Laser Doppler profile sensor with sub-micrometre position resolution for velocity and absolute radius measurements of rotating objects

Abstract

We have investigated the application of a laser Doppler profile sensor for simultaneous measurement of position and velocity on moving rough surfaces. It is shown that, with this technique, the shape of rotating workpieces and components, e.g., turbine blades or turning parts, can be measured absolutely and in-process with only one single sensor. Measurements on different surfaces with defined shape and roughness are presented. The obtained minimum uncertainty in the position is about 250 nm in the centre of the measurement volume. For the velocity, a relative statistical error of 0.02% was obtained. Furthermore, shading effects as occurring for example at triangulation are reduced since illumination and signal detection can be coaxial. Because the measurement occurs contactless and a high temporal resolution is achievable, this sensor can open up new perspectives in the field of real-time production metrology, for example controlling the turning and the grinding process or at tip-clearance measurements in gas turbines.

Interferometric Sensor System for Blade Vibration Measurements in Turbomachine Applications

“…The relative standard uncertainty of the velocity measurement σ v /v has been proven to be a constant factor of approximately σ v /v ≈ 10 −3 [11], [10], [12]. Thus, (5a) and (5b) can be expressed by…”

“…We invented a laser Doppler distance sensor (LDDS) that measures the tip clearance and the tangential blade tip velocity simultaneously [10], [11], [12]. The measurement principle of the LDDS relies on an extension of the laser Doppler velocimeter and is depicted in Fig.…”

“…Vice versa, the radial position and the tangential velocity of the blade tip are obtained from the two measured Doppler frequencies. Further details of the LDDS measurement principle are described in [10]. Since the tangential 0018-9456/$31.00 c 2013 IEEE vibration of the blades is of interest here, only the evaluation of the tangential velocity is considered subsequently.…”

Shape and vibration measurement of fast rotating objects employing novel laser Doppler techniques

“…which is also monotonously varying and does not depend on the velocity v. The inverse function z(q) can therefore be used to determine the axial position z of a scattering object inside the measurement volume 6 . With the known z-position, the actual fringe spacings d 1 and d 2 can be identified via the calibrated fringe spacing curves d 1,2 (z).…”

“…In this contribution, we present a novel laser Doppler position sensor, which allows simultaneous measurement of axial position and tangential velocity of fast rotating objects offering high temporal resolution and high position resolution *thorsten.pfister@tu-dresden.de; phone: +49 351 463-35303; fax: +49 351 463-37716; http://eeemp1.et.tu-dresden.de/ "iitiq •0 simultaneously [6][7][8] . It will be shown that, in contrast to conventional distance measurement techniques, the position uncertainty of this sensor is in principle independent of the object velocity since the determination of the position is attributed to a Doppler frequency measurement.…”