Research On Anti-rollover Control Of Counterbalanced Forklift Based On Stability Region Division And Input Time Delay

With the rapid development of China’s economy,forklifts have played an important role in many industries in China as a handling tool.Due to the complex working environment of counterbalanced forklifts,especially in high-speed steering conditions,they are prone to lateral instability or even rollover,causing casualties and economic losses.Therefore,it is very important to conduct forklift rollover mechanism and anti-rollover control research.In this paper,a forklift rollover dynamics model is established on the basis of forklift structural analysis,and a forklift rollover prevention model predictive control strategy based on the division of stability domains is proposed,and a forklift rollover prevention dynamic output feedback control H∞ strategy considering input time delay is proposed,and carrying out simulation and actual vehicle test verification.The main research contents and results are as follows:(1)Based on the analysis of the structural characteristics and rollover mechanism of the counterbalanced forklift,considering the non-linear characteristics of the tires,a two-stage three-degree-of-freedom rollover dynamics model of the forklift is established:the first stage model with no contact with the limit block LTR1 and the second stage model with the limit block contact LTR2;in order to reduce the complexity of the model,a three-degree-of-freedom rollover dynamics model of the forklift under all working conditions was established;considering the three-point support structure characteristics of the "front drive axle+rear steering axle" of the counterbalanced forklift,the anti-lateralization of the counterbalanced forklift was determined flip control actuator:hydraulic support cylinders,dynamic balance weights and steering cylinders for lateral support,lateral load and active steering control adjustments.(2)Considering the particularity of the counterbalanced forklift’s rollover process,the lateral load transfer rate in the first stage of the roll and the lateral load transfer rate in the second stage are determined as evaluation indicators,and the stability region is divided:stable region,relative stability region,and dangerous region and abnormal danger zone;A hierarchical control strategy for forklift anti-rollover based on the division of stability domains is proposed.The upper stability domain recognition controller recognizes the forklift rollover status;the middle-level model predictive controller MPC takes the vehicle body slip angle and yaw rate as the control target to calculate the required control torque;the lower executive controller adopts an improved chain incremental distribution method to distribute the control torque of the dynamic balance weight,hydraulic support cylinder and steering cylinder to reduce the roll angle and yaw rate during the roll process,and improve the lateral stability of the forklift.(3)Taking into account the input time delay of the actuator,the counterbalanced forklift anti-rollover dynamic output feedback control H∞ is implemented,and the forklift anti-rollover T-S fuzzy system is constructed.The forklift lateral load transfer rate LTR is taken as the control target,and the dynamic output feedback controller H∞is designed.Ensure the asymptotic stability of the closed-loop system with disturbance attenuation level and output constraints;Using Lyapunov theory and linear matrix inequality(LMI)method,the desired dynamic output feedback controller is constructed to reduce the jitter during the recovery of the forklift and improve the robustness of the forklift anti-rollover control system.(4)The hardware and software of the forklift anti-rollover control system are designed and debugged,and the actual vehicle test verification based on the European standard working conditions is carried out.The test results show that the proposed control strategy can effectively improve the active safety of the forklift and the stability of the system.