Programmable Second Skin For Re-Educating Injured Nervous Systems

Abstract

This project is a novel, wearable, bio-inspired cyberphysical assistive device for rehabilitation of injured nervous systems, called the "second skin." The device is characterized by (a) a soft, responsive interface with the body, (b) sensors and actuators that emulate the function of biological components, and (c) a control system based upon distributed networks with modular components. Unlike current exoskeletons that are heavy and structurally like motorized braces, our cyberphysical device is fabricated from soft, elastic, conformable materials. The sensing, actuation, and control functions are each inspired by natural systems. For example, nature uses multiple receptors to transduce body motions in parallel, and at different time scales: a faster time scale that uses mechanical stretch as a signal for regulating individual muscle contractions, and a slower time scale for sensory modulation of the contraction of organized muscle groups in response to changing environmental conditions. And finally, distributed biological networks comprised of modular components are the basis for multifunctionality (using different combinations of the same components) in insects, invertebrates, and vertebrates. The second skin cyberphysical system is designed as a hybrid elastomer-fabric cylinder with embedded sensors and soft actuators. By collectively contracting multiple actuators, the device not only changes its overall shape but also produces pulling or bending forces. Each actuator has its own soft sensor for measuring the local displacement of the actuator. The device is also equipped with multiple inertial measurement units (IMUs) for detecting global shape changes. As the body moves through complicated shape changes, the second skin material stretches and compresses to maintain its conformation. Artificial tendons provide elastic potential energy that is released to assist the biological and synthetic muscle actuation. Each functional unit is composed of a soft actuator and a soft sensor. The soft actuator is a custom-built McKibben-type pneumatic synthetic muscle. When compressed air is supplied to each synthetic muscle, it contracts in its axial direction. Each synthetic muscle is equipped with a hyperelastic strain sensor that abuts one surface to measure the synthetic muscle's contraction. Each strain sensor is fabricated from silicone elastomer and is designed with embedded micro-channel patterns filled with liquid metal (Eutectic Gallium Indium, or EGaIn) that changes overall resistance of the channels as strain is imposed. Electrical resistance increases with axial contraction of the muscle. The system is divided into local and global service layers. The local layer implements fundamental components that manage local resources (clock-driven real-time scheduler, inter-modular communication, and commands to local sensors and actuators). The global layer specifies the application goal with the services provided by the local service layer. The controller network uses a clock-driven scheduling approach to provide predictable timing for achieving device goals. The system parses time into fixed width chunks, called rounds. Each round is further divided into five fixed-order stages: sense, fetch, process, actuate, and emit. The duration of each round is configurable. Since each controller can only communicate with one neighbor at each instant, the controller network relies on a topology-aware scheduling scheme to carry out network-wide communications.

Award ID: 0932015