| In view of the outstanding problems existing in the current ship unloader for bulk grain with the sandwich belt conveyor,namely the relative speed difference of the two belts that cannot be compensated,the lack of relevant basic theoretical research,and the core control technologies such as synchronous air-entrapping that have long been monopolized by foreign countries,this paper studies the vertical lifting section of the ship unloader for bulk grain with sandwich belt conveyor from three aspects: theoretical derivation,physical design and simulated analysis,and obtains the following results:1.Using the improved mathematical model of the lifting stage of the sandwich belt conveyor,a calculation model for the length of the press roll(the outer edge of the belt)is derived.Based on the Hertz Formula,under a certain number of material layers,a mechanical relationship model for the extrusion force on the outermost layer and the center(centroid)of the material cluster is obtained.The viscous flow theory is adopted to determine the theoretical relationship between the diameter of the aeration vent and flow at a given belt speed.2.Based on the special working conditions of the ship unloader for bulk grain at large ports,with the design objective of a hoisting height of 20 m and a transport efficiency of 1000t/h,an overall model of the ship unloader is established.Through analyzing and comparing the advantages and disadvantages of the sandwich belt conveyor’s wrapping pattern of the parallel ring and lantern ring as well as the Z/C type structure,a vertical lifting model with C-type parallel ring suitable for this ship unloader for bulk grain is developed.3.In order to make the "settlement" of the material more efficient and ensure that the material wrapped by the double belt is in a filling state at any moment,a new type of feeding hopper that can allow the materials to overflow automatically is designed in this paper.The adoption of such a feeding hopper can make the structure of the entire lifting mechanism more compact and improve the stability and reliability of the vertical lifting section.At the same time,in order to avoid the throwing and flying of fine materials and dust pollution,a new type of discharge hopper is designed in this paper,which can realize the integration of materials receiving and cleaning and solve the problems that the cleaning of the belt is not thorough and the belt is easily deflected during the discharging process.4.The fuzzy PID control is introduced into the air-entrapping equipment,and a mathematical model of a synchronous air-entrapping device and a fuzzy PID control model are established.Simulink is used to simulate its synchronization effect.The simulation results show that the fuzzy PID air-entrapping equipment is suitable for the ship unloader for bulk grain with the sandwich belt conveyor and can solve the challenge that the air-entrapping equipment of the sandwich belt conveyor is difficult to achieve synchronization. |
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