Robot Manipulators

Robot manipulators are developing more in the direction of industrial robots than of human workers. Recently, the applications of robot manipulators are spreading their focus, for example Da Vinci as a medical robot, ASIMO as a humanoid robot and so on. There are many research topics within the field of robot manipulators, e.g. motion planning, cooperation with a human, and fusion with external sensors like vision, haptic and force, etc. Moreover, these include both technical problems in the industry and theoretical problems in the academic fields. This book is a collection of papers presenting the latest research issues from around the world

Control of Networked Robotic Systems

With the infrastructure of ubiquitous networks around the world, the study of robotic systems over communication networks has attracted widespread attention. This area is denominated as networked robotic systems. By exploiting the fruitful technological developments in networking and computing, networked robotic systems are endowed with potential and capabilities for several applications. Robots within a network are capable of connecting with control stations, human operators, sensors, and other robots via digital communication over possibly noisy channels/media. The issues of time delays in communication and data losses have emerged as a pivotal issue that have stymied practical deployment. The aim of this dissertation is to develop control algorithms and architectures for networked robotic systems that guarantee stability with improved overall performance in the presence of time delays in communication. The first topic addressed in this dissertation is controlled synchronization that is utilized for networked robotic systems to achieve collective behaviors. Exploiting passivity property of individual robotic systems, the proposed control schemes and interconnections are shown to ensure stability and convergence of synchronizing errors. The robustness of the control algorithms to constant and time-varying communication delays is also studied. In addition to time delays, the number of communication links, which prevents scalability of networked robotic systems, is another challenging issue. Thus, a synchronizing control with practically feasible constraints of network topology is developed. The problem of networked robotic systems interacting with human operators is then studied subsequently. This research investigates a teleoperation system with heterogeneous robots under asymmetric and unknown communication delays. Sub-task controllers are proposed for redundant slave robot to autonomously achieve additional tasks, such as singularity avoidance, joint angle limits, and collision avoidance. The developed control algorithms can enhance the efficiency of teleoperation systems, thereby ameliorating the performance degradation due to cognitive limitations of human operator and incomplete information about the environment. Compared to traditional robotic systems, control of robotic manipulators over networks has significant advantages; for example, increased flexibility and ease of maintenance. With the utilization of scattering variables, this research demonstrates that transmitting scattering variables over delayed communications can stabilize an otherwise unstable system. An architecture utilizing delayed position feedback in conjunction with scattering variables is developed for the case of time-varying communication delays. The proposed control architecture improves tracking performance and stabilizes robotic manipulators with input-output communication delays. The aforementioned control algorithms and architectures for networked robotic systems are validated via numerical examples and experiments

An NMPC-ECBF Framework for Dynamic Motion Planning and Execution in vision-based Human-Robot Collaboration

To enable safe and effective human-robot collaboration (HRC) in smart manufacturing, seamless integration of sensing, cognition, and prediction into the robot controller is critical for real-time awareness, response, and communication inside a heterogeneous environment (robots, humans, and equipment). The proposed approach takes advantage of the prediction capabilities of nonlinear model predictive control (NMPC) to execute a safe path planning based on feedback from a vision system. In order to satisfy the requirement of real-time path planning, an embedded solver based on a penalty method is applied. However, due to tight sampling times NMPC solutions are approximate, and hence the safety of the system cannot be guaranteed. To address this we formulate a novel safety-critical paradigm with an exponential control barrier function (ECBF) used as a safety filter. We also design a simple human-robot collaboration scenario using V-REP to evaluate the performance of the proposed controller and investigate whether integrating human pose prediction can help with safe and efficient collaboration. The robot uses OptiTrack cameras for perception and dynamically generates collision-free trajectories to the predicted target interactive position. Results for a number of different configurations confirm the efficiency of the proposed motion planning and execution framework. It yields a 19.8% reduction in execution time for the HRC task considered

Coordinated Control of a Mobile Manipulator

In this technical report, we investigate modeling, control, and coordination of mobile manipulators. A mobile manipulator in this study consists of a robotic manipulator and a mobile platform, with the manipulator being mounted atop the mobile platform. A mobile manipulator combines the dextrous manipulation capability offered by fixed-base manipulators and the mobility offered by mobile platforms. While mobile manipulators offer a tremendous potential for flexible material handling and other tasks, at the same time they bring about a number of challenging issues rather than simply increasing the structural complexity. First, combining a manipulator and a platform creates redundancy. Second, a wheeled mobile platform is subject to nonholonomic constraints. Third, there exists dynamic interaction between the manipulator and the mobile platform. Fourth, manipulators and mobile platforms have different bandwidths. Mobile platforms typically have slower dynamic response than manipulators. The objective of the thesis is to develop control algorithms that effectively coordinate manipulation and mobility of mobile manipulators. We begin with deriving the motion equations of mobile manipulators. The derivation presented here makes use of the existing motion equations of manipulators and mobile platforms, and simply introduces the velocity and acceleration dependent terms that account for the dynamic interaction between manipulators and mobile platforms. Since nonholonomic constraints play a critical role in control of mobile manipulators, we then study the control properties of nonholonomic dynamic systems, including feedback linearization and internal dynamics. Based on the newly proposed concept of preferred operating region, we develop a set of coordination algorithms for mobile manipulators. While the manipulator performs manipulation tasks, the mobile platform is controlled to always bring the configuration of the manipulator into a preferred operating region. The control algorithms for two types of tasks - dragging motion and following motion - are discussed in detail. The effects of dynamic interaction are also investigated. To verify the efficacy of the coordination algorithms, we conduct numerical simulations with representative task trajectories. Additionally, the control algorithms for the dragging motion and following motion have been implemented on an experimental mobile manipulator. The results from the simulation and experiment are presented to support the proposed control algorithms

Analysis and design of a complex-valued sliding mode controller of a 2-link planar manipulator

Robotics and robot manipulators are some common concepts which nowadays are seen as something usual in a lot of industries. However, they are quite young fields in engineering and they include lots of different specialities such as mathematics and mechanical or elec- trical engineering. These lasts decades, the development of new robots and their control techniques have grown a lot, having now a wide variety of knowledge about their behavior and control algorithms that allow them to do their specific tasks with low errors and high performance. This project presents a new strategy in control engineering for the robotics field, which consists of an extension of a sliding mode controller to a complex-valued domain. This controller allows to track the tool center position (TCP) of a 2-link planar manipulator without the direct use of inverse kinematics and working always in the complex space. Hence, the forward kinematics of the end-effector of the robot are modeled with complex variables to design the nonlinear controller and be able to analyze its performance and study the potential of this new approach in this application field. Moreover, three more different controllers (a real-valued sliding mode controller, a state-feedback and a PID con- trol) are also designed so the main controller (Complex-valued sliding mode controller) can be analyzed and compared with other solutions to study the possible benefits and disad- vantages it may have. All the controllers are analyzed and compared with Matlab and simulated with Simulink and the results obtained are studied according to a qualitative and quantitative analysis based on some Key Performance Indicators (KPIs). Finally, all the results obtained during all the development of this project are summarized, discussed and presented with the conclusions extractedLa robòtica i els robots manipuladors són conceptes que actualment es contemplen com a temes habituals en moltes indústries. De totes maneres, es tracta de camps relativa- ment nous en l’enginyeria i inclouen diverses especialitats com la matemàtica i l’enginyeria mecànica o elèctrica. Durant aquestes últimes dècades, el desenvolupament d’aquests robots i les seves tècniques de control han crescut considerablement, arribant a tenir un am- pli coneixement sobre el seu comportament i els algorismes de control que els hi permeten realitzar les seves tasques amb errors baixos i gran rendiment. Aquest projecte presenta una estratègia nova en l’enginyeria de control pel camp de la robòtica, la qual consisteix en una extensió del control per mode de lliscament (sliding mode control, en anglès) en un domini complex. Aquest controlador permet fer un seguiment de la posició final d’un robot manipulador pla de dos braços sense l’ús directe de la cinemàtica inversa i treballant sempre a l’espai complex. D’aquesta manera, la cinemàtica directa del robot s’ha modelat amb variables complexes per tal de dissenyar el controlador no lineal i poder analitzar el seu rendiment i estudiar el potencial d’aquest nou enfocament en aquest camp d’aplicació. A més, s’han dissenyat també tres controladors (un control per mode de lliscament estàndard, un PID i un control per realimentació d’estat) per a poder analitzar i comparar el controlador principal (control per mode de lliscament complex) amb altres solucions i, d’aquesta manera, estudiar les seves possibles avantatges i inconvenients. Tots els controladors s’analitzen i comparen fent servir Matlab i se simulen amb Simulink, estudiant els resultats obtinguts fent una anàlisi qualitativa i quantitativa basada en uns Indicadors Clau de Rendiment (KPIs). Finalment, tots els resultats obtinguts durant el desenvolupament del projecte es re- sumeixen, discuteixen i presenten amb les conclusions extretesLa robótica y los robots manipuladores son conceptos que actualment se contemplan como temas habituales en muchas industrias. De todas maneras, se trata de campos relativa- mente nuevos en la ingeniería e incluyen diversas especialidades como la matemática i la ingeniería mecánica o eléctrica. Durante estas últimas décadas, el desarrollo de estos robots y sus técnicas de control han crecido considerablemente, llegando a tener un amplio conocimiento sobre su comportamiento y los algoritmos de control que les permiten realizar sus tareas con bajo error y gran rendimiento. Este proyecto presenta una estrategia nueva en ingeniería de control para el campo de la robótica, consistente en una extensión de un controlador en modo deslizante (sliding mode control, en inglés) a un dominio de valores complejos. Este controlador permite seguir la posición final de la herramienta de un manipulador plano de 2 eslabones sin el uso directo de la cinemática inversa y trabajando siempre en el espacio complejo. De esta manera, la cinemática directa del efector final del robot se modela con variables complejas para diseñar el controlador no lineal y poder analizar su rendimiento y estudiar el potencial de este nuevo enfoque en este campo de aplicación. Además, también se han disseñado tres controladors (un control en modo deslizante, un PID y un control por realimentación de estado) para poder analizar y comparar el controlador principal (un control en modo deslizante complejo) con otras soluciones y, de esta manera, estudiar sus posibles ventajas e inconvenientes. Todos los controladores se analizan y comparan usando Matlab y se simulan con Simulink, estudiando los resultados obtenidos con un análisis cualitativo y cuantitativo basado en unos Indicadores Clave de Rendimiento (KPIs). Finalmente, todos los resultados obtenidos durante el desarrollo del proyecto se resumen, discuten y presentan junto a las conclusiones extraída