Instantaneous Center of Rotation Trajectory Tracking of A Novel Five-bar Robotic Exoskeleton for Knee Rehabilitation

Knee Exoskeletons provide a way to restore the quality of life in people with knee disorders or after injury. One of the major limitations of these exoskeletons is to mimic the natural polycentric knee joint motion. The design and performance analysis of a novel five-bar mechanism is proposed in this study which can be used in a knee exoskeleton. The purpose of this study was to analyze the instantaneous center of rotation trajectory of the five-bar mechanism mimicking the natural knee center of rotation trajectory during sit to stand motion and compare it with similar existing mechanisms. The position analysis of the mechanism in a simplified configuration and the actual hardware configuration was performed for analyzing the center of rotation trajectory, both theoretically and using a dedicated tool respectively. The motion and the center of rotation trajectory of five-bar mechanism was validated, and the results of the study are presented which show the successful tracking of the reference Instantaneous center of rotation with an error as low as 0.14mm for the simplified configuration and 0.24mm for the actual configuration. These results were then compared with different bar mechanisms showing that our five-bar mechanism had better tracking performance among the available rigid mechanisms.