Double Objectives Optimal Research Of Asymmetric Steering Mechanism Of Four-Wheel Four-Way Forklift Truck

Four-way forklift truck is a kind of industry carrying vehicles, which can be used as counter balanced fork lift truck, side fork lift trucksd and reach trucks etc. From the structure, four-way forklift truck can be divided into two types:three-wheel and four-wheel two types of four-way forklift truck. Compared with three-wheel four-way forklift truck, four-wheel four-way forklift truck has more advantages:more stable moving, safe steering, and greater lifting height etc. Although four-wheel four-way forklift truck has excellent handling performance, but the technology of smooth and reliable four-wheel steering is difficult to achieve, which lead to four-wheel four-way forklift truck has not been widely used. At present, the market also has not domestic four-wheel four-way forklift truck products. Now, a few foreign forklift manufactuer mainly adopts the technology of electric control steering system to implementation steering function of four-wheel four-way forklift truck. But the technology of electric control steering system has some disadvantages, such as steering instability, poor ability of overload protection, high demands on road surface roughness etc. Besides, the electric control steering system prone to stalling phenomenon during four-wheel four-way forklift truck running. Thus it is clear that steering system is the core movement of the four-way forklift truck. A good performance and stable and reliable steering system is the key to improve movement performance of four-wheel four-way forklift truck.The research is based on the Plan Projects for Science and Technology of Ningbo "High-end Storage Industry Vehicle Technology Innovation Team". In this paper, a kind of asymmetric steering mechanism’s (ASM) mechanical behavior was analyzed, and the ASM’s movement mathematics model was established, which based on analyzing the ASM’s steering control and movement principle of a certain type four-wheel four-way forklift truck. In order to reduce the ASM’s steering error, double-objective optimization functions aiming at approaching the Ackermann ideal steering performance were established. The Pareto optimal solution set of ASM’s double-objective optimization functions was obtained using the improved particle swarm optimization (IMPSO) algorithm. The software "Optimal Design System of Asymmetric Steering Mechanism" was created by using of GraphicUser Interface of MATLAB, which provides a complete optimization design theory for four-wheel four-way forklift truck’s ASM.Firstly, the background and significance of the research were introduced, and the research status of four-wheel four-way forklift truck, steering mechanism and multi-objective optimizations were analyzed, and the paper framework and main content were proposed.Secondly, ASM’s system assembly was introduced. The structure and function of ASM’s most important parts were analyzed. The movement principle processes of longitudinal left and right steering, longitudinal driving change to horizontal driving, horizontal left and right steering and horizontal driving change to longitudinal driving were analyzed with emphasis.Thirdly, based on Ackermann ideal four-wheel steering and two-wheel steering, the movement mathematics model of longitudinal four-wheel steering and horizontal two-wheel steering of ASM were established respectively. Double-objective optimization functions, longitudinal four-wheel steering and horizontal two-wheel steering of ASM, were established aiming at approaching the Ackermann ideal steering performance, and the constraint of optimization models was put forwardFourthly, for the problem of ASM’s double-objective optimization, the Pareto optimal solution set was introduced. Based on the standard Particle Swarm Optimization (PSO), the local extremum selection, particle variability and inertia weight of the standard PSO were improved., The suitable algorithm for the problem of ASM’s double-objective optimization was established, which is based on the improved particle swarm optimization (IMPSO) algorithm.Lastly, the software "Optimal Design System of Asymmetric Steering Mechanism" ("Ffsmods" for short) was created by using of GraphicUser Interface of MATLAB. Based on the optimization results of a certain type four-wheel four-way forklift truck’ ASM by using of the software "Ffsmods", the non-dominated solutions of Pareto optimal solution set were analyzed from three aspects:the increased percentage of longitudinal and horizontal steering performance, the relationship between the internal and external steering wheel Angle, and the steering wheel Angle error, which provides choice ways and theoretical principle for ASM’s optimization design size. The successive run test results of prototype showed that, after optimization, both longitudinal four-wheel steering and horizontal two-wheel steering of ASM have good steering performance.