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High-performing legged robots require complex spatial leg designs and controllers to simultaneously implement propulsion, maneuvering and stabilization behaviors. Looking to nature, tails assist a variety of animals with these functionalities separate from the animals' legs. However, prior research into robotic tails primarily focuses on single-mass pendulums driven in a single plane of motion and designed to perform a specific task. In order to justify including a robotic tail on-board a legged robot, the tail should be capable of performing multiple functionalities in the robot's yaw, pitch and roll directions. The aim of this research is to study bioinspired articulated spatial robotic tails capable of implementing maneuvering and stabilization behaviors in quadrupedal and bipedal legged robots. To this end, two novel serpentine tails designs are presented and integrated into prototypes to test their maneuvering and stabilizing capabilities. Dynamic models for these two tail designs are formulated, along with the dynamic model of a previously considered continuum robot, to predict the tails' motion and the loading they will apply on their legged robots. To implement the desired behaviors, outer- and inner-loop controllers are formulated for the serpentine tails: the outer-loop controllers generate the desired tail trajectory to maneuver or stabilize the legged robot, and the inner-loop controllers calculate control inputs for the tail that implement the desired tail trajectory using feedback linearization. Maneuvering and stabilizing case studies are generated to demonstrate the tails' ability to: (1) generate yaw angle turning in both a quadruped and a biped, (2) improve the quadruped's ability to reject an externally applied roll moment disturbance that would otherwise destabilize it, and (3) counteract the biped's roll angle instability when it lifts one of its legs (for example, during its gait cycle). Tail simulations and experimental results are used to implement these case studies in conjunction with multi-body dynamic simulations of the quadrupedal and bipedal legged platforms. Results successfully demonstrate the tails' ability to maneuver and stabilize legged robots, and provide a firm foundation for future work implementing a tailed-legged robot. / Ph. D.

Bipedal robots offer a uniquely flexible platform capable of navigating complex, human-centric environments. This makes them ideally suited for a variety of missions, including disaster response and relief, emergency scenarios, or exoskeleton systems for individuals with disabilities. This, however, requires significant advances in humanoid locomotion and control, as they are still slow, unnatural, inefficient, and relatively unstable. The work of this dissertation the state of the art with the aim was of increasing the robustness and efficiency of these bipedal walking platforms. We present a series of control improvements to enable reliable, robust, natural bipedal locomotion that was validated on a variety of bipedal robots using both hardware and simulation experiments. A huge part of reliable walking involves maximizing the robot's control authority. We first present the development of a model predictive controller to both control the ground reaction forces and perform step adjustment for walking stabilization using a mixed-integer quadratic program. This represents the first model predictive controller to include step rotation in the optimization and leverage the capabilities of the time-varying divergent component of motion for navigating rough terrain. We also analyze the potential capabilities of model predictive controllers for the control of bipedal walking. As an alternative to standard trajectory optimization-based model predictive controls, we present several optimization-based control schemes that leverage more traditional bipedal walking control approaches by embedding a proportional feedback controller into a quadratic program. This controller is capable of combining multiple feedback mechanisms: ground reaction feedback (the "ankle strategy"), angular momentum (the "hip strategy"), swing foot speed up, and step adjustment. This allows the robot to effectively shift its weight, pitch its torso, and adjust its feet to retain balance, while considering environmental constraints, when available. To enable the robot to walk with straightened legs, we present a strategy that insures that the dynamic plans are kinematically and dynamically feasible to execute using straight legs. The effects of timing on dynamic plans are typically ignored, resulting in them potentially requiring significantly bending the legs during execution. This algorithm modifies the step timings to insure the plan can be executed without bending the legs beyond certain angle, while leaving the desired footsteps unmodified. To then achieve walking with straight legs we then presented a novel approach for indirectly controlling the center of mass height through the leg angles. This avoids complicated height planning techniques that are both computationally expensive and often not general enough to consider variable terrain by effectively biasing the solution of the whole-body controller towards using straighter legs. To incorporate the toe-off motion that is essential to both natural and straight leg walking, we also present a strategy for toe-off control that allows it to be an emergent behavior of the whole-body controller. The proposed approach was demonstrated through a series of simulation and experimental results on a variety of platforms. Model predictive control for step adjustment and rough terrain is illustrated in simulation, while the other step adjustment strategies and straight leg walking approaches are presented recovering from external disturbances and walking over a variety of terrains in hardware experiments. We discuss many of the practical considerations and limitations required when porting simulation-based controller development to hardware platforms. Using the presented approaches, we also demonstrated a important concept: using whole-body control frameworks, not every desired motion need be directly commanded. Many of these motions, such as toe-off, may simply be emergent behaviors that result by attempting to satisfy other objectives, such as desired reaction forces. We also showed that optimization is a very powerful tool for walking control, able to determine both stabilizing inputs and joint torques. / Ph. D.

Spur-of-the-moment planetary exploration missions are within our reach. Complex systems and complex missions usually take years of planning and force launches to become incredibly expensive. We argue here for cheap, fast missions using large numbers of mass produced simple autonomous robots that are small by today's standards, perhaps 1 to 2kg. We suggest that within a few years it will be possible, at modest cost, to invade a planet with millions of tiny robots.

京都大学 / 新制・課程博士 / 博士(情報学) / 甲第24266号 / 情博第810号 / 新制||情||136(附属図書館) / 京都大学大学院情報学研究科システム科学専攻 / (主査)教授 大塚 敏之, 教授 石井 信, 教授 森本 淳 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

This dissertation explores the design, and implementation of articulated robotic tail mechanisms onboard reduced degree-of-freedom (DOF) legged robots to augment performance in terms of stability and maneuverability. Fundamentally, this research is motivated by the question of how to improve the stability and maneuverability of legged robots. The conventional approach to address these challenges is to utilize leg mechanisms that are composed of three or more active DOFs that are controlled simultaneously to provide propulsion, maneuvering, and stabilization. However, animals such as lizards and cheetahs have been observed to utilize their tails to aid in these functionalities. It is hypothesized that by using an articulated tail mechanism to aid in these functionalities onboard a legged robot, the burden on the robot's legs to simultaneously maneuver and stabilize the robot may be reduced. This could allow for simplification of the leg's design and control algorithms. In recent years, significant progress has been accomplished in the field of robotic tail implementation onboard mobile robots. However, the main limitation of this work stems from the proposed tail designs, the majority of which are composed of rigid single-body pendulums that provide a constrained workspace for center-of-mass positioning, an important characteristics for inertial adjustment applications. Inspired by lizards and cheetahs that adjust their body orientation using flexible tail motions, two novel articulated, cable driven, serpentine-like tail mechanisms are proposed. The first is the Roll-Revolute-Revolute Tail which is a 3-DOF mechanism, designed for implementation onboard a quadruped robot, that is capable of forming two mechanically decoupled tail curvatures via an s-shaped cable routing scheme and gear train system. The second is a the Discrete Modular Serpentine Tail, designed for implementation onboard a biped robot, which is a modular two-DOF mechanism that distributes motion amongst links via a multi-diameter pulley. Both tail designs utilize a cable transmission system where cables are routed about circular contoured links that maintain equal antagonistic cable displacements that can produce controlled articulated tail curvatures using a single active-DOF. Furthermore, analysis and experimental results have been presented to demonstrate the effectiveness of an articulated tail's ability to: 1) increase the manifold for center-of-mass positioning, and 2) generate enhanced inertial loading relative to conventionally implemented pendulum-like tails. In order to test the tails ability to augment the performance of legged robots, a novel Robotic Modular Leg (RML) is proposed to construct both a reduced-DOF quadrupedal and bipedal experimental platform. The RML is a modular two-DOF leg mechanism composed of two serially connected four-bar mechanisms that utilizes kinematic constraints to maintain a parallel orientation between it's flat foot and body without the use of an actuated ankle. A passive suspension system integrated into the foot enables the dissipation of impact energy and maintains a stable four point-of-contact support polygon on both flat and uneven terrain. Modeling of the combined legged robotic systems and attached articulated tails has led to the derivation of dynamic formulations that were analyzed to scale articulated tails onboard legged robots to maximize inertial adjustment capabilities resulting from tail motions and design a control scheme for tail-aided maneuvering. The tail prototypes, in conjunction with virtual simulations of the quadruped and biped robot, were used in experiments and simulations to implement and analyze the methods for maneuvering and stabilizing the proposed legged robots. Results successfully demonstrate the tails' ability to augment the performance of reduced-DOF legged robots by enabling comparable walking criteria with respect to conventional legged robots. This research provides a firm foundation for future work involving design and implementation of articulated tails onboard legged robots for enhanced inertial adjustment applications. / Ph. D.

No description available.

This thesis addresses the problem of generating smooth and efficiently executable locomotion trajectories for legged robots under contact constraints. In addition, we want the trajectories to have the property that small changes in the foot position generate small changes in the joint target path. The first part of this thesis explores methods to select poses for a legged robot that maximises the workspace reachability while maintaining stability and contact constraints. It also explores methods to select configurations based on a reduced-dimensional search of the configuration space. The second part analyses time scaling strategy which tries to minimize the execution time while obeying the velocity and acceleration constraints. These two parts effectively result in smooth feasible trajectories for legged robots. Experiments on the RoboSimian robot demonstrate the effectiveness and scalability of the strategies described for walking and climbing on a rock climbing wall.

This thesis is about control and balance stability of leggedlocomotion. It also presents a combination of tools that makesit easier to design controllers for large and complicated robotsystems. The thesis is divided into four parts. The first part studies and analyzes how walking machines arecontrolled, examining the literature of over twenty machinesbriefly, and six machines in detail. The goal is to understandhow the controllers work on a level below task and pathplanning, but above actuator control. Analysis and comparisonis done in terms of: i) generation of trunk motion; ii)maintaining balance; iii) generation of leg sequence andsupport patterns; and iv) reflexes. The next part describes WARP1, a four-legged walking robotplatform that has been builtwith the long term goal of walkingin rough terrain. First its modular structure (mechanics,electronics and control) is described, followed by someexperiments demonstrating basic performance. Finally themathematical modeling of the robot’s rigid body model isdescribed. This model is derived symbolically and is general,i.e. not restricted to WARP1. It is easily modified in case ofa different number of legs or joints. During the work with WARP1, tools for model derivation,control design and control implementation have been combined,interfaced and augmented in order to better support design andanalysis. These tools and methods are described in the thirdpart. The tools used to be difficult to combine, especially fora large and complicated system with many signals and parameterssuch as WARP1. Now, models derived symbolically in one tool areeasy to use in another tool for control design, simulation andfinally implementation, as well as for visualization andevaluation—thus going from equation to action. In the last part we go back to“equation”wherethese tools aid the study of balance stability when complianceis considered. It is shown that a legged robot in a“statically balanced”stance may actually beunstable. Furthermore, a criterion is derived that shows when aradially symmetric“statically balanced”stance on acompliant surface is stable. Similar analyses are performed fortwo controllers of legged robots, where it is the controllerthat cause the compliance. <b>Keywords</b>legged locomotion, control, balance, leggedmachines, legged robots, walking robots, walking machines,compliance, platform stability, symbolic modeling