Virtual Machining

Virtual machining systems apply computers and different types of software in manufacturing and production in order to simulate and model the behavior and errors of a real environment in virtual reality systems. This can provide useful means for products to be manufactured without the need of physical testing on the shop floor. As a result, the time and cost of part production can be decreased

Virtual machining considering dimensional, geometrical and tool deflection errors in three-axis CNC milling machines

Virtual manufacturing systems can provide useful means for products to be manufactured without the need of physical testing on the shop floor. As a result, the time and cost of part production can be decreased. There are different error sources in machine tools such as tool deflection, geometrical deviations of moving axis and thermal distortions of machine tool structures. Some of these errors can be decreased by controlling the machining process and environmental parameters. However other errors like tool deflection and geometrical errors which have a big portion of the total error, need more attention. This paper presents a virtual machining system in order to enforce dimensional, geometrical and tool deflection errors in three-axis milling operations. The system receives 21 dimensional and geometrical errors of a machine tool and machining codes of a specific part as input. The output of the system is the modified codes which will produce actual machined part in the virtual environment

Virtual machining considering dimensional, geometrical and tool deflection errors in three-axis CNC milling machines

Virtual manufacturing systems can provide useful means for products to be manufactured without the need of physical testing on the shop floor. As a result, the time and cost of part production can be decreased. There are different error sources in machine tools such as tool deflection, geometrical deviations of moving axis and thermal distortions of machine tool structures. Some of these errors can be decreased by controlling the machining process and environmental parameters. However other errors like tool deflection and geometrical errors which have a big portion of the total error, need more attention. This paper presents a virtual machining system in order to enforce dimensional, geometrical and tool deflection errors in three-axis milling operations. The system receives 21 dimensional and geometrical errors of a machine tool and machining codes of a specific part as input. The output of the system is the modified codes which will produce actual machined part in the virtual environment

Eslamshahr, un nouveau type de banlieue à Téhéran

Eslamshahr est le symbole des nouvelles banlieues iraniennes : après une structure qui ne ménageait aucune transition entre monde rural et villes, puis les cités miséreuses issues de l'industrialisation, émergent désormais des cités populaires prospères, ni urbaines ni rurales, autonomes tout en restant liées aux grandes villes comme Téhéran

Eslamshahr, un nouveau type de banlieue à Téhéran

Eslamshahr est le symbole des nouvelles banlieues iraniennes : après une structure qui ne ménageait aucune transition entre monde rural et villes, puis les cités miséreuses issues de l'industrialisation, émergent désormais des cités populaires prospères, ni urbaines ni rurales, autonomes tout en restant liées aux grandes villes comme Téhéran

Tool Wear Improvement and Machining Parameter Optimization in Non-generated Face-hobbing of Bevel Gears

Face-hobbing is the dominant and the most productive machining process for manufacturing bevel and hypoid gears. Bevel gears are one of the most important power transmission components, in automobile to aerospace industries, where the power is transmitted between two non-parallel axes. In current industries, the face-hobbing process confronts two major challenges, the tool wear and trial and error experiments to select machining parameters. In the present work, these two problems are targeted. The tool wear in face-hobbing happens at the tool corners of the cutting blades due to the multi-flank chip formation and large gradient of working rake and relief angles along the cutting edge at the corners. In addition, the cutting fluid absence contributes in the tool wear phenomena. In the present work, a cutting tool design method is proposed in order to improve the tool wear characteristics especially at the tool corners. The rake and relief surfaces of the conventional cutting blades are re-designed in such a way that normal rake and relief angles during the face-hobbing process are kept constant and consequently the gradients of these two angles are minimized, theoretically to zero. Using mathematical tool wear characterization relationship and also FEM simulation, the improvements in tool wear are approved. In addition, in the present thesis, semi-analytical methods are proposed to optimize the face-hobbing process in order to select appropriate machining settings. The optimization problem is constructed in such a way that the machining time is minimized subject to the tool rake wear or cutting force related constraints. In order to predict the tool rake wear (crater wear depth), methods are proposed to calculate un-deformed chip geometry, cutting forces, normal stresses, interface cutting temperature and chip sliding velocity. The un-deformed chip geometry is obtained using two proposed methods numerically and semi-analytically. In the numerical method, the workpiece in-process model is obtained and then the un-deformed chip geometry is approximated using the in-process model. In the semi-analytical method, an un-deformed chip boundary theory is constructed in such a way that the boundary curves of the un-deformed chip are formulated by closed form equations. The obtained un-deformed chip geometry is discretized along the cutting edge of the blades. Each infinitesimal element is considered as a small oblique cut. The differential cutting forces are predicted for each individual element using oblique cutting transformation theory. The total cutting forces are derived by integrating the differential cutting forces along the cutting edge. The proposed methods are applied on case studies of non-generated face-hobbing of gears to show the capability of the methods to find the un-deformed chip geometry, predict cutting forces and finally find the optimum machining parameters in non-generated face-hobbing

An Examination of the Relationship between Visual Fatigue Symptoms with Flicker Value Variations in Video Display Terminal Users

In most sensitive occupations such as nuclear, military and chemical industries closed circuit systems and visual display terminals (VDTs) are used to carefully control and assess sensitive processes. Visual fatigue is one of the factors decreasing accuracy and concentration in operators causing faulty perception. This study aimed to find out a relationship between visual fatigue symptoms (VFS) of Flicker value variations in video display terminal (VDT) operators. This cross-sectional study, conducted in 2011, aimed to examine visual fatigue and determine the relationship between its symptoms and visual flicker value changes in 248 operators of VDTs in several occupations. The materials used in this study were a visual fatigue questionnaire of VDTs and a VFM-90.1 device. Visual fatigue was measured in two stages (prior to beginning to work and 60 min later). The data were analyzed by SPSS11.5, using descriptive statistics, paired t-test, simple and multiple linear regressions, correlation and recognition coefficients. Then regression equations of changes in flicker value depending on the changes in the main domains and the changes in final score before the questionnaire were obtained. Paired t-test indicated significant differences in the mean score of visual fatigue symptoms and the mean score of flicker value between the two stages, respectively (P ≤ 0.001). Simple and multiple regressions of flicker value variations, for the last visual fatigue changes in questionnaire score and the four main domains of the questionnaire were obtained R2 = 0.851 and R2 = 0.853, respectively. Correlation coefficient in the above tests indicated reverse and significant relationships among flicker value changes with changes in questionnaire score and visual fatigue symptoms. Diagnosing the first symptoms of visual fatigue could be an appropriate warning for VDTs operators in sensitive occupations to react suitably, in behavior and management, to control or treat visual fatigue and prevent errors efficiently

Aircraft Attitude Estimation Using Panoramic Images

This thesis investigates the problem of reliably estimating attitude from panoramic imagery in cluttered environments. Accurate attitude is an essential input to the stabilisation systems of autonomous aerial vehicles. A new camera system which combines a CCD camera, UltraViolet (UV) filters and a panoramic mirror-lens is designed. Drawing on biological inspiration from the Ocelli organ possessed by certain insects, UV filtered images are used to enhance the contrast between the sky and ground and mitigate the effect of the sun. A novel method for real–time horizon-based attitude estimation using panoramic image that is capable of estimating an aircraft pitch and roll at a low altitude in the presence of sun, clouds and occluding features such as tree, building, is developed. Also, a new method for panoramic sky/ground thresholding, consisting of a horizon– and a sun–tracking system which works effectively even when the horizon line is difficult to detect by normal thresholding methods due to flares and other effects from the presence of the sun in the image, is proposed. An algorithm for estimating the attitude from three–dimensional mapping of the horizon projected onto a 3D plane is developed. The use of optic flow to determine pitch and roll rates is investigated using the panoramic image and image interpolation algorithm (I2A). Two methods which employ sensor fusion techniques, Extended Kalman Filter (EKF) and Artificial Neural Networks (ANNs), are used to fuse unfiltered measurements from inertial sensors and the vision system. The EKF estimates gyroscope biases and also the attitude. The ANN fuses the optic flow and horizon–based attitude to provide smooth attitude estimations. The results obtained from different parts of the research are tested and validated through simulations and real flight tests

Spinocerebellar Atrophy Type-3 with Chiari Malformation in a Young Man: A Case Report

Introduction: Chiari malformations are a group of congenital anomalies which involve the hindbrain and the cervical spinal canal. Case presentation: Here, we describe a patient who presented with acute diplopia and gait unsteadiness which was first deigned with Chiari malformation type-1. However due to progression of the ataxia the full neurologic evaluation was considered which established the diagnosis of spinocerebellar ataxia type 3 (Machado-Joseph-Disease). Conclusion: We aim to highlight the importance of careful examination in order to avoid misdiagnosis of even rare diseases