Trajectory Synthesis And Gravity Balance Of Planar Six Bar Mechanism For Rehabilitation Of Lower Limbs

Rehabilitation robots can replace paramedics to help paralyzed patients with highly repetitive rehabilitation exercises.The rehabilitation robot has the advantages of accurate motion positioning and high working intensity.However,at present,many rehabilitation robots do not have a clear track of rehabilitation when performing rehabilitation exercises for patients,but only the affected limbs of the patient are simply flexed and stretched.Many rehabilitation robots use a series mechanical arm structure,which results in a large load on the structure itself,requires multiple motors to work together,and requires high motor control algorithms.Therefore,this subject designed a rehabilitation robot driven by a motor to assist the lower limbs of the human body to walk out of normal gait,and can balance the gravity of the lower limbs of the human body during the rehabilitation process.The structure of the human lower limb rehabilitation robot is established based on the gait of the human lower limb and the six-bar structure of Stephenson III.Five representative points are selected from the natural gait trajectory of the human body,and a comprehensive function generator based on the Stephenson III six-bar structure trajectory is designed.The homotopy algorithm is used to solve the solution of the polynomial equations generated by the function generator,and the solutions that meet the requirements are selected from the obtained multiple sets of solutions.Using MATLAB to simulate the trajectory of the rehabilitation robot,compare the simulation curve with the actual gait of the human body,and select the optimal set of parameters as the rod length parameters of the mechanism.For the load of the lower limbs to the rehabilitation robot,the subsystem method is combined with the zero initial spring to establish the gravity balance model.The analysis of the single-degree-of-freedom member is based on the zero-precision spring to achieve the balance of moment and potential energy when the gravity balance is achieved.The sum of the gravitational potential energy of the multi-rod system is calculated,and then it is decomposed into n subsystems.The pseudo-base is established in each subsystem,and the zero initial spring is combined to make the potential energy conservation of each subsystem achieve the multi-pole gravity balance.The multi-bar gravity balance model is applied to the lower limbs of the human body,and the spring coefficient of the zero initial spring is calculated.The potential energy conservation analysis and the moment balance analysis are performed using MATLAB to verify the implementability of the gravity balance.The kinematics model is established by the closed-loop vector equation.The kinematics analysis is performed on the lower limb rehabilitation robot.The between the original and the follower is obtained by the elimination method.The angular displacement,angular velocity and angular acceleration relationship.The EulerLagrangian equation is used for dynamic modeling analysis.The torque input simulation diagram is compared with or without gravity balance.It is found that the subsystem method combined with the zero initial spring can realize the gravity balance to reduce the output of the motor.Torque.Using Simulink to perform PD control simulation and sliding mode control simulation for lower limb rehabilitation robots,and provide theoretical guidance for subsequent experimentsThe experimental platform is built,the trajectory of human lower limb assisted by the robot is collected,and the trajectory simulation map is compared to determine that the rehabilitation robot based on the Stephenson III six-bar structure design can realize the gait reproduction of the lower limb of the human body.Comparing the magnitude of the motor output torque with or without gravity balance,verifying the gravity balance can optimize the mechanical properties of the structure.