1,846 research outputs found

    Cable Robot Performance Evaluation by Wrench Exertion Capability

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    Although cable driven robots are a type of parallel manipulators, the evaluation of their performances cannot be carried out using the performance indices already developed for parallel robots with rigid links. This is an obvious consequence of the peculiar features of flexible cables-a cable can only exert a tensile and limited force in the direction of the cable itself. A comprehensive performance evaluation can certainly be attained by computing the maximum force (or torque) that can be exerted by the cables on the moving platform along a specific (or any) direction within the whole workspace. This is the idea behind the index-called the Wrench Exertion Capability (WEC)-which can be employed to evaluate the performance of any cable robot topology and is characterized by an efficient and simple formulation based on linear programming. By significantly improving a preliminary computation method for the WEC, this paper proposes an ultimate formulation suitable for any cable robot topology. Several numerical investigations on planar and spatial cable robots are presented to give evidence of the WEC usefulness, comparisons with popular performance indices are also provided

    Air vehicle simulator: an application for a cable array robot

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    The development of autonomous air vehicles can be an expensive research pursuit. To alleviate some of the financial burden of this process, we have constructed a system consisting of four winches each attached to a central pod (the simulated air vehicle) via cables - a cable-array robot. The system is capable of precisely controlling the three dimensional position of the pod allowing effective testing of sensing and control strategies before experimentation on a free-flying vehicle. In this paper, we present a brief overview of the system and provide a practical control strategy for such a system. ©2005 IEEE

    Design, analysis, and control of a cable-driven parallel platform with a pneumatic muscle active support

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    Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugÀnglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The neck is an important part of the body that connects the head to the torso, supporting the weight and generating the movement of the head. In this paper, a cable-driven parallel platform with a pneumatic muscle active support (CPPPMS) is presented for imitating human necks, where cable actuators imitate neck muscles and a pneumatic muscle actuator imitates spinal muscles, respectively. Analyzing the stiffness of the mechanism is carried out based on screw theory, and this mechanism is optimized according to the stiffness characteristics. While taking the dynamics of the pneumatic muscle active support into consideration as well as the cable dynamics and the dynamics of the Up-platform, a dynamic modeling approach to the CPPPMS is established. In order to overcome the flexibility and uncertainties amid the dynamic model, a sliding mode controller is investigated for trajectory tracking, and the stability of the control system is verified by a Lyapunov function. Moreover, a PD controller is proposed for a comparative study. The results of the simulation indicate that the sliding mode controller is more effective than the PD controller for the CPPPMS, and the CPPPMS provides feasible performances for operations under the sliding mode control

    A Bio-Inspired Tensegrity Manipulator with Multi-DOF, Structurally Compliant Joints

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    Most traditional robotic mechanisms feature inelastic joints that are unable to robustly handle large deformations and off-axis moments. As a result, the applied loads are transferred rigidly throughout the entire structure. The disadvantage of this approach is that the exerted leverage is magnified at each subsequent joint possibly damaging the mechanism. In this paper, we present two lightweight, elastic, bio-inspired tensegrity robotics arms which mitigate this danger while improving their mechanism's functionality. Our solutions feature modular tensegrity structures that function similarly to the human elbow and the human shoulder when connected. Like their biological counterparts, the proposed robotic joints are flexible and comply with unanticipated forces. Both proposed structures have multiple passive degrees of freedom and four active degrees of freedom (two from the shoulder and two from the elbow). The structural advantages demonstrated by the joints in these manipulators illustrate a solution to the fundamental issue of elegantly handling off-axis compliance.Comment: IROS 201

    Modeling, Control and Estimation of Reconfigurable Cable Driven Parallel Robots

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    The motivation for this thesis was to develop a cable-driven parallel robot (CDPR) as part of a two-part robotic device for concrete 3D printing. This research addresses specific research questions in this domain, chiefly, to present advantages offered by the addition of kinematic redundancies to CDPRs. Due to the natural actuation redundancy present in a fully constrained CDPR, the addition of internal mobility offers complex challenges in modeling and control that are not often encountered in literature. This work presents a systematic analysis of modeling such kinematic redundancies through the application of reciprocal screw theory (RST) and Lie algebra while further introducing specific challenges and drawbacks presented by cable driven actuators. It further re-contextualizes well-known performance indices such as manipulability, wrench closure quality, and the available wrench set for application with reconfigurable CDPRs. The existence of both internal redundancy and static redundancy in the joint space offers a large subspace of valid solutions that can be condensed through the selection of appropriate objective priorities, constraints or cost functions. Traditional approaches to such redundancy resolution necessitate computationally expensive numerical optimization. The control of both kinematic and actuation redundancies requires cascaded control frameworks that cannot easily be applied towards real-time control. The selected cost functions for numerical optimization of rCDPRs can be globally (and sometimes locally) non-convex. In this work we present two applied examples of redundancy resolution control that are unique to rCDPRs. In the first example, we maximize the directional wrench ability at the end-effector while minimizing the joint torque requirement by utilizing the fitness of the available wrench set as a constraint over wrench feasibility. The second example focuses on directional stiffness maximization at the end-effector through a variable stiffness module (VSM) that partially decouples the tension and stiffness. The VSM introduces an additional degrees of freedom to the system in order to manipulate both reconfigurability and cable stiffness independently. The controllers in the above examples were designed with kinematic models, but most CDPRs are highly dynamic systems which can require challenging feedback control frameworks. An approach to real-time dynamic control was implemented in this thesis by incorporating a learning-based frameworks through deep reinforcement learning. Three approaches to rCDPR training were attempted utilizing model-free TD3 networks. Robustness and safety are critical features for robot development. One of the main causes of robot failure in CDPRs is due to cable breakage. This not only causes dangerous dynamic oscillations in the workspace, but also leads to total robot failure if the controllability (due to lack of cables) is lost. Fortunately, rCDPRs can be utilized towards failure tolerant control for task recovery. The kinematically redundant joints can be utilized to help recover the lost degrees of freedom due to cable failure. This work applies a Multi-Model Adaptive Estimation (MMAE) framework to enable online and automatic objective reprioritization and actuator retasking. The likelihood of cable failure(s) from the estimator informs the mixing of the control inputs from a bank of feedforward controllers. In traditional rigid body robots, safety procedures generally involve a standard emergency stop procedure such as actuator locking. Due to the flexibility of cable links, the dynamic oscillations of the end-effector due to cable failure must be actively dampened. This work incorporates a Linear Quadratic Regulator (LQR) based feedback stabilizer into the failure tolerant control framework that works to stabilize the non-linear system and dampen out these oscillations. This research contributes to a growing, but hitherto niche body of work in reconfigurable cable driven parallel manipulators. Some outcomes of the multiple engineering design, control and estimation challenges addressed in this research warrant further exploration and study that are beyond the scope of this thesis. This thesis concludes with a thorough discussion of the advantages and limitations of the presented work and avenues for further research that may be of interest to continuing scholars in the community

    CABLE-SUSPENDED CPR-D TYPE PARALLEL ROBOT

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    This paper deals with the analysis and synthesis of a newly selected Cable-suspended Parallel Robot configuration, named CPR-D system. The camera carrier workspace has the shape of a parallelepiped. The CPR-D system has a unique Jacobian matrix that maps the relationship between internal and external coordinates. This geometric relationship is a key solution for the definition of the system kinematic and dynamic models. Because of the CPR-D system complexity, the Lagrange principle of virtual work has been adapted. Two significant Examples have been used for the CPR-D system analysis and validation

    Reconfigurable cable driven parallel mechanism

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    Due to the fast growth in industry and in order to reduce manufacturing budget, increase the quality of products and increase the accuracy of manufactured products in addition to assure the safety of workers, people relied on mechanisms for such purposes. Recently, cable driven parallel mechanisms (CDPMs) have attracted much attention due to their many advantages over conventional parallel mechanisms, such as the significantly large workspace and the dynamics capacity. In addition, it has lower mass compared to other parallel mechanisms because of its negligible mass cables compared to the rigid links. In many applications it is required that human interact with machines and robots to achieve tasks precisely and accurately. Therefore, a new domain of scientific research has been introduced, that is human robot interaction, where operators can share the same workspace with robots and machines such as cable driven mechanisms. One of the main requirements due to this interaction that robots should respond to human actions in accurate, harmless way. In addition, the trajectory of the end effector is coming now from the operator and it is very essential that the initial trajectory is kept unchanged to perform tasks such assembly, operating or pick and place while avoiding the cables to interfere with each other or collide with the operator. Accordingly, many issues have been raised such as control, vibrations and stability due the contact between human and robot. Also, one of the most important issues is to guarantee collision free space (to avoid collision between cables and operator and to avoid collisions between cables itself). The aim of this research project is to model, design, analysis and implement reconfigurable six degrees of freedom parallel mechanism driven by eight cables. The main contribution of this work will be as follow. First, develop a nonlinear model and solve the forward and inverse kinematics issue of a fully constrained CDPM given that the attachment points on the rails are moving vertically (conventional cable driven mechanisms have fixed attachment points on the rails) while controlling the cable lengths. Second, the new idea of reconfiguration is then used to avoid interference between cables and between cables and operator limbs in real time by moving one cable’s attachment point on the frame to increase the shortest distance between them while keeping the trajectory of the end effector unchanged. Third, the new proposed approach was tested by creating a simulated intended cable-cable and cable-human interference trajectory, hence detecting and avoiding cable-cable and cable-human collision using the proposed real time reconfiguration while maintaining the initial end effector trajectory. Fourth, study the effect of relocating the attachment points on the constant-orientation wrench feasible workspace of the CDPM. En raison de la croissance de la demande de produits personnalisĂ©s et de la nĂ©cessitĂ© de rĂ©duire les coĂ»ts de fabrication tout en augmentant la qualitĂ© des produits et en augmentant la personnalisation des produits fabriquĂ©s en plus d'assurer la sĂ©curitĂ© des travailleurs, les concepteurs se sont appuyĂ©s sur des mĂ©canismes robotiques afin d’atteindre ces objectifs. RĂ©cemment, les mĂ©canismes parallĂšles entraĂźnĂ©s par cĂąble (MPEC) ont attirĂ© beaucoup d'attention en raison de leurs nombreux avantages par rapport aux mĂ©canismes parallĂšles conventionnels, tels que l'espace de travail considĂ©rablement grand et la capacitĂ© dynamique. De plus, ce mĂ©canisme a une masse plus faible par rapport Ă  d'autres mĂ©canismes parallĂšles en raison de ses cĂąbles de masse nĂ©gligeable comparativement aux liens rigides. Dans de nombreuses applications, il est nĂ©cessaire que l’humain interagisse avec les machines et les robots pour rĂ©aliser des tĂąches avec prĂ©cision et rapiditĂ©. Par consĂ©quent, un nouveau domaine de recherche scientifique a Ă©tĂ© introduit, Ă  savoir l'interaction humain-robot, oĂč les opĂ©rateurs peuvent partager le mĂȘme espace de travail avec des robots et des machines telles que les mĂ©canismes entraĂźnĂ©s par des cĂąbles. L'une des principales exigences en raison de cette interaction que les robots doivent rĂ©pondre aux actions humaines d'une maniĂšre sĂ©curitaire et collaboratif. En consĂ©quence, de nombreux problĂšmes ont Ă©tĂ© soulevĂ©s tels que la commande et la stabilitĂ© dues au contact physique entre l’humain et le robot. Aussi, l'un des enjeux les plus importants est de garantir un espace sans collision (pour Ă©viter les collisions entre des cĂąbles et un opĂ©rateur et Ă©viter les collisions entre les cĂąbles entre eux). Le but de ce projet de recherche est de modĂ©liser, concevoir, analyser et mettre en Ɠuvre un mĂ©canisme parallĂšle reconfigurable Ă  six degrĂ©s de libertĂ© entraĂźnĂ© par huit cĂąbles. La principale contribution de ces travaux de recherche est de dĂ©velopper un modĂšle non linĂ©aire et rĂ©solvez le problĂšme de cinĂ©matique direct et inverse d'un CDPM entiĂšrement contraint Ă©tant donnĂ© que les points d'attache sur les rails se dĂ©placent verticalement (les mĂ©canismes entraĂźnĂ©s par des cĂąbles conventionnels ont des points d'attache fixes sur les rails) tout en contrĂŽlant les longueurs des cĂąbles. Dans une deuxiĂšme Ă©tape, l’idĂ©e de la reconfiguration est ensuite utilisĂ©e pour Ă©viter les interfĂ©rences entre les cĂąbles et entre les cĂąbles et les membres d’un opĂ©rateur en temps rĂ©el en dĂ©plaçant un point de fixation du cĂąble sur le cadre pour augmenter la distance la plus courte entre eux tout en gardant la trajectoire de l'effecteur terminal inchangĂ©e. TroisiĂšmement, la nouvelle approche proposĂ©e a Ă©tĂ© Ă©valuĂ©e et testĂ©e en crĂ©ant une trajectoire d'interfĂ©rence cĂąble-cĂąble et cĂąble-humain simulĂ©e, dĂ©tectant et Ă©vitant ainsi les collisions cĂąble-cĂąble et cĂąble-humain en utilisant la reconfiguration en temps rĂ©el proposĂ©e tout en conservant la trajectoire effectrice finale. Enfin la derniĂšre Ă©tape des travaux de recherche consiste Ă  Ă©tudiez l'effet du dĂ©placement des points d'attache sur l'espace de travail rĂ©alisable du CDPM
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