Sensory-motor impairments due to age or neurological diseases can influence a person's ability to maintain balance, and increase the risk of falls. Recently, wearable Control Moment Gyroscopes (CMGs) have proven to provide effective balance support. Here, we show a new design of a Series-Elastic Control Moment Gyroscope (SECMG) enhanced by an additional passive degree of freedom, namely a second, orthogonal gimbal that is supported by a (visco)elastic element. The design mainly aims to reject disturbances originating from human movement and render a low remaining impedance, as well as to provide more accurate torque sensing, based on angular deflection of the compliant element. Evaluation of the torque tracking performance with regards to a classic rigid Single-Gimbal Control Moment Gyroscope (SGCMG) showed that the device equally exceeds the bandwidth requirements for its application in human augmentation. However, characterization of our current compliant construction also revealed some backlash occluding the torque-deflection relation. In the future, the SECMG could be evaluated in experiments with humans, to validate its predicted low remaining impedance.

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.

One important aspect of gait stability is the control of whole-body centroidal angular momentum H. We recently showed that if sensory-motor impairments affect a person's balance control, control of H can be assisted by control moment gyroscopes (CMGs). However, the effect of CMG technology inherently depends on the size and weight of these actuators, and on the speed of the flywheels they contain. These factors all pose challenges for wearable applications. Here, we show that it is possible to design CMGs light enough for wearable applications, while generating meaningful output torques. Our CMG, weighing 1.187 kg, can exert a peak torque of 15 N m with a torque-tracking bandwidth of 18 Hz. These results are partly due to an integrated model of components and partly to advancements in flywheel velocity control, allowing the speed to safely reach 20 000 rpm. These actuators open up new pathways of building wearable assistive devices for clinical applications.

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.

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.