Cooperative Control of the Two-handed Flexible Exoskeleton for Rehabilitation Based on the Process of Juggling Task

To solve the problems of two-handed flexible exoskeleton in juggling task, such as slow response, an energy transfer model of two-handed juggling process and a hybrid force/position cooperative control system with position feed-forward are proposed. Firstly, an energy transfer model of object-hand collision is established based on the movement characteristics of two-handed juggling process. Then, a mathematical model of coupling between the flexible exoskeleton hand and the human hand is established based on the law of energy conservation and the principle of virtual work. Meanwhile, the rope elongation in the juggling-collision model is deduced, which is considered as the feedforward value in position compensation. For the driving rope, the control system adopts position control at the beginning of juggling process, and switches to force control when the rope elongation remains unchanged and the tension value of the rope continues to increase. Finally, position control and force interaction experiments in juggling an actual object with the two-handed flexible exoskeleton are carried out to prove the dynamic responsiveness and effectiveness of the proposed position feedforward control strategy based on the rope elongation and the stability of fingertip contact force under the force interaction control in the posterior period. The experimental results show that the two-handed flexible exoskeleton for rehabilitation can assist the user to realize the rapid grasp of the objects, and meet the cooperative control requirements for the exoskeleton hand in the juggling task.