Mimicking human motion with a humanoid robot can prove to be useful for studying gaits, designing better prostheses, or assisting the elderly or disabled. Directly mimicking and implementing a motion of a human on a humanoid robot may not be successful because of the different dynamic characteristics between them, which may cause the robot to fall down due to instability. Using the Zero Moment Point as the stability criteria, this work proposes an Analytical Motion Filter (AMF), which stabilizes a reference motion that can come from human motion capture data, gait synthesis using kinematics, or animation software, while satisfying common constraints. In order to determine how the AMF stabilized a motion, the different kinds of instabilities were identified and classified when examining the reference motions. The different cases of instability gave more insight as to why a particular motion was unstable: the motion was too fast, too slow, or inherently unstable. In order to stabilize the gait two primary methods were utilized: time and spatial scaling. Spatial scaling scaled the COM trajectory down towards a known stable trajectory. Time scaling worked similarly by changing the speed of the motion, but was limited in effectiveness based on the types of instabilities in the motion and the coupling of the spatial directions. Other constraints applied to the AMF and combinations of the different methods produced interesting results that gave more insight into the stability of the gait. The AMF was tested using both simulations and physical experiments using the DARwIn miniature humanoid robot developed by RoMeLa at Virginia Tech as the test platform. The simulations proved successful and provided more insight to understanding instabilities that can occur for different gait generation methods. The physical experiments worked well for non-walking motions, but because of insufficient controllability in the joint actuators of the humanoid robot used for the experiment, the high loads during walking motions prevented them from proper testing. The algorithms used in this work could also be expanded to legged robots or entirely different platforms that depend on stability and can use the ZMP as a stability criterion. One of the primary contributions of this work was showing that an entire reference motion could be stabilized using a single set of closed form solutions and equations. Previous work by others considered optimization functions and numeric schemes to stabilize all or a portion of a gait. Instead, the Analytical Motion Filter gives a direct relationship between the input reference motion and the resulting filtered output motion. / Ph. D.

The objectives of this study were to implement force sensors on the feet of a bipedal robot and analyze their response at different conditions. The data will be used to design a control strategy for the robot. The powered joints of the robot are driven by linear motors. A force sensor circuit was made and calibrated with different kinds of weight. A trajectory generator and inverse kinematics calculator for the robot were made to control the robot walking movement in an open-loop manner. The force data were taken at a certain period of time when the robot was in a standing position. Experiments with external disturbances were also performed on the robot. The ZMP position and mass of the robot were calculated by using the data of force sensors. The force sensor circuit was reliable in taking and handling the data from the sensor although the noise from the motors of the robot was present. / <p>Validerat; 20111115 (anonymous)</p>

No description available.

Bipedal locomotion in humanoid robots is a very challenging problem within the field of robot locomotion. In this thesis, we propose and demonstrate an omni-directional walking engine that achieves stable walking using feedback from an inertial measurement unit. Our walking engine generates gaits for which the zero moment point is on the center of the supporting foot. The mechanical structure of CHARLI-L, a humanoid robot used as our test platform in this thesis, is first introduced by describing the inverse kinematics of its legs. The principles of the omni-directional gait generator that creates walking motions and overcomes the robot's mechanical deficiencies is discussed. We develop and implement two kinds of feedback controllers; one is the gait feedback controller and the other is the joint feedback controller. Both feedback controllers use proportional-derivative of the angle of the pelvis from an inertial measurement unit. The results of the experiments are presented the efficacy of our proposed walking engine. / Master of Science

Os dispositivos robóticos bípedes tem um grande potencial de aplicações tanto comerciais como para pesquisa. Dentre as presentes lacunas existentes que limitam a sua aplicabilidade prática tem um destaque especial a incapacidade de realizar uma marcha estável, robusta, versátil e eficiente no ponto de vista energético. No presente estado da arte, existem três principais estratégias de abordagem para o problema e algumas de suas implementações obtiveram sucesso em satisfazer pelo menos um dos requisitos listados, porém nunca todos eles de forma simultânea. Dentro deste cenário, este trabalho se propôs desenvolver um novo critério de estabilidade para marcha bípede que possibilite marchas versáteis, robustas e eficientes. Inicialmente foi realizada uma avaliação de diversos simuladores de código aberto e o Simbody foi definido como o mais apropriado para ser utilizado no desenvolvimento das simulações dinâmicas realizadas nesta Tese. Uma toolbox de MATLAB para auxiliar nos cálculos cinemáticos e dinâmicos foi desenvolvida em conjunto com um módulo de Inter Process Communication para realizar a comunicação entre o MATLAB e o simulador. Foi realizado um estudo da marcha bípede, implementando e avaliando as estratégias do Zero Moment Point e do Limit CycleWalking. Este estudo resultou numa proposta de controlador não linear comutado para robôs em Ciclo Limite. Na procura de um novo critério de estabilidade foi abordado o estudo da marcha humana. Um procedimento para identificar os mecanismos que controlam a estabilidade da marcha humana é analisar a mesma sob perturbações, como tropeços, ou na ultrapassagem de obstáculos. Na literatura existiam bastantes referências sobre este tema, porém, faltou uma comparação da marcha humana sob diferentes condições de visão com a marcha de robôs que utilizam o ZMP. Foi descoberto que os seres humanos privados de visão têm uma estratégia de ultrapassagem de obstáculos semelhante a um robô com ZMP. A partir do conhecimento adquirido deste estudo é proposto e formulado um novo critério de estabilidade, o Step Viability, inspirado na marcha humana e no conceito de N-Step Capturability. O Step Viability baseia-se na definição de restrições que garantem a viabilidade de realizar passos futuros que garantam a convergência para um ponto fixo em tempo finito. O critério foi implementado utilizando-se uma otimização de trajetória multi-fase. Múltiplos testes foram realizados utilizando-se o modelo Compass Gait com diferentes parâmetros (distribuição de massa, torque máximo disponível), com diferentes inclinações e com vários padrões de marcha desejados (periódico, aumento uniforme e até aleatório não periódico). Adicionalmente o critério foi testado em um modelo de 5 segmentos, sintetizando uma marcha com variação tanto linear quanto aleatória. O critério foi bem-sucedido na geração de uma marcha estável em todos os testes e os resultados foram consistentes. A marcha pode ser sintetizada completamente desacoplada do critério de estabilidade, e o modelo renunciou automaticamente do padrão desenhado em favor da estabilidade. / Bipedal robots present a great potential for both commercial and research applications. However, there are some drawbacks that limit their applicability in the real world. The most prominent is the inability to perform a stable, robust, versatile and efficient gait. There are three main state of the art strategies to approach this problem. However, none of them has been successful in satisfying all the listed requirements simultaneously. In this context, this work conducted a study of bipedal gait, both in humans and robots, in order to implement and evaluate existing stability strategies. As a first step, an evaluation of several open source simulators was performed and Simbody was chosen as the most adequate for the dynamic simulations carried out in this Thesis. A MATLAB toolbox to help in the kinematic and dynamic calculations was developed in conjunction with a module of an Inter Process Communication to perform the communication between MATLAB and the simulator. A bipedal gait study was carried out, implementing and evaluating Zero Moment Point and Limit Cycle Walking strategies. This study resulted in a proposed nonlinear switched controller for Limit Cycle robots. In the search for a new stability criterion, human gait was analyzed. A procedure to identify the mechanisms controlling human gait stability is to analyze gait under disturbances such as stumbling or overcoming obstacles. In the literature, there were many references on this subject, however, there was a lack of comparison of the human gait under different vision conditions with the gait of robots that use the ZMP. It was found that vision-deprived humans have an obstacle crossing strategy similar to robots with ZMP. From the knowledge acquired from this study, it is proposed a novel stability criterion, the Step Viability, inspired on human gait and the N-Step Capturability concept. The Step Viability is based on the definition of constraints that ensure the viability of performing future steps that guarantee convergence to a fixed point in finite time. The criterion was implemented using a multi-phase trajectory optimization. Multiple tests were performed using the Compass Gait model with different parameters (mass distribution, maximum available torque), with different slopes and with several desired gait patterns (periodic, uniform increase and even random non-periodic). Additionally, the criterion was tested in a 5-links model, synthesizing a gait with both linear and random velocity variation. The criterion was successful on generating a stable gait in all the tests and the results presented consistent data. The gait could be designed completely uncoupled from the stability criterion, yet the model automatically renounced to follow the desired pattern in favor of maintaining stability.

Os dispositivos robóticos bípedes tem um grande potencial de aplicações tanto comerciais como para pesquisa. Dentre as presentes lacunas existentes que limitam a sua aplicabilidade prática tem um destaque especial a incapacidade de realizar uma marcha estável, robusta, versátil e eficiente no ponto de vista energético. No presente estado da arte, existem três principais estratégias de abordagem para o problema e algumas de suas implementações obtiveram sucesso em satisfazer pelo menos um dos requisitos listados, porém nunca todos eles de forma simultânea. Dentro deste cenário, este trabalho se propôs desenvolver um novo critério de estabilidade para marcha bípede que possibilite marchas versáteis, robustas e eficientes. Inicialmente foi realizada uma avaliação de diversos simuladores de código aberto e o Simbody foi definido como o mais apropriado para ser utilizado no desenvolvimento das simulações dinâmicas realizadas nesta Tese. Uma toolbox de MATLAB para auxiliar nos cálculos cinemáticos e dinâmicos foi desenvolvida em conjunto com um módulo de Inter Process Communication para realizar a comunicação entre o MATLAB e o simulador. Foi realizado um estudo da marcha bípede, implementando e avaliando as estratégias do Zero Moment Point e do Limit CycleWalking. Este estudo resultou numa proposta de controlador não linear comutado para robôs em Ciclo Limite. Na procura de um novo critério de estabilidade foi abordado o estudo da marcha humana. Um procedimento para identificar os mecanismos que controlam a estabilidade da marcha humana é analisar a mesma sob perturbações, como tropeços, ou na ultrapassagem de obstáculos. Na literatura existiam bastantes referências sobre este tema, porém, faltou uma comparação da marcha humana sob diferentes condições de visão com a marcha de robôs que utilizam o ZMP. Foi descoberto que os seres humanos privados de visão têm uma estratégia de ultrapassagem de obstáculos semelhante a um robô com ZMP. A partir do conhecimento adquirido deste estudo é proposto e formulado um novo critério de estabilidade, o Step Viability, inspirado na marcha humana e no conceito de N-Step Capturability. O Step Viability baseia-se na definição de restrições que garantem a viabilidade de realizar passos futuros que garantam a convergência para um ponto fixo em tempo finito. O critério foi implementado utilizando-se uma otimização de trajetória multi-fase. Múltiplos testes foram realizados utilizando-se o modelo Compass Gait com diferentes parâmetros (distribuição de massa, torque máximo disponível), com diferentes inclinações e com vários padrões de marcha desejados (periódico, aumento uniforme e até aleatório não periódico). Adicionalmente o critério foi testado em um modelo de 5 segmentos, sintetizando uma marcha com variação tanto linear quanto aleatória. O critério foi bem-sucedido na geração de uma marcha estável em todos os testes e os resultados foram consistentes. A marcha pode ser sintetizada completamente desacoplada do critério de estabilidade, e o modelo renunciou automaticamente do padrão desenhado em favor da estabilidade. / Bipedal robots present a great potential for both commercial and research applications. However, there are some drawbacks that limit their applicability in the real world. The most prominent is the inability to perform a stable, robust, versatile and efficient gait. There are three main state of the art strategies to approach this problem. However, none of them has been successful in satisfying all the listed requirements simultaneously. In this context, this work conducted a study of bipedal gait, both in humans and robots, in order to implement and evaluate existing stability strategies. As a first step, an evaluation of several open source simulators was performed and Simbody was chosen as the most adequate for the dynamic simulations carried out in this Thesis. A MATLAB toolbox to help in the kinematic and dynamic calculations was developed in conjunction with a module of an Inter Process Communication to perform the communication between MATLAB and the simulator. A bipedal gait study was carried out, implementing and evaluating Zero Moment Point and Limit Cycle Walking strategies. This study resulted in a proposed nonlinear switched controller for Limit Cycle robots. In the search for a new stability criterion, human gait was analyzed. A procedure to identify the mechanisms controlling human gait stability is to analyze gait under disturbances such as stumbling or overcoming obstacles. In the literature, there were many references on this subject, however, there was a lack of comparison of the human gait under different vision conditions with the gait of robots that use the ZMP. It was found that vision-deprived humans have an obstacle crossing strategy similar to robots with ZMP. From the knowledge acquired from this study, it is proposed a novel stability criterion, the Step Viability, inspired on human gait and the N-Step Capturability concept. The Step Viability is based on the definition of constraints that ensure the viability of performing future steps that guarantee convergence to a fixed point in finite time. The criterion was implemented using a multi-phase trajectory optimization. Multiple tests were performed using the Compass Gait model with different parameters (mass distribution, maximum available torque), with different slopes and with several desired gait patterns (periodic, uniform increase and even random non-periodic). Additionally, the criterion was tested in a 5-links model, synthesizing a gait with both linear and random velocity variation. The criterion was successful on generating a stable gait in all the tests and the results presented consistent data. The gait could be designed completely uncoupled from the stability criterion, yet the model automatically renounced to follow the desired pattern in favor of maintaining stability.

This thesis introduces a new measure of balance for bipedal robotics called the foot placement estimator (FPE). To develop this measure, stability first is defined for a simple biped. A proof of the stability of a simple biped in a controls sense is shown to exist using classical methods for nonlinear systems. With the addition of a contact model, an analytical solution is provided to define the bounds of the region of stability. This provides the basis for the FPE which estimates where the biped must step in order to be stable. By using the FPE in combination with a state machine, complete gait cycles are created without any precalculated trajectories. This includes gait initiation and termination. The bipedal model is then advanced to include more realistic mechanical and environmental models and the FPE approach is verified in a dynamic simulation. From these results, a 5-link, point-foot robot is designed and constructed to provide the final validation that the FPE can be used to provide closed-loop gait control. In addition, this approach is shown to demonstrate significant robustness to external disturbances. Finally, the FPE is shown in experimental results to be an unprecedented estimate of where humans place their feet for walking and jumping, and for stepping in response to an external disturbance.

This thesis introduces a new measure of balance for bipedal robotics called the foot placement estimator (FPE). To develop this measure, stability first is defined for a simple biped. A proof of the stability of a simple biped in a controls sense is shown to exist using classical methods for nonlinear systems. With the addition of a contact model, an analytical solution is provided to define the bounds of the region of stability. This provides the basis for the FPE which estimates where the biped must step in order to be stable. By using the FPE in combination with a state machine, complete gait cycles are created without any precalculated trajectories. This includes gait initiation and termination. The bipedal model is then advanced to include more realistic mechanical and environmental models and the FPE approach is verified in a dynamic simulation. From these results, a 5-link, point-foot robot is designed and constructed to provide the final validation that the FPE can be used to provide closed-loop gait control. In addition, this approach is shown to demonstrate significant robustness to external disturbances. Finally, the FPE is shown in experimental results to be an unprecedented estimate of where humans place their feet for walking and jumping, and for stepping in response to an external disturbance.

Malgré le progrès de l'automatisation industrielle, les solutions robotiques ne sont pas encore couramment utilisées dans le secteur du génie civil. Plus spécifiquement, les tâches de ponçage, telles que le désamiantage, sont toujours effectuées par des opérateurs humains utilisant des outils électriques et hydrauliques classiques. Cependant, avec la diminution du coût relatif des machines par rapport au travail humain et les réglementations sanitaires strictes applicables à des travaux aussi risqués, les robots deviennent progressivement des alternatives crédibles pour automatiser ces tâches et remplacer les humains.Dans cette thèse, des nouvelles approches de contrôle de ponçage de surface sont élaborées. Le premier contrôleur est un contrôleur hybride position-force avec poignet conforme. Il est composé de 3 boucles de commande, force, position et admittance. La commutation entre les commandes pourrait créer des discontinuités, ce qui a été résolu en proposant une commande de transition. Dans ce contrôleur, la force de choc est réduite par la commande de transition proposée entre les modes espace libre et contact. Le second contrôleur est basé sur un modèle de ponçage développé et un contrôleur hybride adaptatif position-vitesse-force. Les contrôleurs sont validés expérimentalement sur un bras robotique à 7 degrés de liberté équipé d'une caméra et d'un capteur de force-couple. Les résultats expérimentaux montrent de bonnes performances et les contrôleurs sont prometteurs. De plus, une nouvelle approche pour contrôler la stabilité des manipulateurs mobiles en temps réel est présentée. Le contrôleur est basé sur le « zero moment point », il a été testé dans des simulations et il a été capable de maintenir activement la stabilité de basculement du manipulateur mobile tout en se déplaçant. En outre, les incertitudes liées à la modélisation et aux capteurs sont prises en compte dans les contrôleurs mentionnés où des observateurs sont proposés.Les détails du développement et de l'évaluation des différents contrôleurs proposés sont présentés, leurs mérites et leurs limites sont discutés et des travaux futurs sont suggérés. / Despite the advancements in industrial automation, robotic solutions are not yet commonly used in the civil engineering sector. More specifically, grinding tasks such as asbestos removal, are still performed by human operators using conventional electrical and hydraulic tools. However, with the decrease in the relative cost of machinery with respect to human labor and with the strict health regulations on such risky jobs, robots are progressively becoming credible alternatives to automate these tasks and replace humans.In this thesis, novel surface grinding control approaches are elaborated. The first controller is based on hybrid position-force controller with compliant wrist and a smooth switching strategy. In this controller, the impact force is reduced by the proposed smooth switching between free space and contact modes. The second controller is based on a developed grinding model and an adaptive hybrid position-velocity-force controller. The controllers are validated experimentally on a 7-degrees-of-freedom robotic arm equipped with a camera and a force-torque sensor. The experimental results show good performances and the controllers are promising. Additionally, a new approach for controlling the stability of mobile manipulators in real time is presented. The controller is based on zero moment point, it is tested in simulations and it was able to actively maintain the tip-over stability of the mobile manipulator while moving. Moreover, the modeling and sensors uncertainties are taken into account in the mentioned controllers where observers are proposed. The details of the development and evaluation of the several proposed controllers are presented, their merits and limitations are discussed and future works are suggested.