Modelización teórica de los principios físicos de funcionamiento de las máquinas de medición por coordenadas para la optimización de la precisión de medición alcanzable

Abstract

The optimization and modelling of the measurement accuracy that can be achieved during the verification of mechanical components using coordinate measuring machines (CMMs) is of special relevance for production systems, since these measuring equipment are widely used to check the dimensional properties of the manufactured parts, which are frequently subject to high demands in terms of the dimensional and geometric tolerances and the surface finish that are required for the acceptance of these products during their quality control. For this reason, the optimization of these measuring equipment is essential for the inspection of the dimensional quality of manufactured products within diverse areas of the metal-mechanical sector such as the industry of machinery manufacturing, naval, automobile, aeronautics, aerospace, etc., in all those applications for which the use of coordinate measuring machines is recommendable due to their versatility for verifying different types of dimensional and geometric tolerances. There are numerous authors who have carried out diverse works focused on the analysis of some of the different factors that must be considered to improve the measurement accuracy in CMMs, including those that are dedicated to the development of devices that could help to the increase of precision, the study of the influence of certain factors on the behavior of coordinate measuring machines, and the numerical modelling of the measurement process. This doctoral thesis is especially aimed at defining a methodology that could be used for the study, modelling and prediction of the measurement accuracy of coordinate measuring machines during the dimensional verification of the parts generated from the corresponding manufacturing processes, as a consequence of the effect caused by the geometric and dynamic errors of the linear and angular axes of the CMMs and other types of errors associated with this equipment. For this purpose, it has been included a first methodology oriented to the identification of machine errors, a second methodology that is focused on the proposal of a theoretical model that allows predicting the influence of these factors on the measurement accuracy with a reduced computing time, and a third methodology that provides a second model that is based on a new parameter through which the different error sources can be integrated to facilitate its analysis. Inside the report of this doctoral thesis, at the first chapter it can be found a brief description about the physical principles of operation of coordinate measuring machines, including the main geometric and dynamic errors that are usually present in this equipment, and after that it will be carried out a review about the state of the art related to the works dedicated to the study of these errors and their computational modelling, as well as the definition of the objectives pursued in the doctoral thesis. At the second chapter, with regards to the methodology that is proposed in this doctoral thesis, firstly it will be exposed a procedure to register the level of geometric and dynamic errors that exist at the CMMs to be studied, which will be needed during the theoretical analysis of the behavior of these equipment to be carried out lately. Secondly, it will be defined a traditional numerical model with random errors, which could be employed to analyze with a reduced computing time some of the most common errors in coordinate measuring machines, as well as their influence on the precision that could be achieved in these equipment. In the last part of the proposed methodology, it will be suggested the use of a new error index that will be called equivalent error (EE), and a second numerical model based on the equivalent error in order to facilitate the study of the measurement accuracy of CMMs. Subsequently, this methodology will be employed for a specific application example with different measurement conditions. This application example will be focused on the analysis of the achievable precision in coordinate measuring machines with three linear axes and FXYZ structural configuration, although the proposed methodology could also be applied to other different types of coordinate measuring machines. Finally, in the last part of this doctoral thesis, it will be presented some of the main conclusions that can be extracted from the work developed in relation to the methodology that has been proposed to study the measurement accuracy of coordinate measuring machines.