| Belt conveyors are important transportation equipment in the modern industry and they are moving towards greater capacity,more adaptable and more stably continuous transportation.The dynamic characteristics of the large-scale belt conveyors are complicated.The large dynamic tension of conveyors may cause tearing of the conveyor belt and severe vibration of the conveyors.Therefore,the optimization method of the belt conveyor drive system and the tensioning system appear.Based on the characteristics of large deflection,viscoelasticity,and large transport capacity of belt conveyors,this dissertation analyzes the law of tension distribution of conveyor belts in different operating phases.It also resolves the problem of traditional research on the belt conveyors dynamic tension mainly related to the tension of conveyors at special locations without caring about the whole distribution of tension on conveyors.This dissertation provides a theoretical support for effectively reducing the design safety factor of the conveyor belt and preventing the tearing of the conveyor belt,and provides a basis for the optimization and upgrading of the belt conveyor drive system and the tensioning system.According to the basic characteristics of the belt conveyors,this dissertation analyzes three methods to study the dynamic characteristics of the belt conveyors,respectively Newton's analysis method,finite element analysis method and wave analysis method.For large belt conveyors,the current mainstream research methods are wave analysis method and finite element analysis method.The wave analysis method simplifies the conveyor models too much and ignores many factors that affect the running dynamics of the conveyors,and the solution of the wave equation is too complicated.In contrast,the finite element analysis method can discretize the conveyors,and the degree of discretization depending on the computing power of computer,the higher degree of discretization,the more factors considered,and the results are closer to the true parameters of the conveyors operation.The common discrete models of the conveyor belt are the Maxwell model and the Kelvin-Voigt model,which respectively represent the relaxation characteristics and hysteresis characteristics of the conveyor belt.The hysteresis characteristics of the conveyor belt affect the dynamic characteristics far more than the relaxation characteristics during the operation of the conveyors.So,the Kelvin-Voigt model is used in this dissertation.This dissertation uses AMESim software to set models of belt conveyors discretely and uses Harrison acceleration starting mode to start.Simulation results show the dynamic tension,acceleration and speed of the belt conveyors distributing on the conveyor under the conditions of starting,normal operation and emergency braking,and the three-dimensional curves of them.The simulation results show that the farther away from the drive roller,the speed of conveyor belt fluctuates more violently,but the overall speed distribution characteristics are not obvious.From the phase difference between the tail and head velocity peaks,the propagation velocity of the elastic wave in the conveyor belt can be calculated,which is consistent with the velocity calculated by the wave velocity formula.The acceleration of the conveyors has obvious distribution characteristics during the tensioning phase,no obvious distribution characteristics appear during the operation,and it has been kept at a very low level,and no large flexible impact has appeared on the entire conveyors.The distribution characteristics of dynamic tension on the conveyors are very obvious.During the whole simulation process,the tension is decreasing along the nose to the tail.The tension of the head reaches 2 times the tension of the tail during the uniform driving of the driving roller,and the maximum tension of the head is 1.3 times that of the stable operation.This analysis method takes into account the distribution of the dynamic characteristics of the conveyors,and it is conducive to the optimization of the conveyor system.This dissertation provides a new experimental method to verify the rationality of the belt conveyors simulation method based on AMESim by comparing the tension of the test conveyor belt and the simulation tension.The test stand is a 21 m long,retractable belt conveyor.The sensors include pressure sensors,tension sensors and encoders.The pressure sensor with a small wheel holds the conveyor belt at an included angle.Through the size of the angle,the data of pressure sensor is converted into the tension of the conveyor belt.This method can measure the tension at almost any place on the conveyor belt.The final result shows that the trends of the experimental data curves and the simulated data curves are relatively consistent,indicating that the simulation analysis in this dissertation has certain feasibility.The innovations in this dissertation include the analysis of the distributed dynamic characteristics of conveyors and the rationality of simulation methods verified by experiment. |
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