Research On Energy-saving Technology Of Electric Drive Lifting System For Forklift

Forklifts are widely used in ports,stations,airports,freight yards,factories,workshops,warehouses,circulation centers and distribution centers for their excellent handling capacity.With the rapid development of the logistics industry,the electric forklift sales are increasing rapidly and its market share gains every year.Because energy and environmental problems are becoming more and more serious,the research of energy saving forklift has become the focus of industrial technology development.Therefore,the study of the energy saving technology of electric forlift has great market value and social benefit.Because the lifting frequency is very high when the electric forklift works,a new type of lift energy saving system can improve the energy saving effect of electric forklift further.This research was supported by the National High Technology Research and Development Program 863 named “the key technology and system development of new hybrid construction machinery(Grant No.2009AA044403)”.In this paper,taking the CPD30 electric forklift of Liuzhou Construction Machinery Company as the research object,a new type of lifting energy-saving system for electric forklift was studied deeply based on its actual operating conditions,and the following research contents were achieved.(1)A new type of lifting energy-saving system for electric forklift using ball screw instead of traditional hydraulic cylinder was proposed and designed.The traditional drive mechanism of lifting mechanism adopts hydraulic transmission.The driving chain is storage-battery – motor – oil pump – valve – hydro-cylinder – lifting mechanism.The driving chain of the new type of forklift lifting energy-saving system is storage-battery – motor – ball screw pair – lifting mechanism.Thus the transmission efficiency has been greatly improved.(2)Based on a power bond graph theory,a controllability and observability analysis method of electric drive lifting system was established.This metod can analyze the dynamic characteristics of the electric drive lifting system,including the acceleration of the cargo fork,the constant-speed rise,the deceleration braking and so on,thoroughly.The structural characteristics of the lifting system were analyzed,and its controllability and observability were verified theoretically,which provide a foundation for the control and operation of electric drive lifting system.(3)A brushless DC motor double-loop speed control system based on fuzzy sliding mode variable structure control strategy was designed.Unlike the traditional motor drive mode,when the motor is locked rotor,it provides sufficient torque to the system as well as limits the armature current of the motor.In order to overcome the drawback of the state observer that have slow convergence rate and poor precision,the state observer design idea of the high gain error feedback was proposed in this paper.The fuzzy sliding mode variable structure control method was established,which can solve the chattering of the lifting system.Thus the operation performance of electric drive lifting mechanism reached the same level of hydraulic drive lifting transmission.The response speed and anti-interference ability of this system are significantly improved.(4)Both MATLAB simulation models of hydraulic lifting mechanism and electric drive lifting mechanism were established.The simulation results showed that when the lifting height is 3 meters and the load is 3 tons,the working efficiency of the hydraulic drive forklift lifting mechanism is 49.05%,and the working efficiency of the electric drive forklift lifting mechanism is 72.6%.The high efficiency of the electric driving lifting system was verified by simulation.(5)The first domestic experimental platform of the electric drive forklift lifting mechanism was built.Through the comparison test,the accumulative energy consumption of a complete lifting process of electric forklift was calculated in light load,medium load and full load.Take the load is 3 tons as an example,when the lifting height is 3 meters,the working efficiency of the hydraulic drive forklift lifting mechanism is 46.1%,and the working efficiency of the electric drive forklift lifting mechanism is 63.1%.The working efficiency of the electric drive forklift lifting mechanism is 17% higher than that of the hydraulic drive lifting mechanism.It is obvious that the electric drive forklift lifting mechanism has a bigger superiority in energy-saving.Thus the correctness of the design scheme is verified.