Development of a 4 DOF exoskeleton robot for elbow and wrist rehab

It is important to control impedance between a patient and a robot to maximize the effect of the robot rehabilitation therapy. This paper presents a 4 DOF exoskeleton robot for elbow and wrist rehabilitation, which includes a unified actuator module per each joint. The unified actuator module consists of a frameless motor, an incremental encoder, an absolute encoder, a harmonic drive, a torque sensor, and a motor controller. The interaction force between a patient and the robot can be computed based on the torque signal of each joint. This enables us to design impedance controller to implement proper impedance to the patient. All the components of the unified actuator module were carefully selected to minimize overall weight and size. A second-order state-space model for the unified actuator module is developed via experiments. A H₂ optimal controller was designed based on the state-space model.