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

M. Comm. / One function of skeletal muscle is to serve as the body's shock absorbers and thus dampen rates of loading (ROL) around joints during activities. However, it is not clear whether individuals with strong leg muscles actually demonstrate different ROL during gait than weaker individuals. The aim of this cross-sectional study was to determine the significance of muscle strength on ROL during gait. Females (ages 18 to 50) were solicited via advertisement and screened via phone interviews. Subjects (n=56) were chosen and placed into one of three groups based on training history: Strength Trained (ST), Aerobically Trained (AT), and Sedentary (S). Subjects walked barefoot (10 trials) over an 8 m walkway while ROL was sampled using a 1000 Hz force platform (AMTI OR6-6). Gait speed was controlled between 2.22 - 2.45 m.s -1 using telemetric photocells placed three meters apart. Maximum concentric and eccentric quadriceps and hamstring strength were measured at 90 degrees•s -1 using an isokinetic dynamometer (KINCOM 500H). Peak torque was divided by body weight to determine relative strength (Nrn-kg -1 ). Statistical analyses (p<0.05) included ANOVA and the Bonferroni/Dunn post-hoc test. There were no significant differences in age, height or walking speed across groups. The S group (78.3 ± 15.6 kg, n=18) weighed significantly more than the AT (60.5 ± 8.0 kg, n=19) and ST (63.1 ± 10.7 kg, n=19) groups. Body composition analyses showed that the mean body fat percentage of the S group (34.8 ± 7.3 %, n=18) was significantly higher than both AT (22.3 ± 5.7 %, n=19) and ST (23.2 ± 6.9 %, n=19) groups. Relative concentric and eccentric strength of the quadriceps of the AT (2.02 ± 0.07, n=19; 3.49 ± 0.18, n=19 respectively) and ST (2.1 ± 0.08, n=19; 3.50 ± 0.14, n=19 respectively) groups were significantly greater than the S (1.68 ± 0.07, n=18; 2.63 ± 0.10, n=18 respectively) group. Relative concentric hamstrings strength of both the AT (1.07 ± 0.05, n=19) and ST (1.08 ± 0.04, n=19) groups were significantly greater than the S (0.91 ± 0.04, n=18) group. Relative eccentric hamstring strength of only the ST (1.60 ± 0.07, n=19) group was significantly greater than the (1.34 ± 0.08, n=18) group. There were no significant differences in ROL between the S (2.21 ± 0.15 %Wt.ms -1 , n=18) and AT groups (2.14 ± 0.15 %Wt-ms 1 , n=19) (p=0.70), and the AT (2.14 ± 0.15 %Wt.ms-1 , n=19) and ST (1.82 ± 0.10 %Wt.ms -1 , n=19) (p=0.10) groups. However, the females in the ST (1.82 ± 0.10 %Wt•ms -1 , n=19) group had significantly lower ROL than the females in the S group. In addition, females in the ST group demonstrated a lower frequency of heelstrike transient (HST) occurrence. Seven of the S (n=18) females demonstrated HST while only four of the ST (n=19) females did. In conclusion, strength trained females demonstrated significantly lower rates of loading during gait than those in the sedentary group. High ROL have been associated with knee pain and osteoarthritis. These findings suggest that strength training may decrease the risk for these maladies.

A number of investigators have determined the joint forces acting at the hip and knee for normal human locomotion as related to the design of prosthetic devices. This research has been extended to allow the calculation or estimation of the muscular and ligamentous forces operating at the knee joint for normal walking. The current study expanded upon the past research to evaluate the magnitude and temporal sequence of.the muscle, ligament and articular forces acting at the knee joint for a simulated skating thrust. A skilled ice hockey player was filmed in two reference planes while making a skating thrust from a laboratory force platform. The cine film data was synchronized with the force plate output to allow calculation of the orthogonal forces and moments imposed on the knee joint. The orthogonal force system was determined from a knowledge of the inertial, gravitational and reaction forces acting on the lower limb during the skating thrust. The muscle, ligament and joint forces were determined from equations derived from the conditions of joint equilibrium. The equations of equilibrium were indeterminate and had to be reduced by making assumptions from electromyographic records to allow solution. Forces were calculated for a simplified muscle and ligament system which included the hamstrings, quadriceps and gastrocnemius muscle groups, the collateral ligaments and the cruciate ligaments of the knee joint. In addition, the articular joint force, joint torque and centre of pressure of the joint force were determined. Results of the investigation revealed that the magnitude of the muscle, ligament and joint forces developed in a skating thrust were considerably greater than respective forces exerted during level walking while the temporal sequence of the skating forces was comparable to walking upstairs. The quadriceps muscle group exerted the greatest contractile force while the gastrocnemius and hamstrings groups developed much smaller forces. The largest ligament forces were developed in the collateral ligaments and the posterior cruciate ligament to maintain stability of the joint. The knee joint is subject to the combined effects of a joint force six times body weight and a large joint torque superimposed upon each other during the skating thrust and this fact is considered important when discussing the cause of menisci knee injuries. / Education, Faculty of / Curriculum and Pedagogy (EDCP), Department of / Graduate