Abstract: To analyze the change rule of body center-of-mass momentum during sit-to-stand motion assisted by rehabilitation robot, the trajectory and center-of-mass momentum of human body are measured. A mathematical model of the body center-of-mass momentum is derived based on Lagrangian equation. The position of mass center during standing up is obtained by auxiliary parallelogram method. The trajectory and momentum are measured during standing up with low, normal and fast assisting velocities. A simulation model is built up in Matlab/Simulink based on the proposed mathematical model to simulate the trajectory and momentum. The results show that sit-to-stand motion is carried out steadily with different assistant velocities of the robot. Through the analysis of horizontal and vertical peak center-of-mass momentum, it is found that the horizontal momentum is the determinant of the stable standing up motion, and the vertical momentum is the determinant of the complete sit-to-stand process. The simulation and measuring curves fit well, which demonstrates the effectiveness of the proposed model in predicting body position and center-of-mass momentum during sit-to-stand motion. This work provides references for stable standing up analysis and robot assisted rehabilitation.

Key words: machine design, rehabilitative robot, assistive standing-up, mass center of human body, linear and angular momentum