For in-process shape monitoring of rotating objects such as workpieces in a turning machine, contactless and compact sensors with high temporal resolution are necessary. For this challenging task, we developed a miniaturized and robust nonincremental interferometric fiber-optical distance sensor with dimensions of only 30×40×90 mm3, which enables attaching the sensor head directly to the mount of a turning tool bit. We present the results of in-process 3-D shape measurements of turning parts at a metal working lathe. To proof the accuracy of the measurement results, comparative measurements with tactile and optical sensors were performed. A maximal deviation between the different measurement methods of 2.2 μm was achieved for the determination of the mean height of a radial step.
In-process shape measurements of rotating objects such as turning parts at a metal working lathe are of great importance
for monitoring production processes or to enable zero-error production. Therefore, contactless and compact sensors with
high temporal resolution as well as high precision are necessary. Furthermore, robust sensors are required which
withstand the rough ambient conditions in production environment. Thus, we developed a miniaturized and robust non-incremental
fiber-optic distance sensor with dimensions of only 30x40x90 mm3 which can be attached directly adjacent
to the turning tool bit of a metal working lathe and allows precise in-process 3D shape measurements of turning parts.
In this contribution we present the results of in-process shape measurements during the turning process at a metal
working lathe using a miniaturized interferometric distance sensor. The absolute radius of the turning workpiece can be
determined with micron precision. To proof the accuracy of the measurement results, comparative measurements with
tactile sensors have to be performed.
The precise shape measurement of fast rotating objects is a challenging task in metrology. Deformation measurements of
lightweight composite materials are important to guarantee its robustness e.g. against impacts since they cannot be
simulated reliably. In a high-speed rotor test rig, their elastic and plastic deformations due to centrifugal forces can be
evaluated. Non-contact inspection techniques with micron resolution under vacuum conditions are necessary.
We present for the first time deformation measurements of a high-speed cylindrical rotor by a non-incremental
interferometric array sensor system. Rugged compact sensors were realised by employing optical fibers and diffractive
optics. Unique is the determination of the radial expansion also in the presence of an unsteady tumbling motion of the
rotor which is also monitored.
In this article we present a novel optical sensor allowing simultaneous measurements of axial displacement and
tangential velocity of moving rough solid state objects. The laser Doppler distance sensor with phase coding (P-LDDS)
features multiple interference fringe systems which are superposed slightly tilted. The axial displacement of fast laterally
moving rough solid state surfaces as well as of purely axial moving objects is determined via phase evaluation. Within a
measurement range of 200 μm, the measured maximum systematic displacement error at a laterally moving rough solid
state object is 1.4 μm and the displacement resolution is 240 nm. In contrast to conventional measurement techniques,
such as triangulation, the displacement uncertainty is independent of the lateral object velocity. This unique feature can
be utilized for precise displacement and vibration measurements of high speed objects.
One challenge in micrometrology is to measure precisely the shape of fast moved objects with high temporal resolution.
Deformation measurements of lightweight composite materials are of importance to guarantee its robustness e.g. against
impacts. In a high-speed rotor test rig their elastic and plastic deformations due to centrifugal forces can be evaluated.
Non-contact inspection techniques with micron resolution under vacuum conditions are necessary.
For the first time, we present high-speed deformation measurements of a cylindrical rotor by a non-incremental laser
Doppler distance sensor system using fiber and diffractive optics. Besides the determination of the radial enlargement
also wobbling of the rotor was monitored.
The optical inspection and metrology for non-optics industry gains increasing importance. Several optical sensors are
available for shape measurements of rough surfaces. However, at fast rotating objects such as turbine blades high
temporal resolution is necessary, which often can not be fulfilled by commercially available sensors. The recently
developed laser Doppler distance sensors allow temporal resolutions in the microsecond range. The independence of the
distance measurement uncertainty to the lateral surface velocity is unique. The laser Doppler distance sensors were
realized by the evaluation of the interference signal frequency as well as the interference signal phase. Both sensors have
been employed for high-speed inspection.
KEYWORDS: Sensors, Doppler effect, Calibration, Dynamical systems, Light scattering, Error analysis, Signal to noise ratio, Teeth, Signal detection, Process control
We introduce a simplified laser Doppler distance sensor comprising only one single fan-shaped interference fringe
system for dynamic position and shape measurement of fast moving objects with micrometer precision. Due to its low
complexity, it can be built very compact and cheap, which is crucial for many industrial applications. It will be shown
theoretically as well as experimentally that its position uncertainty is in principle independent of the object velocity in
contrast to conventional distance sensors. In order to evidence its capability, radial and axial shape measurements of
rotating bodies are presented employing a miniaturized sensor setup. An average position resolution of 2.3 μm was
obtained.
In-situ measurement of distances and shapes as well as dynamic deformations and vibrations of fast moving and
especially rotating objects, such as gear shafts and turbine blades, is an important task at process control.
We recently developed a laser Doppler distance frequency sensor, employing two superposed fan-shaped interference
fringe systems with contrary fringe spacing gradients. Via two Doppler frequency evaluations the non-incremental
position (i.e. distance) and the tangential velocity of rotating bodies are determined simultaneously. The distance
uncertainty is in contrast to e.g. triangulation in principle independent of the object velocity. This unique feature allows
micrometer resolutions of fast moved rough surfaces.
The novel sensor was applied at turbo machines in order to control the tip clearance. The measurements at a transonic
centrifugal compressor were performed during operation at up to 50,000 rpm, i.e. 586 m/s velocity of the blade tips. Due
to the operational conditions such as temperatures of up to 300 °C, a flexible and robust measurement system with a
passive fiber-coupled sensor, using diffractive optics, has been realized. Since the tip clearance of individual blades
could be temporally resolved an analysis of blade vibrations was possible. A Fourier transformation of the blade
distances results in an average period of 3 revolutions corresponding to a frequency of 1/3 of the rotary frequency.
Additionally, a laser Doppler distance sensor using two tilted fringe systems and phase evaluation will be presented. This
phase sensor exhibits a minimum position resolution of σz = 140 nm. It allows precise in-situ shape measurements at
grinding and turning processes.
In this contribution a novel laser Doppler distance (LDD) sensor is presented, which allows simultaneous measurement
of axial position and tangential velocity and, thus, determination of the shape of moving and especially rotating objects
with one single sensor. Conventional laser Doppler velocimeters measure only velocities. A concurrent position
measurement can be realized by generating two fan-shaped interference fringe systems with contrary fringe spacing
gradients and evaluating the quotient of the two resulting Doppler frequencies. Alternatively, two tilted fringe systems in
combination with phase evaluation can be employed. It will be shown that, in contrast to conventional distance sensors,
high temporal resolution below 3 μs and high position resolution of about 1 μm can be achieved simultaneously, because
the position uncertainty of the LDD sensor is in principle independent of the object velocity. This is advantageous
especially for monitoring highly dynamic processes e.g. at turbo machines, where in-process measurements of tip
clearance and rotor vibrations are reported for up to 600 m/s blade tip velocity.
This contribution presents novel laser Doppler techniques, which allow simultaneous measurement of radial position and
tangential velocity and, thus, determination of the shape of rotating objects with one single sensor. Conventional laser
Doppler velocimeters measure only velocities. A concurrent position measurement can be realized by generating two
fan-like interference fringe systems with contrary fringe spacing gradients and evaluating the quotient of the two
resulting Doppler frequencies. Alternatively, two tilted fringe systems in combination with phase evaluation can be
employed. It is shown that the position uncertainty of this sensor is not only independent of the surface roughness but,
most notably, that it is in principle independent of the object velocity. Thus, in contrast to conventional distance sensors,
the novel laser Doppler position sensor offers high temporal resolution below 3 &mgr;s and high position resolution in the
micrometer range simultaneously. The sensor was applied to automatic 3D shape measurements of turning parts and to
monitoring rotor unbalance and dynamic deformations. Furthermore, in situ measurements of tip clearance and rotor
vibrations at turbo machines for up to 600 m/s blade tip velocity are reported. The results are in excellent agreement with
those of triangulation and capacitive probes, respectively.
We report about a novel optical method based on laser Doppler velocimetry for position and shape measurements of moved solid state surfaces with approximately one micrometer position resolution. 3D shape measurements of a rotating cylinder inside a turning machine as well as tip clearance measurements at a transonic centrifugal compressor performed during operation at 50,000 rpm and 586 m/s blade tip velocity are presented. All results are in good agreement with conventional reference probes. The measurement accuracy of the laser Doppler position sensor is investigated in dependence of the speckle pattern. Furthermore, it is shown that this sensor offers high temporal resolution and high position resolution simultaneously and that shading can be reduced compared to triangulation. Consequently, the presented laser Doppler position sensor opens up new perspectives in the field of real-time manufacturing metrology and process control, for example controlling the turning and the grinding process or for future developments of turbo machines.
An external cavity laser is assembled by using an antireflection coated laser diode together with the surface of a measurement object. The automatic evaluation of the longitudinal modespacing yields the distance between the laser diode and the measurement object. The measurement resolution is increased by utilizing the resonance effect due to synchronous pumping of the laser diode current. Thus, a distance sensor with interesting properties for industrial applications is set up. Nevertheless, a systematic measurement deviation arises as a result of the nonlinear properties of the laser diode. A fundamental understanding of the processes inside the laser diode is necessary for achieving a measurement uncertainty in the micrometer range. Seen applications are in-situ measurements at grinding processes or the focus control at laser material processing.
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.
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