A region segmentation method to measure multiple features using a tactile scanning probe

Coordinate measuring machines (CMMs) have been widely used in industry to precisely measure parts for inspection or quality control. One of the main barriers to using a CMM touch-trigger probe is the cumbersome programming work required to identify the probing points and for scan path planning. In this paper, we propose a practical data-segmentation method to continuously measure multiple features of the workpiece using a scanning probe. This approach takes advantage of the fast data-capture capability of the scanning probe and, subsequently, the point dataset is segmented using the information extracted from the CAD model of the part. This methodology does not require tedious programming and all desired measurement results can be obtained from a single scan. The principle of the method is presented, and the feasibility of the method is experimentally verified on a bridge-type Hexagon DEA Global CMM equipped with a Leitz LSP-X1 probe. The proposed method avoids manual operation errors and generates more sampling points than traditional methods; therefore, theoretically providing lower measurement uncertainty. The test results also indicate that the new method using a scanning probe is easy to implement and can save more than 90% measurement time in comparison with a conventional touch-trigger method

Vérification et diagnostic des machines à mesurer tridimensionnelles avec découplage machine et palpeur.

RÉSUMÉ Cette recherche est une contribution au diagnostic des sources d’erreurs sur les machines à mesurer tridimensionnelles (MMTs). Le diagnostic des principales sources d’erreurs sur une MMT nécessite une étude dépendante du volume de mesure. Dans un grand volume de mesures, ce sont les erreurs liées au mouvement des axes de la machine qui dominent. Dans un petit volume de mesure, ce sont les erreurs liées au palpeur qui deviennent, souvent, dominants. Ces sources d’erreurs coexistent et affectent la qualité de mesure. Dans un grand volume de mesure, une méthode pour identifier les écarts de perpendicularité et les gains d’échelle a été proposée en utilisant un calibre étagé mesuré dans les sept positions suggérées par le rapport ASME B89.4.10360.2-2008. Ces paramètres permettent d’expliquer partiellement les erreurs mesurées sur le calibre étagé et d’apporter une action corrective à la machine en cas de non-conformité. Dans un petit volume de mesure, une méthode pour séparer les erreurs de palpeur du reste des erreurs de la machine a été proposé. Cette méthode est basée sur le palpage d’une sphère de référence selon plusieurs configurations en faisant un retournement du système de palpage. Les données non expliquées par le modèle de séparation sont traitées afin de séparer les contributions aléatoires des résultats de palpage en fonction de la direction de l'approche de la machine et la direction de déclenchement du palpeur. Enfin, une étude sur le choix de configurations et sur l’échantillonnage de points palpés a été réalisée dans le but de réduire le temps d’exécution de la méthode.----------ABSTRACT The diagnosis of the main sources of errors in a coordinate measuring machine (CMM) requires a study dependent on the measurement volume. In a large measurement volume, the errors related to movement of the machine axes dominate. In a small measurement volume, the errors related to the probe, often, dominate. These error sources coexist and affect the measurement quality. In a large measurement volume, a method for identifying axes out-of-squarenesses and gains of scale is proposed which uses data obtained by measuring a step gauge in the seven positions suggested by the report ASME B89.4.10360.2 -2008. These parameters can partially explain the measured errors on a step gauge and remedial action can be taken if necessary. In a small measurement volume, a method to separate the probe errors from machine errors is proposed. This method is based on redundancy measurements of the machine’s own test sphere. The method was tested on a laboratory machine and the results were confirmed by measuring separately the probe and the machine errors. Data not explained by those error models are used to separate the contributions to the probing results randomness originating from the machine approach direction and from the probe triggering direction. Such information can then be used as input to the estimation of measurement uncertainty. Finally, a study on the choice of configuration and sampling points measured was conducted in order to minimize the test time and reduce the industrial cost of such periodic verification

Integrated tactile-optical coordinate measurement for the reverse engineering of complex geometry

Complex design specifications and tighter tolerances are increasingly required in modern engineering applications, either for functional or aesthetic demands. Multiple sensors are therefore exploited to achieve both holistic measurement information and improved reliability or reduced uncertainty of measurement data. Multi-sensor integration systems can combine data from several information sources (sensors) into a common representational format in order that the measurement evaluation can benefit from all available sensor information and data. This means a multi-sensor system is able to provide more efficient solutions and better performances than a single sensor based system. This thesis develops a compensation approach for reverse engineering applications based on the hybrid tactile-optical multi-sensor system. In the multi-sensor integration system, each individual sensor should be configured to its optimum for satisfactory measurement results. All the data measured from different equipment have to be precisely integrated into a common coordinate system. To solve this problem, this thesis proposes an accurate and flexible method to unify the coordinates of optical and tactile sensors for reverse engineering. A sphere-plate artefact with nine spheres is created and a set of routines are developed for data integration of a multi-sensor system. Experimental results prove that this novel centroid approach is more accurate than the traditional method. Thus, data sampled by different measuring devices, irrespective of their location can be accurately unified. This thesis describes a competitive integration for reverse engineering applications where the point cloud data scanned by the fast optical sensor is compensated and corrected by the slower, but more accurate tactile probe measurement to improve its overall accuracy. A new competitive approach for rapid and accurate reverse engineering of geometric features from multi-sensor systems based on a geometric algebra approach is proposed and a set of programs based on the MATLAB platform has been generated for the verification of the proposed method. After data fusion, the measurement efficiency is improved 90% in comparison to the tactile method and the accuracy of the reconstructed geometric model is improved from 45 micrometres to 7 micrometres in comparison to the optical method, which are validated by case study