Advanced Strategies for Robot Manipulators

Amongst the robotic systems, robot manipulators have proven themselves to be of increasing importance and are widely adopted to substitute for human in repetitive and/or hazardous tasks. Modern manipulators are designed complicatedly and need to do more precise, crucial and critical tasks. So, the simple traditional control methods cannot be efficient, and advanced control strategies with considering special constraints are needed to establish. In spite of the fact that groundbreaking researches have been carried out in this realm until now, there are still many novel aspects which have to be explored

Robotic Arts: Painting a red canvas with a robotic arm

L'objectiu principal de l'art robòtic és crear art alhora que desenvolupar tècniques generals que es puguin utilitzar en altres contextos. En aquesta tesi es presenta un projecte dins l'àmbit de la Pintura Robòtica. Per tal d'iniciar el camí cap a un sistema robòtic de reproducció autònoma d'un quadre, l'objectiu d'aquesta tesi és aconseguir que un robot pinti uniformement un llenç de vermell. Per fer-ho, s'han d'utilitzar diferents tècniques, i el focus principal es posa en la planificació del moviment (motion planning). Presentem una tècnica general que resol el problema de resolució de redundància (redundancy resolution) donada una superfície d'espai de tasques restringit. Aquest és un enfocament basat en gràfics que s'utilitza per trobar un mínim del camí global segons criteris de cost integrals per la ruta. Es basa en un graf de Roadmap precalculat que representa la preimatge de la superfície de l'espai de tasques restringit. Amb aquest graf, es troba primer una solució a un problema aproximat, mitjançant una cerca feta per un graf de capes creat a partir del Roadmap original. Finalment, les solucions s'ajusten amb una optimització final mitjançant grafs factorials (Factor Graphs). Aquest mètode s'aplica amb èxit a la pintura robòtica. Les nombroses reconfiguracions possibles d'un robot entre pinzellades s'eviten mitjançant un ús intel·ligent del Roadmap. Gràcies a això, es mostra la flexibilitat i l'adaptabilitat que aquest mètode aporta en aquest context.El objetivo principal del arte robótico es crear arte a la vez que desarrollar técnicas generales que se puedan utilizar en otros contextos. En esta tesis se presenta un proyecto en el ámbito de la Pintura Robótica. Con el fin de iniciar el camino hacia un sistema robótico de reproducción autónoma de un cuadro, el objetivo de esta tesis es conseguir que un robot pinte uniformemente un lienzo de rojo. Para ello, deben utilizarse diferentes técnicas, cuyo foco principal se pone en la planificación del movimiento (motion planning). Presentamos una técnica general que resuelve el problema de resolución de redundancia (redundancy resolution) dada una superficie de espacio de tareas restringido. Éste es un enfoque basado en gráficos que se utiliza para encontrar un mínimo del camino global según criterios de coste integrales para la ruta. Se basa en un grafo de un Roadmap precalculado que representa la preimagen de la superficie del espacio de tareas restringido. Con este grafo, se encuentra primero una solución a un problema aproximado, mediante una búsqueda hecha en un grafo de capas creado a partir del Roadmap original. Por último, las soluciones se ajustan con una optimización final mediante grafos factoriales (Factor Graphs). Este método se aplica con éxito en la pintura robótica. Las numerosas reconfiguraciones posibles de un robot entre pinceladas se evitan mediante un uso inteligente del Roadmap. Gracias a ello, se muestra la flexibilidad y adaptabilidad que este método aporta en este contexto.The main goal in Robotic Arts is to create art while also developing general techniques that can be used in many other contexts. In this thesis, a project within the field of Robotic Painting is presented. In order to start the path to an autonomous painterly robotic reproduction system, the goal of this thesis is to get a robot to uniformly paint a canvas red. To do so, different techniques have to be used, and the main focus is put on the motion planning. We present a general technique that solves the redundancy resolution problem given a constrained task space surface. This is a graph-based approach used to find a global path minimum according to an integral path cost criteria. It is based on a precomputed Roadmap graph that represents the preimage of the constrained task space surface. With this graph, a solution to an approximate problem is found via a search on a Layered Graph representation of the previous original Roadmap. Finally, solutions are fine-tuned with an ending optimization via factor graphs. This method is then successfully applied to Robotic Painting. The many possible reconfigurations of a robot between strokes are evaded by a clever use of the Roadmap. Thanks to this, the flexibility and adaptability of this general method to this context is shown.Outgoin

Kinematic Performance Measures and Optimization of Parallel Kinematics Manipulators: A Brief Review

This chapter covers a number of kinematic performance indices that are instrumental in designing parallel kinematics manipulators. These indices can be used selectively based on manipulator requirements and functionality. This would provide the very practical tool for designers to approach their needs in a very comprehensive fashion. Nevertheless, most applications require a more composite set of requirements that makes optimizing performance more challenging. The later part of this chapter will discuss single-objective and multi-objectives optimization that could handle certain performance indices or a combination of them. A brief description of most common techniques in the literature will be provided

Solving robotic kinematic problems : singularities and inverse kinematics

Kinematics is a branch of classical mechanics that describes the motion of points, bodies, and systems of bodies without considering the forces that cause such motion. For serial robot manipulators, kinematics consists of describing the open chain geometry as well as the position, velocity and/or acceleration of each one of its components. Rigid serial robot manipulators are designed as a sequence of rigid bodies, called links, connected by motor-actuated pairs, called joints, that provide relative motion between consecutive links. Two kinematic problems of special relevance for serial robots are: - Singularities: are the configurations where the robot loses at least one degree of freedom (DOF). This is equivalent to: (a) The robot cannot translate or rotate its end-effector in at least one direction. (b) Unbounded joint velocities are required to generate finite linear and angular velocities. Either if it is real-time teleoperation or off-line path planning, singularities must be addressed to make the robot exhibit a good performance for a given task. The objective is not only to identify the singularities and their associated singular directions but to design strategies to avoid or handle them. - Inverse kinematic problem: Given a particular position and orientation of the end-effector, also known as the end-effector pose, the inverse kinematics consists of finding the configurations that provide such desired pose. The importance of the inverse kinematics relies on its role in the programming and control of serial robots. Besides, since for each given pose the inverse kinematics has up to sixteen different solutions, the objective is to find a closed-form method for solving this problem, since closed-form methods allow to obtain all the solutions in a compact form. The main goal of the Ph.D. dissertation is to contribute to the solution of both problems. In particular, with respect to the singularity problem, a novel scheme for the identification of the singularities and their associated singular directions is introduced. Moreover, geometric algebra is used to simplify such identification and to provide a distance function in the configuration space of the robot that allows the definition of algorithms for avoiding them. With respect to the inverse kinematics, redundant robots are reduced to non-redundant ones by selecting a set of joints, denoted redundant joints, and by parameterizing their joint variables. This selection is made through a workspace analysis which also provides an upper bound for the number of different closed-form solutions. Once these joints have been identified, several closed-form methods developed for non-redundant manipulators can be applied to obtain the analytical expressions of all the solutions. One of these methods is a novel strategy developed using again the conformal model of the spatial geometric algebra. To sum up, the Ph.D dissertation provides a rigorous analysis of the two above-mentioned kinematic problems as well as novel strategies for solving them. To illustrate the different results introduced in the Ph.D. memory, examples are given at the end of each of its chapters.La cinemática es una rama de la mecánica clásica que describe el movimiento de puntos, cuerpos y sistemas de cuerpos sin considerar las fuerzas que causan dicho movimiento. Para un robot manipulador serie, la cinemática consiste en la descripción de su geometría, su posición, velocidad y/o aceleración. Los robots manipuladores serie están diseñados como una secuencia de elementos estructurales rígidos, llamados eslabones, conectados entres si por articulaciones actuadas, que permiten el movimiento relativo entre pares de eslabones consecutivos. Dos problemas cinemáticos de especial relevancia para robots serie son: - Singularidades: son aquellas configuraciones donde el robot pierde al menos un grado de libertad (GDL). Esto equivale a: (a) El robot no puede trasladar ni rotar su elemento terminal en al menos una dirección. (b) Se requieren velocidades articulares no acotadas para generar velocidades lineales y angulares finitas. Ya sea en un sistema teleoperado en tiempo real o planificando una trayectoria, las singularidades deben manejarse para que el robot muestre un rendimiento óptimo mientras realiza una tarea. El objetivo no es solo identificar las singularidades y sus direcciones singulares asociadas, sino diseñar estrategias para evitarlas o manejarlas. - Problema de la cinemática inversa: dada una posición y orientación del elemento terminal (también conocida como la pose del elemento terminal), la cinemática inversa consiste en obtener las configuraciones asociadas a dicha pose. La importancia de la cinemática inversa se basa en el papel que juega en la programación y el control de robots serie. Además, dado que para cada pose la cinemática inversa tiene hasta dieciséis soluciones diferentes, el objetivo es encontrar un método cerrado para resolver este problema, ya que los métodos cerrados permiten obtener todas las soluciones en una forma compacta. El objetivo principal de la tesis doctoral es contribuir a la solución de ambos problemas. En particular, con respecto al problema de las singularidades, se presenta un nuevo método para su identificación basado en el álgebra geométrica. Además, el álgebra geométrica permite definir una distancia en el espacio de configuraciones del robot que permite la definición de distintos algoritmos para evitar las configuraciones singulares. Con respecto a la cinemática inversa, los robots redundantes se reducen a robots no-redundantes mediante la selección de un conjunto de articulaciones, las articulaciones redundantes, para después parametrizar sus variables articulares. Esta selección se realiza a través de un análisis de espacio de trabajo que también proporciona un límite superior para el número de diferentes soluciones en forma cerrada. Una vez las articulaciones redundantes han sido identificadas, varios métodos en forma cerrada desarrollados para robots no-redundantes pueden aplicarse a fin de obtener las expresiones analíticas de todas las soluciones. Uno de dichos métodos es una nueva estrategia desarrollada usando el modelo conforme del álgebra geométrica tridimensional. En resumen, la tesis doctoral proporciona un análisis riguroso de los dos problemas cinemáticos mencionados anteriormente, así como nuevas estrategias para resolverlos. Para ilustrar los diferentes resultados presentados en la tesis, la memoria contiene varios ejemplos al final de cada uno de sus capítulos

Profile Synthesis Of Planar Variable Joints

Reconfigurable mechanisms provide quick changeover and reduced costs for low volume manufacturing applications. In addition, these mechanisms provide added flexibility in the context of a constrained environment. A subset of planar reconfigurable mechanisms use variable joints to provide this added adaptability. In this dissertation, the profile synthesis of planar variable joints that change from a rotational motion to a translational motion was investigated. A method was developed to perform automated profile synthesis. It was shown that combinations of higher variable joints can be used to create kinematically equivalent variable joints that are geometrically different. The results were used to create two new reconfigurable mechanisms that utilize the synthesized variable joints. The first reconfigurable mechanism is a four-bar mechanism that performs a rigid body guidance task not possible using conventional four-bar theory. The second mechanism uses variable joints in a 3-RPR parallel mechanism for singularity avoidance without adding redundant actuation

Advances in Robot Kinematics : Proceedings of the 15th international conference on Advances in Robot Kinematics

International audienceThe motion of mechanisms, kinematics, is one of the most fundamental aspect of robot design, analysis and control but is also relevant to other scientific domains such as biome- chanics, molecular biology, . . . . The series of books on Advances in Robot Kinematics (ARK) report the latest achievement in this field. ARK has a long history as the first book was published in 1991 and since then new issues have been published every 2 years. Each book is the follow-up of a single-track symposium in which the participants exchange their results and opinions in a meeting that bring together the best of world’s researchers and scientists together with young students. Since 1992 the ARK symposia have come under the patronage of the International Federation for the Promotion of Machine Science-IFToMM.This book is the 13th in the series and is the result of peer-review process intended to select the newest and most original achievements in this field. For the first time the articles of this symposium will be published in a green open-access archive to favor free dissemination of the results. However the book will also be o↵ered as a on-demand printed book.The papers proposed in this book show that robot kinematics is an exciting domain with an immense number of research challenges that go well beyond the field of robotics.The last symposium related with this book was organized by the French National Re- search Institute in Computer Science and Control Theory (INRIA) in Grasse, France