With respect to current manufacturing tolerances, the inspection of screw threads in the field of precision engineering requires measurement uncertainties that cannot be achieved with the standardized measuring procedure in the current EURAMET cg-10 calibration guide. Because the conventional measuring strategy and evaluation method for calibrating screw threads refers only to specific lines along two axial sections, the complexity of the 3D workpiece is not taken into account. The manufacturing industry requires a paradigm shift from line-oriented to areal-oriented measuring strategies. This article presents a holistic approach that starts with the parameterization of complex screw thread geometry, continues with a concept for an areal measuring strategy and ends with the 3D evaluation of the gathered point cloud and the determination of the measurement uncertainty using numerical simulation.
Zusammenfassung
Maß- und Formmessungen an Gewinden, Zahnrädern oder anderen
lückenbehafteten Bauteilen werden häufig in Zweiflankenanlage
durchgeführt. In dem vorliegenden Beitrag werden bisher oft
vernachlässigte Einflüsse durch diese Art der Messpunktaufnahme
beschrieben und Lösungsmöglichkeiten zur Genauigkeitssteigerung
aufgezeigt. Ein wesentlicher Bestandteil ist hierbei das neu entwickelte
Lückennormal.
Modern coordinate measuring machines (CMMs) feature high-precision scanning due to improved mechanics, electronics, control, and software. PTB's Coordinate Metrology department therefore executed a thorough experimental comparison of the performance of scanning and discrete point probing regarding involute gear calibrations. In the last four years, PTB used scanning and discrete point probing to calibrate 29 different gear geometries covering a wide range of industry-relevant workpieces. Based on these extensive experiments and their analysis regarding measurement results, uncertainty and time, PTB decided to use scanning for gear calibrations in the future while guaranteeing the same measurement uncertainties and the same high level of reliability. This paper comprises an overview of tactile CMM scanning technology, PTB's gear calibration strategy, the measurement results, measurement uncertainty analyses, and a discussion of the task-specific advantages and challenges of scanning.
Die Physikalisch-Technische Bundesanstalt (PTB) entwickelt neue Verfahren für die Kalibrierung von Drehmomentaufnehmern mit zeitlich variierendem Drehmoment. Die Rückführung erfolgt dabei auf die Größen Massenträgheitsmoment und Winkelbeschleunigung. Die vorliegende Arbeit beschreibt die experimentelle Bestimmung des beteiligten Massenträgheitsmomentes der NormalMesseinrichtung (NME). Zur Messung wurde ein Torsionspendel aufgebaut und dessen Schwingung mit dem interferometrischen Messsystem der NME erfasst. Schlagwörter: Drehmoment, dynamische Kalibrierung, Torsionspendel, MassenträgheitsmomentThe Physikalisch-Technische Bundesanstalt (PTB), the National Metrology Institute of Germany, is developing new methods for the calibration of torque transducers with dynamic torque. In this case the traceability is based on the measurands of moment of inertia and angular acceleration. This contribution describes the experimental determination of the moment of inertia intrinsic to the standard device. For the measurement a torsional pendulum was realized and its oscillation was traced by the laser interferometric measurement system of the device.
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