Development of standing-up motion assist robot to realize physiotherapist skill for muscle strength maintenance

This paper proposes a method for standing up that utilizes a patient's own power to their fullest extent while allowing the person to stand up easily. Analyzing the skills of physiotherapists, we extracted two skills that we believe allowed them to assist patients in standing up by themselves: (1) promoting a forward-bending posture by making it easier to arch their backs and antevert the pelvis, and (2) providing balance so the patient does not fall down. In order to implement these skills, we propose (1) an inbuilt passive joint using a body holder to hold the patient's upper body which reinforces a natural forward-bending posture, and (2) a horizontal position and vertical force assist control system which guides position control in the horizontal direction and assists with exerting force through force control in the vertical direction. We conducted experiments using linear stage system to assist with standing-up motion and confirmed that it promoted a comfortable and natural forward-bending posture through the inbuilt passive joint. Moreover, we compared standing-up motion using a control system that controls both vertical and horizontal positions with the proposed method, which guides the horizontal direction while assisting with vertical force. We found that in the position control system, when the patient performs the standing-up motion, they stand up at a predetermined constant velocity regardless of the force applied to the robot. On the other hand, the proposed method varied velocity in response to the force the patient applied to the robot. In other words, when velocity increases, the robot's motion changes to apply more lifting force, and when velocity decreases, the robot's motion changes to apply less lifting force. In other words, we confirmed that the system uses the patient's remaining body power while assisting with standing-up motion.