC à deux degrés de redondance. Des schémas de commande adaptés aux RPC, intégrant l'algorithme de distribution des tensions, sont ensuite proposés. Un schéma de commande en espace double est introduit pour compenser la dynamique de la plate-forme et des enrouleurs. Afin de pallier les incertitudes et les variations des paramètres des modèles, une commande adaptative en espace double est finalement proposée. Des résultats expérimentaux prouvent la compatibilité temps-réel des algorithmes et des lois de commande développés dans cette thèse, ainsi que leur stabilité le long de la trajectoire suivie.Cable-driven parallel robots (CDPR) are particularly well adapted for some applications such as handling of heavy payloads over large workspaces. However, in order to fully control all the degrees of freedomof the mobile platformand to obtain large workspace to footprint ratios, redundant actuation may be required, which implies the determination of feasible cable tension distributions. In this thesis, in the case of CDPR with two degrees of actuation redundancy, real-time compatible algorithms capable of efficiently calculating various continuous tension distribution are introduced. Furthermore, efficient control schemes are proposed in order to increase the CDPR tracking performances. First, an dual-space feedforward control scheme is introduced to compensate for the plate-formeand whinches dynamics. In order to deal with parametric variations and incertainties in the models, an adaptive dual-space motion control scheme for CDPR is finally presented. Experimental results validate the reel-time efficiency of the proposed tension distribution algorithmand control schemes as well as their stability along the tracked trajectory
Design and Control of a Redundant Suspended Cable-Driven Parallel Robots
International audienceThis paper introduces a six degree-of-freedom suspended parallel robot driven by eight cables. The determination of an optimal geometry of such a parallel cable robot together with the design of a prototype are briefly outlined. Then, based on usual kinematic modeling, a basic control strategy is presented. Since the parallel cable-driven robot presented here is redundantly actuated, this control strategy has to deal with the problem of cable tension distribution. This latter turns out to be challenging because of the under-constrained nature of the considered cabledriven robot. The extension to these robots of existing tension distribution methods is finally discussed
Dynamics Modelling of Large Suspended Parallel Cable-Driven Robots
This paper proposes a multibody approach to model and simulate the dynamics of
large cable robot, considering hefty cables. Each cable is discretized into finite rigid segments
interconnected by ball joints including small stiffness and damping effects. This finite-segment
model also involves the development of a simple winding model to transfer the mass of the first
translating segment onto the rotating drum. The choice of the required number of segments to
use is a key issue that is also discussed in this work. This discussion is based on the comparison
of ten models involving one to ten segments per cable regarding their static equilibria, their
behavior when the platform is elevated and their eigen frequencies. Finally, an application is
proposed to simulate the control of the chosen model. An existing quasi-static analytical model
is also used for comparison and to devise the control strategy
A Versatile Tension Distribution Algorithm for -DOF Parallel Robots Driven by Cables
International audienceRedundancy resolution of redundantly actuated cable-driven parallel robots (CDPRs) requires the computation of feasible and continuous cable tension distributions along a trajectory. This paper focuses on n-DOF CDPRs driven by n + 2 cables, since, for n = 6, these redundantly actuated CDPRs are relevant in many applications. The set of feasible cable tensions of n-DOF (n + 2)-cable CDPRs is a 2-D convex polygon. An algorithm that determines the vertices of this polygon in a clockwise or counterclockwise order is first introduced. This algorithm is efficient and can deal with infeasibility. It is then pointed out that straightforward modifications of this algorithm allow the determination of various (optimal) cable tension distributions. A self-contained and versatile tension distribution algorithm is thereby obtained. Moreover, the worst-case maximum number of iterations of this algorithm is established. Based on this result, its computational cost is analyzed in detail, showing that the algorithm is efficient and real-time compatible even in the worst case. Finally, experiments on two six-degree-of-freedom eight-cable CDPR prototypes are reported
Magnetic resonance based control of a robotic manipulator for interventions in the beating heart
Abstract Though many women in need of access to HIV preventive regimes are pregnant, there is a dearth of data to guide these care decisions. While oral pre-exposure prophylaxis (PrEP) has been shown to prevent HIV infection in numerous high-risk populations, pregnant women have been excluded from all major prospective trials. We propose for ethical examination a theoretical trial—a prospective, observational study of PrEP for pregnant women at risk for HIV in sub-Saharan Africa—highlighting an ethical tradeoff that characterizes issues faced for advancing research in pregnancy. On the one hand, an “opportunistic” study design has certain ethical advantages: as formally construed, the research activity usually begins after decisions to use PrEP during pregnancy are made in the clinical setting. This minimizes research risks and avoids ethical problems that a randomized controlled trial (RCT) comparing PrEP to placebo would entail, particularly withholding care proven beneficial in other populations. On the other hand, observational studies yield less precise information than RCTs. This raises a broader question about the pace of research with pregnant women, as it typically takes many years after a drug’s approval for use in the general population to determine safety of the medication in pregnancy. Such delays can have the effect of making it impossible to ethically conduct an RCT with pregnant women, reducing the likelihood that the research community is able to obtain robust, pregnancy-specific evidence. While an observational cohort is potentially the most ethically and scientifically justified research design to study PrEP in pregnancy, earlier involvement of pregnant women in studies of newer preventives may lead to evidence that is more timely and robust