Soft Exosuits

We are developing next generation soft wearable robots that use innovative textiles to provide a more conformal, unobtrusive and compliant means to interface to the human body. These robots will augment the capabilities of healthy individuals (e.g. improved walking efficiency) in addition to assisting those with muscle weakness or patients who suffer from physical or neurological disorders. As compared to a traditional exoskeleton, these systems have several advantages: the wearer's joints are unconstrained by external rigid structures, and the worn part of the suit is extremely light.  These properties minimize the suit's unintentional interference with the body's natural biomechanics and allow for more synergistic interaction with the wearer.

Structured functional textiles

suitWe are creating innovative textiles that are inspired by an understanding of human biomechanics and anatomy. These wearable garments provide means to transmit assistive torques to a wearer’s joints without the use of rigid external structures. In order to obtain high-performance soft exosuits, some considerations should be taken into account in the design process. Exosuits should attach to the body securely and comfortably, and transmit forces over the body through beneficial paths such that biologically-appropriate moments are created at the joints.   In addition, these garments can be designed to passively (with no active power) generate assistive forces due to the natural movement of the wear for particular tasks. A key feature of exosuits is that if the actuated segments are extended, the suit length can increase so that the entire suit is slack, at which point wearing an exosuit feels like wearing a pair of pants and does not restrict the wearer whatsoever.


Lightweight and efficient actuation

In order to provide active assistance through the soft interface, we are developing a number of actuation platforms that can apply controlled forces to the wearer by attaching at anchoring points in the wearable garment. We are developing lightweight and fully portable systems and a key feature of our approach is that we minimize the distal mass that is attached to the wearer through more proximally mounted actuation systems and flexible transmissions that transmit power to the joints. While most of our recent work is on cable-driven electromechanical approaches, we have also pursued pneumatic based approaches. This early work with McKibbon actuators in 2013 was the first demonstration that a soft exosuit can have a positive effect on mobility. 



Wearable sensors

New sensor systems that are easy to integrate with textiles and soft components are required in order to properly control and evaluate soft exosuits. Rigid exoskeletons usually include sensors such as encoders or potentiometers in robotic joints that accurately track joint angles, but these technologies are not compatible with soft structures.  Our approach is to design new sensors to measure human kinematics and suit-human interaction forces that are robust, compliant, cost effective, and offer easy integration into wearable garments.  In addition, we use other off the shelf sensor technologies (e.g. gyro, pressure sensor, IMU) that can be used to detect key events in the gait cycle. These wearable sensors can be used as part of the control strategy for the wearable robot or alternatively to monitor and record the movement of the wearer (when wearing the exosuit or as a standalone sensor suit) for tracking changes over time or determining what activities they are performing (e.g. walking vs running).


Intuitive and robust control

We are also developing rapidly reconfigurable multi-actuator systems that provide more flexibility for lab-based studies. Such an approach allows us to rapidly explore the basic science around human-machine interaction with such systems that can then be used to guide the design of our portable systems. A robust, intuitive and adaptive human-machine interface is a necessary component for a wearable robot to interact synergistically with the wearer. Our focus is to provide assistance in a manner that does not disrupt the natural, passive dynamics that make walking or running so efficient. To achieve this, we develop approaches to non-invasively estimate the intent so that any actuation applied assists that from the appropriate biological muscles. A key feature of our approach is to leverage integrated sensors that monitor the wearer interaction with the compliant textile that interfaces to the body as well as other sensors that detect key moment during the gait cycle.


Experimental biomechanics

Our motion capture lab utilizes a Vicon T-series 9-camera system for motion capture, together with a Bertec fully instrumented split-belt treadmill to measure GRFs. By comparing the average profile and range of motion of each joint in the three conditions, we can identify how the soft exosuit itself impacts gait and how the assistance applied by the exosuit changes kinematics. Our hypothesis is that it is desirable that such changes are minimal and in any case not disruptive to natural gait. We study to what extent the active exosuit is assisting the human by analyzing gait dynamics and kinetics (joint moments, power, force delivered by the exosuit). Inverse dynamics is an effective way to determine to what degree the exosuit is augmenting the body function at a joint level. The comparison of joint moments and suit assistive forces allows us to monitor the degree of synchronicity between the user and the robot. Surface electromyography (sEMG) can be used to selectively monitor muscular activity focusing on the muscle groups that are most relevant for the task under consideration. Comparing the ensemble average profiles of sEMG activity between the unpowered, active and no suit conditions allows us to determine effects on the maximum force being delivered by each muscle (peak sEMG activation) and on the energy cost of each muscle activation (integral sEMG). We use the metabolic cost of walking as a global physiological measurement to determine to what extent the suit is assisting the wearer and if assistance offsets the weight of the device. 


Translational applications

In addition to our work on basic research and system development, we are highly interested in pursuing applications of our soft wearable robots. Through our DARPA funded work, we are interested in developing exosuits that can assist soldiers walking while carrying heavy loads. Our belief is we can create passive and active systems that offload the high forces in the muscles and tendons in the leg – thus reducing the risk of injury and increasing the walking efficiency of the wearer. Another translational focus of our group is on gait assistance for medical applications. We foresee soft exosuits being able to restore mobility in patients with muscle weakness (e.g. the elderly) or who suffer from a neurological disease such as multiple sclerosis or stroke. Beyond our active systems, we envision translational potential in the area of sports and recreation where fully passive soft suits with structured functional textiles can provide small amounts of assistance during walking, hiking, running and other activities.


Associated Papers

Stronger, Smarter, Softer: Next-Generation Wearable Robots
A. T. Asbeck, S. De Rossi, I. Galiana, Y. Ding, and C. J. Walsh, “Stronger, Smarter, Softer: Next-Generation Wearable Robots,” IEEE Robotics & Automation Magazine, vol. 21, no. 4, pp. 22-33, 2014. Publisher's VersionAbstract

Exosuits show much promise as a method for augmenting the body with lightweight, portable, and compliant wearable systems. We envision that such systems can be further refined so that they can be sufficiently low profile to fit under a wearer's existing clothing. Our focus is on creating an assistive device that provides a fraction of the nominal biological torques and does not provide external load transfer. In early work, we showed that the system can substantially maintain normal biomechanics and positively affect a wearer's metabolic rate. Many basic fundamental research and development challenges remain in actuator development, textile innovation, soft sensor development, human-machine interface (control), biomechanics, and physiology, which provides fertile ground for academic research in many disciplines. While we have focused on gait assistance thus far, numerous other applications are possible, including rehabilitation, upper body support, and assistance for other motions. We look forward to a future where wearable robots provide benefits for people across many areas of our society.

Assistance magnitude versus metabolic cost reductions for a tethered multiarticular soft exosuit
B. T. Quinlivan, et al., “Assistance magnitude versus metabolic cost reductions for a tethered multiarticular soft exosuit,” Science Robotics, vol. 2, no. 2, 2017. Publisher's VersionAbstract

When defining requirements for any wearable robot for walking assistance, it is important to maximize the user’s metabolic benefit resulting from the exosuit assistance while limiting the metabolic penalty of carrying the system’s mass. Thus, the aim of this study was to isolate and characterize the relationship between assistance magnitude and the metabolic cost of walking while also examining changes to the wearer’s underlying gait mechanics. The study was performed with a tethered multiarticular soft exosuit during normal walking, where assistance was directly applied at the ankle joint and indirectly at the hip due to a textile architecture. The exosuit controller was designed such that the delivered torque profile at the ankle joint approximated that of the biological torque during normal walking. Seven participants walked on a treadmill at 1.5 meters per second under one unpowered and four powered conditions, where the peak moment applied at the ankle joint was varied from about 10 to 38% of biological ankle moment (equivalent to an applied force of 18.7 to 75.0% of body weight). Results showed that, with increasing exosuit assistance, net metabolic rate continually decreased within the tested range. When maximum assistance was applied, the metabolic rate of walking was reduced by 22.83 ± 3.17% relative to the powered-off condition (mean ± SEM).

M. B. Yandell, B. T. Quinlivan, D. Popov, C. Walsh, and K. E. Zelik, “Physical interface dynamics alter how robotic exosuits augment human movement: implications for optimizing wearable assistive devices,” Journal of NeuroEngineering and Rehabilitation, vol. 14, no. 1, pp. 40, 2017. Publisher's VersionAbstract


Wearable assistive devices have demonstrated the potential to improve mobility outcomes for individuals with disabilities, and to augment healthy human performance; however, these benefits depend on how effectively power is transmitted from the device to the human user. Quantifying and understanding this power transmission is challenging due to complex human-device interface dynamics that occur as biological tissues and physical interface materials deform and displace under load, absorbing and returning power.

Here we introduce a new methodology for quickly estimating interface power dynamics during movement tasks using common motion capture and force measurements, and then apply this method to quantify how a soft robotic ankle exosuit interacts with and transfers power to the human body during walking. We partition exosuit end-effector power (i.e., power output from the device) into power that augments ankle plantarflexion (termed augmentation power) vs. power that goes into deformation and motion of interface materials and underlying soft tissues (termed interface power).

We provide empirical evidence of how human-exosuit interfaces absorb and return energy, reshaping exosuit-to-human power flow and resulting in three key consequences: (i) During exosuit loading (as applied forces increased), about 55% of exosuit end-effector power was absorbed into the interfaces. (ii) However, during subsequent exosuit unloading (as applied forces decreased) most of the absorbed interface power was returned viscoelastically. Consequently, the majority (about 75%) of exosuit end-effector work over each stride contributed to augmenting ankle plantarflexion. (iii) Ankle augmentation power (and work) was delayed relative to exosuit end-effector power, due to these interface energy absorption and return dynamics.

Our findings elucidate the complexities of human-exosuit interface dynamics during transmission of power from assistive devices to the human body, and provide insight into improving the design and control of wearable robots. We conclude that in order to optimize the performance of wearable assistive devices it is important, throughout design and evaluation phases, to account for human-device interface dynamics that affect power transmission and thus human augmentation benefits.


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