Lars Buettner

In-process shape and roundness measurements at turning machines using a novel laser Doppler profile sensor

We have investigated the application of a laser Doppler profile sensor for in-process shape and roundness measurements at turning machines. This sensor is an extension of a conventional laser Doppler velocimeter (LDV), where two interference fringe systems with contrary fringe spacing gradients are generated inside the same measuring volume using wavelength division multiplexing. Scattering objects passing the measuring volume generate scattered light signals with two different Doppler frequencies, from which the velocity as well as the position of the objects can be determined via a proper calibration function. Hence, the radius and the tangential velocity and, thus, the shape of rotating work pieces and components, e.g. turbine blades or turning parts, can be measured absolutely and with only one single sensor. Two-dimensional and three-dimensional measurements of shape, excentricity, and roundness on quickly rotating cylinders inside a turning machine are presented. The results are compared with tactile measurements conducted with a coordinate measuring machine.

Measurement of velocity gradients in boundary layers by a spatially resolving laser Doppler sensor

A novel laser Doppler technique is presented to measure flow fields with micro-scale resolution. The realized laser Doppler sensor provides distributed velocity measurements inside a defined measurement volume. Two laser wavelengths are used to accomplish two Doppler frequency measurements, which determine the position and the velocity of a scattering particle. Repeating of these measurements determines the velocity gradient of the flow. One application area is the evaluation of the velocity variations in boundary layers of flows close to a wall. This contribution presents the principle and experimental results of the spatially resolving laser Doppler velocity sensor. Different concepts on the optical arrangements as well as the signal processing technique are discussed. A scheme for the construction of a miniaturized fiber-coupled sensor is presented, which allows its integration into flow channels.

Interferometric Velocity Measurements Using Adaptive Optics and a Fresnel Guide Star

A technique for interferometric velocity measurements through a fluctuating gas-liquid interface is presented. The adaptive optic system for wavefront correction uses the Fresnel reflex as a laser guide star allowing only one optical access.

Fiber optic distributed velocity sensor for precision measurements in microscopic and macroscopic flows

We report about a laser Doppler velocity profile sensor for precision measurements of microfluidic flows. The sensor measures the velocity and position of a tracer particle in the measurement volume, which consists of two superposed interference fringe systems of different wavelength, one with convergent, one with divergent interference fringes. This arrangement was achieved with a special combination of a diffractive and achromatic lenses. Due to fiber-optic beam delivery the sensor can be build compact and offers potential for miniaturization. A spatial resolution in the sub-micrometer range and an uncertainty of the velocity of about 10-4 could be achieved. The sensor offers potential for a variety of applications, like the investigation of shear flows or precise flow rate measurments.