Synthesis of Novel Integrated Actuators Powered by Shape Memory Alloys

In the modern age of miniaturisation, Smart Materials, a type of material that reacts mechanically to a certain stimulus, have become an integral part of this revolution. Among these materials, Shape Memory Alloys (SMAs), which have the highest volumetric work density, are the ideal candidate in creating lightweight and miniature actuators. These alloys, after being deformed, are able to revert back to their original shape when exposed to heat. This exotic behaviour has allowed them to be the core active component in a plethora of applications such as grippers, bio-mimetic robots and surgical instruments.Despite their high work density, their implementation comes with some challenges. While the Shape Memory Effect (SME), the ability to recover strain when a thermal load is applied, is a remarkable behaviour, it is also a complex and multi-physical one. This complicates their design and makes it difficult to predict their behaviour. Furthermore, these alloys are only able to recover strain when deformed at low temperatures. This implies that a biasing element is required to exploit these materials in reversible actuators. Due to these limitations, the work density of SMAs, when implemented as actuators in robotic systems, are often much lower than their theoretical maximum.In this thesis, the various types of SMA actuator implementations from different applications are examined to understand the design requirements and subsystems that are necessary to build an actuator. A holistic approach is, then, used to construct a design methodology to create highly integrated actuators in the hopes of preventing the work density degradation present in traditional SMA-based systems. Here, in this work, the identified subsystems of the SMA actuator are combined to serve as a multi-functional element in the novel integrated actuator.The work employs different strategies to integrate the SMA actuator into robotic systems while also proposing adapted sizing methodologies. The resulting SMA-powered system can be sized to be lightweight, compact and dynamic. Various case studies are presented that utilise the proposed holistic design approach and sizing methodologies to serve as a proof-of-concept and to validate the methodology.In this work, compliant and flexure-based mechanisms are exploited to exclude the need for a dedicated biasing element and create lightweight SMA-powered grippers to demonstrate the advantages of the proposed methodology. Additionally, utilising the mechanical behaviour of the SME, a lightweight mechanically-controlled crawling robot is designed and implemented. Furthermore, with the help of topology optimization and kirigami-inspired design, the work details the creation of compliant SMA structures that allow the material to generate multiple outputs while remaining compact and easy to assemble. Lastly, a novel bistable gripper is designed and sized to experimentally validate the design methodologies proposed in this work.The work demonstrates the different areas in which the degradation of the work density occur in traditional SMA systems. In this regard, design methodologies accompanied with sizing strategies are proposed that allows the creation of lightweight, high bandwidth and integrated SMA-based robotic systems. The results in this thesis, reveal the extraordinary value of SMAs in creating lightweight robotic systems and presents various strategies to allow the further integration of the alloy within the system.

Development and control of interactive reconfigurable robotic systems

Jian-Lin Huang

While reconfigurable robots provide a new promising approach for interactive systems, the complexity of distributed actuation/sensing systems, coupled kinematics and desired functionalities also bring new challenges and questions both in control design and hardware development: What design approaches enable direct human-robot interactions to address the morphological transformations and constraints of multi-DoF distributed activated robotic system? How to implement in-situ, multi-stage, programmable, and controllable actuation for the desired range of motion and functionalities? How to design multi-DoF robotic systems and needed for operation in distinct, real-world applications? These challenges and research questions formulate the objective and framework of my thesis. Namely, I explore for the solutions to provide methodologies for not only building the hardware for reconfigurable interactive systems but also investigating the control algorithm considering human-in-the-loop and evaluating the effectiveness of the integrated system with different application scenarios. In order to address the challenges associated with the development of reconfigurable robotic systems for human interactions, I first outline the concept of an interactive interface between humans and robots. I study the design methods for intuitively and dynamically controlling multi-DoF reconfigurable systems and algorithms for integrating mechanical characteristics of the core robotic components. Then, we investigate the design space and limitation of gesture-based multi-modalities interactions for further exploring the controllability, scalability, and versatility in functions for reconfigurable robotic systems. To realize the reconfigurable interactive robotic system, the design, capability, and limitation of the hardware system need to be established and evaluated. One of my research goals is to take the advantage of current non-conventional manufacturing technologies and materials as well as overcome their limitations. I study and develop compact actuators and unique transmission mechanisms inspired by origami patterns that can be integrated with multi-DoF robotic systems. I start with the design, model, and experimental validation of core functional components. Then, we investigate the fabrication process which has an additive manufactured structure with subtractive manufactured functional components integrated for compact, light-weight, and distributed activated mechanisms. Lastly, I propose the strategies for configuring and controlling the functional components to achieve functionalities like multi-DoF distributed actuation, self-assembly, and tunable stiffness. The achievable functionalities are further examined with several application scenarios. The main contributions of this thesis are: Development of interactive control interface for reconfigurable robotic systems Design and validation of distributed actuation solution and transmission mechanisms for compact multi-DoF robotic systems Study the synergy of additive manufacturing techniques and smart materials for achieving customizable functionalities and overcoming the limitation for conventional robotic systems

EPFL2021

Design Methodology for Engineering Multifunctional Mesoscale Robots

Zhenishbek Zhakypov

In this thesis our research goal is to develop, study and demonstrate multifunctional multi-robot systems in mesoscale. Particularly, our goal is to study and demonstrate terrestrial multi-locomotion and collective behaviours with mesoscale robots, similar to small-scale natural systems, by feeling the gap in the field. Our research objective is to develop, evaluate and demonstrate minimal, compact, variable power and efficient actuation mechanisms for multi-locomotion and rapid fabrication methods for robot multiplicity employing functional materials and composite design. In doing so, we intend to establish a comprehensive and systematic design methodology for designing multifunctional, mass-producible mesoscale robots for various applications. This dissertation first attempts to explore and answer the following key research question: how to achieve variable power, efficient and compact actuation in mesoscale? The relation between performance and physicality is significant for especially mesoscale robot design and is poorly studied. Our goal is to achieve high power, variable speed and high efficiency actuation in mesoscale. We attempt to address this by exploring unconventional active material-based actuation methods using shape memory alloy and composite material. In doing so, we quest of the following: what are the compromises should be made between force, speed, efficiency and size of functional material-based actuators? We investigate and demonstrate new, compact multimaterial actuators and mechanisms that possess power density superior to conventional motors, produce high speed and high force actuation and achieve multifunctionality when distributed and actuated selectively, all with minimal and compact forms and integrity. While we study and develop design methods at the component level, like actuation, based on performance and physical features, we look for the same at the composite level or robotic system level. The next research question we attempt to address is what, if any, is the general design methodology for constructing composite robots?. To address this we formulate and analyze robogami design in terms of mechanisms, geometry, functional components, materials and fabrication to highlight their relation, potential and the challenges, as well as to structure the knowledge in the field. This leads to a systematic design approach that consolidates these critical design features and facilitates robot design and fabrication process. To ensure applicability of our methodology, we analyze the design process of composite robots reported in the literature and design a multi-locomotion mesoscale robot, called Tribot, as a case study. We further investigate the application of the proposed actuation and rapid composite robot design methods by questing of how to achieve multifunctional multi-robot behaviors in mesoscale? We address this by constructing a unique, untethered, multi-locomotion robotic collective to study locomotion and cooperative behaviors. We investigate minimal, compact and tunable mechanisms that generate high power jumping and low power crawling locomotion. We overcome the key trade-off between the actuation power and weight and construct a 10 g palm-sized prototype, the smallest and lightest self-contained, multi-locomotion robot to date, by folding a quasi-2-D mechamatronic composite with locomotion mechanisms, smart actuation and sensing layers, enabling robot multiplicity assembly-free mass-production.

EPFL2019

Shape Memory Effect of Benchmark Compliant Mechanisms Designed With Topology Optimization

Thomas Guillaume Martinez, Yves Perriard, Adrien Jean-Michel Thabuis, Sean Thomas

Shape Memory Alloys (SMA) are a class of Smart Materials that are ideal for creating compact actuators. The complex nature of their behavior results in the use of these materials in simple geometries (wires, sheets) limiting their performances. A design method to develop complex compliant mechanisms made of SMA is proposed in this paper. Using topology optimization for conventional materials, a set of benchmark problems are designed. Finite element modelling is then able to validate the shape memory effect of the designs (with strain retention up to 80%), confirming the notion that this methodology can, in fact, be used to design the next generation of SMA actuators.