| Elevator is a kind of special transportation equipment,plays an important role in people’s life,but with the surge of the number of elevators,and the untimely and nonstandard maintenance measures,elevator accidents also happen frequently.Brake as the first line of defense for emergency stop of elevator.It relies on the friction between brake shoe and brake wheel to stop the speeding car.But the emergency braking process will produce a lot of friction heat,a large amount of friction heat causes the temperature of brake to rise sharply.Excessive temperature will not only cause the friction torque between brake wheel and brake shoe to decline,but also lead to thermal cracks on the surface of brake wheel,which seriously affect the braking ability of the elevator.All these seriously affect the braking ability of the elevator.Therefore,it is of great significance to study and analyze the thermal structure phenomenon of elevator brake in the process of emergency braking,and realize the structural optimization design of the brake by combining approximate model method and multi-objective genetic algorithm,which is of great significance to improve the braking ability of the brake and ensure the safe and stable operation of the elevator.The main research content of this paper is as follows:(1)According to the actual parameters of a certain type of elevator block brake,the three-dimensional model of the brake is established by using Solidworks software and the model is properly simplified.Then the model is imported into ANSYS for material assignment and mesh division.Meanwhile,the braking time and thermal boundary conditions are solved according to the actual working conditions.The pre-processing of thermal-structural coupling model of block brake was completed.(2)Taking the elevators with rated speeds of 1.5m/s,2.0m/s and 2.5m/s as the research object,the emergency braking process of the block brake was numerically simulated,the coupling characteristics of the three-dimensional transient temperature field and stress field of the brake were studied,and the temperature and stress changes of the brake wheel in radial,axial and circumferential directions were analyzed emphatically.(3)Based on the coupling field analysis results,the causes and modes of thermal fatigue failure of brake wheels were analyzed,and the dangerous areas were found out.The principal stress direction was determined by three-way stress analysis of joints,and the thermal fatigue life prediction of brake wheels was completed by using Masson-Coffin fatigue prediction model.(4)An approximate model of the relationship between design variables and optimization objectives was established through AO-BP neural network,and the prediction accuracy of the network model was analyzed.After determining the constraint conditions and objective functions,the mathematical model of block brake structure optimization was established,and the structural optimization design of elevator block brake was realized by combining multi-objective genetic algorithm.Finally,the effectiveness of the optimization results is verified by simulation experiments.The results show that the maximum temperature of the optimized brake wheel during the emergency braking process is 222.09℃,which is 36.71℃ lower than the maximum temperature of 258.8℃ before optimization,with a change rate of 14.2%.The maximum equivalent stress after optimization is 247 MPa,which is 28.88 MPa lower than the maximum equivalent stress before optimization is 275.88 MPa,and the change rate is 10.4%.In addition,the mass of brake wheel is reduced from 58.85 kg to 52.40 kg before optimization,and the thermal fatigue life at the maximum equivalent stress of brake wheel is increased from 59 times before optimization to 94 times. |
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