Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract. Includes bibliographical references (leaves 138-149).

Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S. in Electrical Engineering and M.S. in Systems Engeineering)--Naval Postgraduate School, June 2005. / Thesis Advisor(s): Xiaoping Yun. Includes bibliographical references (p. 93-95). Also available online.

Thèse (Ph.D.)--Université Laval, 2001. / Titre de l'écran-titre (visionné le 22 mars 2004). Bibliogr. Présenté aussi en version papier.

Thèse (M.Sc.)--Université Laval, 2002. / Bibliogr. Publié aussi en version électronique.

Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 124-134). Also available for download via the World Wide Web; free to University of Oregon users.

Undergraduate honors paper--Mount Holyoke College, 2007. Dept. of Biological Sciences. / Includes bibliographical references (leaves 54-55).

In an age where computers challenge the smartest human beings in cognitive tasks, the conspicuous discrepancy between robot and animal locomotion appears paradoxical. While animals can move around autonomously in complex environments, today’s robots struggle to independently operate in such surroundings. There are many reasons for robots’ inferior performance, but arguably the most important one is our missing understanding of complexity. This thesis introduces the notion of discrete actuation for the study of locomotion in robots and animals. The actuation of a system with discrete actuation is restricted to be applied at a finite number of instants in time and is impulsive. We find that, despite their simplicity, such systems can predict various experimental observations and inspire novel technologies for robot design and control. We further find that, through the study of discrete actuation, causal relationships between actuation and resulting behaviour are revealed and become quantifiable, which relates the findings presented in this thesis to the broader concepts of complexity, self-organisation, and self-stability. We present four case studies in Chapters 3-6 which demonstrate how the concept of discrete actuation can be employed to understand the physics of locomotion and to facilitate novel robot technologies. We first introduce the impulsive eccentric wheel model which is a discretely actuated system for the study of hopping locomotion. We find that the model predicts robot hopping trajectories and animal related hopping characteristics by reducing the dynamics of hopping–usually described by hybrid differential equations–to analytic maps. The reduction of complexity of the model equations reveals the underlying physics of the locomotion process, and we identify the importance of robot shape and mass distribution for the locomotion performance. As a concrete application of the model, we compare the energetics of hopping and rolling locomotion in environments with obstacles and find when it is better to hop than to roll, based on the fundamental physical principles we discover in the model analysis. The theoretical insights of this modelling approach enable new actuation techniques and design for robots which we display in Robbit; a robot that uses strictly convex foot shapes and rotational impulses to induce hopping locomotion. We show that such systems outperform hopping with non-strictly convex shapes in terms of energy effective and robust locomotion. A system with discrete actuation motivates the exploitation of shape and the environment to improve locomotion dynamics, which reveals advantageous effect of inelastic impacts between the robot foot and the environment. We support this idea with experimental results from the robot CaneBot which can change its foot shape to induce timed impacts with the environment. Even though inelastic impacts are commonly considered detrimental for locomotion dynamics, we show that their appropriate control improves the locomotion speed considerably. The findings presented in this thesis show that discrete actuation for locomotion inspires novel ways to appreciate locomotion dynamics and facilitates unique control and design technologies for robots. Furthermore, discrete actuation emphasises the definition of causality in complex systems which we believe will bring robots closer to the locomotion behaviour of animals, enabling more agile and energy effective robots.

Lower-extremity amputees face numerous challenges when returning to daily activities. Amongst these challenges is the ability to safely and dynamically transition from one locomotor state to another. Switching between level-ground, ramp, and stair locomotion poses an increased risk as lower-extremity functionality is compromised. Powered prosthetics have been proposed as a solution to this problem. Hypothetically, powered prosthetics would be able to return full functional to the amputated limb. The most common and successful source of information used in algorithms for lower-extremity prosthetics has been electromyography. However, in practice, amputees remain unable to easily actuate the mechanized joints of powered prostheses. Therefore, the current project aimed to identify myoelectric activation differences in lower-extremity musculature during the gait cycles preceding locomotor transition in able-bodied, trans-tibial, and trans-femoral subjects to assist efforts in developing robust classification algorithms for locomotor transitions. Analysis of electromyography was completed to determine if there were periods of activation where classification algorithms could utilize differences in myoelectric activation to appropriately control joint actuation in a subset of eight transitions that included level-ground locomotion and switching to either ramp or stair locomotion and vice versa. Ramp transitions were fundamentally similar to level-ground locomotion and elicited no differences in myoelectric activation. Stair transitions were found to alter muscle activation patterns in able-body and trans-tibial subjects. Trans-femoral subjects differentiated from able-bodied and trans-tibial subjects due to increased recruitment pattern variability. These patterns are distinct and may suggest individual learning patterns within the trans-femoral amputee population. Further investigation of these patterns may be warranted. Findings within able-bodied and trans-tibial subjects suggest common transition based differences within each respective population. Trans-tibial classification algorithms may be developed to utilize this information, using schemes that are focused on important areas during the gait cycle.

The hydrodynamics and mechanics of obliquely swimming characoid species Chilodus punetatus, Nannostomus eques, Nannostomus unifasciatus, Thayeria. boehlkei and Thayeria obliqua are investigated. In Chilodus punctatug, Nannostomus eques and Nannostomus unifasciatus the position of the centre of mass relative to the centre of buoyancy is the reverse of what would be expected from their pitch. The centre of mass is in front of the centre of buoyancy in the two Nannostomus species which swim with a positive pitch and vice versa in Chilodus punctatus which swims with negative pitch. The relative positions of these two centres are in such a way that they help to bring the fish horizontal during fast swimming. Pitch in these species is maintained by the action of the pectoral and caudal fins. In the two Thayeria species the centre of mass is behind the centre of buoyancy and their separation is responsible for the positive pitch. The fins are used to correct for this pitch to the desirable level. The enlarged lower lobe of the caudal fin in Nannostomus species has an epibatic effect and does not contribute to the forces responsible for the pitch in hovering as previously proposed. Relative vertebrae size in Nannostomus eques and Nannostomus unifasciatus when compared to Nannostomus becfordi and Nannostomus trifasciatus which swim horizontally show adaptations towards a strategy of rapid start from rest. / Science, Faculty of / Zoology, Department of / Unknown