Development Of A Compact Walking Assistance Exoskeleton And Research On Gait Generation Method

In China,numerous persons such as stroke patient,spinal-cord injury patient and other elders are suffering from physical and psychological disabilities owing to walking dysfunction.Persons with walking dysfunction need assistance devices to provide basic mobility,reduce complications,and improve the life quality.However,standing assistance devices such as brackets and orthosis cannot achieve the motion function of the lower-limbs.Movement assistance devices such as crutches and wheelchairs cannot provide the sense of walking to users.Wearable exoskeleton is an interactive robot system which is worn on the human body,cooperates with the human limbs,provides the body with support,assists in the movement of the limbs,and improves physical function.In the past decade,extensive research on the field of paramedical medicine has made walking assistance exoskeleton one of the hot topics at home and abroad.However,current walking assistance exoskeletons are not yet practical due to the bulky structure,complex manipulation,and fixed gait.To satisfy the basic requirements of persons with walking dysfunction,this paper develops a compact walking assistance exoskeleton,and aims at the research on stable and natural gait generation method.Based on theoretical research and experiments,the system design,online gait generation method,and natural and stable gait adjustment strategy are researched to promote the adaptability and practicability of the walking assistance exoskeleton.Firstly,the exoskeleton which is designed to assist the p ersons with walking dysfunction to stand and walk upright stably and comfortably should be light and compact.Based on the biomechanics analysis of human movement,the overall scheme of the modular compact exoskeleton for walking assistance is designed by choosing actuated joints,designing the man-machine compatible configuration,and designing overall parameters of function and performance.The modular design scheme has good performances in portability,on and off,interchangeability,and maintainability.Based on the modular design scheme,the mechanical systems including waist module,shank module,and thigh module are designed.Meanwhile,the actuator modules are designed and the performance of actuated joint is tested.Furthermore,the electrical subsystems including the control system,servo system,sensor system,energy system,and human-machine interactive system are designed.The mass of the walking assistance exoskeleton prototype is 10.15 kg.The kinematics and dynamics models of the compact walking assistance exoskeleton are established.The system framework of motion control with three stages,which are joint motion control,gait trajectory generator,and human-machine interaction,is designed.These three stages have clear function differentiation,mutually independent layers,and flexible convertibility.The position closed-loop control method of actuated joint is researched.The motion generation method based on the finite-state machine(FSM)is designed,in which,four basic motion states and seven pre-designed reference motions are defined.Meanwhile,the logical relationships between the basic motion states and the reference motions are established.Moreover,the reference motion trajectories are gathered and designed based on the torque compensation control method to reduce original error.Finally,three human-machine interactive devices,which are the wireless handle,functional crutches,and gait virtual interface,are designed.The stable motion control and gait generation of the walking assistance exoskeleton are achieved.Based on the FSM-based motion generation method,the reference motion trajectories are parameterized via the step-velocity coefficient,step-length coefficient,and step-height coefficient.According to these three parameters,an online adjustment method of the gait trajectory is proposed.Furthermore,the relation equation between the step-length coefficient and the step-height coefficient is established after analyzing the relevance between the characteristic parameters.The coupling relationship between the crutch attitude and lower limb motion position is analyzed.The analysis result reveals that the step length is relevant to the crutch pitch angle during the continuous walking.Therefore,a motion state switch strategy and an online gait generation method of the exoskeleton based on the crutch pitch angle are proposed,and the trigger boundaries of the motion states are obtained through experiment.After that,the stability criterion and stability margin of the human-exoskeleton system are definited to analyze the system stability during the processes of standing up,sitting down,and continuous walking.Based on the system stability analysis,the trigger boundaries of the motion states are calibrated,and the online gait generation method is optimized.As a result,the minimum stable threshold of the system during the continuous walking is promoted with 50 mm.In addition,a stability-orientated motion generation strategy of the exoskeleton is proposed to achieve safely and stably online gait trajectory generation and adjustment.Based on the developed compact walking assisitance exoskeleton and the proposed online gait trajectory generation and adjustment methods,exoskeleton experiments of FSM-based motion with reference trajectory,gait trajectory online parametric adjustment,online gait adjustment and motion states trigger based on the crutch pitch angle,and gait stability of online trajectory adjustment during continuous walking are conducted.The results demonstrates that the compact walking assisitance exoskeleton is able to accomplish the above experiments stably and reliably,and can be worn and manipulated conveniently.Meanwhile,the feasibility of the proposed online gait generation and adjustment methods are verified.Moreover,the stability of the exoskeleton system during continuous walking is significantly promoted utilizing the online gait adjustment method.