# Soft Rehabilitation and Nursing-Care Robots: A Review and Future Outlook
## 2 Mechanical Design  
### Soft Rehabilitation and Nursing-Care Robots Based on Tendon-Driven Actuation  
Soft rehabilitation and nursing-care robots based on tendon-driven actuation are usually driven by cables [17; 18], such as Bowden cable. Cables in robotic structures are used to simulate tendons of human. This kind of SRNCR guides patients to perform rehabilitation exercises by simulating the biomechanical properties of ligaments and tendons. Therefore, SRNCRs based on tendon-driven are usually used for the rehabilitation of upper and lower limbs. Since such robots are driven by cables, this kind of robots has the characteristic of routing diversity, and the payload of such robots is determined by the quality of the cables, which also determines the assistant capability of robots. The application of robotic technology in therapy has been continually explored for decades. Meanwhile, the conventional rehabilitation devices still remain inaccessible outside of a clinical setting because they are cumbersome and expensive. In order to expand the accessibility of rehabilitation robot to those who need it, [PERSON] et al. proposed a design concept of glove for hand rehabilitation in 2013. Then they designed a robotic glove to assist the movement and coordination of grip exercises (Figure 1a) [19]. This glove produces maximum grip strength of 15N. Based on the initial concept and previous work, [PERSON] et al. explored a lightweight, soft, cable-driven design, and fabricated an upper limb rehabilitation exoskeleton with 6 actuated degrees of freedom by adding actuation of the elbow joint and constructing a better new system (Figure 1b) [20]. In the same year, [PERSON] et al. developed a soft wearable rehabilitation robot called Exo-Glove with a soft tendon routing system and an underactuation adaptive mechanism (Figure 1c) [21]. Fabric tapes and Teflon tubes were used in the Exo-Glove instead of mechanical pulley used in the traditional tendon routing system. Exo gloves use Bolton wires to control fingers. In order to improve the energy efficiency of the whole system, a passive brake mechanism was added to the drive units [22; 23]. The Exo-Glove is compact in structure and weighs 194 g. It has 20 N grip force, 40 N package grip force, and 76 mm maximum grip size. The test results show that patients can grasp objects of various shapes without active control by using the under-actuated mechanism to control the Exo-Glove. Subsequently, the team proposed a slack enabling mechanism [24]. They built a prototype and tested it on the Exo-Glove to prove the advantages of the proposed mechanism. The prototype can eliminate tendon pre-tension and minimize friction caused by pre-tension, which improves the efficiency of the system and ensures the safety of the soft tendon routing system. Then, in 2016, [PERSON] et al. proposed a design method of a 3D-printed flexible and high-deformable flexible robot driven by motor-tendon [25]. This modular design approach facilitates rapid fabrication, deployment, and maintenance, and [PERSON] et al. developed an 8-DOF tendon-driven mechanical glove (Figure 1d) [26]. The glove is actuated by a Bowden cable transmission and a brushless motor actuator. For portability, only one motor is used to control the 8-DOF hand. Recently, in 2018, [PERSON] et al. proposed a new lightweight inflatable soft exoskeleton glove called AirexGlove (Figure 1e) [27], which is based on the antagonistic driving principle [28; 29; 30]. The system is based on the previous work done by the group of [PERSON] in [31; 32; 33]. At the same time, [PERSON] et al. proposed a soft hand sheath combined with electromyography (EMG) sensor (Figure 1f) [34]. The soft gloves are optimized based on a tendon-driven glove. The tendon routings of the glove are typically parallel to single fingers, respectively. Compared with the soft gloves driven by tendon, the singularity of motion is avoided.