Flexure Variable Stiffness Actuators

Series elastic actuators (SEAs) and variable elastic actuators (VSAs) provide shock resistance, energy storage, and stable force control. However, they usually require extra springs, mechanical parts, and transmissions, increasing size, weight, number of moving parts, and reducing the mechanical efficiency. In particular, this mechanical complexity is one of the significant challenges in the design of wearable and scalable force feedback devices. In this article, flexure variable stiffness actuators (F-VSAs), which combine kinematic transmission, elasticity, and stiffness modulation via a network of folding patterns using flexure hinges, are presented. Thus, F-VSAs allow the creation of robots benefiting from the advantages of SEAs and VSAs without hindering form factor or mechanical efficiency. To illustrate the design strategy of F-VSAs, a 4-design-of-freedom (DoF) robot that provides stiffness and force output is presented. An analytical model that estimates the inherent stiffness and the end-effector force output for any given configuration of the folding pattern is proposed. Finally, stiffness modulation and force control of the robot are implemented and good agreement with the predictions from the model is observed. Thus, this novel design strategy allows the creation of compact and scalable robots with stiffness and force output for wearable, rehabilitation, and haptic applications.

Development of Essential Components for Soft Wearable Technologies

Amir Firouzeh

The rising demand for safe human-robot interaction in daily tasks has motivated significant research effort in the robotics field towards compliant and conformable robots, capable of replicating complex human movements in applications such as wearable rehabilitative devices and haptic interfaces. Novel manufacturing, actuation, and sensing technologies contributed significantly to this field by providing design and manufacturing frameworks for inherently compliant robots. Although promising, these technologies are still in the early stages of development and base research for refining their design, improving their performance, and defining design criteria is still required for these technologies to reach their full potential. In this thesis, some of the main challenges hindering the effective application of robotics in wearable devices are tackled. We propose the robotic origami (robogami) framework with multiple but finite degrees of freedom (DoFs) for soft wearable devices. Robogamis are low profile robots that provide conformity and compliance with their multiple DoFs driven by soft actuation methods. The finite DoFs in these robots enable better prediction and planning of their motion while highly customizable joint designs, thanks to the layer-by-layer manufacturing and the precise quasi-2D fabrication processes, allows the multiple DoFs to be embedded to achieve the required level of conformity. The main contributions of this thesis are: -Study of the robogami framework as a design platform for soft robots with programmable reconfiguration and compliance. -Design and validation of actuation solutions based on smart materials for independent actuation of robogami joints. -Adoption of the smart materials' variable mechanical properties to adjust the stiffness of robogami joints and the overall compliance of the robot. -Development of customized sensing methods to measure robogami joint angles and stretchable sensors based on the same principles to measure body movements. We believe that these contributions facilitate some of the main challenges for the effective application of robogamis in wearable devices for safe and yet capable interaction with humans. The highly customizable components can also be used in design frameworks other than robogamis and other applications where compliance and conformity are required.

EPFL2017

Comprehensive Interactive Soft Interfaces for Wearable Tactile Feedback

Harshal Arun Sonar

As the field of robotics continues to grow outside the manufacturing environment into our daily lives, the interactions between humans and robots are increasingly becoming close and dynamic. This type of environment requires robots to be less rigid, multi-functional, safer, and compliant with human bodies. Such robotics interfaces are ideally suited for medical rehabilitation, elderly assistance to at-home entertainment devices. However, the traditional rigid robotic devices fail to address some of the design criteria posed for safety, compliance, and physical limitations on the mechanical design. In the case of wearable technologies, the robotic device additionally requires a lightweight, compliant, and safe interface to provide smooth communication and interaction with humans. The traditional robotic systems are fast, accurate, and can handle large torques. However, they are also, application-specific and not suitable as it is for the wearable scenario due to the contradictory design requirements. In the past decade, soft robotics has emerged as a novel approach to solve the complex problems faced by rigid robots using inherent softness and compliant material properties. The design for the future interactive wearable interfaces thus may lie in the intersection of developments in the fields of wearable technology and soft robotics.Designing a wearable interactive interface with soft materials for wearability, portability, cost-effectiveness, and modularity would be one of the ideal solutions to tackle the wearability challenge. It can be a cost-effective solution for at-home assistive rehabilitation or entertainment. It also allows developing novel methods of soft sensing, actuation, control strategies, and human in loop protocols to maximize the utility of inherent material properties and environment around the robotic device.In my Ph.D. research, I develop and create hardware and software towards an immersive interactive soft virtual-tactile environment focusing on the wearability, portability, easy customization, and modularity aspects. I developed a low profile soft pneumatic actuator-skin (SPA-skin) with distributed sensing and actuation capabilities for testing various levels of complex vibrotactile feedback: the multilayer composite of high-sensitivity PZT pressure sensors and vibratory SPA can produce up to 3 N output force at 0-100 Hz. This demonstrated that SPA-skin produces distinctive and dynamic haptic force feedback under modulated varying time, force, and spatial resolution. Furthermore, a complete framework for designing a tactile feedback skin for specific wearable applications is developed, starting from the material selection and actuator design, and concluding with the validation of the subjectâs perceived feedback. As soon as, the SPA-skin is required to be worn by humans, the complexity of the problem multiplies due to lack of proper grounding to ensure the blocked forces. The platform is further optimized for application space in fMRI compliant environment and a user study protocol for somatosensory thresholds is designed. The modulable and controllable nature of SPA-skinâs tactile feedback provides much-needed validation using BOLD signals from brain imaging. SPA-skin and findings presented herein, provide a foundational platform to further investigate the sensitivity of human skin and decipher mechanoreceptor reactions for a diverse range of human-robot interactions and wearable technology.

EPFL2021

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

Comprehensive Interactive Soft Interfaces for Wearable Tactile Feedback

Harshal Arun Sonar

EPFL2021

Development of Essential Components for Soft Wearable Technologies

Amir Firouzeh

EPFL2017

Development and control of interactive reconfigurable robotic systems

Jian-Lin Huang

EPFL2021