Wearable electronics is a rapidly growing field that recently started to introduce successful commercial products into the consumer electronics market. Employment of biopotential signals in wearable systems as either biofeedbacks or control commands are expected to revolutionize many technologies including point of care health monitoring systems, rehabilitation devices, human–computer/machine interfaces (HCI/HMIs), and brain–computer interfaces (BCIs). Since electrodes are regarded as a decisive part of such products, they have been studied for almost a decade now, resulting in the emergence of textile electrodes. This study presents a systematic review of wearable textile electrodes in physiological signal monitoring, with discussions on the manufacturing of conductive textiles, metrics to assess their performance as electrodes, and an investigation of their application in the acquisition of critical biopotential signals for routine monitoring, assessment, and exploitation of cardiac (electrocardiography, ECG), neural (electroencephalography, EEG), muscular (electromyography, EMG), and ocular (electrooculography, EOG) functions.

https://www.mdpi.com/2079-9292/8/5/479/pdf

Wearable and Flexible Textile Electrodes for Biopotential Signal Monitoring: A review

In this article, we present the design of a powered knee–ankle prosthetic leg, which implements high-torque actuators with low-reduction transmissions The transmission coupled with a high-torque and low-speed motor creates an actuator with low mechanical impedance and high backdrivability This style of actuation presents several possible benefits over modern actuation styles in emerging robotic prosthetic legs, which include free-swinging knee motion, compliance with the ground, negligible unmodeled actuator dynamics, less acoustic noise, and power regeneration Benchtop tests establish that both joints can be backdriven by small torques ( $\sim$ 1–3 N $\cdot$ m) and confirm the small reflected inertia Impedance control tests prove that the intrinsic impedance and unmodeled dynamics of the actuator are sufficiently small to control joint impedance without torque feedback or lengthy tuning trials Walking experiments validate performance under the designed loading conditions with minimal tuning Finally, the regenerative abilities, low friction, and small reflected inertia of the presented actuators reduced power consumption and acoustic noise compared to state-of-the-art powered legs

https://par.nsf.gov/servlets/purl/10057954

Design and Benchtop Validation of a Powered Knee-Ankle Prosthesis with High-Torque, Low-Impedance Actuators

Knee exoskeletons for gait rehabilitation and human performance augmentation: A state-of-the-art

High-performance actuators are crucial to enable mechanical versatility of wearable robots, which are required to be lightweight, highly backdrivable, and with high bandwidth. State-of-the-art actuators, e.g., series elastic actuators, have to compromise bandwidth to improve compliance (i.e., backdrivability). In this article, we describe the design and human–robot interaction modeling of a portable hip exoskeleton based on our custom quasi-direct drive actuation (i.e., a high torque density motor with low ratio gear). We also present a model-based performance benchmark comparison of representative actuators in terms of torque capability, control bandwidth, backdrivability, and force tracking accuracy. This article aims to corroborate the underlying philosophy of “design for control,” namely meticulous robot design can simplify control algorithms while ensuring high performance. Following this idea, we create a lightweight bilateral hip exoskeleton to reduce joint loadings during normal activities, including walking and squatting. Experiments indicate that the exoskeleton is able to produce high nominal torque (17.5 Nm), high backdrivability (0.4 Nm backdrive torque), high bandwidth (62.4 Hz), and high control accuracy (1.09 Nm root mean square tracking error, 5.4% of the desired peak torque). Its controller is versatile to assist walking at different speeds and squatting. This article demonstrates performance improvement compared with state-of-the-art exoskeletons.

/pdf/quasi-direct-drive-actuation-for-a-lightweight-hip-2pzpznxwng.pdf

Quasi-Direct Drive Actuation for a Lightweight Hip Exoskeleton With High Backdrivability and High Bandwidth

This letter presents design and control innovations of wearable robots that tackle two barriers to widespread adoption of powered exoskeletons: restriction of human movement and versatile control of wearable co-robot systems. First, the proposed high torque density actuation comprised of our customized high-torque density motors and low ratio transmission mechanism significantly reduces the mass of the robot and produces high backdrivability. Second, we derive a biomechanics model-based control that generates assistive torque profile for versatile control of both squat and stoop lifting assistance. The control algorithm detects lifting postures using compact inertial measurement unit (IMU) sensors to generate an assistive profile that is proportional to the human joint torque produced from our model. Experimental results demonstrate that the robot exhibits low mechanical impedance (1.5 Nm backdrive torque) when it is unpowered and 0.5 Nm backdrive torque with zero-torque tracking control. Root mean square (RMS) error of torque tracking is less than 0.29 Nm (1.21% error of 24 Nm peak torque). Compared with squatting without the exoskeleton, the controller reduces 87.5%, 80% and 75% of the three knee extensor muscles (average peak EMG of 3 healthy subjects) during squat with 50% of human joint torque assistance.

https://par.nsf.gov/servlets/purl/10112267

Design and Control of a High-Torque and Highly Backdrivable Hybrid Soft Exoskeleton for Knee Injury Prevention During Squatting

This letter presents design principles for comfort-centered wearable robots and their application in a lightweight and backdrivable knee exoskeleton. The mitigation of discomfort is treated as mechanical design and control issues and three solutions are proposed in this letter: 1) a new wearable structure optimizes the strap attachment configuration and suit layout to ameliorate excessive shear forces of conventional wearable structure design; 2) rolling knee joint and double-hinge mechanisms reduce the misalignment in the sagittal and frontal plane, without increasing the mechanical complexity and inertia, respectively; 3) a low impedance mechanical transmission reduces the reflected inertia and damping of the actuator to human, thus the exoskeleton is highlybackdrivable. Kinematic simulations demonstrate that misalignment between the robot joint and knee joint can be reduced by 74% at maximum knee flexion. In experiments, the exoskeleton in the unpowered mode exhibits 1.03 Nm root mean square (RMS) low resistive torque. The torque control experiments demonstrate 0.31 Nm RMS torque tracking error in three human subjects.

Comfort-Centered Design of a Lightweight and Backdrivable Knee Exoskeleton

This paper presents the design and evaluation of a soft hand exo-sheath integrated with a soft fabric electromyography (EMG) sensor for rehabilitation and activities of daily living (ADL) assistance of stroke and spinal cord injury (SCI) patients. This wearable robot addresses the limitations of the soft robot gloves with design considerations in terms of ergonomics and clinical practice. Its features include: this exo-sheath is based on electric actuation and has been designed to be compact and portable. It reduces the shear force and avoids kinematic singularity comparing with tendon-driven soft gloves as their tendon routings are typically in parallel with individual fingers. Disparate from conventional robotic gloves, this design optimizes a bio-inspired fin-ray structure to enhance the hand proprioception as the palm is not covered by wearable structures. With a novel self-fastening finger clasp design, wearers can self-don/doff the exoskeleton device simplifying ADL assistance. To develop more intuitive control interface, a soft fabric EMG sensor has been developed to understand human intentions. The functionality of this soft robot has been demonstrated with experimental results using the low-level position control, kinematics evaluation and reliable EMG measurements.

A soft robotic exo-sheath using fabric EMG sensing for hand rehabilitation and assistance

Loss of hand dexterity is a major challenge faced by post-stroke patients who strive to resume their ordinary daily lives. Effective hand function rehabilitation treatment for such population is therefore necessary. A soft robotic glove system operated through SSVEP-based BCI has been reported to be an effective tool for post-stroke hand motor function recovery. This study further evaluated the application of visual stimulation in the alpha band for SSVEP-assisted rehabilitation. We compared the treatment outcome with stimulations within the alpha band to that outside the band. A total of 20 post-stroke patients with severe upper limb dysfunction were randomly assigned to alpha band group and non-alpha band group. The experiment result was assessed with Fugl-Meyer upper limb Motor Assessment (FMAUE) and alpha EEG oscillation analysis. The alpha band group showed slightly but notably higher FMA-UE scores $(\mathrm{P}\lt 0.05)$, and significantly increased alpha wave EEG oscillations $(\mathrm{P}\lt 0.05)$. The result demonstrated the usefulness of alpha band SSVEP for post stroke hand function rehabilitation.

Soft Robotic Glove with Alpha Band Brain Computer Interface for Post-Stroke Hand Function Rehabilitation

This paper presents design principles for comfort-centered wearable robots and their application in a lightweight and backdrivable knee exoskeleton. The mitigation of discomfort is treated as mechanical design and control issues and three solutions are proposed in this paper: 1) a new wearable structure optimizes the strap attachment configuration and suit layout to ameliorate excessive shear forces of conventional wearable structure design; 2) rolling knee joint and double-hinge mechanisms reduce the misalignment in the sagittal and frontal plane, without increasing the mechanical complexity and inertia, respectively; 3) a low impedance mechanical transmission reduces the reflected inertia and damping of the actuator to human, thus the exoskeleton is highly-backdrivable. Kinematic simulations demonstrate that misalignment between the robot joint and knee joint can be reduced by 74% at maximum knee flexion. In experiments, the exoskeleton in the unpowered mode exhibits 1.03 Nm root mean square (RMS) low resistive torque. The torque control experiments demonstrate 0.31 Nm RMS torque tracking error in three human subjects.

Junlin Wang

Papers

Comfort-Centered Design of a Lightweight and Backdrivable Knee Exoskeleton

A soft robotic exo-sheath using fabric EMG sensing for hand rehabilitation and assistance

Soft Robotic Glove with Alpha Band Brain Computer Interface for Post-Stroke Hand Function Rehabilitation

Comfort-Centered Design of a Lightweight and Backdrivable Knee Exoskeleton