Papers by Author: Jian Guo Yang

Abstract: Thermal expansion of ball screw system affects the machining accuracy of machine tools significantly. The objective of this paper is to analyze the thermal behavior and predict the temperature variation pattern of a ball screw based on finite element analysis and experimental investigation. Wireless temperature sensors are used to monitor the temperature variation of the ball screw system under different thermal conditions during both the warm-up and cooldown phases, so as to investigate its temperature variation pattern. Then an exponential algorithm is proposed to analyze and predict the temperature variation of the ball screw based on finite element analysis, and the actual thermal boundary conditions of the ball screw system are exactly defined according to the proposed algorithm and the experimental results. Finally, it was found that the simulation based on the thermal boundary conditions identified herein could match quite well with the experimental results.

Abstract: The CNC milling machine is extensively used in manufacturing of the die and the box-type parts. As the increasing requirement of the mechanical products qualities, the components also need higher and higher precision. However, the cutting force induced error affects the machining accuracy of the machined parts seriously. Furthermore, accurate measurement of the cutting force in CNC machining is very difficult. To solve this problem, a motor current-based cutting force induced error detection and modeling method is proposed in this paper. The motor current is obtained from the window function of the Fanuc CNC system. The cutting force induced error model is established according to the least-square method. The motor current-based error model can implement the cutting force induced error fitting effectively, and the fitting accuracy of X, Y, and Z-axis are 97%, 96%, and 84%, respectively.

Abstract: A distributed numerical control (DNC) strategy for error compensation on Fanuc and Siemens CNC machine tools is proposed. A DNC network is built in multi-Fanuc CNC machine tools and the error compensation of all the machine tools is realized simultaneously. A human machine interface (HMI) is developed for Siemens 840D CNC machine tools, error components are decoupled in the X, Y and Z directions and they are compensated by 840Ds own function of thermal error compensation. Experimental verification is conducted and it proves that the proposed DNC strategy for error compensation is an effective and precision manner to improve the accuracy of machine tools.

Abstract: The error modeling compensation method for improvement the machine tools accuracy has been extensively used in the past decades. To unify the multi-error model for four types CNC machining center, the comprehensive multi-error model of TXYZ type machining center was established based on the homogenous coordinate transformation. According to the analysis of the transmission chain, a unified multi-error model for four types machining center was established based on the Singular Function. Using the unified multi-error model, the mathematical model of four types machining center can be standardized. It is very important for unceasing development of error compensation technology.

Abstract: Based on grey system theory correlation analysis methods, to turning center as an example, the study for the thermal error, the detection of the temperature field, thermal point of error detection and real-time compensation technology optimized, key points of temperature on the machine location was carried out. The most key points of temperature sensors are optimized. A thermal error compensation system was set up, and real-time compensation for the processing of authentication. At this stage the results show that the compensation results are obvious.

Abstract: In this paper, a synthesis modeling method of geometric and thermal error is presented. Through the analysis of machine error data at varying temperatures, the error distribution rule is obtained. Based on the different characteristics of geometric error and thermal error, error separation method has been carried out in the modeling. Using polynomial fitting for geometric error and linear fitting for thermal error, a synthesis mathematical model has been proposed. This error compensation method concerns the variations of geometric errors at different temperatures in the machine working, thus a comprehensive analysis is made on the error and its regularity from the overall temperature rise to the heat steady-state. Both at low and high temperatures in the machine working, the experimental validations show that the positioning errors of the machine tool are reduced effectively after applying the error compensation approach.

Abstract: Weibull distribution is one of the most widely used model in reliability analysis of NC machine tools. In order to assess the reliability of NC machine tool, Generalized Expectation Maximization (GEM) algorithm is used to estimate parameters of mixture Weibull models. Akaike information criterion (AIC) and Bayesian information criterion (BIC) are used as comprehensive criteria to select the number of subpopulations of mixture models. The results show that mixture models are more suitable to assess reliability of NC machine tools than that of single model. Root mean square errors (RMSE) of mixture models reduce by 87.5% than that of single model. Reliability evaluation results of machine tool, such as MTBF etc., are given.

Abstract: This paper studies the modeling method based on RBF (Radial-Basis Function) neural network according to its learning ability, and a new neural network online model has been set up. The comparison and analysis result of the case studies shows that, when changing the working condition, the compensation effect of online modeling method is better than offline modeling method and the online model can better reflect the thermal characteristics of High-speed machine tool.

Abstract: The mathematical model of five-axis NC machine tools was established based on the transformation matrix. A new decoupling and linkage-compensation method for five-axis NC machine tools is proposed. The error caused by linear axes and rotary axes was compensated by using the linkage-compensation approach. In the real-time error compensation process, the rotary axes error was compensated firstly, and then the linear error caused by linear axes and rotary axes was compensated. The new decoupling method can effectively compensate machining errors for five-axis NC machine tools, which was verified by simulation and actual machining.

Abstract: Four key temperature points of a CNC machine tool were obtained in this paper, and a thermal error model based on the four key temperature points was proposed by using based back propagation neural network. A thermal error compensation system was developed based on the proposed model, and which has been applied to the CNC machine tool in daily production. The results show that the thermal error in workpiece diameter has been reduced from 33 to 6 .