Resistive force theory-based analysis of magnetically driven slender flexible micro-swimmers

Resistive force theory is concise and reliable approach to resolve flow-induced viscous forces on submerged bodies at low Reynolds number flows. In this paper, the theory is adapted for very thin shell-type structures, and a solution procedure within a nonlinear finite element framework is presented. Flow velocity proportional drag forces are treated as configuration-dependent external forces and embedded in a commercial finite element solver (ABAQUS) through user element subroutine. Furthermore, incorporation of magnetic forces induced by external fields on magnetic subdomains of such thin-walled structures is addressed using a similar perspective without resolving the magnetic field explicitly. The treatment of viscous drag forces and the magnetic body couples is done within the same user element formalism. The formulation and the implementation are verified and demonstrated by representative examples including the bidirectional swimming of thin strips with magnetic ends

Assembly Modulated by Particle Position and Shape: A New Concept in Self-Assembly

In this communication we outline how the bespoke arrangements and design of micron-sized superparamagnetic shapes provide levers to modulate their assembly under homogeneous magnetic fields. We label this new approach, ‘assembly modulated by particle position and shape’ (APPS). Specifically, using rectangular lattices of superparamagnetic micron-sized cuboids, we construct distinct microstructures by adjusting lattice pitch and angle of array with respect to a magnetic field. Broadly, we find two modes of assembly: (1) immediate 2D jamming of the cuboids as they rotate to align with the applied field (rotation-induced jamming) and (2) aggregation via translation after their full alignment (dipole-dipole assembly). The boundary between these two assembly pathways is independent on field strength being solely a function of the cuboid’s dimensions, lattice pitch, and array angle with respect to field—a relationship which we capture, along with other features of the assembly process, in a ‘phase diagram’. In doing so, we set out initial design rules to build custom made assemblies. Moreover, these assemblies can be made flexible thanks to the hinged contacts of their particle building blocks. This flexibility, combined with the superparamagnetic nature of the architectures, renders our assembly method particularly appropriate for the construction of complex actuators at a scale hitherto not possible

A Fully Implicit Method for Robust Frictional Contact Handling in Elastic Rods

Accurate frictional contact is critical in simulating the assembly of rod-like structures in the practical world, such as knots, hairs, flagella, and more. Due to their high geometric nonlinearity and elasticity, rod-on-rod contact remains a challenging problem tackled by researchers in both computational mechanics and computer graphics. Typically, frictional contact is regarded as constraints for the equations of motions of a system. Such constraints are often computed independently at every time step in a dynamic simulation, thus slowing down the simulation and possibly introducing numerical convergence issues. This paper proposes a fully implicit penalty-based frictional contact method, Implicit Contact Model (IMC), that efficiently and robustly captures accurate frictional contact responses. We showcase our algorithm's performance in achieving visually realistic results for the challenging and novel contact scenario of flagella bundling in fluid medium, a significant phenomenon in biology that motivates novel engineering applications in soft robotics. In addition to this, we offer a side-by-side comparison with Incremental Potential Contact (IPC), a state-of-the-art contact handling algorithm. We show that IMC possesses comparable performance to IPC while converging at a faster rate.Comment: * Equal contribution. A video summarizing this work is available on YouTube: https://youtu.be/g0rlCFfWJ8

형상기억 합금을 이용한 마이크로스케일 고속 구동기의 제작 및 평가

학위논문 (박사)-- 서울대학교 대학원 공과대학 기계항공공학부, 2017. 8. 안성훈.We designed, fabricated, and evaluated a shape memory alloy-based microscale actuator. To achieve complex shape fabrication and an in situ mechanical characterization, a manipulation and characterization platform equipped with high-resolution nanopositioners (with multiple degrees of freedom) and a micro-force sensor was developed. The challenges inherent in precise and accurate fabrication of samples with complex geometry were overcome so that the platform can be used for mechanical property characterization with an in situ method in the high vacuum chamber of a focused ion beam (FIB) system. Using the developed platform, diamond-shaped frame structures 1–1.5 μm in thickness were manufactured using an FIB milling process with a shape memory alloy (SMA). The behavior of these structures under mechanical deformation and changes in thermal conditions was investigated with respect to use as a driving force for a high-speed microscale actuator. Thermal energy was delivered by an optical method, including ion beam irradiation and laser irradiation. Because this method does not require any wiring, unlike other heating methods such as Joule heating, we could realize the fabricated SMA structure without any structural interruptions that could negatively affect the fast actuation motion. As an application, a microscale actuator is proposed. Due to the scale effect, a microscale linear motion actuator can vibrate at over 500 Hz with laser-induced heating. The reaction force and response speed were investigated according to changes in the laser switching speed and power. Additionally, a gripper having a negative Poissons ratio structure could grab small objects and deliver an objective by triggering the shape memory effect. We expect the proposed actuators to contribute to the development of micro- and nanoscale devices for microscale investigations and medical purposes.Chapter 1. Introduction 1.1. Toward miniaturization 1.2. Shape Memory Alloy (SMA) 1.3. Shape memory alloy based microscale actuator 1.4. Focused Ion Beam technique in micro- and nanoscale structuring 1.5. In-situ characterization in SEM/FIB system 1.6. Goals of this research Chapter 2. Platform for manufacturing and test 2.1. Focused Ion Beam (FIB) system 2.2. Platform design of in-situ fabrication and evaluation 2.3. Application of developed platform: Case studies Chapter 3. Fabrication and evaluation of SMA microstructure 3.1. Test platform 3.2. Thin film fabrication using FIB milling. 3.3. Patterning method in FIB milling process 3.4. Prediction of damages at the surface caused by FIB milling process 3.5. Characterization of SMA cells 3.6. Force depend on angle 3.7. Investigation of deformation behavior with computational simulation Chapter 4. Development of SMA based actuator. 4.1. Evaluation of shape memory effect. 4.2. Shape memory effect under ion beam irradiation condition 4.3. Shape memory effect under ambient heating 4.4. Shape memory effect with laser induced heating 4.5. Development of hardware for laser-induced SMA actuation Chapter 5. Development of high-speed micro-actuator and robot 5.1. High-speed linear actuation 5.2. Design and fabrication of Micro Gripper 5.3. High-speed linear vibration actuator 5.4. Actuation with 2-way shape memory effect Chapter 6. ConclusionsDocto

DEVELOPMENT OF A NANOCOMPOSITE SENSOR AND ELECTRONIC SYSTEM FOR MONITORING OF LOCOMOTION OF A SOFT EARTHWORM ROBOT

The ability to detect external stimuli and perceive the surrounding areas represents a key feature of modern soft robotic systems, used for exploration of harsh environments. Although people have developed various types of biomimetic soft robots, no integratedsensor system is available to provide feedback locomotion. Here, a stretchable nanocomposite strain sensor with integrated wireless electronics to provide a feedbackloop locomotion of a soft robotic earthworm is presented. The ultrathin and soft strain sensor based on a carbon nanomaterial and a low-modulus silicone elastomer allows for a seamless integration with the body of the soft robot, accommodating large strains derived from bending, stretching, and physical interactions with obstacles. A scalable, costeffective, screen-printing method manufactures an array of strain sensors that are conductive and stretchable over 100% with a gauge factor over 38. An array of stretchable nanomembrane interconnectors enables a reliable connection between soft strain sensors and wireless electronics, while tolerating the robot’s multi-modal movements. A set of computational and experimental studies of soft materials, stretchable mechanics, and hybrid packaging provides key design factors for a reliable, nanocomposite sensor system. The miniaturized wireless circuit, embedded in the robot joint, offers a real-time monitoring of strain changes on the earthworm skin. Collectively, the soft sensor system shows a great potential to be integrated with other flexible, stretchable electronics for applications in soft robotics, wearable devices, and human-machine interfaces.M.S

Development of a Novel Amphibious Locomotion System for use in Intra-Luminal Surgical Procedures

Colonoscopy is widely considered the gold standard for inspection of the colon. The procedure is however not without issue, current colonoscopes have seen little change or innovation throughout their 40 years of use with patient discomfort still limiting success. The aim of this PhD study was to develop a locomotion system for use on a robotic device that can traverse a liquid filled colon for atraumatic inspection and biopsy tasks. The PhD was undertaken as part of a larger two-centre EU project, which aimed to bring about a change in the way colonoscopy is done by moving to “robotic hydro-colonoscopy”. In this thesis the initial development and testing of an amphibious locomotion concept for use in a procedure known as hydro-colonoscopy is described. The locomotion system is comprised of four Archimedes’ screws arranged in two counter-rotating pairs. These aim to provide propulsion through a fluid-filled colon as well as provide locomotive traction against colonic tissue in partially fluid-filled or collapsed sections of the colon, such as the splenic flexure. Experimental studies were carried out on a single screw system in fluid and dual counter-rotating screws in contact conditions. These show the system’s ability to generate thrust in the two discrete modes of locomotion of the amphibious system. A 2:1 scale prototype of the proposed device was produced and features compliant screw threads to provide atraumatic locomotion. The scale prototype device was tested in ex-vivo porcine colon. The developed system was able to traverse through lumen to limited success, which demonstrated that this concept has the potential for use on an intra-luminal robotic device The key contributions of this research are: variable geometry locomotion system; amphibious locomotion using Archimedes’ screws; experimental assessment of the locomotion in fluid, contact and amphibious states; and analysis of the contact dynamics against tissue