Nuogang Sun

Current-based feed axis condition monitoring and fault diagnosis

A kind of numerical control machine tool feed axis condition monitoring system based on AC servo motor current is proposed. Firstly, the mathematical model between motor current and the fault is established. Then the test principle is profoundly investigated. And the frequency response between the disturbance torque from the fault and motor current is analyzed based on Matlab/SIMULINK. To obtain the motor current information, some different measured methods are suggested. In addition, the wavelet transform technology is proposed to detect the fault. The analysis results of the simulation and experiments show that it is feasible and reliable to use the motor current for monitoring the mechanical parts state, which puts basis for online feed axis condition monitoring and localizing the fault source rapidly.

A New Field Unbalance Estimation Method for Flexible Rotors

Current field unbalance estimation methods regards “flexible rotors with lumped mass” as the main research object, and most of them need a stop running to take trial weights. Due to its test speed closing to the critical speed, the process of balance is really complicated and dangerous. This paper concerns rotors which unbalance state shows a continuous spatial distribution. Firstly, a dynamic finite element (FE) model of the rotor system is built, the inherent relations and differences between the dynamics transfer matrix and influence coefficient (IC) matrix are analyzed, and then, an extended dynamics matrix with arbitrary dimension is obtained based on the principle of IC balancing method. Secondly, the continuous distribution mass eccentricity curve is represented as mass eccentricity point on each FE model node, and the unbalance forces imposing on each FE model node are identified by the extended dynamics matrix. Finally, the theoretic analysis and experiment is presented to verify this method, and the result shows that unbalance forces on all FE model nodes can be identified accurately with less measuring points, and higher order modal components of the distributed unbalance are balanced effectively.© 2011 ASME

Sensorless Simultaneous Rotary-Translational Axis Motion Error Measurement and Trace Based on Virtual Bar

Simultaneous rotary-translational (R-T) axis motion error has significant influence on multi-axis machine tool precision. To improve multi-axis machine tool precision, axis motion error measurement and trace method are investigated in this study. A sensorless R-T axis motion error measurement and trace technology based on virtual bar is proposed. Firstly, the fundamental sensorless test principle is discussed. Then, the virtual-bar-based test path of a circular test though a rotary axis and two translational axes motion is scheduled. The mathematical model of motion error is established. Furthermore, to identify the error source, spatial error charts and some advanced signal processing and feature extraction technologies, such as wavelet transform and frequency analysis, are used. The analysis of experimental results shows that it is practical and efficient to use the virtual bar and the sensorless information to estimate motion error.Copyright

Sensorless Rapid On-line Evaluation for Slide Level

Slide level is one of the most important indexes of CNC machine tool performance. A novel kind of sensorless rapid on-line evaluation technology for machine tool slide level based on linear or rotary scale, motor encoder and AC servo motor current/output torque is proposed. To acquire the level information, the sensorless test principle is profoundly investigated, and the relationship mathematical model between the slide level and the sensorless data is established. Furthermore, according to the Stribeck effect, the various amplitude and velocity triangular wave test curve and a kind of precise nonlinear model identification method are suggested to get the key parameters such as static friction torque, coulomb friction torque, viscous coefficient and total moment of inertia. And then CNC slide level can be identified. The analyses results of the experiments show that it is simple, rapid, feasible and reliable for evaluating slide level.