Research On Adaptive Control Strategies For Chain Tensioning System Of Heavy Scraper Conveyor

Heavy scraper conveyor is the core transportation equipment in the fully mechanized coal-mining face.Heavy scraper conveyor,which is subject to the random dropping coal,is characterized by severe operation environment,large load changes,grievous impact and vibration.It is prone to chain jamming,chain breaking and other faults.The chain tensioning system is the only part of scraper conveyor that can adjust telescopic tail to control the chain tension in real time.It is the key system is to improve the the service life of the scraper chain and reduce the failure rate of the whole equipment.Since the chain tensioning system is subject to its own heavy-tail friction and multiple external disturbances,the traditional tension control methods may not be suitable to the complex operation environment in the mine.Meanwhile,similar researches on the chian tensioning system are not mature at home and abroad.Therefore,the chain tensioning system of heavy scraper conveyor is taken as the research object in this dissertation.This research combined hydraulic transmission theory,system identification algorithm,nonlinear control method and other technologies.The theoretical and experimental research on the modeling,friction compensation,load adaption control,safety tracking control of chian tensioning system are conducted,respectively.It provides the important theoretical support and technical means for the stable and reliable operation of chain tensioning system of scraper conveyor under complex operation conditions.The main research contents include the following parts:Firstly,the composition and operation principle of the chain tensioning system of heavy scraper conveyor studied in this dissertation are introduced.Combined with the operation mode and structural characteristics of the system,the telescopic tail model and valve-controlled tensioning hydraulic cylinder model of chain tensioning system are established based on catenary theory and hydraulic transmission technology.The chain tensioning experimental test system of scraper conveyor is built.The model parameters of the chain tension test system are identified.The main factors affecting the control performance of chain tensioning system are studied via the simulation and experimental test,which lays a foundation for the theoretical and experimental researches on adaptive control strategies for the chain tensioning system of scraper conveyor under complex operation conditions.Secondly,in order to reduce the negative influence of heavy telescopic-tail on the chain tensioning control system,comparative experimental results on the tension tracking of three typical controllers are conducted to reveal the key velocity region of friction compensation in the chain tensioning system.A modified Lu Gre friction model of the heavy telescopic-tail combined with zero velocity crossing window is proposed based on the hyperbolic tangent function.The zero-velocity oscillation of the friction model is reduced.Considering the adverse influence of complex operation environment,the adaptive friction compensation method is proposed for chian tensioning system based on double-structure observer and parameter adaption.By comparing with the experimental results of the traditional and modified friction models,the effectiveness of the proposed friction compensation control method is verified.Thirdly,in order to deal with the poor control accuracy of chain tensioning control system subject to the disturbance of time-varying load caused by random dropping coal,an oblique-section differentiable tension model including linear regression part and nonlinear mapping part is proposed.This model effectively reflects the variable stiffness characteristic of chain and the disturbance of time-varying load,and avoids the real-time measurement of all parameter of the original tension model.The recursive least square method is utilized to identity the equivalent stiffness of system.The input state variables of the controlled system are extended using Levant’s differentiator and state observer.The nonlinear mapping parts are online estimated using neural adaptive method.The tension tracking controller combined with the instruction filter is proposed based on load adaption.The effectiveness of the proposed controller is verified under different load ranges via the comparison of different controllers.Finally,aiming at the violation of position and velocity constraints for chain tensioning system subject to the abnormal conditions,the integral robust position protection controller is conducted based on the discontinuous disturbances.Combined with the second binary switching variable,switched safety tracking control strategy is proposed for chain tension system based on hybrid tension/position switching system.The overshoot and oscillation of controlled system in the switching transient between the position and tension controllers are analyzed.According to the working condition of chain tensioning system,the safe switching rules of the controllers based on hysteresis principle are formulated.The telescopic-tail position correction trajectory suitable for the abnormal condition is designed.The experimental researches on the switched safety tracking control strategies of chain tensioning system are conducted to verify the effectiveness of the proposed controller in pre-tension stage,operation stage and strong disturbance condition.