Design and dynamic analysis of soft pneumatic systems for wearable robots

There are many challenges in the development of pneumatically powered soft robots due to the non-linearities of the materials used, non-linear pneumatic flow, complex non-standard designs, and high compliance that leads to loading-specific mechanical behaviour. As a result, there is still a significant gap towards understanding these robots, as compared to standard well-known actuators such as motors, rigid pneumatic actuators, or voice-coils. This thesis develops a comprehensive system-wide understanding of soft wearable robots through investigation and quantification of their soft actuator mechanical outputs, dynamic performance, and biomechanical effects. Towards this goal, we explore methods for accurate and consistent experimental characterization, modelling of SPA pressure and flow dynamics, and musculoskeletal modelling and analysis of soft wearable robots. First, we present a novel experimental protocol and setup for recreating application-specific loading conditions, in order to accurately capture the mechanical behaviour of soft robots. This concept is based on emulating the physical constraints acting on the soft robot at its contact points, and measuring the mechanical outputs. Then, we analyse the dynamic behaviour of SPAs and its dependency on the PSS and loading conditions. Via simulations and experimental testing, we map a direct relationship between properties of the PSS and SPA, and dynamic performance metrics. Using these relations, we present design optimization of PSSs for simultaneously meeting requirements of performance, portability and additional user-defined metrics such as mass or volume. By further investigating the effect of loading conditions on SPA dynamic behaviour, we introduce a previously unknown property of SPAs, self-sensing, that allows estimation of force and displacement without dedicated sensors. Finally, we investigate the biomechanical effect of soft wearable devices via the design and modelling of a soft exosuit for the human torso. The research in this thesis can be broadly categorized into three sections: quantifying mechanical behaviour of soft robots, modelling pressure dynamics of soft pneumatic actuators, and evaluating biomechanical effect of soft exosuits.

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 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

The Design and Modeling of a Novel Resistive Stretch Sensor With Tunable Sensitivity

Amir Firouzeh, Jamie Paik

Wearable technologies, interactive and safe robotic systems require an effective actuator control that highly depends on the accurate feedback from flexible and dense array of sensors. In this paper, we introduce a novel soft stretch sensor design that is applicable to distributed high strain measurements. The proposed sensor design utilizes 2-D fabrication processes to create specific profiles and stretchable mesh patterns in Constantan-polyimide laminate that are scalable and customizable. In addition to the geometrical parameters of the stretchable mesh pattern, the sensitivity in the proposed design is determined by the metal layer profile. Without considerably affecting its mechanical properties and stretchability, the profile design allows an engineering freedom to choose the scope of measurements and the sensitivity. Similar design principle can eventually produce complete sensor/circuit systems, where the circuitry and the sensing elements can coexist in a single metal laminate. In this paper, we describe the sensor design parameters and the sensor model that include the equations of deformation and resistance change as a function of the stretch. We compare the prototype test results to the model prediction. The findings provide guideline to designing customized sensors that satisfies specific size and stretch requirements.