LQR Optimal Control About Four Wheel Steering Forklifts Based On State Feedback

Four Wheel Steering (4WS) technology of forklifts is that the front wheel steering angle is also added to steering system. It can reduce the steering radius and increase steering sensitivity, therefore it is widely accepted. Linear Quadratic Regulator (LQR) based on state feedback is easy to realize, and has the advantage of small overshoot and short setting time. The control algorithm has been applied into the two degrees of freedom (2DOF) model, but there is less research about three degrees of freedom (3DOF) model. This paper puts forward the following research aimed at this phenomenon.Firstly, handing stability of forklifts was analyzed, three influence factors:side slip angle, yaw rate, roll angle and methods for estimating or measuring have been given.Secondly, the proper cornering stiffness has been chosen by analyzing tire model. Based on the theory of vehicle dynamics, the 2DOF and 3DOF model are established, and steady-state and transient-state response are analyzed under step input of rear wheel steering angle.Lastly, LQR control algorithm based on state feedback is added to the established forklift model. Comparing simulation results of LQR 4WS, proportional 4WS and rear wheel steering (RWS), it shows that side slip angle is reduced under LQR control. On the other side, yaw rate is increased. It indicates that LQR control can keep better control performance.In general, choosing the weight coefficient of LQR reasonably can improve the dynamic response performance and keep a better body attitude. Consequently, the handing stability is enhanced.