Parameter-Dependent Lyapunov Functions for Linear Systems With Constant Uncertainties

Robust stability of linear time-invariant systems with respect to structured uncertainties is considered. The small gain condition is sufficient to prove robust stability and scalings are typically used to reduce the conservatism of this condition. It is known that if the small gain condition is satisfied with constant scalings then there is a single quadratic Lyapunov function which proves robust stability with respect to all allowable time-varying perturbations. In this technical note we show that if the small gain condition is satisfied with frequency-varying scalings then an explicit parameter dependent Lyapunov function can be constructed to prove robust stability with respect to constant uncertainties. This Lyapunov function has a rational quadratic dependence on the uncertainties

Control of a BCI-based upper limb rehabilitation system utilizing posterior probabilities (BBA tabanlı üst uzuv rehabilitasyon sisteminin sonsal olasılık değerleri kullanılarak kontrolü)

In this paper, an electroencephalogram (EEG) based Brain-Computer Interface (BCI) is integrated with a robotic system designed to target rehabilitation therapies of stroke patients such that patients can control the rehabilitation robot by imagining movements of their right arm. In particular, the power density of frequency bands are used as features from the EEG signals recorded during the experiments and they are classified by Linear Discriminant Analysis (LDA). As one of the novel contributions of this study, the posterior probabilities extracted from the classifier are directly used as the continuous-valued outputs, instead of the discrete classification output commonly used by BCI systems, to control the speed of the therapeutic movements performed by the robotic system. Adjusting the exercise speed of patients online, as proposed in this study, according to the instantaneous levels of motor imagery during the movement, has the potential to increase efficacy of robot assisted therapies by ensuring active involvement of patients. The proposed BCI-based robotic rehabilitation system has been successfully implemented on physical setups in our laboratory and sample experimental data are presented

Time independent tracking using 2-D movement flow-based visual servoing

In this paper, the so-called 2-D movement flowbased visual servoing system is proposed, which allows the tracking of trajectories planned in the image space. This method is time-independent, which is useful when problems such as obstructions occur during the tracking. This method allows the tracking of image trajectories assuring the correct behaviour in the 3-D space and avoiding the limitations of the time-dependent systems used up to now for tracking trajectories. This aspect has allowed its application to manipulation tasks in which the trajectory can be obstructed during the tracking.This work is partially supported by the Spanish MCYT project “DESAURO: Desensamblado Automático Selectivo para Reciclado mediante Robots Cooperativos y Sistema Multisensorial” (DPI2002-02103)

Multi-AGV transport of a load: state of art and centralized proposal

[EN] An automatic guided vehicle is a battery powered fully automated industrial transport system. These vehicles are widely used in the industrial sector to substitute manual forklifts and conveyors. The challenge of using AGVs as transport agents in industrial environments goes through providing them with enough intelligence to develop collaborative tasks. Among these collaborative tasks the multi-AGV transport of one object is differentiated from the multi-object multi-AGV transport. This work presents the state of art of cooperative transport solutions of one object between several AGVs. The theoretical fundaments are revised and several proposals for its resolution are classified and described. Finally, an own proposal of one-object multi-AGV transport with omnidirectional AGVs based on centralized remote control is presented.[ES] Un vehículo de guiado automático (Automatic Guided Vehicle –AGV-en inglés) es un sistema de transporte industrial completamente automatizado y alimentado por baterías. Estos vehículos son ampliamente utilizados en el sector industrial para sustituir a carretillas manuales y cintas transportadoras. El reto de la utilización de AGVs como agentes de transporte en entornos industriales pasa por dotarles de la inteligencia suficiente para desarrollar tareas colaborativas. Dentro de estas tareas colaborativas se diferencia el transporte multi-AGV de un objeto del transporte multi-AGV de múltiples objetos. Este trabajo presenta el estado del arte de las soluciones de transporte cooperativo de un objeto entre varios AGVs. Para ello, se revisan los fundamentos teóricos y se clasifican y describen varias propuestas para su resolución. Finalmente se propone una solución de control remoto centralizado para el transporte de una carga con AGVs omnidireccionales.Este trabajo ha sido apoyado parcialmente por la Junta de Castilla y León bajo el proyecto 10/16/BU/0014 y la empresa ASTI Mobile Robotics.Espinosa, F.; Santos, C.; Sierra-García, JE. (2020). Transporte multi-AGV de una carga: estado del arte y propuesta centralizada. Revista Iberoamericana de Automática e Informática industrial. 18(1):82-91. https://doi.org/10.4995/riai.2020.12846OJS8291181Adăscăliţei, F., and Doroftei, I. 2011. Practical Applications for Mobile Robots based on Mecanum Wheels - A Systematic Survey. The Romanian Review Precision Mechanics, Optics & Mechatronics, nº 40.Alonso-Mora, J., Barker, S. and Rus, D. 2017. Multi-robot formation control and object transport in dynamic environments via constrained optimization. The International Journal of Robotics Research. 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Cooperative Mobile Robot Control Architecture for Lifting and Transportation of Any Shape Payload. Chapter book of Distributed Autonomous Robotic Systems pp 177-191. ISBN 978-4-431-55877-4. https://doi.org/10.1007/978-4-431-55879-8_13Hirata, Y., Kosuge, K., 2001. Motion Control of Distributed Robot Helpers Transporting a Single Object in Cooperation with a Human. Lecture Notes in Control and Information Sciences. Experimental robotics. SpringerVerlag. Pp. 313-322. ISBN 3-540-42104-1 https://doi.org/10.1007/3-540-45118-8_32Karim, N.A. and Ardestani, M.A. 2016. Takagi-Sugeno Fuzzy formation control of non-holonomic robots. 4th International Conference on Control, Instrumentation, and Automation (ICCIA), Qazvin, 2016, pp. 178-183. https://doi.org/10.1109/ICCIAutom.2016.7483157Kosuge, K., Oosumi, T., 1996. Decentralized Control of Multiple Robots Handling an Object. Proc. Of 1996 IEEE Int. Conf. on Intelligent Robots and Systems, pp.318-323.Kosuge, K., Sato., M., 1999. 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Passive Velocity Field Control (PVFC): Part II - Application to Contour Following

In contour following applications, the various degrees of freedom of a mechanical system have to be well coordinated, but very often, the speed at which the contour is followed is not critical. Moreover, in the context of machining, the system has to interact closely with its physical environment. When the contour following task is represented by a velocity field on the configuration manifold of the system, the coordination aspect of the problem is made explicit. The passive velocity field control (PVFC) scheme developed in the Part I companion paper [7] can then be applied to track the defined velocity field so that the desired contour is followed, and to ensure that the interaction of the closed-loop system with the physical environment is passive to enhance safety and stability. Unfortunately, for some contours, an encoding velocity field on the configuration manifold does not exist or is difficult to define and, as a consequence, the PVFC cannot be directly applied. For systems whose configuration manifolds are compact Lie groups and the desired contour is represented by a parameterized trajectory, a general methodology is developed, using a suspension technique, to define a velocity field on a manifold related to the configuration manifold of the system for which PVFC can be applied. With this strategy, timing along the contour can be naturally varied on-line by a self-pacing scheme so that the contour tracking performance can be improved. The experimental results for a 2 degree of freedom robot following a Lissajous contour illustrates and verifies the convergence and robustness properties of the PVFC methodology

Design, implementation and control of rehabilitation robots for upper and lower limbs

We present two novel rehabilitation robots for stroke patients. For lower limb stroke rehabilitation, we present a novel self-aligning exoskeleton for the knee joint. The primal novelty of the design originates from its kinematic structure that allows translational movements of the knee joint on the sagittal plane along with the knee rotation. Automatically adjusting its joint axes, the exoskeleton enables a perfect match between human joint axes and the device axes. Thanks to this feature, the knee exoskeleton is not only capable of guaranteeing ergonomy and comfort throughout the therapy, but also extends the usable range of motion for the knee joint. Moreover, this adjustability feature significantly shortens the setup time required to attach the patient to the robot, allowing more effective time be spend on exercises instead of wasting it for adjustments. We have implemented an impedance-type concept of the knee exoskeleton, experimentally characterized its closed-loop performance and demonstrated ergonomy and useability of this device through human subject experiments. To administer table top exercises during upper limb stroke rehabilitation, we present a novel Mecanum-wheeled holonomic mobile rehabilitation robot for home therapy. The device can move/rotate independently on its unlimited planar workspace to provide assistance to patients. We have implemented two different concepts of holonomic mobile platform based on different actuation and sensing principles: an admittance-type mobile robot and a mobile platform with series elastic actuation. The admittance-type robot is integrated with virtual reality simulations and can assist patients through virtual tunnels designed around nominal task trajectories. The holonomic platform with series elastic actuation eliminates the need for costly force sensors and enables implementation of closed loop force control with higher controller gains, providing robustness against imperfections in the power transmission and allowing lower cost drive components to be utilized. For contour following tasks with the holonomic platforms, we have synthesized passive velocity field controllers (PVFC) that ensure coordination and synchronization between various degrees of freedom of the patient arm, while letting patients to complete the task at their own preferred pace. PVFC not only minimizes the contour error but also ensures coupled stability of the human-in-the-loop system

Design and analysis of a brain-computer interface-based robotic rehabilitation system

In this thesis, we have investigated the effect of brain-computer interfaces (BCI) which enable direct communication between a brain and a computer, to increase the patient's active involvement to his/her task in the robotic rehabilitation therapy. We have designed several experimental paradigms using electroencephalography (EEG) based BCIs which can be used to extract information about arm movement imagery in the context of robotic rehabilitation experiments. In particular, we propose a protocol that extracts and uses information about the level of intention of the subject to control the robot continuously throughout a rehabilitation experiment. In this context we have developed and implemented EEG signal processing, learning and classiffication algorithms for o ine and online decision-making. We have used di erent types of controlling methods over the robotic system and examined the potential impact of BCI on rehabilitation, the effect of robotic haptic feedback on BCI, and information contained in EEG about the rehabilitation process. Our results verify that the use of haptic feedback through robotic movement improves BCI performance. We also observe that using BCI continuously in the experiment rather than only to trigger robotic movement may be preferable. Finally, our results indicate stronger motor imagery activity in BCI-based experiments over conventional experiments in which movement is performed by the robot without the subject's involvement

Smart Exercise Adaptive Control of a Three Degree of Freedom Upper-limb Manipulator Robot

An adaptive velocity field controller for robotic manipulators is proposed in this thesis. The control objective is to cause the user to exercise in a manner that optimizes a criterion related to the user’s mechanical power. The control structure allows for passive user-manipulator physical interaction while the adaptive algorithm identifies the user’s biomechanical characteristics as a linear Hill based force-velocity curve defined at each pose of a repetitive exercise motion i.e. a Hill surface. The study of such a surface allows for the characterization of maximal effort exercise tasks and subsequently the control of exercises that is unique to each user. This allows for the intelligent characterization of a user’s abilities such that repetitive exercises defined by velocity fields can be safely performed. Such a study involving a 3DOF manipulator operating in full 3D has not been conducted in literature to the best of author’s knowledge. The proposed control structure is verified through experimentation on a unimanual setup of the BURT rehabilitation manipulator system involving a single user. The manipulator system includes friction, actuator/sensor noise, and unmodelled dynamics