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  • 1.
    Archenti, Andreas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Laspas, Theodoros
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Accuracy and Performance Analysis of Machine Tools2019In: Metrology / [ed] Wei Gao, Singapore: Springer, 2019Chapter in book (Refereed)
    Abstract [en]

    The key to solve manufacturing quality and productivity problems in the machining of parts is to understand the physical attributes’ geometric/kinematic, static, dynamic, and thermal behavior of machine tools. In this chapter basic definitions, error sources, and instruments and methodologies for the identification and evaluation of machine tools’ physical attributes will be outlined.

    The first section presents the background and answers “why” it is important to measure and evaluate machine tools under no-load and loaded condition. Basic concepts and definitions of metrological terms will be given. In the second part, error sources in machine tools are introduced, and in the third part, instruments and methodologies for the accuracy evaluation of machine tools will be given.

  • 2.
    Laspas, Theodoros
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Machine and Process Technology.
    Closed Force Loop Evaluation of Machining Systems2018Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Machine tools accuracy has been a cornerstone in defining machining system capability and directly affecting dimensional and geometrical tolerance of machined parts. The effort for achieving higher precision and accuracy can be distinguished in two general ideas. One is to improve performance of machine tools by designing better, stiffer and more accurate machine tools. The other is to develop tools and methods for evaluating and measuring their behaviour and gain knowledge of their performance. In order to properly control the machine tool characteristics that can affect and improve their accuracy such as static stiffness and static accuracy.This thesis is aiming at establishing and further advancing the idea of loaded testing of machining systems and the concept of Elastically Linked Systems as a framework for measuring, identifying and characterising quasi-static stiffness of machine tools under loaded conditions. This will allow the creation of an improved capability profile of machining system accuracy. The focus is on the implementation of Elastically Linked Systems concept (ELS) through the Loaded Double Bar system, a measurement method that can partly simulate the process-machine interaction by reproducing forces exerted on the machine tool structure for the evaluation of system characteristics under loaded condition. This allows the qualitative and quantitative evaluation and comparison of machine tools for the purpose of accuracy enhancement, identification of weak directions with potential utilization in process planning, machine procurement and maintenance.Through two case studies, the capability to identify the effect of machine components and structure behaviour is shown.

  • 3.
    Laspas, Theodoros
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Archenti, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Investigation of multi-axis system static and kinematic characteristics2016Conference paper (Refereed)
    Abstract [en]

    Multi-axis machine tools performance is essential in achieving high positioning accuracy at the desired feed rate and to withstand mechanical loads induced by the process-machine interaction. In this regard evaluation and characterization of multi-axis machine performance in terms of kinematic and static accuracy under variable load operating conditions poses a challenge.The paper aims to investigate and characterize the kinematic and static accuracy of a multi-axis milling centre under loaded conditions. Employing the concept of Elastically Linked System (ELS) for “off-operational” evaluation, the accuracy due to the interaction between the machine’s structure the machining process loads and the control system is assessed. Using the Loaded Double Ball Bar (LDBB) measurement system the cutting process is emulated by inserting an “elastic link” between the tool and the workpiece that closes the force-loop of the system.A set of workspace positions is selected to perform the LDBB measurements. The positions are selected so as to cover an adequate region of the effective machining workspace and at the same time utilizing a combination of linear and rotational axis positions and orientations to allow the investigation of their behavior and the effect of the machine structure. The captured deformations and their variation within the examined workspace region give a comprehensive view of the machine’s kinematic and static accuracy under the effect of the load induced errors and kinematic inaccuracies.

  • 4.
    Szipka, Karoly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Laspas, Theodoros
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Archenti, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Measurement and analysis of machine tool errors under quasi-static and loaded conditions2018In: Precision engineering, ISSN 0141-6359, E-ISSN 1873-2372, Vol. 51, p. 59-67Article in journal (Refereed)
    Abstract [en]

    Machine tool testing and accuracy analysis has become increasingly important over the years as it offers machine tool manufacturers and end-users updated information on a machine’s capability. A machine tooĺs capability may be determined by mapping the distribution of deformations and their variation range, in the machine tool workspace, under the cumulative effect of thermal and mechanical loads. This paper proposes a novel procedure for the prediction of machine tool errors under quasi-static and loaded conditions. Geometric errors and spatial variation of static stiffness in the work volume of machines are captured and described through the synthesis of bottom-up and top-down model building approaches. The bottom-up approach, determining individual axis errors using direct measurements, is applied to estimate the geometric errors in unloaded condition utilizing homogeneous transformation matrix theory. The top-down approach, capturing aggregated quasi-static deviations using indirect measurements, estimates through an analytical procedure the resultant deviations under loaded conditions. The study introduces a characterization of the position and direction dependent static stiffness and presents the identification how the quasi-static behavior of the machine tool affects the part accuracy. The methodology was implemented in a case study, identifying a variation of up to 27% in the stiffness response of the machine tool. The prediction results were experimentally validated through cutting tests and the uncertainty of the measurements and the applied methodology was investigated to determine the reliability of the predicted errors.

  • 5.
    Szipka, Karoly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Laspas, Theodoros
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Archenti, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Measurement uncertainty associated with the performance of machine tool under quasi-static loaded test condition2017In: Laser Metrology and Machine Performance XII / [ed] L. Blunt & W. Knapp, Renishaw Innovation Centre, UK, 2017Conference paper (Refereed)
    Abstract [en]

    For proper characterisation of different physical quantities in machine tools, it is necessary to report the uncertainties associated to the measurements. The uncertainty evaluation, according to international standards, expresses information of the quality and the reliability of the measurement result. Applications like calibration and compensation are sensitive for the quality of the input data, thus the reliability of the characterisation results need to be interpreted accurately to avoid significant residual errors or overcompensation. General approaches take several factors into consideration during the estimation of measurement uncertainty such as the environmental variations or the uncertainties of the measurement device or the setup. At the same time, various reproducible and non-reproducible error sources associated to the performance testing of the machine tool are ignored. The reason behind it can be the lack of the applicable standardized measurement instruments.

    This paper highlights the significance of the uncertainty sources connected to the performance of the machine tool under quasi-static loaded condition. The variation of the static stiffness of machine tools, the hysteresis and play in the system can be even more significant uncertainty sources than the above mentioned ones. Under the framework of elastically linked systems (ELS), a circular test device, the loaded double ball bar (LDBB), is used in a case study to identify this effect. The LDBB can be used as a double ball bar, with the additional capability of applying a load, thus it enables the measurement of machine tool deviations under quasi-static loaded conditions. A measurement methodology is proposed to properly describe and demonstrate the variation of the contributing uncertainties associated with repeatability performance of the machine tool. With this approach important interdependencies can be expressed as uncertainty sources.

  • 6.
    Szipka, Karoly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Theodoros, Laspas
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Archenti, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Prediction of machine tool errors under quasi-static condition2016Conference paper (Refereed)
  • 7.
    Szipka, Károly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Laspas, Theodoros
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Archenti, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Mechanistic approach for the evaluation of machine tools quasi-static capability2017In: NEWTECH 2017: Proceedings of 5th International Conference on Advanced Manufacturing Engineering and Technologies, Springer Berlin/Heidelberg, 2017, p. 229-243Chapter in book (Refereed)
    Abstract [en]

    One of the greatest challenges in the manufacturing industry is to increase the understanding of the error sources and their effect on machine tool capability. This challenge is raised by the complexity of machining systems and the high requirements on accuracy. In this paper, a mechanistic evaluation approach is developed to handle the complexity and to describe the underlying mechanisms of the machine tools capability under quasi-static condition. The capability in this case is affected by the geometric errors of the multi-axis system and the quasi-static deflections due to process loads. In the assessment of these sources a mechanistic model is introduced. The model is composed of two parts, combining direct and indirect measurements. The direct measurement modelling method was applied to predict the effects of individual axis geometric errors on the functional point of machine tools. First, the direct measurement is employed to allow measuring each single machine tool axis motion error individually. The computational in the direct measurement model calculates the deviations from a given toolpath in the work space. Then, indirect measurements are used to determine the static stiffness and its variation in the workspace of machine tools. A case study demonstrates the applicability of the proposed approach, where laser interferometry was implemented as direct and loaded double ball bar as indirect measurement. The methodology was investigated on a three and a five axis machine tool and the results demonstrate the potential of the approach.

  • 8.
    Theissen, Nikolas Alexander
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Laspas, Theodoros
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Archenti, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Machine and Process Technology.
    Closed-force-loop elastostatic calibration of serial articulated robots2019In: Robotics and Computer-Integrated Manufacturing, ISSN 0736-5845, E-ISSN 1879-2537, Vol. 57, p. 86-91Article in journal (Refereed)
    Abstract [en]

    This paper presents a novel methodology to measure the compliance of articulated serial robots based on the Elastically Linked Systems concept. The idea behind the methodology is to measure serial articulated robots with customized external wrench vectors under a closed-force-loop. The methodology proposes to measure robots in use-case defined configurations to increase the effect of the identified model parameters on their later implementation. The measurement methodology utilizes the Loaded Double Ball Bar to customize wrench vectors and a laser tracker to measure the system response. In particular, the Loaded Double Ball Bar creates the closed-force-loop to create a flow of forces similar to the intended application of the robot. The methodology is applied to an industrial robot with six rotary joints using the LDBB and a laser tracker. Finally, the paper ends on a discussion about the implementation of the model parameters to improve the accuracy of robots as well as challenges to realize a more cost efficient elastostatic calibration.

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