| Because of the bad mining environment and complex coal seam structure,it’s easy to aggravate the vibration of the gear and lead the transmission instability with the long transmission link of the traditional shearer cutting system,then make fatigue damage of gears under long-term work.Therefore,this project attempts to improve the existing cutting transmission system.Combined with the development of rare earth permanent magnet material and motor drive technology,a cutting part transmission system semidirect driven by permanent magnet synchronous motors is proposed.Aiming at the stability and reliability of the new system,the dynamic characteristics of the gear under temperature effects,chaos control,cutting load simulation,and dynamic reliability of the transmission system under failure correlation were successively developed.The main research contents include:(1)In view of the extreme working temperature changes of the shearer,the gear teeth will be thermally deformed,then indirectly affect the normal operation of the gear.Taking the first-stage gear pair of the semi-direct-drive cutting transmission system as the research object,and analyzing the changes in tooth thickness and gear clearance under temperature changes.Then a four-degree-of-freedom torsional vibration dynamic model of gear pair is established by combining the coupling effects of meshing damping,bearing stiffness,and bearing damping.Then dimensionless gear system parameters,and the Runge-Kutta method is used to simulate the model,the dynamic characteristics of the system at different frequencies and temperatures are analyzed.In addition,according to the dynamic transmission error of gear pair,the meshing state under different conditions is studied.For the chaotic state generated by the system,the unstable motion under the temperature effect is effectively controlled by applying the external periodic resonance excitation.(2)Since the complexity of coal seam composition in coal cutting process,the uncertainty of parameters such as quantity,size and distribution of gangue in unit space is fully considered,and the cutting load of drum in coal seam with gangue is simulated.Combined with the electromagnetic torque of PMSM,torsional stiffness and damping of transmission shaft,the bending-torsional dynamic model of the transmission system is established.Then the dynamic response is solved and the dynamic meshing force of each gear is obtained.The bending stress of tooth root is counted by rain flow counting method and the eight-level load spectrum is established.Based on global S-N curve of material and nonlinear fatigue accumulation theory,and considering the influence of different loading sequence of multistage load on material fatigue damage,the residual strength model of root under random load is established.(3)Defined the time-varying distribution characteristics of root bending strength and stress.Based on stress-strength interference theory,the time-varying reliability model of tooth root bending fatigue is established.According to the influence of tooth width,module and number of teeth on root stress and reliability,the optimal design of gear parameters is completed.The influence of time-varying meshing stiffness,static transmission error and torsional stiffness of transmission shaft on dynamic characteristics and reliability of gear is analyzed,which provides reference for structural optimization of transmission system.The correlation between the failure rate curves of each gear is studied,and selected the appropriate correlation function to define the failure correlation between gears.Then analyzed the failure correlation between gear pairs,and finally got the dynamic reliability of the transmission system under the failure correlation of each component.By comparing the analysis results under the condition of failure correlation,complete correlation and mutual independence,the rationality of reliability prediction under failure correlation is proved.(4)Based on the equivalent similarity theory,a transmission test bench as smallscale cutting unit is built.Aiming at the gangue coal mining conditions,a sudden load simulation experiment was first performed.The test results show the good loading performance of the magnetic powder dynamometer and the sensitive dynamic response performance of the PMSM,which verifies the feasibility of the experimental system applied to coal mining load simulation test.Secondly,the gearbox vibration test under different loads were performed,and the results were analyzed by frequency spectrum,which verified the correlation between gear vibration and reliability,reflecting the mechanism of rapid fatigue failure under large load.Finally,the transient dynamic simulation of the final gear pair was performed by ANSYS.The simulation results verified the accuracy of the stresses obtained by numerical calculation.The paper has 78 pictures,17 tables,and 93 references. |
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