Symmetry restoring bifurcations and quasiperiodic chaos induced by a new intermittency in a vibro-impact system

This work was supported by National Natural Science Foundation of China (11272268, 11572263, and 11672249).Peer reviewedPublisher PD

Dynamic Modeling of the Dissipative Contact and Friction Forces of a Passive Biped-Walking Robot

This article belongs to the Special Issue Optimization of Motion Planning and Control for Automatic Machines, Robots and Multibody Systems.This work presents and discusses a general approach for the dynamic modeling and analysis of a passive biped walking robot, with a particular focus on the feet-ground contact interaction. The main purpose of this investigation is to address the supporting foot slippage and viscoelastic dissipative contact forces of the biped robot-walking model and to develop its dynamics equations for simple and double support phases. For this investigation, special attention has been given to the detection of the contact/impact between the legs of the biped and the ground. The results have been obtained with multibody system dynamics applying forward dynamics. This study aims at examining and comparing several force models dealing with different approaches in the context of multibody system dynamics. The normal contact forces developed during the dynamic walking of the robot are evaluated using several models: Hertz, Kelvin-Voight, Hunt and Crossley, Lankarani and Nikravesh, and Flores. Thanks to this comparison, it was shown that the normal force that works best for this model is the dissipative Nonlinear Flores Contact Force Model (hysteresis damping parameter - energy dissipation). Likewise, the friction contact/impact problem is solved using the Bengisu equations. The numerical results reveal that the stable periodic solutions are robust. Integrators and resolution methods are also purchased, in order to obtain the most efficient ones for this model.This work was financially supported by the Spanish Government through the MCYT project "RETOS2015: sistema de monitorización integral de conjuntos mecánicos críticos para la mejora del mantenimiento en el transporte-maqstatus

System Identification of Bipedal Locomotion in Robots and Humans

The ability to perform a healthy walking gait can be altered in numerous cases due to gait disorder related pathologies. The latter could lead to partial or complete mobility loss, which affects the patients’ quality of life. Wearable exoskeletons and active prosthetics have been considered as a key component to remedy this mobility loss. The control of such devices knows numerous challenges that are yet to be addressed. As opposed to fixed trajectories control, real-time adaptive reference generation control is likely to provide the wearer with more intent control over the powered device. We propose a novel gait pattern generator for the control of such devices, taking advantage of the inter-joint coordination in the human gait. Our proposed method puts the user in the control loop as it maps the motion of healthy limbs to that of the affected one. To design such control strategy, it is critical to understand the dynamics behind bipedal walking. We begin by studying the simple compass gait walker. We examine the well-known Virtual Constraints method of controlling bipedal robots in the image of the compass gait. In addition, we provide both the mechanical and control design of an affordable research platform for bipedal dynamic walking. We then extend the concept of virtual constraints to human locomotion, where we investigate the accuracy of predicting lower limb joints angular position and velocity from the motion of the other limbs. Data from nine healthy subjects performing specific locomotion tasks were collected and are made available online. A successful prediction of the hip, knee, and ankle joints was achieved in different scenarios. It was also found that the motion of the cane alone has sufficient information to help predict good trajectories for the lower limb in stairs ascent. Better estimates were obtained using additional information from arm joints. We also explored the prediction of knee and ankle trajectories from the motion of the hip joints

A Foot Placement Strategy for Robust Bipedal Gait Control

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

Tuning and Control of Human Locomotion

Mathematical modeling and analysis have been an integral part of legged locomotion research for many years. While models from the very simple inverted pendulum model of walking and the spring-mass model of running to multi-segmental models with numerous muscles across each joint have been used to explore the process of legged locomotion, they are not always sufficient to explain how human locomotion adapts to a changing environment. Using techniques from dynamical and control systems, I : 1) identify the time scales involved in metabolic minimization in running, 2) explore how stability differs between walking and running, 3) develop an algorithm for optimal control in discrete physical systems, and 4) examine the changes in leg mechanics involved in uphill and downhill running. For the first project, I use ideas from control systems to identify the processes involved in metabolic minimization in running. For the second project, I use ideas of orbital and local stability, measured using Floquet multipliers and finite time Lyapunov exponents, to try to quantify dynamic stability in walking and running at preferred and transition speeds. For the third project, I define a new method for the constrained optimization problem underlying Discrete Mechanics in Optimal Control. For the fourth project, I use a control systems approach to examine the changes in leg dynamics from level to uphill and downhill running. By exploring the adaptations that occur with changing environment, I hope to reveal the mechanisms, and possibly some of the strategies, that lead to stable locomotion

Optimierung der Energieeffizienz zweibeiniger Roboter durch elastische Kopplungen

In dieser Arbeit wird die Optimierung der Energieeffizienz zweibeiniger Roboter durch den Einsatz elastischer Kopplungen untersucht. Die betrachteten Roboter werden als unteraktuierte Systeme modelliert und mittels Ein-Ausgangs-Linearisierung geregelt. Zur Untersuchung des Einflusses der elastischen Kopplungen auf Energieeffizienz sowie Stabilität und Robustheit werden parallel die Bewegungen der Roboter als auch deren elastische Kopplungen unter Anwendung numerischer Algorithmen optimiert