Calibration of Machine Tools Using on Machine Probing of an Indigenous Artefact

RÉSUMÉ Les centres d’usinage cinq axes avec deux axes rotatifs facilitent la production des pièces complexes grâce à la capacité de positionnement et d’orientation de l’outil par rapport à la pièce en cours d’usinage. Cependant, le centre d’usinage est vulnérable à de nombreuses sources d’erreurs. L’inspection périodique du centre d’usinage est un élément clé pour obtenir la pièce finie souhaitée dans les limites de tolérances. Les méthodes d’inspection existantes nécessitent un personnel qualifié, un montage spécial et un temps additionnel pour installer les équipements. Par conséquent, l’objectif de cette thèse est de surmonter ces contraintes et développer une nouvelle méthode pour estimer les erreurs paramétrique inter- et intra-axes par palpage d’un artefact indigène directement sur le centre d’usinage. Les palpeurs de déclenchement tactile sont utilisés pour mesurer des facettes de la table de la machine-outil. Un modèle mathématique a été développé pour modéliser les erreurs d’installation de la sonde et des artefacts afin d’enlever leurs effets lors du processus d’étalonnage. Le temps d'étalonnage est de 1 heure et 30 minutes. La validation de cet étalonnage est effectuée en comparant l’artefact du modèle estimé avec les mesures du même artefact obtenu par mesurage sur une Machine à Mesurer Tridimensionnelle (MMT). La capacité de prédiction des erreurs volumétriques du modèle est également validée en prédisant la position de la touche du stylet dans le repère de la pièce usinée pour d’autres facettes sondées pour fin de validation seulement, et les comparer avec les données mesurées par MMT. La distance résiduelle maximale entre l’artefact prédit par le modèle et l’artefact estimé par le MMT est 139.50 μm sans aucun paramètre estimé, et 6.92 μm avec 86 inter- et intra-axes paramètres estimés par le modèle. La technique de calibration proposée est appliquée au centre d’usinage intégré avec des tables de formes prismatique et sphérique (Mitsui Seiki HU40T et Huron KX8-five). Un schéma est proposé pour examiner les performances de la machine au cours d’une journée et entre les jours. La qualité du schéma est validée avec les incertitudes des paramètres calibrés venant de la covariance de l’ensemble des résultats de cycles de mesures effectuées pendant des jours consécutifs.----------ABSTRACT Five-axis machine tools with two rotary axes facilitate the production of intricate parts due to the position and orientation capability of the tool with respect to the workpiece but this flexibility also renders the machine tool vulnerable to numerous sources of error. Periodic inspection is the key to obtain finished part within the prescribed tolerance limits. Existing machine tool inspection methods require trained personnel, special setups and additional time to setup the test equipments. Therefore, the aim of this thesis is to overcome these limitations and develop a new method to calibrate inter- and intra-axis error parameters by on-machine probing of an indigenous artefact. A touch trigger probe is used to measure facets on the existing machine tool table. A mathematical model is developed to model the probe and the artefact setup errors and remove their effects from the estimation process. The calibration time is 1 hour and 30 minutes. The validation of the calibration is done by comparing the model estimated artefact with the Coordinate Measuring Machine (CMM) measured artefact. The volumetric error prediction capability of the model is also validated by predicting the stylus tip positions in the last workpiece branch frame (rigidly connected to the machine table frame) for each facet probing and comparing them with the CMM measurements. The maximum residual distance between the model predicted artefact and CMM artefact is 139.50 μm with no parameters estimated and 6.92 μm with 86 inter- and intra-axis parameters estimated. The proposed calibration technique is applied to the machine tools integrated with prismatic and cylindrical shape tables (Mitsui Seiki HU40T & Huron KX8-five). A scheme is proposed to investigate the machine performance throughout a day and between days supported by the uncertainties of the calibrated parameters estimated from the pooled covariance of the repeated measurement cycles performed for consecutive days. The calibration performance is also evaluated by investigating the repeatability of the uncalibrated indigenous artefact probing against artefact probing strategy, rotary axes indexations, parameters’ uncertainties and artefact dismount and remount cycle

Modeling and Evaluation of the Volumetric Errors for the 5-Axis Machine Tool

Department of Mechanical EngineeringCNC Machine tools are among the most important means of production in metalworking industries and/ have been most widely used. Since an increasing demand for machinery parts with geometric complexity in high efficiency, multi-axialization and multi-functionalization emerged as technology trends in the machine tools field. As a result, 5-axis machine tools have been extensively used in various manufacturing applications requiring higher machining accuracy. In reality, demand in aerospace, medical, electric vehicle, and precision&semiconductor industries are driving. Based on the order composition of machine tools, the proportion of five-axis machine tools has become large remarkably, and also this trend is expected to continue in the future. While this high flexibility to machine complex parts efficiently could have led the 5-axis machine tool to become a great solution in the metalworking industry, at the same time, 5-axis machine tools have encountered challenges that have to overcome hurdles that come from this flexibility and freedom. As is well known, machine tools' accuracy is one of the most important indicators for the performance of machine tools, and 5-axis machine tools accompany more complexities and require more elements and more assembly processes, so encounter more accuracy problems indispensably. Overcoming these challenges and under the motivation to high-accuracy 5-axis machine tools, modeling and evaluating the volumetric errors for a 5-axis machine tool was set as this research objective. Specifically, in order to model the volumetric error, a study on the kinematic structures and identification for systematic error is carried out beforehand, and based on this, the goal aims to establish an error model of the 5-axis machine tool. Then, the error model established for a 5-axis machine tool is applied to a practical machine tool, and the errors propagating sensitively to volumetric error are determined as key errors. Also, the resultant effect of the individual errors and key errors is evaluated in advance through estimation of volumetric error. To estimate the volumetric error in virtual, stochastic estimation with random variables was conducted to obtain tool points??? coordinates within a workspace, and statistical analysis has carried out. Through these analysis processes, whether machine tools' volumetric error is enhanced under the condition when key errors were specified and assembled is confirmed. Lastly, to confirm the utility of modeling and evaluation for volumetric error in advance, the demonstration was conducted on two actual 5-axis machine tools, and each machine tool had been manufactured under the management to be assembled with the tolerance used in virtual evaluations as same as possible. Depending on whether or not the specified key error tolerance range is fulfilled, it has clearly confirmed the superiority and inferiority of 5-axis machine tools' volumetric error. And also by comparing estimation and experimental results, it is found that the approach and methods used in this study were useful and could be applied to the actual 5-axis machine tool manufacturing process.ope

Traceable onboard metrology for machine tools and large-scale systems

Esta tesis doctoral persigue la mejora de las funcionalidades de las máquinas herramienta para la fabricación de componentes de alto valor añadido. En concreto, la tesis se centra en mejorar la precisión de las máquinas herramienta en todo su volumen de trabajo y en desarrollar el conocimiento para realizar la medición por coordenadas trazable con este medio productivo. En realidad, la tecnología para realizar mediciones en máquina herramienta ya está disponible, como son los palpadores de contacto y los softwares de medición, sin embargo, hay varios factores que limitan la trazabilidad de la medición realizada en condiciones de taller, que no permiten emplear estas medidas para controlar el proceso de fabricación o validar la pieza en la propia máquina-herramienta, asegurando un proceso de fabricación de cero-defectos. Aquí, se propone el empleo del documento técnico ISO 15530-3 para piezas de tamaño medio. Para las piezas de gran tamaño se presenta una nueva metodología basada en la guía VDI 2617-11, que no está limitada por el empleo de una pieza patrón para caracterizar el error sistemático de la medición por coordenadas en la máquina-herramienta. De esta forma, se propone una calibración previa de la máquina-herramienta mediante una solución de multilateración integrada en máquina, que se traduce en la automatización del proceso de verificación y permite reducir el tiempo y la incertidumbre de medida. En paralelo, con el conocimiento generado en la integración de esta solución en la máquina-herramienta, se propone un nuevo procedimiento para la caracterización de la precisión de apunte del telescopio LSST en todo su rango de trabajo. Este nuevo procedimiento presenta una solución automática e integrada con tecnología láser tracker para aplicaciones de gran tamaño donde la precisión del sistema es un requerimiento clave para su buen funcionamiento.<br /

Numerical simulation of the rheological behavior of fresh concrete

This thesis reports recent numerical investigation of the rheological behavior of fresh concrete using the Distinct Element Method (DEM). Some relevant questions of the concrete rheology e.g. the influence of the concrete composition on the rheological behavior of the fresh concrete, the experimental determination of the Bingham rheological constants as well as the use of these constants in the numerical simulation were discussed thoroughly. An important topic of the performed investigation was the development of the numerical model for fresh concrete which enables simple, fast and stable predictive simulation of different technological operations with fresh concrete. Firstly, in a literature survey, the state-of-the-art of the numerical simulation of fresh concrete was presented and critically discussed in order to show advantages and disadvantages of other methods and modeling approaches. Open (unsolved) questions were highlighted and the basis for their investigation is created within this thesis. Fundamental concepts of the rheology were then presented and the basic rheological models of viscoelastic materials were considered; the rheological behaviors of different types of concretes were presented and its influencing factors were discussed. Additionally main methods for scientific investigation and testing of the fresh concrete were shown. The test methods were critically discussed in order to select the test, which has been used as a reference experimental test for the numerical simulations. Chosen reference experimental test was the slump flow test. The slump flow test was thoroughly analyzed and an analytical solution was developed which helps to interpret the results of measurements and provides a link between rheological constants and measured quantities. In a further step an extensive experimental program was carried out in order to investigate the rheological behavior of fresh concrete and get the input data for numerical simulation. Firstly, the experiments on macrolevel were performed. Here the rheological behavior of the fresh concrete flow in different tests was investigated (slump and slump flow tests, L-Box). Further, the experiments on mesolevel with polymer on Carbopol basis and mortar were developed and performed in order to investigate the interaction between distinct particles suspended in a fluid matrix. The necessary material parameters, especially those representative of the fluid suspension micromechanical behavior, i.e. the force-displacement relationship, yield force and bond strength, were determined by these experiments. The slump flow test was used as the basic test to calibrate the model for fresh concrete (key data: slump value, slump flow diameter (for concretes with a soft consistency) and the time of spreading). Thus, the decisive phenomena of the fresh concrete flow were highlighted, control points for a contact model were selected and the initial input data for the development of the contact model was obtained. Next, the user-defined contact model was developed and implemented into the Particle Flow Code ITASCA. The contact model was completely described and its limitations discussed. Then, the set of numerical tools was developed, which enable simplified and stable numerical simulation of the fresh concrete with particular behavior, i.e. automatic generation of the concrete with given particle grading, amount of fibers and air, automatic recalculation of the micromechanical parameters of the contact model from given initial yield stress and plastic viscosity. The model was calibrated by slump flow test simulations and validated by corresponding analytical approach. Further, the role of different model parameters was investigated by simulating the slump flow test. Furthermore, for verification of the model several additional experiments were simulated, i.e. L-Box and LCPC-box test. The results of modeling were compared with experimental results and discussed in detail. All numerical simulations provide qualitatively as well as quantitatively correct results and hence adequately represent the phenomena observed in real experiments. The thesis closes with general conclusions and outlook of the work. In the future, the developed contact model and tools of the “Virtual concrete laboratory” could be modified in order to extend the potential of the laboratory to cover such properties as thixotropic behavior of fresh concrete or simulating hardening of the concrete and behavior of the hardened concrete

Doctor of Philosophy

dissertationShape analysis is a well-established tool for processing surfaces. It is often a first step in performing tasks such as segmentation, symmetry detection, and finding correspondences between shapes. Shape analysis is traditionally employed on well-sampled surfaces where the geometry and topology is precisely known. When the form of the surface is that of a point cloud containing nonuniform sampling, noise, and incomplete measurements, traditional shape analysis methods perform poorly. Although one may first perform reconstruction on such a point cloud prior to performing shape analysis, if the geometry and topology is far from the true surface, then this can have an adverse impact on the subsequent analysis. Furthermore, for triangulated surfaces containing noise, thin sheets, and poorly shaped triangles, existing shape analysis methods can be highly unstable. This thesis explores methods of shape analysis applied directly to such defect-laden shapes. We first study the problem of surface reconstruction, in order to obtain a better understanding of the types of point clouds for which reconstruction methods contain difficulties. To this end, we have devised a benchmark for surface reconstruction, establishing a standard for measuring error in reconstruction. We then develop a new method for consistently orienting normals of such challenging point clouds by using a collection of harmonic functions, intrinsically defined on the point cloud. Next, we develop a new shape analysis tool which is tolerant to imperfections, by constructing distances directly on the point cloud defined as the likelihood of two points belonging to a mutually common medial ball, and apply this for segmentation and reconstruction. We extend this distance measure to define a diffusion process on the point cloud, tolerant to missing data, which is used for the purposes of matching incomplete shapes undergoing a nonrigid deformation. Lastly, we have developed an intrinsic method for multiresolution remeshing of a poor-quality triangulated surface via spectral bisection

39th Aerospace Mechanisms Symposium

The Aerospace Mechanisms Symposium (AMS) provides a unique forum for those active in the design, production, and use of aerospace mechanisms. A major focus is the reporting of problems and solutions associated with the development and flight certification of new mechanisms. Organized by the Mechanisms Education Association, NASA Marshall Space Flight Center (MSFC) and Lockheed Martin Space Systems Company (LMSSC) share the responsibility for hosting the AMS. Now in its 39th symposium, the AMS continues to be well attended, attracting participants from both the United States and abroad. The 39th AMS was held in Huntsville, Alabama, May 7-9, 2008. During these 3 days, 34 papers were presented. Topics included gimbals and positioning mechanisms, tribology, actuators, deployment mechanisms, release mechanisms, and sensors. Hardware displays during the supplier exhibit gave attendees an opportunity to meet with developers of current and future mechanism components