Rehabilitation robot with high backdrivability using a serial-parallel hybrid structure and precise cable drive

Backdrivability can improve the safety and comfort of rehabilitation training robots, thereby facilitating active patient participation. However, existing high-backdrivability systems often result in tradeoffs, including a reduced transmission ratio or lower response bandwidth. To address these issues, a combination of a serial-parallel hybrid structure and a precision cable drive were used in this study. However, a serial-parallel hybrid structure increases the kinematic operation cost. An equivalent KP screw system method was introduced to simplify the hybrid motion chain and reduce the computational cost in the control process. The developed robot has a working space that fully covers the normal range of motion of the human upper limb and provides high motion dexterity, covering the areas required for most rehabilitation training movements. Despite its excellent reverse driving capability (10 cNm), the robot maintained a relatively high transmission ratio (1:24) and good control bandwidth (50 Hz). The rehabilitation training system design is based on the patient’s active intent, and experimental results indicate that the robot achieves high trajectory tracking accuracy (error: ±0.5°).