Ankle-assisted Flexible Exoskeleton System For Stroke Patients

Clinical observations show that most of the patients with stroke suffer from varying degrees of motor dysfunction.Among them,the walking ability and efficiency of patients with ankle plantarflexion/dorsiflexion dysfunction declined,which greatly affects their self-care ability,participation ability and quality of life.Ankle exoskeleton robots can assist such patients in walking,but most of the existing ankle exoskeleton robots adopt rigid design,which is difficult to meet the rehabilitation needs of these patients due to the problems of high weight,large volume and joint misalignments.For the above situation,in order to meet the walking aid needs of patients with ankle dysfunction,this subject designs a flexible exoskeleton robot driven by Bowden cable.The robot adopts Bowden cable to realize flexible transmission,and transfers the power to the wearer's heel or forefoot,which is converted into a torque to assist joint movement and realize the walking aid for the patients.At the same time,based on the motion characteristics of the ankle joint,the methods of robotic walking aids for providing assistance force in the plantarflexion phase and avoiding foot drop in the dorsiflexion phase are put forward to meet the different needs of the two types of patients.The main contents of this paper are as follows:(1)Walking aid principle and structure design of flexible exoskeleton:Firstly,the motion law of human ankle joint is analyzed,and based on the elastic characteristics of human muscles,a human-machine coupled system model is established,and the walking aid principle of the robot is given:by planning the displacement trajectory of Bowden cable guide under the plantarflexion and dorsiflexion transmission methods,it provides pushing power in the stance phase for patients with ankle plantarflexion dysfunction,and avoid foot drop in the swing phase for patients with ankle dorsiflexion dysfunction.Finally,the overall configuration design and structural design of ankle-assisted flexible exoskeleton robot are completed,which provides a basis for robot control and experiment,and realizes the engineering realization of robot prototype from the walking aid principle.(2)Design of the gait detection insole:In order to achieve gait detection during walking,a gait detection insole based on multi-channel plantar force sensors is developed.The arrangement of the sensors,the implementation of the hardware/software and the communication method are studied.The developed insole can obtain the plantar pressure cloud image,gait phase and the center of the plantar force in real time during walking,and can feedback the gait moment in real time,which provides the basis for the real-time control of the flexible exoskeleton robot system.Meanwhile,the insole can also be used to assess the wearer's gait.(3)Research on driving and control method of flexible exoskeleton robot:Firstly,the brushless motor driving method is studied,and the FOC(Field Oriented Control)constant-torque-angle control method is used to realize the complete decoupling of the electromagnetic torque,simplifying the motor control.Then,the decoupled current loop control parameter is used for the "position-current" double closed-loop PID control method to realize the position control of the motor,which can adjust the displacement of Bowden cable guide during dorsiflexion aid walking.Aiming at the requirement of the tension adjustment of Bowden cable guide when the exoskeleton robot providing plantarflexion assistance force,a fuzzy control method is adopted according to the characteristics of uncertainty in human-machine interaction,and the output force of the robot is realized by dynamically adjusting the displacement of Bowden cable guide.By controlling the brushless motor embedded in the modular joint,the walking aid motion of the robot is realized.(4)Experimental studies on ankle-assisted flexible exoskeleton robot:On the basis of the established flexible exoskeleton robot body,the software and hardware of the control system are designed,and then the walking experiments of wearing the robot are carried out,and the effect of walking aid is verified by EMG signal.The experimental results show that when the robot performing plantarflexion assistance,it can provide stable lower limb pushing force,and the average absolute error of the force tracking is less than 10N;when the robot performing dorsiflexion assistance,it can avoid foot drop,and the average absolute error of the displacement track is less than 0.08cm.In the two walking aid processes,the lower limb muscle activity of the wearer decreases significantly compared with helpless walking,which proved the effectiveness of the robot.