Papers by Author: Chun Li Lei

Abstract: In order to control effectively the temperature of the motorized spindle, based on thermodynamics, heat transfer theory and fluid dynamics control theory, the model of motorized spindle with cooling system is established and simulated. Based on the idea of orthogonal experiment and simulation experiment, the comprehensive tests are built, and the optimum matching relation between the heat flux of motor and the flow velocity of cooling liquid is determined in this article. The results show that the flow velocity of coolant can be adjusted according to the heat flux of motor which can control the temperature in the steady range and improves the cooling effect.

Abstract: In order to improve the manufacturing accuracy of NC machine tool, it is crucial to reducing the temperature rise of high-speed motorized spindle. The cooling effect and temperature distribution of water-cooling system are simulated and analyzed based on thermodynamics, heat transfer theory and computational fluid dynamics in this paper. The results show that the cooling system has fine cooling effect; the temperature of cooling liquid is changed from low to high and then to decrease, the highest temperature is at the roundabout of helical water channel and the reason for this phenomenon is found out. The results provide the theory basis for the structure optimization for water-cooling system.

Abstract: Study the linear and nonlinear stiffness dynamic characteristics of ball screw in feed system. According to the structure and the stiffness of ball screw, considering the influence of damping force, elastic force, friction force, driving force and load, establish the dynamic model of feed system. Use Linz Ted- Poincare (L-P) Method of singular perturbation to solve the model, obtain the quadratic approximate solution of the free vibration, analyze the multiple solution phenomenon of the model, and also conduct the numerical simulation analysis for the model.

Abstract: According to the high speed bearing failure problem caused by the high temperature, finite element model of high-speed hybrid ceramic angular contact ball bearing is established in this paper. Quantity of heat and heat transfer coefficient are calculated by using the heat transfer and thermodynamics theory, which are boundary condition for the temperature field simulation analysis of ball bearing. The temperature distribution of bearing is obtained when bearing speed is 12000rad/min. The results can provide a theoretical foundation for lubrication cooling system controlling temperature.

Abstract: Direct at NC machine tool feed system, the article analyzed the influence of the nonlinear friction at each motion joint, and points out that the nonlinear friction are the main factors that influence the positioning accuracy of the feed system. The article have discussed the methods for effectively compensation and controlling of the nonlinear friction respectively from two aspects of flutter compensation and predictly controlling the nonlinear friction, and proved the correctness of the compensation and control method that is proposed in this paper.

Abstract: The model that describes the friction between contact surfaces of motion pair of the feed system has been established use of Stribeck friction theory, it fully reflected the various lubrication conditions. The bifurcation and stability analysis of the model has been done. The experimental methods were used to research the nonlinear dynamics characteristics of the feed system under the external excitation. The influences that friction force to the nonlinear characteristics of the system at the certain parameters condition were analyzed. Utilize the research findings of the dynamical characteristics that caused by friction in the feed system can effectively provide a theoretical basis for designing optimization of complex systems in engineering, fault diagnosis and vibration control.

Abstract: According to the location and number of temperature measuring points of the motorized spindle thermal error, a new method for optimizing the locations of thermal key points is proposed. Firstly, temperature measuring points are divided into groups by using fuzzy clustering method. Secondly, grey correlation model is adopted to analyze emphasis of each measuring point to thermal deformation in temperature field distribution of motorized spindle. Finally, temperature measuring points have been optimally selected based on modified coefficient of determination. Comparing to the conclusion of the existed literature, the results show that this method is feasibility and validity. The method can reduce the temperature variables and modeling time, and supply the theoretic support for the engineering experience.

Abstract: To improve the manufacturing accuracy of NC machine tool, the thermal error model based on multivariate autoregressive method for a motorized high speed spindle is developed. The proposed model takes into account influences of the previous temperature rise and thermal deformation (input variables) on the thermal error (output variables). The linear trends of observed series are eliminated by the first difference. The order of multivariate autoregressive (MVAR) model is selected by using Akaike information criterion. The coefficients of the MVAR model are determined by the least square method. The established MVAR model is then used to forecast the thermal error and the experimental results have shown the validity and robustness of this model.

Abstract: In order to reduce the thermal error of the motorized spindle and improve the manufacturing accuracy of NC machine tool, the thermal error forecasting models based on multivariate autoregressive (MVAR) method and genetic radial basis function (GARBF) neural network method are proposed, respectively. According to different representations of generation mechanism of motorized spindle thermal deformation, operation efficiency and curve fit precision of these two models are compared. The studied results show that under the same temperature rise variable conditions, MVAR model and GARBF neural network model have almost the same convergence and operation time and relative errors of two models are less than 3%. The results also show that the MVAR model has higher forecast precision in the prediction former stages; in contrast, the GARBF neural network model has higher forecast precision in the latter stages.

Abstract: A hybrid manufacturing system which consists of two machines is examined. Unreliable buffers and multiple stochastic failure modes of the machines are introduced to the system. A new method of the system performance evaluation is presented. The states of the system are analyzed in detail based on a discrete model and a new solution technique is given to determine the state probabilities. The method can be used to analyze the cases arising from two or more stochastic events or longer (or more complex)production lines. Numerical results are also offered to testify the method and show some characteristics of the system.