# Soft Rehabilitation and Nursing-Care Robots: A Review and Future Outlook
## 1 Introduction  
In many cases, population aging increases the probability of disability and the number of disabled people in, and the age structure of disabled people is becoming an inverted pyramid [1]. Due to the degeneration of physiological function, the incidence of cardiovascular diseases, osteoarthritis, hemiplegia, and other related diseases increased in the elderly. According to the statistic data from World Health Organization (WHO), stroke kills 6.2 million patients every year, which is more than the combined total of AIDS, tuberculosis, and malaria [2]. Therefore, the treatment and rehabilitation of stroke, hemiplegia, and other related diseases have become a particular concern of the medical community. However, the recovery of these diseases requires long-term treatment. Besides, nursing for the elderly and the disabled is also a topic of high social concern. As a result, the demand for medical resources is high, which leads to a shortage of professional labor-force. Rehabilitation robots, which is able to provide assistant treatment instead of professional labor-force and alleviate the problem, has become a popular research area. Traditional rehabilitation robots typically consist of rigid parts such as rigid drives, actuators and so on [3,4]. They can help patients accomplish rehabilitation training, daily activities, and even restore some loss abilities. The emergence of such robots has created a new collaborative relationship between robots, patients and therapists. This new collaborative relationship has improved the effectiveness of the patient's rehabilitation training and the efficiency of the rehabilitation worker, providing an effective way to address the challenges posed by the trend of an ageing community. Therefore, this kind of robots has a huge potential market in the field of medical rehabilitation. However, the rigid structure of conventional rehabilitation robots makes it difficult forpatients to obtain a good experience when using them, and if the machine malfunctions, it will most likely cause great damages to the patient, which greatly limits the application of the rehabilitation robots. Human beings or animals usually have elaborate structures and unique movement mechanism to achieve varieties of complex behavioral patterns. Inspired by nature, researchers began to study biomimetic robots and soft robots, such as multijoint robotic rat, snake robot, and so on [5; 6; 7], and these new robots have become research hotspots in the filed of robotics nowadays [8]. The flexible of soft robots make this type of robot have higher safety than the rigid robot when interacting with humans. Therefore, soft robots have great advantages in the field of medical robots, and existing research results show that soft robots have great potential in the field of medical rehabilitation and nursing-care due to their inherent compliance and safety. In a narrow sense, Soft Rehabilitation and Nursing-Care Robots (SRNCRs) refer to robots which are designed to provide therapy and assistance for specified persons and are entirely composed of flexible materials. However, due to current technical limitations, it is difficult to obtain an entirely flexible robot. In a broadly sense, SRNCRs are those that include flexible drives and some other rigid components, which are currently the most studied type of soft robots for providing therapy and assistance to persons. Admittedly, the SRNCR in a narrow sense is our ultimate goal, while the research of those in a broad sense will lay a solid technical foundation for us to achieve complete flexibility. The rehabilitation robot based on artificial pneumatic muscles is a typical example, such as [9; 10; 11]. Compared to some rigid rehabilitation robots that have been widely used, such as Lokomat [12; 13] and Welwalk [14], it is hard to find the mature SRNCR products on the market. Furthermore, in the study of SRNCRs, the highly nonlinear and time-varying properties of soft materials cause difficulties for control, which is also a hard problem that must be solved.