No description available.

PURPOSE. To determine the effects of blurring vision on whole-body center-of-mass (CM) dynamics and foot-clearance parameters in elderly individuals performing a single step up to a new level. METHODS. Twelve healthy subjects (mean age, 72.3 ±4.17 years) performed a single step up to a new level (heights of 73 and 146 mm). Trials were undertaken with vision optimally corrected and with vision diffusively blurred by light-scattering lenses (cataract simulation). CM and foot-clearance parameter data were assessed by analyzing data collected by a five-camera, three-dimensional (3-D) motion analysis system. RESULTS. When vision was blurred, subjects took 11% longer to execute the stepping task (P < 0.05), mediolateral displacement of the point of application of the ground reaction force vector (i.e., weighted average of all pressures over the area in contact with the ground; the so called center of pressure, CP) decreased from 37.6% of stance width to 28.3% (P < 0.01), maximum distance between the mediolateral position of the CM and CP decreased by 9.8 mm (P < 0.01), and toe clearance (distance between tip of shoe and edge of step) increased in both the horizontal (28%) and vertical (19%) direction (P < 0.05). CONCLUSIONS. These findings suggest that when vision was blurred, subjects used a twofold safety-driven adaptation: First, to increase dynamic stability they ensured that the horizontal position of their CM was kept close to the center of the base of support and second, they increased horizontal and vertical toe clearance while swinging their lead limb forward to reduce the risk of tripping.

Each year there is an increasing incidence of slip and fall accidents, especially among the elderly population. Existing evidence has identified several aging effects related to slip and fall accidents, yet, the causes of these accidents with advancing age are still little known. The objective of this research was to investigate the factors influencing the initial phase of unexpected slips and falls in younger and older individuals. More specifically, the relationship between ankle strength, the ankle joint power to transfer the whole body center-of-mass during normal gait, and the likelihood of slip-induced falls was identified. The walking experiment and the ankle strength tests were conducted in the Locomotion Research Laboratory, Virginia Tech. Fourteen old (67-79 years old) and 14 young (19-35 years old) individuals participated in this study (7 male and 7 female for each age group).Within a subsequent 20-minute session of natural walking on a linear track, kinematic and kinetic data were collected synchronously. A slippery surface was introduced to the participant on the purpose of unexpected slip event. The ankle strength tests were performed using a dynamometer. The results indicated that ankle strength degradation in older individuals was related to the outcome of slips (i.e., higher frequency of falls). The results also indicated that older individuals' RCOF was less than their younger counterparts. However, older individuals fell more often than younger individuals. It is concluded that friction demand characteristics may not be a total deterministic factor of fall accidents. Thus, the further research should focus not only on the dynamic of slips, but also on the dynamics of falls.</p> / Master of Science

No description available.

Avant de pouvoir interagir avec l'homme, les robots humanoïdes doivent encore être largement améliorés, tant au niveau de leur modélisation, de leur commande que de leur conception. Contrairement aux robots manipulateurs la notion de centre de masse est prédominante chez les robots humanoïdes et sera au centre de la gestion de leur équilibre. C'est donc dans ce cadre que s'inscrit cette thèse dont le but est de proposer une modélisation précise du centre de masse des robots humanoïdes dont la complexité ne cesse d'augmenter. En effet les modèles utilisés aujourd'hui pour définir la trajectoire du centre de masse sont des modèles simplifiés des robots humanoïdes. Les travaux de cette thèse s'articulent autour de trois contributions majeures : la modélisation cinématique et dynamique ainsi que l'estimation du centre de masse de robots humanoïdes. La première contribution propose une transformation de la structure arborescente de l'humanoïde en une chaîne virtuelle série localisant son centre de masse et permettant une commande cinématique adaptée de ce dernier. La dynamique du robot est ensuite exprimée en son centre de masse permettant ainsi une description exacte de ses accélérations. À ce titre, le concept de manipulabilité dynamique du centre de masse est introduit. Enfin grâce à la modélisation sous forme de chaîne virtuelle, une méthodologie qui s'impose aujourd'hui comme référence dans le domaine de l'estimation du centre de masse chez l'humain est proposée. De nombreuses expérimentations illustrent tout au long de cette thèse l'application et l'utilité de ces travaux. / Before they can interact with men, humanoid robots must be strongly enhanced in their modeling, their control and their design. Contrary to manipulator robots, the notion of center of mass is predominant in humanoid robots and will be central to the management of their balance. In this context, this thesis aims to provide accurate modeling of the center of mass of humanoid robots, whose complexity is increasing. Indeed, the models used today to determine the trajectory of center of mass are simplified models of humanoid robots. The works of this thesis revolve around three major contributions : kinematics and dynamics modeling as well as the estimation of the center of mass of humanoid robots. The first part proposes a transformation of the tree structure of the humanoid in a virtual serial chain locating its center of mass and allowing an adapted control of the latter. The dynamics of the robot is then expressed in the center of mass space allowing an accurate description of its acceleration. As such, the concept of dynamic manipulability of the center of mass is introduced. Finally, through the modeling in a virtual chain, a methodology that is today a reference in the field of center of mass estimation in humans is proposed. Many experiments show throughout this thesis the application and usefulness of this work.

Certains besoins de santé spécifiques ont contribué au développement du travail présenté ici, en particulier dans le domaine de la kinésithérapie dans lequel l’étude de l’équilibre postural est étudiée. Les solutions qui existent aujourd'hui sur le marché sont coûteuses, disponibles uniquement dans les grands hôpitaux ou dans des salles dédiées, avec un faible taux de fréquentation de la population, principalement dans des endroits plus éloignés des grands centres urbains. Ce travail a été développé en collaboration avec une équipe constituée de kinésithérapeutes, de chercheurs en génie électrique et en génie mécanique du laboratoire G-SCOP, Grenoble INP, Institut d’Ingénierie, Univ. Grenoble Alpes, France. Cette équipe cherche des solutions à faible coût qui répondent aux besoins de la société en général, en mettant l'accent sur la santé, mais également sur la vulgarisation scientifique, en diffusant ses travaux lors de manifestations de type fête de la Sciences dans la région et pour la communauté. Les travaux ont débuté avec une plateforme de force développée en 2016, conjointement par des chercheurs de l'UNESP (une Université de l'état Sao Paulo au Brésil) et du laboratoire G-SCOP. A cette solution a été ajoutée une nouvelle interface électronique, développée dans le but de fournir des informations sur le déplacement du centre de pression du patient. Un mécanisme a également été mis en place pour assurer la synchronisation entre les informations capturées par les capteurs installés sur la plate-forme et un capteur Microsoft Kinect. De nouveaux outils logiciels ont été proposés pour capturer et analyser les résultats. Le traitement des données permet de créer un modèle tridimensionnel détaillé contenant la cinématique de plusieurs articulations du corps humain et leur comportement respectif en fonction du temps. La mise en œuvre du capteur Kinect synchronisé avec la plate-forme de force permet de comparer le Centre de Pression avec le Centre de masse en vue de proposer un outil plus léger et moins cher à la communauté des praticiens hospitaliers. / Some specific health needs contributed to the development of the work presented here, especially in Physical Therapy in which the Postural Equilibrium is studied. The solutions that exist today in the market are of expensive, available only in large hospitals or in dedicated rooms, with low index of attendance to the population, mainly in places more distant of the great urban centers. This work was developed in cooperation with a team constituted of Phisiotherpists, Electrical Engineering and Mechanical Engineering from of the G-SCOP Laboratory, Grenoble INP, Institute of Engineering Univ. Grenoble Alpes, France. This team seeks low cost solutions that meet the needs of society in general, with a focus on health, but also with a focus on the popularization of science, disseminating its work in basic schools in the region and also in the community. The work began with a strength platform developed in 2016, jointly by researchers from UNESP, Sao Paulo, Brasil, and the G-SCOP Laboratory. To this solution was added a new electronic interface, developed with the purpose of providing information on the displacement of the patient pressure center. A mechanism was also implemented to ensure synchronization between information captured by sensors installed on the platform and a Microsoft Kinect sensor. New software tools were developed to capture and analyze the results. The data treatment allows the creation of a detailed three-dimensional model, containing the kinematics of several joints of the human body and their respective positional behavior, as a function of time. With the implementation of the Kinect sensor, synchronised with the force platform, it is also possible to evaluate the kinematic and positional biomechanical parameters.

In this thesis, the dynamic modeling of a wheelchair-human system is performed, and the effects of steering action and sudden slope changes along the path on the system stability are analyzed for different road and driving conditions. For the cases where the wheelchair system is unstable three methods are proposed for stability augmentation. This study is performed to improve the stability of the wheelchair system under varying road conditions so as to increase the limit of independency for wheelchair users and enhance their life quality. Two separate mathematical models are obtained for the wheelchair driven on constant sloped and changing sloped roads. Matlab Simulink models are constructed with the obtained mathematical models and control structure. The stability of the system is analyzed by case studies and it is seen that the system is unstable in some of these cases. Three methods are used for enhancement of the stability. One is the speed reduction via joystick module during steep turns, by which the speed of the wheelchair is reduced automatically for a safe steering, but the wheelchair follows the desired course. The second method is the use of a shape filter in order to obtain a less jerky response for the speed. As a final method, the center of mass of the wheelchair-human system is shifted gently in a controlled manner to the side where the reaction force on the wheels decreases.

No description available.

Many landing sites of scientific interest on Mars including most of the Southern Hemisphere at elevations above 2km Mars Orbiter Laser Altimeter reference are inaccessible due to current limitations in precision entry guidance and payload deceleration. Precision guidance and large payload deceleration is challenging due to the thin Martian atmosphere, large changes in free stream conditions during entry, and aerothermal and aerodynamic instability concerns associated with control systems with direct external flow field interaction. Such risks have descoped past Mars missions to unguided entry with the exception of Mars Science Laboratory's (MSL) bank angle guidance. Consequently, prior to MSL landing ellipses were on the order of 100's of km. MSL has approached the upper limit of payload deceleration capability for rigid, blunt body sphere cone aeroshells used on all successful Mars entry missions. Hypersonic Inflatable Aerodynamic Decelerators (HIADS) are in development for larger payload deceleration capability through inflated aeroshell diameters greater than rigid aeroshells constrained by the launch rocket diameter, but to date there has been limited dynamics, control, and guidance development for their use on future missions. This dissertation develops internal moving mass actuator (IMMA) control systems for improving Mars precision entry guidance of rigid capsules and demonstrating precision guidance capability for HIADs. IMMAs provide vehicle control moments without direct interaction with the external flow field and can increase payload mass delivered through reducing propellant mass for control and using portions of the payload for the IMMAs. Dynamics models for entry vehicles with rotation and translation IMMAs are developed. IMMA control systems using the models are developed for two NASA vehicle types: a 2.65 m, 602 kg Mars Phoenix-sized entry capsule and an 8.3 m, 5.9 metric ton HIAD approaching payload requirements for robotic precursor missions for future human missions. Linear Quadratic controllers with integral action for guidance command tracking are developed for translation and rotation IMMA configurations. Angle of attack and sideslip guidance laws are developed as an alternative to bank angle guidance for decoupling range and cross-range control for improved precision entry guidance. A new variant of the Apollo Earth return terminal guidance algorithm is implemented to provide the closed-loop angle of attack range control commands. Nonlinear simulations of the entire 8 degree of freedom closed-loop systems demonstrate precision guidance to nominal trajectories and final targets for off-nominal initial entry conditions for flight path angle, range, cross-range, speed and attitude. Mechanical power studies for IMMA motion show rotation IMMA require less total mechanical power than translation actuators, but both systems have low nominal mechanical power requirements (below 100 Watts). Precision guidance for both systems to terminal targets greater than 38 km down-range from an open-loop ballistic entry is shown for low mechanical power, low CM displacement, (< 4.5 in) and at low internal velocities (< 2 in/s) over significant dynamic pressure changes. The collective precision guidance results and low mechanical power requirements show IMMA based entry guidance control systems constitute a promising alternative to thruster based control systems for future Mars landers. / Ph. D.

The versatility of the fish to adapt to diverse swimming requirements has attracted the attention of researchers in studying bioinspired propulsion for developing efficient underwater robotics. The tail/caudal fin is a major source of thrust generation and is believed that the fish modulates its fin stiffness to optimize the propulsive performance. Inspired by the stiffness modulation of fish fins, the objective of this research is to predict and evaluate the effect of flexibility on propulsive performance of flapping fins. The stiffness of the fins vary along their length and optimization studies have been performed to predict the stiffness profiles that maximize performance. Experiments performed on the real fish caudal fins to measure the stiffness variation along their length validate the theoretical optimal stiffness profiles and provide an insight about the evolution of fish fins for optimal performance. Along with the fin stiffness, the stiffness of the joint (caudal peduncle) connecting the fish body to the tail plays a major role in the generation of thrust. The numerical and experimental investigation has shown that there exists an optimal combination of fin and joint stiffness for each operating condition, thus providing the motivation for active stiffness control during locomotion to optimize efficiency. Inspired by nature's ability to modulate stiffness and shape for different operating conditions, an investigation has been carried out on active control of flapping foils for thrust tailoring using Macro Fiber Composites (MFCs). It has been observed that the performance can be enhanced by controlling the deformation, and distributed actuation along fin produces maximum performance through proper selection of the phase difference between heaving and voltage. Flapping fins produce forces which are oscillatory in nature causing center of mass (COM) oscillations of the attached bodies posing problems of control and maneuverability. Optimization studies have revealed that flexibility of the fin plays a major role in reducing the COM oscillations along with the other operating parameters. Based on these studies, the design principles and guidelines that control the performance have been proposed which aid in the development of aerial and underwater robotic vehicles. Additionally, these studies provide some insight in to how fish might modulate its stiffness based on the requirements. / Ph. D.