Research On 6-DOF Foot And Ankle Complex Dynamic Gait Simulation System And Its Control Strategies

The foot and ankle complex(FAC)is in a special location that requires it to form a vital dynamic connection between the human body and the ground.All upright locomotion accomplished by the human being requires the FAC to continually adapt and couple with the body's surroundings.The FAC is highly complicated in both anatomy and function.As an important equipment for the FAC biomechanical research,the dynamic gait simulator could mimic the stance phase of the gait by using the cadaveric foot,and realize accurate internal measurement of the dynamic behaviors of FAC(such as bony motion,bone internal stress distribution,mechanical behaviors of the ligament and tendon,joint contact force,and so on)by using invasive method.The gait simulator is important for investigating the biomechanical mechanism of FAC disease,demonstrating the surgery plan,studying the sport injury and protection,and developing bionic FAC system.Aiming at the biomechanical research requirements of the FAC,the corresponding gait data from the living subject is analyzed,the technical and control indicators of the simulation system are formed,and a cadaveric FAC based six degrees of freedom(6-DOF)dynamic gait simulation system with active tibia control method is proposed.The system includes a base movable 6-DOF parallel manipulator based tibia motion control subsystem,an electro-hydraulic proportional position control system based base driving subsystem,an electro-hydraulic proportional force control system based dynamic tibia loading subsystem,and a 4-axis tendon actuating subsystem driving by servo electric cylinders.The integration of each subsystem and the development of the prototype are completed,and multi-actuator coupling problem of the twelve-axis system during the FAC dynamic gait simulation is analyzed.The kinematics and dynamics of the base movable 6-DOF parallel manipulator are studied.In order to increase the controllable task-space of the end effector along anterior-posterior direction in the sagittal plane,the electro-hydraulic proportional position control system is employed to drive the movable base of the manipulator.When analyzing the inverse kinematics and dynamics of the manipulator,the inertial forces of the manipulator components caused by the motion of the movable base are considered,and the general dynamic equations for the base movable parallel manipulator are derived.Combined with the in-vivo gait data,the driving laws and the driving forces of the manipulator legs are calculated.The nonlinear equations for forward kinematics of the 6-DOF parallel manipulator are generated upon the unknown coordinates of 3 points embedded to the end effector,thus the position and orientation of the end effector can be calculated without rotation matrix.The dynamic simulation study of the gait simulator is carried out in ADAMS by using a multi-segment foot model,and the feasibility of the proposed gait simulation method is preliminarily verified.A radial basis function neural network(RBFNN)based adaptive composite dynamic surface control algorithm is proposed for high accuracy tracking control of the electro-hydraulic proportional position control system.The RBFNN is utilized to estimate and compensate the unknown nonlinear friction of the system online.The command filters are introduced to to process the virtual control signals,the dynamic surface control(DSC)technique is utilized to design the nonlinear controller of the system,and the "explosion of complexity" problem which is inherent in the traditional backstepping control is avoided.Compensating signals are designed to eliminate the effects of the command filter errors,and the corresponding compensated tracking errors and the estimating errors are utilized to design the composite adaptive law for the RBFNN.By using the Lyapunov theory,the stability analysis of the closed-loop system is given,and the coordinated control method for the base driving subsystem is studied to tackle the multi-actuator coupling problem of the gait simulation system.At last,the comparative simulation results have verified the effectiveness and advancement of the proposed control algorithm.An iterative learning mechanism based output feedback dynamic surface control algorithm is proposed for high accuracy dynamic tibia loading of the electro-hydraulic proportional force control system.The high gain observer is utilized to estimate the unmeasured state variables of the hydraulic system,the dynamic surface control is implemented for high accuracy position tracking of the cylinder,and the Lyapunov theory based stability analysis for the closed-loop system is given.The desired cylinder position trajectory can be optimized by a designed proportional-integral-derivative(PID)type iterative learning mechanism such that the tibia loading force in the complex gait simulation process can be as close as possible to the target tibia loading curve after several iterations.Matlab/Simulink based simulation results have verified the effectiveness of the proposed control algorithm.Simultaneously,by combining the living tendon trend during the stance phase,Fuzzy-PID control algorithm is proposed for the tendon actuating subsystem,and the coordinated control method for the force control systems is studied to tackle the multi-actuator coupling problem of the gait simulation system.At last,the control hardware and software for the prototype are constructed.The base driving subsystem,the tibia dynamic loading subsystem,the tendon actuating subsystem and related control algorithms are verified by using the experimental method.The experimental study of the cadaveric gait simulation is carried out to verify the effectiveness and advancement of the proposed 6-DOF FAC dynamic gait simulation system and its control strategies.The research contents are useful for biomechanics investigations of the FAC.