Crinela Pislaru

Modern techniques for condition monitoring of railway vehicle dynamics

A modern railway system relies on sophisticated monitoring systems for maintenance and renewal activities. Some of the existing conditions monitoring techniques perform fault detection using advanced filtering, system identification and signal analysis methods. These theoretical approaches do not require complex mathematical models of the system and can overcome potential difficulties associated with nonlinearities and parameter variations in the system. Practical applications of condition monitoring tools use sensors which are mounted either on the track or rolling stock. For instance, monitoring wheelset dynamics could be done through the use of track-mounted sensors, while vehicle-based sensors are preferred for monitoring the train infrastructure. This paper attempts to collate and critically appraise the modern techniques used for condition monitoring of railway vehicle dynamics by analysing the advantages and shortcomings of these methods.

Hybrid modelling and simulation of a computer numerical control machine tool feed drive

Abstract The paper presents a new approach to the modelling and simulation of a computer numerical control (CNC) machine tool feed drive. The hybrid model of the drive incorporates a distributed load, explicit damping factors and measured non-linear effects in order to achieve a realistic dynamic performance. In this way, the shortcomings of traditional modelling methods applied to CNC machine tool axis drives are overcome. A MATLAB/SIMULINK package was used to simulate this new model for a CNC machine tool feed drive. A novel hybrid model with a distributed load, explicit damping factors, backlash and friction was developed and shown to have a similar dynamic response to the machine tool feed drive system under the same conditions. The simulated results display resonance frequencies, while the lumped-parameter models generate only the response of a second-order element.

Improving the Quality of Technology-Enhanced Learning for Computer Programming Courses

Teaching computing courses is a major challenge for the majority of lecturers in Libyan higher learning institutions. These courses contain numerous abstract concepts that cannot be easily explained using traditional educational methods. This paper describes the rationale, design, development and implementation stages of an e-learning package (including multimedia resources such as simulations, animations, and videos) using the ASSURE model. This training package can be used by students before they attend practical computer lab sessions, preparing them by developing technical skills and applying concepts and theories presented in lecture through supplementary study and exercises.

Modelling and simulation of a feed drive using the transmission line modelling technique

The paper focuses on the modelling and simulation of a test rig and a digital drive is based on the transmission line modelling technique. The rig is a positioning system equivalent to a CNC machine tool feed drive. Accurate representations of dynamic systems included in electromagnetic, power electronic and some mechanical applications have been obtained until now by applying the transmission line modelling technique. The paper proposes a novel application of th~s method for simulation of closed loop control of the position of a test rig. The model includes the distributed parameter dynamics of the feed drive and the effect of mass distribution. This is based on the flexibility of transmission line modelling to develop lumped and distributed parameter systems. Also a transmission line model for the controller integrated into the digital drive is developed. Encouraging simulation results are obtained by using MATLAB. In this way, the CNC machine tools feed drives could be modelled with increasing accuracy as hybrid, distributed-lumped representations using numerical methods.

A New Approach To The Modelling AndSimulation Of A CNC Machine Tool Axis Drive

The paper presents a new approach to the modelling and simulation of a CNC machine tool axis drive. Modules have been created for different parts of the CNC machine tool. This allows greater flexibility in the construction of the model and an investigation of the interaction between model components. In this way all the shortcomings of the traditional methods are overcome. MATLAB / SIMULINK package has been used to simulate this new model for a CNC machine tool. Simulation results are very good, in accordance with CNC machine tool theory. The described approach allows the easy construction of detailed machine tool drive models. It represents the basis for future incorporation of geometric, non-rigid and thermal models of machine tool behaviour.

Evaluating the structural dynamics of a vertical milling machine

Many CNC machine tools are used in general-purpose machining environments, resulting in a wide variety of machining conditions being present at the cutting tool. The requirement for guide-way to bearing clearances and limited mass of the structural elements results in a limited stiffness between the cutter and workpiece. This, coupled with the inertial effect of the structural element masses and drive-system, can lead to complex vibration modes that are affected by the axis positions and machine tool configuration. Therefore, the study of the dynamic behaviour of the machme is important in determining the response of the machines structure to an external force. In this paper, the results and the setup of an experimental modal analysis performed on a vertical milling mache at the Ultra Precision Engineering Centre of the University of Huddersfield are presented. Ths work will be used as the foundation to carry out further activities into the modelling and correction of vibration-induced machining errors on CNC machine tools.

Improving CNC machine tools performance by using modular approach

The paper presents a comparison of single axis simulation results for various stimuli conditions against measurements for the same stimuli conditions on the machme. The results compare well and further comparison can be demonstrated against previously derived lumped parameter models for the same machine. Sinusoidal and CO-sinusoidal inputs are introduced into a complex 2D model including geometric error components measured directly from the machine by laser interferometer. The simulated circular position error traces could then be directly compared with machine measured error traces obtained from using ball bar plots. Measured Bode plots based on the swept sine measurement technique show how the machine is operating across a broad frequency range and provide further information than a step response. A Signal Analyser injects waveforms into the open position loop axis drive and generates Bode diagrams by comparing inputs with outputs. The measured Bode plots compare well with the same diagrams generated from simulated model and in this way the proposed model is validated.

Identification Of Damping Elements In A CNC Machine Tool Drive

An understanding of the dynamic characteristics of a machine tool is a vital element in the control of the machine which has a direct affect on the precision of the machining which can be undertaken. The ways in which energy is dissipated, such as friction and damping, have a significant effect on the dynamic behaviour. This paper outlines an approach to investigating the dynamic characteristics of an axis drive on a CNC milling machme. The torsional behaviour of the motor, belt drive and ballscrew coupled with the axial movement of the table or saddle and the ballscrew nut were considered. The mechanical elements of the drive were modelled as point inertias coupled by springs and dampers using Matlab 1 Simulink. The undamped natural frequencies and their likely mode shapes were determined using an eigenvalue approach in order to act as a guide to the numbers we were likely to get. The effect of the distributed mass in the ballscrew was also investigated. Comparison with measurements gave values of the dynamic stiffness and damping factor governing the lowest of the observed natural frequencies. The approach outlined in the paper is being used as a basis for investigations into other aspects of the dynamic behaviour of machine tool drives.

Computer numerical control vertical machining centre feed drive modelling using the transmission line technique

This study presents a novel application of the Transmission Line Matrix Method (TLM) for the modelling of the dynamic behaviour of non-linear hybrid systems for computer numerical control (CNC) machine tool drives. The application of the TLM technique implies the dividing of the ball-screw shaft into a number of identical elements in order to achieve the synchronisation of events in the simulation, and to provide an acceptable resolution according to the maximum frequency of interest. This entails the use of a high performance computing system with due consideration to the small time steps being applied in the simulation. Generally, the analysis of torsion and axial dynamic effects on a shaft implies the development of independent simulated models. This study presents a new procedure for the modelling of a ball-screw shaft by the synchronisation of the axial and torsion dynamics into the same model. The model parameters were obtained with equipments such as laser interferometer, ball bar, electronic levels, signal acquisition systems, etc. The MTLM models for single and two-axis configurations have been simulated and matches well with the measured responses of machines. The new modelling approach designated the Modified Transmission Line Method (MTLM) extends the TLM approach retaining all its inherent qualities but gives improved convergence and processing speeds. Further work since, not the subject of this paper, have identified its potential for real-time application.

Trends and Policy Issues for the e-Learning Implementation in Libyan Universities

This paper provides an overview the current trends and the policy issues for e-learning implementation in Libyan universities LUs.; where is present a sample model to comparative between two questionnaires in 2009& 2013; as a technique to evolution the e-learning policy implementation process in LUs. The paper emphasizes that in spite of the drawbacks faced by most HE institutions, some have managed to successfully introduce e-learning into their strategies. This paper concludes brief considerations of issues of the implementation policy; difficulties in the process and other challenges. Finally the paper aims into: Provision of a study on overall difficulties of the followed policy initiatives of e-learning implementation into the decision-makers in LUs; provision of conception to the developers to consider the strength and the weakness points when new strategies mode. And provision a set of suggestions for improving the effectiveness of the e-learning systems usage in Libyan HE based on the results of these SWOT analyses.