Design and transparency evaluation of an upper limb rehabilitation robot for physical human-robot interaction

Over the years, there has been a surge in the usage of robotic exoskeletons in clinics to treat patients with neurological impairments and other brain acquired injuries. For a comfortable and safe human-robot interaction, a harmony is required between the motion of exoskeleton and naturalistic movements of the user. To support natural coordination, exoskeletons must be transparent, ensuring natural human movements to proceed unimpeded. A biomimetic exoskeleton design, coupled with effective force control strategies, can help achieve transparency in motion. An upper limb rehabilitation robot is presented in this study to aid in the rehabilitation of upper limb disabilities. The proposed upper limb rehabilitation robot (ULRR) is designed to improve the transparency, incorporating shoulder, elbow, and wrist joints. The proposed ULRR provides six actuated degrees of freedom (DOF) out of which three are associated with the shoulder joint, one with the elbow joint, and two DOF for the wrist joint. The telescopic features at the upper and lower arm of the ULRR allow a close alignment between the elbow joint of the robot and the user. To evaluate the transparency of the ULRR, two comparative studies were conducted with ten healthy subjects. Firstly, the tests were conducted for the motions of the shoulder joint only in all three DOF individually. Later, a trajectory from the active daily life (ADL) was given as a reference and the ULRR was operated in patient-in-charge and robot-in-charge control modes. The force data collected during these experiments were analyzed to assess the transparency of the ULRR for human-robot interaction.