Dynamics Modeling And Control Simulation Research Of Four-wheel Steering-by-wire Forklift

With the rapid development of forklift industry technology and wide application in logistic system,handling stability have been gradually concerned by people.Four-wheel steering(4WS)is an active control technology for effectively improving safety and maneuverability which can reduce steering radius and increase steering sensitivity.The vehicle that assembles steering-by-wire(SBW)system transfers steering control information by electric signal,which not only is environment-friendly but also improves flexibility of design and makes it possible to track desired steering goal.The 4WS forklift with SBW is taken as the controlled object,and then further study on control strategy for 4WS forklift is carried out,cooperating with the preview optimal curvature driver model.Firstly,a nonlinear tire model of forklift is introduced based on magic formula,and on the basis of trie model,three degrees of freedom(3DOF)nonlinear 4WS forklift dynamics model is set up by using vehicle standard coordinate system.Simultaneously,driver model and double lane model are introduced based on forklift characteristics,which offer a favorable simulation modeling platform for design of subsequent controller.Secondly,considering that real-time and accurate access to the key state variables of forklift is the prerequisite for design of 4WS control system and sideslip angle is difficult to measure,sideslip angle estimation model based on two degrees nonlinear dynamics model is established using the extended kalman filter(EKF)and unscented kalman filter(UKF)respectively.Simulation results confirm that the proposed UKF estimation model has good estimation effect under open-loop and closed-loop system.Finally,considering internal system parameter perturbation or external disturbance and other uncertain elements of forklift,based on SBW technology,the sliding mode controller(SMC)is designed to actively control steering angle of front and rear wheel.Simulation analysis is discussed under open-loop and closed-loop system.Simulation results show that SMC is effective on reducing sideslip angle and tracking ideal yaw rate of 4WS forklift,effectively resisting internal system parameter perturbation and external disturbance,which improve handling stability of forklift.