基于零力矩点滑模预测控制的电动前移式叉车稳定性研究

Stability study of electric reach forklift based on zero moment point sliding mode predictive control

考虑了在电动前移式叉车装载货物转向行驶的情况下,其门架受载变形和货物升降共同引起叉车合成质心位置的变化,进而结合叉车合成质心变化模型和叉车三自由度模型建立了叉车动力学模型。针对叉车合成质心位置变化导致其转向稳定性不足的问题,根据零力矩点(Zero Moment Point,ZMP)理论分析了叉车行驶的稳定条件并得到了侧倾指标来判断车辆的稳定性。通过理想跟踪模型得到理想的叉车横摆角速度、质心侧偏角、车身侧倾角和侧倾角速度,以理想值与由叉车动力学模型仿真得到的实际值的差值为输入,设计了一种基于零力矩点的滑模预测控制(Sliding Mode Predictive Control,SMPC)算法,以调节叉车后轮转角的大小。仿真研究表明,在阶跃工况和双移线工况下,当货物升降速度不同时,与滑模控制(Sliding Mode Control,SMC)和无控制相比,基于ZMP滑模预测控制实现了对理想叉车横摆角速度和质心侧偏角的实时快速跟踪,提高了叉车的稳定性。

Considering the change of the synthetic center of mass position of the forklift caused by the deformation of the door frame and the lifting and lowering of the cargo when the electric reach forklift is loaded with goods and turns to drive,and then a forklift dynamics model was established by combining the forklift synthetic center of mass position change model and the forklift three-degree-of-freedom model.Aiming at the problem of insufficient steering stability due to the change of synthetic center of mass position of forklift,the stability conditions of forklift driving were analyzed according to the Zero Moment Point(ZMP)theory and the sway index was obtained to judge the stability of the vehicle.The ideal tracking model was used to obtain the ideal forklift yaw rate,side slip angle,body roll angle and roll angle speed,and the Sliding Mode Predictive Control(SMPC)algorithm based on zero moment point was designed to adjust the magnitude of the rear wheel turning angle of the forklift with the difference between the ideal value and the actual value obtained from the forklift dynamics model simulation as input.The simulation study shows that the sliding mode predictive control based on zero moment point achieves real-time fast tracking of the ideal forklift yaw rate and side slip angle compared with the Sliding Mode Control(SMC)and no control when the cargo lifting and lowering speed is different under the step condition and double shift line condition,which improves the stability of the forklift.