Towards vision-based control of cable-driven parallel robots

International audienceThis paper deals with the vision-based control of cable-driven parallel robots. First, a 3D pose visual servoing is proposed, where the end-effector pose is indirectly measured and used for regulation. This method is illustrated and validated on a cable-driven parallel robot prototype. Second, to take into account the dynamics of the platform and using a Cartesian pose and velocity estimator, a vision-based computed torque control is developed and validated in simulation

A Vision-Based Referencing Procedure for Cable-Driven Parallel Manipulators

In the last three decades, cable-driven parallel robots (CDPRs) have captured a growing attention in the robotics field. Indeed, they promise to bring automation in fields where it is not affirmed yet, granting ease of scaling and reconfigurability. For large-workspace cable robots, accuracy is an important issue. In this paper, a look-and-move procedure is proposed, based on a wireless camera, to refer the coordinate frame of the CDPR platform to another known coordinate frame. Two sample cases are studied and presented. In the first, the proposed vision-based system is employed to let the platform precisely attain its home position. In the second, the platform is referenced to an external coordinate frame, in order to accurately accomplish an assigned task. For both cases, experiments are successfully carried out

Hybrid Modeling of Deformable Linear Objects for Their Cooperative Transportation by Teams of Quadrotors

his paper deals with the control of a team of unmanned air vehicles (UAVs), specifically quadrotors, for which their mission is the transportation of a deformable linear object (DLO), i.e., a cable, hose or similar object in quasi-stationary state, while cruising towards destination. Such missions have strong industrial applications in the transportation of hoses or power cables to specific locations, such as the emergency power or water supply in hazard situations such as fires or earthquake damaged structures. This control must be robust to withstand strong and sudden wind disturbances and remain stable after aggressive maneuvers, i.e., sharp changes of direction or acceleration. To cope with these, we have previously developed the online adaptation of the proportional derivative (PD) controllers of the quadrotors thrusters, implemented by a fuzzy logic rule system that experienced adaptation by a stochastic gradient rule. However, sagging conditions appearing when the transporting drones are too close or too far away induce singularities in the DLO catenary models, breaking apart the control system. The paper’s main contribution is the formulation of the hybrid selective model of the DLO sections as either catenaries or parabolas, which allows us to overcome these sagging conditions. We provide the specific decision rule to shift between DLO models. Simulation results demonstrate the performance of the proposed approach under stringent conditions.This work has been partially supported by spanish MICIN project PID2020-116346GB-I00, and project KK-2021/00070 of the Elkartek 2021 funding program of the Basque Government. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 777720

A cable-driven robot for architectural constructions: a visual-guided approach for motion control and path-planning

Cable-driven robots have received some attention by the scientific community and, recently, by the industry because they can transport hazardous materials with a high level of safeness which is often required by construction sites. In this context, this research presents an extension of a cable-driven robot called SPIDERobot, that was developed for automated construction of architectural projects. The proposed robot is formed by a rotating claw and a set of four cables, enabling four degrees of freedom. In addition, this paper proposes a new Vision-Guided Path-Planning System (V-GPP) that provides a visual interpretation of the scene: the position of the robot, the target and obstacles location; and optimizes the trajectory of the robot. Moreover, it determines a collision-free trajectory in 3D that takes into account the obstacles and the interaction of the cables with the scene. A set of experiments make possible to validate the contribution of V-GPP to the SPIDERobot while operating in realistic working conditions, as well as, to evaluate the interaction between the V-GPP and the motion controlling system. The results demonstrated that the proposed robot is able to construct architectural structures and to avoid collisions with obstacles in their working environment. The V-GPP system localizes the robot with a precision of 0.006 m, detects the targets and successfully generates a path that takes into account the displacement of cables. Therefore, the results demonstrate that the SPIDERobot can be scaled up to real working conditions.This work is partly funded by the project PTDC/ ATP-AQI/5124/2012 - Robotic Technologies for Non-Standard Design and Construction in Architecture. This work is also financed by the ERDF European Regional Development Fund through the COMPETE Programme (operational programme for competitiveness) and by National Funds through the FCT Portuguese Foundation for Science and Technology within project “FCOMP - 01-0124-FEDER-022701”.info:eu-repo/semantics/publishedVersio

Reconfigurable cable driven parallel mechanism

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 personnalisés et de la nécessité de réduire les coûts de fabrication tout en augmentant la qualité des produits et en augmentant la personnalisation des produits fabriqués en plus d'assurer la sécurité des travailleurs, les concepteurs se sont appuyés sur des mécanismes robotiques afin d’atteindre ces objectifs. Récemment, les mécanismes parallèles entraînés par câble (MPEC) ont attiré beaucoup d'attention en raison de leurs nombreux avantages par rapport aux mécanismes parallèles conventionnels, tels que l'espace de travail considérablement grand et la capacité dynamique. De plus, ce mécanisme a une masse plus faible par rapport à d'autres mécanismes parallèles en raison de ses câbles de masse négligeable comparativement aux liens rigides. Dans de nombreuses applications, il est nécessaire que l’humain interagisse avec les machines et les robots pour réaliser des tâches avec précision et rapidité. Par conséquent, un nouveau domaine de recherche scientifique a été introduit, à savoir l'interaction humain-robot, où les opérateurs peuvent partager le même espace de travail avec des robots et des machines telles que les mécanismes entraînés par des câbles. L'une des principales exigences en raison de cette interaction que les robots doivent répondre aux actions humaines d'une manière sécuritaire et collaboratif. En conséquence, de nombreux problèmes ont été soulevés tels que la commande et la stabilité 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 éviter les collisions entre des câbles et un opérateur et éviter les collisions entre les câbles entre eux). Le but de ce projet de recherche est de modéliser, concevoir, analyser et mettre en œuvre un mécanisme parallèle reconfigurable à six degrés de liberté entraîné par huit câbles. La principale contribution de ces travaux de recherche est de développer un modèle non linéaire et résolvez le problème de cinématique direct et inverse d'un CDPM entièrement contraint étant donné que les points d'attache sur les rails se déplacent verticalement (les mécanismes entraînés par des câbles conventionnels ont des points d'attache fixes sur les rails) tout en contrôlant les longueurs des câbles. Dans une deuxième étape, l’idée de la reconfiguration est ensuite utilisée pour éviter les interférences entre les câbles et entre les câbles et les membres d’un opérateur en temps réel en déplaçant un point de fixation du câble sur le cadre pour augmenter la distance la plus courte entre eux tout en gardant la trajectoire de l'effecteur terminal inchangée. Troisièmement, la nouvelle approche proposée a été évaluée et testée en créant une trajectoire d'interférence câble-câble et câble-humain simulée, détectant et évitant ainsi les collisions câble-câble et câble-humain en utilisant la reconfiguration en temps réel proposée tout en conservant la trajectoire effectrice finale. Enfin la dernière étape des travaux de recherche consiste à étudiez l'effet du déplacement des points d'attache sur l'espace de travail réalisable du CDPM

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

Discrete Cosserat Approach for Multi-Section Soft Robots Dynamics

In spite of recent progress, soft robotics still suffers from a lack of unified modeling framework. Nowadays, the most adopted model for the design and control of soft robots is the piece-wise constant curvature model, with its consolidated benefits and drawbacks. In this work, an alternative model for multisection soft robots dynamics is presented based on a discrete Cosserat approach, which, not only takes into account shear and torsional deformations, essentials to cope with out-of-plane external loads, but also inherits the geometrical and mechanical properties of the continuous Cosserat model, making it the natural soft robotics counterpart of the traditional rigid robotics dynamics model. The soundness of the model is demonstrated through extensive simulation and experimental results for both plane and out-of-plane motions.Comment: 13 pages, 9 figure

Sliding Mode Control of Cable-Driven Redundancy Parallel Robot with 6 DOF Based on Cable-Length Sensor Feedback

The sliding mode control of the cable-driven redundancy parallel robot with six degrees of freedom is studied based on the cable-length sensor feedback. Under the control scheme of task space coordinates, the cable length obtained by the cable-length sensor is used to solve the forward kinematics of the cable-driven redundancy parallel robot in real-time, which is treated as the feedback for the control system. First, the method of forward kinematics of the cable-driven redundancy parallel robot is proposed based on the tetrahedron method and Levenberg-Marquardt method. Then, an iterative initial value estimation method for the Levenberg-Marquardt method is proposed. Second, the sliding mode control method based on the exponential approach law is used to control the effector of the robot, and the influence of the sliding mode parameters on control performance is simulated. Finally, a six-degree-of-freedom position tracking experiment is carried out on the principle prototype of the cable-driven redundancy parallel robot. The experimental results show that the robot can accurately track the desired position in six directions, which indicates that the control method based on the cable-length sensor feedback for the cable-driven redundancy parallel robot is effective and feasible