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
We 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.
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.
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.
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.