# Design Approaches of an Exoskeleton for Human Neuromotor Rehabilitation
## 1 Introduction  
Nowadays, exoskeletons have become popular in medical rehabilitation programs and extended their applications as power augmentation systems used in different domains, such as industry or defense. Considering exoskeletons specially designed for human locomotion system recovery, these can be divided into two major categories: one category consists of exoskeletons that serve as robotic systems in an assistive mode for restoring gait patterns for persons who have partial mobility; the other category is represented by exoskeletons specially designed to help elderly persons perform daily activities. The exoskeletons from the first category were specially designed for people with neuromotor disorders or stroke accidents [1; 2; 3; 4; 5; 6; 7; 8]. Others exoskeletons [9; 10; 11; 12; 13; 14; 15] were specially designed to fulfill human walking temporal recovery programs dedicated to persons who were exposed to orthopedic surgical interventions. In both mentioned categories, there are fully actuated exoskeletons [3; 6] for all human lower-limb joints under rehabilitation programs. Considering the exoskeletons used on temporal recovery programs [11; 13], these can have actuated individual joints from the patient locomotion system (one joint actuated, a pair of joints or a group of human lower limb joints). In addition, these are characterized by personalized therapy protocols that can recover a single joint, namely the one that was involved in a surgical intervention. Thus, most of the existing exoskeletons have imposed several design conditions, such comfort during rehabilitation programs, complex actuations, low- or high-cost principles, easy operation features, and user-friendly interfaces. In order to accomplish the aforementioned conditions, some exoskeletons [3; 6] can fulfill a few of them, while other solutions [11; 14] can cover the rest. The latest ones [11; 14] recharacterized by a complex structure, leading to expensive rehabilitation programs for patients. Most of the designed exoskeletons require a qualified rehabilitation team made from a proper physician, a medical engineer, a technician and some medical rehabilitation assistants. By referring to the beginning of an exoskeleton system design, and taking into account the physician-specific requirements, it can be remarked that human exoskeletons are characterized by a complex actuation system that involves mechanisms with a minimum number of actuators [2; 8; 9; 15]. There are also complex rehabilitation systems especially designed for human walking recovery [16; 17] and these have in their structure an exoskeleton with a simplified mechanical structure, but all equivalent human locomotion joints are fully actuated through complex command and control protocols. The criteria imposed by physician requirements in cases of persons disabled due to neuromotor disorders during walking activities must be considered as a starting research point in designing an exoskeleton, as it can be remarked in [18], and it can be observed that there are persons who need to recover some joints from the entire locomotion system. In this case, it is necessary to have an exoskeleton that can perform isolated motions for the affected joints or to have a complete exoskeleton that involves all human locomotion joints for neuromotor rehabilitation processes. Thus, this represents a research challenge for designing an exoskeleton used in both cases. Another argument is the one that the existing exoskeletons [1; 3; 4; 5] need to have a database characterized by locomotion motion law patterns acquired from persons with different anthropometric data, and the therapist needs to choose and adapt these motion patterns for the targeted patient. For accomplishing this argument, most of the exoskeletons were designed in a parameterized form and have segments with variable length and width. These segments can be adjusted through locking/unlocking mechanical devices.