A 3UPS/S Spherical Parallel Manipulator Designed for Robot Assisted Hand Rehabilitation after Stroke

Hand dysfunction is a common symptom in stroke patients. This paper presents a robotic device which assists rehabilitation process in order to reduce the need of physical therapy, i.e., a 3UPS/S parallel robotic device is employed for repetitive robot-assisted rehabilitation. Euler angle representation was used to solve the robot's inverse kinematics. The robot's joint space and rotational workspace are determined for two scenarios. In the first scenario, the workspace is obtained considering the actuator’s stroke limitations, while in the second scenario, the workspace is determined by adding a second condition, i.e. the range of motion of the spherical joints. Singularity analysis is performed using geometric algebra approach. The robot was manufactured using additive manufacturing technology. The solution of the inverse kinematic problem is employed to control the robot. The robot can perform full range of motion during wrist ulnar deviation and radial deviation motions, with the exception of limited wrist flexion and extension motions. The robot has singular configurations within its workspace. Although the spherical joints have roles in reducing the workspace, the primary causes are actuator selection, radiuses of base and moving platforms and the length of the central leg. These factors can be considered to improve the workspace. Singularity can be avoided by carefully selecting the rotation of the moving platform about Z-axis and avoiding same leg lengths.