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

Développement d'un indicateur d'intégrité écologique en milieux anthropisés: application de l'approche par traits fonctionnels

Les écosystèmes urbains subissent de fortes pressions, directes ou indirectes, et sont fortement marqués par la présence d’espèces exotiques. Au-delà de leur composition, ces facteurs interagissent aussi pour en modifier les propriétés écosystémiques, affectant à la fois la capacité des écosystèmes à se maintenir dans le temps et à fournir des services écosystémiques. Les acteurs impliqués dans la prise de décisions font face à de nombreux défis: opérant le plus souvent dans un cadre normatif qui met l’emphase sur l’intégrité écologique, ils utilisent régulièrement des inventaires floristiques détaillés permettant difficilement de capter les variations de ces propriétés écosystémiques. L’approche par traits fonctionnels cherche des liens généralisables entre les propriétés écosystémiques et la composition des communautés écologiques (marqueurs fonctionnels). En combinant les inventaires standard aux données de traits disponibles publiquement, cette approche pourrait ainsi permettre de capter les propriétés de l’écosystème à des coûts minimes. L’objectif principal de cette thèse est de développer un outil permettant de caractériser l’intégrité des propriétés écosystémiques des boisés urbains dans le domaine de la forêt de feuillus tempérée, et ce, de manière à informer directement la prise de décision. Pour y arriver, j’explore d’abord l’applicabilité des outils existant pour quantifier l’intégrité écologique dans les milieux urbain, puis je teste la capacité de l’approche par traits à capter les différences dans les propriétés écosystémiques de ces écosystèmes. Je propose finalement une méthode pour agréger l’information fournie par de tels marqueurs fonctionnels pour l’exprimer sous forme quantitative et informer la prise de décision en milieu urbain. Mes résultats montrent que les modèles conceptuels existants de l’intégrité écologique s’appliquent difficilement aux boisés urbains, justifiant l’adoption d’une approche consultative pour le développement de concepts d’intégrité écologiques à l’échelle régionale. Suivant cette approche, je propose un tel modèle pour les boisés urbains de la région de Montréal. Je montre ensuite que l’approche par traits fonctionnels est en mesure de fournir des marqueurs fonctionnels pour capter les différences dans les propriétés de l’écosystème, mais que ces marqueurs fonctionnels ne sont pas nécessairement les mêmes traits que ceux étant associés avec un gradient d’urbanisation. Mes résultats montrent également que, lorsque réunis pour fournir un portrait multidimensionnel de l’intégrité du fonctionnement des écosystèmes, les marqueurs fonctionnels captent mieux les différences réelles dans les propriétés écosystémiques de mes boisés d’étude que deux autres méthodes de caractérisation plus simples. Pour mesurer l’intégrité des propriétés écosystémiques des boisés urbains, je propose l’utilisation de la distance de Fonctionnelle de Mahalanobis. Cette mesure représente un outil concret permettant d’utiliser les inventaires de végétation déjà collectés lors de la caractérisation des écosystèmes par les acteurs du milieu environnemental pour exprimer l’intégrité des propriétés écosystémique de manière quantitative

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

The Dimensional Synthesis of Planar Parallel Cable-Driven Mechanisms Through Convex Relaxations

The wrench-closure workspace (WCW) of parallel cable-driven mechanisms is the set of poses for which any wrench can be produced at the end-effector by a set of positive cable tensions. In this paper, we tackle the dimensional synthesis problem, namely, that of finding a geometry for a planar parallel cable-driven mechanism (PPCDM) whose WCW contains a prescribed workspace. To this end, we first recall a linear program to determine whether a given pose is inside or outside the WCW of a given PPCDM. The relaxation of this linear program over a box leads to a nonlinear feasibility problem that can only be satisfied when this box is completely inside the WCW. We extend this feasibility problem to find a PPCDM geometry whose WCW includes a given set of boxes. These boxes represent the prescribed workspace or an estimate thereof, which may be obtained through interval analysis. Finally, we introduce a nonlinear program through which the PPCDM geometry is changed while maximizing the scaling factor of the prescribed set of boxes. When the optimum scaling factor is greater or equal to one, the WCW of the resulting PPCDM contains the set of boxes

Designing Multi-Axis Force-Torque Sensors by Minimizing the Amplitudes of Their Nonlinear Displacements

Compliant multi-axis force-torque sensors play a crucial role in many emerging robotic applications, such as telemanipulation, haptic devices and human-robot physical interaction. In order to synthesize the compliant architectures at the core of these sensors, several researchers have devised performance indices from mechanism theory. This paper follows the same approach, but includes the innovation of using the changes in the compliant mechanism geometry as a new performance index. Once external forces are applied, the compliant mechanism deviates from its unloaded configuration, and thus, changes in geometry prevent the sensor from exhibiting a linear response. In order to minimize this nonlinear behavior, the potential sources of error are analyzed by applying linear algebra techniques to the expression of the Cartesian force mapping. Two performance indices are then presented and combined. The first index measures the variations of the Jacobian matrix about the unloaded configuration. The second index measures the amplification of the error arising from the joint displacements measurement. The resulting indices can be expressed symbolically, making them easier to evaluate and synthesize. Finally, we apply the performance indices we have developed to simple compliant mechanisms, and discuss the results

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

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