Research On Mechanical Properties Of Key Structures On Boom-type Roadheader

Boom-type roadheader is the core equipment of comprehensive driving face in coal mine.The reliability of its working performance directly affects the efficiency and safety of coal mine tunnel.The working face of coal roadway is bad,and the cutting head of roadheader will be subjected to large impact loads and random fluctuations,which makes the roadheader show complex and changeable mechanical characteristics.Key structures of boom-type roadheader play a main load bearing role in the working process,which mainly include cutting head,cutting arm,rotary table,lift cylinder and rotary cylinder.The mechanical properties of key structures are the foundations for the stability and reliability of roadheader.In order to make the roadheader work safely and efficiently,key structures must have good static and dynamic mechanical properties.At present,the research on the mechanical properties of key structures on roadheader is not mature enough,many basic technical problems need to be further solved and improved.This thesis takes EBZ160 boom-type roadheader as research object,and a series of research on the mechanical characteristics of key structures are developed,and the actual working load and position data of boom-type roadheader are deeply excavated.This paper explores the spatial stress variation and the static & dynamic characteristics under different operating conditions,load spectrum recognition and reconstruction,kinematics and dynamics of key structures in comprehensive driving face,using a combination of statistical analysis,mathematical modeling,finite element analysis,numerical analysis and virtual prototype simulation method.It is of great theoretical and engineering significance to improve the mechanical performance of key structures and promote the robotization development of roadheader.The main results are as follows:(1)A space load analytical method of key structures is proposed,which suit for any working condition of boom-type roadheaderTo solve the difficulty of measuring the random loads of cutting head in the mine,and the situation of random loads predicting usually using empirical formula,the spatial mechanics model of key structures of roadheader is established by introducing the mapping relationship between the loads of cutting head and cutting pick(involved in cutting),after the internal relationship between the loads of cutting head and driving cylinders and pose parameters of cutting arm is studied,then the equivalent three-axis forces,the three-axis force moments at the rotation center of cutting head and the constrained forces,force moments at the hinge joints are obtained.This paper focuses on the variation of the loads of cutting head with the pose parameters of cutting arm and the loads of cylinders in the condition of cutting head swing in the horizontal direction.The results show that the horizontal angle ? and pitch angle ? mainly affect the cutting resistance FFr,pushing resistance FFa and tangential resistance moment MFt.It shows that the forces,force moments increase first then decrease with the angle ?,the change situation with the angle ? is opposite,and the forces reach the extreme value when the absolute value of the angle ? or the angle ? is minimum.It also points out that the remaining three forces,force moments are mainly positively correlated with the load of lift cylinder and the angle ?.The force FFr can characterize the force in the swing direction better,so it has a maximum value,it can reach 90-100 kN in the upper limit position.According to the degree of the cutting head loads on the rotary cylinder,it can be obtained that it is in dangerous condition when the pitch angle ?=0o?-26o?44o or the angle ? is in the left and right limit positions.The study of theoretical basis can further improve the static characteristics of key structures of roadheader,and it can provide the basis for the optimization of the system structure parameters and the on-line identification of the cutting head loads.(2)The measured loads and load spectrums of key structures on boom-type roadheader are analyzed.The test programs for the working loads of boom-type roadheader in the coal mine are developed based on self-developed large capacity data recorder.Then the loads data of driving cylinders are acquired and pretreated.The load spectrums of driving cylinders of boom-type roadheader are compiled using the method of rainflow counting,frequency extrapolation and fatigue damage equivalence.It realized that the load amplitudes of rotary cylinder obey the two-parameter Weibull distribution W(1.156,3.345)and W(1.081,2.95)by the probability distribution fitting of the counting results.The proposed three-modal normal probability distribution model can identify the mean value of the rotary cylinder load well.At the same time,compared with the distribution parameters of the mean load,the left rotary cylinder has a larger load mean value in the driving process,which is consistent with the law of the increase in energy consumption of coal and rock in reverse cutting process due to a large degree of extrusion.In addition,the amplitude and the mean value of cylinder load in the two conditions are independent.In order to keep the working load characteristics of the rotary cylinder in the whole life cycle,the two-dimensional load spectrum in 8×8 level of the rotary cylinder is established according to the proportion of the time in the push working or pull working condition of the rotary cylinder.Then the one-dimensional load spectrum in 8 level of the rotary cylinder is programed,which provides reliable testing loading information for the prediction of the fatigue life of the rotary cylinder.Finally,the time-domain load history of the driving cylinder is generated using the Monte Carlo method.The results show that the simulated loads can describe the load state of the cylinder in the coal mine.Then the cutting head loads time history of the single cutting section are reconstructed using space load analysis method of key structures,which provides the data support for the dynamics research.(3)Static strength analysis and initial stresses modal analysis of key structures of boom-type roadheader are completed.Since the boundary conditions are difficult to accurately set during simulation research of static and dynamic characteristics of single element,a consideration of nonlinear contact on the hinge joints between components is put forward,and the finite element model coupled by key structures,slewing bearing,body frame and hinge pins of boom-type roadheader is established.According to the analysis of static strength and deformation of key structures in three kinds of dangerous conditions,the conclusions are obtained as follows: the maximum stress value of components is less than the yield strength of the material,the stress of the rotary table is relatively larger and its distribution characteristics are similar under different conditions,more reasonable stress distribution nephogram of the hinge pins can be obtained with the nonlinear contact algorithm to deal with the hinged problems,the overall maximal deflection deformation occurred in the front of cutting head,and the deformation increases with the increase of pitch angle.Initial stresses modal analysis of the overall key structures was conducted on the basis of the finite element static analysis,the former six inherent frequency and the corresponding vibration mode under loads condition are obtained,which reveals the dynamic response of key structures and aims to avoid excitation of key structures vibration mode by some methods such as optimization of the structure and operation.Combined with the one-dimensional program load spectrum and the finite element analysis results and based on the stress fatigue theory,fatigue life analysis of the rotary cylinder was carried out,the result shows that the fatigue life of the maximum stress pin hole on the end of rotary cylinder is about 3.47 years,coinciding with the field application.(4)The dynamic characteristics of key structures of boom-type roadheader are analyzed.This paper analyzed the kinematics characteristics of key structures of boom-type roadheader in the cutting process.A method to establish the kinematic model of key structures based on differential geometry theory is proposed.It not only optimizes the rotation transformation path of the spatial coordinate system,but also avoids multiple operations of trigonometric function and inverse matrices.So it can simplify the derivation process and reduce the computational difficulty.The kinematics equations of key structures are decoupled using numerical solution method by Matlab.Then the movement path of the cutting tooth in the roadway is obtained.The three-dimensional cutting section formed by simulation was waist drum shape,which is consistent with the actual cutting path of the cutting tooth in the cutting section.It also proves the reliability of the differential geometry in the study of movement rule of roadheader.The transformation rule of each component motion response under the right swing condition is mainly studied.The varied range of rotating table angular velocity is small and the angular velocity direction of rotary cylinder changes when piston rod is extended in uniform velocity.The velocity of the rotation center of the cutting head shows a trend of stage linearity,and its velocity in z-direction is significantly correlated with the angular velocity of the rotating table.The acceleration of the cutting tooth is periodically changed under the high speed rotation of the cutting head,and the maximum rate of the change is up to 84%.Since the rotational motion is small in the x-direction,the magnitude of the acceleration in the x-direction is relatively small,and it is positively correlated with the absolute value of the horizontal angle of cutting arm.(5)The dynamics modeling of key structures of boom-type roadheader is completed and the simulation analysis is carried out.In order to improve the forming quality of the cutting section of roadheader and reduce the influence of the uncertain factors on the precise control the tunneling process,the dynamics characteristics of key structures of boom-type roadheader are explored.According to the dynamic response of key structures and the multi-body dynamics theory,the dynamic model of key structures considering redundant actuation is established using Lagrangian method and virtual work principle.Then the relationship between the system motion parameters,the cutting head loads and the cylinder driving forces is obtained.The paper proposes the optimal allocation of redundant actuation force of rotary cylinder by using the minimum principle of norm optimization strategy.To improve the dynamic performance of roadheader,this paper controls the driving force and position collaboratively to improve the drive cylinder bearing the degree of inconsistency.Based on ADAMS software platform,the virtual prototyping model of key structures is established and simulated.The change of cylinder driving force with the planned path,external load under non-redundant or redundant driving is revealed.Combined with the dynamic response curve of the cutting head,the results are consistent with the results obtained by numerical solution,which verified the correctness of the dynamic modeling and simulation analysis method.Based on the simulation results,the stress state of the rotary center of the rotary table is investigated,and it is compared with the calculation results of the space mechanics model.As the swing speed is small and tends to uniform motion,the overall show a similar trend.The results show that the proposed key structures space load analysis method can predict the cutting head loads more accurately.The analytical method,modeling approach and research results of this thesis have strong universality,they can provide theoretical basis for the mechanics characteristics analysis of the same type roadheaders and other comprehensive tunneling equipments.