Adaptive Control Of A Robotic Exoskeleton For Physical Human-Robot Interaction

As a kind of robots aiming at providing service for human,robotic exoskeletons play a more and more important role in the fields of rehabilitation therapies and power assistance.Thus it is important for researchers to study the control development of such robots interacted with human,and enhance the control performance.The major research of this paper is the physical human-robot interaction using impedance control.According to the interaction force,the impedance parameters are tuned online and then the reference trajectory of the robot is generated,which contains the motion intention of human.Consider the uncertainties in the robotic dynamics(including masses and moments of inertial,etc.),corresponding adaptive control is proposed based on the Lyapunov direct theory,which can make the robot track the reference trajectory accurately and simultaneously minimize the required interaction force exerted by the human in order to reduce the operation load of the human.The main research contents of this paper are as follows:(1)Asymmetric bimanual control of a dual-arm exoskeleton is developed,which could be applied in the target tracking training in rehabilitation and enable the disabled patients to enhance the efficiency using the exoskeleton.The operation space is constrained in a specific region.In the cooperative control scheme,human intention and dynamic uncertainties as well as physical limits are taken into consideration.Human intention trajectory is estimated according to the interaction force,while the adaptive online estimation for impedance parameters is employed to deal with the nonlinear and variable stiffness property of the limb model.In order for the robot to follow a specific impedance target,we integrate the motion intention estimation into a barrier Lyapunov function based adaptive impedance control.Compared with the conventional impedance control,the proposed adaptive impedance control is able to reduce the required interaction force by human.(2)Consider the load tasks such as assist operations,an adaptive admittance control scheme with two loops is proposed so as to enable the operator to easily accomplish specific tasks such as lifting something heavy.In the outer loop,the impedance information is estimated according to the relationship of the interaction force and the robot motion,then the reference trajectory is reshaped for the robotic exoskeleton.In the inner loop,an adaptive control scheme is designed for the robot to track the reference trajectory which is the output of the outer loop.In the control scheme,a regressor-based method is used to deal with the uncertain robotic dynamics,while a disturbance observer is used to compensate for the external disturbance of the robot system.A cost function about the interaction force and the position error is considered in the control scheme.Thus the controller is able to achieve satisfactory performance in the interaction task and minimize the interaction force by human as well as guarantee the safety during the task.