| As a kind of wearable intelligent equipment,lower limb exoskeleton robot plays a particularly important role in the field of amplifying human muscle energy,rehabilitation training,and enhancing load bearing abilities of human body.At present,due to the further increase in the number of people with lower limb motor dysfunction in China,long-term bed rest or lack of walking has led to a decrease in their lower limb muscle strength and affected balance,thereby affecting their walking ability and quality of life.Therefore,the lower limb exoskeleton is gradually becoming the most potential,attractive and important intelligent power assist equipment.For a long time,the criteria of walking stability of lower limb exoskeletons have been a hot spot and difficulty in the field of exoskeleton study,unlike bipedal robots,human-robot will continue to be interfered by human-robot interaction force during collaborative movement.Since human-robot interaction force was difficult to be directly measured and unpredictable,it will increase the uncertainty of exoskeleton dynamic stability to a certain extent.In addition,most of the existing exoskeleton stability criteria were based on ZMP theory,which have certain limitations for exoskeleton dynamic stability discrimination.In view of the above issues that human-robot interaction force was difficult to measure and stability criteria have limitations,on the one hand,by establishing human body and human-robot inverted pendulum model,the thesis analyzed the influence of human-robot interaction force on the walking stability of exoskeleton,and constructed the mathematical expression of Co M-Co PCo A.In addition,by using centroid acceleration and plantar pressure to describe human-robot interaction force,which avoided the error caused by direct measurement of human-robot interaction force,and on this basis,the influence of human-robot interaction force on the walking stability of exoskeleton was quantitatively analyzed by Co A(Composition of Acceleration),and an exoskeleton walking stability criterion was proposed.On the other hand,based on the stability criterion,the stability margin of exoskeleton was redefined,and a stability margin evaluation function was proposed to measure the correlation between the walking speeds and the stability margin of the exoskeleton under the influence of human-robot interaction force,so as to match the relative optimal walking speed of the exoskeleton and maximize the stability margin.The specific study content was as follows:(1)Analysis of cooperative walking mechanism of human-robot system.Using human anatomy theory,simplified the human lower limb joint structure,a complete gait cycle was divided,the joint structure design of lower limb assisted exoskeleton robot was introduced,and a multimodal information collection platform was established.(2)Study on stability criterion methods.Aiming at the issues that the stability criterion of exoskeleton was complicated due to the difficulty of direct measurement and uncertainty of human-robot interaction force,the stable motion characteristics of exoskeleton based on human-robot interaction force were constructed and analyzed,and the human-robot interaction force was expressed by integrating human-robot centroid acceleration and plantar pressure.Based on the position relationship between Co A trajectories and gait trajectories,a walking stability criterion of exoskeleton was proposed.The influence of human-robot interaction force on Co A trajectories and gait trajectories was analyzed respectively,which played an important role in improving the walking stability of exoskeleton and laid a foundation for the future study on walking stability control.(3)Study on Stability margin evaluation and optimization.Aiming at the mismatch between exoskeleton walking speed and stability margin,a stability margin evaluation function was proposed by taking the idea of the ratio of the expected region of Co A trajectories to the actual area,and the correlation between exoskeleton walking speed and stability margin under the interference of human-robot interaction force was explored,so as to determine the relative optimal walking speed of exoskeleton robot and improve the safety during exoskeleton walks.(4)Experimental study of exoskeleton walking stability.The experiment was carried out around the two parts of stability discrimination and stability margin optimization of the exoskeleton robot.On the one hand,by collecting experimental data in different walking modes,combining with the mathematical model of Co M-Co P-Co A to obtain the corresponding Co A trajectories and gait trajectories,and judging the stability of exoskeleton robots in different walking modes through the proposed stability criterion,the experimental results verify the effectiveness of the stability discrimination method.On the other hand,by collecting experimental data at different walking speeds to obtain the corresponding Co A trajectories,the proposed evaluation function was used to compare the ratio of the desired region to the actual area,and the walking speed of the exoskeleton was adjusted accordingly according to the ratio size to maximize the stability margin,and the experimental results showed the feasibility of the evaluation function and the stability margin optimization method.Taking the wearable lower limb-assisted exoskeleton robot as researched object,the influence of human-robot interaction excitation on stability was analyzed through the human inverted pendulum model and the human-robot stable walking model,and an exoskeleton walking stability criterion and stability margin evaluation function were proposed,and the exoskeleton-assisted walking stability experiment was carried out,which verified the effectiveness of the stability criterion and stability margin evaluation function,which was helpful to improve the stability and safety in the process of human-robot collaborative walking,and laid a solid foundation for the subsequent exoskeleton fall prevention control strategy. |
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