# Assistance of a Person with Muscular Weakness Using a Joint-Torque-Assisting Exoskeletal Robot
###### Abstract  
Robotic systems for gait rehabilitation have been actively developed in recent years; many of the rehabilitation robots have been commercialized and utilized for treatment of real patients in hospitals. The first generation of gait rehabilitation robots was a tethered exoskeleton system on a treadmill. While these robots have become a new trend in rehabilitation medicine, there are several arguments about the effectiveness of such robots due to the passiveness of the motions that the robots generate, i.e., the continuous passive motions may limit the active involvement of patients' voluntary motion control. In order to let a patient be more actively involved by requiring the self-control of whole-body balance, untethered powered exoskeletons, wearable robots that patients can wear and walk on the ground, are receiving great attention. While several powered exoskeletons have been commercialized already, the question about their effectiveness has not been cleared in the viewpoint of rehabilitation medicine because most of the powered exoskeletons provide still continuous passive motions, even though they are on the ground without tethering. This is due to their control strategy; the joints of a powered exoskeleton are position-controlled to repeatedly follow a predefined angle trajectory. This may be effective when a wearer is completely paraplegic such that the powered exoskeleton must generate full actuation power for walking. For people with muscular weakness due to various reasons, the powered exoskeleton must assist only the lack of muscular force without constraining human motion. For assistance and rehabilitation of people with partial impairment in walking ability, Angel Legs is introduced in this paper. The proposed powered exoskeleton system is equipped with a transparent actuation system such that the assistive force is accurately generated. The overall design and control of Angel Legs are introduced in this paper, and a clinical verification with a human subject is also provided. powered exoskeleton; gait rehabilitation; torque-assist control +
Footnote †: 29 March 2021  
continues to extend. Furthermore, if there is an abnormality in hip abductor muscles, gluteus medius gait occurs, in which the body leans over the opposite leg during the swing phase. Joint pain and weakness due to aging also cause abnormal walking. [PERSON] et al. showed that muscular strength declines with age and decreases by up to 50% by the age 70 [2]. Patients with abnormal walking and balance disorders are afraid of walking and cannot walk for a long time. These mobility disabilities increase the risk of dependency in physical activities in daily living [2,3]. If abnormality is not considerable, balancing can be assisted by a simple walking aid such as canes, walkers, crutches, and so on. Using these, the base of support can be widened to help maintain balance [4]. However, when used for a long time, the arm muscles may become painful. In some cases, an Ankle Foot Orthosis (AFO) or a Knee Ankle Foot Orthosis (KAFO) is used to companate weakness. There are various materials and structures of orthosis; recently, electrical devices that incorporate active joints have been introduced [5]. For people with partial impairment in walking ability, it is mandatory to stand up and perform walking motions frequently with the help of assistive devices (e.g., a harness system, a robotic rehabilitation treatment system, etc. [6]) to maintain health conditions. In this respect, wearable robots enabling the patients with paretic gait walk on the real ground can be used. These robots are effective both for rehabilitation and for an increase in the patients' mobility. In recent years, wearable robots for gait assistance have been developed and commercialized [7]. Among many applications of the wearable robots, ones for assisting people with complete paraplegia may be the mostly popularized.