Nano-to-macroscopically architectured shape memory actuators for wearable human-interactive robotics

Abstract

In the rapidly advancing realm of robotics, human-interactive robotics (HIR) epitomize the quest to amplify the symbiotic relationship between humans and machines. To further enhance user experiences and allow natural movement during interactions, interfaces for HIRs are moving progressively closer to the skin's surface in a wearable form. This thesis delves into the development of shape memory alloy-based wearable human-interactive interfaces that blend intuitive feedback with wearable comfort. When utilized as actuators, shape memory alloys offer benefits like lightness, high force generation, silent operation, and adaptability to diverse shapes. However, their drawback lies in a sluggish cooling rate, which limits their actuation speed. In addition, when designing wearable interfaces that make close contact with the body, it is vital yet challenging to prioritize lightweight, compactness, ergonomic design, and aesthetic appeal. To address the inherent limitations and challenges, a multiscale material engineering approach was adopted by introducing optimal scale-specific architecture designs, in nano to macroscopic levels, to the shape memory alloy-based actuators. Firstly, we aim to enhance the actuation speed of small and intricately structured 3D spring-shaped SMA actuators by directly growing even smaller nanoscale conductive copper nanowires on their surfaces. By increasing the surface area of the SMA in this manner, we intend to promote heat dissipation and achieve faster actuation speeds. Secondly, to improve wearability, we develop a multimodal wearable haptic interface by knotting SMA wires into auxetic meta-structures. This auxetic-architectured interface conforms to the body's curves when worn and provides diverse spatiotemporal tactile feedback. Thirdly, we aim to develop a wearable interface that offers multifunctionality, but at the same time, with considerations for ergonomic design and aesthetic appeal. This interface includes multimodal haptic actuators embedded in a single auxetic meta-structure, where each component operates independently, culminating in the development of an auxetic-architectured wearable multimodal interface. Through nano-to-macroscopically architectured SMA-based actuators, we aim to pave the way for developing user-friendly wearable robotics and interfaces that bridge humans and robots to interact seamlessly and broaden our immersion into virtual, augmented, and mixed realities.