# Modular Design and Decentralized Control of the Recupera Exoskeleton for Stroke Rehabilitation
Most exoskeletons for upper body rehabilitation [28] are heavy and bulky, and, hence, attached to a fixed base or heavy mobile platforms (e.g., ARMIN III [29], ARMEO [30], HARMONY [31]). This either reduces the mobility of patients or forces the patient to carry the weight of the exoskeleton (e.g., RUPERT [32]) which might be problematic for patients with reduced trunk stability. Accordingly, the use of these systems is limited to clinical applications, where patients can practice exercises only with the supervision of a therapist. Lightweight exoskeletons with at least 5 degrees of freedom (DOF) which do not compromise with patient's mobility are sparsely reported (e.g., SUEFUL-6 [33]). Since clinical resources and especially therapist time are limited, it is often not possible to offer more frequent or longer therapy sessions. To make the exoskeleton technology more pervasive in the patient's life, it is important to develop lightweight exoskeletons with high safety assurance that provide possibilities for self-training (such as mirror therapy [34] or teach and replay [35]) so that the total therapy time can be increased. Another important development trend is the development of bilateral systems (e.g., HARMONY [31]) to extend therapy options. In this paper, we present the electro-mechanical design aspects and evaluation results of the bilateral Recupera exoskeleton (Figure 1). It is designed to support the therapy of patients with hemiparetic motor impairments of the upper body after stroke. The system has been developed in close collaboration between engineers, therapists and neurobiologists to support the patient and therapist in an optimal way. Due to novel mechanisms, embedded processing and an advanced control architecture, it can provide a set of different therapy modes and exercise possibilities in clinical or ambulatory therapy or even the private environment. The lightweight design and modularity allows to use the system in different configurations, e.g., (1) as a 10 DOF upper body wheelchair-mounted part system (Figure 1a) or (2) as a 30 DOF full-body system (Figure 1b) with legs to support sitting and standing postures. The wheelchair system is designed to support the hemiparetic stroke patients who are usually bounded to a wheelchair in their early days after stroke. Once they start to recover, they can continue training with the full body exoskeleton system which provides them the possibility to perform upper body exercises while both sitting and standing. Both systems are designed such that the patient does not have to carry the weight of the exoskeleton as the weight of the system is compensated by the controller and transferred to the ground. Furthermore, the mobility of the patient is not compromised. Due to its bilateral design, the system can be used with both left and right sided stroke patients and can provide extended training possibilities e.g., dual arm tasks, and mirror therapy. In the previous work from the authors, the first CAD design ideas of this system were introduced in [36] and detailed analysis of various subsystem modules used in the design were presented in [37; 38; 39; 40]. This paper focuses on the mechatronic design aspects and the control architecture of the commissioned system and presents the experimental results on its rehabilitative aspects. Non-rehabilitative control aspects of the full body configuration such as active balancing, walking etc. will be addressed in future work.