INSPIIRE - A Modular and Passive Exoskeleton to Investigate Human Walking and Balance.

Powered exoskeletons for SCI patients are mainly limited by their inability to balance dynamically during walking. To investigate and understand the control strategies of human bipedal locomotion, we developed INSPIIRE, a passive exoskeleton. This device constrains the movements of able-bodied subjects to only hip and knee flexions and extensions, similar to most current active exoskeletons. In this paper, we detail the modular design and the mechanical implementation of the device. In preliminary experiments, we tested whether humans are able to handle dynamic walking without crutches, despite the limitation of lateral foot placement and locked ankles. Five healthy subjects showed the ability to stand and ambulate at an average speed of 1 m/s after 5 minutes of self-paced training. We found that while the hip abduction/adduction is constrained, the foot placement was made possible thanks to the pelvis yaw and residual flexibility of the exoskeleton segments in the lateral plan. This result points out that INSPIIRE is a reliable instrument to learn sagitally-constrained human locomotion, and the potential of investigating more dynamic walking, which is shown as possible in this implementation, even if only flexion/extension of the hip and knee are allowed.

TWIICE One powered exoskeleton: effect of design improvements on usability in daily life as measured by the performance in the CYBATHLON race.

BACKGROUND: Spinal cord injury leading to paraplegia affects the mobility and physiological well-being of one in a thousand people. Powered exoskeletons can temporarily restore the ability to walk. Their relevance in daily life is still limited because of low performance beyond ground that is even. CYBATHLON is an international competition promoting improvements in assistive technology. In this article, we present the latest design and results of testing of TWIICE One version 2018, one of the competing devices in the 2020 race. METHODS: A person with a motor-complete spinal cord injury at thoracic level T10 participated as race pilot. Training ahead of the race took place over one week at a rate of 2 h per day. The time to perform each of the seven tasks of the competition was recorded together with the number of repetitions. Performance is compared over the training period and against the 2016 race results. RESULTS: Progression was observed in all tasks and accounted for by both user training and technology improvements. Final competition rank was second out of seven participating teams, with a record time of 4'40". This represents an average improvement of 40% with respect to comparable obstacles of the 2016 race, explaining the two ranks of improvement since then. CONCLUSION: These results help understand which features had a positive impact on the real-life performance of the device. Understanding how design affects performance is key information to create devices that really improve the life of people living with paraplegia.

Bioinspired Postural Controllers for a Locked-Ankle Exoskeleton Targeting Complete SCI Users.

Several lower-limb exoskeletons enable overcoming obstacles that would impair daily activities of wheelchair users, such as going upstairs. Still, as most of the currently commercialized exoskeletons require the use of crutches, they prevent the user from interacting efficiently with the environment. In a previous study, a bio-inspired controller was developed to allow dynamic standing balance for such exoskeletons. It was however only tested on the device without any user. This work describes and evaluates a new controller that extends this previous one with an online model compensation, and the contribution of the hip joint against strong perturbations. In addition, both controllers are tested with the exoskeleton TWIICE One, worn by a complete spinal cord injury pilot. Their performances are compared by the mean of three tasks: standing quietly, resisting external perturbations, and lifting barbells of increasing weight. The new controller exhibits a similar performance for quiet standing, longer recovery time for dynamic perturbations but better ability to sustain prolonged perturbations, and higher weightlifting capability.

Balance Control Strategies during Standing in a Locked-Ankle Passive Exoskeleton.

This paper investigates sensorimotor adaptation strategies of sagittal postural control in healthy subjects under kinematic constraints. A passive exoskeleton named CAPTUR, with locked ankle joints and legs motion restrained to the sagittal plane is used to restrict and measure participant's movements. The aim is to assess the role of the orientation of the shank and the trunk segments in maintaining the body center of mass above its support base, while the ankle strategy is inhibited. Five young healthy participants were asked to keep standing, while their balance was challenged by five experimental conditions. Participants mainly regulated quiet standing balance by flexing/extending the knees, in order to affect the shank and feet angles, and move the contact patch along the sagittal axis. In this case, the orientation of the trunk segment changes synchronously with the shank angle to keep an upright posture. Responses to more dramatic excursions of the center of pressure are ensured by changing the trunk tilt angle in opposition of phase with the shank angle. These observations could be used to implement a bioinspired balance controller for such constrained lower-limb exoskeletons.

Bio-inspired standing balance controller for a full-mobilization exoskeleton.

This paper presents a novel method to perform automatic standing balance in a full mobilization exoskeleton. It exploits the locked ankle and the curved foot sole of the exoskeleton TWIICE. The idea is to use the knees to roll the sole and change the position of the contact point with the floor, which allows to stabilize without an actuated ankle.This controller is biologically inspired, originating from a previous experiment with the passive exoskeleton CAPTUR and healthy subjects. Then, a simulation model was built to test the observed balance strategy. Finally, the controller was implemented on the actual actuated exoskeleton, without a wearer for the time being, to experimentally check the basic operation. The next planned step is to test its actual performance with healthy subjects, then paraplegic patients.

TWIICE - A lightweight lower-limb exoskeleton for complete paraplegics.

This paper introduces TWIICE, a lower-limb exoskeleton that enables people suffering from complete paraplegia to stand up and walk again. TWIICE provides complete mobilization of the lower-limbs, which is a first step toward enabling the user to regain independence in activities of the daily living. The tasks it can perform include level and inclined walking (up to 20° slope), stairs ascent and descent, sitting on a seat, and standing up. Participation in the world's first Cybathlon (Zurich, 2016) demonstrated good performance at these demanding tasks. In this paper, we describe the implementation details of the device and comment on preliminary results from a single user case study.

EXiO-A Brain-Controlled Lower Limb Exoskeleton for Rhesus Macaques.

Recent advances in the field of brain-machine interfaces (BMIs) have demonstrated enormous potential to shape the future of rehabilitation and prosthetic devices. Here, a lower-limb exoskeleton controlled by the intracortical activity of an awake behaving rhesus macaque is presented as a proof-of-concept for a locomotorBMI. A detailed description of the mechanical device, including its innovative features and first experimental results, is provided. During operation, BMI-decoded position and velocity are directly mapped onto the bipedal exoskeleton's motions, which then move the monkey's legs as the monkey remains physicallypassive. To meet the unique requirements of such an application, the exoskeleton's features include: high output torque with backdrivable actuation, size adjustability, and safe user-robot interface. In addition, a novel rope transmission is introduced and implemented. To test the performance of the exoskeleton, a mechanical assessment was conducted, which yielded quantifiable results for transparency, efficiency, stiffness, and tracking performance. Usage under both brain control and automated actuation demonstrates the device's capability to fulfill the demanding needs of this application. These results lay the groundwork for further advancement in BMI-controlled devices for primates including humans.