A Cable-Driven Parallel Robot with an Embedded Tilt-Roll Wrist

International audienceThis paper addresses the optimum design, configuration and workspace analysis of a Cable-Driven Parallel Robot (CDPR) with an embedded tilt-roll wrist. The manipulator consists in a tilt-roll wrist mounted on the moving platform of a suspended CDPR. The embedded wrist provides large amplitudes of tilt and roll rotations and a large translational workspace obtained by the CDPR. This manipulator is suitable for tasks requiring large rotation and translation workspaces like tomography scanning, camera-orienting devices and visual surveillance. The moving-platform is an eight-degree-of-freedom articulated mechanism with large translational and rotational workspaces and it is suspended from a fixed frame by six cables. The manipulator employs two bi-actuated cables, i.e., cable loops to transmit the power from motors fixed on the ground to the tilt-roll wrist. Therefore, the manipulator achieves better dynamic performances due to a lower inertia of its moving-platform

Improving cable driven parallel robot accuracy through angular position sensors

Conventionally, a cable driven parallel mechanism (CDPM) pose is obtained through the forward kinematics from measurements of the cable lengths. However, this estimation method can be limiting for some applications requiring more precision. This paper proposes to use cable angle position sensors in addition to cable length measurements in order to improve the accuracy of such mechanisms. The robot pose is first obtained individually by the cable length measurements and the cable angle position measurements. A data fusion scheme combining these two types of measurements is then proposed in order to improve the CPDM accuracy. Finally, simulations and experiments are presented in order to assess the benefits of using cable angle position sensors on the CDPM

Cable interference control in physical interaction for cable-driven parallel mechanisms

Cable interferences and collisions can lead to unpredictable behavior when a human physically interacts with a cable-driven parallel mechanism through its mobile platform. This paper presents an interactive control approach to prevent two cables in interference from folding onto one another, and thus preserve the cable-mechanism geometry. In this approach, the controller generates a repulsive force to prevent the cables from crossing. Therefore, the task is executed within the cable-driven parallel mechanism’s geometric limits. The repulsive force applied by the controller is derived from the gradient of the minimum distance between any pair of cables of the parallel mechanism. In turn, this minimum distance between cables is computed from the Karush-Kuhn-Tucker conditions of the associated optimization problem. The approach was tested and validated on a parallel mechanism driven by seven cables

A compact underactuated gripper with two fingers and a retractable suction cup

Modern industrial applications of robotics such as small-series production and automated warehousing require versatile grippers, i.e., grippers that can pick up the widest possible variety of objects. These objects must often be grasped or placed inside a container, which limits the size of the gripper. In this article, we propose to combine the two most popular gripper technologies in order to maximise versatility: finger grippers and suction-cup (vacuum) grippers. Many researchers and a few companies have followed this same idea in the past, but their gripper designs are often overly complex or too bulky to pick up objects inside containers. Here, we develop a gripper where the suction cup is lodged inside the palm of a two-finger robotic hand. The suction cup is mounted on a retractile rod that can extend to pick up objects inside containers without interference from the two fingers. A single actuator drives both the finger and sliding-rod motions so as to minimise the gripper complexity. The opening and closing sequence of the gripper is achieved by using a planetary gear train as transmission between the actuator, the fingers and the suction cup sliding mechanism. Special attention is paid to minimise the overall gripper size; its diameter being kept to 75 mm, which is that of the end link of the common UR5 robot. A prototype of the gripper is built and its versatility is demonstrated in a short accompanying video

Safer hybrid workspace using human-robot interaction while sharing production activities

In a near future, human and industrial manipulator will work together sharing a common workspace and production activities leading to a potential increase of accident. The research project concerns the adaptation of industrial robot already installed in a flexible manufacturing system in order to make it more interactive with human. The aim concerns the reduction of potential risk of injuries while working with an industrial robot. This paper presents a new inexpensive, non-intrusive, non-invasive, and non-vision-based system, for human detection and collision avoidance. One method investigated for improving safety concerns planning of safe path. This system recognizes human activities and locates operator's position in real time through an instrumented safety helmet. This safety helmet includes an IMU (Inertial Measurement Unit) and an indoor localization system such as RSSI (Received Signal Strength Indication) using industrial wireless equipment. A hybrid workspace including a flexible manufacturing system has been designed in order to practice experiments in an industrial-like environment

A Smart Safety Helmet using IMU and EEG sensors for analysis of worker’s fatigue

It is known that head gesture and mental states can reflect some human behaviors related to a risk of accident when using machine-tools. The research works presented in this paper aim to reduce the number of injury and thus increase worker safety. Instead using camera, this paper presents a Smart Safety Helmet (SSH) in order to track head gestures and mental states of worker able to recognize anomalous behavior. Information extracted from SSH is used for computing risk level of accident (a safety level) for preventing and reducing injury or accidents. The SSH system is an inexpensive, non-intrusive, non-invasive, and non-vision-based system, which consists of 9DOF Inertial Measurement Unit (IMU) and dry EEG electrodes. A haptic device, such as vibrotactile motor, is integrated to the helmet in order to alert the operator when computed risk level (fatigue, high stress or error) reach a threshold. Once the risk level of accident breaks the threshold, a signal will be sent wirelessly to stop the relevant machine tool or process

Etude prospective sur l'agriculture bretonne

Diffusion du document : INRA Unité d'Economie et Sociologie rurales rue Adolphe Bobierre CS 61103 35011 Rennes Cedex (FRA)Cette étude a été conduite à la demande des autorités régionales dans le cadre de la préparation du contrat de plan Etat-Région. La première partie introductive présente l'objectif de l'étude qui est de proposer une vue prospective de l'agriculture bretonne dans un contexte de réexamen de la politique agricole commune (PAC), lié aux contraintes actuelles et anticipées de l'Organisation mondiale du commerce (OMC), à l'élargissement de l'Europe à l'Est, et aux préoccupations environnementales. La deuxième partie dresse un état des lieux de l'agriculture bretonne. On met d'abord l'accent sur l'importance du complexe agro-alimentaire dans l'économie bretonne. On aborde ensuite les structures de production qui ont connu une évolution classique (baisse des effectifs, concentration et gains de productivité) accompagnée de la spécialisation et de la simplification des systèmes de production. Les conséquences de la concentration et de la spécialisation sur l'environnement sont ensuite analysées ainsi que les politiques environnementales mises en oeuvre. Un bilan des industries agro-alimentaires est également fait. La troisième partie fait le point sur les évolutions fondamentales qui vont affecter l'agriculture et celle de la Bretagne en particulier, notamment l'évolution du comportement du consommateur-citoyen, l'intensification des échanges internationaux, les réglementations sanitaires et phytosanitaires ainsi que les politiques environnementales. La quatrième partie tente de cerner les enjeux de la contribution de l'agriculture bretonne à un développement régional durable, face aux risques externes (montée de la concurrence internationale) et internes (forte spécialisation, effets d'image négatifs liés à la dégradation de l'environnement). Elle donne également des principes pour l'action publique. Les aspects prospectifs sont prolongés par des projections d'impact de la future réforme de la PAC (Agenda 2000) sur les résultats économiques du secteur agricole breton. Compte tenu des aides nouvelles, le revenu brut d'exploitation par actif en termes réels devrait augmenter entre 1996 et 2005. Enfin, des initiatives régionales sont proposées visant le maintien du système productif du complexe agroalimentaire breton, la diversification mais aussi la mise au point de produits à vocation universelle rattachés à l'origine régionale, la mise en place d'un système de suivi crédible des pratiques environnementales et d'un zonage complet de l'espace rural pour atténuer les conflits d'usage, la mise en valeur du potentiel de l'espace rural

Conception d'accéléromètres multiaxiaux avec architectures simpliciales pour l'estimation de la pose et du visseur instantané d'un corps rigide

Accelerometer arrays are used in biomechanics and other fields to estimate the rigid-body acceleration field and, thence, all kinematic variables describing the rigid-body displacements. However, the progress of this technology has been limited by that of micromachined gyroscopes, which turn out to be more accurate than accelerometer arrays in most applications. The work reported in this thesis aims at improving the accuracy of the angular velocity estimates provided by accelerometer arrays. The approach is twofold: A class of accelerometer mechanical architectures is proposed, with the goal of reducing the accelerometer cross-axis sensitivity, and robust algorithms are proposed to estimate the angular velocity from some or all components of the rigid-body acceleration field. The novel class of accelerometers is inspired from parallel-kinematics-machine (PKM) architectures, taking the accelerometer proof mass to be the PKM moving platform, and the accelerometer frame the PKM base. A common characteristic of the proposed PKM architectures is that their moving platforms are connected to their bases by n + 1 legs each, n = 1, 2, 3 being their respective number of sensitive directions. For this reason, the resulting class of accelerometers is referred to as "Simplicial Multiaxial Accelerometers" (SMA). A micro-scale version of the Simplicial Biaxial Accelerometer (SBA) was devised, designed, fabricated, and tested. Furthermore, the theory behind the estimation of the angular velocity from acceleration measurements is revisited. Hence, four algorithms are proposed, which allow for the estimation of the rigid-body angular velocity from centripetal acceleration measurements alone. Based on Kalman filtering, another method is proposed in order to obtain a rigid-body angular-velocity estimate from both the centripetal and tangential components of the rigid-body acceleration field.Les assemblages d'accéléromètres sont utilisés entre autres en biomécanique afin d'estimer le champ des accélérations d'un corps rigide et, de là, les variables cinématiques décrivant les déplacements dudit corps rigide. On remarque toutefois que le progrès de cette technologie a été limité par celui des gyroscopes micro-usinés, lesquels sont plus précis que les assemblages d'accéléromètres dans la plupart des applications. Le but des recherches décrites dans cette thèse est d'améliorer la précision des estimés de vitesse angulaire produits par les assemblages d'accéléromètres. Les développements proposés portent sur deux aspects : une classe d'architectures mécaniques d'accéléromètres est proposée ayant pour but de réduire la sensibilité des capteurs aux accélérations transverses, des algorithmes robustes étant également proposés afin d'estimer la vitesse angulaire à partir de certaines ou de toutes les composantes du champ d'accélération du corps rigide. La classe d'accéléromètres proposée est inspirée des architectures de machines à cinématique parallèle (MCP) en assimilant la masse d'épreuve et le support d'un accéléromètre à l'organe terminal et à la base d'une MCP, respectivement. Une caractéristique commune aux MCP proposées ici est que leurs organes terminaux et leurs bases sont reliées par n+1 chaînes cinématiques simples, n = 1, 2, 3 étant leurs nombres de directions sensibles respectifs. Pour cette raison, on appelle accéléromètres simpliciaux multiaxiaux les capteurs résultant de ces MCP. Une version microusinée de l'accéléromètre simplicial biaxial est conçue, fabriquée et testée. En outre, la théorie permettant l'estimation de la vitesse angulaire d'un corps rigide à partir de mesures d'accélérations est réexaminée. De cette révision, quatre algorithmes permettant l'estimation de la vitesse angulaire à partir de mesures d'accélération centripète sont proposés. Enfin, un algorithme permettant l'estimation de la vitesse angulaire d'un corps rigide à partir de mesures d'accélérations centripète et tangentielle et reposant sur le filtrage de Kalman est proposé