Michelle C. Yuen

Active Variable Stiffness Fibers for Multifunctional Robotic Fabrics

In this letter, we introduce active variable stiffness fibers that are made from shape memory alloy and thermally responsive polymers. This combines the actuation of shape memory alloy with the variable stiffness of a thermoplastic using electric current as the stimulus. By combining both actuation and variable stiffness functions, the multifunctional fibers can move to a new position then hold that position without requiring additional power. We explore the possibility of tuning the fibers to meet varying structural and performance demands by selecting different thermoplastics with different glass transition temperatures. Finally, we integrate the active variable stiffness fibers into a fabric to demonstrate multifunctional robotic fabrics that can control the motion of soft, compliant bodies from their surface.

Conformable actuation and sensing with robotic fabric

Future generations of wearable robots will include systems constructed from conformable materials that do not constrain the natural motions of the wearer. Fabrics represent a class of highly conformable materials that have the potential for embedded function and are highly integrated into our daily lives. In this work, we present a robotic fabric with embedded actuation and sensing. Attaching the same robotic fabric to a soft body in different ways leads to unique motions and sensor modalities with many different applications for robotics. In one mode, the robotic fabric acts around the circumference of the body, and compression of the body is achieved. Attaching the robotic fabric in another way, along one surface of a body for example, bending is achieved. We use thread-like actuators and sensors to functionalize fabric via a standard textile manufacturing process (sewing). The actuated fabric presented herein yields a contractile force of 9.6N and changes in length by approximately 60% when unconstrained. The integrated strain sensor is evaluated and found to have an RMS error of 14.6%, and qualitatively differentiates between the compressive and bending motions demonstrated.

Sensor Skins: An Overview

Sensor skins can be broadly defined as distributed sensors over a surface to provide proprioceptive, tactile, and environmental feedback. This chapter focuses on sensors and sensor networks that can achieve strains on the same order as elastomers and human skin, which makes these sensors compatible with emerging wearable technologies. A combination of material choices, processing limitations, and design must be considered in order to achieve multimodal, biocompatible sensor skins capable of operating on objects and bodies with complex geometries and dynamic functionalities. This chapter overviews the commonly used materials, fabrication techniques, structures and designs of stretchable sensor skins, and also highlights the current challenges and future opportunities of such sensors.

Fabric sensory sleeves for soft robot state estimation

In this paper, we describe the fabrication and testing of a stretchable fabric sleeve with embedded elastic strain sensors for state reconstruction of a soft robotic joint. The strain sensors are capacitive and composed of graphite-based conductive composite electrodes and a silicone elastomer dielectric. The sensors are screenprinted directly into the fabric sleeve, which contrasts the approach of pre-fabricating sensors and subsequently attaching them to a host. We demonstrate the capabilities of the sensor-embedded fabric sleeve by determining the joint angle and end effector position of a soft pneumatic joint with similar accuracy to a traditional IMU. Furthermore, we show that the sensory sleeve is capable of capturing more complex material states, such as fabric buckling and non-constant curvatures along linkages and joints.

OmniSkins: Robotic skins that turn inanimate objects into multifunctional robots

Robotic skins are planar substrates with embedded actuation and sensing that can wrap around soft objects to turn them into robots. Robots generally excel at specific tasks in structured environments but lack the versatility and the adaptability required to interact with and locomote within the natural world. To increase versatility in robot design, we present robotic skins that can wrap around arbitrary soft bodies to induce the desired motions and deformations. Robotic skins integrate actuation and sensing into a single conformable material and may be leveraged to create a multitude of controllable soft robots with different functions or gaits to accommodate the demands of different environments. We show that attaching the same robotic skin to a soft body in different ways, or to different soft bodies, leads to distinct motions. Further, we show that combining multiple robotic skins enables complex motions and functions. We demonstrate the versatility of this soft robot design approach in a wide range of applications—including manipulation tasks, locomotion, and wearables—using the same two-dimensional (2D) robotic skins reconfigured on the surface of various 3D soft, inanimate objects.

Fabricating Microchannels in Elastomer Substrates for Stretchable Electronics

As flexible devices and machines become more ubiquitous, there is a growing need for similarly deformable electronics. Soft polymers continue to be widely used as stretchable and flexible substrates for soft electronics, and in particular, soft sensing. These soft sensors generally consist of a highly elastic substrate with embedded microchannels filled with a conductive fluid. Deforming the substrate deforms the embedded microchannels and induces a change in the electrical resistance through the conductive fluid. Microchannels, thus, are the foundation of flexible electronic devices and sensors. These microchannels have been fabricated using various methods, where the manufacturing method greatly impacts device functionality. In this paper, comparisons are made between the following methods of microchannel manufacturing: cast molding, 3D printing of the elastomer substrate itself, and laser ablation. Further processing of the microchannels into flexible electronics is also presented for all three methods. Lastly, recommended ranges of microchannel sizes and their associated reproducibility and accuracy measures for each manufacturing method are presented.