In this paper, we present the design, control, and preliminary evaluation of the Symbitron exoskeleton, a lower limb modular exoskeleton developed for people with a spinal cord injury. The mechanical and electrical configuration and the controller can be personalized to accommodate differences in impairments among individuals with spinal cord injuries (SCI). In hardware, this personalization is accomplished by a modular approach that allows the reconfiguration of a lower-limb exoskeleton with ultimately eight powered series actuated (SEA) joints and high fidelity torque control. For SCI individuals with an incomplete lesion and sufficient hip control, we applied a trajectory-free neuromuscular control (NMC) strategy and used the exoskeleton in the ankle-knee configuration. For complete SCI individuals, we used a combination of a NMC and an impedance based trajectory tracking strategy with the exoskeleton in the ankle-knee-hip configuration. Results of a preliminary evaluation of the developed hardware and software showed that SCI individuals with an incomplete lesion could naturally vary their walking speed and step length and walked faster compared to walking without the device. SCI individuals with a complete lesion, who could not walk without support, were able to walk with the device and with the support of crutches that included a push-button for step initiationOur results demonstrate that an exoskeleton with modular hardware and control allows SCI individuals with limited or no lower limb function to receive tailored support and regain mobility.

This work was devoted to preliminary test the Achilles ankle exoskeleton and its NeuroMuscular Controller (NMC) with a test pilot affected by incomplete spinal cord injury. The customization of the robot controller, i.e. a subject-specific tailoring of the assistance level, was performed and a 10-session training to optimize human-robot interaction was finalized. Results demonstrated that controller tuning was in line with the functional clinical assessment. NMC adapted to the variable walking speed during the training and the test pilot was successfully trained in exploiting robotic support and also improved his performance in terms of walking speed and stability. After the training, a higher speed could also be achieved during free walking and hence a slight unexpected rehabilitation effect was evidenced.

The main goal of the Symbitron project was to develop a safe, bio-inspired, personalized wearable exoskeleton that enables SCI patients to walk without additional assistance, by complementing their remaining motor function. Here we give an overview of major achievements of the projects.

In this study, our goal was to improve the standing balance of people with a spinal cord injury by using a wearable exoskeleton that has ankle and knee actuation in the sagittal plane. Three test-pilots that have an incomplete spinal cord injury wore the exoskeleton and tried to maintain standing balance without stepping while receiving anteroposterior pushes. Two balance controllers were tested: One providing assistance based on the subject's body sway and one based on the whole body momentum. For both controllers, the balance performances of the test-pilots wearing the exoskeleton were assessed based on the center of mass kinematics and compared to the condition in which the device did not provide any assistance. One of the test-pilots was not able to maintain balance without assistance, but could withstand small pushes when any of the balance controllers was implemented. For this test-pilot the recovery time and sway amplitude hardly varied with the type of balance controller that was used. For the other two test-pilots the recovery time and the sway amplitude were smallest using the body sway controller. In conclusion, the wearable exoskeleton with balance controller was able to improve the balance performance of the test-pilots by reducing the recovery time after a perturbation and by enabling one of the test-pilots to maintain balance, who could not maintain balance by himself.

Improving stability of people wearing a lower extremity Wearable Exoskeleton (WE) is one of the biggest challenges in the field. The goal of this preliminary study was to improve balance recovery from perturbations in people with incomplete Spinal Cord Injury (SCI) assisted by a WE with specifically developed balance controller. The WE has actuated ankle and knee joints, which were controlled by using a body sway-based balance controller. Two test pilots participated in 5 training sessions, devoted to enhance the use of the robot, and in pre/post assessments. Their balance during quiet standing was perturbed through pushes in forward direction. The controller was effective in supporting balance recovery in both tests pilots as reflected by a smaller sway amplitude and recovery time when compared with a minimal impedance controller. Moreover, the training resulted in a further reduction of the sway amplitude and recovery time in one of the test pilots whereas it had not an additional beneficial effect for the other subject. In conclusion, the novel balance controller can effectively assist people with incomplete SCI in maintaining standing balance and a dedicated training has the potential to further improve balance.