# Current State of Robotics in Hand Rehabilitation after Stroke: A Systematic Review
## 2 Materials and Methods
### Drive Mode of Hand Rehabilitation Robot  
The choice of drive mode directly affects the system solutions, such as structural design and control system, and is the basis for the design of hand rehabilitation robots. Currently, common drive modes are hydraulic drive, motor drive, pneumatic drive, and new intelligent drive materials [69; 70]. We summarized different drive modes in Table 2, in which we only summarized three types of drive modes, namely motor drive, pneumatic drive, and new intelligent drive materials because the hydraulic drive is not commonly used in hand rehabilitation. At present, most of the rehabilitation hand rehabilitation robots use motor drive mode, which has many advantages compared with other drive modes, such as easy control, no pollution, and low noise. Among the new drive modes, there is another widely used drive mode, pneumatic artificial muscle drive [71]. Pneumatic artificial muscle by air as the driving source generally consists of an easily deformable rubber capsule and the external play to limit the deformation of the mesh support. When the air pressure decreases, the pneumatic artificial muscle will return to its original length by the elasticity of the rubber and the external load. Figure 10 shows the pneumatic artificial muscle produced by FESTO. With the development of science and technology, the drive method has been developing more and more in the direction of flexibility, lightweight and high efficiency from the traditional electric motor, to pneumatic drive, and now to the new intelligent material drive [72]. Hydraulic drives now have some insurmountable constraints in some applications, many scholars at home and abroad hope to develop new drive materials to replace the traditional drive methods, which has given rise to many new intelligent drive materials, which have played their unique roles in different fields. Among the existing new intelligent drive materials, dielectric elastomers, IPMC, piezoelectric ceramics and shape memory alloy wires are the most typical drive materials. New intelligent drive materials, which are developed by scholars at home and abroad to overcome the traditional drive methods, are one of the development directions of drive innovation for future hand rehabilitation robots. Motor drive, pneumatic drive and new intelligent drive materials will have their own advantages and disadvantages, so researchers need to choose the most suitable drive mode in combination with the design requirements and continuously innovate. Dielectric elastomer is often used to do research on bionic muscles, it is a new functional material with the advantages of high plasticity, flexibility, low noise, etc., and has a high efficiency of electrical and mechanical energy conversion [73], The dielectric elastomer bionic skeletal muscle experiment is shown in Figure 11a below. Some scholars hope to use it as a driving source for rehabilitation applications, but its driving conditions are very demanding, requiring ultra-high voltage to drive (-100 MV/m), and the poor robustness of control and low driving efficiency, seriously limit its application in rehabilitation driving; ion exchange membrane metal composite (IPMC), is formed by a class of precious metal cation exchange membrane, such as platinum through the chemical coating. When energized, the IPMC film will be bent and deformed in the direction of the anode, and the larger the energized voltage, the more obvious the bending amplitude. If an alternating current is applied, the film will oscillate as the positive and negative poles keep changing. Using its special deformation response, it can be applied in some driving fields, as shown in Figure 11b for IPMC bionic gripper. It requires a low driving voltage of only 5 V to drive, but it must be driven in a humid environment or in a conductive environment, such as  
Figure 10: The pneumatic artificial muscle produced by FESTO [71]. electrolyte, which is very demanding for the environment, and the mechanical conversion efficiency is relatively low.