# Current State of Robotics in Hand Rehabilitation after Stroke: A Systematic Review
## 2 Materials and Methods
### Control Strategy of Hand Rehabilitation Robot
#### 2.3.1 Interactive Control Based on Force Signals
Impedance control is divided into two different control results based on force and position; force-based impedance control is achieved by controlling the joint drive torque to adjust the end contact force and displacement; while position-based impedance control is achieved by adjusting the position of the robot end according to the deviation of the contact force between the robot and the environment. In the force-based impedance control method, the robot reflects the end impedance characteristics of the robot by controlling the robot joint torque through feedback based on the contact force between the end and the environment. In practical applications, the robot end position and contact force are detected in real-time, the desired force output is generated by the grid feedback position and desired impedance model, the difference between the desired force and the actual contact force is taken, and the control torque is calculated by the robot dynamics model based on the force error as the joint driving force so that the robot's system behaves as the desired impedance model characteristics. Therefore, the force-based impedance control must first determine the exact robot dynamics model before the desired impedance model and the exact contact force control can be achieved. The position-based impedance control consists of two parts, the inner loop of position control and the outer loop of impedance control. The inner loop of position control processes the three data of the desired position, position compensation amount, and actual position to make the actual position of the robot track up to the desired position. The impedance control outer loop is to process the difference between the desired force and the actual force to get the position correction amount, and these will continuously adjust the target impedance model parameters by actually detecting the force between the robot and the environment, and then control the robot's position through the position controller to achieve force control. The literature mainly addresses the problems of the robot arm in terms of unstable impedance control force and position control safety collision avoidance and designs an impedance controller with linear decoupling position control in the operation space as the inner loop and uses the force error to adjust the reference trajectory in real-time to achieve effective force tracking impedance control and collision avoidance control of the robot arm. In the literature, an impedance control method based on the position inner loop was proposed for the gripping force tracking of the end-effector double-finger grasping of fruits and vegetables to reduce the damage of the robot in the picking process, which realized the flexible grasping of the robot, reduced the damage of the grasped fruits and vegetables, and ensured the picking quality. Most of the current research on hand function rehabilitation robot systems focuses on function realization in the bionic structure power source which mainly adopts a micro DC motor, a transmission method selects a linkage mechanism or rope wheel mechanism, and currently, for the selection of degrees of freedom, quality, institutional efficiency is to be further improved. In terms of control methods, based on multi-rigid body robot control methods, most scholars focus on the study of motion control of hand-functional rehabilitation robot systems, or the study of rehabilitation training patterns based on motion control, and a few scholars focus on the study of human-machine contact forces for hand-functional rehabilitation robots. There is a lack of in-depth research regarding human-machine interface modeling and contact force control methods for hand-functional rehabilitation robots.