# Soft Rehabilitation and Nursing-Care Robots: A Review and Future Outlook
## 4 Discussion and Outlook  
Due to the inherent compliance and safety, soft robots shows a great potential in rehabilitation and nursing-care and has broad application prospects. Although many SRNCRs have initially demonstrated their assistant rehabilitation ability, there are still many problems to be solved. Firstly, as a rehabilitation robot, its rehabilitation effect is the most important standard of measure. Although there are many kinds of rehabilitation robots and exoskeletons, most of them were only experimented in the laboratory, not put into the rehabilitation clinic and real life to get more validation. Especially for the SRNCR, there is no mature product on the market so far. Secondly, for rehabilitation equipment, the original intention of the design is to help more patients, so the production cost of the SRNCR must be considered. Some existing rehabilitation robots such as HAL and ReWalk are still expensive, which hinders their wide use. SRNCRs are complex systems with multiple degrees of freedom. Traditional rehabilitation robots are often complex and cumbersome. For wearable rehabilitation robots, patients are generally required to carry the weight of the equipment for rehabilitation training. So it will be inconvenient for the patient to wear and use due to the complexity and the heavy weight of the devices. Therefore, an ideal SRNCR needs to have a lighter mechanical body, which requires researchers to optimize the  
Figure 7: Types of control strategies and their percentage in this review. (**a**) Overall proportion of SRNCRs; (**b**) Proportion of SRNCRs based on tendon-driven; (**c**) Proportion of SRNCRs based on soft intelligent materials. mechanical structure of rehabilitation robots to reduce the weight of SRNCR. The development of new soft-smart materials is an viable option, such as full fabric material, carbon fiber and titanium alloy, which is a common method of weight reduction. However, flexible materials are often less durable than rigid materials, which hinders the practical application of SRNCRs [112; 113]. So the durability of soft materials is also a practical problem need to be solved. The development of new sensing devices and sensing technologies to reduce the number of sensors in robots is another viable option, and some new measurement techniques may be used. As a robot that needs to assist the patients with dyskinesia, from the current research results, the response speed and motion accuracy of SRNCRs still need to be improved to achieve better therapeutic effects and comfort of human-robot interaction. In addition, some rehabilitation robots still contain a few rigid components, which may affect patient comfort, and researchers need to explore more softer components. For example, soft heater based on carbon fiber contributes [110] to development of lighter and thinner sensors. Furthermore, most SRNCRs have a limited range of assistance output and motion angles. This problem may not have a obvious impact in the early stages of rehabilitation. However, when the rehabilitation treatment enters the later stage, further rehabilitation of the patient with certain abilities will be precluded. All in all, the structural design of SRNCRs should be flexible and comfortable. As far as the modeling methods and control strategies of rehabilitation robots are concerned, most of the current SRNCRs use relatively simple control methods and rough models with numerous assumptions. Modeling and control work of soft materials is difficult due to the high nonlinearity, time-varying characteristics and response delay characteristics. Because the traditional theories are mostly not applicable to soft materials, researchers need to make a series of assumptions when modeling. These factors bring uncertainties and disturbances to the control system. The patient's feeling during the training process is also an important factor that needs to be considered. Designing more advanced sensors and combining appropriate control strategies may be a viable direction.