Aiming at steering stability and wheel angle tracking of steer-by-wire (SBW) three wheeled forklift, steering dynamic model and SBW system mathematical model of three wheeled forklift are established. A control strategy for the ideal transmission ratio is introduced based on this model, which ensures forklift steering gain invariant. A sliding mode controller can then be designed based on the bound information of uncertain system parameters, uncertain self-aligning torque, and external disturbances. The results of simulation show the control strategies above can effectively reduce the sideslip angle when the forklift is steering and improve the sensitivity and stability of the steering forklift; at the same time can effectively restrain the parameter perturbation of internal system and external disturbance, which improves the tracking performance of the wheel angle.
IntroductionThe forklift usually works in small working space to handle cargo with low speed, so more need to ensure the steering maneuverability and handling stability [1] . The three wheeled forklift has the characteristic of small size, it uses advanced dual-front technology and rear wheel active steering technology, can achieve 90-degree steering, has advantage of small turning radius, more effort to operate, so very suitable for working in narrow space.Conventional forklifts, which are mechanical steering, can't take the initiative to control the angular transmission characteristics and force transfer characteristics of the steering system. The Steer-by-Wire (SBW) system eliminates the mechanical connection between steering handle and steering wheels in a conventional steering system and transmits the control signals via electrical signals, so that can be freely designed [2][3][4][5].Nowadays, the research on the vehicle steering system is mostly based on the variable transmission ratio and the strategy of yaw stability control, and does not take into account the tracking performance of the wheel angle of SBW system. In this paper, for the three wheeled forklift equipped with SBW system, the stability of the steering forklift and the problem of wheel angle tracking are considered. Based on the ideal transmission ratio control which the yaw rate gain is fixed, sliding mode angle tracking controller based on variable parameters is designed. Through simulation experiments, it is verified that the proposed scheme can improve the stability of the steering forklift and the tracking performance of wheel angle.
Modeling of SBW System for Three Wheeled ForkliftIn this paper, a three wheel steering model with 2DOF (which are lateral and yaw) was established.
Three Wheeled Forklift Steering Dynamics Model Based on Ground Coordinate SystemAs shown in Fig.1, oc is