Robot-Assisted Upper Limb Rehabilitation System Based on Variable Admittance Control

This paper introduces a robotic rehabilitation system for upper limb therapy, utilizing a manipulator controlled through variable admittance control. The proposed approach allows dynamic modulation of the patient's mobility within a predefined spatial tolerance region, which is set by the therapist at the beginning of each session based on the patient's capabilities. The system adjusts movement constraints based on the applied force, promoting guidance along the intended path. Specifically, it supports motion along the path tangent while increasing resistance to deviations, but only when the applied force pushes the patient away from the trajectory. Conversely, when the movement is directed toward realignment, the system permits greater freedom in all directions that facilitate a return to the predefined path. To validate the proposed approach, an experimental study was conducted to analyze the system's behavior in practice. The results demonstrate the system's effectiveness in modulating movement assistance and resistance based on patient interaction, ensuring both guidance and adaptability within the rehabilitation process.