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.@en

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.@en

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.@en

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.@en

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.@en

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.@en

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.@en

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.@en

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.@en

For optimal control of wearable lower limb exoskeletons the sensory information flow should also be (partly) restored, especially when the users are Spinal Cord Injury subjects. Several methods, like electrotactile or electromechanical vibrotactile stimulation, to provide artificial sensory feedback have been studied thoroughly and showed promising results. Pneumatic tactile stimulation might be an alternative to these methods, because the stimulation amplitudes can be larger and in cases of force feedback, the modality of stimulation and sensing can be matched. In this study we have developed a setup that can provide pneumatic feedback with four feedback levels via three stimulation modalities: (1) amplitude modulation, (2) position modulation and (3) frequency modulation. The differences in subject stimulus perception between these three stimulation modalities were evaluated through a magnitude estimation task performed with 10 healthy subjects. Percentages correctly identified feedback levels were significantly higher for frequency modulation than the other two stimulation modalities. Also through questionnaires the subjects indicated that feedback through frequency modulation was the most intuitive and the only method where addition of an extra feedback level was indicated as possible. The results of this study show that pneumatic feedback is feasible, can provide high percentages of feedback level discrimination that are at least comparable to vibrotactile stimulation and therefore encourages further research to optimize the pneumatic setup.@en