Experimental comparison of control strategies for trajectory tracking for mobile robots

The purpose of this paper is to implement, test and compare the performance of different control strategies for tracking trajectory for mobile robots. The control strategies used are based on linear algebra, PID controller and on a sliding mode controller. Each control scheme is developed taking into consideration the model of the robot. The linear algebra approaches take into account the complete kinematic model of the robot; and the PID and the sliding mode controller use a reduced order model, which is obtained considering the mobile robot platform as a black-box. All the controllers are tested and compared, firstly by simulations and then, by using a Pioneer 3DX robot in field experiments.Fil: Capito, Linda. Escuela Politécnica Nacional; EcuadorFil: Proaño, Pablo. Escuela Politécnica Nacional; EcuadorFil: Camacho, Oscar. Escuela Politécnica Nacional; EcuadorFil: Rosales, Andrés. Escuela Politécnica Nacional; EcuadorFil: Scaglia, Gustavo Juan Eduardo. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentin

Sliding mode control applied in trajectory-tracking of WMRs and autonomous vehicles

Tese de doutoramento apresentada à Fac. de Ciências e Tecnologia da Universidade de CoimbraThe thesis is structured as follows: • Chapter 2: Trajectory tracking problems are summarized. • Chapter 3: Kinematic and dynamic modeling of theWMRs and car-like robots are presented. • Chapter 4: The concept of sliding mode are first introduced. Then the fundamentals of SMC are summarized, including basic definitions, methods of sliding surface and control law design, robustness properties and the methods on handling chattering problems. New sliding-mode trajectory-tracking and slidingmode path-following controllers for WMRs and car-like vehicles, are also proposed in this chapter. • Chapter 5: The trajectory/path planning are developed, including the velocity profile. • Chapter 6: A model with two freedom degrees is considered for the HNC model. The user comfort is examined not only in the time domain, but also in the frequency domain. • Chapter 7: Experimental results obtained with the implementation of the proposed controllers in RobChair are summarized and discussed. • Chapter 8: Finally, conclusions are drawn and some suggestions for future work are provided

Perception Based Navigation for Underactuated Robots.

Robot autonomous navigation is a very active field of robotics. In this thesis we propose a hierarchical approach to a class of underactuated robots by composing a collection of local controllers with well understood domains of attraction. We start by addressing the problem of robot navigation with nonholonomic motion constraints and perceptual cues arising from onboard visual servoing in partially engineered environments. We propose a general hybrid procedure that adapts to the constrained motion setting the standard feedback controller arising from a navigation function in the fully actuated case. This is accomplished by switching back and forth between moving "down" and "across" the associated gradient field toward the stable manifold it induces in the constrained dynamics. Guaranteed to avoid obstacles in all cases, we provide conditions under which the new procedure brings initial configurations to within an arbitrarily small neighborhood of the goal. We summarize with simulation results on a sample of visual servoing problems with a few different perceptual models. We document the empirical effectiveness of the proposed algorithm by reporting the results of its application to outdoor autonomous visual registration experiments with the robot RHex guided by engineered beacons. Next we explore the possibility of adapting the resulting first order hybrid feedback controller to its dynamical counterpart by introducing tunable damping terms in the control law. Just as gradient controllers for standard quasi-static mechanical systems give rise to generalized "PD-style" controllers for dynamical versions of those standard systems, we show that it is possible to construct similar "lifts" in the presence of non-holonomic constraints notwithstanding the necessary absence of point attractors. Simulation results corroborate the proposed lift. Finally we present an implementation of a fully autonomous navigation application for a legged robot. The robot adapts its leg trajectory parameters by recourse to a discrete gradient descent algorithm, while managing its experiments and outcome measurements autonomously via the navigation visual servoing algorithms proposed in this thesis.Ph.D.Electrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58412/1/glopes_1.pd

Semi-autonomous robotic wheelchair controlled with low throughput human- machine interfaces

For a wide range of people with limited upper- and lower-body mobility, interaction with robots remains a challenging problem. Due to various health conditions, they are often unable to use standard joystick interface, most of wheelchairs are equipped with. To accommodate this audience, a number of alternative human-machine interfaces have been designed, such as single switch, sip-and-puff, brain-computer interfaces. They are known as low throughput interfaces referring to the amount of information that an operator can pass into the machine. Using them to control a wheelchair poses a number of challenges. This thesis makes several contributions towards the design of robotic wheelchairs controlled via low throughput human-machine interfaces: (1) To improve wheelchair motion control, an adaptive controller with online parameter estimation is developed for a differentially driven wheelchair. (2) Steering control scheme is designed that provides a unified framework integrating different types of low throughput human-machine interfaces with an obstacle avoidance mechanism. (3) A novel approach to the design of control systems with low throughput human-machine interfaces has been proposed. Based on the approach, position control scheme for a holonomic robot that aims to probabilistically minimize time to destination is developed and tested in simulation. The scheme is adopted for a real differentially driven wheelchair. In contrast to other methods, the proposed scheme allows to use prior information about the user habits, but does not restrict navigation to a set of pre-defined points, and parallelizes the inference and motion reducing the navigation time. (4) To enable the real time operation of the position control, a high-performance algorithm for single-source any-angle path planning on a grid has been developed. By abandoning the graph model and introducing discrete geometric primitives to represent the propagating wave front, we were able to design a planning algorithm that uses only integer addition and bit shifting. Experiments revealed a significant performance advantage. Several modifications, including optimal and multithreaded implementations, are also presented

Controle por modo deslizante de robôs móveis sobre rodas

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia de Automação e Sistemas, Florianópolis, 2013O controle de robôs móveis não holonômicos é um problema para o qual existem lacunas a serem preenchidas. As principais técnicas de controle têm desempenho limitado no tocante à robustez e implementação prática e ainda dificuldades no tratamento de restrições não holonômicas. O controle por modo deslizante é uma técnica que se mostra bastante adequada para tratar este problema, devido a sua característica de oferecer robustez restringindo o sistema. Todavia, a implementação prática da sua forma clássica, o controle por modos deslizantes de primeira ordem, sofre com efeitos de chattering, devido à excitação de dinâmicas rápidas negligenciadas e a limitação na frequência de chaveamento do sinal de controle. Algumas soluções conhecidas para compensar o chattering têm como desvantagem a redução de robustez. Uma técnica de controle por modo deslizante de segunda ordem é considerada como solução, pois minimiza o chattering mantendo suas propriedades de robustez. Trata-se do algoritmo super- twisting que além das características enumeradas, possui implementação simples e tem bom desempenho numérico. Neste trabalho, aborda-se o problema de controle de rastreamento de trajetória para um robô móvel sujeito a restrições não holonômicas cuja representação de estado é feita com um modelo cinemático em cascata com um modelo dinâmico. A solução proposta nesta tese é a síntese de uma estrutura de controle composta por um controlador cinemático e um controlador dinâmico. O controlador cinemático é sintetizado com a técnica de controle super-twisting e tem como principal produto restrições que ao serem impostas ao sistema garantem o rasteamento robusto de trajetórias. Para isso, gera um sinal de controle em velocidade a ser rastreado pelo controlador dinâmico, que consiste de uma lei de controle por dinâmica inversa com um controlador externo proporcional e derivativo (PD). O controle PD auxilia na redução de chattering, pois sua ação diminui a influência das dinâmicas negligenciadas. Para ilustrar as características dos controladores propostos, são apresentados resultados de simulação e experimentos obtidos em ensaios com um robô móvel sobre rodas diferencial de médio porte The control of mobile robots is still an open problem. The main control techniques have limited performance with respect to robustness and practical implementation and yet some difficulties in handlind nonholonomic restrictions. The sliding mode control is a technique that proves to be quite adequate to address this problem, due to its characteristic of offering robustness by constraining the system. However, the practical implementation of the classic form of this technique, the first order sliding mode control, suffers from chattering effects, due to the excitation of neglected fast dynamic and frequency limitation of the switching control signal. Some known solutions to overcome the chattering has the disadvantage of reducing the ideal robustness of the technique. A second order sliding mode control technique is considered as a solution since it minimizes this problem maintaining its robustness properties. This is the super-twisting algorithm that in addition to the features listed, its implementation is simple and has good numerical performance. This work addresses the trajectory tracking control problem for a mobile robot subject to nonholonomic constraints and represented in the state space by a kinematic model in cascade with a dynamic model. The proposed solution in this thesis is the synthesis of a control structure comprising a kinematic controller and a dynamic one. The kinematic controller is designed with the super-twisting control technique and has as main product restrictions that when imposed to the system ensure the robust trajectory tracking. For that, it generates a velocity control signal to be tracked by the dynamic controller, which consists of an inverse dynamic control law with proportional plus derivative (PD) control. The additional PD control law plays an important role in assisting in the reduction of chattering, as its action decreases the influence of neglected dynamics. To illustrate the characteristics of the proposed controllers, simulation and also experimental results are obtained in trials with a differential wheeled mobile robot

Control Methods for Compensation and Inhibition of Muscle Fatigue in Neuroprosthetic Devices

For individuals that suffer from paraplegia activities of daily life are greatly inhibited. With over 5,000 new cases of paraplegia each year in the United States alone there is a clear need to develop technologies to restore lower extremity function to these individuals. One method that has shown promise for restoring functional movement to paralyzed limbs is the use of functional electrical stimulation (FES), which is the application of electrical stimulation to produce a muscle contraction and create a functional movement. This technique has been shown to be able to restore numerous motor functions in persons with disability; however, the application of the electrical stimulation can cause rapid muscle fatigue, limiting the duration that these devices may be used. As an alternative some research has developed fully actuated orthoses to restore motor function via electric motors. These devices have been shown to be capable of achieving greater walking durations than FES systems; however, these systems can be significantly larger and heavier. To develop smaller and more efficient systems some research has explored hybrid neuroprostheses that use both FES and electric motors. However, these hybrid systems present new research challenges. In this dissertation novel control methods to compensate/inhibit muscle fatigue in neuroprosthetic and hybrid neuroprosthetic devices are developed. Some of these methods seek to compensate for the effects of fatigue by using fatigue dynamics in the control development or by minimizing the amount of stimulation used to produce a desired movement. Other control methods presented here seek to inhibit the effects of muscle fatigue by adding an electric motor as additional actuation. These control methods use either switching or cooperative control of FES and an electric motor to achieve longer durations of use than systems that strictly use FES. Finally, the necessity for the continued study of hybrid gait restoration systems is facilitated through simulations of walking with a hybrid neuroprosthesis. The results of these simulations demonstrate the potential for hybrid neuroprosthesis gait restoration devices to be more efficient and achieve greater walking durations than systems that use strictly FES or strictly electric motors

TOWARDS SUSTAINABLE AUTONOMOUS VEHICLES

Ph.DDOCTOR OF PHILOSOPH