## 2 Materials and Methods  
### Design of Hand Function Rehabilitation Robot  
#### 2.1.1 Hand Structure and Structure Design of Rehabilitation Robot  
Hand dysfunction is one of the most common dysfunctions in stroke patients. It is one of the main factors hindering patients' normal life, work and social life, as well as returning to family and society, causing a heavy burden on patients and families. The function of the hand is complex, including many functions such as movement and sensation, and is also closely related to the advanced functions of the brain such as cognition. Its movement has the characteristics of a large range of activities and complex and diverse forms of movement. It is the most important effector organ of purposeful and instrumental movement [31; 32].  
Of the 206 bones in the human body, 54 are in the hand, equivalent to a quarter of the total number of human bones; The muscle structures that drive them are also extremely complex. At the same time, the joints of fingers have more degrees of freedom and various motion functions. In order to use robots to realize these functions, many dexterous anthropomorphic robot hands have been developed. In order to perform an effective grasping action, many effective manipulators with adaptive grasping or low degree of freedom (DOF) have been developed [33; 34; 35].  
In different existing architectures, we decided to adopt the exoskeleton based on connecting rod coupling linkage. The connecting rod driving mechanisms have inherent advantages, such as ruggedness, easy manufacture and maintenance; however, they also have disadvantages, such as the difficulty in carrying out multi-degree of freedom motions in a small space while maintaining sufficient workspace. Therefore, it is of great significance to realize a linkage-driven robot finger mechanism with human-like finger motions.  
The motion transmission is based on the linkage mechanism to realize the coupling motion of each joint of the finger. The rod can transmit tensile and compressive loads. Therefore, each finger can only use one degree of freedom, that is, it can perform the extension (the most needed motion in rehabilitation) and flexion (auxiliary) motion of the finger.  
Specifically, the designed exoskeleton rehabilitation robot is mainly composed of four identical finger modules, which drive the index finger, middle finger, ring finger and little finger, respectively. Each finger module has a degree of freedom actively driven by a linear driver.  
The structural design drawing is shown in Figure 1. The linear driver is constrained on the fixed frame and connected with the proximal phalanx fixed block of the finger. When the driver moves in a straight line, it drives the proximal phalanx fixed block of the finger to move around the circular guide rail with the shaft, and then drives the connecting rod to move. The load transmitted by the connecting rod drives the middle phalanx fixed block to move along the circular guide rail, so as to drive the middle phalanx fixed block to move, realizing the bending action of the finger. Similarly, the linear driver moves in the opposite direction to complete the extension movement of the finger.  
Figure 1: Overall design of exoskeleton hand rehabilitation robot. (**a**) A simplified model of single finger structure with joint linkage; (**b**) structure design of rehabilitation training for single finger; (**c**) composition of control host, interactive interface and control hardware; (**d**) frame design for finger mounting; (**e**) assembled whole robot; (**f**) the whole structure of hand rehabilitation robot.