Application of a differentiator-based adaptive super-twisting controller for a redundant cable-driven parallel robot

In this paper we present preliminary, experimental results of an Adaptive Super-Twisting Sliding-Mode Controller with time-varying gains for redundant Cable-Driven Parallel Robots. The sliding-mode controller is paired with a feed-forward action based on dynamics inversion. An exact sliding-mode differentiator is implemented to retrieve the velocity of the end-effector using only encoder measurements with the properties of finite-time convergence, robustness against perturbations and noise filtering. The platform used to validate the controller is a robot with eight cables and six degrees of freedom powered by 940 W compact servo drives. The proposed experiment demonstrates the performance of the controller, finite-time convergence and robustness in tracking a trajectory while subject to external disturbances up to approximately 400% the mass of the end-effector

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

A Case Study on Vestibular Sensations in Driving Simulators

Motion platforms have been used in simulators of all types for several decades. Since it is impossible to reproduce the accelerations of a vehicle without limitations through a physically limited system (platform), it is common to use washout filters and motion cueing algorithms (MCA) to select which accelerations are reproduced and which are not. Despite the time that has passed since their development, most of these algorithms still use the classical washout algorithm. In the use of these MCAs, there is always information that is lost and, if that information is important for the purpose of the simulator (the training simulators), the result obtained by the users of that simulator will not be satisfactory. This paper shows a case study where a BMW 325Xi AUT fitted with a sensor, recorded the accelerations produced in all degrees of freedom (DOF) during several runs, and data have been introduced in mathematical simulation software (washout + kinematics + actuator simulation) of a 6DOF motion platform. The input to the system has been qualitatively compared with the output, observing that most of the simulation adequately reflects the input to the system. Still, there are three events where the accelerations are lost. These events are considered by experts to be of vital importance for the outcome of a learning process in the simulator to be adequat

Function Design of Mechatronic Systems for Human-Robot Collaboration

Traditionally, robots have been caged off from human activity but, recently, improvements in advance robotic technology as well as the introduction of new safety standards, have allowed the possibility of collaboration between human workers and robotic systems. The introduction of Human-Robot Collaboration has the potential to increase the quality and the flexibility of the production process while improving the working condition of the operators. However, traditional industrial robots are typically characterized by small payload and small reachable workspace that reduce the range of possible applications. These drawbacks can overcome the advantages related to a collaborative task and make the collaboration not effective. This work aims at analyzing innovative mechatronic solutions capable of increasing the workspace and the versatility of the system with the final goal of creating effective collaborations with humans. Cable driven Parallel Robots (CDPRs) are considered a promising technology able to satisfy these requirements. In fact, compared to rigid serial and parallel robots, they have several advantages such as large workspaces, high payloads per unit of weight, ease of construction, versatility and affordable costs. This work presents two innovative solutions of CDPR able to enlarge the workspace, improve the versatility and reduce the collisions risk. The first solution consists of a cable-suspended parallel robot with a reconfigurable end-effector whereas the second solution is an innovative model of cable-driven micro-macro robot. In the first part of the thesis, the kinematic and dynamic models of these innovative systems are presented and analyzed in order to characterize their capability. Trajectory planning and optimal design are addressed with the purpose of maximizing the performance of the systems. The last part of the thesis deals with the design of a novel family of Intelligent CAble-driven parallel roBOTs whose architecture and control are conceived to maximize the robot versatility to the task to be performed and the environment in which the robot is intended to operate

Kinematics and statics of cable-driven parallel robots by interval-analysis-based methods

In the past two decades the work of a growing portion of researchers in robotics focused on a particular group of machines, belonging to the family of parallel manipulators: the cable robots. Although these robots share several theoretical elements with the better known parallel robots, they still present completely (or partly) unsolved issues. In particular, the study of their kinematic, already a difficult subject for conventional parallel manipulators, is further complicated by the non-linear nature of cables, which can exert only efforts of pure traction. The work presented in this thesis therefore focuses on the study of the kinematics of these robots and on the development of numerical techniques able to address some of the problems related to it. Most of the work is focused on the development of an interval-analysis based procedure for the solution of the direct geometric problem of a generic cable manipulator. This technique, as well as allowing for a rapid solution of the problem, also guarantees the results obtained against rounding and elimination errors and can take into account any uncertainties in the model of the problem. The developed code has been tested with the help of a small manipulator whose realization is described in this dissertation together with the auxiliary work done during its design and simulation phases.Negli ultimi decenni il lavoro di una parte sempre maggiore di ricercatori che si occupano di robotica si è concentrato su un particolare gruppo di robot appartenenti alla famiglia dei manipolatori paralleli: i robot a cavi. Nonostante i numerosi studi al riguardo, questi robot presentano ancora oggi numerose problematiche del tutto (o in parte) irrisolte. Lo studio della loro cinematica nello specifico, già complesso per i manipolatori paralleli tradizionali, è ulteriormente complicato dalla natura non lineare dei cavi, i quali possono esercitare sforzi di sola trazione. Il lavoro presentato in questa tesi si concentra dunque sullo studio della cinematica dei robot a cavi e sulla messa a punto di tecniche numeriche in grado di affrontare parte delle problematiche ad essa legate. La maggior parte del lavoro è incentrata sullo sviluppo di una procedura per la soluzione del problema geometrico diretto di un generico manipolatore a cavi basata sull'analisi per intervalli. Questa tecnica di analisi numeirica, oltre a consentire una rapida soluzione del problema, permette di garantire i risultati ottenuti in caso di errori di cancellazione e arrotondamento e consente di considerare eventuali incertezze presenti nel modello del problema. Il codice sviluppato è stato testato attraverso un piccolo prototipo di manipolatore a cavi la cui realizzazione, avvenuta durante il percorso di dottrato, è descritta all'interno dell'elaborato unitamente al lavoro collaterale svolto durante la fase di progettazione e simulazione.Pendant les dernières décennies, le travail d'une partie toujours croissante de chercheurs qui s'occupent de robotique s'est focalisé sur un groupe spécifique de robots qui fait partie de la famille des manipulateurs parallèles: les robots à câbles. Malgré les nombreux études que l'on a consacré à ce sujet, ces robots présentent encore aujourd'hui plusieurs problématiques complètement ou partiellement irrésolues. En particulier l'étude de leur cinématique, qui se révèle déjà complexe pour les manipulateurs parallèles traditionnels, est rendu encore plus compliqué par la nature non linéaire des câbles qui peuvent seulement exercer des efforts de traction. Le travail présenté dans ma thèse concentre donc son attention sur l'étude de la cinématique des robots à câbles et sur la mise au point de techniques numériques capables d'aborder une partie des problématiques liées à cela. La plupart du travail se concentre sur l'élaboration d'un algorithme pour la résolution du problème géométrique direct d'un manipulateur à câbles général qui se fonde sur l'analyse par intervalles. Cette technique d'analyse permet non seulement de résoudre rapidement le problème mais également de garantir les résultats obtenus en cas d'erreur de cancellation et d'arrondi et de prendre en considération les incertitudes éventuellement presentes dans le modèle du problème. Le code développé a été testé grâce à un petit prototype de manipulateur à câbles dont la réalisation, qui a eu lieu pendant le parcours de doctorat, est décrite à l'intérieur du devoir en accord avec la phase de conception du projet et de simulation

Modeling, Control and Estimation of Reconfigurable Cable Driven Parallel Robots

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-driven parallel mechanisms for minimally invasive robotic surgery

Minimally invasive surgery (MIS) has revolutionised surgery by providing faster recovery times, less post-operative complications, improved cosmesis and reduced pain for the patient. Surgical robotics are used to further decrease the invasiveness of procedures, by using yet smaller and fewer incisions or using natural orifices as entry point. However, many robotic systems still suffer from technical challenges such as sufficient instrument dexterity and payloads, leading to limited adoption in clinical practice. Cable-driven parallel mechanisms (CDPMs) have unique properties, which can be used to overcome existing challenges in surgical robotics. These beneficial properties include high end-effector payloads, efficient force transmission and a large configurable instrument workspace. However, the use of CDPMs in MIS is largely unexplored. This research presents the first structured exploration of CDPMs for MIS and demonstrates the potential of this type of mechanism through the development of multiple prototypes: the ESD CYCLOPS, CDAQS, SIMPLE, neuroCYCLOPS and microCYCLOPS. One key challenge for MIS is the access method used to introduce CDPMs into the body. Three different access methods are presented by the prototypes. By focusing on the minimally invasive access method in which CDPMs are introduced into the body, the thesis provides a framework, which can be used by researchers, engineers and clinicians to identify future opportunities of CDPMs in MIS. Additionally, through user studies and pre-clinical studies, these prototypes demonstrate that this type of mechanism has several key advantages for surgical applications in which haptic feedback, safe automation or a high payload are required. These advantages, combined with the different access methods, demonstrate that CDPMs can have a key role in the advancement of MIS technology.Open Acces

Modelización de un exoesqueleto de rehabilitación propulsado por cables con capacidad de desplazamiento espacial

En la actualidad miles de personas en nuestro país y en el mundo se enfrentan a las enfermedades cerebrovasculares y a sus devastadoras consecuencias sobre la vida humana. Aquellos que sobreviven se ven obligados a sufrir diversas secuelas permanentes, de las cuales aquellas que afectan a la movilidad física son de las que más situaciones de dependencia producen. El aumento de la frecuencia de este tipo de males lo convierten en una de las principales preocupaciones de la medicina moderna La esperanza de los pacientes con reducción de la movilidad se centra en las terapias de rehabilitación, las cuales exigen gran cantidad de medios y horas de esfuerzo que a menudo no se encuentran al alcance de los especialistas. La ingeniería robótica ha proporcionado un gran apoyo a estos procesos mediante los exoesqueletos de rehabilitación, pero su investigación se mantiene hoy en pleno desarrollo y aún existen muchos inconvenientes en el uso de sus sistemas. Una nueva línea de investigación de robots de cables ha surgido demostrando poder resolver muchos de estos inconvenientes y propone un futuro prometedor. Sus sistemas aún sufren grandes restricciones al movimiento que hacen que todavía estos exoesqueletos de cables no posean todas las capacidades que la medicina de rehabilitación requiere. El proyecto “Modelización de un exoesqueleto de rehabilitación propulsado por cables con capacidad de desplazamiento espacial” tiene como objetivo ampliar las posibilidades de los exoesqueletos de cables actuales mediante la modelización y simulación de un sistema completo de tres grados de libertad capaz de desplazarse en el espacio tridimensional.Nowadays thousands of people in our country and in the world face cerebrovascular diseases and its devastating consequences on human life. Those who survive are forced to suffer different kinds of permanent sequelae. Among them, mobility disabilities are those who produce more dependency situations. The increase in the frequency of this type of illness makes it one of the main concerns of modern medicine. The hope of patients with reduced mobility is focused on rehabilitation therapies, which require a great deal of means and hours of effort that are often not available to specialists. Robotic engineering has provided great support to these processes through rehabilitation exoskeletons, but its research is still in a developing state and there are many drawbacks in the use of these systems. A new line of research on cable-driven robots has emerged showing that it can solve many of these problems and it seems to have a bright future. Their systems still suffer great restrictions to movement that mean that these cable exoskeletons still do not have all the capabilities that rehabilitation medicine requires. The project "Modelling a cable-driven rehabilitation exoskeleton with space displacement capacity" aims to expand the possibilities of current cable exoskeletons by modelling and simulating a complete system of three degrees of freedom capable of movement in three-dimensional spaceUniversidad de Sevilla. Grado en Ingeniería Electrónica, Robótica y Mecatrónic

Kinematics and Robot Design I, KaRD2018

This volume collects the papers published on the Special Issue “Kinematics and Robot Design I, KaRD2018” (https://www.mdpi.com/journal/robotics/special_issues/KARD), which is the first issue of the KaRD Special Issue series, hosted by the open access journal “MDPI Robotics”. The KaRD series aims at creating an open environment where researchers can present their works and discuss all the topics focused on the many aspects that involve kinematics in the design of robotic/automatic systems. Kinematics is so intimately related to the design of robotic/automatic systems that the admitted topics of the KaRD series practically cover all the subjects normally present in well-established international conferences on “mechanisms and robotics”. KaRD2018 received 22 papers and, after the peer-review process, accepted only 14 papers. The accepted papers cover some theoretical and many design/applicative aspects

Virtual reality and body rotation: 2 flight experiences in comparison

Embodied interfaces, represented by devices that incorporate bodily motion and proprioceptive stimulation, are promising for Virtual Reality (VR) because they can improve immersion and user experience while at the same time reducing simulator sickness compared to more traditional handheld interfaces (e.g.,gamepads). The aim of the study is to evaluate a novel embodied interface called VitruvianVR. The machine is composed of two separate rings that allow its users to bodily rotate onto three different axes. The suitability of the VitruvianVR was tested in a Virtual Reality flight scenario. In order to reach the goal we compared the VitruvianVR to a gamepad using perfomance measures (i.e., accuracy, fails), head movements and position of the body. Furthermore, a series of data coming from questionnaires about sense of presence, user experience, cognitive load, usability and cybersickness was retrieved.Embodied interfaces, represented by devices that incorporate bodily motion and proprioceptive stimulation, are promising for Virtual Reality (VR) because they can improve immersion and user experience while at the same time reducing simulator sickness compared to more traditional handheld interfaces (e.g.,gamepads). The aim of the study is to evaluate a novel embodied interface called VitruvianVR. The machine is composed of two separate rings that allow its users to bodily rotate onto three different axes. The suitability of the VitruvianVR was tested in a Virtual Reality flight scenario. In order to reach the goal we compared the VitruvianVR to a gamepad using perfomance measures (i.e., accuracy, fails), head movements and position of the body. Furthermore, a series of data coming from questionnaires about sense of presence, user experience, cognitive load, usability and cybersickness was retrieved