A diversity of animals move on and bury within dry and wet granular media, such as dry desert sand or rainforest soils. Little is known about the biomechanics and neural control strategies used to move within these complex terrains. Burial and subsurface locomotion provides a particularly interesting behavior in which to study principles of interaction because the entire body becomes surrounded by the granular environment. In this dissertation, we used three model organisms to elucidate control principles of movement within granular substrates: the sand-specialist sandfish lizard which dives into dry sand using limb-ground interactions, and swims subsurface using body undulations; the long-slender shovel-nosed snake which undulates subsurface in dry sand with low slip; and the ocellated skink, a desert generalist which buries into both wet and dry substrates. Using muscle activation measurements we discovered that the sandfish targeted optimal kinematics which maximized forward speed and minimized the mechanical cost of transport. The simplicity of the sandfish body and kinematics coupled with a fluid-like model of the granular media revealed the fundamental mechanism responsible for neuromechanical phase lags, a general timing phenomenon between muscle activation and curvature along the body that has been observed in all undulatory animals that move in a variety of environments. Kinematic experiments revealed that the snake moved subsurface using a similar locomotion strategy as the sandfish, but its long body and low skin friction enabled higher performance (lower slip). The ocellated skink used a different locomotor pattern than observed in the sandfish and snake but that was sufficient for burial into both wet and dry media. Furthermore, the ocellated skink could only reach shallow burial depths in wet compared to dry granular media. We attribute this difference to the higher resistance forces in wet media and hypothesize that the burial efficacy is force-limited. These studies reveal basic locomotor principles of burial and subsurface movement in granular media and demonstrate the impact of environmental interaction in locomotor behavior.

Ce mémoire présente le développement de l’architecture et des algorithmes de commande d’une interface de locomotion utilisant un mécanisme parallèle à câbles. Cette interface de locomotion permet d’améliorer l’expérience de la réalité virtuelle en recréant la topologie du monde virtuel. Tout d’abord, une revue de littérature sur les interfaces de locomotion est présentée. Par la suite, l’architecture globale du système est présentée. Les définitions de base sous-jacentes à la compréhension des algorithmes de commande ainsi que l’analyse cinématique du mécanisme sont ensuite présentées. L’architecture logicielle et les algorithmes de commande sont enfin présentés. Des améliorations au point de vue des mécanismes à câbles sont aussi présentées. Ces améliorations permettent d’améliorer la précision de la commande en position des mécanismes à câbles. Enfin, les résultats présentent l’aboutissement des travaux en montrant le fonctionnement d’un prototype à trois degrés de liberté de l’interface de locomotion réalisé. / Québec Université Laval, Bibliothèque 2019

In this dissertation, we developed predictive models for legged and limbless locomotion on dry, homogeneous granular media. The vertical plane Resistive Force Theory (RFT) for frictional granular fluids accurately predicted the reaction forces on intruders (with complex geometries) translating and rotating at low speeds ( < 0.5 m/s). Using RFT and multibody simulation, we predicted the forward moving speed of legged robots. During the locomotion of lightweight robots and animals where instantaneous limb penetration speed can reach values greater than ~0.5 m/s, a Discrete Element Method (DEM) simulation was developed to capture the limb-ground interaction. We demonstrated that hydrodynamic-like forces generated by accelerated particles can balance the robot weight and inertia, and promote the rapid movement on granular media. Forces from the environment can not only determine locomotion dynamics, but also affect the locomotion strategy. We studied and simulated the limbless locomotion of snakes in a heterogeneous environment and demonstrated how touch sensing was used to adjust the movement pattern. In heterogeneous environments, the long-term locomotion dynamics is also poorly understood. We presented a theory for transport and diffusion in such settings.

The objective of this research is to discover principles of ambulatory locomotion on homogeneous and heterogeneous granular substrates and create models of animal and robot interaction within such environments. Since interaction with natural substrates is too complicated to model, we take a robophysics approach – we create a terrain generation system where properties of heterogeneous multi-component substrates can be systematically varied to emulate a wide range of natural terrain properties such as compaction, orientation, obstacle shape/size/distribution, and obstacle mobility within the substrate. A schematic of the proposed system is discussed in detail in the body of this dissertation. Control of such substrates will allow for the systematic exploration of parameters of substrate properties, particularly substrate stiffness and heterogeneities. With this terrain creation system, we systematically explore locomotor strategies of simplified laboratory robots when traversing over different terrain properties. A key feature of this proposed work is the ability to generate general interaction models of locomotor appendages with such complex substrates. These models will aid in the design and control of future robots with morphologies and control strategies that allow for effective navigation on a large diversity of terrains, expanding the scope of terramechanics from large tracked and treaded vehicles on homogeneous ground to arbitrarily shaped and actuated locomotors moving on complex heterogeneous terrestrial substrates.

Studying animal mechanics is crucial in order to understand how signals in the neuromuscular system contribute to an organism’s behaviour and how force-sensing organs and sensory neurons interact. In particular, the connection between the nerves and the muscles responsible for the force generation in the neuromuscular system needs to be established. Knowledge of the locomotion forces can be beneficial for the development of therapies for muscle disorders, neurodegenerative and human genetic diseases, such as muscular dystrophy. The simplicity of the nematode Caenorhabditis elegans’ (C. elegans) nervous system, which is limited to 302 neurons, has made it an excellent model organism for studying animal mechanics which include mechanosensation and locomotion at the neuronal level. The advent of miniaturized force sensing devices has led to the proposal of various approaches for measuring C. elegans locomotion forces. However, these existing devices are relatively complex, involving complicated microfabrication procedures and are incapable of measuring forces exerted by C. elegans in motion. This thesis addresses these shortcomings by introducing a force sensor capable of continuously measuring the forces generated by C. elegans in motion. The system consists of a micropillar-based device made of polydimethylsiloxane (PDMS) only and a vision-based algorithm for resolving the worm force from the deflection of the cantilever-like pillars. The measured force is horizontal and equivalent to a point force acting at half of the pillar height. The microdevice, sub-pixel resolution for visual tracking of the deflection, and experimental technique form an integrated system for measuring dynamic forces of moving C. elegans with force resolution of 3.13 uN for worm body width of 100 um. A simple device fabrication process based on soft-lithography and a basic experimental setup, which only requires a stereo microscope with off-the-shelf digital camera mean that this method is accessible to most biological science laboratories. The results demonstrate that the proposed device is capable of quantifying multipoint forces of moving C. elegans rather than single-point forces for a worm sample. This allows one to simultaneously collect force data from up to eight measurements points on different worm body parts. This is a significant step forward as it enables researchers to explicitly quantify the relative difference in forces exerted by the worm’s different body segments during the worms’ movements. The device’s capability to determine multipoint forces during nematode motion can also generate meaningful data to compare forces associated with different worm body muscles, gaining new understanding on how these muscles function. The forces measured during locomotion in the micropillars could also be used to differentiate mutant phenotypes. Apart from locomotion forces, the device is also capable of conducting concurrent measurement of other locomotion parameters such as speed, body amplitude and wavelength, as well as undulation frequency. This additional information can be useful to further quantify phenotypic behaviour of C. elegans and deepen the understanding of the theory behind worm locomotion forces. The relationship between C. elegans locomotion forces and their environment has also been analyzed by variation of the pillar arrangement and spacing. The results indicate that the microstructured environment significantly affects the worm’s contraction force, locomotion speed and the undulation frequency. In addition, an alternative measurement technique was provided to measure worm forces on other substrates, such that worm locomotion behaviour in varying environments can be investigated further. The combination of the conventional measurement technique with the findings of worm locomotion on a glass substrate reported show promise for biological measurements and other sensing application such as tactile force. Additional functions of on-chip worm selection, sorting, and imaging have also been integrated with the device, rendering its potential to accommodate for high-throughput application of C. elegans force measurement and locomotion studies in the future. The primary contributions of this thesis are centered around four topics: the development of the PDMS micropillar array and its application to study C. elegans locomotion forces, the analysis of C. elegans muscular forces and locomotion patterns in microstructured environments, the investigation of the worm locomotion forces using different substrates and finally the integration of the PDMS micropillar with PDMS microvalve for on-chip worm selection and imaging. Although the results presented in this thesis focus on wild type C. elegans, the method can be easily applied to its mutants and other organisms.

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A major function of the central nervous system (CNS) during locomotion is the ability to maintain dynamic stability during threats to balance. The CNS uses reactive, predictive, and anticipatory mechanisms in order to accomplish this. Previously, stability has been estimated using single measures. Since the entire body works as a system, dynamic stability should be examined by integrating kinematic, kinetic, and electromyographical measures of the whole body. This thesis examines three threats to stability (recovery from a frontal plane surface translation, stepping onto and walking on a compliant surface, and obstacle clearance on a compliant surface). These threats to stability would enable a full body stability analysis for reactive, predictive, and anticipatory CNS control mechanisms. From the results in this study, observing various biomechanical variables provides a more precise evaluation of dynamic stability and how it is achieved. Observations showed that different methods of increasing stability (eg. Lowering full body COM, increasing step width) were controlled by differing CNS mechanisms during a task. This provides evidence that a single measure cannot determine dynamic stability during a locomotion task and the body must be observed entirely to determine methods used in the maintenance of dynamic stability.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.