Research On Operating Characteristics Of Cutting Mechanism Of Full Hydraulic Opencast Shearer

Coals play a dominant role in China's energy supplies.The coal in open-pit mines is an important part of China's coal resources.Compared with other major coal-producing countries,the proportion of production capacity of coals from open-pit mines is always comparatively low.There are a number of reasons for this situation.Firstly,the coal seam occurrence in China is particularly unique.And secondly,the manufacture level of domestic mining equipments used in open-pit coal mines is low compared to overseas advanced manufacture level due to the lack of key technologies.The full hydraulic opencast shearer in this thesis is a new generation of mining equipments for large open-pit coal mines,which is characterized by function integration of high-efficient cutting,continuous transportation and direct crushing.It enables the production of large open-pit coal mines to reach centralizations.The cutting mechanism is the main component of full hydraulic opencast shearer.Its operating characteristics have an important influence on the performance of full hydraulic opencast shearer.The operating characteristics of cutting mechanism of full hydraulic opencast shearer and the related key technologies were emphasized in this thesis,which were believed to be of high engineering and academic value.In this thesis,a control strategy that combines the variable damping accumulator with the interval type of speed controller was proposed to solve the problems of pressure impact and cutting drum's stalling in the cutting-driven hydraulic system.Moreover,a switched multimode control method was developed to coordinate working situations of the starting controller,the constant power controller and the interval type of speed controller.The starting controller was used when the cutting-driven hydraulic system starts to work.The constant power controller was employed when operating in normal situations.The interval type of speed controller becomes the dominate controller when facing extreme loads.When the proposed control strategy was applied,the numerical experiments showed that the pressure peak in the cutting-driven hydraulic system was reduced by 22.81%from 51.3MPa to 39.6MPa.The adaptability to multi-kinds of loads of the cutting drum was enhanced significantly.The speed range of the cutting drum was reduced by 12.33%and the speed support capacity of the cutting drum was improved by 59.72%.A concept of coal pile's average distance was defined to make some quantitative evaluations of the load effect of different cutting trajectories.The calculation formulation of coal pile's average distance was put forward.When the vertical plane through the pin connecting the arm to the mainframe was specified as a reference,the average distance between the reference and the coal's landing place was just the so-called coal pile's average distance.It is related to the initial speed and height if the coal was cut down in the manner of horizontal projectile motion.Three kinds of typical cutting trajectory were presented in this thesis,such as the outer arc cutting trajectory,the straight cutting trajectory,and the inner arc cutting trajectory.The corresponding coal pile's average distances are figured out as 4.195m,3.594m and 3.265m,respectively.Three kinds of typical cutting trajectory were evaluated from the view of loading effect,structure interference,and hauling speed.A conclusion was drawn that the overall performance of the straight cutting trajectory was the best among three typical cutting trajectories.In order to improve the accuracy of flow rate inferential measurement method to reduce the time of non-cutting stroke,a reverse compensation principle was proposed to perfect the flow rate calculation process.Firstly,an offline numerical experiment was conducted when using an ideal flow-meter with infinite frequency responses to regulate the accumulator'^ flow rate in the form of closed-loop control.Secondly,the flow rate through the main control valve was depicted in detail.Thirdly,the flow rate through the main control valve was used to calculate the spool displacement of the main control valve and the pressure in pilot valves.The error of the pressure in pilot valves was eliminated by this way and thus,the accuracy of flow rate inferential measurement method was improved.Numerical analysis showed that the reverse compensation principle was valid.After adopting the proposed method,the accumulator's flow rate could be regulated well and the time of non-cutting stroke was reduced from 30 seconds to 25 seconds.The efficiency of non-cutting stroke was raised by 16.67%.If the time of cutting stroke and walking stroke remains the same,the total working time of a cycle of operation could be reduced from 180 seconds to 175 seconds.The efficiency of full hydraulic opencast shearer was improved by 2.78%.The thesis is outlined as follows:In chapter 1,the status of mining techniques and mining equipments both at home and abroad was introduced.The key technologies about full hydraulic opencast shearer were reviewed,including cutting mechanisms,full hydraulic driven systems,simulation of complicated coal seams,cutting loads,hydraulic pressure impact,flow rate inferential measurement.The aims and the research contents in the thesis were discussed.In chapter 2,structural components and workflows of full hydraulic opencast shearer were elaborated explicitly.The full hydraulic driven circuits were designed and the choices of the hydraulic components consisting of the circuits were accomplished.A numerical model to simulate the complicated coal seams including stone bands,inclusions and fractures was developed.Force analyses of conical picks and cutting drums were performed and the cutting load of full hydraulic opencast shearer was obtained.In chapter 3,the heat balance of the cutting-driven hydraulic system was analyzed.A controlstrategy that combines the variable damping accumulator with the interval type of speed controller was proposed and a switched multimode control method was developed.The cutting-driven hydraulic system was redesigned with the help of the proposed method.The validity of the proposed method was checked by numerical simulation.In chapter 4,kinematics analysis and dynamic analysis of the cutting mechanism were completed.Several typical operating conditions were chosen as the analysis example.The outer arc cutting trajectory,the straight cutting trajectory,and the inner arc cutting trajectory were presented in the thesis.A concept of coal pile's average distance was defined to evaluate load effects and its calculation formulation was put forward.A straight cutting trajectory was achieved by controlling the displacements of the arm cylinder and forearm cylinder.In chapter 5,a scheme utilizing the accumulator whose flow rate was under control to compensate the inadequacy of the flow rate in rapid non-cutting stroke was proposed.Flow rate inferential measurement method was employed to control the flow rate of accumulator.A reverse compensation principle was proposed to improve the accuracy of flow rate inferential measurement.The rapid non-cutting stroke was implemented by using the proposed method.In chapter 6,all the research contents and the innovations were summarized.Some future work was discussed in the end.