Biped Locomotion Systems Analysis, Modeling and Control

This dissertation concerns the analysis, modeling and control of the human locomotion with a view to the design of advanced systems supporting natural mobility, and, thus, promoting inclusivity and quality of life. It starts with an overview of the state-of-the-art in modeling and control of the human locomotion, as well as a review of key background in nonlinear control and hybrid systems framework. Then, an analysis of human motion is performed in order to extract requirements to be satisfied by a motion control system. This leads to the specification of the overall control architecture and to some control design options that are discussed in detail. In order to properly formulate the associated control problems, a detailed and comprehensive kinematic and dynamic motion modeling is done by resorting to the so called DH method (Kinematics), Euler-Lagrangian method (dynamics), and techniques of impact mechanics. Finally, some simulation results of the implemented models are presented and some conclusions are taken. A preliminary observation of locomotion quickly reveals its huge complexity. It is cyclic but composed of two major phases: double support and single support. Both of the phases encompass several stages, such as heel strike, midstance and push-off. The more significant changes occur in the sagittal plane. To avoid falling down when standing still, the body autonomously maintains its COG inside the support base formed by the feet. All the body segments have a role in system stability and accomplishments. Humanoid robots can already walk at human speed and go up and down stairs or slopes.Multiple control methods were tested, often based on ZMP stability criterion. The industry dedicated to the development of mobility solutions for disabled people is a growing sector of the economy, despite the current financial situation worldwide. For people that walk with abnormal gait due to muscle weakness, balance issues or similar issues, the state of the art solution is a hand-made carbon fiber frame with gyroscopes and a lock /unlock controller in the knee. Other solutions exist for paraplegics or amputees.Nowadays, most of the solutions involve electronics and, for this reason, they follow international standards for electromagnetic compatibility and low voltage levels, among others. The idealized system presents a distributed architecture organized by layers as a way to guarantee adaptivity, robustness and (sub-)optimality. The low level controllers make use of a nonlinear technique to track the reference provided by the MPC, which is responsible for their optimization and for the feasibility verification in the upper layers. When the system safety is at risk or the a priori motion plan is impossible to archive the walking parameters or references can be adapted. The walking machine model is composed by three sub-system (stance leg, swing leg and trunk) that cooperate to allow that the abstraction of balance, that constitutes a virtual system, to converge to a limit cycle. The simulations done in the different domains proved sometimes the need of a different or additional approach/features. Once they were introduced, the requirements looked plausible.