Passive Actuation of a Planetary Rover to Assist Sandy Slope Traverse

This thesis introduces the design of a novel locomotive methodology. The problem being addressed is the traverse of unmanned locomotion over sandy inclined traverses. This is a special terramechanical issue regarding terrain or regolith that is non-cohesive in nature. The method uses a planetary exploration rover, Solar Rover 2 as its base. The proposed solution methodology includes a passively-actuated leg affixed to the rover to assist in slope traversal. Proposed physical implementations are designed and virtual representations are created, studied, and simulated in SolidWorks. This solution is justified through the use of a simulation designed in MATLAB

A Tendon-Driven Origami Hopper Triggered by Proprioceptive Contact Detection

We report on experiments with a laptop-sized (0.23m, 2.53kg), paper origami robot that exhibits highly dynamic and stable two degree-of-freedom (circular boom) hopping at speeds in excess of 1.5 bl/s (body-lengths per second) at a specific resistance O(1) while achieving aerial phase apex states 25% above the stance height over thousands of cycles. Three conventional brushless DC motors load energy into the folded paper springs through pulley-borne cables whose sudden loss of tension upon touchdown triggers the release of spring potential that accelerates the body back through liftoff to flight with a 20W powerstroke, whereupon the toe angle is adjusted to regulate fore-aft speed. We also demonstrate in the vertical hopping mode the transparency of this actuation scheme by using proprioceptive contact detection with only motor encoder sensing. The combination of actuation and sensing shows potential to lower system complexity for tendon-driven robots. For more information: Kod*lab (link to kodlab.seas.upenn.edu

Mathematical models for biological motility: From peristaltic crawling to plant nutations

In this thesis we propose mathematical models for the motility of one-dimensional crawlers moving along a line and for growing slender plant organs, which are applied to the study of peristaltic crawling and nutations of plant shoots, respectively. The first chapter contains a theoretical analysis of metameric worm-like robotic crawlers, and it investigates optimal actuation strategies. Our main result is that peristalsis, i.e., muscle extension and contraction waves propagating along the body, is an optimal actuation strategy for locomotion. We give a rigorous mathematical proof of this result by solving analytically the optimal control problem in the regime of small deformations. We show that phase coordination arises from the geometric symmetry of a 1D system, exactly in the periodic case and approximately, due to edge-effects, in the case of a crawler of finite length. In the second chapter we introduce the general framework of morphoelastic rods to model elongating slender plant organs. This chapter is intended as preparatory to the third one, where we derive a rod model that is exploited to investigate the role of mechanical deformations in circumnutating plant shoots. We show that, in the absence of endogenous cues, spontaneous oscillations might arise as system instabilities when a loading parameter exceeds a critical value. Moreover, when oscillations of endogenous nature are present, their relative importance with respect to the ones associated with the former mechanism varies in time, as the biomechanical properties of the shoot change. Our findings suggest that the relative importance of exogenous versus endogenous oscillations is an emergent property of the system, and that elastic deformations play a crucial role in this kind of phenomena

THE EFFECTS OF BODY SIZE ON SOFT-BODIED BURROWERS

Burrowing is a difficult form of locomotion due to the abrasive, heterogeneous, and dense nature of many substrates. Despite the challenges, many vertebrates and invertebrates spanning multitudes of taxa and body sizes burrow in a variety of terrestrial and aquatic substrates. Unlike terrestrial burrowers and modern digging equipment, many invertebrate burrowers lack rigid elements, and instead possess a fluid-filled hydrostatic skeleton. Soft-bodied burrowing invertebrates range in size from several hundred micrometers in length (e.g. nematodes) to several meters in length (e.g. earthworms), and burrow in environments ranging from muds to sands to soils. However, relatively little of the burrowing literature available has focused the effect of size on burrowing mechanics, and it is possible that the physical characteristics of soil may impose size-dependent constraints on burrowers. My research has found significant changes in morphology, soil stiffness, and burrowing behavior in Lumbricus terrestris earthworms during ontogeny. My results suggest that many aspects of the hydrostatic skeleton may change shape during growth to compensate for the ecological context of the organism. Specifically, I found that soil stiffness and resistance may become a significant challenge for soft-bodied burrowers as they increase in size, and must strain a greater volume of soil in order to form a burrow.Doctor of Philosoph

Towards tactile sensing active capsule endoscopy

Examination of the gastrointestinal(GI) tract has traditionally been performed using tethered endoscopy tools with limited reach and more recently with passive untethered capsule endoscopy with limited capability. Inspection of small intestines is only possible using the latter capsule endoscopy with on board camera system. Limited to visual means it cannot detect features beneath the lumen wall if they have not affected the lumen structure or colour. This work presents an improved capsule endoscopy system with locomotion for active exploration of the small intestines and tactile sensing to detect deformation of the capsule outer surface when it follows the intestinal wall. In laboratory conditions this system is capable of identifying sub-lumen features such as submucosal tumours.Through an extensive literary review the current state of GI tract inspection in particular using remote operated miniature robotics, was investigated, concluding no solution currently exists that utilises tactile sensing with a capsule endoscopy. In order to achieve such a platform, further investigation was made in to tactile sensing technologies, methods of locomotion through the gut, and methods to support an increased power requirement for additional electronics and actuation. A set of detailed criteria were compiled for a soft formed sensor and flexible bodied locomotion system. The sensing system is built on the biomimetic tactile sensing device, Tactip, \cite{Chorley2008, Chorley2010, Winstone2012, Winstone2013} which has been redesigned to fit the form of a capsule endoscopy. These modifications have required a $360^{o}$ cylindrical sensing surface with $360^{o}$ panoramic optical system. Multi-material 3D printing has been used to build an almost complete sensor assembly with a combination of hard and soft materials, presenting a soft compliant tactile sensing system that mimics the tactile sensing methods of the human finger. The cylindrical Tactip has been validated using artificial submucosal tumours in laboratory conditions. The first experiment has explored the new form factor and measured the device's ability to detect surface deformation when travelling through a pipe like structure with varying lump obstructions. Sensor data was analysed and used to reconstruct the test environment as a 3D rendered structure. A second tactile sensing experiment has explored the use of classifier algorithms to successfully discriminate between three tumour characteristics; shape, size and material hardness. Locomotion of the capsule endoscopy has explored further bio-inspiration from earthworm's peristaltic locomotion, which share operating environment similarities. A soft bodied peristaltic worm robot has been developed that uses a tuned planetary gearbox mechanism to displace tendons that contract each worm segment. Methods have been identified to optimise the gearbox parameter to a pipe like structure of a given diameter. The locomotion system has been tested within a laboratory constructed pipe environment, showing that using only one actuator, three independent worm segments can be controlled. This configuration achieves comparable locomotion capabilities to that of an identical robot with an actuator dedicated to each individual worm segment. This system can be miniaturised more easily due to reduced parts and number of actuators, and so is more suitable for capsule endoscopy. Finally, these two developments have been integrated to demonstrate successful simultaneous locomotion and sensing to detect an artificial submucosal tumour embedded within the test environment. The addition of both tactile sensing and locomotion have created a need for additional power beyond what is available from current battery technology. Early stage work has reviewed wireless power transfer (WPT) as a potential solution to this problem. Methods for optimisation and miniaturisation to implement WPT on a capsule endoscopy have been identified with a laboratory built system that validates the methods found. Future work would see this combined with a miniaturised development of the robot presented. This thesis has developed a novel method for sub-lumen examination. With further efforts to miniaturise the robot it could provide a comfortable and non-invasive procedure to GI tract inspection reducing the need for surgical procedures and accessibility for earlier stage of examination. Furthermore, these developments have applicability in other domains such as veterinary medicine, industrial pipe inspection and exploration of hazardous environments

The hydrodynamics of swimming microorganisms

Cell motility in viscous fluids is ubiquitous and affects many biological processes, including reproduction, infection, and the marine life ecosystem. Here we review the biophysical and mechanical principles of locomotion at the small scales relevant to cell swimming (tens of microns and below). The focus is on the fundamental flow physics phenomena occurring in this inertia-less realm, and the emphasis is on the simple physical picture. We review the basic properties of flows at low Reynolds number, paying special attention to aspects most relevant for swimming, such as resistance matrices for solid bodies, flow singularities, and kinematic requirements for net translation. Then we review classical theoretical work on cell motility: early calculations of the speed of a swimmer with prescribed stroke, and the application of resistive-force theory and slender-body theory to flagellar locomotion. After reviewing the physical means by which flagella are actuated, we outline areas of active research, including hydrodynamic interactions, biological locomotion in complex fluids, the design of small-scale artificial swimmers, and the optimization of locomotion strategies.Comment: Review articl

Continuum Mechanical Models for Design and Characterization of Soft Robots

The emergence of ``soft'' robots, whose bodies are made from stretchable materials, has fundamentally changed the way we design and construct robotic systems. Demonstrations and research show that soft robotic systems can be useful in rehabilitation, medical devices, agriculture, manufacturing and home assistance. Increasing need for collaborative, safe robotic devices have combined with technological advances to create a compelling development landscape for soft robots. However, soft robots are not yet present in medical and rehabilitative devices, agriculture, our homes, and many other human-collaborative and human-interactive applications. This gap between promise and practical implementation exists because foundational theories and techniques that exist in rigid robotics have not yet been developed for soft robots. Theories in traditional robotics rely on rigid body displacements via discrete joints and discrete actuators, while in soft robots, kinematic and actuation functions are blended, leading to nonlinear, continuous deformations rather than rigid body motion. This dissertation addresses the need for foundational techniques using continuum mechanics. Three core questions regarding the use of continuum mechanical models in soft robotics are explored: (1) whether or not continuum mechanical models can describe existing soft actuators, (2) which physical phenomena need to be incorporated into continuum mechanical models for their use in a soft robotics context, and (3) how understanding on continuum mechanical phenomena may form bases for novel soft robot architectures. Theoretical modeling, experimentation, and design prototyping tools are used to explore Fiber-Reinforced Elastomeric Enclosures (FREEs), an often-used soft actuator, and to develop novel soft robot architectures based on auxetic behavior. This dissertation develops a continuum mechanical model for end loading on FREEs. This model connects a FREE’s actuation pressure and kinematic configuration to its end loads by considering stiffness of its elastomer and fiber reinforcement. The model is validated against a large experimental data set and compared to other FREE models used by roboticists. It is shown that the model can describe the FREE’s loading in a generalizable manner, but that it is bounded in its peak performance. Such a model can provide the novel function of evaluating the performance of FREE designs under high loading without the costs of building and testing prototypes. This dissertation further explores the influence viscoelasticity, an inherent property of soft polymers, on end loading of FREEs. The viscoelastic model developed can inform soft roboticists wishing to exploit or avoid hysteresis and force reversal. The final section of the dissertations explores two contrasting styles of auxetic metamaterials for their uses in soft robotic actuation. The first metamaterial architecture is composed of beams with distributed compliance, which are placed antagonistic configurations on a variety of surfaces, giving ride to shape morphing behavior. The second metamaterial architecture studied is a ``kirigami’’ sheet with an orthogonal cut pattern, utilizing lumped compliance and strain hardening to permanently deploy from a compact shape to a functional one. This dissertation lays the foundation for design of soft robots by robust physical models, reducing the need for physical prototypes and trial-and-error approaches. The work presented provides tools for systematic exploration of FREEs under loading in a wide range of configurations. The work further develops new concepts for soft actuators based on continuum mechanical modeling of auxetic metamaterials. The work presented expands the available tools for design and development of soft robotic systems, and the available architectures for soft robot actuation.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163236/1/asedal_1.pd

Mechanics of Burrowing in Muddy Sediments

Marine muds are elastic solids through which animals move by propagating a crack-shaped burrow. Dilations previously considered anchors serve to exert dorsoventral compressive stresses on the burrow walls that, through elastic behavior of the medium, focus strongly at the tip of the burrow. This focused stress breaks adhesive or cohesive bonds, propagating a crack for the animal to follow. The force exerted by the polychaete, Nereis virens, to propagate a crack has been measured in gelatin, an analogue of muddy sediment, through photoelastic stress analysis. Finite element analysis was used to convert measured forces to those exerted in natural sediments based on differences in stiffnesses between gelatin and mud. From linear elastic fracture mechanics theory, it is predicted that a crack propagates when the stress intensity factor, a measure of stress amplification at the crack tip, exceeds a critical value, the fracture toughness. Stress intensity factors, calculated from measured forces using finite element modeling, fall within the range of critical values measured in gelatin and exceed those in natural sediments. Stress intensity factors were also calculated from the shapes of worms burrowing in transparent gels with varied mechanical properties, and fell close to or exceeded respective critical values. These results, using two independent measurements, strongly support that the mechanism underlying burrowing is crack propagation. Behavioral differences were observed by worms burrowing in gels with different mechanical properties, and can be explained by the differences in mechanics. This mechanism of burrowing by fracture is consistent with descriptions of burrowing across phyla and helps explain long-puzzling anatomies and behaviors of burrowing animals. Understanding of this mechanism raises questions about the reputed high energetic cost of burrowing, feeding guild classifications—specifically surface deposit feeders, and identifies some potential artifacts in benthic studies of chemistry and bioturbation. Both behaviors of burrowers and responses of sediments to forces exerted by burrowers depend on the mechanical properties (stiffness and fracture toughness), and understanding of that relationship will lead to advances in automaton modeling of bioturbation. Any serious mechanical analysis of swimming involves relevant physical properties of the medium. Going forward, the same will now be true of burrowing

Nature-inspired soft robotics: On articial cilia and magnetic locomotion

Inspired by micro-organisms in nature, people imagined using micro-scale soft robots to work inside the human body for therapeutic drug delivery, minimally invasive surgery, or diagnostic biochemical sensing. To create these robots is challenging due to their small size, viscosity environment, and soft constituting materials. In addition, the mechanisms of operation are quite different from the conventional rigid macro-scale robots that we are familiar with. In this PhD project, we focused on the computational analysis and design of micro-scale soft robots. Working closely with experimental groups, we studied artificial cilia and micro-swimmers that can realize particle manipulation, fluid transport, fluid mixing, or magnetic locomotion. Various cilia systems are considered, including soft inflatable cilia which could be controlled individually and programmable magnetic cilia featuring phase shifts and collective metachronal patterns. We also analyze micro-swimmers that are soft and adaptive in confined spaces. Driven by different external magnetic fields, the swimmer's motion can be changed between undulation crawling, undulation swimming, and helical crawling. By using computational modeling, we analyze the transport mechanisms of the soft robots and study the effect of different parameters to provide guidelines for the design of the robots in specific applications. By studying the physical mechanisms of micro-organisms in nature, we are not only able to understand more clearly their functional behaviour, it also opens the possibility of biomimetic design of soft robotic cilia and micro-swimmers