Controle de força de robos manipuladores interagindo com ambientes de elasticidade não linear

Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro TecnologicoEste trabalho tem como objetivo principal o controle simultâneo de força e posição robusto de robôs manipuladores em contato com ambientes de elasticidade não linear. A finalidade do controlador é a automação do manuseio de peças flexíveis nos mais diversos tipos de linhas de montagem, proporcionando então, um avanço tecnológico na indústria de manufatura. A estratégia usada é o controle híbrido de força e posição. Este esquema atende simultaneamente trajetórias de referências de força e de posição especificadas no espaço de tarefa. Para proporcionar robustez ao controlador, os sub-controladores são implementados utilizando controladores de modos deslizantes. Na apresentação da teoria de estrutura variável é implementado um controlador de posiçao no espaço de juntas num robô SCARA industrial. O controlador híbrido de força e posição projetado é simulado numericamente, apresentando resultados satisfatórios com relação à estabilidade e à robustez

Kraftsensorlose Manipulator Kraftsteuerung zur Abtastung unbekannter, harter Oberflächen

Die vorliegende Arbeit zeigt ein Verfahren zur kraftgesteuerten Kontaktierung unbekannter harter Freiformflächen mit einem Standard–6DOF-Industriemanipulator (z.B. Manutec R2). Die bisher entwickelten Verfahren auf dem Gebiet der Manipulatorkraftregelung waren auf teure, fragile, mehrdimensionale Kraft-/Momentensensoren am Manipulator-Endeffektor angewiesen, die bei dem in dieser Arbeit entwickelten Ansatz der sensorlosen Kraft-/Geschwindigkeitsregelung überflüssig werden. Die Einstellung der gewünschten Kontaktkraft zu der unbekannten Umgebung erfolgt ausschließlich über eine robuste, beobachtergestützte Regelung der Motorströme der Gelenkantriebe. In freien Bewegungsphasen garantierte eine kaskadierte Kraft-/Geschwindigkeitsregelung vordefinierte Heranfahrgeschwindigkeiten an die unbekannte Kontaktoberfläche. Hierdurch eröffnen sich vollkommen neue Einsatzszenarien für die kraftkontrollierte Kontaktierung und Bearbeitung unbekannter Oberflächen oder Werkstücke beliebiger Härte und Steifigkeit

A passivity-based approach to force regulation and motion control of robot manipulators

This paper deals with the design of control schemes for a robot manipulator in contact with a compliant surface. A passivity-based approach is adopted in the task space, where the control law contains a nonlinear model-based term and a linear term obtained as the sum of a position action and a force action. The force control action dominates the position control action along the constrained task space direction so as to achieve force regulation at the expense of a steady-state position error. Motion control along the unconstrained task space directions is ensured. In the case of imperfect model compensation, the scheme is made adaptive with respect to a set of dynamic parameters. Numerical case studies are developed for an industrial robot manipulator

A passivity-based approach to force regulation and motion control of robot manipulators

This paper deals with the design of control schemes for a robot manipulator in contact with a compliant surface. A passivity-based approach is adopted in the task space, where the control law contains a nonlinear model-based term and a linear term obtained as the sum of a position action and a force action. The force control action dominates the position control action along the constrained task space direction so as to achieve force regulation at the expense of a steady-state position error. Motion control along the unconstrained task space directions is ensured. In the case of imperfect model compensation, the scheme is made adaptive with respect to a set of dynamic parameters. Numerical case studies are developed for an industrial robot manipulator

Design and validation of a system for controlling a robot for 3D ultrasound scanning of the lower limbs

Peripheral arterial disease (PAD) is a common circulatory problem featured by arterial narrowing or stenosis, usually in the lower limbs (i.e. legs). Without sufficient blood supply, in the case of PAD, the patient may suffer from intermittent claudication, or even require an amputation. Due to the PAD’s high prevalence yet low public awareness in the early stages, its diagnosis becomes very important. Among the most common medical imaging technologies in PAD diagnosis, the ultrasound probe has the advantages of lower cost and non-radiation. Traditional ultrasound scanning is conducted by sonographers and it causes musculoskeletal disorders in the operators. In addition, the data obtained from the manual operation are unable for the three-dimensional reconstruction of the artery needed for further study. Medical ultrasound robots release sonographers from routine lifting strain and provide accurate data for three-dimensional reconstruction. However, most existing medical ultrasound robots are designed for other purposes, and are unsuited to PAD diagnosis in the lower limbs. In this study, we present a novel medical ultrasound robot designed for PAD diagnosis in the lower limbs. The robot platform and the system setup are illustrated. Its forward and inverse kinematic models are solved by decomposing a complex parallel robot into several simple assemblies. Singularity issues and workspace are also discussed. Robots need to meet certain accuracy requirements to perform dedicated tasks. Our robot is calibrated by direct measurement with a laser tracker. The calibration method used is easy to implement without requiring knowledge of advanced calibration or heavy computation. The calibration result shows that, as an early prototype, the robot has noticeable errors in manufacturing and assembling. The implemented calibration method greatly improves the robot's accuracy. A force control design is essential when the robot needs to interact with an object/environment. Variable admittance controllers are implemented to adapt the variable stiffness encountered in human-robot interaction. An intuitive implementation of the passivity theory is proposed to ensure that the admittance model possesses a passivity property. Finally, experiments involving human interaction demonstrate the effectiveness of the proposed control design

Robotic Trajectory Tracking: Position- and Force-Control

This thesis employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control. In a first phase, the focus is put on the following of a freeform surface in a discontinuous manner. Next to resulting switching constraints, disturbances and uncertainties, the case of unknown robot models is addressed. In a second phase, once contact has been established between surface and end effector and the freeform path is followed, a desired force is applied. In order to react to changing circumstances, the manipulator needs to show the features of an intelligent agent, i.e. it needs to learn and adapt its behaviour based on a combination of a constant interaction with its environment and preprogramed goals or preferences. The robotic manipulator mimics the human behaviour based on bio-inspired algorithms. In this way it is taken advantage of the know-how and experience of human operators as their knowledge is translated in robot skills. A selection of promising concepts is explored, developed and combined to extend the application areas of robotic manipulators from monotonous, basic tasks in stiff environments to complex constrained processes. Conventional concepts (Sliding Mode Control, PID) are combined with bio-inspired learning (BELBIC, reinforcement based learning) for robust and adaptive control. Independence of robot parameters is guaranteed through approximated robot functions using a Neural Network with online update laws and model-free algorithms. The performance of the concepts is evaluated through simulations and experiments. In complex freeform trajectory tracking applications, excellent absolute mean position errors (<0.3 rad) are achieved. Position and torque control are combined in a parallel concept with minimized absolute mean torque errors (<0.1 Nm)

Commande des systèmes sous frottement utilisant le formalisme LMI : application aux systèmes robotiques avec contact et aux actionneurs pneumatiques

Le frottement présente systématiquement un risque accablant dans l'altération des performances de mouvement des systèmes mécaniques. La mise-en-place d'un système de contrôle efficace pour dissiper ce genre d'anomalie constitue encore un sujet d'actualité dans les domaines de la recherche et de l'ingénierie. Les mécaniciens, les tribologues, spécialistes de la théorie de frottement, et les automaticiens oeuvrent pour l'étude de ce phénomène des points de vue: caractérisation, modélisation et compensation. Une revue assez exhaustive de ces travaux est présentée dans le chapitre 1. Dans le présent travail de thèse, nous proposons un schéma général de contrôle des systèmes sous frottement que nous pouvons utiliser dans plusieurs applications. En respectant les paradigmes standards de stabilité, de robustesse et d'optimisation (de types H2, H∞ , etc.), ce shéma est basé sur l'estimation en boucle fermée du frottement dynamique, selon le modèle de LuGre, et la structure dynamique de contrôle linéaire par retour de sortie. La synthèse de cette commande repose sur les outils numériques des inégalités matricielles linéaires. En plus, pour tenir compte de la variété des structures dynamiques de mouvement et aussi de force dans les différents dispositifs en question, le schéma de la commande que nous proposons peut comprendre des termes d'actions statiques (ou) dynamiques, linéaires (ou) non linéaires et éventuellement robustes. Une illustration simple de la commande de mouvement d'une masse, sur une surface sous frottement, est exposée dans le chapitre 2. Il s'agit d'une généralisation du principe de commande stabilisante par rétroaction statique introduit par Canudas et al.(1995). Ensuite, nous appliquons notre schéma dans des cas plus complexes (non linéarités, incertitudes et couplages de force/position non négligeables). Pour ce faire, nous proposons dans le chapitre 3 l'étude de la commande hybride de position/force du robot manipulateur dont l'élément final est en contact sous frottement avec une surface donnée. Dans le chapitre 4, nous développons le schéma de contrôle de force (i.e. de pression) de l'actionneur pneumatique. Et dans le chapitre 5, nous présentons le schéma détaillé de contrôle de position de ce type d'installation qui renferme plusieurs points de contact avec frottement. Des résultats expérimentaux sont présentés pour valider notre approche de commande et aussi la comparer à d'autres schémas de commande et/ou de compensation de frottement. Pour conclure ce travail, nous recommandons, en particulier, l'extension de l'approche proposée en utilisant un modèle de frottement encore plus générale comme celui de glissement généralisé de Maxwell (GMS) dans une suite logique et aussi ambitieuse de ce travail