Peng Fangyu

On-line chatter detection using servo motor current signal in turning

Chatter often poses limiting factors on the achievable productivity and is very harmful to machining processes. In order to avoid effectively the harm of cutting chatter, a method of cutting state monitoring based on feed motor current signal is proposed for chatter identification before it has been fully developed. A new data analysis technique, the empirical mode decomposition (EMD), is used to decompose motor current signal into many intrinsic mode functions (IMF). Some IMF’s energy and kurtosis regularly change during the development of the chatter. These IMFs can reflect subtle mutations in current signal. Therefore, the energy index and kurtosis index are used for chatter detection based on those IMFs. Acceleration signal of tool as reference is used to compare with the results from current signal. A support vector machine (SVM) is designed for pattern classification based on the feature vector constituted by energy index and kurtosis index. The intelligent chatter detection system composed of the feature extraction and the SVM has an accuracy rate of above 95% for the identification of cutting state after being trained by experimental data. The results show that it is feasible to monitor and predict the emergence of chatter behavior in machining by using motor current signal.

Closed-loop stiffness modeling and stiffness performance analysis for multi-axis process system

General stiffness performance of manufacturing process system directly affects machining accuracy and stability. When machining complex surface, general stiffness performance changes with tool posture that is determined by machining position and feed direction. In order to analyze general stiffness performance including machine tool, cutter and workpiece, a closed loop stiffness model is established by Jacobi matrix and finite element method. It is a general stiffness model for multi-axis process system, which can be used to evaluate general stiffness performance in workspace. The distribution law of stiffness performance can be evaluated by isoclines map of stiffness index plotted in workpiece coordinate system. The result helps engineers plan tool path based on both geometric and physics constrains.

Notice of Retraction A fast error measurement system for CNC machine tools based on step-gauge

Traditional error measuring methods for CNC machine tools are often restricted by repeated alignment in set-up, high price and strict measuring environment. In order to develope a convenient and fast error measuring system, research about the principle of error measurement based on step-gauge has been done. The proposed equipment is convenient for it has no demand for installation accuracy and working environment. It can identify the gesture of step-gauge with its own measuring function. And automatic correction of micrometer and step-gauges gesture can eliminate interference caused by installation, which has greatly enhanced the efficiency. Temperature difference compensation enables the equipment to perform in the workshop. This method is fast with accuracy within 2~3 μm, which can be applied to measure position error of economy machine tools. In addition, it can generate corresponding compensation files for various CNC system.