Design And Motion Control Research On Parallel Redundant Soft Ankle Rehabilitation Robot

The ankle is one of the important components of the human body,and it also plays a vital role in ensuring the balance of people walking.More and more people have already suffered from ankle injury due to illness or other safety incidents.The patient's rehabilitation training for ankle also requires higher control precision,better repeatability,and more diverse training modes.Therefore,it is more and more difficult for traditional rehabilitation doctors to assist patients in rehabilitation training to meet the needs of patients.The rehabilitation robot has the advantages of high precision of training track control,good repeatability and diversified training modes,which can better meet the rehabilitation needs of patients.The actuators of the existing ankle rehabilitation robots are mostly rigid,and have problems such as insufficient flexibility and poor safety,and the soft pneumatic muscle driver has the advantages of good flexibility and light weight.Therefore,the application of a Soft pneumatic muscle driver to an ankle rehabilitation robot has many advantages.However,pneumatic muscle drivers have strong nonlinearities and timevarying characteristics,and pneumatic muscle drivers can only provide tensile force,which makes it difficult to control the position of pneumatic muscles.In view of the above problems,the main research contents of this paper are as follows:(1)Aiming at the need of ankle rehabilitation,the driving characteristics of soft pneumatic muscle driver which can not provide thrust,a soft ankle rehabilitation robot driven by five pneumatic muscles is designed that can provide sufficient range of motion in dorsiflexion/plantarflexion,inversion/eversion,and adduction/abduction.Then the inverse kinematics and dynamics model are studied.On this basis,the relationships among the rotation angle of the end platform,the expected output moment of the end platform,the displacement of the pneumatic muscle driver and the pull force of the pneumatic muscle driver are established.Finally,the complete software and hardware control system of the parallel ankle rehabilitation robot is established.(2)In order to accurately control the position of the pneumatic muscle-driven ankle rehabilitation robot,a three-element model of the pneumatic muscle driver was established.Due to the strong nonlinearity of pneumatic muscle actuators,in order to improve the accuracy of position control,this paper studies the backstepping-based sliding mode control method for nonlinear systems.On this basis,in the process of rehabilitation training,a nonlinear disturbance observer is designed for the disturbance of the patient's limb disturbance,the modeling error of the pneumatic muscle driver and the friction between the devices.At the same time,an adaptive backstepping sliding mode control method based on nonlinear disturbance observer is proposed.The unpredictable interference problem in the robot-assisted training process will be solved,so that the position control accuracy can be effectively improved.(3)In view of the fact that the pneumatic muscle driver can only provide the tensile force and the characteristics of each pneumatic muscle driver of the ankle rehabilitation robot to maintain the tensile force at all times,this paper studies the force distribution algorithm of a redundant parallel soft ankle rehabilitation robot based on the Jacobian matrix and Karush-Kuhn-Tucker(KKT)conditions.Then the analysisiteration algorithm is used to derive the optimal solution of the force distribution algorithm.Based on this,a force/position hierarchical control method including a position control loop and a force control loop is proposed.While ensuring the positional tracking accuracy of the soft ankle rehabilitation robot,all pneumatic muscle drivers are always stretched to ensure the safety and controllability of the rehabilitation process.