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 /

Method for Accuracy Assessment of the Length Measurement Unit of Laser Tracking Systems

Laser tracking systems are widely used in large-scale metrology of geometric quantities. Their importance is confirmed by the fact that one of the parts of the ISO 10360 series of standards has been devoted to the issue of assessing their accuracy (ISO 10360-10). A laser tracker is a device whose final measurement result is calculated using indications from various subsystems included in it, such as devices for measuring length and angle. The analysis of these individual impacts can be useful in creating simulation models of accuracy which, in regard to the Industry 4.0 concept, seem to be the most justified in terms of speed of operation and ease of use. For this reason, it may be particularly important to undertake research on the accuracy of this component in isolation from other factors affecting the measurement of the coordinates of the point. The article describes a method that allows separation of the length measurement error from the other components. The method uses a high-accuracy interferometer which is treated as a reference system that allows for the comparison of indications obtained using the tested distance measurement system. Thanks to the proposed method, it is possible to minimize errors from the optical system and other measuring systems. The use of a precise linear guide allows the reduction of errors related to the implementation of linear motion. The article presents the test method and the results obtained from performed experiments, as well as formulates conclusions and the directions of further development

Method for Accuracy Assessment of the Length Measurement Unit of Laser Tracking Systems

Laser tracking systems are widely used in large-scale metrology of geometric quantities. Their importance is confirmed by the fact that one of the parts of the ISO 10360 series of standards has been devoted to the issue of assessing their accuracy (ISO 10360-10). A laser tracker is a device whose final measurement result is calculated using indications from various subsystems included in it, such as devices for measuring length and angle. The analysis of these individual impacts can be useful in creating simulation models of accuracy which, in regard to the Industry 4.0 concept, seem to be the most justified in terms of speed of operation and ease of use. For this reason, it may be particularly important to undertake research on the accuracy of this component in isolation from other factors affecting the measurement of the coordinates of the point. The article describes a method that allows separation of the length measurement error from the other components. The method uses a high-accuracy interferometer which is treated as a reference system that allows for the comparison of indications obtained using the tested distance measurement system. Thanks to the proposed method, it is possible to minimize errors from the optical system and other measuring systems. The use of a precise linear guide allows the reduction of errors related to the implementation of linear motion. The article presents the test method and the results obtained from performed experiments, as well as formulates conclusions and the directions of further development

Dimensional measurements in the shipbuilding industry: on‑site comparison of a state‑of‑the‑art laser tracker, total station and laser scanner

Thanks to recent technological innovations, some large-volume-metrology measuring instruments—that would have been considered out of context one/two decades ago—are now efective for the shipbuilding industry, where dimensional errors of a few millimetres are generally tolerated. This paper considers three state-of-the-art instruments: a laser tracker, a total station, and a laser scanner, all with the latest generation of technology. While the frst instrument type has long been widespread for applications in industrial metrology, the last two have traditionally been used in other felds, such as as-built surveying, civil engineering, architecture and topography. Instruments are compared using experimental tests concerning the dimensional verifcation of cruise-ship modules in the relatively under-explored context of the construction of the hull, which represents the ship’s framework. The comparison is structured based on several qualitative and quantitative criteria, including but not limited to (i) simplicity of use for operator(s), (ii) time of acquisition/analysis of measurement data, (iii) metrological performance, and (iv) cost. The main contribution of this article is the on-site testing of instruments of interest, in the typical (unfavourable) working conditions of shipyards

Uncertainty Modelling of High-precision Trajectories for Industrial Real-time Measurement Applications

Within the field of large volume metrology, kinematic tasks such as the movement of an industrial robot have been measured using laser trackers. In spite of the kinematic applications, to date most research has focused on static measurements. It is crucial to have a reliable uncertainty of kinematic measurements in order to assess spatiotemporal path deviations of a robot. With this in mind an approach capable of real-time was developed, to determine the uncertainties of kinematic measurements

Laser tracker kinematic error model formulation and subsequent verification under real working conditions

A kinematic model of the Laser Tracker (LT) based on the Denavit-Hartenberg method has been developed. In this model, error matrices have been included with error parameters for linear and rotary joints. The calibration method is based on the measurement of a mesh of reflectors measured by a LT from different positions. Error parameters are calculated knowing that distances between every pair of reflectors is the same regardless the LT position. The absence of nominal data prevents us from knowing the calibration behaviour and its suitability. Although synthetic data tests show a good accuracy improvement, it is not possible to know if this will work with under real working conditions. An experiment has been made to check the calibration procedure. A set of 17 reflectors have been placed on a Coordinate Measuring Machine (CMM) and have been measured by a LT from 5 different positions. Reflector positions have also been measured with the CMM to calculate the initial errors. With LT measurements we calculate the error parameters. LT measurements are recalculated considering the kinematic error model and compared with the CMM measurements to get the residual error. Two errors have been calculated; distances error between reflectors and their position error compared with CMM data

Traceability of on-machine tool measurement: a review

Nowadays, errors during the manufacturing process of high value components are not acceptable in driving industries such as energy and transportation. Sectors such as aerospace, automotive, shipbuilding, nuclear power, large science facilities or wind power need complex and accurate components that demand close measurements and fast feedback into their manufacturing processes. New measuring technologies are already available in machine tools, including integrated touch probes and fast interface capabilities. They provide the possibility to measure the workpiece in-machine during or after its manufacture, maintaining the original setup of the workpiece and avoiding the manufacturing process from being interrupted to transport the workpiece to a measuring position. However, the traceability of the measurement process on a machine tool is not ensured yet and measurement data is still not fully reliable enough for process control or product validation. The scientific objective is to determine the uncertainty on a machine tool measurement and, therefore, convert it into a machine integrated traceable measuring process. For that purpose, an error budget should consider error sources such as the machine tools, components under measurement and the interactions between both of them. This paper reviews all those uncertainty sources, being mainly focused on those related to the machine tool, either on the process of geometric error assessment of the machine or on the technology employed to probe the measurand

A New Methodology for Kinematic Parameter Identification in Laser Trackers

In recent years, there has been an increasing interest in measurement systems such as laser trackers (LT) for the verification of large-scale parts in the aeronautic, spatial or naval sectors because of their advantages in terms of portability, flexibility, high speed in data acquisition, accuracy, and reliability. These systems present systematic errors caused by geometrical misalignments, environmental conditions, mechanical wear and tear and other unpredictable variables. Different standards such as the ASME B89.4.19 and the VDI 2617-10 suggest tests to calculate the geometric errors of the LT. In this work, we present an alternative calibration method based on a new errors model. The LT can be considered as an open kinematic chain, so it is possible to shape a kinematic model of the LT. Once the kinematic model has been set, the error model is defined. The model has been validated with synthetic data. Then, experimental tests based on the measurement of a mesh of reflectors placed at suitable places for different locations of the LT have been performed to ensure the reliability of the method proposed. A sensitivity analysis shows the best experimental setup to perform a calibration test. The calibration results have been validated with nominal data

A framework for flexible integration in robotics and its applications for calibration and error compensation

Robotics has been considered as a viable automation solution for the aerospace industry to address manufacturing cost. Many of the existing robot systems augmented with guidance from a large volume metrology system have proved to meet the high dimensional accuracy requirements in aero-structure assembly. However, they have been mainly deployed as costly and dedicated systems, which might not be ideal for aerospace manufacturing having low production rate and long cycle time. The work described in this thesis is to provide technical solutions to improve the flexibility and cost-efficiency of such metrology-integrated robot systems. To address the flexibility, a software framework that supports reconfigurable system integration is developed. The framework provides a design methodology to compose distributed software components which can be integrated dynamically at runtime. This provides the potential for the automation devices (robots, metrology, actuators etc.) controlled by these software components to be assembled on demand for various assembly applications. To reduce the cost of deployment, this thesis proposes a two-stage error compensation scheme for industrial robots that requires only intermittent metrology input, thus allowing for one expensive metrology system to be used by a number of robots. Robot calibration is employed in the first stage to reduce the majority of robot inaccuracy then the metrology will correct the residual errors. In this work, a new calibration model for serial robots having a parallelogram linkage is developed that takes into account both geometric errors and joint deflections induced by link masses and weight of the end-effectors. Experiments are conducted to evaluate the two pieces of work presented above. The proposed framework is adopted to create a distributed control system that implements calibration and error compensation for a large industrial robot having a parallelogram linkage. The control system is formed by hot-plugging the control applications of the robot and metrology used together. Experimental results show that the developed error model was able to improve the 3 positional accuracy of the loaded robot from several millimetres to less than one millimetre and reduce half of the time previously required to correct the errors by using only the metrology. The experiments also demonstrate the capability of sharing one metrology system to more than one robot