Research On Key Technologies Of Active Power-assist Lower Limb Exoskeleton Robot

The exoskeleton robot is a kind of specific robot worn on the human body.It achieves the function of compensating and strengthening the human body,and have shown great potential for application.To meet the new needs of the elderly assisting and soldire physical fitness enhancing,active power-assist technology is required.Active assist is a challenging study in the exoskeleton field that requires exoskeleton robots to actively estimate the wearer’s need for force and energy assistance and to help the wearer complete the limb motion in order to reduce the wearer’s muscle fatigue and physical energy consumption.In order to solve the problem of active assist of exoskeleton,based on the perception of human motion i ntention,this paper explored the active assist mechanism,constructed the human-machine cooperative motion control architecture,and designed a prototype of lower limb active-assist exoskeleton robot with strong human-machine coupling characteristics.Experiments about the effectiveness of active-assist were also carried out.A motion intention perception method based on human dynamics model was proposed.This paper analyzed the generation,transmission and expression of human intentions from the perspective of bionics,and demonstrated the feasibility of using joint torques to represent human motion intentions to achieve active assist.The parametric model of the humanbody was established.In order to solve the problem of the abrupt change of dynamic moder of support phase and swing phase,the error accumulation of mutiple joints in series and the internal force confrontation between two legs,a mothod of measuring the contace force of human foot is proposed.The five bar dynamics of the human body is reduced to a two bar dynamics solution.After acquiring the current motion information and foot contact force of the human body,the exoskeleton controller can solve the joint torque required by the human body in the current motion state in real time.The human motion information is obtained through human-machine motion mapping,and the human inverse dynamics solving method is optimized for feasibility,accuracy and adaptability.The experimental results compared with the motion capture system showed that the proposed method can adapt to various complex movements of different wearers with high accuracy.Active power-assist method is researched.Based on the analysis of the mechanism of muscle energy consumption during human motion,the feasibility of reducing the muscle force to achieve the goal of active assistance was determined.The simulation on the Muscular Torque Proportion Compensation(MTPC)was carried out,and the active assist conditions was determined.The MTPC method causes improper load in human bone and skin.Thus an improved active assist method based on man-machine coupling point which called Equivalent Force on Connection(EFOC)was proposed.Through equivalent transformation,the joint target assist moment is converted into the target contact force/moment at the human-machine connection point,and the human motion intention is mapped to the exoskeleton control command.The simulation results of human-machine joint dynamics show that EFOC can achieve the similar effect with MTPC,and can achieve the goal of active assistance and overcome the shortcomings of MTPC.This paper analyzed the inherent characteristics of human-in-loop control and proposed a hierarchical human-machine cooperative control architecture.The deliberative layer obtains human motion information from sensors,realizes the perception of human motion intention,and converts motion intention into target human-machine contact force through the EFOC power assisted method.The reflective layer establishes human-machine contact Force feedback and closed-loop control to ensure the accuracy of active power assisted.The autodynamic feedforward of exoskeleton is used to reduce the interference of exoskeleton weight on human-machine contact force servo.The tropism layer solves the problem of redundant driving caused by simultaneous support of both legs by optimizing the bearing capacity of both sides of the legs,and converts the PID deviation correction result of human-machine contact force into the target torque of each joint of the exoskeleton robot through force balance equation.Finally,the outputs are torques of the dynamic joints.The framework enables the exoskeleton to interact with the human body only in the form of force/torque,but does not actively interfere with the human motion trajectory,so as to achieve the goal of " human-dominated,robot-secondary and human-machine cooperation".The active power-assist lower limb exoskeleton system was designed.This paper analyzed the inherent characteristics of the strong human-machine coupling of the exoskeleton,and puts forward the design requirements The angles,velocities,torques,power and other data of lower limb joints were obtained through experiments,which provide data support to the system design.The exoskeleton mechanical system was designed around the characteristics of strong coupling between human and machine.The exoskeleton configuration was designed with reference to the structural parameters of human body.Human-machine coupling mechanism based on three-point connection was proposed.Human-computer motion mapping was established.Force/energy coupling between the human body and the exoskeleton in the trunk and feet was realized.The perception and control system of the exoskeleton was built.Hip and knee dynamic joints based on hydraulic flexible drive units were developed.System integration and prototype development of the whole machine were completed.This system meet the requirement of the active power-assisted technical framework by combining the requirements of the active power-assist technology system on human body motion information,man-machine load conduction,various sensor signals and flexible drive.It provides a prototype platform for experimental verification.The active power efficiency is studied experimentally.In the human-machine contact force experiment,the human-machine back contact force showed a trend of lifting the human body upward under three kinds of movements,namely treading in situ,squatting and jumping.The full force of the human body dec reased by 188.1N,176.8N and 184.1N respectively,accounting for 24.9%,23.4% and 24.4% of the gravity of the human body,which is very close to the predefined assist factor of 0.25,indicating the successful realization of motion intention perception and EFOC power method.In the experiment of joint assist moment and assist power,the equivalent joint moment provided by exoskeleton is similar to the curve shape of joint moment required by human body.The assist moment is positive in most cases.The assist energy increases continuously with the movement.This indicates that the transient response and the overall power effect of exoskeleton are good.In the power efficiency statistical analysis experiment,five experimenters repeated three exercise patterns 30 times each.The period of statistical positive assist time accounted for 84.6% of the mean.The ratio of positive and negative impulse moments obtained by the joint during the gait period is 90.1%.The total assist impulse moment is 93.1%.The total assist energy is all positive.This shows that the technical indicators of active assistance are good.In the walking experiment in a complex environment,the subjects moved flexibly in various road conditions.It shows that the exoskeleton can support the complex and varied motion of the human body.It embodies the characteristics of "thinking as human thought and assisting as human need" and "human-dominated,robot-secondary and human-machine cooperation".