Research On The Mechanism Of Influence Of Goods On Stability And Control Strategy For Forklift

With the rapid development of logistics industry and the demand for the maneuverability of modern forklift,the stability control of forklift has caused great interest in the research field.As the operation space become smaller and the operation requirements become higher,the requirements for the stability control of forklift also become higher.However,the traditional control of forklift regards forklift as the general vehicle,which lacks the particularity of the control object.Especially it does not consider the impact of cargo on the stability of forklift.Relevant data shows that a considerable part of forklift accidents are caused by the loaded goods.On the one hand,the lifting height of the cargo will lead to forklift overturns.On the other hand,the change of composite center of forklift gravity,which caused by the loading of goods,also will affect the lateral forklift stability.Each of them will bring serious security risks.In order to improve the influence of cargo on the forklift stability,the lateral stability model and longitudinal stability model of forklift are analyzed and a lateral stability control strategy for forklift based on longitudinal boundary is also proposed to improve the safety and stability of forklift.In this paper,based on the traditional two degree of freedom model of vehicle,the lateral dynamic model of forklift considering the lifting of goods is established.At the same time,a special working condition which causes the longitudinal overturning of forklift is analyzed,namely the acceleration caused by the sudden stop and start of forklift.Transfer function between driving force and pitch angle is proposed and the simulation results verify the proposed dynamic model.It also shows that it is necessary to control the forklift stability considering the goods to improve its stability and provides a theoretical basis for the design of controller subsequently.Secondly,based on the lateral dynamic model of the forklift considering the goods,the steering angle of the front and rear wheels of the forklift is modified to improve the movement posture of the forklift by using the four-wheel steer by wire technology and the nonlinear sliding mode controller.The nonlinear sliding mode controller designed is directed against the lateral dynamic model of forklift with nonlinear and uncertain parameters.The lateral stability control problem of forklift is transformed into the stability design problem of a known uncertain linear system by separating the parameters of the system.The designed nonlinear sliding mode control system is asymptotically stable under Lyapunov formula and it also has a good suppression effect on external interference.Finally,on the basis of sliding mode controller of forklift lateral stability,the maximum height of goods is introduced to form the controller of forklift lateral stability based on longitudinal boundary.Through the hypothesis analysis of the forklift longitudinal stability model,the controller obtains the longitudinal stability boundary of the forklift.On the one hand,it provides a guarantee for the longitudinal forklift stability.On the other hand,it also provides a prerequisite for the design of the sliding mode controller.The effectiveness of the designed lateral stability controller based on the longitudinal boundary is verified under the operation conditions of double lane change.Under the prerequisite of ensuring the stability of pitch angle guaranteed,it can further optimize the yaw rate and sideslip angle and improve the lateral forklift stability under the condition of driving with cargo up-and-down.