Dimension Synthesis And Performance Analysis Of A Reconfigurable Knee Exoskeleton

The exoskeleton robot is one of the typical representatives of intelligent robots,it can realize the combination of human intelligence and machine power,enhance the comprehensive ability of the body,relieve fatigue caused by heavy loads and long time work.The exoskeleton robot can be applied to improve the marching velocity and movement flexibility of soldiers carrying more materials,ammunition,and operation equipment.It can also be applied to industries,construction,rescue,disaster relief,and other scenes with high labor intensity and inconvenient mechanized operations,to improve the ability of wearers to prevent muscle strain and occupational diseases.The lower limb exoskeleton robot mechanism is connected to the lower limb side by side through an auxiliary device,this requires the lower limb exoskeleton robot to synchronize with the lower limbs of the wearer.Because the axis of rotation of the knee joint is variable and the axis of rotation of the knee joint exoskeleton with a single hinge pair is fixed,the motion trajectory between them cannot achieve real-time coincidence(also known as axis misalignment).Axis misalignment affects the lower limb exoskeleton in many ways.On the one hand,the degree of axis misalignment will increase with the increase of movement velocity.The worse the coordination between the two movements,the more difficult the humancomputer interaction force will be,and the wearer will face safety risks under the action of the binding device.On the other hand,the axis misalignment between the wearer and the exoskeleton robot will also affect power assist efficiency and wearing comfort.As a result,this paper provides a structural design method for reconfigurable knee exoskeleton and examines the performance of the knee exoskeleton based on the coupler curve synthesis theory of the planar four-bar mechanism.The main research content is as follows.Firstly,a four-bar linkage trajectory synthesis method is proposed to meet the highefficiency requirements of the variable axis structure design of the knee exoskeleton and lay a theoretical foundation for the design of the knee exoskeleton based on the reconfigurable mechanism.The main difficulty of linkage trajectory synthesis is that the trajectory synthesis equations are nonlinear equations with nine elements and eight elements.By studying the parameter relation of the trajectory synthesis equation and the elimination of the non-linear equation,an independent quaternion cubic nonlinear equation set is obtained without adding or subtracting the roots,which reduces the difficulty of solving the equation and improves the efficiency of solving the equation.A unified synthesis method of sequence paths and a hybrid synthesis method of attitude points and path points are also proposed in the theory of linkage trajectory synthesis.Secondly,a knee exoskeleton structure is acquired using the proposed reconfigurable synthesis method based on the functional combination principle.The visual tracking system is used to record the trajectory of the knee joint at three velocities,and the experimental trajectory is synthesized.For each motion trajectory,the parameter distribution range is confirmed by the atlas method.The parameter value is calculated based on the optimization algorithm and reserved for the results under different errors.The trajectory synthesis equations corresponding to distinct findings are generated,and the analytical approach is used to solve the trajectory synthesis equations' answers.All the equation solutions are the homologous mechanism of the parameter group,which expanded the samples of parameters of the link with different velocities.The linkage parameter groups at different velocities are combined and screened using the image method.The aggregation of image parameters is observed to obtain the structural parameters of the reconfigurable knee-exoskeleton to realize the combination of four-bar mechanisms at different velocities.The displacement of the flexible element of the fixed hinge,based on the rigid reconfigurable construction,is designed to lessen the degree of dislocation during the moving process.Finally,an analysis method for the safety and comfort of the knee exoskeleton is proposed based on the axis misalignment calculation.The degree of freedom of the knee exoskeleton and the angle of movement of the knee exoskeleton is taken as the specific analysis parameters,and compared with the range of motion of the human knee joint,the safety of the exoskeleton structure was proved.By calculating the trajectory errors between the knee exoskeleton and the knee joint,the average dislocation distance at different speeds is 1.608 mm.The humancomputer interaction force is used to improve the comfort of the exoskeleton,and the humancomputer interaction force is calculated by the Voight element-binding formula.The results showed that the comfort of the reconfigurable knee exoskeleton is 10.85 times higher than that of the single hinge pair.