Design And Active Control Of Three-dimensional Vibration Damping Device Of Military Vehicle Seat Based On Parallel Mechanism

In the process of military vehicles’ driving,the braking causes the vehicle body to vibrate forward and backward,the uneven road surface causes the body to bump up and down,and the turning causes the body to vibrate left and right.Overall,these vibrations can be regarded as three-dimensional vibration.Long-term exposure to low frequency and high intensity whole body vibration will not only affect the ride comfort of the driver and crews,but also cause temporary or even permanent injuries.Based on the principles of multi-dimensional motion of parallel mechanism,this thesis proposes a multiDOF(Degrees of Freedom)vibration damping seat with 3-PCR parallel mechanism as the main body,which is equipped with spring damping device at the prime mover of the mechanism to achieve better vibration isolation and vibration damping effect in three directions of the vehicle seat,and improve the ride comfort of the occupants.Firstly,a three-dimensional vibration damping’s matrix model of vehicle seat is established,and analysis of DOF is conducted on the vibration damping’s matrix based on the mechanism topology theory.Numerical method is used to solve the inverse kinematics and obtain the length value of the driving rod.PSO-BPNN and newtonraphson algorithms are used to solve the kinematics of the parallel mechanism.The velocity and acceleration of vibration absorber are analyzed based on the motion constraint equation.Considering the limiting factors such as the length of the driving rod,the rotation angle of the pair and the interference between the connecting rods.The threedimensional stereogram and section diagram of the working space of the vibration absorber are obtained by using space search method and MATLAB software.According to the stereogram and section diagram,the vibration absorber’s matrix has a large working space in the vertical direction.Therefore,the 3-PCR parallel mechanism is finally determined as the matrix of three-dimensional vibration damping device of vehicle’s seats.Secondly,Lagrange method is used to construct the matrix dynamic model of the seat’s vibration damping device,and the driving balance force of the moving accessory joint is derived according to the principle of virtual work.Three-dimensional model of Seat’s vibration damping device is constructed by using Solidworks software,and import the model into ADAMS to build a virtual prototype.Based on the virtual prototype model,using the space spiral motion curve equation as a function input of multi-DOF driven,getting the displacement,velocity and acceleration curve and driving balance force curve by simulation.The curve is smooth,whice means vibration damping device’s matrix has good movement stability.There is nor big shock when acceleration changes,and the system is convenient for real-time control.Then,the matrix transformation method is used to do modal analysis of decoupling of the seat vibration absorber system.Ignoring the moment of inertia and second-order small amount of velocity of the rod,a simplified closed-loop dynamic model of the vibration isolation system is established by using Newton Euler equation and the vibration response is analyzed.Force is impacted on the vehicle seat vibration reduction platform X,Y,Z three directions.The dynamic platform acceleration curves and the corresponding amplitude-frequency characteristic curves are drew.According to the acceleration curves,at the beginning of applying the impulse force,the acceleration response of the dynamic platform changes dramatically.Under the action of the damping force,the acceleration in X,Y and Z directions quickly tends to be stable within 3s.It is found that the vibration damping platform has good vibration damping performance.Acceleration amplitude frequency characteristic curves show that low frequency vibration will remain for a period of time to stabilize due to mutual coupling of three branched chain of parallel mechanism.It is found that natural frequency of the seat vibration damping system whose matrix is parallel mechanism is changing.To avoid the resonance frequencies of the human body,the appropriate spring stiffness and an appropriate initial position of parallel mechanism can be chosed.Finally,the vibration control model of the vibration damping platform is established.In order to optimize the performance of the system,the LQG controller of the seat threedimensional vibration damping device is designed based on the optimal control theory.Considering the problem that weight coefficient of conventional LQG controller is difficult to determine,the method that weight coefficient of LQG controller is optimized by using GA and MPGA algorithms respectively is put forward.Regarding the weight coefficients of LQG controller as variables,regarding relative displacement of fixed platform and speed of moving platform as optimize targets,based on the weight coefficients,multi-objective optimization mathematical model is established to make each objective reach the optimal.From the simulation results of the active seat vibration damping device,compared with the GA algorithm,using MPGA algorithm for optimizing weight coefficients,attenuation degree of root mean square value of displacement of moving platform is better,so is moving platform’s acceleration,which can effectively avoid premature phenomenon,whose control effect is more close to the optimal solution,which prove the validity of the optimization method.