| The research direction of exoskeleton robots has two main branches:rehabilitation exoskeleton and assisted exoskeleton.The former is mainly used in the medical field.In the process of human-machine coordinated exercise,the movement of rehabilitation exoskeleton is the active movement,and the one of human body is the passive movement.Assisted exoskeleton is the walking and assisting robot,which is mainly worn on a normal human body.Through the exoskeleton robot mechanical mechanism,the load is transferred to the ground to achieve power.When the booster exoskeleton robot together with the wearer is in human-machine coordinated movement,the movement of human body is the active movement,and the one of the exoskeleton robot is the passive movement.This paper mainly studies the lower limb assisted exoskeleton robot.The assist of the exoskeleton robot not only enhances the endurance of the human body,increases the speed of movement,but also improves the body's ability to resist loads.Therefore,studying the dynamic stability characteristics of human-machine coordinated movement of exoskeleton robots is of great significance for realizing human-machine coordination and the synergy effect of exoskeleton robots.The design scheme of the mechanical body of the lower extremity exoskeleton robot driven by single degree of freedom is proposed,which reduces the number of drives and simplifies the structure of the lower extremity exoskeleton robot.Under different motion attitudes,with reference to CGA human motion data,the degrees of freedom of each joint are defined,and the range of motion angles of each joint is given.The multi-attitude dynamic motion characteristics of human-machine system were analyzed by D-H kinematics analysis method and Lagrangian dynamics analysis method.The motion simulation was carried out by using MATLAB and ADAMS analysis software,and the theoretical and simulation comparison results were obtained:when the attitude motion is converted,the motion parameters are greatly abrupt.From the curve trajectory,the fluctuation is obvious,and the overall system stability is low.Based on the zero moment point balance theory,the stability criterion based on ZMP biped projection polygon method is proposed,the variation law of stable polygon in single step motion is constructed,and the multi-pose stability characteristics of human-machine system are qualitatively analyzed.Based on the stability criterion of ZMP biped projection polygon method,combined with the stability calculation method of the shortest distance stability margin,the instability rate is proposed.It is known from the definition of the instability rate that the stability of the interior of the stable polygon and the form of instability appearing are different.Therefore,starting from the centroid of the stable polygon,the vertices of the stable polygon are respectively connected,and the stable polygon is divided into several triangles.Within several triangles,the dynamic stability characteristics of each attitude are analyzed,and the quantitative calculation of the stability degree is carried out.From the focus of COG,the influence of its multi-attitude dynamic stability characteristics on human-machine system is analyzed,and the center-of-gravity COG and zero-torque point ZMP space coordinate system and three-dimensional space inverted pendulum model are established.The force analysis is carried out,and the spatial position relation expression between the center of gravity COG and the zero moment point ZMP is obtained.Based on the ZMP theory of zero moment point,the force model of Z-direction man-machine system is established,and the relationship between plantar pressure and mechanical model is obtained.Then,the relationship between zero-torque point ZMP and plantar pressure COP is derived.Based on the above two points,the foot pressure-zero moment point-center of gravity algorithm is proposed,and the flow chart of the plantar pressure-zero moment point-center of gravity algorithm is drawn,and the relationship between the plantar pressure COP and the center of gravity COG is obtained.In the multi-pose motion environment,the influence of the center of gravity COG on the dynamic stability characteristics of each attitude is analyzed.In the picking up posture,a simplified model of the inverted posture is established.The relationship between the center of gravity COG and the zero moment point ZMP is analyzed by using the concepts of momentum and angular momentum.In the walking attitude,the telescopic inverted pendulum model of human-machine system is established.The relationship between the center of gravity of the sagittal plane COG-zero and moment point ZMP is analyzed from the initial acceleration period,the two-leg support period,the deceleration phase and the acceleration phase,and the COG displacement and velocity change trajectory of the center of gravity are obtained.In the stair attitude,a 6-step stair action diagram was established,focusing on the step-up process in the middle stage.With the inverted pendulum model and theory,a virtual variable height inverted pendulum model was established,the influence factors ? and ? of the inverted pendulum Z-direction height are defined,and the centroid polynomial of the center of gravity COG is established and solved.A multi-attitude motion test platform was built to test the stability characteristics of multi-pose motion.Through the plantar pressure sensor,the plantar pressure during each attitude movement is collected.Combined with the pressure center point-zero,moment point-center and point algorithm,the comparative test and theoretical results are analyzed.The results show that during the motion process,the man-machine system can meet the stability characteristic requirements,and the stability degree tends to approach the stable boundary locally.Therefore,further research on stability control strategies is needed to enhance the overall stability of human-machine systems.A multi-attitude motion test platform is built to test the stability characteristics of multi-pose motion.The plantar pressure during the three posture movements of picking up,walking and going up the stairs is obtained.Combined with the COP-ZMP-COG algorithm,the test results and theoretical analysis results are analyzed and compared.The results showed that during the exercise,the man-machine system can meet the requirements of stable characteristics,and the degree of stability has a tendency to approach the stable boundary locally.Therefore,further research on the stability control strategy is needed to strengthen the comprehensive stability of the human-machine system.In this paper,the trajectories of the center of gravity during human-machine motion in squatting,walking and ascending stairs were obtained by means of Multi-Attitude motion test platform and human motion data measurement system,which provide experimental basis for verifying the accuracy of biped projection polygon method and center of pressure-zero Moment point-center of gravity algorithm.The validity of the biped projection polygon method and center of pressure-zero Moment point-center of gravity algorithm are verified by comparing the experimental and theoretical results,which provide a new idea and method for the study of the stability characteristics of biped walking robot. |
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