An earthworm-like modular soft robot for locomotion in multi-terrain environments

Robotic locomotion in subterranean environments is still unsolved, and it requires innovative designs and strategies to overcome the challenges of burrowing and moving in unstructured conditions with high pressure and friction at depths of a few centimeters. Inspired by antagonistic muscle contractions and constant volume coelomic chambers observed in earthworms, we designed and developed a modular soft robot based on a peristaltic soft actuator (PSA). The PSA demonstrates two active configurations from a neutral state by switching the input source between positive and negative pressure. PSA generates a longitudinal force for axial penetration and a radial force for anchorage, through bidirectional deformation of the central bellows-like structure, which demonstrates its versatility and ease of control. The performance of PSA depends on the amount and type of fluid confined in an elastomer chamber, generating different forces and displacements. The assembled robot with five PSA modules enabled to perform peristaltic locomotion in different media. The role of friction was also investigated during experimental locomotion tests by attaching passive scales like earthworm setae to the ventral side of the robot. This study proposes a new method for developing a peristaltic earthworm-like soft robot and provides a better understanding of locomotion in different environments

Design and Development of Soft Earthworm Robot Driven by Fibrous Artificial Muscles

Earthworm robots have proven their viability in the fields of medicine, reconnaissance, search and rescue, and infrastructure inspection. These robots are traditionally typically hard-shelled and must be tethered to whatever drives their locomotion. For this reason, truly autonomous capabilities are not yet feasible. The goal of this thesis is to introduce a robot that not only sets the groundwork for autonomous locomotion, but also is safe for human-robot interaction. This was done by ensuring that the actuation principle utilized by the robot is safe around humans and can work in an untethered design. Artificial muscle actuation allowed for these prerequisites to be met. These artificial muscles are made of fishing line and are twisted, wrapped in conductive heating wire, and then coiled around a mandrel rod. When electrical current passes through the heating wire, the artificial muscles expand or contract, depending on how they were created. After the muscles were manufactured, experiments were done to test their functionality. Data was collected via a series of experiments to investigate the effect of various processing parameters on the performance, such as the diameter of the mandrel coiling rod, the applied dead weight, the applied current, cyclic tests, and pulse tests. After acquiring data from the artificial muscles, a prototype was designed that would incorporate the expansion and contraction artificial muscles. This prototype featured two variable friction end caps on either side that were driven via expansion muscles, and a central actuation chamber driven via an antagonistic spring and contraction artificial muscle. The prototype proved its locomotion capabilities while remaining safe for human-robot interaction. Data was collected on the prototype in two experiments – one to observe the effect of varying induced currents on axial deformation and velocity, and one to observe the effect of varying deadweights on the same metrics. The prototype was not untethered, but future research in the implementation of an on-board power source and microcontroller could prove highly feasible with this design

Large Deformable Soft Actuators Using Dielectric Elastomer and Origami Inspired Structures

There have been significant developments in the field of robotics. Significant development consists of new configurations, control mechanisms, and actuators based upon its applications. Despite significant improvements in modern robotics, the biologically inspired robots has taken the center stage. Inspired by nature, biologically inspired robots are called ‘soft robots’. Within these robots lies a secret ingredient: the actuator. Soft robotic development has been driven by the idea of developing actuators that are like human muscle and are known as ‘artificial muscle’. Among different materials suitable for the development of artificial muscle, the dielectric elastomer actuator (DEA) is capable of large deformation by applying an electric field. Theoretical formulation for DEA was performed based upon the constitutive hyperelastic models and was validated by using finite element method (FEM) using ABAQUS. For FEM, multistep analysis was performed to apply pre-stretch to the membrane before applying actuation voltage. Based on the validation of DEA, different configurations of DEA were investigated. Helical dielectric elastomer actuator and origami dielectric elastomer actuator were investigated using theoretical modeling. Comparisons were made with FEM to validate the model. This study focus on the theoretical and FEM analysis of strain within the different configuration of DEA and how the actuation strain of the dielectric elastomer can be translated into contraction and/or bending of the actuator

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

The diversity of hydrostatic skeletons

A remarkably diverse group of organisms rely on a hydrostatic skeleton for support, movement, muscular antagonism and the amplification of the force and displacement of muscle contraction. In hydrostatic skeletons, force is transmitted not through rigid skeletal elements but instead by internal pressure. Functioning of these systems depends on the fact that they are essentially constant in volume as they consist of relatively incompressible fluids and tissue. Contraction of muscle and the resulting decrease in one of the dimensions thus results in an increase in another dimension. By actively (with muscle) or passively (with connective tissue) controlling the various dimensions, a wide array of deformations, movements and changes in stiffness can be created. An amazing range of animals and animal structures rely on this form of skeletal support, including anemones and other polyps, the extremely diverse wormlike invertebrates, the tube feet of echinoderms, mammalian and turtle penises, the feet of burrowing bivalves and snails, and the legs of spiders. In addition, there are structures such as the arms and tentacles of cephalopods, the tongue of mammals and the trunk of the elephant that also rely on hydrostatic skeletal support but lack the fluid-filled cavities that characterize this skeletal type. Although we normally consider arthropods to rely on a rigid exoskeleton, a hydrostatic skeleton provides skeletal support immediately following molting and also during the larval stage for many insects. Thus, the majority of animals on earth rely on hydrostatic skeletons

Developing Design and Analysis Framework for Hybrid Mechanical-Digital Control of Soft Robots: from Mechanics-Based Motion Sequencing to Physical Reservoir Computing

The recent advances in the field of soft robotics have made autonomous soft robots working in unstructured dynamic environments a close reality. These soft robots can potentially collaborate with humans without causing any harm, they can handle fragile objects safely, perform delicate surgeries inside body, etc. In our research we focus on origami based compliant mechanisms, that can be used as soft robotic skeleton. Origami mechanisms are inherently compliant, lightweight, compact, and possess unique mechanical properties such as– multi-stability, nonlinear dynamics, etc. Researchers have shown that multi-stable mechanisms have applications in motion-sequencing applications. Additionally, the nonlinear dynamic properties of origami and other soft, compliant mechanisms are shown to be useful for ‘morphological computation’ in which the body of the robot itself takes part in performing complex computations required for its control. In our research we demonstrate the motion-sequencing capability of multi-stable mechanisms through the example of bistable Kresling origami robot that is capable of peristaltic locomotion. Through careful theoretical analysis and thorough experiments, we show that we can harness multistability embedded in the origami robotic skeleton for generating actuation cycle of a peristaltic-like locomotion gait. The salient feature of this compliant robot is that we need only a single linear actuator to control the total length of the robot, and the snap-through actions generated during this motion autonomously change the individual segment lengths that lead to earthworm-like peristaltic locomotion gait. In effect, the motion-sequencing is hard-coded or embedded in the origami robot skeleton. This approach is expected to reduce the control requirement drastically as the robotic skeleton itself takes part in performing low-level control tasks. The soft robots that work in dynamic environments should be able to sense their surrounding and adapt their behavior autonomously to perform given tasks successfully. Thus, hard-coding a certain behavior as in motion-sequencing is not a viable option anymore. This led us to explore Physical Reservoir Computing (PRC), a computational framework that uses a physical body with nonlinear properties as a ‘dynamic reservoir’ for performing complex computations. The compliant robot ‘trained’ using this framework should be able to sense its surroundings and respond to them autonomously via an extensive network of sensor-actuator network embedded in robotic skeleton. We show for the first time through extensive numerical analysis that origami mechanisms can work as physical reservoirs. We also successfully demonstrate the emulation task using a Miura-ori based reservoir. The results of this work will pave the way for intelligently designed origami-based robots with embodied intelligence. These next generation of soft robots will be able to coordinate and modulate their activities autonomously such as switching locomotion gait and resisting external disturbances while navigating through unstructured environments

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

Verfahren und Anlagenprototyp zur Herstellung dünnwandiger Hohlzylinder aus Silikonelastomer mit integrierten Fluidkammern und –kanälen

Die minimal-invasive Chirurgie gewinnt innerhalb der invasiven Therapieverfahren weiterhin an Bedeutung, verspricht man sich davon doch eine schnellere Genesung des Patienten, verbunden mit einer Reduktion der finanziellen Aufwände für das Gesundheitssystem. Zu diesem Zweck werden Lokomotionssysteme benötigt, die sich aktiv in den natürlichen Körperhöhlen des Patienten fortbewegen können, um Arbeitskanäle und Operationswerkzeuge des Chirurgen von außen zum gewünschten Operationsfeld zu transportieren. Vollständig nachgiebige, miniaturisierte Systeme mit wurmartiger Fortbewegung sind dabei im Fokus der internationalen Entwicklungen. Eine wesentliche Limitation bei der Entwicklung und weiteren Miniaturisierung solcher Lokomotionssysteme besteht durch die verfügbaren Herstellverfahren. Die vorliegende Arbeit stellt ein neues Verfahren und einen Anlagenprototyp zur Herstellung dünnwandigen Hohlzylinders aus Elastomer vor, in deren Wandung im Rahmen des Verfahrens Fluidkammern und –kanäle integriert werden. Durch Befüllung der Miniaturfluidsysteme mit Fluid und Steuerung des ein- bzw. ausgepumpten Fluidvolumens, kann eine zielgerichtete Verformung der Kammern erzeugt werden. Durch Ausstattung des Hohlzylinder mit einer ganzen Reihe von Kammern und Kanälen soll so im Rahmen weiterer Entwicklungen eine peristaltische Sonde entstehen, die sich wurmartig im Wirbelkanal fortbewegen kann. Das vorgestellte Verfahren besteht aus den folgenden Schritten: 1. Auf einen Metallstab wird durch Tauchen (Dip-Coating) eine lösbare Trennschicht aus Photoresist aufgebracht. 2. Anschließend wird auf der Trennschicht und ebenfalls durch Tauchen eine erste, die innere Schicht aus Silikonelastomer erzeugt. 3. Diese Silikonschicht wird durch Aufsprühen (Spray-Coating) unter Nutzung spezieller Prozeßparameter mit Photoresist beschichtet, welches anschließend mittels Laser-Lithografie belichtet wird. 4. Nach dem Entwickeln, Spülen und Trocknen verbleiben auf der Oberfläche der Silikonschicht Resiststrukturen, die die späteren Fluidkammern und Zuläufe repräsentieren. 5. Diese Resiststrukturen sind Platzhalter für das innere, später mit Fluid gefüllte Volumen, wenn in einem weiteren Schritt erneut durch Tauchen die äußere Silikonelastomerschicht aufgebracht wird. In Anlehnung an die klassische Gießerei- und an die Mikrosystemtechnik können die Resiststrukturen auch als Opferstrukturen bezeichnet werden. 6. Anschließend wird der entstandene Silikonkörper mit entsprechenden Schlauchzuleitungen verbunden und über diese wird Lösungsmittel zugeführt, welches die Resiststrukturen auflöst. 7. Nach dem Spülen der Kammern und Zuläufe können diese mit dem Arbeitsfluid (z.B. sterile, isotonische Kochsalzlösung) befüllt werden